We report on measurements and modeling of the mode structure of tunable Fabry-Pérot optical microcavities with imperfect mirrors. We find that non-spherical mirror shape and finite mirror size lead to loss, mode deformation, and shifted resonance frequencies at particular mirror separations. For small mirror diameters, the useful cavity length is limited to values significantly below the expected stability range. We explain the observations by resonant coupling between different transverse modes of the cavity and mode-dependent diffraction loss. A model based on resonant state expansion that takes into account the measured mirror profile can reproduce the measurements and identify the parameter regime where detrimental effects of mode mixing are avoided.
We demonstrate laser-written concave hemispherical structures produced on the endfacets of optical fibers that serve as mirror substrates for tunable open-access microcavities. We achieve finesse values of up to 250, and a mostly constant performance across the entire stability range. This enables cavity operation also close to the stability limit, where a peak quality factor of $1.5\times 10^4$ is reached. Together with a small mode waist of $2.3\; \mathrm{μm}$, the cavity achieves a Purcell factor of $C \sim 2.5$, which is useful for experiments that require good lateral optical access or ot…
A narrow linewidth laser operating at the telecommunications band combined with both fast and wide-band tuning features will have promising applications. Here, we demonstrate a single-mode (both transverse and longitude mode) continuous microlaser around 1535 nm based on a fiber Fabry-Pérot microcavity, which achieves wide-band tuning without mode hopping to 1.3 THz range and fast tuning rate to 60 kHz, yields a frequency scan rate of $1.6\times10^{17}$ Hz/s. Moreover, the linewidth of the laser is measured as narrow as 3.1 MHz. As the microlaser combines all these features into one fiber comp…
We propose a fiber-based environmental sensor that exploits the reflection phase shift tunability provided by the use of layered coatings composed of dielectric slabs spaced by conducting membranes. A transfer matrix study is done in a simplified theoretical model, for which an enhanced sensitivity of the reflection interference pattern to the output medium is demonstrated, in the typical refractive index range of liquid media. An experimental configuration using a cascaded Fabry-Perot microcavity coated by a graphene oxide/polyethylenimine (GO/PEI) multilayered structure is demonstrated. Its …
Exciton-polaritons in semiconductor microcavities generate fascinating effects such as long-range spatial coherence and Bose-Einstein Condensation (BEC), which are attractive for their potential use in low threshold lasers, vortices and slowing light, etc. However, currently most of exciton-polariton effects either occur at cryogenic temperature or rely on expensive cavity fabrication procedures. Further exploring new semiconductor microcavities with stronger exciton photon interaction strength is extensively needed. Herein, we demonstrate room temperature photon exciton strong coupling in hyb…
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 demonstrate in open microcavities with broken chiral symmetry, quasi-degenerate pairs of co-propagating modes in a non-rotating cavity evolve to counter-propagating modes with rotation. The emission patterns change dramatically by rotation, due to distinct output directions of CW and CCW waves. By tuning the degree of spatial chirality, we maximize the sensitivity of microcavity emission to rotation. The rotation-induced change of emission is orders of magnitude larger than the Sagnac effect, pointing to a promising direction for ultrasmall optical gyroscopes.
