A Novel Approach to Interface High-Q Fabry-P\'erot Resonators with Photonic Circuits

TL;DR

This paper introduces a numerically optimized polarization-splitting grating coupler that efficiently integrates high-Q Fabry-Pérot resonators with silicon photonic circuits, enabling stable frequency locking and back reflection suppression.

Contribution

It presents a novel reflection cancellation circuit with a multi-port polarization-splitting grating coupler designed via inverse methods for high efficiency and back reflection suppression in integrated photonic systems.

Findings

Achieved 55% coupling efficiency with the grating coupler.

Realized 5.8 dB insertion loss and over 9 dB back reflection suppression.

Demonstrated integration with various off-chip reflective devices.

Abstract

The unique benefits of Fabry-P\'erot resonators as frequency-stable reference cavities and as an efficient interface between atoms and photons make them an indispensable resource for emerging photonic technologies. To bring these performance benefits to next-generation communications, computation, and timekeeping systems, it will be necessary to develop strategies to integrate compact Fabry-P\'erot resonators with photonic integrated circuits. In this paper, we demonstrate a novel reflection cancellation circuit that utilizes a numerically optimized multi-port polarization-splitting grating coupler to efficiently interface high-finesse Fabry-P\'erot resonators with a silicon photonic circuit. This circuit interface produces spatial separation of the incident and reflected waves, as required for on-chip Pound-Drever-Hall frequency locking, while also suppressing unwanted back reflections from the Fabry-P\'erot resonator. Using inverse design principles, we design and fabricate a polarization-splitting grating coupler that achieves 55% coupling efficiency. This design realizes an insertion loss of 5.8 dB for the circuit interface and more than 9 dB of back reflection suppression, and we demonstrate the versatility of this system by using it to interface several reflective off-chip devices.