It is common both in the classical and quantum optics to describe the optical field as a superposition of plane waves. However, it is well known that optically active materials emit photons vastly dominantly in the electric dipole approximation. The photons emitted in the electric dipole transitions are not plane waves, but spherical photon states corresponding to eigenstates J = 1 of the total angular momentum and M = ±1 of the z component of the total angular momentum. In addition, electric dipole photons are separated from the magnetic photons by the state index η = e for electric photons in distinction to η = m for magnetic photons. In this work, we study the far-field of light that is generated when a two-dimensional matrix of atoms emits electric dipole photons and compare this far-field at large distance from the emitting matrix with a plane wave. The goal of our work is to find out if the light emitted from the electric dipole transitions carry the memory of being electric dipole photons when they are far from the emitting atoms. In particular, it is well known that a plane wave includes all angular momentum components corresponding to quantum numbers J = 1, 2, 3, …, while the far field of the emitting matrix can include only the angular momentum component J = 1. Although the two-dimensional atomic matrix used as a light source in our simulations is certainly nontrivial to fabricate, it is nevertheless fully physical and we expect that with some modifications, the conclusions from the present simulations can be generalized to atomic light sources that are more easy to realize experimentally.
The recently introduced mass-polariton (MP) theory of light describes light in a medium as a coupled state of the field and matter [Phys. Rev. A 95, 063850 (2017)]. In the MP theory, the optical force density drives forward an atomic mass density wave (MDW) that accompanies electromagnetic waves in a medium. The MDW is necessary for the fulfilment of the conservation laws and the Lorentz covariance of light. In silicon at wavelength λ_{0} = 1550 nm, the atomic MDW carries 92% of the total momentum and angular momentum of light. The MDW of a light pulse having field energy E propagating in a dielectric also transfers a net mass equal to δM = (n_{p}n_{g} − 1)E/c^{2} , where n_{p} and n_{g} are the phase and group refractive indices. In this work, we present a schematic experimental setup for the measurement of the MDW in a silicon crystal. This setup overcomes many challenges that have been present in previously introduced setups and that have made the experimental observation of the MDW effect difficult due to its smallness in comparison with other effects, such as the momentum transfer by absorption and reflections. The present setup also overcomes challenges with elastic relaxation effects while extending possible measurement time scales beyond the time scale of sound waves in the setup geometry. For the proposed setup, we also compare the predictions of the MP theory of light to the predictions of the conventional Minkowski theory, where the total momentum of light is carried by the electromagnetic field. We also aim at optimizing experimental studies of the MDW effect using the proposed setup.
We have recently introduced the mass-polariton (MP) theory of light to describe the coupled dynamics of the field and matter when a light pulse propagates in a transparent medium. The theory is based on combining the electrodynamics of continuous media and continuum mechanics, which are both widely used standard theories in their fields of physics. The MP theory shows that a light pulse propagating in a transparent medium is accompanied by a mass density wave (MDW) of atoms set in motion by the optical force density of the light pulse. In the corresponding quantum picture, the covariant coupled state of the field and matter is described as the MP quasiparticle, which has coupled field and medium components. We study a schematic experimental setup that would enable measurements of the atomic displacements and the excess mass density related to the MDW of a Gaussian MP pulse propagating in an optical fiber made of fused silica.
We have recently developed the mass-polariton (MP) theory of light to describe propagation of light in dielectric materials [Phys. Rev. A 95, 063850 (2017)]. The MP theory considers a light wave simultaneously with the dynamics of the medium atoms driven by optoelastic forces between the field-induced dipoles and the electromagnetic field. The MP theory combines the well-known optical forces with the Newtonian dynamics of the medium. Therefore, it can be applied to any inhomogeneous, dispersive, and lossy materials. One of the key observations of the MP theory of light is that a light pulse propagating in a nondispersive dielectric transfers an increased atomic density such that the total transferred mass is equal to δM = (n^{2} − 1)E/c^{2} , where n is the refractive index and E is the electromagnetic energy of the pulse. This mass is transferred by an atomic mass density wave (MDW) where the atoms are spaced more densely inside the light pulse as a result of the optical force. Another key observation is that, in common semiconductors, most of the linear and angular momenta of light is transferred by the semiconductor atoms in the MDW moving under the influence of the optical force. In this work, we use the electric and magnetic fields of selected Laguerre-Gaussian mode beams to calculate the optical force density, which is used in the optoelastic continuum dynamics to simulate the dynamics of medium atoms in edge-supported free-standing thin film structures. The goal of our work is to find out how the different force components related to the reflection, transmission, absorption, and the atomic MDW bend and twist the film. The simulations also aim at optimizing experimental studies of the atomic dynamics in the thin film and to relating the measurements to the properties of incoming light.
