JP2002082309A - Optical isolator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact optical isolator having high productivity. SOLUTION: In the optical isolator provided with a 1st polarizer, a Faraday rotator, a 2nd polarizer, ad a permanent magnet arranged at the outside of the Faraday rotator, the permanent magnet has a cylindrical outer shape and a polygonal through-hole and the isolator has a display, such that the direction of the major diameter or minor diameter of an optical beam having an elliptical or an oblong cross-sectional shape can be detected easily from its appearance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical component used in an optical communication system or an optical measuring instrument, and more particularly to an optical isolator that transmits light in one direction with low loss and blocks light in the opposite direction.

[0002]

2. Description of the Related Art In an optical communication system, an optical fiber amplifier for directly amplifying an optical signal without replacing the optical signal with an electric signal, or transmitting optical signals of a plurality of wavelengths through one optical fiber. Technologies such as wavelength division multiplexing optical communication have been put to practical use. In this case, many optical isolators that transmit signal light in the forward direction and block return light in the reverse direction are used in various optical modules constituting an optical communication system.

In an optical communication system, various optical modules that perform a series of processes such as branching, amplification, and multiplexing on an optical signal are used in combination. Each optical module includes various optical devices such as an optical connector, a lens, an optical isolator, and an optical switch. Among them, the optical isolator is an optical device including an optical element such as a polarizer, a Faraday rotator, and an analyzer and a permanent magnet which is a means for applying a magnetic field to the Faraday rotator. A conventional example is shown in FIG.

FIG. 4A is a cross section perpendicular to the central axis of the optical isolator, and the cross section is shown in FIG.
FIG. 4B is a cross-sectional view having a cross-section including the central axis of the optical isolator.

[0005] A Faraday rotator 42 having a square cross section is disposed inside a cylindrical permanent magnet 41 having a round hole, and a first polarizer 43a and a second polarizer 43b are provided before and after the Faraday rotator 42b. Provided. Further, a holder 44 for fixing those elements is used. Such a form was common in the conventional example.

[0006]

The optical isolator for optical communication shown as a conventional example has a configuration in which a permanent magnet is arranged around a Faraday rotator. This is a general shape of an optical isolator, but in this configuration, in order to satisfy both of the two requirements of downsizing the optical isolator and securing a transmitted light area, it is necessary to reduce the thickness of the permanent magnet in the diameter direction. is necessary. However, to obtain a polarization plane rotation of 45 ° by the Faraday rotator,
Generally, since a considerably strong magnetic field must be applied, there is a limit to the reduction in thickness.

When the Faraday rotator is a ferromagnetic material such as a bismuth-substituted magnetic garnet, the applied magnetic field needs to have a magnetic field strength of a certain level or more necessary for magnetically saturating the Faraday rotator.

[0008] On the other _{hand, Cd 1-u-v Mn} u Hg v Te (0 <
u <1, 0 <u + v <1) In the case of a paramagnetic material such as a single crystal or a polycrystal, the Faraday rotation angle required for rotating the transmitted light polarization plane by 45 ° is proportional to the applied magnetic field strength. If the total length of the Faraday rotator is increased, the strength of the applied magnetic field can be saved. However, this method results in an increase in the overall length of the optical isolator, which goes against the purpose of miniaturization. As described above, in miniaturizing the optical isolator, it is difficult to reduce the size of the permanent magnet which is a constituent element.

Accordingly, an object of the present invention is to provide a compact and highly productive optical isolator.

[0010]

According to the present invention, by improving the shape of a permanent magnet which is an element constituting an optical isolator, the strength of an applied magnetic field in a region where a Faraday rotator is installed is not reduced, and The outer dimensions of the permanent magnet can be reduced without reducing the dimensional limit of the transmission area of the transmitted light beam in the Faraday rotator. The shape of the improved permanent magnet is described below.

The Faraday rotator used for the optical isolator is often used in a shape having a square optical surface due to processing problems and the like. However, the through-hole for transmitting the light of the permanent magnet disposed on the outer periphery is conventionally circular. That is, there is a space around the Faraday rotator that does not contribute to light transmission or magnetic field application. Therefore, the shape of the through hole of the permanent magnet is made to be a polygon that matches the outer shape of the Faraday rotator, and a wasteful space that has existed conventionally is used so as to contribute to the application of the magnetic field.

Further, the beam shape of the signal light emitted from the semiconductor laser and transmitted through the optical isolator is often elliptical or elliptical, and the longitudinal direction of this beam is the same as the diagonal direction of the Faraday rotator. When assembling the optical isolator, the positional relationship between the polarizer and the analyzer is specified so that they match. By these measures, the cross-sectional area of the through hole of the permanent magnet is reduced as compared with the conventional circular hole, the volume of the permanent magnet itself is increased, and the strength of the magnetic field applied to the through hole can be increased. Also, there is no need to reduce the beam size of the transmitted light.

