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Optics and Photonics: Essential Technologies for Our Nation (2013)

Chapter:Appendix C: Additional Technology Examples

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Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
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C

Additional Technology Examples

ENABLING TECHNOLOGIES

This appendix gives examples of additional technologies in the area of optics and photonics as they relate to many of the fields described in the chapters of this report. The Committee on Harnessing Light: Capitalizing on Optical Science Trends and Challenges for Future Research believes that this compilation puts additional emphasis on how optics and photonics truly are enabling technologies, and at the same time it provides the reader with further examples that highlight the many complex ways that optics and photonics support the foundation of many common areas not always directly associated with the fields of optics and photonics.

DEFENSE AND NATIONAL SECURITY

This section discusses the changes in many of the areas that were addressed in “Optics in National Defense,” Chapter 4 of the National Research Council’s (NRC’s) 1998 Harnessing Light: Optical Science and Engineering in the 21st Century.1 The subsections below provide an update for the areas of surveillance, night vision, laser systems operating in the atmosphere and in space, fiber-optic systems, and special techniques (e.g., chemical and biological species detection, laser gyros, and optical signal processing).

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1 National Research Council. 1998. Harnessing Light: Optical Science and Engineering for the 21st Century. Washington, D.C.: National Academy Press.

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
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Surveillance

Surveillance still plays a critical role in the detection and assessment of hostile threats to the United States. High-resolution imaging satellites have been deployed for more than 50 years to provide critical data for U.S. defense experts over denied airspace. The progress in optical sensors over the past decade has created an exponential growth in intelligence, surveillance, and reconnaissance (ISR) data from both passive and active sensors. This progress includes not just an increase in area coverage rate, but also an increase in sensor capabilities and performance. Material advances have made collection at new wavelengths feasible, and improved components provide new data signatures including vibrometry, polarimetry, hyper-spectral signatures, and three-dimensional data that mitigate camouflage for targets of interest.

A key advance since the NRC’s 1998 study is the dramatic increase in the application of active optical sensors for surveillance. The primary impetus for this increase has been the advances made in laser technology, including advances in robustness, efficiency, and optical power (see Figure C.1) for many wavelengths. In order for optical sensors to be widely fielded, they must also meet eye-safety requirements, which have driven advances in sources and amplifiers for 1.5 and 2 µm wavelength lasers.

In order to maximize atmospheric transmission, there has been a push for longer wavelength amplifiers in regimes with efficient detectors. Recent advances in thulium (Tm)-doped fiber amplifiers enable laser sensor operation in the 1.9 to 2.1 µm wavelength range. Average power levels are approaching the kilowatt level, and pulsed amplifiers with peak powers approaching 100 kW have been demonstrated.2,3,4,5 Several vendors are offering lasers with output powers up to 150 W. There are also several vendors offering narrow line-width, rapidly tunable 2.1 µm laser sources. The atmospheric transmission at this wavelength combined with the availability of commercial amplifiers, sources, and detectors makes 2.1 µm an attractive wavelength for long-range laser sensing. The efficiency of the current

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2 Cristensen, S., G. Frith, and B. Samson. 2008. “Developments in Thulium-Doped Fiber Lasers Offer Higher Powers.” SPIE Newsroom. DOI: 10.1117/2.1200807.1152. Available at http://spie.org/x26003.xml. Accessed July 31, 2012.

3 Moulton, P.F., G.A. Rines, E.V. Slobodtchikov, K.F. Wall, G. Firth, B. Samson, and A.L.G. Carter. 2009. Tm-doped fiber lasers: Fundamentals and power scaling. IEEE Journal of Selected Topics in Quantum Electronics 15(1):85-92.

4 Sudesh, V., T.S. McComb, R.A. Sims, L. Shah, M. Richardson, and J. Stryjewsky. 2009. Latest developments in high power, tunable, CW, narrow line thulium fiber laser for deployment to the ISTEF. Proceedings of SPIE 7325:73250B.

5 McComb, T.S., R.A. Sims, C.C.C. Willis, P. Kadwani, V. Sudesh, L. Shah, and M. Richardson. 2010. High-power widely tunable thulium fiber lasers. Applied Optics 49(32):6236.

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
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image

FIGURE C.1 Progress in output power for 1 µm, 1.5 µm, and 2 µm optical amplifiers. This plot tracks the historical progress in output power from a single fiber amplifier. Ytterbium (Yb)-fiber amplifiers (1 µm) have a significant lead over other technologies primarily due to their low quantum defect and the abundance of high-brightness pump sources at 915 to 975 nm. However, thulium (Tm)-fiber amplifiers (1.9 to 2.1 µm) have been demonstrated with average output powers approaching 1 kW and pulsed operation approaching 100 kW without sacrificing beam quality. There are several commercial units available with an average power ∼150 W. Their efficiency is set by the efficiency of the pump source, which should continue to improve over time as demand for Tm-lasers increases. SOURCE: Cristensen, S., G. Frith, and B. Samson. 2008. “Developments in Thulium-Doped Fiber Lasers Offer Higher Powers.” SPIE Newsroom. DOI: 10.1117/2.1200807.1152. Available at http://spie.org/x26003.xml. Reprinted with permission.

commercial amplifiers is approximately 6.25 percent6 limited by the efficiency of the pump source. However, there have been many investments made in these areas, which should improve the efficiency over time.

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6 See, for example, IPG Photonics, “2 Micron CW Fiber Lasers.” Available at http://www.ipgphotonics.com/products_2microns.htm. Accessed July 31, 2012.

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
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Night Vision

Night-vision capabilities continue to be an important tactical tool for the warfighter. In fact, the proliferation of equipment over the past few decades has led to a significant amount of surplus equipment available at very low cost, which has eroded the tactical advantage for the United States that existed for some time. During the First Gulf War, the United States “owned the night,” with U.S. night-vision systems significantly outperforming Iraqi night-vision sensors.7 However, the current commercially available night-vision sensors are nearly equivalent to the best U.S. night-vision systems. Since the NRC’s 1998 Harnessing Light8 study, there have been substantial improvements in sensitivity, performance for uncooled systems, and expanded wavelength applicability, which have enabled practical thermal imaging systems for size, weight, and power (SWaP)-constrained platforms.

Laser Rangefinders, Designators, Jammers, and Communicators

The significant increase in laser diode efficiency coupled with the decrease in cost has enabled recent advances in laser designators. However, similar advances in night vision and imaging detector arrays have limited the use of laser designators and led to ground force casualties in recent engagements. Therefore, there is a greater push for SWaP improvements to enable designators on small unmanned platforms (e.g., micro-unmanned aerial vehicles [UAVs]), which will also carry over to active sensors and optical communication systems. Early laser designator systems used neodymium-doped yttrium aluminum garnet (Nd=YAG) lasers at 1 µm. However, improvements in laser materials and efficiency have enabled a wider range of wavelengths to be implemented.

A large investment in laser communications had been made prior to publication of the NRC’s 19989 report and has continued since that time. Optical communication in fibers has been steadily advancing in the past decade. The high carrier frequency of light, combined with the low attenuation in fiber, makes it attractive for telecommunications applications. For free-space applications, the short wavelength improves directivity by minimizing diffraction when compared to radio-frequency (RF) communications. This is one of the key motivators for moving to optical communications, which minimize the probability of interception, jamming, and detection while dramatically minimizing the power needed for a given communication bandwidth, since most of the energy can be focused on the receiver.

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7 National Research Council. 2010. Seeing Photons: Progress and Limits of Visible and Infrared Sensor Arrays. Washington, D.C.: The National Academies Press.

