Download II. Semiconductor optical amplifier

International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
All-Optical Logic Gates (AND, OR, XOR) at
10Gbps by using a single Semiconductor Optical
Amplifier
Chaw Chaw

Abstract- All-optical logic gates (AND, OR and XOR) are
described at 10 Gb/s using the single semiconductor optical
amplifier and several optical Gaussian band pass filter. These
logic gates are illustrated in the same power setting but different
bandwidth and offset spacing. The cross phase modulation
method of semiconductor optical amplifier is used to produce the
optical logic gates of the system. All-optical logic gates (AND,
OR, XOR) are demonstrated with 0.4dB, 1.2dB and 2.1dB
power penalty at 10-9 BER in the same power. Both data signals
have a pulse width of 20ps with peak power of 2mW and probe
power of 0.1mW is modulated at 10 Gb/s. The bit error rate, Q
factor and power penalty are measured for all-optical logic
gates. The Q factor is near approximately 6.
integration and low power consumption. Two inputs logic
gates (AND, OR, XOR) based on single SOA and several
optical band pass filters. Two data signals and a probe signal
are injected into the SOA at the same time to improve cross
phase modulation (XPM) effects. The probe spectrum will be
broadened, and designed optical filters are used to filter out
different frequency components, which contain different logic
output, such as logic (AND, OR, XOR). The bit error rate
(BER), Q factors and power penalty are measured for
all-optical logic gates.
II. SEMICONDUCTOR OPTICAL AMPLIFIER
Index Terms—Semiconductor Optical Amplifier, All-optical
logic gates, Cross phase modulation, Band pass filter
I. INTRODUCTION
In the next communications networks, optical explanations
to logic applications are expected to present an alternative to
current electronic signal processing because of quicker
response [1]. The optical logic functionalities in the networks
are very simple, i.e. consisting of very few Boolean logic
gates. To date many techniques have been illustrated to
understand various logic functions (AND, OR, XOR) in
optical communication system [2, 3]. Logic gates can enable
many improved functions such as all-optical bit pattern
recognition [4], all-optical bit-error rate monitoring [5],
all-optical packet address and payload separation [6],
all-optical label swapping [7] and signal regeneration,
addressing, header recognition, data encoding and encryption
[8]. All-optical logic device can be produced by the three
types of materials such as the nonlinearity based on fibers,
wavelength conversion based on a semiconductor optical
amplifier and optical waveguides. All of them, the logic gates
are produced by using the semiconductor optical amplifier
have the more advantages of compactness, monolithic
Manuscript received April 30, 2014.
Chaw Chaw, Department of Electronic Engineering, and Mandalay
Technological University (e-mail: [email protected]).
Mandalay, Myanmar.
Semiconductor optical amplifiers (SOA) are the key element
for the all-optical signal processing applications studied and
proposed in this system. The optical signals in SOA is
classified via gain and phase change. SOA based non-linear
effects: cross gain or phase modulation (XGM, XPM); cross
polarization rotation (XPR); and four-wave mixing (FWM).
III. CROSS PHASE MODULATION IN SOA
Cross phase modulation as the using wavelength converter
present more advantages when compared to other schemes:
high conversion efficiency and output extinction ration;
different techniques can be applied to permit conversion after
the SOA temporal response; and the output signal information
is logically non-inverted. In a single SOA, the many refractive
index change occurs at the wavelength the SOA gain is
maximized. Since the changes in the refractive index lead to
the desired phase changes which cause cross phase
modulation, the maximum gain wavelength is usually chosen
to be the operating wavelength of technique relying on such
non-linear effect. The frequency of a probe signal at the SOA
output is achieved when a pulse is propagated at a different
wavelength. When the input signal is at constant power level
(either high or low power), the CW probe signal wavelength is
unchanged. For the leading edged of an optical pulse, the
pump signal shifts to upper wavelengths (a red-wavelength).
The trailing edges of the optical pulse occurs a blue
wavelength. Continuous wave (CW) probe wavelength shifts
to lower value. And so, the probe spectrum is broadened.
