Tunable Microcavity Research Articles

Coherent Coupling of a Diamond Tin-Vacancy Center to a Tunable Open Microcavity

Efficient coupling of optically active qubits to optical cavities is a key challenge for solid-state-based quantum optics experiments and future quantum technologies. Here we present a quantum photonic interface based on a single tin-vacancy center in a micrometer-thin diamond membrane coupled to a tunable open microcavity. We use the full tunability of the microcavity to selectively address individual tin-vacancy centers within the cavity mode volume. Purcell enhancement of the tin-vacancy center optical transition is evidenced both by optical excited state lifetime reduction and by optical linewidth broadening. As the emitter selectively reflects the single-photon component of the incident light, the coupled emitter-cavity system exhibits strong quantum nonlinear behavior. On resonance, we observe a transmission dip of 50% for low incident photon number per Purcell-reduced excited state lifetime, while the dip disappears as the emitter is saturated with higher photon number. Moreover, we demonstrate that the emitter strongly modifies the photon statistics of the transmitted light by observing photon bunching. This work establishes a versatile and tunable platform for advanced quantum optics experiments and proof-of-principle demonstrations on quantum networking with solid-state qubits. Published by the American Physical Society 2024

Hybrid cavity-antenna architecture for strong and tunable sideband-selective molecular Raman scattering enhancement.

Plasmon resonances at the surface of metallic antennas allow for extreme enhancement of Raman scattering. Intrinsic to plasmonics, however, is that extreme field confinement lacks precise spectral control, which would hold great promise in shaping the optomechanical interaction between light and molecular vibrations. We demonstrate an experimental platform composed of a plasmonic nanocube-on-mirror antenna coupled to an open, tunable Fabry-Perot microcavity for selective addressing of individual vibrational lines of molecules with strong Raman scattering enhancement. Multiple narrow and intense optical resonances arising from the hybridization of the cavity modes and the plasmonic broad resonance are used to simultaneously enhance the laser pump and the local density of optical states, and are characterized using rigorous modal analysis. The versatile bottom-up fabrication approach permits quantitative comparison with the bare nanocube-on-mirror system, both theoretically and experimentally. This shows that the hybrid system allows for similar SERS enhancement ratios with narrow optical modes, paving the way for dynamical backaction effects in molecular optomechanics.

Combining three sources of optical anisotropy in a tunable open-access microcavity: From theory to experiment

Photonic spin–orbit (SO) coupling is an important physical mechanism leading to numerous interesting phenomena in the systems of microcavity photons and exciton-polaritons. We report the effect of SO coupling in a tunable open-access microcavity embedded with anisotropic active media. The SO coupling associated with the TE–TM splitting results in an emergent anisotropy, which further leads to fine energy splittings allowing clear observation of the full set of eigenstates, in sharp contrast with the isotropic situation which leads to the isotropic eigenstates of spin vortices. We show that the photonic potential can be engineered by playing with the relation between the emergent anisotropy and the cavity ellipticity. All the experimental results are well reproduced by the degenerate perturbation theory. Our results constitute a significant extension to the research field of microcavity spinoptronics, with potential applications in polarization control and optical property measurement of photonic devices and materials.

Polaritonic Photocatalysis and Polariton-driven Control of Energy Relaxation Pathways in a Tunable Microcavity

Polaritonic Photocatalysis and Polariton-driven Control of Energy Relaxation Pathways in a Tunable Microcavity

Silicon-Based On-Chip Tunable High-Q-Factor and Low-Power Fano Resonators with Graphene Nanoheaters.

Tunable and low-power microcavities are essential for large-scale photonic integrated circuits. Thermal tuning, a convenient and stable tuning method, has been widely adopted in optical neural networks and quantum information processing. Recently, graphene thermal tuning has been demonstrated to be a power-efficient technique, as it does not require thick spacers to prevent light absorption. In this paper, a silicon-based on-chip Fano resonator with graphene nanoheaters is proposed and fabricated. This novel Fano structure is achieved by introducing a scattering block, and it can be easily fabricated in large quantities. Experimental results demonstrate that the resonator has the characteristics of a high quality factor (∼31,000) and low state-switching power (∼1 mW). The temporal responses of the microcavity exhibit qualified modulation speed with 9.8 μs rise time and 16.6 μs fall time. The thermal imaging and Raman spectroscopy of graphene at different biases were also measured to intuitively show that the tuning is derived from the joule heating effect of graphene. This work provides an alternative for future large-scale tunable and low-power-consumption optical networks, and has potential applications in optical filters and switches.

