JPH09325297A - Optical isolator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily assemble an optical isolator with high reliability in arranging an optical element with inclination to the optical axis, as for the optical isolator. SOLUTION: The optical isolator is provided with a polarizer 1, a Faraday rotator 2-1 and an analyzer 3-1 as optical elements. Among the optical elements, at least the optical element positioned on the incident side in a forward direction is arranged so as to be inclined to the optical axis of the forward transmitted light at a prescribed angle from a vertical position. And, each optical element is individually mounted on a holder which can be rotated in a plane vertical to the optical axis, and in each holder, recessed parts for storing and fixing the optical elements are formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical isolator mainly used in optical communication, and more particularly to an optical isolator having a structure in which reflected light does not return to the forward side.

[0002]

2. Description of the Related Art Generally, in an optical communication system, use of an optical fiber amplifier which directly amplifies an optical signal as it is without replacing the optical signal with an electric signal has been studied. The amplified light is obtained by transmitting the signal light to be amplified and the pumping light through the Er-doped optical fiber having a length. In such an optical fiber amplifier, the use of an optical isolator is indispensable because only the transmitted light in the forward direction is transmitted with low loss and the returned light in the reverse direction is blocked.

By the way, when the forward transmitted light of the optical isolator becomes the reflected light on the surface of each optical element, that is, the transmitted light is the incident side surface of the incident side polarizer and the emitting side surface which is the rear surface thereof, and then When reflected by the incident side surface of the Faraday rotator located at, and returned to the incident side as reflected light, this reflected light becomes the return light in the opposite direction, and this return light has a significant value compared to the isolation of the optical isolator. In that case, there is no point in using an optical isolator.

In general, the isolation of the optical isolator is 30 dB or more for the one-stage type and 60 dB or more for the two-stage type, and the intensity of the reflected light on each optical element surface must be sufficiently smaller than the isolation. However, generally, the amount of surface reflection of each optical element used in the optical isolator for communication is 0.
It is difficult to fall below 02%. This value (surface reflection amount) is about 27 dB, which is a value that can be a sufficient problem even if it is considered that the light actually returning to the incident side out of the reflected light on each optical element surface is a part of it. is there.

In order to prevent surface reflection in the optical isolator as described above, for example, Japanese Unexamined Patent Publication No. 62-11831.
The technique described in Japanese Patent Publication No. 5 is known. here,
Each optical element forming the optical isolator is installed at a predetermined angle from the vertical position with respect to the optical axis in the forward direction (see FIG. 6). That is, as shown in FIG. 6, the optical isolator includes a polarizer 41, a Faraday rotator 42, and an analyzer 43, and the polarizer 41, the Faraday rotator 42, and the analyzer 43 are respectively a holder 44 and a permanent member. The magnet 45 and the holder 46 are held by being tilted at a predetermined angle from the vertical position with respect to the optical axis in the forward direction (the polarizer 41 and the analyzer 43 and the Faraday rotator 42 have different tilt directions).

As described above, by installing each optical element at a predetermined angle from the vertical position with respect to the optical axis in the forward direction, the reflected light on the surface of the optical element of the transmitted light incident from the forward direction is It is reflected in a direction different from the axial direction.
Therefore, the returning light to the incident side can be reduced to such an extent that there is no practical problem.

[0007]

By the way, long-term reliability is especially required for optical isolators for optical communication.
Therefore, as for the assembly method, the most common method is to use metal bonding (welding, soldering, etc.), which is superior in terms of reliability, and organic bonding that is low in cost but inferior in reliability is not often used. Not not.

However, the conventional optical isolator structure has a problem that it is difficult to assemble it by metal bonding.
That is, at the time of metal bonding, a method of heating the bonding part to a considerably high temperature to melt the metal and then cooling it to fix the bonding part is taken. There is no choice but to use a structure in which molten metal is filled between the holder and the permanent magnet, and more molten metal is required.

