Abstract:
This invention provides polarization independent magnetooptic switches. Input optical signals are switched to different output ports via polarization manipulation utilizing magnetically switchable Faraday rotators, polarization beam splitters (PBS) and polarization beam combiners (PBC). The Faraday rotators are Bi-substituted magnetic garnet with small coercivity, and PBS/PBC made from birefringence crystals. The switching Faraday rotator is mounted inside a soft magnetic ferrite core, which is magnetized by an electric coil outside. To ensure a high switching speed, the selected ferrite core exhibits high frequency characteristic. Based on the same principle of polarization manipulation, a latching magnetooptic switch (only a current pulse is required) can be built using a latchable Faraday rotator as a switching control unit. The advantages of these magnetooptic switches are high speed (˜μs or faster), low insertion loss, low PDL and PMD, compactness in size, no moving parts and no liquid in the device.

Description:
CROSS-RELATED APPLICATION 
     This application claims priority under 35 U.S.C. §119(e) of provisional patent application No. 60/291,956, filed May 21, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     Optic switches are indispensable in future all-optical broadband telecommunication systems. The current optical switches include optical mechanical switches (OMS) including MEMS, thermooptic switches (TOS); liquid crystal switches (LCS) and electro-optic switches (EOS). The drawback of OMS/MEMS, TOS and LCS are their low speed (switching time ˜10 ms or longer) and poor mechanical reliability. Although EQS is fast (switching speed can be a few nano-seconds), its complicated fabrication process, polarization dependence and huge optical insertion loss limit its applications. 
     The magnetooptic switches in accordance with the present invention are based on light polarization manipulation using Faraday rotators and polarization beam splitters/combiners, and will not have the above drawbacks. 
     SUMMARY OF THE INVENTION 
     The magnetooptic switches (MOS) in accordance with the present invention are based on magnetooptic effects in Faraday rotators. In particular, switching Faraday rotators are utilized in combination with polarization beam splitters/combiners (PBS) and walk-off plates. The mechanism of the magnetooptic switches is based on light polarization manipulation. The Faraday rotators are Bi-substituted magnetic garnets with small saturation fields, and the PBS is made from birefringence crystals (such as TiO2, YVO4, . . . ). The switching Faraday rotator is mounted inside a magnetically soft ferrite core, which is magnetized by an electric coil surrounding the ferrite core when an electrical current is applied to the electric coil. To ensure high switching speed, the ferrite core is selected to exhibit high frequency (&gt;10 MHz) characteristics. When a magnetic field is generated by the electric current in the coil, the ferrite core will be magnetized to produce a magnetic field large enough to switch the Faraday rotator, which, in turn, changes the polarization rotation of the linearly polarized lights. Based on the same principle of polarization manipulation, a latching magnetooptic switch (only a current pulse is required) can be built using a latchable Faraday rotator as a switching control unit. The magnetooptic switch can be either a transmissive or reflective type. The advantage of a reflective-type switch is the fact that less optical parts are needed and also a leak portion can be used as a monitoring signal. The advantages of these magnetooptic switches include: high speed (˜μs or faster), low insertion loss, low polarization dependent loss (PDL) and polarization mode dispersion (PMD), compactness in size, no moving parts, and no liquid and organic materials in the optical path. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The various designs of magnetooptic switches are schematically illustrated in the following figures: 
     FIG. 1 illustrates a Wollaston prism which splits an un-polarized light into two separate (o- and e-) beams (with polarization direction mutually perpendicular). 
     FIG. 2 illustrates a pair of Faraday rotators in accordance with the present invention. 
     FIG. 3 illustrates a combination of the pair of Faraday rotators and the Wollaston prism in accordance with the present invention. 
     FIG. 4 illustrates a 2×2 polarization dependent switch comprising an addition of one more Wollaston prisms to the combination illustrated in FIG. 3 in accordance with the present invention. 
     FIG. 5 illustrates a top view and a side view of a first preferred embodiment of a polarization independent 1×2 magnetooptic switch in accordance with the present invention. 
     FIG. 6 illustrates the polarization states and positions of the light after passing through each component of the switch illustrated in FIG.  5 . 
     FIG. 7 illustrates a top view and a side view of a second embodiment of a polarization independent 1×2 magnetooptic switch in accordance with the present invention. 