[0013] The process that led to the solution of the problem will be further described. As described above, the permanent magnet for applying a magnetic field used in a conventional optical isolator often has a columnar structure with a circular through hole formed therein as described above. This is mainly due to the fact that the structure has such a shape that a permanent magnet can be easily manufactured. On the other hand, a design to make the Faraday rotator circular was also considered according to the shape of the through-hole, but it has been put into practical use due to problems such as difficulty in processing into a circular shape and a large amount of waste when cutting out. Absent. However, the configuration in which the through-holes of the permanent magnet are square can be sufficiently realized by using a non-cutting manufacturing method such as improvement of cutting technology or sintering.

Further, when the optical surface of the Faraday rotator is square, the optical isolator is assembled by adjusting the longitudinal direction of the beam of the forward transmitted light so as to match the diagonal direction of the Faraday rotator. It is also possible to further reduce the area of the Faraday rotator as compared with the conventional case.

When passing through the Faraday rotator,
The polarization plane of the elliptical or elliptical transmitted light rotates by 45 °, but the shape of the beam does not change in particular, so the angle between the direction of the polarization plane of the beam and the longitudinal direction of the beam is 45 °.
Will change. In general, the angle between the two in the signal light is different depending on the case, so the arrangement angle of the polarizer, the analyzer and the square Faraday rotator needs to be appropriately set according to the case where the optical isolator is used. .

According to the above method, the cross-sectional area of the through hole of the permanent magnet for applying a magnetic field is calculated to be 36% smaller than that of the circular hole when the Faraday rotator having the same shape and square cross section is used. If the length and the outer dimensions are the same, the volume of the permanent magnet increases accordingly. As a result, how the applied magnetic field intensity changes near the Faraday rotator depends on the relationship between the thickness (difference between the outer diameter and the inner diameter) and the length of the permanent magnet, but is generally used in optical isolators. It has been found that a ring-shaped permanent magnet having a small thickness and a short length greatly contributes to an increase in applied magnetic field strength.

When the Faraday rotator is a paramagnetic material such as a CdMnHgTe element, the Faraday rotation angle is proportional to the intensity of the applied magnetic field. In addition to this, it can also contribute to the improvement of the insertion loss of the optical isolator.

Conversely, if it is not necessary to increase the intensity of the applied magnetic field, the outer dimensions of the permanent magnet can be reduced, which contributes to the downsizing of the optical isolator.

Further, as for the material of the permanent magnet, it is necessary to select a material which can be processed in accordance with not only the magnetic properties but also the shape and precision required in the optical isolator.

In other words, the optical isolator according to the present invention is disposed outside the Faraday rotator, the first polarizer, the Faraday rotator, the second polarizer, which are sequentially disposed in the light transmission direction. An optical isolator including a permanent magnet, wherein the permanent magnet has a cylindrical shape and a shape having a polygonal through hole, and has an elliptical or elliptical beam shape that can transmit through the optical isolator. The display has a display that allows the direction of the major axis or minor axis of the light beam to be easily understood from the appearance.

The optical surface of the Faraday rotator has a square shape, and the direction of the diagonal line of the optical surface is displayed as the direction of the major axis of the light beam that can be transmitted so that it can be easily seen from the outside. It can be.

Further, the material of the permanent magnet is samarium.
It can be a cobalt-based magnet.

The material of the permanent magnet may be a neodymium / iron / boron magnet.

Further, the Faraday rotator can be made of a paramagnetic material.

Further, the Faraday rotator may be a magneto-optical element made of a _{Cd 1-x Mn x Te (} 0 <x <1) single crystal or polycrystal composed by blending Mn.

Further, the Faraday rotator may be a magneto-optical element made of a single crystal or polycrystal of Hg _{1- y} MnyTe (0 <y <1) mixed with Hg.

Further, the Faraday rotator can be a magneto-optical element made of a single crystal or polycrystal of Hg _1-z Cd _z Te (0 <z <1) mixed with Hg.

Further, the Faraday rotator is blended Mn and Hg comprising _{Cd 1-u-v Mn u} Hg v Te (0
<U <1, 0 <u + v <1) A magneto-optical element made of a single crystal or polycrystal can be used.

[0029]

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view showing the shapes of a Faraday rotator and a permanent magnet according to an embodiment of the present invention, and FIG. 2 is a perspective view showing the appearance of an optical isolator according to the embodiment of the present invention.

FIG. 1A is a perspective view showing a Faraday rotator combined with a permanent magnet, and has a wavelength of 0.98 μm.
At m, the element operates as a 45 ° Faraday rotator. Reference numeral 11 denotes a permanent magnet.
It is made of a cobalt-based magnet and has an outer dimension of φ7 × 3.5mm
And the hole is a 1.4 mm square shape, and at the four corners,
Processing of relief is made.

