Supercontinuum generation in optical fibers · 2012. 6. 2. · Silica Glass Optical Fibers, dispersion tuning Silica cladding n ~ 1.45 more complex profiles to tune dispersion “high”

INAOE, 27/04/2011 1

Supercontinuum generation in optical

fibers

E.A.Kuzin

INAOE, Puebla, Mexico

INAOE, 27/04/2011 2

Outline

• Short historical background on

supercontinuum.

• Introduction to nonlinear effects involving in

the process of supercontinuum generation.

• Some latest results on supercontinuum and its

applications.

• Some results of the investigations in INAOE

• Conclusions

INAOE, 27/04/2011 3

What is supercontinuum?

Supercontinuum generation is a process where

laser light is converted to light with a very broad spectral

bandwidth, whereas the spatial coherence remains high.

Lasers:– Narrow range of frequencies– Very bright• Natural light:– Wide frequency range– Not very bright• Supercontinuum light:– Very bright– White

INAOE, 27/04/2011 4

First observation.

R.R.Alfano and S.L.Shapiro, 1970

filaments

The spectrum

400 nm to 800 nm.

1-GW, 532 nm, 5 ps pulse

Frequency doubled

Nd:Glass mode-locked

laser

Several filaments were formed in the sample and broad band light was detected

at the sample output. Four wave mixing and self phase modulation were supposed

to be responsible for the effect.

Glass

INAOE, 27/04/2011 5

Optical fiber vs bulk materials

L

S

Nonlinear effects ~L*P/S

D

Fiber is very effective

nonlinear material !!!

/SL

Several mm2 in fibers

INAOE, 27/04/2011 6

First experiment with fibers

(1976)

In 1976 Lin and Stolen reported a new nanosecond source that produced

continua with a bandwidth of 110-180 nm centered on 530 nm at output

powers of around a kW [Appl. Phys. Lett., v.28, pp. 216 -218 (1976).

The system used a 10-20 kW dye laser producing 10 ns pulses with 15-20 nm

of bandwidth to pump a 19.5 m long, 7 μm core diameter silica fiber.

INAOE, 27/04/2011 7

Super continuum in fibers is effective at anomalous

dispersion.

Telcom fibers >1300 nm

M.N.Islam, G.Sucha, I.Bar-Joseph, M.Wegener, J.P.Gordon, D.S.Chemla, 1989

NaCl color

center laser

λ = 1.5 µm

Pulse width 14 ps

INAOE, 27/04/2011 8

J. K. Ranka, R. S. Windeler, A. J. Stentz, Optics Letters (2000).

The 75-cm section of microstructure fiber with the 1.7 µm diameter of

nuclear. The dashed curve shows the spectrum of the initial 8-kW 100-fs

pulse from Ti-sapphire laser.

First SC experiment in Photonic Crystal Fibers

INAOE, 27/04/2011 9

T. A. Birks, W. J. Wadsworth, and P. St. J. Russell, Optical Letters (2000).

SC in tapered fibers

9 cm

2-µm waist

Ti:sapphire, 100-fs laser

380 W

210 W60 W

INAOE, 27/04/2011 10

Theoretical background

INAOE, 27/04/2011 11

Spectrum of pulses

DfDt

Dt Dt

t

Af

DD

A=0.46 for Gaussian pulse

A=0.32 for secant hyperbolic

if the pulse and spectrum width are measured

as the Full Width at Half Maxima (FWHM).

pulse spectrum

At Dt=1 ps D=4 nm

(1550 nm)

Propagation of pulsos, phase velocity, group

velocity

)( 00,,zti

etzAtzE

tzA ,

f0; se mueve con

velocidad de fase

Se mueve con

velocidad de grupo

n

c

phv

d

ndn

c

d

d

d

dvg

1

12INAOE, 27/04/2011

nc

2

INAOE, 27/04/2011 13

Dispersion relation,

group velocity dispersion

....)(2

1)()()( 2

02

2

00

grv

11

....)(2

)()( 2

02

010

d

vd gr/1

2

2

2

grph vv

0

;0 ;0

grv

0

;0 ;0

grv

0

An interval of frequencies

in our process

red)n faster tha islight (blue

dispersion anomalous 0;

blue)n faster tha islight (red

dispersion normal 0;

2

2

INAOE, 27/04/2011 14

Another definition of group velocity

dispersion

LDtt 2121

t=0

t2

t1

22

2

cD

2

1

fiber

Anomalous dispersions; D>0 (2<0)

INAOE, 27/04/2011 15

Super continuum in fibers is effective at

anomalous dispersion.

