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