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INVITED: Optical clock recovery methods: Review
Abstract
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.
... However, Alexander PDe has nonlinear transfer characteristic compared with Hogge PDe, but it is difficult to interface the Hogge PDe with the digital path. 18,19 There is an approach to connect an analog to digital converter to the Hogge PDe for generating a digital output, 20 but the analog to digital converter increases the complexity of the design. The controller uses the early and late signals and provides the control signals. ...
... There are many techniques that have been proposed for implementing the OCDR, quantum dash lasers, 18 SP lasers, and filter-based techniques. 19,20 In this section, we propose and develop 2 techniques for OCDR: SP using DBRL and filtering using FBG. These methods exhibit excellent performance and lower implementation cost compared with those of the other OCDR methods. ...
Clock and data recovery (CDR) is an essential part in high-speed telecommunication systems. The CDR is used to extract the clock and re-time the received data, which allows a synchronous operation to recover the transmitted signal. In optical access networks, electrical CDR or optical CDR implementations can be used. However, there are no clear guidelines or recommendations on which CDR implementation should be adopted for better performance. These missing clear recommendations are because the electrical CDR requires electronics design expertise whereas the optical CDR requires optical design expertise. Consequently, in this paper, an all-digital CDR, designed and implemented on the field-programmable gate array platform, and an optical CDR, developed by using fiber Bragg grating technology on the OptiSystem platform, are presented. Furthermore, the integration of these 2 CDR implementations with the optical access network is implemented, and their performance is evaluated for various transmission rates and communication distances. Finally, a comparative study in terms of the bit error rate between the all-digital CDR and the optical CDR is presented.
... To improve OCDMA system performance further with autocorrelation time gating [1] the receiver synchronisation is critical. Implementations of a wide variety of signal extraction techniques [2] for synchronisation were developed mostly in WDM [3] and OTDM [4], however their application in OCDMA is limited. Clock and data recovery for OCDMA was reported for example in [5,6]; however these approaches were not implemented all-optically. ...
... Realisation of a suitable all-optical clock extraction circuit which can recover a timing signal from an incoming OCDMA data stream and produce an optical clock without an intermediate electronic stage is needed. In principle, recovering an optical clock from incoming data at given bit rates means extracting a new periodic signal with a period reciprocal of the bit rate, while free of information carried by data and without phase noise [2]. Laboratory testing usually relies on a global clock and fast photodetector to detect the autocorrelation peaks and to avoid the degradation due to the multi-access interference (MAI). ...
A receiver that incorporates an all-optical clock recovery approach for synchronisation suitable for use in incoherent OCDMA transmission is demonstrated. The developed solution was implemented and tested in a multiuser environment using the 2D-WHTS coding scheme on incoherent OCDMA transmission with 2.5 Gbit/s data rate. The receiver with built-in all-optical clock recovery was tested by taking the BER for the received data when synchronised with the all-optically recovered clock from the incoming OCDMA traffic and when an RF synthesiser was used to the generate the clock. Improvement of ~7.5 dBm was observed with the all-optical clock recovery approach. The related eye diagrams and the wavelength spectrum were also recorded.
... Accurate and "dynamic" synchronization of the receiver is needed to improve OCDMA signal detection to ensure that the OCDMA receiver is as little as possible affected by the timing jitter. A clock recovery for the receiver synchronization is a well-known approach for addressing this issue and clock recovery subsystems have been recognized as essential for high speed detection systems [2], [7,8]. Implementations of wide variety of clock extraction techniques [8] for use in receiver synchronization were predominantly developed for wavelength division multiplexing (WDM) [9,10] and optical time division multiplexing (OTDM) [11,12] systems. ...
... A clock recovery for the receiver synchronization is a well-known approach for addressing this issue and clock recovery subsystems have been recognized as essential for high speed detection systems [2], [7,8]. Implementations of wide variety of clock extraction techniques [8] for use in receiver synchronization were predominantly developed for wavelength division multiplexing (WDM) [9,10] and optical time division multiplexing (OTDM) [11,12] systems. However, their application in OCDMA using picosecond pulses is limited or often impossible. ...
A novel incoherent OCDMA receiver with incorporated all-optical clock
recovery for self-synchronization of a time gate for the multi access
interferences (MAI) suppression and minimizing the effect of data time
jitter in incoherent OCDMA system was successfully developed and
demonstrated. The solution was implemented and tested in a multiuser
environment in an out of the laboratory OCDMA testbed with
two-dimensional wavelength-hopping time-spreading coding scheme and
OC-48 (2.5 Gbp/s) data rate. The self-clocked all-optical time gate uses
SOA-based fibre ring laser optical clock, recovered all-optically from
the received OCDMA traffic to control its switching window for cleaning
the autocorrelation peak from the surrounding MAI. A wider eye opening
was achieved when the all-optically recovered clock from received data
was used for synchronization if compared to a static approach with the
RF clock being generated by a RF synthesizer. Clean eye diagram was also
achieved when recovered clock is used to drive time gating.
... One of the basic requirements of an OPLL is that the summed linewidths of the master and slave lasers should be smaller than to phase-amplitude coupling [25][26][27][28]. Therefore, OPLL demonstrations have typically been performed using specialized lasers such as solid-state lasers [5][6][7][8][9], gas lasers [10], external cavity lasers [11][12][13][14][15][16] or specialized multisection SCLs [17][18][19][20][21][22][23] [5,6,17,18,[31][32][33][34][35][36], clock generation and transmission [14,19,[37][38][39], synchronization and recovery [21,40]. More recent work has investigated applications of OPLLs in intersatellite communications [9], optical frequency standards [41][42][43] and phase-sensitive amplification [15,44], to name a few. ...
... 40) where f c denotes the corner frequency of the thermal response and depends on thedevice material and structure, and b = K th /K el − 1 denotes the relative strength of the thermal and electronic responses. For typical SCLs, b > 0, and f c lies in the range of 0.1-10 MHz. ...
This thesis explores the precise control of the phase and frequency of
the output of semiconductor lasers (SCLs), which are the basic building
blocks of most modern optical communication networks. Phase and
frequency control is achieved by purely electronic means, using SCLs in
optoelectronic feedback systems, such as optical phase-locked loops
(OPLLs) and optoelectronic swept-frequency laser (SFL) sources.
Architectures and applications of these systems are studied. OPLLs with
single-section SCLs have limited bandwidths due to the nonuniform SCL
frequency modulation (FM) response. To overcome this limitation, two
novel OPLL architectures are designed and demonstrated, viz. (i) the
sideband-locked OPLL, where the feedback into the SCL is shifted to a
frequency range where the FM response is uniform, and (ii) composite
OPLL systems, where an external optical phase modulator corrects excess
phase noise. It is shown, theoretically and experimentally, and in the
time and frequency domains, that the coherence of the master laser is
"cloned" onto the slave SCL in an OPLL. An array of SCLs, phase-locked
to a common master, therefore forms a coherent aperture, where the phase
of each emitter is electronically controlled by the OPLL. Applications
of phase-controlled apertures in coherent power-combining and
all-electronic beam-steering are demonstrated. An optoelectronic SFL
source that generates precisely linear, broadband, and rapid frequency
chirps (several 100 GHz in 0.1 ms) is developed and demonstrated using a
novel OPLL-like feedback system, where the frequency chirp
characteristics are determined solely by a reference electronic
oscillator. Results from high-sensitivity biomolecular sensing
experiments utilizing the precise frequency control are reported.
Techniques are developed to increase the tuning range of SFLs, which is
the primary requirement in high-resolution three-dimensional imaging
applications. These include (i) the synthesis of a larger effective
bandwidth for imaging by "stitching" measurements taken using SFLs
chirping over different regions of the optical spectrum; and (ii) the
generation of a chirped wave with twice the chirp bandwidth and the same
chirp characteristics by nonlinear four-wave mixing of the SFL output
and a reference monochromatic wave. A quasi-phase-matching scheme to
overcome dispersion in the nonlinear medium is described and
implemented.
