High extinction ratio and low loss polarization beam splitter based on multimode interference for PICs

Area of Science:

• Photonics
• Integrated Optics
• Semiconductor Devices

Background:

• Polarization beam splitters (PBS) are essential components in optical systems.
• Traditional PBS designs often face limitations in extinction ratio, insertion loss, and bandwidth.
• Silicon-on-insulator (SOI) platforms offer advantages for integrated photonic devices.

Purpose of the Study:

• To propose and experimentally demonstrate a novel polarization beam splitter (PBS) based on cascaded multimode interference (MMI).
• To achieve a high extinction ratio (ER) and low insertion loss (IL) for both TE and TM polarizations.
• To evaluate the device's performance over a broad wavelength range and assess its fabrication tolerance.

Main Methods:

• Design of a PBS utilizing cascaded MMI structures on a silicon-on-insulator platform.
• Experimental demonstration and characterization of the fabricated PBS.
• Utilizing the eigenmode expansion method to analyze fabrication tolerances.

Main Results:

• The proposed PBS achieved high extinction ratios of 22.3 dB (TE) and 25.6 dB (TM) at 1550 nm.
• Low insertion losses of 0.7 dB (TE) and 0.1 dB (TM) were recorded.
• A broad operational bandwidth of 60 nm (1520-1580 nm) was demonstrated with ER > 16 dB for both polarizations.
• Significant fabrication tolerances were identified: ±40 nm for MMI width and ±1500 nm for MMI length.

Conclusions:

• The cascaded MMI-based PBS on SOI offers superior performance compared to conventional MMI structures.
• The device exhibits excellent polarization splitting capabilities with high ER and low IL over a broad bandwidth.
• The demonstrated fabrication tolerance makes the proposed PBS a practical candidate for mass production in silicon photonic integrated circuits for polarization division multiplexing applications.