SWIFTS Waveguide Micro-Spectrometer Integrated on Top of a 1D-NbN SNSPD Array

The SWIFTS integrated waveguide device (Stationary Wave Integrated Transform Spectrometer) has been designed on top of a 1D parallel array of 50-nm-width single stripe Superconducting Nanowire Single Photon Detectors (SNSPD). Colored light, around 1.55-μm wavelengths, is introduced inside PE-CVD deposited and patterned Si3N4 monomode rib waveguides, in order to produce a counter-propagative stationary wave over the Nanowire array. Optical power losses are reported, mainly due to waveguide sidewall roughness scattering, end-fire fiber coupling and mode coupling mismatch. Simulations and measurements over waveguide bending, coupling and roughness quantify the loss contributions of the different factors. E-beam lithography has been re-optimized on 4-inch sapphire and NbN passivating nano-layers added for elaborating SWIFTS devices with 24 Nanowires each of 50-nm widths, capable of directly sampling the stationary wave profile. Process compatibility has been demonstrated, thanks to the MgO layer protecting NbN Nanowires before SiN deposition. Each SNSPD should operate separately at 4K in the single photon counting regime for sampling the guided standing wave, introduced by the high precision mechanical alignment of a fiber in the test set-up.