AN INTERACTIVE ENVIRONMENT FOR SIMULATION AND …
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Transcript AN INTERACTIVE ENVIRONMENT FOR SIMULATION AND …
Bit Error Rate Performance of All
Optical Router Based on SMZ
Switches
Razali Ngah, and Zabih Ghassemlooy
Optical Communication Research Group
School of Engineering & Technology
Northumbria University, United Kingdom
http: soe.unn.ac.uk/ocr/
1
Contents
Introduction
OTDM
All optical switches
Symmetric Mach-Zehnder (SMZ) switch
All OTDM Router
Simulations and Results
Conclusion
2
Introduction
Multiplexing:
• Electrical
• Optical
Drawbacks with Electrical:
Speed limitation beyond 40 Gb/s (80 Gb/s future) of:
Electo-optics/opto-electronics devices
High power and low noise amplifiers
Router congestion and reduced throughputs: Due to optical-electronic-optical
conversion
Limited modulation bandwidth of light sources, and modulators
Solution: All optical transmission, multiplexing, switching, processing, etc.
3
Multiplexing - Optical
Wavelength division multiplexing (WDM)
Optical time division multiplexing (OTDM)
Hybrid WDM-OTDM
4
OTDM
Flexible bandwidth on demand at burst rates of 100 Gb/s/
The total capacity of single-channel OTDM network = DWDM
Overcomes non-linear effects associated with WDM:
(i) Self Phase Modulation (SPM) – The signal intensity of a given channel
modulates its own refractive index, and therefore its phase
(ii) Cross Phase Modulation (XPM) – In multi-channel systems, other
interfering channels also modulate the refractive index of the desired channel and
therefore its phase
(iii) Four Wave Mixing (FWM) – Intermodulation products between the WDM
channels, as the nonlinearity is quadratic with electric field
Less complex end node equipment (single-channel Vs. multichannels)
Can operate at both:
1500 nm (like WDM) due to EDFA
1300
5
OTDM - Principle of Operation
Multiplexing is sequential, and could be carried out in:
A bit-by-bit basis (bit interleaving)
A packet-by-packet basis (packet interleaving)
Data (10 Gb/s)
Data (10 Gb/s)
Rx
Span
N*10 Gb/s
10 GHz
Rx
Network
node
Light
source
N
Rx
Drop
Clock
Add
Clock
recovery
Transmitter
Receiver
Fibre delay line
Modulators
Amplifier
OTDM MUX
OTDM DEMUX
Fibre
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All Optical Switches
x
SLA
Long fibre
loop
Control
coupler
Control
pulse
CW
Fibre
loop
CCW
Data
In s
Coupler
Data in
Port 1
Control
Pulse c
Port 2
PC Data
out
Non-linear Optical
Loop Mirror (NOLM)
CW
CCW
Data
out
Coupler
PC
Terahertz Optical Asymmetric
Demultiplexer (TOAD)
7
All Optical Switches – contd.
Mach-Zehnder Interferometer (MZI)
Colliding pulse
Mach-Zehnder
(CPMZ)
Symmetric Mach
Zehnder (SMZ)
8
SMZ Switch: Principle
(i) No control pulses
Control Pulse
Input Port 1
SOA1
OTDM Signal Pulses
Control Pulse
Input Port 2
Output
Port 2
3 dBCoupler
SOA2
(ii) With control pulses
Control Pulse
(switch-on)
SOA1
Output
Port 1
OTDM Signal Pulses
Optical
filter
Tdelay
Control Pulse
(switch-off)
3 dBCoupler
SOA2
9
SMZ : Switching Window
1
W (t ) G1 (t ) G2 (t ) 2 G1 (t )G2 (t ) . cos (t )
4
G1 and G2 are the gains profile of the data signal at the output of the SOA1 and SOA2
and ΔФ is the phase difference between the data signals
Gain Profile of Gc1(__) and Gc2(--)
20
SMZ switching window
25
18
20
16
SMZ gain
15
Gain
14
10
12
5
0
40
10
45
50
55
60
Time (ps)
65
70
75
8
6
4
2
40
45
50
55
60
65
Time (ps)
70
75
80
85
90
10
1x2 All OTDM Router
( a)
( c)
SMZ1
(clock
extract)
(e)
SMZ2
(read
address)
Port 1
(f)
SMZ3
(route
payload )
( b)
Port2
(d)
(a) OTDM Signal
(b) Extracted Clock
(c) Address + Payload
(d) Address
(e) Payload
(f) Payload
11
Performance Issues
(1) Relative Intensity Noise (RIN)
Relative timing jitter between the control and the signal pulses
induces intensity fluctuations of the demultiplexed signals
12
Relative Intensity Noise (RIN)
The output signal can be described by:
w(t )
T
x
(t ) p(t )dt
where Tx(t) is the switching window profile and p(t) is the input data profile
The expected of the output signal energy is given as:
E ( )
w(t ) p (t )dt
t
pt(t) probability density function of the relative signal pulse arrival time:
1
pt (t )
e
2 t RMS
1 t
2 t RMS
2
where tRMS is the root mean square jitter
13
Relative Intensity Noise (RIN) – contd.