     FIG. 8 illustrates the polarization states and positions of the light after passing through each component of the switch illustrated in FIG.  7 . 
     FIG. 9 illustrates a first preferred embodiment of a 2×2 magnetooptic switch in accordance with the present invention. 
     FIG. 10 illustrates the polarization states and positions of the light after passing through each component of the switch illustrated in FIG.  9 . 
     FIG. 11 illustrates a polarization beam splitter combined with a rotator in accordance with the present invention. 
     FIG. 12 illustrates a reflective switching Faraday rotator mounted in a ferrite core and electric coil in accordance with the present invention. 
     FIG. 13 illustrates a reflective polarization independent 1×2 magnetooptic switch using a polarization walk-off plate in accordance with the present invention. 
     FIG. 14 illustrates the polarization states and positions of the light after passing through each component of the switch illustrated in FIG.  13 . 
     FIG. 15 illustrates a polarization independent 2×2 magnetooptic switch utilizing a cubic polarization beam splitter (Glan-Thompson) and two reflective switching Faraday rotators in accordance with the present invention. 
     FIG. 16 illustrates a top view and a side view of a polarization independent 2×2 magnetooptic switch utilizing a special-shape polarization beam splitter (Glan-Thompson) and one reflective-type switching Faraday rotator in accordance with the present invention. 
     FIG. 17 illustrates large port (2×4, 4×4, 8×8, and 16×16) magnetooptic switches which can be made from the preferred embodiments of the 1×2 and 2×2 switches, discussed in FIGS. 2-16, in accordance with the present invention. 
    
    
     DESCRIPTION OF THE INVENTION 
     The present invention provides polarization independent magnetooptic switches. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the preferred embodiment will be readily apparent to those skilled in the art and the generic principles herein may be applied to other embodiments. Thus, the present invention is not intended to be limited to the embodiment shown but is to be accorded the widest scope consistent with the principles and features described herein. 
     To more particularly describe the features of the present invention, please refer to FIGS. 1 through 17 in conjunction with the discussion below. 
     FIG. 1 illustrates a Wollaston prism  102  which splits an un-polarized light into two separate (o- and e-) beams, with polarization directions mutually perpendicular. The functioning of a Wollaston prism is well known in the art and will not be further described here. 
     FIG. 2 illustrates a pair of Faraday rotators in accordance with the present invention. The pair of Faraday rotators comprises a latched Faraday rotator  202  which comprises a permanent magnetic garnet. The latched Faraday rotator  202  is Bi-substituted with a thickness which is enough to achieve about a 45 degree rotation at a given wavelength (such as 1550 nm). The pair of Faraday rotators also comprises a switching Faraday rotator  204  which comprises a Faraday rotator  211  mounted within a ferrite core  212 , and an electric coil  213  surrounding the ferrite core  212 . A current may be provided to the electric coil  213 , creating a magnetic field. The current-produced magnetic field is enhanced by the ferrite core  212 , which is large enough to cause the Faraday rotator  211  to rotate a polarization direction of a light either about 45 degree clockwise (CW) or counter-clockwise (CCW), depending on the direction of the current. The switching Faraday rotator  204  should have a small saturation field so that only a small current is needed. The Faraday rotator  211  can be either non-latched or latched with a hysteresis loop. For a latched Faraday rotator  211 , only a pulsed current is needed to set the polarization 
     By combining the latched Faraday rotator  202  and the switchable Faraday rotator  204 , the polarization angle of a light traversing therethrough can be either about 0 degrees when the magnetic field in the switching Faraday rotator  204  is opposite to that of the latched Faraday rotator  202 , or about 90 degrees when the magnetic field in the switching Faraday rotator  204  is in the same direction as in the latched Faraday rotator  202 . The position of the latched Faraday rotator  202  and the switching Faraday rotator  204  can be exchanged without affecting the output. 
     FIG. 3 illustrates a combination of a pair of Faraday rotators and a Wollaston prism in accordance with the present invention. The latched Faraday rotator  202  and the switching Faraday rotator  204  are combined with the Wollaston prism  102 . With a current provided to the electric coil  213  in a particular direction, the Wollaston prism  102  deflects the o-beam in one direction and the e-beam in another direction. 
