Coupling of Photonic Waveguides to Integrated Detectors Using 3D Inverse Tapering
We report on the design, fabrication, and characterization of a Silicon Nitride (SiN)-based integrated photonic chip in which the dielectric waveguides are coupled to photodetectors integrated homogeneously into the Silicon substrate. The photonic-electronic coupling was realized by a 3D inverse tapering of SiN waveguides. The novelty of our approach consists in tapering the waveguide in the vertical direction by means of an engineered wet chemical etching. This allows for a smooth transition from a full-height to an arbitrarily thin waveguide thickness at the detector location, expanding adiabatically the optical mode towards the latter. The measured chips showed a responsivity R≈109μ A/mW and a corresponding quantum efficiency of 16% at an excitation wavelength of 850 nm. Our technological solution offers a versatile method for a top-down monolithic integration of lightwave circuitries with substrate-located photon sensing devices.
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