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Transmission of a true single polarisation 40 Gbit/s soliton data signal over 205 km using a stabilised erbium fibre ring laser and 40 GHz electronic timing recovery
Electronics Letters
Abstract
Four independently modulated 10 Gbit/s channels were transmitted over 205 km with a penalty of less than 1.5 dB. The pulse source comprised a stabilised 10 GHz erbium fibre ring laser, multiplexed to 40 Gbit/s in a single polarisation by four independent lithium niobate modulators. Following transmission the requirement to kick start the demodulator is avoided using a 40 GHz electronic clock recovery circuit with a 10 GHz output. The experiment is performed entirely with commercial components and semiconductor laser diodes.
... Das optische Datensignal wird direkt mit einer Photodiode gewandelt und anschließend in einer elektrischen PLL gefiltert, um das Taktsignal zu generieren [42]. Da eine PLL auf sehr schwache Signale rasten kann, ist es mit dieser Methode möglich, höhere Datenraten zu extrahieren, als es die 3-dB-Bandbreite der Photodiode vermuten lässt. ...
Die Arbeit beschreibt den Aufbau, die Charakterisierung und den experimentellen Test einer optischen Taktrückgewinnung für optische Zeitmultiplex-Datensignale (OTDM) bei einer Datenrate von 160 Gbit/s. Die Aufgabe der Taktrückgewinnung besteht in der Generierung eines zum Datenstrom synchronen Taktsignals lediglich mit Hilfe des Datenstroms selbst. Die Taktrückgewinnung wurde für den Einsatz im Empfänger von glasfaserbasierten optischen 160-Gbit/s-Übertragungssystemen entwickelt. Da bestehende Empfangssysteme einen Takt von 160 GHz nicht verarbeiten können, wurde das rückgewonnene Taktsignal als elektrisches Hochfrequenzsignal mit der zum Datensignal subharmonischen Frequenz von 10 GHz zur Verfügung gestellt. Für die Taktrückgewinnung wurde ein neuartiger Phasenkomparator mit optisch differentieller Signalverarbeitung entwickelt und in einer linearen Phasenregelschleife (PLL) eingesetzt. In dieser Arbeit wurde die Entwicklung dieses neuen Phasenkomparators und seiner Komponenten beschrieben. Seine Kennlinie wurde experimentell untersucht und theoretisch bestimmt. Eine Einbettung in die Theorie der linearen PLL war möglich. Aus der Theorie ließ sich das Regelverhalten der Taktrückgewinnung bei einem Phasensprung sowie die Stabilität und der zeitliche Jitter des rückgewonnenen Taktsignals in Abhängigkeit von der optischen Eingangsleistung bestimmen. Die theoretischen Berechnungen waren in guter Übereinstimmungen mit experimentellen Ergebnissen, die an der Taktrückgewinnung mit einem 40-GHz-Eingangssignal ohne Datenmodulation gemessen wurden. Die in dieser Arbeit beschriebene Taktrückgewinnung wurde in unterschiedlichen OTDM-Übertragungsexperimenten bei einer Datenrate von 160 Gbit/s eingesetzt. Dabei zeigte sich besonders ihre Robustheit gegenüber Signalverzerrungen und eine hohe Langzeitstabilität. Der zeitliche Jitter des rückgewonnenen Taktsignals konnte je nach Art des eingesetzten optischen Senders sogar verringert werden. Auch in einem 320-Gbit/s-Übertragungsexperiment konnte die Taktrückgewinnung erfolgreich eingesetzt werden, jedoch zeigte sie dabei eine deutlich geringere Robustheit als bei der Datenrate 160 Gbit/s. Ebenfalls ließ sich die Taktrückgewinnung in einem Optischen Samplingsystem für 320 Gbit/s erfolgreich einsetzen. Gedruckte Version im Verlag Dr. Hut [http://www.dr.hut-verlag.de/] erschienen.
