High-performance lithium-niobate-on-insulator optical filter based on multimode waveguide gratings.

Area of Science:

• Photonics and Optical Engineering
• Materials Science (Lithium Niobate)

Background:

• Optical filters are crucial components in various photonic systems.
• Existing filter technologies face limitations in performance metrics like sidelobe suppression and insertion loss.
• The lithium-niobate-on-insulator (LNOI) platform offers unique advantages for integrated photonics.

Purpose of the Study:

• To propose and realize a novel high-performance optical filter.
• To utilize multimode waveguide gratings (MWG) and two-mode multiplexers on the LNOI platform.
• To achieve superior performance characteristics, including low loss and high sidelobe suppression.

Main Methods:

• Design and fabrication of an optical filter based on multimode waveguide gratings (MWG).
• Integration of two-mode multiplexers on an x-cut lithium-niobate-on-insulator (LNOI) platform.
• Gaussian apodization technique applied for optimized filter response.
• Cascading of two identical MWGs to further enhance performance.

Main Results:

• Theoretical analysis predicted a low excess loss of 0.05 dB and a sidelobe suppression ratio (SLSR) of 32 dB.
• Fabricated filters demonstrated a box-like response with a 1-dB bandwidth of 6-23 nm, excess loss of ~0.15 dB, and SLSR >26 dB.
• Cascading two MWGs improved performance to an SLSR of 48 dB with an excess loss of ~0.25 dB.

Conclusions:

• The proposed MWG-based optical filter on LNOI is a novel and high-performance solution.
• The device achieves excellent sidelobe suppression and low excess loss, outperforming previous integrated optical filters.
• This technology holds promise for advanced applications in optical communications and signal processing.