Backside-etched SNSPDs with enhanced system detection efficiency at 1064 nm

A system detection efficiency (SDE) of up to 90% is commonly reported for superconducting nanowire single-photon detectors (SNSPDs) coupled with single-mode fibers at 1550 nm. However, achieving stable and high-performance SDE for practical multimode fiber-coupled SNSPDs at 1064 nm, a wavelength widely used in lidar, remains a significant challenge. This difficulty arises primarily from two factors: first, the backside-illuminated structure, which is designed to focus incident light from fibers onto the photosensitive area of the SNSPD, induces substantial absorption loss in the silicon substrate; second, the nanowire absorption efficiency exhibits pronounced polarization sensitivity, and a front-side-illuminated structure also has relatively limited fabrication process compatibility, which makes it challenging to achieve polarization insensitivity and high SDE. In this paper, we report a backside-etched SNSPD design with improved SDE performance at 1064 nm. Specifically, a titanium dioxide layer was incorporated into the optical cavity to effectively suppress the polarization sensitivity. Concurrently, an additional dry etching step was implemented on the silicon substrate, reducing the silicon substrate's intrinsic absorption loss from 25% to less than 5%. Experimentally, an SDE of 67% was achieved for our sample device at 1064 nm, with the minimum SDE exceeding 64% for all polarization states. This study demonstrates a high-performance solution optimized for 1064 nm, a wavelength offering superior atmospheric transmission and far-field beam characteristics, enabling broad applications in lidar, satellite laser ranging, and industrial manufacturing.