Photon-phonon Interaction Research Articles

A complete multifluid model for bipolar semiconductors, with interacting carriers, phonons, and photons

If electrons (e) and holes (h) in metals or semiconductors are heated to the temperatures $$T_\mathrm{e}$$ and $$T_\mathrm{h}$$ greater than the lattice temperature, the electron–phonon interaction causes energy relaxation. In the non-uniform case a momentum relaxation occurs as well. In view of such an application, a new model, based on an asymptotic procedure for solving the kinetic equations of carriers, phonons, and photons, is proposed, which gives naturally the displaced Maxwellian at the leading order. Several generation–recombination (GR) events occur in bipolar semiconductors. In the presence of photons the most important ones are the radiative GR events, direct, indirect, and exciton-catalyzed. Phonons and photons are treated here as a participating species, with their own equation. All the phonon–photon interactions are accounted for. Moreover, carrier–photon (Compton) interactions are introduced, which make complete the model. After that, balance equations for the electron number, hole number, energy densities, and momentum densities are constructed, which constitute now a system of macroscopic equations for the chemical potentials (carriers), the temperatures (carriers and bosons), and the drift velocities (carriers and bosons). In the drift–diffusion approximation the constitutive laws are derived and the Onsager relations recovered, even in the presence of an external magnetic field.

Light-sound interconversion in optomechanical Dirac materials

Analyzing the scattering and conversion process between photons and phonons coupled via radiation pressure in a circular quantum dot on a honeycomb array of optomechanical cells, we demonstrate the emergence of optomechanical Dirac physics. Specifically we prove the formation of polaritonic quasi-bound states inside the dot, and angle-dependent Klein tunneling of light and emission of sound, depending on the energy of the incident photon, the photon-phonon interaction strength, and the radius of the dot. We furthermore demonstrate that forward scattering of light or sound can almost switched off by an optically tuned Fano resonance; thereby the system may act as an optomechanical translator in a future photon-phonon based circuitry.

Simulation of an optomechanical quantum memory in the nonlinear regime

A full quantum simulation of the photon-phonon interaction in an optomechanical system is developed. The implications for the quantum storage of coherent states are discussed, showing that even with current experimental parameters, unexpectedly strong nonlinear effects can dominate spectral features and reduce the quantum memory fidelity.

Investigation of the thermal photocarrier interaction–recombination in ZnO nanostructures fabricated by the hydrothermal method

The characteristics of the photocarrier transfer process in ZnO nanostructures fabricated on silicon substrates by the hydrothermal method are studied using temperature-dependent photoluminescence (PL) measurements. The luminescence shows distinct features arising from the dynamics of the excited carriers which occur as a consequence of the different size distributions of the ZnO nanostructures. It is found that the temperature-dependent photoluminescence phenomena can be attributed to the carrier-thermalization processes that occur in the ZnO nanostructures. The photogenerated carrier redistribution leads to a blueshift in the emission energy of the radiative transitions in the ZnO nanostructures. The random configuration of the photogenerated carriers in the ZnO nanostructures can be qualitatively understood in terms of the transition enthalpy and the transition entropy in the photocarrier transfer process. The oxygen vacancy induced emission with the trapping of electrons and spontaneous fluctuations of ZnO nanostructures has an influence on the variation of the full width at half maximum (FWHM). The carrier thermal escape and retrapping anomalies affect the temperature-dependence of the photoluminescence phenomena. The activation energy is larger for ZnO nanostructures with larger size distributions and the carrier confinement is better. Thermally-related spectroscopy allowed observation of the photon-phonon interactions associated with ZnO nanostructures with different size distributions.

Multi-path photon-phonon converter in optomechanical system at single-quantum level.

Based on photon-phonon nonlinear interaction, a scheme of controllable photon-phonon converters is proposed at single-quantum level in a composed quadratically coupled optomechanical system. With the assistance of the mechanical oscillator, the Kerr nonlinear effect between photon and phonon is enhanced so that the single-photon state can be converted into the phonon state with high fidelity even under the current experimental condition that the single-photon coupling rate is much smaller than mechanical frequency (g ≪ ωm). The state transfer protocols and their transfer fidelity are discussed analytically and numerically. A multi-path photon-phonon converter is designed by combining the optomechanical system with low frequency resonators, which can be controlled by experimentally adjustable parameters. This work provides us a potential platform for quantum state transfer and quantum information.

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.

