Squeezing of the mechanical motion and beating 3 dB limit using dispersive optomechanical interactions

We study an optomechanical system consisting of an optical cavity and movable mirror coupled through dispersive linear optomechanical coupling (LOC) and quadratic optomechanical coupling (QOC). We work in the resolved side band limit with a high quality factor mechanical oscillator in a strong coupling regime. We show that the presence of QOC in the conventional optomechanical system (with LOC alone) modifies the mechanical oscillator’s frequency and reduces the back-action effects on mechanical oscillator. As a result of this the fluctuations in mechanical oscillator can be suppressed below standard quantum limit thereby squeeze the mechanical motion of resonator. We also show that either of the quadratures can be squeezed depending on the sign of the QOC. With detailed numerical calculations and analytical approximation we show that in such systems, the 3 dB limit can be beaten.     

Negative effective mass,optical multistability and Fano line-shape control via mode tunnelling in double cavity optomechanical system

ABSTRACT

We theoretically investigate the optical and mechanical properties of a double cavity optomechanical system with one stationary and two harmonically bound mirrors. We show that it is possible for the mechanical mirrors in this system to possess negative effective mass. Working within the strong coupling and the resolved sideband regime, we show that the displacement of the middle resonator is multistable under certain constrains. We also point to the existence of optomechanically induced absorption (OMIA) and Fano resonance. Owing to the negative effective mass, our scheme can be exploited in the study of quantum optomechanical metamaterials.     

Quantifying quantumness of correlations using Gaussian Rényi-2 entropy in optomechanical interfaces

Using the Gaussian Rényi-2 entropy, we analyse the behaviour of two different aspects of quantum correlations (entanglement and quantum discord) in two optomechanical subsystems (optical and mechanical). We work in the resolved sideband and weak coupling regimes. In experimentally accessible parameters, we show that it is possible to create entanglement and quantum discord in the considered subsystems by quantum fluctuations transfer from either light to light or light to matter. We find that both mechanical and optical entanglement are strongly sensitive to thermal noises. In particular, we find that the mechanical one is more affected by thermal effects than that optical. Finally, we reveal that under thermal noises, the discord associated with the entangled state decays aggressively, whereas the discord of the separable state (quantumness of correlations) exhibits a freezing behaviour, seeming to be captured over a wide range of temperature.     

Coherent coupling between an optomechanical membrane and an interacting photon Bose–Einstein condensate

In this paper, we study theoretically the optomechanical interaction of an interacting condensate of photons with an oscillating mechanical membrane in a microcavity. We show that in the Bogoliubov approximation, due to the large number of photons in the condensate, there is a linear strong effective coupling between the Bogoliubov mode of the photonic Bose–Einstein condensate (BEC) and the mechanical motion of the membrane which depends on the photon–photon scattering potential. This coupling leads to the cooling of the mechanical motion, the normal mode splitting (NMS), the squeezing of the output field and the entanglement between the excited mode of the cavity and the mechanical mode. Since the photon condensation occurs at room temperature, this hybrid system can be potentially considered as a room temperature source of squeezed light as well as a suited candidate for exploring the quantum effects. We show that, on one hand, the non-linearity of the photon gas increases the degree of the squeezing of the output field of the microcavity and the efficiency of the cooling process at high temperatures. On the other hand, it reduces the NMS in the displacement spectrum of the oscillating membrane and the degree of the optomechanical entanglement. In addition, the temperature of the photonic BEC can be used to control the above-mentioned phenomena.     

Dynamic manipulation of nanomechanical resonators in the high-amplitude regime and non-volatile mechanical memory operation

The ability to control mechanical motion with optical forces has made it possible to cool mechanical resonators to their quantum ground states. The same techniques can also be used to amplify rather than reduce the mechanical motion of such systems. Here, we study nanomechanical resonators that are slightly buckled and therefore have two stable configurations, denoted 'buckled up' and 'buckled down', when they are at rest. The motion of these resonators can be described by a double-well potential with a large central energy barrier between the two stable configurations. We demonstrate the high-amplitude operation of a buckled resonator coupled to an optical cavity by using a highly efficient process to generate enough phonons in the resonator to overcome the energy barrier in the double-well potential. This allows us to observe the first evidence for nanomechanical slow-down and a zero-frequency singularity predicted by theorists. We also demonstrate a non-volatile mechanical memory element in which bits are written and reset by using optomechanical backaction to direct the relaxation of a resonator in the high-amplitude regime to a specific stable configuration.     