Telcom fibers >1300 nm


NaCl color

center laser

λ = 1.5 µm

Pulse width 14 ps

INAOE, 27/04/2011 16

Nonlinear index refraction

Wmn

A

Pnnn

eff

/103~

~

220

2

20

At high power of light the refraction

index is changed

eff

NL

eff

A

Pn

c

A

Pnn

cn

c

2

20

~

~

D

At high power of light the wave

number is changed; phase and group

velocities are changed.

Equations for pulse propagation

Ait

tzAi

t

tzA

z

tzANL D

...

),(

2

),(),(2

2

21

;' 1ztt

A – amplitude of

field

fiberinput

't't

output

Retarded time frame

AAnc

iAit

tzAi

z

tzANL

2

22

2

2~),(

2

),( D

17INAOE, 27/04/2011

0 0

Effects of nonlinearity (n2) and

group velocity dispersion (2)

INAOE, 27/04/2011 18

INAOE, 27/04/2011 19

Nonlinear chirp in the pulse at 2=0

Self Phase Modulation, SPM

dt

tdP

An

cdt

td

eAeAeAtzE

eff

tiztizti

)(1~)(

,

20

)(

000000

D

Z

leading edge, dP/dt>0

ω< ω0

tailing edge, dP/dt<0

ω> ω0

Broadening of the spectrum because of chirp

1 ps pulse; 20 m fiber; D=0

INAOE, 27/04/2011

20

50 W100 W500 W

D, nm

1 ps

Low power pulse propagation in fiber;

1-W power pulse; D = 18 ps/nm-km

INAOE, 27/04/2011 21

0 meters5 meters10 meters20 meters50 meters100 meters

Time, ps

A 100 W power pulse propagation in fiber with

anomalous dispersion; D=18 ps/nm-km

INAOE, 27/04/2011 22

0 meters5 meters10 meters20 meters50 meters100 meters

Time, ps

INAOE, 27/04/2011 23

Soliton

00 //0

2)/(sec)(

TtTtee

TthtE

102

2

2

00

ñT

A

P

eff

The condition for the

pulse to be soliton

1-ps FWHM soliton

P = 44 W at D = 18 ps/nm-km

The shape of soliton is not changed in propagation,

dispersion must be anomalous

Propagation of a 20-W 50-ps pulse through

the fiber with anomalous dispersion

INAOE, 27/04/2011 24

input50-m length150-m length200-m length

Time, ps

200-m length input

output

Modulation instability (MI) at anomalous dispersion

causes the amplification of fluctuation and pulse

breakupgLeionamplificat

2/1

2

0max

2

P

0max 2 Pg

25INAOE, 27/04/2011

Propagation of a 20-W, 50-ps pulse through

the 200-m fiber with normal dispersion

INAOE, 27/04/2011 26

Pulse Spectrum

Behavior of the pulse in the fiber is affected

drastically by the sign of the dispersion.

D>0: normal dispersion

D<0: anomalous dispersion

Small anomalous dispersion is favorable for

supercontinuum !!!

