Silicon photonic contradirectional couplers using subwavelength grating waveguides.

Area of Science:

• Photonics and Optical Engineering
• Integrated Optics
• Waveguide Technology

Background:

• Conventional contradirectional couplers face challenges with undesired codirectional coupling and intrawaveguide reflections.
• Subwavelength grating (SWG) structures offer unique optical properties for waveguide design.

Purpose of the Study:

• To propose and demonstrate a novel contradirectional coupler design utilizing a subwavelength grating (SWG) waveguide.
• To investigate the impact of SWG waveguide parameters on coupler performance.
• To enhance suppression of codirectional coupling and expand the operating range of optical couplers.

Main Methods:

• Fabrication of devices on a silicon-on-insulator (SOI) platform.
• Integration of a subwavelength grating (SWG) waveguide into a contradirectional coupler.
• Experimental characterization of spectral properties, including coupling suppression and operating bandwidth.
• Systematic study of the effects of SWG period, waveguide gap distance, and coupling length.

Main Results:

• Achieved over 35 dB suppression of undesired codirectional coupling.
• Demonstrated an operating range exceeding 120 nm, free from intrawaveguide reflections.
• Showcased a large optical phase-mismatch between the SWG and continuous waveguides.
• Observed tunable bandwidths from 18.2 nm down to 0.9 nm by varying the gap distance (100 nm to 500 nm).

Conclusions:

• The novel SWG waveguide design significantly improves contradirectional coupler performance.
• The device offers robust suppression of unwanted coupling and a broad, reflection-free operating range.
• Tailoring SWG parameters provides effective control over coupler bandwidth and spectral characteristics.