An 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. In Physics, the space surrounding an Electric charge or in the presence of a time-varying Magnetic field has a property called an electric field (that can The term encompasses a number of distinct phenomena, which can be subdivided into
- a) change of the absorption
- electroabsorption: general change of the absorption constants
- Franz-Keldysh effect: change in the absorption shown in some bulk semiconductors
- Quantum-confined Stark effect: change in the absorption in some semiconductor quantum wells
- electro-chromatic effect: creation of an absorption band at some wavelengths, which gives rise to a change in colour
- b) change of the refractive index
- Pockels effect (or linear electro-optic effect): change in the refractive index linearly proportional to the electric field. In Physics, absorption of electromagnetic radiation is the process by which the Energy of a Photon is taken up by matter typically the electrons of an The Franz-Keldysh effect is a change in optical absorption by a Semiconductor when an Electric field is applied The Stark effect is the shifting and splitting of Spectral lines of atoms and molecules due to the presence of an external static Electric field. A quantum well is a Potential well that confines particles which were originally free to move in three dimensions to two dimensions forcing them to occupy a planar region The refractive index (or index of Refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves is reduced inside the medium The Pockels effect, or Pockels electro-optic effect produces Birefringence in an optical medium induced by a constant or varying Electric field. Only certain crystalline solids show the Pockels effect, as it requires inversion asymmetry
- Kerr effect (or quadratic electro-optic effect, QEO effect): change in the refractive index proportional to the square of the electric field. The Kerr effect or the quadratic electro-optic effect ( QEO effect) is a change in the Refractive index of a material in response to an Electric field All materials display the Kerr effect, with varying magnitudes, but it is generally much weaker than the Pockels effect
- electro-gyration: change in the optical activity. The electrogyration effect is the spatial dispersion Phenomenon, that consists in the change of Optical activity (gyration of crystals by a constant or time-varying Optical rotation or optical activity is the rotation of linearly polarized Light as it travels through certain materials
It should be noted that changes in absorption can have a strong effect on refractive index for wavelengths near the absorption edge, due to the Kramers–Kronig relation. The Kramers–Kronig relations are mathematical properties connecting the real and imaginary parts of any complex function which is analytic
Using a less strict definition of the electro-optic effect allowing also electric fields oscillating at optical frequencies, one could also include nonlinear absorption (absorption depends on the light intensity) to category a) and the optical Kerr effect (refractive index depends on the light intensity) to category b). The Kerr effect or the quadratic electro-optic effect ( QEO effect) is a change in the Refractive index of a material in response to an Electric field Combined with the photoeffect and photoconductivity, the electro-optic effect gives rise to the photorefractive effect. Introduction When a Metallic surface is exposed to Electromagnetic radiation above a certain threshold Frequency, the light is absorbed and Electrons Photoconductivity is an optical and electrical phenomenon in which a material becomes more conductive due to the absorption of electro-magnetic radiation The photorefractive effect is a nonlinear optical effect seen in certain Crystals and other materials that respond to Light by altering their
The term "electro-optic" is often erroneously used as a synonym for "optoelectronic". Optoelectronics is the study and application of electronic devices that source detect and control Light, usually considered a sub-field of Photonics.
Main applications
Electro-optic modulators
Electro-optic modulators are usually built with electro-optic crystals exhibiting the Pockels effect. Electro-optic modulator (EOM is an optical device in which a signal -controlled element displaying Electro-optic effect is used to modulate a Beam of In Telecommunications, modulation is the process of varying a periodic Waveform, i The transmitted beam is phase modulated with the electric signal applied to the crystal. Phase modulation (PM is a form of Modulation that represents information as variations in the instantaneous phase of a Carrier wave. Amplitude modulators can be built by putting the electro-optic crystal between two linear polarizers. Amplitude modulation ( AM) is a technique used in electronic communication most commonly for transmitting information via a Radio Carrier wave A polarizer is a device that converts an unpolarized or mixed- Polarization beam of Electromagnetic waves (e
Electro-optic deflectors
Electro-optic deflectors utilize prisms of electro-optic crystals. In Optics, a prism is a transparent optical element with flat polished surfaces that refract Light. The index of refraction is changed by the Pockels effect, thus changing the direction of propagation of the beam inside the prism. Electro-optic deflectors have only a small number of resolvable spots, but possess a fast response time. There are few commercial models available at this time. This is because of competing acousto-optic deflectors, the small number of resolvable spots and the relatively high price of electro-optic crystals. Acousto-optics is a branch of Physics that studies the interactions between sound waves and light waves especially the Diffraction of Laser Light
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