Invited Article: Acousto-optic finite-difference frequency-domain algorithm for first-principles simulations of on-chip acousto-optic devices

We introduce a finite-difference frequency-domain algorithm for coupled acousto-optic simulations. First-principles acousto-optic simulation in time domain has been challenging due to the fact that the acoustic and optical frequencies differ by many orders of magnitude. We bypass this difficulty by formulating the interactions between the optical and acoustic waves rigorously as a system of coupled nonlinear equations in frequency domain. This approach is particularly suited for on-chip devices that are based on a variety of acousto-optic interactions such as the stimulated Brillouin scattering. We validate our algorithm by simulating a stimulated Brillouin scattering process in a suspended waveguide structure and find excellent agreement with coupled-mode theory. We further provide an example of a simulation for a compact on-chip resonator device that greatly enhances the effect of stimulated Brillouin scattering. Our algorithm should facilitate the design of nanophotonic on-chip devices for the harnessing of photon-phonon interactions.

Capacity Evaluation of a Quantum-Based Channel in a Biological Context.

Nanotechnology, as enabler of the miniaturization of devices in a scale ranging from 1 to few hundreds of nm , represents a viable solution for " alternative" communication paradigms that could be effective in complex networked systems, as body area networks. Traditional communication paradigms are not effective in the context of joint body and nano-networked systems, for several reasons, and then novel approaches have been investigated such as nanomechanical, electromagnetic, acoustic, molecular, etc. On the other hand, quantum phenomena represent a natural direction for developing nanotechnology, since it has to be considered as a new scale where new phenomena can occur and can be exploited for information purpose. Specific quantum particles are phonons, the quanta of mechanical vibrations (i.e., acoustic excitations), that can be analyzed as potential information carriers in a body networked context. In this paper we will focus on the generation of phonons from photon-phonon interaction, by irradiating a sample of human tissue with an electro-magnetic field, and then we will theoretically derive the information capacity and the bit rate in the frequency range [103 - 1012] Hz.

High-mechanical-frequency characteristics of optomechanical crystal cavity with coupling waveguide.

Optomechanical crystals have attracted great attention recently for their ability to realize strong photon-phonon interaction in cavity optomechanical systems. By far, the operation of cavity optomechanical systems with high mechanical frequency has to employ tapered fibres or one-sided waveguides with circulators to couple the light into and out of the cavities, which hinders their on-chip applications. Here, we demonstrate larger-centre-hole nanobeam structures with on-chip transmission-coupling waveguide. The measured mechanical frequency is up to 4.47 GHz, with a high mechanical Q-factor of 1.4 × 103 in the ambient environment. The corresponding optomechanical coupling rate is calculated and measured to be 836 kHz and 1.2 MHz, respectively, while the effective mass is estimated to be 136 fg. With the transmission waveguide coupled structure and a small footprint of 3.4 μm2, this simple cavity can be directly used as functional components or integrated with other on-chip devices in future practical applications.

Resonance fluorescence spectra from coherently driven quantum dots coupled to slow-light photonic crystal waveguides

Using a polaron master equation approach we investigate the resonance fluorescence spectra from coherently driven quantum dots (QDs) coupled to an acoustic phonon bath and a photonic crystal waveguide with a rich local density of photon states (LDOS). Resonance fluorescence spectra from QDs in semiconductor crystals are known to show strong signatures of electron-phonon interactions, but when coupled to a structured photonic reservoir, the QD emission properties are also determined by the frequency dependence of the LDOS of the photon reservoir. Here, we investigate the simultaneous role of coupled photon and phonon baths on the characteristic Mollow triplet spectra from a strongly driven QD. As an example structured photonic reservoir, we first study a photonic crystal coupled cavity waveguide, and find that photons and phonons have counter-interacting effects near the upper mode-edge of the coupled-cavity waveguide, thus establishing the importance of their separate roles in determining the emission spectra. The general theory is developed for arbitrary photonic reservoirs and is further applied to determine resonance the fluorescence spectra from a realistic, disordered W1 photonic crystal waveguide showing important photon-phonon interaction effects that are directly relevant to emerging experiments and theoretical proposals.

Brillouin scattering self-cancellation.

The interaction between light and acoustic phonons is strongly modified in sub-wavelength confinement, and has led to the demonstration and control of Brillouin scattering in photonic structures such as nano-scale optical waveguides and cavities. Besides the small optical mode volume, two physical mechanisms come into play simultaneously: a volume effect caused by the strain-induced refractive index perturbation (known as photo-elasticity), and a surface effect caused by the shift of the optical boundaries due to mechanical vibrations. As a result, proper material and structure engineering allows one to control each contribution individually. Here, we experimentally demonstrate the perfect cancellation of Brillouin scattering arising from Rayleigh acoustic waves by engineering a silica nanowire with exactly opposing photo-elastic and moving-boundary effects. This demonstration provides clear experimental evidence that the interplay between the two mechanisms is a promising tool to precisely control the photon–phonon interaction, enhancing or suppressing it.

