Optical isolator

Abstract: The present invention relates to an optical isolator having a plurality of Faraday rotators with a structure, which allows an accurate and easy assembly. The optical isolator relating to the present invention, comprises: Faraday rotators (2A,2B) and birefringent crystal plates (1A,3A,1B,3B) arranged on both sides of the each rotator; a plurality of magnets (4A,4B) arranged on the sides of the each rotator; a plurality of magnets arranged on the the circumference of the Faraday rotators for magnetizing the Faraday rotators; and a housing body (5) arranged on the circumference of the plurality of magnets, the plurality of magnets being integrally formed, and the optical isolating unit being integrally fixed with the integrally formed magnets.

Description: The present invention relates to an optical isolator having a structure which allows accurate and easy assembling. EP-A-0 611 980 describes an optical isolator comprising first through fourth plate-like birefringement substances, each for receiving and transmitting an incident beam of light. Each plate-like birefringement substance has a corresponding optical axis which is inclined with respect to a direction of the incident beam of light. The optical isolator also includes first and second magneto-optical materials, each for rotating a plane of polarization of the incident beam of light. Finally, the optical isolator includes a magnetized element for magnetizing the first and second magneto-optical materials. In one embodiment, the magnetizing element is composed of two magnets arranged around the periphery of the optical elements and separated by a spacer. EP-A-0 364 968 describes an optical isolator comprising a cylindrical magnet magnetized in a direction parallel to the optical axis of rotational symmetry thereof, a Faraday rotator disposed in a center space of said cylindrical magnet,-and a pair of polarizers on both sides of said Faraday rotator with an inclination of 45° relative to each other. The Faraday rotator and the polarizers are supported by a center holder having a lateral opening which extends parallel to the axis for insertion of the rotator and the polarizers. JP-A-4 093 814 describes an optical isolator comprising prism holders and prisms as well as a permanent magnet holder, a permanent magnet and a magneto-optical crystal respectively bonded by the fusion of low melting glass. The permanent magnet holder and the prism holders are integrated by welding. JP-A-6 194 604 describes an optical isolator consisting of polarizing elements, Faraday rotors and permanent magnets for impressing magnetic fields, disposed with condenser lenses for coupling incident and exit light at both ends thereof. The optical elements thereof are contained in a housing body. The conventional optical isolator as shown in Fig. 10, for instance, provides respective birefringent crystal plates, 1A, 3A, 1B and 3B,each on both sides of Faraday rotators, 2A and 2B, and magnets 20 are provided on Faraday rotators' circumference[Japanese Patent Laying-Open No. 6-242403 (1994)]. Lenses 21A and 21B, and optical fibers,22A and 22B, are provided on the both sides of the optical isolator. When one Faraday rotator is provided, the isolation of the optical isolator is at the highest, about 40 dB . On the other hand, when a plurality of Faraday rotators are provided, the isolation of the optical isolator is further improved (The Electronic Information Transmission Society: Proceeding 90/5 Vol. J73-C-1 No. 5). In order to manufacture an optical isolator having a plurality of Faraday rotators , assembly must be accurately made of many optical elements and must be small. Further, a plurality of magnets must be assembled into the optical isolator accurately and easily. Reciprocation action between magnets makes changeful the position of magnets. It makes more difficult the adjustment of magnets and Faraday rotators and the fixation a main body's optical isolator on a housing body. The purpose of the present invention is to provide an optical isolator structured to allow a plurality of magnets being assembled into the optical isolator accurately and easily. Accordingly, the present invention provides an optical isolator, having a structure as defined in claim 1. According to this structure, the assembling of a plurality of magnets into an optical isolator can be simplified, thereby allowing accurate and easy assembling. Fig. 1 is a sectional drawing showing a structure of an optical isolator not forming part of the present invention. Fig. 2 is