The variance of the output signal, depending on the relative arrive time is:
Var( )
2
2
w
(
t
)
p
(
t
)
dt
E
( )
t
Assuming that the mean arrival time of the target channel is at the centre
of the switching window, RIN induced by the timing jitter of the output
signal can be expressed as:
RIN( )
Var ( )
E 2 ( )
The total RIN for the router is three times the value of single SMZ
14
Performance Issues – contd.
(2) Channel Crosstalk (CXT)
Due to demultiplexing of adjacent non-target channels to the output port
when the switching profile overlaps into adjacent signal pulses
15
Channel crosstalk (CXT) – contd.
CXT is defined by the ratio of the transmitted
power of one non-target channel to that of a
target channel
Et is the output signal energy due to the
target channel
Ent is the output signal energy due to the
nontarget channel
The total crosstalk for the router
Ent
CXT 10 log
Et
Et
tc TD / 2
T
x
(t ) p (t t c )dt
tc TD / 2
E nt
tc T TD / 2
T
x
(t ) p (t t c )dt
tc TD / 2
CXT (1 CXT )3 1
16
BER Analysis
Assuming 100% energy switching ratio for SMZ and the probability of mark
and space are equal, the mean photocurrents for mark Im and space Is are:
__
__
I m I sig [1 CXTn ]
I s I sig [CXTn ]
___
I sig Rino u tGLPsig
where R is the responsivity of the photodetector, ηin and ηout are the input and output
coupling efficiencies of the optical amplifier, respectively; G is the optical amplifier
internal gain, L is optical loss between amplifier and receiver, and Psig is the preamplified average signal power for a mark (excluding crosstalk)
The variance of receiver noise for mark and space:
2
rec, x
_
4
KT
k
s2 th2 2q( I x I ASE ) Be
ia2 Be
RL
___
17
BER Analysis – cont.
The noise variance of optical amplifier
The noise variance of RIN
2
RIN , m
2
2
I m RINT Be I sig RINROUTER
The average photo-current equivalent of ASE
The expression for calculating BER is given as:
___
where
and
Q
___
Im Is
2
amp , x
2
4I x I ASE Be I ASE
Be (2Bo Be )
Bo
Bo2
2
RIN , s
2
I s RIN T Be
I ASE Nsp (G 1)out qBo L
BER
1 exp(0.5Q 2 )
Q
2
2
Total
The total variance
2
2
2
2
2
Total
rx2 ,m rx2 ,s amp
,m
amp ,s
RIN ,m
RIN ,s
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Results
Block diagram of a router with a receiver
Incoming
OTDM
Signal
Pin
Receiver
1x2 Router
t = st
Pk
SMZ
1
SMZ
2
Photodetector
SMZ
3
BER
Filter
Optical
Amp.
Clock
Address
Optical path
Electrical path
System Parameters
Parameter
Value
in
-2
dB
out
-2
dB
out
Gain
(overall)
25 dB
L
-2
dB
R
1
A/W
RL
50
Tk
293
K
Nsp
2
RINT
10-15
Hz-1
Bo
400
GHz
Ia2
100
pA2
/Hz
RINR
OUTER
RMSji
CXT
tter
n
-21
dB
1 ps
-25
dB
Be
0.7
Rb
19
Results – RIN and CXT
0
-8
OTDM router
SMZ demultiplexer
FWHM = 2ps
-10
-5
-10
-12
SMZ crosstalk (dB)
Relative intensity noise (dB)
-15
-14
-16
-18
-20
-25
-30
-20
-35
-22
-40
-24
-26
OTDM router
SMZ demultiplexer
FWHM = 2ps
-45
-50
0
2
4
6
8
10
12
Control signals separation (ps)
14
16
18
RIN against control pulse separation for a
single SMZ and a router
20
0
2
4
6
8
10
12
Control signals separation (ps)
14
16
18
20
CXT against control pulse separation for a
single SMZ and a router
20
Results - BER
10Gb/s baseline
10Gb/s with router
-2
10
-4
10
Bit error rate
-6
10
-8
10
-10
10
-12
10
-44
-42
-40
-38
-36
-34
-32
-30
Average received optical power (dBm)
-28
-26
-24
-22
BER against average received power for baseline and with an optical router
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Conclusions
Relative intensity noise and channel crosstalk of 1x2
router is investigated
BER analysis has been performed.
As expected the BER increases with the number of SMZ
stages due to the accumulation of ASE noise in the SOAs
hence, resulting the RIN increases.
22
THANK YOU
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