400%/W second harmonic conversion efficiency in 14 μm-diameter gallium phosphide-on-oxide resonators

Area of Science:

• Integrated photonics
• Nonlinear optics
• Semiconductor materials

Background:

• Efficient frequency conversion is crucial for various photonic applications, including optical communications and spectroscopy.
• Gallium phosphide (GaP) offers a promising platform for integrated nonlinear optics due to its high nonlinear coefficient and transparency in the visible and near-infrared spectrum.
• Previous efforts in integrated nonlinear photonics have faced challenges in achieving high conversion efficiencies due to factors like low mode confinement and phase-matching limitations.

Purpose of the Study:

• To demonstrate high-efficiency second harmonic generation (SHG) in a novel gallium phosphide on oxide integrated photonic platform.
• To investigate the role of resonant cavities and mode confinement in enhancing nonlinear optical processes.
• To explore pathways for further improving SHG efficiency in integrated photonic devices.

Main Methods:

• Fabrication of doubly-resonant, phase-matched ring resonators on a gallium phosphide on oxide platform.
• Characterization of resonator quality factors (Q ∼ 10⁴) and mode volumes (V ∼ 30(λ/n)³).
• Measurement and simulation of second harmonic conversion efficiency from 1550 nm to 775 nm.

Main Results:

• Demonstrated second harmonic conversion efficiency of 400% W^-1.
• Achieved high quality factors and low mode volumes, leading to significant nonlinear mode overlap.
• Simulations predict a potential 20-fold increase in conversion efficiency by optimizing waveguide-cavity coupling for critical coupling.

Conclusions:

• The GaP on oxide platform enables highly efficient second harmonic generation through doubly-resonant ring resonators.
• The demonstrated efficiency highlights the potential of this platform for integrated nonlinear photonic applications.
• Further optimization of device coupling presents a clear route to substantially enhance conversion efficiencies.