Fiber Lasers and their Applications

Prof. Dr Ir Patrice MÉGRETFaculté Polytechnique de Mons

Electromagnétisme et Télécommunications Boulevard Dolez 31

7000 MONS

Basic principles

A laser is an oscillator and thus needs three ingredients

• Amplifying medium (need external power)• Noise (to start)• Feedback resonator

Noise Amplifier

Feedback

+

Output

Optical Amplification

Three interaction mechanisms are always simultaneously present

from Senior, "Optical Fiber Communications", Prentice Hall, 1992

1. (stimulated) absorption2. spontaneous emission3. stimulated emission

• a) ==> optical detectors

• b) ==> LED (incoherent)

• c) ==> LD (coherent)

Population inversion is needed to build a amplifier

from Senior, "Optical Fiber Communications", Prentice Hall, 1992

• to produce the population inversion, it is necessary to excite atoms from level 1 to level 2. • This process is called pumping and is achieved using an external energy source (which can be electrical, optical, chemical, ...)

3

3

2121211

212

21221221

12112

8

c

hfBAB

g

gB

ANBNR

BNR

f

f

Three and four level systems are commonly used

from Senior, "Optical Fiber Communications", Prentice Hall, 1992

the terminal level is the ground state==> high pumping necessary

the terminal level is an intermediaire state==> moderate pumping

Light amplification in fiber is an old story

• Optical amplification in a Neodymium-doped fiber [C. Koester, E. Snitzer, 1963]

• Fiber laser at 1.3 µm [J. Stone, C. Burrus, 1974]• Erbium-doped fiber [Southampton University, 1985]• Erbium-doped fiber amplifier [Southampton University, 1986]• ...

pump pump

Laser Effect in a Single-Mode Fiber

signal signal

Introduction

The two types of optical fiber amplifier have common features

• Erbium-Doped Fiber Amplifiers 3rd telecommunication window (1.55 µm) now a mature technology

• Praseodymium-Doped Fluoride Fiber Amplifiers• 2nd telecommunication window (1.31 µm) rely on fluoride fiber progresses but commercial devices

available

• Main features of optical fiber amplifiers High optical intensities achievable in singlemode fibers Geometrical compatibility with fiber links High gain, large bandwidth, high output power Quantum limit noise, high linearity, absence of crosstalk Transparency to bit rate and data format

Er+3 or Pr3+ ions absorb and emit light in different bands

Cross sections of transitions of Er3+ around 1.5 µm

0.0E+00

1.0E-25

2.0E-25

3.0E-25

4.0E-25

5.0E-25

6.0E-25

7.0E-25

8.0E-25

9.0E-25

1.40 1.45 1.50 1.55 1.60 1.65Wavelength (µm)

Cro

ss s

ectio

ns (

m²) Absorption

Emission

Rare-earth dopants Absorption Fluorescence

Er3+ (silica) 810, 980, 1530 nm 1530 nm Pr3+ (ZBLAN) 1015, 1500 nm 1325 nm

Light is amplified through stimulated emissions

hphs

hs

hs

h

PumpingStimulated absorption of

pump photons

(Ground State Absorption)

AmplificationStimulated emission of signal photons that are coherent (E,,k) with

incident photons

hh

NoiseSpontaneous emission of

photons which are not coherent but can be amplified

by stimulated emission

(Amplification of Spontanteous Emission)

Erbium-doped fiber amplifier is a 3-level laser system

p = 980 nm

s

p = 1480 nm

(a) (b) (c) (d)

Excited state

Metastable state

Fundamental state

1500 1510 1520 1530 1540 1550 1560 1570 1580 1590-45

-40

-35

-30

-25

-20

-15

-10

-5

0

Wavelength (nm)

Pow

er (d

Bm

)

• Rapid non-radiative desexcitation from 3 to 2 : N3=0 (two-level laser system)