... All-optical clock recovery for data rates up to 320 Gbps for on-off-keyed (OOK) modulation has been demonstrated using various schemes [13]. One of the most common methods is based on the injection-locking of a mode-locked laser, which is advantageous because of large wavelength tunability and low timing jitter. ...
We report all-optical clock recovery from 10 GBaud NRZ shaped lightwave signals in QPSK and 16QAM formats through injection mode-locking of an Erbium-doped fiber laser. Since these optical NRZ phase modulated coherent signals lack in the strength of the clock-tones, a pre-processing stage for the enhancement of these clock-tones based on a nonlinear semiconductor optical amplifier (SOA) is employed. Optical clock recovery is demonstrated experimentally for both modulation formats, along with wavelength tunability of the scheme over the entire C-band. Resilience of the clock recovery process to input OSNR conditions is also demonstrated. The RMS timing jitter of the recovered clock is measured to be
ps. We also report the performance analysis of the scheme for coherent modulation formats with respect to the dispersion-induced degradation in practical links through simulations and experiments.
... The detection of the relative timing of two signals is commonly required in a wide range of optical measurements and devices, such as in light detection and ranging (LIDAR)-based measurements [1] and clock recovery [2] in optical communication systems. Optical time division multiplexing requires precise relative timing to achieve interleaving accuracy in optical data streams [3]. ...
The functionality of a pulse timing discriminator, which is commonly required in optical communication systems and artificial neuromorphic engineering, was implemented into chalcogenide phase-change materials. GeSbTe (GST) and GeCuTe (GCT), which exhibit opposite refractive index behavior in their respective crystalline and amorphous phases, were employed. A GST/GCT double layer enabled the order of arrival of two counter-propagating femtosecond pulses to be encoded as a difference in the degree of amorphization of the GCT layer, i.e., either a brighter or darker contrast of the amorphized area with respect to the crystalline background. Nonthermal ultrafast amorphization contributed to a picosecond time resolution in the discrimination of the pulse arrival order.
... All-optical clock recovery is a key requirement for 3R regeneration in next generation digital communication systems. Several methods of performing all-optical clock recovery have been discussed in the past [1]. One of the simplest methods is to extract the clock tone of the signal using a passive filter. ...
Abstract: We demonstrate all-optical clock recovery on a 10 Gbps NRZ-OOK optical signal
by filtering the clock tone using a Fabry-Perot fiber Bragg grating (FP-FBG), with its free
spectral range (FSR) matched to the data rate.
OCIS codes: 060.4510, 060.3735.
... OCDR is capable of synchronizing, and reshaping (regenerating) the data along the fiber cable. This will help to significantly expand the transmission distance as well as boost the transmission rate, achieving small Bit Error Rate (BER) at the receiver end [1] [2]. Several solutions have been reported for all-optical clock recovery, such as quantum dash lasers [3], self-pulsating lasers [4] and passive filtering techniques [5] [6]. ...
All-Optical Clock and Data Recovery (OCDR) is an important function for future optical networks and optical signal processing. The OCDR realizes a long-distance optical data transmission system by restoring the incoming data and then re-transmitting. The Self-Pulsating (SP) lasers are the promising technologies to enable fast and high-speed data recovery system in an optical domain. In this paper, we design and implement the OCDR based on two SP laser types, Amplified Feedback Laser (AFL) and Distributed Bragg Reflector Laser (DBRL). A comparative study and measurement of the network performance for the two types have been presented.
... OCDR is capable of synchronizing, and reshaping (regenerating) the data along the fiber cable. This will help to significantly expand the transmission distance as well as boost the transmission rate, achieving small Bit Error Rate (BER) at the receiver end [1] [2]. Several solutions have been reported for all-optical clock recovery, such as quantum dash lasers [3], self-pulsating lasers [4] and passive filtering techniques [5] [6]. ...
... OCDR can expand the transmission distance by synchronizing, and reshaping the data along the optical fiber. Consequently the presence of the OCDR achieve small Bit Error Rate (BER) at the receiver end [1] [2]. Several methods are used to implement the OCDR such as: quantum dash lasers [3], self-pulsating lasers [4] and passive filtering techniques [5] [6]. ...
All-Optical Clock and Data Recovery (OCDR) is considered the most promising technique to increase the optical networks distance and the data rate by synchronizing and regenerating the data along the fiber cable, consequently achieving small Bit Error Rate (BER) at the receiver end. In this paper, we design and implement the OCDR using two different techniques, Self-Pulsating (SP) using Distributed Bragg Reflector laser (DBRL) and Filtering based using Fiber Brag Grating (FBG). A comparative study and measurement of the network performance for the two methods have been presented. The experimental results show clearly the increase either transmission distance or the bitrate.
... All-optical clock recovery is a key ingredient of all-optical signal processing such as 3R generation and network synchronization in the next generation high speed optical networks. Several optical timing extraction techniques suitable for high speed operation have been demonstrated [1]. Optical CR methods may be divided into two main categories: active pulsating and passive filtering techniques. ...
In this paper, we propose and simulate all optical clock recovery at bit rates up to 100 Gbit/s using FabryPerot filters based on fiber Bragg gratings. Simulations performed for Return to Zero (RZ) data format at 10, 40 and 100 Gbit/s show that the technique is quite simple and promising. Based on such results, we have fabricated Fabry-Perot filters for optical clock recovery and report the relevant results.
... OCDR is capable of synchronizing, and reshaping (regenerating) the data along the fiber cable. This will help to significantly expand the transmission distance as well as boost the transmission rate, achieving small Bit Error Rate (BER) at the receiver end [1] [2]. Several solutions have been reported for all-optical clock recovery, such as quantum dash lasers [3], self-pulsating lasers [4] and passive filtering techniques [5] [6]. ...
All-Optical Clock and Data Recovery (OCDR) is an important function for future optical networks and optical signal processing. The OCDR realizes a long-distance optical data transmission system by restoring the incoming data and then retransmitting. The Self-Pulsating (SP) lasers are the promising technologies to enable fast and high-speed data recovery system in an optical domain. In this paper, we design and implement the OCDR based on two SP laser types, Amplified Feedback Laser (AFL) and Distributed Bragg Reflector Laser (DBRL). A comparative study and measurement of the network performance for the two types have been presented
... All-optical clock recovery is critical for 3R regeneration in optical communication systems [1]. One of the simplest ways to perform all-optical clock recovery is by injection-locking a mode-locked laser using the incoming data signal. ...
We perform injection-locking of a passively mode-locked Fabry-Perot quantum dash laser at 40 GHz using 10 Gbps PRBS data in NRZ-OOK format after spectral enrichment and thus demonstrate all-optical clock recovery through sub-harmonic injection-locking.
... OCDR is capable of synchronizing, and reshaping (regenerating) the data along the fiber cable. This will help to significantly expand the transmission distance as well as boost the transmission rate, achieving small Bit Error Rate (BER) at the receiver end [1] [2]. Several solutions have been reported for all-optical clock recovery, such as quantum dash lasers [3], self-pulsating lasers [4] and passive filtering techniques [5] [6]. ...
All-Optical Clock and Data Recovery (OCDR) is an important function for future optical networks and optical signal processing. The OCDR realizes a long-distance optical data transmission system by restoring the incoming data and then re-transmitting. The Self-Pulsating (SP) lasers are the promising technologies to enable fast and high-speed data recovery system in an optical domain. In this paper, we design and implement the OCDR based on two SP laser types, Amplified Feedback Laser (AFL) and Distributed Bragg Reflector Laser (DBRL). A comparative study and measurement of the network performance for the two types have been presented.
