Optical Communication

Optical communication is very much useful in telecommunication systems, data processing and networking. It consists of a transmitter that encodes a message into an optical signal, a channel that carries the signal to its desired destination, and a receiver that reproduces the message from the received optical signal. It presents up to date results on communication systems, along with the explanations of their relevance, from leading researchers in this field. The chapters cover general concepts of optical communication, components, systems, networks, signal processing and MIMO systems. In recent years, optical components and other enhanced signal processing functions are also considered in depth for optical communications systems. The researcher has also concentrated on optical devices, networking, signal processing, and MIMO systems and other enhanced functions for optical communication. This book is targeted at research, development and design engineers from the teams in manufacturing industry, academia and telecommunication industries

Hybrid entanglement for quantum communication

A dissertation submitted to the Faculty of Science in partial fulfillment of the requirements for the Degree of Master of Science School of Physics University of Witwatersrand November 1, 2017The generation and detection of entangled photons is a topic of interest in quantum communication. With current state-of-the-art methods it is possible to manipulate any degree of freedom (DoF) of photons, e.g, polarisation, transverse momentum, orbital angular momentum and energy. Furthermore, it is possible to combine these DoF to realise hybrid entanglement { entanglement between the DoF of photons. In this dissertation we focus on hybrid entanglement between photon states of coupled orbital angular momentum and polarisation. We engineer hybrid-entanglement using geometric phase control between spatially separated photons produced from spontaneous parametric down conversion. We present a new type of quantum eraser that does not rely on physical path interference. We show that in principle any other degree of freedom can be used and demonstrate this e ectively through polarisation control. The use of high dimensional hybrid photon states in quantum communication, particularly in quantum cryptography, is still in its infancy. Here we tailor photon states that are coupled in their polarisation and spatial DoF (orbital angular momentum) to realise high dimensional encoding alphabets. We show how photons entangled in their internal DoF can be generated and deterministically detected. We exploit them in a demonstration of a high dimensional quantum key distribution protocol and show that our scheme generates secure keys at high rates.MT 201

Síntesi de camps vectorials de llum amb polarització tridimensional no uniforme mitjançant holografia digital