• Rather long lifetime of ions in the metastable level : 21 =10 ms

p= 980 (1480) nm

s= 1530 nm

An optical fiber amplifier is a rather compact device

Pump Source

• Pump and signal are injected into rare-earth doped fiber using WDM couplers

• Forward, backward or bidirectional pumping schemes

• Single-pass or double-pass (with a mirror) amplification schemes

Doped fiberPin WDM WDM

Pump Source

Pout

Isolator

Erbium doped fiber

Pin

Pump laser diodeat 980 nm or 1480 nm

WDM

Mirror forsignal and/or pump

Pout

EDFA: double pass configuration

Feedback = resonator

Optical waves interfere when they are present simultaneously in the same

region of space

Case of two monochromatic waves of the same frequency i

)()()()()()()()()()( 2*1

*21

2

2

2

1

2

21

2rrrrrrrrrr UUUUUUUUUI

U I ei ij i Complex amplitudes :

I I I I I 1 2 1 22 cos( )

Depending on : constructive or destructive interference

I I I

2 1 420 0

2cos( ) cos In the case of I1 = I2 = I0 : • I = 4 I0 when = 0

• I = 0 when =

Interferometers can measure small variations of distance, refractive index,

wavelength

I I I nd

2 1 2 1 20 0

0

cos( ) cos

U I e jkz1 0

U I e jk z d2 0 ( )

Mach-Zehnder Michelson Sagnac

In an optical resonator, light is confined and stored at certain

resonance frequencies

filter spectrum analyser generation of pulsed or CW laser light (with active medium inside the

cavity)

• Light circulates or is repeatedly reflected within the cavity

• Wavelength selectivity is due to optical feedback

Fabry-Perot cavity

Mirror

Optical fibre ring cavity

Fiber

Coupler

Isolator

Fabry-Perot cavity is the simplest planar resonator

• Resonator modes as standing waves • Resonator modes as travelling waves

r r+1r-1d

r=100 %

m=

no loss

mode = sol. of Hemholtz eq. satisfying boundary cond.

mode = wave that reproduces itself after a single round trip

U z A k zr r( ) sin( )

2 2 0

0 0 0

U z k U z

U z U z d

( ) ( ) ,

( ) , ( )

k md

mr

, ,2,...1

r mc

dm

21, ,2, ...

F

c

d

2

k d m m2 2 1, ,2,...

condition of positive feedback

F is the mode spacing

Losses in a real cavity are not zero

Let r² be the intensity attenuation factor introduced by the two mirror reflections and by the absorption in the medium during a round trip (phase shift )

jrehh

UUhhUUU

,

1... 0

02

00

I UU

re

I

r r

Ij F

2 0

2

20

2 22

2 2 221 1 4 1

( ) sin ( ) ( ) sin ( )

max

II

rmax ( )

0

21F

r

r

1

Finesse of the resonator

II

FF

max

( ) sin ( )1 2 2 2

k d

d

c2

4

Large value of F means sharp resonance peaks

0

10

20

30

40

50

60

70

80

90

100

-3 -2 -1 0 1 2 3

Phase shift (multiple of pi)

I/I0

(a.u

.)

R=0.9 F=29.8

FWHMF

FF

( )1

0

10

20

30

40

50

60

70

80

90

100

-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5

Frequency shift (GHz)

I/I0

(a.u

.)

R=0.9 F=29.8

Fabry-Perot with an active medium has a threshold for

amplification

M1 M2E+(z)

E-(z)r'1

r'2

E z E j z kn j g

E r E E L r E L

r r j knL g L

r r g L knL q

( ) ( ) exp

( ) ( ) ( ) ( )

exp exp

exp

01

2

0 0

2 1

1 2 2

1 2

1 2

1 2 1 2

gL r r

f qc

nL

th 1

2

1

2

1 2

lnr r ji i iexp( )

Continuous Wave Fiber Lasers

A lot of structures have been used

Noise Amplifier

Feedback

+Output

pump

Optical fiber FP cavity

Output 1Output 2

Active Fiber

pumpIsolator

Optical fiber ring cavity

Fiber

outputActive Fiber

Polarization controler

pump

output

Figure 8 cavity fiber laser

ActiveFiber

50:50

Fiber laser with two FBG, 5 m of doped fiber and a total length of 13 m

(realized by students)

MULTIPLEXEUR

RESEAU DE BRAGG (R= 20%)

RESEAU DE BRAGG (R= 99%) ISOLATEUR

Bras à 980 nm Bras à 1550/980 nm Bras à 1550 nm Fibre dopée à l’erbium

ISOLATEUR

POMPE

SOUDURE

Polarization beam splitter and Faraday rotator are some key elements

B

Faradayrotator

MirrorInputlight

Outputlight

/4

Polarizing beamsplitter (PBS): two prisms from the same anisotropic (uniaxial) material cemented with orthogonal optic axes

