Polarization Drift Channel Model for Coherent Fibre-Optic Systems

A theoretical framework is introduced to model the dynamical changes of the state of polarization during transmission in coherent fibre-optic systems. The model generalizes the one-dimensional phase noise random walk to higher dimensions, accounting for random polarization drifts, emulating a random walk on the Poincar\'e sphere, which has been successfully verified using experimental data. The model is described in the Jones, Stokes and real four-dimensional formalisms, and the mapping between them is derived. Such a model will be increasingly important in simulating and optimizing future systems, where polarization-multiplexed transmission and sophisticated digital signal processing will be natural parts. The proposed polarization drift model is the first of its kind as prior work either models polarization drift as a deterministic process or focuses on polarization-mode dispersion in systems where the state of polarization does not affect the receiver performance. We expect the model to be useful in a wide-range of photonics applications where stochastic polarization fluctuation is an issue.Comment: 15 pages, 4 figure

Modeling and Compensation of Polarization Effects in Fiber-Optic Communication Systems

Optical communication systems that exploit the orthogonality between two polarizations of light convey information over optical fibers by modulating data over the two polarizations. In an idealized scenario, the two polarizations propagate through the fiber without interfering. However, this is not the case for practical fibers, which suffer from various imperfections that lead to polarization-related interference between the two polarizations. This thesis is concerned with polarization effects that arise in communication systems over optical fibers. In particular, we consider modeling and compensation of such effects, and their impact on and improvement of nonlinearity mitigation algorithms.The impact of an impairment on the performance of a transmission system can be understood via a channel model, which should describe the behavior of the channel as accurately as possible. A theoretical framework is introduced to model the stochastic nature of the state of polarization during transmission. The model generalizes the one-dimensional carrier phase noise random walk to higher dimensions, modeling the phase noise and state of polarization drift jointly as rotations of the electric field and it has been successfully verified using experimental data. Thereafter, the model is extended to account for polarization-mode dispersion and its temporal random fluctuations. Such models will be increasingly important in simulating and optimizing future systems, where sophisticated digital signal processing will be natural parts.The typical digital signal processing solution to mitigate phase noise and drift of the state of polarization consists of two separate blocks that track each phenomenon independently and have been developed without taking into account mathematical models describing the impairments. Based on the proposed model for the state of polarization, we study a blind tracking algorithm to compensate for these impairments. The algorithm dynamically recovers the carrier phase and state of polarization jointly for an arbitrary modulation format. Simulation results show the effectiveness of the proposed algorithm, having a fast convergence rate and an excellent tolerance to phase and polarization noise.The optical fiber is a nonlinear medium with respect to the intensity of the incident light. This effect leads to nonlinear interference as the intensity of light increases, which made nonlinear interference mitigation techniques to be an intensively studied topic. Typically, these techniques do not take into account polarization-mode dispersion, which becomes detrimental as the nonlinear effects interact with polarization-mode dispersion. We study digital-domain nonlinear interference mitigation algorithms that take into account polarization-mode dispersion by i) reversing the polarization effects concurrently with reversing the nonlinear effects and by ii) mitigating only the polarization-insensitive nonlinear contributions. These algorithms will be increasingly important in future optical systems capable of performing large bandwidth nonlinear interference mitigation, where even small amounts of polarization-mode dispersion become a limiting factor

