1 Razali Ngah, and Zabih Ghassemlooy Optical Communication Research Group School of Engineering & Technology Northumbria University, United Kingdom http:

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


Symmetric Mach-Zehnder (SMZ)

Symmetrical switching window profile Integratable structure

13


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


33

Data packet at the transmitted output of SMZ1


Add Payload

34

Address bit at the reflected output of SMZ2


35

Payload at the transmitted output of SMZ2


36

Payload at the port 1 of SMZ3


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


Rel

ativ

e in

tens

ity n

oise

(dB

)


0 2 4 6 8 10 12 14 16 18 20-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0


SM

Z cr

osst

alk

(dB

)


0 2 4 6 8 10 12 14 16 18 20-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0


SM

Z cr

osst

alk

(dB

)


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

Documents

1 Razali Ngah, and Zabih Ghassemlooy Optical Communication Research Group School of Engineering & Technology Northumbria University, United Kingdom http: