Optomechanical Crystal Cavity Research Articles

Comprehensive review of the directed design of optomechanical crystal cavities using intelligent algorithms

Optomechanical crystal cavities are devices based on optomechanical interactions to manipulate photons and phonons on periodic subwavelength structures, enabling precise measurement of the force and displacement. The performance of the target structures varies when applied to different applications. Optomechanical crystal cavities now rely on an empirical forward design, which is inefficient. Therefore, a desired shift is toward directed design with a “problem-oriented” strategy. The directed optimization problem’s nonconvex nature and extensive parameter space necessitate substantial computational resources, driving the need for intelligent algorithms in a sub-wavelength structure design. Intelligent algorithms can surpass the constraints of traditional methods and discover novel structures that are effective in different materials, topologies, modes, and wavelengths. This paper provides an extensive overview of intelligent algorithms for guiding the directed design of optomechanical crystal cavities. It presents a systematic classification of 15 algorithmics, including, but not limited to, topology algorithms, particle swarm optimization algorithms, convolutional neural networks, and generative adversarial networks. The article provides a comprehensive review and thorough analysis of the principle and current application state, as well as the advantages and disadvantages of each intelligent algorithm. By using these intelligent algorithms, researchers can enhance the efficiency and accuracy of optimizing optomechanical crystal cavities in a broader design space.

Optomechanical Frequency Comb Based on Multiple Nonlinear Dynamics.

Phonon-based frequency combs that can be generated in the optical and microwave frequency domains have attracted much attention due to the small repetition rates and the simple setup. Here, we experimentally demonstrate a new type of phonon-based frequency comb in a silicon optomechanical crystal cavity including both a breathing mechanical mode (∼GHz) and flexural mechanical modes (tens of MHz). We observe strong mode competition between two approximate flexural mechanical modes, i.e., 77.19 and 90.17MHz, resulting in only one preponderant lasing, while maintaining the lasing of the breathing mechanical mode. These simultaneous observations of two-mode phonon lasing state and significant mode competition are counterintuitive. We have formulated comprehensive theories to elucidate this phenomenon in response to this intriguing outcome. In particular, the self-pulse induced by the free carrier dispersion and thermo-optic effects interacts with two approximate flexural mechanical modes, resulting in the repetition rate of the comb frequency-locked to exact fractions of one of the flexural mechanical modes and the mode hopping between them. This phonon-based frequency comb has at least 260 comblines and a repetition rate as low as a simple fraction of the flexural mechanical frequency. Our demonstration offers an alternative optomechanical frequency comb for sensing, timing, and metrology applications.

Realization of quantum ground state in an optomechanical crystal cavity

Realization of quantum ground state in an optomechanical crystal cavity

Heterogeneous optomechanical crystal cavity coupled by a wavelength-scale mechanical waveguide

Integrated optomechanical crystal (OMC) cavities provide a vital device prototype for highly efficient microwave to optical conversion in quantum information processing. In this work, we propose a novel heterogeneous OMC cavity consisting of a thin-film lithium niobate (TFLN) slab and chalcogenide (ChG) photonic crystal nanobeam coupled by a wavelength-scale mechanical waveguide. The optomechanical coupling rate of the heterogeneous OMC cavity is optimized up to 340 kHz at 1.1197 GHz. Combined with phononic band and power decomposition, 17.38% energy from the loaded RF power is converted into dominant fundamental horizontal shear mode (SH0) in the narrow LN mechanical waveguide. Based on this fraction, as a result, 3.51% power relative to the loaded RF energy is scattered into the fundamental longitudinal mode (L0) facing the TFLN-ChG heterogeneous waveguide. The acoustic breathing mode of the heterogeneous OMC is successfully excited under the driving of the propagating L0 mode in the heterogeneous waveguide, demonstrating the great potentials of the heterogeneous piezo-optomechanical transducer in high-performance photon–phonon interaction fields.

Design of an ultra-low mode volume piezo-optomechanical quantum transducer.

