Active Optical Cavity Research Articles

Metasurface-tunable lasing polarizations in a microcavity

Manipulating polarization states of microlasers is essentially important in many emerging optical and biological applications. Strategies have been focused on using external optical elements or surface nanostructures to control the polarization state of laser emission. Here we introduce a strategy for manipulation of laser polarization based on metasurfaces through round trips of photons confined inside an active optical cavity. The roles of intracavity metasurfaces and light–meta-atom interactions were investigated under a stimulated emission process in a microcavity. Taking advantage of strong optical feedback produced by the Fabry–P e ´ rot optofluidic microcavity, light–meta-atom interactions are enlarged, resulting in polarized lasing emission with high purity and controllability. Depending on the metasurface structural orientation, the polarization state of lasing emission can be actively modulated as linearly polarized or elliptically polarized with different degrees of circular polarization at a source within the microcavity. This study provides insight into fundamental laser physics, opening possibilities by bridging metasurfaces into microlasers.

Wafer-Scale High-Quality Microtubular Devices Fabricated via Dry-Etching for Optical and Microelectronic Applications.

Mechanical strain formed at the interfaces of thin films has been widely applied to self-assemble 3D microarchitectures. Among them, rolled-up microtubes possess a unique 3D geometry beneficial for working as photonic, electromagnetic, energy storage, and sensing devices. However, the yield and quality of microtubular architectures are often limited by the wet-release of lithographically patterned stacks of thin-film structures. To address the drawbacks of conventionally used wet-etching methods in self-assembly techniques, here a dry-release approach is developed to roll-up both metallic and dielectric, as well as metallic/dielectric hybrid thin films for the fabrication of electronic and optical devices. A silicon thin film sacrificial layer on insulator is etched by dry fluorine chemistry, triggering self-assembly of prestrained nanomembranes in a well-controlled wafer scale fashion. More than 6000 integrated microcapacitors as well as hundreds of active microtubular optical cavities are obtained in a simultaneous self-assembly process. The fabrication of wafer-scale self-assembled microdevices results in high yield, reproducibility, uniformity, and performance, which promise broad applications in microelectronics, photonics, and opto-electronics.

Burst mode MHz repetition rate inverse free electron laser acceleration

The capability of accelerating electron bunches at high repetition rate is one of the key performance criteria for all high average power particle accelerator applications. High gradient laser-driven acceleration holds the potential for greatly reducing size and costs of future machines, but typically requires very high peak laser powers. On the other hand, MHz pulse trains of TW-class laser beams are much beyond the state of the art, so that laser recycling and recirculation is a necessary step to bridge that gap. In this experiment we demonstrate for the first time an inverse free electron laser accelerator (IFEL) operating within an active optical cavity showing the ability to laser-accelerate electron bunch trains in burst mode at $g20\text{ }\text{ }\mathrm{MHz}$ repetition rate. The experimental setup, synchronization challenges and acceleration results are presented. It is found that careful control of the dispersive properties of the cavity is required in order to sustain high accelerating gradients over many passes in the laser pulse train.

Dissipative quantum phase transition in a biased Tavis–Cummings model**Project supported by the National Natural Science Foundation of China (Grant Nos. 11934010, U1801661, U1930402, and 11847087) and the National Key Research and Development Program of China (Grant No. 2016YFA0301200).

We study the dissipative quantum phase transition (QPT) in a biased Tavis–Cummings model consisting of an ensemble of two-level systems (TLSs) interacting with a cavity mode, where the TLSs are pumped by a drive field. In our proposal, we use a dissipative TLS ensemble and an active cavity with effective gain. In the weak drive-field limit, the QPT can occur under the combined actions of the loss and gain of the system. Owing to the active cavity, the QPT behavior can be much differentiated even for a finite strength of the drive field on the TLS ensemble. Also, we propose to implement our scheme based on the dissipative nitrogen-vacancy (NV) centers coupled to an active optical cavity made from the gain-medium-doped silica. Furthermore, we show that the QPT can be measured by probing the transmission spectrum of the cavity embedding the ensemble of the NV centers.

