No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Influence of free-running characteristics on optical clock in all-optical clock recovery using a self-pulsating semiconductor laser
Abstract
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.
... There are three kinds of compact devices such as mode-locked laser diodes (MLLD) [1], dual-mode laser with two different DFB-sections (TS-DFB) [2] and amplified feedback DFB lasers (AFL) [3,4,5,6] reported as all-optical clock recovery devices. The oscillating frequency of MLLDs is almost fixed by the lengths of their cavity, so the limitation of the fabrication accuracy makes it difficult to achieving precise frequency control. ...
... [3] in 2006, Dae-Su Yee, Y. A. Leem et al. fabricated a three-section AFL realized 10Gbs clock recovery based on passive mode locking mechanism. [4]In 2007, they published [5], which reported a three-section AFL as a 33Gbs clock regenerator. ...
We report all optical clock recovery based on a monolithic integrated four-section amplified feedback semiconductor laser (AFL), with the different sections integrated based on the quantum well intermixing (QWI) technique. The beat frequency of an AFL is continuously tunable in the range of 19.8-26.3 GHz with an extinction ratio above 8 dB, and the 3-dB linewidth is close to 3 MHz. All- optical clock recovery for 20 Gb/s was demonstrated experimentally using the AFL, with a time jitter of 123.9 fs. Degraded signal clock recovery was also successfully demonstrated using both the dispersion and polarization mode dispersion (PMD) degraded signals separately.
... In order to generate high quality optical microwave, the M-B with narrow linewidth is equally necessary besides the characteristics of wide frequency tunability. It was experimentally demonstrated that the quality of the recovered clock signal depend greatly on the free-running M-B linewidth characteristics [33]. In Fig. 12, blue line shows the RF spectrum of the free-running M-B at 39.9 GHz. ...
The dynamics of monolithically integrated amplified feedback lasers (AFL) is investigated through numerical simulation and experimental verification. The period-doubling route to chaos and high-frequency microwave generation are demonstrated through simulation. Then, we design and fabricate monolithically integrated AFLs. Mappings of dynamic states and oscillation frequency in the parameter space of phase section current $I_{rm P}$ and amplifier section current $I_{rm A}$ are depicted. For relative small $I_{rm A}$, the period doubling evolution to chaos is presented with the increase of $I_{rm P}$ . For the relative large $I_{rm A}$, a high-frequency mode-beating (M-B) pulsation can be observed under suitable value of $I_{rm P}$. The oscillation frequency of period-one is about 10 GHz and the frequency of M-B pulsation is over 40 GHz for the device with a total length of 780 μm.
... Operation speed of the three-section device have been demonstrated up to 40 GHz [76][77][78][79][80][81]. In on-going development the multisection laser diodes have incorporated four [82,83], and five [84,85] separate sections. ...
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.
A compact and simple approach to realizing tunable high-frequency photonic microwave using a directly-modulated dual-wavelength amplified feedback laser (AFL) diode is demonstrated. By directly modulating the AFL at the 1/2 sub-harmonic frequency of its fundamental mode spacing, frequency-doubled microwave is generated. At a low RF driven power of 2.8 dBm, tunable microwave outputs ranging from 15 GHz to 33 GHz are obtained with 2-GHz locking range. The phase noise and frequency stability of the generated microwave signal are also investigated. The proposed scheme requires much lower RF driven power and can be a viable choice for situations where high power and high frequency RF signal is not available.
We demonstrate a monolithically integrated dual-mode laser (DML) with narrow-beat-linewidth and wide-beat-tunability. Using a monolithic DFB laser subjected to amplified feedback, photonic microwave generation of up to 45?GHz is obtained with higher than 15?GHz beat frequency tunability. Thanks to the high phase correlation of the two modes and the narrow mode linewidth, a RF linewidth of lower than 50?kHz is measured. Simulations are also carried out to illustrate the dual-mode beat characteristic. Furthermore, using the DML, an all-optical clock recovery for 40? Gbaud NRZ-QPSK signals is demonstrated. Timing jitter of lower than 363?fs (integrated within a frequency range from 100?Hz to 1?GHz) is obtained.