Coherent transduction of quantum states from the microwave to the optical domain can play a key role in quantum networking and distributed quantum computing. We present the design of a piezo-optomechanical device formed in a hybrid lithium niobate on silicon platform, that is suitable for microwave-to-optical quantum transduction. Our design is based on acoustic hybridization of an ultra-low mode volume piezoacoustic cavity with an optomechanical crystal cavity. The strong piezoelectric nature of lithium niobate allows us to mediate transduction via an acoustic mode which only minimally interacts with the lithium niobate, and is predominantly silicon-like, with very low electrical and acoustic loss. We estimate that this transducer can realize an intrinsic conversion efficiency of up to 35% with <0.5 added noise quanta when resonantly coupled to a superconducting transmon qubit and operated in pulsed mode at 10 kHz repetition rate. The performance improvement gained in such hybrid lithium niobate-silicon transducers make them suitable for heralded entanglement of qubits between superconducting quantum processors connected by optical fiber links.

Semiconductor-on-diamond cavities for spin optomechanics.

Optomechanical cavities are powerful tools for classical and quantum information processing that can be realized using nanophotonic structures that co-localize optical and mechanical resonances. Typically, phononic localization requires suspended devices that forbid vertical leakage of mechanical energy. Achieving this in some promising quantum photonic materials such as diamond requires non-standard nanofabrication techniques, while hindering integration with other components and exacerbating heating related challenges. As an alternative, we have developed a semiconductor-on-diamond platform that co-localizes phononic and photonic modes without requiring undercutting. We have designed an optomechanical crystal cavity that combines high optomechanical coupling with low dissipation, and we show that this platform will enable optomechanical coupling to spin qubits in the diamond substrate. These properties demonstrate the promise of this platform for realizing quantum information processing devices based on spin, phonon, and photon interactions.

Engineering Multiple GHz Mechanical Modes in Optomechanical Crystal Cavities

Optomechanical crystal cavities (OMCCs) are fundamental nanostructures for a wide range of phenomena and applications. Usually, optomechanical interaction in such OMCCs is limited to a single optical mode and a unique mechanical mode. In this sense, eliminating the single-mode constraint---for instance, by adding more mechanical modes---should enable more complex physical phenomena, giving rise to a context of multimode optomechanical interaction. However, a general method to produce in a controlled way multiple mechanical modes with large coupling rates in OMCCs is still missing. In this work, we present a route to confine multiple GHz mechanical modes coupled to the same optical field with similar optomechanical coupling rates---up to 400 kHz---by OMCC engineering. In essence, we increase the number of unit cells (consisting of a silicon nanobrick perforated by circular holes with corrugations at both its sides) in the adiabatic transition between the cavity center and the mirror region. Remarkably, the mechanical modes in our cavities are located within a full phononic band gap, which is a key requirement to achieve ultrahigh mechanical $Q$ factors at cryogenic temperatures. The multimode behavior in a full phononic band gap and the easiness of realization using standard silicon nanotechnology make our OMCCs highly appealing for applications in the classical and quantum realms.

Giant injection-locking bandwidth of a self-pulsing limit-cycle in an optomechanical cavity

Locking of oscillators to ultra-stable external sources is of paramount importance for improving close-to-carrier phase noise in free running oscillators. In most of them, such as Micro-Electro-Mechanical-Systems or LC circuit-based oscillators, the locking frequency range is limited by the robustness of their natural frequency, which comes explicitly related with intrinsic parameters of the system. In this work we report the synchronization of an optically-driven self-pulsing limit-cycle taking place in a silicon optomechanical crystal cavity to an external harmonic signal that modulates the driving laser. Because of the extreme ductility of the natural self-pulsing frequency (several tens of MHz), the injection-locking mechanism is highly efficient and displays giant relative bandwidths exceeding 60%. The external modulation reveals itself as a knob to explore dynamical attractors that are otherwise elusive and, in particular, as a means to initialize a mechanical resonator into a state of self-sustained oscillations driven by radiation pressure forces. Moreover, we exploit the large anharmonicity of the studied limit-cycle to induce injection-locking to integer multiples and fractions of the frequency of the external reference, which can be used for frequency conversion purposes in nano-electro-opto-mechanical systems.

