High-efficiency bident edge coupler based on thin film lithium niobate

Area of Science:

• Photonics
• Materials Science
• Integrated Optics

Background:

• Thin-film lithium niobate (TFLN) is a key platform for photonic integrated circuits (PICs) due to its high nonlinear coefficients and electro-optic response.
• Efficient optical fiber coupling to TFLN chips is crucial but challenging due to fabrication complexity and alignment precision requirements of existing edge couplers.

Purpose of the Study:

• To propose and demonstrate a high-efficiency, fabrication-friendly, and alignment-tolerant bident edge coupler for TFLN devices.
• To overcome the limitations of current edge coupler designs in terms of performance and manufacturing.

Main Methods:

• Design of a novel bident edge coupler comprising facet coupling, beam combining, and adiabatic taper regions.
• Fabrication using a simplified single overlay process.
• Characterization of coupling efficiency, spectral performance across the C-band, and alignment tolerance.

Main Results:

• Achieved a measured coupling efficiency better than -1.52 dB per facet at 1550 nm.
• Demonstrated an average coupling efficiency between -1.85 dB and -1.6 dB across the C-band.
• Obtained a mode field diameter of approximately 4 μm and a large alignment tolerance of ±1 μm.

Conclusions:

• The proposed bident edge coupler offers a practical and high-performance solution for optical interface packaging in TFLN devices.
• The design simplifies fabrication, requiring only a single overlay step, making it suitable for mass production.
• This advancement facilitates the integration of TFLN-based PICs with optical fibers, enabling broader applications.