POLARIZING ELEMENTS

Abstract: A polarizing element comprises a transparent flat plate (31) havig two parallel faces, a polarizing separate layer (32) provided on a portion of one of those faces, and an optical reflecting material (33) provided on a portion of the other face. Such use of a flat plate facilitates miniaturization.

Description: POLARIZING ELEMENTS The present invention relates to polarizing elements, for example to a polarizing element for use in an optical switch, optical circulator, etc. An optical switch comprising a polarizing element and a Faraday rotator is well known. Further, an optical circulator comprising a polarizing element and a Faraday rotator is also well known. Such a polarizing element used in an optical switch and an optical circulator provides polarized light beams or rays that are separated by a distance which is undesirably large, for example approximately ten millimeters. In the structure of a conventional polarizing element, it is difficult to make the distance less than one millimeter. It is desirable to provide a miniature or compact polarizing element at a reasonably low cost. An embodiment of the present invention can provide a polarizing element comprising a transparent flat plate having at least two parallel surfaces, a polarizing separate layer provided on a portion of one parallel surface of the transparent flat plate, and an optical reflecting material provided on a portion of the other parallel surface of the transparent flat plate. It is preferred that the transparent flat plate be a glass plate. It is also preferred that the thickness of the transparent flat plate range from 0.2 to 1.5 mm. As the polarizing separate layer, a dielectric multi layer is advantageously used. The dielectric multilayer may be made of TiO2 and SiO2. It is preferred that the reflecting layer be a dielectric multi layer or a metal layer. The dielectric multi layer may be made of TiO2 and Si02. The metal layer is advantageously made of copper having a thickness of about 3000 A. The present invention can be embodied in a polarizing element comprising a first rectangular prism and a second rectangular prism, the polarizing separate layer being disposed between the first rectangular prism and the transparent flat plate and the optical reflecting material being disposed between the transparent flat plate and the second rectangular prism. It is preferred that the polarizing separate layer is disposed between a surface of the first rectangular prism not forming (i.e. facing towards) a right angle and one surface of the transparent flat plate, and the optical reflecting layer is disposed between a surface of the second rectangular prism not forming a right angle and the other surface of the transparent flat plate. In another embodiment the polarizing separate layer is disposed between a surface of first rectangular prism not forming a right angle and one surface of the transparent flat plate, and the optical reflecting layer is disposed between a surface of the second rectangular prism forming a right angle and the other surface of the transparent plate. In an example of such preferred embodiments there may be provided a wave plate adhered to the first rectangular prism by a transparent adhesive having substantially the same refractive index as that of the rectangular prism. An embodiment of the pesent invention can provide a polarizing element which can be efficiently used for near infrared rays. Reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a schematic view of an optical switch incorporating a prior polarizing element. Figure 2 is a schematic view of the structure of a prior polarizing element. Figure 3 is a schematic view of an embodiment of a polarizing element according to the present invention. Figures 4A and 4B are schematic views of another embodiment of a polarizing element according to the present invention. Figure 5 is a schematic view of an example of an optical switch which makes use of the polarizing element shown in Fig. 4B. Figure 6 is a schematic view of another example of an optical switch which makes use of another polarizing element embodying the present invention. Figures 7 and 8 are schematic views of other embodiments of polarizing elements according to the present invention. Referring to Figure 1, a horizontal polarization ray passes through a polarizing separate film la and is reflected by a reflection surface lb, and the horizontal polarization ray is transmitted to a Faraday rotator 3. On the other hand, a vertical polarization ray is reflected by the polarizing separate film la and is transmitted to the Faraday rotator 3. Conventionally, the distance dl between the optical paths of horizontal polarization ray and vertical polarization ray separated by a polarizing element 1 is approximately ten millimeters. The distance dl is based on the geometric size of the polarizing element 1, namely, the distance between the surface of the polarizing separate film la and the reflection surface lb. The structure of a conventional polarizing element is composed of segments A and B as shown in Fig. 2. The segments A and B are separately produced. The