High-power and high-stable
Yb fiber laser for KAGRA
Jeongmin Lee, Gwang Hoon Jang and Tai Hyun Yoon
thyoon@korea.ac.kr
2nd Korea-Japan Workshp on KAGRA
May 29, 2012, ICRR, Japan
Laser Physics Laboratory
Department of Physics
Korea University
Field
Korean
Laser
Tai Hyun Yoon
Yong-Ho Cha
Japanese
Norikatsu Mio
Items
•
•
High power amplifier
Pre-stabilization with
fiber ring cavity
MCMC parameter
estimation
EM follow up
MVC
Data Analysis
Hyung Won Lee
HideyukiTagoshi
•
•
•
•
Data Branch
Gungwon Kang
Nobuyuki Kanda
•
In progress
Feedforward control
Gravity gradient
noise
Vibration Isolation
Jaewan Kim
Ryutaro Takahashi
•
•
•
Interferometer
Donghyun Cho
Kyuman Cho
Seiji Kawamura
-> Yoichi Aso
•
•
Exchange
information
•
Exchange
information
Quantum Optics
Jai-Min Choi
Seiji Kawamura
KAGRA Input Optics
Isolator for backward light
Mode Cleaner
ETMy
Pre Mode Cleaner
Intensity stabilization
ITMy
PRM
PR2
Laser
BS
ITMx
PR3
SR2
Mode matching
Alignment
Modulator
AOM
Beam shutter
Variable attenuator
EOPM
AOM
Laser
AOM
Laser
Reference Cavity
Mode cleaning
Phase lock
SR3
SRM
ETMx
KGWG-LCGT Laser Experiments
• Master laser frequency stabilization: frequency
stabilization of NPRO with a fiber ring cavity
• High power Yb fiber laser & amplifier
• Optical frequency comb metrology: Absolute
long distance measurement
Fiber ring cavity for laser frequency stabilization
E1
E3
coupler
E2
E4
- 2×2 fiber coupler
Ei
1
3
Er
2
4
coupler
r = coupler insertion loss
k = coupling coefficient
a = splice loss
α = fiber loss per unit length
L = length of the fiber ring resonator
n = refractive index in the fiber core

Et
E3  1  r
2
- Fabry-Perot cavity
Ei
2
(1  r ) E 1  E 2
E3
E1

2

2
 E3  E4
1  k E1  i k E 2



k (k  1  A)
 1  r   1 

1/ 2
(1  k ) (1  A  2 A cos(  L )) 