[cat] La introducció dels feixos amb polaritzacions no uniformes ha aportat grans avenços en multitud d'àrees. En un nivell més fonamental, ha permès entendre la naturalesa de la llum d'una manera més amplia, estenent les teories òptiques conegudes, com ('escalar, a d'altres més precises com la vectorial. La síntesi de feixos amb una distribució no uniforme de la polarització segueix sent una tasca desafiant. Mentre que algunes tècniques utilitzen sistemes totalment òptics, en aquesta tesi, s'ha optat per incorporar dispositius optoelectrònics per modular la llum, obtenint així una major flexibilitat a la hora de dissenyar el feix. Per altra banda, el muntatge òptic utilitzat està basat en un interferòmetre de Mach-Zehnder per tal de manipular les dues components del feix, d'una manera independent, en cada braç de l'interferòmetre. D'aquesta manera, utilitzant en cada braç de l'interferòmetre un modulador de cristall líquid, tenim la capacitat de modular ambdues components del feix incident. Aquests moduladors són els proporcionats per Holoeye, concretament el model HEO 0017, els quals treballen en transmissió. Compten amb una configuració pixelada, dotant-nos d'una capacitat de modulació espacial amb una resolució de 32gm. Complementant aquesta modulació amb una tècnica d'holografia digital, som capaços de modular tant l'amplitud com la fase d'ambdues components del camp i, per tant, d'esculpir qualsevol forma amb qualsevol distribució de la polarització. Per tal de mostrar aquesta flexibilitat, s'ha sintetitzat un conjunt de feixos amb diversos perfils i diverses distribucions de la polarització. Els feixos generats s’han avaluat mitjançant un analitzador, compost d’una làmina retardadora λ/4 i un polaritzador lineal, enfront d’una càmera CCD de 14 bits de rang dinàmic del model Stingray F080B A5G. D’aquesta manera, s’han obtingut les distribucions dels paràmetres d’Stokes en el pla de la càmera. Aprofitant aquesta capacitat de modulació, s’ha dissenyat una tècnica d’encriptació hologràfica utilitzant el mateix sistema òptic amb lleugeres modificacions. Les claus secretes, que garanteixen la seguretat en la codificació, són màscares de polarització. Per incrementar el nivell de seguretat del sistema, s’han afegit dos paràmetres físics necessaris per poder desencriptar la informació. A més, s’ha simulat, sobre els resultats experimentals obtinguts, la resposta del sistema sota condicions de molt baixa il·luminació. Aquestes condicions, sovint utilitzades en treballs previs, augmenten significativament la robustesa del mètode d’encriptació. Un cop garantida la correcta manipulació d’ambdues components d’un feix paraxial, s’ha procedit a desenvolupar un marc teòric per sintetitzar feixos altament focalitzats amb una polarització tridimensional arbitrària. Per tal d’obtenir aquests feixos, s’ha utilitzat un objectiu de microscopi amb una obertura numèrica de NA=0.85, on s’ha modulat el camp en la pupil·la d’entrada mitjançant el mètode hologràfic anterior. El disseny del camp en la zona focal, en funció de la distribució de la polarització en la pupil·la d’entrada, s’ha realitzat en el marc de la teoria vectorial desenvolupada per B. Richards i E. Wolf. Per avaluar el funcionament del sistema, s’ha sintetitzat un feix altament focalitzat amb polarització circular en qualsevol pla, i s’ha comparat els resultats obtinguts experimentalment amb els extrets numèricament. La definició del grau de polarització en feixos altament focalitzats, encara ara, genera certs debats degut a que no es pot expandir d’una manera inequívoca com una suma directa del camp totalment polaritzat i del camp totalment despolaritzat. En aquesta tesi, hem fet l’estudi en el marc dels paràmetres d’Stokes generalitzats, obtenint una correspondència entre la distribució del paràmetres d’Stokes en la pupil·la d’entrada i la distribució del paràmetres d’Stokes de la contribució transversal del camp focalitzat. S’ha proposat un feix paraxial, que, un cop focalitzat, genera un camp amb les components transversals despolaritzades i que compta amb una component longitudinal no nul·la. Aquests tipus de feixos són de gran utilitat, entre d’altres camps, en la confecció de capes de invisibilitat.[eng] Non uniformly polarized beams have provided great strides in many areas. The synthesis of arbitrary polarized beams remains a challenging task. While some techniques use full optics systems, in this dissertation we introduce a system where optoelectronic devices modulate the light, providing more flexibility in the beam design. Complementing this modulation with a digital holography method, we modulate both amplitude and phase of the field. Moreover, the optical assembly is based on a Mach-Zehnder interferometer where the two components of the field can be independently manipulated in each arm of the interferometer. Applying an arbitrary modulation in both compontents, we can sculpt any profile with any distribution of polarization. To show this flexibility, a set of beams with multiple profiles and polarization distribution have been presented. In addition, taking this modulation capability, we introduce an holographic encryption technique where the secret keys are polarization masks. Two physical parameters are necessary to decrypt the information, increasing the security of the system. We have simulated the system response under very low illumination. Once guaranteed the flexibility in the design of paraxial beams with arbitrary polarization distribution, a theoretical framework to synthesize highly focused beams with an arbitrary three-dimensional polarization has been developed. The B. Richards y E. Wolf theory relates the polarization distribution on the entrance pupil of a microscope objective with the vectorial structure of the field in the focal region. To evaluate the performance of the system we have implemented a highly focused beam (NA=0.85) with circular polarization in any plane. The definition of the degree of polarization in highly focused beams even now generates some discussion because it can not be expanded unequivocally as a direct sum of completely polarized fields and completely depolarized fields. In this thesis, we have made the study within the frame of generalized Stokes parameters. We have obtained a correspondence between the distribution of the Stokes parameters in the entrance pupil and the distribution of the transverse Stokes parameters in the focused field. We have proposed a paraxial beam, which once focused, it generates a field with the transverse components depolarized and a non-zero longitudinal component

Doppler Encoded Excitation Patterning (DEEP) Microscopy

Traditional optical imaging systems rely on lenses and spatially-resolved detection to probe distinct locations on the object. We develop a novel computational approach to 2D and 3D imaging that instead measures the object\u27s spatial Fourier transform using a single-element detector and without requiring precision optics. This wide-field technique can be used to image biological and synthetic structures in fluoresced or scattered light using coherent or broadband illumination. It employs dynamic structured illumination, acousto-optics, RF electronics, and tomographic algorithms to circumvent several trade-offs in conventional imaging, such as the dependence of the optical transfer function on the imaging lenses and the coupling of resolution and depth of field. We use Fourier optics concepts to derive the dynamic optical transfer function, evaluate different Fourier sampling strategies, and investigate and compare tomographic algorithms for 2D and 3D image synthesis. We also develop conceptual and analytical models to describe imaging of fluorescent as well as amplitude and phase scattering objects, the effects of broadband and spatially-incoherent illumination, and nonlinear wide-field super-resolution imaging. We consider sources of noise, analyze and simulate SNR behavior for several types of noise and Fourier sampling strategies, and compare the sensitivity of the technique to conventional imaging. We describe several experimental proof-of-concept systems and present two-dimensional high-resolution tomographic image reconstructions in both scattered and fluoresced light demonstrating a thousandfold improvement in the depth of field compared to conventional lens-based microscopy. Finally, we explore approaches for high-speed Fourier sampling and propose several related sensing techniques, including wide-field fluorescence imaging in scattering media

