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A 4 × 5 Gb/s Transmission System with All-Optical Clock Recovery
Abstract
The authors demonstrate successful 5 Gb/s operation of an all-optical clock extraction circuit in a 20 Gb/s optical time division multiplexing OTDM system. An optical clock signal was obtained by synchronizing a self-pulsating 1.56 mu m laser diode to a 5 GB/s RZ data signal, demultiplexed from a 4*5 Gb/s OTDM transmission system. Synchronization was achieved for pseudo-random-bit sequences from 2/sup 7/-1 to 2/sup 31/-1. At 2/sup 7/-1 full system bit-error-ratio (BER) measurement on one of the 5 GB/s channels using the extracted optical clock for synchronization were made with no observed penalty over transmitter clock measurements. Such clock extraction techniques may be of great importance in a wide variety of telecommunications applications.< >
... When there is a large enough difference in the carrier lifetimes between the two sections, self-pulsing may take place [3]. It is well known that SPL's can be effectively injection-locked by a superimposed RF signal [4], with a straightforward extension to digitally modulated signals [5], [6]. ...
... Here an external sine wave having a known frequency is superimposed onto the DC bias applied to the gain section, and with a slight change in the DC bias applied to the gain section, injection locking does take place. This locking procedure is a well-known characteristic of the laser [4], but the novelty is using this device to distinguish between desired and unwanted frequencies [9]. The authors were only interested in pulsation and stable regions, but the model could also predict regions of bistability. ...
We demonstrate tuneable optoelectronic bandpass filtering of an ASK modulated subcarrier data stream, using a two-section laser. Gain enhancement of 15dB is measured when the laser is locked to a 697MHz and 1100MHz carrier frequency.
... All-optical timing extraction from a demultiplexed channel in a four-channel 20 Gbs/s OTDM system has been demonstrated [4]. In this case the extracted clock has a frequency of 5 GHz. ...
... In principle, therefore, it is possible to easily reconfigure the operation of such a timing extraction system, a feature which may be of significant importance in future transparent optical networks. The highest reported data rate for timing extraction with self-pulsating laser diodes is 5 Gb/s [4], demonstrating the potential of the technique for high speed optical networks. ...
All-optical timing extraction from a coded line signal with division of the extracted clock frequency is demonstrated using a single twin-section self-pulsating laser diode. Either the bit-rate clock or a submultiple of the bit-rate clock can be extracted, depending only on the DC biases applied to the self-pulsating laser diode. Timing extraction is carried out for the first time without optical injection locking of the self-pulsating laser diode by the optical data source.< >
... The operation in the seminal work was demonstrated for a moderate data rate of 200 Mbit/s that was limited by the carrier lifetime of the SA region. When this region is doped with suitable dopant, such as Zn or N, and the SA region is suitably biased the carrier lifetime could be reduced and the operation was demonstrated for data rates of 5 Gbit/s [51][52][53][54], and 10 Gbit/s [55,56], respectively. The impact of SA biasing conditions for MLL performance has been studied in Ref. [57]. ...
Clock recovery is a fundamental operation in digital telecommunications systems, where the receiver synchronizes itself to the transmitter timing. In optical clock recovery, this operation is made using optical signal processing methods. This paper reviews the physical principles and classifies the various optical clock recovery methods developed during the last 20 years.
... One approach to high-speed clock extraction is the injection mode locking technique, in which optical clock signal is obtained by launching the pulse trains into the cavity of a selfpulsating laser [3,4]. Another approach is based on the four wave mixing (FWM) phenomenon [5]. ...
In this paper, we demonstrate clock recovery from a patterned optical-time-division-multiplexed (OTDM) return-to-zero (RZ) data stream. A cascaded LiNbO3 Mach-Zehnder modulator is employed as an efficient optical-electrical mixer. A phase-locked-loop (PLL) is used to lock the cross-correlation component between the optical signal and a local oscillating signal. As a result, clock signal at 10GHz is extracted from the 160Gb/s optical TDM signal. The measured root-mean-square (RMS) timing jitter of the 10GHz clock signal is ~ 130fs.
... Control pulses synchronized with address bits are needed for the routing system to operate correctly. Therefore, the synchronization between control pulses and address bits is one of the important issues in constructing all-optical routing systems [5], [6]. In the works reported so far, the synchronous signal can be regenerated under a certain condition in an alloptical manner. ...
