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divider and other SiGe ILFDs; the proposed ring-oscillator-based
ILFD has wider-locking-range percentage.
A new small die area ring-oscillator-based ILFD circuit has
been proposed and implemented in the 0.35 lm SiGe BiCMOS
technology. The ILFD consists of four-stage of differential am-
plifier to construct an eight-phase oscillator, and the injection
signal is applied to the tails of the differential amplifiers. The
proposed ILFD provides an eight-phase output and wide-locking
range from 12.7 to 15.25 GHz. The locking-range percentage of
the proposed ILFD is the largest among the published SiGe
1. A. Joseph, J. Dunn, G. Freeman, D. Harame, D. Coolbaugh, R.
Groves, K. Stein, R. Volant, S. Subbanna, V. Marangos, S. St.
Onge, E. Eshun, P. Cooper, J. Johnson, J.-S. Rieh, B. Jagannathan,
V. Ramachandran, D. Ahlgren, D. Wang, and X. Wang, Product
applications and technology directions with SiGe BiCMOS, IEEE J
Solid State Circuits 38 (2003), 1471–1478.
2. A. Rylyakov and T. Zwick, 96-GHz static frequency divider in SiGe
bipolar technology, IEEE J Solid State Circuits 39 (2004),
3. H. Knapp, M. Wurzer, T.F. Meister, K. Aufinger, J. Bock, S.
Boguth, and H. Schafer, 86 GHz static and 110 GHz dynamic fre-
quency dividers in SiGe bipolar technology, IEEE MTT-S Int Dig 2
4. J.C. Chien, C.S. Lin, L.H. Lu, H. Wang, J. Yeh, C.Y. Lee, and J.
Chern, A harmonic injection-locked frequency divider in 0.18 lmSiGe BiCMOS, IEEE Microwave Wireless Compon Lett 10 (2006),
5. J.K. Nakaska and J.W. Haslett, An integrated 6.2–11GHz SiGe
inductorless injection locked frequency divider, Eur Microwave
Conf 1 (2005), 669–672.
6. S.-L. Jang, K.-C. Shen, C.-W. Chang, and M.-H. Juang, A 6-phase
�3 injection locked frequency divider in SiGe BiCMOS technology,
Microwave Opt Technol Lett 51 (2009), 1555–1557.
7. S.-L. Jang, C.C. Liu, and C.-W. Chung, A tail-injected divide-by-4
SiGe HBT injection locked frequency divider, IEEE Microwave
Wireless Compon Lett 19 (2009), 236–238.
8. F. Herzel and W. Winkler, A 2.5 GHz eight-phase VCO in SiGe
BiCMOS technology, IEEE Trans Circuits Syst II 52 (2005),
9. X. Guan, H. Hashemi, and A. Hajimiri, A fully integrated 24-GHz
eight-element phased-array receiver in silicon, IEEE J Solid State
Circuits 39 (2004), 2311–2320.
10. J.J. Kim and B. Kim, A low-phase-noise CMOS LC oscillator with
a ring structure, IEEE ISSCC Dig Tech Papers 38 (2000), 430–431.
11. R. Tang and Y.-B. Kim, A novel 8-phase PLL design for PWM
scheme in high speed I/O circuits, IEEE Int SOC Conf (2006),
12. Y.-H. Chuang, S.-H. Lee, S.-L. Jang, J.-J. Chao, and M.-H. Juang,
A ring-oscillator-based wide locking range frequency divider, IEEE
Microwave Wireless Compon Lett 16 (2006), 470–472.
VC 2009 Wiley Periodicals, Inc.
DEMONSTRATION AND ANALYSISOF DUAL-WAVELENGTH CLOCKRECOVERY BASED ON STIMULATEDBRILLOUIN SCATTERING
Ming Chen,1,2 and Shui-sheng Jian1,21 Key-Laboratory of All-Optical Networks and AdvancedCommunication Networks, Ministry of Education, Beijing 100044,China; Corresponding author: [email protected] Institute of Lightwave Technology, Beijing Jiaotong University,Beijing 10004, China
Received 29 April 2009
ABSTRACT: Dual-wavelength clock recovery (CR) based on
Stimulated Brillouin Scattering is realized. The maximum frequencyspacing of two channels is theoretically analyzed and experimentally
demonstrated. The total wavelength span of the CR scheme isinvestigated to be about 3.37 nm in experiment. Multiwavelength CRcan be implemented within the span. VC 2009 Wiley Periodicals, Inc.
