Fig. 1. (a) Energy level diagram of redshifted SRS and blueshifted SARS with the vibrational state of the gain medium. νPump, νSRS, νSARS, and νVibration correspond to the frequencies of pump, SRS, SARS, and vibrational optical phonon, respectively. (b) Schematic image of generated SRS (red) and SARS (blue) with pump (purple) in on-chip metal-doped silica hybrid toroid resonator with tapered optical fiber waveguide.

Fig. 2. COMSOL Multiphysics FEM simulation results. (a) Optical field distribution in the coated toroidal microcavity. The major and minor diameters of the silica toroid are 55 and 6 μm, respectively. The refractive indices of coatings are 1.454 for undoped and 1.520 for metal-doped layer (either Zr or Ti) with thickness of 400 nm. (b) Fundamental mode area as a function of the refractive index of coating (ncoating) and the minor diameter. The coating thickness is fixed to 400 nm, and the wavelength is 1550 nm.

Fig. 3. (a) SEM image of a solgel-coated device indicating major (D) and minor (d) diameters; (b) schematic image of testing setup with a laser, a tapered optical fiber, a photodetector (PD) connected to an O-scope, an OSA, and on-chip silica microcavity. EDS spectra from (c) Zr- and (d) Ti-doped silica hybrid devices. The silicon (purple) has peaks at 1.740 and 3.49 keV. The oxygen (green) has a peak at 0.523 keV. The Zr (red) and Ti (blue) have peaks at 2.042 and 4.510 keV, respectively. Each peak is fitted to a Gaussian.

Fig. 4. Intrinsic Q of a series of undoped, Zr-doped, and Ti-doped silica hybrid devices.

Fig. 5. Emission spectra of (a) undoped, (b) Zr-, and (c) Ti-doped devices with similar coupled power (∼1.5  mW) into the devices obtained via OSA. Zoom-in spectra below show generated SARS.

Fig. 6. Generated SRS (hollow symbol) and SARS (solid symbol) shift from various devices. As expected, the Stokes and anti-Stokes shifts are identical, providing evidence that the upconverted photons are the result of the anti-Stokes process.

Fig. 7. (a) SRS and (b) SARS power as a function of the coupled power into the devices; (c) ratio of SARS versus SRS power from various devices.

Fig. 8. (a) Threshold and (b) efficiency values of SRS, and (c) threshold and (d) efficiency values of SARS from various devices.