Self-aligned multi-channel superconducting nanowire single-photon detectors.

We describe a micromachining process to allow back-side coupling of an array of single-mode telecommunication fibers to individual superconducting nanowire single photon detectors (SNSPDs). This approach enables a back-illuminated detector structure which separates the optical access and electrical readout on two sides of the chip and thus allows for compact integration of multi-channel detectors. As proof of principle, we show the integration of four detectors on the same silicon chip with two different designs and their performances are compared. In the optimized design, the device shows saturated system detection efficiency of 16% while the dark count rate is less than 20 Hz, all achieved without the use of metal reflectors or distributed Bragg reflectors (DBRs). This back-illumination approach also eliminates the cross-talk between different detection channels.