Nano-optomechanical System Research Articles

Isolation of optomechanical nonlinearities in nanomechanical cantilevers

In this paper we study the nonlinearities present in a nano-optomechanical system consisting of a cantilever coupled to a racetrack resonator. We show that higher-order harmonics in the mechanical frequency spectrum are indicative of a readout nonlinearity and we connect these harmonics to the optical cavity transmission with detuning function and its derivatives. We also show that there are optical force nonlinearities that cause a Duffing-type response in the driven mechanical signal. The Duffing-type nonlinearity produces a nonlinear softening when the probe laser is blue detuned, and a nonlinear stiffening when the probe laser is red detuned. The optical force and readout nonlinearities are difficult to separate using a purely experimental approach. We demonstrate the use of a numerical model of the pump-and-probe system to analyze the nonlinearities independently. The numerical model also allows us to estimate the amplitude of the system, predicting the exact detuning where nonlinearities cancel each other to produce higher critical amplitude, and ultimately gives a prospective mass sensitivity level of $83\phantom{\rule{0.28em}{0ex}}\mathrm{yg}/{\mathrm{Hz}}^{1/2}$. The numerical model provides a rich understanding of the complexities of the nano-optomechanical system and is much needed for the development of sensors with increased dynamic range and overall performance.

Dynamical Invariant Applied on General Time-Dependent Three Coupled Nano-Optomechanical Oscillators

A quadratic invariant operator for general time-dependent three coupled nano-optomechanical oscillators is investigated. We show that the invariant operator that we have established satisfies the Liouville-von Neumann equation and coincides with its classical counterpart. To diagonalize the invariant, we carry out a unitary transformation of it at first. From such a transformation, the quantal invariant operator reduces to an equal, but a simple one which corresponds to three coupled oscillators with time-dependent frequencies and unit masses. Finally, we diagonalize the matrix representation of the transformed invariant by using a unitary matrix. The diagonalized invariant is just the same as the Hamiltonian of three simple oscillators. Thanks to such a diagonalization, we can analyze various dynamical properties of the nano-optomechanical system. Quantum characteristics of the system are investigated as an example, by utilizing the diagonalized invariant. We derive not only the eigenfunctions of the invariant operator, but also the wave functions in the Fock state.

Probing optical mode hybridization in an integrated graphene nano-optomechanical system

We propose a scheme for sensitive local monitoring of mode hybridization in vertically asymmetric waveguides with a nano-optomechanical probe based on graphene. Extracting local information about mode hybridization is challenging using intensity measurements at the output or scanning optical probes over the waveguide. Transferring the information about the guided field profiles into the mechanical mode of graphene (with ultra-low-force sensitivity) using the optical gradient force allows for sensitive probing of the mode hybridization. In our proposed scheme, we estimate that a 100% change in the TE fraction of the fundamental quasi-TM waveguide mode would cause a change in the vibration amplitude of graphene on the order of 1000 pm. The limit of detection of the TE fraction is approximately 0.001. The change in the TE fraction due to index perturbations in the core and cladding can also be used for index sensing with responsivity on the order of 1000 pm change in vibration amplitude per refractive index unit and a limit of detection of 2 × 10 − 4 refractive index units. This work provides novel methods for applications in optomechanical modulation and sensing.

Synthetic gauge fields for phonon transport in a nano-optomechanical system.

Gauge fields in condensed matter physics give rise to nonreciprocal and topological transport phenomena and exotic electronic states1. Nanomechanical systems are applied as sensors and in signal processing, and feature strong nonlinearities. Gauge potentials acting on such systems could induce quantum Hall physics for phonons at the nanoscale. Here, we demonstrate a magnetic gauge field for nanomechanical vibrations in a scalable, on-chip optomechanical system. We induce the gauge field through multi-mode optomechanical interactions, which have been proposed as a resource for the necessary breaking of time-reversal symmetry2-4. In a dynamically modulated nanophotonic system, we observe how radiation pressure forces mediate phonon transport between resonators of different frequencies. The resulting controllable interaction, which is characterized by a high rate and nonreciprocal phase, mimics the Aharonov-Bohm effect5. We show that the introduced scheme does not require high-quality cavities, such that it allows exploring topological acoustic phases in many-mode systems resilient to realistic disorder.