     FIG. 4 illustrates a 2×2 polarization dependent switch comprising an addition of one more Wollaston prisms to the switching Faraday rotator illustrated in FIG. 3 in accordance with the present invention. By adding the second Wollaston prism  402  to the combination of FIG. 3, switching one or more lights of arbitrary polarization may be provided through the second Wollaston prism  402 . 
     FIG. 5 illustrates a top view and a side view of a first preferred embodiment of a polarization independent 1×2 magnetooptic switch in accordance with the present invention. The switch  500  is a reflective-type and comprises three collimators  501 , one for an input port  1  and two for output ports  1 ′ and  2 ′. The collimators  501  are aligned at the same height. The switch  500  also comprises a polarization beam splitter  502  (PBS), two latched rotators  503  and  508 , a switching Faraday rotator  504 , a Wollaston prism  505 , and a reflector  506 . The PBS  502  has an optical axis tilted approximately 45 degrees towards the “bottom”  507 . The latched rotator  503  rotates a polarization direction of a light about 45 degrees CW, and the latched rotator  508  rotates a polarization direction of a light about 45 degrees CCW. The switching Faraday rotator  504  rotates a polarization direction of a light either about 45 degrees CW or 45 degrees CCW. It comprises a ferrite core  509  and an electric coil  510  surrounding the ferrite core  509 , and functions similarly to the switching Faraday rotator  204 , described above. The reflector  506  is made either from a high-reflective metallic film (such as thin film Ag or Au) or dielectric multilayer. The advantage of the switch  500  is that the lateral distance between the neighboring input port  1  and exit ports  1 ′ and  2 ′ can be adjusted by moving the reflector  506  toward or away from the Wollaston prism  505 . 
     FIG. 6 illustrates the polarization states and positions of the light after passing through each component of the switch  500  illustrated in FIG.  5 . The states and positions illustrated at each letter A-F correspond to locations A-F at the switch  500 , as labeled in FIG.  5 . The upper two diagrams illustrate a light as it travels between port  1  and port  1 ′. The lower two diagrams illustrate a light as it travels between port  1  and port  2 ′. 
     Referring to both FIGS. 5 and 6, a light with arbitrary polarization traverses from the input port  1  and is collimated by the collimators  501  at location A. The PBS  502  (e.g. YVO4 crystal with its optical axis 45 degree tilted downward with respect to the input optical beam) splits the arbitrarily polarized (could be any polarization state) input beam into o-(ordinary) and e-(extra-ordinary) beams (refer to the side view) at location B. The o- and e-beams further traverse the pair of latched rotators  503 ,  508  with opposite rotational angles at location C. The latched rotators  503 ,  508  could be made from a pair of half wave plates (with a tilting angle of about 22.5 degrees CW and 22.5 degrees CCW with respect to the polarization direction of the o-beam) or a pair of latched Faraday rotators (higher coercivity is preferred) with opposite rotation angles of about 45 degrees. After passing through the latched rotators  503 ,  508 , the two parallel beams enter the switching Faraday rotator  504  with its rotation angle set at either about 45 degrees CW or at 45 degrees CCW, depending on the direction of current applied to the electric coil  510  surrounding the ferrite core  509  at location D. In the upper two diagrams of FIG. 6, the switching Faraday rotator  504  rotates the polarization direction of the light by about 45 degrees CCW. In the lower two diagrams of FIG. 6, the switching Faraday rotator  504  rotates the polarization direction of a light by about 45 degrees CW. The switching Faraday rotator  504  has a small saturation field (preferably Hs&lt;100 Oe). Following the switching Faraday rotator  504  is a Wollaston prism  505  which guides the polarized light moving either “upwards” or “downwards” depending on the polarization state of the light at location M. Then, the light will be reflected back at location F to the Wollaston prism  505  by the reflector  506  with a lateral shift at location D, which defines the separation distance between input port  1  and output ports  1 ′ or  2 ′. The switching Faraday rotator  504  rotates the polarization direction of the lights by about 45 degrees CW at location C. The latched rotator  503  rotates the polarization direction of the upper beam about 45 degrees CW while the latched rotator  508  rotates the lower beam about 45 degrees CCW at location B. (See side view in FIG. 5) The PBS  502  combines the o- and e-beams at location A. The combined light is collected/collimated to exit ports  1 ′ or  2 ′, depending on the switching current of the switching Faraday rotator  504 . 
