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4 Defense and National Security INTRODUCTION Many technological opportunities have been made possible by the advances in optics and photonics since the National Research Council’s (NRC’s) publication in 1998 of Harnessing Light: Optical Science and Engineering for the 21st Century.1 Because optics and photonics are playing an increasingly important role in national defense, the United States is at a critical juncture in maintaining technological superiority in these areas. The gap between sophisticated and less sophisticated adversaries is not as large as it once was, and provides little or no advantage in several key technical areas, such as conventional night-vision equipment. Sensor systems are becoming the next “battleground” for dominance in intelli- gence, surveillance, and reconnaissance (ISR), with optics-based sensors represent- ing a significant fraction of ISR systems.2 In addition, laser weapons are poised to cause a revolution in military affairs, and integrated optoelectronics is on the verge of replacing many traditional integrated circuit functions. Sophisticated platforms have reduced the need for a large set of traditional warfighters, but there is an in- creased need for a high-tech workforce to support those platforms. This workforce 1 National Research Council. 1998. Harnessing Light: Optical Science and Engineering for the 21st Century. Washington, D.C.: National Academy Press. 2 Details of additional defense and national security technologies may be found in Appendix C in this report. Topics covered include surveillance; night vision; laser rangefinders, designators, jam- mers, and communicators; laser weapons; fiber-optic systems; and special techniques focusing on chemical and biological species detection, laser gyros for navigation, and optical signal processing. 102
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Defense and N at i o na l S e c u r i t y 103 relies on advanced training in technical areas with a basis in science, technology, engineering, and mathematics (STEM), which are precisely the areas in which it is becoming more difficult to find continued optics and photonics education in the United States. The ability of U.S. defense forces to leverage technology for dominance while using a small force is also threatened by an ongoing migration of optics and photonics capabilities to offshore manufacturing sites. This means that the United States may lose both first access and assured access to new optics and photonics defense capabilities. Although conventional night-vision imagers have become commodities avail- able to anyone with money, more sophisticated optical-based surveillance systems have made major progress in the past decade and provide a great opportunity. A number of very-wide-field-of-view passive sensor systems have been developed and are discussed in this chapter. It is now possible by using such systems to view large areas with moderate to high resolution, especially during the day. Large por- tions of a city can thus be continuously monitored and the data from the system stored. If something of interest occurs, it is possible to re-examine that event to determine exactly what happened. Once areas of interest have been detected, it would be useful to have exquisite detail in certain critical areas, highlighted by the wide-area detection sensor. There have recently been long-range identifica- tion demonstrations using active electrooptical (EO) systems called laser radar, or ladar. Although synthetic aperture radar (SAR) has been around for decades, it is only recently that synthetic aperture ladar systems have been flown. These are briefly discussed below. Multiple sub-aperture-based, potentially conformal, active sensor developments are also discussed. This is a developing technology that will allow lighter-weight, long-range imaging systems that can also be applied to laser weapons. After an object has been detected and identified, it may be recognized as a threat that has to be dealt with. “Speed-of-light” weapons are ideal choices for certain applications, such as for a boosting missile. These laser weapons can destroy a boosting ballistic missile, causing whatever warhead is on the missile to fall back on the nation that fired the missile. Recently the Airborne Laser Test Bed (ALTB)3 shot down a boosting ballistic missile with an onboard laser for the first time. Although this was a highly successful test, it was done with a chemical laser, using a mixture of oxygen iodine as the gain medium. There is strong interest in and great potential for laser weapons that run on electricity. If sufficient electricity can be generated from onboard fuel, one could use the same fuel, already in use. Multiple all-electric laser options are briefly discussed below. The three areas just referred to have made major progress over the last decade, 3 More information on the Airborne Laser Laboratory is available at http://www.fas.org/spp/ starwars/program/all.htm (accessed November 22, 2011) and http://boeing.mediaroom.com/index. php?s=43&item=1075 (accessed November 7, 2012).
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104 Optics and Photonics: Essential Technologies for O u r N at i o n but they have been pursued as stovepiped activities. A laser weapon needs to detect a potential target, the target must be identified, and an aim point must be selected and maintained. Additionally, as communication between sensors producing “in- put” about a situation and systems taking action (output) needs to be faster, there is a technological need to put these sensors and systems as close together as possible. The committee believes that there is significant synergy between these activities and that photonics technologies will be an integral part of this new integrated system capability. Over the last decade, significant work has evolved on silicon photonics, to closely integrate optics and electronics in a cost-effective manner, as was discussed in the previous chapter, on communications. Most of this work has been driven by communications needs, but it will be an enabler for the defense arena as well. Optics is becoming integrated in defense systems other than optical systems, such as into microwave radars, using radio-frequency (RF) photonics. It is anticipated that more and more areas of defense “electronics” will become defense optoelectronics. OPTICS AND PHOTONICS: IMPACT ON DEFENSE SYSTEMS There is virtually no part of a modern defense system that is not impacted in some way by optics and photonics, even when the system is not optically based. Modern defense systems are migrating toward optically based imaging, remote sensing, communications, and weapons. This trend makes maintaining leadership in optics and photonics vital to maintaining the U.S. position in defense applica- tions. Additional areas of impact include the following: precision laser machining, optical lithography for electronics, optical signal interconnects, solar power for remote energy needs, and generation of a stable timebase for the Global Positioning System (GPS). Even when the actual sensor is not optics-based, in many cases optics plays an important role, such as the migrating of RF photonics into microwave radar systems mentioned above. TECHNOLOGY OVERVIEW There have been significant advances in optics and photonics for national de- fense both in components and in systems since the publication of Harnessing Light in 1998.4 Some of the key areas include surveillance, night vision, laser systems, fiber-optics systems, chemical and biological detection, and optical processing. One example of a significant advance in component technologies is laser diode efficiency, which has directly impacted the efficiency of laser systems. In addition, there has been significant progress in both laser power and available wavelengths 4 National Research Council. 1998. Harnessing Light.
