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Razali Ngah, and Zabih Ghassemlooy

Optical Communication Research Group

School of Engineering & Technology

Northumbria University, United Kingdom

http: soe.unn.ac.uk/ocr/

The Performance of An OTDM Demultiplexer Based on SMZ Switch

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Contents

Introduction OTDM All optical switches Simulations and results Conclusions

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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

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Multiplexing - Optical

Wavelength division multiplexing (WDM)

Optical time division multiplexing (OTDM) Hybrid WDM-OTDM

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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

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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

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All Optical Switches

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

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All Optical Switches – contd.

Symmetric Mach-Zehnder (SMZ)

Symmetrical switching window profile Integratable structure

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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]

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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

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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

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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

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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

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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

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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 normarlised transmission powerAgainst linewidth enhancement factor

On-off ratio at different data rate

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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

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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

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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

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Application of SMZ switch: 1x2 All OTDM Router

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

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Conclusions

An all optical demultiplexer based on SMZ has been implemented in a simulation environment using VPI.

BER analysis has been performed. The power penalty of the demultiplexer is mainly

due to the ASE noise in the SOAs of the SMZ. The application of low noise SOA will reduce the

power penalty.

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Acknowledgement

Thanks to the University of Teknologi Malaysia for sponsoring the research.

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THANK YOU