Optimization of diamond optomechanical crystal cavities

Due to recent development of growing and processing techniques for high-quality single crystal diamond, the large scale production of diamond optomechanical crystal cavities has become feasible, enabling optomechanical devices that can operate in higher mechanical frequencies and can be coupled to two-level systems based on diamond color centers. In this paper we describe a design optimization method to produce diamond optomechanical crystal cavities operating at the high-cooperativity regime (close to unity) at room temperature.

Testing Optomechanical Microwave Oscillators for SATCOM Application

The realization of photonic microwave oscillators using optomechanical cavities has recently become a reality. By pumping the cavity with a blue-detuned laser, the so-called phonon lasing regime - in which a mechanical resonance is amplified beyond losses - can be reached and the input signal gets modulated by highly-coherent tones at integer multiples of the mechanical resonance. \textcolor{Red}{Implementing optomechanical cavities on released films with high index of refraction can lead to optical modes at telecom wavelengths and mechanical resonances in the GHz scale, resulting in highly-stable signals in the microwave domain upon photodetection}. Owing to the extreme compactness of such cavities, application in satellite communications (SATCOM) seems highly appropriate, but no experiments have been reported so far. In this paper, an optomechanical microwave oscillator (OMO) built on a micron-scale silicon optomechanical crystal cavity is characterized and tested in a real SATCOM testbed. Using a blue-detuned laser, the OMO is driven into a phonon lasing state where multiple harmonics are generated, reaching tones up to 20 GHz. Under this regime, its practical applicability, remarkably addressing its performance as a photonic local oscillator, has been validated. The results, in addition with the advantages of extreme compactness and silicon-technology compatibility, make OMOs very promising candidates to build \textcolor{Red}{ultra-low} weight photonics-based microwave oscillators for SATCOM applications.

Structural imperfections on characteristics of optomechanical crystal nanobeam cavity

We present a theoretical analysis of the influence of structural imperfections on the device performance of optomechanical crystal nanobeam cavity. The quality factor, resonant frequency and optomechanical coupling properties are investigated statistically according to the various defects of the positions, radii, alignments, and surface roughness. Our results reveal the predominant influence and suggest an approach of manipulation towards these parameters, which provide important information for engineering a desired optomechanical crystal nanobeam cavity.

Multistability and Fano resonances in a hybrid optomechanical photonic crystal microcavity

We investigate the optical response of a hybrid cavity quantum-electrodynamics system consisting of a quantum dot embedded in an optomechanical photonic crystal cavity. The system is coupled to an auxiliary cavity via a waveguide that can support a single optical mode. We demonstrate the possibility of generating tunable optical bistability, double-bistabilty and tristability which can be utilized to design all-optical-switch and multi-valued logic circuits eventually forming a part of a large scale quantum communication platform. The proposed system has also found to exhibit the Mollow triplet and the Fano resonances modified by an optomechanical interaction. The optomechanically induced transparency (OMIT) is superimposed on the Fano resonance (OMIT-Fano resonance) having the transparency window occurring exactly at the point where the probe detuning becomes equal to the mechanical oscillator's resonant frequency.

Phonon lasing in a hetero optomechanical crystal cavity

Micro- and nanomechanical resonators have emerged as promising platforms for sensing a broad range of physical properties, such as mass, force, torque, magnetic field, and acceleration. The sensing performance relies critically on the motional mass, mechanical frequency, and linewidth of the mechanical resonator. Herein, we demonstrate a hetero optomechanical crystal (OMC) cavity based on a silicon nanobeam structure. The cavity supports phonon lasing in a fundamental mechanical mode with a frequency of 5.91 GHz, an effective mass of 116 fg, and a mechanical linewidth narrowing in the range from 3.3 MHz to 5.2 kHz, while the optomechanical coupling rate is as high as 1.9 MHz. With this phonon laser, on-chip sensing can be predicted with a resolution of δ λ / λ = 1.0 × 10 − 8 . The use of a silicon-based hetero OMC cavity that harnesses phonon lasing could pave the way toward high-precision sensors that allow silicon monolithic integration and offer unprecedented sensitivity for a broad range of physical sensing applications.