... All-optical clock recovery (CR) plays a fundamental and key role in all digital communications, and various kinds of methods based on different physical principles for CR have been proposed and demonstrated [1][2][3][4]. The passive CR schemes, such as the Fabry-Pérot (FP) etalon, had received great interests in the past [5,6], due to the lower cost and complexity. ...
We fabricate and demonstrate a compact polarization insensitive filter for all-optical clock recovery (CR) based on silicon-on-insulator (SOI), which consists of a microring resonator (MRR) and two modified two-dimensional (2D) grating couplers. The distributed Bragg reflectors (DBRs) are introduced to improve the coupling efficiency of the 2D grating coupler. The MRR works as a comb filter for CR, while the 2D grating couplers serve as the polarization diversity unit to achieve a polarization insensitive operation. A subsequent semiconductor optical amplifier (SOA) performs the amplitude equalization. Based on this scheme, a good clock signal with 970 fs timing jitter can be achieved at 44 Gb/s from input signals with arbitrary polarization states.
... All-optical clock recovery is a key requirement for 3R regeneration in next generation digital communication systems. Several methods of performing all-optical clock recovery have been discussed in the past [1]. One of the simplest methods is to extract the clock tone of the signal using a passive filter. ...
Fabry-Perot filters based on fiber Bragg gratings are widely used as optical narrowband filters and as sensors. Here we propose and demonstrate all optical clock recovery (10Gbit/s, 40Gbit/s & 100Gbit/s) with Fabry-Perot filters made up of fiber Bragg gratings.
... A LL-OPTICAL clock recovery (CR) is a fundamental and important operation performed in all digital communication systems ranging from optical transciever to the processing functions, including 3R regeneration, signal synchronization, modulation format conversion, logical operation and optical demultiplexing. During the last 20 years a wide variety of optical CR methods based on different physical principles have been proposed and demonstrated [1]. The active schemes can usually provide a high quality clock at the expense of high complexity and costs [2]- [6]. ...
An all-optical clock recovery (CR) scheme with wide locking range is demonstrated, based on a silicon microring resonator (MRR) and a semiconductor optical amplifier (SOA). The MRR with a free spectral range of 40 GHz works as a comb filter, which removes the modulation information, whereas the SOA operating in the saturation regime performs amplitude equalization to achieve a good optical clock signal. The design of the MRR is investigated according to the tolerance of the subsequent equalizer. Based on the fabricated MRR, single and dual channels CR from 40 Gb/s input data streams can be achieved successfully with root mean square time jitter of . Because of the moderate finesse of the MRR, the CR can be achieved with a wide range of several gigahertz.
... All-optical 3R (reamplifying, reshaping, and retiming) regenerators can directly handle degraded signals resulting from fiber loss, dispersion, nonlinearity and the amplified spontaneous emission (ASE) noise of erbiumdoped optical fiber amplifiers (EDFAs), and overcome the bandwidth bottleneck of optic-electric-optic (O/E/O) processing systems. Previous research works show that the clock extraction can be obtained through Fabry-Pérot (FP) filters, self-pulsating threesection distributed feedback lasers (SP-DFBs), nonlinear-optical loop mirrors (NOLMs) and fiber optical parametric oscillators (FOPOs) [1][2][3]. The self-phase modulation (SPM), cross-phase modulation (XPM) and four-wave mixing (FWM) are used to achieve a nonlinear decision gate [4][5][6]. ...
... The pumps and signals are usually independent with each other, and therefore a supplementary functionality of clock recovery is required for the synchronization between pumps and signals. Fortunately, various optical clock recovery methods have been developed, including the use of phase-locked loops, self-pulsating lasers, and filtering methods [70]. Optical clock recovery from DPSK signals has also been studied [71][72][73][74]. ...
Data exchange, namely bidirectional information swapping, provides enhanced flexibility compared to the unidirectional information transfer. To fulfill the rapid development of high-speed large-capacity optical communications with emerging multiplexing/demultiplexing techniques and advanced modulation formats, a laudable goal would be to achieve data exchange in different degrees of freedom (wavelength, time, polarization), for different modulation formats (OOK, DPSK, DQPSK, pol-muxed), and at different granularities (entire data, groups of bits, tributary channels). Optical nonlinearities are potentially suitable candidates to enable data exchange in the wavelength, time, and polarization domains. In this paper, we will review our recent works towards robust data exchange by exploiting miscellaneous optical nonlinearities, including the use of cSFG/DFG in a PPLN waveguide for time- (groups of bits) and channel-selective data exchange and tributary channel exchange between two WDM+OTDM signals, nondegenerate FWM in an HNLF for phase-transparent data exchange (DPSK, DQPSK), bidirectional degenerate FWM in an HNLF for multi-channel data exchange, and Kerr-induced nonlinear polarization rotation in an HNLF for tributary channel exchange of a pol-muxed DPSK OTDM signal. The demonstrated data exchanges in different degrees of freedom, for different modulation formats, and at different granularities, open the door for alternative approaches to achieve superior network performance.
... Optical clock recovery from data signals is essential for optical signal processing applications in digital communication systems, such as 3R (reamplifation, retiming, and reshaping) regeneration, format conversion, optical logic gates, and signal demultiplexing [1]. Previously, optical clock recovery from a high-speed digital signal was reported using injection-locked mode-locked lasers [2][3][4], selfpulsing lasers [5], phase-locked loops [6] or optoelectronic oscillators (OEOs) [7][8][9]. ...
A novel scheme to implement clock recovery from degraded signals is proposed and demonstrated based on an optoelectronic oscillator and a dual-wavelength mode-locked fiber ring laser with distributed dispersion cavity. The scheme can obtain wavelength-tunable optical clocks at two wavelengths, which is highly desirable for composite optical logic gates, cascaded optical signal processing modules or optical signal processing modules that need synchronized pulses at multiple wavelengths. In addition, the scheme can operate in both RZ and NRZ systems. The feasibility of the method is demonstrated by an experiment, in which dual-wavelength 10-GHz optical clock with a timing jitter less than 170fs is obtained from 10-Gb/s degraded RZ and NRZ signals. The optical clocks can be tuned from 1530 to 1565nm.
... In this proof-of-concept experiment, we manually set the clock stream to have an antiphase relation with the data stream by adjusting the position of mirror M1. In practice, an optical phase-locked loop (OPLL) [27] can be employed to sense the phase of the incoming data stream, the antiphase clock stream could then be derived from the OPLL. ...
We experimentally demonstrate optical retiming of a 10.7 Gb/s data stream utilizing the property of bound soliton pairs (or “soliton molecules”) to relax to an equilibrium temporal separation after propagation through a nonlinear dispersion alternating fiber span. Pulses offset up to 16 ps from bit center are successfully retimed. The results of the experiment are in agreement with numerical simulations. An enhanced version of this retiming scheme is analyzed using numerical simulations.
... A broad variety of concepts and implementations have been proposed [1], among which one popular optical clock recovery device is the optical tank circuit [2]. The optical tank circuit consists of a simple Fabry-Pérot resonator. ...
In this paper we discuss the bit pattern effect on optical clock signals recovered using tank circuits and using birefringent resonators. For the first time we compare the bit pattern dependence of the clock signals recovered from both schemes. We show that a birefringent resonator can recover the clock for the same number of consecutive zeros as the optical tank circuit. We also show quantitatively that the fluctuation of the clock signal amplitude is less for the birefringent resonator than the optical tank circuit. These results are obtained numerically and confirmed experimentally.