When the amount of the molten metal used is increased in this way, the molten metal may inevitably flow out and cover the inner surfaces of the holder and the permanent magnet. In such a situation, a bonding jig, which must be installed adjacent to the bonding portion due to its structure, is fixed by the molten metal, or the optical element is displaced, resulting in defective products. The possibility increases.

As described above, the conventional optical isolator has a problem that it is difficult to assemble the optical element with high reliability when arranging the optical element at an angle with respect to the optical axis.

It is an object of the present invention to provide an optical isolator which can be easily assembled with high reliability when an optical element is arranged tilted with respect to the optical axis.

[0012]

According to the present invention, in a holder for holding an optical element that is installed at an angle from a plane perpendicular to the optical axis of forward-direction transmitted light, the optical element is a rectangle formed in the holder or An optical isolator is constructed as a structure that is installed in a hollow of a cylindrical shape or a combination thereof, and the bottom surface of this hollow is tilted from a plane perpendicular to the optical axis of forward transmitted light. By adopting a structure in which the optical element is tilted, the problem of defects occurring during manufacturing is improved.

According to the structure of the optical isolator according to the present invention, it is possible to avoid the problems that have been conventionally caused when metal-bonding the holder constituting the optical isolator and the optical element bonded and fixed thereto. That is, in the case of the optical isolator according to the present invention, the joint portion with the holder can be provided not at the side surface portion of the optical element but at the surface end portion thereof. In the case of joining at the surface end portion, unlike the case of the side surface portion, it is generally possible to make the thickness of the molten metal layer at the joint portion considerably thin. This is because the optical element can be pressed against the holder dent at the time of joining via a jig or the like.If both the bottom surface of the dent of the holder and the optical element are flat, the pressing force can be adjusted to adjust the molten metal. The layer thickness can be controlled quite freely.

Therefore, by appropriately setting the amount of molten metal to be initially applied and the pressing force, it is possible to prevent the molten metal from overflowing and to prevent defective joining. Furthermore, when pressing the optical element against the bottom surface of the recess of the holder, the joint and the jig will be located on the opposite sides of the optical element respectively, preventing molten metal from sticking to the jig. It is possible.

The depression of the above-mentioned holder must have a shape that is inclined with respect to the optical axis of the forward direction transmitted light.
The optical element installed there has a structure in which the bottom surface portion is in close contact.

When the permanent magnet is attached to the holder in which the optical element is installed, if the permanent magnet has, for example, a cylindrical shape, the inner wall of the permanent magnet has the optical element even if the holder has no recess. It will act as a mounting recess.

[0017]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described below with reference to the drawings.

Referring first to FIG. 1, the illustrated optical isolator includes a polarizer 1, a Faraday rotator 2-1, and an analyzer 3.
-1. The polarizer 1, the Faraday rotator 2-1, and the analyzer 3-1 are held by the holder 11, the holder 12-1, and the holder 13-1, respectively.
At this time, in FIG. 1, the polarizer 1 is supported by being tilted at a predetermined angle from the vertical position with respect to the optical axis 7 of the forward direction transmitted light.

As shown in the figure, the holder 11 has, for example, a cylindrical shape, the holder 11 is formed with a recess 11a having an inclined surface inclined from the vertical position with respect to the optical axis 7, and the polarizer 1 is recessed. It is fixed in contact with the inclined surface of 11a.
The holder 12-1 has a ring shape, and as shown in FIG. 1A, an annular flange portion 12a extending in the optical axis 7 direction.
The inner peripheral surface of the annular permanent magnet 8 is abutted and fixed to the outer peripheral surface of the flange portion 8, and the permanent magnet 8 forms a recess. The Faraday rotator 12-1 is arranged and fixed in the permanent magnet 8, and the Faraday rotator 12-1
One surface is in contact with the tip of the flange portion 12a. The holder 13-1 has a cylindrical shape and is formed with a recess 13a having a vertical surface on which the analyzer 3-1 is abutted and fixed.
The analyzer 3-1 is in contact with and fixed to the vertical surface of the recess 13a.

