Ultra-compact dual-band grating coupler for visible wavelengths with shape-optimized spot size converter

Area of Science:

• Photonics and Optical Engineering
• Integrated Optics
• Nanophotonics

Background:

• Efficient light coupling is crucial for integrated photonic devices.
• Existing grating couplers often lack dual-band functionality or are bulky.
• Silicon nitride (Si3N4) offers a robust platform for visible light applications.

Purpose of the Study:

• To present the first ultra-compact dual-band grating coupler for visible wavelengths.
• To achieve simultaneous light coupling at 729 nm and 860 nm.
• To demonstrate the device's potential for integrated ion qubit systems.

Main Methods:

• Theoretical and numerical analysis of a silicon nitride (Si3N4) platform.
• Design of a one-dimensional (1D) grating coupler integrated with shape-optimized spot-size converters (SSCs).
• Adjoint method optimization for mode conversion and spot-size matching.

Main Results:

• Achieved coupling efficiencies of -4.12 dB at 729 nm and -5.5 dB at 860 nm for the grating coupler.
• Obtained total coupling efficiencies of -4.28 dB at 729 nm and -5.57 dB at 860 nm with SSCs.
• Device size is ultra-compact, measuring approximately 65 μm × 10 μm.

Conclusions:

• The developed dual-band grating coupler is highly efficient and ultra-compact.
• The device enables simultaneous coupling of two visible wavelengths.
• This technology is promising for interfacing light sources with in-plane multi-wavelength ion trap devices in CMOS-compatible systems.