A broadband and low-power light-control-light effect in a fiber-optic nano-optomechanical system.

The coupling of the optical and mechanical degrees of freedom using optical force in nano-devices offers a novel mechanism to implement all-optical signal processing. However, the ultra-weak optical force requires a high pump optical power to realize all-optical processing. For such devices, it is still challenging to lower the pump power and simultaneously broaden the bandwidth of the signal light under processing. In this work, a simple and cost-effective optomechanical scheme was demonstrated that was capable of achieving a broadband (208 nm) and micro-Watt (∼624.13 μW) light-control-light effect driven by a relatively weak optical force (∼3 pN). In the scheme, a tapered nanofiber (TNF) was evanescently coupled with a substrate, allowing the pump light guided in the TNF to generate a strong transverse optical force for the light-control-light effect. Additionally, thanks to the low stiffness (5.44 fN nm-1) of the TNF, the light-control-light scheme also provided a simple method to measure the static weak optical force with a minimum detectable optical force down to 380.8 fN. The results establish TNF as a cost-effective scheme to break the limitation of the modulation wavelength bandwidth (MWB) at a low pump power and show that the TNF-optic optomechanical system can be well described as a harmonic oscillator.

A proposal for realization of MIR to NIR up-conversion process based on nano-optomechanical system

In this work, a nanoscale optomechanical system driven by optical force resulted from light scattering is designed and demonstrated. The proposed system is able to control and manipulate the propagating light in single-mode waveguides in the structure. The optical part of the guiding wave structure consists of two coupled single-mode optical waveguides and a series of nanogold metallic spheres on a silica substrate. The structure is illuminated with a plane wave with a wavelength of 4.3 μm. The resonance of the nanogold spheres due to the incidence plane wave provides scattering and thus the optical force can be generated and causes the two waveguides to deform and start bending toward each other. The generated optical force has been calculated with a maximum value of 34.37pN/μm/W. The designed system could achieve a maximum waveguide displacement of 963 nm. The change in the power of the incident plane wave allows controlling the displacement of the waveguides hence the amount of the NIR (850 nm) light power coupled between the two waveguides can be controlled. Here, the electromagnetic wave with a wavelength of 850 nm has been utilized to propagate in the single-mode waveguides. The induced optical force changes the distance between the single-mode optical waveguides and this causes the coupling of the optical power (NIR) into another waveguide. By choosing the distance between the two waveguides it is possible to couple any desired fraction of the NIR input light from one waveguide to another. Therefore, any changes in the incident MIR light power will affect and change the distance between the two optical waveguides and thus the NIR coupled light changes accordingly. Finally, we have calculated a linear relationship between the coupled light in NIR band and the incident light power in MIR using the proposed structure and in fact this is an optomechanical up-conversion system.

Accurate measurement of nanomechanical motion in a fiber-taper nano-optomechanical system

The hybrid systems that couple optical and mechanical degrees of freedom in nanoscale devices offer an unprecedented opportunity and development in laboratories worldwide. A nano-optomechanical (NOM) system that converts energy directly/inversely between optics and mechanics opens an approach to control the behavior of light and light-driven mechanics. An accurate measurement of the mechanical motion of a fiber-taper NOM system is a critical challenge. In this work, an optical microscope was used to measure the nanoscale mechanical motion of the fiber taper by introducing white light interference. The resolution of mechanical motion monitoring achieved 0.356 nm with an optomechanical efficiency of >20 nm/μW. This paper describes an approach to characterize NOM transducers between optical and mechanical signals in both classical and quantum fields.

Porous Nanophotonic Optomechanical Beams for Enhanced Mass Adsorption.