... For carrier-suppressed modulation schemes, a Costa's loop can be used [8]. OPLLs are commonly used for optical clock recovery in digital telecommunication systems [9] . They have also been developed for generation of stable channel offsets in dense wavelength-division multiplexed (DWDM) systems [10]. ...
We present the design, fabrication, and results from the first monolithically integrated optical phase-locked loop (OPLL) photonic integrated circuit (PIC) suitable for a variety of homodyne and offset phase locking applications. This InP-based PIC contains two sampled-grating distributed reflector (SG-DBR) lasers, semiconductor optical amplifiers (SOAs), phase modulators, balanced photodetectors, and multimode interference (MMI)-couplers and splitters. The SG-DBR lasers have more than 5 THz of frequency tuning range and can generate a coherent beat for a wide spectrum of frequencies. In addition, the SG-DBR lasers have large tuning sensitivities and do not exhibit any phase inversion over the frequency modulation bandwidths making them ideal for use as current controlled oscillators in feedback loops. These SG-DBR lasers have wide linewidths and require high feedback loop bandwidths in order to be used in OPLLs. This is made possible using photonic integration which provides low cost, easy to package compact loops with low feedback latencies. In this paper, we present two experiments to demonstrate proof-of-concept operation of the OPLL-PIC: homodyne locking and offset locking of the SG-DBR lasers.
... On the other hand, the timing or clock recovery (CR) is necessary to the high symbol rate direct detection systems [14], because one symbol is sampled only once to make the symbol decision that requires the sampling rate strictly synchronous to the symbol rate or tracking the symbol rate variation. Lack of DSP, the timing extraction has to be implemented by the hardware running at the symbol rate instead of software algorithm, which casts a great challenge to the clock recovery devices [15][16][17]. ...
A cost effective clock recovery scheme simultaneously providing signal performance monitoring is proposed for high speed electrical time domain multiplexing (ETDM) transmission systems to release the bandwidth requirement on the involved electrical devices. In the scheme, we first convert the clock frequency down in the optical domain using electroptic modulation, and then extract the clock with a phase locked loop (PLL) after photo-detection. All the devices involved are operated at frequencies lower than half of the symbol rate. Furthermore, we use a quadrature phase detector in the PLL to create a monitor signal which characterizes the transmitted signal performance in terms of optical-to-noise ratio (OSNR) and accumulated chromatic dispersion (ACD). This scheme is applied to a 112-Gbit/s none-return-to-zero (NRZ) differential quadrature phase shift keying (DQPSK) system. Experimental results show that the clock can be recovered in a dispersion range of −40 to 40 ps/nm, and the evaluated OSNR, over a range of 18~36 dB, has a deviation smaller than 1 dB compared to the measured one based on the optical spectrum method. The bit error ratio remains below 10⁻⁹ for 12 hours in the back-to-back case and 2 hours after transmission over 100-km standard single mode fiber (SSMF).
... All-optical clock recovery is a key ingredient of all-optical signal processing such as 3R generation and network synchronization in the next generation high speed optical networks. Several optical timing extraction techniques suitable for high speed operation have been demonstrated [1]. Optical CR methods may be divided into two main categories: active pulsating and passive filtering techniques. ...
Electro-optical feedback circuit is presented and analyzed. The method realizes a closed-loop positive feedback by feeding the electrodes of a Mach-Zehnder interferometer with the voltage produced by its own detection circuit. In its basic form, it is shown to act as a multi-level opto-electric quantizer. The quantization behavior disclosed herein is realized via the opto-electric conversion process itself. The circuit is modeled by an equivalent electronic representation with which the static and dynamic behavior of the circuit is characterized. A component-level electro-optical simulation is included, supporting the theoretical results.
In this Letter, we present a high-strain resolution fiber laser-based sensor (FLS) by a novel optical phase-locked loop (OPLL) interrogation technique based on a root mean square detector (RMSD). The sensor consists of a distributed feedback (DFB) fiber laser as a master laser for strain sensing and a fiber Fabry–Perot interferometer (FFPI) as a reference. The laser carrier locks to the reference by the PDH technique, and the single sideband laser working as a slave laser locks to the DFB sensing element using the OPLL technique, respectively. A strain resolution of 8.19 pε/√Hz at 1 Hz and 35.5 pε in 10 s is achieved in the demonstrational experiments. Significantly, the noise behaves a 1∕f distribution below 0.2 Hz due to the very low pump power for the DFB sensor and an active thermostat testing environment. The proposed OPLL interrogation brings new thinking for the demodulation of FLS. This strain sensor based on FLS has a great performance in strain measurement and can be a powerful tool for geophysical research.
We propose a scheme of all-optical clock recovery (AOCR) based on ultrahigh-order mode locking by a semiconductor optical amplifier (SOA), which can directly extract the optical clock from non-return-to-zero (NRZ) pseudo-random-binary-sequence (PRBS) data. Firstly we demonstrate that the active mode locking system can generate stable high repetition frequency ultrashort pulse train, and adjusting the modulator’s bias voltage and polarization states one can realize doubling the repetition frequency. Due to robust mode locking configuration, we successfully realize the AOCR up to 40 Gbits/s from the PRBS (2³¹-1) NRZ optical signals without NRZ to RZ conversion, while the signal to noise ratio of the recovered optical clock is more than 20 dB with high stability, and the pulse width is short as 1.85 ps. Owing to the ultrafast nonlinear polarization rotation in the SOA, our scheme can execute AOCR for data rate of 100 Gbits/s and more.
Single dissipative Kerr soliton (DKS) formed in microresonator shows few-cycle femtosecond pulses along with smooth and phase-coherent comb spectra that easily reaching an octave spanning. Such unique characteristics lead to revolutionary breakthrough in advanced communications, spectroscopy, metrology, etc. However, as hidden deepest inside the multistable states of driven-damped microresonator, the single DKS state remains challenging to generate deterministically and straightforwardly. Here, we theoretically show that a train of energetic pulse trigger imposed on an external continuous-wave driving pump can quickly kick start the cavity to deterministically evolve into a single DKS state. Neither the pump frequency nor the cavity resonance frequency requires to be scanned, thus possessing the potential for turnkey soliton microcombs generation. The additional degrees of freedom given by the combined pump enables the manipulation of multi-DKS and even perfect soliton crystals generation in the same microresonator. The proposed pulse train triggering method can also be harnessed for ultrahigh speed all-optical clock recovery with a potential rate up to terahertz. Our results open up a new path for manipulating single and multi-DKS in microesonators and a robust optical clock recovery module simultaneously possessing ultrahigh speed, on-chip integration, and cost-efficiency.
The design of a digital optical link involves many interrelated operating characteristics of the fiber, source, photodetector, and other components in the link. In carrying out an optical fiber link analysis, several iterations with different device characteristics may be required before the analysis is completed satisfactorily. The two basic analyses that usually are carried out to ensure that the desired system performance can be met are the link power budget and the system rise-time analysis. In addition to discussing these two analyses, this chapter addresses procedures for detecting and controlling errors in a digital data stream in order to improve the reliability of a communication link.
The design of an optical receiver can be quite sophisticated because the receiver must be able to detect weak, distorted signals and make decisions on what type of data was sent based on an amplified and reshaped version of this distorted signal. In the photodetection processes, various noises and distortions will unavoidably be introduced, which can cause signal interpretation errors. Noise considerations are thus important in the design of optical receivers, because the noise sources operating in the receiver generally set the lowest limit for the signal levels that can be processed. This chapter describes the origins of these noises and their effect on link performance.
