Optomechanical Devices Research Articles

Two‐Photon Nanomachining of a Micromechanically Enhanced Optical Cavity Sensor on an Optical Fiber Tip

Herein, a two‐photon nanostructuring process that is employed to monolithically integrate dynamic three‐dimensional (3D) micromechanical features into Fabry–Pérot cavity (FPC) sensors on an optical fiber tip is demonstrated. These features represent a breakthrough in the integration and fabrication capabilities of micro optomechanical devices and systems. The demonstrated dynamic optical surface enables directional thin‐film deposition onto obscured areas. The rotation of the dynamically movable mirror to deposit a thin reflective coating onto the inner surfaces of a FPC with curved geometry is leveraged. The reflective coating in conjunction with the dynamically rotatable mirror greatly improves the quality factor of the FPC and enables a new class of highly integrated multipurpose sensor systems. A unique open cavity geometry on an optical fiber tip is used to demonstrate temperature and refractive index sensing with sensitivities of 2045 ± 39 nm/RIU and 366 ± 22 pm °C−1, respectively. A gold reflective coating sputtered onto the inner surfaces of the FPC improves the quality factors of the cavity by more than 800%. This technology presents a path forward for utilizing 3D design freedom in micromechanically enhanced optical systems to facilitate versatile processing and advantageous geometries beyond the current state of the art.

Elastic bilayer phononic crystal

Inspired by twisted bilayer graphene, we present an elastic bilayer consisting of a plate with two honeycomb lattices of mechanical resonators on both sides of the plate. Surface acoustic waves (SAW), which can interact depending on the thickness of the plate, are supported by each side of the plate. Beyond twisting a lattice with respect to the other, the coupling strengths between the two sides can be controlled via the plate thickness, which strongly affects the dispersion of elastic waves in the bilayer structure. The dispersion relationship of the SAW is theoretically characterized by calculating the band structure for the cases of AA and AB stacking configurations, as well as for special cases of twisting angles that produce sublattices with even and odd symmetries. Furthermore, we explore the topological characteristics of the bands and uncover a possible mechanism of creating topological elastic Valley states. The proposed bilayer plate could constitute a promising platform for manipulating mechanical waves and exploring quantum analog phenomena which could open routes toward innovative mechanical and optomechanical devices at the microscale, for instance.

Development of an Optomechanical Device with Extremely Low Optical Energy Loss

Development of an Optomechanical Device with Extremely Low Optical Energy Loss

Single‐Photon Emitters in Layered Van der Waals Materials

Single‐photon emitters (SPEs) have recently been discovered in various atomically thin materials. Their properties, controllability, and the possibility of their monolithic integration in electronic and photonic device structures make them attractive candidates for a wide range of applications in quantum information and communication, and also in other fields of physics and technology. In this review article, an overview of SPEs in layered van der Waals materials and their physical properties is given, theoretical concepts for the modeling of their level structure and their coupling to phonons are presented, and techniques for the creation and localization of these emitters in the host material are described. Perspectives for their application in various fields, such as their coupling to photonic resonators and waveguides, their control by external electric fields or strain, and their integration in optomechanical devices are discussed. Finally, functionalities relying on properties beyond single‐photon emission are briefly addressed.

Four-wave-cooling to the single phonon level in Kerr optomechanics

Cavity optomechanics has achieved groundbreaking control and detection of mechanical oscillators, based on their coupling to linear electromagnetic modes. Recently, however, there is increasing interest in cavity nonlinearities as resource in radiation-pressure interacting systems. Here, we present a flux-mediated optomechanical device combining a nonlinear superconducting quantum interference cavity with a mechanical nanobeam. We demonstrate how the Kerr nonlinearity of the circuit can be used to enhance the device performance by suppressing cavity frequency noise, and for a counter-intuitive sideband-cooling scheme based on intracavity four-wave-mixing. With a large single-photon coupling rate of up to g0 = 2π ⋅ 3.6 kHz and a high mechanical quality factor Qm ≈ 4 ⋅ 105, we achieve an effective four-wave cooperativity of {{{{{{{{mathcal{C}}}}}}}}}_{{{{{{{{rm{fw}}}}}}}}}, > , 100 and demonstrate four-wave cooling of the mechanical oscillator close to its quantum groundstate. Our results advance the recently developed platform of flux-mediated optomechanics and demonstrate how cavity Kerr nonlinearities can be utilized in cavity optomechanics.