We have developed a porous silicon nanocantilever for a nano-optomechanical system (NOMS) with a universal sensing surface for enhanced sensitivity. Using electron beam lithography, we selectively applied a V2O5/HF stain etch to the mechanical elements while protecting the silicon-on-insulator photonic ring resonators. This simple, rapid, and electrodeless approach generates tunable device porosity simultaneously with the mechanical release step. By controlling the porous etchant concentration and etch time, the porous etch depth, resonant frequency, and the adsorption surface area could be precisely manipulated. Using this control, cantilever sensors ranging from nonporous to fully porous were fabricated and tested as gas-phase mass sensors of volatile organic compounds coming from a gas chromatography stream. The fully porous cantilever produced a dramatic 10-fold increase in sensing signal and a 6-fold improvement in limit of detection (LOD) compared to an otherwise identical nonporous cantilever. This signal improvement could be separated into mass responsivity increase and adsorption increase components. Allan deviation measurements indicate that a further 4-fold improvement in LOD could be expected upon speeding up characteristic peak response time from 1 s to 50 ms. These results show promise for performance enhancement in nanomechanical sensors for applications in gas sensing, gas chromatography, and mass spectrometry.

Appearance and Disappearance of Quantum Correlations in Measurement-Based Feedback Control of a Mechanical Oscillator

Quantum correlations between imprecision and back-action are a hallmark of continuous linear measurements. Here we study how measurement-based feedback can be used to improve the visibility of quantum correlations due to the interaction of a laser field with a nano-optomechanical system. Back-action imparted by the meter laser, due to radiation pressure quantum fluctuations, gives rise to correlations between its phase and amplitude quadratures. These quantum correlations are observed in the experiment both as squeezing of the meter field fluctuations below the vacuum level in a homodyne measurement, and as sideband asymmetry in a heterodyne measurement, demonstrating the common origin of both phenomena. We show that quantum feedback, i.e. feedback that suppresses measurement back-action, can be used to increase the visibility of the sideband asymmetry ratio. In contrast, by operating the feedback loop in the regime of noise squashing, where the in-loop photocurrent variance is reduced below the vacuum level, the visibility of the sideband asymmetry is reduced. This is due to feedback back-action arising from vacuum noise in the homodyne detector. These experiments demonstrate the possibility, as well as the fundamental limits of measurement-based feedback as a tool to manipulate quantum correlations.

Single laser modulated drive and detection of a nano-optomechanical cantilever

To reduce the complexity in a nano-optomechanical system a pump and probe scheme using only a single input laser is used to both coherently pump and probe the nanomechanical device. The system operates similarly to the traditional two laser system, but instead of using a constant power to probe the device and a separate, modulated laser to drive it with an optical gradient force, a single laser is utilized for both functions. A model of the measurement scheme’s response is developed which matches the experimental data obtained in the optomechanical Doppler regime and low cavity power limit. As such, the unconventional response still yields useful device information such as the resonant frequency of the device and its mechanical quality factor. The device is driven with low noise and its frequency is tracked using a phase-locked loop. This demonstrates its potential use for dynamic frequency measurements such as nanomechanical inertial mass loading. In such a system, the estimated mass resolution of the device is 6 zg and consistent with other detection methods.

Monolayer-molybdenum-disulfide-based nano-optomechanical transistor and tunable nonlinear responses**Project supported by the National Natural Science Foundation of China (Nos. 11404005, 51502005, 61272153, 61572035), the Key Foundation for Young Talents in College of Anhui Province (No. 2013SQRL026ZD), and the Foundation for PhD in Anhui University of Science and Technology.

Atomically thin two-dimensional semiconductor nanomaterials have attained considerable attention currently. Here, we present a nano-optomechanical system based on a suspended monolayer molybdenum disulfide (MoS2). The linear and nonlinear coherent optical properties of this system, and the phenomenon of phonon-induced transparency are demonstrated. The transmission of the probe field can be manipulated by the power of a second ‘gating’ (pump) field, which indicates a promising candidate for an optical transistor. We further study the nonlinear effect of the system, and the optical Kerr effect of the monolayer MoS2 resonator can be regulated under different parameter regimes. This scheme proposed here may indicate potential chip-scale applications of monolayer MoS2 resonator in quantum information with the currently popular pump-probe technology.

