in manufacturing (for example, in lithography, machining, cutting, and welding), which have provided improved devices that are used to make improved sensors. That spiral threading of improvements feeds itself. Although the United States tends not to compete well in high-volume manufacturing, there is now a market opportunity for leveraging the application of these improved capabilities, as in the examples above, from consumer devices to address lower-volume niche sensor markets.
There has been a steady progression from RF to optically based sensing, which has advanced significantly since the Harnessing Light appeared in 1998. One example is in synthetic aperture imaging. Synthetic aperture radar (SAR) has been used since the 1950s; however, only in the last decade have advances in photonics enabled simultaneously agile and stable optical sources that have made SAR viable at optical wavelengths. The move to optically based sensing is partially due to the potential for improved resolution made possible by the much shorter wavelength. However, in many systems the resolution requirements are modest. In those cases, the primary motivations are to achieve easily interpreted imaging and improve illumination efficiency. The shorter wavelength enables a smaller illumination area because of diffraction, and the reflectivity at optical wavelengths closely matches what we are accustomed to viewing with our eyes. In contrast, typical SAR images require significant training for interpreting the resulting data.
Since the NRC’s 1998 study, there have been significant advances in emitter and detector materials for practical sources and sensors at new wavelengths. One example is the substantially improved capability at wavelengths near 2 µm, which is important for atmospheric research and military sensing. Significant advances in devices have also enabled photon-counting detectors to be extended to Geiger-mode detector arrays and to photon-number-resolving Geiger-mode detectors. Such advanced photon-counting techniques need to be expanded not only to higher count rates but to exploitation of novel quantum states of light in advanced optical sensors that are likely to come onto the horizon in the next decade or so.3,4,5 Moreover, current research will potentially provide a true linear-mode single-photon detector that will open new doors for sensing, imaging, and metrology.
3 An example is the planned incorporation of squeezed quantum states of light in the advanced Laser Interferometer Gravitational Wave Observatory (LIGO). Johnston, Hamish. 2008. Prototype gravitational-wave detector uses squeezed light. Physics World. Available at http://physicsworld.com/cws/article/news/33755. Accessed August 1, 2012.