[Saleh, Fundamentals of Photonics]

Different refraction angles at the interface for both polarization components

Spatially separates orthogonal polarization states

Inputlight

Faraday rotation mirror (FRM): a 45° Faraday rotator followed by a conventional mirror

After reflection and double-pass through the rotator, light is returned at the input port (the only port of the FRM) with a 90° polarization rotation

Optical isolator is based on Faraday rotator and can be polarization

independent

[Saleh, Fundamentals of photonics]

Single-polarization isolator

/2

/2

Single-polarizationisolator

PBS

PBS

Polarization-independent isolator

Pumping is realized at 980 nm and creates amplification at 1550 nm

0

50

100

150

200

0 50 100 150 200 250 300

Intensité du courant [mA]

Pu

iss

an

ce

de

so

rtie

[m

W]

Two Bragg gratings are used for feedback (same wavelengths but

different reflectivities)

1st grating 2nd grating

R=99%

R=20%

-1,6

-1,4

-1,2

-1

-0,8

-0,6

-0,4

-0,2

0

1540 1545 1550 1555 1560

longueur d'onde [nm]

pu

iss

an

ce

de

so

rtie

[d

B]

Tuneability is achievable by:• Temperature tuning of FBG• Strain tuning of FBG

Optical spectra at the two outputs

-60.000

-50.000

-40.000

-30.000

-20.000

-10.000

0

10.000

20.000

1.480.000 1.500.000 1.520.000 1.540.000 1.560.000 1.580.000 1.600.000 1.620.000

l ongueur d'onde [nm]

caractéristique du laser (co-propagatif )

-60.000

-50.000

-40.000

-30.000

-20.000

-10.000

0

1.480.000 1.500.000 1.520.000 1.540.000 1.560.000 1.580.000 1.600.000 1.620.000

longueur d'onde [nm]pu

issa

nce

de s

ortie

[dB]

caractéristique du laser (contra-propagatif)

Efficiency is of the order of 23.5%

0

5

10

15

20

25

30

35

40

0 50 100 150 200 250

intensité de courant [mA]

pu

iss

an

ce

de

so

rtie

[m

W]

Pulsed Fiber Lasers

How to get pulses from a laser?

External modulation : CW laser + external switch or modulator energy is blocked during the off-time of the pulse train peak pulse power < CW power

Internal modulation : turning the laser itself on and off energy is stored during the off-time of the pulse train peak pulse power >> CW power different methods :

• gain switching : gain control by turning the laser pump on and off• Q-switching : periodic loss increase (absorber inside the resonator) • cavity dumping : loss modulated by altering mirror transmittance• mode locking : coupling laser modes and locking their phases

In a free-running laser, modes normally oscillate independently

Free-running modes

r r+1r-1

F

a comb of equally spaced modes (F) of random phases => train of identical bursts of incoherent light, spaced by rep= F = 1/ F

t

rep= 1/ F

Coupling modes and locking their phases force them to oscillate together

Locked modes

r r+1r-1

F

a comb of equally spaced modes (F) in phase => train of very intense and short bursts of light, spaced by rep= F = 1/ F

rep= 1/ F

t

p=1rep : repetition rate

Peak sharpness increases with the number of locked modes

• period of pulse train = round trip time = F (repetition rate = mode spacing = F)

• pulse width = p=1 (for Er3+:silica = 4 THz => p = 250 fs)

• peak intensity (M²|A|²) is M times higher than average intensity (M|A|²)

0

50

100

150

200

250

300

350

400

-150.0E-9 -100.0E-9 -50.0E-9 000.0E+0 50.0E-9 100.0E-9 150.0E-9

t (s)

I(z=

0)/|A

|²

M = 10

M = 20

F= 100 ns

How the modes can be locked together ?

