Subwavelength grating couplers for an ultrathin silicon waveguide

Area of Science:

• Photonics and Optical Engineering
• Materials Science

Background:

• Subwavelength grating (SWG) structures are crucial for integrated optical devices due to their small size and tunable refractive index.
• Efficient light coupling is essential for advancing optical device performance.

Purpose of the Study:

• To design and experimentally validate a novel subwavelength grating (SWG) coupler for a 70-nm-thick silicon waveguide.
• To evaluate the coupling efficiency, bandwidth, and backreflection of the proposed SWG coupler.

Main Methods:

• Device design utilizing particle swarm optimization algorithm.
• Three-dimensional finite-difference time-domain (3D FDTD) simulations for performance prediction.
• Experimental characterization of the SWG coupler at 1550 nm wavelength for transverse-electric (TE) polarization.

Main Results:

• Achieved a peak coupling efficiency of -7.0 dB.
• Observed a 1-dB bandwidth of approximately 40 nm.
• Measured backreflection of approximately -18.7 dB.
• Minimum feature size of the SWG coupler is ~210 nm.

Conclusions:

• The developed SWG coupler demonstrates effective performance for integrated optical devices.
• The ultrathin, simple, and reproducible device structure is suitable for cost-effective sensing and optoelectronic integration.
• This technology holds promise for advancing miniaturized optical systems.