1

Raman and Parametric mediated

amplification and all optical

processing for high speed fiber

optics communication systems

David Dahan

Electrical Engineering Department

Technion 27/06/2005

2

Acknowledgements My supervisor : Prof. Gadi Eisenstein

Former and current students

Dr. Kobi Lasri

Dr. Alberto Bilenca

Evgeny Shumakher

Robert Alizon

Din Hadass

Ido Ben-Aroya

Laboratory staff

Dr. Mark Sogolov

Dr. Boris Levit

Dr. Alex Bekker

Vladimir Smulakovsky

Scholarships and prices

Technion: Martin Prosserman fellowship Ministry of Science: Levy Eskhol scholarship

IEEE/LEOS: Graduate student fellowship award (2005)

3

Research Topics

Stimulated Raman Scattering (SRS) in fiber

ASE Noise properties of saturated Raman Fiber amplifier in CW regime

Inter band Raman mediated wavelength converter and reshaper

Parametric Processes in fibers for optical pulse source generation A Self Starting Ultra Low Jitter Pulse Source Using Coupled Optoelectronic

Oscillators with an Intra Cavity Fiber Parametric Amplifier

Multi wavelength pulse sources based on saturated OPA without spectral broadening

SRS + Parametric processes All optical tunable delay line via Slow and fast light propagation in a narrow

band parametric amplifier : a route to optical buffering

4

Motivations

1300 1400 1500 1600

U Fiber Type

Standard

AllWave

Fib

er

Loss (

dB

/km

)

0.15

EDFA 0.25

0.35

C L S+ S

TDFA

GS-TDFA

GS-EDFA

Raman,

OPA

Optical Wavelength (nm)

How can we cope with the increasing demand in

information capacity?

Motivations Operation over these extremely large optical

bandwidths requires that several key

components be developed !

All optical processing devices : Wavelength converter and re-shapers

All optical buffers

High bit rate stable optical pulse sources Low jitter self starting source

Multi wavelength source

Wide Band Amplifiers (Raman, OPA) Noise properties

6

Inter band Raman - Mediated

Wavelength Converter with Noise

Reduction Capabilities

7

Raman wavelength converter :

Principle of operation Signal at wavelength λs

t

t

P1s

P0s

Ppr

t

t Probe : λpr~ λs-100 nm,

Ppr<<P1s

Optical fiber

(L km)

Large detuning may degrade the conversion because of large walk off

Need to operate almost symmetrically around the zero dispersion wavelength

8

Raman wavelength converter :

Principle of operation

Fast Raman response - few fs

Strong depletion regime (Ps>>Ppr)

(0) exp (0)

(0)exp

pr s

s R s eff

pr pr

P LD P C P L

P L

1 exp( )s seff

s

LL

R p s

R

eff

g f fC

KA

9

Experimental set up: wavelength conversion

λ λ 0~1536.3 nm

λs λpr

Highly Nonlinear Fiber : γ~ 10.6 W-1/km, λ0~1536.3 nm ,S0~ 0.018 ps/(nm2-km)

~100 nm

10

Experimental result :

wavelength conversion

Ram

an i

nd

uce

d d

eple

tion

at

14

83

nm

in

CW

reg

ime

[dB

]

-5 10 15 20 25 -16

0 5

-14

-12

-10

-8

-6

-4

-2

0

0

2

4

6

8

10

12

14

16

Theory

Measurements

Input Power at 1584 nm [dBm]

Ex

tin

ctio

n r

atio

at

10

Gb

/s

fo

r p

rob

e si

gn

al at

14

91

nm

[d

B]

ER Measurements +

CR~3.7 W-1

/Km extracted from CW measurement

11

Experimental set up : wavelength conversion with reshaping capabilities

12

Converted Signal, p=1500 nm

Reshaping results @ 10 Gbit/s

Original Signal, s=1581 nm

13

Reshaping results @ 10 Gbit/s

Original Signal, s=1581 nm Converted Signal, p=1490 nm

14

Reshaping results @ 10 Gbit/s

Original Signal, s=1581 nm Converted Signal, p=1480 nm

15

Reshaping results @ 10 Gbit/s

Original Signal, s=1581 nm Converted Signal, p=1470 nm

16

BER measurement at 10 Gbit/s : Large crosstalk : -13 dB

-28 -26 -24 -22 -20 -18 -16 -14 -14

-12

-10

-8

-6

-4

-2

0

Received optical power [dBm]