A novel mode-beating DBR laser with dual-mode lasing is fabricated. The
DBR laser has four parts, a front gain section, a phase section, a DBR
grating section, and a rear gain section. When the current of the front
gain section is above the threshold, the device is working in
single-mode. Dual-mode lasing can be obtained by adjusting the current
of the rear gain section. The power difference between the two modes can
be less than 1 dB. An optical down-conversion technique was used to
measure the beating frequency. The mode-beating frequency of the two
modes is about 93 GHz, and the 3- dB linewidth of the mode-beating RF
spectrum of the laser when free-running is about 5 MHz. Moreover, the
wavelength of the dual-mode can be tuned synchronously when the current
injected into the DBR grating section is adjusted. The wavelength tuning
range of the device is at least 3 nm.
In this letter, we report a novel mode-beating distributed Bragg reflector (DBR) laser with dual-mode output. Both the working wavelengths and mode spacing of the dual-mode laser can be tuned when the currents injected into the DBR laser are adjusted. The tuning ranges of the laser wavelength and mode-beating frequency are [1527.20 nm, 1531.04 nm] and [91.88 GHz, 94.02 GHz] , respectively. A fourth harmonic injection locking is also demonstrated to achieve a synchronized RF output at 93.23 GHz. The phase noise of the RF output is measured by using the down-conversion method. A single sideband phase noise of 96.92 dBc/Hz with 1-MHz offset at a down-converted frequency of 13.23 GHz is achieved.
We present and demonstrate all-optical clock recovery (CR) from the input single- and multiwavelength return-to-zero (RZ) data, using a single multiquantum-well Fabry–Pérot semiconductor optical amplifier (FP-SOA) with no additional amplitude equalization measures. The influence of the FP-SOA facet reflectivity on the amplitude equalization of the recovered clock was numerically investigated. A stable 36.55 GHz optical clock with an extinction ratio of 11.0 dB and a root-mean-square timing jitter of 575 fs was extracted from the input, which consisted of $2^{23} {-}1$ pseudorandom binary sequences of RZ data. The presented scheme has the potential to perform CR from more than 100 Gbit/s of RZ data, and it has the advantage of wideband and parallel operation.
All-optical clock recovery is a key technology in all-optical 3R signal regeneration (Re-amplification, Retiming, and Reshaping) process. In this paper, a monolithic integrated three-section amplified feedback semiconductor laser (AFL) is demonstrated as an all optical clock regenerator. We fabricated a three-section AFL using quantum well intermixing process without regrowth instead of butt-joint process. The tunable characteristics of three-section AFL were investigated, and all optical clock recovery for 40Gb/s return to zero (RZ) 2<sup>31</sup>−1 pseudorandom binary sequence (PRBS) is demonstrated experimentally using AFL with time jitter about 689.2fs.
Monolithic self-pulsating semiconductor lasers called amplified feedback lasers (AFLs) can generate high-frequency self-pulsations according to the concept of a single-mode laser with shortly delayed optical feedback, which consist of a distributed-feedback (DFB) laser, a phase control, and an amplifier section. Since mode degeneracy of the DFB section, which should operate as a single-mode laser, affects the self-pulsation, single-mode characteristics of the DFB section are critical for the self-pulsation. The effect of a complex coupling in the DFB section on the self-pulsation is numerically analyzed to reveal that the complex coupling provides a wide operation range for the self-pulsation. Also, self-pulsating AFLs based on a loss-coupled DFB laser are experimentally demonstrated to verify the self-pulsation characteristics and the capability for all-optical clock recovery.
An experimental and theoretical investigation of the fluctuations of the pulses from continuous-wave mode-locked lasers is presented. It is shown that these fluctuations can be detected and quantitatively characterized from measurements of the power spectrum of the light intensity. Such power spectra can be measured with great accuracy by shining the laser output on a suitable photodetector and by processing the detector signal with the use of an electronic spectrum analyzer. Different types of noise such as fluctuations of the pulse energy, pulse repetition time, and pulse duration, can be readily recognized from their characteristic spectral signature. Experimental results of noise measurements are presented for a synchronously mode-locked dye laser pumped by an acousto-optically mode-locked argon ion laser, and also for a colliding pulse passively mode-locked dye laser.