Conventional theories of electromagnetic waves in a medium assume that only the energy of the field propagates inside the medium. Consequently, they neglect the transport of mass density by the medium atoms. We have recently presented foundations of a covariant theory of light propagation in a nondispersive medium by considering a light wave simultaneously with the dynamics of the medium atoms driven by optoelastic forces [Phys. Rev. A 95, 063850 (2017)]. In particular, we have shown that the mass is transferred by an atomic mass density wave (MDW), which gives rise to mass-polariton (MP) quasiparticles, i.e., covariant coupled states of the field and matter having a nonzero rest mass. Another key observation of the mass-polariton theory of light is that, in common semiconductors, most of the momentum of light is transferred by moving atoms, e.g., 92% in the case of silicon. In this work, we generalize the MP theory of light for dispersive media and consider experimental measurement of the mass transferred by the MDW atoms when an intense light pulse propagates in a silicon fiber. In particular, we consider optimal intensity and time dependence of a Gaussian pulse and account for the breakdown threshold irradiance of the material. The optical shock wave property of the MDW, which propagates with the velocity of light instead of the velocity of sound, prompts for engineering of novel device concepts like very high frequency mechanical oscillators not limited by the acoustic cutoff frequency.
Conventionally, theories of electromagnetic waves in a medium assume that only the energy of the field propagates in a transparent medium and the medium is left undisturbed. Consequently, the transport of mass density and the related kinetic and elastic energies of atoms is neglected. We have recently presented foundations of a covariant theory of light propagation in a medium by considering a light wave simultaneously with the dynamics of the medium atoms driven by optoelastic forces between the induced dipoles and the electromagnetic field. In the previously discussed mass-polariton (MP) quasiparticle approach, we considered the light pulse as an isolated coupled state between the photon and matter and showed that the momentum and the transferred mass of MP follow unambiguously from the Lorentz invariance and the fundamental conservation laws of nature. In the present work, we combine the electrodynamics of continuous media and elasticity theory to account for the space and time dependent dynamics of the light pulse and the associated mass and momentum distributions of the mass density wave (MDW). In this optoelastic continuum dynamics (OCD) approach, we obtain a numerically accurate solution of the Newtonian continuum dynamics of the medium when the light pulse is propagating in it. For an incoming Gaussian light pulse having total energy E_{0} in vacuum, the OCD simulations of the light pulse propagating in a crystal having refractive index n give the same momentum p = nE_{0}/c and the transferred mass δm = (n^{2}-1)E_{0}/c^{2} as the MP quasiparticle approach. Since the elastic forces are included in our theory on equal footing with the optical forces, our theory also predicts how the mass and thermal equilibria are re-established by elastic waves.
During the past century the electromagnetic field momentum in material media has been under debate in the Abraham-Minkowski controversy as convincing arguments have been advanced in favor of both the Abraham and Minkowski forms of photon momentum. Here we study the photon momentum and optical forces in cavity structures in the cases of dynamical and steady state fields. In the description of the single-photon transmission process we use a field-kinetic one-photon theory. Our model suggests that in the medium photons couple with the induced atomic dipoles forming polariton quasiparticles with the Minkowski form momentum. The Abraham momentum can be associated to the electromagnetic field part of the coupled polariton state. The polariton with the Minkowski momentum is shown to obey the uniform center of mass of energy motion that has previously been interpreted to support only the Abraham momentum. When describing the steady state non-equilibrium field distributions we use the recently developed quantized fluctuational electrodynamics (QFED) formalism. While allowing detailed studies of light propagation and quantum field fluctuations in interfering structures, our methods also provide practical tools for modeling optical energy transfer and the formation of thermal balance in nanodevices as well as studying electromagnetic forces in optomechanical devices.