• Passive mode locking : use of a saturable absorber

• Active mode locking : use of an AM or FM modulator (e.g. electro-optic mod.) with modulation frequency equal to (or a multiple of) the mode spacing F

Frequency domain

r r+1r-1

fmod= F

phase information of a mode is passed to its neighbours through the modulation

sidebands

Time domain

F

t

cavity loss

laser output

pulse builds up after each round trip because cavity loss is minimum at each passage of the pulse

Pin

Pout

t

t

Harmonic mode locking allows to get high repetition rates with reasonable

fibre length

• For high repetition rates, the fibre length that is required is too short in practice

if fmod= F then F = c0/(nL) = 1 GHz => L = 20 cm

• Harmonic mode locking can be used for high repetition rates

if fmod= N F and N = 100 then F = c0/(nL) = 1 GHz => L = 20 m

• N pulses per round trip rep= (1/N)F

• N supermodes are susceptible to oscillate together => beating between supermodes=> amplitude fluctuations in the pulse train

r r+1r-1

F- N F + N F

Electro-optic effects are useful to realize some devices

Electro-optic effect = small change in refractive index n induced by a DC or low frequency electrical field E applied to the material

• n(E) proportional to E = (linear) Pockels effect

• n(E) proportional to E² = (nonlinear) Kerr effect

Electrically controllable optical devices useful in optical communication and optical signal-processing

• lens with controllable focal length

• phase modulator, dynamic wave retarder

• intensity modulator, switch

A phase modulator in a Mach-Zehnder interferometer ...

LiNbO3 waveguide

V

0

IiApplied electric field

I0

I I I Ii i i021

2

1

2 2

cos( ) cos

1 2 10 2 0

V

V

V

V

... can act as a linear intensity modulator or as an optical switch

0.0

0.5

1.0

-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0

V (volts)

phi0 = pi/2, Vpi = 2 V

Linear intensity modulator (0=/2) Switch (0=2)

0.0

0.5

1.0

-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0

V (volts)

phi0 = 2*pi, Vpi = 2 V

T VI

I

V

Vi

( ) cos

0 2 0

2 2

RF-driven Mach Zehnder electro-optic intensity modulator is the key element

for pulsed fiber lasers

V

t

0

1 rf driving voltage

T

V

t

Intensity modulation

0

To cancel PM modulation:= and opposite voltages applied to the arms

DC bias

RF input

IN

OutputY-coupler

+V

-V

OUT(AM only) Dual-output MZM

:OUT 1

OutputX-coupler

OUT 2

IN

DC bias

RF input

(AM + PM)

50/50

50/50

Principle: linear electro-optic effect (Pockels effect):

n V

Er-doped fiber lasers as an alternative to semiconductor lasers for pulse train

generationStructure of an actively mode-locked erbium-doped fiber ring laser (AML-EDFL):

Optical filter

Erbium-doped fiber

rf amplifier

rf generator

Optical isolator

Pumplaser diode

Output

coupler

WDM coupler

Amplitude

modulator

DC

F.P.Msfondée en 1837

ELECTROMAGNETISMETELECOMMUNICATIONS

F.P.Msfondée en 1837

ELECTROMAGNETISMETELECOMMUNICATIONS

Optical pulse train

Intracavity pulse shaping

(e.g., solitons)External reference availableFlexibility

Advantages:

Drawback:

Very sensitive to perturbations,several noises affect the pulse train

Sigma cavity includes both a PM ring and a non-PM branch

Unidirectional, PM ring: Modulator Isolator Filter...

Double-pass, non-PM branch:

Er-doped fiber DCF / DSF Fiber under strain Filter...

PM sectionNon-PM section

1 3

2

PM-FBG

OC

DC

RF

Opticalfilter

Opticalfilter

Er-dopedfiber

Opticalisolator

Pump LD

OutputCoupler

WDMCoupler

AMModulator

PiezodrumFaraday

mirror

Polarizingbeamsplitter

Stabilization scheme

90°splice

8.4 m DCF/200 m DSF

OUT 2

The sigma laser: a virtually polarization-maintaining cavity

FRMOpticalisolator

PBS

/2splice

PBS transmits

reflects

L = LR + 2LB

PM fiber (e.g.: PANDA) : linear polarization along one of the polarization axes is maintained

Standard fiber : Intrinsic + stress-induced refractive index anisotropiesPolarization changes randomly during propagationHowever: Thanks to the 90° polarization rotation at the FRM, both orthogonal polarization

components experience the same delay after one round-trip in the non-PM branchHence, initially linear polarization is returned linear to the PBS, rotated by 90°