A  (1  a )(1  k )(1  r ) e
splice
2
2 L
  n   / c  n  2 f / c
P hase condition :  L  p 2  , p  1, 2, 3,   
- Fiber
E ring cavity
r
k r  1  (1  r )(1  a ) e
2 L
- Fiber ring cavity
E. Her and T. H. Yoon, MOC 2011
High Finesse fiber ring cavity for laser frequency
stabilization: F = 1000
(b)
(a)
Optical fiber
protection sleeve
Cavity
Coupler
Insulated package
Coupler
TEC
(c)
Thermistor
TEC
Thermal insulator
cavity
Acrylic cover
Vibration isolating
rubber plate
Aluminum plate
Rubber plate
(d)
Frequency stabilization of NPRO Nd:YAG laser
Signal
generator 2
DC voltage
controller
AOM
8 V → 130 MHz
0 V → 160 MHz
-8 V → 190 MHz
Laser
driver
HWP
BS
AOM
driver
Loop Filter
FM
Error in
PBS
Nd:YAG laser
(λ=1064 nm)
PD 2
sweep in
Block
AOM
QWP
BS
BS
AOM : acousto-optic modulator
EOM : electro-optic modulator
PD : fast photo diode
QWP : quarter-wave plate
HWP : half-wave plate
PBS : polarization beam splitter
BS : beam splitter
CL : collimation lens
Signal
generator
M
Temperature
controller
QWP
CL
M
EOM
Cavity
PD
Power
splitter
Lock-in
amp.
12
12
6
6
Signal (V)
Signal (V)
Pound-Drever-Hall error signal
6.15 MHz
0
-6
-12
-8
6.15 MHz
0
-6
-4
0
4
Frequency Detuning (MHz)
8
-12
-8
-4
0
4
Frequency Detuning (MHz)
Before environmental isolation, modulation
frequency = 6.15 MHz
After environmental isolation, acoustic
noise, temperature stabilization
S/N ratio 20 : 1
S/N ratio 100 : 1
Slope of central error signal: 7.92 V/MHz
8
Short-term frequency stability
2
0.31 V
Signal (V)
1
 40 kH z
7.92 V /M H z
40 kHz
0
-1
10
-2
0
100
200
300
400
Allan deviation
-1
500
Time (s)
Frequency (MHz)
190
-2
10
-3
10
Out of tuning range
-4
10
185
0.1
1
10
100
Gate time (s)
180
175
Allan deviation of beat frequency at 160 MHz
170
0
175
350
Time (s)
525
700
8×10-4 @ 1 s
1000
Chirped pulse amplifier: Ti:Sapphire Laser
• In CPA systems the effect of self-phase modulation on the pulse is small.
However, recompression of the amplified, stretched pulses can
affected by phase modulation.
Yb fiber mode-locked laser with a SESAM
Chip PZT
976 nm
Pump laser
100
SESAM
AQWP
All PM fiber
CFBG
R= 12.5 %
1030 nm
YDF
Output
Reflectance (%)
R = 70 ~ 90 %
WDM
Multi-pulsing
95
Single-pulsing
90
Saturation fluence
85
80
75
70
65
1
10
100
1000
10000
2
Fluence (J/cm )
- Self-starting mode-locking via SESAM
without Q-switching operation
- In-line fiber output coupler (CFBG)
- All-normal-dispersion (~ 0.08 ps2)
- Environmentally-stable operation
(single polarization operation by controlling AQWP angle
G. H. Jang and T. H. Yoon, Laser Phys. 20, 1463 (2010))
- Temperature controlled compact system
(All system can be integrated within A4 size plate)
Two-photon absorption regime
Nonlinear Reflectance of SESAM


F
R  1 

 Lns
1 F / F
Ftp
s

Modulation depth (μ) = 0.10562
Non-saturation loss (Lns) = 0.0679
Saturation fluence (Fs) = 70.7 μJ/cm2
TPA fluence (Ftp) = 75 mJ/cm2