     The switch  500  is described above for a light traversing through the switch  500  in a forward direction. The switch  500  is bi-directional, thus it also will function for a light traversing through the switch  500  in a reversed direction, i.e., from port  1 ′ to port  1  or from port  2 ′ to port  1 , occurs in a similar manner. 
     FIG. 7 illustrates a top view and a side view of a second preferred embodiment of a polarization independent 1×2 magnetooptic switch in accordance with the present invention. The switch  700  is a reflective type and comprises collimators  701 , a PBS  702 , three latched rotators  703 ,  707 ,  708 , a switching Faraday rotator  704 , a Wollaston prism  705 , and a reflector  706 . The collimators  701  are optically coupled to the input port  1 , which sits at an upper level, and the two output ports  1 ′ and  2 ′, which sit at the lower level. The latched rotators  703  and  708  rotate a polarization direction of a light about 45 degrees in a first direction. The latched rotator  707  rotates a polarization of a light about 45 degrees in an opposite direction. The switching Faraday rotator  704  rotates a light either about 45 degrees CW or 45 degrees CCW. It comprises a ferrite core  710  and an electric coil  711  surrounding the ferrite coil  710 , and functions similarly to the switching Faraday rotator  204 , described above. The reflector  706  is slightly tilted so that the reflected light bends “down” to the lower ports  1 ′ and  2 ′. 
     FIG. 8 illustrates the polarization states and positions of the light after passing through each component of the switch  700  illustrated in FIG.  7 . The states and positions illustrates illustrated at each letter A-F correspond to locations A-F at the switch  700 , as labeled in FIG.  7 . The upper two diagrams illustrate a light as it travels between port  1  and port  1 ′. The lower two diagrams illustrate a light as it travels between port  1  and port  2 ′. Note that the beams in this diagram move in two-dimensions, in contrast to that of FIG.  6 . 
     Referring to both FIGS. 7 and 8, a light with arbitrary polarization traverses from the input port  1  and is collimated by the collimators  701  at location A. The PBS  702  splits the arbitrarily polarized input beam into o- and e- beams at location B. The o- and e-beams further traverse the latched rotators  703  and  707  with opposite rotational angles at location C. The o-beam is rotated by the latched rotator  703  by about 45 degrees CW. The e-beam is rotated by the latched rotator  707  by about 45 degrees CCW. The two beams are now parallel. After passing through the latched rotators  703  and  707 , the two beams enter the switching Faraday rotator  704  with its rotation angle set at either about 45 degrees CW or at 45 degrees CCW, depending on the direction of current applied to the electric coil  711  surrounding the ferrite core  710  at location D. In the upper two diagrams of FIG. 8, the switching Faraday rotator  704  rotates the polarization direction of the light by about 45 degrees CCW. In the lower two diagrams of FIG. 8, the switching Faraday rotator  704  rotates the polarization direction of a light by about 45 degrees CW. The switching Faraday rotator  704  has a small saturation field. Following the switching Faraday rotator  704  is a Wollaston prism  705  which guides the polarized light moving either “upwards” or “downwards” depending on the polarization state of the light at location M. Then, the light will be reflected back by the reflector  706  at location F to the Wollaston prism  705  with a lateral shift at location D, which defines the separation distance between input port  1  and output ports  1 ′ or  2 ′. The switching Faraday rotator  704  rotates the polarization direction of the lights by about 45 degrees CW at location C. The latched rotator  708  rotates the polarization direction of the beam passing through it about 45 degrees CW while the latched rotator  707  rotates the beam passing through it about 45 degrees CCW at location B. The PBS  702  combines the o- and e-beams at location A. The combined light is collected/collimated to exit ports  1 ′ or  2 ′, depending on the switching current of the switching Faraday rotator  704 . 
     The switch  700  is described above for a light traversing through the switch  700  in a forward direction. The switch  700  is bi-directional, thus it also will function for a light traversing through the switch  700  in a reversed direction, i.e., from port  1 ′ to port  1  or from port  2 ′ to port  1 , occurs in a similar manner. 