Solitons in optomechanical arrays.

We show that optical solitons can be obtained with a one-dimensional optomechanical array that consists of a chain of periodically spaced identical optomechanical systems. Unlike conventional optical solitons, which originate from nonlinear polarization, the optical soliton here stems from a new mechanism, namely, phonon-photon interaction. Under proper conditions, the phonon-photon induced nonlinearity that refers to the optomechanical nonlinearity will exactly compensate the dispersion caused by photon hopping of adjacent optomechanical systems. Moreover, the solitons are capable of exhibiting very low group velocity, depending on the photon hopping rate, which may lead to many important applications, including all-optical switches and on-chip optical architecture. This work may extend the range of optomechanics and nonlinear optics and provide a new field to study soliton theory and develop corresponding applications.

Collapse of the superradiant phase and multiple quantum phase transitions for Bose-Einstein condensates in an optomechanical cavity

We investigate the multiple stable macroscopic quantum states of a Bose-Einstein condensate in an optomechanical cavity with pump-cavity field detuning and atom-photon interaction following the experimental realization of the quantum phase transition [Nature (London) 464, 1301 (2010)]. The spin-coherent-state variational method is useful in exploring the multistability since it has the advantage of including both normal and inverted pseudospin states. In the blue detuning regime the usual transition from normal to superradiant phases still exists, however, when the atom-field coupling increases to a certain value, called the turning point, the superradiant phase collapses due to the resonant damping of the mechanical oscillator. As a consequence, the system undergoes at this point an additional phase transition to the normal phase of the atomic population inversion state. In particular, the superradiant phase disappears completely at strong photon-phonon interaction, resulting in the direct atomic population transfer between two atomic levels. Moreover, the coupling-induced collapse and revival of the superradiant state are also found in the red detuning region.

Stimulated Brillouin Scattering in Photonic Integrated Circuits: Novel Applications and Devices

The last few years have seen major progress in harnessing on-chip photon-phonon interactions, leading to a wide range of demonstrations of new functionalities. Utilizing not only the optical response of a nonlinear waveguide-but also acoustic resonances-enables the realization of microwave devices with unprecedented performance, otherwise hard to achieve in all-optical processing schemes or electronically. Here, we overview on-chip stimulated Brillouin scattering (SBS) with special emphasis on microwave sources and microwave signal processing schemes. We review the different material platforms and structures for on-chip SBS, ranging from chalcogenide rib waveguides to hybrid silicon/silicon-nitride structures, high-Q photonic-phononic silica microresonators, and suspended silicon nanowires. We show that the paradigm shift in SBS research-from long length of fibers to chip-scale devices-is now moving toward fully integrated photonic-phononic CMOS chips.

Phoxonic crystals and cavity optomechanics

Abstract Phoxonic crystals are dual phononic/photonic crystals exhibiting simultaneously band gaps for both types of excitations. Therefore, they have the ability to confine phonons and photons in the same cavity and in turn allow the enhancement of their interaction. In this paper, we review some of our theoretical works on cavity optomechanical interactions in different types of phoxonic crystals, including two-dimensional, slab, and nanobeam structures. Two mechanisms are behind the phonon–photon interaction, namely the photoelastic and the moving interface effects. Coupling rates of a few MHz are obtained with high-frequency phonons of a few GHz. Finally, we give some preliminary results about the optomechanical interaction when a metallic nanoparticle is introduced into the cavity, giving rise to coupled photon–plasmon modes or, in the case of very small particles, to an enhancement of the electric field at the position of the particle.

Net on-chip Brillouin gain based on suspended silicon nanowires

The century-old study of photon–phonon coupling has seen a remarkable revival in the past decade. Driven by early observations of dynamical back-action, the field progressed to ground-state cooling and the counting of individual phonons. A recent branch investigates the potential of traveling-wave, optically broadband photon–phonon interaction in silicon circuits. Here, we report continuous-wave Brillouin gain exceeding the optical losses in a series of suspended silicon beams, a step towards selective on-chip amplifiers. We obtain efficiencies up to the highest to date in the phononic gigahertz range. We also find indications that geometric disorder poses a significant challenge towards nanoscale phonon-based technologies.