When assembling the optical isolator, the polarizer 11, the Faraday rotator 2-1, and the analyzer 3-1 are attached to the holder 11, the holder 12-1, and the holder 13-1, respectively, and then, as shown in FIG. As described above, the holder 11, the holder 12-1, and the holder 13-1 are combined and fixed.

Now, the polarizer 1 in which the transmitted light 21 from the forward direction is bonded to the holder 11 which constitutes the optical isolator
When the light is incident on the polarizer 1, since the polarizer 1 is inclined and installed, the reflected light 22 and the reflected light 23 on the front and rear surfaces of the polarizer 1 are reflected in a direction different from the optical axis 7 of the forward transmitted light, and are reflected. There is no returning light.

Since the Faraday rotator 2-1 joined to the holder 12-1 is arranged perpendicularly to the optical axis 7 of the forward transmitted light, the reflected light on both surfaces of the Faraday rotator 2-1. 24-1 and the reflected light 25-1 return to the same direction as the optical axis 7, that is, to the incident point of the transmitted light, and thus may be reflected return light.

However, due to the effect of the Faraday rotator, the plane of polarization of the reflected light 25-1 is rotated by 90 °, so that the polarizer 1 cannot be transmitted and the reflected light 25-1 can be returned. Will only be.

Further, since the analyzer 3-1 joined to the holder 13-1 is arranged perpendicularly to the optical axis 7 of the forward direction transmitted light, the reflected light on both surfaces of the analyzer 3-1 is reflected. 26-1 and reflected light 27-1 are reflected in the same direction as the optical axis 7, but these reflected light 26-1 and reflected light 27-1
Has a polarization plane of 90 ° due to the effect of the Faraday rotator.
Since it rotates, it cannot pass through the polarizer 1.

In the illustrated optical isolator, the reflected light 24-
Although only 1 becomes the return light, the amount of the reflected return light due to this return light is sufficiently smaller than the isolation of the optical isolator, so there is no practical problem.

Although the holder 12-1 has no recess for accommodating the optical element, as described above, the Faraday rotator 2-
1, a permanent magnet 8 is joined to it, and the inner wall of the permanent magnet 8 plays the role of a recess for accommodating the Faraday rotator 2-1. A metal film is formed in advance in a region other than the central light transmitting part on the periphery of the surface end of the Faraday rotator 2-1, and is bonded to the holder 12-1 by metal bonding such as soldering. The gap between the permanent magnet 8 and the permanent magnet 8 is not filled with the joining metal, and the Faraday rotator 2-1 is joined only at the surface end. It has become.

Next, referring to FIG. 2, in FIG. 2, the same components as those in FIG. 1 are designated by the same reference numerals. The holder 12-2 has an annular flange portion 12b.
The outer peripheral surface of the flange portion 12b is inclined with respect to the optical axis 7. Therefore, the permanent magnet 8 is attached to the outer peripheral surface.
When the inner peripheral surface of the above is abutted and fixed, the inner wall of the permanent magnet 8 plays a role of a recess for inclining and accommodating the Faraday rotator 2-2. The holder 13-2 has an analyzer 3-2.
Is formed so as to have an inclined surface on which the abutment is fixed, and the analyzer 3-2 is fixed on the inclined surface of the depression 13b.

Since the Faraday rotator 2-2 joined to the holder 12-2 is installed so as to be tilted with respect to the optical axis 7, the reflected light 24-2 and the reflected light 25- on both surfaces thereof.
Similarly to the case where the polarizer 2 is the polarizer 1, the reflected light is reflected in a direction different from the optical axis 7 and returns to a point different from the incident point of the transmitted light, so that it does not become reflected return light. However, as in the case of FIG.
Due to the effect of the Faraday rotator, the plane of polarization is rotated by 90 °, so that the reflected light 25-2 cannot pass through the polarizer 1. Also, the reflected light 26- on both surfaces of the analyzer 3-2
2 and the reflected light 27-2 are also reflected in a direction different from the optical axis 7.

