1. Supervised by : Prof. Magdy Ibrahim

2. Contents
• Modulation.
• Electro-optic Effect.
• Electro-optic Modulator (EOM).
• Acousto-optic Effect.
• Acousto-optic Modulator (AOM).

3. Contents
• Modulation.
• Electro-optic Effect.
• Electro-optic Modulator (EOM).
• Acousto-optic Effect.
• Acousto-optic Modulator (AOM).

4. Modulation

5. Modulation
Modulation of Binary Signals
1. Amplitude modulation
• used for:
o up to 1200bps on voice grade lines
o very high speeds over optical fiber

6. Modulation
Modulation of Binary Signals
2. Frequency Modulation
• Binary PSK: Two phases represent two binary digits.
3. Phase Modulation
• Two binary values represented by two different frequencies.

7. Contents
• Modulation.
• Electro-optic Effect.
• Electro-optic Modulator (EOM).
• Acousto-optic Effect.
• Acousto-optic Modulator (AOM).

8. Electro-optic Effect
• Definition
A change in the optical properties of a material in response to an electric field.
• Types
1. Change of the absorption.
2. Change of the Refractive index (n).
• Pockels Effect
The change in the refractive index linearly with the electric field.
• Pockels Cells
Voltage-controlled wave plates.

9. Electro-optic Effect
Pockels Cells
• Geometry
Longitudinal devices Transverse devices
• Material
β-barium borate (BBO) : for high average power and high switching frequencies.
• Half-Wave Voltage ( V π )
The voltage required for inducing a phase change of π (Relatively high) .

10. Contents
• Modulation.
• Electro-optic Effect.
• Electro-optic Modulator (EOM).
• Acousto-optic Effect.
• Acousto-optic Modulator (AOM).

11. Electro-optic Modulator (EOM)
• Definition
An optical device in which a signal-controlled element displaying electro-
optic effect is used to modulate a beam of light.
• Types of EOMs
1. Phase Modulation
2. Amplitude Modulation
3. Polarization Modulation
4. Frequency Modulation

12. Electro-optic Modulator (EOM)
• Definition
An optical device in which a signal-controlled element displaying electro-
optic effect is used to modulate a beam of light.
• Types of EOMs
1. Phase Modulation
2. Amplitude Modulation
3. Polarization Modulation

13. Electro-optic Modulator (EOM)
1. Phase Modulation

14. Electro-optic Modulator (EOM)

15. Electro-optic Modulator (EOM)
2. Amplitude Modulation
• Using Mach–Zehnder Interferometer

16. Electro-optic Modulator (EOM)
3. Polarization Modulation
Depending on the type and orientation of the nonlinear crystal, and
on the direction of the applied electric field, the phase delay can
depend on the polarization direction.

17. Contents
• Modulation.
• Electro-optic Effect.
• Electro-optic Modulator (EOM).
• Acousto-optic Effect.
• Acousto-optic Modulator (AOM).

18. Acousto-Optic Effect
• Definition
It is a change of a material's permittivity (ε) due to a mechanical strain
• Materials
Fused silica, arsenic trisulfide, lead silicate, and other materials.
• Acousto optic Devices
o Acousto-optic Filter
By tuning the frequency of the acoustic wave, the desired wavelength of the optical
wave can be diffracted acousto-optically.
o Acousto-optic Deflector
Controls the optical beam spatially. the power driving the acoustic transducer is
kept on, at a constant level, while the acoustic frequency is varied to deflect the
beam to different angular positions.
o Acousto-optic Modulator

19. Contents
• Modulation.
• Electro-optic Effect.
• Electro-optic Modulator (EOM).
• Acousto-optic Effect.
• Acousto-optic Modulator (AOM).

20. Acousto-Optic Modulator (AOM)
Definition
• A device which can be used for controlling the power, frequency or spatial
direction of a laser beam with an acoustic wave.

21. Summary
• Modulation is the process of varying one or more properties of a high-
frequency periodic waveform with a modulating signal which typically
contains information to be transmitted.
• Electro-optic effect is a change in the optical properties of a material in
response to an electric field that varies slowly compared with the
frequency of light.
• EOM is an optical device in which a signal-controlled element displaying
electro-optic effect is used to modulate a beam of light.
• The acousto-optic effect is a change of a material's permittivity (and
refractive index), due to a mechanical strain.
• AOM is a device which can be used for controlling the power, frequency
or spatial direction of a laser beam with an acoustic wave.

22. References
• Modulation:
• “Communication Systems 4Th Edition” by Simon Haykin – Chapter 2.
• Electro-Optic effect:
• http://www.rp-photonics.com/electro_optic_effect.html
• Acousto-Optic effect:
• http://en.wikipedia.org/wiki/Acousto-optics
• http://www.mt-berlin.com/frames_ao/descriptions/ao_effect.htm
• Electro-optic modulator:
• http://en.wikipedia.org/wiki/Electro-optic_modulator
• http://www.rp-photonics.com/electro_optic_modulators.html
• “Photonics Optical Electronics for Modern Communications” by AMNON YARIV – Chapter 9.
• Acousto-optic Modulator:
• http://www.rp-photonics.com/acousto_optic_modulators.html