Photon Phonon Research Articles

Thermal Optofluidics: Principles and Applications

AbstractThermal optofluidics is an emerging field that promises to create numerous research and application opportunities in biophysics, biochemistry, and clinical biology. Innovation in plasmonic optics has led to the development of various invaluable tools in the fields of biosensing and microfluidic manipulation. The optothermal effect originates from light–matter interactions during photon–phonon conversion, which can lead to micro‐ or nanoscale inhomogeneities in the thermal distribution. This further induces a series of hydrodynamic phenomena such as natural convection, Marangoni convection, thermophoresis, the electrolyte Seebeck effect, depletion forces, and interfacial effects in colloidal particles. Light–matter interactions are particularly important for three aspects of microfluidics, namely the motion of colloidal particles, fluidic actuation, and biochemical reactions. This review first systematically elucidates the role of both nanoscale plasmonic thermal generation and heat‐induced fluidic motion in optofluidic microsystems. Then, recent state‐of‐the‐art thermal optofluidic applications of the above‐listed three aspects are presented. The paper aims to provide an insightful reference for future research in optofluidic biochemical systems.

Retraction Note: Photon–phonon anti‑stokes upconversion of a photonically, electronically, and thermally isolated opal

The Editor-in-Chief has retracted this article because post-publication review has shown that there are serious flaws with respect to the acquisition of data through the instrumentation used. The lack of sufficient information on experimental procedures makes it impossible to reproduce the author’s approach. For example, it is not defined which portion of light is analysed in the spectral measurements shown in the article. As a consequence the interpretation of the results (e.g. in terms of “microlasing”) must be considered unsound. The author does not agree with this retraction.

First- and second-order photon–phonon interactions and optical parameters of ZnTe crystal: a broadband terahertz time-domain spectroscopy study

We performed broadband terahertz (THz) time-domain spectroscopy measurements to study the photon–phonon interactions and frequency-resolved optical parameters of bulk ZnTe. Using laser-induced plasma as the source of THz radiation and a GaP bulk wafer as the sensor crystal, a broadband THz response of bulk ZnTe wafer with thickness of 0.1 millimeter within the frequency range from 0.1 to 7.5 THz was obtained. Comparing the measured photon absorption spectrum with phonon dispersion curves obtained from ab initio calculations, we identified the first- and second-order photon–phonon interactions of ZnTe crystal. The frequency-resolved optical parameters including the complex refractive index, dielectric response and conductivity of ZnTe crystal within the frequency range between 0.1 and 7.0 THz were derived from the measured THz transmitted field. By fitting the frequency dependent dielectric functions with the Lorentz oscillator model, a static permittivity of 10.5 along with a transverse optical phonon frequency of 5.9 THz and a phonon lifetime of 1.25 picosecond were obtained for ZnTe crystal.

Squeezed states of coupled photons and phonons in nanoscale waveguides

We investigate the generation of photon–phonon entangled states by exploiting stimulated Brillouin scattering in nanoscale waveguides. The squeezing type Hamiltonian that represents creation and annihilation of photon–phonon pairs is obtained out of the multimode photon–phonon interaction Hamiltonian in the presence of a pump field. The Bogoliubov eigenstates of the Hamiltonian, which are a coherent mix of propagating photons and phonons, show squeezing properties in the uncertainties of the collective quadrature operators. The measurement of the photonic component can provide a controllable source of single phonons in demand.

On-Chip Rolling Design for Controllable Strain Engineering and Enhanced Photon-Phonon Interaction in Graphene.

On-chip strain engineering is highly demanded in 2D materials as an effective route for tuning their extraordinary properties and integrating consistent functionalities toward various applications. Herein, rolling technique is proposed for strain engineering in monolayer graphene grown on a germanium substrate, where compressive or tensile strain could be acquired, depending on the designed layer stressors. Unusual compressive strains up to 0.30% are achieved in the rolled-up graphene tubular structures. The subsequent phonon hardening under compressive loading is observed through strain-induced Raman G band splitting, while distinct blueshifts of characteristic peaks (G+ , G- , or 2D) can be well regulated on an asymmetric tubular structure with a strain variation. In addition, due to the strong confinement of the local electromagnetic field under 3D tubular geometry, the photon-phonon interaction is highly strengthened, and thus, the Raman scattering of graphene in rolled-up tubes is enhanced. Such an on-chip rolling approach leads to a superior strain tuning method in 2D materials and could improve their light-matter interaction in a tubular configuration, which may hold great capability in 2D materials integration for on-chip applications such as in mechanics, electronics, and photonics.

