High-sensitivity 3 to 5 micron PPLN LADAR wavelength converter system

Abstract

Remote sensing systems, such as LIDAR, have benefited greatly from nonlinear sources capable of generating tunable mid-infrared wavelengths (3-5 microns). Much work has focused on improving the energy output of these sources so as to improve the system's range. We present a different approach to improving the range by focusing on improving the receiver of a LADAR system employing nonlinear optical techniques. In this paper, we will present results of a receiver system based on frequency converting mid-infrared wavelengths to the 1.5 µm region using Periodically-Poled Lithium Niobate (PPLN). By doing so, optical amplifiers and avalanche photodetectors (APDs) developed for the fiber optics communications industry can be used, thus providing very high detection sensitivity and high speed without the need for cryogenically cooled optical detectors. We will present results of laboratory experiments with 3 µm, 2.5 ns FWHM LADAR pulses that have been converted to 1.5 µm. Detection sensitivities as low as 1.5 x 10 -13 Joules have been demonstrated. The performance of the Peltier-cooled 1.5 µm InGaAs APD quasi photon-counting receiver will be described.