Polarization-independent waveguide grating coupler using an optimized polysilicon overlay.

Area of Science:

• Photonics
• Integrated Optics
• Nanotechnology

Background:

• Waveguide grating couplers are essential for interfacing optical fibers with integrated photonic circuits.
• Achieving polarization-independent performance in grating couplers remains a significant challenge in integrated optics.
• Existing designs often suffer from polarization-dependent losses, limiting their applicability.

Purpose of the Study:

• To propose and validate a novel design for a polarization-independent waveguide grating coupler.
• To utilize an optimized polysilicon overlay on a silicon grating structure for improved performance.
• To demonstrate low insertion loss for both transverse electric (TE) and transverse magnetic (TM) polarizations.

Main Methods:

• Design and simulation of a silicon grating coupler with a polysilicon overlay.
• Photolithography was employed for device fabrication via a commercial multi-project wafer service.
• Experimental characterization of coupling efficiency for both TE and TM polarizations.

Main Results:

• Simulations predicted high coupling efficiencies of -3.6 dB (TE) and -3.5 dB (TM).
• Fabricated devices exhibited measured coupling losses of -3.96 dB (TE) and -3.93 dB (TM).
• The results demonstrate near-identical performance for both polarizations, confirming polarization independence.

Conclusions:

• The proposed polysilicon overlay on a silicon grating coupler effectively achieves polarization-independent operation.
• The demonstrated low coupling losses are competitive with existing state-of-the-art devices.
• This approach offers a promising solution for robust optical interconnects in integrated photonic systems.