8 National Research Council. 1998. Harnessing Light.

9 National Research Council. 1998. Harnessing Light.

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
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Laser Weapons

The Missile Defense Agency demonstrated the potential use of directed energy to defend against ballistic missiles when the Airborne Laser Test Bed (ALTB) successfully destroyed a boosting ballistic missile on February 11, 2010.10 The experiment, conducted at Point Mugu Naval Air Warfare Center-Weapons Division Sea Range off the coast of central California, served as a proof-of-concept demonstration for the directed-energy technology. The ALTB is a pathfinder for the nation’s directed-energy program and its potential application for missile defense technology. For the demonstrations, a short-range threat-representative ballistic missile was launched from an at-sea mobile launch platform. Within seconds, the ALTB used onboard sensors to detect the boosting missile and used a low-energy laser to track the target. A second low-energy laser was fired to measure and compensate for atmospheric disturbances. Finally, the ALTB fired its megawatt-class high energy laser, heating the boosting ballistic missile to critical structural failure. The entire engagement occurred within 2 minutes of the target missile launch, while its rocket motors were still thrusting. This was the first directed-energy lethal interception demonstration against a liquid-fuel boosting ballistic missile target from an airborne platform. This revolutionary use of directed energy is very attractive for missile defense, with the potential to attack multiple targets at the speed of light, at a range of hundreds of kilometers, and at a low cost per interception attempt compared to the cost with current technologies.

Fiber-Optic Systems

Fiber-optic systems have continued to evolve to achieve higher performance with lower power in a smaller volume. Fiber-optic systems (e.g., gyros, communication links) have several attractive attributes including low loss, high transmission rates, and freedom from electromagnetic interference. Therefore, they have continued to be adopted into military platforms as they are upgraded.

Special Techniques

The special techniques (i.e., chemical and biological species detection, laser gyros, and optical signal processing) evaluated in the NRC’s 199811 report have evolved in different ways. Optical signal processing has also advanced, but not at the pace forecasted at that time. Importantly, recent advances in optical integrated

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10 Missile Defense Agency, U.S. Department of Defense. 2010. “Airborne Laser Test Bed Successful in Lethal Intercept Experiment.” MDANews Release. Available at http://www.mda.mil/news/10news0002.xhtml. Accessed August 2, 2012.

11 National Research Council. 1998. Harnessing Light.

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
×

circuits should enable significant advances in optical signal processing over the next decade.

Chemical and Biological Species Detection

Weapons of mass destruction, including nuclear, biological, and chemical weapons, continue to be a high-priority threat. Long-range chemical and biological detection has advanced considerably since the 1998 report.12 One example is the Joint Biological Stand-off Detection System (JBSDS), a light detection and ranging (LIDAR)-based system that is designed to detect aerosol clouds out to 5 km in a 180 arc and to discriminate clouds with biological content from clouds without biological material at distances of 1 to 3 km or more. This system will provide advance warning of the presence of potential biological weapon aerosol cloud hazards so that a commander can implement individual and collective protective measures for assigned forces.

Laser Gyros for Navigation

Laser gyros were already very mature at the time of the 1998 report.13 They are critical in maintaining precision navigation when the Global Positioning System (GPS) is unavailable due to platform constraints or jamming. A new advance since the 1998 report is in the area of star-trackers, which can augment inertial navigation systems to improve long-term stability.

Optical Signal Processing

Optical processing has not changed very much since the NRC’s 1998 study.14 It continues to be very promising, since some mathematical functions can be performed very rapidly using optical analog techniques. One example is optical correlations that rely on Fourier transforms. Optical correlators compare two-dimensional image data at very high speeds. They were invented in the mid-1960s and have traditionally been used in high-cost military applications such as the analysis of satellite photographs. With recent advances in liquid-crystal technology, optical correlators have become more commercially viable—at a fraction of the high costs previously associated with such high-performance systems. Image data that are entered into the optical system are compared during the correlation process in terms of two criteria, similarity and relative position. Typically, the comparison

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12 National Research Council. 1998. Harnessing Light.

13 National Research Council. 1998. Harnessing Light.

14 National Research Council. 1998. Harnessing Light.

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
×

is done between a reference image (e.g., from a database) and an input image (e.g., from an external camera or sensor).

ENERGY

Cost of Solar Technology

In a 2008 study, leading experts in the solar field working on various technologies were asked to estimate the probability of any technology reaching two different “dollars per watt” benchmarks.15 The two price benchmarks were $1.20/W installed cost, the point at which a technology can be considered commercially viable, and $0.30/W installed cost, the point at which a technology would likely emerge as dominant in supplying utility-scale energy. The experts were asked to gauge the probability that any solar technology would meet these price points by the years 2030 and 2050. The results of this study are shown in Figure C.2, in which a larger circle corresponds to a larger number of experts giving this probability.

Hybrid Solar and Wind Power Systems

Another approach to harvesting the Sun’s energy is a solar updraft tower, which uses the greenhouse effect to create a hybrid of solar and wind power. This technology uses a large base area sealed by a transparent material. The air heats to approximately 70°C due to the greenhouse effect. This air is then forced out of the high central tower, referred to as a “solar chimney,” as shown in Figure C.3. This is expected to produce wind, which will then be used to power turbines. Two 200-MW plants have been proposed for installation in western Arizona.16

Supporting Technologies for Solar Power

The solar power industry has several supporting technologies that are crucial to further development but not directly involved in converting the Sun’s energy into electric power. Technologies such as mounts for solar modules and electronics are also crucial to the commercialization of solar power technologies.

Work has been done to model the competitiveness of a given solar technology quantitatively given the variability of many uncertain factors. Several modeling programs are being developed, one of which has become widely available: the Solar

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15 Curtright, A., M. Granger Morgan, and D. Keith. 2008. Expert assessments of future photovoltaic technologies. Environmental Science and Technology 42(24):9031-9038.

16 Southern California Public Power Authority. 2008. “La Paz Solar Tower Project.” Available at http://www.scppa.org/pages/projects/lapaz_solartower.xhtml. Accessed July 30, 2012.

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
×

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FIGURE C.2 Estimates of the probability of any solar technology reaching two dollars-per-watt price points—$1.20/W and $0.30/W—by 2030 and 2050, according to experts in the solar field. Larger circles correspond to a larger number of experts giving this probability. SOURCE: Estimates based on Curtright, A., M. Granger Morgan, and D. Keith. 2008. Expert assessments of future photovoltaic technologies. Environmental Science and Technology 42(24):9031-9038. Reprinted with permission.

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FIGURE C.3 An updraft solar tower power plant scheme. SOURCE: Redrawn and slightly modified by Cryonic07. Original jpg-drawing made by fr:Utilisateur:Kilohn limahn.

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
×

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FIGURE C.4 A sample output graph produced from the Solar Advisor Model. SOURCE: Mooney, D., M. Mehos, N. Blair, C. Christensen, S. Janzou, and P. Gilman. 2006. “Solar Advisor Model (SAM) Overview.” P. 23 in 16th Workshop on Crystalline Silicon Solar Cells and Modules: Materials and Processes; Extended Abstracts and Papers. Sopori, B.L., ed. Proceedings of the NREL/BK-520-40423 workshop held August 6-9, 2006, in Denver, Colorado. Golden, Colo.: National Renewable Energy Laboratory. Reprinted with permission.

Advisor Model (SAM), produced by the National Renewable Energy Laboratory (NREL) and Sandia National Laboratories.17 This system considers a wide range of module performance options, financing options, and government subsidies and will calculate the levelized cost of energy (LCOE) for an expected situation. A sample output of SAM is shown in Figure C.4, although the program produces an enormous amount of information and only a small part of the output is represented in the figure.

Models that can predict the performances of solar power relative to alternate sources of energy have been developed. Among these is the program ALTSim, developed at Hobart and William Smith Colleges to determine the viability of

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17 Mooney, D., M. Mehos, N. Blair, C. Christensen, S. Janzou, and P. Gilman. 2006. “Solar Advisor Model (SAM) Overview.” P. 23 in 16th Workshop on Crystalline Silicon Solar Cells and Modules: Materials and Processes; Extended Abstracts and Papers. Sopori, B.L., ed. Proceedings of the NREL/BK-520-40423 workshop held August 6-9, 2006, in Denver, Colo. Golden, Colo.: National Renewable Energy Laboratory.

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
×

biofuels competing with fuels such as oil and coal.18 Elaboration and integration of economic modeling programs such as these would enable more quantitative comparisons among technologies and allow more informed investment decisions.

