Power-efficient polarization-insensitive tunable microring filter on a multi-layer Si₃N₄-on-SOI platform.

Area of Science:

• Photonics and Optical Engineering
• Materials Science (Silicon Nitride/Silicon Platforms)
• Integrated Optics

Background:

• Existing optical filters often suffer from polarization dependence, high insertion loss, and limited tunability.
• Microring resonators (MRRs) offer compact solutions for optical filtering but require careful design for performance.
• Silicon nitride (Si3N4) on silicon-on-insulator (SOI) platforms provide a robust base for integrated photonic devices.

Purpose of the Study:

• To develop and demonstrate a non-duplicate polarization-diversity tunable bandpass optical filter.
• To leverage the bi-directional transmission of add-drop dual-coupled MRRs for enhanced filter performance.
• To improve the thermo-optic tuning efficiency and overall device characteristics for practical applications.

Main Methods:

• Utilized a multi-layer Si3N4-on-SOI platform with add-drop dual-coupled MRRs.
• Implemented compact Si3N4 MRRs with Euler-bends for reduced footprint and loss.
• Employed a suspended micro-heater design to enhance thermo-optic tuning efficiency.

Main Results:

• Achieved low fiber-to-fiber insertion loss of 4.3 dB (1.7 dB on-chip) and polarization-dependent loss < 0.5 dB.
• Demonstrated high extinction ratio (> 30 dB) and low differential group delay (< 2.5 ps).
• Experimentally validated a wavelength tuning range of ~2 nm and a 3-dB bandwidth tuning range of 20 GHz with high tuning efficiency (33 pm/mW).

Conclusions:

• The developed filter is reconfigurable, polarization-insensitive, and exhibits low loss and crosstalk.
• The suspended micro-heater design significantly improves tuning efficiency (~7.5x higher than previous designs).
• This device shows strong potential for practical applications in optical communication and signal processing.