High-performance, ultra-broadband silicon polarization beam splitter utilizing mode conversion Bragg gratings

Area of Science:

• Photonics
• Integrated Optics
• Materials Science

Background:

• High-performance polarization beam splitters (PBSs) are crucial for signal integrity in photonic systems.
• Existing PBS designs often face limitations in bandwidth and performance on silicon platforms.

Purpose of the Study:

• To experimentally demonstrate a high-performance, ultra-broadband on-chip silicon PBS.
• To integrate a mode conversion Bragg grating (MC-BG) with an adiabatic asymmetric directional coupler (ADC) for enhanced functionality.

Main Methods:

• Utilizing a mode conversion Bragg grating (MC-BG) etched into a multimode waveguide to route and convert polarization modes.
• Employing an adiabatic asymmetric directional coupler (ADC) to extract the converted higher-order mode.
• Fabricating the device on a standard 220nm silicon-on-insulator (SOI) wafer using a single-step etching process.

Main Results:

• Achieved an ultra-broadband PBS with theoretical extinction ratios (ER) >30 dB/15 dB and insertion losses (IL) <0.9 dB/2 dB over significant bandwidths.
• Experimentally verified a bandwidth exceeding 220 nm for ERs >30 dB on a 91.7 μm device.
• Demonstrated the first PBS on a 220nm SOI platform with experimentally verified ER >30 dB over a >200 nm bandwidth.

Conclusions:

• The integrated MC-BG and ADC design offers a high-performance, ultra-broadband PBS solution on a standard SOI platform.
• The demonstrated device represents a significant advancement for integrated photonic applications requiring precise polarization control.
• Further improvements are possible with the addition of a TM2 mode stripper, potentially extending the 30 dB bandwidth to nearly 295 nm.