Polarization-independent narrow-band integrated add-drop filter for the short near-infrared wavelength range

Photonic integrated circuits operating at short near-infrared wavelengths are gaining relevance in applications such as on-chip single-photon sources and two-photon microscopy. These systems significantly benefit from compact, low-loss, and polarization-insensitive components. In this work, we design and experimentally demonstrate a polarization-independent single-channel optical add-drop filter operating at a center wavelength of 926 nm. The device is based on a compact grating contra-directional coupler fabricated on a 400-nm-thick silicon nitride (SiN) platform using a standard CMOS-compatible process. Experimental results show a polarization-dependent loss of less than 0.85 dB over a 1.5 nm bandwidth and an extinction ratio greater than 15 dB for both transverse-electric (TE) and transverse-magnetic (TM) polarizations. The proposed filter provides an efficient solution for short-wavelength near-infrared photonic integrated circuits and will enable advancements in on-chip quantum networks and lab-on-chip systems.