We have exploited the artificial atom-like properties of epitaxially grown self-assembled quantum dots (QDs) for the development of high operating temperature long wavelength infrared (LWIR) focal plane arrays (FPAs). QD infrared photodetectors (QDIPs) are expected to outperform quantum well infrared detectors (QWIPs) and are expected to offer significant advantages over II-VI material based FPAs. We have used molecular beam epitaxy (MBE) technology to grow multi-layer LWIR Dot-in-a-Well (DWELL) structures based on the InAs/InGaAs/GaAs material system. This hybrid quantum dot/quantum well device offers additional control in wavelength tuning via control of dot-size and/or quantum well sizes. DWELL QDIPs were also experimentally shown to absorb both 45o and normally incident light. Thus we have employed a reflection grating structure to further enhance the quantum efficiency. The most recent devices exhibit peak responsivity out to 8.1 microns. Peak detectivity of the 8.1 μm devices has reached ~ 1 x 1010 Jones at 77 K. Furthermore, we have fabricated the first long-wavelength 640x512 pixels QDIP imaging FPA. This QDIP FPA has produced excellent infrared imagery with noise equivalent temperature difference of 40 mK at 60K operating temperature.

The purpose of this work is to explore mid-infrared (IR) photodetector materials that can operate at room temperature. Shorter-period InAs/GaSb superlattices (SLs) have larger intervalance band seperations, which is beneficial for reducing Auger recombination and tunneling current, thus making room temperature operation possible. To test these possibilities, several short-period SLs ranging from 50 to 11 Å were designed for 4 μm detection threshold and molecular beam epitaxy was used to grow specially designed structures. Since morphological degradation is generally expected in shorter-period SLs, their structural qualities were monitored by transmission electron microscopy. The effect of layer properties on the optical and electrical properties was studied using low temperature photoconductivity measurements and magnetic field dependent Hall measurements. The samples with larger-periods (50 to 31 Å) showed excellent structural qualities, leading to sharper photoresponse band edge (5 meV) and lower residual background carrier concentrations (8x10¹⁰ cm^-2). As the period approached 24 Å, slight layer thickness undulations within the SLs were observed and these undulations intensified as the period further reduced to 17 Å. Evidently, these structural degradations strongly influence their optical properties causing significant broadening in photoresponse band edge (9 meV). In the thinner samples with the period below 17 Å, no optical signal was detected. With slower growth rates, samples with periods as thin as 19 Å were grown without significant layer thickness variations.

High quality infrared (IR) quantum detectors are important for several applications, such as atmospheric remote sensing, chemical detection and absorption spectroscopy. Although several IR detectors are commercially available, with different materials and structures, they provide limited performance regarding the signal-to-noise ratio and the corresponding minimum detectable signal. InGaAsSb/AlGaAsSb heterojunction based phototransistors show strong potential for developing IR sensors with improved performance. In this paper, the performance of a novel n-p-n InGaAsSb/AlGaAsSb heterojunction phototransistor is presented. This performance study is based on experimental characterization of the device dark current, noise and spectral response. Detectivity of 1.7x10⁹ cmHz ^1/2/W at 2-μm was obtained at 100°C temperature and 2 V bias voltage. This corresponds to a responsivity of 94.7 A/W and an internal gain of 156 with about 38% quantum efficiency. Reducing the temperature to -30°C allows to increase the bias to 3V and enhance the detectivity to 8.7x10¹⁰ cmHz^1/2/W at the same wavelength, which corresponds to a responsivity of 386.5 A/W and an internal gain of 288.2 with about 83% quantum efficiency. The device impulse response and linearity, including the corresponding dynamic range, also are presented. Impulse response analysis indicated a settling time of about 1.1 μs at 2V and 100°C, while linearity measurements indicated a constant responsivity in the radiation intensity range of 1.6x10^-7 W/cm² and 31.6 mW/cm².

L-3 Communications InfraredVision Technology Corporation (ITC) has developed a high performance (25μm) 640x480 microbolometer Uncooled Focal Plane Array (UFPA). ITC offers this high-performance VO_x microbolometer-based detector (ITC-2000) to camera manufacturers requiring a state-of-the-art uncooled infrared detector. The ITC-2000 has ten bits of on-chip NonUniformity Correction (NUC) to extend both dynamic range and sensitivity. A serial interface allows programmable gain and global offset to tailor output to the application. The sensor is capable of frame rates up to 30 Hz, non-interlaced. The output is differential to reject common-mode noise. Two temperature sensors are available on chip for monitoring temperature drift. A thermal electric stabilizer is provided in the detector package, if the camera manufacturer requires temperature stabilization. The lightweight package provides a mounting bracket capable of precision alignment to the focal plane array. The addition of the ITC-2000 large-format detector complements ITC's existing ITC-1000 series detector module that addresses both imaging and radiometric commercial-camera applications.

