Inverse-Designed Grating Couplers with Tunable Wavelength via Scaling and Biasing

TL;DR

This paper introduces inverse-designed, broadband grating couplers with tunable wavelength capabilities, demonstrating significant efficiency improvements through systematic scaling and biasing, facilitating wafer-scale testing and adaptable photonic applications.

Contribution

The work presents a novel inverse design method for broadband grating couplers with tunable wavelength, including a systematic scaling and biasing technique to recover efficiency lost due to fabrication deviations.

Findings

Achieved up to 52% simulated efficiency, with 32% measured at 1540 nm.

Systematic scaling and edge biasing improve efficiency up to eightfold.

Enables post-design correction for fabrication variations, supporting large-scale photonic integration.

Abstract

Photonic integrated circuits are heavily researched devices for telecommunication, biosensing, and quantum technologies. Wafer-scale fabrication and testing are crucial for reducing costs and enabling large-scale deployment. Grating couplers allow non-invasive measurements before packaging, but classical designs rely on long tapers and narrow bandwidths. In this work, we present compact, inverse-designed grating couplers with broadband transmission. We optimized and fabricated arrays of devices and characterized them with a 4f-scanning setup. The nominal design reached simulated efficiencies of 52 %, while measurements confirmed robust performance with up to 32 % efficiency at the target 1540 nm wavelength and 46 % at shifted wavelengths. Without scaling and contour biasing, the measured efficiency at the target wavelength drops to only 4.4 %. Thus, a key finding is that systematic scaling and edge biasing recover up to an eightfold improvement in efficiency. These inverse-designed grating couplers can be efficiently corrected post-design, enabling reliable performance despite fabrication deviations. This approach allows simple layout adjustments to compensate for process-induced variations, supporting wafer-scale testing, cryogenic photonic applications, and rapid design wavelength tuning.