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Defense and N at i o na l S e c u r i t y 105 for applications important to national defense. These advances in laser technology have also enabled several significant system advances. One example is the area of optical aperture synthesis, which rapidly went from the laboratory to flight sys- tem demonstrations within several years during the period since Harnessing Light appeared. While the advances described above have enabled new capabilities for the United States, they have also narrowed the technology gap for adversaries. Impor- tantly, the proliferation of low-cost, high-powered lasers has provided inexpensive countermeasures for adversaries. One example is the use of high-powered handheld laser pointers as laser dazzlers against helicopter pilots, causing a bedazzled pilot to become temporarily blinded or disoriented. The low cost and abundance of these devices put them in anyone’s reach. Changes Since the Harnessing Light Study This section briefly discusses the changes in each of the areas that were ad- dressed in Chapter 4, “Optics in National Defense” in the NRC’s 1998 report Har- nessing Light. For a more detailed discussion of these topics, see Appendix C in this report. The most significant changes have been due to the advances made in optical components that have enabled new sensors to be developed and demonstrated (see the section below entitled “Identification of Technological Opportunities from Recent Advances”). The following subsections 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). Surveillance Surveillance still plays a critical role in detecting and assessing hostile threats to the United States. The progress in optical sensors over the past decade has created an exponential growth in ISR data from both passive and active sensors, including an increase in area coverage rate and an increase in sensor capabilities and performance. As the Defense Advanced Research Projects Agency (DARPA) chief Regina Dugan puts it, “We are swimming in sensors and drowning in data.”5 Materials advances have made collection at new wavelengths feasible, and improved components provide new data signatures, including vibrometry, polarimetry, hy- per-spectral signatures, and three-dimensional data that mitigate camouflage for targets of interest. 5 Comment can be found in Norris, P. 2010. Watching Earth from Space: How Surveillance Helps Us—and Harms Us. Chichester, U.K.: Praxis Publishing.
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106 Optics and Photonics: Essential Technologies for O u r N at i o n Night Vision The proliferation of night-vision equipment over the past few decades has led to a significant amount of surplus equipment available at very low cost. This equipment has eroded the tactical advantage that the United States previously had in this area of warfare during the night. Laser Rangefinders, Designators, Jammers, and Communicators The significant increase in laser diode efficiency coupled with the decrease in cost has enabled recent advances in the area of laser designators. One of the key motivators for moving to, for example, optical communications, is that they minimize the probability of interception, jamming, and detection, while dramati- cally minimizing the power needed. The improved efficiency and availability of high-powered lasers at a broader range of wavelengths has also enabled the de- velopment of countermeasure systems for several applications, including defense against the now-prolific man portable air defense systems (MANPADS) capabilities that threaten commercial and military aircraft. The specific developments are not covered in detail in this report. Laser Weapons The Missile Defense Agency demonstrated the potential use of directed energy to defend against ballistic missiles when the Airborne Laser Test Bed successfully destroyed a boosting ballistic missile on February 11, 2010. As discussed in a Missile Defense Agency news release,6 this revolutionary use of directed energy is very at- tractive 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 current technologies (see Figure 4.1). Since publication of the 1998 NRC report, there have also been other successful demonstrations, including the Tactical High Energy Laser (THEL),7 the Mobile Tactical High Energy Laser (MTHEL), and the Maritime Laser Demonstrator (MLD).8 6 Missile Defense Agency, U.S. Department of Defense. 2010. “Airborne Laser Test Bed Successful in Lethal Intercept Experiment.” MDA news release. Available at http://www.mda.mil/news/10news 0002.html. Accessed August 2, 2012. 7 Shwartz, J., J. Nugent, D. Card, G. Wilson, J. Avidor, and E. Behar. 2003. Tactical high energy laser. Journal of Directed Energy 1(1):34-47. 8 More information is available through the Office of Naval Research, at http://www.onr.navy.mil/ Media-Center/Press-Releases/2011/Maritime-Laser-MLD-Test.aspx. Accessed June 4, 2012.
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Defense and N at i o na l S e c u r i t y 107 (a) (b) FIGURE 4.1 Airborne Laser Test Bed (ALTB). (a) The ALTB is a platform for the Department of De- fense’s directed-energy research program. Two solid-state lasers and a megawatt-class chemical oxygen iodine laser (COIL) are housed aboard a modified Boeing 747-400 Freighter. (b) An infrared image of the Missile Defense Agency’s Airborne Laser Test Bed (at right in the image) destroying a threat representative short-range ballistic missile (at left in the image). SOURCE: Images available from the Missile Defense Agency, at http://www.mda.mil/news/gallery_altb.html. Fiber-Optic Systems Fiber-optic systems have continued to evolve to achieve higher performance with lower power in a smaller volume. In addition, fiber-based supercontinuum sources have significantly advanced since the advent of photonic-crystal fibers (PCFs) in 1996.9 PCFs simultaneously provide high nonlinearity and a variable zero dispersion wavelength for a broadband continuum that can span more than an octave. Since the NRC’s 1998 report Harnessing Light, these sources have gone from concept, to demonstration, and finally to commercial products. Special Techniques The special techniques (i.e., chemical and biological species detection and opti- cal signal processing) evaluated in the 1998 Harnessing Light 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 circuits should enable significant advances in optical signal processing over the next decade. Chemical and Biological Species Detection. Weapons of mass destruction, includ- ing nuclear, biological, and chemical weapons, continue to be a high-priority threat. Long-range chemical and biological detection has advanced considerably since the 9 Knight, J., T. Birks, P. Russell, and D. Atkin. 1996. All-silica single-mode optical fiber with pho- tonic crystal cladding. Optics Letters 21:1547.
