The characteristics that one looks for in a Faraday rotator optic include a high Verdet constant, low absorption coefficient, low non-linear refractive index and high damage threshold. The most important optical element in an isolator is the Faraday rotator. The rays were traced using an ordinary refractive index of 2, and an extraordinary refractive index of 3. The forward travelling light is shown in blue, and the backward propagating light is shown in red. In the isolated direction the beam is split, and then diverged, so it does not focus at the collimator.įigure 3 shows the propagation of light through a polarization independent isolator. In the transmitted direction the beam is split and then combined and focused into the output collimator. Typically collimators are used on either side of the isolator. Instead of being focused by the second birefringent wedge, the rays diverge. Now the o-ray is at 90°, and the e-ray is at 0°. The Faraday Rotator again rotates both the rays by 45°. Light traveling in the backward direction is separated into the o-ray at 45, and the e-ray at −45° by the birefringent wedge. The output birefringent wedge then recombines the two components. This means the o-ray is now at 45°, and the e-ray is at −45°.
The Faraday rotator rotates both the o-ray and e-ray by 45°. Light traveling in the forward direction is split by the input birefringent wedge into its vertical (0°) and horizontal (90°) components, called the ordinary ray (o-ray) and the extraordinary ray (e-ray) respectively. The polarization independent isolator is made of three parts, an input birefringent wedge (with its ordinary polarization direction vertical and its extraordinary polarization direction horizontal), a Faraday rotator, and an output birefringent wedge (with its ordinary polarization direction at 45°, and its extraordinary polarization direction at −45°). Polarization independent isolatorįigure 3: Polarization independent isolator Hence the angle of polarization will lead to a loss. In optical fibre systems, the polarization direction is typically dispersed in non polarization maintaining systems. This is because the polarization of the source is typically maintained by the system.
Uses for an optical isolator free#
Polarization dependent isolators are typically used in free space optical systems. The Faraday rotator is chosen to give a 45° rotation. For a polarization dependent isolator, the angle between the polarizer and the analyser,, is set to 45°. Since the polarizer is vertically aligned, the light will be extinguished.įigure 2 shows a Faraday rotator with an input polarizer, and an output analyser. This means the light is polarized horizontally (the rotation is sensitive to direction of propagation). The Faraday rotator will again rotate the polarization by 45°. Light traveling in the backward direction becomes polarized at 45° by the analyser. The analyser then enables the light to be transmitted through the isolator. The Faraday rotator will rotate the polarization by 45°. Light traveling in the forward direction becomes polarized vertically by the input polarizer. The polarization dependent isolator, or Faraday isolator, is made of three parts, an input polarizer (polarized vertically), a Faraday rotator, and an output polarizer, called an analyser (polarized at 45°). A 77, 062507 (2008).Figure 2: Faraday rotator, with a polarizer and an analyser Böer, A Survey of Semiconductor Physics, 2nd ed.
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