This paper reports on timing-jitter analysis of an all-optical clock-recovery scheme at 40 GHz using self-pulsating (SP) lasers. Based on the analogy with injection locking of oscillators, theoretical investigations on phase-noise properties of the recovered clock lead to the demonstration of a filtering function with slope that is compliant with the International Telecommunications Union (ITU) standards and allow us to underline the dependence of the cutoff frequency of the filtering transfer function on the spectral linewidth of the free running SP laser. From this phase-noise analysis, an analytical expression of the timing jitter of the recovered clock is derived, including the optical signal-to-noise ratio (OSNR) of the injected signal. A set of experiments on all-optical clock recovery at 40 GHz is then presented and demonstrates the crucial role of the spectral linewidth on the timing-jitter-filtering function of the SP laser. In good agreement with theoretical results, the impact of the OSNR degradation of the injected signal on the timing jitter is also demonstrated. Finally, the all-optical clock-recovery operation using a quantum-dot SP laser is shown to be standard compliant in terms of timing jitter, even for highly degraded OSNR.
High-speed all-optical clock recovery using a two-section gain-coupled distributed feedback laser is demonstrated operating in the coherent and the incoherent modes. It is found that the coherent mode has a much better performance compared with the incoherent mode. The performance of the coherent clock recovery scheme at 12 and 40 Gb/s, including wavelength and polarization insensitivity, timing jitter, and phase noise; power penalty; sensitivity; dynamic range; locking bandwidth; detuning range of the injection wavelength; and lockup time are described in detail. A comparison between the performances of the two modes of operation is also presented.
This paper investigates the impact of saturable absorption (SA) on the performance of optical clock recovery using a mode-locked multisection laser diode. Optical clock at 40 GHz is recovered from the multisection laser with SA section operated under a range of bias conditions. The dependence of extinction ratio and timing jitter of the recovered clock on required optical injection power, data rate detuning, and mark ratio is also evaluated under these operation conditions. The experimental results show that strong SA effect in laser cavity improves extinction ratio and suppresses timing jitter of the recovered clock, while weak or no SA effect in laser cavity offers clock recovery with larger date rate detuning range defined by timing jitter and less dependence on the variation of data mark ratio for extremely low mark ratio.
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
Modelling of self-pulsations based on phase controlled mode beating (PhasCOMB) shows a speed potential of 160 GHz. A first device is fabricated. A frequency tuning range of 25 to 82 GHz is obtained and all optical clock recovery at 80 Gb/s PRBS sequence is demonstrated.
A 160 GHz optical clock signal was successfully recovered from a 160 Gbit/s data stream using a modelocked laser diode. The timing jitter of the recovered clock was suppressed to less than 0.2 ps over a wide input wavelength range in the C-band. Furthermore, a wide locking range of over 700 MHz was achieved owing to the integrated chirped distributed Bragg reflector.
All-optical clock recovery from 80 Gbit/s data stream has been
demonstrated using a two-section gain-coupled DFB laser. Wavelength and
polarisation insensitive operation was realised by wavelength conversion
using a semiconductor optical amplifier
An all-optical clock recovery module is developed and tested in a
100 Gbit/s 105 km transmission experiment. A penalty free function of
the optical clock relative to an electronic phase-locked loop is
demonstrated. The compact module is wavelength and polarisation
insensitive and requires no electrical radiofrequency equipment.
