While InGaAs-based SWIR imaging technology has been improved dramatically over the past 10 years, the motivation
remains to reduce Size Weight and Power (SWaP) for applications in Intelligence Surveillance and Reconnaissance
(ISR). Goodrich ISR Systems, Princeton (Sensors Unlimited, Inc.) has continued to improve detector sensitivity.
Additionally, SUI is working jointly with DRS-RSTA to develop innovative techniques for manufacturing dual-band
focal planes to provide next generation technology for not only reducing SWaP for SWIR imagers, but also to combine
imaging solutions for providing a single imager for Visible Near-SWIR (VNS) + LW imaging solutions. Such
developments are targeted at reducing system SWaP, cost and complexity for imaging payloads on board UASs as well
as soldier deployed systems like weapon sights. Our motivation is to demonstrate capability in providing superior image
quality in fused LWIR and SWIR imaging systems, while reducing the total system SWaP and cost by enabling Short
Wave and Thermal imaging in a single uncooled imager.
Under DARPA MTO awarded programs, a LW bolometer (DRS-RSTA) is fabricated on a Short Wave (SW) InGaAs
Vis-SWIR (SUI-Goodrich) Imager. The combined imager is a dual-band Sensor-Chip Assembly which is capable of
imaging in VIS-SWIR + LW. Both DRS and Goodrich have developed materials and process enhancements to support
these dual-band platform investigations. The two imagers are confocal and coaxial with respect to the incident image
plane. Initial work has completed a single Read Out Integrated Circuit (ROIC) capable of running both imagers. The
team has hybridized InGaAs Focal planes to 6" full ROIC wafers to support bolometer fabrication onto the SW array.
InGaAs-based focal plane arrays are an unrivaled uncooled SWIR technology. Prior analytical models of InGaAs have
been inaccurate at predicting the ultimate dark current limits for tight-pitch arrays. By going back to first-principles, we
have developed an improved analytic model. This model clarifies how tight pitch arrays suppress diffusion current and
why bulk generation-recombination is not a limiting factor in today's devices. We can thus explain our experimental
arrays with dark currents of 0.5nA/cm2 at 20C and <0.1nA/cm2 at 7C as well why we believe another order of
magnitude decrease in dark current is theoretically possible.
There are few choices when identifying detector materials for use in the SWIR wavelength band. We have exploited the
direct-bandgap InGaAs material system to achieve superior room temperature (293°K) dark current. We have
demonstrated sensitivity from 400nm through 2.6um with this material system and thus provide the opportunity to sense
not only the visible, but also the J-band (1.25um), H-band (1.65um) and K-band (2.2um) windows. This paper discusses
the advantages of our hybridized CMOS-InGaAs material system versus other potential SWIR material systems.
The monolithic planar InGaAs detector array enables 100% fill factor and thus, high external quantum efficiency. We
have achieved room-temperature pixel dark current of 2.8fA and shot noise of 110 electrons per pixel per second. Low
dark current at +300K allows uncooled packaging options, affording the system designer dramatic reductions in size,
weight (cameras <28grams), and power (<2.5W). Commercially available InGaAs pin arrays have shown diode lifetime
mean time between failures (MTBF) of 1011hours for planar InGaAs detectors1, far exceeding telecom-grade reliability
requirements. The use of a hybrid CMOS-InGaAs system allows best of breed materials to be used and permits efficient, cost-effective,
volume integration. Moreover, we will discuss how the InGaAsP material system is compatible with CMOS monolithic
integration. Taken together, these advantages, we believe, make InGaAs the obvious choice for all future SWIR
systems.
The effectiveness of utilizing spatial light modulators (SLMs), developed at Sanders, for reducing some of the critical bottlenecks inherent within the Hyperspectral Imaging (HSI) chain will be presented. Specifically, the more common classification, detection, and endmember selection algorithm used in HSI, which are suitable for optical implementation, are presented here. These algorithms were reformulated for implementation on a compact Vander- Lugt correlator based on Sanders' multi-level quantum well (MQW) spatial light modulator (SLM). Sanders devices are GaAs Fabry-Perot vertical cavity multiple quantum well (MQW) SLMs consisting of MQW optical chips flip-chip bonded to Si/CMOS driver circuitry. Details of the reformation of Pixel Purity Index, an endmember selection algorithm, to the optical correlator is presented as well as a projection of its performance based on software simulations. In addition, hardware results are presented for Spectral Angle Mapper based on a Vander-Lugt implementation using Sanders 128 X 128 binary SLMs. An opto-electronic hyperspectral workstation accelerator is proposed which is based on a Vander-Lugt correlator using Sanders' MQW-SLMs and FPGA- based compute nodes and has the capability of 6.4 Million 1D correlations per second for HSI endmember selection, classification and detection.
2D Parallel Optical Interconnects are capable of providing large connectivity between elements in computing and switching systems. Using this technology we have demonstrated a bi-directional optical interconnect between two PCBs containing optoelectronic VLSI circuits. The OE- VLSI circuits were constructed using VCSELs and photodiodes flip-chip bump bonded to a 0.35 micrometers CMOS chip. The CMOS was comprised of 256 Vertical Cavity Surface Emitting Laser (VCSEL) drivers, 256 receivers, and the requisite buffer and control circuits required to operate the large transceiver array. This is the first system, to our knowledge, to send bi-directional data optically between optoelectronic VLSI chips which have both VCSELs and photodiodes co-integrated on the same substrate.
