JP2003090984A - Embedded optical isolator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily manufacture an optical fiber with high accuracy. SOLUTION: An optical isolator is produced by inserting and adhering an optical fiber into the through hole of an outer supporting body, forming a groove crossing the optical fiber in the supporting body; preparing a composite body of an optical element composed of a polarizer and a Faraday rotator with a reinforcing member which surrounds the above optical element and fills the groove into the thickness to allow the composite body to fit in the groove, and then fitting and adhering the composite body in the groove. The reinforcing member is made of the same material as the outer supporting body or made of a permanent magnet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical isolator used in optical communication and optical measurement.

[0002]

2. Description of the Related Art It is known that a semiconductor laser used as a light source of various optical systems has unstable oscillation due to reflected return light from an optical system coupled thereto.
Isolators are used to prevent this. With the rapid expansion of optical communication systems in recent years, there is an increasing demand for miniaturization and cost reduction of isolators. The structure of a conventional basic isolator is shown in FIG. Polarizers 10a and 10b are arranged on both sides of the Faraday rotator 11, and a magnet 12 for magnetizing the Faraday rotator is arranged around the Faraday rotator 11, and two condenser lenses 9a are provided between the optical fibers 8a and 8b. , 9b are required. With this configuration,
Light incident in the forward direction (direction of arrow C in the figure) is transmitted and light entering in the reverse direction (direction of arrow D in the figure) is blocked, so that the function as an isolator can be realized. It requires many optical elements and the overall configuration is large.

On the other hand, a method using a simple method instead of such a complicated method is described in JP-A-3-63606 and JP-A-4-307512. This method is called "embedded type", and is manufactured by fixing a groove on a substrate with a resin or the like and embedding the optical fiber with a dicing saw, and then embedding and fixing the element. According to this, there is an advantage that the optical axis alignment is not required for manufacturing the optical isolator and the manufacturing is significantly facilitated. However, on the other hand, when the light output from the optical fiber passes through the element portion, diffraction occurs, which causes a problem that the thickness of the element becomes a neck and the insertion loss increases. On the other hand, a method such as enlarging the core of the optical fiber by local heating to reduce the diffractive power is taken.

[0004]

In order to realize the optical isolator described in the above patent publication, a capillary ferrule as a support of the optical fiber is provided with a predetermined TEC optical fiber having an optical fiber core enlarged by local heating. Insert and bond in position. After that, perform PC polishing on both end faces of the capillary and embed the optical isolator element consisting of the Faraday rotator and the polarizer adhered to both sides of the capillary. Apply to the ferrule. The optical isolator element to be inserted into the grooved portion needs to have a size equal to or larger than the mode field diameter emitted from the optical fiber, but the mode field diameter passing through this groove portion is several tens of μm.
Therefore, the device size may be about 100 μm or more. However, it is preferable that the size is as small as possible in order to reduce the cost by taking a large number of optical elements.

When a small optical element is inserted into and bonded to the grooved surface, a large space is opened in the groove portion, so that the inside of the groove where there is no element is covered with the adhesive. Therefore, there is a problem that deterioration such as peeling of the adhesive is likely to occur due to curing shrinkage distortion of the adhesive, external thermal shock, or the like from a place where the adhesive is present in a large amount. Further, it is difficult to dispose and bond the minute element to an appropriate portion of the grooved portion. Therefore, an object of the present invention is to provide a highly reliable optical isolator with excellent workability.

[0006]

SUMMARY OF THE INVENTION According to the present invention, a polarizer is formed by inserting a fiber into a through hole of an external support and then forming a groove so that a polarization direction is 45 ° on both sides of a Faraday rotator in advance. By inserting into the groove, a composite of an optical element (optical isolator element) in which the elements are arranged and fixed and a structural reinforcing member (reinforcing member) that surrounds the element and has a thickness that fills the groove is provided, thereby reducing the size and reliability. High optical isolator. Here, the reinforcing member is made of a member having the same material as that of the external support, or is composed of a magnet for applying a predetermined magnetic field to the Faraday rotator.