Light localization in finite one-dimensional graphite-GaN heterostructures

The properties of light localization in finite one-dimensional photonic heterostructures composed of alternating layers of graphite and wurtzite GaN are studied theoretically. Results are obtained within the transfer-matrix formalism for both transversal-magnetic and transversal-electric polarizations of the incident electromagnetic wave in the infrared region of the electromagnetic spectrum. A structural disorder is introduced into the system by assuming that the width of the slabs in the heterostructure may randomly fluctuate around its mean value. For oblique incidence and transversal-magnetic polarization, a coupling of the infrared photon modes with the longitudinal optical phonons is discussed. This photon–phonon coupling gives rise to signatures of the phonon-polariton modes in the transmission and localization properties of the system, which are observed in the cases of low and moderate levels of structural disorder. The dependence of the properties of the light localization on the number of graphite-GaN double layers is also analyzed.

Analysis of Forward Stimulated Brillouin Scattering in Nanoscale SiGe Waveguides by Tailoring Optical Forces

We propose and design SiGe strip waveguides and silicon waveguides with SiGe cover layers to tailor optical forces. The forward stimulated Brillouin scattering (FSBS) in these SiGe waveguides are analyzed by considering the effects of SiGe concentration on the optical forces. In the radiation-enhanced configuration, electrostrictive forces can constructively add to or destructively interfere with radiation pressure, depending on the concentration. The silicon waveguides with graded-varying cover layers provide a means of enhancing photon–phonon interaction and rewriting the selection rule of excited acoustic modes. The numerical simulation results indicate that SiGe strip waveguides can realize the largest net Stokes’ amplification up to 10.32 dB. Compared to traditional pure silicon waveguides, the silicon waveguides with graded-varying cover layers have an improvement of about 40% on Brillouin gain and at least 2.5 dB on net Stokes’ amplification. Our proposed SiGe waveguides offer an effective approach to implement flexible FSBS in silicon-based chip.

High-order sideband generation in a two-cavity optomechanical system with modulated photon-hopping interaction

The high-order sideband generation in a two-cavity optomechanical system is discussed, where photon hopping between the two cavity modes is modulated sinusoidally. We show that the high-order sideband generation can be induced originating from two processes: the parametric frequency conversion between the photon–photon interactions and the nonlinear optomechanical interactions between the photon–phonon interactions. Both the modulation amplitude and frequency of photon hopping between the two cavities have flexible manipulation on the high-order sideband generation at the low pump power level. With the modulation amplitude varying, we are able to obtain a robust comb-type spectral structure and a weak spectral structure, which can be amplified by tuning the modulation frequency. Selective generation of particular sidebands may also been achieved via transforming the modulation frequency when the parametric conversion process is dominant. Moreover, the dependence of the high-order sideband generation on other important parameters is also discussed in detail, including the cavities linewidthes, the frequency detuning of the two input laser fields and the intensity of control field. These results may provide further insights into the understanding of the high-order sideband generation, and find applications in optical frequency converters and optical frequency combs.

Cross-correlation between photons and phonons in quadratically coupled optomechanical systems

We study photon, phonon statistics, and the cross-correlation between photons and phonons in a quadratically coupled optomechanical system. Photon blockade, phonon blockade, and strong anticorrelation between photons and phonons can be observed in the same parameter regime with the effective nonlinear coupling between the optical and the mechanical modes, enhanced by a strong optical driving field. Interestingly, an optimal value of the effective nonlinear coupling strength for the photon blockade is not within the strong nonlinear coupling regime. This abnormal phenomenon results from the destructive interference between different paths for two-photon excitation in the optical mode with a moderate effective nonlinear coupling strength. Furthermore, we show that phonon (photon) pairs or correlated photons and phonons can be generated in the strong nonlinear coupling regime with a proper detuning between the weak mechanical driving field and mechanical mode. Our results open up a way to generate anticorrelated and correlated photons and phonons, which may have important applications in quantum information processing.

Long-range optical trapping and binding of microparticles in hollow-core photonic crystal fibre

Optically levitated micro- and nanoparticles offer an ideal playground for investigating photon–phonon interactions over macroscopic distances. Here we report the observation of long-range optical binding of multiple levitated microparticles, mediated by intermodal scattering and interference inside the evacuated core of a hollow-core photonic crystal fibre (HC-PCF). Three polystyrene particles with a diameter of 1 µm are stably bound together with an inter-particle distance of ~40 μm, or 50 times longer than the wavelength of the trapping laser. The levitated bound-particle array can be translated to-and-fro over centimetre distances along the fibre. When evacuated to a gas pressure of 6 mbar, the collective mechanical modes of the bound-particle array are able to be observed. The measured inter-particle distance at equilibrium and mechanical eigenfrequencies are supported by a novel analytical formalism modelling the dynamics of the binding process. The HC-PCF system offers a unique platform for investigating the rich optomechanical dynamics of arrays of levitated particles in a well-isolated and protected environment.