Directional amplifier in an optomechanical system with optical gain

Directional amplifiers are crucial nonreciprocal devices in both classical and quantum information processing. Here we propose a scheme for realizing a directional amplifier between optical and microwave fields based on an optomechanical system with optical gain, where an active optical cavity and two passive microwave cavities are, respectively, coupled to a common mechanical resonator via radiation pressure. The two passive cavities are coupled via hopping interaction to facilitate the directional amplification between the active and passive cavities. We obtain the condition of achieving optical directional amplification and find that the direction of amplification can be controlled by the phase differences between the effective optomechanical couplings. The effects of the gain rate of the active cavity and the effective coupling strengths on the maximum gain of the amplifier are discussed. We show that the noise added to this amplifier can be greatly suppressed in the large cooperativity limit.

Dual-wavelength dispersion characterization of confocal Fabry-Perot interferometers.

Optical resonators simultaneously resonating at different wavelengths are of interest in passive as well as active optical cavities. Dual-wavelength lasers, optical parametric amplifiers and spectrometers, e.g., in high spectral resolution lidar (HSRL) are effectively improved by employing multiply resonant cavities. In particular, HSRL allows us to measure aerosol optical properties without a priori hypotheses. Here we analyze optical dispersion in a HSRL prototype, based on a confocal Fabry-Perot interferometer (CFPI), developed to work at 532 nm (the lidar excitation wavelength). The presence of dispersion should be accounted for when realizing an effective HSRL because a second beam is required to obtain sufficient locking stability. We have performed an experiment in order to measure the dispersion contributions coming from cavity mirror coating and air and evaluate the stability of the transmission peaks in order to optimize the performances of HSRL.

Distant entanglement enhanced in PT -symmetric optomechanics

We study steady-state continuous variable entanglement in a three-mode optomechanical system consisting of an active optical cavity (gain) coupled to a passive optical cavity (loss) supporting a mechanical mode. For a driving laser which is blue-detuned, we show that coupling between optical and mechanical modes is enhanced in the unbroken-$\mathcal{PT}$-symmetry regime. We analyze the stability and this shows that steady-state solutions are more stable in the gain and loss systems. We use these stable solutions to generate distant entanglement between the mechanical mode and the optical field inside the gain cavity. It results in a giant enhancement of entanglement compared to what is generated in the single lossy cavity. This work offers the prospect of exploring quantum state engineering and quantum information in such systems. Furthermore, such entanglement opens up an interesting possibility to study spatially separated quantum objects.

Transparent Perfect Mirror

A mirror that reflects light fully and yet is transparent appears paradoxical. Current so-called transparent or “one-way” mirrors are not perfectly reflective and thus can be distinguished from a standard mirror. Constructing a transparent “perfect” mirror has profound implications for security, privacy, and camouflage. However, such a hypothetical device cannot be implemented in a passive structure. We demonstrate here a transparent perfect mirror in a non-Hermitian configuration: an active optical cavity where a certain prelasing gain extinguishes Poynting’s vector at the device entrance. At this threshold, all vestiges of the cavity’s structural resonances are eliminated and the device presents spectrally flat unity-reflectivity, thus, becoming indistinguishable from a perfect mirror when probed optically across the gain bandwidth. Nevertheless, the device is rendered transparent by virtue of persisting amplified transmission resonances. We confirm these predictions in two photonic realizations: a compact integrated active waveguide and a macroscopic all-optical-fiber system.

High duty cycle inverse Compton scattering X-ray source

Inverse Compton Scattering (ICS) is an emerging compact X-ray source technology, where the small source size and high spectral brightness are of interest for multitude of applications. However, to satisfy the practical flux requirements, a high-repetition-rate ICS system needs to be developed. To this end, this paper reports the experimental demonstration of a high peak brightness ICS source operating in a burst mode at 40 MHz. A pulse train interaction has been achieved by recirculating a picosecond CO2 laser pulse inside an active optical cavity synchronized to the electron beam. The pulse train ICS performance has been characterized at 5- and 15- pulses per train and compared to a single pulse operation under the same operating conditions. With the observed near-linear X-ray photon yield gain due to recirculation, as well as noticeably higher operational reliability, the burst-mode ICS offers a great potential for practical scalability towards high duty cycles.

