International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
Polarization-Insensitive Tunable Wavelength
Converter for Two-WDM Channels by using
Four-wave Mixing
Aye Nilar Win

Abstract— Wavelength conversion plays an important
function in wavelength division multiplexing (WDM) networks.
The WDM has become an effective solution to increase traffic
flow in optical communication networks. It is common to find
that there are not enough different wavelengths to satisfy the
requirements of the whole system. This paper demonstrates
polarization-insensitive wavelength converter by utilizing
four-wave mixing (FWM) process for two-WDM channels. For
the proposed wavelength converter, bit-error-rate (BER)
measurement is carried out for a 10-Gb/s converted
nonreturn-to-zero (NRZ) signal, and a polarization-insensitive
property is investigated with the different input signal
polarization states.
Index Terms— Wavelength converter, WDM, four-wave
mixing, polarization diversity.
I.
INTRODUCTION
In optical communication systems, when a high power
optical signal is launched into the fiber cable, there is
nonlinear effect which is due to the third-order electric
susceptibility [1]. Nonlinear effects in optical fiber are
stimulated raman scattering (SRS), stimulated brillouin
scattering (SBS), self-phase modulation (SPM), cross-phase
modulation (XPM), and four-wave mixing (FWM), all of
which originate from the Kerr effect. These effects have the
various applications such as pulse compression, solitons,
optical tunable delays, optical switching, pulse retiming, and
wavelength conversion. Wavelength conversion is a very
useful function for translating data carried on one wavelength
to another in advanced optical systems. Several all-optical
wavelength conversions are based on nonlinearities in
semiconductor optical amplifiers, in optical fibers, in crystals
and so on [2]. All optical wavelength converters have become
key components in the future broadband networks. They are
important functions for avoidance of wavelength blocking in
optical cross connects in wavelength division multiplexed
(WDM) networks. The converters are increased the flexibility
and the capacity of the network for a fixed set of wavelengths
[3].
In this paper, polarization-insensitive tunable wavelength
conversion has been demonstrated utilizing four-wave mixing
(FWM) in a highly nonlinear fiber (HNLF). All-optical
wavelength conversion based on FWM in optical fiber has the
Manuscript received April 30, 2014.
Aye Nilar Win, Department of Electronic Engineering, Mandalay
Technological University (e-mail: ayenilar.ec2010@gmail.com).
Mandalay, Myanmar.
following potential advantages: 1) it eliminates
optical-electrical-optical conversion and, thus, enables
transparent all-optical networks; 2) it is ultrafast and
transparent to both modulation format and bit rate; 3) it
induces negligible signal degradation since there is little chirp
or added noise; and 4) the optical fiber itself is low cost, low
loss, and seamlessly compatible with the transmission fiber
[4]. In particular, four-wave mixing (FWM) is a promising
technique for wavelength conversion owing to its ultrafast
response and high transparency to both bit rate and
modulation format. Polarizing beam splitter (PBS) is also
used to have the polarization-insensitive properties. With the
scheme of polarization diversity, the input polarization
sensitivity can be reduced [5]. By using Optisystem software,
signal waveform, spectrum, Q factor, and bit error rate (BER)
measurements has been analyzed. This paper is organized as
follows, Section II explains theory of FWM and then in
section III, principle of wavelength conversion by using
FWM is described. Section IV mentions simulation setup of
the proposed system and in section V, the performance of the
comparison with PBS and without PBS is analyzed. Finally,
section VI concludes the paper.
II.
THEORY OF FWM
The origin of FWM process lies in the nonlinear response
of bound electrons of a material to an applied optical field.
ω3
ω1
ω2
ω4
Fig.1 FWM of two wave ω1 and ω2 [6].
Fig: 1 illustrates a simple example of mixing of two waves at
frequency ω1 and ω2. When these waves mixed up, they
generate sidebands at ω3 and ω4 such that (ω1+ω2 = ω3+ω4).
Similarly, three propagation waves will appear nine new
optical sideband waves at frequencies given by Eq: (1). These
sidebands travel along with original waves and will grow at
the expense of signal-strength depletion. In general for N
wavelengths launched into fiber, the number of generated
mixed products M is,
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All Rights Reserved © 2012 IJSETR
International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
IV.
M
N
( N  1)
2
(1)
Where, M = number of new generated wavelengths
N = number of launched wavelengths into fiber
III.