In recent years, experimental work has shown that significant luminescence enhancement can be obtained from quantum-well (QW) light-emitting diodes (LEDs) by using metallic grating, which diffracts efficiently optical modes and resonances trapped in these structures and converts surface plasmon (SP) modes into radiative modes. We employ a powerful simulation tool to provide a deep insight into the physics of plasmonic enhancement and present guidelines on how to optimize light-extraction in III-nitride LED structures incorporating an emitting InGaN QW located in the vicinity of a grated silver surface. The model uses first-principle theory, coupling the dyadic Green’s function formalism for solving Maxwell’s equations to fluctuational electrodynamics, and employs a recursive and transparent solution method allowing the fields to be written in a closed form. We demonstrate the significant effect of the type of the periodic grating and layer structure on light-extraction efficiency by simulating various structures with different grating shapes and dimensions. Careful optimization of the grating features shows that the maximum enhancement can reach a factor of around 8 as compared to the flat semiconductor structure and that the plasmonic losses can be significantly reduced.
Recent measurements have generated a need to better understand the physics of hot carriers in III-Nitride (III-N) lightemitting diodes (LEDs) and in particular their relation to the efficiency droop and current transport. In this article we present fully self-consistent bipolar Monte Carlo (MC) simulations of carrier transport for detailed modeling of charge transport in III-N LEDs. The simulations are performed for a prototype LED structure to study the effects of hot holes and to compare predictions given by the bipolar MC model, the previously introduced hybrid Monte Carlo–drift-diffusion (MCDD) model, and the conventional drift-diffusion (DD) model. The predictions given by the bipolar MC model and the MCDD model are observed to be almost equivalent for the studied LED. Therefore our simulations suggest that hot holes do not significantly contribute to the basic operation of multi-quantum well LEDs, at least within the presently simulated range of material parameters. With the added hole transport simulation capabilities and fully self-constistent simulations, the bipolar Monte Carlo model provides a state-of-the-art tool to study the fine details of electron and hole dynamics in realistic LED structures. Further analysis of the results for a variety of LED structures will therefore be very useful in studying and optimizing the efficiency and current transport in next-generation LEDs.
It has very recently been suggested that asymmetric coupling of electromagnetic fields to thermal reservoirs under nonequilibrium conditions can produce unexpected oscillatory behavior in the local photon statistics in layered structures. Better understanding of the predicted phenomena could enable useful applications related to thermometry, noise filtering, and enhancing optical interactions. In this work we briefly review the field quantization and study the local steady state temperature distributions in optical cavities formed of lossless and lossy media to show that also local field temperatures exhibit oscillations that depend on position as well as the photon energy.
Performance of III-N based solid-state lighting is to a large extent limited by current transport effects that are also expected
to contribute to the efficiency droop in real devices. To enable studying the contributions of electron transport in drooping
more accurately, we develop and study a coupled Monte Carlo–drift-diffusion (MCDD) method to model the details of
electron current transport in III-N optoelectronic devices. In the MCDD method, electron and hole distributions are first
simulated by solving the standard drift-diffusion (DD) equations. The hole density and recombination rate density obtained
from solving the DD equations are used as inputs in the Monte Carlo (MC) simulation of the electron system. The MC
simulation involves solving the Boltzmann transport equation for the electron gas to accurately describe electron transport.
As a hybrid of the DD and MC methods, the MCDD represents a first-order correction for electron transport in III-N LEDs
as compared to DD, predicting a significant hot electron population in the simulated multi-quantum well (MQW) LED
device at strong injection.
The unique properties of surface plasmons (SPs) are expected to provide a great improvement of light extraction in light-emitting diodes (LEDs). Surface plasmon modes are characterized by a high local density of states, and if scattered by gratings, significantly high emission enhancement is achievable. We investigate the physical role of SPs in improving light extraction from GaN quantum-well (QW) light-emitting structures incorporating metallic grating, by using first-principle theory based on Maxwell's equations and fluctuational electrodynamics. We demonstrate how careful nano-engineering, specifically by choosing the right nano-grating period, can reduce absorption losses and provide optimal enhancement; in the investigated test geometries, light extraction is increased by a factor of four, with the plasmonic losses being reduced from ~ 90% to below ~ 60% thanks to the metallic grating. While the results confirm a strong enhancement and reduction in the plasmonic losses, the overall losses still represent a significant obstacle for plasmonic-enhanced emission. With further optimization of the structure, the grating shapes and the materials, a much larger enhancement and lower losses are expected to be possible.