... In particular, ultralow phase noise yielding -ps rms jitter is required to achieve 100 Gb/s transmission. The highest operating speed of currently used electrical timing extraction circuits is as high as 40 GHz, determined by the microwave mixer used as a phase detector in II TABLE III a phase-lock loop (PLL) circuit [58]. To increase the operating speed, many approaches based on photonic technology have been studied, as shown in Table III. ...
Recent progress toward multiterabit/s optical transmission systems
employing all-optical ultrafast signal-processing technologies is
described. Focus is placed on optical time-division multiplexing (OTDM),
as well as optical time- and wavelength-division multiplexing (OTDM/WDM)
technologies leading to multiterabit/s transmission capacity. The key
technologies, including ultrafast pulse generation, all-optical
multiplexing/demultiplexing, and optical timing extraction techniques,
are also described, together with state-of-the-art performances and
future prospects
All-optical time-division-multiplexed (TDM) transmission technologies will be essential for future ultrahigh-speed all-optical networks. They include ultrashort transform-limited (TL) pulse generation, all-optical modulation/ time-division multiplexing, high-speed timing extraction and all-optical time-division demultiplexing. In this paper, the TDM transmission technologies that use ultrahigh-speed optical nonlinear phenomena are reviewed. A recent 100 Gbit/s, 200 km optical transmission experiment [1] is shown and problems that must be overcome to achieve > 100 Gbit/s transmission are also discussed.
Ultra-high speed optical time-division- multiplexed (TDM) networks, operating at single stream data rates of 100 Gb/s, may offer unique advantages over wavelength division multiplexed systems. These advantages include the ability to provide integrated services (including packet service) to high-end users, multiple quality of service (QoS) levels and truly flexible bandwidth- on-demand. Realization of these high performance TDM networks requires development of a number of key technologies such as high-speed optical sources, all-optical switches, buffers and rate converters. In this paper, we will give an overview of an ultra-high-speed TDM network architecture, its well as describe recent key technology developments.
Characteristics of single channel 80-Gbit/s optical signal transmissions using a standard single mode fiber (SMF) are discussed including the effect of alternate polarization multiplexing at the sending end. Allowable values of transmission line length, input optical powers to th SMF, and dispersion margin are evaluated based on bit error rate measurements for three line configurations, unrepeated lines, lines having a repeater with a 100-km spacing, and multiply repeated lines with a 60-km spacing. As for the transmission line length, error free transmissions are experimentally possible for the total lengths of 160 km, 200 km, and 300 km for the individal cases. Unrepeated 160-km transmission experiments where an 80-Gbit/s optical signal with a single polarization is launched in the SMF are made for comparison. Superiority of the alternate polarization multiplexing is confirmed through the measuremets of input optical power, optical pulse amplitude fluctuation, and optical spectrum broadening.
A review of nonlinear optical phenomena in fibres is presented. The chapter briefly describes important linear properties of single mode fibres including dispersion and incorporates a discussion on amplified long haul communication systems. Fundamental nonlinear short pulse effects in fibres are described and applications to all-optical processing presented. Solitons as the stable digital modulation format for long haul systems are described and limitations on the information carrying capacity of soliton systems identified.
Potential advantages of ultra-high speed optical time-division-multiplexed (TDM) systems, operating at single stream data rates of 100 Gbit/s, include increased intelligence within the network, provision of packet service to high-end users, and truly flexible bandwidth-on-demand. A number of key technologies must come together to realize high performance TDM networks. High-speed optical sources, all-optical switches, buffers and rate converters are all required. In this talk, we will give an overview of an appropriate architecture for ultra-high-speed TDM networks, as well as describe recent key technology developments.
