Z. Ghassemlooy , H. Le Minh, and Wai Pang Ng Optical Communications Research Group
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Transcript of 1 Razali Ngah, and Zabih Ghassemlooy Optical Communication Research Group School of Engineering &...
1
Razali Ngah, and Zabih Ghassemlooy
Optical Communication Research Group
School of Engineering & Technology
Northumbria University, United Kingdom
http: soe.unn.ac.uk/ocr/
An All Optical OTDM Router Based On SMZ Switch
2
Contents
Aim and objectives Introduction Optical time division multiplexing (OTDM) Ultrafast optical time-domain technology - Issues All optical switches All OTDM router Simulations and results Conclusions + further work Publications
3
Aim and Objectives
Aim: To develop a novel synchronization technique using all optical switches for ultra high speed OTDM networks
Objectives:1. To study the requirement of ultra high
speed OTDM packet switching2. To investigate all optical demultiplexing
techniques and devices3. To develop a novel synchronization
technique using all optical switch
4
Introduction
Solution: All optical transmission, multiplexing, switching, processing, etc.
Multiplexing:- To extend a transmission
capacity
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
Bandwidth bottleneck due to optical-electronic-optical conversion
Ch2 M U X
Ch1
ChN
Ch1
D E M U X
ChN
Ch2
Ch2 M U X
Ch1
ChN
Ch1
D E M U X
ChN
Ch2
5
Multiplexing : Optical
Wavelength division multiplexing (WDM)
Optical time division multiplexing (OTDM) Hybrid WDM-OTDM
6
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. multi-channels) Can operate at both:
1500 nm 1300 nm
OTDM
7
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)
Clock
ReceiverTransmitter
Clockrecovery
LightsourceLight
source
Data (10 Gb/s)
N
Networknode
Networknode
Drop Add
Rx
Rx
Rx
10 GHzN*10 Gb/s
Data (10 Gb/s)
OTDM DEMUXOTDM MUXAmplifierModulatorsFibre delay line
Fibre
Span
8
OTDM : Multiplexing of Clock Signal
Clock(Sync.)
Address Payload Guard band
Space division multiplexing: separate transmission fibre time varying differential delay & high cost
Wavelength division multiplexing: different wavelength only practical for predetermined path
Orthogonal polarization: orthogonally polarized clock pulse polarization mode dispersion and other non linear effects
Intensity division multiplexing: higher intensity for clock pulse difficult to maintain in long distance transmission
Time division multiplexing: self-synchronization - clock is located at the beginning of the packet)
9
Synchronization (all optical clock recovery) Clock recovery: using all optical switch
combined with optical feedback Contention resolution
Type: Optical buffering, deflection routing & wavelength conversion
Routing strategies Switch-level routing and contention resolution
Ultrafast optical time-domain technology : Issues
10
Key components required in all optical signal processing for ultrahigh speed OTDM networks
Applications: Optical cross-connects: provisioning of lightpaths Protection switching : rerouting a data stream in
the event of system or network failure Optical Add/Drop multiplexing: insert or extract
optical channels to or from the optical transmission system
Optical signal monitoring
All Optical Switches
11
All Optical Switches – contd.
Control pulse
Data in Data out
Coupler
CW CCW
Long fibre loop
Port 1 Port 2
Control coupler
PC
x
Data In s
Data out
Coupler
SLA
CW CCW
Fibre loop
Control Pulse c
PC
Non-linear Optical Loop Mirror (NOLM) Terahertz Optical Asymmetric Demultiplexer (TOAD)
Requires high control pulse energy and long fiber loop Asymmetrical switching window profile
due to the counter-propagating nature of the data signals
12
All Optical Switches – contd.
Symmetric Mach-Zehnder (SMZ)
Symmetrical switching window profile Integratable structure
13
All Optical Switches – contd.
Device SwitchingTime
RepetitionRate(GHz)
Noise Figure(dB)
Ease of Integration
?
