Development of PPLN Based Mid-Wave Infrared Transmitter and Receiver for SatCom

Abstract

Recent advances in optical satellite communication (SatCom) have demonstrated the potential of laser-based systems to surpass traditional radio-frequency methods in terms of data rates, size, weight, and power efficiency (SWaP). A series of international proof-of-concept missions over the past several decades have showcased the feasibility of optical SatCom, most utilizing short-wave infrared (SWIR, 0.8-1.7 μm) wavelengths due to their favorable atmospheric transmission and the maturity of terrestrial telecom-derived technologies. However, SWIR systems suffer from severe performance degradation under adverse weather conditions such as haze, fog, and clouds. This remains an unsolved challenge that limits system reliability. This thesis addresses this challenge by proposing a novel optical transmitter/receiver pair operating in the mid-wave infrared band (MWIR, 3–5 μm), which is significantly less affected by atmospheric scattering and turbulence. The key innovation lies in leveraging nonlinear optical processes to achieve compact, high-speed wavelength conversion. A proprietary intracavity design enables efficient conversion of 1550 nm C-band laser light into 3.4 μm (MWIR) at the transmitter, and then back into 810 nm SWIR light at the receiver, using difference frequency generation (DFG) and sum frequency generation in a periodically poled lithium niobate (PPLN) nonlinear crystal, respectively. This two-stage conversion strategy allows the use of commercially available, high-speed C-band laser sources and high-performance SWIR silicon detectors, preserving the information bandwidth of the original signal throughout the optical link while offering significant gains in overall detectivity versus direct MWIR detectors. In this thesis, a proof-of-principle prototype for the transmitter and receiver system is designed, built, and experimentally characterized. A novel model that combines a spatially dependent rate equation laser simulation with a two-dimensional gaussian nonlinear three-wave coupling simulation is presented as well. The experimental results agree well with the model, and further optimizations relating to cavity design and beam overlap in the nonlinear medium are identified for future work.