INAOE, 27/04/2011 27

protective

polymer

sheath

Silica Glass Optical Fibers, dispersion tuning

Silica cladding

n ~ 1.45

more complex profiles

to tune dispersion

“high” index

doped-silica core

n ~ 1.46

“LP01”

confined mode

field diameter ~ 8µmPossibilities of dispersion tuning

are restricted by properties of

glasses

28INAOE, 27/04/2011

Calculated dispersion for small core fiber

INAOE, 27/04/2011 29

From J. K. Ranka, R. S. Windeler, A. J. Stentz, 2000

2 m core

diameter; Dn=0.3

1 m core

diameter; Dn=0.1

D>0, anomalous dispersion

Photonic Crystal Fiber (PCF)

Microstructured Fiber (MSF)

Microstructured Fiber (MSF)

Class 1

Glass

Holes

Large mode area

(LMA)

High Nonlinear

(HNL)

High Numerical Aperture

(HNA)

30INAOE, 27/04/2011

Some examples of PCF from

Universidad de Valencia

25 m5 m

35 m

31INAOE, 27/04/2011

INAOE, 27/04/2011 32

First Supercontinuum Experiment in

Photonic crystal fibers

From J. K. Ranka, R. S. Windeler, A. J. Stentz, 2000

Squares – measured PCF

Circles – standard fiber

Ti:supphiere 1.6 kW, 100 fs

pulses were used for pump

Dispersion for tapered fiber and

supercontinuum generation

INAOE, 27/04/2011 33

1 m1.5 m2.5 m

Standard fiber60 W210 W

380 W

Ti:supphiere 100 fs pulses were

used for pump

T. A. Birks, W. J. Wadsworth, and P. St. J. Russell, OL , 415 (2000)

Stimulated Raman scattering

Pump

Stokes

Depleted

pump

Amplified

Stokes

S>P

zA

Pg

SSeff

P

ePzP )0()(

g – Raman gain coefficient

34INAOE, 27/04/2011

New spectral lines shifted by appr. 12 THz

to “red” may appear as a result of SRS

INAOE, 27/04/2011 35

Raman self-frequency shift

PPPPP AAi

T

Ai

z

A 2

2

2

2

2

Equation for pulse propagation

P

P

RPPPPP A

T

ATAAi

T

Ai

z

A

2

2

2

2

2

2

Raman term

TR = 3 fs input2-m 4-m6-m8-m

LT 4

0

1D

This part

as pump

Spectrum of

the 100 fs

pulse

This part

as Stokes

INAOE, 27/04/2011 36

Modulation instability starts pulse break and soliton

formation. Solitons are shifted to the red by soliton

self frequency shift.

AT

ATAi

T

Ai

z

AR

2

2

2

2

2

2

Basic equation for

supercontinuum

Time, ps Wavelength shift, nm

The 20-W, 50-ps pulse after 1-km of fiber

INAOE, 27/04/2011 37

Four wave mixing

cnnnnk

kkkkk

/

0)(

22114433

2143

2143

D

D

ω

ω

4

ω

3

ω

1

ω

2

The phase matching conditions is the principal problem to solve for effective

FWM process.

The longer the fiber the less is tolerance to phase mismatching.

INAOE, 27/04/2011 38

Preliminary summary of nonlinear effects

involved to SC generation

Self phase modulation. It occurs at any dispersion; the pulse

duration has to be shorter than 1 ps.

Soliton self frequency shift. Anomalous dispersion is required.

It is effective for pulses shorter than 1 ps.

Modulation instability. It requires the anomalous

dispersion; it is effective for long

pulses including cw.

FWM. It is more effective for anomalous

dispersion nearly the point of zero

dispersion and for short fibers.

INAOE, 27/04/2011 39

Part2

Experimental results on SC

INAOE, 27/04/2011 40

Preliminary summary of nonlinear effects

involved to SC generation

Self phase modulation. It occurs at any dispersion; the pulse

duration has to be shorter than 1 ps.

Soliton self frequency shift. Anomalous dispersion is required.

It is effective for pulses shorter than 1 ps.

Modulation instability. It requires the anomalous

dispersion; it is effective for long

pulses including cw.

FWM. It is more effective for anomalous

dispersion nearly the point of zero

dispersion and for short fibers.

INAOE, 27/04/2011 41

First observation

R.R.Alfano and S.L.Shapiro, 1970

filaments

The spectrum

400 nm to 800 nm.

