Geiger-mode ladar cameras

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The performance of Geiger-mode LAser Detection and Ranging (LADAR) cameras is primarily defined by individual pixel attributes, such as dark count rate (DCR), photon detection efficiency (PDE), jitter, and crosstalk. However, for the expanding LADAR imaging applications, other factors, such as image uniformity, component tolerance, manufacturability, reliability, and operational features, have to be considered. Recently we have developed new 32×32 and 32×128 Read-Out Integrated Circuits (ROIC) for LADAR applications. With multiple filter and absorber structures, the 50-μm-pitch arrays demonstrate pixel crosstalk less than 100 ppm level, while maintaining a PDE greater than 40% at 4 V overbias. Besides the improved epitaxial and process uniformity of the APD arrays, the new ROICs implement a Non-uniform Bias (NUB) circuit providing 4-bit bias voltage tunability over a 2.5 V range to individually bias each pixel. All these features greatly increase the performance uniformity of the LADAR camera. Cameras based on these ROICs were integrated with a data acquisition system developed by Boeing DES. The 32×32 version has a range gate of up to 7 μs and can cover a range window of about 1 km with 14-bit and 0.5 ns timing resolution. The 32×128 camera can be operated at a frame rate of up to 20 kHz with 0.3 ns and 14-bit time resolution through a full CameraLink. The performance of the 32×32 LADAR camera has been demonstrated in a series of field tests on various vehicles.