At previous SPIE meetings, we reported on an optoelectronic device that measures the complete polarization state of incident infrared light in a single pixel and in a single frame for a narrow wavelength band (δλ<0.05 μm). Using at least four quantum-well stacks and four linear gratings, each stacked alternating above the other, the device uses the interference among light paths to create a distinct pattern of photocurrents at each quantum-well stack coding for a specific polarization. In this paper, we will model the performance of this device, a quantum-well infrared single-pixel polarimeter (QWISPP), in the setting of a Fourier transform infrared (FTIR) imager. We model one column of QWISPP pixels detecting an inferferogram. Using an FTIR with randomly varying QWIsPP pixels to detect the interferogram, we discovered a technique that allows an 100x improvement in measured spectral-polarization uncertainty compared to the use of identical QWISPP pixels in an FTIR or grating spectrometer. The technique also enables a 15x improvement in the uniformity of the error across a sample spectrum. In other words, we turn into an advantage the imperfections in fabricating an FPA of QWISPPs.
In the Advanced Detectors Research Group within the Space-Based Optical Sensing Center of Excellence in the Spacecraft Technology Division of the Air Force Research Laboratory’s Space Vehicles Directorate, we look to enhance existing detector technologies and develop new detector capabilities for future space-based surveillance missions. To that end, we present some ideas for tuning the wavelength response of detectors throughout the IR (using applied electric or magnetic fields or via a lateral biasing technique). We also present a concept for detecting the full polarization vector of a signal within a single pixel of a quantum well detector.
By layering quantum well stacks separated by partially transmissive linear gratings, similar to a multi-color QWIP, one may be able to detect the full Stokes vector at a single pixel. Such a detector would greatly aid polarization-based automated algorithms to detect targets from earth-gazing platforms. We report results from a theoretical calculation of normally incident infrared light absorbed by quantum wells in an eight-layer quantum-well/grating structure. The structure consists of four quantum-well stacks, of 50 quantum wells each, separated by contact layers and lamellar gratings. The gratings following the first three quantum well stacks are formed by perfectly conducting rectangular strips separated by a transparent dielectric that allows some light to be transmitted. The top grating, following the fourth quantum well stack, is completely reflective. Each of the four lamellar gratings is oriented at a different angle. Incident radiation is diffracted and reflected to different orders and at different angles at each of the four gratings. The model is based on a uniaxial-optics transfer-matrix technique. We calculate the energy absorbed by each of the layers. This in turn allows one to predict and compare which layers will respond for partially- and fully-polarized incident light of either linear or circular polarization.