We present a joint theoretical and experimental characterization of thermo-refractive noise in high quality factor ($Q$), small mode volume ($V$) optical microcavities. Analogous to well-studied stability limits imposed by Brownian motion in macroscopic Fabry-Perot resonators, microcavity thermo-refractive noise gives rise to a mode volume-dependent maximum effective quality factor. State-of-the-art fabricated microcavities are found to be within one order of magnitude of this bound. We confirm the assumptions of our theory by measuring the noise spectrum of high-$Q/V$ silicon photonic crystal cavities and apply our results to estimate the optimal performance of proposed room temperature, all-optical qubits using cavity-enhanced bulk material nonlinearities.
Microcomb generation with simultaneous $χ^{(2)}$ and $χ^{(3)}$ nonlinearities brings new possibilities for ultra-broadband and potentially self-referenced integrated comb sources. However, the evolution of the intracavity field involving multiple nonlinear processes shows complex dynamics that is still poorly understood. Here we report on strong soliton regulation induced by fundamental-second-harmonic (FD-SH) mode coupling. The formation of solitons from chaos is extensively investigated based on coupled Lugiato-Lefever equations. The soliton generation shows more deterministic behaviors in t…
Whispering gallery mode (WGM) microcavities have been widely used for high-sensitivity ultrasound detection, due to their optical and mechanical resonances enhanced sensitivity. The ultrasound sensitivity of the cavity optomechanical system is fundamentally limited by the thermal noise. In this work, we theoretically and experimentally investigate the thermal-noise-limited sensitivity of a WGM microdisk ultrasound sensor, and optimize the sensitivity by varying the radius and thickness of the microdisk, as well as using a trench structure around the disk. Using a microdisk with a radius of 300…
The simultaneous control of optical and mechanical waves has enabled a range of fundamental and technological breakthroughs, from the demonstration of ultra-stable frequency reference devices to the exploration of the quantum-classical boundaries in laser-cooling experiments. More recently, such an opto-mechanical interaction has been observed in integrated nano-waveguides and microcavities in the Brillouin regime, where short-wavelength mechanical modes scatters light at several GHz. Here we engineer coupled optical microcavities spectra to enable a low threshold excitation of mechanical trav…
High-Q ring resonators with contacts to the waveguide core provide a versatile platform for various applications in chip-scale optomechanics, thermo- and electro-optics. We propose and demonstrate a novel approach to implement azimuthally periodic contacted ring resonators based on multi-mode Bloch matching that support contacts on both the inner and outer radius edges with small degradation to the optical Q. Radiative coupling between degenerate modes of adjacent transverse spatial order leads to imaginary frequency (Q) splitting and a scatterer avoiding high-Q "wiggler" supermode field. We e…
We propose a scheme for efficient cavity-enhanced nonlinear THz generation via difference-frequency generation (DFG) processes using a triply resonant system based on photonic crystal cavities. We show that high nonlinear overlap can be achieved by coupling a THz cavity to a doubly-resonant, dual-polarization near-infrared (e.g. telecom band) photonic-crystal nanobeam cavity, allowing the mixing of three mutually orthogonal fundamental cavity modes through a chi(2) nonlinearity. We demonstrate through coupled-mode theory that complete depletion of the pump frequency - i.e., quantum-limited con…
We report on the development of on-chip microcavities and show their potential as a platform for cavity quantum electrodynamics experiments. Microcavity arrays were formed by the controlled buckling of SiO2/Ta2O5 Bragg mirrors, and exhibit a reflectance-limited finesse of 3500 and mode volumes as small as 35lambda^3. We show that the cavity resonance can be thermally tuned into alignment with the D2 transition of 87Rb, and outline two methods for providing atom access to the cavity. Owing to their small mode volume and high finesse, these cavities exhibit single-atom cooperativities as high as…
Observations of polariton condensation in semiconductor microcavities suggest that polaritons can be exploited as a novel type of laser with low input-power requirements. The low-excitation regime is approximately equivalent to thermal equilibrium, and a higher excitation results in more dominant nonequilibrium features. Although standard photon lasing has been experimentally observed in the high excitation regime, e-h pair binding can still remain even in the high-excitation regime theoretically. Therefore, the photoluminescence with a different photon lasing mechanism is predicted to be diff…
Optical microcavities have received much attention over the last decade from different research fields ranging from fundamental issues of cavity QED to specific applications such as microlasers and bio-sensors. A major issue in the latter applications is the difficulty to obtain directional emission of light in the far-field while keeping high energy densities inside the cavity (i.e. high quality factor). To improve our understanding of these systems, we have studied the annular cavity (a dielectric disk with a circular hole), where the distance cavity-hole centers, d, is used as a parameter t…
We performed measurements of photon correlation [$g^{(2)}(τ)$] in driven nonlinear high-$Q$ silicon (Si) photonic crystal (PhC) microcavities. The measured $g^{(2)}(τ)$ exhibits a damped oscillatory behavior when input pump power exceeds a critical value. From comparison between experiments and simulations, we attribute the measured oscillation of $g^{(2)}(τ)$ to self-pulsing (a limit cycle) emerging from an interplay between photon, carrier, and thermal dynamics. Namely, the oscillation frequency of $g^{(2)}(τ)$ corresponds to the oscillation period of the limit cycle, while its finite cohere…