The optical phase locked loop (OPLL) technology is used to lock not only the central frequency but also the optical phase of a laser onto a highly stable low noise laser. It is used to transfer laser frequency arbitrarily not only to another statically operated stable laser, but also to a dynamically frequency modulated laser, which is an important function in laser technology. Sect. 8.1 gives an explicit introduction to OPLL and its related devices. Sect. 8.2 discusses main applications of OPLL, including coherent optical communications, transportation of time and frequency standards, microwave photonics, and physical researches. Sect. 8.3 gives a brief introduction to the frequency comb, which is an important progress in optics and a powerful tool in laser frequency transfer and laser spectroscopy. Sect 8.4 describes some of related applications of the optical frequency comb.
An all-optical clock recovery has been demonstrated numerically with single and double ring microring resonators from 40 Gbit/s return-to-zero on-off keying optical signal. The influence of device cascadability on amplitude fluctuation caused by patterning effects of extracted clock values have been evaluated. Open source simulation toolbox Optilux was used for simulations. The results show that these fluctuations related to patterning effects are considerably reduced after processing with five cascaded single ring microring resonators.
We propose a novel notch-filtering scheme for bit-rate transparent all-optical NRZ-to-PRZ format conversion. The scheme is based on a two-degree-of-freedom optimally designed fiber Bragg grating. It is shown that a notch filter optimized for any specific operating bit rate can be used to realize high-Q-factor format conversion over a wide bit rate range without requiring any tuning.
In this paper, a new all optical phase-locked loop (OPLL) is proposed and analyzed. The scheme relies on using two optical Kerr shutters to reveal the OPLL's error signal. The set of optical Kerr shutters and the subsequent low-speed photodetectors realize two nonlinear cross-correlations between the local clock pulse stream (called pump in Kerr shutter notations) and the time-shifted replicas of the incoming received data signal (called probe). The outputs of the cross-correlators are subtracted to form the error signal of the OPLL. We characterize the mathematical structure of the proposed OPLL and identify its two intrinsic sources of phase noise, namely, randomness of the received optical data pulses and the photo-detectors’ shot noises. The effects of the noise sources on the proposed OPLL performance are investigated, using the power spectral densities (PSDs) of the signals involved in the OPLL. Finally, PSDs are used to obtain a mathematical expression for the timing jitter. The analytical results show that only the shot noises due to photodetectors affect the OPLL performance, whereas the randomness nature of the incoming data signal has no effect on timing jitter of the proposed OPLL. The numerical results exhibit a sub-femtosecond timing jitter, which is considered to be extremely low and negligible in comparison to the extrinsic noises to OPLL usually originated from the electronic devices.
We investigate theoretically the design of a phase-only (all-pass) filter using a Fiber Bragg Grating (FBG) to implement energy-efficient all-optical clock recovery from RZ-OOK data signals.
We report on a novel technique for all-optical clock recovery from RZ OOK data based on phase-only filtering, significantly enhancing the recovered clock quality and energy-efficiency compared to the use of a Fabry-Perot filter.
We report on a novel, efficient technique for all-optical clock recovery from RZ-OOK data signals based on spectral phase-only (all-pass) optical filtering. This technique significantly enhances both the recovered optical clock quality and energy efficiency in comparison with conventional amplitude optical filtering approaches using a Fabry–Perot filter. The proposed concept is validated through recovery of the optical clock from a 640 Gbit / s RZ-OOK data signal using a commercial linear optical waveshaper.
Implementing time gating in ultra-high speed OCDMA networks over long distance transmissions will require precise synchronization in order to suppress the influence of timing jitter on the OCDMA receiver. To implement optical gating, an optical clock is needed to control a switching window i.e., “a time gate” to pass the desired autocorrelation peak while blocking the MAI noise. We demonstrate that the use of a network global clock distribution is not necessary if the receiver synchronization is done via optical clock recovery. In our experimental demonstration a wider eye opening with power budget improvement of ~7.5 dB was achieved when using all-optical clock recovery compare to clock distribution.
An all-optical clock recovery scheme with wide range of ~12GHz is proposed and demonstrated using a silicon microring resonator assisted by an amplitude equalizer. Single and dual channel clock recovery at 40Gb/s has been achieved.
All-optical clock recovery by a two-section DFB laser with different injection wavelengths is demonstrated experimentally at 38.5 GHz. An optical clock with a root-mean-square timing jitter of 250 fs and an extinction ratio of 12.1 dB is obtained with 1551 nm injection. The timing jitter of the recovered clock is further investigated for various intensity ratios of the two DFB emission modes.
In this letter, a novel simultaneous demultiplexing and clock recovery unit based on EAMs and clock recovery module is presented and experimentally demonstrated for a high speed OTDM system. The 10GHz clock signal with low jitter is extracted from 80Gbit/s and 160Gbit/s OTDM signal, and every channel of the OTDM signal is successfully demultiplexed using this unit. The power penalty is lower than 3dB at BER of 10-9.
A clock recovery scheme simultaneous providing polarization de-multiplexing is proposed and demonstrated in a 160-Gbit/s polarization multiplexed NRZ-DQPSK system by employing optical domain frequency down-conversion with standard RF devices. © 2010 Optical Society of America OCIS codes: (060.2330) Fiber optics communications; (230.2090) Electro-optical devices
A simple and flexible simultaneous clock extraction for WDM signals with mixed modulation formats and bit-rates is proposed and demonstrated using a single commercial arrayed waveguide grating (AWG), which acts both detuned multi-channel filter and demultiplexer for the input signals. By using an AWG with 100GHz spacing, clock extraction from transmitted multi-channel nonreturn to zero (NRZ) and NRZ differential phase shift keying (NRZ-DPSK) signals at mixed bit-rates from 10 to 40Gb/s with 200GHz spacing is achieved simultaneously. By cascading a clock recovery module, clock signal can be easily recovered from the preprocessed signals with enhanced clock tones.
In this dissertation I investigated a multi-channel and multi-bit rate all-optical clock recovery device. This device, a birefringent Fabry-Perot resonator, had previously been demonstrated to simultaneously recover the clock signal from 10 wavelength channels operating at 10 Gb/s and one channel at 40 Gb/s. Similar to clock signals recovered from a conventional Fabry-Perot resonator, the clock signal from the birefringent resonator suffers from a bit pattern effect. I investigated this bit pattern effect for birefringent resonators numerically and experimentally and found that the bit pattern effect is less prominent than for clock signals from a conventional Fabry-Perot resonator. I also demonstrated photonic balancing which is an all-optical alternative to electrical balanced detection for phase shift keyed signals. An RZ-DPSK data signal was demodulated using a delay interferometer. The two logically opposite outputs from the delay interferometer then counter-propagated in a saturated SOA. This process created a differential signal which used all the signal power present in two consecutive symbols. I showed that this scheme could provide an optical alternative to electrical balanced detection by reducing the required OSNR by 3 dB. I also show how this method can provide amplitude regeneration to a signal after modulation format conversion. In this case an RZ-DPSK signal was converted to an amplitude modulation signal by the delay interferometer. The resulting amplitude modulated signal is degraded by both the amplitude noise and the phase noise of the original signal. The two logically opposite outputs from the delay interferometer again counter-propagated in a saturated SOA. Through limiting amplification and noise modulation this scheme provided amplitude regeneration and improved the Q-factor of the demodulated signal by 3.5 dB. Finally I investigated how SPM provided by the SOA can provide a method to reduce the in-band noise of a communication signal. The marks, which represented data, experienced a spectral shift due to SPM while the spaces, which consisted of noise, did not. A bandpass filter placed after the SOA then selected the signal and filtered out what was originally in-band noise. The receiver sensitivity was improved by 3 dB.
