Stimulated Brillouin scattering and Brillouin-coupled four-wave-mixing in a silica microbottle resonator

Free-access optomechanical liquid probes using a twin-microbottle resonator

Cavity optomechanics provides high-performance sensor technology, and the scheme is also applicable to liquid samples for biological and rheological applications. However, previously reported methods using fluidic capillary channels and liquid droplets are based on fixed-by-design structures and therefore do not allow an active free access to the samples. Here, we demonstrate an alternate technique using a probe-based architecture with a twin-microbottle resonator. The probe consists of two microbottle optomechanical resonators, where one bottle (for detection) is immersed in liquid and the other bottle (for readout) is placed in air, which retains excellent detection performance through the high optical Q (~10⁷) of the readout bottle. The scheme allows the detection of thermomechanical motion of the detection bottle as well as optomechanical drive and frequency tracking with a phase-locked loop. This technique could lead to in situ metrology at the target location in arbitrary media and could be extended to ultrasensitive biochips and rheometers.

Numerical characterization of soliton microcomb in an athermal hybrid Si3N4-TiO2 microring

We theoretically investigate the athermal constructions to cancel the thermorefractive effect of a hybrid Si₃N₄-TiO₂ microring, which merges two materials with opposite thermo-optical coefficients (TOCs). The analytical and numerical results predict that the thermorefractive effect can be reduced under the appropriate parameters. In addition, the soliton state is easily accessed under the athermal condition. The thermorefractive noise due to the fluctuation of the microresonator temperature caused by the heat exchange between the microresonator and the surrounding environment is also suppressed by one order of magnitude, which is critical for the potential applications of soliton microcombs, such as spectroscopy, optical clocks and microwave generation.

High-power, low-noise Brillouin laser on a silicon chip

We realize a chip-based Brillouin microlaser with remarkable features of high power and low noise using a microtoroid resonator. Our Brillouin microlaser is able to output a power of up to 126 mW with a fundamental linewidth down to 245 mHz. Additionally, in the course of Brillouin lasing we observe an intriguing power saturation-like effect, which can be attributed to complex thermo-optic-effect-induced mode mismatch between the pump and Brillouin modes. To have a quantitative understanding of this phenomenon, we develop a model by simultaneously considering Brillouin lasing and the thermo-optic effect occurring in the microcavity. Of importance, our theoretical results match well with experimentally measured data.

Brillouin-Kerr Soliton Frequency Combs in an Optical Microresonator

By generating a Brillouin laser in an optical microresonator, we realize a soliton Kerr microcomb through exciting the Kerr frequency comb using the generated Brillouin laser in the same cavity. The intracavity Brillouin laser pumping scheme enables us to access the soliton states with a blue-detuned input pump. Because of the ultranarrow linewidth and the low-noise properties of the generated Brillouin laser, the observed soliton microcomb exhibits narrow-linewidth comb lines and stable repetition rate. Also, we demonstrate a low-noise microwave signal with phase noise of -49  dBc/Hz at 10 Hz, -130  dBc/Hz at 10 kHz, and -149  dBc/Hz at 1 MHz offsets for a 10.43 GHz carrier with only a free-running input pump. The easy operation of the Brillouin-Kerr soliton microcomb with excellent performance makes our scheme promising for practical applications.

Diamond Raman oscillator operating at 1178 nm

In this contribution, we report high-power Raman frequency downconversion based on an Yb-doped fiber amplifier and a linear external diamond Raman cavity. A maximum output power of 136 W with nearly diffraction-limited beam quality was achieved by pumping in quasi-continuous-wave mode with 10% duty cycle and 10 ms on-time duration. For continuous-wave operation, we achieved record average power of 46 W centered at 1178 nm. The emergence of stimulated Brillouin scattering in diamond is further investigated. This technology shows the potential to extend the spectral range of fiber lasers to reach uncommon wavelengths at high power levels.

Nonlinear Optics in Microspherical Resonators

Nonlinear frequency generation requires high intensity density which is usually achieved with pulsed laser sources, anomalous dispersion, high nonlinear coefficients or long interaction lengths. Whispering gallery mode microresonators (WGMRs) are photonic devices that enhance nonlinear interactions and can be exploited for continuous wave (CW) nonlinear frequency conversion, due to their capability of confine light for long time periods in a very small volume, even though in the normal dispersion regime. All signals must be resonant with the cavity. Here, we present a review of nonlinear optical processes in glass microspherical cavities, hollow and solid.

