An optical isolator is a non-reciprocal optical element, it is only allowed in one direction through the beam, the reflected light has a strong blocking effect. In the CATV optical transmission systems, the role of fiber optic connectors, fiber splices, optical elements and the presence of Rayleigh scattering of the fiber itself, there is always the reflection light, the system performance adversely affected, so you must use light isolators eliminate the influence of the reflected wave, the reflected light machines, optical amplifiers are equipped with an optical isolator,
  Isolator consists of a polarizer, rotator and an analyzer consists of three parts. Polarizer is an optical device, when the light beam is incident to it, the output beam into a linearly polarized light in one direction, which direction is the polarization axis of the polarizer. When the polarization axis perpendicular to the polarization direction of the incident light and time polariser can not pass, so the polarizer can be Used as an analyzer. Rotator from optically active material and a sleeve on the outside of the permanent magnets, with the magneto-optical effect, rotation occurs through its polarization direction of light a certain extent.

  Optical isolator works as follows: polarizer and analyzer polarization axis difference 45o, when the incident light through the polarizer is linearly polarized, and then by the rotator, its plane of polarization is rotated 45o, just consistent with the direction of polarization of the analyzer, then the optical signal can pass through the optical isolator into the optical path. If the reflected light occurs when the light reflected by the analyzer and after the rotator, the direction of polarization whose polarization direction of the polarizer can not be orthogonal to the polarizer, so as to achieve the purpose of isolating the reflected light, each stage optical isolator loss of light is reflected up to 35dB above.

  In the optical isolator CATV system performance requirements are: positive low loss, high reverse isolation, high return loss, the device is small, good environmental performance. Since the optical isolator relatively expensive, it is generally applied in the light source, not in the optical fiber line, so do not just do not need, but from cost considerations. If the optical isolator cheap, insertion loss and small, can be applied in line in order to improve system performance.

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