Ultralow-loss silicon waveguide crossing using Bloch modes in index-engineered cascaded multimode-interference...

Area of Science:

• Photonics and Optical Engineering
• Integrated Optics
• Nanophotonics

Background:

• Multimode-interference (MMI) couplers are essential components in integrated photonic circuits.
• Waveguide crossings are critical for dense circuit layouts but often suffer from high insertion loss.
• Reducing insertion loss in waveguide crossings is key for developing compact and efficient photonic devices.

Purpose of the Study:

• To investigate the loss mechanisms in three-moded MMI couplers.
• To propose and demonstrate a compact and low-loss waveguide crossing structure using cascaded MMI couplers.
• To minimize insertion loss in broadband silicon waveguide crossing arrays.

Main Methods:

• Design and fabrication of a 101x101 waveguide crossing array using cascaded MMI couplers.
• Integration of lateral subwavelength nanostructures to reduce insertion loss.
• Experimental characterization of insertion loss, crosstalk, and transmission spectrum.

Main Results:

• Demonstrated broadband silicon waveguide crossing arrays with insertion loss as low as ~0.02 dB per crossing.
• Achieved crosstalk below -40 dB at a 1550 nm operating wavelength.
• Exhibited a broad transmission spectrum from 1520 to 1610 nm.

Conclusions:

• The proposed MMI coupler-based waveguide crossing structure offers a viable solution for compact and low-loss integrated photonic circuits.
• Subwavelength nanostructures effectively reduce insertion loss in waveguide crossings.
• The demonstrated performance enables advanced photonic integrated circuit designs with improved efficiency.