Towards space qualified spatial light modulators for optical compact instrumentation

Spatial Light Modulators (SLM) are electro-optical devices based on liquid crystal (LC) properties. One of the most common type is the reflective LC on a ship display, where the LC molecules are sandwiched between a silicon pixel, and a transparent electrode. Upon illumination, the phase of the light reflected is modulated according to the molecular alignment, which is controlled, pixel by pixel, using a CMOS backplane. These devices have a high potential for space applications due to the fact that they allow to introduce any tailored wavefront distortion in an imaging instrument. Indeed, image reconstruction methods as phase diversity, for example, can be used to determine inflight the Point Spread Function and, later, introduce a corrective wavefront distortion to correct deviations of the expected optical quality. On top of that, adaptive optical systems, focusing correction, beam steering or communication systems based on modulating phase/polarization can be easily implemented using this technology. Moreover, the compactness and low power requirements of SLMs can be of great advantage for small satellites with onboard optical instrumentation. SLMs can save complexity and weight and it also reduces the risk associated to the wear of moving parts. However this technology has not been qualified for space applications. Our group has a solid background on the development of liquid crystal devices for space applications (i.e.: the polarization modulators onboard two instruments of the Solar Orbiter mission). Thus we aim to use our knowledge to obtain a full space qualified SLM. In this work we have explored the robustness of different SLM models under environmental tests of particular interest in space applications. The tests concerned with this work are a vibration test (sinusoidal and random), an operative thermo-vacuum test with a range of temperature from 30°C to 60°C; and a gamma irradiation test with accumulative doses up to 100 krad(Si). Several indicators, such as the retardance versus voltage curve, the optical flatness and time response, are monitored before and after each environmental test. Out-gassing and a non-operative thermal test have been also investigated. The SLMs successfully passed all the tests and no degradation was observed. These space simulation tests show that SLM is a valid and robust technology with a large potential to perform a great number of optical space applications. This is also a previous step towards a specifically application designed and space qualified SLM.