A large portion of the module cost for solar applications, particularly those that require concentration, comes from the tracker that the system must be mounted on. These systems must be able to keep accurate alignment with the Sun, moving a large panel area. Maintaining the proper alignment is made more difficult by the requirement that the system stay aligned despite the significant wind loading generated by the solar panel carried. The tracker can comprise approximately half the cost of a current concentrating system. Reducing this cost while not compromising the performance or lifetime of a tracker would make these systems much more commercially viable.

Although the majority of the cost for a solar plant is the solar collection module, the electronics required to interface with the power grid and power storage still form a substantial portion of the cost. Solar panels produce direct current (DC) power, which must be transformed into alternating current (AC) to be sent into the power grid, requiring the use of an inverter. In some cases solar power can be matched to the load—for example, in the southwestern United States, where air conditioning drives peak load. Solar power up to some level can be used to handle this peak and is thus matched to the load. If solar power is also to be used at night, however, photovoltaic (PV) devices require a battery, or some other method of storage to store the power produced to be used when the system is not producing power. Charging a battery requires a charge controller, further adding to the system costs. Improving the performance or reducing the cost of any of these devices will make solar power more cost-effective. An approximate cost breakdown of these components is presented in Table C.1.19

The electronics cost is substantially reduced for concentrating solar power (CSP) systems, as the generator can produce AC power directly to the grid and the battery is unnecessary. These systems do have a large additional cost of thermal storage systems for on-demand generation, which costs approximately 30 percent as much as the solar module.20 Technical or manufacturing advances in this field will drive the cost of CSP plants down.

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18 Drennen, T., R. Williams, and A. Baker. 2009. Alternative Liquid Fuels Simulation Model (AltSim). Sandia Report SAND2009-7602. Albuquerque, N. Mex.: Sandia National Laboratories.

19 Solarbuzz. 2011. “Solar Buzz Retail Pricing.” SB_Retail_Pricing_111013.xls. Available at http://www.solarbuzz.com/facts-and-figures/retail-price-environment/module-prices. Accessed June 22, 2011.

20 Greenpeace International. 2009. “Global Concentrating Solar Power Outlook 09.” Available at http://www.greenpeace.org/international/en/publications/reports/concentrating-solar-power-2009/. Accessed July 31, 2012.

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
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TABLE C.1 Approximate Cost Breakdown Between Module Cost and Various Complementary Electronics Required


Module Unit September 2010 September 2011

Module US$/Wp (?125W) $3.61 $2.65
  Euro€/Wp (?125W) $3.23 $2.43
Inverter US $/continuous Watt S0.715 $0,714
  Euro€/continuous Watt $0.558 $0.500
Battery US $/output Watt hour S0.207 $0,213
  Euro€/output Watt hour $0.161 $0.149
Charge Controller US $/Amp S5.87 $5.93
  Euro€/Amp $4.58 $4.15
Solar Systems Residential c/kWh 34.28 29.53
  Commercial 0/kWh 24.32 19.97
  Industrial c/kWh 18.95 15.56

SOURCE: Frost and Sullivan analysis.

HEALTH AND MEDICINE

The roles played by imaging, optics, and photonics in modern medicine are mentioned in Chapter 6. Some of the details of the technologies used are examined below.

Optics and Photonics in the Emergency Room

In the modern emergency room, the technologies mention take advantage of photons with energies chosen so that they can penetrate deep into the human body. The performance of present-day CT instruments has improved dramatically over the past decades owing to advances in x-ray sources and the introduction of sophisticated multi-element, high-efficiency x-ray detectors. These instruments provide images with submillimeter resolution over large volumes of the body in mere seconds. These almost instantaneous three-dimensional images provide visual evidence of life-threatening disorders, saving precious minutes in life-and-death situations in the emergency room.

Optics and Photonics in Diagnostics

The high-speed blood work mentioned in Chapter 6 can also help determine the status of the patient’s immune system. When the AIDS epidemic was first detected in the early 1980s, the cause of the disease was unknown. It took several years for the human immunodeficiency virus (HIV) to be identified as the infectious agent and several more years for the affected immune system cell types to

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
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be determined. Optical methods based on laser spectroscopy of stained immune system cells provided the key technology that enabled the identification of the specific immune system cells impacted by the virus, out of the dozens of circulating cell types in the immune system. Currently, optical methods based on flow cytometry are still the standard of care for monitoring the immune system status of HIV patients and determining the efficacy of specific antiviral agents used to control the viral load in the patient’s bloodstream.

Pathologists also utilize optics and photonics. Today’s microscopes are interfaced to computers to speed diagnosis, assist the pathologist in recognizing diseased tissue, and provide a permanent electronic record of the images of tissue biopsies. Computerized microscopes combined with genetically engineered fluorescent antibody stains highlight the tumor region, identifying and quantifying the specific mutations and molecular changes in the tissue that are contributing to tumor growth. Knowing the molecular makeup of a tumor helps guide the physician and patient in choosing the most appropriate drug therapies. Although the microscope was invented more than 300 years ago, it still plays a major role as a primary diagnostic tool in the clinical laboratory.

The Human Genome Project Outcomes

One of the major motivations for sequencing of the human genome was to find the particular genes that determine the likelihood that individuals will develop specific diseases. Optical instrumentation was essential for the successful completion of the Human Genome Project (HGP). Using the HGP data, researchers have demonstrated conclusively that mutations in DNA repair genes (BRCA1 and BRCA2) dramatically increase the risk of breast cancer in both men and women. Individuals with these mutations can choose mastectomy or other preventive measures to reduce greatly their risk of developing tumors. Mutations in other genes (P450) are used to predict a patient’s ability to tolerate chemotherapy, allowing the oncologist to determine the optimal dosage more precisely. These key portions of a patient’s genome are measured today in optical instruments that can quantify millions of sequences in a single test using optical lithography technology, which was developed originally to manufacture integrated circuits and was modified to work with DNA molecules. The activity levels of specific genes can provide insight into the causes of tumor growth and thus allow oncologists to prescribe the most effective drugs. The activity or expression levels of specific genes can be measured from tumor biopsies using extremely sensitive fluorescence techniques based on amplifying and measuring the activity levels of genes using a technique called real-time polymerase chain reaction (RT-PCR). This technique is so sensitive and specific that it can detect in a sample the presence of a single molecule with a unique genetic sequence, even in the presence of billions of DNA molecules with slightly

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
×

different sequences. Doctors can evaluate data indicating gene expression levels in a tumor biopsy and use these results to predict the aggressiveness of certain types of cancer and the response of specific tumors to hormonal therapy, thus helping to determine the optimal drug options for each patient.

Biomedical Optics in Everyday Life

Glucose Monitors

Optical methods are also used to monitor chronic conditions, such as the monitoring of the glucose level in diabetic patients by means of compact, cell-phone-sized, battery-operated readers that analyze the concentration in the blood serum. These devices use optically active reagents that react with glucose in a small blood sample placed on a very inexpensive disposable paper strip and change the optical properties of the strip depending on the amount of glucose in the sample. These measurements can be done in a few seconds using a device that easily fits in a shirt pocket or purse, providing people who have diabetes with portable methods for measuring and maintaining safe levels of blood sugars.

Cosmetic Biomedical Optics

Far-infrared lasers are selectively absorbed at the surface of the skin, providing a sterile method for removing or modifying large areas of skin either to serve cosmetic purposes or to aid in the recovery of burn victims. Subsequent healing and regrowth can provide a smooth, more physically appealing surface. Hair follicles also selectively absorb certain infrared (IR) wavelengths emitted by solid-state lasers. Heating follicles above 50°C destroys the cells that cause hair to grow, thus eliminating unwanted hair without surgery.

Both nearsighted and farsighted patients can be treated with precision shaping of the cornea with lasers, which can also correct for astigmatism and other eye aberrations, eliminating the need for glasses in many patients. Contact lenses and standard eyewear provide both disposable and permanent options for correcting vision for those who prefer to avoid surgery.