1-GW, 530 nm, 5 ps pulse

Several filaments were formed in the sample and broad band light was detected

at the sample output. Four wave mixing and self phase modulation were

supposed to be responsible for the effect.

Glass

INAOE, 27/04/2011 42

Soliton self-frequency shift in fibers


NaCl color

Center laser

λ = 1.5 µm

Pulse width 14 ps

500-m fiber with

anomalous dispersion

100-fs solitons were generated and soliton self frequency shift

caused the spectrum broadening

INAOE, 27/04/2011 43

J. K. Ranka, R. S. Windeler, A. J. Stentz, 2000

First observation of super continuum in photonic a

crystal fiber

Ti:supphiere 100 fs pulses were used for pump

First supercontinuum obsevation in

tapered fiber

INAOE, 27/04/2011 44

Ti:supphiere 100 fs pulses were used for pump

60 W210 W

380 W

T. A. Birks, W. J. Wadsworth, and P. St. J.Russell (2000).

INAOE, 27/04/2011 45

Nanosecond supercontinuum in PCF

Experiments used a microchip laser

producing 0.8-ns-duration pulses at 532 nm

with an average output power of 5 mW.

the extent of the spectral broadening is

explained in terms of the interplay

between Raman scattering and FWM

ZDW = 770 nm

Long pulses and cw supercontinuum

INAOE, 27/04/2011 46

A. V. Avdokhin*, S. V. Popov, and J. R. Taylor, OL, 1353 (2003)

10 mW cw laser at 1065 nm was modulated

and amplified by Yb amplifier.

Pulse durations available are of 1 ns to

several tens ns, or continuous wave (CW)

Yb modelocked laser as a source of

pulses for SC generation

INAOE, 27/04/2011 47

60kW peak - 8W average-power 2.2 ps

duration and 40 MHz repetition rate pulses

were generated at the output

Yb amplifier Yb amplifier

A. B. Rulkov, M. Y. VyatkinS. V. Popov, J. R. Taylor, Optics Express 2005

INAOE, 27/04/2011 48

The Yb source was spliced to PCF with zero dispersion at 1040nm , mode field

diameter of 3.2μm and attenuation of less than 2dB/km

A. B. Rulkov, M. Y. VyatkinS. V. Popov, J. R. Taylor, Optics Express 2005

SC in 1550 nm region is also investigated

INAOE, 27/04/2011 49

Takashi Hori, Jun Takayanagi, Norihiko Nishizawa, and Toshio Goto, Optics Express, 2004

Pulse compression

INAOE, 27/04/2011 50

Possible configuration for SC generation - 1;

direct pumping

Ju Han Lee and Kazuro Kikuchi, Optics Express, 4848 (2005)

0.185 W

2.18 W


Er laser with high nonlinear (HNL) fiber in a cavity

INAOE, 27/04/2011 51


0.185 W

2.18 W

Er-doped fiber laser


Raman laser with high nonlinear (HNL) fiber in a

cavity.

INAOE, 27/04/2011 52

2.18 W

0.185 W


PCF at 1550 nm pumping

INAOE, 27/04/2011 53

J. W. Nicholson,1,* R. Bise,1 J. Alonzo et al, Optics Letters, 28 (2008)

High average power SC

INAOE, 27/04/2011 54

J. C. Travers, A. B. Rulkov, B. A. Cumberland, S. V. Popov and J. R. Taylor, Optics Express (2008)

Application of SC

INAOE, 27/04/2011 55

Ultra high resolution optical coherence tomography

(OCT) for bio-medical investigations

INAOE, 27/04/2011 56

Traditional OCT is based on superluminescent diode

light sources; resolution 10 – 15 m

Broadband modelocked Ti:Al2O3 lasers have been demonstrated

to extend the axial resolution to 1-5 μm in tissue. However these systems are

expensive

All fiber SC generator can be a good choice.

