Semiconductor-based all-optical switching for optical time-division multiplexed networks

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.Includes bibliographical references.All-optical switching will likely be required for future optical networks operating at data rates which exceed electronic processing speeds. Switches utilizing nonlinearities in semiconductor optical amplifiers (SOA) are particularly attractive due to their compact size, low required switching energies, and high potential for integration. In this dissertation we investigate the practical application of such semiconductor-based all-optical switches in next-generation optical networks. We present both theoretical and experimental studies of SOA-based interferometric switches. A detailed numerical model for the dynamic response of an SOA to an intensity-modulated optical signal is described. The model is validated using novel pump-probe techniques to measure the time-domain response of an SOA subject to various levels of saturation. The model is then used to evaluate the performance of three common SOA-based interferometric all-optical switches. The use of SOAs in optical transmission systems has been limited due to the deleterious effects of pattern-dependent gain saturation. We develop a statistical model to study the system impact of variations of the SOA optical gain in response to a random intensity-modulated optical signal. We propose the use of pulse-position modulation (PPM) as a means for mitigating gain saturation effects in SOA-based optical processors. We present techniques for modulation and detection of optical PPM signals at data rates in excess of 100 Gbit/s. We demonstrate demultiplexing, wavelength conversion, and format conversion of optical PPM signals at data rates as high as 80 Gbit/s. Finally, we report on experimental demonstrations of an optical interface for slotted OTDM networks.(cont.) We implement head-end and transmitter nodes capable of producing fully loaded optical slots at an aggregate network data rate of 112.5 Gbit/s. We demonstrate a fully functional receiver node which utilizes semiconductor-based all-optical logic for synchronization, address processing, and rate conversion.by Bryan S. Robinson.Ph.D