Nonsuspended optomechanical crystal cavities using As2S3 chalcogenide glass

An optomechanical crystal cavity with nonsuspended structure using As 2 S 3 material is proposed. The principle of mode confinement in the nonsuspended cavity is analyzed, and two different types of optical and acoustic defect modes are calculated through appropriate design of the cavity structure. An optomechanical coupling rate of 82.3 kHz is obtained in the proposed cavity, and the designed acoustic frequency is 3.44 GHz. The acoustic mode coupling between two nonsuspended optomechanical crystal cavities is also demonstrated, showing that the proposed cavity structure has great potential for realizing further optomechanical applications in multicavity systems.

Optomechanical crystals for spatial sensing of submicron sized particles

Optomechanical crystal cavities (OMC) have rich perspectives for detecting and indirectly analysing biological particles, such as proteins, bacteria and viruses. In this work we demonstrate the working principle of OMCs operating under ambient conditions as a sensor of submicrometer particles by optically monitoring the frequency shift of thermally activated mechanical modes. The resonator has been specifically designed so that the cavity region supports a particular family of low modal-volume mechanical modes, commonly known as -pinch modes-. These involve the oscillation of only a couple of adjacent cavity cells that are relatively insensitive to perturbations in other parts of the resonator. The eigenfrequency of these modes decreases as the deformation is localized closer to the centre of the resonator. Thus, by identifying specific modes that undergo a frequency shift that amply exceeds the mechanical linewidth, it is possible to infer if there are particles deposited on the resonator, how many are there and their approximate position within the cavity region. OMCs have rich perspectives for detecting and indirectly analysing biological particles, such as proteins, viruses and bacteria.

Novel one-dimensional optomechanical crystal nanobeam with high optomechanical coupling rate under different defect states

Optomechanical crystals can simultaneously modulate elastic waves and electromagnetic waves as well as localizing phonons and photons to enhance the acousto-optic interaction. In this work, a new type of optomechanical crystal nanobeam cavity is designed by periodically arranging the unit cells with double holes on both sides of a hexagonal prism. Considering the moving boundary effect and the photoelastic effect as well as using the first-order electromagnetic perturbation theory and the optomechanical coupling coefficient calculation method, the optomechanical coupling rate of the structure is calculated. The result shows that the overlap between the optical mode and the mechanical mode can be improved by changing the number of defects and optimizing the geometric structure. For the nanobeam cavity structures with different numbers of the like defects, the number of defects will only affect the action mode of the moving boundary effect and photoelastic effect in the optomechanical coupling rate, but will not change the coupling rate too much. In particular, the optomechanical coupling rate of the single defect optomechanical crystal nanobeam cavity can reach –1.29 MHz, and the equivalent mass is 42.6 fg. Moreover, the designed structure is simple and easy to process and fabricate. The coupling rate of even-symmetric optomechanical crystal nanobeam cavity based on gradient defect can reach 2.25 MHz, and the coupling rate of odd symmetric structure can reach 2.18 MHz, in which the moving boundary effect is dominant. Based on the symmetry analysis of the vibration modes of the optomechanical crystal nanobeam cavity with gradient defects, it is worth noting that only the even symmetrical vibration modes of &lt;i&gt;x&lt;/i&gt;-&lt;i&gt;y&lt;/i&gt;, &lt;i&gt;x&lt;/i&gt;-&lt;i&gt;z&lt;/i&gt; and &lt;i&gt;y&lt;/i&gt;-&lt;i&gt;z&lt;/i&gt; can strongly couple with the optical modes. The surface density of the moving boundary effect is calculated and analyzed, and it is found that the surface density of the acoustic resonance mode with high symmetry also possesses high symmetry. However, when the surface density of the moving boundary effect in the defect state appears adjacent to each other and cancels out each other, it will destroy the coupling mode of the moving boundary effect and reduce the coupling rate, whether the symmetry is high or low. In addition, the designed optomechanical crystal nanobeam can also improve the quality factor of the resonant cavity by optimizing the defect structure while maintaining a high optomechanical coupling rate. Therefore, this research provides an effective means to find a structure with high optomechanical coupling rate, and also presents the ideas for designing the space sensors.

