Subwavelength grating-assisted silicon nitride edge coupler with relaxed alignment tolerance.

Area of Science:

• Photonics and Optical Engineering
• Materials Science
• Nanotechnology

Background:

• Edge couplers are essential for interfacing optical fibers with photonic integrated circuits.
• Conventional edge couplers often suffer from stringent alignment requirements, limiting their practical application.
• Silicon nitride (SiN) is a promising material for photonic integrated circuits due to its low loss and broad transparency window.

Purpose of the Study:

• To propose and demonstrate a novel silicon nitride (SiN) edge coupler with enhanced alignment tolerance.
• To improve the ease of packaging and integration of SiN photonic devices.
• To achieve efficient optical coupling with relaxed alignment sensitivity.

Main Methods:

• Integration of a subwavelength grating (SWG) tri-tip structure into a SiN edge coupler.
• Design of intermediate bridge waveguides for adiabatic mode transitions.
• Fabrication and characterization of the proposed edge coupler at 1550 nm wavelength.
• Coupling with standard SMF-28 optical fiber.

Main Results:

• Achieved a 1-dB horizontal alignment tolerance of ±3 μm with SMF-28 fiber.
• Measured coupling efficiency of -3.8 dB/facet.
• Demonstrated significantly wider horizontal tolerance compared to conventional single-tip inverse-tapered edge couplers.
• Validated the effectiveness of the SWG tri-tip design in expanding the input acceptance region.

Conclusions:

• The proposed SWG tri-tip SiN edge coupler effectively enhances alignment tolerance while maintaining high coupling efficiency.
• The design is suitable for practical packaging and integration in SiN photonic platforms.
• This advancement contributes to the development of more robust and user-friendly photonic devices.