Optical time domain add-drop multiplexing employing fiber nonlinearities

Het in dit proefschrift beschreven onderzoek richt zich op het ontrafelen van in het tijdsdomein gestapelde optische signalen, ook wel optical time division multiplexing (OTDM) genoemd, en de bijbehorende technologische uitdagingen. Dit werk richt zich in het bijzonder op het toevoegen en extraheren van een specifieke datastroom uit een OTDM signaal. De component die deze functie uitvoert kan worden aangeduid als een add-drop multiplexer (ADM). Deze ADMs kunnen worden onderverdeeld in twee categorieën. De eerste categorie is gebaseerd op oplossingen die gebruik maken van halfgeleider materiaal en de tweede categorie benut de niet-lineariteit van een glasvezel. Een onderzochte halfgeleider materiaal ADM techniek is gebaseerd op het crossabsorption modulation (XAM) effect in een electro-absorptie modulator (EAM). Een model, gebaseerd op propagatie-vergelijkingen in halfgeleider materiaal, is ontwikkeld om de invloed van het XAM effect te kunnen simuleren. Resultaten verkregen met dit model komen goed overeen met experimenteel verkregen resultaten. Foutvrij extraheren (demultiplexen) van een 10 Gb/s datakanaal uit een 80 Gb/s OTDM signaal, met behulp van XAM in een EAM is experimenteel aangetoond. Een nieuw concept genaamd cross-polarisatie rotatie (XPR) is geïntroduceerd om het contrast ratio van de EAM demultiplexer te verbeteren. Ondanks verbetering van het contrast ratio van de demultiplexer is er geen significante verbetering van de prestatie waarneembaar. Mogelijkheden om de EAM in een 160 Gb/s demultiplexer configuratie te gebruiken zijn onderzocht. De kwaliteit van de EAM als optische schakelaar is sterk afhankelijk van het maximaal toegestane ingangsvermogen. Een hoger vermogen van het optische kloksignaal leidt tot een sterker absorptie verzadigingseffect. De snelheid van de EAM als optische schakelaar is begrensd door de hersteltijd van de vrije elektronen en gaten in de halfgeleider, gezamenlijk de carriers genoemd. Een verhoging van de negatieve biasspanning leidt tot een verkorting van de carrier hersteltijd. Een nadeel van het gebruik van een hogere biasspanning is de bijkomende hogere absorptie wat resulteert in een hoger vereist ingangsvermogen om de absorptie te verzadigen, omdat anders een verslechtering van de signaal-ruis verhouding onvermijdelijk is. Een belangrijk deel van het proefschrift richt zich op ADMs die de niet-lineariteit van een glasvezel benutten. Een van de meest veelbelovende oplossingen is gebaseerd op de nonlinear optical loop mirror (NOLM). Een geheel optische tijdsdomein ADM gebaseerd op een NOLM structuur is voor het eerst gedemonstreerd op datasnelheden boven de 80 Gb/s. Simulaties en experimenteel onderzoek zijn uitgevoerd op 160 Gb/s en 320 Gb/s. De prestatie limiterende factoren in de NOLM gebaseerde ADM zijn overspraak van naburige kanalen voor het extraheren van een kanaal en incomplete verwijdering van het geëxtraheerde kanaal voor het toevoegen van een nieuw kanaal. De jitter op het controle- en datasignaal en een niet geoptimaliseerde NOLM ingangskoppelaar verslechteren de kwaliteit van de ADM. De behaalde resultaten openen mogelijkheden om in de toekomst het systeem op te waarderen naar 640 Gb/s. De conversie van twee 10 Gb/s non-return to zero (NRZ) golflengte gestapelde kanalen (WDM) naar één 20 Gbs return-to-zero (RZ) OTDM signaal is experimenteel gekarakteriseerd. Het conversie principe is gebaseerd op four-wave mixing (FWM) in een sterk niet-lineare vezel (HNLF). Een voordeel van deze conversie techniek is dat er geen extra NRZ naar RZ conversiestap vereist is. Een tweede voordeel is de transparantie van FWM ten opzichte van de gebruikte modulatie techniek. Zo is deze techniek bijvoorbeeld ook geschikt voor fasegemoduleerde datasignalen. De beperkingen van deze conversie techniek zijn onderzocht. Conversie van 2x10 Gb/s WDM naar 20 Gb/s OTDM is experimenteel aangetoond, maar simulaties wijzen uit dat deze techniek niet geschikt is voor conversie van 4x40 Gb/s WDM naar 160 Gb/s OTDM, omdat het optische vermogen van het geconverteerde signaal erg laag is als gevolg van de lage efficiëntie van het FWM proces. Een alternatieve ADM techniek die ook bestudeerd is, is gebaseerd op cross-phase modulatie (XPM) spectrale verbreding in combinatie met filtering. Het voordeel van deze techniek is het geringere aantal benodigde componenten voor de constructie van een complete ADM in vergelijking met een ADM gebaseerd op een NOLM of een Kerr shutter. Simulaties en experimenteel werk demonstreren de mogelijkheden van deze techniek. Een geheel optische tijddomein ADM voor fasegemoduleerde signalen is voor de eerste maal aangetoond. Add-drop multiplexing van een 80 Gb/s RZ-DPSK OTDM signaal gebaseerd op de Kerr shutter met 375 meter HNLF is experimenteel gedemonstreerd. De fase-informatie in het signaal is behouden in de complete ADM. Praktische beperkingen in de experimentele set-up begrensden de datasnelheid tot 80 Gb/s. Een ADM experiment op 320 Gb/s met amplitude gemoduleerde signalen geeft een indicatie van de mogelijkheden van de Kerr shutter als ultrasnelle schakelaar

Optical pulse generation and signal processing for the development of high-speed OTDM networks