Low coherence interferometry

INAOE, 27/04/2011 57

Input light

detector

displacement

mirror

Signal appears

only if L1 = L2

within the coherence length

L1

L2

INAOE, 27/04/2011 58

Special calculations were done to choose the PCF

characteristics and obtain desirable SC spectrum

Aaron D. Aguirre, Norihiko Nishizawa, James G. Fujimoto, Wolfgang

Seitz, Max Lederer, Daniel Kopf, Optics Express, 2006

Theoretical

INAOE, 27/04/2011 59

800 nm 1300 nm

Example of the tomography of skin

INAOE, 27/04/2011 60

800-nm supercontinuum 1300-nm supercontinuum

INAOE, 27/04/2011 61

All Fiber Source of Supercontinuum for

Optical Tomography

N.Nishizawa, A.D.Aguirre, J.G.Gujimoto, 2006

INAOE, 27/04/2011 62

Experimental Results Obtained with Al-

fiber SC Source

Spectrum of the radiationHuman skin

Optical Frequency Measurements

INAOE, 27/04/2011 63

Examples of two different optical frequency standards:

657 nm (456 THz) standard using laser-cooled Ca atoms;

282-nm (1064-THz) standard using a single trapped and laser-cooled Hg ion.

How to measure the frequency with high accuracy?

Laser mode frequency comb may be used for very exact measurements

Th. Udem, J. Reichert, R. Holzwarth, and T. W. H¨ansch, Optics Letters (2001)

The use of the laser

INAOE, 27/04/2011 64

0

frequency

Beating between lines can be

measured very accurate

1 GHz

1 2 N

frequency

0

Unknown displacement

N

repN Nfff 0

The measurement of f0

65

frequency

0


N

repN Nfff 0Second harmonic

generationrepN Nfff 222 0

frequency

0


N

f0

Broad band laser pulses are required Supercontinuum

Laser system for presision frequency

measurement

INAOE, 27/04/2011 66

Leo Hollberg, Associate Member, IEEE, Chris W. Oates, E. Anne Curtis, Eugene N. Ivanov, Scott A. Diddams,

Thomas Udem, Hugh G. Robinson, James C. Bergquist, Robert J. Rafac, Wayne M. Itano, Robert E. Drullinger, and

David J. Wineland, IEEE QE 2001

INAOE, 27/04/2011 67

Investigations in INAOE

E.A.Kuzin, B. Ibarra-Escamilla, INAOE

R.Rojas-Laguna, University of Guanajuato

O.Pottiez, CIO

J.W.Haus, Dayton University

M.V.Andres, Valencia Spain

INAOE, 27/04/2011 68

Two stage amplifier of pump pulses

10-m EDF

1549-nm FBG

15-m EDF

980-nm pumpInput from

DFB laser

980-nm pump

1:99 coupler

output

monitor

circulator

0 10 20 30 400

5

10

15

20

25

Pow

er,

W

Time, ns

pulse curent, mA

8

7

6

5

4

INAOE, 27/04/2011 69

Development of the modulation instability.

The 210-m long fiber.

1535 1540 1545 1550 1555-40

-35

-30

-25

-20

-15

-10

-5

0

No

rma

lize

d P

ow

er,

dB

Wavelength, nm

Pplateau

= 4 W

Pplateau

= 10 W

1536 1540 1544 1548 1552 1556 1560-40

-35

-30

-25

-20

-15

-10

-5

0

No

rma

lize

d P

ow

er,

dB

Wavelength, nm

Ppeak

=10 W

Ppeak

=30 W

Plateau Peak

INAOE, 27/04/2011 70

Raman enhanced supercontinuum generation.

The 9.13-km long fiber, 18 pump power.

1550 1600 1650 17000

200

400

600

800

1000

Sp

ectr

al po

we

r, a

.u.

Wavelength, nm

3 ns

30 ns

1550 1600 1650 1700-4

-3

-2

-1

0

Log o

f pow

er,

a.u

.Wavelength,nm

T0=3 ns

T0=30 ns

The F8L with the polarization splitter

used for the output

71

0.0 0.2 0.4 0.6 0.8 1.0 1.20.0

0.1

0.2

0.3

0.4

0.5

Tra

nsm

issio

n

Pin/Pcr

Nonlinear dependence

for transmitted pulses

-75 -50 -25 0 25 50 750.0

0.2

0.4

0.6

0.8

1.0

35. 71 ps

Am

plit

ude, a. u.

