vladimir kalosha ultra-short pulse operation of all-optical fiber passively mode-locked yb lasers...
TRANSCRIPT
Vladimir KaloshaVladimir Kalosha
Ultra-short pulse operation of Ultra-short pulse operation of
all-optical fiber passively mode-locked all-optical fiber passively mode-locked
Yb lasersYb lasers
Fiber Optics GroupFiber Optics Group
Dept. of Physics, U. of OttawaDept. of Physics, U. of Ottawa
to be published in to be published in Optics ExpressOptics Express (May 2006) (May 2006)
CoauthorCoauthors:s:
L. L. ChenChen
X. BaoX. Bao
Acknowledgment to:Acknowledgment to:
CIPICIPI NSERCNSERC Research Chair ProgramResearch Chair Program
Outline
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
Yb- vs Er-doped fiber lasersYb- vs Er-doped fiber lasers
Generation
975…1200nm
Generation
975…1200nm
Pump
860-1064 nm
by diodes
Pump
860-1064 nm
by diodes
No ESANo ESA
No
concentration
quenching
No
concentration
quenching
Higher
pump
conversion
Higher
pump
conversion
Broader gain
band
Broader gain
band
Ultra-short
high-energy
pulses
Ultra-short
high-energy
pulses
Positive GVD
Photonic Crystal Fibers
Absorption & Emission cross-Absorption & Emission cross-sections of Ybsections of Yb+3+3 in Ge:SiO in Ge:SiO22
glassglass
Passive mode-locking in Yb-doped fiber Passive mode-locking in Yb-doped fiber laserslasers
Tuennermann Tuennermann et al.et al. OE 13, 9346 (2005): OE 13, 9346 (2005): SESAM,SESAM, self-similar self-similar pulsed pulsed
regimeregime Wise Wise et al.et al. OE 11, 3550 (2003): OE 11, 3550 (2003): NPE,NPE, stretched-pulsed stretched-pulsed
regime,regime,
36-fs, 2-nJ pulses by extra-36-fs, 2-nJ pulses by extra-cavitycavity
compressioncompression Wise Wise et al.et al. OE 13, 3460 (2005): OE 13, 3460 (2005): NPE, PCF, sub-100-fs pulsesNPE, PCF, sub-100-fs pulses Okhotnikov Okhotnikov et al.et al. OE 14, 4368 (2006): OE 14, 4368 (2006): SESAM, both regimesSESAM, 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 SESAMTheory: to study generated pulse parameters in dependence on Laser parameters for both regimes
Schematic of passive mode-locked Yb-Schematic of passive mode-locked Yb-doped fiber laserdoped fiber laser
YDF: Yb-doped fiberSMF: single-mode fiberDCF: photonic crystal fiber as a dispersion-compensating fiberSBR: saturable Bragg reflector/SESAMOUT: output couplerPUMP: pump coupler/WDM
Dispersion @ 1050 nm: YDF, SMF DCF
Round-trip model of the laser Round-trip model of the laser generation:generation:
evolution equations in the intra-cavity fibers…evolution equations in the intra-cavity fibers…
YDF:
SMF & DCF:
GVD2>0 & 2<0
GVD 2>0Kerr
nonlinearity
Loss
Saturated bandwidth-limited
gain
……and in the intra-cavity passive modulatorand in the intra-cavity passive modulator
SESAM:
Ref.: Kutz et al. JOSA B 14, 2681 (1997)
Fast response to pulse intensity
Slow responseto pulse energy
parameters as for SESAM from BATOP
Intra-cavity fiber parameters used in Intra-cavity fiber parameters used in the simulations of the laser dynamicsthe simulations of the laser dynamics
Characteristics of silica fibers used in Characteristics of silica fibers used in the simulations of the laser dynamicsthe simulations of the laser dynamics
YDF, SMF: Analytics for step-index fiberDCF: Vectorial FEM for photonic crystal fiber (inset)
Normal GVD of YDF & SMF and anomalous GVD of DCF @ 1050 nm
Steady-state spectrum, spectral peak location and duration vs. DCF lengthLYDF=LSMF=0.7m; LDCF=60…115cm
Complete intra-cavity dispersion compensationComplete intra-cavity dispersion compensationin the case w/o fiber nonlinearityin the case w/o fiber nonlinearity
LDCF=115cm
A complete compensation ofintra-cavity GVD!