How to pass round the biggest drawback of fiber lasers

f

Length of Er-doped fiber ring lasers ~ 10 - 100 m=> FSR ~ 1 - 10 MHz << GHz repetition rates

Solution: Modulation frequency fm (= repetition rate) = NFSR with N >>

=> Modes no longer locked to their closest but to their Nth closest neighbors (N ~ 103-104)

= Harmonic Mode Locking (HML)

rtm T

NFSRNf

Rational harmonic mode locking for repetition rate multiplication

2fm

0 0.2 0.4 0.6 0.8 1Time (ns)

(a)

0 0.2 0.4 0.6 0.8 1Time (ns)

(b)

RHML3 or + :Pulse-to-pulse fluctuations

fm = (N+R/P)FSR=> fp = Pfm = (NP+R)FSR

RHML2 (P = 2) : fm = (N+1/2)FSREqual pulses [RK et al., OL 25, p. 1439, 2000]

The pulse train repetition rate fp can be multiplied P times modulation frequency fm if fm is detuned from optimal HML frequency by a fraction of the FSR :

(a)

0 0.2 0.4 0.6 0.8 1Time (ns)

(a)

0 0.2 0.4 0.6 0.8 1Time (ns)

(b)

Bias doubling is another technique to double the repetition rate

t

t

T

0 V

1

V

rf driving voltage

Intensity modulation

1/fm

1/2fm

0

(b)

t

t

T

0

V

1

V rf driving voltage

Intensity modulation

1/fm

1/2fm

(a)

t

t

T

0

1

V

rf driving voltage

Intensity modulation

1/fm

1/2fm

0

(b)

V T

t

t

T

0

V

1

V rf driving voltage

Intensity modulation

1/fm

(a)

V

t1 t

2

Cavity length is stabilized by minimizing average interpulse noise

L

P

(a)

(a)

(c)

(c)

(b)

(b)

0.1 s

0.1 s t

t

Glue

Glue

Average interpulse noise is measured at output 2 of the dual-output Mach-Zehnder modulator

V V/2 -V/2 t

t

0

T

0

1

0.5

RF

driving voltage

Intensity modulation

OUT 1

OUT 2

This noise is minimal for optimal cavity length tuning (L = 0)

Fiber has some elasticity => can be adjusted thanks to a piezoelectric crystal

Implementation of the feedback loop

Faradaymirror

Opticalfilter

Erbium-dopedfiber

Opticalisolator

Pump LD

Outputcoupler

WDMcoupler

AMmodulator

Piezodrum

Polarizingbeamsplitter

DC

RF

90°splice

PR

10-Hz

ditheringHVA

1 2

Detuning is detected through the measurement of average interpulse noise

A 10-Hz dithering is applied to the piezo in order to determine the sign of the correction

The stabilization scheme operates also in RHML2 regime [Kiyan et al., OL 24, p. 1029, 1999]

Stabilization feedback loop is needed

Opticalfilter

Erbium-dopedfiber

Opticalisolator

Pump LD

Outputcoupler

WDMcoupler

AMmodulator

PiezodrumFaraday

mirror

Polarizingbeamsplitter

DC

RF

90°splice

PR

10-Hz dithering

HVA

1 2

L

P

(a)

(a)

(c)

(c)

(b)

(b)

0.1 s

0.1 s t

t

Pulse train measurement and characterization is

complicated

90:10 coupler50:50 coupler

Photodiode

OSASamplingoscilloscope

ESA

VSA

EDFAAuto

correlator

Electronics

Polarization

controller

Computer

Powersplitter

Sampling scope traces(fm = 3 GHz)

(a)

0 0.2 0.4 0.6 0.8 1

0 0.2 0.4 0.6 0.8 1

Time (ns)

HML

RHML2

Several typical noise contributions are identified in the radio-frequency

spectrum

fm 5fm Frequency

Pow

er

2.95 3 3.05-100

-80

-60

-40

-20

Frequency (GHz)

Pow

er (

dBm

) Supermode

noiseAmplitude jitter

(Phase jitter)

-30 -20 -10 0 10 20 30

-100

-80

-60

-40

-20

Frequency offset (kHz)

Pow

er (

dBm

)

