Transcript Fiber Optics Communication

Supercontinuum Light Generation in
Nano- and Micro-Structured Fibers
Mustafa Yorulmaz
Bilkent University
Physics Department
1/9/2007
Bilkent University, Physics Department
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Outline

Fiber Nonlinearities:



Self Phase Modulation (SPM)



History
Examples
Simulation Methodology: Split-step Fourier Method


Phase modulation due to intensity dependence of refractive
index
Supercontinuum Light Generation in Microstructured
Fibers


Third order susceptibility
Intensity dependence of refraction
Numerical solution of pulse propagation inside a fiber
Results
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Fiber Nonlinearity

Polarization dependence on electric field is
not linear

P   0  1  E    2 : EE   3 EEE 


Third order susceptibility: intensity dependent
refractive index

n w, E
2
  n  w  n
2
E
2
n2 (silica)= 2.36 x 10-20 m2/W @1.319 µm
n2 (As2Se3)= 2.3 x 10-17 m2/W @1.55 µm
Chalcogenide glasses have very high n2 values.
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Self-Phase Modulation



Change in the phase of an optical pulse due to the
nonlinearity of refractive index of material medium.
Propagation of pulse through the fiber
E  A( z, t )exp(k0 z  0t )
Varying optical index depending on optical power
P
n  n  n2 E  n(t )  n  n2 I (t ) n(t )  n  n2
Aeff
2

Phase fluctuations due to the change in optical
power.   nk L  (n  n E 2 )k L
0
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Selp-Phase Modulation: Broadening of the
Pulses
The intensity-dependent nonlinear phase shift generates new
frequencies for pulsed light. Because the intensity becomes time
dependent. In this case, SPM broadens the bandwidth of the
pulses, because the frequency is given by
 dNL (t )
dI (t )
 (t ) 
  n2 kL
dt
dt
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Supercontinuum Light Generation in
Microstructured Fibers

Supercontinuum light generation is a result of
complicated combinations of nonlinear optical effects.
It is characterized by the dramatic spectral broadening
of intense light pulses propagating through a nonlinear
material.

It was first demonstrated by Ranka et al.

air–silica microstructure fiber.
Optical spectrum of the continuum generated in a 75-cm section of microstructure fiber.
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Supercontinuum Light Generation
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In recent experiment, with
photonic crystal fibers and
air-silica microstructured
fibers.
High-intensity femtosecond
pulses.
Supercontinuum generation
is observed by usage of
different types of fibers
We see an example of
broad spectrum in air-silica
microstructured fiber.
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Scanning electron microscope image of the end of a photonic crystal fiber.
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Simulation Methodology

The numerical solution to the pulse propagation
problem is needed.
A
i
2 A 
2
   2 2  A  i A A
z

2
t
2
Symmetrized Split-step Fourier Method:
A( z , t )
 ( L  N ) A( z , t )
z
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i
2 A 
L   2 2  A
2
t
2
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N  i A
2
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Simulation Methodology
In the solution of pulse propagation equation, the
nonlinearity is included in the middle of the segment.
 z h

h 
h 
A( z  h, T )  exp  L  exp   N ( z ')dz '  exp  L  A( z, T )
2 
2 
 z

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Pulse propagation through optical fiber
n2 = 0, D= nonzero
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Pulse Propagation
Zero nonlinearity.
The GVD is that
expected for As2Se3. Only the time domain is
shown. No change in the spectrum occurs
during dispersion.
Zero dispersion.
The only length scale of interest is LD.
The only length scale of interest is LNL.
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The nonlinearity is that
expected for As2Se3. Only the spectral domain
is shown. No change in the time domain occurs
during spectral broadening.
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THANK YOU
1/9/2007
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