     FIG. 9 illustrates a first preferred embodiment of a 2×2 magnetooptic switch in accordance with the present invention. The switch  900  is a transmissive type and comprises collimators  901  and  910 , PBS&#39;s  902  and  909 , rotators  903  and  908 , Wollaston prisms  904  and  907 , a latched Faraday rotator  905 , and a switching Faraday rotator  906 . The collimators  901  are optically coupled to the input ports  1  and  2 , and the collimators  910  are optically coupled to the output ports  1 ′ and  2 ′. The rotators  903  and  908  rotate the polarization direction of light by approximately 90 degrees. They may comprise either Faraday rotators or half-wave plates. The latched Faraday rotator  905  rotates the polarization direction of light by approximately 45 degrees. The switching Faraday rotator  906  rotates the polarization direction of light either by approximately 45 degrees CW or 45 degrees CCW. 
     FIG. 10 illustrates the polarization states and positions of the light after passing through each component of the switch  900  illustrated in FIG.  9 . The states and positions illustrated at each letter A-I correspond to locations A-I at the switch  900 , as labeled in FIG.  9 . The upper two diagrams illustrate lights when they travel between port  1  and port  2 ′, and between port  2  and port  1 ′(i.e., cross connection). The lower two diagrams illustrate lights when they travel between port  1  and port- 1 ′ and between port  2  and port  2 ′(i.e., parallel connection). 
     Referring to both FIGS. 9 and 10, a first arbitrarily polarized light is input through the input port  1  and collimated by collimators  901  at location A. The first PBS  902  separates the light into an o-beam and an e-beam (bent “downward” as illustrated in FIG. 9) at position B. The rotator  903  rotates the polarization direction of the e-beam about 90 degrees, turning it into an o-beam at location C. The two beams then travel in parallel to location D. The paths of the two parallel beams bend when they travel through the first Wollaston prism  904 . They are rotated by about 45 degrees CW after passing through the latched Faraday rotator  905  at location E. They are rotated by about 45 degrees CCW after passing through the switching Faraday rotator  906  at location F, turning them into o-beams. Their paths are bent “downward” when they travel through the second Wollaston prism  907  at location G. After passing through the rotator  908 , one of the o-beams is rotated about 90 degrees, switched into an e-beam, while the other o-beam remains unchanged at location H. The o- and e-beams are combined when they traverse through the second PBS  909  at location I. The combined beam is output to port  2 ′. 
     The switching Faraday rotator  906  can rotate the two beams by about 45 degrees CW rather than CCW. As illustrated in the lower two diagrams of FIG. 10, the two beams traversing therethrough would become e-beams at location F. One of the e-beams is rotated by about 90 degrees by the rotator  908 , switching it to an o-beam, while the other e-beam remains unchanged at location H. The o- and e-beams are combined and output to port  1 ′. In the same principle of polarization manipulation, an input beam from port  2  can arrive at either at port  1 ′ or  2 ′ simply by changing the rotation direction of the switching Faraday rotator  906 , i.e., 45 degrees CW or CCW. 
     The switch  900  is bi-directional, i.e., when light travels in a reversed direction, and port  1 ′ and  2 ′ are used as input ports and ports  1  and  2  are used as output ports, the switch  900  still functions. 
     FIG. 11 illustrates a polarization beam splitter combined with a rotator in accordance with the present invention. The PBS  1101  splits a light with arbitrary polarization into an o- and an e-beam and displaces the e-beam. The rotator  1102  rotates the polarization direction of the e-beam by approximately 90 degrees, changing it into an o-beam. The rotator  1102  can be either a half-wave plate with its optical axis tilted 45 degrees with respect to the polarization direction of the e-beam, or a latched Faraday rotator. Two beams exit the PBS  1101 /rotator  1102  combination in parallel. 
     FIG. 12 illustrates a reflective switching Faraday rotator mounted in a ferrite core/coil in accordance with the present invention. The reflective switching Faraday rotator  1200  comprises a Faraday rotator  1201 , a ferrite core  1202 , and an electric coil  1206  surrounding the ferrite core  1202 . The back side of the Faraday rotator  1201  is coated with a high reflection layer  1204 . The polarization direction of a light traversing through the reflective switching Faraday rotator  1200  is rotated by either 0 degrees or 45 degrees, approximately, in a forward traverse through the Faraday rotator  1201 . The light is then reflected by the high reflection layer  1204 . The polarization direction of the light is further rotated by either 0 degrees or 45 degrees, approximately, in the reverse traverse through the Faraday rotator  1201 , resulting in a total rotation of either about 0 degrees or 90 degrees. 