2
Operation of Yb fiber mode-locked laser
2.0
Epulse up
Epulse down
Pulse energy (nJ)
1.8
1.6
1.4
1.2
Self-starting
mode-locking
1.0
0.8
117 MHz
0.6
0.4
8
6
Chirped
Gaussian
4
2
0
-8
186 MHz
0.2
0.0
- Interferometric autocorrelation output pulse
Autocorrelation signal (a.u.)
- Out pulse energy of Yb fiber mode-locked laser vs. Pump power
-6
-4
-2
0
2
Delay (ps)
4
6
8
- Optical spectrum of Yb fiber mode-locked laser
0
100
200
300
400
500
2.5
Pump power (mW)
Power (mW)
- Self-starting mode-locking at 200 mW pump
- Picosecond chirped gaussian pulse shape
- Gaussian spectrum with over 20 nm width
- Pulse width and spectral width is increased
by increasing pulse energy
2.0
Gaussian
1.5
1.0
0.5
0.0
1000
1020
1040
Wavelength (nm)
1060
Environmentally-stable operation
- Measured RF spectra of Yb mode-locked fiber laser
0
RBW = 500 kHz
VBW = 500 kHz
Power (dBm)
Power (dBm)
0
- The fundamental carrier of 186 MHz repetition frequency
-20
-40
-60
RBW = 1 Hz
-20 VBW = 1 Hz
fc = 186.643 187 MHz
-40
-60
-80
-100
-125 -100 -75 -50 -25
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
0
25
fc-f (Hz)
Frequency (GHz)
50
75
- Allan deviation of 186 MHz fundamental carrier
-6
10
-7
10
Allan deviation
- Single polarization laser operation
(Polarization maintaining fiber)
- Fundamental RF carrier was 186 MHz,
and it’s stability is 2.8×10-11 at 1-s
averaging time with phase lock circuit.
- High repetition frequency achievable
(210 MHz)
-8
10
-9
10
-10
10
-11
10
-12
10
-13
10
1
10
100
1000
Gate time (s)
10000
Yb Optical Frequency Comb at Korea University
GPS
Synthesizer
14
Yb doped fiber amplifer
PL
L
C
M
C
M
DM
SL
I
L
L
FCMAS
YDF
L
M
M
PL: 25 W, 976 nm pump laser, SL: 300 mW, 1030 nm
seed laser, M: Mirror, DM: Dichroic mirror, I: Isolator, L:
Lens, FCMAS: Fiber chuck multi axis stage, YDF:
Ytterbium doped fiber, C:Clamp.
Core Absorption ratio @ 976 nm
1200 dB/m
Cladding Absorption ratio @ 976 nm
30 dB/m
Core diameter
20 μm
Cladding diameter
125 μm
YDF length
1.85 m
Absorption
55.5 dB
Characteristics of
single-stage18-W Yb fiber amplifier
collimation lens
25 W, 976 nm
Pump
mirror
coupling lens
mirror
300 mW, 7.7 MHz
Yb fiber mode
-loced laser
optical isolator
mirror -30
collimation lens
for seed oscillator
seed oscillator
Pout (W)
-40
Power (dBm)
20
Pout = η (Ppump - Pth)
η = 0.81
Pth = 1.83 W
15
multi axis stage
dichroic mirror
Double cladding
Yb doped fiber
10
-50
output
collimation lens
Amplified laser
Pout=18 W
λc=1035 nm
Δλ=8.9 nm
Seed laser
λc=1032 nm
Δλ=5.1 nm
-60
-70
5
0
-80
980
0
5
10
15
Ppump (W)
20
25
1000
1020
1040
1060
1080
1100
Wavelength (nm)
16
High power Yb-doped fiber amplifier
(Y.-H. Cha, KAERI)
Structure of rod-type PCF
55 or 80 cm
Glass support
- f = 1.7 mm
- No outer coating
Pump clad, air gap
- f = 285 mm
- NA ~ 0.6
Signal core,Yb-doped, PM
- f = 100 mm, MFD = 76 m
- NA ~ 0.02
- Pump absorption@ 976 nm
End capped on both ends ~ 30 dB/m (small signal)
- Material: fused silica
- Length: 8 mm
- Diameter: 8.2 mm
- AR coated
Yb-fiber MOPA system
DFB
20 mW, 1056 nm
LD
0.5 W
LD
5W
NPRO Nd:YAG
x
OI
Master Laser
x
LD
25W
x
DL
Main Amplifier
(Rod-PCF)
All fiber set-up
Easy to handle
2m
x
x
Absolute frequency
AOM
stabilization
PM-SC
Yb Fiber
(6/125)
Line-width reduction by
ULE(or fiber) ring cavity
Pulse Generation &
Pre-Amplifier
BPF
x
Free Space
Coupling
O.I.
O.I. BPF
7m
PM-DC
Yb Fiber
(5/130)
3m
PM-PCF
Yb Fiber
(40/200)
Mid-Amplifier
BPF
Main amplifier with a rod PCF
240
220
200
180
160
140
120
100
80
60
40
20
0
100
90
80
70
60
0
50
100
150
200
250
300
350
Absorbed Pump Power (W)
Pump LD
- 976 nm
F=300 mm
- 450 W
NA: 0.22
Amplified
Lens
output
Pump absorption ratio (%)
Amplified output power(W)
For 200 W cw laser
Need to active research
- Wavelength: 1056 nm
- Repetition rate: 150 kHz
- Max. amp. Power: 230 W (Ep = 1.5 mJ)
- Pump absorption decreases at high-power
- Max. SBS power: ~ 8 W at 230 W power
- Pulse width: ~ 5 ns
SBS monitor
1056 nm
5-6 W (150 kHz)
Isolator Isolator
Transmitted
Pump
Rod PCF (80 cm)
SWP Lens
Lens SWP
Conclusion
• We have developed mode-locked Yb fiber laser
oscillator with high stability & efficiency: 200 MHz
& 7.7 MHz.
• Optical frequency comb generation with more
than one octave is almost completed.
• 18-W stretching-free amplification has been
demonstrated for positively chirped dissipative
soliton laser.
20