Reconfigurable optomechanical circulator and directional amplifier

Non-reciprocal devices, which allow non-reciprocal signal routing, serve as fundamental elements in photonic and microwave circuits and are crucial in both classical and quantum information processing. The radiation-pressure-induced coupling between light and mechanical motion in travelling-wave resonators has been exploited to break the Lorentz reciprocity, enabling non-reciprocal devices without magnetic materials. Here, we experimentally demonstrate a reconfigurable non-reciprocal device with alternative functions as either a circulator or a directional amplifier via optomechanically induced coherent photon–phonon conversion or gain. The demonstrated device exhibits considerable flexibility and offers exciting opportunities for combining reconfigurability, non-reciprocity and active properties in single photonic devices, which can also be generalized to microwave and acoustic circuits.

Coherence and entanglement dynamics of vibrating qubits

We investigate the dynamics of coherence and entanglement of vibrating qubits. Firstly, we consider a single trapped ion qubit inside a perfect cavity and successively we use it to construct a bipartite system made of two of such subsystems, taken identical and noninteracting. As a general result, we find that qubit vibration can lead to prolonging initial coherence in both single-qubit and two-qubit system. However, despite of this coherence preservation, we show that the decay of the entanglement between the two qubits is sped up by the vibrational motion of the qubits. Furthermore, we highlight how the dynamics of photon–phonon correlations between cavity mode and vibrational mode, which may serve as a further useful resource stored in the single-qubit system, is strongly affected by the initial state of the qubit. These results provide new insights about the ability of systems made of moving qubits in maintaining quantum resources compared to systems of stationary qubits.

Fragmentation of twisted light in photon–phonon nonlinear propagation

Twisted light, or orbital angular momentum (OAM) carrying light, has been gradually becoming an important subfield of nonlinear optics. Compared with ordinary light, its chiral phase front provides an additional interface for shaping the phase-matching condition of nonlinear interactions and in consequence reveals a feasible way to tailor light's transverse structure. Here, we explore the nonlinear propagation of twisted light during focused stimulated Brillouin scattering (SBS). Unlike ordinary light that will experience a time-reversal nonlinear reflection, OAM carrying light will break up into corresponding petal-like degenerate OAM modes that carry no net OAM, whereas the superposed OAM modes that carry no net OAM, as the input field, are still time–reversed in focused-SBS. This unexpected phenomenon, resulting from a unique OAM selection rule of noise-initiated SBS, gives more insight into the underlying principle of OAM conservation in electromagnetic interactions and provides an approach to shaping light via nonlinear propagation.

Multi-functional quantum router using hybrid opto-electromechanics

Quantum routers engineered with multiple frequency bands play a key role in quantum networks. We propose an experimentally accessible scheme for a multi-functional quantum router, using photon–phonon conversion in a hybrid opto-electromechanical system. Our proposed device functions as a bidirectional, tunable multi-channel quantum router, and demonstrates the possibility to route single optical photons bidirectionally and simultaneously to three different output ports, by adjusting the microwave power. Further, the device also behaves as an interswitching unit for microwave and optical photons, yielding probabilistic routing of microwave (optical) signals to optical (microwave) outports. With respect to potential application, we verify the insignificant influence from vacuum and thermal noises in the performance of the router under cryogenic conditions.

Optomechanically Induced Transparency and Cooling in Thermally Stable Diamond Microcavities

Diamond cavity optomechanical devices hold great promise for quantum technology based on coherent coupling between photons, phonons, and spins. These devices benefit from the exceptional physical properties of diamond, including its low mechanical dissipation and optical absorption. However, the nanoscale dimensions and mechanical isolation of these devices can make them susceptible to thermo-optic instability when operating at the high intracavity field strengths needed to realize coherent photon–phonon coupling. In this work, we overcome these effects through engineering of the device geometry, enabling operation with large photon numbers in a previously thermally unstable regime of red-detuning. We demonstrate optomechanically induced transparency with cooperativity >1 and normal mode cooling from 300 to 60 K and predict that these devices will enable coherent optomechanical manipulation of diamond spin systems.

