OECC 2006 7C1-2-1
All-optical clock recovery using erbium-doped
fiber ring laser incorporating an electro-absorption
modulator and a linear optical amplifier
Lixin Xu,1,2 L. F. K. Lui,1 P. K. A. Wai,1 and H. Y. Tam,3
1
Photonics Research Centre and Department of Electronic and Information Engineering,
The Hong Kong Polytechnic University, Hung Hom, Hong Kong
Phone: +852 2766-6231, fax: +852 2362-8439, email: enwai@polyu.edu.hk
2
Department of Physics, University of Science and Technology of China, Hefei, 230026, China
3
Photonics Research Centre and Department of Electrical Engineering,
The Hong Kong Polytechnic University, Hung Hom, Hong Kong
Abstract
recovery which composes of an EAM, an LOA, a 12
We demonstrated 10-GHz all-optical clock recovery using
meter long erbium-doped fiber, a bandpass filter, a
an
an
circulator, two isolators, a 980 nm/1550 nm WDM
electro-absorption modulator and linear optical amplifier.
coupler, a 1550 nm band 90:10 coupler, and a polarization
Stable clock pulses with peak power of 200 mW and
controller (PC). The EAM is biased at a DC voltage of
pulsewidth of 6 ps are obtained.
−1.015 V. A 10 Gb/s data stream is injected into the
erbium-doped
fiber
laser
incorporating
EAM through the circulator (C) in the direction opposite
to the circulating direction of the laser cavity. The fiber
1 Introduction
All-optical clock recovery circuit is a key component
laser could be mode-locked and output the optical clock
for system synchronization in all-optical communication
of the data stream if the parameters of the laser are chosen
systems.
Several technologies including tank circuit,
properly. The data stream is generated by modulating a
injection locking, all-optical phase-locked loop have been
10 GHz mode-locked laser source, which has a
proposed to address this issue [1]. Among these
pulsewidth of ~1.8 ps, using an M-Z modulator. The laser
technologies, injection locking in a fiber ring laser is a
gain is provided by the LOA and EDFA.
promising approach because of its capability to generate
operates at a current of 233 mA with a gain of ~13.5 dB,
high-intensity ultrashort optical pulses [2]. Recently, we
and a saturation output power of 13 dBm. The linearity
have implemented a novel 10 GHz mode-locked fiber
of the LOA gain renders the laser system less susceptible
laser that incorporates an electro-absorption modulator
to the transients due to the variations in the ambient
(EAM), a linear optical amplifier (LOA), and an Er-doped
conditions.
fiber amplifier (EDFA) [3].
The mode-locked fiber laser
ring laser output is therefore reduced. The EDFA was
can have stable output pulses at very high peak power
pumped at 980 nm through the 980 nm/1550 nm WDM
with pulse duration of 2.4 ps [3].
The LOA
Amplitude jitter of the mode-locked fiber
In this paper, we use
coupler. The bandpass filter is centered at 1555 nm with
the fiber laser demonstrated in [3] to implement ultra-fast
a bandwidth of 6 nm and side mode suppression of 20 dB.
all-optical clock recovery. Stable clock pulse at 10 GHz
The PC is used to optimize the polarization states of the
with peak power of 200 mW and pulsewidth of 6 ps are
cavity modes because the EAM has a small polarization
obtained. The timing jitter is less than 1 ps.
dependent loss. Ten percent of the cavity energy was
coupled to output through the 90:10 coupler.
2 Experimental results and discussion
Figure 1 shows the configuration for all-optical clock
The
output
pulses
were
measured
using
a
YOKOGAWA Optical Sampling Oscilloscope (OSO)
OECC 2006 7C1-2-2
(model AQ7750). Figure 2(a) shows the 10 Gb/s input
an LOA. Stable pulses with peak power of 200 mW and
data pattern 1001001010. Figure 2(b) shows a 10 Gb/s
pulsewidth of 6 ps are obtained. The timing jitter is less
pseudorandom binary sequence (PRBS)
input signal.
than 1 ps. The external data stream is used to optically
Figure 2(c) is the recovered 10 GHz optical clock when
drive the EAM and actively mode-locked the fiber laser.
the input data is the fixed data pattern shown in Figure
Since no electronic components are involved, our
2(a). The output peak power and the pulsewidth of the
configuration can potentially operate at clock rate beyond
optical clock are 150 mW (1.5 W inside the cavity) and 10
10 GHz.
ps respectively. Figure 2(d) shows the 10 GHz recovered
optical clock coresponding to the PRBS input data shown
in Figure 2(b).
The output peak power and the
a.
b.
c.
d.
pulsewidth of the optical clock are 200 mW (2 W inside
the cavity) and 6 ps respectively. Figure 2 show that the
optical clock is recovered successfully. The timing jitter
of the output clock is measured to be less than 1 ps.
Stable optical clock output can still be observed when the
input data rate varies within 3 MHz (60% of the
foundamental frequency which is about 5 MHz in our
setup).
Figure 3(a) is the output spectrum when the
input data rate is 9.9580 GHz. The wavelength of the
Fig. 2. Timing diagrams at resolution of 100ps/div. (a) 10 Gb/s
input data pattern; (b) the 10 Gb/s PRBS input signal. (c)
recovered 10 GHz optical clock using the fixed data pattern in (a);
(d) recovered 10 GHz optical clock using PRBS as shown in (b).
optical clock is 1556.19 nm while the wavelength of the
input data stream is 1546.64 nm. The bandwidth
0
of
a.
Power(dBm)
the optical spectrum is measured to be 1.87 nm. The
-20
pulsewidth measured from the OSO is 6 ps. The output
clock pulses were significantly chirped.
Figure 3(b)
beyond 48 dB.
Pump
LOA
10 Gb/s
data
AMP
9.965
References
L. Poti, M. Luise and G. Prati, “Ultrafast optical clock
recovery:
90:10
9.960
Fig. 3 Optical Output spectrum and RF output Spectrum. Output
RF spectrum with the resolution bandwidth 10 kHz
F
I2
9.955
RF frequency(GHz)
1.
WDM Er Fiber
-80
9.950
4
I1
C
EAM
∼
12 m
-60
-100
gives the corresponding RF spectrum with a resolution
bandwidth of 10 kHz. The sidemode suppression ratio is
b.
-40
towards
a
system
perspective,”
IEE
Proc.-Circuits Devices Syst., Vol. 150, pp. 506-511, 2003.
2.
PC
H. Kurita, T. Shimizu, and H.Yokoyama, “All-optical clock
extraction at bit rates up to 80 Gbit/s with monolithic
10%
Output
mode-locked laser diodes”. Digest of CLEO’97, Vol. 11,
pp.96-96, 1997.
Fig. 1. Experimental setup of the all-optical clock recovery
circuit; F: band pass filter; I1, I2: isolator; EAM:
electroabsorption modulator; C: circulator; LOA: linear
optical amplifier.
3.
Lixin Xu, L. F. K. Lui, P. K. A. Wai, H. Y. Tam, and M. S.
Demokan, “10 GHz actively mode-locked erbium-doped
fiber ring laser using an electro-absorption modulator and a
linear optical amplifier” Proc. of OFC’2006, paper OWI27,
3 Summary
We demonstrated 10-GHz all-optical clock recovery using
an erbium-doped fiber laser that incorporates an EAM and
2006.