Efficiency Enhanced Grating Coupler for Perfectly Vertical Fiber-to-Chip Coupling.

Area of Science:

• Photonics
• Nanotechnology
• Materials Science

Background:

• Efficient fiber-to-chip optical coupling is crucial for integrated photonic circuits.
• Traditional grating couplers face limitations in efficiency and back-reflection.

Purpose of the Study:

• To propose and optimize a bidirectional grating coupler for enhanced vertical coupling efficiency.
• To reduce optical back-reflection into the fiber.
• To achieve a cost-effective and wide-bandwidth solution for Wavelength Division Multiplexing (WDM) systems.

Main Methods:

• A silicon nitride (Si3N4) layer was integrated above a uniform grating to enhance performance.
• A genetic algorithm (GA) was employed for simultaneous optimization of the grating and Si3N4 layer.
• A backside metal mirror was utilized to further improve coupling efficiency.

Main Results:

• The optimized design achieved an average in-plane coupling efficiency of 68.5%, up from 57.5%.
• Average back-reflection in the C band was reduced from 17.6% to 7.4%.
• With a backside mirror, average and peak coupling efficiencies reached 87% and 89.4%, respectively. The device exhibits a 1-dB bandwidth of 64 nm and 3-dB bandwidth of 96 nm.

Conclusions:

• The proposed grating coupler design offers a significant improvement in coupling efficiency and a reduction in back-reflection.
• The design's minimum feature size (266 nm) allows for cost-effective fabrication using deep-UV lithography.
• This technology provides an efficient and economical solution for vertical fiber-to-chip optical coupling in WDM applications.