Is it possible in the presence of Kerr nonlinearity in the fibers?
LDCF=60cm
dechirpedpulse
generated
3
Importance of Kerr nonlinearity Importance of Kerr nonlinearity in intra-cavity DCFin intra-cavity DCF
1, no DCF2, DCF with GVD w/o Kerr nonlinearity3, DCF with GVD and Kerr nonlinearity
2
1 1
2
3
N.B.: vertical scale for frequency and delay should be relative to 0th intensity levels
“Similariton”: parabolic topsteep edgeslinear chirp
Pulse duration dependence on intra-Pulse duration dependence on intra-cavity cavity DCF with KerrDCF with Kerr nonlinearity nonlinearity
LDCF=84cm
=85cm
=85.6cm
=88cm
=1.96/0.09ps
=1.30/0.06ps
=0.29/0.09ps
=2.70/0.13ps
LDCF
Shorter,less phase-modulated,Stretched-pulse regime
Long,phase-modulated,red-shifted pulses‘similaritons’
Zero total dispersion
Norm
al net
GV
DA
nom
alo
us
net
GV
D
Multi-pulsed regimeUnstable regime
Normal net Normal net GVDGVD
Pulse duration dependence on laser gainPulse duration dependence on laser gain
Anomalous net GVDAnomalous net GVD
Similar-pulse regimeSimilar-pulse regime Stretched-pulse regimeStretched-pulse regime
Generated pulse duration
Dechirped Pulse duration
DiscussionDiscussionDifferent mechanisms of ultra-short pulse generation at Different mechanisms of ultra-short pulse generation at
PML in fiber lasers:PML in fiber lasers: Dispersion and nonlinearity compensation (Dispersion and nonlinearity compensation (solitonsoliton))11
Interrelation of finite bandwidth gain and positive Interrelation of finite bandwidth gain and positive
dispersion (dispersion (similaritonsimilariton))22 Stretched pulse mechanism (Stretched pulse mechanism (dispersion-managed dispersion-managed
solitonssolitons))33
For shortest-pulse generation these effects For shortest-pulse generation these effects
should be combined with pulse shortening byshould be combined with pulse shortening by
passive modulator and effect of finite gain passive modulator and effect of finite gain
bandwidthbandwidth 1EL 27, 544 (1991)2PRL 84, 6010 (2000)3OL 18, 1080 (1993)
Pulse transformation along the cavityPulse transformation along the cavity Normal net GVDNormal net GVD LLDCFDCF=86cm, =86cm,
gg00=0.5dB/m=0.5dB/m
Anomalous net GVDAnomalous net GVD LLDCFDCF=87cm, g=87cm, g00=0.6dB/m=0.6dB/m
ConclusionConclusion
Generation model for all-fiber Yb laser includes Generation model for all-fiber Yb laser includes interrelation of PML/SESAM + saturable finite interrelation of PML/SESAM + saturable finite bandwidth gain + dispersion + Kerr nonlinearitybandwidth gain + dispersion + Kerr nonlinearity
Dispersion compensation by intra-cavity photonic Dispersion compensation by intra-cavity photonic crystal fiber is shown crystal fiber is shown
Laser parameters were found provided generation Laser parameters were found provided generation of sub-ps phase-modulated pulsesof sub-ps phase-modulated pulses
Development of an all-fiber passively mode-locked Development of an all-fiber passively mode-locked Yb laser system is under wayYb laser system is under way