Due to the continued growth of the Internet and the introduction of new broadband services, it is anticipated that individual channel data rates may exceed lOOGbit/s in the next 5-10 years. In order to operate at such high line rates new techniques for optical pulse generation and optical signal processing will have to be developed. As the overall data rate of an OTDM network is essentially determined by the temporal separation between data channels, an optical pulse source that is capable of producing ultra-short optical pulses at a high repetition rate and with wavelength tunability will be important, not only for OTDM, but for vanous applications in WDM and hybrid WDM/OTDM networks. This work demonstrates that by using the gain-switching technique, commercially available laser diodes can be used in the development of nearly transform-limited optical pulses that are wavelength tunable over nearly 65nm with durations ranging from 12-30ps and a Side-Mode Suppression Ratio (SMSR) exceeding 60dB. New optical signal processing techniques will also have to be developed in order to operate at individual data rates in excess of lOOGbit/s. Only nonlinear optical effects, present in fibres, semiconductors and optical crystals, can be employed as these occur on time scales in the order of a few-femtoseconds (10“15 5), with an example being Two-Photon Absorption (TPA) in semiconductors. This thesis describes a specially designed microcavity that can enhance the Two-Photon Absorption (TPA) response by over three orders of magnitude at specific wavelengths. A theoretical model demonstrating error-free demultiplexing of a 250Gbit/s OTDM signal via a TPA microcavity has been developed. Experimental work is also presented demonstrating the use of a TPA microcavity for optical sampling of 100GHz signals with a temporal resolution of 1 ps9 and system sensitivity of 0 009 (mW)2 This value for the sensitivity is the lowest ever reported for a TPA-based sampling system

Generation and optimization of picosecond optical pulses for use in hybrid WDM/OTDM networks

The burgeoning demand for broadband services such as database queries, home shopping, video-on-demand, remote education, telemedicine and videoconferencing will push the existing networks to their limits. This demand was mainly fueled by the brisk proliferation of Personal Computers (PC) together with the exceptional increases in their storage capacity and processing capabilities and the widespread availability of the internet. Hence the necessity, to develop high-speed optical technologies in order to construct large capacity networks, arises. Two of the most popular multiplexing techniques available in the optical domain that are used in the building of such high capacity networks, are Wavelength Division Multiplexing (WDM) and Optical Time Division Multiplexing (OTDM). However merging these two techniques to form very high-speed hybrid WDM/OTDM networks brings about the merits of both multiplexing technologies. This thesis examines the development of one of the key components (picosecond optical pulses) associated to such high-speed systems. Recent analysis has shown that RZ format is superior to conventional NRZ systems as it is easier to compensate for dispersion and nonlinear effects in the fibre by employing soliton-like propagation. In addition to this development, the use of wavelength tunability for dynamic provisioning is another area that is actively researched on. Self-seeding of a gain switched Fabry Perot laser is shown to one of the simplest and cost effective methods of generating, transform limited optical pulses that are wavelength tunable over very wide ranges. One of the vital characteristics of the above mentioned pulse sources, is their Side Mode Suppression Ratio (SMSR). This thesis examines in detail how the pulse SMSR affects the performance of high-speed WDM/OTDM systems that employ self-seeded gain-switched pulse sources

High speed nonlinear optical components for next-generation optical communications

Electronic signal processing systems currently employed at core internet routers require huge amounts of power to operate and they may be unable to continue to satisfy consumer demand for more bandwidth without an inordinate increase in cost, size and/or energy consumption. Optical signal processing techniques may be deployed in next-generation optical networks for simple tasks such as wavelength conversion, demultiplexing and format conversion at high speed (≥100Gb.s-1) to alleviate the pressure on existing core router infrastructure. To implement optical signal processing functionalities, it is necessary to exploit the nonlinear optical properties of suitable materials such as III-V semiconductor compounds, silicon, periodically-poled lithium niobate (PPLN), highly nonlinear fibre (HNLF) or chalcogenide glasses. However, nonlinear optical (NLO) components such as semiconductor optical amplifiers (SOAs), electroabsorption modulators (EAMs) and silicon nanowires are the most promising candidates as all-optical switching elements vis-à-vis ease of integration, device footprint and energy consumption. This PhD thesis presents the amplitude and phase dynamics in a range of device configurations containing SOAs, EAMs and/or silicon nanowires to support the design of all optical switching elements for deployment in next-generation optical networks. Time-resolved pump-probe spectroscopy using pulses with a pulse width of 3ps from mode-locked laser sources was utilized to accurately measure the carrier dynamics in the device(s) under test. The research work into four main topics: (a) a long SOA, (b) the concatenated SOA-EAMSOA (CSES) configuration, (c) silicon nanowires embedded in SU8 polymer and (d) a custom epitaxy design EAM with fast carrier sweepout dynamics. The principal aim was to identify the optimum operation conditions for each of these NLO device configurations to enhance their switching capability and to assess their potential for various optical signal processing functionalities. All of the NLO device configurations investigated in this thesis are compact and suitable for monolithic and/or hybrid integration

