JP2881441B2 - Optical isolator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to an optical isolator applied to an optical communication system.

(Prior Art) A configuration as shown in FIG. 7 is known as an example of an optical communication system. 1 is a laser light source, 2 is an optical isolator, 3 is a lens, 4 is an optical fiber, and the light oscillated by the laser light source 1 is incident on the lens 3 via the optical isolator 2 and condensed here. 4 and transmitted to a desired communication destination.

In such an optical communication system, if the transmitted laser light is reflected from the outside and returned for some reason and is incident on the laser light source 1, the oscillation of the laser light source 1 becomes unstable, which hinders communication. Come to come. For this reason, the optical isolator 2 is used to prevent the reflected light from entering the laser light source 1 and perform safe laser oscillation.

FIG. 8 shows the structure of a first example of a conventional optical isolator disclosed in Japanese Patent Application Laid-Open No. Sho 62-118315, wherein 5 is a first polarizer comprising a prism, and 6 is a second polarizer comprising a prism. , A Faraday rotator disposed therebetween, 8 a polarizer holder for the first polarizer 5, 9 a polarizer holder for the second polarizer 6, and 10 a permanent magnet. According to this structure, when light is incident on the first polarizer 5 from the laser light source in the forward direction, the incident light passes only a light component having a constant polarization plane with respect to the optical axis L indicated by the broken line. . Similarly, when the reflected light is incident on the second polarizer 6 in the opposite direction, only the polarized light component is transmitted. These two polarization components are rotated by 45 degrees in the direction of the polarization plane by the Faraday rotator 7. Since this rotation direction is irreversible with respect to the traveling direction of the light, the light exits the Faraday rotator 7 in the forward and reverse directions. Also, the polarization planes of the same polarization component will differ by 90 °. Therefore, the light from the opposite directions in the first and second polarizers 5 and 6 does not return to the incident light direction but is scattered by the polarizer in the direction perpendicular to the optical axis. As a result, only the polarized light component in the forward direction is focused on the optical fiber, and in the reverse direction, both polarized light components do not return to the incident light direction, so that the influence of the reflected light can be prevented.

FIG. 9 shows a structure of a second example of a conventional optical isolator, which is also shown in Japanese Patent Application Laid-Open No. Sho 62-118315, in which a first polarizer is arranged with respect to a vertical plane of an optical axis L indicated by a broken line. 5, second
Of the respective elements of the polarizer 6 and the Faraday rotator 7 of FIG.

FIG. 10 shows a structure of a third example of a conventional optical isolator disclosed in Japanese Utility Model Laid-Open No. 55-137118, in which a Faraday rotator 7, a first polarizer 5 and a second polarizer 6 are shown. Are fixed by optical adhesive layers 11 and 12. 1
Reference numerals 3 and 14 are antireflection films.

(Problems to be Solved by the Invention) The conventional optical isolators have the following problems, respectively.

First, in the first structure shown in FIG.
Since the end faces of the respective elements of the polarizers 5, 6 and the Faraday rotator 7 are all parallel to each other and perpendicular to the optical axis L, the reflected light goes back at the end faces. It cannot be prevented enough.

Next, in the second structure shown in FIG. 9, the above-mentioned disadvantage is solved, but the end faces of the first and second polarizers 5, 6 and the Faraday rotator 7 are inclined with respect to the vertical plane of the optical axis L. Since the assembling is performed in the assembled state, the assembling work becomes complicated.

Next, since the optical bonding layers 11 and 12 are used in the third structure of FIG. 10, the bonding surface is likely to shift when the ambient temperature condition changes. For this reason, a shift occurs in the optical axis, and the amount of light incident on the optical fiber varies.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide an optical isolator that can solve each conventional problem.

[Constitution of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention provides a first polarizer, a second polarizer, a Faraday rotator disposed therebetween, and a stainless steel. In an optical isolator in which a sleeve made of stainless steel and a holder made of stainless steel are integrally fixed, each of the elements is arranged so as to be oblique with respect to a perpendicular to an optical axis of light entering and exiting each of the elements. The light input and output surfaces of all are parallel, the outer peripheral surface of the sleeve is asymmetrical with respect to the perpendicular of the light input and output surface of each element, and each element, the sleeve and the holder,
In addition to being integrally fixed by welding and / or brazing, each element is fixed to the sleeve via a holder fixed to the sleeve by welding.