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108 Optics and Photonics: Essential Technologies for O u r N at i o n NRC’s 1998 Harnessing Light report. 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 kilometers (km) in a 180-degree arc and to discriminate clouds with biological content from clouds without biological material at distances of 1 to 3 km or more. Optical Signal Processing. Optical signal processing has not changed very much since the NRC’s 1998 report was issued. Optical processing 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. The most promising advances are discussed below, in the section entitled “Integrated Optoelectronics.” Identification of Technological Opportunities from Recent Advances As the military capabilities of other countries have been expanding quickly, sensor systems are becoming the next battleground for dominance in ISR, as noted above. Advanced systems have reduced the reliance on the traditional warfighter so that now there is a need for a more technologically focused personnel. The data generated by deployed sensor systems have grown significantly due to the advances in sensor capabilities. This change has allowed new intelligence data products, but it has also driven the need for more sophisticated data processing and transmission in order to handle these data rates. The following subsections provide an overview of opportunities in synthetic aperture laser radar, multi-mode laser sensing, sparse aperture laser sensing, wide-area surveillance sensors, Geiger-mode imaging, and hyper-spectral sensing. Synthetic Aperture Laser Radar The diffraction limit presents a significant limitation on cross-range resolution for long-range remote sensing applications. Synthetic aperture sensing and analysis techniques provide a method of overcoming this limitation in some applications requiring high-resolution coherent images at great distances. These techniques have been employed in the RF domain for many years in synthetic aperture radar systems. Only in the past several years have advances in simultaneously stable and widely tunable coherent optical systems enabled the application of SAR techniques to the optical domain, allowing a potential for greatly improved illumination ef- ficiency and image acquisition time. As pointed out by Beck et al. in their paper “Synthetic-Aperture Imaging Laser Radar: Laboratory Demonstration and Signal Processing,” the first Synthetic Aperture Imaging Ladar (SAIL) image of a fixed, dif-
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Defense and N at i o na l S e c u r i t y 109 fusely scattering target with a moving aperture10 demonstrated the use of a chirped optical source to provide a demonstration with 60-micron-range resolution and 50-micron cross-range resolution. The earliest synthetic aperture experiments11 in the optical domain were performed at the United Aircraft Research Laboratories in the late 1960s, using inverse techniques to focus a moving point target. Another experiment12 used a technique to perform synthetic aperture imaging in two di- mensions. A later effort13 used a continuous wave Nd:YAG microchip laser to dem- onstrate inverse-SAIL imaging in one dimension together with diffraction limited conventional imaging in the other dimension (with an asymmetric high-aspect- ratio aperture) to produce two-dimensional images. Other demonstrations14,15 achieved one-dimensional SAIL imaging of a point target, using a continuous wave CO2 system, and a two-dimensional inverse-SAIL image of a translated target.16 More recent efforts include the DARPA Synthetic Aperture Ladar for Tactical Im- aging (SALTI) Program.17 The progress from laboratory to flight demonstration within several years shows that optical synthetic aperture imaging is becoming a valuable technology, with several recent additional advancements in combining synthetic aperture imag- 10 Beck, S.M., J.R. Buck, W.F. Buell, R.P. Dickinson, D.A. Kozlowski, N.J. Marechal, and T.J. Wright. 2005. Synthetic-aperture imaging laser radar: Laboratory demonstration and signal processing. Ap- plied Optics 44:7621-7629. 11 Lewis, T.S., and H.S. Hutchins. 1970. A synthetic aperture at 10.6 microns. Proceedings of the IEEE 58:1781-1782. 12 Aleksoff, C.C., J.S. Accetta, L.M. Peterson, A.M. Tai, A. Klossler, K.S. Schroeder, R.M. Majewski, J.O. Abshier, and M. Fee. 1987. Synthetic aperture imaging with a pulsed CO2 TEA laser. In Laser Radar II. Becherer R.J., and R.C. Harney, eds. Proceedings of the SPIE 783:29-40. 13 Green, T.J., S. Marcus, and B.D. Colella. 1995. Synthetic-aperture-radar imaging with a solid- state laser. Applied Optics 34(30):6941-6949. 14 Yoshikado, S., and T. Aruga. 2000. Short-range verification experiment of a trial one-dimensional synthetic aperture infrared laser radar operated in the 10-µm band. Applied Optics 39(9):1421-1425. 15 Bashkansky, M., R.L. Lucke, E. Funk, L.J. Rickard, and J. Reintjes. 2002. Two-dimensional syn- thetic aperture imaging in the optical domain. Optics Letters 27:1983-1985. 16 Using 10 nm of near-linear optical chirp at 1.5 microns with an analog reference channel (to mit- igate waveform uncertainties) with path length exactly matched to the target channel’s path length. 17 Dierking, M., B. Schumm, J.C. Ricklin, P.G. Tomlinson, and S.D. Fuhrer. 2007. Synthetic aperture LADAR for tactical imaging overview. Proceedings of the 14th Coherent Laser Radar Conference 191- 194. Available at http://toc.proceedings.com/05549webtoc.pdf. Accessed June 27, 2012.