Laser written mirror profiles for open-access fiber Fabry-Perot microcavities.

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 200, 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 × 104 is reached. Together with a small mode waist of 2.3 µm, the cavity achieves a Purcell factor of C ∼ 2.5, which is useful for experiments that require good lateral optical access or otherwise large separation of the mirrors. Laser-written mirror profiles can be produced with a tremendous flexibility in shape and on various surfaces, opening new possibilities for microcavities.

A highly stable and fully tunable open microcavity platform at cryogenic temperatures

Open-access microcavities are a powerful tool to enhance light–matter interactions for solid-state quantum and nanosystems and are key to advance applications in quantum technologies. For this purpose, the cavities should simultaneously meet two conflicting requirements—full tunability to cope with spatial and spectral inhomogeneities of a material and highest stability under operation in a cryogenic environment to maintain resonance conditions. To tackle this challenge, we have developed a fully tunable, open-access, fiber-based Fabry–Pérot microcavity platform that can be operated under increased noise levels in a closed-cycle cryostat. It comprises custom-designed monolithic micro- and nanopositioning elements with up to mm-scale travel range that achieve a passive cavity length stability at low temperature of only 15 pm rms in a closed-cycle cryostat and 5 pm in a more quiet flow cryostat. This can be further improved by active stabilization, and even higher stability is obtained under direct mechanical contact between the cavity mirrors, yielding 0.8 pm rms during the quiet phase of the closed-cycle cryocooler. The platform provides the operation of cryogenic cavities with high finesse and small mode volume for strong enhancement of light–matter interactions, opening up novel possibilities for experiments with a great variety of quantum and nanomaterials.

Doubly resonant second-harmonic generation in a fiber-based tunable open microcavity

Doubly resonant second-harmonic generation in a fiber-based tunable open microcavity

Electrically tunable Berry curvature and strong light-matter coupling in liquid crystal microcavities with 2D perovskite.

The field of spinoptronics is underpinned by good control over photonic spin-orbit coupling in devices that have strong optical nonlinearities. Such devices might hold the key to a new era of optoelectronics where momentum and polarization degrees of freedom of light are interwoven and interfaced with electronics. However, manipulating photons through electrical means is a daunting task given their charge neutrality. In this work, we present electrically tunable microcavity exciton-polariton resonances in a Rashba-Dresselhaus spin-orbit coupling field. We show that different spin-orbit coupling fields and the reduced cavity symmetry lead to tunable formation of the Berry curvature, the hallmark of quantum geometrical effects. For this, we have implemented an architecture of a photonic structure with a two-dimensional perovskite layer incorporated into a microcavity filled with nematic liquid crystal. Our work interfaces spinoptronic devices with electronics by combining electrical control over both the strong light-matter coupling conditions and artificial gauge fields.

Electrically Tunable Polymer Whispering-Gallery-Mode Laser.

Microlasers hold great promise for the development of photonics and optoelectronics. At present, tunable microcavity lasers, especially regarding in situ dynamic tuning, are still the focus of research. In this study, we combined a 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) piezoelectric crystal with a Poly [9,9-dioctylfluorenyl-2,7-diyl] (PFO) microring cavity to realize a high-quality, electrically tunable, whispering-gallery-mode (WGM) laser. The dependence of the laser properties on the diameter of the microrings, including the laser spectrum and quality (Q) value, was investigated. It was found that with an increase in microring diameter, the laser emission redshifted, and the Q value increased. In addition, the device effectively achieved a blueshift under an applied electric field, and the wavelength tuning range was 0.71 nm. This work provides a method for in situ dynamic spectral modulation of microcavity lasers, and is expected to provide inspiration for the application of integrated photonics technology.

