Resonant Cavity Enhanced Photo-Diodes for LWIR Communications

ABSTRACT:The LWIR spectrum is well suited for moderate- to long-range free space communications because of its atmospheric window and low scattering by dust, haze, precipitation, and fog. The recent impressive laser development of QCLs is poised to provide the high speed LWIR transmitter for such a free space communication system; a corresponding advance in LWIR detectors is needed to enable the high-speed receiver. The specifics of the LWIR detector requirements are: 8-12 micron wavelength response, GHz bandwidths, and D*=10^13 Jones. The wavelength response and bandwidth requirements are already met by existing detectors, however present detectors are 100 X away from meeting the D* requirement. Meeting the needed 100 X improvement in D* will require 10^4 improvements in both dark current and background current of detectors. This program will develop a detector breakthrough, which will accomplish the 100 X improvement in D*, using an advanced type of resonant cavity-enhanced photodiode (RCE-PD). The RCE-PD developed in this program will have narrow spectral response (at LWIR wavelengths) to limit background current, a thin active region to reduce dark current, and multi-GHz bandwidth.BENEFIT:The detector advance developed in this program is aimed at low noise, high-speed detection of LWIR lasers. In addition to the DoD use of such a detector for free space communications, these detectors are ideally suited for all applications involving detection of both MWIR and LWIR lasers signals. IR monitoring of gases is an especially important example of a commercial application that requires detection of MWIR and LWIR lasers. Rapidly growing applications of such IR gas sensors involve monitoring of green house gases, toxic leaks at refineries and pipe lines, and breath analysis.