This paper describes the optical circuit that enables to extract address from a transmitted cell in an all-optical manner. Nonlinear optical loop mirrors (NOLM's) are used as all-optical switches in order to confirm the operation of the proposed circuit. The control pulses synchronized with address bits are generated from the transmitted cell. The address bits are successfully extracted without any electronic control circuit. The factors that limit an attainable bit rate are discussed. If we use NOLM composed of a 2-km-long fiber, 110 Gb/s is attainable for the 4 ps FWHM input pulse with RZ format
This chapter concentrates on receivers intended for the direct detection of digital data consisting of a stream of light pulses, where the presence and the absence of a pulse correspond to the transmission of a binary mark and space, respectively. The block diagram of a basic telecommunications receiver is depicted in Fig. 8.1.
The Situation of todays optical telecommunications is a curious contrast between the potential bandwidth and the actually utilized bandwidth of optical fibers. It is well known that the bandwidth of the fiber within the 1.3 and 1.55 μm window is in the order of 37 THz, a number which is nearly infinite compared with the bandwidth used in practice. Although it represents a great success that most of the terrestrial communication highways have been occupied by fiber connections, displacing analogue coaxial cable systems with a repeater spacing of 1.5 km and microwave links, the larger amount, consisting of customer access lines, is still monopolized by copper lines. For some time it has been widely agreed that the next big step for optical communications is within the local loop (fiber to the home). It is well known that actual bit rates on customer lines are very low, ranging from 64 kbit/s for plain old telephone services (POTs) to some Mbit/s for cable television (CATV). Therefore cost intensive point-to-point fiber connections have to compete with the very inexpensive copper lines. At several previous conferences 1, the break-even point for fiber and copper has been projected for the next 3 years but break-even has not been attained in any country.
The coming broadband network (B-ISDN) era will require ultrahigh speed technologies not only for transmission lines, but also for transmission nodes. The goal is to handle signal rates of more than 100-Gbit/s, so that vast amounts of information including data and pictures, can be provided to many subscribers through optical fiber cables. To this end, all-optical time-domain signal processing technologies are being studied for realizing ultrahigh-bit-rate optical time-division-multiplexing (TDM) transmission systems. They include high-speed picosecond optical pulse generation, all-optical multi/demultiplexing (MUX/DEMUX) and optical timing extraction techniques. Here, recent advances in these essential technologies and applications to 100Gbit/s optical TDM transmission will be described together with major issues and future prospects.
The tunable optoelectronic bandpass filtering of an ASK modulated subcarrier data stream was demonstrated using a two-section laser was demonstrated. The optical gain was measured by keeping the laser locked to a .697 Ghz and 1.1 GHz carrier frequency. The well known rate equation model which allowed the verification of the pulsation frequency range and the injection process was presented. It was found that the frequency range depended on the SPL characteristics and could be extended into the Bluetooth (2.4 GHz) and HIPERLAN2 (5GHz) ranges.
In this paper, we demonstrate clock recovery from a patterned 160Gb/s optical-time-division-multiplexed (OTDM) return-to-zero (RZ) data stream. A cascaded LiNbO3 Mach-Zehnder modulator is employed as an efficient optical-electrical mixer. A phase-locked-loop (PLL) is used to lock the cross-correlation component between the optical signal and a local oscillating signal. As a result, clock signal at 10GHz is extracted from the 160Gb/s optical TDM signal. The measured root-mean-square (RMS) timing jitter of the 10GHz clock signal is ~ 130fs.
In this work, we demonstrate clock recovery from a patterned 160Gb/s optical-time-division-multiplexed (OTDM) return-to-zero (RZ) data stream. A cascaded LiNbO3 Mach-Zehnder modulator is employed as an efficient optical-electrical mixer. A phase-locked-loop (PLL) is used to lock the cross-correlation component between the optical signal and a local oscillating signal. As a result, clock signal at 10GHz is extracted from the 160Gb/s optical TDM signal. The measured root-mean-square (RMS) timing jitter of the 10GHz clock signal is ~ 130fs.
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.
As one of the methods for data transmission and/or address recognition without electronic and logic circuits in all optical ATM, we propose the optical circuit which enables separation of the transmitted pulse stream into data and address bits in an all optical manner. It is successfully demonstrated that the address bits are separated without electronic control and logic circuits.