Relaxation

oscillations

Amplitude jitter

101 102 103 104-110

-100

-90

-80

-70

-60

Frequency offset (Hz)

Pow

er (

dBm

)

Low-frequency noise

Amplitude jitter

Phase jitter

Pulse width jitter

Optical spectrum and autocorrelation trace

Optical spectra of 3-GHz and 6-GHz

pulse trains

fm = 3 GHz

Resolution = 0.02 nm

Background-free optical

autocorrelation

1540 1540.5 1541 1541.5 1542 1542.5-70

-65

-60

-55

-50

-45

Wavelength (nm)

Pow

er (

dBm

)

1540 1540.5 1541 1541.5 1542 1542.5-70

-65

-60

-55

-50

-45

Pow

er (

dBm

)

Wavelength (nm)

HML RHML

(FWHM)

-10 -5 0 5 100

0.2

0.4

0.6

0.8

1

Delay (ps)

Rel

ativ

e in

tens

ity

qAC

(FWHM)

0 2 4 6 8 1010

-5

10-4

10-3

10-2

10-1

100

Delay (ps)

Rel

ativ

e in

tens

ity

qAC/2

gaussian

solitonic

qAC q

0.648

2/2

Transform-limited (chirp-free)

q 0.3150.441

Exotic configurations

Pulsed fiber lasers with Brillouin mirrors

Q-switched fiber lasers

Such fiber lasers could be realized from the use of rare-earth-doped fibers in combination with non-fiber elements (AOM, EOM…) [J.A. Alvarez-Chavez et al. “High-energy, high-power ytterbium-doped Q-switched fiber laser”, Opt.Lett. 25, 37-39(2000)].

Diode pump~976 nm AOM

Yb-Doped fiber

Pulses 0.1 – 1 µs

Q-switched fiber lasers:passive & all-fiber solutions

• Self-pulsing in Er-laser (due to quenching):• 0.1-ms-pulses with ms-period [P. Le Boudec et al., Opt.Lett. 18, 1890 (1993)]

• Q-switching in Yb-laser due to a saturable absorber (Sm-doped fiber):• 0.5-µs pulses with ~20 µs period [A. A. Fotiadi et al., CLEO-Europe (2005)]

• Q-switching with Brillouin mirror: the most effective!!!

• 1-ns-pulses with 200-µs-period [S.Chernikov et al., Opt.Lett.22, 298, 1997]; Ns-pulse generation

Peak/average power contrast >105

Universal method

Pulse-to-pulse stability is rather poor

Stimulated Brillouin scattering is a good candidate for Q-switching

• SBS is low threshold process: ~10 Wm• Switching time ~ hypersound delay time: ~10 ns

• High switching contrast (up to ~ exp(~20) ~ 85 dB)

~ exponential intensity grows with power

0exp L

S S

PP P g L

S

0 0,P

1 1,P

0k

1k

0q

0 1 0

0 1 SBS

k k q

Rayleigh scattering supports SBS

0

1

600RS outP P P ,RS RSP

0 0,P

0 0RS f

RS mirror causes strong narrowing of the laser line

Optical fiber

RS mirror

GAIN

mirror

Fiber laser

Traditional single-longitude-modesolid-state laser

mirror

GAIN

Set of parallelquartz plates

0 1%RS R RP L P R

- fast varying function

Self-Q-switched fiber laser (simplest configuration)

• Principle of operation is Rayleigh-SBS mechanism

• Has been used for Raman Q-switched laser

Rare-earth-dopedfiber amplifier

Single-modeoptical fiber

Cavitymirror

Laser cavity

Cavitymirror

Output

Self-Q-switched fiber laser(configuration with a ring mirror)

Rare-earth-dopedfiber amplifier

Single-modeoptical fiber

Fiber ringresonator

Cavitymirror

Laser cavity Fiber coupler

Cavitymirror

Output

Rare-earth-dopedfiber amplifier

Single-modeoptical fiber

Fiber ringresonator

Cavitymirror

Laser cavity Fiber coupler

Cavitymirror

Output

• Principle of operation is Rayleigh-SBS mechanism

• For resonance ring frequencies it is equivalent to previous

Self-Q-switched fiber laser

2 ms/div.