(Operation) Since each element is obliquely fixed via the sleeve and the holder so that each end face is obliquely arranged with respect to the optical axis, backward movement of reflected light can be prevented. Further, since each element is fixed by welding a sleeve and a holder made of the same material (stainless steel), the optical axis does not shift even when ambient temperature conditions change.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing an embodiment of an optical isolator according to the present invention, in which a first polarizer 5 and a second polarizer 6 are made of, for example, a rutile polarizing prism, and a first and a second polarizer holder, respectively.
8 and 9 are brazed by, for example, solder 17. The first and second polarizer holders 8, 9 are made of, for example, stainless steel and have hollow portions 8a, 9a, respectively. The hollow portion 9a of the second polarizer holder 9 has a step formed on the inner surface thereof. The Faraday rotator 7 is disposed so as to be in contact with the portion 9b, and the Faraday rotator 7 is pressed by the pressing plate 16 to the back of the step portion 9b. Also, the holding plate 16 is formed by, for example,
Is fixed to the inner surface of the polarizer holder 9. As the Faraday rotator 7, for example, a GGG (gadolinium gallium garnet: Gd ₃ Ga ₅ O ₁₂₎ substrate having a high lattice constant and a liquid phase epitaxial thick film (LPE thick film) formed thereon is used.

The oblique sleeve 15 is made of, for example, stainless steel similarly to the first and second polarizer holders 8 and 9, and has a hollow portion 15c having an inner surface 15b inclined with respect to the surface 15a. Is inclined with respect to the optical axis L, and an angle θ °, for example, about 8 ° exists between both axes. On the inner surface 15b of the oblique sleeve 15, a first polarizer holder 8 and a second polarizer 6 to which the first polarizer 5 is brazed are brazed, and a Faraday rotator 7 is attached. The second polarizer holder 9 is fixed by, for example, welding. Further, a permanent magnet 10 is attached between the step 9c formed on the surface of the second polarizer holder 9 and the first polarizer holder 8 so as to be in contact with the inner surface 15b of the oblique sleeve 15. In the figure, the fixing position by welding is indicated by a black circle. It should be noted that, in each of the components used above, a surface for processing the slope, except for the inner surface 15b of the slanted sleeve 15, is considered to be unnecessary.

By attaching the first and second polarizers 5, 6 and the Faraday rotator 7 to the oblique sleeve 15 along the central axis C via the first and second polarizer holders 8, 9 in this manner, The end faces of these elements 5, 6, and 7 are also arranged obliquely at an angle θ ° with respect to the optical axis L.

Next, a method of assembling the optical isolator according to the present embodiment will be described. FIG. 2 shows an arrangement diagram of each component before assembling the optical isolator.
5, a permanent magnet 10, a first polarizer holder 8 to which a first polarizer 5 is brazed, a second polarizer holder 9 to which a second polarizer 6 is brazed, and a second polarizer holder Faraday rotator 7 and holding plate 16 to be arranged in step 9b in hollow 9a of 9
Is prepared. First polarizer 5 is connected to first polarizer holder 8
In brazing, a metallized layer 18 is formed in advance on the brazed surface of the first polarizer 5 as shown in FIG. 3 and then brazed to the metallized layer 18 with solder 17. Will be The same applies to the case where the second polarizer 6 is brazed to the second polarizer holder 9. In attaching the Faraday rotator 7 to the second polarizer 9, the fifth
As shown in the figure, in a state where the Faraday rotator 7 is pressed by the pressing plate 16 behind the step 9b in the hollow portion 9a of the second polarizer holder 9, the pressing plate 16 is Installation is performed by welding and fixing to the inner surface as shown by the mark ●.

First, as shown in FIG.
The permanent magnet 10 is inserted into 15c so as to be in contact with the inner surface 15b. Next, as shown in FIG. 6B, the second polarizer 6 is brazed to the hollow portion 15c of the oblique sleeve 15 from the right side in the drawing as shown in FIG. Then, the second polarizer holder 9 to which is attached is inserted so that the step 9c is in contact with the permanent magnet 10. Subsequently, as shown in FIG. 6 (c), the first polarizer holder to which the first polarizer 5 is brazed as shown in FIG. 3 from the left side of the hollow portion 15C of the oblique sleeve 15 as shown in FIG. 8 is inserted into contact with the permanent magnet 10. Subsequently, the optical isolator having the structure shown in FIG. 1 is assembled by welding the contact surfaces between the first polarizer holder 8 and the second polarizer holder 9 and the inner surface 15C of the oblique sleeve 15 as indicated by a black circle. .

 Next, the operation of the embodiment will be described.

In the optical isolator shown in FIG. 1, for example, when light is incident on the first polarizer 5 from the laser light source along the optical axis L in a forward direction from the left, the incident light is constant with respect to the optical axis L. Only light components having a plane of polarization are transmitted. Similarly, when the reflected light is incident on the second polarizer 6 in the opposite direction, only the polarized light component is transmitted. Both of these polarization components are rotated by 45 ° in the direction of the polarization plane by the Faraday rotator 7, and this rotation direction is irreversible with respect to the traveling direction of the light. Therefore, the light exits the Faraday rotator 7 in the forward and reverse directions. The polarization planes of the same polarization component are different by 90 °. Therefore, the light from the opposite directions in the first and second polarizers 5 and 6 does not return to the incident light direction but is scattered in a direction inclined with respect to the optical axis L. Therefore, only the polarized light component in the forward direction is emitted and enters the optical fiber, and in the reverse direction, neither polarized light returns to the incident light direction.

