Electrically Programmable On-Chip Equivalent-Phase-Shifted Waveguide Bragg Grating on Silicon

We report an electrically programmable equivalent-phase-shifted (EPS) waveguide Bragg grating implemented on silicon with programmable spectral response. Equivalent phase shift through nonuniform sampling in a Bragg grating is an effective solution to realize a phase-shifted Bragg grating, which significantly reduces the requirement for fabrication accuracy by three orders of magnitude as compared with the fabrication of a conventional phase-shifted Bragg grating. In this paper, an EPS Bragg grating with an equivalent phase shift introduced by increasing one sampling period in the grating center by a half sampling period is proposed, and the tuning of the phase shift is enabled by incorporating two independent PN junctions in each sampling period. Through controlling the bias voltages applied to the PN junctions, the spectral response of the EPS Bragg grating is tuned. The proposed EPS waveguide grating is fabricated and its performance is experimentally evaluated. A multichannel EPS Bragg grating with programmable spectral response is demonstrated. The key advantages of implementing EPS Bragg gratings include largely reduced fabrication constraint and strong multichannel tuning capability, which opens new avenues for on-chip Bragg gratings for programmable multichannel signal processing.