Optomechanical strong coupling between a single photon and a single atom

Single atoms coupled to a cavity offer unique opportunities as quantum optomechanical devices because of their small mass and strong interaction with light. A particular regime of interest in optomechanics is that of ‘single-photon strong coupling’, where motional displacements on the order of the zero-point uncertainty are sufficient to shift the cavity resonance frequency by more than its linewidth. In many cavity QED platforms, however, this is unfeasible due to the large cavity linewidth. Here, we propose an alternative route in such systems, which instead relies on the coupling of atomic motion to the much narrower cavity-dressed atomic resonance frequency. We discuss and optimize the conditions in which the scattering properties of single photons from the atom-cavity system become highly entangled with the atomic motional wave function. We also analyze the prominent observable features of this optomechanical strong coupling, which include a per-photon motional heating that is significantly larger than the single-photon recoil energy, as well as mechanically-induced oscillations in time of the second-order correlation function of the emitted light. This physics should be realizable in current experimental setups, such as trapped atoms coupled to photonic crystal cavities, and more broadly opens the door to realizing qualitatively different phenomena beyond what has been observed in optomechanical systems thus far.

Enhancing the nonlinearity of optomechanical system via multiple mechanical modes.

We theoretically investigate the nonlinear dynamics of an optomechanical system, where the system consists of N identical mechanical oscillators individually coupled to a common cavity field. We find that the optomechanical nonlinearity can be enhanced N times through theoretical analysis and numerical simulation in such a system. This leads to the power thresholds to observe the nonlinear behaviors (bistable, period-doubling, and chaotic dynamics) being reduced to 1/N. In addition, we find that changing the sign (positive or negative) of the coupling strength partly does not affect the threshold of driving power for generating corresponding nonlinear phenomena. Our work may provide a way to engineer optomechanical devices with a lower threshold, which has potential applications in implementing secret information processing and optical sensing.

Mechano-optical Modulation of Excitons and Carrier Recombination in Self-Assembled Halide Perovskite Quantum Dots.

Mechanically modulating optical properties of semiconductor nanocrystals and organic molecules are valuable for mechano-optical and optomechanical devices. Halide perovskites with excellent optical and electronic properties are promising for such applications. We report the mechanically changing excitons and photoluminescence of self-assembled formamidinium lead bromide (FAPbBr3) quantum dots. The as-synthesized quantum dots (3.6 nm diameter), showing blue emission and a short photoluminescence lifetime (2.6 ns), form 20-300 nm 2D and 3D self-assemblies with intense green emission in a solution or a film. The blue emission and short photoluminescence lifetime of the quantum dots are different from the delayed (ca. 550 ns) green emission from the assemblies. Thus, we consider the structure and excitonic properties of individual quantum dots differently from the self-assemblies. The blue emission and short lifetime of individual quantum dots are consistent with a weak dielectric screening of excitons or strong quantum confinement. The red-shifted emission and a long photoluminescence lifetime of the assemblies suggest a strong dielectric screening that weakens the quantum confinement, allowing excitons to split into free carriers, diffuse, and trap. The delayed emission suggests nongeminate recombination of diffusing and detrapped carriers. Interestingly, the green emission of the self-assembly blueshifts by applying a lateral mechanical force (ca. 4.65 N). Correspondingly, the photoluminescence lifetime decreases by 1 order of magnitude. These photoluminescence changes suggest the mechanical dissociation of the quantum dot self-assemblies and mechanically controlled exciton splitting and recombination. The mechanically changing emission color and lifetime of halide perovskite are promising for mechano-optical and optomechanical switches and sensors.

Terahertz cavity optomechanics using a topological nanophononic superlattice.

