IR Detectors: Heterodyne and Direct

In recent years there have been considerable advances in the performance of wide-bandwidth infrared detectors, both for direct and heterodyne detection. In this paper I will discuss briefly the major areas of current detector development, compare various aspects of heterodyne and direct detection, discuss amplifier considerations for wide-bandwidth detection operation, and describe state-of-the-art performance in direct and heterodyne detection. In addition, differences and trade-offs between photodiodes and photoconductors will be discussed, in particular the operating temperature dependence of direct and heterodyne detectors at 10 μm. The content of this paper will be limited to photodiodes and photoconductors in the 1- to 20-μm region with bandwidths in the range of 1 to 100 MHz. This encompasses most of the present detector needs of LIDAR systems for wavelengths beyond the range of efficient photomultipliers.