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110 Optics and Photonics: Essential Technologies for O u r N at i o n ing and digital holography.18,19,20 Another flight demonstration21 has shown that the techniques are well understood and can be implemented with near-real-time processing. Applying aperture synthesis techniques to the optical domain provides two significant advantages: (1) improved image acquisition time and (2) illumination efficiency.22 Improvement in illumination efficiency can be understood by consid- ering that illuminating only a 10-m-diameter area of interest with a 10 gigahertz (GHz) signal at a range of 100 km would require a transmit aperture of approxi- mately 300 m for the RF case, compared to approximately 1.5 centimeters (cm) for an optical system with a wavelength of 1.5 microns. It is clear that this technology has the potential to be further developed and that it can provide additional benefits if it is combined directly with defensive systems. Multi-Mode Laser Sensing Multi-function sensors seek to exploit the maximum information that a laser- based sensor can obtain by incorporating several functions into a single sensor (e.g., three-dimensional imaging, vibrometry, polarimetry, aperture synthesis, agile apertures, etc.). Ideally these sensors utilize waveforms matched to the require- ments of both the hardware (e.g., optical amplifiers, modulators) and the targets being imaged. Recent demonstrations23 have achieved 7-millimeter (mm)-range resolution (0.1-mm-range precision) along with simultaneous vibrometry.24 The inherent multi-functionality of these systems allows maximal use of available ap- erture, volume, and power. Therefore, a multi-function system will enable practi- cal, high-performance ladar remote sensing systems with scalable, reconfigurable 18 Stafford, J.W., B.D. Duncan, and M.P. Dierking. 2010. Experimental demonstration of a stripmap holographic aperture ladar system. Applied Optics 49:2262. 19 Duncan, B.D., and M.P. Dierking. 2009. Holographic aperture ladar. Applied Optics 48:1168. 20 Rabb, D.J., D.F. Jameson, J.W. Stafford, and A.J. Stokes. 2010. Multi-transmitter aperture synthe- sis. Optics Express 18:24937. 21 Krause, B., J. Buck, C. Ryan, D. Hwang, P. Kondratko, A. Malm, A. Gleason, and S. Ashby. 2011. “Synthetic Aperture Ladar Flight Demonstration.” Conference paper. CLEO: Applications and Tech- nology (CLEO: A and T), Baltimore, Md., May 1, 2011. Available at http://www.opticsinfobase.org/ abstract.cfm?uri=CLEO:%20A%20and%20T-2011-PDPB7. Accessed June 27, 2012. 22 For a given cross-range resolution, the image acquisition time scales with the carrier wavelength. For an RF system with l = 3 cm, vplatform = 100 m/s, R = 100 km, and dx = 1 cm, the image collection time would be 1500 sec for the required baseline of 150 km. For an optical system with l = 1550 nm, the same specifications require a baseline of 7.75 m with an image collection time of 78 ms. 23 Buck, J., A. Malm, A. Zakel, B. Krause, and B. Tiemann. 2007. High-resolution 3D coherent laser radar imaging. Proceedings of the SPIE 6550:655002. 24 Buck, J., A. Malm, A. Zakel, B. Krause, and B. Tiemann. 2007. Multi-function coherent ladar 3D imaging with S3. Proceedings of the SPIE 6739:67390F.
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Defense and N at i o na l S e c u r i t y 111 operating modes to obtain spectral, spatial, and temporal information about a target along with information about the target’s depolarization properties. This combined information set can provide an unprecedented ability to characterize targets with a single sensor and shows a possible path for the future development of more complex systems. Sparse Aperture Laser Sensing The use of small-aperture modules can lead to revolutionary optical sens- ing and communications approaches, eliminating large, complex, and expensive apertures.25,26,27,28 Many sub-aperture modules have a much shorter focal length than one large EO aperture with the same F number. As a result, the overall aperture array will be much shallower and will weigh much less than the monolithic system. Phased-array approaches will enable using optical apertures along the surface of a vehicle because of the shallow aperture depth. Small, standard modules can en- able responsive space, with an array of modules stored and ready to be configured and launched. Conformal and structural optical sensing and communications approaches (i.e., those that can be implemented on a platform without modify- ing its skin and thereby avoiding the impacting of platform aerodynamics) can be developed. RF systems already have conformal and structural weight-bearing RF apertures. A conformal array system is robust to element failure, which is impor- tant for system operation in hazardous environments. In conformal systems, beam focusing and retargeting can be performed using fast control of wave-front phase tip and tilt at each conformal system sub-aperture.29 This would allow orders-of- magnitude faster retargeting of the outgoing or received optical waves. With con- formal optical systems, atmospheric turbulence-induced phase distortions can be pre-compensated using adaptive optics (AO) elements that are directly integrated 25 McManamon, P.F. 2008. “Long Range ID Using Sub-Aperture Array Based Imaging.” Confer- ence paper. Coherent Optical Technologies and Applications (COTA), Boston, Mass., July 13, 2008. 26 McManamon, P.F., and W. Thompson. 2003. Phased array of phased arrays (PAPA) laser systems architecture. Fiber and Integrated Optics 22(2):79-88. 27 McManamon, P.F. 2004. “The Vision of Optical Phased Array and Phased Array of Phased Ar- rays.” Conference paper. SPIE Great Lakes Photonics Symposium, Cleveland, Ohio, June 8, 2004. 28 McManamon, P.F., and W. Thompson. 2002. Phased array of phased arrays (PAPA) laser systems architecture. IEEE Aerospace Conference Proceedings 3:1465-1472. 29 Vorontsov, M.A., T. Weyrauch, L. Beresnev, G. Carhart, L. Liu, S. Lachinova, and K. Aschenbach. 2009. Adaptive array of phase-locked fiber collimators: Analysis and experimental demonstration. IEEE Journal of Selected Topics in Quantum Electronics 15:269-280.