[0007]

The optical isolator according to the present invention requires only a very small amount of adhesive to fix the optical element inserted in the groove of the external support member in the groove, so that the curing shrinkage distortion of the adhesive, external thermal shock, etc. Since the adhesive is not peeled off due to deterioration, it is possible to provide a stable optical isolator. Further, since the optical isolator of the present invention is inserted into the groove of the external support as a composite in which the reinforcing member is fixed in advance around the optical element consisting of the polarizer and the Faraday rotator, the fiber, the polarizer and the Faraday rotator are Positioning during assembly is greatly simplified because no precise position adjustment is required. Further, according to the configuration of the present invention, since the distance between the optical fibers is short, a condenser lens is not required, and the size of the optical isolator becomes small. In addition, by adjusting and bonding with a large polarizer and Faraday rotator beforehand,
Since many elements can be cut out from it and used, mass productivity is also excellent. Furthermore, since the area through which light passes is extremely small, the required size of the polarizer and Faraday rotator is also small, and by embedding it inside the groove together with the surrounding inorganic material, a highly reliable and extremely compact optical isolator is realized. it can.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment) An optical isolator according to the present invention will be described with reference to the drawings. 1 and 2 are a top view and a cross-sectional configuration diagram of one embodiment of the present invention, respectively. A ferrule made of zirconia, crystallized glass, or the like can be used as the external support 5 having the through hole 6. After inserting one optical fiber 4 into the through hole 6 and adhering it, a groove 7 is formed in the external support 5 so as to cross the optical fiber 4. This groove can be easily formed with a dicing saw or a slicer. At this time, the reflected return light can be reduced by forming a groove at a predetermined angle with respect to the optical axis of the optical fiber 4 as shown in FIG.
By forming the groove 7, the optical fiber is divided into 4a and 4b. In addition, if the mode field diameter is expanded in advance by heat treatment or the like to the divided portion of the optical fiber, the coupling efficiency of the optical fiber is improved and the loss can be reduced.

An optical isolator element is inserted in the groove 7,
It is glued and fixed. The optical isolator element is composed of a Faraday rotator 1 and polarizers 2a and 2b adhered to both surfaces thereof. For the Faraday rotator 1, YIG, Bi-substituted rare earth garnet, or the like is used, and the thickness is adjusted so that a rotation angle of 45 ° can be obtained by applying a magnetic field. The polarizers 2a and 2b are adjusted so that the transmission polarization directions thereof form an angle of 45 °, and are bonded to both surfaces of the Faraday rotator 1 with an optical adhesive. Since the mode field diameter of light when passing through the groove 7 is about several tens of μm,
The size of the optical element including the Faraday rotator 1 and the polarizers 2a and 2b is about several hundreds of μm, and a large number of optical elements can be produced by cutting out the optical element to a required size using a dicing saw or the like. .

The width of the groove 7 is the Faraday rotator 1 and the polarizer 2.
It is formed to be slightly larger than the thickness of the optical element so that the optical element composed of a and 2b is closely fitted. Therefore, the cut-out optical element is placed on the optical axis without any precise position adjustment by simply inserting it near the center of the groove 7, and by pouring an optical adhesive around the optical element, the position is cut. Fixed to. Since the optical element is smaller than the size of the groove cross-section, as shown in FIG. (Although it may be a magnet as described in 1.), the embedding work is simplified and the deformation of the groove portion is suppressed, so that the reliability is improved.

On the Faraday rotator 1, a cylindrical magnet 3 having a strength sufficient to obtain a rotation angle of 45 ° and capable of applying a magnetic field in the same direction as the optical axis is arranged on the Faraday rotator. The magnet 3 does not necessarily have to be cylindrical, and may be used as the reinforcing member 8 in FIG. 3 to have a shape surrounding the optical element. In this case, as shown in FIGS. 4 and 5, since the magnet 3 is also embedded in the groove 7, it is possible to realize a smaller optical isolator with high reliability without adjustment.

The operation of the optical isolator constructed as above will be described below. Light entering the optical fiber 4a in the forward direction (the direction of the arrow A in the figure) absorbs a polarization component in one direction by the polarizer 2a, and has only the same polarization direction as the transmission polarization direction of the polarizer 2a. Become light. Since this polarization direction is rotated by 45 ° by passing through the Faraday rotator, the polarization direction of light after passing through the Faraday rotator 1
The transmission polarization directions of the polarizer 2b are the same, and the incident light can be transmitted as it is. On the other hand, the light incident from the optical fiber 4b in the opposite direction (the direction of the arrow B in the figure) is reflected by the polarizer 2
The polarized light component in one direction is absorbed by b, and becomes light in the same polarized direction as the transmitted polarized direction of the polarizer 2b. This polarization direction is rotated by 45 ° by passing through the Faraday rotator, but since the rotation direction by the Faraday rotator is the same regardless of the traveling direction of light, the polarization of the light after passing through the Faraday rotator 1 is The wave direction and the transmission polarization direction of the polarizer 2a are orthogonal to each other by 90 °. Therefore, light in the opposite direction is absorbed and does not return to the optical fiber 4a.