polarization separate film la is provided on part of the segment A and then the segment B is laminated to the segment A since it is necessary that the surfaces 4 and 5 of Fig. 2 be kept precisely parallel and that the surfacs 6, 7, 8, and 9 of Fig. 2 be precisely and plainly polished. Further, the segments A and B are assembled so that the surface 6 of the segment A and the surface 7 of the segment B are aligned on the same level. Thus, it is not easy to miniaturize the polarizing element, particularly whilst maintaining the precise structure thereof as mentioned above. In Fig. 3 which shows a basic polarizing element structure embodying the invention, reference numeral 31 denotes a glass plate having a thickness of about 1 mm and a parallel plane. On a portion of a surface of the glass plate 31, a polarizing separate layer 32 consisting of a dielectric multilayer of, for example, Ti02 and Si02 is formed. On a portion of the opposite surface of the glass plate 31, a reflecting layer 33 consisting of a metal layer of, for example, copper or a dielectric multilayer of, for example, Ti02 and Si02 is formed. Particularly, if copper is used as the reflecting layer, the polarizing element can be used in a wavelength ranging from 1.3Fm to 1.55m. The polarizing separate layer 32 and the reflecting mirror 33 can be formed by ordinal vacuum evaporation or sputtering and a photoetching process. In the obtained polarizing element, incident light from the direction X3 is separated and passed therethrough in the direction Y 3 with respect to horizontal polarization and in the direction Y4 with respect to vertical polarization in accordance with the line. On the other hand, incident light from the direction X4 is separated and passed through the polarizing element in the direction Y 4 with respect to horizontal polarization ray and in the direction Y3 with respect to vertical polarization ray. In this case, the distance d2 between the incident light Y3 and Y4 is calculated from the following equation: d2 = 2t.cose.sin8/ (n2 - sin20) 1/2 in which e is an incident light angle formed by light X3 transmitted to the polarizing element, t is the thickness of the glass plate 31, and n is the refractive index thereof. When the values of t, e, and n are 1 mm, 450, and 1.5, respectively, the value of d2 calculated from the above equation is approximately equal to 1.26 mm. If the parallelism of both surfaces of the glass 31 is maintained, a polarizing element using a glass 31 having a thin thickness can be used so that the distance d2 can be decreased in accordance with the thinness of the glass. Figures 4A and 4B show an example of a polarizing element wherein a glass plate 31 provided with the polarizing separate layer 32 and the reflecting layer 33 shown in Fig. 3 is assembled with right-angled triangular prisms 41 and 42 having the same refractive index as that of the glass plate 31 so that the glass plate 31 is disposed between the respective hypotenuse faces of the rectangular prisms 41 and 42. Figure 4A is a perspective view of the rectangular prisms and glass plate before the assembly thereof, and Fig. 4B is a view thereof after the assembly thereof. Since the light from the direction X3 and X4 is transmitted to the respective surfaces 43 and 44 of a polarizing element substantially vertically as shown in Fig. 4B, reflection loss on the incident surface 43 or 44 is reduced so that the incident light angle and the reflection angle are increased at the interface between the polarizing separate layer 32 and the glass plate 31. Thus, the separation property in polarization can be improved. The polarizing element shown in Fig. 4B is used as an optical switch a as shown in Fig. 5. The optical switch is composed of polarizing elements 51 and 52 and a Faraday rotator of, for example, yttrium-iron-garnet (YIG). The same refeence numerals in Fig. 5 as those in Figs. 4A and 4B denote the same elements. The optical systems are indicated by the broken lines. In Fig. 6, another type of optical switch is shown. The optical switch in fig. 6 is composed of other examples of polarizing elements 61 and 62, a Faraday rotator 63 of, for example, YIG, and a wave plate 64. Reference numerals 65 and 66 are input optical systems, and reference numerals 67 and 68 are output optical systems. The polarizing element 61 and 62 consist of a glass plate 31 a polarizing separate layer 32, a reflecting layer 33, and right angled triangular prisms 60 and 69. The polarizing separate layer 32 is disposed between a surface of the glass plate 31 and the hypotenuse face of the prism 69, and the reflecting layer 33 is disposed between a surface of the glass plate 31 and one of the two faces bounding the right angle of the rectangular prism 60. The structure of an optical switch as shown in Fig. 6 can be advantageously used so that the optical system can be arranged in a direction parallel to the input rays and the output rays. Therefore, the structure of the optical switch can make the optical switch compact. The wave plate 64 is advantageously provided to adjust a polarizing angle of an output ray to obtain the angle of 900 when the polarizing angle