1/9/2007bilkent university, physics department1 supercontinuum light generation in nano- and...
TRANSCRIPT
1/9/2007Bilkent University, Physics
Department 1
Supercontinuum Light Generation in Nano- and Micro-Structured Fibers
Mustafa Yorulmaz
Bilkent University
Physics Department
1/9/2007Bilkent University, Physics
Department 2
Outline Fiber Nonlinearities:
Third order susceptibility Intensity dependence of refraction
Self Phase Modulation (SPM) Phase modulation due to intensity dependence of refractive
index Supercontinuum Light Generation in Microstructured
Fibers History Examples
Simulation Methodology: Split-step Fourier Method Numerical solution of pulse propagation inside a fiber
Results
1/9/2007Bilkent University, Physics
Department 3
Fiber Nonlinearity Polarization dependence on electric field is
not linear
Third order susceptibility: intensity dependent refractive index
1 2 30 :P E EE EEE
2 2
2,n w E n w n E
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.
1/9/2007Bilkent University, Physics
Department 4
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
Varying optical index depending on optical power
Phase fluctuations due to the change in optical power.
0 0( , ) exp( )E A z t k z t
2
2 2( ) ( )n n n E n t n n I t
2
0 2 0( )nk L n n E k L
2( )eff
Pn t n n
A
1/9/2007Bilkent University, Physics
Department 5
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
2
( ) ( )( ) NLd t dI tt n kL
dt dt
1/9/2007Bilkent University, Physics
Department 6
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.
Optical spectrum of the continuum generated in a 75-cm section of microstructure fiber.air–silica microstructure fiber.
1/9/2007Bilkent University, Physics
Department 7
Supercontinuum Light Generation 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.
Scanning electron microscope image of the end of a photonic crystal fiber.
1/9/2007Bilkent University, Physics
Department 8
Simulation Methodology
The numerical solution to the pulse propagation problem is needed.
Symmetrized Split-step Fourier Method:
22
2 22 2
A i AA i A A
z t
( , )( ) ( , )
A z tL N A z t
z
2
2 22 2
i AL A
t
2
N i A
1/9/2007Bilkent University, Physics
Department 9
Simulation Methodology
( , ) exp exp ( ') ' exp ( , )2 2
z h
z
h hA z h T L N z dz L A z T
In the solution of pulse propagation equation, the nonlinearity is included in the middle of the segment.
1/9/2007Bilkent University, Physics
Department 10
Pulse propagation through optical fiber
n2 = 0, D= nonzero
1/9/2007Bilkent University, Physics
Department 11
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.
The only length scale of interest is LD.
Zero dispersion. The nonlinearity is that expected for As2Se3. Only the spectral domain is shown. No change in the time domain occurs during spectral broadening.
The only length scale of interest is LNL.
1/9/2007Bilkent University, Physics
Department 12
THANK YOU