Nano-Optomechanical Systems for Gas Chromatography

Microgas chromatography (GC) is promising for portable chemical analysis. We demonstrate a nano-optomechanical system (NOMS) as an ultrasensitive mass detector in gas chromatography. Bare, native oxide, silicon surfaces are sensitive enough to monitor volatile organic compounds at ppm levels, while simultaneously demonstrating chemical selectivity. The NOMS is able to sense GC peaks from derivatized metabolites at physiological concentrations. This is an important milestone for small-molecule quantitation assays in next generation metabolite analyses for applications such as disease diagnosis and personalized medicine. The optical microring, which plays an important role in the nanomechanical signal transduction mechanism, can also be used as an analyte concentration sensor. Different adsorption kinetics regimes are realized at different temperatures allowing temporary condensation of the analyte onto the sensor surfaces. This effect amplifies the signal, resulting in a 1 ppb level limit of detection, without partition enhancement from absorbing media. This sensitivity bodes well for NOMS as universal, ultrasensitive detectors in micro-GC, breath analysis, and other chemical-sensing applications.

Multi-dimensional single-spin nano-optomechanics with a levitated nanodiamond

A hybrid nano-optomechanical system — a nanodiamond levitated in an optical dipole trap that contains a single nitrogen vacancy centre — shows the ability to simultaneously control multidimensional optical, phononic and spin degrees of freedom. Considerable advances made in the development of nanomechanical and nano-optomechanical devices have enabled the observation of quantum effects1,2,3,4, improved sensitivity to minute forces5,6, and provided avenues to probe fundamental physics at the nanoscale7,8,9. Concurrently, solid-state quantum emitters with optically accessible spin degrees of freedom have been pursued in applications ranging from quantum information science10,11 to nanoscale sensing12. Here, we demonstrate a hybrid nano-optomechanical system composed of a nanodiamond (containing a single nitrogen–vacancy centre) that is levitated in an optical dipole trap. The mechanical state of the diamond is controlled by modulation of the optical trapping potential. We demonstrate the ability to imprint the multi-dimensional mechanical motion of the cavity-free mechanical oscillator into the nitrogen–vacancy centre fluorescence and manipulate the mechanical system's intrinsic spin. This result represents the first step towards a hybrid quantum system based on levitating nanoparticles that simultaneously engages optical, phononic and spin degrees of freedom.

Graphene-based nanoresonator with applications in optical transistor and mass sensing.

Graphene has received significant attention due to its excellent properties currently. In this work, a nano-optomechanical system based on a doubly-clamped Z-shaped graphene nanoribbon (GNR) with an optical pump-probe scheme is proposed. We theoretically demonstrate the phenomenon of phonon-induced transparency and show an optical transistor in the system. In addition, the significantly enhanced nonlinear effect of the probe laser is also investigated, and we further put forward a nonlinear optical mass sensing that may be immune to detection noises. Molecules, such as NH3 and NO2, can be identified via using the nonlinear optical spectroscopy, which may be applied to environmental pollutant monitoring and trace chemical detection.

Nano-opto-mechanical effects in plasmonic waveguides

In order to achieve interaction between light beams, a mediating material object is required. Nonlinear materials are commonly used for this purpose. Here a new approach to control light with light, based on a nano-opto-mechanical system integrated in a plasmonic waveguide is proposed. Optomechanics of a free-floating resonant nanoparticle in a subwavelength plasmonic V-groove waveguide is studied. It is shown that nanoparticle auto-oscillations in the waveguide induced by a control light result in the periodic modulation of a transmitted plasmonic signal. The modulation depth of 10% per single nanoparticle of 25 nm diameter with the clock frequencies of tens of MHz and the record low energy-per-bit energies of 10−18 J is observed. The frequency of auto-oscillations depends on the intensity of the continuous control light. The efficient modulation and deep-subwavelength dimensions make this nano-optomechanical system of significant interest for opto-electronic and opto-fluidic technologies.

Static and dynamic wavelength routing via the gradient optical force

We propose and demonstrate an all-optical wavelength routing approach that uses a tuning mechanism based upon the optical gradient force in a specially designed nano-optomechanical system. The resulting mechanically compliant ‘spiderweb’ resonator realizes seamless wavelength routing over a range of 3,000 times the intrinsic channel width, with a tuning efficiency of 309 GHz mW−1, a switching time of less than 200 ns, and 100% channel quality preservation over the entire tuning range. These results indicate the potential for radiation pressure actuated devices to be used in a variety of photonics applications, such as channel routing/switching, buffering, dispersion compensation, pulse trapping/release and widely tunable lasers.