Imaging instruments with state-of-the-art HgCdTe MWIR and LWIR detectors often have limited cooling resources. Therefore, they may need to deal with large detector dark currents and/or optics thermal emission currents. The sum of dark and thermal emission currents form an undesirable "offset" to the desired signal current, which can be orders of magnitude greater than the signal. With modest instrument thermal stability, the offset current change is small over instrument line imaging times on the order of 10 seconds. This allows cancellation or subtraction of the offset by injecting an equal and opposite current into the integration node. The exact value of this cancellation current can be simultaneously measured and stored for every pixel in a self calibrating deep space (negligible signal) scan cycle, leaving only the desired signal current when the aperture is subsequently scanned across the scene. Offset subtraction dramatically reduces the dynamic range requirements of the Readout Integrated Circuit (ROIC) signal chain at the cost of additional ROIC shot noise. However, this shot noise is rarely dominant in MWIR and LWIR applications so overall NEDT performance does not suffer. By subtracting the offset and dramatically reducing ROIC dynamic range requirements, the integration capacitor and overall ROIC size are greatly reduced, power dissipation is decreased, and linearity is greatly improved. The end result is similar NEDT performance at higher detector and instrument temperatures. An ROIC with automatic, low-noise, in unit cell offset subtraction has been developed and demonstrated with LWIR (15 micron cutoff) HgCdTe detectors operating at 67K. The offset, which is 20X the desired signal, is subtracted in less than 10 ms with better than 99% accuracy. The subtraction current drift is less than 0.0015%/s.

An interferometric method for measuring the two-dimensional distribution of the state of polarization (SOP) of light is presented. A pair of Savart plates, a half-wave plate, and an analyzer are inserted between the lenses of a double-diffraction imaging system, so that multiple interference fringes are generated over the video camera. The Fourier analysis of the image obtained from the video camera allows us to determine the two-dimensional distributions of the four Stokes parameters over the object plane. No mechanical or active components for polarization control are required and two dimensional distributions of any parameters related to SOP can be determined from the single image. Principle of this method is experimentally demonstrated by measuring the SOP distribution of the light transmitted by a liquid crystal cell.

A spectropolarimeter utilizing an Oriel MIR8000 Fourier Transform Spectrometer in the MWIR is demonstrated. The use of the channeled spectral technique, originally developed by K. Oka, is created with the use of two AR coated Yttrium Vanadate (YVO₄) crystal retarders with a 2:1 thickness ratio. A basic mathematical model for the system is presented, showing that the Stokes parameters are directly present in the interferogram. Theoretical results are then compared with real data from the system, an improved model is provided to simulate the effects of absorption within the crystal, and error between reconstructions with phase-corrected and raw interferograms is analyzed.

We report on processing techniques to effectively control the data bandwidth in larger format Focal Plane Array (FPA) sensors. Bandwidth reduction techniques are possible using image processing functions near or on the FPA. We have developed image processing techniques that give a controlled reduction in the data rate via simple circuit that estimate Activity on the FPA image plane. By filtering on the FPA and sensing pixel signal changes, this allows only transmitting pixel data that are have less interest, and more efficiently manages data flow from the FPA. We describe and demonstrate results of "Activity Sensing" processing near the FPA. The associated computational efficiency with this type of on FPA processing allows data rate reduction from > 20 Mbytes/sec to under 10Kbytes/sec . We report on the continuing development and performance benefits expected from an Activity Sensing algorithm using recorded infrared (IR) data from a large format 1024 x 1024 variable acuity¹ FPA.

Remote sensing applications make use of the optical polarization characteristics of a scene to enhance target detection and discrimination. Imaging polarimeters typically utilize polarizing arrays located in front of a focal plane array as a means of extracting polarization information from the optical scene. Over the last few years, technology development efforts have resulted in FPAs that integrate the polarizer with the infrared focal plane array (FPA). This paper will report on the radiometric and polarization characterization of a micro-grid polarizer FPA from DRS Infrared Technologies, L.P. (DRS). These measurements were performed to evaluate the radiometric performance and the polarization characteristics of the FPA.