Signal @1581 nm

Converted signal @1495 nm

Converted signal @1485 nm

Converted signal @1480 nm

Converted signal, p =1495 nm, Q=8

Original Signal,

s =1581 nm, Q=3.5

Lo

g10(B

ER

)

17

BER measurement at 10 Gbit/s : Moderate crosstalk : -18 dB

Converted signal @1495 nm Converted signal @1485 nm

-28 -26 -24 -22 -20 -18 -16 -18

-16

-14

-12

-10

-8

-6

-4

-2

0

Received optical power [dBm]

Converted Signal,

p=1495 nm Q=10

Signal @1581 nm

Original Signal,

s=1581 nm Q=5.5

Converted Signal,

p =1485 nm, Q=9.6

Log

10(B

ER

)

18

Numerical simulations : operational bandwidth

Converted Wavelength [nm]

Ou

tpu

t Q

fac

tor

[dB

]

1470 1480 1490 1500 1510 1520 7

8

9

10

11

12

13

14

15

Extinction Ratio

7

8

9

10

11

12

13

14

15 Q factor

Ou

tpu

t E

xti

nct

ion

Rat

io [

dB

]

λs=1581 nm, Ps=21 dBm, Q=7.8

Operational conversion bandwidth = 35 nm

19

Slow and fast light propagation via

narrow band optical parametric

amplifier : a route to optical

buffering

20

Motivations

Tunable optical pulse delays are of central importance to

numerous fields including optical coherence tomography,

ultra-fast pulse metrology, and optical communications.

Next Internet Router generation will be based on all

optical packet switching : Need to develop all optical

buffering devices.

Promising approach : controlling the velocity of optical

pulses through dispersive media, a concept termed as

slow and fast light

21

Speed of light

The velocity of a pulse of light is determined by the

group index ng : vg=c/ng with c the speed of light in

vacuum (c=300 000 km /s).

The group index is determined not only by the refractive

index of the medium but also by the dispersive

characteristics of the structure :

g

nn n

Refractive index

Dependence of

refractive index on

the light frequency

22

Dispersion Near a Resonance

refractive index

n n in ' " 1 2

group index ng

(max) 105

n(max) . 01

!!

Index, Re(χ)

Group index ng

Absorption, Im(χ)

Narrower absorption line

Larger index slope

23

Slow Light Observations of Hau et al.

The speed of light can be slowed down using the absorption rays in an

ultra cold atomic gas : this requires a complex experimental set up which

is not practical for commercial application

24

Other media SC Waveguide (Passive and active) – Limited by carrier

life time. Maximum delay one bit.

Ruby Crystal – large delay narrow bandwidth

Rubidium vapor – Large delays ultra narrow bandwidth

and large attenuation

Nonlinearities in optical fibers may, on the other hand,

offer optical gain in addition to other advantages such as

a broad range of operating wavelengths, operation at

room temperature and flexible length

25

Slow and Fast Light via Stimulated Brillouin Scattering

Positive and negative delays up to 30 ns have been obtained

for pulse with large width (20 ns) using Stimulated Brillouin

Scattering in fiber. (Boyd et. Al)

The Stimulated Brillouin scattering can be used only for wide

pulses (several ns). This is not practical for high bit rate

applications which require pulse width of 100 ps and lower.

Need to find another process to generate a narrow

band gain spectrum in the fiber but large enough to

amplified picosecond pulses

26

Narrow band Optical Parametric Amplifier

(OPA) A partially degenerated OPA usually operates in the

anomalous dispersion regime of the fiber.

A significant parametric gain is obtained as usual for

frequencies satisfying -4γP0<Δk<0

With

When the pump wave propagates in the normal dispersion

regime of the fiber (β2>0) with a negative fourth order

dispersion parameter (β4<0) the phase matching condition

occurs far from the pump wavelength.