SIMULATION SETUP
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PRINCIPLE OF POLARIZATION-INSENSITIVE TUNABLE
WAVELENGTH CONVERSION USING FWM
Simulation setup for the polarization-insensitive tunable
wavelength converter is illustrated in Fig.4. The two signals at
1549.6 nm and 1551.2 nm wavelengths with the power of 0
dBm are combined with the wavelength tunable
continuous-wave pump laser at 1543.2 nm (1539.2 nm –
1547.2 nm) wavelength with a power of 0 dBm by using a
coupler. These signals and pump also pass through the EDFA
with the power of 18.316 dBm. Then, the amplified signal
enters into the polarizing beam splitter (PBS) to be insensitive
the polarization properties. And, 0.5-km long highly
nonlinear fiber (HNLF) is used as the nonlinear medium to
obtain the FWM process. Finally, 1535.2 nm and 1536.8 nm
optical bandpass filter (OBPF) with the bandwidth of 40 G Hz
is also utilized to filter out the converted signals and then
wavelength conversion is achieved. At the receiver, 10-Gb/s
BER measurements are carried out to see the performance of
the wavelength conversion.
Fig.2 Setup the polarization-insensitive tunable wavelength
converter. PC: Polarization controller, EDFA: Erbium- doped
fiber amplifier, PBS: Polarizing beam splitter, HNLF: highly
nonlinear fiber.
The operation of the polarization-insensitive tunable
wavelength converter is shown in fig: (2). The input signal is
modulated by using a Mach-Zehnder interferometer (MZI)
modulator. This input signal is combined with a wavelength
tunable continuous-wave pump laser using a coupler. The
combined signal is launched into a gain-flattened
erbium-doped fiber amplifier (EDFA) with a power of 18.316
dBm. Then, the amplified signal is injected into port A of the
polarizing beam splitter (PBS). PBS plays an important role
in numerous optical systems. It can split an incident beam into
two orthogonally polarized beams and also insensitive
polarization properties. A segment of the highly nonlinear
fiber (HNLF) is placed in a loop connecting Ports B and C of
the PBS. The length of the HNLF is utilized 0.5-km to obtain
FWM process. The HNLF used in proposed system has a
dispersion 0ps/ (km. nm) at 1543.2 nm with a dispersion slope
of 0.032ps/ (km. nm2). The attenuation of the fiber is 0.47dB/
km in the 1543.2 nm range. In this polarization diversity
scheme, polarizing beam splitters split both signal (S) and
pump (P) into two orthogonal polarization states. Pump (P) is
polarized at 45̊ with respect to the PBS axis so that the pump
power is equally split. Therefore, in each propagation
direction, the signal undergoes separate FWM in the HNLF
and the output will exit from Port D of the PBS. Finally, an
optical band-pass filter (OBPF) with a bandwidth of 40G Hz
is used to filter out the converted signal and then wavelength
conversion is obtained. But, only one signal is described in fig:
(2). Really, instead of single signal, two signals are used in the
proposed system. At the receiver, a 10-Gb/s BER
measurement is performed to investigate the performance of
the digital signal of the wavelength converter.
Fig. 3 (a) Spectral analysis obtained at the input of the HNLF.
Fig. 3 (b) Spectral analysis obtained at the output of the
HNLF.
Fig. 3 (c) Waveform obtained at the output of the HNLF.
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All Rights Reserved © 2012 IJSETR
International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
Fig.4 Simulation setup for polarization-insensitive wavelength converter.
V. PERFORMANCE OF THE COMPARISON WITH PBS AND
WITHOUT PBS
Fig.5 Comparison of conversion efficiency with PBS and
without PBS.
Fig.5 illustrates the relationship between the conversion
efficiency and the converted output wavelength with PBS and
without PBS at the wavelengths of 1535.2 nm and 1536.8 nm.
Figure shows the conversion efficiency using PBS is lower
than the conversion efficiency without PBS because of the
loss of PBS. The conversion efficiency is defined as the ratio
of the converted signal power to the input signal power. In this
figure, the signal wavelength is fixed and the pump
wavelength is tuned from 1533 nm to 1543nm approximately
with 1-nm spacing to achieve the various outputs. A 3-dB
tuning range of 10 nm is obtained with the peak conversion
efficiency is about -25 dB in using PBS.
Fig.6 (a) BER versus the average received power without
PBS at 1535.2 nm.
Fig.6 (b) BER versus the average received power with PBS at
1535.2 nm.
Fig.6 (c) Comparison of bit-error-rate with PBS and without
PBS at 1535.2 nm.
In order to measure the performance of the digital signal of
the wavelength converter, a 10-Gb/s BER measurement is
performed. The measured bit-error-rate against the average
received power using 10-Gb/s NRZ data signal are illustrated
in fig: 6 (a), (b), and (c) respectively. These figures are shown
the BER measurements according to the converted
wavelengths of signal (S) and pump (P) as shown in fig: 5.
The power penalty for the converted signal compared to the
original signal is measured to be 0.7 dB at 10 -9 BER level.