Time, ps

72

The soliton transmission for

different EDFA amplifications

The maximum transmission moves

towards longer soliton durations as the

amplification increases. The

calculations were done for 40-m long

fiber in the loop

EDFA

TwistedFiber

NOLMOutput

50/50

α – QWR

angle

Input linear

solitons

50-m

QWR

Total transmission is shown

Basic configuration for investigation

of pulse breakup

Fiber 1

Fiber 2

EDFA PC

TwistedFiber

OutputPulse NOLM

Output

50/50

QWR

OpticalAttenuator

Dispersive fiber

73

T

AATAAi

T

Ai

z

AR

22

22

2

-20 -10 0 10 200

20

40

60

80

Po

we

r, W

Time, ps

T=0.8 ps

Pulses at the NOLM output and at the

end of the 500-m dispersive fiber

74

-20 -10 0 10 200

20

40

60

80

Po

we

r, W

Time, ps

T=0.8 ps

Output of the NOLMOutput of the

dissipative fiber

-20 -10 0 10 200

10

20

30

Pow

er,

W

Time, ps

Amplification

x 2

T=1.1 ps

-20 -10 0 10 200

40

80

120

160P

ow

er,

W

Time, ps

Amplification

x3

T=0.9 ps

-20 -10 0 10 20 300

5

10

15Atenuation = 2

Po

we

r, W

Time, ps

-40 -20 0 20 400

10

20

30

40Attenuation=3

Pow

er,

W

Time, ps

T=1.4 ps

Experimental setup used for

extraction of solitons

75

Effect the amplification of

EDFA-2

-15 -10 -5 0 5 10 150,0

0,2

0,4

0,6

0,8

1,0

Am

plit

ud

e,

a.u

.

Time, ps

Amplification of

EDFA 2

2 times

3 times

4 times

5 times

Autocorrelation traces

At the NOLM output

Transmission at

different amplifications

76

Autocorrelation functions at the

NOLM input and output

-40 -20 0 20 400

1

Time, ps-40 -20 0 20 400

1

Time, ps

-15 -10 -5 0 5 10 150

1

T=2.25 ps

Time, ps-15 -10 -5 0 5 10 150

1

Tac=1.86 ps

Time, ps

-30 -20 -10 0 10 20 300

1

T=2.01 ps

Time, ps

NOLM

input

NOLM

output

10 W pump 15 W pump 20 W pump

77

A red line shows an

autocorrelation

function of the pump

pulse

A red line shows an

Sech2 profile

-60 -40 -20 0 20 40 600

1

Time, ps

Autocorrelation functions at the NOLM

output and the dispersive fiber output

-15 -10 -5 0 5 10 150.0

0.2

0.4

0.6

0.8

1.0 (a)

Tac=2.25 ps

Sech2 profile

Am

plit

ude, a.u

.

Time, ps

-16 -12 -8 -4 0 4 8 12 160,0

0,2

0,4

0,6

0,8

1,0

Tac=1.53 ps

Am

plit

ud

e, a

.u.

Time, ps

Sech2 profile

The NOLM outputThe dispersive fiber output

78

Soliton power is estimated as 100 W, 5 times

higher than the input pulse power. This value

corresponds to theoretical estimations20-W input pulse was applied

Conclusions

INAOE, 27/04/2011 79

The SC can be generated using many source of light: fs lasers, ns

lasers, cw laser.

Extremely important is the choice of the fiber with appropriate

group velocity dispersion preferably in the anomalous dispersion

region.

Generally the mechanisms responsible for SC generation look to

be clear, however many details are still for understanding.

First commercial applications appear in last years.

Documents

Supercontinuum generation in optical fibers · 2012. 6. 2. · Silica Glass Optical Fibers, dispersion tuning Silica cladding n ~ 1.45 more complex profiles to tune dispersion “high”