2 4

2 4 12s p s pk

27

Phase mismatching as a function of the wavelength

λ0=1539 nm, λp=1530 nm, γ=2.5 W-1km-1, P0=10W, λs1=1377 nm, λs2=1721 nm

1400 1500 1600 1700-50

0

50

100

150

200

Wavelength [nm]

Δk/γ

P0

β4<0

β4>0

λ0

β2>0 β2<0

λs1 λs2

Phase matching

28

ASE and gain spectra using 200 m long DSF with λ0=1539 nm

The spectral separation between this narrow gain spectrum and λp increases while its

width decreases as the spectral separation λ0-λp increases.

The parametric process is coupled to Stimulated Raman Scattering (SRS) for |λp-λs| up

to 150 nm.

The narrow gain spectra are very sensitive to the longitudinal variations of λ0 along the

fiber and lead to local variations of the group index

29

System Set up

30

Delay in high gain regime without SRS (|λp- λs |>150 nm)

2

3

2 426

2g p p

c d k c d kn c

d d

Short wavelength side Long wavelength side

1400 1500 1600 1700-50

0

50

100

150

200

Wavelength [nm]

Δk/γ

P0

0g g

g g

cn v

n n

0g g

g g

cn v

n n

Pulse delay Pulse

advancement

Slow light Fast light

31

Theoretical gain and delay spectra

Wavelength [nm]

OP

A G

ain

[d

B]

Tim

e D

ela

y [p

s]

1376 1376.5 1377 1377.5 1378

-5

0

5

10

15

20

25

30

35

40

-15

-10

-5

0

5

10

15

20

25

30

(a)

Wavelength [nm]

Tim

e D

ela

y [p

s]

OP

A G

ain

[d

B]

(b)

1720 1720.5 1721 1721.5 1722 1722.5

-5

0

5

10

15

20

25

30

35

40

-15

-10

-5

0

5

10

15

20

25

30

(b)

λp=1530 nm, P0=10 W, 200 m long DSF

In both spectral regimes, the same maximum gain value of 34 dB and the

maximum absolute value of the induced timing delay is 19 ps.

Both delay spectra are large and quite flat over some 40 GHz where the gain

exceeds 25 dB.

32

Theoretical gain and delay spectra

in Raman assisted OPA

Wavelength [nm]

OP

A G

ain

[d

B]

Tim

e D

ela

y [p

s]

1425 1426 1427 1428 1429 1430 1431

-10

0

10

20

30

40

-5

0

5

10

15

20

(a)

Wavelength [nm]

OP

A G

ain

[d

B]

Tim

e D

ela

y [p

s]

1656 1657 1658 1659 1660 1661 1662

5

10

15

20

25

30

35

40

-7.5

-5

-2.5

0

2.5

5

7.5

10

(b)

λp=1535 nm, P0=10 W, 200 m long DSF

When |λp-λs|<150 nm, the parametric process is coupled with SRS

It causes enhancement of the delay in the short wavelength side

whereas it reduces the time advancement at the long wavelength

side

33

Slow light observations - spectra

The spectra broaden and shift towards shorter wavelengths (since

β4<0) as predicted by the numerically calculated gain spectra .

The coupling between the parametric process and SRS widens the

gain spectra especially on the short wavelength side .

The somewhat wider experimental spectra are attributed once more

to a longitudinal variation of λ0 along the fiber.

1425 1426 1427 1428 1429 1430 1431-20

-10

0

10

20

30

40

50

60

70

1425 1426 1427 1428 1429 1430 1431-70

-60

-50

-40

-30

-20

Wavelength [nm]

Raman assisted parametric gainParametric gain only

Wavelength [nm]

G=49 dB

G=44 dB

G=42 dB

G=37 dB

G=31 dB

G=25 dB

P0

+

AS

E P

ow

er

[dB

m]

Ga

in [d

B]

P0

+

λs λs

34

Slow light observations

Time [ps]

0 50 100 150 200 250

0

0.2

0.4

0.6

0.8

1

Nor

mal

ized

inte

nsity

(a)(1)(2)(3)(4)

0 100 200 300 400

0

0.2

0.4

0.6

0.8

1

0 100 200 300 400

0

0.2

0.4

0.6

0.8

1

Nor

mal

ized

inte

nsity

Nor

mal

ized

inte

nsity

Time [ps] Time [ps]