Optical frequency combs generated mechanically

An elongated bottle microresonator with nanoscale parabolic effective radius variation can possess a series of dense equally spaced optical eigenfrequencies whose separation can match the eigenfrequency of its axially symmetric acoustic mode. It is shown that this acoustic mode can parametrically excite optical modes and give rise to a highly equidistant and moderately broadband optical frequency comb with the teeth spacing independent of the input laser power and the amplitude of mechanical vibrations.

Tunable Raman laser in a hollow bottle-like microresonator

A tunable Raman laser in the hollow bottle-like microresonator is demonstrated. By controlling the pump laser frequency, we have demonstrated continuous Raman laser frequency tuning. We also have studied the interesting transient mode evolution with Raman gain by sweeping the pump and probe laser, and verified the thermal tuning mechanism by theoretical simulations. By mechanically stretching the resonator, we have achieved the large range frequency tuning of the Raman laser, with the tuning range of 132 GHz with the resolution about 85 MHz. The demonstrated tunable Raman laser can be used as a source for future optical applications.

Stimulated Brillouin scattering suppression of thulium-doped fiber amplifier with fiber superfluorescent seed source

We investigate the stimulated Brillouin scattering (SBS) effect in high-power thulium-doped fiber amplifier seeded with a narrow-linewidth fiber superfluorescent source or a conventional narrow-linewidth fiber laser. No random backward SBS pulses are observed when using a narrow-linewidth fiber superfluorescent source as the seed. The corresponding average power and peak power reach 153 W and 3.4 kW, respectively, only limited by the available pump power. This gives the average power and peak power extraction from the thulium-doped fiber amplifier with 17 fold enhancement, in comparison with the situation using the conventional narrow-linewidth fiber laser with similar central wavelength and spectral linewidth as the seed. This work indicates that using low coherent fiber superfluorescent sources is a good solution for power scaling in narrow-linewidth fiber amplifier system in order to overcome the limitation of SBS effect.

Multiple nonlinear resonances and frequency combs in bottle microresonators

We introduce the generalized Lugiato-Lefever equation describing nonlinear effects in the bottle microresonators. We demonstrate that the nonlinear modes of these resonators can form multiple coexisting and overlapping nonlinear resonances and that their instabilities lead to the generation of the low repetition rate frequency combs.

Efficient frequency generation in phoXonic cavities based on hollow whispering gallery mode resonators

We report on nonlinear optical effects on phoxonic cavities based on hollow whispering gallery mode resonators pumped with a continuous wave laser. We observed stimulated scattering effects such as Brillouin and Raman, Kerr effects such as degenerated and non-degenerated four wave mixing, and dispersive wave generation. These effects happened concomitantly. Hollow resonators give rise to a very rich nonlinear scenario due to the coexistence of several family modes.

External cavity lasing pumped stimulated Brillouin scattering in a high Q microcavity

Stimulated Brillouin scattering (SBS) in a microcavity is usually realized by employing a wavelength tunable external cavity diode laser (TECDL) as the pump source. In this Letter, we report the observation of SBS in a high Q microcavity based on a TECDL-free scheme. The microcavity is employed as a mode-reflecting mirror for constructing a fiber-ring laser and, simultaneously, pumped by the fiber-ring lasing with intrinsic resonance latching. Several regimes are observed in a microcavity with a diameter of ∼215  μm, such as single lasing pumped SBS and multiple regular lasing pumped SBSs (single or cascaded). The microwave signals from the beat notes of the composite output lasing are measured with full-width at half-maximum on the scale of kilohertz at ∼11 and ∼22  GHz, indicating the high coherence between the pump and the Brillouin lasing.

Visible light emission from a silica microbottle resonator by second- and third-harmonic generation

We report the first observation of nonlinear harmonic generation and sum frequency generation (SFG) coupled with stimulated Raman scattering (SRS) via the second-order (χ⁽²⁾) and the third-order (χ⁽³⁾) nonlinearities in a silica microbottle resonator. The visible light emission due to third-harmonic generation (THG) was observed in both the output of a tapered fiber and the optical microscope images, which can be used to identify the axial mode profiles. SFG enabled by three- and four-wave mixing processes between the pump light and the light generated via SRS was also observed. Second-harmonic generation (SHG) and the SFG are enabled by χ⁽²⁾ induced in silica by surface effects and multipole excitations.