Measuring coherence properties of exciton-polaritons with homodyne detection

Für die Quantentechnologie sind hybride Systeme gefragt, die verschiedene physikalische Systeme verbinden, z.B. ein Materiesystem zur Informationsverarbeitung und Licht zur Kommunikation. Für die Verbindung zwischen Halbleitern und Licht erforscht die Halbleiter-Quantenoptik, wie Licht den Quantenzustand des Halbleiters beeinflusst und wie der Zustand des Halbleiters über das emittierte Licht gemessen werden kann. Zur Messung des Quantenzustands von Licht wird in der Quantenoptik die vielseitige Methode der optischen Homodyn-Tomographie (OHT) verwendet. Ihre Anwendung auf die Emission von Halbleitern wird jedoch häufig durch das Fehlen einer festen Phasenreferenz für nicht-resonante Lumineszenz und durch die schnellen Zeitskalen des Systems verhindert. Diese Herausforderungen werden in dieser Arbeit angegangen. Wir stellen die Anwendung von OHT auf Halbleiterlumineszenz ohne feste Phasenreferenz vor, um die Kohärenz-Eigenschaften und den Quantenzustand zu untersuchen. Dabei ermöglichen ein gepulster Lokaloszillator und schnelle Detektoren eine hohe Zeitauflösung. Als Testumgebung für die Methode untersuchen wir die Emission eines Exziton-Polariton-Kondensats in einer GaAs-Mikrokavität. Konkret zeigt diese Arbeit, welche Informationen durch die Verwendung von einem, zwei und drei Homodyn-Detektionskanälen gewonnen werden können. Mit einem Kanal wird die Photonenkorrelationsfunktion zweiter Ordnung g(2)(0) gemessen, mit zwei Kanälen messen wir die phasengemittelte Husimi-Funktion und quantifizieren den Grad der Quantenkohärenz im Polaritonensystem, und mit drei Kanälen rekonstruieren wir die regularisierte P-Funktion abhängig von postselektierten Anfangsbedingungen und verfolgen den zeitlichen Zerfall der Quantenkohärenz.For quantum technology, hybrid systems are needed to connect different physical systems, e.g. a matter system for information processing and light for communication. For connecting semiconductors and light, semiconductor quantum optics investigates how light influences the quantum state of the semiconductor and how the state of the semiconductor can be measured via the emitted light. To measure the quantum state of light, optical homodyne tomography (OHT) is a versatile technique that is widely applied in quantum optics. But its application to semiconductor emission is often prevented by the lack of a fixed phase reference for nonresonant luminescence and by the fast time scales of the system. These challenges are tackled in this work. We present the application of OHT to semiconductor luminescence without a fixed phase reference in order to investigate coherence properties and the quantum state. Thereby, a pulsed local oscillator and fast detectors enable a high time resolution. As a testbed for the method, we investigate the emission from an exciton-polariton condensate in a GaAs microcavity. Specifically, this work shows which information can be gained by using one, two and three homodyne detection channels. With one channel, the second-order photon correlation function g(2)(0) is measured. Via two channels, we measure the phase-averaged Husimi function and quantify the amount of quantum coherence in the polariton system. With three channels, we reconstruct the regularized P function, depending on postselected initial conditions, and track the temporal decay of quantum coherence