Tunable microcavities coupled to rare-earth quantum emitters

Electro-optical control of on-chip photonic devices is an essential tool for efficient integrated photonics. Lithium niobate on insulator (LNOI) is an emerging platform for on-chip photonics due to its large electro-optic coefficient and high nonlinearity. Integrating quantum emitters into LNOI would extend their versatility in classic photonics to quantum computing and communication. Here, we incorporate rare-earth ion (REI) quantum emitters into electro-optical tunable lithium niobite (LN) thin films and demonstrate control of LN microcavities coupled to REIs over a frequency range of 160 GHz with 5 µs switching speed. Dynamic control of the cavities enables modulation of the Purcell enhancement of REIs with short time constants. Using Purcell enhancement, we show evidence of detecting single Y b 3 + ions in LN cavities. Coupling quantum emitters in fast tunable photonic devices is an efficient method to shape the waveform of the emitter. It also offers a platform to encode quantum information in the integration of a spectral–temporal–spatial domain to achieve high levels of channel multiplexing, as well as an approach to generate deterministic single-photon sources.

Tunable Polarized Microcavity Characterized by Magnetic Circular Dichroism Spectrum.

Tunable resonator is a powerful building block in fields like color filtering and optical sensing. The control of its polarization characteristics can significantly expand the applications. Nevertheless, the methods for resonator dynamic tuning are limited. Here, a magnetically regulated circular polarized resonant microcavity is demonstrated with an ultrathin ferrimagnetic composite metal layer Ta/CoTb. We successfully tuned the cavity resonant frequency and polarization performance. A huge magnetic circular dichroism (MCD) signal (∼3.41%) is observed, and the microcavity valley position shifts 5.41 nm when a small magnetic field is applied. This resonant cavity has two-stable states at 0 T due to the magnetic remanence of CoTb film and can be switched using a tiny magnetic field (∼0.01 T). Our result shows that the ferrimagnetic film-based tunable microcavity can be a highly promising candidate for on-chip magneto-optical (MO) devices.

Tunable Microcavities Coupled to Rare-Earth Quantum Emitters

Tunable Microcavities Coupled to Rare-Earth Quantum Emitters

Tunable Microcavities Coupled to Rare-Earth Quantum Emitters

Tunable Microcavities Coupled to Rare-Earth Quantum Emitters

Pattern-tunable synthetic gauge fields in topological photonic graphene

Abstract We propose a straightforward and effective approach to design, by pattern-tunable strain-engineering, photonic topological insulators supporting high quality factors edge states. Chiral strain-engineering creates opposite synthetic gauge fields in two domains resulting in Landau levels with the same energy spacing but different topological numbers. The boundary of the two topological domains hosts robust time-reversal and spin-momentum-locked edge states, exhibiting high quality factors due to continuous strain modulation. By shaping the synthetic gauge field, we obtain remarkable field confinement and tunability, with the strain strongly affecting the degree of localization of the edge states. Notably, the two-domain design stabilizes the strain-induced topological edge state. The large potential bandwidth of the strain-engineering and the opportunity to induce the mechanical stress at the fabrication stage enables large scalability for many potential applications in photonics, such as tunable microcavities, new lasers, and information processing devices, including the quantum regime.

Condensation of 2D exciton-polaritons in an open-access microcavity

We establish a tunable open-access microcavity consisting of two planar distributed Bragg reflectors (DBRs) individually controlled by nanopositioners. By varying the cavity length, such configuration enables variation of the light–matter coupling strength by a factor of 2, while keeping in microresonators the same active region and cavity mirrors. Polariton condensation was demonstrated over a large range of Rabi splittings and the corresponding threshold diagram was derived as a function of cavity-exciton detuning, which fits well with theoretical simulations. The results show that for various light-matter coupling strengths, optimal detunings featured by the lowest condensation threshold always occur at a fixed depth of energy trap between the exciton reservoir and the polariton ground state, which enables the most efficient exciton–exciton scattering into the condensate state in the driven-dissipative polaritonic system.