Cavity optomechanical systems operating at the quantum ground state provide a novel way for the ultrasensitive measurement of mass and displacement and provide a new toolbox for emerging quantum information technologies. The high-frequency optomechanical devices could reach the quantum ground state at a high temperature because the access to high frequency is favorable for the cavity optomechanical devices to decouple from the thermal environment. However, reaching ultra-high frequency (THz) is extremely difficult due to the structure of cavity optomechanical devices and properties of materials. In this paper, by introducing acoustic topological interface states, we designed a THz mechanical frequency semiconductor pillar microcavity optomechanical device based on a GaAs/AlAs nanophononic superlattice. In the optomechanical system, multi-optical cavity modes are obtained and the frequency separation between adjacent optical modes is equal to the frequency of the mechanical mode (optomechanical frequency matching). By detuning the laser pump to a lower (higher) energy-resolved sideband to make a spontaneously scattering photon doubly resonate with optical cavity modes at an anti-Stokes (Stokes) frequency and pump frequency, we can achieve an anti-Stokes (Stokes) scattering efficiency 2600 (1800) times larger than that of Stokes (anti-Stokes) scattering, which provides potential for laser cooling and low threshold phonon lasing in the optomechanical system.

Positive and Negative Pull-Back Instabilities in Mode Splitting Optomechanical Devices

Optical gradient forces play an essential role in optomechanical systems. The systems based on coupled microresonators are of great importance for applications in signal processing, sensors, and actuators. Here, we theoretically and experimentally studied, for the first time, positive and negative pull-back instabilities originating from attractive and repulsive optical gradient forces, respectively, in an optomechanical device based on coupled microrings. The device consists of two coupled free-standing waveguides in two identical microrings, fabricated in the silicon-on-insulator process. The coupling between the two microrings results in the symmetric and antisymmetric resonances showing in the transmission spectrum of the device. By measuring the wavelength difference between the self-referenced symmetric and antisymmetric resonances, the wavelength tuning due to the optomechanical actuation is decoupled from the tuning due to the thermo-optical effect. It is demonstrated theoretically and experimentally that the positive pull-back instability originates from the attractive optical gradient force and the negative pull-back instability originates from the repulsive optical gradient force when the pump wavelength increases. The positive pull-back instability significantly increases the wavelength difference between the symmetric and antisymmetric resonances. On the contrary, the negative pull-back instability significantly decreases the wavelength difference.

Visible light photostriction in Kagome staircase zinc ortho-vanadate

Ferroelectric materials have been widely explored for photostrictive action, but their high performance being limited to ultra violet light demands to look for efficient visible light photostrictive materials. Transition metal vanadates, exhibiting the Kagome structural features besides being active in visible light, are the interesting materials for the photostriction study. Here, we investigate the photostriction of the non-magnetic member zinc ortho-vanadate Zn3(VO4)2 or Zn3V2O8. Corresponding to the photostriction response of ∼10−3 under a 405 nm laser (response time, τ = 5.7 s) and ∼10−4 (τ = 5.8 s) under a 665 nm laser, it exhibits a large photostriction efficiency of ∼10−11 and ∼10−12 m3/W, respectively. Thermal expansion investigation indicates that the non-thermal strain dominants the photostriction of Zn3V2O8 ceramics. The peak shift in x-ray diffraction (XRD) pattern as well as in Raman spectra under external laser irradiance revealing, increased anisotropic distortions with increasing stretching and vibrations in the bonds of ZnO6 octahedrons and VO4 tetrahedrons, is proposed as the underlying mechanism of the photostriction response in Zn3V2O8. The good visible light photostriction, rapid response time, and stability functionalities make it a potential candidate for future generation optoelectronics, such as light driven micro-actuators, robots, relays, and other optomechanical devices.

Optomechanical dynamics in the PT - and broken- PT -symmetric regimes

We theoretically study the dynamics of typical optomechanical systems, consisting of a passive optical mode and an active mechanical mode, in the $\mathcal{PT}$- and broken-$\mathcal{PT}$-symmetric regimes. By fully analytical treatments for the dynamics of the average displacement and particle numbers, we reveal the phase diagram under different conditions and the various regimes of both $\mathcal{PT}$-symmetry and stability of the system. We find that by appropriately tuning either mechanical gain or optomechanical coupling, both phase transitions of the $\mathcal{PT}$-symmetry and stability of the system can be flexibly controlled. As a result, the dynamical behaviors of the average displacement, photons, and phonons are radically changed in different regimes. Our study shows that $\mathcal{PT}$-symmetric optomechanical devices can serve as a powerful tool for the manipulation of mechanical motion, photons, and phonons.