Nonlinear refractive index seen by one wave depends on
the intensity of the other wave as
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All Rights Reserved © 2012 IJSETR
International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
Δn NL = n2 (|A1|2+b|A2|2)
Total nonlinear phase shift in a fiber length L
ϕNL= (2ПL/λ)n2 [I1(t)+bI2(t)]
An optical beam changes its own phase and other phase
Nonlinear effect of XPM causes among overlapping optical
pulses
The output is high only when one or both of the data inputs
are at logic high and the output logic is low when both the
inputs are low in the OR operation. When both the data inputs
are high and one input is high, the modulated probe will
receive the red-shift in the strong saturation regime. The band
pass filter can be applied to select the red-shift in the strong
saturation regime. And so, an OR gate is understood.
The output is high when both the inputs are not the same
and the output is low when both the inputs are the same in the
XOR operation. When one control pulse is high the
modulated probe will receive the weaker red-shift. The band
pass filter can be applied to select a weaker red-shift caused
by one control pulse. And so, an XOR gate is understood.
Fig.1. Operation principle of the proposed system
IV. OPERATION PRINCIPLE OF THE PROPOSED SYSTEM
A probe (continuous wave, CW) and two modulated
optical return-to-zero (RZ) control signals (pulsed) are
induced into the SOA. The control signals (Data1 and Data2)
might be the same wavelength with the different wavelength
CW probe. The falling edge of the probe is changed in the
SOA as the longer wavelength (red-shift), while the rising
edge is changed into shorter wavelength (blue-shift) because
of non-linear effect of cross phase modulation method. And
so, the probe wavelength spectrum is broadened. As the
control pulses produce red-shift for the probe light, an optical
filter can be applied to select the red-shift spectrum of the
probe light, so that the probe can only pass through the optical
filter when the control signal is present. All-optical
wavelength conversion at 10 Gbps has been illustrated. The
amount of the injected red-shift can be controlled by the
power of the level input light (Data1, Data2 and probe). The
different logic functions can be understood by adjusting the
power levels and the filter centre wavelength.
When both the data inputs are high, the output logic is high
and when one or both the pulses are low, the output logic is
zero in the AND operation. When both the data inputs are
high, the modulated probe will receive a much stronger
red-shift. The band pass filter is used to select a stronger
red-shift caused by two control pulses. And so, an AND gate
is understood.
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All Rights Reserved © 2012 IJSETR
Fig. 2 .Simulation model for all-optical logic gates (AND, OR, XOR) in the
same input signal powers
V. RESULT AND DISCUSSION
(a)
(b)
International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
only when one or both of the data inputs are at logic high and
the output logic is low when both the inputs are low in the OR
gate operation (d) The output is high when both the input
signals are not the same and the output is low when both the
input signals are the same in the XOR gate operation (e)
When both the data input signals are high, the output logic is
high and when one or both the pulses are low, the output logic
(c)
is zero in the AND operation
Logic
PCW (mW)
P Data (mW)
Offsets
Bandwidth of
BPF (GHZ)
AND
0.1
2
1.7
40
OR
0.1
2
0.7
50
XOR
0.1
2
0.3
20
(d)
Fig.3. Output optical spectra (a) the output spectrum of the probe signal
before BPF, (b)-(d) are the output spectra when the optical band pass filter
has a detuning of 0.3nm, 0.7nm, and 1.7nm for the same input
signal
powers
The output spectrum of the probe signal before optical
band pass filter is shown in fig. 3. (a). When the optical
Gaussian band pass filter is used to select the red-shift at the
offset value of o.3nm and the bandwidth of 20GHZ, the best
logic XOR gate is achieved in fig. 3. (b). If the optical
Gaussian band pass filter selects a red-shift at the offset value
of 0.7nm and the bandwidth of 50GHZ, the best logic OR gate
is realized in fig. 3. (c). When the optical band pass filter is
applied to select a red-shift at the offset value 0f 1.7nm and
the bandwidth of 40GHZ in fig.3. (d).
