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High performance infrared focal plane arrays (FPAs) play a critical role in a wide range of imaging applications. However the high cost associated with the required cooling and serially processed die-level hybridization is major barrier that has thwarted Mid-wavelength Infrared (MWIR) detector technology from penetrating largevolume, low-cost markets. Under the Defense Advanced Research Projects Agency (DARPA) WIRED program, the HRL team has developed a wafer level integration schemes to fabricate large format Antimonidebased MWIR FPAs on Si Read Out Integrated Circuit (ROIC) as a means to achieve significant fab cost reduction and enhanced production scalability. The DARPA-hard challenge we are addressing is the thermal and stress management in the integration of two dissimilar materials to avoid detector and ROIC degradation and to maintain structure integrity at the wafer scale. In addition, a digital ROIC with extremely large well capacity was designed and taped-out, in order to increase the operating temperature of the FPAs. In this talk, we discuss our progress under the DARPA WIRED program.

Recent advances over the last several years in III-V strained-layer superlattice-based infrared detectors have lead this material system to emerge as a solid alternative to HgCdTe for dual-band focal plane arrays (FPAs). Rapid development of superlattice-based detectors has been realized by capitalizing on mature, III-V foundry-compatible processing. Furthermore, superlattice-based epitaxial wafers exhibit a high degree of lateral uniformity with low macroscopic defect densities (< 50 cm-2) and can achieve dark current levels comparable to HgCdTe detectors. In this paper, we review our recent efforts towards producing HD-format (1280x720, 12 μm pitch) superlattice-based, dual-band MWIR/LWIR FPAs. For a representative FPA, characterization was conducted in a pour-fill dewar at 80K, f/3 and using a blackbody range of 22°C to 32°C. For the MWIR band, the noise equivalent temperature difference (NETD) was 14.9 mK with a 3x median NETD operability of 99.91%. For the LWIR band, the median NETD was 28.1 mK with a 3x median NETD operability of 99.66%. To illustrate the manufacturability of superlattice technology, we will present results on 1280x720, 12 μm pitch MWIR/LWIR FPAs built over the last year at HRL through multiple fabrication lots utilizing 4" epiwafers.

A 3D multiphysics solver which combines beam propagation with chemical kinetics for simulating self-propagating photopolymer waveguides is presented. The solver is shown to predict various experimentally observed phenomena and is used to simulate the formation of micro-truss structures consisting of intersecting photopolymer waveguides.

We present a new algorithm that improves the prediction accuracy of the maximum charge and discharge power capabilities, i.e. state of power ( SOP ), of a battery state estimator (BSE) using an equivalent-circuit representation of a battery. For short time (high frequency) operation, lithium ion traction batteries are often dominated by ohmic and interfacial kinetic resistance, and conventional equivalent circuits employing resistors and capacitors (RC circuits) work well to characterize the system. However, for longer times, diffusion resistance becomes important and conventional BSEs based on RC elements fail to provide useful power predictions. In order to take into account diffusion in the SOP prediction, we propose to incorporate a nonlinear resistance into the power prediction formulas that are otherwise based on an RC circuit formulation; The diffusion effect is addressed with this nonlinear resistance whose value is proportional to the square root of time. The new approach is implemented in a vehicle-simulation environment (a hardware-in-the-loop setup) to predict the SOP of a lithium-ion battery. Simulation results demonstrate that this revised estimator provides much more accurate power prediction without compromising the regression performance of the original BSE.

We report the development of an adaptive, multi-parameter battery state estimator based on the direct solution of the differential equations that govern an equivalent circuit representation of the battery. The core of the estimator includes two sets of inter-related equations corresponding to discharge and charge events respectively. Simulation results indicate that the estimator gives accurate prediction and numerically stable performance in the regression of model parameters. The estimator is implemented in a vehicle-simulated environment to predict the state of charge (SOC) and the charge and discharge power capabilities (state of power, SOP) of a lithium ion battery. Predictions for the SOC and SOP agree well with experimental measurements, demonstrating the estimator's application in battery management systems. In particular, this new approach appears to be very stable for high-frequency data streams.

Planar beam-steering apertures for laser-transmitter applications require a true-time-delay (TTD) subsystem for enhanced data-rate performance. The requirements for such a subsystem depend on the overall aperture size, field-of-view, beam-steering switching speed, and data pulse duration. The reprogramming speed of this 8-bit module (1-ps minimum resolvable time increment, and 0-256-ps range) is measured to be /spl sim/400 /spl mu/s, and the upper limit of the dispersion produced by the device is measured to be 0.125 ps/cm/spl middot/nm. Using a TTD chip-scale module for temporal simultaneity, a demonstration of free-space 1.55-/spl mu/m beam-steering over /spl plusmn/30/spl deg/ field-of-view is reported, wherein 2-ps-long laser pulses are emitted from two subapertures.