Optomechanical synchronization across multi-octave frequency spans

Experimental exploration of synchronization in scalable oscillator microsystems has unfolded a deeper understanding of networks, collective phenomena, and signal processing. Cavity optomechanical devices have played an important role in this scenario, with the perspective of bridging optical and radio frequencies through nonlinear classical and quantum synchronization concepts. In its simplest form, synchronization occurs when an oscillator is entrained by a signal with frequency nearby the oscillator’s tone, and becomes increasingly challenging as their frequency detuning increases. Here, we experimentally demonstrate entrainment of a silicon-nitride optomechanical oscillator driven up to the fourth harmonic of its 32 MHz fundamental frequency. Exploring this effect, we also experimentally demonstrate a purely optomechanical RF frequency divider, where we performed frequency division up to a 4:1 ratio, i.e., from 128 MHz to 32 MHz. Further developments could harness these effects towards frequency synthesizers, phase-sensitive amplification and nonlinear sensing.

ПРИМЕНЕНИЕ АВТОМАТИЗИРОВАННОГО ОПТИКО-МЕХАНИЧЕСКОГО УСТРОЙСТВА ДЛЯ ТОМОГРАФИЧЕСКОГО ИССЛЕДОВАНИЯ ДЕСНЫ ПОД ВОЗДЕЙСТВИЕМ ВНЕШНИХ АГЕНТОВ

The work highlights the use of the developed automated optical-mechanical device for tomographic studies of the gums treated with special types of toothpastes. The optical parameters of the gum depth were measured under and without the influence of external agents. This task is relevant and important for therapeutic dentistry. The paper reveals the scheme of an automated opto-mechanical device and its operation, as well as the technical characteristics of the device. The objects of the study were determined and data on the distribution of the reflection coefficient from the subsurface layers (depth 0.5 mm) were obtained. A section of the upper gum area with an area of (1×1) cm2 after treatment with gum pastes in 15 minutes at a wavelength of 0.83 microns was analyzed.

Optomechanical circulator with a polaritonic microcavity

We study theoretically optomechanical interactions in a semiconductor microcavity with embedded quantum well under the optical pumping by a Bessel beam, carrying a non-zero orbital momentum. Due to the transfer of orbital momentum from light to phonons, the microcavity can act as an acoustic circulator: it rotates the propagation direction of the incident phonon by a certain angle clockwise or anticlockwise. Due to the optomechanical heating and cooling effects, the circulator can also function as an acoustic laser emitting sound with nonzero angular momentum. Our calculations demonstrate the potential of semiconductor microcavities for compact integrable optomechanical devices.

Review of coherent phonon and heat transport control in one-dimensional phononic crystals at nanoscale

Phononic crystals are the acoustic analogs of photonic crystals and aim at manipulating phonon transport using phonon interference in periodic structures. While such periodic structures are typically two-dimensional, many applications require one-dimensional (1D) wire-like or bulk structures instead. In this Research Update, we summarize the past decade of theoretical and experimental studies of coherent control of phonon and heat transport in one-dimensional phononic crystals. At the hypersonic frequencies, phononic crystals successfully found applications in optomechanical devices at the microscale. However, at higher terahertz frequencies, experimentalists struggle to demonstrate that coherent thermal transport at room temperature is possible at length scales of hundreds of nanometers. Although many theoretical works predict a reduction in the thermal conductivity in 1D phononic crystals due to coherent effects, most observations conclude about the incoherent nature of heat conduction at least at room temperature. Nevertheless, experiments on superlattices and carbon nanotubes have demonstrated evidence of coherent heat conduction even at room temperature in structures with the periodicity of a few nanometers. Thus, further miniaturization and improving fabrication quality are currently the main challenges faced by 1D phononic nanostructures.

