Light interference detection on-chip by integrated SNSPD counters

Abstract

A SWIFTS device (Stationary Wave Integrated Fourier Transform Spectrometer) has been realized with an array of 24 Superconducting Nanowire Single Photon Detectors (SNSPD), on-chip integrated under a Si3N4 monomode rib-waveguide interferometer. Colored light around 1.55μm wavelength is introduced through end-fire coupling, producing a counter-propagative stationary interferogram over the 40nm wide, 120nm spaced, 4nm thick epi-NbN nanowire array. Modulations in the source bandwidth have been detected using individual waveguide coupled SNSPDs operating in single photon counting mode, which is a step towards light spectrum reconstruction by inverse Fourier transform of the stationary wave intensity. We report the design, fabrication process and in-situ measurement at 4.2K of light power modulation in the interferometer, obtained with variable laser wavelength. Such micro-SWIFTS configuration with 160nm sampling period over 3.84μm distance allows a spectral bandwidth of 2μm and a wavelength resolution of 170nm. The light interferences direct sampling ability is unique and raises wide interest with several potential applications like fringe-tracking, metrology, cryptography or optical tomography.