Abstract

Most earlier work on optical heterodyne receivers has concentrated on detection devices operating in the 10-micron region^1–4. In view of the growing interest in eye-safe, solid state coherent laser radars using Thulium and Holmium based lasers, we have investigated the heterodyne detection characteristics of room-temperature semiconductor detectors operating in the 2-micron wavelength region. A detector characterization system has been designed and developed at NASA/MSFC that enables the accurate characterization of 2-micron detection devices for evaluating their performance as heterodyne detectors and determining their optimum operating parameters. The measured quantities will provide all the necessary detector parameters for specifying the optimum optical local oscillator power incident on the detector, the detector optimum bias voltage, and the parameters of the detector interface electronics. The detector characterization system is also capable of direct measurement of the detector heterodyne quantum efficiency η_HQE as a function of the IF signal frequency. In a coherent lidar, the signal-to-noise ratio is directly proportional to the detector heterodyne quantum efficiency, therefore knowledge of the detector heterodyne quantum efficiency is necessary for initial calibration of coherent lidars and predicting their performance.

© 1995 Optical Society of America