Continuous frequency tuning from 5 to 22 GHz indicates the potential for
bit rate flexible clock recovery
A 40 Gbit/s time-division multiplexed signal was demultiplexed to
10 Gbit/s using a single modelocked semiconductor laser as the clock
source. The pulses of the laser directly control an all-optical switch
for demultiplexing
A comprehensive summary of the operation of two-contact
semiconductor self-pulsating laser diode (SP-LD) in both return-to-zero
(RZ) and non-return-to-zero (NRZ) optical transmission systems is
presented. Results demonstrate that this type of device has great
potential as the basis for all-optical clock recovery circuits at
multi-Gbits rates for switching applications. Results describe the basic
device behaviour showing how zinc doping the shorter (absorber) of the
device enables repeatable and controlled GHz pulsations, within the
range ~0.6 GHz and tunability (via the DC gain current) over many GHz,
to be achieved. Experimental results show that the SP-LD can be locked
with μW of incident power to produce a locked oscillator with a
linewidth of <10 Hz at 5 GHz and with 20 dB power gain across the
device. New results, addressing the pattern dependence, demonstrate that
long breaks (up to ~30 `zeros') in the clock can be accommodated without
significant degradation of the locked clock purity; the length of break
being dependent on the initial state of locking. Other new results show
that time for such circuits is of the order of 100 clock cycles. System
performance is investigated using these devices within a 20 Gbit/s
(4×5 Gbit/s) optical-time-division-multiplexed demonstrator; the
results showing no significant degradation of the bit-error-ratio
performance. Other system results at 3.2 Gbit/s show that this technique
can be applied to NRZ systems when also utilising a nonlinear effect
within a similar device biased below threshold, and identifying the
differences from RZ operation. These results show that such an approach
could provide major benefits in developing the next generation of
telecommunications networks
The injection-locking properties of self pulsation in
semiconductor lasers are studied, using a phenomenological approach,
based on an analogy with laser models. It has been found that the
locking range is directly proportional to the input power, rather than
to the square root of the input power as in injection-locked microwaves
or laser oscillators; the locking range is symmetric with respect to the
self-pulsation frequency in the free-running case; in the locking state,
the spectral linewidth of the self-pulsation peak is equal to that of
the incoming signal. These theoretical results agree very well with
experimental ones, obtained on a distributed feedback three-section
laser
A novel self-pulsation regime is observed in multisection laser diodes which consist of a loss-coupled distributed-feedback (DFB) section, a phase control section, and gain sections, where 10-GHz self-pulsation due to compound cavity mode beating has been reported with the DFB section operated as a single-mode laser. When the DFB section is below threshold current, the devices give the self-pulsation in a very wide operating range. We attribute the pulsation to passive mode-locking and also confirm that this structure is applicable to 40-GHz operation
Monolithic amplified feedback semiconductor lasers are demonstrated as a new solution to 10-GHz optical pulsation, where self-pulsations are generated according to the concept of a single-mode laser with shortly delayed optical feedback. They consist of a loss-coupled distributed feedback section operating as a single-mode laser and an integrated feedback cavity including a phase control, an amplifier, and a transparency section. The pulsation frequency is continuously tunable in the range of 7-11.5 GHz with an extinction ratio above 6.5 dB, which indicates that precise control of a cavity length is not needed.
All-optical clock extraction at 160 Gb/s was successfully achieved using a monolithic colliding-pulse mode-locked laser diode module. Low excess timing jitter less than 0.1 ps was achieved at the injection power of data signal from -3.5 to 3 dBm without any degradation of the pulse characteristics of the output clock pulses.
The dynamics of coherent clock recovery (CR) using self-pulsing two-section distributed feedback (TS-DFB) lasers have been investigated. Both simulation and experimental results indicate fast lockup and walk-off of the clock-recovery process on the order of nanoseconds. Phase stability of the recovered clock from a pseudorandom bit sequence (PRBS) signal can be achieved by limiting the detuning between the frequency of free-running self-pulsation and the input bit rate. The simulation results show that all-optical clock recovery using TS-DFB lasers can maintain a better than 5% clock phase stability for large variations in power, bit rate, and optical carrier frequency of the input data and therefore is suitable for applications in optical packet switching.
We describe the phase dynamics of a timing extraction system based on direct optical injection locking of a multifrequency oscillator employing an InGaAs/InP heterojunction bipolar phototransistor. We present a general model for the locking range, jitter transfer function, and output phase noise. The model is confirmed by a series of locking experiments. We consider first fundamental timing extraction, that is, a 10-GHz oscillator extracting the clock from a 10-Gbit/s data stream. Second, we address superharmonic timing extraction where 40-Gbit/s data lock the fourth harmonic of the 10-GHz oscillator. In the superharmonic timing extraction case, a clock is extracted at 40 GHz as well as its subharmonics at 10, 20, and 30 GHz.
The performance characteristics of a pulse injection locked,
passively mode-locked (PML) external-cavity semiconductor laser system
for all-optical clock recovery are investigated in detail. It is
important to characterize the clock recovery dynamics to understand the
fundamental capabilities and limitations of the clock recovery system.
It is experimentally shown that these devices offer robust clock
recovery with low phase and amplitude noise, low injected data power
requirements, large frequency locking bandwidth, large phase tracking
bandwidth, short lockup time, long dephasing time and immunity to
bit-pattern-effects. Harmonic clock generation and subharmonic clock
generation are demonstrated for data-rate conversion applications