We propose, analyze and demonstrate the optoelectronic phase-locking of optical waves whose frequencies are chirped continuously and rapidly with time. The optical waves are derived from a common optoelectronic swept-frequency laser based on a semiconductor laser in a negative feedback loop, with a precisely linear frequency chirp of 400 GHz in 2 ms. In contrast to monochromatic waves, a differential delay between two linearly chirped optical waves results in a mutual frequency difference, and an acoustooptic frequency shifter is therefore used to phase-lock the two waves. We demonstrate and characterize homodyne and heterodyne optical phase-locked loops with rapidly chirped waves, and show the ability to precisely control the phase of the chirped optical waveform using a digital electronic oscillator. A loop bandwidth of ∼ 60 kHz, and a residual phase error variance of < 0.01 rad² between the chirped waves is obtained. Further, we demonstrate the simultaneous phase-locking of two optical paths to a common master waveform, and the ability to electronically control the resultant two-element optical phased array. The results of this work enable coherent power combining of high-power fiber amplifiers—where a rapidly chirping seed laser reduces stimulated Brillouin scattering—and electronic beam steering of chirped optical waves.
We propose and experimentally demonstrate the temporal-Talbot-effect (TTE)-based preprocessing for the pattern-effect reduction in the all-optical clock recovery using a semiconductor-optical-amplifier (SOA)-based fiber ring laser (SOA-FRL). The TTE-based preprocessing successfully reduced the pattern effects of the recovered clock pulses, so that the 10-GHz clear optical clock pulses were recovered from a 10-Gbit/s return-to-zero on–off keying (RZ-OOK) pseudo-random bit sequence (PRBS) optical signal. “Peak variation” and “Pattern-dependent intensity noise (PDIN)” were proposed and were utilized as parameters to quantitatively evaluate the pattern effects, from which recovered clock pulses suffer, in the temporal domain and the frequency domain, respectively. Peak variation was reduced from 77.2% to 36.2%, and PDIN was improved from −103 dBc/Hz to −110 dBc/Hz with the aid of the TTE-based preprocessing. Furthermore, we examined the tolerance of the proposed technique by intentionally deviating the input signal’s bit-rate by ±190 Mbit/s (±2% of the bit-rate) from the optimum condition for the TTE. As compared with the PDIN value for the pulse train obtained by the direct injection of the non-processed signal into the SOA-FRL, the PDIN of the recovered clock pulses using the preprocessed signal indicated improvements over the entire measurement range of ±190 Mbit/s, which corresponds to the wavelength-dispersion deviation of ±56 ps/nm (±4% of the wavelength-dispersion applied to the input signal) from the optimum value.
The bandwidth and residual phase noise of optical phaselocked loops (OPLLs) using semiconductor lasers are typically constrained by the nonuniform frequency modulation response of the laser, limiting their usefulness in a number of applications. It is shown in this work that additional feedback control using an optical phase modulator
improves the coherence between the master and slave lasers in the OPLL by achieving bandwidths determined only by the propagation delay in the loop. A phase noise reduction by more than a factor of two is demonstrated in a proof-of-concept experiment using a commercial distributed feedback semiconductor laser.
All optical clock recovery has been experimentally demonstrated by an actively mode-locked fiber ring based on the semiconductor optical amplifier (SOA) from a 10-Gb/s NRZ data stream. The system exploits the cross-gain modulation (XGM) nonlinear effect in SOA, and a Fabry–Perot etalon suitably inserted in the loop improves the mode-locking stabilization and efficiency. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 42: 435–437, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20328
We present a traveling-wave large-signal simulation of the spatiotemporal dynamics of two-section distributed feedback lasers, emphasizing the self-pulsation phenomenon. For index-coupled lasers, self-pulsation is a result of the interaction of two modes, each spatially confined primarily to one section. For partially gain-coupled lasers, self-pulsation is a result of the interaction of two modes, one that is spatially confined primarily to one section and another that belongs to both sections. The self-pulsation frequency-tuning range and the modulation index of partially gain-coupled lasers are found to be substantially larger than those of index-coupled lasers. Experimentally, self-pulsation with a frequency-tuning range from 20 to 60 GHz in two-section partially gain-coupled distributed-feedback lasers has been characterized in the electrical domain. The noise of self-pulsation was reduced experimentally by optical feedback.
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.
We demonstrate an optical clock recovery circuit that extracts the line rate component on a per packet basis from short data packets at 40 Gb/s. The circuit comprises a Fabry-Perot filter followed by a novel power limiting configuration, which in turn consists of a 5m highly nonlinear bismuth oxide fiber in cascade with an optical bandpass filter. Both experimental and simulation-based results are in close agreement and reveal that the proposed circuit acquires the timing information within only a small number of bits, yielding a packet clock for every respective data packet. Moreover, we investigate theoretically the scaling laws for the parameters of the circuit for operation beyond 40 Gb/s and present simulation results showing successful packet clock extraction for 160 Gb/s data packets. Finally, the circuit’s potential for operation at 320 Gb/s is discussed, indicating that ultrafast packet clock recovery should be in principle feasible by exploiting the passive structure of the device and the fsec-scale nonlinear response of the optical fiber.
We report on a passive all-optical clock recovery technique based on data signal filtering with a Fabry-Perot filter, tested in a 40 Gb/s transmission system. We have simulated the clock recovery principle to choose the filter finesse and then investigate with experiment the method for 43 Gbit/s RZ signal clock recovery ahead of a receiver. We use Bit Error Rate assessment to demonstrate its system compatibility and to evaluate both its pattern sequence length tolerance and, for the first time, its clock locking range.
We present and evaluate a compact, all-optical Clock and Data Recovery (CDR) circuit based on integrated Mach Zehnder interferometric switches. Successful operation for short packet-mode traffic of variable length and phase alignment is demonstrated. The acquired clock signal rises within 2 bits and decays within 15 bits, irrespective of packet length and phase. Error-free operation is demonstrated at 10 Gb/s.
We demonstrate a 40 Gb/s self-synchronizing, all-optical packet clock recovery circuit designed for efficient packet-mode traffic. The circuit locks instantaneously and enables sub-nanosecond packet spacing due to the low clock persistence time. A low-Q Fabry-Perot filter is used as a passive resonator tuned to the line-rate that generates a retimed clock-resembling signal. As a reshaping element, an optical power-limiting gate is incorporated to perform bitwise pulse equalization. Using two preamble bits, the clock is captured instantly and persists for the duration of the data packet increased by 16 bits. The performance of the circuit suggests its suitability for future all-optical packet-switched networks with reduced transmission overhead and fine network granularity.
In this paper, we proposed and demonstrated all-optical clock recovery at 10GHz with switchable wavelengths. Very stable clock signals corresponding to the bit rate of the injection data have been obtained by injecting 10Gbit/s 2³¹-1 PRBS data signals into the ring cavity. Wavelength switching among eight wavelengths is achieved by merely tuning the delay time of the intra-cavity optical delay line. The proposed clock recovery method is experimentally demonstrated to be insensitive to the polarization changes of the input data.
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.
In this paper, we present a scheme for extracting a 10GHz clock from the 80Gb/s optical time division multiplexed (OTDM) return to zero (RZ) data stream. The proposed clock recovery is based on the offset locking technique. By using the input data composed of a repeating “10100000” pattern, residue jitter free operation for clock recovery is demonstrated. The method utilizes a LiNbO3 Mach-Zehnder (MZ) intensity modulator for cross-correlation detections.
A passive all-optical scheme for clock extraction from non return-to-zero (NRZ) data has been proposed based on narrow-band filtering. Two equally effective embodiments of the proposed scheme have been demonstrated experimentally. A carrier-to-noise ratio (CNR) of 30 dB has been achieved at 40 Gbit/s using fiber Bragg gratings (FBG).
We demonstrate simultaneous demultiplexing, data regeneration and clock recovery at 10 Gbits/s, using a single semiconductor optical amplifier–based nonlinear-optical loop mirror in a phase-locked loop configuration.
