Highly efficient Raman fiber laser

Collaborators:E. BélangerM. BernierB. DéryD. Faucher

Réal Vallée

OUTLINE

I: Raman scattering and gainII: Raman fiber lasers (two generations)III: Standard Model

IV: Experimental set-upV: Results & discussionVI: Conclusion

I: Raman fiber laser (RFL)

Raman scattering

( )sp s v

dIgI I I

dz

0pg I z

s sI I e

s pI gI I z Spontaneous

Stimulated

D.J. Dougherty, et al. Opt. Lett. 20, (1995) 31-33.

1/Rg

13( ) 10 /R MAXg m W

13.2R THz

4 5R THz

2SiO fiber

Raman gain spectrum

@ = 1μm

Pump

Stokes

Evolution of the Stokes and pump signals

0 16cr

R eff

eff

g P L

A : Forward SRS

2. Time-dispersion tuning:

C. Lin et al. Appl. Phys. Lett. 31 (1977) 97-99

CW

1. Angular tuning:

Raman fiber lasers: 1st generation

R. Stolen et al. Appl. Phys. Lett. 30, (1977) 340

Raman fiber lasers: 2nd generation

Key elements were developed for the 2Key elements were developed for the 2ndnd generation of RFL generation of RFL

• Fiber Bragg gratingsproviding reduced losses, spectral selectivity & tunability

• Low loss fibersstandard or with high Ge or P content

• High power Ytterbium fiber lasers providing power, reliability and spectral bandwidth

1117 1175 1240 1315 1395 1480 (nm)11751240131513951480

Yb Fiber laserOUTPUT1480 nm

1117 nm

Fiber Bragg gratingsFiber coil

Raman fiber lasers: 2nd generation

Nested cavities

Spectral coverage

E.M. Dianov et al., Quantum Electron. 35, 435-441 (2005)

Pp

Psf

Psb

PpIN

PsOUT

0 L Z

PpIN Ps

OUTR1 R2

1108nm

1165nm

Bragg gratings

Standard numerical model

bsfsp

eff

R

s

ppp

p PPPA

gP

dz

dP

fsp

eff

Rfss

fs PP

A

gP

dz

dP b

speff

Rbss

bs PP

A

gP

dz

dP

(0) INp pP P

)0()0( 1bs

fs PRP )()( 2 LPRLP f

sbs

Boundary conditions:

Standard numerical model

Propagation equations:

0123456789

10

0 10 20 30 40 50 60

OC Reflectivity (%)

Ou

tpu

t P

ow

er (

W)

RIC= 99%

Laser optimisation vs ROC

Laser optimisation vs L

RIC = 99%ROC= 26%

II: Highly efficient FRL

(15 W)(15 W)

CorningHI980 (9% Ge)

Experimental set-up

Corning HI 980 Specialty Fiber Typical Attenuation Spectra

0

2

4

6

8

10

12

950 1050 1150 1250 1350 1450 1550 1650

Wavelength (nm)

dB

/km

Pump Stokes

Parameters used in simulation OC1 configuration OC2 configuration

Fiber attenuation losses @ p 0.941 dB/km 0.941 dB/km

Fiber attenuation losses @ s 0.811 dB/km 0.811 dB/km

Splicing losses 0.03 dB 0.03 dB

IC gray losses 0.04 dB 0.04 dB

IC cladding-mode losses @ s eff eff

OC gray losses 0.01 dB 0.01 dB

OC cladding-mode losses @ s 0.00 dB 0.00 dB

IC reflectivity 99.6 % 99.6 %

OC reflectivity Reff /55 % Reff /26 %

Spectral broadening

First configuration: OC1

Laser curve with OC1

0,0

1,0

2,0

3,0

4,0

5,0

6,0

7,0

8,0

0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10,0

Absorbed Pump Power (W)

Ou

tpu

t P

ow

er (

W)

Stokes vs absorbed pump with OC1

81%

Second configuration: OC2

IC

OC2

Laser curve with OC2

0,0

1,0

2,0

3,0

4,0

5,0

6,0

7,0

8,0

0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10,0

Absorbed Pump Power (W)

Ou

tpu

t P

ow

er (

W)

93%

Stokes vs absorbed pump with OC2

Effective reflectivity

0

0,05

0,1

0,15

0,2

0,25

0,3

0 2 4 6 8 10

Stokes Power (W)

Eff

ecti

ve R

efle

ctiv

ity

Effective reflectivity (OC2)

( )eff

R S d

R

S d

Cladding-mode losses (IC)

Cladding-mode losses (IC)

0,0

0,5

1,0

1,5

2,0

2,5

3,0

0 1 2 3 4 5 6 7 8

Stokes Power (W)

Eff

ecti

ve L

oss

es (

%)

Effective losses (IC/OC2)

( )eff

S d

S d

Laser curve with OC2

Tuning of FBGs : Set-up

Tuning curve

Conclusion

RFL with efficiencies approaching quantum limit can be obtained using well designed FBGs.

The standard model (AuYeung & Yariv) can be used provided effective R and are considered.

10 W output is achievable from an optical fiber with a moderate Ge content.

Tunability over tens of nm is expected.