On-chip integration of a tunable metalens and deformed multimode waveguide for a speckle spectrometer.

We proposed and demonstrated a silicon photonic speckle spectrometer by integration of a thermo-optic on-chip tunable metalens and a deformed multimode waveguide based on a multimode interferometer (MMI) with edge defects. The tunable metalens enables selective excitation of the MMI from 11 input waveguides while maintaining a much more compact footprint than a conventional optical switch array. The artificially introduced edge defects facilitate the scrambling of the optical waves in the multimode region, which improves the resolution of the speckle spectrometer. The device is fabricated by a standard silicon photonic foundry process. A spectral resolution of 0.85 nm over an operational bandwidth of 100 nm is achieved. This work provides an alternative structure for on-chip integrated speckle spectrometer.