It may be better to optimize that polarizer's orientation for maximum isolation, while accepting a somewhat higher insertion loss in forward direction. If the rotation angle of the Faraday rotator somewhat deviates from 45° (either due to fabrication errors or due to operation away from the design wavelength), the orientation of the output polarizer may still be adjusted for maximum transmission, but in that case the degree of isolation is reduced. Note that the output polarizer (pol 2) is important if light may be reflected back with a modified polarization state. Then, however, its polarization direction is rotated by another 45° in the Faraday rotator, so that this light will be blocked at the input polarizer, or can be sent to the separate output port. When light is reflected back to the output port of the isolator with an unchanged polarization state, it can fully transmit the output polarizer (pol 2). The photograph was kindly provided by GMP Switzerland. Figure 2: A selection of Faraday isolators for different power levels. The double arrows indicate the polarization directions of a forward and backward-propagating beam. Figure 1: Setup of a polarization-sensitive Faraday isolator, containing a Faraday rotator between two polarizers. Here, a properly polarized and collimated input beam passes a first polarizer (pol 1 in Figure 1) with minimum loss, then a 45° Faraday rotator, and finally another polarizer (pol 2) with its transmitting axis being rotated by 45°, such that the transmission losses are small. The simplest type of Faraday isolator is polarization-sensitive in the sense that it works only when the input beam has a prescribed direction of linear polarization. Light injected into port 1 will exit at port 2, while input at port 2 will be sent to port 3, and input at port 3 to port 1. Faraday isolators are based on Faraday rotators and constitute the technologically most important type of optical isolators.Ī variant is an optical circulator, having at least three optical ports.
#Micro faraday isolator how to
How to cite the article suggest additional literatureĪ Faraday isolator is a kind of optical isolator, i.e., a device which transmits light in a certain direction while blocking light in the opposite direction. Definition: optical isolators based on the Faraday effectĬategories: general optics, photonic devices
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