Modulation Transfer Function (MTF) is an important quantitative measure of imaging quality of an infrared camera system. It provides quantitative description on how infrared camera system transfers contrast from object to image space. The higher the MTF values as a function of spatial frequency, the better the reconstruction of fine detail of the object space. Therefore, MTF is a good metric of performance measure for infrared camera systems. However, for QWIP Focal Plane Array (FPA) there is little comprehensive MTF result that has been reported. The over-sampled tilted knife-edge technique to generate the MTF plot is the most common method to measure MTF. Thus we have developed a method to construct the edge function from the image of tilted knife-edge. This construction is reversible since the tilted knife-edge image can be reconstructed from the edge function. Unfortunately, the knife-edge technique requires knowledge of the lens' MTF. The lens MTF is removed from the total system MTF to derive the detector and electronic MTF. In order to validate the knife-edge technique, an interferometric and small spot illumination method of MTF measurement was conducted. In the interferometric method the QWIP FPA was placed at the pupil plane, and therefore diffraction limitation was avoided. The interferogram also provides a high-resolution plot of the spectral response of the detector. The spot illumination mimics the point-spread function. Since spot illumination requires re-imaging of point source by lenses, it also requires lens' MTF that needs to be divided out. The objective of this paper is to report on an extensive MTF characterization of large format QWIP FPA.
Focal plane arrays (FPAs), which are two-dimensional array of detectors hybridized to Read Out Integrated
Circuits (ROIC), present unique challenges in characterization and functionality tests. Parameters such as temporal
and spatial NEΔT, detectivity (D*), quantum efficiency (η), spectral response (R(λ)), etc., are generally the typical
figures of merits. However, detailed operational information extractable from the electro-optical properties of the
FPAs normally requires very time-consuming data analyses. One major difficulty in analyzing large format FPAs is
the volume of data that are present in dealing with individual or group of pixels. Additional complications arise from
circuit and subsystems that are an integral part of the FPA operations, and analyzing their effect individually
requires detailed knowledge of the ROIC properties and the driving electronics. The noise analyses add another
complexity in understanding the characteristics since noises can be generated externally as well as internally. The
characterization techniques presented in this paper are performed specifically for very large format 1Kx1K LWIR
QWIP FPA but will also be applicable to other types of FPAs.
In recent years quantum well infrared (IR) photodetector (QWIP) focal plane array (FPA) technology has developed to the point where it may be considered a candidate for insertion into 3rd generation FLIR systems. Large format 1024x1024 pixels FPAs have been produced using QWIP technology. We report on the application of a large format FPAs to the challenges facing today's military. These include the collection of signatures of military vehicles for long-range target detection/identification. The FPA used was a 1024x1024 pixel array which is available commercially. from QWIP Technologies, Inc. We show imagery of military targets at ranges from 500 m to 5 km acquired in the field. The results of the performance in the field are compared to that predicted by computer models and the performance of the large format QWIP FPA will be evaluated in terms of the capabilities of a notional 3rd generation FLIR system.
Quantum Well Infrared Photodetectors (QWIPs) based infrared focal plane arrays (FPAs) are commercially available in the single color. QWIP Technologies, Inc. provides a number of QWIPCHIPTM FPAs available in the single-color, dual-color and even multiple-color, as well as varieties of physical formats in the infrared range. In this paper, we discuss the research and development efforts currently ongoing at QWIP Technologies on dual-color, visible-NIR/LWIR FPAs, and the development of a four-color QWIP-based FPA. These multicolor systems are being developed to meet the needs of a number of military applications including land mine detection. Land mines inhibit the safe movement of troops and produce chaos in countries struggling for socio-economic stability long after the cessation of hostilities. This paper will describe the efforts to develop a near multi-color QWIP sensor for mine detection. The core of the discussion will include highlights of a two-color LWIR QWIP sensor system designed to provide uniform, high spatial resolution, multi-color co-registered imagery and possess negligible spectral cross-talk. Through these efforts, The Defense Advanced Research Projects Agency (DARPA) is completing the development of a visible/infrared mine detection system, which when deployed on an airborne platform, would increase the war fighting effectiveness has sponsored the current developments.
Quantum Well Infrared Photodetectors (QWIPs) based infrared focal plane arrays (FPAs) have been widely researched and investigated in the 3-5 μm and 6-20 μm wavelength ranges. The demonstrations of QWIP FPAs include single-color, dual-color and even multiple-color, as well as varieties of physical formats in the infrared range. In this paper, we discuss the research and development efforts currently undergoing at QWIP Technologies on dual-color, visible-NIR/LWIR FPAs, as an interim step for a project sponsored by DARPA (Defense Advanced Research Project Agency) to develop a four-color QWIP-based FPA. To the best of our knowledge, this is the first reported result on visible/LWIR QWIP imager, as well as the first reported GaAs PIN diode-based FPA. This device consists of a GaAs/AlGaAs based PIN diode grown on a GaAs substrate, and subsequently a stack of multiple quantum wells (MQWs), epitaxially grown on top of the PIN structure. This VISA (visible/infrared sensor array) structure is sensitive in the 500nm-890nm as well as in the 8um-12 um wavelength ranges. Very high sensitivities are observed from both visible PIN diode and LWIR QWIP; both visible and LWIR images obtained from this device are presented in this paper.
Land mines, and other buried explosive devices, are widely deployed all over the world. As such, they pose a significant threat to dismounted soldiers, vehicles, and civilians. Land mines inhibit the safe movement of troops and produce chaos in countries struggling for socio-economic stability long after the cessation of hostilities. Consequently, there has been much investigation into how buried explosives might be detected and safely neutralized. Many different electro-optical and radar sensor systems have been considered for the detection of buried land mines. These include ground penetrating radars, polarization detectors, and visible/thermal infrared (IR) imagers. This paper will describe the efforts to develop a near IR/LWIR mine detection system. The core of the discussion will include highlights of a two-color LWIR QWIP sensor system designed to provide uniform, high spatial resolution, multi-color co-registered imagery and possess negligible spectral cross-talk. The current developments have been sponsored by the Defense Advanced Research Projects Agency (DARPA) for developing a visible/infrared mine detection system, which when deployed on a TUAV would increase the war fighting effectiveness of any rapid deployment force by facilitating ground penetration into hostile territory.