Integrated gallium phosphide nonlinear photonics

TL;DR

This paper introduces GaP-on-insulator as a new platform for integrated nonlinear photonics, demonstrating low-loss waveguides, high-Q resonators, and various nonlinear optical phenomena including frequency combs and Raman lasing.

Contribution

It presents the first implementation of GaP-on-insulator platform with integrated waveguides and resonators, enabling nonlinear photonics applications at telecommunication wavelengths.

Findings

Achieved 1.2 dB/cm loss in GaP waveguides

Observed Kerr frequency comb generation with low threshold powers

Demonstrated broadband frequency combs and Raman lasing

Abstract

Gallium phosphide (GaP) is an indirect bandgap semiconductor used widely in solid-state lighting. Despite numerous intriguing optical properties---including large $\chi^{(2)}$ and $\chi^{(3)}$ coefficients, a high refractive index ($>3$), and transparency from visible to long-infrared wavelengths ($0.55-11\,\mu$m)---its application as an integrated photonics material has been little studied. Here we introduce GaP-on-insulator as a platform for nonlinear photonics, exploiting a direct wafer bonding approach to realize integrated waveguides with 1.2 dB/cm loss in the telecommunications C-band (on par with Si-on-insulator). High quality $(Q> 10^5)$, grating-coupled ring resonators are fabricated and studied. Employing a modulation transfer approach, we obtain a direct experimental estimate of the nonlinear index of GaP at telecommunication wavelengths: $n_2=1.2(5)\times 10^{-17}\,\text{m}^2/\text{W}$. We also observe Kerr frequency comb generation in resonators with engineered dispersion. Parametric threshold powers as low as 3 mW are realized, followed by broadband ($>100$ nm) frequency combs with sub-THz spacing, frequency-doubled combs and, in a separate device, efficient Raman lasing. These results signal the emergence of GaP-on-insulator as a novel platform for integrated nonlinear photonics.