Get documents about "An Optical Fiber Mode-Locked Figure Eight Laser
Document Sample
An Optical Fiber Mode-Locked Figure Eight Laser
K-State Physics REU
Daniel Nickel
Mentor: Brian Washburn
Overview
• Mode locked lasers
– Produce soliton-like pulses
• The soliton
– The optical soliton
Dispersion
Self-phase modulation
• The figure eight laser
– Description
– Principles of operation
– Results
Pulse Train from a Mode-Locked Laser
Gain
S D
A C
DC = Dispersion Compensation
SA = Saturable Absorber
The Soliton
• First Observation
– John Scott Russell, 1834
– Deemed the “Wave of Translation”
Photos courtesy of www.amath.washington.edu/~bernard/kp/waterwaves
The Optical Soliton
• F8L produces soliton-like pulses
• Balance between Self-Phase Modulation (SPM)
and Dispersion
1
0.8 sech2
0.6
0.4
0.2
0
-4 -2 0 2 4
Material Dispersion
Characterized by the mode propagation constant:
1 d m
n( ) ( ) 0 ( 0 ) m
m m! d
m
c
• Positive (normal)
– High frequencies: slow
– Low frequencies: fast
• Negative (anomalous)
– High frequencies: fast
– Low frequencies: slow
Temporal Spreading
1.0 1.0
Temporal Phase (radians)
Temporal Phase (radians)
1.0 1.0
Temporal Intensity
Temporal Intensity
0.8 0.8
0.5 0.5
(a) (b)
0.6 0.6
0.0 0.0
0.4 0.4
-0.5 -0.5
0.2 Intensity -1.0 0.2
Intensity -1.0
Phase Phase
0.0 0.0
-400 -300 -200 -100 0 100 200 300 400 -400 -300 -200 -100 0 100 200 300 400
Time (fs) Time (fs)
d d
0 finite
dt dt
Self-Phase Modulation
Arises from the
Optical Kerr Effect
n( I ) n0 n2 I
d
Leading edge shifts
to lower frequencies dt
Trailing edge shifts
to higher frequencies
Net negative dispersion needed in F8L
cavity to form solitons
The Figure Eight Laser
980 nm pump
PC Er fiber
isolator
isolator
50/50 NALM
50/50
PC
PZT
Output
NALM: nonlinear amplifying loop mirror
The Optical Coupler (50/50)
Beamsplitter Directional Coupler
b2 a1 b1
a1 b1
a2 a2 b2
Both 4 port devices
Coupler needs a π phase difference between pulses to completely
switch out of one port
Nonlinear Loop Mirror: Linear Operation
A PC
PC
50/50
Gain
B
Linear Operation:
No phase shift between interferometer arms
Nonlinear Loop Mirror: Nonlinear Operation
A PC
PC
50/50
Gain
B
Nonlinear Operation:
Phase Difference: n2 (G 1) I (t ) L
Building the Figure Eight Laser
• Fiber length requirements
– Net negative (anomalous) dispersion
– NALM π phase shift
• Fiber splicing using arc fusion splicer
– Spliced fibers and components together
– Spliced fiber that the polarization
controllers broke
• Mode-locking
– Many days of manipulating the PC’s until
sech2 shaped spectrum appeared
Results
• Mode-locked Operation
– Inherently Stable 1.0
Spectral FWHM : 12.9 nm
– Tunable
Normalized Intensity
0.8
0.6
Center Wavelength = 1567 nm
0.4
Bandwidth (FWHM)= 12.9 nm
0.2
Repetition Rate= 57.753 MHz 0.0
Power = 10 mW 1540 1550 1560 1570 1580 1590 1600
Wavelength (nm)
Kelly Sidebands
Results
• Nearly transform-limited
pulses 1.0 AC FWHM : 322 fs
2
Sech FWHM : 209 fs
– Shortest possible
Normalized Intensity
pulse with the given 0.8
bandwidth
– From the uncertainty 0.6
principle
0.4
Transform limited pulse: 0.2
t 0.315 0.0
for sech2 pulses
-600 -400 -200 0 200 400 600
Our pulses: AC Delay (fs)
t 0.329
What’s Next?
• Amplification and compression to < 70 fs pulses
Amplifier
LD LD
from
EDFL
SMF EDF SMF
section 1 section 2
Thanks for your time.
References:
1. I. Duling III, Opt. Lett. 16, 539 (1991)
2. M.E. Fermann, F. Haberl, M. Hofer, and H. Hochreiter, Opt. Lett. 15,
752 (1990)
Related docs