As described above, in the optical isolator shown in FIG. 2, the reflected light 22 and the reflected light 2 on the front and rear surfaces of the polarizer 1 are shown.
Not only 3 but also the reflected light 24-2 on the front surface of the 2-2 Faraday rotator 2-2 is reflected in a direction different from the optical axis 7, and therefore, neither of them becomes reflected return light.

A metal film is formed in the peripheral portion of the surface end of the Faraday rotator 2-2 in a region other than the central light transmitting portion, and the holder 12 is formed by metal joining such as soldering.
-2, the gap with the permanent magnet 8 that functions as a guide is not filled with the joining metal, and the Faraday rotator 2-2 is joined only at the surface end. .

FIG. 3 shows an example of a two-stage optical isolator according to the present invention.

In FIG. 3, the optical isolator shown in FIG. 2 is used as the first-stage optical isolator section, and the optical isolator shown in FIG. 1 is used as the second-stage optical isolator section. In the optical isolator section of the first stage, the reflected light of the transmitted light 21 from the forward direction is reflected in the direction different from the optical axis 7 on both surfaces of each optical element, so that it does not become reflected return light.

On the other hand, when the transmitted light 21 from the forward direction is incident on the polarizer 4 joined to the second-stage holder 14, the polarizer 4 is installed so as to be inclined. The reflected light 28 and the reflected light 29 are reflected in a direction different from the optical axis 7 of the forward transmitted light, and do not become reflected return light.

By the way, since the Faraday rotator 5-3 joined to the holder 15-3 is perpendicular to the optical axis 7 of the forward direction transmitted light, the reflected light 30 on both surfaces of the Faraday rotator 5-3. -3 and the reflected light 31-3 return to the same direction as the optical axis, that is, to the incident point of the transmitted light, and may be reflected return light. However, since the plane of polarization of the reflected light 31-3 is rotated by 90 ° due to the effect of the Faraday rotator, it cannot actually pass through the polarizer 4,
Only the reflected light 30-3 can be returned.

In the optical isolator of FIG. 3, the reflected light 30-
Since the amount of reflected return light by 3 is sufficiently smaller than the isolation of the optical isolator, there is no practical problem. It should be noted that the holder 15-3 does not have a recess for accommodating the optical element.
The permanent magnet 9 is joined to the holder 15-3, and the inner wall of the permanent magnet 9 plays a role of a recess for accommodating the Faraday rotator 5-3. The Faraday rotator 5-3 has a metal film formed in advance on the peripheral portion of the surface end portion other than the central light transmitting portion, and the holder 15-is formed by metal joining such as soldering.
Although it is joined to the Faraday rotator 5-3, the gap between the permanent magnet 9 and the permanent magnet 9 that functions as a guide is not filled with the joining metal.

Another example of the two-stage optical isolator according to the present invention will be described with reference to FIG.

In the illustrated two-stage optical isolator, the optical isolator shown in FIG. 2 is used for both the first-stage optical isolator section and the second-stage optical isolator section. In the illustrated example, in the first-stage optical isolator unit, all the reflected light of the transmitted light 21 from the forward direction is reflected in a direction different from the optical axis 7 on both surfaces of each optical element. It never happens.

Since the Faraday rotator 5-4 joined to the holder 15-4 is installed so as to be inclined with respect to the optical axis 7 of the forward direction transmitted light, reflection on both surfaces of the Faraday rotator 5-4. The light 30-4 and the reflected light 31-4 are reflected in a direction different from the optical axis 7 as in the case of the polarizer 4, and are returned to a point different from the incident point of the transmitted light, so that they become reflected return light. There is no. However, as in the case of FIG. 3, since the plane of polarization is rotated by 90 ° due to the effect of the Faraday rotator, the reflected light 31-4 cannot pass through the polarizer 4.

