Fano resonances in a multimode waveguide coupled to a high-Q silicon nitride ring resonator

Area of Science:

• Integrated Optics
• Photonics
• Materials Science

Background:

• Silicon nitride (Si3N4) offers low-loss optical properties for integrated photonic circuits.
• Optical ring resonators are key components in manipulating light on-chip.

Purpose of the Study:

• To investigate light transmission through a silicon nitride ring resonator coupled to a multimode waveguide.
• To explore the excitation and probing of waveguide modes using single-mode fibers.
• To analyze the resulting Fano resonances and their tunability.

Main Methods:

• Coupling single-mode fibers to input and output ports of a Si3N4 waveguide.
• Selective excitation and probing of waveguide modes.
• Observation and analysis of transmission spectra.
• Development of a coupled mode theory model.

Main Results:

• Strong asymmetric Fano resonances were observed in the transmission spectra.
• The asymmetry of the Fano resonance was tunable by adjusting fiber positions.
• The Fano resonance arises from interference between waveguide modes and the ring resonator.
• A theoretical model based on coupled mode theory accurately described the experimental findings.

Conclusions:

• Silicon nitride ring resonators coupled to multimode waveguides exhibit tunable asymmetric Fano resonances.
• The observed Fano resonances are a result of mode interference.
• The tunability and the extended nature of optical modes make this system highly promising for optical sensing applications.