Multicomponent Bose-Einstein condensates, quantum Hall systems, and chiral magnetic materials display twists and knots in the continuous symmetries of their order parameter, known as Skyrmions. Originally discovered as solutions to the nonlinear sigma model in quantum field theory, these vectorial excitations are quantified by a topological winding number dictating their interactions and global properties of the host system. Here, we report the first experimental observation of a stable individual second order meron, and antimeron, appearing in an electromagnetic field. These complex textures …
We report on the thermomechanical and thermal tuning properties of curved-mirror Fabry-Perot resonators, fabricated by the guided assembly of circular delamination buckles within a multilayer a-Si/SiO2 stack. Analytical models for temperature dependence, effective spring constants, and mechanical mode frequencies are described and shown to be in good agreement with experimental results. The cavities exhibit mode volumes as small as $\sim10λ^3$, reflectance-limited finesse $\sim3\times10^3$, and mechanical resonance frequencies in the MHz range. Monolithic cavity arrays of this type might be of…
We describe the use of monolithic, buckled-dome cavities as ultrasound sensors. Patterned delamination within a compressively stressed thin film stack produces high-finesse plano-concave optical resonators with sealed and empty cavity regions. The buckled mirror also functions as a flexible membrane, highly responsive to changes in external pressure. Owing to their efficient opto-acousto-mechanical coupling, thermal-displacement-noise limited sensitivity is achieved at low optical interrogation powers and for modest optical (Q ~ 10^3) and mechanical (Q ~ 10^2) quality factors. We predict and v…
Owing to their dual-resonance enhanced sensitivity, cavity optomechanical systems provide an ideal platform for ultrasound sensing. In this work, we realize high sensitivity air-coupled ultrasound sensing from kilohertz (kHz) to megahertz (MHz) frequency range based on whispering gallery mode microcavities. Using a 57 um-diameter microtoroid with high optical Q factor (~10^7) and mechanical Q factor (~700), we achieve sensitivities of 46 uPa Hz^{-1/2}-10 mPa Hz^{-1/2} in a frequency range of 0.25-3.2 MHz. Thermal-noise-limited sensitivity is realized around the mechanical resonance at 2.56 MHz…
Exciton polaritons in semiconductor microcavities exhibit many fundamental physical effects, with some of them amenable to being controlled by external fields. The polariton transport is affected by the polaritonic spin-orbit interaction, which is caused by the splitting of transverse-electric and transverse-magnetic (TE-TM) modes. This is the basis for a polaritonic Hall effect, called optical spin Hall effect (OSHE), which is related to the formation of spin/polarization textures in momentum space, determining anisotropic ballistic transport, as well as related textures in real space. Owing …
Optical microcavities are often used to realize enhanced nonlinear optical interactions for highly efficient second-harmonic generation. With increased pump power, the efficiency of nonlinear frequency conversion can be increased further, while some other unwanted nonlinear effects will also emerge, leading to complicated dynamics or instability. Here, we study the interplay between cascaded second- and third-order nonlinear processes and investigate their impact on the second-harmonic generation in microcavities. It is found that the non-degenerate optical parametric oscillation (OPO) appears…
Optical frequency combs are crucial for both fundamental science and applications demanding wide frequency spanning and ultra-precision resolutions. Recent advancements of nonlinear Kerr effect based optical frequency combs in microcavities open up new opportunities in a compact platform, however, internal cavity-enhanced nonlinearities are still unclear. Here we demonstrate transient nonlinear dynamics during optical frequency comb formation inside a Kerr microcavity. We show that gain spiking forms due to nonlinear phase modulation, causing comb lines' self-detuning nearby a cavity resonance…
Whispering gallery mode (WGM) microcavities strongly enhance nonlinear optical processes like optical frequency comb, Raman scattering and optomechanics, which nowadays enable cutting-edge applications in microwave synthesis, optical sensing spectroscopy, and integrated photonics. Yet, tunability of their resonances, mostly via coarse and complicated mechanism through temperature, electrical or mechanical means, still poses a major challenge for precision applications as above. Here we introduce a new passive scheme to finely tune resonances of WGMs at MHz precision with an external probe. Suc…
Sensors that are able to detect and track single unlabelled biomolecules are an important tool both to understand biomolecular dynamics and interactions at nanoscale, and for medical diagnostics operating at their ultimate detection limits. Recently, exceptional sensitivity has been achieved using the strongly enhanced evanescent fields provided by optical microcavities and nano-sized plasmonic resonators. However, at high field intensities photodamage to the biological specimen becomes increasingly problematic. Here, we introduce an optical nanofibre based evanescent biosensor that operates a…
In astronomy, interferometry of light collected by separate telescopes is often performed by physically bringing the optical paths together in the form of Young's double-slit experiment. Optical loss severely limits the efficiency of this so-called direct detection method, motivating the fundamental question of whether one can achieve a comparable performance using separate optical measurements at the two telescopes before combining the measurement results. Using quantum mechanics and estimation theory, here I show that any such spatially local measurement scheme, such as heterodyne detection,…