Proteomic Analysis Through Protein and Tissue Arrays

High-throughput protein-detection instruments that trap individual protein molecules on microscopic beads have recently been developed. These protein molecules are in turn detected by genetically engineered enzymes that bind to the proteins and efficiently generate a fluorescent signal. This signal is highly concentrated near the microscopic bead and can be detected using high-sensitivity, low-

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
×

noise, charge-coupled-device (CCD) imaging devices. Very low concentrations of protein molecules can be detected with such high efficiency that individual protein molecules can be counted digitally, providing very high accuracy and precision. This technology increases the sensitivity of the detection of proteins by almost three orders of magnitude. Such improvements in sensitivity provide the possibility of detecting early signs of cancer recurrence. Medical studies are currently underway to use these new approaches to look for low levels of prostate-specific antigen (PSA) in prostate cancer patients who have had their prostates removed. The presence of PSA is evidence that prostate cells maybe proliferating in other organs, which indicates a recurrence of the cancer through metastasis. Another potential application of protein-detection technology would allow the early detection in peripheral blood of very low levels of proteins indicative of Alzheimer’s disease. The current protocol involves proteomic analysis of spinal fluid requiring much more invasive lumbar puncture procedures.

Ophthalmology

Excessive blood vessel growth is one symptom of diabetic retinopathy (DR), one of the most common causes of late-onset vision loss. A common method for diagnosing retinal disease such as DR involves photographing the blood vessels in the retina. Current methods use an injectable fluorescent dye (sodium fluorescein) and excite the dye in the retina using flash photography or a scanning laser system that raster scans over the patient’s retina. Adverse reactions to the intravenous dye occur in a significant fraction of elderly patients and particularly in those with hypertension. Intravenous administration of fluorescein can cause nausea, vomiting, hives, acute hypotension, and anaphylactic shock. A version of optical coherence tomography (OCT), called phase variance optical coherence tomography (PVOCT), appears to have the potential to eliminate the need for the administration of an intravenous fluorescent dye, thus making this procedure much safer. PVOCT measures the changes in the light reflected from the retina due to the motion of the blood flowing through the retina. These signals can be detected without using fluorescent dyes, and the resulting images have resolution and contrast comparable to the standard dye-based procedures. An additional advantage of the PVOCT protocol is that three-dimensional information about the vasculature is obtained, providing further valuable information that can aid in diagnosis of retinal disease.21

Head trauma can result in partially detached retinas, which can be “welded” back in place using pulsed lasers. Occluded lenses caused by cataracts can be sectioned

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21 Kim, D.Y., J. Fingler, J.S. Werner, D.M. Schwartz, S.E. Fraser, and R.J. Zawadzki. 2011. In vivo volumetric imaging of human retinal circulation with phase-variance optical coherence tomography. Biomedical Optics Express 2(6):1504-1513.

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
×

and more easily removed using pulsed lasers. Using lasers with different output colors, doctors can repair almost every major element in the eye: cornea, lens, and retina.

Millions of individuals have had their vision permanently corrected using the photorefractive keratectomy (PRK) procedure that uses excimer lasers to modify the lens in the eye precisely. New methods involving ultrafast lasers allow the removal of an ultrathin corneal flap prior to PRK surgery (laser-assisted in situ keratomileusis, or LASIK). This flap is placed over the machined cornea and helps protect the corneal surface and promotes faster healing. LASIK eliminates the use of a scalpel to cut this sensitive tissue and provides a much more precise and thinner flap covering the surgical incision. Moreover, in the LASIK procedure the precise laser incision allows a tab to be retained, which assists in repositioning the flap over the incision. This process reduces the risk of infection by eliminating physically touching the eye with a scalpel and provides a much more precise method for determining the diameter and symmetry of the incision; see Figure C.5.

One of the most common causes of visual impairment is the development of cataracts or cloudiness in the eye lens, which leads to reduced visual acuity and difficulty in seeing at night. The standard treatment procedure involves the surgical removal of the clouded lens and its replacement with a clear plastic lens. Common cataract procedures involve cutting the lens capsule surrounding the lens and then segmenting the occluded lens prior to manual removal by the surgeon. Current methods require making an incision in the eye and inserting scissors to cut the lens capsule surrounding the clouded lens manually. This method can often be imprecise and result in uneven or torn lens capsules, which compromise the placement of the replacement lens. This process can now be performed with phenomenal precision using laser surgery guided by OCT data.22

Advances in Endoscopic Surgery

Prosthetic devices can restore hearing in many older adults who have experienced degenerative hearing loss and in children born with hearing deficits. Inserting these devices often requires delicate surgery in the close environment of the ear canal, surrounded by very delicate tissue structures. Far-infrared lasers can be used to resculpt the inner ear to allow effective incorporation of a prosthetic device. The tissues in the ear canal strongly absorb mid-infrared (mid-IR) laser light, which can be used to cut and oblate tissue to allow insertion of the prosthetic device. Until recently lasers were not easily employed in this application, since directing the beam into the ear canal was complicated by the complex physiology and small confines of the ear canal. Building on advances in fiber-optic technology stimulated by the

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22 See Chapter 6 in the main text of this report for a description.

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
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image

image

FIGURE C.5 (a) Steps in the photorefractive keratectomy (PRK) procedure. (b) Steps in the laser-assisted in situ keratomileusis (LASIK) procedure.

telecommunications industry, several new types of fiber-optic cables have been developed that allow the effective delivery of mid- and far-IR lasers, wavelengths that are highly absorbed by soft tissue, into previously inaccessible portions of the human anatomy like the inner ear. Thus mid-IR lasers can now be used in a variety of surgical procedures that were not previously possible. Novel fiber optic designs use nanostructured geometries to confine the far-IR light of a carbon dioxide (CO2) laser into a flexible fiber cable, as shown in Figure C.6. These geometries

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
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image

FIGURE C.6 Omniguide fiber for otology. SOURCE: Courtesy of OmniGuide, Inc.® Cambridge, Massachusetts. Reprinted with permission.

utilize submicron layers of optical materials surrounding a hollow core, which allows the far-IR light from the CO2 laser to be delivered to delicate bone and tissue structures of the inner ear. This new fiber-coupled source has found great utility in otology, providing effective methods for the surgical implantation of prosthetic devices restoring hearing to adults and children who have hearing impairments. These advances have relied heavily on fundamental research in nanophotonics and photonic crystal devices, technology originally developed primarily for the telecommunications industry.

Similarly, kidney stones can be very effectively fragmented using fiber-coupled, near-IR pulsed lasers. High-energy, short pulses from these lasers are absorbed by the kidney stone, creating a thermal shock wave, disrupting the stone. New, low-water-content fibers allow a holmium-doped (Ho):YAG laser to be focused into an optical fiber, which is incorporated into a flexible endoscope. This endoscope can be threaded through the urethra and guided to the kidney stone. This laser effectively fragments kidney stones and provides a low-morbidity, less expensive, and highly effective alternative to previous treatments using high-intensity sound shock waves to disrupt the stones.

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
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Advances in Oxygen Saturation Measurements

When firefighters come upon an unconscious person, they must often assess whether the victim has been subjected to high levels of carbon monoxide (CO). A rapid assessment of the levels of CO in the blood is critical so that intervention can take place before brain damage occurs. Exposure to CO and the effect of a number of common drugs on the blood’s ability to transport oxygen throughout the body alter the spectroscopic properties or color of the blood, providing key indications of the cause and expediting the appropriate intervention. Exposure to CO reduces the oxygen-carrying capacity of blood and causes the IR transmission of the blood to increase, whereas exposure to certain drugs decreases the absorption in the orange region of the visible spectrum. These optical signatures, as indicated in Figure C.7, can be used to diagnose quickly and noninvasively the cause of hypoxia and can help determine the most effective treatment.

Rapidly growing tumors require high blood flow to supply sufficient nutrients and oxygen to support tumor growth. Using near-IR wavelengths of light, which can penetrate through most normal tissues but are absorbed preferentially by highly oxygenated blood, tumors can be detected by monitoring the increase in oxygenated blood flow to regions of tissue deep beneath the surface of the skin.