We demonstrate coherent combination of two high-gain and high-power single-mode 1 μm fiber amplifiers via direct pump current modulation. Each all-fiber amplifier channel, which is built as a master oscillator-multiple amplifier architecture, can operate either continuous waves or 4 ns, 1 MHz pulses with average power of 50 W and more than 55 dB gain. These two amplifiers are coherently combined by modulating the pump currents of the preamplifiers in a multidither arrangement. The key feature of the scaling scheme is the insertion of a designated second stage preamplifier between the first stage preamplifier and the final power amplifier stage, so as to improve the coherency and to minimize the gain variation of the preamplifier to the power amplifier. Otherwise, overall phase control of the fiber amplifiers with this method is not possible at such a high power level.

We present a prototype photodetector in which the built-in "tunneling structure" serves as an internal gain mechanism for photon detection. Initial feasibility studies demonstrated that the new photon detector offers an optical responsivity as high as 3000 A/W peaked at λ=1.3 μm at less than 1 V bias applied. The measurements were carried out using a photospectrometer setup in a continuous mode at room-temperature. Very strong (> 1000) responsivity is also measured from visible to SWIR even with a simple optical coupling scheme that utilizes very thin absorber layers in the prototype devices. The dark current density is ~ 5×10 -10 A/μm 2 at the operating bias. Room-temperature NEP was calculated based on a shot noise measurement, yielding NEP of 4~ 5×10 -15 W/Hz 1/2 and D* of 2~3×10 12 cmHz 1/2 /W, peaked at a bias of 0.3 V at a fixed wavelength of λ=1.3 μm.

We operate our laboratory-demonstrated coherent seven-sub-aperture transmitter on our 408 meter free-space range, and demonstrate phase-locking while simultaneously measuring turbulence. The received signal enhancement is near what is expected from analysis.

Using a true-time-delay chip-scale module, free-space 1.55-/spl mu/m beam-steering over /spl plusmn/40/spl deg/ field-of-view with 2-ps laser pulses is reported. The measured reconfiguration speed of this 8-bit-programmable module (0 ps to 256 ps, 1-ps increments) is /spl sim/400/spl mu/s.

We describe our concept for a power scalable transmitter with built in high-speed (>1 kHz) atmospheric aberration correction capability also. We have demonstrated this concept in the laboratory using seven 1 W fiber amplifiers for the transmitter and phase locked them with a simple and robust method to give spatially coherent output at the receiver. We report the near and far field of the transmitter beam shapes and automatic small angle steering capability for the transmitter beam to follow the slight motions of the receiver. The airborne laser link platform presents difficult engineering problems. The system must be simple, light and rugged, yet provide sufficient power for high-bandwidth communications. The solution we propose naturally fits this application. Phased fiber arrays are a recognized simple solution to power scaling. The inclusion of the corrections of the fiber phase, atmospheric path aberrations, and steering in the same feedback loop is particularly elegant. The proposed transmitter requires substantially less power than an uncorrected transmitter to achieve same link margin, and uses COTS fiber components. Our transmitter can be scaled in power to 100 W and beyond and can correct even turbulence-induced aberrations because of its high-speed response capability.

We report our first experimental demonstration of an all-fiber true-time-delay (TTD) system integrated into our free-space laser-communication laboratory breadboard. Using far-field interference fringes at the target to monitor both temporal and spatial coherence, we demonstrated optical beam steering over nearly ±40° FOV with our high-bandwidth TTD system (i.e., 2.7-ps optical pulses at 10 GHz repetition frequency). The planar output aperture of the optical beam-steering device has an overall aperture-diameter of ~4 cm, while the TTD architecture utilized piezo fiber-stretcher components for low-cost, efficient programmable time-delay performance.

A multi-fiber network is shown to provide programmable time delays so that an ensemble of pulselets can be temporally synchronized over a large field-of-view, leading to high-bandwidth, multi-aperture beam-steering systems, including MEMS and liquid crystal arrays.

We report a laser link that can correct atmospheric aberrations. We use a fiber collimator array, fed by a master oscillator with multiple fiber amplifiers (MOMA), and accomplish phase adjustment via pump diode current control. Each of seven channels is tagged by a different 1-20 kHz diode current dither. At the receiver, each channel's phase information is extracted from the ~100 km-range scenarios is the correction bandwidth limited by light's travel time. The low dither frequencies and amplitudes do not interfere with the typically GHz laser communications signal. Importantly, our system reduces transmitter power requirements by correcting small pointing errors and atmospheric-path aberrations. Of course the multiple-fiber amplifier array also enables power scaling. We describe our near- and far-field beam measurements in the laboratory.

We report laboratory experiments demonstrating a phase-compensating 70-mm-diameter aperture transceiver that comprises a hexagonally close-packed array of seven 23-mm-diameter fiber collimator subapertures. Other than the collimators, the transceiver uses only fiber optics, connected as a master oscillator-multiple amplifier. The master oscillator is a fiber-coupled 1.5-µm diode laser, which is split and fed to 1-W fiber amplifiers before it exits the collimators. To obtain a phase-coherent far field we control each subaperture's phase by adjusting the current to its amplifier's pump diodes in a multidither arrangement, maximizing the signal at the receiver. We achieve a diffraction-limited coherent beam combination in the far field that produces 1.4 W of power in the main lobe, in agreement with theory.