Speed limitations of conventional transmission and future research directions are discussed. There has been steady progress for both optical devices and transmission techniques toward transmission above 2.5 Gb/s. Erbium fiber amplifiers, with their extremely wide bandwidth, have provided increased performance for both optical transmitters and receivers as well as offering efficient line amplifiers. Such devices and techniques now make it possible to demonstrate the feasibility of practical systems up to 10 Gb/s, and there are interesting possibilities for doubling and even tripling this rate. At such rates, proper consideration must be given to source spectral characteristics, even for short systems. On very long repeatered systems, such as submarine cables, nonlinear effects also become significant and could severely limit performance. However, by careful design these can be made to counter chromatic dispersion to provide a soliton system
We investigate optical synchronization with frequency multiplication and division of self-pulsating laser diodes. Using a simple rate equation model to describe self-pulsation we show that synchronization with frequency multiplication can be accompanied by large variations in the period of the emitted laser pulses over the injected pulse cycle. These variations are not obvious in the frequency domain treatment of synchronization. By applying a frequency division synchronizing signal to our model, we also show that the sensitivity of the phase difference between the injected signal and laser emission to power increases with increasing frequency division ratio and leads to the presence of power synchronization ranges.
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.
Base rate optical clock recovery of an 8 GHz clock signal from a 32 Gb/s (4×8 Gb/s) OTDM data stream was demonstrated by incorporating injection locking of a short cavity Fabry-Perot laser diode with opto-electronic feedback.
This paper reports a technical assessment of an all-optical
4×10 Gbps clock extraction technique in the context of fiber optic
digital communication systems. The technique consists in putting a 1320
nm semiconductor laser in a self pulsating mode through injection
locking to a CW source. The pulsations are triggered by a fast drive
current step. The useful self pulsation region has been explored after
extensive simulation providing a valuable knowledge for on-going
experiments. Actual synchronization with the optical data stream was
observed both considering all ones and pseudo-random sequences. Phase
sustaining of the clock over moderate-length sequences of zeros was
noticed as the most encouraging result of this work
First Page of the Article
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
Ultrafast all-optical signal processing techniques are expected to
play a major role in future ultrafast single-carrier soliton systems,
because they remove the electronics bottleneck. In this paper, two
all-optical devices, the nonlinear optical loop mirror (NOLM) and the
Kerr fiber modulator (KFM), are used to achieve major functions related
to high bit rate soliton links. At the interface with existing networks,
conversions from data at the nonreturn-to-zero (NRZ) format to
return-to-zero (RZ) and soliton data, and vice-versa are required. These
two conversions are demonstrated through NOLMs, and their limitations
investigated. However, the main part of this paper is devoted to in-line
soliton regeneration through synchronous modulation. Synchronous
modulation requires both clock recovery and in-line optical modulation.
In the following, all-optical approaches for these two functions are
considered separately, before being associated in a true all-optical
regenerator. All-optical clock recovery techniques are first reviewed.
An experimental implementation of one of these techniques is described.
On the other hand, all-optical modulation can be done either with
intensity or phase modulators. We initially proposed the NOLM as
all-optical intensity modulator. We analyze it theoretically, both from
the component and the system application viewpoints. A modified
configuration of the NOLM, having two optical controls, removes some
limitations pertaining to the single-control configuration, yielding
even higher performance. The other all-optical synchronous modulator
considered here is the KFM, which is a pure phase modulator. Its
potential is demonstrated in a 20-Gb/s soliton transmission experiment,
when driven by an optoelectronic optical clock generation device. Issues
specific to the implementation of both types of all-optical fiber-based
modulators are discussed. Finally, a true all-optical synchronous
regenerator, combining all-optical clock recovery circuit and KFM, is
tested in an actual soliton transmission experiment at 20 Gb/s
Review current OTDMA technology, with the emphasis on optical clock recovery and time demultiplexing. Various optical switching techniques are surveyed, and they are compared by taking account of the potential feasibility of engineering implementation. The architectures for OTDMA networks are described, and we look at all-optical clock recovery schemes that are based on traveling-wave (TW) semiconductor laser amplifiers, self-pulsating laser diodes, EO switches, mode locking of a fiber ring laser, and four-wave mixing (FWM). We also review various optical switching techniques for ultrafast time demultiplexing
A novel phase-lock type clock recovery technique based on a terahertz optical asymmetric demultiplexer (TOAD) is proposed. The technique is compatible with the conventional time-division multiplexing (TDM) timing techniques but does not require the ultrahigh-speed optical detector nor ultrafast electrical components. Further, it can readily be used to achieve frame synchronization, upon which a complete self-timing demultiplexer can be demonstrated.
This paper reports for the first time direct off-air detection and transmission from the radio frequency through to the optical domain using a substrate antenna and a self-pulsating laser. The injection-locking property of self-pulsating lasers is exploited and used to lock onto a 1.393-GHz carrier amplitude shift key modulated with 155-Mb/s pseudorandom data. Tunable selection of carriers at 1.409 and 1.630 GHz is demonstrated, with the resultant injection-locked signals being amplified by ∼20 dB.