Microwave Opt Technol Lett 52: 204–207, 2010; Published online in
Wiley InterScience (www.interscience.wiley.com).
Key words: all-optical clock recovery; stimulated Brillouin scattering(SBS); optical signal processing
All-optical signal processing is inevitably developed as the most
promising scheme for ultra-high-speed data transmission and
processing systems because of its potential of high speed
response. All-optical clock recovery (CR) is one of the corre-
sponding fundamental technology in signal processing for system
synchronization such as all-optical regeneration, all-optical time-
division switching systems, and all-optical demultiplexers. Sev-
eral optical timing extraction techniques suitable for high-speed
operations have been demonstrated using self-pulsating lasers ,
optical passive tank circuit based on Fabry-Perot resonator [2, 3],
multisection laser diodes , two-photon absorption , and opti-
cal phase-lock loop [6, 7]. Most of these methods require prior
knowledge of the bit rate. An exception is an active optical filter
based on the comb-shaped gain spectrum according to Stimulated
Brillouin Scattering (SBS) [8, 9]. In Ref. 8, Kawakami et al. used
several extra continuous-wave (CW) lights with different center
frequencies as pumps to amplify multiple clock-related line spec-
tral components of the optical data signal; however, the center
frequencies of the CW laser must be tuned carefully in the band-
width range of Brillouin Gain (20–40 M) and automatic fre-
quency control (AFC) should be applied. In Ref. 9, Butler et al.
directly used the comb spectral components of the signal light as
the pump lights, and the clock can be recovered in optical domain
without the knowledge of the incoming data bit rate. Besides, as
the optical fiber in a dense wavelength-division-multiplexing sys-
tem hosts multiple wavelength channels, it is especially desirable
to extend this parallelism to signal processing by finding means
of all-optical CR. A multiwavelength clock-recovery device can
greatly simplify costs by eliminating the need to have a separate
regenerator for each wavelength, which has been researched in
In this study, multiwavelength all-optical CR based on SBS is
realized. According to the CR scheme, the maximum frequency
spacing is theoretical analyzed and demonstrated in our experi-
ment, correspondingly, for the first time, with low clock jitter and
204 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 52, No. 1, January 2010 DOI 10.1002/mop
without pattern dependence. Meanwhile, the scheme presents an
idea for the measurement of the gain bandwidth of SBS.
2. PRINCIPLE OF OPERATION
SBS as the nonlinearity is utilized for all-optical CR and the
measurement of the gain bandwidth of SBS because it has a
long interaction time (narrow bandwidth) and a lower threshold
than other optical nonlinearities in fibers. The process of SBS
can be described classically as a nonlinear interaction between
the pump and the backward-propagating Stokes fields through
an acoustic wave, which is generated by the pump field through
the process of electrostriction. When the pump power is higher
than the SBS threshold, the stimulated scattering process trans-
forms most of the energy of the pump light to the counter-prop-
agating wave. The gain of each spectral component in the
Stokes signal is related to the power in the corresponding spec-
tral components of the pump. The result is an active filter that
selects and amplifies only the most intense spectral components,
facilitating the extraction of the appropriate frequency compo-
nents in the optical domain.
Here, an input data stream is split into two beams with oppo-
site directions using a directional coupler. The larger one works
as the pump; the other beam is downshifted by the Brillouin shift
of a dispersion shift fiber (DSF) using a modulator. As long as
the clock-related CW tones in the downshifted seed wave (Stokes
wave) have sufficient power to exceed the Brillouin threshold,
the data portion of the seed spectrum is attenuated relative to the
clock, and then the clock component can be extracted. Because
of the additional modulation, the variation of the pump detuning
due to the signal frequency has been discussed in Ref. 13. With
the extra modulation, the modulation frequency used to down-
shift the signal is designed to be fixed, so control over the fre-
quency of the seed signal is unnecessary. Furthermore, the
scheme based on SBS is without pattern effect. Meanwhile, as all
single wavelength Brillouin active filters can be introduced owing
to the narrow Brillouin gain bandwidth of the DSF fiber (about
20 MHz) and each seed signal is only allowed to interact with its
own unshifted pump signal, thus, multiwavelength CR is possi-
ble, if each channel’s clock tone power levels are all above the
Brillouin threshold, which can be satisfied by using high gain er-
bium-doped fiber amplifier (EDFA).
