Thermal Stability of SU-8 Low-Loss Optical Coupling Interconnects at 850 nm

Ultra-low-loss optical coupling between photonic circuits and components is crucial in many applications such as photonic quantum computing, sensing and optical communications. This letter presents the thermal stability of a SU-8 based taper optical interconnect by characterizing its optical coupling efficiency (CE) and structural robustness after exposure to elevated temperatures. The taper is heated from 280 °C to 400 °C for duration from 1 min to 120 min. The experimental results reveal that CE loss is linear with the duration of the high temperature, while the relation between the temperature and duration adheres to a logarithmic model at a specific CE loss level. This offers a valuable means to predict the maximum temperature and duration before exceeding a CE loss threshold, enabling the determination of material processing. A limit temperature-duration curve for a maximum 0.1 dB optical coupling degradation is derived. This analysis demonstrates that the SU-8 tapers can withstand a temperature of 300 °C for 9 min and 350 °C for 1min and 30 s with less than 0.1 dB optical loss. The structural mechanical stability of the taper is confirmed up to 400 °C for 1 hour, well above the aforementioned optical limit.