     FIG. 13 illustrates a reflective polarization independent 1×2 switch using a polarization walk-off plate in accordance with the present invention. The switch  1300  utilizes the reflective switching Faraday rotator  1200  illustrated in FIG. 12 to create a reflective-type switch. The switch  1300  comprises collimators  1301 , the PBS  1101 , the rotator  1102 , a polarization walk-off plate  1302 , and a reflective switching Faraday rotator  1200 . The collimators  1301  are optically coupled to an input port  1  and output ports  1 ′ and  2 ′. Box  1304  illustrates a cross-sectional view of the collimators  1301 , showing their positions. The PBS  1101  and rotator  1102  function in the same manner as described above with reference to FIG.  11 . The combined beams are rotated and reflected by the reflective switching Faraday rotator  1200 , as described above with reference to FIG.  12 . The beams then traverse through the polarization walk-off plate  1302  which displaces the beams, the rotator  1102 , the PBS  1101 , and the collimator  1301 , in a reverse direction. The light is output to either port  1 ′ or  2 ′, depending upon the direction of the current provided to the electric coil  1206  of the reflective switching Faraday rotator  1200 . 
     FIG. 14 illustrates the polarization states and positions of the light after passing through each component of the switch  1300  illustrated in FIG.  13 . The states and positions illustrated at each letter A-F correspond to locations A-F at the switch  1300 , as labeled in FIG.  13 . The upper two diagrams illustrate a light when it travels from port  1  to port  1 ′. The lower two diagrams illustrate a light when in travels from port  1  to port  2 ′. 
     Referring to both FIGS. 13 and 14, a light with arbitrary polarization is input through the input port  1 , and collimated by collimators  1301  at location A. The PBS  1101  splits the light with arbitrary polarization into an o- and an e-beam and displaces the e-beam at location B. The rotator  1102  rotates the polarization direction of the e-beam by approximately 90 degrees, changing it into an o-beam. The two o-beams exit the rotator  1102  in parallel at location C. The polarization directions of the parallel beams are rotated by either about 0 degrees or 45 degrees by a forward traverse through the Faraday rotator  1200  at location F. In the upper diagram of FIG. 14, the switching Faraday rotator  1200  rotates the polarization direction of the parallel beams by about 0 degrees. In the lower diagram of FIG. 14, the switching Faraday rotator  1200  rotates the polarization direction of the parallel beams by about 45 degrees. The beams are then reflected by the high reflection layer  1204 . The polarization direction of the beams is further rotated by either about 0 degrees or 45 degrees by a reverse traverse through the Faraday rotator  1201  at location E, resulting in a total rotation of either about 0 degrees or 90 degrees. The polarization walk-off plate  1302  displaces the beams at location C. The latched rotator  1102  rotates a polarization direction of one beam by about 90 degrees while the other beam remained unchanged at location B. The PBS  1101  combines the two beams at location A. The combined beams are output to either port  1 ′ or  2 ′, depending upon the rotation direction of the switching Faraday rotator  1200 . 
     The switch  1300  is bi-directional, i.e., when light travels in a reversed direction, and port  1 ′ or  2 ′ is used as an input port and port  1  is used as an output port, the switch  1300  still functions. 
     FIG. 15 illustrates a polarization independent 2×2 magnetooptic switch utilizing a cubic polarization beam splitter (Glan-Thompson) and two reflective switching Faraday rotators in accordance with the present invention. The switch  1500  comprises a cubic PBS  1502  and two reflective switching Faraday rotators  1200 A and  1200 B. The two reflective switching Faraday rotators  1200 A and  1200 B each has the same structure, and function in the same manner, as the reflective switching Faraday rotator  1200 , described above with reference to FIG.  12 . The switch  1500  further comprises two dual-fiber collimators  1508  and  1510 . The collimators  1508  and  1510  may be GRIN lenses. The collimator  1508  is optically coupled to a first input port  1  and a first output port  1 ′. The collimator  1510  is optically coupled to a second input port  2  and a second output port  2 ′. 
