Optical Cryocooling for Space-borne Sensors

ABSTRACT: We propose to develop a light weight, compact, vibration-less and micro-scale cooler for space-mission conditions based on optical refrigeration using an all-fiber approach. Specifically, we will use a Tm+3-doped fiber laser to pump Tm+3-doped glass fibers, which provide the cooling action on the affixed heat source. The cooling fiber is attached to the heating sample e.g., EO-IR detector or any kind of space-borne sensor. NP Photonics'high electrical- to-optical efficiency thulium-doped fiber lasers (>20% E-O) offer power up to 100W and beyond. This fits the scope of Phase I, and also allows for scaling to much higher cooling requirements in Phase II. Our system has several key advantages compared to conventional bulk glass systems: 1) its cooling power benefits from high optical confinement in the fiber core; 2) fiber Bragg gratings are transparent to the waste photons and thus minimize fluorescence reabsorption; they will be used for enhancing pump absorption; and 3) the all-fiber system can conveniently transfer part of the heat to a remote location. In Phase I, we will investigate cooling fibers based on germanate and tellurite host glasses, with possibility to extend to ZBLAN fibers later. Theoretical modeling of optical cooling in our fiber and thermal modeling of the entire fiber cooler will be performed in parallel with the experiments. BENEFIT: Using all-fiber optical cooling techniques provide a vibration less cooler that would be a substantial advantage in satellite and space applications. Fiber-based optical cooling or thermal management could find applications in a variety of commercial applications, such as broadcast transmitters and other concentrated radiators, or other heat limited electronic or opto-electronic devices such as microprocessors or semiconductor receivers. One of the challenges associated with scaling-up the power output of fiber lasers toward and beyond the kW level is thermal management in the active fiber. One promising direction is optical cooling using laser sources to cool down the fiber and enable alternate approaches for thermal dissipation strategies in high power fiber lasers. Cooling and thermal dissipation using fibers and fiber lasers would not only apply to the space-borne sensors specifically targeted in this program, but many other electronic and opto-electronic applications where conventional proximity cooling is inconvenient or unsuitable.