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FIGURE C.7 Blood changes color depending on the hemoglobin status. The absorption profiles of four different hemoglobin statuses are shown. Simple disposable probes that can be mounted on a patient’s finger can precisely measure the absorption level of the blood at different wavelengths and help determine the extent and cause of hypoxia. SOURCE: Masimo. 2012. “Rainbow SET Pulse CO-Oximetry.” Available at http://www.masimo.co.uk/Rainbow/about.htm. Reprinted with permission.

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
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This increased blood flow can be measured and tumor images can be generated by positioning multiple sources and detectors around the affected tissue and observing “shadows” of the tumor due to this increased blood flow required by the tumor.

Biomedical Optics in Research

The polymerase chain reaction (PCR) was discovered in the early 1980s. The PCR provides one of the most sensitive and specific methods for measuring nucleic acid molecules in vitro. Using high-efficiency fluorescent organic dyes and low-noise detectors, single DNA molecules with specific sequences can be detected even when contained in a sample with a large concentration of background DNA molecules. This high sensitivity and specificity have allowed the development of techniques that separate the sample into multiple individual wells, where the number of wells is large enough that only a single molecule is likely to be in any individual well. The absolute number of molecules in the original sample can be determined simply by counting the number of wells in which single molecules are detected. This approach to quantitative PCR, called digital PCR, allows a significant increase in the accuracy with which low levels of specific nucleic acid molecules can be detected. Digital PCR may also provide a method for developing precise standard reference materials and detection protocols for ultra-low trace concentrations of nucleic acids.

Cancer biopsies often contain heterogeneous mixtures of various types of normal and tumor cells. It is thought that even within a tumor, specific tumor cells (cancer stem cells) have an enhanced ability to reproduce and to survive chemotherapy treatment, leading to the post-treatment regrowth of the tumor. Cancer stem cells are rare and are located close to both normal tissue and non-stem tumor cells. Studying these rare cells requires isolating and removing them from the surrounding tissue sample. Automated laser-based methods for performing these micro-dissections have been developed, providing a fast and precise method for excising single cells from the complex tissue environment found in most biopsies. These methods combine ultraviolet (UV) lasers used for isolating the single cells, with IR lasers which capture the cells, and allow an efficient method for extraction of the sample from the biopsy. Automated laser capture micro-dissection (LCM) has been combined with microfluidic technology, allowing the macromolecules to be extracted efficiently from the micro-dissected samples and reagents that provide a means to copy and thus amplify specific target molecules of messenger ribonucleic acid (mRNA) or DNA within the microscopic samples to allow precise quantification. The abilities to isolate, extract, and analyze single cells on the basis of optical imaging and laser technologies have created the new field of microgenomics, which has found applications in many fields of research including microbiology, neuroscience, developmental biology, and forensics.

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
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ADVANCED MANUFACTURING

CNC Grinding and Polishing

Computer numerically controlled (CNC) grinding and polishing have brought a deterministic approach to centuries-old processes. Applying technology from the machine tool industry, CNC grinding and polishing have made significant advancements in the ability to produce precision aspheric components. Aspheric geometry is much more difficult to generate and polish than are spheres, however. Five-axis CNC grinding and polishing equipment, as shown in Figure C.8, makes it possible to produce these challenging geometries. Computer controllers dynamically adjust cutting paths for tool wear and can be programmed for edging, beveling, sagging, concave, and convex surface grinds.

Polymer Molding

Molded plastic lenses have become commonplace in consumer and commercial products. Mobile phones, DVD players, digital cameras, and conferencing systems have incorporated polymer lenses. Hydraulic injection molding presses and injection compression molding presses are now employed by most optical

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FIGURE C.8 (Left) A commercially available 5-axis computer numerically controlled grinder. (Right) A closeup image of the grinding head. SOURCE: Courtesy of Optipro.

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
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component molding shops. Presses in the 20- to 50-ton range are frequently used and have excellent process control. Single- and multiple-cavity (2 and 4 cavities) molding tools with replaceable inserts are standard in the industry. For components associated with higher-volume products which have a long product life, higher tool cavitation can often be justified. In these cases, molds of 16, 18, or 20 cavities may be employed. Automation to pick and degate parts is employed for high-volume products in an effort to reduce costs.

In the past few years, several new materials have been proven to be moldable. Table C.2 indicates some of the polymers commonly used today. The capability of the molding process has also been advanced. Depending on material, lens type, and size, newer polymer molding processes routinely hold tight tolerances of 1 fringe accuracy during testing.

TABLE C.2 Table of Commonly Used Polymers


  Unit Acrylic Acrylic Copolymer Polystyrene Polyetherimide

Trade name   Plexiglas UVT Styron Ultem
Refractive Index
nf (486.1 nm)   1.497   1.604 1.689
nd (589 nm)   1.419 1.49 1.59 1.682
nc (656.3 nm)   1.486   1.585 1.653
Abbe value Vd   57.2 50–53 30.8 18.94
Transmission 1% 92–95 92–95 87–92 82
Maximum continuous service temp. °F 161 190 180 338
  °C 72 88 82 170
Water absorption 3% 0.3 0.25 0.2 0.25
Haze % 1–2 2 2–3  
dN/dNx 10-5 /°C -8.5 -10 to-12 -12  
           
Color/tint   Water clear Water clear Water clear Amber
Benefit 1   High transmission and purity High transmission and purity High index Impact resistant
Benefit 2   Scratch resistance Chemical resistance Excellent UV properties Clarity Thermal and chemical resistance
Benefit 3   High Abbe value Low dispersion High melt flow 82% transmission at 924–301 nm. 1 mm CT   High index

SOURCE: Courtesy of Syntec.

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
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Glass Molding

Glass molding technology, first developed in the early 1970s, has become increasingly available in the past decade. Prior to the turn of the century, most glass molding technology was proprietary and only available to the corporations that developed it. During the past decade, domestic and offshore manufacturers have marketed systems capable of producing precision-molded glass lenses. Figure C.9 shows a molding machine developed and produced in the United States and commercially available around the world, and Figure C.10 shows molding inserts and molded asphere lenses.

Not all glass is moldable. Several factors are important in the determination of moldability. Constituents in the glass and the glass transition temperature are factors to be considered. Molding trials are conducted to ensure moldability. Figure C.11 shows glass types that are moldable by one U.S. manufacturer with its


Polycarbonate Methylpentene ABS Cyclic Olefin Polymer Nylon NAS SAN

Lexan TPX Acrylon Zeonex Polyamide Methyl Styrene Acrylonitrile
1.593 1.473   1.537   1.595 1.578
1.586 1.467 1.538 1.53 1.535 1.533–1.567 1.567–1.571
1.58 1.464   1.527   1.558 1.563
34 51.9   55.8   35 37.8
85–91 90 79–90.6 90–92 88 90 88
255     253 179.6 199.4 174–190
124     123 82 93 79–88
0.15     <0.01 3.3 0.15 0.2–0.35
1–3 5 12 1–2 7 3 3
-11.8 to     -8   -14 -11
-14.3            
Water clear Slight yellow Durable Water clear   Water clear Water clear
Impact strength Chemical resistance   High transmission and purity Chemical resistance Good index range Stable
Temperature resistance     Low moisture absorption      
      Good thermal stability      

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
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FIGURE C.9 Commercially available glass molding machine. SOURCE: Courtesy of Moore Nanotech, LLC.

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
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FIGURE C.10 Generic molding inserts and molded asphere lenses. SOURCE: Courtesy of Rochester Precision Optics.

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FIGURE C.11 Moldable glasses types available from Rochester Precision Optics. SOURCE: Courtesy of Rochester Precision Optics.

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
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proprietary process. Figure C.11 indicates that lenses can be produced from glass with indices of refraction that range from approximately 1.48 to above 1.9, with Abbe numbers from 84.47 to 20.88, respectively.

The quality of lenses produced from the glass molding process is highly dependent on the ability to produce molding tools. Molding inserts are single-point diamond turned or ground and post-polished. The resulting inserts and tools are very capable with surface roughness as low as 5 A root mean square (RMS) and a surface accuracy of 1/10 λ. High-precision tools are capable of producing lenses with tolerances for power of 3 fringes and irregularity of ½ fringe.

