Study On On-Chip Integrated Polarization Beam Splitters

As the demand for information processing continues to increase,the transmission capacity of on-chip optical interconnect networks is challenged.To solve this issue,multi-dimensional optical multiplexing technology provides a promising solution.As a key component in polarization division multiplexing system,the polarization beam splitter separating two orthogonal polarization modes is highly desired.Due to the high compatibility with the CMOS fabrication process,low transmission loss and high-index contrast,silicon-based optoelectronic devices have gained increased attention.Thus,in this thesis,several on-chip integrated polarization beam splitters are studied.The main contents and innovations are described below:1.A design of polarization beam splitter using metasurface-assisted silicon nitride Y-junction for mid-infrared wavelengths is presented.The finite difference time domain method and particle swarm optimization algorithm are used for optimizing structural parameters so that the input TM₀and TE₀ modes can be efficiently separated from each other.Simulation results show that TM₀-to-TE₁ and TE₀-to-TM₀ conversion efficiencies can be up to 97.4%and 97.6%.At 2500 nm wavelength,for the designed device with the input TE₀ and TM₀ modes,insertion losses are respectively 0.31 and 0.21 dB,the corresponding polarization extinction ratios are 27.61 dB and27.45 dB,and the crosstalk are-33.55 dB and-53.77 dB.Within a bandwidth from 2450 to 2550nm,the insertion loss is less than 1.41 dB,the polarization extinction ratio is greater than 19.48 dB,and the crosstalk is less than-33.07 dB.2.A design of switchable polarization beam splitter using GST-on-silicon waveguides is presented.The particle swarm optimization algorithm and finite difference time domain method are utilized to optimize the presented device’s parameters by meeting the mode-hybridization and phase-matching conditions so that the input TE₀ and TM₀ modes can be separated and switched as desired.Simulation results reveal that the designed device can have a broad bandwidth,low crosstalk,and high polarization extinction ratio.Within a bandwidth from 1535 nm to 1565 nm,the crosstalk lower than-23.40 dB and the polarization extinction ratio larger than 21.35 dB can be obtained in the case of the amorphous GST,while in the case of the crystalline GST the crosstalk is less than-27.37 dB and the polarization extinction ratio is greater than 21.37 dB.3.A design of compact and high-polarization-extinction-ratio polarization beam splitter based on a counter-tapered coupler is proposed.By meeting phase-matching condition,structural parameters are optimized based on the particle swarm optimization algorithm and finite difference time domain method so that the TM₀ mode is coupled and exits from the cross port and the TE₀mode propagates forward and emerges from the bar port.The coupling length of the designed device is only 5μm.By using electron-beam lithography and inductively coupled plasma etching,the designed device is experimental demonstrated.At 1550 nm wavelength,when TE₀ and TM₀modes are input,the polarization extinction ratios of the fabricated device are respectively 28.1 dB and 23.0 dB.