It has recently been shown that multiphoton absorption in cavities containing an emitter and a nonlinear mirror or a two photon absorber can be used to create antibunched photons (i.e. nonclassical light). We investigate the generation of nonclassical photon states using nonlinear laser cavities where the excitation has been modified so that it consists of short current pulses. The light fields in the studied setups are ideally formed of superpositions of zero photon and one photon states. Our goal is to study and develop single photon sources which are needed e.g. in quantum information processing and quantum computing, and fundamental quantum optical experiments. We investigate the effect of exciting the photon emitter with time dependent current pulses to provide single-photon-on-demand sources. We maximize the probability of the single photon state by optimizing the strengths of linear losses, nonlinear absorption, photon emission, and the length of the current injection pulse into the amplifier. Furthermore, we analyze the output photon statistics and waiting times using Monte Carlo simulations. This type of a setup is technologically attractive since it potentially provides room temperature realization of photon antibunching with essentially standard optoelectronic materials and processing techniques.
According to the fundamental laws of quantum optics, noise is necessarily added to the system when one tries to clone or amplify a quantum state. However, it has recently been shown that the quantum noise related to the operation of a linear phase-insensitive amplifier can be avoided when the requirement of a deterministic operation is relaxed. Nondeterministic noiseless linear amplifiers are therefore realizable. Usually nondeterministic amplifiers rely on using single photon sources. We have, in contrast, recently proposed an amplification scheme in which no external energy is added to the signal, but the energy required to amplify the signal originates from the stochastic fluctuations in the field itself. Applying our amplification scheme, we examine the amplifier gain and the success rate as well as the properties of the output states after successful and failed amplification processes. We also optimize the setup to find the maximum success rates in terms of the reflectivities of the beam splitters used in the setup. In addition, we discuss the nonidealities related to the operation of our setup and the relation of our setup with the previous setups.
Surface plasmons (SPs) have recently gained substantial attention due to their sub-wavelength localization and strong interactions in the near-field. Their unique properties are expected to be essential for the next-generation photonic nanodevices, for instance, to improve light extraction in light-emitting diodes (LEDs). We discuss and develop a rigorous and transparent method to model luminescence enhancement and absorption in grated multilayer structures. The method is based on Green's functions, obtained as a perturbative solution to Maxwell's equations, and the fluctuational electrodynamics description of the structures. The model provides an analytical alternative to numerical methods such as finite-element methods and gives insight beyond the numerical solutions, offering a direct means of studying emission and luminescence from the periodic structures. The model is applied to answer key fundamental questions regarding luminescence enhancement, absorption and reflection in realistic
plasmonic GaN light-emitting diode (LED) structures. Two aspects are considered in particular: (1) modeling the reflectometry measurements of grated LED structures to explain and map the interference patterns observed experimentally by our collaborators, and (2) modeling the enhancement in plasmonic structures where the emission takes place in quantum wells in the vicinity of the metallic grating. The results clearly reveal e.g. the SP-related luminescence enhancement in InGaN quantum well structures incorporating periodic silver grating.
LED structures based on nanowires (NWR) have recently received much attention as a potential way to increase the output power and efficiency of GaN LEDs. We introduce a diffusion-assisted carrier injection scheme for III-Nitride optoelectronic devices, which may open up new current injection methods e.g. for free-standing nanowire emitters (FSNWR) and other structures where the active region is located outside the pn junction and the conventional current path. We simulate the charge transport numerically in selected InGaN/GaN nanowire structures as well as present a simplified analytical model for the current transport. We also discuss the basic characteristics of the bipolar diffusion injection scheme and the factors that make it more sensitive to the dimensions and materials of the current-spreading layers than the conventional LED injection scheme. Our results show that bipolar diffusion enables high efficiency current injection to free-standing nanowires with no top contacts and may also be beneficial to more conventional quantum well structures.