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…
We study the interplay between rotation and openness for mode coupling in wavelength-scale microcavities. In cavities deformed from a circular disk, the decay rates of a quasi-degenerate pair of resonances may cross or anti-cross with increasing rotation speed. The standing-wave resonances evolve to traveling-wave resonances at high rotation speed, however, both the clockwise (CW) and counter-clockwise (CCW) traveling-wave resonances can have a lower cavity decay rate, in contrary to the intuitive expectation from rotation-dependent effective index. With increasing rotation speed, a phase lock…
Optical microcavities allow to strongly confine light in small mode volumes and with long photon lifetimes. This confinement significantly enhances the interaction between light and matter inside the cavity, with applications such as optical trapping and cooling of nanoparticles, single-photon emission enhancement, quantum information processing, and sensing. For many applications, open resonators with direct access to the mode volume are necessary. Here we report on a scalable, open-access optical microcavity platform with mode volumes < 30 $λ^3$ and finesse approaching $5x10^5$. This result …
We investigate the optical properties of microcavities with suspended subwavelength structured mirrors, such as high-contrast gratings or two-dimensional photonic crystals slabs, and focus in particular on the regime in which the microcavity free-spectral range is larger than the width of a Fano resonance of the highly reflecting structured mirror. In this unusual regime, the transmission spectrum of the microcavity essentially consists in a single mode, whose linewidth can be significantly narrower than both the Fano resonance linewidth and the linewidth of an equally short cavity without str…
The emission of light of an efficient single-photon emitter (SPE) should have a high-count rate into a well-defined spatio-temporal mode along with an accessible numerical aperture (NA) to increase the light extraction efficiency that is required for effective coupling into optical waveguides. Based on a previously developed experimental approach to fabricate hybrid Fabry-Perot microcavities (Further information is available [F. Ortiz-Huerta et al, Opt.Express 26, 33245 (2018)]), we managed to find analytical and finite-difference time-domain (FDTD) values for the, experimentally achievable, g…
We demonstrate non-perturbative coupling between a single self-assembled InGaAs quantum dot and an external fiber-mirror based microcavity. Our results extend the previous realizations of tunable microcavities while ensuring spatial and spectral overlap between the cavity-mode and the emitter by simultaneously allowing for deterministic charge control of the quantum dots. Using resonant spectroscopy, we show that the coupled quantum dot cavity system is at the onset of strong coupling, with a cooperativity parameter of 2. Our results constitute a milestone towards the realization of a high eff…
Optical cavities can support many transverse and longitudinal modes. A paraxial scalar theory predicts that the resonance frequencies of these modes cluster in different orders. A non-paraxial vector theory predicts that the frequency degeneracy within these clusters is lifted, such that each order acquires a spectral fine structure, comparable to the fine structure observed in atomic spectra. In this paper, we calculate this fine structure for microcavities and show how it originates from various non-paraxial effects and is co-determined by mirror aberrations. The presented theory, which appl…
We present experimental and numerical studies of broad-area semiconductor lasers with chaotic ray dynamics. The emission intensity distributions at the cavity boundaries are measured and compared to ray tracing simulations and numerical calculations of the passive cavity modes. We study two different cavity geometries, a D-cavity and a stadium, both of which feature fully chaotic ray dynamics. While the far-field distributions exhibit fairly homogeneous emission in all directions, the emission intensity distributions at the cavity boundary are highly inhomogeneous, reflecting the non-uniform i…
The spontaneous emission of atoms can be controlled by placing them between two mirrors that form an optical cavity. Rapid advances in material processing techniques in the last 10 years have made it possible to fabricate microscopic optical cavities that can be finely tuned into resonance with the emitter. This has enabled progress in single-photon sources, nano-lasers and spectroscopy of new nano-emitters such as semiconductor quantum dots and Nitrogen-vacancy centres in diamond. Here we introduce a step-by-step method for computing the Purcell factor of the latest generation of open tunable…
Fiber-based optical microcavities exhibit high quality factor and low mode volume resonances that make them attractive for coupling light to individual atoms or other microscopic systems. Moreover, their low mass should lead to excellent mechanical response up to high frequencies, opening the possibility for high bandwidth stabilization of the cavity length. Here, we demonstrate a locking bandwidth of 44 kHz achieved using a simple, compact design that exploits these properties. Owing to the simplicity of fiber feedthroughs and lack of free-space alignment, this design is inherently compatible…
