More efficient second harmonic generation of whispering gallery modes by selective out-coupling

TL;DR

This paper demonstrates significantly improved second harmonic generation efficiency in lithium niobate whispering gallery mode resonators by selectively controlling mode out-coupling, achieving over 5%/mW efficiency.

Contribution

It introduces a method for independent control of pump and signal mode coupling, enhancing SHG efficiency in whispering gallery resonators.

Findings

Achieved 5.28%/mW SHG efficiency from 1555.4 nm to 777.7 nm.

Theoretical analysis shows optimal independent control of pump and signal modes.

Experimental verification confirms efficiency improvement by over an order of magnitude.

Abstract

We demonstrate second harmonic generation (SHG) in an $x$-cut congruent lithium niobate (LN) whispering gallery mode resonator. We first show theoretically that independent control of the coupling of the pump and signal modes is optimal for high conversion rates. A scheme based on our earlier work in Ref. [1] is then implemented experimentally to verify this. Thereby we are able to improve on the efficiency of SHG by more than an order of magnitude by selectively out-coupling using a LN prism, utilizing the birefringence of it and the resonator in kind. We report 5.28%/mW efficiency for SHG from 1555.4 nm to 777.7 nm.