Optimum Integrated Heterodyne Photoreceiver for Coherent Lidar Applications
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Optimum Integrated Heterodyne Photoreceiver for Coherent Lidar Applications Farzin Amzajerdiana, Diego Pierrottetb,Upendra Singh a, and Michael Kavaya a a NASA Langley Research Center, Hampton VA 23681 b Coherent Applications, Inc., Hampton VA, 23669
ABSTRACT Many coherent lidar applications, particularly airborne and space-based applications, impose stringent power and size constraints while requiring high levels of sensitivity. For this reason, optimization of the lidar heterodyne photoreceiver is one of the critical steps in ensuring full utilization of limited resources to achieve the required sensitivity. The analysis of 2-micron heterodyne receivers shows that substantial improvement of the order of 3 dB can be obtained by proper optimization of the receiver key control parameters and elimination of its parasitic capacitances by integrating the detector, its bias circuit, and the preamplifier on a single substrate. This paper describes analytical steps for defining optimum heterodyne receiver design parameters and development of experimental devices operating at 2-micron wavelength.
INTRODUCTION Coherent lidar has proven to be a powerful tool for a wide range of remote sensing applications capable of measuring atmospheric wind velocity, turbulence, aerosol concentration, cloud height and velocity, and CO2 concentration. However, most coherent lidar applications continue to demand smaller and more efficient instruments. Optimization of the lidar heterodyne photoreceiver is one of the critical steps in ensuring full utilization of limited resources and achieving the required sensitivity. Analysis of heterodyne photoreceivers has projected an improvement of about 3dB in lidar sensitivity by reducing the parasitic capacitances associated with the detector and its interfacing preamplifier and properly adjusting the local oscillator power level [1-2]. This improvement in lidar sensitivity directly translates to a factor of 2 reduction in either the transmitter laser power or the telescope area. The key areas that must be considered in optimization of a heterodyne photoreceiver are the effects of the detector non-linearity, the parasitic capacitances of the circuit, and the amplifier gain and noise characteristics. This paper describes these effects, their interactions, and their impact on the photoreceiver performance. Using this analysis, the optimum design parameters for 2-micron heterodyne photoreceivers are defined and the status of the development of a series of experimental devices operating at different bandwidths is reported.
HETERODYNE PHOTORECEIVER MODEL The performance of any heterodyne photoreceiver is established by the operating and intrinsic parameters of its detection device and its interfacing preamplifier. Figure 1 shows a typical photoreceiver topology where the detector output current is amplified by a transimpedance amplifier. The detector is operated in reverse-biased mode for increased
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frequency response. The performance of photoreceivers is best described by their Trans
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