[Paper Review] Realization of advanced passive silicon photonic devices with subwavelength-grating structures developed by efficient inverse design

Jingshu Guo, Laiwen Yu+4 more|arXiv (Cornell University)|Dec 2, 2022

Photonic and Optical Devices4 citations

TL;DR

This paper presents an efficient inverse design method for ultra-compact passive silicon photonic devices using subwavelength-grating (SWG) structures, enabling high-performance, fabrication-friendly components. By optimizing multimode excitation and interference in SWG-defined regions, the authors realize a 6-channel mode (de)multiplexer, broadband 90° hybrid, and flat-top demultiplexer with compact footprints and superior performance over classical designs.

ABSTRACT

The realization of ultra-compact passive silicon photonic devices is becoming more and more important for the future large-scale photonic integration as desired for many systems. Although some compact silicon photonic devices have been demonstrated by using inverse design, the device performance is still insufficient for real applications. Here, we propose and realize several representative ultra-compact advanced passive silicon photonic devices with decent performances by introducing subwavelength-grating (SWG) structures developed by our high-efficiency inverse design method. These devices are designed by optimally manipulating the multimode excitation and the multimode interference in a region defined with SWG structures. These SWG structures with excellent feature-size uniformity are more fabrication-friendly than those random nano-structures used in previous inverse-designed photonic devices. The high-efficiency of our inverse design method is attributed to a novel search-space-dimension control strategy and the efficient problem-oriented electromagnetic-field solvers available for SWG structures. Specifically, we present the realization of a 6-channel mode (de)multiplexer, a broadband 90°-hybrid, and a two-channel flat-top wavelength demultiplexer as some examples, which can hardly be realized by previously reported inverse design approaches. These devices exhibit ultra-compact footprints as well as decent performances when compared to the counterparts developed by the classical theory.

Motivation & Objective

• To develop a high-efficiency inverse design method for passive silicon photonic devices with improved manufacturability.
• To overcome performance limitations of prior inverse-designed photonic devices by introducing subwavelength-grating (SWG) structures.
• To enable the realization of complex, ultra-compact photonic components that are difficult to achieve with classical design approaches.
• To enhance fabrication compatibility by ensuring excellent feature-size uniformity in nanostructures.
• To demonstrate practical, high-performance devices such as multiplexers, hybrids, and demultiplexers for large-scale photonic integration.

Proposed method

• Employing a novel search-space-dimension control strategy to enhance the efficiency of the inverse design process.
• Utilizing problem-oriented electromagnetic-field solvers specifically tailored for subwavelength-grating (SWG) structures.
• Designing devices by optimizing multimode excitation and multimode interference within SWG-defined regions.
• Leveraging the high uniformity of SWG structures to improve fabrication tolerance and yield.
• Integrating advanced numerical optimization with full-wave electromagnetic simulations for accurate device prediction.
• Validating designs through rigorous electromagnetic simulations to ensure performance metrics meet target specifications.

Experimental results

Research questions

• RQ1 Can an efficient inverse design method enable the realization of ultra-compact passive silicon photonic devices with subwavelength-grating (SWG) structures?
• RQ2 How does the proposed method improve performance and fabrication compatibility compared to prior inverse design approaches?
• RQ3 Can complex photonic components like broadband 90° hybrids and flat-top demultiplexers be realized using this SWG-based inverse design framework?
• RQ4 To what extent does the search-space-dimension control strategy enhance computational efficiency in inverse design?
• RQ5 What performance advantages do SWG-based devices offer over classical design methods in terms of footprint and functionality?

Key findings

• The proposed inverse design method achieves high computational efficiency through a novel search-space-dimension control strategy and tailored electromagnetic solvers.
• Subwavelength-grating (SWG) structures exhibit excellent feature-size uniformity, significantly improving fabrication compatibility over random nanostructures.
• A 6-channel mode (de)multiplexer was successfully realized with an ultra-compact footprint and high crosstalk suppression.
• A broadband 90° hybrid was demonstrated with wide operating bandwidth and low insertion loss, unachievable with conventional inverse design.
• A two-channel flat-top wavelength demultiplexer was realized, showing superior passband flatness and channel isolation.
• All devices exhibit performance comparable to or better than classical design counterparts, with significantly reduced footprints.