Inverse-designed Grating Couplers Achieve 52% Efficiency and 46% Performance at Shifted 1540nm Wavelengths

Grating couplers represent a critical component in photonic integrated circuits, enabling efficient light transfer for applications ranging from telecommunications to biosensing, but traditional designs often suffer from limited bandwidth and bulky structures. Lorenz J. Sauerzopf, Fabian Becker, and Kai Müller demonstrate a significant advance in this field with the development of compact, inverse-designed grating couplers capable of broadband transmission and tunable wavelength operation. The team achieves remarkably high efficiencies, reaching 52% in initial designs and maintaining robust performance with up to 32% efficiency at a target wavelength and 46% at shifted wavelengths, a substantial improvement over conventional couplers. Crucially, the researchers demonstrate that systematic scaling and edge biasing techniques recover up to an eightfold increase in efficiency, enabling reliable performance even with fabrication variations and paving the way for wafer-scale testing, cryogenic applications, and rapid design adaptation.

Photonic integrated circuits represent heavily researched devices for applications including telecommunication, biosensing, and quantum technologies. Wafer-scale fabrication and testing prove crucial for reducing costs and enabling large-scale deployment. Grating couplers facilitate non-invasive measurements before packaging, but conventional designs typically rely on long tapers and narrow bandwidths. This work presents compact, inverse-designed grating couplers exhibiting broadband transmission. The team optimized and fabricated arrays of these devices, subsequently characterizing them with a specialized scanning setup. Simulations initially predicted efficiencies of 52%, and measurements confirm these results, demonstrating a significant advancement in the field.

Wafer Scale Cryogenic Grating Coupler Fabrication

This research centers on inverse design techniques to create grating couplers, essential components in integrated photonics used to efficiently couple light between optical fibers or free space and nanoscale waveguides on a chip. A key motivation is developing couplers that enable efficient and automated testing of photonic chips directly on the wafer before they are separated, which is crucial for high-volume manufacturing. The study also addresses the need for couplers that maintain performance at cryogenic temperatures, essential for applications like quantum computing where material properties and fabrication tolerances change at low temperatures. The team emphasizes the importance of designs that are robust to fabrication variations and transferable across different fabrication platforms.

Researchers demonstrate that scaling, uniformly changing the size of the coupler features, and edge biasing, adjusting the feature sizes near the edges, are effective post-design strategies to compensate for fabrication errors and maintain performance. This provides a practical and relatively simple approach to improve robustness. The designs are optimized to maintain high efficiency even at cryogenic temperatures, critical for quantum applications, and operate over a broad range of wavelengths, making them versatile for different applications. Improved grating couplers facilitate automated wafer-scale testing, reducing manufacturing costs and improving quality control. This research provides a practical and effective approach to designing robust and high-performance grating couplers for a wide range of photonic applications, with a particular focus on enabling scalable manufacturing and cryogenic operation. The techniques developed are broadly applicable to any integrated photonic system requiring efficient light coupling.

Optimized Grating Couplers Achieve 57% Efficiency

Scientists achieved peak simulated efficiencies of 57% at 1540nm using an optimized design for inverse-designed grating couplers, demonstrating a significant advancement in photonic integrated circuit technology. Detailed analysis revealed that systematic adjustments to the design, specifically scaling and edge biasing, dramatically influence the spectral response and overall efficiency of the couplers. Simulations demonstrated that negative edge biases shift the peak transmission to shorter wavelengths, while positive biases shift it to longer wavelengths, providing a powerful method for wavelength tuning. Experiments confirmed these simulated spectral shifts, with measurements showing clear red and blue shifts corresponding to positive and negative edge biases respectively.

Crucially, measurements revealed a substantial performance drop to only 4. 4% efficiency at the target 1540nm wavelength when the devices were fabricated without scaling or edge biasing. However, applying systematic scaling and edge biasing recovered performance, delivering up to an eightfold improvement in efficiency, highlighting the robustness of this approach against fabrication deviations. These inverse-designed grating couplers, characterized with arrays of devices ranging from 86% to 114% scale and -20nm to 40nm bias, provide a pathway to compensate for process-induced variations, supporting wafer-scale testing, cryogenic photonic applications, and rapid design wavelength tuning. This work establishes a robust method for achieving high-performance grating couplers, even in the presence of fabrication imperfections, paving the way for more reliable and efficient photonic integrated circuits.

Inverse Design Boosts Grating Coupler Efficiency

This research demonstrates the successful development of compact, inverse-designed grating couplers with broadband transmission characteristics. The team achieved efficiencies of up to 32% at 1540nm and 46% at shifted wavelengths, representing a significant advancement in photonic integrated circuit technology. Crucially, the study establishes that systematic scaling and edge biasing are essential for recovering up to an eightfold improvement in efficiency, effectively compensating for variations introduced during the fabrication process. These inverse-designed grating couplers offer a robust solution for wafer-scale testing and cryogenic photonic applications, eliminating the need for time-consuming fiber alignment.

Researchers confirmed that scaling and biasing reliably counteract fabrication-induced variations, as demonstrated by consistent spectral shifts observed in both simulations and experiments. While acknowledging potential limitations, including waveguide losses, the team suggests that optimizing the fabrication process could further enhance device performance. Future work could explore maintaining high polarization extinction to enable versatile excitation and detection schemes, and facilitate cross-polarization measurements.