Monte-carlo computations for predicted degradation of photonic devices in space environment

Photonic systems are more and more used for aerospace applications and most of these systems require reliable optoelectronic emitters or photodetectors such as Laser diodes or phototransistors. Examples of satellite applications including such devices consist in time reference (atomic clock), attitude control (Fiber Optic Gyroscope) and telecommunications (inter-satellite links and satellite-downlinks). In order to ensure reliability of photonic devices for space applications, a critical issue requires to correctly evaluate their degradation with respect to the constraints of various mission profiles. In particular, the wide range of satellite missions for LEO (Low Earth Orbit), GEO (Geostationary Earth Orbit) or MEO (Medium Earth Orbit) environment, makes currently qualification activities very challenging. Selection tests and life-testing are specifically based on optical telecommunication standards (ex. Telcordia GR-468 CORE) for reliability prediction. Basically, this approach uses the extrapolation of degradation from electrical or optical parameters monitoring and occasionally physics of failure on a weak statistic population allowing both strong test time reduction and long-term reliability prediction. Unfortunately in the case of mature technology, there is a huge complexity in order to calculate average lifetime and failure rates (FITs) using aging tests in particular due to extremely low failure rates. For instance, regarding Laser diode technologies, times to failure tend to be 106 hours under typical conditions (10 mW, 80°C). These aging tests must be performed on more than 100 components aged during 10,000 hours mixing different temperatures and drive current conditions conducting to acceleration factor above 300. Such conditions are high-cost, time consuming, cannot give a complete distribution of times to failure and highlight that predicted lifetime based on previous standards is no longer effective. In the case of radiation aspects for space environment, the correct estimation of the key performance degradation as a function of the total ionizing dose (TID) and/or the displacement damage dose (DDD) received by the devices in the framework of a specific mission profile, remains also a crucial point to face. In this paper, we demonstrate the relevance of Monte-Carlo based computations to predict degradation, extrapolate lifetime distribution and failure rates in operating conditions of specific photonic devices for space applications mixing physical parameters of experimental degradation laws and statistic tools. Firstly, Distributed Feedback single mode Laser diodes used for 1550 nm telecommunication applications operating at 2.5 Gb/s transfer rate are addressed and potentially for optical switching of RF/microwave signals developed for enhancing the reconfiguration capabilities of future telecom satellites in Ka-band with multiple antenna beams. Electrical and optical parameters have been measured before and after aging tests, performed at constant current, according to Telcordia GR-468 standards. Cumulative failure rates and lifetime distributions are computed using statistic calculations and equations of drift mechanisms versus time fitted from experimental measurements. We also demonstrate that Monte-Carlo approach can be associated with a dedicated Design of Experiments (DoE) methodology in order to predict End-Of-Life performance of silicon based photo transistors arrays used in optical encoders to monitor the angular position, speed and acceleration of mechanisms by means of CMGs (Control Moment Gyroscope) controlling the orientation of spacecrafts and exposed to a wide range of space environments. The proposed test plan allows to model the degradation of the main performances (mainly photo and dark current) of silicon based phototransistors arrays with respect to TID and DDD. Our approach does not need any accurate physical modeling of the device degradation that would be very complex to obtain anyway. In addition it does not require any specific knowledge regarding the device technology which makes it very useful for the definition of qualification strategies.