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All Rights Reserved © 2012 IJSETR
International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
(a)
(b)
Fig.7 Eye diagram using PBS at 1535.2 nm (a) for back to
back; (b) after wavelength conversion.
Fig. 10 Plot of the converted signal power against the input
signal polarization states.
(a)
(b)
Fig.8 Eye diagram without PBS at 1535.2 nm (a) for back to
back; (b) after wavelength conversion.
Fig:7 (a) and (b) are illustrated eye diagrams with PBS at
the wavelength of 1535.2 nm for back to back and after
wavelength conversion of the system. And then, eye patterns
without using PBS at 1535.2 nm wavelength for back to back
and after wavelength conversion are shown in fig: 8 (a) and
(b) respectively.
Fig: 10 shows the converted signal power versus the input
signal polarization states with PBS and without PBS at the
wavelengths of 1535.2 nm and 1536.8 nm respectively. The
converted output wavelength is measured at the different
input
signal
polarizations
to
demonstrate
polarization-insensitive operation of the wavelength
converter. As shown in figure, the converted signal power
using PBS seems to be lower than the converted signal power
without using PBS in both wavelengths. However, the
converted signal power with PBS is achieved with the flat
power. The input polarization rotation is done by using an
electrical-driven polarization controller (PC). In using PBS,
the power variation of the output is obtained to be less than
0.8 dB for the wavelength of 1535.2 nm and 0.3 dB for 1536.8
nm wavelength as the input signal polarization was rotated
from -90̊ to 90̊.
VI. CONCLUSION
Fig. 9 Plot of the bit-error-rate versus the input signal
polarization states in a 10-Gb/s BER measurement.
Fig: 9 illustrates the BER against the input signal
polarization states with PBS and without PBS at wavelengths
of 1535.2 nm and 1536.8 nm respectively. As seen in the
figure, although the input signal polarization states change bit
error rate using PBS is obtained with the flat values because
the proposed system uses the polarizing beam splitter (PBS).
It can be insensitive the polarization properties. The input
polarization rotation is done by using an electrical-driven
polarization controller (PC).
A tunable polarization-insensitive wavelength converter
for two WDM channels has been investigated based on
four-wave mixing (FWM) in a highly nonlinear fiber (HNLF).
A tuning range over 10 nm of the converted signal with a
conversion efficiency of -25 dB and good flatness from 1533
nm to 1543 nm approximately has been achieved with the
polarization sensitivity to be less than 0.8 dB for the
wavelength of 1535.2 nm and 0.3 dB for 1536.8 nm
wavelength. Also, the power penalty for the converted signal
compared to the original signal is measured to be 0.7 dB at
10-9 BER level for wavelength conversion. The results show
that such converters with highly nonlinear fiber (HNLF) can
use for wavelength conversion applications in all-optical
networks.
REFERENCES
[1]
[2]
[3]
[4]
Osamu Aso*, Masateru Tadakuma * and Shu Namiki*, “Four-Wave
Mixing in Optical Fibers and Its Applications”.
Lalit Kishor Tyagi, Arvind Kumar Jaiswal#, Mukesh Kumar#,
Tripuresh Joshi, “Performance Analysis of Four Wave Mixing Based
Wavelength Conversion in Commercial Optical Fibers”.
1Anupjeet Kaur, 2Kulwinder Singh, 3Bhawna Utreja, “Wavelength
Converter in Optical Communication Systems”.
C. Yu, Student Member, IEEE, Z. Pan, Student Member, IEEE, Y.
Wang, Student member, IEEE, Y. W. Song, Student Member, IEEE, D.
Gurkan, Student Member, IEEE, M. C. Hauer, Student Member, IEEE,
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All Rights Reserved © 2012 IJSETR
International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
[5]
[6]
D. Starodubov, and A. E. Willner, Fellow, IEEE,
“Polarization-Insensitive All-Optical Wavelength Conversion Using
Dispersion-Shifted Fiber With a Fiber Bragg Grating and a Faraday
Rotator Mirror”.
T. Hasegawa, K. Inoue, and K. Oda, “Polarization independent
frequency conversion by fiber four-wave mixing with a polarization
diversity technique,” IEEE Photon. Technol. Lett., vol. 5, no. 8, pp.
947-949, Aug. 1993.
Nazmi A. Mohammed, Mahmoud M. Ragab, and Moustafa H. Aly,
“FOUR-WAVE-MIXING BASED WAVELENGTH CONVERSION
USING DIFFERENT TYPES OF FIBERS”.
Aye Nilar Win received her Bachelor of Technology (B.Tech) degree in
2009and Bachelor of Engineering (B.E) degree in 2010 in Electronic
Engineering from Meikhtila Technological University, Myanmar. She is
now Master of Engineering (M.E) student in Mandalay Technological
University, Myanmar.
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