Dispersive optomechanics of supercavity modes in high-index disks.

In this work, we study the dispersive coupling between optical quasi-bound states in the continuum at telecom wavelengths and GHz-mechanical modes in high-index wavelength-sized disks. We show that such cavities can display values of the optomechanical coupling rate on par with optomechanical crystal cavities (g0/2π≃800kHz). Interestingly, optomechanical coupling of optical resonances with mechanical modes at frequencies well above 10 GHz seems attainable. We also show that mechanical leakage in the substrate can be extremely reduced by placing the disk over a thin silica pedestal. Our results suggest a new route for ultra-compact optomechanical cavities that can potentially be arranged in massive arrays forming optomechanical metasurfaces for application in signal processing or sensing.

Microwave oscillator and frequency comb in a silicon optomechanical cavity with a full phononic bandgap

Abstract Cavity optomechanics has recently emerged as a new paradigm enabling the manipulation of mechanical motion via optical fields tightly confined in deformable cavities. When driving an optomechanical (OM) crystal cavity with a laser blue-detuned with respect to the optical resonance, the mechanical motion is amplified, ultimately resulting in phonon lasing at MHz and even GHz frequencies. In this work, we show that a silicon OM crystal cavity performs as an OM microwave oscillator when pumped above the threshold for self-sustained OM oscillations. To this end, we use an OM cavity designed to have a breathing-like mechanical mode at 3.897 GHz in a full phononic bandgap. Our measurements show that the first harmonic of the detected signal displays a phase noise of ≈−100 dBc/Hz at 100 kHz. Stronger blue-detuned driving leads eventually to the formation of an OM frequency comb, whose lines are spaced by the mechanical frequency. We also measure the phase noise for higher-order harmonics and show that, unlike in Brillouin oscillators, the noise is increased as corresponding to classical harmonic mixing. Finally, we present real-time measurements of the comb waveform and show that it can be fitted to a theoretical model recently presented. Our results suggest that silicon OM cavities could be relevant processing elements in microwave photonics and optical RF processing, in particular in disciplines requiring low weight, compactness and fiber interconnection.

Two-dimensional optomechanical crystal cavity with high quantum cooperativity

Optomechanical systems offer new opportunities in quantum information processing and quantum sensing. Many solid-state quantum devices operate at millikelvin temperatures—however, it has proven challenging to operate nanoscale optomechanical devices at these ultralow temperatures due to their limited thermal conductance and parasitic optical absorption. Here, we present a two-dimensional optomechanical crystal resonator capable of achieving large cooperativity C and small effective bath occupancy nb, resulting in a quantum cooperativity Ceff ≡ C/nb > 1 under continuous-wave optical driving. This is realized using a two-dimensional phononic bandgap structure to host the optomechanical cavity, simultaneously isolating the acoustic mode of interest in the bandgap while allowing heat to be removed by phonon modes outside of the bandgap. This achievement paves the way for a variety of applications requiring quantum-coherent optomechanical interactions, such as transducers capable of bi-directional conversion of quantum states between microwave frequency superconducting quantum circuits and optical photons in a fiber optic network.

Optomechanical microwave oscillator and frequency comb generation in a full phononic bandgap 1D optomechanical crystal cavity

In this work we show that a silicon optomechanical crystal cavity can be used as an optomechanical oscillator when driven to the phonon lasing condition with a blue-detuned laser. The optomechanical cavity is designed to have a breathing like mode vibrating at Ωm/2π =3.897 GHz in a full phononic bandgap. Our measurements show that the first harmonic displays a phase noise of -100 dBc/Hz at 100 kHz. Stronger bluedetuned driving leads eventually to the formation of an optomechanical frequency comb, with lines spaced by the mechanical frequency. The measured phase noise grows up with the harmonic number, as in classical harmonic mixing. We present real-time measurements of the comb waveform and show that it can be adjusted to a theoretical model recently presented. Our results suggest that silicon optomechanical cavities can play a role in integrated microwave photonics.