The subject of this thesis is ultrahigh capacity optical communication systems. Such systems will use a combination of techniques for dense wavelength-division multiplexing (D-WDM) and ultrahigh speed all-optical time-division multiplexing (O-TDM). The work may be separated into two parts; the first part aims at ultra-high bit-rate applications involving clock-recovery and high speed O-TDM field transmission experiments. Two single channel field experiments with line rates of 40 and 80 Gbit/s over 400 and 172 km respectively are demonstrated using soliton pulses in a high loss, high polarization-mode dispersion (PMD) environment. The reported line rate of 80 Gbit/s was the first single channel transmission experiment above 40 Gbit/s over installed fiber. Furthermore, nonlinear crosstalk due to four-wave mixing in D-WDM systems are studied under the influence of PMD. The second part deals with a novel type of amplifiers based on fiber optical parametric amplification. One important feature of these amplifiers is that they may be tailored to operate at a specific wavelength and they may thus open up new, previously unused, transmission bands. A cw pumped fiber based parametric amplifier is demonstrated with 39 dB black box gain. This is the first demonstration of a cw pumped fiber based parametric amplifier showing a net black box gain. The very fast relaxation time (∼fs) may be used for all-optical signal processing. Three signal processing applications based on a fiber optical parametric amplifier are proposed and demonstrated; a 40-10 Gbit/s O-TDM demultiplexer with more than 40 dB gain, a 40 GHz pulse source providing wavelength tunable pulses below 4 ps and an all-optical sampling system with a temporal resolution of 1.6 ps demonstrating visualization of 300 Gbit/s data. Finally, a simple technique for increasing the maximum launched power into an optical fiber by increasing the stimulated Brillouin scattering threshold is proposed and evaluated.
All-optical signal processing is a powerful tool for the processing of communication signals and optical network applications have been routinely considered since the inception of optical communication. There are many successful optical devices deployed in today’s communication networks, including optical amplification, dispersion compensation, optical cross connects and reconfigurable add drop multiplexers. However, despite record breaking performance, all-optical signal processing devices have struggled to find a viable market niche. This has been mainly due to competition from electro-optic alternatives, either from detailed performance analysis or more usually due to the limited market opportunity for a mid-link device
. For example a wavelength converter would compete with a reconfigured transponder
which has an additional market as an actual transponder enabling significantly more economical development. Never-the-less, the potential performance of all-optical devices is enticing. Motivated by their prospects of eventual deployment, in this chapter we analyse the performance and energy consumption
of digital coherent transponders, linear coherent repeaters and modulator based pulse shaping/frequency conversion, setting a benchmark for the proposed all-optical implementations.
40 Gb/s signal transmission over up to more than 3000 km standard fiber by use of midway optical phase conjugation is predicted with a power penalty of below 5 dB and an eye closure of below 1 dB. This suggests that optical phase conjugation seems to be a very attractive technique in compensating for signal distortion for high speed long-haul standard fiber transmission systems.
Three kinds of clock recovery circuit for 40-Gbit/s optical RZ signals are fabricated and their characteristics are compared. The three schemes comprise a phase lock loop (PLL) including a voltage-controlled oscillator, an injection locking, and a logic operation by T-flip-flop. The injection-locking scheme is then applied for 80-Gbit/s signals, where the input optical signal is converted into a 40-GHz signal by an optical modulator driven by the output of the locking circuit. Characteristics as hold-in rage, frequency response, and phase noise are measured and compared among the schemes. The properties of the PLL and the injection locking circuit were relatively similar and those of the TFF circuit were uncharacteristic compared with others. Performance of the circuits was confirmed by error free transmission and by stable phase noise over 24 hours. Phase noise transfer properties of the three schemes are briefly discussed.
Recent progress toward ultrahigh-bit-rate optical fibre transmission systems employing optical time-division multiplexing (TDM) techniques is reviewed. Focus is placed on 100 Gbit s-1 optical TDM transmission systems and the related technologies studied in Japan. Successful 100 Gbit s-1 TDM transmission experiments over 200-500 km and the key technologies are described, including ultrashort optical pulse generation, all-optical multiplexing-demultiplexing and optical timing extraction techniques, together with state-of-the-art performances and future prospects.