Magnetorheological Finishing

The use of magnetorheological finishing (MRF) has increased in the fabrication of optical components. MRF requires the starting surfaces to be polished and is a deterministic polishing process that uses interferometry to provide feedback to the polishing tools. Figure C.12 shows a schematic of the polishing process. Ferrous-laden fluid passes through an electromagnetic field where its viscosity is stiffened, allowing the creation of a precise and repeatable polishing tool. When the fluid rotates out of the magnetic field, it is collected and recirculated. Constant monitoring of the polishing process parameters such as pressure and flow rate and

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FIGURE C.12 Magnetorheological finishing polishing. SOURCE: Reprinted with permission from Photonics Tech Briefs.

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
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the addition of process fluids provides for a predictable removal rate. Very accurate surfaces, particularly aspheric surfaces, can be produced using the MRF process. Surface accuracies of better than 1/20 λ peak to valley are standard for this process.

Single-Point Diamond Turning

Single-point diamond turning (SPDT) as a fabrication process for optical components has grown in popularity since the mid-1970s. SPDT is now routinely used to produce finished optical elements as well as mold inserts for polymer lenses and glass molding. The machining process uses single-crystal diamond cutting tools combined with nanometer-precision positioning to generate spherical surface geometries as well as more complex geometries such as toroids, aspheres, and diffractives.

The materials best suited to SPDT include metals, crystals, and polymers. Box C.1 provides a list of optical materials that have been demonstrated to be machinable. It is important to note that Box C.1 is not an exhaustive list of the materials that are machinable in the SPDT process, but rather a general listing. It is known that ferrous metals generate excessive tool wear; non-ferrous metals are thus the preferred metals. Metals such as aluminum 6061 and electroless nickel can be machined to produce a very high quality optical surface. As demand has increased for optical components that transmit in the infrared, the capability to machine IR materials has improved. Single-crystal materials such as those listed in Box C.1 can be reliably machined to

BOX C.1
Materials Suitable for Single-Point Diamond Turning

Metals Nonmetals Polymers

Aluminum Calcium Fluoride Cyclic Olefin
Brass Magnesium Fluoride Polymethylmethacrylate
Copper Cadmium Telluride Polycarbonates
Beryllium Copper Zinc Selenide Polyimide
Bronze Zinc Sulphide Polystyrene
Gold Gallium Arsenide  
Silver Sodium Chloride  
Lead Calcium Chloride  
Platinum Germanium  
Tin Strontium Fluoride  
Zinc Sodium Fluoride  
Electroless Nickel Potassium di-hydrogen phosphate
Potassium titanyl phosphate
Silicon
 
Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
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produce the required components. Polycrystalline materials are more difficult to machine and generally considered not diamond-machinable. Polymers have become popular in optical systems. SPDT provides an excellent solution for the manufacture of polymer prototypes, low and mid production, and inserts for polymer molds.

Optical Coating

Optical thin-film coatings technology has been advanced in response to requirements in multiple and diverse markets including telecommunications, health and medical, biometrics and defense markets. Evaporation deposition processes in which materials are deposited by means of a transformation from solid to vapor back to solid have been the most widely used processes in the optical industry. Although the coatings satisfy requirements, they are often porous and sensitive to humidity and thermal conditions. The ion-assisted deposition (IAD) process, as highlighted in Figure C.13, more tightly “packs” coating layers, yielding a more robust coating. These evaporation processes, both assisted and unassisted, are widely

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FIGURE C.13 Ion-assisted deposition with sources, heaters, and substrates labeled as well as detectors for monitoring the process. SOURCE: Courtesy of Edmunds Optics, Inc.

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
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used for antireflection coatings, mirrors, filters, and beam splitters, all typically with less than 100 layers.

Responding to industry requirements for higher-precision coatings, ion beam sputtering (IBS) was developed. This process uses an ion gun to excite ions such that they collide with the source, resulting in sputtering of material from the source to the part being coated. The process provides very high quality coatings, although the cost of the equipment and its maintenance is high relative to IAD. IBS is often chosen for high- and ultrahigh-precision coatings.

In the past few years a technology newer than IBS, advanced plasma reactive sputtering (APRS), has been developed and is especially effective for complex coatings of more than 200 layers per run totaling more than 20 µm. Figure C.14 shows the APRS system from Leybold Optics. The APRS system uses two dual-magnetron sources, which operate at mid-frequency. Material oxidation occurs when the part being coated passes through an oxygen plasma. The deposition rate of approximately 0.5 nm/sec is similar to the deposition rates experienced with evaporation; however, the resultant coatings are denser and more stable.

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FIGURE C.14 HELIOS advanced plasma reactive sputtering tool. SOURCE: Courtesy of Leybold Optics.

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
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Metrology

Metrology is an important enabling technology in the optics industry. It has long been said, “If you can’t measure it, you can’t make it.” Over the past decade there have been advances in interferometry improving the ability to measure increasingly more challenging optics, particularly aspheres. Extremely tight tolerances for some of these aspheric geometries are the challenge for available metrology. Testing variability for ultrahigh-precision optics, as in optics for lithographic applications, often needs to be 3 to 5 times smaller than the tolerance of the optic being measured. Recent advancements, for example in stitching interferometry, shown in Figure C.15, have provided the industry with the capability of making

image

image

FIGURE C.15 Stitching interferometer of QED Technologies. (Top) A sub-aperture lattice covers the entirety of a high-numerical-aperture part. (Bottom) Simulated fringe patterns for an approximately 50 micon-depatture asphere: (a) the lack of data shows because the fringes are not resolved; (b) magnification allows for some resolution; (c) correct choice of local best-fit sphere increases fringe resolution even further. SOURCE: Images provided courtesy of QED Technologies International, Inc.

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
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image

FIGURE C.16 The Verifire Asphere system of Zygo combines interferometer technology. SOURCE: Courtesy of Zygo Corporation. Reprinted with permission.

full-aperture measurements on optics exceeding 200 mm in diameter including aspheres with up to 650 microns of aspheric departure. Another advancement, shown in Figure C.16, combines laser Fizeau interferometry and displacement-measuring interferometry to reduce measurement uncertainty.

Gray-Scale Lithography for Diffractive- and Micro-Optic Components

Gray-scale lithography has become an important method for the fabrication of diffractive- and micro-optical components for optical systems applications spanning the range from the deep UV (193 nm) to the infrared (10.6 µm). The process involves the exposure of photoresist coated on a substrate. The photoresist is exposed using a focused laser beam, which is scanned across the surface of the photoresist using air-bearing translation stages. As the laser beam is scanned, the intensity is modulated, so that when the photoresist is developed, the desired surface-relief pattern is obtained. In the early work in the 1980s, surface-relief profiles were typically in the range of 1 to 5 µm; now one can obtain virtually any continuous, surface-relief profile with depths up to 100 to 120 µm. The developed photoresist master can then be replicated using UV cast and cure materials, or it can be used to create a nickel electroform, which in turn can be used in high-volume manufacturing processes, such as polymer-injection molding and roll-to-

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
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roll film manufacturing. Examples of surface-relief optical components, produced using this gray-scale lithography manufacturing method, are shown in Figure C.17.

Numerous and important applications exist for these lithographically generated, surface-relief optical components: for example, efficient extraction and distribution of light from LED sources for general lighting, laser-beam shaping for sensors systems, front- and rear-projection screens, and imaging and display systems. Or, one can also place the substrate with the patterned photoresist into a reactive-ion etcher chamber in which ions are used to bombard the surface and transfer (or etch) the surface-relief pattern directly into the substrate material. Common substrate materials for reactive-ion-etched optical components include fused silica, silicon, and germanium.

image

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FIGURE C.17 Different types of regular microlens arrays. SOURCE: Reprinted, with permission, from Fan, Xiqiu, Honghai Zhang, Sheng Liu, Xiaofeng Hu, and Ke Jia. 2006. NIL—A low-cost and high-throughput MEMS fabrication method compatible with IC manufacturing technology. Microelectronics Journal 37(2):121-126.