Practicality
SMZ < 1 ps 100+ GHz 6 YES HIGH
TOAD < 1 ps 100+ GHz 6 YES MEDIUM
NOLM 0.8 ps 100+ GHz 0 NO LOW
UNI < 1 ps 100+ GHz 6 NO MEDIUM
Comparative study of all optical switches [Prucnal’01]
14
3 dBCoupler
Tdelay
OTDM Signal Pulses
Control Pulse (switch-on)
Optical filter
Control Pulse (switch-off)
SOA1
SOA2
Output Port 1
SMZ Switch : Principle
3 dBCoupler
OTDM Signal Pulses
Control Pulse Input Port 1
Control Pulse Input Port 2
SOA1
SOA2
Output Port 2
(i) No control pulses
(ii) With control pulses
15
SMZ : Switching Window
)(cos.)()(2)()(4
1)( 2121 ttGtGtGtGtW
40 45 50 55 60 65 70 75 80 85 902
4
6
8
10
12
14
16
18
20
Gain Profile of Gc1(__) and Gc2(--)
Time (ps)
Gain
40 45 50 55 60 65 70 750
5
10
15
20
25SMZ switching window
Time (ps)
SM
Z g
ain
G1 and G2 are the gains profile of the data signal at the output of the SOA1 and
SOA2, ΔФ is the phase difference between the data signals, and LEF is linewidth enhancement factor
)/ln(5.0 21 GGLEF
16
SMZ : Switching Window (simulation)
TABLE I. SIMULATION PARAMETERSParameter ValueSOA. LengthLSOA 0.3 mm. Active area, 3.0x10-13 m2
. Transparent carrier density, No
1.0x1024 m-3
. Confinement factor, 0.15
. Differential gain, g 2.78x1020 m2
. Linewidth enhancement, 4.0
. Recombination coefficient A1.43x108 1/s. Recombination coefficient B1.0x10-16 m3/s. Recombination coefficient C3.0x10-41 m6/s. Initial carrier density 2.8x1024 m-3
. Total number of segments 50Data and control pulses. Wavelength of control & data 1550 nm. Pulse FWHM 2 ps. Control pulse peak power 1.2 W. Data pulse peak power 2.5 µW
17
SMZ : Switching Window (comparison)
45 50 55 60 65 70 750
5
10
15
20
SMZ switching window (Cross)
Time (ps)
SM
Z ga
in
2.025 2.03 2.035 2.04 2.045 2.05 2.055 2.06
x 10-9
5
10
15
20
Time (s)
SM
Z G
ain
SMZ Switching Window
Theoretical Simulation
18
SMZ : Switching Window (experimental)
Experimental switching window profile of the SMZ [Toliver’00 Opt. Comm]
19
The ratio of the output power in the on-state to the output power in the off-state
SMZ : On-Off Ratio
Input signal of the SMZ Transmitted output of the SMZ
Crosstalk
Target signal
20
SMZ : On-Off Ratio – contd.
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7
Linewidth enhancement factor
On
-off
ra
tio
(d
B)
0.00
0.20
0.40
0.60
0.80
1.00
1.20
No
rma
lise
d t
ran
sm
issio
n p
ow
er
0
2
4
6
8
10
12
14
16
18
20
10 40 80 100 160
Bit rate (Gb/s)
On
-off
ra
tio
(d
B)
On-off ratio and normalised transmission powerAgainst linewidth enhancement factor
On-off ratio at different data rate
21
SMZ : BER Performance
___________________________________Parameter Value
Pre-amplifierMode Gain controlledNoise Figure 4 dBGain 25 dB
PIN detector Responsivity 1 A/WThermal noise 10 pA/Hz1/2
Cutoff frequency 7.0x109 Hz__________________________________________
Receiver parameters
22
SMZ : BER Performance – contd.