a sectional drawing showing another structure of an optical isolator not forming part of the present invention. Fig. 3 is a perspective drawing showing a main body's structure of an optical isolator in relation to the present invention. Fig. 4 is a drawing showing a plurality of magnets fixed to a spacer. Fig. 5 is a drawing showing a structure of an optical isolator in relation to the present invention. Fig. 6 is a sectional drawing showing another main body's structure of an optical isolator in relation to the present invention. Fig. 7 is a sectional drawing showing another main body's structure of an optical isolator in relation to the present invention. Fig. 8 is a drawing showing astructure of a housing body and a plurality of magnets fixed thereto. Fig. 9 is a drawing showing another structure of a housing body and a plurality of magnets fixed thereto. Fig. 10 is a drawing describing a conventional optical isolator. Explanation of the present invention in relation to the attached drawing follows after the embodiment. Omitting redundant explanation, in this case, the same element is attached with the same code in the explanation of the drawing. Fig. 1 shows a sectional drawing showing a structure in case of a conventional optical Isolator having two Faraday rotators, wherein each first and second birefringent crystal plates, 1A, 3A, 1B, and 3B, respectively, are installed on both sides of Faraday rotators, 2A and 2B. Those optical elements are independently assembled and adjusted and are integrally fixed with the light-transmitting adhesive. Ultraviolet curing resin or thermosetting resin is used. The adoption of this structure enables down-sizing of an optical isolator unit and simplification of assembly work, which therefore allows accurate and easy assembly. The thickness of second birefringent crystal plates, 3A and 3B, is designed to be (1+ 2 ) times the thickness of the first birefringent crystal plates, 1A and 1B. The Faraday rotators, 2A and 2B, are magnetized by magnets, 4A and 4B, respectively,in opposite directions, at which the polarized wave aspects of transmitting light rotate by +45' and -45 ' respectively. Respective cylindrical magnets, 4A and 4B, are formed by a magnetic body such as ferrite or the like . The place of them are selected so that respective Faraday rotators, 2A and 2B, can be positioned at approximately midway between them. The end faces of magnet, 4A and 4B, are integrally fixed with adhesive, which allows accurate and easy assembly of the subsequent stage. In such a manner, forming integrally the plurality of magnets simplifies the fixing work with adhesive 6 by inserting the optical isolator unit composed of integrally formed optical elements into an integrally formed cylinder-type magnets, followed by adjustment to a predetermined position. Lastly, the circumference of the cylinder-type magnet is covered with a metallic cylinder-type housing body, followed by fixing with an adhesive. The cylinder-type housing body holds the magnets and the spacers inside at a predetermined position and protects them. Fig. 2 is a sectional drawing showing another structure of a conventional optical isolator. The above-mentioned Faraday rotators,2A and 2B, and birefringent crystal plates, 1A, 3A, 1B, and 3B, are inserted into slots which are processed on the surface of silicon substrate 7 in the form of comb. Since the adhesive is not used in a path through which light passes these optical elements, the light path is not shut by the burning or alteration of the adhesive caused by transmitting light even if high energy light is transmitted, and reliability is high. Other points of this embodiment are the same as shown in Fig. 1. A rectangular plate is used for the optical element, while a square tube or plate is used for the magnets other than a cylinder. Fig. 3 shows an example of main body's structure of an optical isolator or the present invention formed integrally using rectangle plates. Fig. 4 shows a case of an integrally formed magnets in which magnetic spacer 8 is arranged between cylindrical magnets, 4A and 4B, where they are integrally fixed by screws 9. The spacer is preferably made of magnetic body. The spacer 8 is arranged between magnets and adjusted so that the Faraday rotators are positioned at the center of each magnet. As physical means fixing other than with screws, welding or adhesive can be applied. Fig. 5 shows a sectional drawing of a structure of another optical isolator in relation to the present invention, which forms a housing body by providing a