Generalized noise terms for the quantized fluctuational electrodynamics

The quantization of optical fields in vacuum has been known for decades, but extending the field quantization to lossy and dispersive media in nonequilibrium conditions has proven to be complicated due to the position-dependent electric and magnetic responses of the media. In fact, consistent position-dependent quantum models for the photon number in resonant structures have only been formulated very recently and only for dielectric media. Here we present a general position-dependent quantized fluctuational electrodynamics (QFED) formalism that extends the consistent field quantization to describe the photon number also in the presence of magnetic field-matter interactions. It is shown that the magnetic fluctuations provide an additional degree of freedom in media where the magnetic coupling to the field is prominent. Therefore, the field quantization requires an additional independent noise operator that is commuting with the conventional bosonic noise operator describing the polarization current fluctuations in dielectric media. In addition to allowing the detailed description of field fluctuations, our methods provide practical tools for modeling optical energy transfer and the formation of thermal balance in general dielectric and magnetic nanodevices. We use the QFED to investigate the magnetic properties of microcavity systems to demonstrate an example geometry in which it is possible to probe fields arising from the electric and magnetic source terms. We show that, as a consequence of the magnetic Purcell effect, the tuning of the position of an emitter layer placed inside a vacuum cavity can make the emissivity of a magnetic emitter to exceed the emissivity of a corresponding electric emitter

Noiseless amplification of weak coherent fields without external energy

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.Comment: arXiv admin note: substantial text overlap with arXiv:1309.428

Thermal balance and photon-number quantization in layered structures

The quantization of the electromagnetic field in lossy and dispersive dielectric media has been widely studied during the last few decades. However, several aspects of energy transfer and its relation to consistently defining position-dependent ladder operators for the electromagnetic field in nonequilibrium conditions have partly escaped the attention. In this work we define the position-dependent ladder operators and an effective local photon-number operator that are consistent with the canonical commutation relations and use these concepts to describe the energy transfer and thermal balance in layered geometries. This approach results in a position-dependent photon-number concept that is simple and consistent with classical energy conservation arguments. The operators are formed by first calculating the vector potential operator using Green's function formalism and Langevin noise source operators related to the medium and its temperature, and then defining the corresponding position-dependent annihilation operator that is required to satisfy the canonical commutation relations in arbitrary geometry. Our results suggest that the effective photon number associated with the electric field is generally position dependent and enables a straightforward method to calculate the energy transfer rate between the field and the local medium. In particular, our results predict that the effective photon number in a vacuum cavity formed between two lossy material layers can oscillate as a function of the position suggesting that also the local field temperature oscillates. These oscillations are expected to be directly observable using relatively straightforward experimental setups in which the field-matter interaction is dominated by the coupling to the electric field

Monte Carlo study of non-quasiequilibrium carrier dynamics in III–N LEDs

Hot carrier effects have been observed in recent measurements of III–Nitride (III–N) light-emitting diodes. In this paper we carry out bipolar Monte Carlo simulations for electrons and holes in a typical III–N multi-quantum well (MQW) LED. According to our simulations, significant non-quasiequilibrium carrier distributions exist in the barrier layers of the structure. This is observed as average carrier energies much larger than the 1.5kBT1.5kBT corresponding to quasi-equilibrium. Due to the small potential drop over the MQW being modest, the non-quasiequilibrium carriers can be predominantly ascribed to nnp and npp Auger processes taking place in the QWs. Further investigations are needed to determine the effects of hot carriers on the macroscopic device characteristics of real devices

Modeling transmitters, amplifiers and nonlinear circuits for the next generation optical networks