Monolithic Subwavelength High-Index-Contrast Grating VCSEL

In this letter, we propose and numerically investigate a new vertical-cavity surface-emitting laser (VCSEL) structure consisting of a nearly lambda-thick active optical cavity sandwiched between two planar monolithic subwavelength high-index-contrast gratings (MHCGs) etched directly into the semiconductor layers surrounding the optical cavity. The structure allows the reduction of the vertical thickness of the subsequent MHCG VCSEL to roughly 0.6 $\mu \text{m}$ for emission at 980 nm. Compared with a conventional all-semiconductor VCSEL with distributed Bragg reflector mirrors, the MHCG VCSEL has a shorter effective cavity length and thus a shorter roundtrip cavity time. Our proposed design enables the fabrication of VCSELs with lattice-matched mirror layers in all common semiconductor optoelectronic material systems, or alternatively VCSELs with hybrid HCGs.

Optofluidic FRET microlasers based on surface-supported liquid microdroplets

We demonstrate optofluidic microlasers using highly efficient non-radiative Förster resonance energy transfer (FRET) for pumping of gain medium placed within liquid microdroplets situated on a superhydrophobic surface. Microdroplets generated from a mixture of ethylene glycol, glycerol, and water and stained with the FRET donor–acceptor dye pair Rhodamine 6G-Rhodamine 700 serve as active optical resonant cavities hosting high-quality whispering gallery modes. Upon direct optical pumping of the donor with a pulsed laser, lasing is observed in the emission band of the acceptor as a result of efficient FRET coupling between the acceptor and donor molecules. FRET lasing is characterized for different acceptor and donor concentrations, and threshold pump fluences of acceptor lasing as low as 6.3 mJ cm−2 are demonstrated. We also verify the dominance of the non-radiative FRET over cavity-assisted radiative energy transfer for the range of parameters studied in the experiments.

Spectral tuning of lasing emission from optofluidic droplet microlasers using optical stretching

We introduce tunable optofluidic microlasers based on active optical resonant cavities formed by optically stretched, dye-doped emulsion droplets confined in a dual-beam optical trap. To achieve tunable dye lasing, optically pumped droplets of oil dispersed in water are stretched by light in the dual-beam trap. Subsequently, resonant path lengths of whispering gallery modes (WGMs) propagating in the droplet are modified, leading to shifts in the microlaser emission wavelengths. Using this technique, we present all-optical, almost reversible spectral tuning of the lasing WGMs and show that the direction of tuning depends on the position of the pump beam focus on the droplet. In addition, we study the effects of temperature changes on the spectral position of lasing WGMs and demonstrate that droplet heating leads to red-tuning of the droplet lasing wavelength.

Topological solitons in active optical cavities: Fundamental properties and possible applications

Fundamental properties of topological spatial solitons existing in active cavities with high (above 100) Fresnel numbers, laser and/or parametric amplification, and saturated absorber were numerically and experimentally studied. Writing and erasing of bi- and tristable laser solitons (fundamental solitons [1, 2] and vortex solitons [3]) using an external control light pulse were considered in various regions of the laser cross section. The existence of optical domain walls (separated phase domains which are in antiphase) in the form of expanding spiral waves and the localized domain soliton rotating about the Neel defect (in this connection, we called it the “Neel soliton”) in active cavities with mixed laser and parametric amplification was shown in a numerical experiment for the first time. We proposed potential possibilities of using topological solitons in optical data processing, storage, and transmission.