ring-shape collar 12 on both ends of a cylindrical body 11 made of metal such as soft-iron, etc. After inserting magnets, 4A and 4B, into a cylindrical body 11 preserving a clearance 10, the collar 12 is fixed. Both ends of the inserted magnets, 4A and 4B, are securely fixed at the collar 12, which is effective when both magnets are arranged so that repulsion is generated. Indeed, there may be a case of introducing a spacer 8 to a position of clearance 10. Fig. 6 and Fig. 7 show sectional drawings of a main body's structure of another optical isolator. In Fig. 6, optical elements and magnets are fixed by passing a screw 14 through a screw hole 13 provided in a cylinder-type spacer 8. Each optical element is integrally fixed with these contact surfaces by use of an ultraviolet curing resin 15, while a spacer 8 as well as magnets, 4A and 4B, are also fixed by use of a thermosetting adhesive. Fig. 7 shows a structure as shown in Fig. 6, in which a hole 16 is provided in a cylinder-type spacer 8, and optical elements and magnets are fixed by applying an adhesive 17 in this hole. Others are the same as those in Fig. 6. Fig. 8 and Fig. 9 show a structure of integrally formed magnets,4A and 4B, and a spacer 8 which are integrally fixed in a cylindrical-type housing body 5. Fig. 8 shows that the housing body 5 and the spacer 8 (even the magnets 4A and 4B may suffice this need) are subjected to direct through-welding, 18A and 18B, by use of a YAG laser, etc. Furthermore, Fig. 9 shows that, by providing a hole 19 on a housing body 5, the housing body and the magnets are fixed by physical means such as welding, adhesive or screws through this hole. When making the optical isolator as shown in Fig. 1 by use of the method described above, favourable characteristics were obtained with an insertion loss of 0.1 dB and an isolation of 60dB.

Claims: An optical isolator, comprising: an optical isolator unit having a plurality of optical elements, wherein said plurality of optical elements include at least two Faraday rotators (2A, 2B) and a plurality of birefringent crystal plates (1A, 1B, 3A, 3B) arranged on both sides of each rotator; an assembly of magnets comprising a plurality of magnets fixed to a spacer arranged between the magnets, said assembly of magnets being arranged around the periphery of the Faraday rotators for magnetizing the Faraday rotators ; and a housing body (5) arranged around the periphery of the plurality of magnets, wherein the optical isolator unit further comprises a means for fixing the assembly of magnets, on the one hand to the housing body and on the otherhand to the said optical Isolator unit, at the location of the spacer. An optical isolator as claimed in Claim 1, wherein the plurality of optical elements are adhered to each other by use of light-transmitting adhesive (6). An optical isolator as claimed in Claim 1, further comprising a substrate (7) having a slot provided in the surf thereof in which a respective one of said optical elements is fixedly inserted. An optical isolator as claimed in Claim 1, wherein the plurality of magnets (4A, 4B) are fixed to the spacer (8) by means selected from the group consisting of welding, screws (9), or adhesive. An optical isolator as claimed in Claim 1, wherein the spacer (8) is made of a magnetic material. An optical isolator as claimed in Claim 1, wherein the optical isolator unit and the plurality of magnets (4A, 4B) are fixed to each other by means selected from the group consisting of welding, screws (14), or adhesive (17). An optical isolator as claimed in Claim 1, wherein the housing body (5) consists of a cylinder (11) or a cylinder (11) having collars (12) on both ends thereof. An optical isolator as claimed in Claim 1, wherein the housing body (5) is provided with a through hole (19A, 19B) and the plurality of magnets (4A, 4B) are fixed to the housing body by means selected from the group consisting of welding (18A, 18B), screws, or adhesive. An optical isolator as claimed in Claim 1, wherein the housing body (5) is made of metal and said fixing means for fixing said housing body to the spacer (8) is constituted by through-welding means.

Inventors: HIRAI SHIGERU, SASAKI TAKASHI, SEMURA SHIGERU, YUI DAI, HIRAI, SHIGERU, SASAKI, TAKASHI, SEMURA, SHIGERU, YUI, DAI, HIRAI, SHIGERU, C/O YOKOHAMA WORKS, Sasaki, Takashi, c/o Yokohama Works, Semura, Shigeru, c/o Yokohama Works, YUI, DAI, C/O YOKOHAMA WORKS
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LTD
Application year: 1995
Main classification: G02F1
IPC codes: G02B6, G02F1