Efficient Simulation of 3D Electro-optical Waveguides Using the Effective Refractive Index Method

Abstract: 3D FEM simulation of millimeterscale, complex electro-optically induced waveguide based devices demands the use of grids with more than several million nodes. Hence, the simulation could take substantial time and require large amounts of available memory. This paper presents a computation algorithm based on the conversion of an initial 3D waveguide structure into an analogous 2D structure, where the wave propagation on the 'reduced' dimension is described by an effective refractive index. It is shown that with the proposed algorithm the computing efficiency could be improved. Moreover the algorithm could be successfully used to simulate large-size passive or electro-optically active waveguide structures. For an electro-optical waveguide coupler, we could demonstrate a good agreement between simulated and calculated coupling length

Overcoming asymmetrical communication delays in line current differential protection circuits

Communications asymmetry leads to current differential protection relay misoperation by causing relays at either end of a power line to sample load current waveforms at different moments in time. The increased use of current differential protection and developments in communication technologies in power systems has led to the increase likelihood of relay misoperation due to communication delay asymmetry. The main cause of communication delay asymmetry is split-path-communications, whereby transmit and receive directions of a communications channel take separate paths with different delays. Split-path-communications are the result of faults in one direction of a communications channel, causing that direction only to switch from main to alternate paths. This project studies AusNet Services’ communications network and those similar to it, to find the typical sources of communication delays. Delays are measured between a variety E1 interfaces in the AusNet Services network, and the results used to calculate the per unit delays through given types of cross-connections. These are used in conjunction with a current differential relay response calculator, to create a model that displays a relay’s response to a communications channel with specified attributes. The chance of split-path-communications can be avoided by using communications equipment with bidirectional switching capabilities. The Avara DB4 family of branching E1 cards have this capability; however, this project reveals that a fault in the DB4 firmware code means that they may still cause protection relays to misoperate due to asymmetry. The DB4 firmware was updated, and further testing proved that it now prevented relay misoperation

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

Utilising optical Kerr microresonators for polarisation control, logic gates, and quantum optics applications

When high intensities of light are focused inside of a medium, strange effects occur. Light can self-interact. It can be slowed down based on how bright it is, it can be made to go in one direction but not the other, and it can even be made to c change colour. It is hard to imagine how the world would look if these were effects that we experienced in our everyday lives. Fortunately, it takes a significant amount of effort to make the conditions right for such events to occur, specifically, with high optical intensities required. This thesis details some of these efforts. In this work, I present some applications of Kerr microresonantor based nonlinear and quantum optics. Microresonators are minute devices that can be integrated in photonic circuits. They trap and guide light on a repeating path, with each roundtrip leading to an increase in intensity until nonlinear effects start to occur. I start by explaining how such resonators work, are fabricated, and how nonlinear effects can manifest. Next, an all-optical polarisation controller is introduced, in which the nonlinear splitting of otherwise degenerate polarisation modes is employed. This device could find application in integrated photonic circuits that require fast response times. A similar effect, but this time for counter-propagating light, is then used to demonstrate an all-optical, universal logic gate. Interestingly, a set of such logic gates could be used for the on-chip routing of optical signals to provide low-latency communications for telecoms and distributed computing. Finally, the quantum nature of these nonlinearities is explored, first with the calculation of multi-modal entanglement metrics before then discussing work that is progressing towards a single-photon source. These phenomena show promise for integration into future quantum technologies, in particular in secure quantum communications and for state generation for quantum information processing.Open Acces