Amorphous-silicon visible-light detector integrated on silicon nitride waveguides

Visible light integrated photonics is emerging as a promising technology for the realization of optical devices for applications in sensing, quantum information and communications, imaging and displays. Among the existing photonic platforms, high-index contrast silicon nitride (Si₃N₄) waveguides offer broadband transparency in the visible spectral range and a high scale of integration. As far as the complexity of photonic integrated circuits (PICs) increases, on-chip detectors are required to monitor their working point for reconfiguration and stabilization operations. In this work we present a compact in-line power monitor integrated in Si₃N₄ waveguides that operates in the red-light wavelength range (660 nm). The proposed device exploits the photoconductivity of an hydrogenated amorphous silicon (a-Si:H) film employed as a coating layer of the optical waveguide. Experimental results show a responsivity of 30 mA/W, a sensitivity of – 45 dBm and a sub-μs time response. These features enable the use of the proposed photoconductor for high-sensitivity monitoring and control of visible-light Si₃N₄ PICs.