Heat transfer mediated by the dynamical Casimir effect in an optomechanical system

Heat transfer in an optomechanical system consisting of one optical cavity and two movable mirrors with or without a laser field is studied by using the quantum master-equation method. The radiation-pressure interaction between the cavity and the mirrors contains the single-photon optomechanical coupling (SPOC) and the dynamical Casimir effect (DCE). When the laser is not applied to the cavity, the heat transfer is induced by a nonlocal interaction between mirrors that builds up only due to the presence of the DCE. Once the monochromatic field is turned on, both the SPOC and the DCE can be used to modify the energy transfer process. In both cases, the heat transfer can be drastically enhanced at resonant conditions manifested by the DCE. Our results can motivate further studies to actively control heat transfer mediated by the DCE in optomechanical devices.

Aluminium nitride integrated photonics: a review

Abstract Integrated photonics based on silicon has drawn a lot of interests, since it is able to provide compact solution for functional devices, and its fabrication process is compatible with the mature complementary metal-oxide-semiconductor (CMOS) fabrication technology. In the meanwhile, silicon material itself has a few limitations, including an indirect bandgap of 1.1 eV, transparency wavelength of >1.1 μm, and insignificant second-order nonlinear optical property. Aluminum nitride (AlN), as a CMOS-compatible material, can overcome these limitations. It has a wide bandgap of 6.2 eV, a broad transparency window covering from ultraviolet to mid-infrared, and a significant second-order nonlinear optical effect. Furthermore, it also exhibits piezoelectric and pyroelectric effects, which enable it to be utilized for optomechanical devices and pyroelectric photodetectors, respectively. In this review, the recent research works on integrated AlN photonics in the past decade have been summarized. The related material properties of AlN have been covered. After that, the demonstrated functional devices, including linear optical devices, optomechanical devices, emitters, photodetectors, metasurfaces, and nonlinear optical devices, are presented. Last but not the least, the summary and future outlook for the AlN-based integrated photonics are provided.

High-Resolution Imaging of Cold Atoms through a Multimode Fiber

We developed an ultra-compact high-resolution imaging system for cold atoms. Its only in-vacuum element is a multimode optical fiber with a diameter of $230\,\mu$m, which simultaneously collects light and guides it out of the vacuum chamber. External adaptive optics allow us to image cold Rb atoms with a $\sim 1\,\mu$m resolution over a $100 \times 100\,\mu$m$^2$ field of view. These optics can be easily rearranged to switch between fast absorption imaging and high-sensitivity fluorescence imaging. This system is particularly suited for hybrid quantum engineering platforms where cold atoms are combined with optical cavities, superconducting circuits or optomechanical devices restricting the optical access.

Quantum limits for stationary force sensing

State-of-the-art sensors of force, motion and magnetic fields have reached the sensitivity where the quantum noise of the meter is significant or even dominant. In particular, the sensitivity of the best optomechanical devices has reached the Standard Quantum Limit (SQL), which directly follows from the Heisenberg uncertainty relation and corresponds to balancing the measurement imprecision and the perturbation of the probe by the quantum back action of the meter. The SQL is not truly fundamental and several methods for its overcoming have been proposed and demonstrated. At the same time, two quantum sensitivity constraints which are more fundamental are known. The first limit arises from the finiteness of the probing strength (in the case of optical interferometers - of the circulating optical power) and is known as the Energetic Quantum Limit or, in a more general context, as the Quantum Cram\'{e}r-Rao Bound (QCRB). The second limit arises from the dissipative dynamics of the probe, which prevents full efficacy of the quantum back action evasion techniques developed for overcoming the SQL. No particular name has been assigned to this limit; we propose the term Dissipative Quantum Limit (DQL) for it. Here we develop a unified theory of these two fundamental limits by deriving the general sensitivity constraint from which they follow as particular cases. Our analysis reveals a phase transition occurring at the boundary between the QCRB-dominated and the DQL regimes, manifested by the discontinuous derivatives of the optimal spectral densities of the meter field quantum noise. This leads to the counter-intuitive (but favorable) finding that quantum-limited sensitivity can be achieved with certain lossy meter systems. Finally, we show that the DQL originates from the non-autocommutativity of the internal thermal noise of the probe and that it can be overcome in non-stationary measurements.