Channel-tunable mode-locked laser transmitter for OTDM networks and modeling of mode-locked semiconductor laser.

by Hung Wai.Thesis (M.Phil.)--Chinese University of Hong Kong, 2000.Includes bibliographical references (leaves 69-[73]).Abstracts in English and Chinese.Chapter 1 --- Introduction --- p.1Chapter 1.1 --- All Optical Multi-Access Network --- p.1Chapter 1.2 --- Multi-access Techniques --- p.2Chapter 1.2.1 --- Wavelength-Division Multi-access (WDMA) --- p.2Chapter 1.2.2 --- Subcarrier Multi-Access (SCMA) --- p.3Chapter 1.2.3 --- Time-Division Multi-Access(TDMA) --- p.3Chapter 1.3 --- Numerical Modelling of Semiconductor Mode-locked laser --- p.4Chapter 1.4 --- Objective of this Thesis --- p.5Chapter 2 --- Optical TDMA networks --- p.7Chapter 2.1 --- Introduction --- p.7Chapter 2.2 --- OTDM --- p.8Chapter 2.3 --- Network Architecture --- p.9Chapter 2.3.1 --- Broadcast Networks --- p.9Chapter 2.3.2 --- Switch-based networks --- p.10Chapter 2.4 --- Key technologies for optical TDMA Network --- p.13Chapter 2.4.1 --- High Repetition Rate Short Pulse sources --- p.13Chapter 2.4.2 --- Multiplexer and de-multiplexers --- p.15Chapter 2.4.3 --- Optical Clock Recovery --- p.17Chapter 2.4.4 --- All optical logic gates --- p.18Chapter 2.5 --- Summary --- p.19Chapter 3 --- A Channel-Tunable Mode-locked Laser Transmitter for OTDM Networks --- p.20Chapter 3.1 --- Introduction --- p.20Chapter 3.2 --- Principle of Operation --- p.21Chapter 3.3 --- Experimental Demonstration --- p.23Chapter 3.4 --- The Channel Tuning Transient --- p.25Chapter 3.5 --- Experimental Investigation of channel-tuning transient --- p.28Chapter 3.6 --- Summary --- p.37Chapter 4 --- Modeling of Mode-Locked Semiconductor Laser --- p.38Chapter 4.1 --- Introduction --- p.38Chapter 4.2 --- Principle of Mode-Locking --- p.39Chapter 4.3 --- Simulation Model --- p.41Chapter 4.3.1 --- Travelling Wave Rate Equation Analysis --- p.41Chapter 4.3.2 --- Large Signal Time Domain Mode-locked Laser Model --- p.42Chapter 4.3.3 --- Modeling of Spontaneous Noise --- p.44Chapter 4.3.4 --- Modeling of Self-phase Modulation --- p.44Chapter 4.3.5 --- Frequency Dependent Gain Profile --- p.45Chapter 4.3.6 --- Computation Procedure --- p.45Chapter 4.4 --- Device Parameters --- p.47Chapter 4.5 --- Simulation Results on Passive Mode-locking --- p.48Chapter 4.5.1 --- Pulse Repetition Rate under Passive Mode-locking --- p.48Chapter 4.5.2 --- The effect of Differential Gain and Differential Absorption on Mode-locking Regimes --- p.50Chapter 4.5.3 --- The Effects of Linewidth Enhancement Factor and Ab- sorber Carrier Lifetime on Mode-locking Pulse Width --- p.53Chapter 4.6 --- Simulation Results on Hybrid and Subharmonic Mode-locking --- p.54Chapter 4.6.1 --- Modeling the Effect of Modulation on Absorber Section --- p.54Chapter 4.6.2 --- Modulation Phase Change Dynamics --- p.55Chapter 4.6.3 --- Subharmonc Mode-Locking Induced Amplitude Modulation --- p.62Chapter 4.7 --- Summary --- p.64Chapter 5 --- Conclusion --- p.66Chapter 5.1 --- Summary of the Thesis --- p.66Chapter 5.2 --- Future Work --- p.67Bibliography --- p.6