-44 -42 -40 -38 -36 -3410
-20
10-18
10-16
10-14
10-12
10-10
10-8
10-6
10-4
10-2
100
Received power (dBm)
BE
R
back-to-back 10Gb/sSMZ 4x10Gb/s SMZ 8x10 Gb/s SMZ 16x10 Gb/s
BER against the average received power for (a) back-to-back without demultiplexer, (b) 40 – 10 Gb/s demultiplexer, (c) 80 – 10 Gb/s demultiplexer and (d) 160 – 10 Gb/s demultiplexer
23
SMZ : BER Performance – contd.
Ngah’04 Tekin’02
IWC4
Diez’00
Elec. Lett
Hess’98
PTL
Jahn’95
Elec. lett
Back-to-back
(10 Gb/s)
Sensitivity
-38 dBm
-35 dBm
-35 dBm
-34 dBm
-37 dBm
40-10 Gb/s
demux.
Power penalty1.2 dB NA NA 0 dB 2.5 dB
80-10 Gb/s
demux.
Power penalty1.4 dB 1 dB 1.2 dB 4 dB NA
160-10 Gb/s
demux.
Power penalty1.5 dB 3.5 dB 2.8 dB NA NA
Comparison with experimental results
24
Port 1
Port2
SMZ1 (clock
extract)
SMZ2 (read
address)
SMZ3 (route
payload )
( a)
( b)
( c) (e)
(d)
(f)
(a) OTDM Signal
(b) Extracted Clock
(c) Address + Payload
(d) Address
(e) Payload
(f) Payload
1x2 All OTDM Router
25
OTDM Router : Synchronization
PC
3 dBCoupler
OTDM Signal
Control Pulse (switch-on)
Optical filter
Control Pulse (switch-off)
SOA1
SOA2
Output Port 1
OFDL
OFDL
Self-synchronization: low hardware costs and control control complexity require a single pulse in the first bit position of the packet
Clock, Address and payloads have the same intensity, polarization, width and wavelength
26
OTDM Router : Synchronization (simulation)
27
OTDM Router : Simulation Results
OTDM packet signal Extracted clock from the OTDM packet
Crosstalk
28
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
200 400 600 800 1000 1200
Bits Period (ps)
On
-Off
Ra
tio
(d
B)
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
200 400 600 800 1000 1200
Bits Period (ps)
On
-Off
Ra
tio
(d
B)
The on-off ratio against the bit period
OTDM Router : Simulation Results –contd.
29
Demultiplexed payload at the transmitted port
OTDM Router : Simulation Results – contd.
Clock extraction and demultiplexing for OTDM
packet signal
Crosstalk
30
OTDM Router : Simulation
31
OTDM Router : Simulation Results
OTDM input packet
Clk Add Payload
32
Extracted clock signal at the reflected output of SMZ1
OTDM Router : Simulation Results – contd.
33
Data packet at the transmitted output of SMZ1
OTDM Router : Simulation Results – contd.
Add Payload
34
Address bit at the reflected output of SMZ2
OTDM Router : Simulation Results – contd.
35
Payload at the transmitted output of SMZ2
OTDM Router : Simulation Results – contd.
36
Payload at the port 1 of SMZ3
OTDM Router : Simulation Results – contd.
37
Performance Issues
(1) Relative Intensity Noise (RIN)
Relative timing jitter between the control and the signal pulses induces intensity fluctuations of the demultiplexed signals
38
Relative Intensity Noise (RIN)
The output signal can be described by:
dttptTtw x )()()(
dttptwE t )()()(
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:
pt(t) probability density function of the relative signal pulse arrival time:2
2
1
2
1)(
RMSt
t
RMS
t et
tp
where tRMS is the root mean square jitter
39
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:
)(
)()(
2
E
VarRIN
The variance of the output signal, depending on the relative arrive time is:
)()()()( 22 EdttptwVar t
Relative Intensity Noise (RIN) – contd.
The total RIN for the router is three times the value of single SMZ
40
(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
Performance Issues – contd.