All-fiber integrated format Standard telecom components Low-pump power (~120mW) Peak/average power contrast:

500W/25 mW (up to ~105) Poor pulse-to-pulse stability

Diode WDM

12.7-GHzFBG

~5m~10.5m ~5m

~2.25m

EDFA SMF

Coupler10/90

Opticalisolator

Output 2Output 1

~980nm160 mW

Diode WDM

12.7-GHzFBG

~5m~10.5m ~5m

~2.25m

EDFA SMF

Coupler10/90

Opticalisolator

Output 2Output 1

~980nm160 mW

~80% ~20%

1480nm~120 mW

5/95

~1.25m~1m~5 m

~1m

Pulse shape and spectrum

Pulse Peak/average power

~500W/25mW

Pulse duration ~10ns

Spectrum Linewidth ~0.25nm 3 Brillouin components (~11GHz)

1555.75 1556.00 1556.25 1556.501555.75 1556.00 1556.25 1556.50 P

ower

, a.u

.

Wavelength, nm

FBG

10 ns/div.10 ns/div.

Peak: ~500W

band

Synchronization of SBS components

Diode WDM

12.7-GHzFBG

~5m~10.5m ~5m

~2.25m

EDFA SMF

Coupler10/90

Opticalisolator

Output 2Output 1

~980nm160 mW

Diode WDM

12.7-GHzFBG

~5m~10.5m ~5m

~2.25m

EDFA SMF

Coupler10/90

Opticalisolator

Output 2Output 1

~980nm160 mW

~80%34-GHz

FBG~20%

Time 200 ns/div.

Output 2

A

C

Output 2

1533.6 nm -16.5GHz/div.

~10 GHz

Pulses and spectra (FBG width 12.5 GHz)

Output 2

Output 1

40 ns/div.

Output 2

Output 1

1

2

31

2

3

FBG1 2 3, , ,FBG are equidistant 11SBS GHz

~300 W~15ns

Experiment and simulations(FBG width 12.5 GHz)

-160

-80

0

80

160

0

80

160

240

Time, ns

40 ns/div.

2

1 3

Output 1

Output 2

Power, W

Simulations Experiment

40 dB/div.

Output 2

Output 1

1

2

3

40 ns/div.

~300 W

[A.A.Fotiadi, P.Mégret, M.Blondel, Opt.Lett., Vol.29, N10, 2004, pp. 1078-1080.]

All-Fiber Ytterbium Laser Employing Samarium Fiber as

Saturable Absorber

In collaboration with

USTL, Lille, France

and FORC, Moscow, Russia

(EU patent is applied for, CLEO-EUROPE; submitted to CLEO’2006, USA)

Absorption spectrum of Sm-doped fiber

1000 1100 1200 13000

20

40

60

80

100

Abs

orpt

ion,

dB

/m

Wavelength, nm

Isolator Pump/signal filter

Saturable absorber (1020-1100

nm) ~1064 nm ~1085 nm

Suitable for many other wavelengths

976nm 1064nm

1085nm

Yb

Yb, absorptionYb, emission

Principle configuration

All fiber spliced configuration! Pump up to ~20W at ~976nm FBG: at 1085nm and 1064nm The use of a Sm-doped fiber as an optical isolator 1-3 m as a saturable absorber 10 cm

Diodepump

at ~976nm

Sm-doped fiber

Sm-doped fiber

HRFBG

Yb-doped double-clad fiber

optical filter saturable absorber

Outputat

~1085 nm(~1064 nm)

LRFBG

Yb-doped fiber Inner clad:

125x125 µ2

Core Ø: ~6 µ Sm-doped fiber

Clad Ø: ~125 µ Core Ø: ~6 µ

Pulse train

Similar behavior is observed at 1040-1100nm

Pow

er, a

.u.

Time, 10 µs/div

Pow

er, a

.u.

Time, 10 µs/div

All-fiber pulsed laser source Passive pulse operation High stability Performance characteristics

Wavelength: 1085 nm Pump: ~7 W Average power: ~2.5 W Peak power: ~30 W Pulse duration: ~600 ns Period: ~8 µs

Thank you for your kind attention

Olivier Deparis*, Roman Kiyan*, Andréi Fotiadi, Olivier Pottiez*, Gautier Ravet, Marc Wuilpart,

Christophe Caucheteur, Sébastien Bette, Véronique Moeyeart