(c) (d)(1) (2)(3)(4)(5)(6) (1) (2)(3)(4)(5)(6)

Nor

mal

ized

inte

nsity

Time [ps]

0 50 100 150 200 250 300 350

0

0.2

0.4

0.6

0.8

1(1) (2)(3)(4)(5)(6)(b)

200 m 500 m

1000 m 2000 m

λs=1428.6 nm λp=1535 nm

35

Measured delays as a function of parametric

gain for different fiber lengths

For a fixed gain level, the delay increases with fiber length. However, the

obtainable delay range decreases for very long fibers due to saturation.

There exists therefore an optimal length : 500 m long DSF offers a tunability

range 146 % larger than the minimum delay.

Del

ay [p

s]

0 10 20 30 40 500

50

100

150

200

Gain [dB]

L=200m

L=500m

L=1000m

L=2000m

36

Delay versus fiber length

200 m and 2000 m long Raman assisted OPA provide the same gain at λs

The overall delay which is the accumulative effect of the group index

distribution is larger in the long fiber as predicted

The small tuning range of long fibers results from the fact that their minimum

delay is large and they saturate rapidly

0 500 1000 1500 2000 0

0.5

1

1.5

2

2.5 x 10

-5

DSF length [m] G

r o u p

i n

d e x v

a r i

a t i o

n s

λ s

λ s

λ peak

Wavelength [nm]

1426.5 1427 1427.5 1428 1428.5 1429 -20

-10

0

10

20

30

40

50

60

70

O P

A G

a i n

[ d

B ]

-5

2000 m long DSF

200 m long DSF

λ s

λ peak

37

Delay versus pump wavelength

The combined effects of SRS and parametric gain enhance the time delay

at the spectral edges while the gain is decreased.

A slight signal broadening is noticeable in two cases:

When the signal is close to the peak gain, broadening is cause by saturation

when it is located at the spectral edge, there are strong group index variations

which induce dispersion.

1428 1429 1430 1431 1432 -70

-65

-60

-55

-50

-45

-40

-35

-30

Wavelength [nm]

λ s

A S

E P

o w

e r

[ d B

m ]

(a) λp =1535 nm λp =1535.1 nm

λp =1535.15 nm λp =1535.18 nm

0 50 100 150 200

0

0.2

0.4

0.6

0.8

1

1.2

Time [ps]

(b)

No gain

G=30.4 dB, d= 11.3 ps

G=24.5 dB, d=16.2 ps G=11.2dB, d=22.2 ps G=-5 dB, d=29.1 ps

38

Fast light observations

0 50 100 150 200

0

0.2

0.4

0.6

0.8

1

Time [ps]

No

rma

lize

d In

ten

sity

No gain

G=24 dB, d= - 4.7 ps

(a)

0 50 100 150 2000

0.2

0.4

0.6

0.8

1

Time [ps]N

orm

aliz

ed

In

ten

sity

No gain

G=27 dB, d= - 11 ps

(b)

For the present system, negative delay (fast light) occurs at wavelengths

longer than the pump wavelength.

The longest available single mode laser operated at 1600 nm where the

negative delay per unit length is small. Using 2 and 3 km long DSF we have

demonstrated a pulse advancement of 4 and 11 ps respectively.

39

Parametric Processes in

fibers for optical pulse

source generation

40

A Self Starting Ultra Low Jitter

Pulse Source Using Coupled

Optoelectronic Oscillators with an

Intra Cavity Fiber Parametric

Amplifier

41

Background and motivation

Timing stability is a performance limiter

Known sources of highly stable pulse trains

Self-starting optoelectronic oscillators

Optoelectronic oscillator with an EO modulator

Interlocked microwave and mode locked diode

lasers based optoelectronic oscillators

Jitter level :

Several tens of fs at 10 GHz

repetition rate

Actively mode locked laser ( fiber or diode )

Jitter level is dictated by high quality external

drive microwave source Jitter level :