Photonic Laser Propulsion: Proof-of-Concept Demonstration

T HE propulsion concept of photonic propulsion (i.e., the direct transfer of the momentum of photons to a spacecraft that emits them) has been around since the beginning of the 20th century [1]. According to special relativity, the largest velocity of any kind of rocket exhaust particles is the velocity of light, c 2:99 10 m=s. Photons are the propellant with the largest specific impulse Isp 3:06 10 s, but with the smallest thrust-to-power ratio T=P 3:34 10 9 N=W. Photonic propulsion is highly inefficient in thrust generation at a given power. Thus, the applications proposed for its implementation require high-power photon beams and extremely large space platforms, with power generation from large solar collectors [2], nuclear power generators [3], or from antimatter power generators [4]. Implementation of these large complex systems is many decades away. One approach to enhance practicality of photonic propulsion involves overcoming its inherent inefficiency through amplification of photon momentum transfer. This may be accomplished by bouncing or trapping photons between two high-reflectance (HR) mirrors that form an optical cavity between two space platforms. There have been two types of optical cavities considered for this purpose: 1) passive resonant optical cavities and 2) nonresonant optical cavities. In a passive resonant optical cavity, a laser beam is injected into the cavity. Because the passive resonant optical cavity requires a high-power single-frequency laser (which is itself inefficient) for efficient power injection into the cavity, and because the passive resonant optical cavity is highly sensitive to small changes in cavity length [5] and deterioration in mirror quality, it is impractical for photonic propulsion. The sensitivity to cavity length was exemplified in a gravitational detection system with a high Q passive optical cavity, in which even a 1-nm perturbation in cavity length thwarted the resonance condition and canceled the force exerted on mirrors [6]. The nonresonant optical cavity approach [7,8], as in Herriot cells, requires tightly focused laser beam spots on each mirror to avoid the beam interference that may result in optical resonance in the cavity. However, as the cavity length and the number of laser beam reflections increase, the laser beam focal spot diameter projected on mirrors increases, which requires extremely large mirrors to avoid beam interferences. Once the laser beam spots start to interfere, the nonresonant cavity becomes the passive resonant cavity that is impractical for photonic propulsion. An attempt to demonstrate an amplified photonic propulsion concept based on the nonresonant optical cavity was performed by Gray et al. [9]. They reported measurement of an amplified photon thrust of 0:4 N using a 300Wcontinuous-waveNd:YAG laser and a photon thrust amplification factor of 2:6. The much-lower-than-expected performance probably resulted from the previously mentioned technical difficulties. Therefore, the previously proposed photonic propulsion concepts seemed to be impractical, and the search for a new viable photonic propulsion concept continues. Photonic laser propulsion (PLP) is a new and innovative photonic propulsion concept [10,11] that is based on forming an active resonant optical cavity between two space platforms. The laser gain medium is located in the optical cavity, in contrast to the passive resonant cavity concept, in which the laser gain medium is located outside of the optical cavity. In PLP, the photon thrust FT produced on each mirror is given by

A build-up cavity for Fourier transform emission experiments

We have recorded electronic spectra of some diatomic species (I 2, K 2, and NaK), to illustrate the potential power of the combination of two high resolution techniques: intra-cavity laser induced fluorescence (ICLIF) and Fourier transform (FT) spectroscopy. Active and passive optical cavities have been used, working with visible continuous wave (cw) laser sources. The active cavity is a modified commercial ring dye laser, allowing for a sample up to 25 cm in length. Dispersed fluorescence spectra recorded on a Bomem Fourier transform spectrometer showed a signal enhancement of about 10 when a molecular source was placed within the resonator. The system was tested with a heatpipe source, producing alkali metal vapour at about 300 °C. These experiments illustrate enhanced cascade excitation mechanisms in K 2; the highest vibrational levels of the electronic ground state of K 2 can be observed with surprising ease. The increase in available power within the cavity has also led to the observation of fluorescence in NaK excited by a two-photon transition ( Q (66) 6 1Σ + ← X 1Σ + transition). Spatial limitations have driven us to build a more versatile ring cavity able to accommodate larger sources. This broad-band (590–650 nm) build-up cavity is locked by a Hänsch–Couillaud servo-loop to an input laser of (instantaneous) bandwidth ∼1 MHz. Power enhancement factors of around 30 have been obtained with a 2.6% input coupler. The performance of the build-up cavity has been tested by recording FT spectra of intra-cavity laser induced fluorescence of iodine. The technique clearly has useful applications for weakly absorbing species, or for those whose electronic states are inaccessible to single-photon absorption techniques. This paper describes the arrangement we have used, highlighting some of the advantages and describing some of the particular difficulties we have encountered.

