This document summarizes an electro-optic modulator final project. It describes three types of optic modulators including electro-optic modulators, which use an external voltage to modify a nonlinear crystal's refractive index. Pockels cells are described as using this electro-optic effect to modulate laser beams for applications like optical communication. The document outlines different electro-optic modulator types including phase and intensity modulators built using Pockels cells and interferometers. It provides details on design considerations, materials like lithium niobate, and evaluates a research paper on building a polarization-insensitive waveguide modulator.

1. ELECTRO-OPTIC MODULATOR
Final Project
Başak Esin Köktürk
120206021

2. OPTİC MODULATOR TYPES
 Electro-optic modulator
 Acousto-optic modulator
 Magneto-optic modulator

3. WHAT IS ELECTRO-OPTİC
MODULATOR
 An electro-optic modulator (EOM) is a device
which can be used for controlling the power,
phase or polarization of a laser beam with an
electrical control signal.
 Electro-optic effect is the modificatiın of
refractive index of a nonlinear crystal by an
external voltage.

4. POCKELS EFFECT AND KERR EFFECT
 The Pockels effect is the linear electro-optic effect,
where the refractive index of a medium is modified
in proportion to the applied electric field strength.
 The Kerr Effect or quadratic electro-optic effect is
a change in refractive index of metarial refractive
index with an electric field.
 The difference between Pockels effect and Kerr
effect; Pockels effect refractive index is changed
proportionally with the square of electric field but in
Kerr effect it changes with magnitude of the field.

5. POCKELS CELLS
 A Pockels cell is a device consisting of an
electro-optic crystal through which a light beam
can propagate. The phase delay in the crystal can
be modulated by applying a variable electric
voltage.
 Half-wave voltage (Vπ) is very important
parameter for Pockels cells, half-wave voltage is
the voltage value for requiring π phase shift.

6. Longitudinal devices
Transverse devices
Source : http://www.rp-photonics.com/img/pockels_cell_l.png

7. ELECTRO-OPTİC MODULATOR TYPES
 Phase Modulators
The simplest type of electro-optic modulator is
a phase modulator containing only a Pockels cell,
where an electric field changes the phase delay of a
laser beam sent through the crystal
φ= n(E)koL=2πn(E)L/λo
Source :
Uri Cummings , LINEARIZED AND HIGH FREQUENCY ELECTROOPTIC MODULATORS ,
CALIFORNIA INSTITUTE OF TECHNOLOGY, 2005

8. INTENSİTY MODULATORS
Amplitude modulation with Pockels cell and
polarizers is based on Pockels cell modify the
polarization state and polarizer convert this into
change in transmitted optical amplitude and
power Using phase modulation in
optical communication isn’t
easy. Because
photodetectors are only
sensetive to intensity.
Because of this phase
modulation must be
convert to intensity
modulation. This can be
Source : http://www.rp- made by using
photonics.com/img/amplitude_modulator.png
interferometer.

9. MACH­ZEHNDER
INTERFEROMETERS
The Mach–Zehnder interferometer
benefit from the changing refractive
index with different distance path.
Source :
Uri Cummings , LINEARIZED AND HIGH FREQUENCY ELECTROOPTIC
MODULATORS , CALIFORNIA INSTITUTE OF TECHNOLOGY, 2005

10. USAGE AREA OF ELECTRO-OPTIC
MODULATORS
 Modulating a laser beam ; e.g. laser printing,high-
speed digital data recording,high-speed optical
communication
 In laser frequency stabilization shemes
 Q switching of solid-state lasers
 Active-mode locking
 Switching pulses in pulse pickers

11. IMPORTANT PROPERTIES OF ELECTRO-OPTIC
MODULATORS BEFORE PURCHASING
 There must be large open aperture
 Crystal length ,metarial and beam radius are important
where device is used for switching ultrashort pulses
because of Kerr nonlinearity and chromatic dispersion
 Depending on design an phase modulator can be generate
unwanted amplitude modulations
 In switching applications, unwanted ringing effect can be
occured because of the material specifications,orientation
and direction
 The crystals should have anti-reflection coatings, designed
for the required range of operation wavelength

12. This is an example for electro optic phase
modulator
Part Number : EO-PM-NR-C3 *
Weight : 0.75 kg
Price: € 2.032,10
Source : http://www.thorlabs.com/thorProduct.cfm?partNumber=EO-PM-NR-C3

13. OVERVIEW OF REFERENCE STUDIES
STUDY
“Polarization­insensitive strip­loaded
waveguide for electro­optic modulators and
switches” by Jie Sun,Changming Chen, Lei Gao,
Xiaoqiang Sun,Weinan Gao,Chunsheng Ma and
Daming Zhang pressed on Optics Communication
282(2009) 2255­2258.

14. A GLANCE TO STUDY
 Study aim is design a polarisation-insensitive
strip-loaded waveguide with thin EO film and
SU-8 photoresist and demonstrate it.
 In the study EO waveguide is introduced ,
needed metarials for design polarisation-
insensitive strip-loaded waveguide with thin EO
film and SU-8 photoresist are explained and
design properties and fabrication procedures are
presented

15. WHAT IS SU-8 PHOTORESİST?
SU-8 is a commonly used epoxy-based
negative photoresist.
SU-8 was originally developed
as a photoresist for microelectronics
industry, to provide a high-resolution
mask for fabrication of semiconductor
devices.
It is now mainly used in the fabrication
of microfluidics and MEMS parts.
SU-8 molecule

16. METARIALS AND THEIR PRODUCING
STEPS
 Organic and inorganic hybrid material is synthesized by
sol-gel method.Sol-gel method is prefered because film
fabrication is easy and it has high stability
 The sol-gel TiO2 / SiO2 hybrid film is processed.
However, fabricating this sol–gel TiO2/SiO2 film into a
single-mode waveguide is difficult, because the material is
too rigid to form thick film which is more than 2 lm.
Cracks will appear if the thickness increases. To overcome
this material limitation, the strip-loaded waveguide
structure is devised.
 SU-8 is purchased from MicroChem Corp. Choosen SU-8
has high sidewall quality,low curing temprature, simple

17. DESİGN PROCEDURE
 Normally in waveguides; core has bigger refractive
index than cladding. Contrast to normal waveguide
designs, in this study core divided two parts; EO film
and SU-8. And also multilayer part divided four
parts; the bottom cladding,the EO core,the strip-
loaded rib and the top cladding.

18.  When adjusting the
waveguide size ; the
effective refractive
index of TE and TM
modes are very close and
this is good for
polarisation-insensitive
waveguide because of
the similar propagation
constant between the
two modes.
 In the study ; effective
refractive index of TE
and TM modes are 1.568
and 1.563 where the
refractive index of

19. TE and TM modes are analyzed by conformal
mapping theorem with using MATLAB and
outputs are
Output mode profiles of the strip-loaded structure TM mode and TE mode.

20. FABRİCATİON PROCEDURE

21. MEASUREMENT
 In order to measure the polarisation-insensitive
characteristics, an M–Z interferometer intensity
modulator based on this waveguide is fabricated
and measured.
The upper signal is the
voltage source and the
lower is the intensity
modulation response. The
half-wave voltage Vπ is 7 V.

22.
Thank You!