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112 Optics and Photonics: Essential Technologies for O u r N at i o n into individual sub-apertures. This enables the cost-effective integration of AO capabilities into conformal optical systems.30,31 Spatial heterodyne, a form of digital holography, is also being developed as a method of active imaging with high-resolution multiple sub-apertures and framing cameras.32,33,34,35 This is a new area with potential significant advantages, and it is anticipated that multiple-sub-aperture-based imaging will grow over time. Wide-Area-Surveillance Sensors One of the developments that will make a difference in U.S. military capa- bility is wide-area surveillance, especially for cities. The U.S. military has a great surveillance capability in open spaces, but cities, in which there are many non- combatants, present a new problem. From a security point of view, in cities there is a large amount of “clutter” in terms of buildings and people. The ability to watch everything all the time in a city improves the ability to do surveillance, especially when one can store the imagery and replay it at any time. A number of wide-area- surveillance systems are being developed. One example is an airborne system de- veloped in concert with the Philadelphia Police Department to show the value of such a system.36 The system was flying over a troubled neighborhood for one day as a test. When a woman got home from work she called the police to report that her house had been broken into during the day. The police reviewed the imagery collected that day and could see someone enter and leave the house around 2:00 p.m. They could trace the person who left the house to another house 8 blocks away. This imagery provided sufficient proof for a warrant to search the house to which the person was traced, and there the stolen goods were found and an arrest 30 Vorontsov, M.A., and S.L. Lachinova. 2008. Laser beam projection with adaptive array of fi- ber collimators. I. Basic considerations for analysis. Journal of the Optical Society of America A 25:1949-1959. 31 Lachinova, S.L., and M.A. Vorontsov. 2008. Laser beam projection with adaptive array of fiber collimators. II. Analysis of atmospheric compensation efficiency. Journal of the Optical Society of America A 25:1960-1973. 32 Marron, J.C., and R.L. Kendrick. 2007. Distributed aperture active Imaging. Proceedings of the SPIE 6550:65500A. 33 Rabb, D.J., D.F. Jameson, A.J. Stokes, and J.W. Stafford. 2010. Distributed aperture synthesis. Optics Express 18:10334-10342. 34 Marron, J.C., R.L. Kendrick, N. Seldomridge, T.D. Grow, and T.A. Höft. 2009. Atmospher- ic turbulence correction using digital holographic detection: Experimental results. Optics Express 17:11638-11651. 35 Miller, N.J., J.W. Haus, P. McManamon, and D. Shemano. 2011. Multi-aperture coherent imag- ing. Proceedings of the SPIE 8052:8052-8056. 36 Written communication to the committee, October 25, 2011, from the President of Persistent Surveillance Systems.
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116 Optics and Photonics: Essential Technologies for O u r N at i o n Hyper-Spectral Sensing Hyper-spectral imaging is an extreme form of color imaging. People are very familiar with color imaging. We all know that spotting a bright red object lying on a green lawn is much easier than seeing a green object on a green lawn. Color in an image can be divided into many wavebands for more resolution. One of the significant issues associated with multi- or hyper-spectral imaging is whether or not one needs to see at night. Daytime viewing uses the visible and near-infrared regions of the spectrum, where as nighttime viewing requires detectors for longer wavelengths. Although there is a phenomenon called night glow46 in the near- infrared, and often in man-made lighting or light from the Moon, reliable view- ing requires moving to the mid- or long-wave infrared (IR). Most of the current commercial applications of spectral, or hyper-spectral, imaging use the visible and near-IR regions. Multi- or hyper-spectral imaging can be used for telling the status of crops, for finding minerals, and for surveillance. Spectral information is always valuable for looking at surface material properties. In addition, hyper-spectral imaging technol- ogy is very useful for search-and-rescue applications.47 One of the disadvantages of hyper-spectral imaging is signal availability, because the narrow bands provide limited signal for a passively illuminated scene. For hyper-spectral imaging, the resolution of the sensor must be traded with the available signal levels. Defense Systems Defense systems (laser weapons) have made great progress since the 1998 NRC report was issued. The Airborne Laser Laboratory (ABL) intercepted two ballistic missiles in February 2010 (see Figure 4.1)48 with the megawatt-class oxygen iodine laser emitted from the nose of the aircraft. After this successful test, ABL was con- verted to the Airborne Laser Test Bed to explore issues associated with potential follow-on activities. As of this writing, no follow-on activity has been identified. Until April 2009, ABL was on a path to deployment in small numbers. However, 46 Barber, D.R. 1957. A very early photographic observation of the spectrum of the night glow. Nature 179(4556):435. 47 Eismann, M.T., A.D. Stocker, and N.M. Nasrabadi. 2009. Automated hyperspectral cueing for civilian search and rescue. Proceedings of the IEEE 97(6):1031-1055. 48 Wolf, Jim, and David Alexander. 2010. “U.S. Successfully Tests Airborne Laser on Missile.” Available at http://www.reuters.com/article/2010/02/12/usa-arms-laser-idUSN1111660620100212? type=marketsNews. Accessed October 26, 2011.
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Defense and N at i o na l S e c u r i t y 117 at that time the second ABL aircraft was recommended for cancellation, with the program to return to a research and development effort.49 Another major laser weapons effort was the advanced tactical laser (ATL), a short-range weapon for use on a gunship-like aircraft, with the laser replacing a gun. In August 2008, the first test-firing of the “high-energy chemical laser” mounted in a Hercules transport plane was announced. In August 2009, a ground target was “defeated” from the air with the ATL aircraft.50 This laser weapon is also based on an oxygen iodine laser, requiring hauling hazardous chemicals to the field. At the time of this writing, there is no planned follow-on effort. Because of the interest in electric-powered lasers that do not require a spe- cialized logistics tail, the High Energy Laser-Joint Technology Office (HEL-JTO) initiated a program to demonstrate a 100-kilowatt (kW)-output, electric-powered laser capable of being used in a laser weapon system, called the Joint High Power Solid State Laser (JHPSSL). As discussed in the December 2010 news release from DARPA entitled “Compact High-Power Laser Program Completes Key Milestone,”51 JHPSSL operated above the rated 100-kW power level for 6 hours.52,53 The goal of the High Energy Liquid Laser Area Defense System (HELLADS) is to demonstrate 150 kW of power in a lightweight package. In June 2011, DARPA completed the laboratory testing of a fundamental building block for HELLADS, a single laser module that successfully demonstrated the ability to achieve high power and beam quality from a significantly lighter and smaller laser.54 Another DARPA program that is developing an approach to laser weapons is the Adaptive Photonic Phase Locked Elements (APPLE) program.55 APPLE uses a modular system (Figure 4.4) to scale the available power, which requires high-powered lasers with sufficiently 49 Gates, Dominic. 2009. “Boeing Hit Harder than Rivals by Defense Budget Cuts. Available at http://seattletimes.nwsource.com/html/localnews/2008997361_defensecuts07.html. Accessed Octo- ber 26, 2011. 50 Boeing. 2009. “Boeing Advanced Tactical Laser Defeats Ground Target in Flight Test.” Available at http://boeing.mediaroom.com/index.php?s=43&item=817. Accessed June 27, 2012. 51 DARPA. 2011. “Compact High-Power Laser Program Completes Key Milestone.” Available at http://www.darpa.mil/NewsEvents/Releases/2011/2011/06/30_COMPACT_HIGH-POWER_LASER_ PROGRAM_COMPLETES_KEY_MILESTONE.aspx. Accessed October 26, 2011. 52 JHPSSL first achieved the 100-kW power levels in March 2009. More information is available at http://www.irconnect.com/noc/press/pages/news_releases.html?d=161575. Accessed June 4, 2012. 53 Optics. 2010. “Northrop’s 100 kW Laser Weapon Runs For Six Hours.” Available at http://optics. org/news/1/7/13. Accessed October 26, 2011. 54 DARPA. 2011. “Compact High-Power Laser Program Completes Key Milestone.” 55 Dorschner, Terry A. 2007. “Adaptive Photonic Phase Locked Elements: An Overview.” Raytheon Network Centric Systems presentation. Available at http://www.dtic.mil/cgi-bin/GetTRDoc?Location =U2&doc=GetTRDoc.pdf&AD=ADA503733. Accessed June 27, 2012.