Considering that the Brillouin shift varies inversely with the
pump wavelength, we focus on the analysis of the maximum
frequency spacing for CR from two channel signals based on
SBS. Figure 1 shows the sketched analysis principle. This
pump-induced index grating scatters the pump light through
Bragg diffraction. Scattered light is downshifted in frequency
because of the Doppler shift associated with a grating moving at
the acoustic velocity mA. The antidirection Brillouin shift is, fB¼ 2nmA/kp, where n is the refractive index at the pump wave-
length kp. It is obvious that the Brillouin shifts are different
according to two channel signals with different central fre-
quency (expressed as f1 and f2). However, if f1 is close to f2, theinduced Brillouin shifts can be reasonably assumed to equal,
which means fB1 ¼ fB2. The seed signals are downshifted by the
modulation frequency fm, where fm ¼ fB1; thus, the multiwave-
length clocks can be recovered simultaneously without any diffi-
culty. As Figure 1(a) shows, although the Brillouin shift fB2becomes bigger going with the increase of f2, the downshifted
seed signal deviate from the centre of the Brillouin-gain band-
width for the DSF used in the scheme under the condition of fm¼ fB1; therefore, the SBS gain is reduced for this clock tone.
More direct current components exist in the extracted clock,
even make it impossible for CR. It is necessary to make sure
that the two seed signals with frequency of f1 � f 0m and f2 � f 0mare both adjusted to the range of gain bandwidth of SBS, so fmis changed to f 0m as shown in Figure 1(b). Then, the multiwave-
length clock can still be extracted even if the quality of the
clock is degraded. Figure 1(c) shows the ultimate situation that
both f1 � f 0m and f2 � f 0m totally exceed the Brillouin-gained
spectrum; it is unable to realize the multiwavelength CR. Here,
fm ¼ fB1 þ 1
2DmB ¼ fB2 � 1
where DmB is the gain bandwidth of SBS, and fBi ¼ 2nmA/ki,fi ¼ c/ki, so the maximum frequency spacing is given by
f2 � f1 ¼ DmB � c=2nmA; (2)
if vA, n is set to be 5.96 km/s and 1.44, respectively, the values
appropriate for silica fibers, DmB ¼ 24 MHz at kp ¼ 1.55 lm,
the calculated maximum frequency spacing (f2�f1) is about 416
GHz, and the corresponding wavelength span for multiwave-
length CR is 3.4 nm.
Some points are necessary to illuminate:  The CR scheme
is based on SBS effect, and the Brillouin-gained bandwidth
depends on the fiber, accordingly the maximum frequency spac-
ing just relates to the fiber medium;  Only central frequency
of the signal is used for analysis as shown in Figure 1; if con-
sidering the spectral broadening induced by high-speed modula-
tion, the modulation rate fdm should subtract from f2�f1. For
example, in 10 Gbps optical system, the corresponding wave-
length span is changed to 3.3–0.08 nm . The ideal upper
bound of data rate for the single channel clock extraction is also
about 416 Gbps because the pump is obtained directly from the
incoming signal . The data rates of each wavelength need not
be the same. The only cost of adding each additional wave-
length channel is that the input power to the Brillouin active fil-
ter or the gain of the EDFA in the scheme must be increased by
3 dB  for each additional wavelength.
3. EXPERIMENTAL SETUP AND RESULTS
Figure 2 shows the experimental setup. Two channels 9.953 Gb/
s optical RZ data stream is generated by modulating the CW
output of a distributed feedback fiber laser with a cascaded
LiNbO3 Mach-Zehnder modulator (MZM) driven by pattern
generator (Agilent N4901B) with 223�1 bits length. A high gain
EDFA is used to increase the power of the signal above 100
Figure 1 Principle of the maximum frequency spacing
DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 52, No. 1, January 2010 205
mW to exceed the SBS threshold. Then, the multiwavelength
signals are injected to a directional coupler. As SBS is an inter-
action involving two counterpropagating waves, i.e., the pump
and the Stokes, that are separated in frequency from each other
by the acoustic phonon frequency of the medium, therefore, in
our system, we split the amplified data stream into two counter-
propagating signals and then downshift one of them by the
acoustic resonance to the Stokes frequency. Here, the clockwise
propagating signal is modulated by the Brillouin shift (10.480
GHz) of DSF using the MZM to be the Stokes wave, and the
anticlockwise signal with 95% of the total power functions as
the pump. The pump with frequency unshifted retains most of
the power of the input data stream so that the Stokes wave expe-
riences strong gain during the SBS interaction. The polarization
controllers maintained the same polarization state for the pump
and Stokes waves. Optical isolators are used to prevent the
Stokes signal from re-entering into the input or appear in the
forward direction. The performance of the system is investigated
by a digital sampling oscilloscope (Agilent DCA 86100 B).