A novel all-optical time-channel routing device for synchronous networks is presented. The routing device is optically programmable: channels that are present during the device start-up are routed to one output port, channels that are introduced subsequently are routed to the other output port. Experimental results showing the routing operation and start-up behaviour are presented. It is shown that several devices can be combined to create an optically programmable network with flexible granularity and aggregate bit-rate.
In this paper, we present ultrafast slotted optical time-division multiplexed networks as a viable means of achieving a highly capable next generation all-optical packet-switched network which provides simple network management, the ability to support variable quality-of-service, self-routing of packets, scalability in the number of users, and the use of digital regeneration, buffering, and encryption. We have reviewed all-optical switch and Boolean logic gate implementations using an ultrafast nonlinear interferometer that is capable of stable, data pattern independent operation at speeds in excess of 100 Gbit/s. We have expanded the capability provided by the ultrafast nonlinear interferometer beyond switching and logic demonstrations to include system-level functions such as packet synchronization, address comparison, and rate conversion. We have used these advanced all-optical signal processing capabilities to demonstrate a slotted OTDM multi-access network testbed operating at 112.5 Gbit/s line rates with inherent scalability in the number of users and system line rates. We have also investigated long- haul propagation of short optical pulses in fiber and all-optical 3R regeneration as a viable cost-effective means of extending the long-haul distance of our OTDM network to distances much greater than 100 km.
The history of the proposal that solitons be used for optical fiber
communications and of the technical developments toward making soliton
transmission practical is reviewed. The causes of bit errors in
long-distance soliton transmission are presented and the methods for
reducing them are described. A perturbation theory suited for soliton
analysis is developed. Current status and future prospects of
long-distance repeaterless fiber communications are stated.
Optical time division multiplexing (OTDM) technique was investigated for increasing the transmission capacity of the fiber using monolithic Mach-Zehnder interferometer with integrated semiconductor optical amplifiers (MZI-SOA). High speed optical demultiplexers and add/drop multiplexers were used to process high bit rate data streams. Demultiplexing experiments were employed for the functionality of the OTDM systems. The results show the full applicability of the OTDM devices for increasing the transmission speed of optical fibers in real network environments.
During the past two decades, great progress has been achieved in optical fibre communications technologies toward higher capacity
and longer repeaterspan transmission, leading to very economical trunk transmission systems for public communications networks.
In particular, newly evolved technologies including erbium-doped fibre amplifiers have made very-high-speed 10 Gbit/s optical
transmission systems of practical use. However, because these transmission techniques still rely on electronics for processing
the high-speed signals, it is anticipated that the operational speed and transmission bit rate will hit the upper limit in
the near future. Moreover, to accommodate the coming broadband network (B-ISDN) era, very-high-speed technologies must be
developed not only for transmission lines, but also transmission nodes. The goal is to handle signal rates of over ITbit/s,
so that vast amounts of information, including data and pictures, can be provided to many subscribers through optical-fibre
cables. To this end, novel all-optical signalprocessing technologies capable of superseding conventional electron-based technologies
are urgently required.Figure 9.1 illustrates a future ultrafast optical time-division-multiplexing (OTDM) transmission system
that fully utilises all-optical high-speed signal processing technology.
A single electroabsorption modulator was used to demultiplex a 10 Gbit/s channel from a 40 Gbit/s OTDM data stream, whilst simultaneously recovering the 10 GHz electrical clock. This was achieved using a new bi-directional operation of the EA modulator, combined with a simple phase-locked loop feedback circuit. Excellent system performance was achieved, indicating that operation up to and beyond 100 Gbit/s is possible using current technology.
Using a fiber-optic stimulated-Brillouin-scattering amplifier as an active filter, we have demonstrated optical clock recovery from 5-Gbit/s return-to-zero-format optical data. Definite patterns and pseudorandom bit sequences were tested. This scheme requires no prior knowledge of the clock frequency and is well suited for operation at higher data rates.