     A first light with arbitrary polarization is input from the first input port  1 . It traverses the collimator  1508  to the cubic PBS  1502 . The cubic PBS  1502  decomposes the light based on it its polarity. The portion of the light vertical to a plane  1512  in the cubic PBS  1502  is reflected toward the first reflective switching Faraday rotator  1200 A. The portion of the light parallel to the plane  1512  is transmitted to the second reflective switching Faraday rotator  1200 B. The reflective switching Faraday rotators  1200 A and  1200 B manipulate the polarization of the portions, as described above with FIG. 12, and reflects the light either with a polarization rotation of about 0 degrees or 90 degrees. If there is no polarization rotation, the cubic PBS  1502  lets the light travel to output port  1 ′. If there is a 90 degree polarization rotation, the light will be reflected by the cubic PBS  1502  and exit output port  2 ′. Similarly, input light from port  2  can be switched to either  1 ′ or  2 ′ depending on the polarization rotation of the reflective switching Faraday rotators  1200 A and  1200 B. 
     The switch  1500  is bi-directional, i.e., when light travels in a reversed direction, and port  1 ′ and  2 ′ are used as input ports and ports  1  and  2  are used as output ports, the switch  1500  still functions. 
     FIG. 16 illustrates a top view and a side view of a polarization independent 2×2 magnetooptic switch utilizing a special-shape polarization beam splitter (Glan-Thompson) and a reflective-type switching Faraday rotator in accordance with the present invention. The switch  1600  comprises a dual fiber collimator  1610 , a special Glan-Thompson PBS  1602 , and a switching Faraday rotator  1604 . The switching Faraday rotator  1604  can comprises of two Faraday rotators, one latching rotator (45 degrees) and one switching rotator (45 degrees), as illustrated in the upper two diagrams. The switching Faraday rotator  1604  can also be comprised of one Faraday rotator  1608  (45 degrees) with the other 45 degree rotation being provided by another latched Faraday rotator  1606  external to the switching Faraday rotator  1604 , as illustrated in the bottom diagram. The switching Faraday rotator  1604  rotates a polarization direction of a light either by a total of about 0 degrees or 90 degrees in the same manner as the switching Faraday rotator  1200 , illustrated in FIG.  12 . The switching Faraday rotator  1604  can also be used in the switches  1300  and  1500 , illustrated in FIGS. 13 and 15, or with any other reflective type magnetooptic switch. 
     The special-shape PBS  1602  splits an arbitrarily polarized input beam into o- and e- beams. The o and e-beams traverse to the reflective switching Faraday rotator  1604 , which manipulate the polarization of the portions, as described above with FIG. 12, and reflects the light either with a polarization rotation of about 0 degrees or 90 degrees. If there is no polarization rotation, the special-shaped PBS  1602  lets the light travel to output port  1 ′. If there is a 90 degree polarization rotation, the light will be reflected by the special-shaped PBS  1602  and exit output port  2 ′. Similarly, input light from port  2  can be switched to either  1 ′ or  2 ′ depending on the polarization rotation of the reflective switching Faraday rotator  1604 . Unlike the switch  1500 , the switch  1600  only require one reflective switching Faraday rotator  1604 . 
     The switch  1600  is bi-directional, i.e., when light travels in a reversed direction, and port ‘ 1  and  2 ’ are used as input ports and ports  1  and  2  are used as output ports, the switch  1600  still functions. 
     FIG. 17 illustrates large port (2×4, 4×4, 8×8, and 16×16) magnetooptic switches which can be made from the preferred embodiments of the 1×2 and 2×2 switches, discussed in FIGS. 2-16, in accordance with the present invention. Any of the described embodiment may be used in any combination to create these large port magnetooptic switches. A polarization independent magnetooptic switch has been disclosed. The switch utilizes a switching Faraday rotator comprising a Faraday rotator, a ferrite core, and an electric coil surrounding the ferrite core. A direction of a current provided to the electric coil determines the direction of polarization rotation of a light traversing through the switching Faraday rotator. When used in combination with polarization beam splitters/combiners, polarization walk-off plates, and rotators, a fast polarization independent magnetooptic switch is provided. Both transmissive and reflective switches may be created. In addition to high speed, the switch in accordance with the present invention also provides low insertion loss, low PDL, and low PMD. It is compact in size, with no moving parts and no liquid or organic material in the optical path. 
     Although the present invention has been described in accordance with the embodiments shown, one of ordinary skill in the art will readily recognize that there could be variations to the embodiments and those variations would be within the spirit and scope of the present invention. Accordingly, many modifications may be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims.