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Characterisation of an optical clock recovery method based on a mode-locked laser diode using spectrographic pulse measurement
Optics Express
Abstract
As channels rates in optical networks are expected to exceed 100 Gb/s in the near future, new optical techniques for clock recovery will have to be developed for optical regeneration. This paper describes an optical clock recovery method based on a mode-locked laser diode. Experimental results show that a 42 GHz high quality optical clock can be retrieved from a 170 Gb/s OTDM data signal. Chirp transfer between the incident signal and the recovered clock signal is investigated using the SHG-FROG method. Results demonstrate that this clock recovery technique is invariant to input dispersion varying between +/-75 ps/nm, making it ideal for use in 3R regenerators.
We proposed and demonstrated a novel, simple, and low cost method for all-optical clock recovery based on the switching between two injection-locked longitudinal modes in a dc-biased multi-quantum-well Fabry-Perot laser diode (FP-LD). The dc biased FP-LD is simultaneously injection-locked by a return-to-zero data signal at one of the longitudinal modes of the FP-LD and self-seeded at another longitudinal mode by using a uniform fiber Bragg grating as a feedback component. The powers and detunes of the data signal and self-seeding signal are chosen such that self-seeding is realized in the FP-LD only when data signal power is low. Clock signals of data streams at different data rates can be obtained by tuning the optical delay line in the external self-seeding loop. We have demonstrated all-optical clock recovery at 10 GHz. The pulse width, time-bandwidth product, side mode suppression ration, root mean square timing jitter, and average power of the recovered clock signals are 50 ps, 0.5, 50 dB, 248 fs, and 3.6 dBm, respectively. Clock recovery is possible at wavelength within the gain band of the FP-LD. We also find and explore in the experiment the influence of detune between the external data signal and the nearest FP-LD longitudinal mode to the recovered clock.
We summarize the problem of measuring an ultrashort laser pulse and describe in detail a technique that completely characterizes a pulse in time: frequency-resolved optical gating. Emphasis is placed on the choice of experimental beam geometry and the implementation of the iterative phase-retrieval algorithm that together yield an accurate measurement of the pulse time-dependent intensity and phase over a wide range of circumstances. We compare several commonly used beam geometries, displaying sample traces for each and showing where each is appropriate, and we give a detailed description of the pulse-retrieval algorithm for each of these cases. © 1997 American Institute of Physics.
We demonstrate for the first time, thanks to a quantum-dots Fabry-Perot laser, the compliance of an all-optical 40 GHz clock recovery with ITU-T standards on time jitter removal for frequencies larger than 4 MHz.
Bit-error-rate assessment of a multi-rate all-optical clock recovery (OCR) based on a narrow linewidth mode-locked quantum-dot (QD) Fabry-Perot laser is presented in this letter. OCR has been achieved without external feedback. We use a QD Fabry-Perot semiconductor laser designed for 40-GHz clock extraction. We then present OCR performance with 40-, 80-, and 160-Gb/s input data signal and demonstrate that clock recovery has been obtained thanks to subharmonic locking process. Results are presented through penalty measurement using an original characterization based on recovered clock remodulation with electrical data from the transmitter. This technique allows us to evaluate the quality of the recovered clock.
All-optical clock recovery from 180-Gb/s data streams has been demonstrated using a self-pulsing multisection gain-coupled distributed feedback laser. The laser produces self-pulsations with a tuning range of more than 230 GHz. The recovered clock has a jitter of less than 410 fs over a dynamic range of 7 dB.
Clock recovery (CR) from a 160-Gb/s data signal is demonstrated using a single unidirectional electroabsorption modulator in a cost-effective phase-locked loop configuration consisting entirely of commercially available components. The CR exhibits a root mean square time jitter of 205 fs, a holding range of 10 MHz, a wavelength-independent performance of 10 nm, and an input dynamic range of 10 dB. Demultiplexing experiments of transmitted 160-Gb/s data through installed fiber links over 275.4 km verified the excellent performance of the proposed CR. All 16 10-Gb/s channels were demultiplexed error-free.
The authors describe the design and performance of an ultrafast optical clock recovery system that is based on two-photon absorption (TPA) in a silicon avalanche photodiode. Unlike many other optical clock recovery techniques, the system is shown to be polarization insensitive, broadband, low jitter, and scalable to high data rates. Moreover, the system is simple, economical, and suitable for integration with silicon electronics. Successful operation of the system is reported for speeds up to 80 Gb/s and transmission distances up to 840 km using a recirculating loop. The authors introduce a new dithering detection scheme that dramatically improves the dynamic range and decreases polarization and wavelength dependence, without introducing an additional timing jitter. The system achieves a dynamic range of 10 dB and optical bandwidth exceeding 35 nm.
