Ultrahigh-Q lithium niobate microring resonator with multimode waveguide.

Area of Science:

• Photonics
• Materials Science
• Optical Engineering

Background:

• Lithium niobate (LN) microresonators are crucial for photonic applications but suffer from high propagation loss due to etching difficulties.
• Achieving high quality factor (Q) microresonators in LN requires sophisticated fabrication processes.

Purpose of the Study:

• To fabricate a multimode LN microring resonator with significantly reduced propagation loss and high Q-factor.
• To demonstrate the effectiveness of Euler bends in suppressing higher-order modes.
• To implement a bandpass microwave photonic filter using the fabricated microresonator.

Main Methods:

• Fabrication of a multimode microring resonator using advanced etching techniques.
• Utilizing Euler bends to suppress higher-order mode excitation.
• Characterization of resonator performance, including Q-factor and free spectral range (FSR).
• Implementation and testing of a bandpass microwave photonic filter.

Main Results:

• Achieved an intrinsic Q-factor of 6 × 10⁶.
• Demonstrated a propagation loss 50 times lower than single-mode LN microring resonators.
• Successfully suppressed higher-order modes using Euler bends.
• Implemented a microwave photonic filter with a 47.5 MHz bandwidth and 2-26.5 GHz tuning range.

Conclusions:

• The developed multimode LN microring resonator offers a significant reduction in propagation loss.
• Euler bends are effective in controlling mode excitation in LN resonators.
• This work facilitates improved performance in ultrahigh-Q LN microresonator applications like frequency combs and quantum photonics.