Open Fabry-Perot microcavities represent a promising route for achieving a quantum electrodynamics (cavity-QED) platform with diamond-based emitters. In particular, they offer the opportunity to introduce high purity, minimally fabricated material into a tunable, high quality factor optical resonator. Here, we demonstrate a fiber-based microcavity incorporating a thick (> 10 μm) diamond membrane with a finesse of 17,000, corresponding to a quality factor Q ~ $10^6$. Such minimally fabricated, thick samples can contain optically stable emitters similar to those found in bulk diamond. We observe…
Planar microcavities allow the control and manipulation of spin-polarization, manifested in phenomena like the optical spin Hall effect due to the intrinsic polarization mode splitting. Here, we study a transparent microcavity with broken rotational symmetry, realized by aligning the optical axis of a uniaxial cavity material in the cavity plane. We demonstrate that the in-plane optical anisotropy gives rise to exceptional points in the dispersion relation, which occur pair-wise, are circularly polarized, and are cores of polarization vortices. These exceptional points are a result of the non-…
A theoretical variation between the two distinct light-matter coupling regimes, namely weak and strong coupling, becomes uniquely feasible in open optical Fabry-Pérot microcavities with low mode volume, as discussed here. In combination with monolayers of transition-metal dichalcogenides (TMDCs) such as WS2, which exhibits a large exciton oscillator strength and binding energy, the room-temperature observation of hybrid bosonic quasiparticles, referred to as exciton-polaritons and characterized by a Rabi splitting, comes into reach. In this context, our simulations using the transfer-matrix me…
The polarization exchange effect in a twisted-nematic Fabry-Pérot resonator is experimentally confirmed in the regimes of both uniform and electric-field-deformed twisted structures. The polarization of output light in the transmission peaks is shown to be linear rather than elliptical. The polarization deflection from the nematic director grows from $0^\circ$ to $90^\circ$ angle and exchanges the longitudinal and transverse directions. Untwisting of a nematic by a voltage leads to the rotation of the polarization plane of light passing through the resonator. The polarization exchange effect a…
Photoinduced Kerr rotation by more than $π/2$ radians is demonstrated in planar quantum well microcavity in the strong coupling regime. This result is close to the predicted theoretical maximum of $π$. It is achieved by engineering microcavity parameters such that the optical impedance matching condition is reached at the smallest negative detuning between exciton resonance and the cavity mode. This ensures the optimum combination of the exciton induced optical non-linearity and the enhancement of the Kerr angle by the cavity. Comprehensive analysis of the polarization state of the light in th…
A Mach-Zehnder interferometer with absorbing Fabry-Pérot cavities is used to measure the optical phase differences upon rotation around a vertical axis. The details of the expected experimental results are described based on the idea that a conducting medium can introduce phase differences due to changes in material conductivity that are expected to occur when a medium moves with respect to a reference frame. Experimental details and results are discussed.
Hybrid light-matter states, polaritons, are one of the central concepts in modern quantum optics and condensed matter physics. Polaritons emerge as a result of strong interaction between an optical mode and a material resonance, which is frequently realized in molecular, van der Waals, or solid-state platforms (1-7). However, this route requires accurate (nano)fabrication and often lacks simple means for tunability, which could be disadvantageous in some applications. Here, we use a different approach to realize polaritonic states by employing a stable equilibrium between two parallel gold nan…
Optical gyroscope based on the Sagnac effect have excellent potential in the application of high-sensitivity inertial rotation sensors. In this paper, we demonstrate that for an optical resonance gyroscope with normal dispersion, the measurement sensitivity can be increased by two orders of magnitude through coupling into a squeezed vacuum light, which is different from that in the classical situation. When the system is operated under critical anomalous dispersion condition, injecting a squeezed vacuum light allows the measurement sensitivity beyond the corresponding standard quantum limit by…
We study the frequency splitting of the polarization eigenmodes of the fundamental transverse mode in CO2 laser-machined, high-finesse optical Fabry-Perot cavities and investigate the influence of the geometry of the cavity mirrors. Their highly reflective surfaces are typically not rotationally symmetric but have slightly different radii of curvature along two principal axes. We observe that the eccentricity of such elliptical mirrors lifts the degeneracy of the polarization eigenmodes. The impact of the eccentricity increases for smaller radii of curvature. A model derived from corrections t…
