By:

Hojjatollah Sarvari

Department of Electrical Engineering

Shiraz University, Shiraz-Iran

January-2009

All-Optical Switch andTunable

Filter with Photorefractive Crystal

INTRODUCTION

WDM network systems increase bandwidth & bit rate

Tunable optical filter is a important device in telecommunication

Use KNbO3 as Photorefractive crystal

Tunable optical filter with photorefractive waveguide

Using transmission grating

Adjusting the period of the grating by changing the incident angel, wavelength or

phase distribution of the control beams

Analytical model for tunable optical filter using

transmision grating

Gaussian beam as inut with:

maximum value of intensity Is 1.0W/cm²

Radius is 0.5mm

The incident angle is θs=5.5°

The index grating induced by the

control beams with spatial range

of z=0mm and z=8mm

Intensity ratio of the control beam to

signal beam as Ic/Is=5

We analyze signal beam propagation in a photorefractive material using a

Fnite Dimensional Beam Propagation Method (FD-BPM)

We investigate diffraction efficiency and bandwidth of an output signal

Signal beam propagation in photorefractive material and

its relative permittivity distribution

signal beam is diffracted toward c-axis

signal beam is diffracted toward anti-c-axis

Simulation results for Tunable optical filter using

transmision grating

The diffraction efficiency has a maximum value 0.92 and 0.79 at z=3.8mm and 4.6mm

in case of diffraction toward c-axis and anti c-axis

The difference between these maximum diffraction efficiencies or these optimum

interaction lengths decrease as the intensity of the control beam increases

because the index grating induced by the signal beam becomes small

relatively to that induced by the control beam

Considering the D.E & Lopt & I it may be concluded that it is preferable to use the

optical configuration of diffraction toward C-axis

Simulation results for Tunable optical filter using

transmision grating

Diffraction Efficiency has maximum value for L=4 & 5 mm

Compare FWHM with D.E (previous picture) for optimum intraction length

The minimum values of FWHM are 2, 1.8, 1.5nm at L=5, 6, 6mm

Intensity ratio of the control beams is adjusted to 1:1, 1:5 and 1:10

The maximum diffraction efficiencies are 0.91, 0.88 and 0.85

Using reflection grating

Tunable optical filter with photorefractive waveguide

Analytical model for optical filter using reflection grating

φc is the phase difference between the interference pattern and the index

modulation .It is equal to -π / 2 or π / 2

Reflection efficiency against interaction length and beam

intensity ratio of control beam to signal beam

Reflection efficiency normalized by the maximum value

against wavelength of the signal beam

λ=532nm for signal beam for satisfying phase matching

For satisfying phase matching condition Δκ=2κ-κg=0

Experimental result of optical filter using transmision

gratingYAG/SHG laser (λ=532nm)

He : Ne laser (λ=633nm)

BaTiO3 bulk crystal as PR material whose size

is 5mm×5mm

Dofference between theory and exprimental:

1-Energy loss due to absorption and

optical reflection on the crystal surface

2-Non-linear scattering of the

diffracted signal beam toward the c-axis

of the crystal via fanning effect

CONCLUSIION

It is able to select the required wavelength components and control the bandwidth of the signal beam by adjusting the period and the width of the grating

The diffraction efficiency of the signal beam against the interaction length using the transmission grating is largerthan that using the reflection grating

FWHM of the filter using the transmission grating is much broader than that using the reflection grating

Ultra-narrowband optical filter with FWHM under 0.1nmcan be achieved using the reflection gratingconfiguration

Reference

[1] “Tunable optical filter for wavelength division multiplexing using

photorefractive planar waveguide” Satoshi Honma, Hirokazu Ito, Mitsuhiro

Komatsu,Shinzo Muto,Atsushi Okamoto; Proc. of SPIE Vol. 6582,

65821S, (2007)

Thanks for your attention