The idea of varying the axial distribution of dispersion along a length of optical fibre as a means of manipulating and controlling the soliton supporting nature of the fibre and thereby the characteristics of soliton pulses propagating through the medium has been around for some while. A number of specific applications have been suggested in particular techniques for bright and dark soliton generation, pulse compression and most notably techniques for high frequency soliton transmission. The experimental realisation of most of these techniques however has been hindered by difficulties in the reliable fabrication of dispersion varying fibres. A technique for the fabrication of such fibres was first developed by workers at General Physics Institute, Moscow. Control of the waveguide dispersion was achieved by active control of fibre diameter during the pull. Fibre lengths of up to 2km were fabricated and successfully used in the first experimental demonstrations of high frequency (>60 GHz) bright soliton generation and pulse compression. Subsequent to these first experimental results a number of other groups have commenced fabrication programs on such fibres, extending the techniques to fibre lengths of 40km. In this presentation we describe our latest achievements in Dispersion Decreasing Fibre (DDF) fabrication and report on two applications of the technology. Firstly, we describe a robust, diode-pumped, 40 GHz bright soliton transmitter, and secondly we demonstrate loss compensation in a 38km loss-matched dispersion varying fibre
L'objectif de cette thèse est de réaliser un système de transmission optique bas coût en multiplexage temporel (OTDM), pour un débit global de 10 Gb/s. Le train de pulses optique nécessaire au système a été généré par modulation externe d'une source optique continue, avec une modulateur d'intensité. Les simulations ont été concluantes quant à la faisabilité du système étudié. Une étude théorique a permis de résoudre le problème lié aux interférences cohérentes dues à la nature de la source utilisée. Les performances du système de multiplexage expérimental ont été comparées pour deux sources optiques différentes. Le démultiplexage est réalisé avec un modulateur à électroabsorption (EAM). Des valeurs de Taux d'Erreur Binaire (TEB) inférieures à 10-10 ont été obtenues expérimentalement sur chaque canal extrait. Le système est adapté pour une combinaison avec la technique de multiplexage en longueur d'onde (WDM).
The use of dispersion-managed solitons has permitted the transmission of 20 Gb/s data over 14,000 km and 10 Gb/s over 24,500 km at low error rates without using active controls or frequency shifting filters. Experiments propagating 20 Gb/s data over 20,000 km were performed with a bit error rate <1×10 -9. These results and a Monte Carlo simulation of the experiment indicate that with the system parameters, pulse-to-pulse interactions do not have a significant impact on communication performance.
A technological approach is presented for a compact optical 3R
regenerator consisting of a monolithic InP Mach-Zehnder interferometer
decision gate, incorporating semiconductor optical amplifiers, and an
electronic clock recovery unit driving a simplistic 40 GHz optical clock
source. Bit error rate measurements for 10 Gbit/s regeneration
demonstrate a penalty <2 dB over a wide wavelength range
The transmission of 20 Gbit/s data over distances of 20000 km was
achieved using dispersion-managed solitons without significant
impairment due to pulse-to-pulse interactions. Error rates of
<10-9 were achieved over the entire distance
measured
Error free operation of all 10 independently modulated channels in
a 100 Gbit/s OTDM system is demonstrated. Electroabsorption modulators
are used to extract 10 Gbit/s channels from the 100 Gbit/s data stream,
the highest speed reported for such a device
The error ratio performance of soliton like transmission over a 68
km distributed erbium fibre link is reported. The transmission link had
a net gain of only 2 dB, with remarkably low signal power excursions and
a penalty of <1 dB was observed at 40 Gbit/s
The authors demonstrate the highest reported repetition rate
regeneration of an optical data stream, using a mode lacked fibre ring
laser for clock recovery, and an optical decision circuit based on
non-linear polarisation rotation. Error ratio measurements of the