First, the central wavelength of two channels is set to
1554.948 and 1555.754 nm, respectively, and the spectrums are
shown in Figure 3 with the dashed lines. Each channel’s clock
tone power levels are above the Brillouin threshold after ampli-
fied by a high gain EDFA. So, SBS interaction works as an
active filter to extract clock. The solid lines in Figure 3 show
the spectrum of the multiwavelength recovered clock. The tiny
frequency shift compared to the spectrum of input RZ signals is
due to the additional modulation at the Brillouin shift (10.480
GHz). Figure 4 shows the eye-diagrams of recovered clock at
1554.948 nm (the top trace) and 1555.754 nm (the bottom one).
The time jitters were 2.34 and 2.41 ps, respectively, which origi-
nated mainly from amplitude fluctuations. A broadband optical
filter for restraining amplified spontaneous emission from the
high gain EDFA should be applied. Besides, if the amplifier is
unsaturated, a small amount of noise can create substantial am-
plitude variations in the recovered clock signal because of the
exponential nature of the gain, and this may be overcome by
increasing the Stokes power. It is also helpful to utilize another
optical filter in the output. Or cascaded CR module based on
SBS is introduced.
Next step is to increase the frequency spacing by changing
the output wavelength of fiber laser. The multiwavelength clock
can still be extracted, even if the quality is degraded. However,
when the wavelengths are adjusted to the 1554.34 and 1557.71
nm, it became so hard to recover the two channel clocks. The
spectrum of output signals is shown in Figure 5. Here, we can
see, only one frequency component suffers the Brillouin-gain for
each channel, and not all clock tones are amplified; thus neither
clock can be recovered. This situation is homologous to upper
analysis illuminated in Figure 1(c). Then, we decrease the wave-
length span a little; the clock of one channel can be extracted as
shown in Figure 6, with high time jitter and huge noise.
The maximum wavelength span for two channels is demon-
strated to be 3.37 nm in our experiment. Once exceed this span,
Figure 3 Spectrums of multiwavelength RZ signal and extracted clock
Figure 4 The measured eye-diagram of multiwavelength recovered
clock. Time scale: 50 ps/div. [Color figure can be viewed in the online
issue, which is available at www.interscience.wiley.com]
Figure 5 The output spectrum of the clock recovery device
Figure 2 Experimental setup of multiwavelength clock recovery.
EDFA, erbium-doped fiber amplifier; ISO, isolator; PC, polarization con-
troller; DSF, dispersion shift fiber; MZM, M–Z modulator; AWG,
arrayed waveguide grating
206 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 52, No. 1, January 2010 DOI 10.1002/mop
the clock tones of two channels are out of the Brillouin gain
spectrum and not able to experience the process of SBS. The
experiment results are in good agreement with the theoretical
Although the measured wavelength span of our clock-recov-
ery device was about 3.37 nm, this span could be increased by
introducing strain into the DSF  or replaced by another fiber
loop with a larger Brillouin-gain bandwidth. Besides, multiple
modulators and corresponding wavelength filters that provide
different modulation shifts for different wavelength bands may
fundamentally extend the span.
Meanwhile, according to Eq. (2), a rough method for the
measurement of gain bandwidth of SBS can be presented, which
is given by
DmB ¼ f2 � f1ð Þ � 2nmA=c; (3)
The Brillouin-gain bandwidth can be calculated by using the ex-
perimental value of the maximum frequency spacing.
Maximum frequency spacing for dual-wavelength all-optical CR
based on SBS is demonstrated experimentally and understood
theoretically. The maximum wavelength span is 3.37 nm accord-
ing to the DSF we used in the experiment. Multiwavelength
clock can be recovered within the span. The all-optical CR
scheme can be extended to high speed and parallel all-optical
processing of multiple channels’ even more simultaneous data
rates (e.g., 160 Gbps in addition to 10 and 40 Gbps).
This work is supported by Excellent Doctoral Scientific Innovation
Projects of Beijing Jiaotong University (No. 141051522), National
863 High Technology Projects of China (No. 2007AA01Z258,
2008AA01Z15). The authors acknowledge the optical transmission
group in Institute of Lightwave Technology in Beijing Jiaotong
University for their helpful discussion and support throughout the
1. P. Barnsley, H. Wickes, G. Wickens, and D. Spirit, All-optical clock
recovery from 5 Gbit/s RZ data using a self-pulsating 1.56 _m laser
diode, IEEE Photon Technol Lett 3 (1991), 942–945.
