Development of High Gain, High Sensitivity Imaging Detectors for Laser Radar Systems

High performance, high gain, uncooled detectors and detector arrays working at eye safe wavelengths are necessary or the development of low cost laser radar systems for imaging and targeting applications. Imaging arrays with the capability of acquiring and processing true time delay information at the pixel level for ranging is extremely important for obtaining the 3D imagery with laser radar systems. For very low level signal readout, some gain on the detector element will be very useful. This can be achieved by using the APDs. PES proposes to develop 2D arrays of APD type of detectors with on wafer microlenses to reduce the detector area and improve the signal to noise performance. In addition to improving the signal to noise ratio, the effective reduction of detector area can be used to increase the temperature of operation while maintaining good signal to noise ratio. An improvement by two orders of magnitude or more of signal to noise ration has been obtained in the past by many researchers. On wafer microlenses and microlens arrays combined with photodetectors have been fabricated by Princeton Electronic Systems (PES) in the past for imaging array applications using quantum Well IR Photodetectors (QWIP) and InGaAs PIN types of detectors. PES has developed a very sophisticated technique for fabrication of the microlenses on semiconductor wafers and on the FPAs. This technology can be used to develop imaging array for LADAR applications with readout circuits which will process time delay information for 3D imaging. In phase I, PES wants to develop a 128x128 element array InGaAs APDs with microlenses as well as study the requirements for the detectors for the application. The technology of the microlenses can be applied to any types of detectors in phase II. In phase II, the imaging array with a suitable detector with the microlenses and the readout electronics with time delay readout capability will be fabricated for AF applications.