Mimicking a hybrid-optomechanical system using an intrinsic quadratic coupling in conventional optomechanical system

We consider an optical and mechanical mode interacting through both linear and quadratic dispersive couplings in a general cavity-optomechanical set-up. The parity and strength of an intrinsic quadratic optomechanical coupling (QOC) provides an opportunity to control the optomechanical (OM) interaction. We quantify this interaction by studying normal-mode splitting (NMS) as a function of the QOC's strength. The proposed scheme exhibits NMS features equivalent to a hybrid-OM system containing either an optical parametric amplifier or a Kerr medium. Such a system in reality could offer an alternative platform for devising state-of-art quantum devices with requiring no extra degrees-of-freedom as in hybrid-OM systems.     

Optical coupling of deep-subwavelength semiconductor nanowires

Systems of coupled resonators manifest a myriad of exciting fundamental physical phenomena. Analogous to the synthesis of molecules from single atoms, the construction of photonic molecules from stand-alone optical resonators represents a powerful strategy to realize novel functionalities. The coupling of high quality factor (Q) dielectric and semiconductor microresonators is by now well-understood and chipscale applications are abound. The coupling behavior of low-Q nanometallic structures has also been exploited to realize high-performance plasmonic devices and metamaterials. Although dense arrays of semiconductor nanoparticles and nanowires (NWs) find increasing use in optoelectronic devices, their photonic coupling has remained largely unexplored. These high refractive index nano-objects can serve as low-Q optical antennas that can effectively receive and broadcast light. We demonstrate that the broad band antenna response of a pair of NWs can be tuned significantly by engineering their optical coupling and develop an intuitive coupled-mode theory to explain our observations.     

Integration of photonic and silver nanowire plasmonic waveguides

Future optical data transmission modules will require the integration of more than 10,000 x 10,000 input and output channels to increase data transmission rates and capacity. This level of integration, which greatly exceeds that of a conventional diffraction-limited photonic integrated circuit, will require the use of waveguides with a mode confinement below the diffraction limit, and also the integration of these waveguides with diffraction-limited components. We propose to integrate multiple silver nanowire plasmonic waveguides with polymer optical waveguides for the nanoscale confinement and guiding of light on a chip. In our device, the nanowires lay perpendicular to the polymer waveguide with one end inside the polymer. We theoretically predict and experimentally demonstrate coupling of light into multiple nanowires from the same waveguide, and also demonstrate control over the degree of coupling by changing the light polarization.     

Nonreciprocal behaviour between photon and phonon in coupled optomechanical systems

It is shown that the asymmetry coupling between two coupled optomechanical cavities leads to special class of PT-symmetric model for optomechanical structure. Under these conditions, Hamiltonian is considered in blue and red sideband regime. In these cases, the asymmetric coupling between two cavities has been transferred such that the asymmetric beam-splitter or squeezing interaction is generated between optical and mechanical modes. Then, the amount of entanglement between the different optical and mechanical modes is calculated. The results define that PT-symmetry can improve the entanglement in special conditions. The proposed system provides good condition to investigate the nonreciprocal interaction between photon and phonon.     

Controllable optical bistability and Fano line shape in a hybrid optomechanical system assisted by kerr medium: possibility of all optical switching

We theoretically analyse the optical and optomechanical nonlinearity present in a hybrid system consisting of a quantum dot(QD) coupled to an optomechanical cavity in the presence of a nonlinear Kerr medium, and show that this hybrid system can be used as an all optical switch. A high degree of control and tunability via the QD-cavity coupling strength, the Kerr and the optomechanical nonlinearity over the bistable behaviour shown by the mean intracavity optical field and the power transmission of the weak probe field can be achieved.The results obtained in this investigation has the potential to be used for designing efficient all-optical switch and high sensitive sensors for use in Telecom systems.     