In such an optical isolator of the present embodiment, the first
Each element of the second polarizers 5, 6 and the Faraday rotator 7 is fixed to the inner surface 15b of the oblique sleeve 15 via the polarizer holders 8, 9, so that each end face is inclined by θ ° from the optical axis L. Since they are arranged, it is possible to sufficiently prevent the reflected light from going backward as in the conventional structure shown in FIG. Further, it is unnecessary to assemble the first and second polarizers 5, 6 and the Faraday rotator 7 with the end faces inclined with respect to the optical axis L as in the conventional structure shown in FIG. Element is polarizer holder 8, 9
Each end face is arranged obliquely with respect to the optical axis L by fixing to the inner surface 15b of the slanted sleeve 15 through the slanted sleeve. it can. As a result, an increase in cost can be avoided, and a strong and safe structure can be obtained and the size can be reduced. Further, each element is placed in the oblique sleeve 15 by welding the polarizer holders 8 and 9 made of the same material and the oblique sleeve 15 without using the optical adhesive layers 11 and 12 as in the conventional structure of FIG. Since it is fixed, the optical axis does not deviate even when the ambient temperature condition changes. Therefore, it is possible to eliminate variations in the amount of light incident on the optical fiber.

In this embodiment, the first and second polarizers 5, 6 are fixed to the respective polarizer holders 8, 9 by brazing. However, as shown in FIG. Can also. That is, a U-shaped pressing plate 16 'is used and, for example, the first polarizer 5 is pressed against the first polarizer holder 8 by the pressing plate 16' and welded as indicated by a black circle.

Examples of the materials of the first and second polarizers 5, 6 and the Faraday rotator 7 have been described by way of example. However, the present invention is not limited thereto, and any material can be selected as long as the material is used for this purpose. Further, the assembling method of FIGS. 6A to 6C is an example, and the order of inserting the components can be changed as appropriate.

[Effects of the Invention] According to the present invention as described above, since the light entrance / exit surface of each element is arranged so as to be oblique with respect to the perpendicular to the incident optical axis, it is possible to sufficiently prevent the backward movement of the reflected light. In addition to the conventionally known effects, each element is fixed to the sleeve via the holder fixed to the sleeve using the holder and the sleeve made of the same material system of stainless steel, so that the fixing between the sleeve and the holder is performed. The thermal stress due to the temperature change applied to the part can be minimized, and since the fixing part is welded, the strength of the fixing part is much higher than that of the solder. Therefore, by using a combination of "using a sleeve and a holder made of the same material" and "fixing the sleeve and the holder by welding", it is possible to efficiently prevent the occurrence of optical axis deviation due to a change in ambient temperature. it can.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of an optical isolator according to the present invention, FIG. 2 is a layout diagram of components used for assembling the present embodiment, and FIGS. 3 and 4 are polarized lights used in the present embodiment. FIG. 5 is a cross-sectional view showing an example of fixing a polarizer to a polarizer holder, FIG. 5 is a cross-sectional view showing an example of mounting a Faraday rotator used in this embodiment on a polarizer holder, and FIGS. 6 (a) to (c). FIG. 7 is a sectional view showing an example of assembly of the present embodiment, FIG. 7 is a block diagram showing an example of an optical communication system, and FIGS. 8 to 10 are sectional views showing examples of a conventional optical isolator. 5 ... first polarizer, 6 ... second polarizer, 7 ... Faraday rotator, 8 ... first polarizer holder, 9 ... second
Polarizer holder, 10 permanent magnet, 15 oblique sleeve, L optical axis, C central axis of oblique sleeve.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02B 27/28 G02B 7/00

Claims (1)

(57) [Claims] 1. An optical isolator in which a first polarizer, a second polarizer, a Faraday rotator, a sleeve made of stainless steel, and a holder made of stainless steel, which are arranged therebetween, are integrally fixed. The respective elements are arranged such that the light incident / emitted surfaces of the respective elements are oblique to the perpendicular to the incident optical axis, and the light incident / emitted surfaces of the respective elements are all parallel, and the outer peripheral surface of the sleeve. Is asymmetric with respect to the perpendicular of the light entrance / exit surface of each element, and each element, the sleeve and the holder are integrally fixed by welding and / or brazing, and each element is An optical isolator fixed to the sleeve via a holder welded to the sleeve.