The branch of physics which deals with the influence of an electric field on the optical properties of matter, especially in its crystalline form. These properties include transmission, emission, and absorption of light.
An electric field applied to a transparent crystal can change its refractive indexes and, therefore, alter the state of polarization of light propagating through it. When the refractive-index changes are directly proportional to the applied field, the phenomenon is termed the Pockels effect. When they are proportional to the square of the applied field, it is called the Kerr effect. See Kerr effect, Polarized light, Refraction of waves
The Pockels effect is used in a light modulator called the Pockels cell. This device (see illustration) consists of a crystal C (usually potassium dihydrogen phosphate, or KDP) placed between two polarizers P1 and P2 whose axes are crossed. Ring electrodes bonded to two crystal faces allow an electronic driver V to apply an electric field parallel to the axis OZ along which a light beam (for example, a laser beam) is made to propagate. Pockels cells can be switched on and off in well under 1 nanosecond. See Laser, Optical modulators
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The linearity and high-speed response of the Pockels effect within an electrooptic crystal make possible a unique optical technique for measuring the amplitude of repetitive high-frequency (greater than 1 GHz) electric signals that cannot be measured by conventional means. The technique, known as electrooptic sampling, employs a special traveling-wave Pockels cell between crossed polarizers. It is used to analyze ultrafast electric signals such as those generated by high-speed transistors and optical detectors.
A self-electrooptic-effect device (SEED) is a combination of a quantum-well electrooptic modulator with a photodetector which, when light shines on it, changes the voltage on the modulator. Although the device relies internally on an electrooptic effect, the output from the modulator is controlled by the light shining on the photodetector, giving an optically controlled device with an optical output. Most of these devices rely on the quantum-confined Stark effect in semiconductor quantum-well heterostructures as the electrooptic mechanism and utilize the changes in optical absorption resulting from this mechanism. See Semiconductor heterostructures, Stark effect
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