2. M. Jinno and T. Matsumoto, Optical tank circuits used for all-opti-
cal timing recovery, IEEE J Quantum Electron 28 (1992), 895–900.
3. G. Contestabile, A. D’Errico, M. Presi, and E. Ciaramella, 40-GHz
all-optical clock extraction using a semiconductor-assisted Fabry-
Perot filter, IEEE Photon Technol Lett 16 (2004), 2523–2525.
4. I. Kim, C. Kim, G. Li, P. LiKamWa, and J. Hong, 180-GHz clock
recovery using a multisection gain-coupled distributed feedback
laser, IEEE Photon Technol Lett 17 (2005), 1295–1297.
5. R. Salem and T.E. Murphy, Broad-band optical clock recovery sys-
tem using two-photon absorption, IEEE Photon Technol Lett 16
6. S. Kawanishi and M. Saruwatari, Ultrahigh-speed PLL-type clock
recovery circuit based on all-optical gain modulation in travelling-
wave laser diode amplifier as a 50 GHz detector, Electron Lett 24
7. O. Kamatani and S. Kawanishi, Ultrahigh speed clock recovery with
phase locked loop based on four-wave mixing in a traveling-wave
laser diode amplifier, J Lightwave Technol 14 (1996), 1557–1568.
8. H. Kawakami, Y. Miyamoto, T. Kataoka, and K. Hagimoto, All-op-
tical timing clock extraction using multiple wavelength pumped
Brillouin amplifier, IEICE Trans Com E78-B (1995), 694–701.
9. D.L. Butler, J.S. Wey, M.W. Chbat, et al., Optical clock recovery
from a data stream of an arbitrary bit rate by use of Stimulated Bril-
louin Scattering, Opt Lett 20 (1995), 560–562.
10. C. Johnson, K. Demarest, C. Allen, R. Hui, K.V. Peddanarappagari,
and B. Zhu, Multiwavelength all-optical clock recovery, IEEE Pho-
ton Technol Lett 11 (1999), 895–897.
11. D.V. Kuksenkov, S. Li, M. Sauer, and D.A. Nolan, Nonlinear fiber
devices operating on multiple WDM channels, 31st Eur Conf Opt
Commun (ECOC) Mo3.5.1 (2005), 51–54.
12. T. von Lerber, J. Tuominen, H. Ludvigsen, S. Honkanen, and F.
Kueppers, Multichannel and rate all-optical clock recovery, IEEE
Photon Technol Lett 18 (2006), 1395–1397.
13. X. Zhou, H.H.M. Shalaby, L. Chao, et al., A performance analysis
of all-optical clock extraction circuit based on stimulated Brillouin
scattering, J Lightwave Technol 18 (2000), 1453–1466.
VC 2009 Wiley Periodicals, Inc.
STABLE OPERATION OF MICROWAVEPHOTONIC FILTERS CONSTRUCTEDWITH TWO CASCADED HI-BI FIBERS
H. Dong,1 J. Q. Zhou,2 S. Aditya,2 Y. D. Gong,1 and P. Shum2
1 Institute for Inforcomm Research, 1 Fusionopolis Way, # 21-01Connexis, Singapore 138632; Corresponding author:[email protected] Technology Research Centre, Nanyang TechnologicalUniversity, Singapore 637553
Received 6 April 2009
ABSTRACT: For the microwave photonic filters constructed with twocascaded Hi-Bi fibers, we demonstrate theoretically and experimentally
a new technique that uses a dual- or tri-wavelength spacing-tunablelaser source to greatly suppress the sensitivity of the filter response toenvironmental perturbations without the introduction of the phase-
induced intensity noise. VC 2009 Wiley Periodicals, Inc. Microwave Opt
Technol Lett 52: 207–212, 2010; Published online in Wiley InterScience
(www.interscience.wiley.com). DOI 10.1002/mop.24844
Key words: microwave photonic filter; Hi-Bi fiber; differential groupdelay; multi-wavelength laser
Microwave and millimeter-wave signal processing using micro-
wave photonic filters (MPF) offer various advantages like large
time–bandwidth product, electromagnetic interference immunity,
and inherent low loss due to the use of optical components .
To achieve a stable operation free from environmental
Figure 6 The measured eye-diagram of degraded recovered clock.
Time scale: 50 ps/div. [Color figure can be viewed in the online issue,
which is available at www.interscience.wiley.com]
DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 52, No. 1, January 2010 207