As described above, in the optical isolator shown in FIG. 4, the reflected light 28 and the reflected light 2 on the front and rear surfaces of the polarizer 4 are shown.
Not only 9 but also the reflected light 30-4 on the front surface of the Faraday rotator 5-4 is reflected in a direction different from the optical axis 7 of the forward transmitted light, so that none of them becomes reflected return light. Note that the holder 15-4 does not have a recess for accommodating an optical element. The permanent magnet 9 is joined to the holder 15-4, and the inner wall of the permanent magnet 9 serves as a recess for accommodating the Faraday rotator 5-4. Faraday rotator 5-
A metal film is formed in advance in the area other than the central light transmitting portion in the peripheral portion of the surface end portion of 4 and is joined to the holder 15-4 by metal joining such as soldering, but the permanent magnet functions as a guide. The gap between the Faraday rotator 5-4 and the Faraday rotator 5-4 is joined only by the joining metal, and the gap is not filled with the joining metal.

With reference to FIG. 5A, when the optical element 35 has a quadrangular shape, the recess 34a formed in the holder 34 naturally matches the shape of the optical element 35. That is, the depression 34a has a quadrangular shape, and circular circular cutouts are provided at its four corners. This notch prevents the corners from becoming rounded when creating the dent (the rounded corners make the optical element that can be stored smaller than the shape of the dent), and the same element when storing the optical element. This is to secure a space for attaching / detaching a jig for grasping.

Referring to FIG. 5B, when the optical element 37 has a disc shape, the recess 36a of the holder 36 has a circular shape. At this time, circular cutouts are provided at four portions of the recess 36a. This notch is used to secure an attachment / detachment space for a jig that holds the optical element when the optical element is stored.

In the optical isolator shown in FIGS. 1 and 2, the analyzer 3 metal-bonded to the holder 13 is used.
Due to the effect of the Faraday rotator, each reflected light on both surfaces of the polarization plane of the reflected light is 90 ° with respect to the transmitted light 21 from the forward direction.
Since it is rotating, it cannot pass through the polarizer 1,
It does not become a reflected return light. Therefore, it is not necessary to install the analyzer 3 inclining with respect to the vertical plane of the optical axis 7 of the forward transmitted light, but from the viewpoint of preventing the reflected return light from being reflected back to the emission side and the holder 11 and the holder. Due to the design of the optical isolator and the like, it is desirable to install the same with the analyzer 3 and the polarizer 1 in a tilted manner.

On the other hand, the same can be said for each optical element in the second stage in the case of the two-stage optical isolator. That is, as in the case of the single-stage optical isolator, it is desired to share the parts of the holder 11, the holder 13, and the holder 14 and the holder 16 in order to prevent the reflected return light from being reflected to the emission side again. For reasons of design of the optical isolator, etc., it is actually desirable to install the analyzer 6 with the same inclination as the polarizer 4.

[0044]

As described above, according to the present invention, in an optical isolator used as a component device in an optical amplifier or the like, it is possible to prevent reflected light from an optical element of transmitted light from the forward direction from becoming reflected return light. Therefore, the isolation of the optical isolator can be improved.

Further, according to the present invention, since each optical element is bonded to the recess provided in each holder at the surface end thereof, the behavior of the bonding material such as the bonding metal cannot be sufficiently controlled when the optical isolator is assembled. Therefore, it is possible to prevent a defect that a defect occurs.

[Brief description of drawings]

FIG. 1 is a diagram showing a first example of an optical isolator according to the present invention, in which (a) is a sectional view and (b) is a perspective view.

2A and 2B are diagrams showing a second example of the optical isolator according to the present invention, wherein FIG. 2A is a sectional view and FIG. 2B is a perspective view.

3A and 3B are diagrams showing a third example of the optical isolator according to the present invention, in which FIG. 3A is a sectional view and FIG. 3B is a perspective view.