Complex optical systems such as high-quality microcavities enabled by advanced lithography and processing techniques paved the way to various light-matter interactions (LMI) studies. Without lattice-matching constraints in epitaxy, coating techniques or shaky open cavity constructions, sub-micrometer-precise lithographic development of a polymer photoresist paves the way to polymer microcavity structures for various spectral regions based on the material's transparency and the geometrical sizes. We introduce a new approach based on 3D nanowriting in photoresist, which can be employed to achiev…
High-finesse, open-geometry microcavities have recently emerged as a versatile tool for enhancing interactions between photons and material systems, with a range of applications in quantum optics and quantum information science. However, mechanical vibrations pose a considerable challenge to their operation within a closed-cycle cryostat, particularly when spatial tunability and free-space optical access are required. Here, we present the design and characterization of a system that can achieve $\sim$16 pm-rms passive mechanical stability between two high-finesse mirrors while permitting both …
Aggregation-engineered loss-tolerant strong coupling in metallic microcavities
European Laboratory for Non-Linear Spectroscopy (LENS), Università di Firenze（佛罗伦萨大学非线性光谱欧洲实验室）；Advanced Materials and Life Science Division, Istituto Nazionale di Ricerca Metrologica (INRiM)（意大利国家计量研究所先进材料与生命科学部）；Department of Industrial Engineering (DIEF), University of Florence & INSTM RU of Florence（佛罗伦萨大学工业工程系及INSTM佛罗伦萨研究单元）；Institute of Chemistry of Organometallic Compounds (ICCOM-CNR)（金属有机化合物化学研究所）；Department of Chemistry ‘Ugo Schiff ’ DICUS & INSTM Research Unit, University of Florence（佛罗伦萨大学乌戈·席夫化学系及INSTM研究单元）；Dipartimento di Fisica e Astronomia, Università di Firenze（佛罗伦萨大学物理与天文学系）；Consiglio Nazionale delle Ricerche, Istituto Nazionale di Ottica, CNR-INO（意大利国家研究委员会国家光学研究所）
The use of low-dimensional objects in the field of cavity optomechanics is limited by their low scattering cross section compared to the size of the optical cavity mode. Fiber-based Fabry-Pérot microcavities can feature tiny mode cross sections and still maintain a high finesse, boosting the light-matter interaction and thus enabling the sensitive detection of the displacement of minute objects. Here we present such an ultrasensitive microcavity setup with the highest finesse reported so far in loaded fiber cavities, $\mathcal{F} = 195\,000$. We are able to position-tune the static optomechani…
We report studies of optical Fabry-Perot microcavities based on semiconducting single-wall carbon nanotubes with a quality factor of 160. We experimentally demonstrate a huge photoluminescence signal enhancement by a factor of 30 in comparison with the identical film and by a factor of 180 if compared with a thin film containing non-purified (8,7) nanotubes. Futhermore, the spectral full-width at half-maximum of the photo-induced emission is reduced down to 8 nm with very good directivity at a wavelength of about 1.3 $μ$m. Such results prove the great potential of carbon nanotubes for photonic…
Whispering-gallery microcavity laser possesses ultralow threshold, whereas convenient free-space optical excitation and collection suffer from low efficiencies due to its rotational symmetry. Here we analytically study a three-dimensional microsphere coupled to a nano-sized scatterer in the framework of quantum optics. It is found that the scatterer is capable of coupling light in and out of the whispering-gallery modes (WGMs) without seriously degrading their high-Q properties, while the microsphere itself plays the role of a lens to focus the input beam on the scatterer and vice versa. Our a…
Spin-orbit interactions which couple spin of a particle with its momentum degrees of freedom lie at the center of spintronic applications. Of special interest in semiconductor physics are Rashba and Dresselhaus spin-orbit coupling (SOC). When equal in strength, the Rashba and Dresselhaus fields result in SU(2) spin rotation symmetry and emergence of the persistent spin helix (PSH) only investigated for charge carriers in semiconductor quantum wells. Recently, a synthetic Rashba-Dresselhaus Hamiltonian was shown to describe cavity photons confined in a microcavity filled with optically anisotro…
The achievable instrument sensitivity is a critical parameter for the continued development of THz applications. Techniques such as Cavity-Enhanced Techniques and Cavity Ring Down Spectroscopy have not yet been employed at THz frequency due to the difficulties to construct a high finesse Fabry-Pérot cavity. Here, we describe such a THz resonator based on a low-loss oversized corrugated waveguide with highly reflective photonic mirrors obtaining a finesse above 3000 around 620 GHz. These components enable a Fabry-Perot THz Absorption Spectrometer with an equivalent interaction length of one kil…
