Fiber-chip grating coupler based on interleaved trenches with directionality exceeding 95.

Area of Science:

• Photonics and Optical Engineering
• Nanofabrication and Integrated Optics

Background:

• Efficient fiber-to-chip coupling is crucial for integrated photonic circuits.
• Existing grating couplers often require complex fabrication or additional components to achieve high directionality.

Purpose of the Study:

• To design and analyze a fiber-chip grating coupler with enhanced upward directionality and coupling efficiency.
• To achieve fabrication compatibility with standard deep-UV lithography.

Main Methods:

• Interleaving standard full and shallow etch trenches in a 220 nm silicon layer.
• Implementing a transverse subwavelength structure in the initial grating periods.
• Optimizing trench separation for constructive interference in the upward direction.

Main Results:

• Achieved upward directionality exceeding 95%.
• Calculated coupling efficiency (CE) of -1.05 dB with a 1 dB bandwidth of 30 nm.
• Minimum feature size of 100 nm, compatible with deep-UV lithography.
• Directionality is independent of bottom oxide thickness and does not require bottom reflectors or overlays.

Conclusions:

• The proposed grating coupler design offers a robust and efficient solution for fiber-chip light coupling.
• The design simplifies fabrication by eliminating the need for specialized etch depths or additional optical components.
• This advancement is significant for the development of practical and high-performance integrated photonic devices.