Table.1. Parameters for all-optical logic gates (AND, OR, XOR) in the same
input signal powers
This table is shown as the parameters for all-optical logic
gates (AND, OR, XOR) at the same input power setting of the
two input signal powers and the CW probe power but
different bandwidth and offset spacing by using a single
semiconductor optical amplifier and several optical band pass
filters. The XOR gate bandwidth is narrow and the time
waveform is wide.
2
Data 1
0
(a)
2
Optical Power (mW)
Data 2
0
T
(b)
(a)
(b)
60
OR
0
(c)
45
XOR
0
(d)
3
AND
(c)
(d)
(e)
0
2
0
5
8
11
(e)
Time(ns)
Fig. 4. Simulation results for two- input logic gates, (a) and (b) are input data
signals, (c)-(e) are logic OR, XOR and AND gates for the same input signal
powers.
The simulation results of two-input logic gates are shown
as the bit sequences in Fig4 (a) and (b). The time output
waveform by the optical time domain (c) The output is high
Fig. 5. Eye patterns measured for the RZ format: (a) back-to-back 1, (b)
back-to-back 2, (c) XOR gate, (d) OR gate(e) AND gate at in the same power
setting.
The eye-diagrams show the BER pattern at the same average
power of -22.369dBm. Fig. 5. (a) and (b) are the eye patterns
of two inputs data signal. The output eye patterns of(c) XOR
gate (d) OR gate and AND gate are shown.
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All Rights Reserved © 2012 IJSETR
International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
signal and probe are 1550nm and 1560nm. To improve cross
phase modulation effect, the SOA is biased at 500mA.
Understanding of the all-optical logic gates will provide not
only increased speed and capacity telecommunication
systems, but also various applications including optical
packet switching, add/drop, decision making, bit extraction,
and many other optical applications system.
ACKNOWLEDGMENT
The author would like to express sincere appreciation to
the Rector of Mandalay Technological University for kind
Permission to prepare for this journal. The author would also
like to give special thanks to my supervisor and all teachers in
EC Department and all who willingly helped the author
throughout the preparation of the journal. This journal is
dedicated to the author’s parents for continual and full support
on all requirements and moral encouragement.
REFERENCES
[1]
Fig. 6. BER measurement for all-optical logic gates (AND, OR, XOR) for
the same input signal powers
AND gate operation is the best result in the BER
measurements for all-optical logic gates (AND, OR, XOR)
based on single SOA and BPF at the10-9 but it is not good
beyond at the 10-12. All-optical logic gates (AND, OR, XOR)
are demonstrated with 0.4dB, 1.2dB and 2.1dB power penalty
at 10-9 BER in the same input signal power. BER curve are
measured back to back1, back to back2, XOR gate, OR gate
and AND gate by placing at the same average power. If the
input signal is received at the output with the little power, the
receiver sensitivity is good.
V. CONCLUSION
All-optical logic gates (AND, OR, XOR) are described at
10 Gb/s using the single semiconductor optical amplifier and
several optical Gaussian band pass filter. All-optical logic
gates (AND, OR, XOR) capable of working with 10Gbps RZ
modulated data streams based on cross phase modulation
effect of the single SOA in the same power setting but
different bandwidth and offset spacing. The BER for
all-optical logic gates is produced in the same power setting,
an AND gate is the best logic gate at10-9 but beyond 10-12 it is
not good. All-optical logic gates (AND, OR, XOR) are
demonstrated with 0.4dB, 1.2dB and 2.1dB power penalty at
10-9 BER in the same power setting but different bandwidth
and offset spacing. Both data signals have a pulse width of
20ps with peak power of 2mW and probe power of 0.1mW is
modulated at 10 Gb/s. The bit error rate, Q factor and power
penalty are measured for all-optical logic gates. The Q factor
is near approximately 6. The wavelengths of two inputs data
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All Rights Reserved © 2012 IJSETR
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[4]
[5]
[6]
[7]
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1. Chaw Chaw received her Bachelor of Technology (B.Tech) degree in
2006 and Bachelor of Engineering (B.E) degree in 2007 in Electronic
Engineering from Monywa Technological University, Myanmar. She is now
Master of Engineering (M.E) student in Mandalay Technological University,
Myanmar. Her research interests include optical fiber communications and
digital communications.