Generating EPR-type entanglement of degenerate optomechanical parametric oscillators

Einstein–Podolski–Rosen (EPR) entanglement states are achievable by combining two single-mode position and momentum squeezed states at a 50:50 beam splitter (BS). To generate the EPR mechanical entanglement, we consider the system consisted of two parametric optomechanical resonators, where two mechanical oscillators are linearly coupled. The linear coupling forms the symmetric and antisymmetric combinations of two mechanical modes, parallel to a 50:50 BS mixing. In the weak optomechanical coupling regime and via applying the opposite phases of parametric interactions, the symmetric and antisymmetric mechanical modes can be position and momentum squeezed, respectively. Therefore, two original mechanical modes are EPR entangled. Moreover, the mechanical thermal noise can decrease the entanglement. But with the parametric interaction enhanced optomechanical cooling, the influence of thermal noise on entanglement can be significantly suppressed, and the mechanical entanglement can be generated under a relatively high temperature. We also discuss the critical thermal occupation where the entanglement disappears, which is proportional to the optomechanical cooperativity parameter.     

Design of light scattering in nanowire materials for photovoltaic applications

We experimentally investigate the optical properties of layers of InP, Si, and GaP nanowires, relevant for applications in solar cells. The nanowires are strongly photonic, resulting in a significant coupling mismatch with incident light due to multiple scattering. We identify a design principle for the effective suppression of reflective losses, based on the ratio of the nondiffusive absorption and diffusive scattering lengths. Using this principle, we demonstrate successful suppression of the hemispherical diffuse reflectance of InP nanowires to below that of the corresponding transparent effective medium. The design of light scattering in nanowire materials is of large importance for optimization of the external efficiency of nanowire-based photovoltaic devices.     

Decoherence and the conditions for the classical control of quantum systems

We find the conditions for one quantum system to function as a classical controller of another quantum system: the controller must be an open system and rapidly diagonalized in the diagonal basis of the controller variable that is coupled to the controlled system. This causes decoherence in the controlled system that can be made small if the rate of diagonalization is fast. We give a detailed example based on the quantum optomechanical control of a mechanical resonator. The resulting equations are structurally similar to recently proposed models for consistently combining quantum and classical stochastic dynamics.     

Mechanical behaviour of Al2O3–ZrO2 minicomposite reinforced glass matrix optomechanical composite

Abstract

To understand the effect of a 'mesh-structured reinforcement' on the optical and mechanical properties of optomechanical composites, a unidirectional Al₂O₃ fibre–ZrO₂ matrix minicomposite reinforced glass matrix optomechanical composite has been fabricated. By regular alignment of the minicomposites in the glass matrix as part of the 'mesh structure' a high degree of optical transparency is obtained in the composite; this transparency is proportional to its 'optical window' regions. The mesh structured reinforcement composed of millimetre order widely spaced minicomposites is effective in improving the fracture resistance of the resulting composites primarily through an intact minicomposite bridging mechanism. Use of the minicomposite type of reinforcement is one possible means of improving the mechanical properties of brittle matrix optomechanical composites.     

Imaging in diffuse media with pulsed-ultrasound-modulated light and the photorefractive effect

Acousto-optic imaging in diffuse media is a dual wave-sensing technique in which an acoustic field interacts with multiply scattered laser light. The acoustic field causes a phase modulation in the optical field emanating from the interaction region, and this phase-modulated optical field carries with it information about the local optomechanical properties of the media. We report on the use of a pulsed ultrasound transducer to modulate the optical field and the use of a photorefractive-crystal-based interferometry system to detect ultrasound-modulated light. The use of short pulses of focused ultrasound allows for a one-dimensional acousto-optic image to be obtained along the transducer axis from a single, time-averaged acousto-optic signal. The axial and lateral resolutions of the system are controlled by the spatial pulse length and width of the ultrasound beam, respectively. In addition, scanning the ultrasound transducer in one dimension yields two-dimensional images of optical inhomogeneities buried in turbid media.     