4A and 4B are diagrams showing a fourth example of the optical isolator according to the present invention, in which FIG. 4A is a sectional view and FIG. 4B is a perspective view.

FIG. 5 is a view for explaining the shape of a recess when fixing the optical element to the holder in FIGS. 1 to 4;
(A) is a figure which shows a square-shaped hollow, (b) is a figure which shows a circular recess.

FIG. 6 is a sectional view showing a configuration of a conventional optical isolator.

[Description of Reference Signs] 1,4,41 Polarizers 2-1, 2-2,2-3,2-4,5-3,5-4,4
2 Faraday rotators 3-1, 3-2, 3-3, 3-4, 6-3, 6-4, 4
3 Analyzer 7,47 Optical axis of forward direction transmitted light 8,9,45 Permanent magnet 11, 12-1 to 12-4, 13-1 to 13-4,
14-3, 14-4, 15-3, 15-4, 16-3,
16-4, 44, 46 Holder 21 Transmitted light from forward direction 22, 23 24-1 to 24-4, 25-1 to 25
-4, 26-1 to 26-4, 27-1 to 27-4,
28, 29, 30-3, 30-4, 31-3, 31-
4,32-3,, 32-4,33-3,33-4 Reflected light

Claims (8)

[Claims] 1. An optical isolator comprising a polarizer, a Faraday rotator, and an analyzer as optical elements, wherein the polarizer, the Faraday rotator, and the analyzer are arranged in this order, and at least one of the optical elements is provided. The optical element located on the incident side in the forward direction is arranged so as to be inclined at a predetermined angle from the vertical position with respect to the optical axis of the forward transmitted light, and each of the optical elements rotates in a plane perpendicular to the optical axis. An optical isolator, characterized in that the optical isolator is attached to each possible holder, and each of the holders has a recess for accommodating and fixing the optical element. 2. The optical isolator according to claim 1, wherein each of the optical elements is inserted and fixed in a recess of the holder, and the holders are bonded and integrated with each other. Isolators. 3. The optical isolator according to claim 1 or 2, wherein the holder to which the Faraday rotator is fixed is provided with a permanent magnet. 4. The optical isolator according to claim 3, wherein the permanent magnet has a hollow portion, and the hollow portion forms the recess. 5. A first polarizer, a first Faraday rotator, and a first analyzer are provided as a first optical element, and the first polarizer, the first Faraday rotator, and A first optical isolator portion arranged in the order of the first analyzer, and a second optical isolator portion located at a stage subsequent to the first optical isolator portion.
Of the second polarizer, the second Faraday rotator, and the second analyzer as a second optical element, and the second polarizer, the second Faraday rotator, and the second analyzer In an optical isolator having a second optical isolator section arranged in order, each of the first optical elements of the first optical isolator section is tilted at a predetermined angle from a vertical position with respect to the optical axis of forward transmitted light. The second optical element of the second optical element of the second optical isolator, which is located at least on the forward incident side, is inclined by a predetermined angle from the vertical position with respect to the optical axis of the forward transmitted light. And each of the first and second optical elements is attached to a respective first and second holder that is rotatable in a plane perpendicular to the optical axis. Each of the holders has a first optical A first recess for accommodating and fixing the child is formed, and a second recess for accommodating and fixing the second optical element is formed in each of the second holders. Optical isolator. 6. The optical isolator according to claim 5, wherein each of the first and second optical elements is inserted and fixed in the first and second recesses, and the first and second optical elements are inserted and fixed. An optical isolator in which two holders are bonded and integrated with each other. 7. The optical isolator according to claim 5 or 6, wherein the first and second holders, to which the first and second Faraday rotators are fixed, respectively have a first and a second, respectively. An optical isolator comprising the permanent magnet of 8. The optical isolator according to claim 7, wherein the first and second permanent magnets each have a hollow portion, and the hollow portion forms the first and second recessed portions. An optical isolator characterized by the above.