We study the quantized electromagnetic (EM) field in cavities and cavity like structures and develop models
to describe EM energy transfer. Our starting point is based on including the quantum mechanical field-matter
interaction in the traveling wave (TW) formalism with appropriate boundary conditions accounting for the
interference to obtain the spatially resolved quantized field operators. This allows evaluating the Poynting vector
to calculate e.g. the energy fluxes through a cavity structure, the energy emitted and absorbed by an element
placed in a leaky cavity and the formation of its steady state.
We present a transport equation model for the light emission and transport in light-emitting diodes. Using the
model, we compare the brightness and quantum efficiency of LEDs with light extraction through a smooth, light
scattering or perfectly transparent planar surface. We show that surface roughened LEDs can perform almost
ideally and that the thickness of the active region in LEDs has a large effect on the photon extraction and the
overall efficiency.
We have developed a quantum trajectory model for describing the evolution of an optical mode interacting with
optoelectronic devices. Our model includes the field-material coupling, the pumping rate of the material, the loss
rate of the material, and also the mirror losses of the cavity. We derive a relation between the model parameters
and semiconductor material and device properties and apply the model to calculate the photon statistics of
semiconductor devices. We show that depending on the material and device parameters the setup can operate
as a light emitting diode or as a laser. In addition to the steady state solutions, the model can be applied to
calculate the transient phenomena of the density operator of the optical field. It can also be applied to model
the single photon detectors coupled to a cavity field.
In thermophotonic cooling (TPC) the requirement of efficient photon extraction out of the semiconductor material
is removed by the absorption of the light within the semiconductor structure. TPC cooling currently offers
one of the most viable approaches to observing electroluminescent cooling of semiconductors in practice. We
discuss a detailed numerical model that accounts for the current and photon transport as well as various loss
mechanisms like the mirror losses and the nonradiative losses in the structure. The model essentially consists of
the semiconductor equations for current transport and the radiative transfer equation for the photon transport.
Electron blocking layers (EBLs) are commonly used to reduce the leakage current in modern multi-quantum
well (MQW) InGaN light-emitting diodes (LEDs). We study the effect of the EBL and doping on the operation
and efficiency of LEDs. We simulate both conventional MQW LEDs with AlGaN EBL, LEDs with quaternary
AlInGaN EBL and LEDs without EBL. We show that the elimination of the polarization charges at the EBL
interface greatly enhances the injection efficiency and that the hole injection in MQW lattice can be optimized
by doping. The efficiency droop limiting the high power operation is also analyzed to determine the underlying
mechanisms in the simulated MQW structures. Based on these results, we discuss the measures to increase the
overall efficiency MQW structures.
We have recently proposed a solid state heat pump based on photon mediated heat transfer between two large-area light emitting diodes (LEDs) coupled by the electromagnetic field and enclosed in a semiconductor structure with a nearly homogeneous refractive index. We have shown that ideally the thermophotonic heat pump (THP) allows heat transfer at Carnot efficiency and studied the factors that in practice limit the efficiency. In this paper we link the previously parametrized loss mechanisms to the observed nonradiative loss mechanisms in LEDs and study the requirements of observing electroluminescent cooling by using the THP structure. Our results show that a very simple structure that optically couples two LEDs and fabricated using current standard fabrication methods should enable electroluminescent cooling.
We have fabricated InGaAsP/InP separate confinement heterostructure multiple quantum-well lasers emitting at 1.43 μm, which corresponds to a local absorption maximum of liquid water. We have carried out the modeling of the laser, including the calculation of gain, optical confinement factor, and threshold current. The laser structure was grown by atmospheric-pressure all-organometallic vapor-phase epitaxy. The study of the laser structure growth indicates that tertbutylphosphine partial pressure of 2.0 Torr or larger is necessary for the growth of layers with mirrorlike surface morphology. Photoluminescence measurements show that the optimum purge time between the growth of quaternary quantum-well and barrier layers is from 0.5 to 2.5 s. Lattice-matched 500-μm-long devices with three quantum wells lased at a threshold current density of 1.35 kA/cm^{2} with external quantum efficiency of about 25% per facet. These results are comparable with the results reported for lattice-matched 1.3- and 1.55-μm devices, and are in agreement with the values obtained with laser modeling.
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