Design of an all hollow fiber‐coupled middle infrared laser heterodyne radiometer (LHR)

Abstract

An integrated optics method, using hollow fibers which easily ensures optimal beam alignment of the local oscillator (LO) and incoherent solar radiation and promotes high photomixing efficiency, is proposed for a compact, rugged, and high-efficiency all hollow fiber-coupled photomixing assembly in the midinfrared (IR). The method is adopted for the design of an all-hollow fiber-coupled mid-IR laser heterodyne radiometer (LHR) using an 8 µm external-cavity quantum cascade laser as LO. Coupling efficiency, attenuation coefficients, total-loss transmission, and output beam divergence of the HE 11 mode in hollow fibers for the all hollow fiber-coupled mid-IR LHR are discussed in detail and are shown to highly depend on the launch conditions.