The potential for using inexpensive compact disc laser diodes as
optical clock extraction elements in transparent networks has led to an
increase in research into the dynamics of self-pulsating laser diodes.
We use a rate-equation model to simulate the synchronization of the
self-pulsating laser output pulses to a periodic optical signal, In
particular, we investigate the time it takes for the laser to
synchronize to the input signal and also, the time taken for the laser
to unlock when the signal is removed. The effect of varying the power of
the optical signal and the detuning of the input signal frequency
relative to the laser's self-pulsation frequency are determined. Our
results enable us to identify important issues which need to be
addressed when a self-pulsating laser diode is used in a clock
extraction subsystem, In particular, we find that the signal frequency
and laser free-running frequency must be as close as possibility to
minimize errors. Also, the higher the signal power the quicker the laser
synchronizes to the signal, although we find that if the power becomes
too large the laser can no longer lock, which would cause a significant
increase in detection errors
In this paper we propose BER measurements allowing to demonstrate the ultra-low sensitivity of an all-optical clock recovery on a quantum-dash Fabry-Perot Laser to chromatic dispersion and optical noise on the injected data signal.
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
A fast, compact optical clock recovery device that uses a regeneratively modelocked semiconductor laser had been developed, and a 40 GHz optical clock signal was successfully recovered from a 160 Gbit/s data stream. It was confirmed that the regeneration loop is effective in achieving stable operation with low timing jitter.
A novel all-optical clock recovery scheme in which an optical data stream is used to mode-lock a fibre laser at (or at integer multiple of) the line rate is experimentally demonstrated. A length of data transmission fibre is shared with the fibre laser and mode locking occurs through the process of crossphase modulation.
All-optical timing extraction from an intensity modulated 196
Mbit/s return to zero optical data stream by the injection locking
technique, using a 1.5 μm self-pulsating multielectrode DFB laser
diode (LD) is demonstrated. A frequency lock-in range, which depends
upon both the injection signal level and the length of space
continuation is investigated
We present ultrafast slotted optical time-division multiplexed networks as a viable means of implementing a highly capable next-generation all-optical packet-switched network. Such a network is capable of providing simple network management, the ability to support variable quality-of-service, self-routing of packets, scalability in the number of users, and the use of digital regeneration, buffering, and encryption. We review all-optical switch and Boolean logic gate implementations using an ultrafast nonlinear interferometers (UNIs) that are capable of stable, pattern-independent operation at speeds in excess of 100 Gb/s. We expand the capability provided by the UNI beyond switching and logic demonstrations to include system-level functions such as packet synchronization, address comparison, and rate conversion. We use these advanced all-optical signal processing capabilities to demonstrate a slotted OTDM multiaccess network testbed operating at 112.5 Gb/s line rates with inherent scalability in the number of users and system line rates. We also report on long-haul propagation of short optical pulses in fiber and all-optical 3R regeneration as a viable cost-effective means of extending the long-haul distance of our OTDM network to distances much greater than 100 km.
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
The field of high speed semiconductor lasers has undergone substantial advances since the first demonstration of a laser with modulation bandwidth beyond 1OGHz[1]. Much of the present understanding on the high speed modulation of semiconductor lasers comes from a small signal analysis of the laser rate equations, which is basically a book-keeping of the rate of supply, annihilation and creation of carriers and photons inside the laser cavity and describes laser dynamics in a most basic manner. The resulting small signal bandwidth is given by the now standard formula [1]
Retiming and reshaping behaviors in an all-optical clock extraction operation at 160 Gb/s using a monolithic 160-GHz mode-locked laser diode was investigated in detail. The investigation of the basic clock extraction performance revealed that the clock extraction was stable against the input of data signals with a long zero sequence and with a poor extinction ratio. The clock extraction performance when the input data had random intensity and timing fluctuations was also discussed. We revealed that the generated clock pulse train absorbed well the intensity and timing fluctuations of the input data. Stable clock extraction remained even when the input data had 25% of the peak-intensity fluctuations. A timing jitter reduction from 0.85 to 0.32 ps was also achieved. The detailed investigation in the frequency-domain analysis of the jitter spectra revealed that the timing jitter reduction originated from the short-term stability of the slave 160-GHz mode-locked laser diode.