High-efficiency second-harmonic generation in doubly-resonant χ(²) microring resonators

Area of Science:

• Photonics
• Nonlinear Optics
• Computational Electromagnetics

Background:

• Second Harmonic Generation (SHG) is a key nonlinear optical process for frequency conversion.
• Achieving high SHG efficiency in integrated photonic devices is crucial for optical communications and signal processing.

Purpose of the Study:

• To numerically demonstrate high-efficiency SHG in a microscale doubly-resonant ring resonator coupled to waveguides.
• To investigate the operational characteristics, including conversion efficiency and bandwidth, at telecom wavelengths.
• To explore the nonlinear behaviors, such as limit-cycle and bistability, in the high-efficiency regime.

Main Methods:

• Direct numerical simulation of Maxwell's equations using the finite-difference time-domain (FDTD) method.
• Analysis of device performance including conversion efficiency and bandwidth.
• Comparison of simulation results with coupled-mode theory predictions.

Main Results:

• Achieved SHG conversion efficiency greater than 94% at telecom wavelengths.
• Demonstrated high efficiency with milliwatt incident powers and high quality factor (Q ~ 1000s) resonators.
• Observed limit-cycle or bistable behavior above a threshold incident power.
• Numerical results showed excellent agreement (within a few percent) with coupled-mode theory.

Conclusions:

• The proposed microscale ring resonator structure enables highly efficient SHG.
• The device exhibits complex nonlinear dynamics, including bistability, at high efficiencies.
• The findings are well-supported by both FDTD simulations and coupled-mode theory, validating the design approach.