Fabrication error tolerant broadband mode converters and their working principles

Area of Science:

• Photonics and Nanophotonics
• Integrated Optics
• Computational Design

Background:

• Nanophotonic devices require compact designs without performance compromise.
• Reducing computational cost and improving fabrication robustness are key challenges in inverse design.
• Silicon-on-insulator (SOI) platform is widely used for integrated photonic devices.

Purpose of the Study:

• To experimentally demonstrate TE0-TE1 and TE1-TE3 mode converters (MCs) designed with computationally efficient inverse design.
• To evaluate the performance of these MCs in terms of conversion efficiency, insertion loss, and crosstalk.
• To assess the robustness of the designed MCs to fabrication imperfections and demonstrate their suitability for high-speed optical communications.

Main Methods:

• Utilized a computationally efficient shape optimization method for inverse design of MCs.
• Fabricated the designed MCs on a silicon-on-insulator platform.
• Experimentally characterized the mode conversion efficiency, insertion loss, and modal crosstalk across a wavelength range.
• Investigated the device robustness to dimensional variations (over/under etch).
• Performed time-domain transmission experiments using 28 Gbps OOK and 20 GBaud PAM-4 signals.

Main Results:

• Achieved mode conversion efficiencies exceeding 95% for both TE0-TE1 and TE1-TE3 MCs.
• Observed insertion losses between 0.3 dB and 1 dB over an 80 nm wavelength span (1.5-1.58 µm).
• Measured maximum modal crosstalk below -19 dB in the C-band.
• Demonstrated good robustness, with conversion efficiency dropping by at most 2.2% for 10 nm etch variations.
• Validated device performance in high-speed data transmission (28 Gbps OOK, 20 GBaud PAM-4) with Q-factors of 8 dB.

Conclusions:

• Computationally efficient inverse design enables the creation of high-performance, compact nanophotonic mode converters.
• The demonstrated MCs offer excellent conversion efficiency, low loss, and robustness, suitable for integrated photonic applications.
• These devices show significant potential for enabling high-throughput optical data communication systems.