Coherent control and manipulation of quantum degrees of freedom such as spins forms the basis of emerging quantum technologies. In this context, the robust valley degree of freedom and the associated valley pseudospin found in two-dimensional transition metal dichalcogenides is a highly attractive platform. Valley polarization and coherent superposition of valley states have been observed in these systems even up to room temperature. Control of valley coherence is an important building block for the implementation of valley qubit. Large magnetic fields or high-power lasers have been used in th…
We present a monolithic semiconductor microcavity design for enhanced light-matter interaction and photon extraction efficiency of an embedded quantum emitter such as a quantum dot or color center. The microcavity is a hemispherical Fabry-Perot design consisting of a planar back mirror and a top curved mirror. Higher order modes are suppressed in the structure by reducing the height of the curved mirror, leading to efficient photon extraction into a fundamental mode with a Gaussian far-field radiation pattern. The cavity finesse can be varied easily by changing the reflectivity of the mirrors …
Tunable open-access Fabry-Pérot microcavities enable the combination of cavity enhancement with high resolution imaging. To assess the limits of this technique originating from background variations, we perform high-finesse scanning cavity microscopy of pristine planar mirrors. We observe spatially localized features of strong cavity transmission reduction for certain cavity mode orders, and periodic background patterns with high spatial frequency. We show in detailed measurements that the localized structures originate from resonant transverse-mode coupling and arise from the topography of th…
The high refractive index of ZnS (about 2.4 in the visible range) makes ZnS microstructures good candidates for the fabrication of light guides and resonant microcavities. Light guiding behaviour has been studied in several ZnS structures. In particular, in this work the behavior of rods and plates has been investigated and it is has been shown that the morphology of the studied structures plays a determinant role on the supported resonant modes. In ZnS:Ga and ZnS:In structures investigated in the present work Fabry-Perot as well as Whispering Gallery resonant modes are supported. A good agree…
Nanoantennas offer the ultimate spatial control over light by concentrating optical energy well below the diffraction limit, whereas their quality factor (Q) is constrained by large radiative and dissipative losses. Dielectric microcavities, on the other hand, are capable of generating a high Q-factor through an extended photon storage time but have a diffraction-limited optical mode volume. Here we bridge the two worlds, by studying an exemplary hybrid system integrating plasmonic gold nanorods acting as nanoantennas with an on-resonance dielectric photonic crystal (PC) slab acting as a low-l…
Although experimental efforts have been active for about 30 years now, a direct laboratory observation of vacuum magnetic birefringence, an effect due to vacuum fluctuations, still needs confirmation. Indeed, the predicted birefringence of vacuum is $Δn = 4.0\times 10^{-24}$ @ 1~T. One of the key ingredients when designing a polarimeter capable of detecting such a small birefringence is a long optical path length within the magnetic field and a time dependent effect. To lengthen the optical path within the magnetic field a Fabry-Perot optical cavity is generally used with a finesse ranging fro…
Optical microcavities are a powerful tool to enhance spontaneous emission of individual quantum emitters. However, the broad emission spectra encountered in the solid state at room temperature limit the influence of a cavity, and call for ultra-small mode volume. We demonstrate Purcell-enhanced single photon emission from nitrogen-vacancy (NV) centers in nanodiamonds coupled to a tunable fiber-based microcavity with a mode volume down to $1.0\,λ^{3}$. We record cavity-enhanced fluorescence images and study several single emitters with one cavity. The Purcell effect is evidenced by enhanced flu…
We present a cryogenic setup where an optical Fabry-Perot resonator is coupled to a single-mode optical fiber with coupling efficiency above 90% at mK temperatures without realignment during cooling down. The setup is prealigned at room temperature to compensate for the thermal contraction and change of the refractive index of the optical components during cooling down. The high coupling efficiency is achieved by keeping the setup rotation-symmetric around the optical axis. The majority of the setup components are made of Invar (FeNi36) which minimizes the thermal contraction. High coupling ef…
Synthesized micro- and nanotubes composed of transition metal dichalcogenides (TMDCs) such as MoS$_2$ are promising for many applications in nanophotonics, because they combine the abilities to emit strong exciton luminescence and to act as whispering gallery microcavities even at room temperature. In addition to tubes in the form of hollow cylinders, there is an insufficiently-studied class of twisted tubes, the flattened cross section of which rotates along the tube axis. As shown by theoretical analysis, in such nanotubes the interaction of electromagnetic waves excited at opposite sides of…
