Vladimir Kalosha - PowerPoint PPT Presentation

Ultra-short pulse operation of

all-optical fiber passively mode-locked

Yb lasers

Fiber Optics Group

Dept. of Physics, U. of Ottawa

to be published in Optics Express (May 2006)

• L. Chen
• X. Bao

• CIPI
• NSERC
• Research Chair Program

Acknowledgment to:

• Motivation
• Advantages: Yb- vs Er-doped fiber lasers
• Mode-locked Yb fiber lasers: SESAM vs. NPE
• Round-trip Model
• Results on dynamics modeling
• Particular emphasis: How to generate ultimate shortest pulses directly from the cavity?
• Discussion
• Conclusion

• Tuennermann et al. OE 13, 9346 (2005): SESAM,self-similar pulsed

regime

• Wise et al. OE 11, 3550 (2003): NPE,stretched-pulsed regime,

36-fs, 2-nJ pulses by extra-cavity

compression

• Wise et al. OE 13, 3460 (2005): NPE, PCF, sub-100-fs pulses
• Okhotnikov et al. OE 14, 4368 (2006): SESAM, both regimes
• …

• The aim: to create an environmentally robust all-fiber Yb fiber laser
• generating high-power sub-ps pulses directly from the cavity,
• with intra-cavity dispersion compensation by PCF,
• with mode-locking by SESAM
• Theory: to study generated pulse parameters in dependence on
• Laser parameters for both regimes

YDF: Yb-doped fiber

SMF: single-mode fiber

DCF: photonic crystal fiber

as a dispersion-compensating fiber

SBR: saturable Bragg reflector/SESAM

OUT: output coupler

PUMP: pump coupler/WDM

Dispersion @ 1050 nm: YDF, SMFb2>0

DCFb2<0

YDF:

GVD b2>0

Loss

Kerr

nonlinearity

Saturated

bandwidth-limited

gain

SMF & DCF:

GVD b2>0 & b2<0

Fast response

to pulse intensity

SESAM:

parameters as for SESAM from BATOP

Slow response

to pulse energy

Ref.: Kutz et al. JOSA B 14, 2681 (1997)

Intra-cavity fiber parameters used in the simulations of the laser dynamics

Characteristics of silica fibers used in the simulations of the laser dynamics

YDF,SMF:Analytics for step-index fiber

DCF:Vectorial FEM for photonic crystal fiber (inset)

Normal GVD of YDF & SMF and anomalous GVD of DCF @ 1050 nm

Complete intra-cavity dispersion compensationin the case w/o fiber nonlinearity

Steady-state spectrum, spectral peak location and duration vs. DCF length

LYDF=LSMF=0.7m; LDCF=60…115cm

LDCF=115cm

dechirped

pulse

generated

LDCF=60cm

A complete compensation of

intra-cavity GVD!

Is it possible in the presence of Kerr nonlinearity in the fibers?

Importance of Kerr nonlinearity in intra-cavity DCF

“Similariton”:

tparabolic top

tsteep edges

tlinear chirp

3

3

1

1

2

2

1, no DCF

2, DCF with GVD w/o Kerr nonlinearity

3, DCF with GVD and Kerr nonlinearity

N.B.: vertical scale for frequency and delay should be relative to 0th

intensity levels

Pulse duration dependence on intra-cavity DCF with Kerr nonlinearity

Long,

phase-modulated,

red-shifted pulses

‘similaritons’

LDCF=84cm

t=2.70/0.13ps

Normal net GVD

=85cm

=1.96/0.09ps

Zero total dispersion

=85.6cm

Shorter,

less phase-modulated,

Stretched-pulse regime

=1.30/0.06ps

Anomalous net GVD

=88cm

=0.29/0.09ps

Multi-pulsed regime

Unstable regime

LDCF

Pulse duration dependence on laser gain

• Anomalous net GVD

• Normal net GVD

Generated pulse duration

Dechirped Pulse duration

• Stretched-pulse regime

• Similar-pulse regime

Different mechanisms of ultra-short pulse generation at

PML in fiber lasers:

• Dispersion and nonlinearity compensation (soliton)1
• Interrelation of finite bandwidth gain and positive

dispersion (similariton)2

• Stretched pulse mechanism (dispersion-managed

solitons)3

For shortest-pulse generation these effects

should be combined with pulse shortening by

passive modulator and effect of finite gain

bandwidth

1EL 27, 544 (1991)

2PRL 84, 6010 (2000)

3OL 18, 1080 (1993)

• Anomalous net GVD
• LDCF=87cm, g0=0.6dB/m

• Normal net GVD
• LDCF=86cm, g0=0.5dB/m

• Generation model for all-fiber Yb laser includes interrelation of PML/SESAM + saturable finite bandwidth gain + dispersion + Kerr nonlinearity
• Dispersion compensation by intra-cavity photonic crystal fiber is shown
• Laser parameters were found provided generation of sub-ps phase-modulated pulses
• Development of an all-fiber passively mode-locked Yb laser system is under way