(Prototype Example) An optical isolator was prototyped according to the above-described embodiment. A crystallized glass ferrule with a diameter of 1.25 mm was used as the external support 5, and the optical fiber 4 was inserted into the through hole 6 and bonded. In this optical fiber, the mode field diameter at the groove forming portion was 40 μm. After that, a groove 7 having a width of 410 μm was formed in the center of the ferrule 5 with a precision slicer at an angle of 1.75 ° with respect to the direction perpendicular to the optical axis. In addition, the Faraday rotator 1 uses a Bi-substituted rare earth garnet having a thickness of 250 μm, which has a rotation angle of 45 ° at a wavelength of 1.31 μm, and has polychromatic polarizers 2a and 2b on both sides thereof, and transmission polarization directions are mutually different. An optical element was manufactured by adjusting so as to form an angle of 45 ° and adhering it with an optical adhesive. 0.3mm × this element
A large number of slices each having a size of 0.3 mm were taken and fitted into a square notch of the magnet 3 (having the shape of the reinforcing member 8 in FIG. 3) having the same thickness as the obtained optical element. A composite of an optical element and a magnet was formed by bonding and bonding. The composite was inserted and bonded into the groove 7 so that the optical element was aligned with the optical fiber to obtain an optical isolator. When the optical characteristics were measured, an insertion loss of 0.6 dB and an isolation of 28 dB were obtained. The magnet was completely embedded in the groove, resulting in a very compact and highly reliable optical isolator. As can be seen from the examples and prototypes, the present invention does not use a condenser lens. This is because the end of the optical fiber is in direct contact with both surfaces of the optical isolator element and the thickness of the optical isolator element is sufficiently thin.

Alternatively, instead of the magnet, the reinforcing member may be made of the same crystalline glass as the ferrule, and the optical element may be fitted into the square notch as shown in FIG. 3 and fixed with an adhesive. In this case, the magnets are arranged on the outer peripheral portions of the optical element and the reinforcing member as in the conventional case.

[0015]

According to the structure of the present invention, not only the condenser lens is not required, but also the fine adjustment of the positions of the optical fiber, the polarizer and the Faraday rotator is unnecessary. To be simplified. Also, adjust in advance using a large polarizer and Faraday rotator,
By adhering, a large number of devices can be cut out from the device and used, so that mass productivity is also excellent. further,
Since the region through which light passes is extremely small, the required size of the polarizer and the Faraday rotator is also small, and by embedding the inside of the groove together with the surrounding inorganic material, a highly reliable and extremely small optical isolator can be realized.

[Brief description of drawings]

FIG. 1 is a top view of an embodiment of the present invention.

FIG. 2 is a cross-sectional configuration diagram of an embodiment of the present invention.

FIG. 3 is a structural example of an optical element section.

FIG. 4 is a top view showing a structure in which a magnet is embedded.

FIG. 5 is a cross-sectional configuration diagram when a magnet is embedded.

FIG. 6 is a configuration diagram of a conventional optical isolator.

[Explanation of symbols]

1, 11 Faraday rotator 2a, 2b, 10a, 10b Polarizer 3, 12 magnets 4a, 4b, 13a, 13b optical fiber 5 External support 6 through holes 7 groove 8 Reinforcement member 9a, 9b lens

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[Procedure amendment]

[Submission date] September 6, 2002 (2002.9.6)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction content]

[0006]

According to the present invention, an optical fiber is provided in a through hole.
Insert the fiber into the bonded ferrule to attach the optical fiber.
Form a groove in the ferrule transversely,
Surrounding the optical element consisting of a Laday rotator and the optical element
Fitting a composite with a reinforcing member filling the groove into the groove
Make sure that the one formed to the thickness is fitted and bonded in the groove.
The characteristic optical isolator or the reinforcing member is
Optical isolator characterized by the same material as the rule
And an optical eye characterized in that the reinforcing member is a magnet.
Regarding Solator.

Claims (3)

[Claims] 1. An optical element comprising a polarizer and a Faraday rotator, in which a groove is formed in an outer support body in which an optical fiber is inserted and bonded in a through hole of the outer support body, the groove being formed across the optical fiber. An optical isolator, wherein a composite of a reinforcing member that surrounds the optical element and fills the groove is formed in a thickness that fits in the groove, and is fitted and bonded in the groove. 2. The optical isolator according to claim 1, wherein the reinforcing member is made of the same material as the external support. 3. The optical isolator according to claim 1, wherein the reinforcing member is a magnet.