regenerated 40 Gbit/s output confirm the fidelity of the technique
Experimental field transmissions of solitons at 20 Gbit/s over
2000 km have been successfully demonstrated using part of the Tokyo
metropolitan optical network consisting of conventional
dispersion-shifted fibre cables. The soliton pulse width was 10 ps and a
polarisation-insensitive MQW electroabsorption modulator was used for
demultiplexing. The power penalty at a BER of 1010 was ~3.5
dB
A fully packaged electroabsorption modulator is used to generate
transform limited 4.1 ps pulses at a 20 GHz repetition rate. The
feasibility of using this component for short pulse generation and
demultiplexing in a four channel 80 Gbit/s OTDM system is
discussed
The authors report the first error-free direct optical modulation
of 40 GHz pulses generated by a low-jitter beat frequency to soliton
train conversion source
The cascadability of 690×20 Gbit/s OTDM D&I network
nodes is demonstrated. This demonstration employs electro-optic
modulators for optical routing and soliton control to realise almost
unlimited scalability
Experimental field transmissions of solitons at 10 Gbit/s over
2000 km have been successfully demonstrated using part of the Tokyo
metropolitan optical loop network. The network is composed of
conventional dispersion-shifted 200 core optical fibre cable which was
not originally intended for soliton transmission. However, with the
dispersion-allocated soliton transmission technique, an error-free 13 ps
soliton data train was successfully transmitted over 2000 km. The power
penalty at a BER of 10-10 was 3.1 dB
A single channel, single polarisation 200 Gbit/s
time-division-multiplexed optical transmission experiment is
successfully demonstrated using optical short pulses generated by
supercontinuum. A prescaled clock is recovered directly from the 200
Gbit/s signal to drive an all-optical demultiplexer
The authors discuss the performance of a low-timing-jitter,
diode-driven, Nd:YLF pumped 5 ps, 30-40 GHz soliton source based on
beat-signal conversion in a dispersion-decreasing fibre. In addition,
the first experimental demonstration is reported of long-distance (205
km) propagation of such pulse streams in an amplified transmission line
incorporating three amplifiers at 50 km amplifier spacing
The authors demonstrate for the first time the transmission of a
4×10 Gbit/s OTDM data sequence over two unrepeatered links of 100
km of nondispersion shifted fibre. The experiment is enabled using
midspan spectral inversion and electroabsorption modulator sources and
demultiplexers, and results in a record bit-rate-distance product of 8.1
Tbit/s km for a single channel over standard fibre
The first field demonstration using optical duobinary signalling
at 10 Gbit/s over installed fibres is reported. Transmission over 138 km
of standard fibre is demonstrated without repeaters or dispersion
compensation and with a penalty of only 2.5 dB. This technique
significantly increases the bit rate distance product without changing
any specifications of the existing fibre network. The influence of fibre
nonlinearity on system performance is also investigated
Active transmission control has been used to allow error free
propagation of a 20 Gbit/s soliton data stream over 125 Mm in a
recirculating loop. The use of a synchronous amplitude modulator in the
transmission path suppressed the accumulation of both timing jitter and
amplitude noise and also allowed the amplifier spacing to approach the
soliton period
A new approach to all-optical time-division multiplexing is
proposed and experimentally demonstrated. A 100 GHz 1.547 μm signal
is modified by time-delayed 6.3 Gbit/s signals to generate subchannels
in a 1.557 μm 100 Gbit/s signal via four-wave mixing
The authors demonstrate, for the first time, a three node
optically time division multiplexed network with a maximum capacity of
40 Gbit/s. Electro-optical switches were used for both `drop and insert'
and demultiplexing, and electronic clock recovery provided
synchronisation throughout the network
All-optical clock recovery at bit rates up to 40 Gbit/s using a modelocked fibre ring laser is demonstrated. The configuration simultaneously performs timing extraction and pulse reshaping to give a continuous stream of closely transform limited picosecond duration pulses.