41
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 t
nt
E
ECXT log10
Et is the output signal energy due to the target channel
2/
2/
)()(Dc
Dc
Tt
Tt
cxt dtttptTE
Ent is the output signal energy due to the nontarget channel
2/
2/
)()(Dc
Dc
TTt
Tt
cxnt dtttptTE
The total crosstalk for the router 1)1( 3 CXTCXT
42
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:
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 pre-amplified average signal power for a mark (excluding crosstalk)
The variance of receiver noise for mark and space:
eaL
keASExths Bi
R
KTBIIq
xrec
_2
___222 4
)(2,
]1[__
nsigm CXTII ][__
nsigs CXTII
sigoutinsig GLPRI ___
43
The noise variance of optical amplifier
BER Analysis – cont.
2
22
,
)2(4
o
eoeASE
o
eASExxamp B
BBBI
B
BII
The average photo-current equivalent of ASE LqBGNI ooutspASE )1(
The expression for calculating BER is given as:
where 2
______
Total
sm IIQ
Q
QBER
)5.0exp(
2
1 2
The noise variance of RIN
ROUTERsigeTmmRIN RINIBRINI22
2, eTssRIN BRINI
22, and
2,
2,
2,
2,
2,
2,
2sRINmRINsampmampsrxmrxTotal The total variance
44
BER: Theoretical Results
SMZ 1
Clock Address
SMZ 2
SMZ 3
Photo- detector
BER
1x2 Router Incoming OTDM Signal
Pin
Filter
t = ts
Pk
Receiver
Optical Amp.
Optical path Electrical path
Block diagram of a router with a receiver
System Parameters
Parameter in out out L R RL Tk Nsp RINT Bo Ia2 RINR
OUTER
RMSjitter
CXTn
Be
Value -2 dB
-2 dB
Gain (overall)25 dB
-2 dB
1 A/W
50
293 K
2 10-15 Hz-1
400
GHz
100
pA2
/Hz
-21 dB
1 ps -25 dB
0.7Rb
45
RIN and CXT : Results
0 2 4 6 8 10 12 14 16 18 20-26
-24
-22
-20
-18
-16
-14
-12
-10
-8
Control signals separation (ps)
Rel
ativ
e in
tens
ity n
oise
(dB
)
OTDM router SMZ demultiplexerFWHM = 2ps
0 2 4 6 8 10 12 14 16 18 20-26
-24
-22
-20
-18
-16
-14
-12
-10
-8
Control signals separation (ps)
Rel
ativ
e in
tens
ity n
oise
(dB
)
OTDM router SMZ demultiplexerFWHM = 2ps
0 2 4 6 8 10 12 14 16 18 20-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Control signals separation (ps)
SM
Z cr
osst
alk
(dB
)
OTDM router SMZ demultiplexerFWHM = 2ps
0 2 4 6 8 10 12 14 16 18 20-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Control signals separation (ps)
SM
Z cr
osst
alk
(dB
)
OTDM router SMZ demultiplexerFWHM = 2ps
RIN against control pulse separation for a single SMZ and a router
CXT against control pulse separation for a single SMZ and a router
46
BER : Results
BER against average received power for baseline and with an optical router
-44 -42 -40 -38 -36 -34 -32 -30 -28 -26 -24 -22
10-12
10-10
10-8
10-6
10-4
10-2
Average received optical power (dBm)
Bit
erro
r ra
te
10Gb/s baseline 10Gb/s with router
47
BER : Simulation Results
-44 -42 -40 -38 -36 -34 -32 -30 -28 -26 -24 -2210
-20
10-18
10-16
10-14
10-12
10-10
10-8
10-6
10-4
10-2
100
Received power (dBm)
BE
R
10Gb/s back-to-back10Gb/s with router
BER against average received power for baseline and with an optical router
BER increases with the number of SMZ stages due to the accumulation of ASE noise in the SOAs hence, resulting the RIN increases.
48
Conclusions
All optical demultiplexer and 1x2 router based on SMZ has been implemented in a simulation environment using VPI.