A new phase lock loop (PLL) is proposed and demonstrated for clock
recovery from an ultrahigh-speed time-division multiplexed (TDM) optical
signal. A traveling-wave laser-diode amplifier (TW-LDA) is used as a
phase detector, and the cross-correlation component between the optical
signal and an optical clock pulse train is detected as a
four-wave-mixing (FWM) signal generated in the TW-LDA. A timing clock
from a TDM signal is extracted as a prescaled electrical clock, and this
prescaled clock is directly recovered from a randomly modulated TDM
optical signal. A prescaled 6.3 GHz clock is successfully extracted from
a 100 Gb/s signal using the timing comparison output obtained as the
cross-correlation between the optical signal and a short (<10 ps) 6.3
GHz optical clock pulse train in the generated FWM light. A comparison
of the PLL phase noise with a previously reported gain modulation method
is also shown, and the possibility of the Tbit/s operation of this PLL
is also considered in the experiments
All-optical signal regularizing/regeneration using a nonlinear
fiber Sagnac interferometer switch (NSIS) that employs signal-clock
walk-off is investigated. The NSIS realizes all-optical signal
regeneration, including timing and amplitude regularizing, by switching
clock pulses with amplified input signals using a walk-off-induced,
wide, square switching window and intensity-dependent transmittance of
the device. First, characteristics (in both the temporal and spectral
domains) of the all-optical signal regeneration achieved with the NSIS
are investigated theoretically and experimentally. They certify that if
clock pulses are within the square switching window obtained with
signal-clock walk-off, the clock pulses can be modulated according to
the data that the input signals carry and retain their temporal and
spectral profiles. This means that if clock pulses can be prepared that
meet the system requirements, the NSIS can convert input signals that
may not satisfy system requirements into high-quality output signals.
Limitations on the switching contrast due to the cross-phase modulation
of counterpropagating reference pulses is also discussed. Second, two
possible applications of NSIS-based all-optical signal
regularizing/regeneration, 1) an all-optical multiplexer with an optical
clock and 2) an all-optical regenerative repeater, are discussed.
Preliminary experiments with ~10-ps pulses at bit rates of ~5 Gb/s that
use locally prepared optical clock pulses, show that the NSIS provides
an error-free regeneration function with a certain tolerance for
pulse-period irregularity if a proper optical clock is obtained
A new phase lock loop (PLL) is developed for very-high-speed
optical timing extraction using traveling-wave laser-diode amplifier
(TW-LDA) as a phase detector. The all-optical gain modulation of the
TW-LDA is utilized to detect the relative phase difference between an
optical signal and an optical clock The frequency response of the
optical gain modulation measured with the optical heterodyne technique
agrees with the theoretical results based on a rate equation model. With
the developed PLL, 10-GHz optical timing clock is successfully extracted
from randomly modulated optical signal pulses and the measured
bit-error-rate performance shows no power penalty. Influence of the
received optical noise on the phase variance of the PLL is also
evaluated and it is concluded that 100 GHz operation is possible by
increasing the input optical power to 10 mW
The coming broadband era will require very high-speed technologies that can handle more than 100-Gb/s for both transmission lines and transmission nodes. Novel all-optical signal processing technologies that offer unsurpassed performance are urgently required. This article briefly reviews the essential photonic technologies required for high-speed optical TDM transmission, including ultrashort optical pulse generation, all-optical multiplexing/demultiplexing, and optical timing extraction techniques. Recent all-optical TDM transmission experiments up to 100 Gb/s are introduced together with major issues and future prospects.< >
Challenges of next-generation transmission technologies are
summarized in the context of creating future terabit-per-second
networks. The technologies will be realized through both the separate
and combined evolution of inherent lightwave capabilities along with
time-, wavelength-, and space-domain optical processing techniques.
Optical signal processing techniques in the tens of gigabit per second
range for future high-speed transmission systems and broadband networks
are reviewed
The behavior of a 1.55-μm InGaAsP distributed feedback (DFB)
self-pulsating (SP) laser diode (LD) when injected with either
unmodulated or modulated light from an external LD is investigated
numerically. When subjected to weak injection of unmodulated light, the
SP-LD exhibits mostly chaotic behavior with some regions of
self-sustained-pulsations and multiple-peak periodic oscillations. As
the strength of optical injection increases, the SP-LD transits from
chaos to multiple-peak periodic oscillations followed by high-frequency
self-oscillations before reaching an equilibrium state (i.e., a steady
level). When injected with modulated light, the output of the SP-LD is
dominated by either quasi-periodicity or chaos depending on the
modulation current of the injected optical signal
Conditions have been analyzed for the occurrence for self‐sustained pulsations and bistabilities in semiconductor lasers having a saturable absorber region. It is shown that there are three crucial parameters, namely ratios of differential gain and carrier lifetime between amplifying region and absorbing region, and ratio of absorbing magnitude in absorbing region to the cavity loss. Ranges of these three parameters are determined in which bistabilities and self‐sustained pulsations take place.
