Seeing Photons Progress and Limits of Visible and Infrared Sensor Arrays (2010) / Chapter Skim
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4 Emerging Technologies with Potentially Significant Impacts
4 Emerging Technologies with Potentially Significant Impacts
Pages 91-133
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From page 91... ...
The detector material generally consists of two or more thin layers grown in succession on a substrate. Epitaxial growth implies that the crystal structure of the layers is aligned with that of the substrate, a necessary requirement for good material quality and appropriate electrical characteristics.
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Also, the ability to grow MCT on silicon has enabled the fabrication of very large focal plane arrays (FPAs)
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Further improvements in the MBE technique are needed to minimize the populations of point defects that limit the carrier lifetimes in SLS material. The large experience base in the growth and design of electronic and photonic devices using bandgap engineering -- the incorporation of multiple functional layers into device structures -- opens new avenues for optimizing device performance.
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4Available at www.nano.gov/NNI_FY09_budget_summary.pdf. Accessed March 25, 2010.
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From page 95... ...
The combination of graphene's attractive electronic and photonic properties holds great promise for visible detector applications. In fact, recent results have demonstrated the use of graphene detectors in a 10 gigabit per second optical link with an external photoresponsivity of 6.1 mA/W at 1.55 µm wavelength.6 The same group also reports 6 T
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From page 96... ...
Graphene's high switching speed combined with a broadband photoresponse underscores its potential to have a disruptive impact on future detector performance. The promise of a material that may surpass the performance of silicon for many electronic applications has focused a significant body of research on graphene because the mechanisms of transport in this material are not fully understood.
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From page 97... ...
and surface plasma wave chemical-biological sensors.14 Additional discussion of the application to infrared detectors is presented in the following section. Electronics The broad applicability of nanotechnology to electronics is obvious; for example, the use of cathodic electron field emission from an assemblage of nanotubes for high-power microwave transmitters15 and other vacuum electronic applications offers copious production of electrons; this particular technology may find immediate application in fielded systems.
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Still the ultimate payoff of a fully integrated sensor element with nanoscale processing requires ongoing monitoring of global improvement and activity. Sensor Elements Quantum sensor elements receive an incoming photon and free a bound electron(s)
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Sommerfeld was the first to recognize the existence of a bound surface mode at the interface between a lossless dielectric and a lossy metal in his analysis of Marconi's wireless transmission experiments (there the loss was associated with currents in Earth's surface) .20,21,22 More recently, interest in plasmonics has been rekindled with the discovery of anomalous transmission through a metal slab perforated with a 2-D array of holes.23,24 This transmission is associated with resonances involving the coupling of the incident radiation to surface plasma waves (SPW)
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The difficulty is finding the appropriate combination of SPW coupling, hole transmission, and angular and spectral bandwidth while still retaining the ability to collect the photo- or plasmon-generated carriers. FINDING 4-1 An emerging trend in focal plane array technologies is multispectral band sens ing enabling enhanced system capability through a single aperture.
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From page 101... ...
The primary drivers for this research are the need for achieving large absorption cross section together with high field localization and/or enhancement for applications in nanoscale imaging and spectroscopy, solar energy conversion, and coherent control of light emission and/or absorption.31 It is difficult to speculate on the 31An overview of the current research on optical antennas as well as a discussion of their potential applications can be found in Palash Bharadwaj, Bradley Deutsch, and Lukas Novotny.
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2007. Negative refractive index at optical wavelengths.
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emerging technologies Potentially significant imPacts 0 with Au Dipoles Niobium Detector Niobium d detector Au Dipoles to Amp SiO2 h Silicon substrate a Substrate b Au backplane for MOS cap a) Cross Section View b)
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From page 104... ...
Visible detectors are superior to all subbands of infrared detectors in almost all aspects. The concept of wavelength conversion from an infrared wavelength to the visible would make these inexpensive, superior, focal planes available to detect radiation at infrared wavelengths.
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Simultaneous impingement of a strong pump signal and an emitted weak detected signal are necessary requirements. Photonic materials provide this effect and might help isolate extraneous pump signal noise and improve the overall quantum efficiency.
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Optics Express 17(20)
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Last accessed March 25, 2010. • Memis, Omer Gokalp, and Hooman Mohseni.
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2009. Noise analysis and comparison of analog and digital readout integrated circuits for infrared focal plane arrays.
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Integration of Optics with Focal Plane Arrays Novel optical configurations, specifically configurations in which optical components are integrated with the detector, can provide new and improved levels of
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In the TOMBO configuration, the minilenses are the imaging element. In a typical example, a focal plane array of detectors (for example 1280 × 1024)
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Compressive Sensing The idea of compressive sensing is to measure only the data you will keep.47,48 The concepts behind compressive sensing began only a few years ago.49,50,51,52 A precursor to compressed sensing was seen in the 1970s, when seismologists constructed images of reflective layers within the Earth based on data that did not seem to satisfy the sampling criterion.53 Compressive sensing could have a major effect on detector use in systems because a smaller number of detectors could image over a large area. While the size of detector arrays is ever increasing, if it were possible to use the same array and obtain an image similar to that obtained from a much larger array, this would have major impact at the systems level.
