Synthetic single-crystal diamond has recently emerged as a promising material for nonlinear photonics due to its large bandgap (~5.5eV) resulting in an ultrawide transparency window (UV - THz), large linear (~2.4) & nonlinear (similar to SiN) refractive indices, absence of multi-photon & free-carrier absorption losses, and high power-handling capability via excellent thermal properties (largest thermal conductivity and small thermo-optic coefficient).

Scanning electron micrograph of an array of waveguide-coupled diamond microring resonators on a silica substrate

We have developed novel nanofabrication techniques to make low-loss nanowaveguides and high quality-factor (Q ~ 1 million) microresonators in an integrated, on-chip diamond-on-insulator platform.

Our goal is to build novel light sources across a broad spectrum using nonlinear optical interactions in diamond for applications ranging from spectroscopy, sensing and biomedical to telecommunication and classical & quantum information processing. As an example, we have demonstrated a multi-color 'frequency-comb' source at telecom wavelengths (~1600nm) through cascaded four-wave-mixing due to diamond's parametric third-order nonlinearity in high-Q microring resonators integrated onto a silicon chip [Nature Photon. 8, 369 (2014)].

A strong monochromatic pump laser coupled into a resonance of the diamond microring generates coherent light at additional wavelengths at equally spaced adjacent cavity resonances (FSR ~ 100s of GHz in our case). We observed such a frequency comb of 20 new wavelengths spanning a bandwidth of ~10% of the center frequency with <100mW of input pump power. Our work was highlighted in the Sep. 2014 issue of Laser Focus World. We are currently working towards extending this on-chip frequency-comb technology in diamond to novel wavelength ranges in the optical spectrum, particularly the visible frequency range where it has been difficult to achieve with other traditional nanophotonic materials.

The generated optical parametric oscillation (OPO) spectra from a 20-μm radius diamond ring resonator is shown for two different pump positions, 1553nm and 1599nm.

As another example, we have demonstrated an on-chip Raman laser operating at the highly-sought-after ~2 micron wavelength range, identified for next-generation telecommunication networks, using integrated, high-Q, oval-shaped long path-length racetrack microresonators in diamond [Optica 2, 924 (2015)].

Schematic of diamond microresonator based on-chip Raman laser (green represents pump wave and orange represents Raman-shifted Stokes output)

Diamond's giant Raman shift (~40THz) and large Raman gain (~10cm/GW) coupled with the availability of synthetically-grown, low-cost single-crystal diamond plates have piqued interest in diamond-based Raman lasers. Our telecom-laser-pumped on-chip device operated in continuous-wave mode and reduced the threshold power by orders of magnitude to <100mW. We further showed discrete tuning capability (in steps of the microcavity FSR) over >5% of the center frequency of operation, and also continuous tuning of the diamond Raman laser over a range of ~10 GHz. Our work was highlighted in the Oct. 2015 issue of Optics & Photonics News. We are working towards extending this on-chip Raman laser technology in diamond to novel wavelength ranges in the optical spectrum, particularly the visible frequency range.

Output spectrum and threshold characteristics of telecom-pumped on-chip diamond Raman laser operating at ~2 microns.