We present successful extraction of a 10 GHz clock from single-wavelength 160 and 320 Gbps OTDM data streams, using an opto-electronic phase-locked loop based on three-wave mixing in periodically-poled lithium niobate as a phase comparator.
Self-pulsation at 45 GHz repetition frequency has been demonstrated in 1.5 μm monolithic single-section quantum dot Fabry-Perot semiconductor lasers without saturable absorber. The mode-beating exhibits a narrow linewidth below 100 kHz, demonstrating high phase correlation between these modes. Such modelocked lasers open ways to low timing-jitter components for clock recovery or millimetre-wave generation in wireless transmission applications.
Optical clock recovery and clock division is demonstrated from a pseudo-data pattern at 20 Gb/s, using a semiconductor optical amplifier fibre ring laser. The ring laser is capable of generating 4.7 ps pulses at 20 GHz repetition rate and less than 3 ps pulses at the divided clock frequencies of 10 and 5 GHz, over a 16 nm tuning range. The effect of the input data pattern on the recovered clock signal is investigated. The extinction ratio of the recovered clock signal to the clock sub-harmonics was found to be as high as 40 dB despite the long series of consecutive zeros of input pattern.
For optical clock recovery of nonreturn-to-zero (NRZ) signals more than 40 Gb/s, we propose and experimentally demonstrate a simple clock recovery scheme using beat processing. Through the proposed scheme, we square the adjustment range of the variable optical attenuator (VOA) and achieved an enhanced clock-to-noise ratio (CNR) of more than 15 dB in the experiment, compared to a system without the proposed scheme.
cw assist light in the gain region or at transparency wavelength of a semiconductor optical amplifier (SOA) is introduced into an SOA-based clock recovery circuit to overcome the pattern effect. A numerical model considering intraband effects in the SOA, such as carrier heating and spectrum hole burning, is constructed to study the pattern effect on clock recovery. The pattern effect reductions for different injection powers and wavelengths of cw assist light and different bias currents of the SOA are simulated to optimize this system. In an experiment, high-quality clock pulses were recovered from a (231-1)-pseudorandom-bit sequence (PRBS) at 20 and 40 Gbit/s by using cw assist light. Simulation and experimental results show that a lower pattern effect can be effectively obtained by using a cw assist light with highest power near the highest-gain wavelength when the SOA works at a high current level. In this respect, cw assist light in the gain region is superior to light at the transparency wavelength. This scheme can be applied to SOA-based all-optical clock recovery and other all-optical signal processing for pattern effect reduction.
We present a scheme for recovering a 10-GHz clock from a 40- and 80-Gb/s time-division-multiplexed (TDM) return-to-zero (RZ) data stream. The proposed clock recovery is successfully demonstrated using an electrical phase-locked loop (PLL). The jitter of the recovered clock is estimated to be around 50 fs. The key part in the proposed clock recovery circuit is a LiNbO3 Mach-Zehnder modulator, which is shown to be highly effective in optical to electrical down conversion. (C) 2004 Society of Photo-Optical Instrumentation Engineers.
A 40Gbit/s optical 3R regenerator is proposed and demonstrated. The 3R regenerator consists of a dual-ring injection mode-locked fiber ring laser as the clock recovery module and an electroabsorption modulator (EAM) as the decision gate. The clock recovery module extracts the optical short pulse clock with low timing jitter from degraded 40Gbit/s optical data streams, while the decision gate restores their signal quality. A numerical model describing the cross-absorption modulation effect in a bulk EAM is developed to explore the operating conditions, such as bias voltage, pump signal power. The timing jitter tolerance for the EAM optical gate is also investigated. Significantly improvement of BER is obtained from 40Gbit/s RZ signals which are degraded by polarization mode dispersion or chromatic dispersion.
An optical clock has been experimentally recovered by an actively mode-locked fiber ring based on a semiconductor optical amplifier (SOA) from a 10-Gb/s NRZ data stream after propagation on 100 km of installed fiber (either DS, or NZD, or SR). The results indicate the flexibility and robustness of the technique, which seems well suited for application in optical networks. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 44: 264–266, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20606
We propose and demonstrate nonreturn-to-zero (NRZ) to pseudoreturn-to-zero (PRZ) data format conversion at 10 Gb/s based on transverse-magnetic (TM) mode absorption and self-phase modulation (SPM) in a Fabry-Pe´rot laser diode (FP-LD). An FP-LD has absorption nulls for TM mode injected beam and the beam having NRZ data experiences SPM, which induces a frequency chirp at every rising edge and falling edge. By extracting the chirp components, all-optical NRZ-to-PRZ format conversion has been achieved. The resultant PRZ data gives well-defined 10-Gb/s clock signal. This method will be very useful in all-optical clock recovery of high-speed optical communication systems.
A scheme for wavelength and polarization insensitive all-optical clock extraction and enhancement of nonreturn-to-zero (NRZ) data is proposed and demonstrated. At 10 Gbit/s, more than 7-dB clock enhancement and 19-dB clock-to-data suppression ratio (CDSR) enhancement have been realized using a semiconductor optical amplifier (SOA) and a reflective fiber Bragg grating (FBG) over a 30-nm input wavelength range. (C) 2004 Society of Photo-Optical Instrumentation Engineers.
A novel scheme for all-optical frequency multiplication/recovery based on a semiconductor optical amplifier ring cavity is proposed and investigated numerically. The results show, for a 2.5 GHz driving pulse train, it can be generated 5-25 GHz repetition rate pulse trains with low clock amplitude jitter, polarization independence and high peak power. Furthermore, the extraction of the clock signal from a pseudorandom bit sequence signal can be realized based on the proposed scheme. (c) 2005 Elsevier B.V. All rights reserved.
We propose a novel configuration for clock extraction by converting the NRZ data into the PRZ data and by employing a polarization-maintaining fibre loop mirror (PMFLM) which is usually used as an optical comb filter. It is found that the PMFLM can simply be constructed by a polarization controller and polarization-maintaining fibre (PMF). We theoretically analyse the principle of PMFLM for the NRZ-to-PRZ conversion. Experimentally we demonstrate 10 Gbit/s all-optical clock recovery through our proposed setup. It is shown that recovered clock signal with an extinction ratio above 10 dB can be achieved.
All-optical clock recovery is performed using a multisection semiconductor laser that can generate two kinds of self-pulsation due to compound cavity mode beating and passive mode locking. To investigate factors to influence quality of optical clock, optical clocks recovered from an optical data are compared by using various self-pulsations with different characteristics. It is experimentally demonstrated that characteristics of optical clock depend on free-running characteristics of a RF linewidth and amplitude noise. In particular, optical clock with a subpicosecond jitter is recovered by use of a self-pulsation with a narrow linewidth and low amplitude noise of the monolithic semiconductor laser in the 10 GHz regime. The free-running characteristics can be utilized as a criterion of a potential of self-pulsating semiconductor lasers for all-optical clock recovery.
A novel clock recovery scheme using two-ring injection mode-locked fiber ring laser based on all 10 GHz bandwidth components was demonstrated. With this scheme, the clock with low timing jitter was obtained from a degraded 10 Gb/s optical data stream. Optical clock recovery was also achieved from a degraded 20 Gb/s optical data train when the clock division technique in the opto-electronic oscillator (OEO) and the rational harmonic mode-locking technique in the fiber ring laser were applied. No pattern effect was observed in the experiments.
10 GHz clock recovery from 40 Gbps optical time-division-multiplexed (OTDM) signal pulses is experimentally demonstrated using optical phase lock loop based on a terahertz optical asymmetric demultiplexer (TOAD) with a local-reference-oscillator-free electronic feedback circuit. The clock pulse that was used as the control pulse had energy of 800 fJ and the SNR of the time-extracted 10 GHz RF signal to the side components was larger than 40 dB.
