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Polarization
Published in Myeongkyu Lee, Optics for Materials Scientists, 2019
While the transmitted light is also horizontally polarized, its intensity is a quarter of the intensity of the incident unpolarized light. After passing through the quarter-wave plate, the light becomes circularly polarized. Thus its E-field component parallel to the x-axis can pass through the second polarizer. An optical isolator is a device that allows the transmission of light in only one direction. It is useful for preventing reflected light from returning back to the source. A simple isolator system can be constructed by a quarter-wave plate combined with a polarizing beam splitter. Figure 7.17 illustrates a simplified diagram of the isolator system used for optical storage devices (CD, DVD). Linearly polarized light from a laser source passes through a polarizing beam splitter and then becomes circularly polarized by a quarter-wave plate. The optic axis of the quarter-wave plate is at 45° with respect to the polarization direction of the incident light. After reflection from the storage medium, light crosses the quarter-wave plate again. This converts circularly polarized light back into linearly polarized light. Since the returning light has passed through the quarter-wave plate twice, it is linearly polarized but has a polarization direction orthogonal to that of the incident light. The polarizing beam splitter blocks the reflected light and deflects it toward a detector, as shown. In this system, the quarter-wave plate rotates the polarization direction of the incoming light by 90° and thus acts as a half-wave plate.
Passive Fibre Optic Devices
Published in Abdul Al-Azzawi, Photonics, 2017
Figure 27.12 illustrates the isolator operation. An optical isolator is composed of a magnetic garnet crystal acting as a Faraday rotator; a permanent magnet for applying a designated magnetic field; and polarizing elements that permit only forward light to pass, while shutting out backward light. For this reason, optical isolators are indispensable devices for eliminating the adverse effect of back reflection in fibre optic systems. The optical isolator consists of two polarization elements and a 45° Faraday rotator placed between the polarization elements. The polarizer and the analyzer have a 45° difference in the direction of their light transmission axes. Forward light passing the optical isolator undergoes the following: When passing through the polarizer, the incident light is transformed into linearly polarized light.When passing through the Faraday rotator, the polarization plane of the linearly polarized light is rotated 45°.This light passes through the analyzer without loss, since the light polarization plane is now in the same direction as the light transmission axis of the analyzer, which is tilted 45° from the polarizer in the direction of Faraday rotation.
Passive Fibre Optic Devices
Published in Abdul Al-Azzawi, Fibre Optics, 2017
Figure 6.12 illustrates the isolator operation. An optical isolator is composed of a magnetic garnet crystal acting as a Faraday rotator; a permanent magnet for applying a designated magnetic field; and polarizing elements that permit only forward light to pass, while shutting out backward light. For this reason, optical isolators are indispensable devices for eliminating the adverse effect of back reflection in fibre optic systems. The optical isolator consists of two polarization elements and a 45° Faraday rotator placed between the polarization elements. The polarizer and the analyzer have a 45° difference in the direction of their light transmission axes. Forward light passing the optical isolator undergoes the following: When passing through the polarizer, the incident light is transformed into linearly polarized light.When passing through the Faraday rotator, the polarization plane of the linearly polarized light is rotated 45°.This light passes through the analyzer without loss, since the light polarization plane is now in the same direction as the light transmission axis of the analyzer, which is tilted 45° from the polarizer in the direction of Faraday rotation.
A Real-Time Application of Modified Inductor Coupled KY Converter Topology in Speed Control of E-Bikes
Published in Electric Power Components and Systems, 2019
Varun Krishnan K. S., Preethi Thekkath
The driver circuit consist of Opto-Isolator IC and Driver IC. Opto-Isolator provides an optical isolation between the low voltage control side and the high voltage power circuit side. Driver IC provides an adequate lift in the voltage level of PWM signal (PWM amplitude = 5 V), sufficient to turn on the MOSFETs (VGS = 10 to 20 V).