Photon–phonon parametric oscillation induced by quadratic coupling in an optomechanical resonator

A direct photon–phonon parametric effect of quadratic coupling on the mean-field dynamics of an optomechanical resonator in the large-scale-movement regime is found and investigated. Under a weak pumping power, the mechanical resonator damps to a steady state with a nonlinear static response sensitively modified by the quadratic coupling. When the driving power increases beyond the static energy balance, the steady states lose their stabilities via Hopf bifurcations, and the resonator produces stable self-sustained oscillation (limit-circle behavior) of discrete energies with step-like amplitudes due to the parametric effect of quadratic coupling, which can be understood roughly by the power balance between gain and loss on the resonator. A further increase in the pumping power can induce a chaotic dynamic of the resonator via a typical routine of period-doubling bifurcation, but which can be stabilized by the parametric effect through an inversion-bifurcation process back to the limit-circle states. The bifurcation-to-inverse-bifurcation transitions are numerically verified by the maximal Lyapunov exponents of the dynamics, which indicate an efficient way of suppressing the chaotic behavior of the optomechanical resonator by quadratic coupling. Furthermore, the parametric effect of quadratic coupling on the dynamic transitions of an optomechanical resonator can be conveniently detected or traced by the output power spectrum of the cavity field.

Thermal Brillouin noise observed in silicon optomechanical waveguide

Stimulated Brillouin scattering was recently observed in nanoscale silicon waveguides. Surprisingly, thermally-driven photon–phonon conversion in these structures had not yet been reported. Here, we inject an optical probe in a suspended silicon waveguide and measure its phase fluctuations at the output. We observe mechanical resonances around 8 GHz with a scattering efficiency of and a signal-to-noise ratio of 2. The observations are in agreement with a theory of noise in these waveguides as well as with stimulated measurements. Our scheme may simplify measurements of mechanical signatures in nanoscale waveguides and is a step towards a better grasp of thermal noise in these new continuum optomechanical systems.

Dicke phase transition and collapse of superradiant phase in optomechanical cavity with arbitrary number of atoms

We in this paper derive the analytical expressions of ground-state energy, average photon-number, and the atomic population by means of the spin-coherent-state variational method for arbitrary number of atoms in an optomechanical cavity. It is found that the existence of mechanical oscillator does not affect the phase boundary between the normal and superradiant phases. However, the superradiant phase collapses by the resonant damping of the oscillator when the atom–field coupling increases to a so-called turning point. As a consequence the system undergoes at this point an additional phase transition from the superradiant phase to a new normal phase of the atomic population-inversion state. The region of superradiant phase decreases with the increase of photon–phonon coupling. It shrinks to zero at a critical value of the coupling and a direct atomic population transfer appears between two atom-levels. Moreover we find an unstable nonzero-photon state, which is the counterpart of the superradiant state. In the absence of oscillator our result reduces exactly to that of Dicke model. Particularly the ground-state energy for N=1 (i.e. the Rabi model) is in perfect agreement with the numerical diagonalization in a wide region of coupling constant for both red and blue detuning. The Dicke phase transition remains for the Rabi model in agreement with the recent observation.

Photon-phonon Interaction in a Microfiber Induced by Optical and Electrostrictive Forces

Stimulated Brillouin scattering (SBS) via electrostrictive force is a fundamental interaction between light and sound which limits the power in conventional optical fibers. The emergence of optical microfibers with subwavelength diameter, ultralight mass and an intense light field, provides a new platform for photon–phonon coupling, resulting in the radiation pressure mediated contribution of SBS. This study examines the optomechanical system in cylindrical coordinates, reveals the theoretically radiation pressure induced analogous, and demonstrates contrary effect compared with electrostrictive force in solid or hollow silica microfibers. The finding shows that the photon-phonon coupling, which is related to SBS, can be suppressed in a solid microfiber, and even be completely cancelled in a hollow microfiber.

Anderson localization of composite excitations in disordered optomechanical arrays

Optomechanical (OMA) arrays are a promising future platform for studies of transport, many-body dynamics, quantum control and topological effects in systems of coupled photon and phonon modes. We introduce disordered OMA arrays, focusing on features of Anderson localization of hybrid photon–phonon excitations. It turns out that these represent a unique disordered system, where basic parameters can be easily controlled by varying the frequency and the amplitude of an external laser field. We show that the two-species setting leads to a non-trivial frequency dependence of the localization length for intermediate laser intensities. This could serve as a convincing evidence of localization in a non-equilibrium dissipative situation.