2007. Investigation of multiwavelength clock recovery based on heterodyne beats of sideband-filtered signal. Optics Communications, volume 271, number 1, pages 87-90. Abstract We investigate a new parallel all-optical clock recovery scheme based on heterodyne beats of an optical sideband-filtered signal. The oscillating clock signal is recovered when the filtered sideband is combined with a stable local oscillator. The filtering is performed with an optical resonator, which by nature provides possibility for multiwavelength operation. The local oscillator could be realized by a mul-tiwavelength laser, whose emission wavelengths are injection seeded with carrier wavelengths of the input data. The output signal of such a configuration benefits from a reduced bit-pattern effect and a stable offset level. The sideband filtering is demonstrated for 23 simul-taneous channels at 100 GHz DWDM grid, each hosting a data stream of 10 Gbit/s.
A novel NRZ-to-PRZ converter consisting of an SOA and an AWG is proposed. The parameters are investigated through numerical analysis to optimize its performance. In the experiments, all-optical clock recovery from NRZ data and NRZ-to-RZ format conversion are successfully demonstrated at 10 Gb/s, which further proves that the proposed scheme is applicable. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 516–521, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21396
For optical clock recovery of nonreturn-to-zero (NRZ) signals of more than 40 Gb/s, we propose and experimentally demonstrate a simple clock recovery scheme through beating process between the carrier frequency component and one of the clock frequency components in modulated NRZ signals. The proposed scheme consists of a circulator, a variable optical attenuator (VOA), and two fiber Bragg grating (FBG) filters. With FBG filters and a VOA, the proposed scheme can equalize the amplitudes of two extracted frequency components for a maximum clock-to-noise ratio (CNR). Through this scheme, we have squared the adjustment range of the VOA and achieved an enhanced CNR of more than 15 dB before the receiver in experiment. Bit error rate (BER) curves for back-to-back and 80 km transmissions showed that BERs of less than 10−11 can be obtained without error floors for both cases. We expect that the proposed scheme can operate as an efficient clock extraction system for high-speed optical communications.
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.
A novel all-optical frequency multiplication/recovery technique based on a repetitive pulse intensity matching is proposed and demonstrated. Unlike a rational harmonic mode locking requiring additional stabilizing functions, this technique can be used to generate stable and input polarization independent optical pulse trains with the repetition rates of 2.5–12.5 GHz from 2.5 GHz driving pulse. Also, this scheme can be applied to the extraction of the clock signal from a pseudorandom bit sequence signal.
All optical bit clock recovery is one of the key technologies for all optical 3R recovery. In this paper, a simple method applying the combination of Fabry–Perot (F–P) filter and semiconductor optical amplifier (SOA) for clock recovery is proposed. The effect of the F–P filter finesse on the clock recovery and the reduction in the amplitude fluctuation of the clock pulse by the SOA are discussed theoretically. With this technology clock recovery with equal amplitude and wavelength transparency was realized experimentally.
A new phase lock loop (PLL) is proposed and demonstrated for clock recovery from 40 Gbps time-division-multiplexed (TDM) optical signal using simple optical phase lock loop circuit. The proposed clock recovery scheme improves the jitter effect in PLL circuit from the clock pulse laser of harmonically-mode locked fiber laser. 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 SOA. The lock-in frequency range of the clock recovery is found to be within 10 KHz.
We report a wavelength-tunable clock recovery scheme for all-optical 3R regeneration and simultaneous wavelength conversion. The scheme is based on a fiber-optic parametric oscillator, in which dynamic gain results from the four-wave mixing process in the fiber. In our implementation, 2.9 ps clock pulses are recovered from the incident pseudo-random data stream with the clock wavelength being tunable over the whole erbium-doped-fiber-amplifier bandwidth. RF spectrum measurements show that the recovered clock has less timing jitter than the incident data stream. We also present a two-channel clock recovery experiment, which demonstrates the feasibility of our scheme at 100 Gbit/s data rate.
The advent of optical fibers has greatly impacted the modern technology landscape. Most notably, existing telecommunications infrastructure relies on optical fiber networks, which have the ability to transmit high-bandwidth data over considerable distances. Optical fibers have also visible foothold in the field of metrology, where they are used as sensors in various applications. An optical resonator is a basic building block of many optical devices, such as lasers, measurement probes, and optical signal processing equipment. In this dissertation we propose new methods and tools for metrology and general telecommunications sciences based on fiber optical resonators. Compared to conventional free-space technology, fiber resonators enable easy connectivity and they are shown to be robust against ambient perturbations. This thesis consists of two parts that concentrate on optical measurement and signal processing technology, respectively. The first part introduces new measurement schemes for fiber loss and minute birefringence quantification. A loss of an optical fiber medium is measured using a so-called fiber cavity ring-down method. In presence of an external source of loss, such as fiber bending or degradation, one may obtain information about the environment of the probe. Another scheme measures birefringence and, thus, the beat length of a short fiber section. We also suggest a computational method for resonator photon lifetime (also called resonator time constant) extraction under noisy signal conditions. We demonstrate that the developed algorithm may yield meaningful results even when conventional methods fail. The second part of the thesis deals with all-optical signal processing and temporal data synchronization. In a proof-of-principle experiment we perform an all-optical clock recovery for 21 parallel wavelength channels at two simultaneous data rates. The method relies on a birefringent optical resonator, whose transmission spectrum is used to filter carrier and sideband frequencies of return-to-zero-modulated data for multiple wavelength channels. In another clock recovery experiment we investigate the possibility to use sideband filtered signal, combined with a continuous wave light emitted at the carrier wavelength. TKK dissertations, ISSN 1795-4584; 84
All-optical clock recovery (CR) from 10 Gbps non-return-to-zero differential phase-shift-keying (NRZ-DPSK) signal is demonstrated experimentally, with the chromatic dispersion induced clock tone and semiconductor optical amplifier (SOA)-based mode-locked fiber ring laser. The good performance of our proposed configuration is fulfilled with a 20 km standard single mode fiber to regenerate clock tone of the NRZ-DPSK signal. The recovered clock signal with the extinction ratio over 17 dB and the root-mean-square timing jitter of 718 fs is achieved under 231-1 pseudorandom binary sequence NRZ-DPSK signals measurement.
Operating principles and experimental testing results are reviewed for several multiple-WDM channel nonlinear fibre devices: optical clock recovery, 2R regenerator and dynamic residual dispersion compensator.
We describe an optical clock recovery circuit that employs a traveling-wave electroabsorption modulator-based ring oscillator. This approach provides synchronized optical clock and the original optical data signal from the same output at separate wavelengths, eliminating additional timing adjustments for the subsequent nonlinear decision gate for reamplifying, reshaping, and retiming (3R) regeneration. Furthermore, additional retiming and lateral reshaping of the original data signal can be realized along with optical clock recovery by synchronized modulation. We present a general model of jitter transfer and locking dynamics for the clock recovery circuit and compare with experimental results. Theoretical results indicate that by using hybrid integration to shorten the cavity length, nanosecond-order locking time can be achieved, which is critical for a variety of applications such as protection switching, optical burst and optical packet switching. Experimental demonstrations of 40-Gb/s optical clock recovery and its application for optical 3R regeneration are presented. The recovered 40-GHz optical clock has 500-fs timing jitter and 8-ps pulsewidth, and within 0.3 μs locking time. 3R experiment is implemented by using the OCR combined with a subsequent regenerative wavelength converter, which provides vertical reshaping function. 3R regeneration is demonstrated with a reduced timing jitter.
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
Pre-scaled clock recovery of a serial 640 Gbit/s data signal is demonstrated using a quasi-phase-matching periodically poled lithium niobate module as an ultrafast phase comparator in an optoelectronic phase- locked loop.