Recent advances in dual band infrared focal plane technology now enable the design and testing of a dual infrared band snapshot imaging spectrometer, the first-ever of its kind. A review of proof of concept results from a dual-visible-band Computed Tomographic Imaging Spectrometer (CTIS) system is presented. The dual-visible system demonstrates that it is possible to reconstruct two spatially co-registered hyperspectral data cubes covering different spectral bands. Based on the visible band CTIS proof of concept, a similar infrared system is now proposed. Critical to the CTIS system is the design of the Computer Generated Holographic (CGH) disperser. Several different (CGH) designs are considered. A first order optical design for the dual infrared band CTIS is presented.

This paper covers the design and construction of a snapshot imaging spectropolarimeter for use in the long wave infrared, 8 to 12 micron region. This imaging device is unique in the fact that system is nonscanning, contains no moving parts, and in a single integration period is able to record spectral data as well as the polarization state as a function of wavelength from every spatial location in a 2D image. The system is based on the Computed Tomographic Imaging Spectrometer, commonly referred to as CTIS, and has been modified to incorporate components of Channeled Spectropolarimetry. The paper presents an overview of how both the CTIS and the CTICS (Computed Tomographic Imaging Channeled Spectropolarimeter) systems work, details on the specific components used in the LWIR system, and preliminary results from a completed LWIR CTIS system, which is the first of its kind.

We propose a new imaging device for the long infrared spectral range, inspired by the natural eye of a lobster. Such a lobster-eye lens is composed of reflecting channels with a square cross section capable of wide angle of view and practically omni-directional imaging. As in large-aperture lenses, aberrations can significantly degrade the image. We show two methods of reducing aberrations: by selecting proper material for the mirrors and by making channels with absorbing sections.

Hyperspectral imaging in the infrared bands is traditionally performed using a broad spectral response focal plane array, integrated in a grating or a Fourier transform spectrometer. This paper describes an approach for miniaturizing a hyperspectral detection system on a chip by integrating a Micro-Electro-Mechanical-System (MEMS) based tunable Fabry Perot (FP) filter directly on a photodetector. A readout integrated circuit (ROIC) serves to both integrate the detector signal as well as to electrically tune the filter across the wavelength band. We report the first such demonstration of a tunable MEMS filter monolithically integrated on a HgCdTe detector. The filter structures, designed for operation in the 1.6-2.5 μm wavelength band, were fabricated directly on HgCdTe detectors, both in photoconducting and high density vertically integrated photodiode (HDVIP) detectors. The HDVIP detectors have an architecture that permits operation in the standard photodiode mode at low bias voltages (≤0.5V) or in the electron avalanche photodiode (EAPD) mode with gain at bias voltages of ~20V. In the APD mode gain values of 100 may be achieved at 20 V at 200 K. The FP filter consists of distributed Bragg mirrors formed of Ge-SiO-Ge, a sacrificial spacer layer within the cavity and a silicon nitride spacer membrane for support. Mirror stacks fabricated on silicon, identical to the structures that will form the optical cavity, have been characterized to determine the optimum filter characteristics. The measured full width at half maximum (FWHM) was 34 nm at the center wavelength of 1780 nm with an extinction ratio of 36.6. Fully integrated filters on HgCdTe photoconductors with a center wavelength of approximately 1950 nm give a FWHM of approximately 100 nm, and a peak responsivity of approximately 8 × 10⁴ V/W. Initial results for the filters on HDVIP detectors exhibit FWHM of 140 nm.

This paper reports new performance data for SWIR HgCdTe 256x256 hybrid Focal Plane Arrays with cutoff wavelengths of 2.6-2.7 μm, operating at temperatures of 190 K to 220 K. The unit cell size is 30x30 μm². Back-illuminated SWIR HgCdTe P-on-n photodiode arrays were fabricated from two-layer LPE films grown on CdZnTe substrates. Response uniformity is excellent, with σ/μ=3-4%, and response operabilities are better than 99.9%. At a temperature of 190 K and a background photon flux of 6.8x10¹¹ ph/cm²-s, the median NEI is 1.1x10⁹ ph/cm²-s, which is 1.4 times the BLIP NEI. NEI operabilities are better than 98.8%. Quantum efficiencies for large-area test diodes are 69% to 78%, close to the 79% upper limit imposed by reflection from the non-antireflection-coated CdZnTe substrate.

How to meet the functional schedule of specifications of an IR instrument, as we know that the parameters of such an instrument, such as the diameter of pupil, the integration time, the wavelengths, bandwidths and focal plane array are not only interdependent, and also depend on the functional schedule of specifications. The complexity of an IR instrument, with its environment, and the observation geometry in movement force us to make choices that are sometimes difficult and often contradictory. We manage this complexity by building abacuses which make it possible to show how the system evolves/moves according to possible choices. Those abacuses thus enable us to determine the preliminary design of the instrument which will enable us it possible to meet its functional schedule of specifications.