Andrew Kirk, David Plant, Ted Szymanski, Z. Vranesic, John Trezza, Frank Tooley, D. Rolston, Michael Ayliffe, Frederic Lacroix, D. Kabal, Brian Robertson, Eric Bernier, D. Filiatrault-Brosseau, Feras Michael, E. Chuah
We describe the design and implementation of a free-space optical interconnect for multi-processor and backplane applications. The system is designed to interconnect 4 nodes in a unidirectional ring, with a total of 256 data channels propagating from node to node. Each node contains an array 512 GaAs electro-absorption modulators and 512 photodetectors, hybridly attached to a silicon integrated circuit. Light is relayed between nodes with a rigid micro- optical system. System results are presented.
Marc Chateauneuf, Michael Venditti, Emmanuelle Laprise, Julien Faucher, Kevan Razavi, Frederic Thomas-Dupuis, Andrew Kirk, David Plant, Tsuyoshi Yamamoto, John Trezza, W. Luo
A vertical-cavity surface-emitting laser (VCSEL) based free- space parallel optical interconnect is presented. The rigid optical link interconnects bi-directionally two PCBs over a distance of 3 inches. The 512 optical channels were grouped in 4 by 8 clusters on a 750-micrometers pitch, where each cluster is a 4 by 4 array of channels on a 125-micrometers pitch. Modules combining both microlenses and minilenses were used to propagate light from the VCSELs to the detectors. Details of the optical design and assembly process are presented.17
We review GaAs Fabry-Perot vertical cavity multiple quantum well (MQW) spatial light modulators (SLMs) developed at Sanders, a Lockheed Martin Company, and demonstrate their use in optical image correlation. These MQW SLMs are reflective- mode modulators using electrically-tunable absorption to modulate the reflected intensity. The operation of the MQW SLMs with a newly-developed Labview graphical user interface is described. A compact Vander-Lugt image correlator is described which was configured using MQW SLMs: binary 128 X 128 pixel image input with a binary filter plane. In addition, the architecture of 8-bit gray-scale MQW-SLM module developed at Sanders is discussed. The performance of the image correlator was characterized using amplitude-encoded binary phase-only filters and various test targets including test imagery supplied by US Army AMCOM, and is compared with simulations for peak-to-secondary efficiencies on these data. Finally, high-speed (250,000 frames per second) target recognition of 128 X 128 pixels binary input imagery is demonstrated.
We review GaAs Fabry-Perot vertical cavity electro-optical devices constructed at Lockheed Martin Sanders, with particular attention to spatial light modulators and discuss a number of their applications. Our manufacturing processes enable the construction of large format, highly-uniform optical modulator and smart pixel arrays integrated with silicon CMOS VLSI circuitry. These devices can be used for a wide variety of applications including: optical computing for target recognition and signal processing, optical data routing, optical interconnect systems, and optical memory storage and access.
GaAs asymmetric Fabry-Perot vertical cavity modulators are useful in a wide variety of applications. Vertical cavity devices have employed amplitude or phase modulation for optical switching. Amplitude modulators have been demonstrated in large format arrays. Additional uses for the pixels include directional modulation, detection, and light- emitting capability. When arrays of these deices are integrated with electronic circuits - most significantly silicon CMOS VLSI - at the pixel level, large, complex optical spatial light modulators, detectors, transceivers, computation devices, and emitters can be created for a wide variety of applications. These applications range from target recognition to SAR radar processing, to optical data routing, to optical interconnect systems, to optical memory access.
GaAs asymmetric Fabry-Perot vertical cavity modulators are useful in a wide variety of applications. Such modulators have been demonstrated in large format arrays. The majority of vertical cavity devices have employed amplitude modulation to produce optical switching. Additional uses for the pixels include detection, phase modulation, directional modulation, and light-emitting capability. When arrays of these devices are integrated with electronic circuits-most significantly silicon CMOS VLSI-at the pixel level, large, complex optical spatial light modulators, detectors, transceivers, computation devices, and emitters can be created for a wide variety of applications. These applications range from target recognition to SAR radar processing, to optical data routing, to optical interconnect systems, to optical memory access.
We have developed a conservative and reversible optoelectronic intensity modulator. Two of the inputs are optical and the third in the device's initial implementation is an electrical control signal. The device is essentially a controllable optical routing element. In one state beams incident from opposite sides of the device are reflected and in the other state they are transmitted. Using arrays of these devices, various switching networks can be constructed, including crossbar switches and other regular or irregular architectures. The device itself is composed of quantum wells in a Fabry-Perot cavity. Our device is grown using molecular beam epitaxy (MBE) and can be realized using several materials systems, so that varying wavelengths of operation can be obtained. In addition, the radial thickness non uniformity due to rotation during MBE growth can be exploited to obtain devices operating at different wavelengths on the same wafer. The design of the devices or arrays of devices can be focused on optimizing bandwidth, modulation ratio, voltage, or change in reflectivity, depending on the desired application. In this work we will describe the use of the devices for several systems applications and discuss some further refinements to the device that make it more useful in a systems context.
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