Optical pulse processing towards Tb/s high-speed photonic systems

Due to the continued growth of high-bandwidth services provided by the internet, there is a requirement to operate individual line rates in excess of 100 Gb/s in next generation optical communications systems. Thus, to implement these high-speed optical networks all-optical processing techniques are necessary for pulse shaping and pulse routing. Two sub-systems (pulse generation and wavelength conversion), which exploit optical processing techniques are explored within this thesis. Future systems will require high-quality pulse sources and this thesis develops the pulse generation technique of gain switching to provide simple and cost efficient pulse sources. The poor pulse quality typically associated with gain switching is enhanced by developing all-optical methods. The main attribute of the first pulse generation scheme presented is its wavelength tunability over 50 nm. The novelty of the second scheme lies in the ability to design a grating which has a nonlinear chirp profile exactly opposite to the gain-switched pulses. This grating used in conjunction with the gain-switched laser generates transform limited pulses suitable for 80 Gb/s systems. Furthermore the use of a vertical microcavity-based saturable absorber to suppress detrimental temporal pulse pedestals of a pulse source is investigated. Next generation networks will require routing of data in the optical domain, which can be accomplished by high-speed all-optical wavelength converters. A semiconductor optical amplifier (SOA) is an ideal device to carry out wavelength conversion. In this thesis pulses following propagation through an SOA are experimentally characterised to examine the temporal and spectral dynamics due to the nonlinear response of the SOA. High-speed wavelength conversion is presented using SOA-based shifted filtering. For the first time 80 Gb/s error-free performance was obtained using cross phase modulation in conjunction with blue spectral shifted filtering. In addition an important attribute of this work experimentally examines the temporal profile and phase of the SOA-based shifted filtering wavelength converted signals. Thus the contribution and effect of ultrafast carrier dynamics associated with SOAs is presented

High-speed and Robust Integrated Silicon Nanophotonics for On-Chip Interconnects

Optical interconnects offer advantages over electrical interconnects such as higher bandwidth, low power, reduced interconnects delay, and immunity to electro-magnetic interference and signal crosstalk. However, in order for optical interconnects to be widely adopted, the technology must be made cost effective and must be simple to implement with CMOS electronics. Silicon photonics offers a great promise due to its inexpensive material and its compatibility with the current CMOS fabrication technology. Moreover, Silicon as a platform has the ability to integrate with different types of the optical components such as photodetector, modulator, light source, and waveguide to form a photonics integrated circuit. The goal of this work is to develop and fabricate devices that utilize a hybrid electronic-photonic integration to enable high performance optoelectronic computing and communication systems that overcome the barriers of electronics and dramatically enhance the performance of circuits and systems. We experimentally demonstrate a novel broadband optical time division multiplexer (OTDM) on a silicon chip. The system has a footprint× 700 micrometer and is inherently broadband with a bandwidth of over 100nm making it suitable for high-speed optical networks on chip. Also, we propose and fabricate a novel design to demultiplex the high bit rates of OTDM data using two differentially operated 5Gb/s modulators. Moreover, we propose a high-speed hybrid optical-time-division-multiplexing (OTDM) and wavelength-division-multiplexing (WDM) system that seamlessly generates high bit-rate data (\u3e200Gbit/s) from a low speed (5Gbit/s) quantum-dot mode locked laser pulse source. By utilizing time and wavelength domains, the proposed design is a promising solution for high-speed, compact and low-power consumption optical networks on chip. And finally, we experimentally demonstrate a robust, low insertion loss, compact Silicon ring resonator electro-optic modulator for Binary Phase Shift Key (BPSK) coding/decoding that encodes data in the phase of light. Our design improves significantly over recently demonstrated PSK modulator designs in terms of insertion loss and stability