The InfraRed staring arrays are more and more compact and offer system solutions in the different IR wavebands. The HgCdTe (Mercury Cadmium Telluride / MCT) material and process, as well as the hybridization technology, have been taken to an even more advanced level of sophistication to achieve these new staring arrays high performances. Latest developments allow progress at different stages of products offered by SOFRADIR. Uniformity of Focal Plan Arrays (FPA) is improved, read-out circuits propose new functions as the analogic to digital conversion, and the reliability of the whole dewar detector and cooler assembly is increased. New products take advantages on these progresses. In mid-wave (MWIR), 1280x1024 MCT detector available in a tactical dewar is presented.

A high performance prototype CMOS imager is introduced. Test data is reviewed for different array formats that utilize 3T photo diode, 5T pinned photo diode and 6T photo gate CMOS pixel architectures. The imager allows several readout modes including progressive scan, snap and windowed operation. The new imager is built on different silicon substrates including very high resistivity epitaxial wafers for deep depletion operation. Data products contained in this paper focus on sensor's read noise, charge capacity, charge transfer efficiency, thermal dark current, RTS dark spikes, QE, pixel cross- talk and on-chip analog circuitry performance.

Irradiation of a photodetector by very short laser pulses was presented as a technique that can remotely alter detector's performance [1]. Recent experimental data demonstrated that energy of femto-second laser pulse transforms almost entirely into thermal energy. Thermal energy may inflict long-lasted changes in the detector that based on lattice structural changes or disorder [2], and semiconductor compound heats up. Those changes may result in detector's responsivity change - to induce a spectral shift that may prevent detection at specific wavelengths and in overall noise increase. Both phenomena may contribute into ultimately non-compensated losses in detectivity. Effect completely reversible if energy level is below energy threshold for melting E_th -therefore integrity of the photodetector is protected during the alteration. In the paper we demonstrate that much longer laser pulses can be used to inflict similar effects in photo- detectors. Laser pulse can be arranged in such a way that combination of energy per pulse, repetition rate, pulse dwell time and duty cycle will not destroy detector or generate signal, but just inflict responsivity shift and noise variance increase. Technique of noise generation by ultra-fast laser is described and analyzed in details with respect to newly presented experimental data.

Pyroelectric detectors for infrared radiation are thermal sensors operating at ambient temperature, unlike semiconductor detectors, which require cooling. They have a uniform spectral response in a wide range of wavelengths, including main band of infrared transmission of the earth's atmosphere. The effective sensitivity and performance depend not only on the sensor material characteristics but also on the thermal performance of the complete structure of a detector. Recently, it has been proposed that bimorph (two pyroelectric materials stacked together) detector structure shall show better pyroelectric performance than the monomorph. Thus, a one-dimension thermal diffusion equation has been solved for nlayered structure for pyroelectric bimorph films. In such a system, performance of any number of layers of a detector structure can be derived, predicted, and optimized using these computations. Using viable bimorph element sensor configurations and materials parameter, the calculated and predicted current responsivity and other parameters are presented. It is predicted that greater enhancement of the bimorph current responsivity relative to that of monomorph using well-known pyroelectric materials, require higher modulating frequency or thicker bottom (lower) pyroelectric layer of the bimorph detector structure.

CMOS imagers based on Active Pixel Sensors (APS) are very important among others because of their possible technical innovations leading to ultra-low power image acquisition or efficient on-chip image preprocessing. Implementation of the image processing tasks (focal plane preprocessing and subsequent image processing) can be done effectively only with the consideration of known transfer characteristics of the imager itself. Geometrical Point Spread Function (PSF) depends on the certain geometric shape of active area in the particular design of CMOS APS. In this paper, the concept of Modulation Transfer Function (MTF) analysis is generalized to be applicable to the sampled structures of CMOS APS. Recalling theoretical results, we have analytically derived the detector MTF in the closed form for some special active area shapes. The paper also deals with the method based on pseudorandom image pattern with uniform power spectral density (PSD). This method allows to evaluate (in contrast to other methods) spatially invariant MTF including sampling MTF. It is generally known that a signal acquired by image sensor contains different types of noises. The superposition of these noises produces noise with a Gaussian distribution. The denoising method based on Bayesian estimator for implementation into the smart imager is presented.