Below 10 fs at 10 GHz repetition rate

42

500 m HNLF

MZ ModulatorPolarization Controller

TL1 EDFA EDFA

AWG

TL2

50%

50%

OSA/PSA/AC

OBPF3

Polarization Controller

Polarization Controller

OBPF2

OBPF1

(0.4 nm)

p=1543.5 nm

PowerAmplifier G

IM

Bias-T

Photo-HBT

Bias-T

VB

VC

BPF

10 GHz

Directional

coupler

G

Experimental set up

OPA based pulse generating mechanism

( Hansyrd, 2001 )

s=1559 nm

43

500 m HNLF

10 km DSF

MZ ModulatorPolarization Controller

TL1 EDFA EDFA

AWG

TL2

50%

50%

OSA/PSA/AC

EDFA

OBPF3

Polarization Controller

Polarization Controller

OBPF2

OBPF1

(0.4 nm)

p=1543.5 nm

OBPF4

PM

BER

PowerAmplifier G

IM

Bias-T

Photo-HBT

Bias-T

VB

VC

BPF

10 GHz

Directional

coupler

G

Experimental set up

Additional source is needed for PM in

order to elevate SBS threshold

s=1559 nm

44

500 m HNLF

10 km DSF

MZ ModulatorPolarization Controller

TL1 EDFA EDFA

AWG

TL2

50%

50%

OSA/PSA/AC

EDFA

OBPF3

Polarization Controller

Polarization Controller

OBPF2

OBPF1

(0.4 nm)

p=1543.5 nm

OBPF4

PowerAmplifier G

IM

Bias-T

Photo-HBT

Bias-T

VB

VC

BPF

10 GHz

Directional

coupler

G

Nonlinear pump modulation reduces the

need for phase modulation

Experimental set up

s=1559 nm

45

Nonlinear pump modulation

0 2 4 6 8 10 0

0.2

0.4

0.6

0.8

1

Theory

Measurements t

t

Norm

aliz

ed tra

nsm

issio

n function

Driving voltage V

Mach-Zehnder

modulator biased

at transmission

maximum

46

Nonlinear pump modulation

0 2 4 6 8 10 0

0.2

0.4

0.6

0.8

1

Theory

Measurements

f [GHz]

10-10

fopt

20

GHz

fc

Norm

aliz

ed tra

nsm

issio

n function

Driving voltage V

Driven by 10 GHz

sinusoidal input

produces optical

pulses at 20 GHz

Pulses are

distorted by

Mach-Zehnder

imperfections

47

Initial spectrum has more spectral components

Broader spectrum reduces the need for PM

Spectral lines at 10 GHz far from the carrier cause time

domain distortion

0 50 100 150 2000

0.5

1

1.5

2

1542.5 1543 1543.5 1544 1544.5

-40

-20

0

20

Nonlinear pump modulation

Wavelength nm Time ps

Optical pow

er

dB

m

De

tecte

d p

ow

er

mW

p

Nonlinearly modulated pump Filtered pump

48

Spectral lines at 10 GHz far from the carrier cause time domain

distortion

Around 1the spectrum is of 10 GHz pulse train

Two missing lines cause the 20 GHz sub-pulses

0 50 100 150 2000

0.5

1

1.5

2

0 50 100 150 2000

0.5

1

1.5

2

1542.5 1543 1543.5 1544 1544.5

-40

-20

0

20

Nonlinear pump modulation

Wavelength nm Time ps

1542.5 1543 1543.5 1544 1544.5

-40

-20

0

20

Optical pow

er

dB

m

De

tecte

d p

ow

er

mW

p 1

Nonlinearly modulated pump Filtered pump

49

-60 -40 -20 0 20 40 600

0.2

0.4

0.6

0.8

1

-60 -40 -20 0 20 40 600

0.2

0.4

0.6

0.8

1

1510 1530 1550 1570 1590

-5

5

15

25

35

45

Pulse generation using OPA

Wavelength nm Time ps

Gain

dB

Norm

aliz

ed p

ow

er

Pp = 30.4 dBm

Pp = 23.9 dBm

Parametric gain level and bandwidth depend on pump power

acts as a discriminator eliminating the 20 GHz sub-pulses

At signal wavelength ( s ), 7.6 ps wide pulses are obtained.

