No abstract

Chalcogenide glasses, with high nonlinearity and low loss, have captured research interest as an integrated device platform for near- and mid-infrared nonlinear optical devices. Compared to silicon-based microfabrication technologies, chalcogenide fabrication processes are less mature and a major challenge is obtaining high quality devices. In this paper, we report a hybrid resonator design leveraging a high quality silica resonator to achieve high Q factors with chalcogenide. The device is composed of a thin chalcogenide layer deposited on a silica wedge resonator. The hybrid resonators exhibit loaded Q factors up to 1.5 x 10 in the near-infrared region. We also measured the effective thermo-optic coefficient of the device to be 5.5x10/K, which agreed well with the bulk value. Thermal drift of the device can be significantly reduced by introducing a titanium dioxide cladding layer with a negative thermo-optic coefficient.

We report a ∼3-fold enhancement of third-harmonic generation (THG) conversion efficiency using indium tin oxide (ITO) nanoparticles on the surface of an ultra-high-Q silica microsphere. This is one of the largest microcavity-based THG enhancements reported. Phase-matching and spatial mode overlap are explored numerically to determine the microsphere radius (∼29 µm) and resonant mode numbers that maximize THG. Furthermore, the ITO nanoparticles are uniformly bonded to the cavity surface by drop-casting, eliminating the need for complex fabrication. The significant improvement in THG conversion efficiency establishes functionalized ITO microcavities as a promising tool for broadband frequency conversion, nonlinear enhancement, and applications in integrated photonics.

High nonlinearity optical devices are of interest for compact, low power devices. Whispering gallery mode (WGM) microresonators offer strong nonlinear optical responses due to high quality factors and the small mode volume. To achieve high nonlinearity with these WGM devices, both a material with a high nonlinear index as well as a high quality factor is required. Indium tin oxide (ITO) is an excellent nonlinear material due to an exceptionally high nonlinear refractive index found at the epsilon-near-zero wavelength. However, ITO’s enormous absorption at this point prohibits having a resonator with a high quality factor. Here, we present a novel ITO nanoparticle-coated silica microsphere with significantly enhanced nonlinearity while maintaining high quality factors. Nonlinear refractive index and quality factor of the ITO nanoparticle-coated silica microsphere are obtained by fitting the measured transmission spectra with a theoretical model that includes thermal and Kerr effects. By controlling the number of particles on a silica surface, we achieve 39–187 times higher nonlinear indices compared with a pure silica microsphere and quality factors between 106 and 107. The study establishes a new avenue toward novel nonlinear optical devices based on ITO nanoparticles, which can be readily incorporated in a variety of geometries.

We report Ge23Sb7S70 chalcogenide wedge resonators with a high quality factor and broadband dispersion which is induced by an exceedingly smooth and varying-angle wedge surface.