Telecommunication Systems

This book is based on both industrial and academic research efforts in which a number of recent advancements and rare insights into telecommunication systems are well presented. The volume is organized into four parts: "Telecommunication Protocol, Optimization, and Security Frameworks", "Next-Generation Optical Access Technologies", "Convergence of Wireless-Optical Networks" and "Advanced Relay and Antenna Systems for Smart Networks." Chapters within these parts are self-contained and cross-referenced to facilitate further study

Optical angular momentum in air core fibers

As data consumption continues to grow, the backbone of the internet, comprising single mode fiber (SMF)-based infrastructure, is fundamentally limited by nonlinear optical effects. One strategy to address this bottleneck, space division multiplexing (SDM), utilizes multiple modes in a single fiber as independent data channels. Orbital Angular Momentum (OAM) carrying modes, which have twisting phase fronts tracing out helices as the beams propagate, have recently received tremendous attention as a means of achieving low-crosstalk, digital signal processing (DSP)-free transmission with enhanced capacity. Terabit-scale transmission using 4 OAM modes over 1.1km has been demonstrated, but questions remain – how many OAM modes can fibers support, and how stable is propagation over longer lengths? In this thesis, we investigate angular momentum carrying modes in a novel class of fibers featuring an air core. We find that high-order OAM states, although arising in degenerate pairs, counterintuitively resist mode coupling due to OAM conservation, pointing to a unique stability inherent to OAM modes in fibers. We achieve OAM propagation up to 13.4km lengths, and achieve mode purities greater than 15dB at data-center length-scales. We use these fibers to transmit wavelength-division multiplexed data with 25 GHz channel spacing, 10 GBaud rates and quadrature-phase-shift keyed modulation formats in 12 modes simultaneously, over 1.2km, and over a large number of wavelengths across the C-band (1530-1565nm). However, transmission over every mode in every channel of the C-band was prevented by the accidental degeneracy of OAM states with undesired modes. To achieve a larger ensemble of stable modes over a larger wavelength range, we study new fiber designs that avoid this accidental degeneracy problem. We find that the most scalable modal eigenbasis is a set of states that carry non-integer amounts of average OAM, also called spin-orbit coupled modes in analogy with similar effects observed in atomic physics. We demonstrate excitation and transmission of 24 such modes over device lengths (10m). The achievement of a record number of uncoupled modes in fibers confirms the viability of angular momentum states as data carriers, and potential applications include links in data centers, high capacity optical amplifiers, and quantum communications links.2017-09-09T00:00:00

Optics in Our Time

Optics, Lasers, Photonics, Optical Devices; Quantum Optics; Popular Science in Physics; History and Philosophical Foundations of Physic

Recent Progress in Optical Fiber Research

This book presents a comprehensive account of the recent progress in optical fiber research. It consists of four sections with 20 chapters covering the topics of nonlinear and polarisation effects in optical fibers, photonic crystal fibers and new applications for optical fibers. Section 1 reviews nonlinear effects in optical fibers in terms of theoretical analysis, experiments and applications. Section 2 presents polarization mode dispersion, chromatic dispersion and polarization dependent losses in optical fibers, fiber birefringence effects and spun fibers. Section 3 and 4 cover the topics of photonic crystal fibers and a new trend of optical fiber applications. Edited by three scientists with wide knowledge and experience in the field of fiber optics and photonics, the book brings together leading academics and practitioners in a comprehensive and incisive treatment of the subject. This is an essential point of reference for researchers working and teaching in optical fiber technologies, and for industrial users who need to be aware of current developments in optical fiber research areas

Quantum information with structured light

We investigate structured photons as carriers of quantum information. We describe our implementation of quantum cryptography with orbital angular momentum, and present our results on efficient implementation of quantum state tomography for structured light fields