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
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DISPLAYS

Polarization in Liquid-Crystal Displays

If two pieces of polarized material are placed in series between an observer and a light source and then rotated relative to one another, at one point the transmission of light will be blocked as the polarization of the two pieces of material is perpendicular. If from that point they are rotated another 90°, the polarizers will be aligned and about half the light will pass (with the other half absorbed by the first polarizer). A variable amount of light can be passed by rotating the polarizers in between the extreme perpendicular and aligned positions, as shown in Figure C.18. This form of light modulation automatically loses a factor of two in the best case unless the initial light source is polarized.

A liquid-crystal display (LCD) works roughly the same way; however, rather than rotating the polarizers, the light itself is rotated by a liquid crystal. Light from a source is passed through two fixed polarizers with liquid crystal in between. The polarizers are crossed, but in the absence of electric current, the thickness of the liquid-crystal layer is such that it rotates the polarization by 90°, so light is passed. Applying an electric field alters the alignment of the liquid crystal so that the light is not rotated and light is thus blocked. Varying the strength of the field varies the degree of alignment and thus the amount of light passed, as indicated in Figure C.19. A wide variety of colors can be achieved by varying the amount of light passed through each of the three subpixels.

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FIGURE C.18 Polarized light waves. SOURCE: Image created by Bob Mellish.

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
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image

FIGURE C.19 Liquid-crystal changing polarization. NOTE: TFT, thin-film transistor; ITO, indium tin oxide. SOURCE: © Merck KGaA, Darmstadt, Germany. Reprinted with permission.

Three-Dimensional Technology in LCDs

One method used to achieve a three-dimensional effect using an LCD display that was mention in Chapter 10 alternates showing an image for one eye, then a slightly displaced image for the other eye. Wireless connection between a pair of glasses and the display keeps the polarization of glasses in sync, only passing light to the intended eye. The first-generation three-dimensional LCD televisions used such active shutter glasses, seen in Figure C.20.

The shutter glasses were themselves crude LCDs, consisting of a single large pixel per eye. One of the challenges of this approach is brightness. In an LCD, the entire screen is not switched at once, but the screen is painted line by line, typically from top to bottom. As the screen is being refreshed for one eye, the top of the display shows the desired image for that eye, but the bottom of the display still shows the previous image for the other eye. The display is constantly refreshing, so only for an instant during each cycle would the screen show an image for only one eye. To overcome this problem, an image for a given eye was shown twice in succession and the shutter glasses opened during the second painting. Unfortunately,

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
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image

FIGURE C.20 Shutter glasses blocking left image from entering right eye. Image courtesy of E. Svedberg.

this solution meant that the shutter glasses for any one eye were passing light only during one out of four frames. Thus, the apparent brightness of the display was only one-quarter that of the same display when used in a two-dimensional mode without glasses.

More recently an alternative approach to three-dimensional displays has been introduced, placing a patterned optical retarder on the face of the display. The role of this retarder is to continually twist the polarization of every other row, as shown in Figure C.21. To view the display in three dimensions, observers wear passive glasses that have polarizers 90° opposed. The left eye can then only observe the odd rows, say, while the right eye can only observe the even rows. The screen brightness is thus increased because both eyes are constantly receiving signal.

Unfortunately, the trade-off of this alternate scheme is a reduction in vertical resolution. Rather than each eye receiving the 1,080 rows of a standard high-definition set, each receives only 540 rows. This reduction in vertical resolution has motivated some to suggest that future sets be made with the standard 1,920 horizontal pixels but with double the number of vertical pixels, to 2,160, so that each eye then can receive full high definition when viewing in three-dimensional mode. In two-dimensional mode, the even and odd row pairs could mimic one another to result in standard high definition, as input sources with doubled vertical resolution may be rare.

Another possible approach for creating three-dimensional displays puts two

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
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image

FIGURE C.21 Highly simplified view of patterned retarder and the observer’s passive glasses. Image courtesy of E. Svedberg.

liquid-crystal displays in series. In this active retarder scheme, the rear display has the traditional role, while the role of the front display is to rotate the polarization on a frame-by-frame basis. The viewer then wears passive glasses to filter out images not intended for a given eye.

One might expect brightness to be an issue with an active retarder as it is with active shutter glasses. However, the brightness issue can be greatly reduced by synchronizing the two displays and segmenting the backlight. That is, during the refreshing of a given row or set of rows, the backlight can be turned off. As the set of rows is updated for the alternate eye, both in terms of image from the rear display and polarization from the front display, the backlight is turned on for those

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
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rows. The dark period is then only during the refreshing of a set of rows rather than affecting the entire display.

Other Three-Dimensional Display Methods

The discussion of three-dimensional displays so far has involved glasses of one sort or another. Unfortunately, the need for glasses, even the relatively more comfortable passive glasses, is thought to be stifling the broad adoption of these displays. So the question arises as to how to create three-dimensional displays without the need for glasses. There are actually two cases to consider: that of the individual observer and that involving a group of observers. Of the two, the case of the individual observer is the easier, provided that the position from which the individual is observing is known. This may be a reasonable assumption when considering a handheld device. In such a situation, there are several means of alternating the delivery of a left image only to the left eye and a right image only to the right eye. For example, the backlight might have an illumination source on the left and right side within the display, with those sources alternating and being steered by some projection film to one eye, then the other. The far more difficult problem is having a three-dimensional display without the need for glasses when multiple viewers can be positioned in a wide variety of locations. As was mentioned in Chapter 10, the most popular approach is the use of viewing zones created by lenticular arrays.

Touch Displays

The signal detection in capacitive touch displays is dependent on the grid of unit cells, defined by a unique combination of row and column electrodes. When a signal is applied to a row electrode, the proximity of column electrodes results in coupling that can be measured. By sweeping through the rows, measurement can be made of the entire screen.

As illustrated in Figure C.22, the signal radiates a small distance through non-conductive materials, such as the cover glass, and one might say that such coupling projects through the cover glass. This coupling is attenuated by a finger touching the cover glass, which provides a path to ground through the body. This reduction in capacitive coupling can be measured, and based on the readings from each unit cell the center of the touch position or positions can be interpolated to higher resolution than the cell spacing. This imaging of the touch positions has enabled the multi-touch capability.

While the conductors inside the display aperture area must be transparent, outside the display aperture, and beneath the black border that commonly surrounds the display, are metal conductors that have lower resistivity than the ITO, providing for reduced signal loss en route to an integrated circuit (not shown)

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
×

image

FIGURE C.22 Projected capacitive touch operation. (Top) The electric field couples between the source and drain through the dielectric touch panel. (Bottom) A grounding by means of touch effects the coupling and can be used to sense position of the touch. (Not to scale.)

mounted to a flex circuit bonded to the sensor glass with anisotropic conductive film, as shown in Figure C.23.

There have been efforts within the industry to eliminate the separate substrate that is dedicated to the touch sensor function. Of the existing substrates considered for integration with this function, the leading candidates are the underside of the cover glass and the face of the color filter glass.

Although the underside of the cover may seem quite attractive, subtle aspects work against this choice. In particular, touch sensors based on dedicated substrates are typically fabricated on large glass sheets, which are then diced into the smaller sheets needed for the display, even though such large-scale lithography runs counter to the manner in which cover glass is made.

The common way for cover glass to be fabricated achieves high retained strength so that it can survive damage inflicted by everyday use. This is done by putting all surfaces under compression. After cutting the cover to shape, it is then dipped into an ion exchange acid bath where smaller sodium ions are exchanged for larger potassium ions, putting all surfaces under compression. Since glass fails

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
×

image

FIGURE C.23 Dedicated touch sensor glass. SOURCE: Courtesy of Zytronic Displays Limited.

under tension, not compression, the compressive stress layer increases damage resistance.

