Low-loss chalcogenide photonic devices with a secondary coating method

Abstract

In the traditional dry etching process for photonic device fabrication, the etching effect is influenced in many ways, usually resulting in relatively large sidewall roughness and high transmission loss. In this study, an effective method, namely the secondary coating method, is proposed to reduce the transmission loss of a Ge-Sb-Se chalcogenide waveguide and increase the quality factor (Q-factor) of a Ge-Sb-Se chalcogenide micro-ring resonator. The Ge-Sb-Se waveguide and micro-ring resonator are fabricated by ultraviolet exposure/electron beam lithography and inductively coupled plasma etching technology. Afterward, a 10 nm-thick Ge-Sb-Se thin film is deposited by thermal evaporation. The measurements show that after secondary coating, the sidewall roughness of the waveguide is reduced from 11.96 nm to 6.52 nm, with the transmission loss reduced from 2.63± 0.19 dB/cm to 1.86± 0.11 dB/cm at 1.55 µm wavelength. Keeping an equal coupling condition with equal radius and coupling distance, the Q-factor of the micro-ring resonator is improved by 47.5% after secondary coating. All results indicate that the secondary coating method is a feasible way to generate low-loss and high Q-factor integrated chalcogenide photonic devices.