No abstract

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 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.

Reconfigurable optical devices provide new opportunities for integrated photonics. The use of chalcogenide glasses, with large refractive index nonlinearity and photosensitivity, in conjunction with the microresonator platform has proven to be a powerful tool in the study and application of nanophotonics. Here, we report cavity-enhanced photo-induced writing and erasing of gratings in a chalcogenide As 2 S 3 microresonator. Grating writing is implemented with self-enhanced standing wave modes, while the erasing of written gratings as well as removing of intrinsic back-scattering is achieved by Kerr-nonlinearity-induced symmetry breaking in the microresonator. These findings pave the way for future reconfigurable photonic devices and reveal exciting new possibilities for nonlinear photonics and microresonators.

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.