Acousto-optic coupling in phoxonic crystal nanobeam cavities with plasmonic behavior.

Acousto-optic (AO) coupling in a two-layer GaAs/Ag heterogeneous phoxonic crystal nanobeam cavity with plasmonic behavior is studied numerically. Because of the Ag metal layer, the cavity structure hybridizes photons and surface plasmons, squeezing the optical energy into small regions near the GaAs/Ag interface; the phononic cavity modes can be simultaneously tailored to highly match the photonic cavity modes at reduced regions in the cavity. Consequently, AO coupling is enhanced at near-infrared wavelengths. Boosting of the interface effect by the acoustic displacement field mainly contributes to the AO coupling enhancement. The simultaneous small photonic mode volume and high spatial matching of photonic and phononic cavity modes enhance the photonic resonance wavelength shift by one order of magnitude. This study enables applications of strong AO or photon-phonon interaction in subwavelength nano-structures.

Nanophotonic cavity optomechanics with propagating acoustic waves at frequencies up to 12 GHz

Strong coherent interactions between colocalized optical and mechanical eigenmodes of various cavity optomechanical systems have been explored intensively toward quantum information processing using both photons and phonons. In contrast to localized modes, propagating mechanical waves are another form of phonons that can be guided and manipulated like photons in engineered phononic structures. Here, we demonstrate sideband-resolved coupling between multiple photonic nanocavities and propagating surface acoustic waves up to 12 GHz. Coherent and strong photon–phonon interaction is manifested with electro-optomechanically induced transparency, absorption, and amplification, and phase-coherent interaction in multiple cavities. Inside an echo chamber, it is shown that a phonon pulse can interact with an embedded nanocavity for multiple times. Our device provides a scalable platform to optomechanically couple phonons and photons for microwave photonics and quantum photonics.

Strong Optomechanical Interaction in Hybrid Plasmonic-Photonic Crystal Nanocavities with Surface Acoustic Waves.

We propose dynamic modulation of a hybrid plasmonic-photonic crystal nanocavity using monochromatic coherent acoustic phonons formed by ultrahigh-frequency surface acoustic waves (SAWs) to achieve strong optomechanical interaction. The crystal nanocavity used in this study consisted of a defective photonic crystal beam coupled to a metal surface with a nanoscale air gap in between and provided hybridization of a highly confined plasmonic-photonic mode with a high quality factor and deep subwavelength mode volume. Efficient photon-phonon interaction occurs in the air gap through the SAW perturbation of the metal surface, strongly coupling the optical and acoustic frequencies. As a result, a large modulation bandwidth and optical resonance wavelength shift for the crystal nanocavity are demonstrated at telecommunication wavelengths. The proposed SAW-based modulation within the hybrid plasmonic-photonic crystal nanocavities beyond the diffraction limit provides opportunities for various applications in enhanced sound-light interaction and fast coherent acoustic control of optomechanical devices.

Subcell Debye behavior analysis of order–disorder effects in triple-junction InGaP-based photovoltaic solar cells

Analysis was made of the Subcell Debye behavior of the order–disorder effects in triple-junction InGaP-based photovoltaic solar cells fabricated by a metal organic vapor phase epitaxy (MOVPE) system with careful adjustment of the growth conditions. The order–disorder configurations of the InGaP subcells were investigated after post-annealing treatment at various temperatures in a nitrogen atmosphere. Temperature-dependent photoluminescence (PL) measurements over a broad temperature range provided insight into the roles of the thermophysical phenomena connected with the ordering and disordering in the InGaP alloys. The thermally-related spectroscopic observations associated with the ordering effects on the photon–phonon interactions were confirmed by the McCumber–Sturge theory. The variations of both the full width at half-maximum (FWHM) and shift in the peak of PL with temperature were analyzed. According to the width-related PL observations the effective photon–phonon coupling coefficient and the Debye temperature were 0.53meV and 424K, respectively; according to shift-related PL observations of the as-grown sample they were 0.3247eV and 430K, respectively, for the width-related PL observation they were 0.29meV and 421K; and from the shift-related PL observations for the as-grown ordered samples they were 0.3142eV and 425K, respectively, implying that the spontaneously disordered InGaP heterostructures met the demand for improvement of photovoltaic devices. Both the effective photon–phonon coupling coefficient and the Debye temperatures were characterized as functions of the annealing temperature. The Debye temperatures obtained for the disordered and ordered top subcells were consistent with the universal Gruneisen–Bloch relation.