is not 900 between the polarizing surface before passing through Faraday rotator and the polarizing surface after passing through the Faraday rotator. It is preferred that a wave plate 73 (Fig. 7) be adhered to the rectangular prism 69 with a bonding medium 71. Further, in order to prevent the surface of the wave plate from undergoing mechanical shock, etc; a glass plate 72 may be adhered to the wave plate 73 as shown in Fig. 7. Such a structure can make a polarizing element having a wave plate compact. Referring to Fig. 8, on one side surface of the glass plate 31 having parallel surfaces, a polarizing separate layer 32 is provided in such a manner that the polarizing separate layer is disposed between a rectangular prism 82 and the glass plate 31. However, on the opposite side surface of the glass plate 31, a reflecting layer is not provided. In place of a reflecting layer, only a prism 83 is provided on the surcface of the glass so that a plane surface f of the prism 83 is parallel to a plane surface 81 of the glass plate 31. In the polarizing element shown in Fig. 8, the ray I transmitted vertically onto a surface h of the prism 83 is reflected on the surface f. Then the reflected ray I is passed through the glass plate 31 to the polarizing separate layer 32. A horizontal polarization ray is passed through the polarizing separate layer 32. On the other hand, a vertical polarization ray is reflected on the polarizing separate layer 32 and is passed through the glass plate 31. Then the vertical polarization ray is reflected on a surface g of the glass plate 31, which surface forms a boundary between the air and the glass, i.e. the ray I is separated into a horizontal polarization namely, and a vertical polarization S. The ray I' is also separated into a horizontal polarization P' and a vertical polarization S'. The polarizing element shown in Fig. 8 is also used in an optical switch.

Claims: CLAIMS. 1. A polarizing element comprising a transparent flat plate having at least two parallel surfaces, a polarizing separate layer provided on a portion of one parallel surface of the transparent flat plate, and a layer of optical reflecting material provided on a portion of the other parallel surface of the transparent flat plate. 2. A polarizing element according to claim 1, wherein the transparent flat plate is a glass plate. 3. A polarizing element according to claim 1 or 2, wherein the thickness of the transparent flat plate ranges from 0.2 to 1.5 mm. 4. A polarizing element according to claim 1, 2 or 3, wherein one or each of the polarizing and reflecting layers is a dielectric multi layer. 5. A polarizing element according to claim 1, 2 or 3, wherein one or each of the polarizing and reflecting layers is a dielectric multi layer made of Ti02 and Si02. 6. A polarizing element according to any preceding claim, wherein the reflecting layer is a metal layer. 7. A polarizing element according to claim 6, wherein the metal layer is made of copper. 8. A polarizing element as claimed in any preceding claim, wherein the transparent flat plate is interposed between two right-angled triangular prisms. 9. A polarizing element according to claim 8, wherein the polarizing separate layer is disposed between the flat plate and the hypotenuse face of one of the prisms, and the optical reflecting layer is disposed between the flat plate and the hypotenuse face of the other prism. 10. A polarizing element according to claim 8, wherein the polarizing separate layer is disposed between the flat plate and the hypotenuse face of one of the prisms, and the reflecting layer is disposed between the flat plate and one of the two faces of the other prism that bound the right-angle thereof. 11. A polarizing element according to claim 9 or 10, further comprising a wave plate adhesively secured to the said one of the prisms by a transparent adhesive having substantially the same refractive index as that one prism. 12. A polarizing element, including a transparent member (31) having a plane surface on which is provided a polarization discriminating layer (32) which, when the element is in use, separates light that is incident thereon into first and second components of different respective polarizations so that one (?3) of the components is directed from the discriminating layer away from the said transparent member whilst the other component (Y4) is directed into that member to undergo reflection at another, parallel surface of the said transparent member, with the result that the two components leave the element as adjacent but laterally separated respective beams that are parallel to one another, characterised in that the said transparent member is a flat plate, the two main faces of which constitute respectively the said plane surface and the other, parallel surface of the member, and in that a portion of the said other surface is provided with a layer of optically reflective material (33) at which the said reflection of the said other component takes place when the element is in use.

Inventors: SHIRASAKI, MASATAKA
Applicants: FUJITSU LIMITED
Application year: 1983
Main classification: G02B27
IPC codes: G02B5, G02B27