In the current optical networks nonlinear interaction of optical signals with matter is often a nuisance in the operation of amplifiers, optical fibers and other linear devices. The next generation optical networks, on the other hand, need nonlinear optical components with signal processing capabilities. To create components that meet the demands of tomorrow, it is necessary to understand, control, exploit and enhance the available weak nonlinearities. In this thesis the dynamic properties of quantum dot lasers and linear optical amplifiers are investigated. Additionally, optical memories and logic ports exploiting a new type of nonlinearity based on gain clamped optical amplifiers and interferometers are proposed. The properties of quantum dot lasers are studied by using a parametrized model for the bandstructure of the dots and the surrounding layers. The model is used to calculate the absorption spectrum, refractive index and other properties of the lasers at different excitation levels. The properties of linear optical amplifiers, conventional gain clamped amplifiers and semiconductor optical amplifiers are described by a stochastic traveling wave rate equation model. The gain clamped optical amplifiers used together with interferometers are shown to provide a new fast nonlinearity, which can be used to construct coherent nonlinear optical circuits, including optical regenerators, flip-flop memories and logic gates. The speed of the nonlinear devices presented in this thesis is limited by the modulation response of the gain clamped optical amplifiers above the laser threshold in the regime where there always is a large photon population in the laser mode. The speed may therefore reach values in excess of 100 GHz, or even higher values if the level of optical technologies evolves closer to the level of silicon technology. In principle the flip-flop structure developed in this thesis is suitable for integration.Optisten signaalien epälineaarinen vuorovaikutus väliaineen kanssa on usein ongelmallista optisten kuitujen, vahvistimien ja monien muiden optisten verkkojen komponenttien kannalta. Toisaalta seuraavan sukupolven optisissa verkoissa tarvitaan epälineaarisia signaalin käsittelyyn kykeneviä optisia komponentteja. Tulevaisuudessa tarvittavien komponenttien valmistamiseksi on tarpeen ymmärtää, hallita ja hyödyntää komponenteissa käytettyjen materiaalien heikkoja epälineaarisuuksia. Tässä väitöskirjassa on tutkittu kvanttipistelasereiden ja lineaaristen optisten vahvistimien dynamiikkaa. Lisäksi on kehitetty ja mallinnettu uudentyyppisiä optisia muisteja sekä logiikkaportteja, joiden toiminta perustuu vahvistuslukittujen optisten vahvistimien ja interferometrien epälineaarisiin ominaisuuksiin. Kvanttipistelasereiden ominaisuuksia on tutkittu käyttämällä parametrisoitua vyörakennemallia, jossa on huomioitu kvanttipisteiden lisäksi myös ympäröivät materiaalikerrokset. Vyörakennemallia käyttäen on laskettu kvanttipistelaserin absorptio- ja taitekerroinspektri sekä laserin muita ominaisuuksia erilaisilla varauksenkuljettajien injektiotasoilla. Lineaaristen optisten vahvistimien, perinteisten vahvistuslukittujen vahvistimien ja optisten puolijohdevahvistimien ominaisuuksia on kuvattu stokastisella etenevän aallon rate-yhtälömallilla. Koherenttien vahvistuslukittujen optisten vahvistimien käyttö yhdessä interferometrien kanssa mahdollistaa uudenlaisen nopean epälineaarisuuden, jonka avulla voidaan toteuttaa optisia piirejä kuten optisia regeneraattoreita, flip-flop muisteja ja logiikkaportteja. Väitöskirjassa kuvattujen epälineaaristen piirien nopeutta rajoittaa optisten vahvistuslukittujen vahvistimien modulaationopeus laserointikynnyksen yläpuolella alueella, jossa laseroivassa moodissa on jatkuvasti suuri fotonipopulaatio. Siitä johtuen epälineaarisuus voi toimia yli 100 GHz nopeudella, tai jopa nopeammin optisen teknologian tason kehittyessä lähemmäs piiteknologian tasoa. Väitöskirjassa kehitetyt komponentit soveltuvat periaatteessa integroitaviksi.reviewe

Lock-in thermography approach for imaging the efficiency of light emitters and optical coolers

Developing optical cooling technologies requires access to reliable efficiency measurement techniques and ability to detect spatial variations in the efficiency and light emission of the devices. We investigate the possibility to combine the calorimetric efficiency measurement principles with lock-in thermography (LIT) and conventional luminescence microscopy to enable spatially resolved measurement of the efficiency, current spreading and local device heating of double diode structures (DDS) serving as test vessels for developing thermophotonic cooling devices. Our approach enables spatially resolved characterization and localization of the losses of the double diode structures as well as other light emitting semiconductor devices. In particular, the approach may allow directly observing effects like current crowding and surface recombination on the light emission and heating of the DDS devices.Peer reviewe

Bipolar Monte Carlo Simulation of Hot Carriers In III-N LEDs

We carry out bipolar Monte Carlo (MC) simulations of electron and hole transport in a multi-quantum well light-emitting diode with an electron-blocking layer. The MC simulation accounts for the most important interband recombination and intraband scattering processes and solves self-consistently for the non-quasiequilibrium transport. The fully bipolar MC simulator results in better convergence than our previous Monte Carlo-drift-diffusion (MCDD) model and also shows clear signatures of hot holes. Accounting for both hot electron and hot hole effects increases the total current and decreases the efficiency especially at high bias voltages. We also present our in-house full band structure calculations for GaN to be coupled later with the MC simulation in order to enable even more detailed predictions of device operation

Photon momentum and optical forces in cavities

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 nonequilibrium 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