Swept-Cavity Ringdown Absorption Spectroscopy: Put Your Laser Light In and Shake It All About

Cavity ringdown (CRD) absorption spectroscopy with continuous-wave (cw) tunable coherent light sources provides a convenient, sensitive, and precise way to measure very weak optical absorption spectra and to analyze trace gas concentrations. Several recently introduced innovations in cw-CRD spectroscopy are described. Our approach involves one or more single-mode tunable diode laser sources, a rapidly swept ringdown cavity, and a simple optical heterodyne detected approach (based on the dynamics of coherent light reflected from such an active optical cavity). This offers high performance in a relatively simple, low-cost, compact instrument that is facilitated by fibre optic and other standard photonics or telecommunications components. New experimental results are reported, comprising CRD spectra of water vapour in the 0.815 µm wavelength region and of mixtures of CO2 and CO in the range of 1.56–1.59 µm. Promising applications of such techniques include chemical analysis of trace gases in medicine, agriculture, industry, and the environment.

Single Nanowire Lasers

Ultraviolet lasing from single zinc oxide nanowires is demonstrated at room temperature. Near-field optical microscopy images quantify the localization and the divergence of the laser beam. The linewidths, wavelengths, and power dependence of the nanowire emission characterize the nanowire as an active optical cavity. These individual nanolasers could serve as miniaturized light sources for microanalysis, information storage, and optical computing.

InGaAs/GaAs structures with quantum dots in vertical optical cavities for wavelengths near 1.3 µm

Semiconductor heterostructures with vertical optical cavities with active regions, based on arrays of InAs quantum dots inserted in an external InGaAs quantum well, have been obtained by molecular-beam epitaxy on GaAs substrates. The dependences of the reflection and photoluminescence spectra on the structural characteristics of the active region and optical cavities have been investigated. The proposed heterostructures are potentially suitable for optoelectronic devices at wavelengths near 1.3 µm.

Diffraction-limited 1.3-μm-wavelength tapered-gain-region lasers with >1-W CW output power

Diode lasers have been fabricated in InGaAsP-InP multiple-quantum-well material grown by atmospheric-pressure organometallic vapor-phase epitaxy with an active optical cavity consisting of a ridge-waveguide region coupled to a tapered gain region. Over 1 W of CW output power was obtained with 85% of the power in the central lobe of a diffraction-limited far-field radiation pattern.

Cavity design for improved electrical injection in InAlGaP/AlGaAs visible (639–661 nm) vertical-cavity surface-emitting laser diodes

A novel optical cavity design for improved electrical injection in visible vertical-cavity surface-emitting laser (VCSEL) diodes employing an InGaP/InAlGaP strained quantum-well active optical cavity and AlAs/Al0.5Ga0.5As distributed Bragg reflectors (DBRs) is described. The cavity design was determined by measuring the lasing threshold current density of visible edge-emitting laser diodes with AlAs/Al0.5Ga0.5As DBR cladding layers. By inserting InAlP spacer layers between the active region and the DBR cladding, significant improvement in the performance of the edge-emitting lasers was achieved. This approach was then applied to the design of visible VCSEL diodes, and resulted in the first demonstration of room-temperature electrically injected lasing, over the wavelength range 639–661 nm. The visible VCSELs, with a diameter of 20 μm, exhibit pulsed output power of 3.4 mW at 650 nm, and continue to lase at a duty cycle of 40%. The threshold current was 30 mA, with a low threshold voltage (2.7 V) and low series resistance (<15 Ω).