Axicon-based Bessel resonator: analytical description and experiment

We present a new scheme for an optical resonator for production of Bessel and Bessel-Gauss light beams. The resonator with Bessel modes is composed of two plane mirrors with an axicon placed close to one of them. If this mirror is concave, the modes are Bessel-Gauss light beams. Analytical expressions relating parameters of the resonator and characteristics of its modes are obtained and analyzed. The results are verified with the Fox-Li algorithm. The resonator scheme was implemented in an experiment to confirm the possibility of the generation of zero-order Bessel beams. It was found that multipass modes can also oscillate in the resonator if its apertures are large enough.     

Organic Microcavity Photodiodes

The interaction of light and matter lies at the heart of the principle of optoelectronic devices. By tuning the strength of the electric field component of the light wave, one can gain control over this interaction. A simple way of achieving this is by employing microcavities, which are one‐dimensional photonic structures. These give rise to an effective quantization of the light field in one direction. The largest enhancements in the strength of light–matter coupling are achieved for cavities with dimensions on the order of the effective wavelength of light. As organic materials have the very large oscillator strengths required for light–matter coupling, as well as excellent thin film forming properties, they are ideal materials with which to exploit tunable electron–photon coupling. We demonstrate the influence of the optical field strength in organic microcavity photodiodes. Besides allowing tunability of the response spectrum by varying the effective resonator thickness, a large increase in the photocurrent sensitivity is observed below the absorption threshold of the optically active material. The microcavity induced field enhancement plays a particularly important role under two‐photon excitation. In this case we observe a 500‐fold increase in the photocurrent response with respect to a non‐cavity device. This opens up a range of applications for organic microcavity photodiodes as nonlinear detector elements.     

Ring resonator for lasers with annular gain media

A ring resonator for lasers with annular gain media is presented. The resonator consists of two annular mirrors. While the radiation is reflected back and forth between the two annular mirrors, diffraction effects induce an additional azimuthal radiation flux. Output coupling is obtained through a decentered coupling aperture on the circumference of one of the two mirrors. The azimuthal radiation flux permits the extraction of optical power from the whole gain volume through the coupling aperture. The azimuthal radiation flux can revolve in two directions. The associated modes are degenerate, and random jumping between unidirectional and bidirectional operation is observed. Unidirectional operation has been stabilized but remains very sensitive to mirror alignment. High extraction efficiencies have been demonstrated experimentally with this resonator with a diffusion-cooled CO(2) laser and 2 times diffraction-limited beams have been obtained. An empty resonator model that shows the effect of edge diffraction at the coupling aperture on the resonator modes is also given.     

布里渊光纤陀螺光纤环形腔研究

提出了一种用于布里渊光纤陀螺的光纤环形腔设计方法。在分析了布里渊光纤陀螺原理的基础上,利用琼斯矩阵光学的理论以及光纤中的受激布里渊散射理论,详细研究了布里渊光纤环形腔的特性。通过对腔内外光强的细致分析,得出布里渊光纤陀螺环形腔对于腔的耦合系数及输入光强的要求。实验结果表明,该方法用于设置布里渊光纤陀螺工作点,能够保证斯托克斯光的最大传输效率,并有效抑制光路中的散粒噪声。     

High‐order DGTD methods for dispersive Maxwell's equations and modelling of silver nanowire coupling

A high‐order discontinuous Galerkin time‐domain (DGTD) method for Maxwell's equations for dispersive media of Drude type is derived and then used to study the coupling of 2D silver nanowires, which have potential applications in optical circuits without the restriction of diffraction limits of traditional dielectric waveguides. We have demonstrated the high accuracy of the DGTD for the electromagnetic wave scattering in dispersive media and its flexibility in modelling the plasmon resonant phenomena of coupled silver nanowires. Specifically, we study the cross sections of coupled nanowires, the dependence of the resonance on the number of nanowires with more resolved resonance information than the traditional FDTD Yee scheme, time‐domain behaviour of waves impinging on coupled silver nanowires of a funnel configuration, and the energy loss of resonant modes in a linear chain of circular and ellipse nanowires. Copyright © 2006 John Wiley & Sons, Ltd.