Unfortunately, dipping the entire cover in the acid bath results in all exposed glass surfaces becoming ion exchanged, not just the large front and back faces. If a large sheet of uncut cover glass were to be ion exchanged, after which the transparent conductors were patterned, dicing individual covers from the large sheet would be difficult because the sheet already had been ion exchanged. Even if success in dicing were achieved, this still would be problematic because none of the exposed edges would have been ion exchanged, and thus central tension would be exposed. As integrating touch into the cover is difficult, the face of the color filter glass is an alternative location to consider. However, the fundamental challenge here is that the switching noise from the transistors painting the display image can be coupled

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
×

into the touch electrodes. Designers of touch ICs have made some progress toward devising schemes to avoid and/or reject such noise.23

One of the implications of integrating touch into the face of the LCD’s color filter glass is the elimination of air gaps. Although the dedicated touch substrate is commonly bonded directly to the cover glass, the bonded assembly itself is only sometimes bonded to the front polarizer of the display. Such direct bonding results in additional coupling of display noise, which is a particularly challenging problem with larger displays, like those of tablets, since ITO is such a poor conductor. As a result, although direct bonding can improve optical transmission by eliminating Fresnel reflections on either side of the air gap, eliminating the air gap is more challenging with larger displays because of problems with achieving high yields with this process.

These weaknesses and those mentioned in Chapter 10 have motivated inventors to look for other technologies to compete with projected capacitive.

As mentioned in Chapter 10, optical touch displays have limitations. However, the size and conductivity of the touching object in such a system are immaterial, and there is no reduction in optical transparency as there is with the not-completely-transparent conductors and any air gap of a projected capacitive touch system; see Figure C.24. However, optical touch capability has not been achieved on a large scale and—while the multi-touch experience is now commonly expected because of the widespread use of modern handheld devices—has yet to be developed.

Display Frames

A trend in the use of LCDs in arrays is the reduction in the gap, or bezel, between the pixels of adjacent displays for application in video walls. Although still not completely seamless, gaps have been reduced to the single-digit millimeter range, as represented in Figure C.25. This change benefits the image quality, but it has repercussions for touch. In particular, a cover glass can be bonded to a relatively wide bezel, but as that bezel shrinks, it becomes less feasible to use the bezel as a mount. Although very narrow brackets might be used to affix cover glass to large-format displays, in time that might change to direct bonding of cover glass.

This prospect has numerous challenges, such as cutting the glass after ion exchange as mentioned above in the discussion of integrated touch. Thermal expansion would be an additional challenge, as current color filter substrates match the thermal expansion of the glass with the thin-film transistors (TFTs), which are

_________________

23 See, for example, “Development of IPS LCD with Integrated Touch-Panel by Hitachi Displays.” 2010. Available at http://japantechniche.com/2010/10/08/development-of-ips-lcd-with-integrated-touch-panel-by-hitachi-displays/. Accessed July 27, 2012.

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
×

image

FIGURE C.24 Optical sensors in the upper corners of the array detecting touch. SOURCE: NextWindow. 2012. “Optical Touch Overview.” Available at http://www.nextwindow.com/optical/. Reprinted with permission.

image

FIGURE C.25 Narrow-bezel liquid-crystal display array. SOURCE: Courtesy of NEC Display Solutions of America.

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
×

switched to control the light valves that form the image. As these transistors are based on silicon, the glass substrate material is chosen to match the coefficient of thermal expansion of silicon, which is relatively low. Cover glass, by contrast, has relatively high thermal expansion, as this is currently thought necessary to achieve a glass capable of ion exchange. Nevertheless, if an internal polarizer were to be achieved, researchers would be highly motivated to create a glass that combines cover and color filter functionality.

OLED Displays

In order to form a light-emitting device, the light-emitting organic layer of an organic light-emitting diode (OLED) requires several other layers. These include a transparent substrate, which can be either rigid or flexible, depending on the application; a transparent conducting anode; a conducting organic layer; the organic light-emitting layer; and a cathode, which may or may not be transparent, depending on the application.

In operation, an electrical potential is applied across the OLED by connecting a battery or other power source between the cathode and the anode, causing a current to flow. The current flow results in electrons being removed from the molecules in the emissive organic layer, creating holes. When these holes are filled at the interface with the conducting organic layer, the electrons give up their excess energy as photons. The intensity of the emitted light is determined by the total current flow, and the color is determined by the energy level of the hole that is filled by the electrons. This, in turn, is determined by the properties of the organic molecules, allowing OLEDs to be used in color displays.

OLEDs can be made on transparent substrates to form an all-transparent display, or on an opaque or reflective substrate. In the former case, it makes possible what is known as a heads-up display, since only the displayed information interrupts the visual field.

Flexible Displays

“Flexible display technology” is a term used for a desirable technology for the next generation of cell phones, military devices, and reading devices. A device with flexible display technology would enable the user to overcome the fear of breaking, bending, or scratching the device.

One type of flexible display technology uses organic films constructed from OLEDs, which in turn are made from layers of organic material and the conductive materials needed to inject electrons and holes. When a voltage of proper polarity is applied to the conductive layers, electrons from one layer combine with the holes

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
×

from the other, releasing light. If these OLEDs were constructed from polymers with high flexibility, they could be the basis of lightweight, portable, rollup displays, or displays that could be used on curved surfaces.

Another promising material technology is amorphous oxides. Some amorphous oxides can form thin films that are transparent and electrically conductive, which is why they already serve as the see-through electrode layer in displays and solar cells. It was this combination of qualities that led to the surge in research that began in 1996, when Hideo Hosono and his colleagues at the Tokyo Institute of Technology first noted the merits of amorphous transparent conducting oxides. The biggest problem when amorphous silicon is deposited on flexible plastic is switching and drifts.

Amorphous oxides could do more than simply serve as passive electrodes. They could also replace amorphous silicon as the active semiconducting material in TFTs. The advantages of oxide semiconductors over amorphous silicon are motivating much work in the display industry. Only 2 years after the first oxide-based transistors were reported, Korea’s LG Electronics Co. revealed a prototype OLED display that used indium gallium zinc oxide (IGZO) transistors to drive its pixels. Other companies followed quickly, with oxide-based displays of their own. The U.S. $100 billion flat-panel-display industry has been built on amorphous silicon, and the new materials will have to compete with its 30-year head start. However, amorphous silicon is a mature technology, and most limitations arise from fundamental physical and chemical properties requiring breakthroughs.

Amorphous oxide semiconductors will likely challenge amorphous silicon. When this will happen depends mainly on the development time for a large-scale

image

FIGURE C.26 Crystalline, polycrystalline, and amorphous atomic structures. SOURCE: Reprinted, with permission, from Wager, J.F., and Hoffman, R. 2011. Thin, fast, and flexible. IEEE Spectrum 48(5). Copyright 2011 by IEEE.


Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
×

manufacturing capability incorporating these materials. However, the oxide TFT fabrication process is very similar to that used for amorphous (for atomic structures, see Figure C.26) silicon devices; thus the display industry can leverage much of the existing infrastructure and know-how. A key advantage amorphous oxides hold over amorphous silicon is their higher charge-carrier mobility.

Suggested Citation:"Appendix C: Additional Technology Examples." National Research Council. 2013. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press. doi: 10.17226/13491.
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Optics and photonics technologies are ubiquitous: they are responsible for the displays on smart phones and computing devices, optical fiber that carries the information in the internet, advanced precision manufacturing, enhanced defense capabilities, and a plethora of medical diagnostics tools. The opportunities arising from optics and photonics offer the potential for even greater societal impact in the next few decades, including solar power generation and new efficient lighting that could transform the nation's energy landscape and new optical capabilities that will be essential to support the continued exponential growth of the Internet.

As described in the National Research Council report Optics and Photonics: Essential Technologies for our Nation, it is critical for the United States to take advantage of these emerging optical technologies for creating new industries and generating job growth. The report assesses the current state of optical science and engineering in the United States and abroad--including market trends, workforce needs, and the impact of photonics on the national economy. It identifies the technological opportunities that have arisen from recent advances in, and applications of, optical science and engineering. The report also calls for improved management of U.S. public and private research and development resources, emphasizing the need for public policy that encourages adoption of a portfolio approach to investing in the wide and diverse opportunities now available within photonics.

Optics and Photonics: Essential Technologies for our Nation is a useful overview not only for policymakers, such as decision-makers at relevant Federal agencies on the current state of optics and photonics research and applications but also for individuals seeking a broad understanding of the fields of optics and photonics in many arenas.

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