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LACOSTE-coded aperture imaging technology focused on achieving a very wide instantaneous field of regard using multiple simultane 54 Emmanuel Candès, Justin Romberg, and Terence Tao.
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2008. Adaptive coded aperture imaging in the infrared: towards a practical implementation.
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If the phase and amplitude of the light wave are known in the pupil plane, they can be digitally converted to the image plane by taking a Fourier transform. This is the essence of so-called lensless imaging.
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Lensless imaging may not be completely lensless. If the detector focal plane array is the size of the aperture being used, no optics will be required.
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research suggest the potential for breakthroughs that may ultimately transform the use of TE coolers in detector systems. These developments include the demon stration of thin-film thermoelectrics with performance that is two to three times greater than conventional bulk materials at or near room temperature and new understandings of how nanostructurer can improve thermoelectric performance at cryogenic temperatures.
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SOURCE: Rama Venkatasubramanian, and colleagues, RTI International, Research Triangle Park, N.C. 4-7 w-replacement type.eps FIGURE 4-8 Advanced thin-film superlattice thermoelectric modules for FPA applications.
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funded research to specifi cally address thermoelectric development for cryogenic temperatures. FINDING 4-6 Thin-film thermoelectric devices have the potential to substantially reduce size, weight, and power requirements of the active cooling component for room-temperature focal plane arrays.
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From page 119... ...
Additionally, the flexible nature of the 2-D phononic crystal topology could allow one to uniquely tailor the electronic structure of the silicon to facilitate improved Seebeck coefficients over those of nanowire topologies.71,72 Laser Cooling Laser cooling refers to one of several mechanisms by which laser light interacts with matter in a way that results in a net reduction in temperature. The reduction in temperature is associated with absorption and emission processes that result in a net loss of momentum at the atomic or molecular level.
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2010. Laser cooling of solids to cryogenic temperatures.
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On the other hand, the emergence of single-chip multicore processor architectures may allow significant local pre-processing of sensor data before they are transmitted from the remote sensor, reducing the bandwidth required and allowing the use of sensors with improved precision (e.g., the number of pixels in a focal plane array) or higher scan rates, each of which may be valuable in some applications.
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Once the raw data or derived information have reached the ground processing station, there are fewer limitations in terms of power re quirements, computer power, and communication bandwidth. The technologies that address data transmission limitations on communication bandwidth belong to two major classes: (1)
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The same concepts are also being explored in the design of a new generation of imagers that employ compressive sensing at the optical-analog layer. In this new concept of sensing a smaller number of measurements is acquired, and each measurement corresponds to a quantity in the transformed space that is optically accomplished as the inner product of the scene with the basis functions.
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In the IR and high-performance visible imaging area, fully digital focal planes are just entering the market. In some cases their performance exceeds that of tra ditional analog focal planes coupled to discrete electronics.
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identify and transmit only small amounts of high-level "actionable information" rather than large numbers of raw data bits. Architectural bottlenecks occur when steps in digital signal processing are mismatched in their performance.
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In addition, ARGUS-IS uses a spread-spectrum jam-resistant CDL wireless data link of 274 megabit per sec ond capacity. If the wireless data link is fully utilized, the on-board systems must achieve a data rate reduction of 423,936/274 or more than 1,500, which is difficult to achieve with compression technologies alone.
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From page 127... ...
The significant advances in high-performance computing over the last decade are making real-time onboard processing a reachable reality. However, the complexity of programming these powerful processors and achieving their potential computer power has significantly increased -- both the exploitation of the available parallelism and the memory organization of the computation are subtle and require significant effort.
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The switch engine in each tile completely offloads the tile processing engine from iMesh™ network routing and protocol handling, and provides buffering and flow control so that tiles can perform processing in an asynchronous manner. Each network link is full duplex.
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.87 FINDING 4-7 Scaling the data throughput of focal plane sensor systems involves not only the sensor chip but also the detector-processor interface, signal processing and compression, and the communication link (wireless for remote air- and space-borne missions)
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Three specific methods for sensor fusion include raw data fusion, feature level fusion, and decision-level fusion. The highest level of fusion occurs when the multiple images are combined into a single multivalue image that is then exploited.
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Fusion techniques that operate in this mode are known as raw data fusion as well as centralized data fusion methods, and they typically assume a common image projection plane for the multiple sensors. Multi- and hyperspectral sensors are well matched for this type of fusion approach.95,96 Centralized data fusion is not typically applied to sensors that do not share a common imaging plane such as synthetic aperture radar (SAR)
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In a decision-level fusion, also known as distributed data fusion, an independent decision is made based on a single data modality and the decisions are passed to the fusion node where a global decision is made using a variety of algorithms including Bayesian inferencing. Feature-level fusion is a hybrid between raw data fusion and decision-level fusion.
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Emerging detector and related system-level technologies have significant potential for advancing sensor systems and deserve attention from the intelligence community in assessing present and future global sensor system capabilities.
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