Upgrade of a core telecommunications network by means of
wavelength division multiplexing has not up to now appeared
operationally attractive. Influential factors have been the lack of
suitable wavelength defined sources and the increased losses of the
multiplexing elements which limit the system range. Solutions to these
problems are in the form of higher power, wavelength definable DFB
lasers, higher sensitivity receivers and optical amplifiers (either
semiconductor lasers or fibre types). The authors show that wavelength
multiplexed systems can be interconnected to form an optical
transmission network infrastructure that offers similar planning
flexibility to those currently used but with increased bandwidth. With
the progress of optical switching technology it is possible to foresee
how flexibility can be added to these networks to provide automatic
routing and protection of high capacity channels. Some network
structures are examined and their attributes discussed
For the first time, all-optical clock extraction from 2.5 Gbit/s NRZ data is demonstrated using a two contact InGaAsP semiconductor selfpulsating laser diode (SP-LD) for what the authors believe to be the first time. The saturable absorber region of the device was doped with Zn ions to reduce the carrier lifetime such that strong selfpulsations at frequencies up to 4 GHz were obtained. Injection of a 10 mu W optical data signal at a wavelength approximately 15 nm lower than the lasing wavelength was sufficient to synchronise the selfpulsations to the incoming NRZ data stream. Similar effects were seen for RZ formated data. Such all-optical clock extraction techniques will find application in future multigigabit per second optical networks and for OEIC applications.
100-channel optical FDM transmission/distribution at 622 Mbit/s is demonstrated for a fibre length of 50 km. A polarisation-insensitive waveguide frequency-selection-switch with 10 GHz intervals and an FSK/direct-detection scheme using a Mach-Zehnder filter type optical frequency discriminator are verified as feasible.
A 20 Gbit/s optical time division multiplexed transmission system based on components and subsystems operating at not more than 5 GHz repetition rate is reported. Full BER measurements indicate a penalty of only 0.8 dB after transmission through 205 km of dispersion-shifted fibre. The penalty was mostly attributed to the accumulation of noise from erbium-doped fibre repeater amplifiers in the system.
An optical retiming regenerator is demonstrated using two 1.5 mu m wavelength multielectrode (ME) DFB LDs at 200 Mbit/s. The regenerator consists of an injection-locked self-pulsating ME DFB LD for timing recovery and a bistable ME DFB LD for retimed regeneration.
All-optical clock extraction from 5 Gb/s RZ data is demonstrated using a two-contact InGaAsP semiconductor self-pulsating laser diode. The saturable absorber region of the device was doped with zinc ions to reduce the carrier lifetime in this region such that strong self pulsations at frequencies up to 5.2 GHz were obtained. Injection of a 10- mu W optical data signal at a wavelength close to one of the Fabry-Perot wavelengths was sufficient to synchronize the self pulsations to the incoming data stream. The measured 3-dB RF electrical bandwidth of the synchronized optical clock signal was 10 Hz, approximately the same as that of the electrical transmitter clock. Initial bit-error-rate measurements for 2/sup 7/-1 5 Gb/s data result in a 0.5-dB receiver sensitivity penalty when using the optical clock signal compared to the transmitter clock.< >
A novel approach to clock extraction for non-return-to-zero (NRZ) formatted data is demonstrated using two contact semiconductor nonlinear optical amplifiers (NLOAs). The NLOA amplifies the transmitted data (fiber-fiber approximately 5 dB) and due to the absorptive nonlinearity, induced by bleaching a region of saturable absorption within the NLOA, an electrical clock component is generated at the absorber electrical contact. Narrow bandpass electrical filtering of the absorber contact electrical RF spectrum is all that is required in order to extract a stable clock signal. Bit-error-rate measurements at 155.6 Mb/s showed no receiver sensitivity penalty when using the NLOA extracted clock compared to the transmitter clock. Using quantum well material strong clock component generation has been achieved at modulation rates from < 100 Mb/s up to 5 Gb/s.< >
An ultrafast all-optical timing extraction method using an optical tank circuit is described, and experimental results at 2 Gb/s are reported. A Fabry-Perot resonator, whose free spectral range is equal to the clock frequency of the incoming optical data stream, is utilized as the optical tank circuit. Its fully passive structure and ultra-high-bit-rate operation ( approximately Tb/s) is possible through decreasing resonator length.< >