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118 Optics and Photonics: Essential Technologies for O u r N at i o n FIGURE 4.4 Overview of the Adaptive Photonic Phase Locked Elements (APPLE) system, which uses a distributed fiber laser with a master oscillator power amplifier (MOPA) train and coherently combined beams to scale the optical power while correcting for wavefront errors. NOTE: Stochastic parallel gradient descent (SPGD). SOURCE: Raytheon Co. Reprinted with permission. narrow linewidth for phasing. There are several other efforts to investigate electric laser-based defense systems.56,57,58,59 Free-Space Laser Communications The Air Force 405B program started the thrust toward free-space laser com- munications in 1971 with a goal of 1 gigabit per second (Gb/s) free-space laser communications, with a flight demonstration in 1979. The Department of Defense (DOD) is interested in free-space laser communications for high-speed com- munications with mobile platforms (e.g., aircraft, satellites, ground vehicles, dis- mounted solders). Although the DOD can and does make use of the Internet, there is a strong need to extend high-bandwidth communications to mobile platforms, with RF communications used as the baseline for mobile DOD communications. 56 Optics. 2010. “Northrop’s 100 kW Laser Weapon Runs for Six Hours.” 57 DARPA. 2011. “Compact High-Power Laser Program Completes Key Milestone.” 58 Dorschner, Terry A. 2007. “Adaptive Photonic Phase Locked Elements: An Overview.” 59 Page, Lewis. 2007. “DARPA Looking to Kickstart Raygun Tech.” Available at http://www. heregister. t co.uk/2007/08/23/darpa_laser_blast_cannon_plan. Accessed October 26, 2011.
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Defense and N at i o na l S e c u r i t y 119 At the 2011 Defense Security and Sensing Symposium Fellows luncheon, Larry Stotts, from DARPA, pointed out that the DOD owns 300 megahertz (MHz) of RF bandwidth for communications, which represents the total extent of RF bandwidth legally available to the DOD for communications. The primary disadvantage of free-space optical communications is the limited penetration of significant cloud depths, resulting in DOD programs combining RF and optical communications to maintain continuous link management. Because the technology for laser com- munications is very similar to that of laser radar sensors, both areas have jointly benefited from the advances in each.60 However, it is also believed that there is possible synergy by fully merging optical surveillance technology, laser weapon technology, and free-space laser technology based on the reduced communication paths, close integration of sensors, and increased reliability. Traditionally these areas have been addressed as separate technologies, but since progress has been made in many of these fields, integration can clearly result in additional synergies. Solar Power for Military Applications The military uses a substantial amount of energy in various forms, with sig- nificant logistics complications due to the remote deployment of forces. Reducing the overall cost of energy along with simplifying remote energy-supply methods represents a promising application of solar technologies. The dismounted soldier going into remote areas typically carries a heavy backpack, with batteries represent- ing a significant fraction of the weight. Therefore, the remote charging of batteries is the simplest application of solar power. Because solar power represents one of the primary energy sources for space-based platforms, solar power for space has been one of the sources of funding for very high efficiency solar cells. There is a strong military interest in developing long-dwell platforms, such as the DARPA Vulture program.61 Vulture is supposed to fly continuously for 5 years at an altitude above 60,000 ft and is expected to be solar-powered. Another, similar effort is the NASA Helios work, which has performed demonstration flights of a prototype (see Figure 4.5). Integrated Sensor Is Structure (ISIS) is another long- dwell, high-altitude DARPA program; it uses a blimp with solar cells for power.62 60 Stotts, L.B., L.C. Andrews, P.C. Cherry, J.J. Foshee, P.J. Kolodzy, W.K. McIntire, M. Northcutt, R.L. Phillips, H.A. Pike, B. Stadler, and D.W. Young. 2009. Hybrid optical RF airborne communications. Proceedings of the IEEE 97(6):1109-1127. 61 Defense Industry Daily. 2010. “DARPA’s Vulture: What Goes Up, Needn’t Come Down.” Avail- able at http://www.defenseindustrydaily.com/DARPAs-Vulture-What-Goes-Up-Neednt-Come- Down-04852/. Accessed October 26, 2011. 62 Defense Industry Daily. 2011. “USA’s HAA & ISIS Projects Seek Slow, Soaring Surveillance Su- periority.” Available at http://www.defenseindustrydaily.com/darpas-isis-project-seeks-slow-soaring- surveillance-superiority-updated-02189/. Accessed October 26, 2011.