Properties of III-Nitride-Based Polariton and Spin Polariton Diode Lasers

The cavity electrodynamic regime of strong coupling of emitter-photon interactions in a semiconductor microcavity gives rise to new light-matter entangled quasiparticles, also known as exciton-polaritons. The non-linear nature of the energy-momentum dispersions of these composite bosons has been suitably engineered and efficiently utilized to demonstrate inversionless coherent emission, or polariton lasing in submicron-scale optical cavities. Previous theoretical as well as experimental work on Gallium Arsenide and Cadmium Telluride-based systems operated at cryogenic temperatures, have shown the central importance of the nature of the output polarization of the emitted light originating from the radiative decomposition of these polaritons. Room-temperature operation of these lasers necessitates the use of wide-band gap semiconductors such as Gallium Nitride, because of their large free excitonic binding energies and oscillator strengths, which consequently lead to stronger and more robust exciton-photon strong coupling. Thus, the steady state output polarization characteristics of Gallium Nitride-based microcavity polariton lasers operated with unpolarized electrical injection, have been examined at room temperature. The output is essentially unpolarized below the nonlinear threshold injection current and is linearly polarized above it with a maximum degree of polarization of ∼ 22%. Besides other advantages, a spin-polarized laser offers inherent control of the output circular polarization. Electrical spin injection in a bulk Gallium Nitride-based microcavity polariton diode laser enables the realization of an electrically modulated low-energy circularly-polarized coherent light source. Successful electrical spin injection in bulk Gallium Nitride, which is the active layer of the polariton diode laser, has been independently confirmed from room-temperature four-terminal Hanlè spin precession measurements made on Gallium Nitride-based spin valves, and observation of hysteretic circular polarization in III-nitride-based light-emitting diodes. The optical selection rules governing the operation of the latter have also been elucidated. Electrical injection of spin polarized electrons is accomplished in all the above-mentioned devices via a n-type Cobalt Iron alloy/Magnesium Oxide spin injector contact. The output polarization characteristics of this polariton diode laser have been examined at room temperature. A degree of output circular (linear) polarization of ~ 25 (33) % is recorded under remanent magnetization. The helicity as well as the degree of the steady-state circular polarization is deterministically governed by the magnetizing field used to magnetize the ferromagnetic contacts. The variation of output circular and linear polarization with spin-polarized injection current has been analyzed employing two distinct spin-dependent rate equation models, and there is good agreement between measured and calculated data in both cases. The present work also theoretically explores other optoelectronic properties of these spin polariton lasers. Optical effects arising from spin-induced gain anisotropy such as threshold reduction and emission intensity enhancement have been theoretically predicted for these diode lasers. An electrical excitation mechanism has also been formulated, which can potentially magnify the degree of a deterministic circular polarization of the output emission by an order of magnitude, compared to the injected electron spin polarization. The dissertation concludes with the discussion of the observation of a non-linear enhancement in the excitation-dependent photocurrent characteristics of the microcavity diodes with a threshold, which is consistent with the polariton lasing threshold. This is explained in the framework of an Auger-like process of excitonic dissociation into its constituent electron-hole pairs, which can be stimulated by the occupation of the polariton lasing states and the observed effect is therefore a unique manifestation of the bosonic final-state stimulation effect in polariton lasers.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/145800/1/anirudb_1.pd

Spatial channel characterization for smart antenna solutions in FDD wireless networks

This paper introduces a novel metric for determining the spatial decorrelation between the up- and down-link wireless bearers in frequency division duplex (FDD) networks. This metric has direct relevance to smart or adaptive antenna array base-station deployments in cellular networks, which are known to offer capacity enhancement when compared to fixed coverage solutions. In particular, the results presented were obtained from field trial measurement campaigns for both urban and rural scenarios, with the observations having a direct impact on the choice of down-link beamforming architecture in FDD applications. Further, it is shown that significant spatial decorrelation can occur in urban deployments for bearer separations as small as 5 MHz. Results are presented in terms of both instantaneous characteristics as well as time averaged estimates, thus facilitating the appraisal of smart antenna solutions in both packet and circuit switched network

Frequency and time profiles of metric wave isolated Type I solar noise storm bursts at high spectral and temporal resolution

Type I noise storms constitute a sizeable faction of the active-Sun radio emission component. Observations of isolated instances of such bursts, in the swept-frequency-mode at metric wavelengths, have remained sparse, with several unfilled regions in the frequency coverage. Dynamic spectra of the burst radiation, in the 30 - 130 MHz band, obtained from the recently commissioned digital High Resolution Spectrograph (HRS) at the Gauribidanur Radio Observatory, on account of the superior frequency and time resolution, have unravelled in explicit detail the temporal and spectral profiles of isolated bursts. Apart from presenting details on their fundamental emission features, the time and frequency profile symmetry, with reference to custom-specific Gaussian distributions, has been chosen as the nodal criterion to statistically explain the state of the source regions in the vicinity of magnetic reconnections, the latent excitation agent that contributes to plasma wave energetics, and the quenching phenomenon that causes damping of the burst emission.Comment: 9 pages 7 black and white / grey-scale figures (inclusive of 3 composite). MNRAS - accepte