Triple-resonant Frequency Conversion in Gallium Phosphide Integrated Photonic Resonators

Abstract

The development of scalable quantum repeaters to extend entanglement distributionbeyond the transmission range of single photons is vital to the implementation large-scale quantum networks, which could be used to secure communications with quantum key dis- tribution among other applications. Quantum emitters that can be entangled remotely, such as the diamond nitrogen-vacancy (NV) center, can be used as memory-based quantum repeaters. However, the maximum practical distance between repeaters is limited by high attenuation in optical fiber at the emission wavelength of NV centers (637 nm) and similar emitters. Scalable frequency conversion of single photons from the emission wavelength to a low-loss telecom band would extend the remote entanglement range, reducing cost and improving performance of a fiber-based quantum repeater network. As a step toward low-power visible-to-telecom single-photon frequency conversion for diamond NV centers, this thesis presents frequency conversion of coherent light inputs with quasi-phase matched multi-resonant enhancement in gallium phosphide (GaP) nonlinear ring resonators on a silicon oxide substrate. The methods for designing, fabricating, and testing the GaP ring resonators and input/output coupling structures are presented, including tests for quickly and reliably identifying devices that are close to double or triple resonance. In the first two design generations, double-resonant quasi-phase matched (QPM) second harmonic genera- tion (SHG) from telecom (1550 nm) to near-visible (775 nm) wavelengths is demonstrated with a small-signal conversion efficiency of up to 400%/W. In the third design generation, triple-resonant, quasi-phase matched sum-frequency generation (SFG) from the telecom C- band (1532 nm) to visible red (647 nm) is realized with a small-signal photon conversion efficiency of 2100-4000%/W. On-chip conversion efficiencies as high as 45,000%/W are pro- jected to be attainable in GaP ring resonators, indicating that GaP nonlinear resonators are a promising and competitive platform for extending entanglement range by frequency conversion.