The intrinsic thermal noise in optical fibers is the ultimate limit of fiber-based systems. However, at infrasonic frequencies, the spectral behavior of the intrinsic thermal noise remains unclear so far. We present the measurements of the fundamental thermal noise in optical fibers obtained using a balanced fiber Michelson interferometer. When an ultra-stable laser is used as the laser source and other noise sources are carefully controlled, the 1/f spectral density of thermal noise is observed down to infrasonic frequencies and the measured magnitude is consistent with the theoretical predic…
The ability to control the spin-orbit interaction of light in optical microresonators is of fundamental importance for future photonics. Organic microcrystals, due to their giant optical anisotropy, play a crucial role in spin-optics and topological photonics. Here we realize controllable and wavelength-dependent Rashba-Dresselhaus spin-orbit interaction, attributed to the anisotropic excitonic response in an optical microcavity filled with an organic microcrystalline. We also investigate the transition of the spin-orbit interaction from dominant photonic type caused by the splitting of the tr…
Liquid droplet whispering-gallery-mode microresonators open a new research frontier for optomechanics and photonic devices. At visible wavelengths, where most liquids are transparent, a major contribution to a droplet optical quality factor is expected theoretically from thermal surface distortions and capillary waves. Here, we investigate experimentally these predictions using transient cavity ring-down spectroscopy. In this way, the optical out-coupling and intrinsic loss are measured independently while any perturbation induced by thermal, acoustic and laser-frequency noise is avoided thank…
Non-Hermitian Hamiltonians describing open systems can feature singularities called exceptional points (EPs). Resonant frequencies become strongly dependent on externally applied perturbations near an EP which has given rise to the concept of EP-enhanced sensing in photonics. However, while increased sensor responsivity has been demonstrated, it is not known if this class of sensor results in improved signal-to-noise performance. Here, enhanced responsivity of a laser gyroscope caused by operation near an EP is shown to be exactly compensated by increasing sensor noise in the form of linewidth…
Thermal noise of optical cavities limits the accuracy of many experiments on precision laser spectroscopy and interferometry. The study of the physical properties of this noise opens opportunities for the creation of more stable cavities, reduction of phase noise of optical radiation, and performance of accurate optical studies. The paper proposes a method of partial recording of TEM00 mode thermal noise of a Fabry-Perot cavity using two "probe" modes of higher order. The method allows partial compensation of noise in the fundamental mode. Mathematical modeling is performed, which confirms the…
We present numerical studies of two photonic crystal membrane microcavities, a short line-defect cavity with relatively low quality ($Q$) factor and a longer cavity with high $Q$. We use five state-of-the-art numerical simulation techniques to compute the cavity $Q$ factor and the resonance wavelength $λ$ for the fundamental cavity mode in both structures. For each method, the relevant computational parameters are systematically varied to estimate the computational uncertainty. We show that some methods are more suitable than others for treating these challenging geometries.
We demonstrate the existence of fundamental and dipole interface solitons in one-dimensional thermal nonlinear media with a step in linear refractive index. Fundamental interface solitons are found to be always stable and the stability of dipole interface solitons depends on the difference in linear refractive index. The mass center of interface solitons always locates in the side with higher index. Two intensity peaks of dipole interface solitons are unequal except some specific conditions, which is different from their counterparts in uniform thermal media.
The radiance of thermal emission, as described by Planck law, depends only on the emissivity and temperature of a body, and increases monotonically with the temperature rise at any emitted wavelength. Nonthermal radiation, such as photoluminescence, is a fundamental light matter interaction that conventionally involves the absorption of an energetic photon, thermalization, and the emission of a redshifted photon. Such a quantum process is governed by rate conservation, which is contingent on the quantum efficiency. In the past, the role of rate conservation for significant thermal excitation h…
Metamaterials and meta-surfaces represent a remarkably versatile platform for light manipulation, biological and chemical sensing, nonlinear optics, and even spaser lasing. Many of these applications rely on the resonant nature of metamaterials, which is the basis for extreme spectrally selective concentration of optical energy in the near field. The simplicity of free-space light coupling into sharply-resonant meta-surfaces with high resonance quality factors Q>>1 is a significant practical advantage over the extremely angle-sensitive diffractive structures or inherently inhomogeneous high-Q …
Optically levitated rotors are prime candidates for torque sensors whose precision is limited by the fluctuationsof the rotation frequency. In this work we investigate an optically levitated rotor at its fundamental thermal limitof frequency stability, where rotation-frequency fluctuations arise solely due to coupling to the thermal bath.
Thermal Deformation Reduction in High-Power Interferometry with Higher-Order Laser Modes
Université Paris Cité, CNRS, Astroparticule et Cosmologie（巴黎西岱大学，法国国家科学研究中心，粒子与宇宙学）；University of Florida（佛罗里达大学）；Institute for Gravitational Wave Astronomy, Henan Academy of Sciences（河南省科学院引力波天文研究所）；School of Physics and Astronomy, Beijing Normal University（北京师范大学物理与天文学院）；Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University（北京师范大学天文与前沿科学研究院）