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120 Optics and Photonics: Essential Technologies for O u r N at i o n FIGURE 4.5 Overview of long-dwell platforms. (Top) The NASA Helios prototype during its test- flight over the Pacific Ocean. SOURCE: Defense Industry Daily. 2010. “DARPA’s Vulture: What Goes Up, Needn’t Come Down.”Available at http://www.defenseindustrydaily.com/DARPAs-Vulture-What- Goes-Up-Neednt-Come-Down-04852/. (Bottom) A depiction of the DARPA Integrated Sensor Is the Structure (ISIS) concept. SOURCE: Defense Industry Daily. 2011. “USA’s HAA & ISIS Projects Seek Slow, Soaring Surveillance Superiority.” Available at http://www.defenseindustrydaily.com/ darpas-isis-project-seeks-slow-soaring-surveillance-superiority-updated-02189/.
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Defense and N at i o na l S e c u r i t y 121 Integrated Optoelectronics For more than 40 years, fulfillment of the promise of a truly integrated opto- electronic circuit—that is, a single-crystal monolithically integrated circuit com- bining lasers, waveguides, modulators, detectors, and amplifiers—has been awaited. Such an advance would enable unprecedented capability for optical systems, much in the same way that electronics have evolved using integrated circuits.63 It is also known that electronic components are susceptible to being influenced by stray electromagnetic radiation, whereas optical components are not affected by most microwave radiation. As more and more of the “circuit” components are converted from electronics to optics, the vulnerability of the U.S. military’s electronic systems to electromagnetic pulse and other electronic vulnerabilities is being reduced. In order for computing power to continue to adhere to Moore’s law, it is likely that the integration of optics and electronics in a single chip will be required (see the discussion in Chapter 3 in this report). However, as speed increases, it is important to integrate optics and electronic functions seamlessly in very close proximity, reducing communication time between functions best done in optics and functions best done in electronics. The most promising advances for defense applications have been in the development of indium phosphide (InP)-based subsystems, which, although more costly than silicon, allow the needed subsystems to be created with a single material. There is currently very little InP work being done in the United States, and limited trusted foundries are suitable for these ap- plications. The potential for scaling processing power beyond that possible with electronics, along with the reduction in electromagnetic interference and power requirements, makes this a very promising technology for dealing with the large data rates being generated with new optical sensors. MANUFACTURING In order for the United States to maintain leadership in advanced defense systems, it is critical for the nation to be at the forefront of both research and manufacturing. Defense systems have unique needs that require both first access and assured access to important technology components, and both types of access are compromised if the manufacturing capabilities do not exist within the United States. There has been a steady migration of photonics manufacturing overseas64 at precisely the same time that these technologies are becoming critical in defense applications. Some of this migration has been driven by the need to cut costs for high-volume consumer products, but there is an alarming shift of manufacturing 63 Yariv, A. 1981. Integrated optoelectronics. Engineering and Science 44(3):17-20. 64 NAS-NAE-IOM. 2007. Rising Above the Gathering Storm: Energizing and Employing America for a Brighter Economic Future. Washington, D.C.: The National Academies Press.
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122 Optics and Photonics: Essential Technologies for O u r N at i o n for critical items due to the International Traffic in Arms Regulations (ITAR). Al- though these regulations were originally designed to keep critical technologies out of the hands of adversaries, their current implementation has created an incentive for companies to move manufacturing overseas in order to be well positioned for commercial applications of their technologies. This has resulted in some companies moving the related research and development efforts to be near the manufactur- ing for a more rapid development cycle. A previous National Research Council study has reported on the impacts of ITAR controls on U.S. technology.65 With insufficient funding from the DOD to maintain first and assured access to many critical photonics components, companies are unable to maintain a manufacturing capability when potentially larger commercial markets are restricted. Manufactur- ing for cutting-edge photonics has become increasingly globalized over the past several years, and ITAR controls have not been changed to reflect these shifts. The committee understands that the ITAR issue is very complex in scope and cannot even begin to be fully addressed in this report, but the committee also recognizes that the issue directly affects the defense optics and photonics community in a negative fashion. Another important consideration for manufacturing related to defense tech- nologies is the spiral threading of innovations in optics and photonics that feeds itself. For example, improvements in lasers (i.e., stability, agility, and efficiency) and detectors (i.e., arrays, expanded wavelengths, improved efficiency, bandwidth) have enabled new remote sensing capabilities over the past decade. The developments in lasers and detectors have also led to the improved manufacturing of devices, which further improves the devices for sensors, and also improves manufacturing, in a continuous loop. Thus, there are secondary impacts as a consequence of the progressive loss of photonics manufacturing in the United States. U.S. GLOBAL POSITION For many years, the United States has taken for granted its position as one of the leaders in defense technologies. However, several trends have been developing over the past few decades that seriously threaten that position. The military capa- bilities of other countries have been expanding quickly, as sensor systems become the next battleground for dominance in ISR, with optics- and photonics-based sen- sors representing an increasing fraction of ISR systems. During difficult economic times, long-term R&D is an easy target for cuts in favor of shorter-term applica- tions. However, it is the long-term developments that provide the most significant 65 National Research Council. 2008. Space Science and the International Traffic in Arms Regulations: Summary of a Workshop. Washington, D.C.: The National Academies Press.
