The magnet ring for a RIG FR is usually axially magnetized, as shown in Fig.1(a). The TGG rotator (including magnet rings and TGG crystal) need elaborate design to obtain the required strength of magnetic field with a minimal magnet. (2), a high strength magnetic field is required, which is to be generated by a big magnet. The Verdet constant of TGG crystal is V=0.002º/(G The thickness of 10~15mm excludes wedge-type structure. Thus we know, for high power applications, TGG is required instead of RIG. The assembly of the device is difficult and the two forward rays can’t be received by the output collimator simultaneously. If the TGG rotator is used in the wedge-type isolator, the lateral offset and walk-off of the rays are too much. Moreover, the thickness of TGG crystal (10~15mm) is much more than that of RIG FR. While for a TGG rotator, the magnet ring needs to be elaborately designed to provide a precise rotatory angle. A RIG FR just needs a small magnet ring providing magnetic field more than saturation (usually 200Oe). The thickness of a 45º FR is about 0.36mm (including the substrate thickness). The film thickness is doubled for a 90º rotator than a 45º rotator. The actual rotatory angle depends on the thickness of the RIG film epitaxially grown on a substrate. (2).įor the RIG FR in telecom applications, the rotatory angle is fixed under a saturated magnet field. Usually, the magnet field is not uniform, thus Eq. The rotatory angle by the TGG crystal depends on Verdet constant, crystal thickness and magnetic field strength, as Eq. Thus TGG (terbium gallium garnet) crystal is used for optical rotation as the substitution due to its endurance to high optical power. The RIG film will be damaged by high power laser. The FR for telecom applications is a thin film of Bi-substituted rare-earth iron garnet single crystals (RIG) grown by liquid phase epitaxy. The reason is that the FR for telecom applications can’t be used anymore. While for some applications under high optical power, BD-type in-line optical isolator is employed instead of wedge-type. For some applications under relatively low optical power, wedge-type in-line optical isolator is employed, just with more consideration on heat dissipation. Depending on the actual applications, different types of optical isolator are employed. Optical isolators are important devices to ensure the reliability of fiber lasers. doi: 10.1038/064577e0.The research and application of fiber lasers flourish in recent years. "On the Magnetic Rotation of Light and the Second Law of Thermo-Dynamics". "Faraday Isolators and Kirchhoff's Law: A Puzzle" (PDF). For a polarization dependent isolator, the angle between the polarizer and the analyzer, β : CS1 maint: archived copy as title ( link) Since the polarizer is vertically aligned, the light will be extinguished.įigure 2 shows a Faraday rotator with an input polarizer, and an output analyzer. This means the light is polarized horizontally (the direction of rotation is not sensitive to the 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 analyzer. The analyzer 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 analyzer (polarized at 45°). It is made of three parts, an input polarizer, a Faraday rotator and an analyzer. Figure 2: Faraday isolator allows the transmission of light in only one direction.
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