> 26 dB 6.5 dB

Pump

Signal

Compressed

signal

50

-60 -40 -20 0 20 40 600

0.2

0.4

0.6

0.8

1

-60 -40 -20 0 20 40 600

0.2

0.4

0.6

0.8

1

-60 -40 -20 0 20 40 600

0.2

0.4

0.6

0.8

1

1510 1530 1550 1570 1590

-5

5

15

25

35

45

Pulse generation using OPA

Wavelength nm Time ps

Gain

dB

Norm

aliz

ed p

ow

er

Pp = 30.4 dBm

Pp = 23.9 dBm

Pulses are chirped and can be linearly compressed

Pump

Signal

Compressed

signal

51

1557 1558 1559 1560 1561

-60

-40

-20

0

1557 1558 1559 1560 1561

-60

-40

-20

0

1526 1527 1528 1529 1530

-60

-40

-20

0

0 50 100 150 2000

1

2

3

4

Pulse source spectra

Broad signal and idler spectra :

FWHM of 1.4 nm - 1.5 nm

Wavelength nm Time ps

Optical pow

er

dB

m

Dete

cte

d p

ow

er

mW

Signal

Idler

0.01 nm resolution

30 GHz detection bandwidth

52

-20 -10 0 10 20

0

0.2

0.4

0.6

0.8

1

-20 -10 0 10 20

0

0.2

0.4

0.6

0.8

1

Autocorrelation traces

Experiment

Accumulated dispersion ps/nm

FW

HM

p

s

0 5 10 15 2

4

6

8

10

12

14

Simulation

Delay ps

Inte

nsity

a.u

.

Raw

Comp.

Signal

Idler

Signal : TFWHM = 3.4 ps ( 7.6 ps ) , TBP = 0.58

Idler : TFWHM = 3.0 ps ( 7.8 ps ) , TBP = 0.57

Pump induced XPM causes significant chirping

can be compensated linearly by an anomalous dispersion

53

Comparison with results using sinusoidal pump modulation

with phase modulation @ 500 Mbps

Wavelength [nm]

1542 1543 1544 -60

-40

-20

0

[dB

m]

1526 1527 1528 -70

-50

-30

-10

10

1557 1558 1559 1560 -70

-50

-30

-10

10

[dB

m]

[d

Bm

]

100 ps

Pum

p

Sig

nal

Idle

r

Δλs=0.41 nm

TFWHM=9.5 ps

(after compression)

TBP=0.45

Δλs=0.39 nm

TFWHM=9 ps

(after compression)

TBP=0.47

Δλs=0.16 nm

TFWHM=37 ps

54

Phase noise ( timing jitter ) is substantially

reduced

500 m HNLF

10 km DSF

MZ ModulatorPolarization Controller

TL1 EDFA EDFA

AWG

TL2

50%

50%

OSA/PSA/AC

EDFA

OBPF3

Polarization Controller

Polarization Controller

OBPF2

OBPF1

(0.4 nm)

p=1543.5 nm

OBPF4

PowerAmplifier G

IM

Bias-T

Photo-HBT

Bias-T

VB

VC

BPF

10 GHz

Directional

coupler

G

Pulse spectra doesn’t undergo any noticeable

change when system becomes locked

500 m HNLF

MZ ModulatorPolarization Controller

TL1 EDFA EDFA

AWG

TL2

50%

50%

OSA/PSA/AC

OBPF3

Polarization Controller

Polarization Controller

OBPF2

OBPF1

(0.4 nm)

