Electro-optic Modulator

Supervised by : Prof. Magdy Ibrahim

ELECTRO-OPTIC MODULATOR

• Modulation.

• Electro-optic Effect.

• Electro-optic Modulator (EOM).

• Acousto-optic Effect.

• Acousto-optic Modulator (AOM).

Contents

• Modulation.

• Electro-optic Effect.

• Electro-optic Modulator (EOM).

• Acousto-optic Effect.

• Acousto-optic Modulator (AOM).

Contents

The Carrier

can be:

1. Amplitude Modulated (AM)

2. Angle Modulated.

1. Frequency Modulated (FM)

2. Phase Modulated (PM)

Modulation

Modulation of Binary Signals

1. Amplitude modulation

• used for:o up to 1200bps on voice grade lineso very high speeds over optical fiber

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.

Modulation

• Modulation.

• Electro-optic Effect.

• Electro-optic Modulator (EOM).

• Acousto-optic Effect.

• Acousto-optic Modulator (AOM).

Contents

• Definition A change in the optical properties of a material in response to an electric field.

• Types1. Change of the absorption.

2. Change of the Refractive index (n).

• Pockels EffectThe change in the refractive index linearly with the electric field.

• Pockels CellsVoltage-controlled wave plates.

Electro-optic Effect

Pockels Cells

• Geometry

• Materialβ-barium borate (BBO) : for high average power and high switching frequencies.

• Half-Wave Voltage ( Vπ )

 The voltage required for inducing a phase change of π (Relatively high) .

Electro-optic Effect

Longitudinal devices

Transverse devices

• Modulation.

• Electro-optic Effect.

• Electro-optic Modulator (EOM).

• Acousto-optic Effect.

• Acousto-optic Modulator (AOM).

Contents

• DefinitionAn 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

Electro-optic Modulator (EOM)

• DefinitionAn 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

Electro-optic Modulator (EOM)

1. Phase Modulation

Electro-optic Modulator (EOM)

1. Phase Modulation

Refractive index:

Longitudinal Electric Field:

Carrier angle becomes:

Phase Shift is:

And the Output light is:

Electro-optic Modulator (EOM)

2. Amplitude Modulation• Using Mach–Zehnder Interferometer

Electro-optic Modulator (EOM)

3. Polarization ModulationDepending 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. 

Electro-optic Modulator (EOM)

• Modulation.

• Electro-optic Effect.

• Electro-optic Modulator (EOM).

• Acousto-optic Effect.

• Acousto-optic Modulator (AOM).

Contents

• Definition It is a change of a material's permittivity (ε) due to a mechanical strain

• MaterialsFused silica, arsenic trisulfide, lead silicate, and other materials.

• Acousto optic Deviceso 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

Acousto-Optic Effect

• Modulation.

• Electro-optic Effect.

• Electro-optic Modulator (EOM).

• Acousto-optic Effect.

• Acousto-optic Modulator (AOM).

Contents

Definition

• A device which can be used for controlling the power, frequency or spatial direction of a laser beam with an acoustic wave.

Acousto-Optic Modulator (AOM)

• 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.

Summary

• 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

References