Graphene/Epoxy Composite Based Broadband All-Optical Tunable Fiber Microcavity Filter

A graphene/epoxy composite based broadband all-optical tunable fiber microcavity filter is presented. The graphene/epoxy composite based microcavity shows the excellent all-optical controlability. Since the light acts on the graphene/epoxy composite directly, the microcavity has stronger optical Kerr effect and photothermal effect induced by the optical pump. Experimental results show that its wavelength tuning range and tuning step reach 25.54 nm and −832 pm/mW, respectively. It is expected to be applied in the fields of tunable optical filters, optical communication, optical sensors, fiber lasers, and spectrum scanning.

Nanophotonic Materials for Twisted-Light Manipulation.

Twisted light, an unbounded set of helical spatial modes carrying orbital angular momentum (OAM), offers not only fundamental new insights into structured light-matter interactions, but also a new degree of freedom to boost optical and quantum information capacity. However, current OAM experiments still rely on bulky, expensive, and slow-response diffractive or refractive optical elements, hindering today's OAM systems to be largely deployed. In the last decade, nanophotonics has transformed the photonic design and unveiled a diverse range of compact and multifunctional nanophotonic devices harnessing the generation and detection of OAM modes. Recent metasurface devices developed for OAM generation in both real and momentum space, presenting design principle and exemplary devices, are summarized. Moreover, recent development of whispering-gallery-mode-based passive and tunable microcavities, capable of extracting degenerate OAM modes for on-chip vortex emission and lasing, is summarized. In addition, the design principle of different plasmonic devices and photodetectors recently developed for on-chip OAM detection is discussed. Current challenges faced by the nanophotonic field for twisted-light manipulation and future advances to meet these challenges are further discussed. It is believed that twisted-light manipulation in nanophotonics will continue to make significant impact on future development of ultracompact, ultrahigh-capacity, and ultrahigh-speed OAM systems-on-a-chip.

Tunable self-assembled Casimir microcavities and polaritons.

Spontaneous formation of ordered structures-self-assembly-is ubiquitous in nature and observed on different length scales, ranging from atomic and molecular systems to micrometre-scale objects and living matter1. Self-ordering in molecular and biological systems typically involves short-range hydrophobic and van der Waals interactions2,3. Here we introduce an approach to micrometre-scale self-assembly based on the joint action of attractive Casimir and repulsive electrostatic forces arising between charged metallic nanoflakes in an aqueous solution. This system forms a self-assembled optical Fabry-Pérot microcavity with a fundamental mode in the visible range (long-range separation distance about 100-200 nanometres) and a tunable equilibrium configuration. Furthermore, by placing an excitonic material in the microcavity region, we are able to realize hybrid light-matter states (polaritons4-6), whose properties, such as coupling strength and eigenstate composition, can be controlled in real time by the concentration of ligand molecules in the solution and light pressure. These Casimir microcavities could find future use as sensitive and tunable platforms for a variety of applications, including opto-mechanics7, nanomachinery8 and cavity-induced polaritonic chemistry9.

Strong exciton−photon coupling with colloidal quantum dots in a tunable microcavity

Polariton emission from optical cavities integrated with various luminophores has been extensively studied recently due to the wide variety of possible applications in photonics, particularly promising in terms of the fabrication of low-threshold sources of coherent emission. Tunable microcavities allow extensive investigation of the photophysical properties of matter placed inside the cavity by deterministically changing the coupling strength and controllable switching from weak to strong and ultra-strong coupling regimes. Here, we demonstrate room-temperature strong coupling of exciton transitions in CdSe/ZnS/CdS/ZnS colloidal quantum dots with the optical modes of a tunable low-mode-volume microcavity. Strong coupling is evidenced by a large Rabi splitting of the photoluminescence spectra depending on the detuning of the microcavity. A coupling strength of 154 meV has been achieved. High quantum yields, excellent photostability, and scalability of fabrication of quantum dots (QDs) pave the way to practical applications of coupled systems based on colloidal QDs in photonics, optoelectronics, and sensing.