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.
Electro-optic EffectPockels 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) .
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 EOMs1. Phase Modulation2. Amplitude Modulation3. Polarization Modulation4. Frequency Modulation
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 EOMs1. Phase Modulation2. Amplitude Modulation3. Polarization Modulation
Electro-optic Modulator (EOM)1. Phase Modulation
Electro-optic Modulator (EOM)
Electro-optic Modulator (EOM)2. Amplitude Modulation • Using Mach–Zehnder Interferometer
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.
Acousto-Optic Effect• Definition It is a change of a materials 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
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.
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 materials 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.
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