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Defense and N at i o na l S e c u r i t y 123 advantages for defense applications. The current U.S. position relies on leadership in research, which is also being negatively impacted by the manufacturing trends. The U.S. defense STEM workforce in photonics and other areas will be signifi- cantly diminished owing to retirements over the next decade, whereas the technical workforce of potential adversaries is expanding rapidly.66 For example, the College of Optics and Photonics at the University of Central Florida has only approximately 40 percent U.S. nationals in its graduate optics program,67 and according to the 2009 Program for International Student Assessment (PISA), the United States ranks 17th in science and 25th in mathematics education. Figure 4.6 shows the percent age of U.S. national PhDs in physics in U.S.-based institutions of higher learning between 1969 and 2008. Although optics accounts for only one part of the physics student population, this trend should give a good idea of the percentage of foreign optics graduate students in U.S. graduate schools. These trends in the STEM workforce are creating a tipping point for photonics defense work, with fewer individuals who are capable of obtaining security clear- ances being trained in the United States. If the United States continues to shrink its STEM workforce and market share in photonics, innovations in research will bolster the economy and the defense technology of countries poised to take ad- vantage of those advances. The trends in manufacturing are further straining the U.S. position in photon- ics. It is critical for the United States to be at the forefront of both research and manufacturing in order to maintain a leadership position in photonics for defense applications. The need for first and assured access combined with ITAR controls imposes an additional need on the United States for a U.S.-based manufacturing capability for these technologies. ITAR controls have also hastened the steady migration of photonics manufacturing for advanced technologies overseas, where companies want to be positioned for commercial applications of those technolo- gies. These companies have also begun moving research groups overseas to facilitate a rapid development cycle for such capabilities. Although the ITAR controls were meant to keep critical technologies out of the hands of adversaries, they are reduc- ing the effectiveness of technology development for defense applications. When coupled with the workforce trends, the U.S. position in photonics for defense ap- plications is potentially reaching a tipping point, which must be reversed in order to maintain leadership in critical areas for defense. 66 NAS-NAE-IOM. 2007. Rising Above the Gathering Storm: Energizing and Employing America for a Brighter Economic Future. Washington, D.C.: The National Academies Press. 67 Private communication with Dr. M.J. Soileau, Vice President for Research and Professor of Op- tics, Electrical and Computer Engineering, and Physics, at the University of Central Florida.
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124 Optics and Photonics: Essential Technologies for O u r N at i o n FIGURE 4.6 Citizenship of physics PhDs in U.S. institutions of higher learning from 1969 through 2008. SOURCE: Reprinted, with permission, from Mulvey, Patrick J., and Starr Nicholson. 2011. Phys- ics Graduate Degrees: Results from the Enrollments and Degrees and the Degree Recipient Follow-up Surveys, available at http://www.aip.org/statistics/trends/reports/physgrad2008.pdf. FINDINGS AND CONCLUSIONS Finding: The committee notes that there have been several areas of optics and photonics with significant advancement for defense and security since the NRC’s report Harnessing Light: Optical Science and Engineering for the 21st Century was published in 1998. These areas include the following: · Long-range, laser-based identification capabilities, including multiple ap- erture and synthetic aperture demonstrations, wide-area passive surveil- lance capabilities in the visible and infrared regions, and signal processing capabilities to handle some of the new sensor data; · Long-range, high-powered laser demonstrations from flight platforms for
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Defense and N at i o na l S e c u r i t y 125 intercepting ballistic missiles. Although these programs have had successful demonstrations, the DOD has not set a roadmap for this technology; and · High-speed free-space laser communication. Key Conclusion: There is possible synergy between optical surveillance technol- ogy, laser weapon technology, and free-space laser technology. Because of orga- nizational and funding issues within the Department of Defense, these technical areas have been pursued mostly as separate technologies. Great progress has been made, as highlighted above, but it is likely that a higher level of cooperation can result in additional synergies. Conclusion: The findings of previous National Research Council studies report- ing the potential workforce shortages for the United States in the areas of science, technology, engineering, and mathematics are consistent for the areas of optics and photonics in relation to defense and security. There are additional constraints for the defense workforce, which requires either a sufficient number of qualified U.S. nationals or a new way of leveraging uncleared individuals in the U.S. defense workforce, and will be significantly impacted by a decrease of senior personnel due to the retirement of a disproportionately older workforce over the next 15 years. Conclusion: It is possible that the United States is losing both first access and as- sured access to critical optics and photonics technologies at precisely the same time that these capabilities are becoming a crucial defense technological advantage. This problem, which is not unique to photonics within defense-related technologies and systems, is believed to be primarily due to these factors: · The ongoing migration of optics and photonics capabilities offshore as the manufacture and assembly of these components and systems becomes increasingly globalized; and · The inability of companies to maintain a U.S.-based manufacturing ca- pability for critical technologies when the larger commercial markets are restricted due to ITAR controls, which have not been changed to reflect the globalization of manufacturing for cutting-edge photonics systems and components. Key Finding: Silicon-based photonic integration technologies offer great potential for short-distance applications and could have a great payoff in terms of enabling continued growth in the function and capacity of silicon chips if optics for inter- connection could be seamlessly included in the silicon complementary metal oxide semiconductor (CMOS) platform. It is also highly likely that integrated optoelec-
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126 Optics and Photonics: Essential Technologies for O u r N at i o n tronics in InP is a critical development area with significant growth potential for continuing the advance of defense systems. RECOMMENDATION AND GRAND CHALLENGE QUESTIONS On the basis of the conclusions presented above, the committee makes the following recommendation in order to enable the United States to maintain a competitive position in optics and photonics for security and defense: Key Recommendation: The U.S. defense and intelligence agencies should fund the development of optical technologies to support future optical systems capable of wide-area surveillance, exquisite long-range object identification, high-bandwidth free-space laser communication, “speed-of-light” laser strike, and defense against both missile seekers and ballistic missiles. Practical application for these purposes would require the deployment of low-cost platforms supporting long dwell times. These combined functions will leverage the advances that have been made in high-powered lasers, multi-function sensors, optical aperture scaling, and algo- rithms that exploit new sensor capabilities, by bringing the developments together synergistically. These areas have been pursued primarily as separate technical fields, but it is recommended that they be pursued together to gain synergy. One method of maintaining this coordination could include reviewing the coordination efforts among agencies on a regular basis. This key recommendation leads directly to the third grand challenge question: 3. ow can the U.S. military develop the required optical technologies to sup- H port platforms capable of wide-area surveillance, object identification and improved image resolution, high-bandwidth free-space communication, laser strike, and defense against missiles? Optics and photonics technologies used synergistically for a laser strike fighter or a high-altitude platform can provide comprehensive knowledge over an area, the communications links to download that information, an ability to strike targets at the speed of light, and the ability to robustly defend against missile attack. Clearly this technological opportunity could act as a focal point for several of the areas in optics and photonics (such as camera development, high-powered lasers, free-space communication, and many more) in which the United States must be a leader in order to maintain national security.