BER analysis has been performed. The application of low noise SOA will reduce
the power penalty. SMZ switch becomes a key component for
ultra high speed OTDM networks.
49
Publications
(1) R. Ngah, Z. Ghassemlooy, G. Swift, T. Ahmad and P. Ball, “Simulation of an all Optical Time Division Multiplexing Router Employing TOADs”, 3rd Annual Postgraduate Symposium on the Convergence of Telecommunications, Networking & Broadcasting, Liverpool, 17-18 June 2002, pp. 415-420.
(2) R. Ngah, Z. Ghassemlooy, and G. Swift, “Simulation of an all Optical Time Division Multiplexing Router Employing Symmetric Mach-Zehnder (SMZ),” 7th IEEE High Frequency Postgraduate Student Colloquium, London, 8-9 Sept. 2002, pp. 133-139.
(3) R. Ngah, Z. Ghassemlooy, and G. Swift, “40 Gb/s All Optical Router Using Terahertz Optical Asymmetric Demutiplexer (TOADs)” International Conference on Robotics, Vision, Information and Signal Proceeding, Penang Malaysia, 22-24 Jan 2003, pp. 179-183.
(4) R. Ngah, Z. Ghassemlooy, and G. Swift, “Simulation of 1 X 2 OTDM router employing Symmetric Mach-Zehnder (SMZ)” Postgraduate Research Conference in Electronic, Photonics, Communication & Networks, and Computing Science, Exeter, 14-16 April, pp 105-106.
(5) R. Ngah, Z. Ghassemlooy, and G. Swift, “Comparison of Interferometric all-optical switches for router applications in OTDM systems” 4th Annual Postgraduate Symposium on Convergence of Telecommunications, Networking and Broadcasting, Liverpool, 16-17 June 2003, pp. 81-85.
(6) A. Als, R. Ngah, Z. Ghassemlooy, and G. Swift, “Simulation of all-optical recirculating fiber loop buffer employing a SMZ switch” 7th World Multiconference on Systemics, Cybernetics, and Informatics, Florida, 27-30 July 2003, pp 1-5.
(7) R. Ngah, and Z. Ghassemlooy, “BER performance of an OTDM demultiplexer based on SMZ switch” Postgraduate Research Conference in Electronic, Photonics, Communication & Networks, and Computing Science, Hetfordshire, 5-7 April 2004, pp 228 –229.
(8) R. Ngah, and Z. Ghassemlooy, “Bit Error Rate Performance of All Optical Router Based on SMZ Switches,” First IFIP International Conference on Wireless and Optical Communications Networks (WOCN 2004), Oman, 7 – 9 June 2004, Accepted for publications.
(9) R. Ngah, and Z. Ghassemlooy, “The Performance of an OTDM Demultiplexer Based on SMZ Switch,” IEE Seminar on Future Challenges and Opportunities for DWDM and CWDM in the Photonic Networks, University of Warwick, 11 June 2004, Accepted for publications.
(10) R. Ngah, and Z. Ghassemlooy, “Simulation of Simultaneous All Optical Clock Extraction and Demultiplexing for OTDM Packet Signal Using SMZ Switches,” 9th European Conference on Networks & Optical Communications (NOC 2004), Eindhoven, 29 June – 1 July 2004, Accepted for publications.
(11) R. Ngah, and Z. Ghassemlooy, “Noise and Crosstalk Analysis of SMZ Switches,” International Symposium on Communication Systems, Networks and Digital Signal Processing, University of Newcastle, 20 - 22 Juuly 2004, Accepted for publications.
Conference
50
Journal(1) R. Ngah, and Z. Ghassemlooy, “Simulation of 1x2
OTDM Router Employing Symmetric Mach-Zehnder Switches” Accepted for publications in IEE Proceeding Circuits, Devices & Systems.
Publications – contd.
51
Acknowledgement
Thanks to the University of Teknologi Malaysia for sponsoring the research.
52
THANK YOU