p=1543.5 nm

PowerAmplifier G

IM

Bias-T

Photo-HBT

Bias-T

VB

VC

BPF

10 GHz

Directional

coupler

G

Experimental set up

s=1559 nm

55

Signal jitter estimation

102

103

104

105

106

-120

-100

-80

-60

0 1 2 3 4 50

0.5

1

1.5

2

0 1 2 3 4 50

0.5

1

1.5

2

100 Hz – 15 kHz

500 Hz – 1 MHz

100 Hz – 1 MHz

Measured

Curve fitted

1st harmonics

2nd harmonics

3rd harmonics

4th harmonics

Offset frequency Hz

Phase n

ois

e dB

c/H

z

Harmonics number σ

2 ·

10

4

Estimated jitter levels

100 Hz – 15 kHz : 29.6 fs

500 Hz – 1 MHz : 28.9 fs

100 Hz – 1 Mhz : 39.8 fs

56

0 1 2 3 4 5-0.5

0

0.5

1

1.5

2

2.5

0 1 2 3 4 5-0.5

0

0.5

1

1.5

2

2.5

102

103

104

105

106

-120

-100

-80

-60

Idler jitter estimation

100 Hz – 15 kHz

500 Hz – 1 MHz

100 Hz – 1 MHz

Measured

Curve fitted

1st harmonics

2nd harmonics

3rd harmonics

4th harmonics

Offset frequency Hz

Phase n

ois

e dB

c/H

z

Harmonics number σ

2 ·

10

4

Estimated jitter levels

100 Hz – 15 kHz : 49.7 fs

500 Hz – 1 MHz : 34.3 fs

100 Hz – 1 Mhz : 58.8 fs

57

Multi wavelength pulse sources

based on saturated OPA without

spectral broadening

58

Motivations

For high bit rates and long transmission

distances RZ format is more robust than NRZ format

In RZ-WDM systems , it is necessary to develop laser pulsed sources at high bit rate for each channel

A cost effective way is to use CW sources and to create RZ pulses for all the channels simultaneously

59

Multi-wavelength pulse source :

principle of operation

HNLF

CW

CW

MZ

Pump

λp λs

Signal

λp λs λid1 λid2 λid3 λid5 λid4

A high input CW signal saturates the

OPA : high FWM orders are generated

60

2Δf 3Δf

Phase modulation induced spectral

broadening Phase modulating the pump to increase SBS threshold

leads to severe spectral broadening for FWM product

waves.

Channel quality degraded through phase to intensity

noise conversion via dispersion

λp λs

λid2

λid1 λid3

Δf Δf

61

2Δf 3Δf

Phase modulation induced spectral

broadening

The degradation is enhanced with the FWM order

λp λs

λid2

λid1 λid3

Δf Δf

62

Experimental Set up

63

OPA spectrum

1480 1500 1520 1540 1560 1580 1600 1620-70

-60

-50

-40

-30

-20

-10

0

10

20

wavelength [nm]

Optical pow

er

[dB

m]

no signal

Ps in=-17 dBm

Ps in=-7 dBm

Ps in=3 dBm

signal Idler 1

Idler 2 Idler 3 Pump

64

Channel pulse sources at 10 GHz

Δ λ= 0.98 nm 1558 1560 1562 1564

-60

-40

-20

0

Optical pow

er

[dB

m]

1538 1540 1542 1544 1546

-60

-40

-20

0

Δ λ= 0.9 nm

1567 1569 1571 1573 1575 -60

-40

-20

0

Δλ=0.9 nm

1529 1531 1533 1535

-50

-30

-10

10

Wavelength [nm]

Δλ=0.9 nm

Sig

nal

λs=

15

61.n

m

Idle

r 1

λid

1=

154

2 n

m

Idle

r2

λid

2=

157

1 n

m

Idle

r 3

λid

3=

153

1.5

nm

ΔT=6ps

Δf ΔT=0.72

ΔT=5.6ps

Δf ΔT=0.64

ΔT=5.8ps

Δf ΔT=0.63

ΔT=6ps

Δf ΔT=0.69

65

Timing Jitter estimations

0

50

100

150

100 Hz – 15 kHz

500 Hz – 1 MHz

100 Hz – 1 MHz

Tim

ing J

itte

r [f

s]

Signal Idler 1 Idler 2 Idler 3

66

Conclusion Various aspects of Raman and parametric mediated amplification

and all optical processing have been investigated.

Beside its use for Raman amplification, SRS can be used in absorption regime as inter band wavelength converter with reshaping capabilities.

Tunable all optical delay and advancement can be produced via narrow band gain spectra produced through Raman assisted optical parametric amplification

Parametric effects offer quantitative and qualitative methods for high bit rate and low jitter pulse sources.

All these all optical devices provide key tools toward the development of the next generation high bit rate optical fiber systems