Transmission of a 4×10Gbit/s optically time division
multiplexed data signal over an unrepeatered link comprising 80km of
standard non-dispersion shifted fibre is demonstrated. The 1300pns/nm
dispersion of the link is balanced using a length of dispersion
compensating fibre located at the OTDM transmitter, and the signal is
demultiplexed to 10Gbit/s using a semiconductor optical amplifier
A polarisation insensitive GaInAsP near travelling wave Semiconductor laser amplifier is used as the nonlinear element in a nonlinear optical loop mirror. With this compact configuration, the authors demonstrate a continuously tunable switching window, and report, for the first time using semiconductor materials, error ratio measurements for a demultiplexing operation from 40 to 10 Gbit/s, with a receiver sensitivity of -23 dBm.
Successful operation of a phaselocked loop is demonstrated using a travelling-wave laser-diode amplifier as a 50 GHz phase detector. Optical gain modulation in the laser diode amplifier and an all-optical clock multiplication technique using a silica-based guided-wave optical circuit are used to achieve the extremely highspeed operation. Also discussed is the possibility of more than 100 GHz operation.
The paper presents optical duobinary signalling as an alternative
to the binary format for improved transmission performance in
dispersion-limited systems and summarises results achieved from both
experimental and theoretical investigations. The potential advantages of
duobinary transmission for dispersion accommodation in high capacity
systems are demonstrated in both laboratory experiments and installed
optical fibres. Unrepeatered transmission at 10 Gbit/s without
dispersion compensation was achieved with penalties of only 1.5 dB after
120 km and 2.5 dB after 138 km. Initial indications of the influence of
self-phase modulation (SPM) and stimulated Brillouin scattering (SBS) on
duobinary transmission are also presented. Two channel, 2×10
Gbit/s wavelength division multiplex (WDM) operation with mixed binary
and duobinary transmission was demonstrated in a field trial. This is
the world's first demonstration of using both duobinary and binary
signallings at a total capacity of 20 Gbit/s over installed fibre. The
investigations show that duobinary signalling should become an important
transmission format for future wideband networks where system
performance is primarily dispersion dominated
A three-node optical time-division multiplexing (OTDM) network is demonstrated that utilizes electroabsorption (EA) modulators as the core elements. Each node is self contained and performs its own clock recovery and synchronization. "Drop and insert" functionality is demonstrated for the first time with an EA modulator by completely removing a 10-Gb/s channel from a 40-Gb/s OTDM data stream. A different 10-Gb/s channel was subsequently inserted into the vacant time slot. Clock recovery is achieved by using an EA modulator in a novel bidirectional configuration. Bit-error-rate (BER) measurements are presented for each of the 10-Gb/s OTDM channels.
A novel optical phase-locked loop (PLL), which utilizes four wave mixing in a fiber as a phase detector, is proposed to track a data rate clock in an optically time-division-multiplexed (TDM) data stream, and to generate a prescaled electric clock directly. An optical TDM 20 Gb/s-105 km transmission experiment has been successfully performed with the optical PLL.< >
An all-optical signal processor based on the self-wavelength conversion of Raman solitons is described. The processor consists of an erbium-doped fiber amplifier (EDFA), a highly nonlinear fiber, and an optical bandpass filter. The timing-jitter-free demultiplexing of the processor was demonstrated by an 80-km transmission experiment. Error-free bit error rate (BER) performance was achieved. Transmitted fourfold optical time-division multiplexing (OTDM) signals with a large timing jitter of about 16 ps for an OTDM signal interval of 25 ps were demultiplexed to 9.95-Gb/s signals without signal degradation.
A novel method to suppress noise in a high harmonic mode-locked erbium fibre laser is proposed and realised for the first time, dithering the cavity length at a kilohertz rate. This method makes only one supermode in the laser dominant and suppresses the others. A fibre laser so stabilised has enabled 2.5 Gbit/s soliton transmission over 205 km fibre remaining error free for 100 min, and in a recirculating loop achieving a 10-9 bit error rate at 12000 km, respectively.
Nonlinear pulse compression has been used to achieve transmission beyond the linear dispersion limit for 20 Gbit/s optical time-division-multiplexed data. Error free system operation has been achieved over an operating wavelength range of 10 nm above the wavelength of zero dispersion, in the anomalous dispersion regime.