Monitoring of JUICE optical fibers during thermal cycles keeping the optical connectors at different stable temperatures in 3-chambers setup

Two types of multimode fibers (50μm and 400μm) are going to be used for the scalar sensor of the JUICE (Jupiter Icy Moon Explorer program) magnetometer. This optical sensor will be placed at the end of a boom and these multimode fibers will be used to transmit modulated laser light through the sensor, the light source and the detector electronics being located within the spaceship. The fibers will be exposed to very low temperatures while the optical connectors will be more protected. The simulation of the optical budget did not allow to assure that the optical power transmitted through the fibers would be OK within the entire thermal range. A 3-chambers thermal cycling test was proposed to thermally cycle in a synchronized way to different temperature plateaus, both high and low, while monitoring the transmitted optical power. Some pieces of fibers and mating connectors were stabilized to one temperature while others were at other values. The temperature ranges for each chamber were: -190ºC to 120ºC for one chamber, -160ºC to 100ºC for the second one and -80ºC to +45ºC for the third one. The light source used for the test was developed by the institute of experimental physics at TUG Graz using exactly the same lasers that will be used for JUICE. The stability of the setup was assured using a reference path. This paper presents the main challenges for this test and the results obtained.