Reference numeral 12 denotes a Faraday rotator, which is made of a CdMnHgTe crystal having a square optical cross section, and has a size of 1.3 × 1.3 × 2.5 mm. The broken elliptical shape shown on the optical surface of the Faraday rotator 12 indicates the cross-sectional shape of the elliptical light beam that can be transmitted.

An optical isolator is manufactured by combining the 45 ° Faraday rotator thus manufactured and two polarizing elements. FIG. 3 shows a cross-sectional view of the optical isolator. 31 is a permanent magnet, 32 is a Faraday rotator, 33a
Is the first polarizer, 33b is the second polarizer, and 34
Is a holder.

Means for displaying the direction of an elliptical or elliptical light beam that can pass through the optical isolator will be described with reference to FIG. In FIG. 2A, 21a, 21
b is a holder for a polarizer, and 23 is a holder for a permanent magnet. In this embodiment, the polarizer holder 21a has a circular aperture hole 24, and the surface of the polarizer holder 21a is provided with round depressions 22a and 22b, and the direction of a straight line passing through these holes is an ellipse through which the light can pass. The shape or the shape of the elliptical light beam is indicated as the major axis direction.

FIG. 2B is a perspective view showing another display mode. 25a and 25b are polarizer holders;
Reference numeral 7 denotes a permanent magnet holder. In this embodiment, the polarizer holder 25a has an elliptical or oblong aperture hole 2.
8 is provided. Even in this case, in the actual assembling process, it is necessary to accurately adjust the direction of the major axis of the transmitted beam in order to improve the yield rate. Accordingly, grooves 26a and 26a are formed on the surface of the polarizer holder 25a.
b is provided, and the direction of a straight line along the groove is indicated as the major axis direction of an elliptical or oblong light beam that can be transmitted.

By the way, as such display means,
Not only round recesses and grooves, but especially when the optical isolator assembling device has a visual recognition device or when assembling by hand, it can be easily recognized from the appearance of the optical isolator. I just want it.

Next, another embodiment of the permanent magnet and the Faraday rotator according to the present invention will be described with reference to FIG. Reference numeral 14 denotes a permanent magnet, 15 denotes a Faraday rotator, and 16 drawn by an elliptical broken line denotes a cross-sectional shape of a light beam that can be transmitted.

In this embodiment, since the optical surface of the Faraday rotator has a hexagonal shape, there is a problem that the number of processing steps increases and the number of elements obtained from the material crystal decreases. Since the cross-sectional area can be increased,
This is an effective form when the outer diameter of the optical isolator is limited to a small size.

Next, still another embodiment of the permanent magnet and the Faraday rotator according to the present invention will be described with reference to FIG. Reference numeral 17 denotes a permanent magnet, 18 denotes a Faraday rotator, and 19 drawn by an elliptical broken line denotes a cross-sectional shape of a light beam that can be transmitted.

In this embodiment, the portion of the Faraday rotator through which light does not pass is further reduced to increase the sectional area of the permanent magnet. This enables further miniaturization of the optical isolator.

Further, when a small magnet is required and the characteristics at high temperatures are not strict, neodymium permanent magnets can be used as permanent magnets.
Iron-boron magnets can be used.

In the optical isolator of the present invention,
The indication of the major axis or minor axis of an elliptical or elliptical beam that can be transmitted is different from the commonly used indication of the polarization direction of the polarizer, and the shape of the hole of the permanent magnet and the Faraday rotator are different. This is to prevent vignetting of the light beam by the Faraday rotator due to the shape.

[0043]

As described above, according to the present invention,
A small optical isolator can be provided.

Further, according to the present invention, it is possible to provide an optical isolator capable of improving the yield rate in the production process.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a permanent magnet and a Faraday rotator according to an embodiment of the present invention. FIG. 1A shows a permanent magnet having a square hole shape and a Faraday rotator having a square optical surface, and FIG. 1B shows a permanent magnet having a hexagonal hole shape and hexagonal optics. FIG. 1C is a diagram illustrating a case of a Faraday rotator having a surface, and FIG. 1C is a diagram illustrating a case of a Faraday rotator having an octagonal optical surface and a permanent magnet having an octagonal hole shape.

FIG. 2 is a diagram showing an appearance of an optical isolator according to the embodiment of the present invention. In FIG. 2A, the direction of the major axis of the light beam is indicated by a round depression. In FIG. 2B, the direction of the major axis of the light beam is indicated by a groove.

FIG. 3 is a sectional view showing an optical isolator according to the embodiment of the present invention. The cut plane includes the central axis of the optical isolator.

FIG. 4 is a sectional view showing a conventional optical isolator. FIG.
4A is a cross section perpendicular to the central axis of the optical isolator, and FIG. 4B is a cross section including the central axis of the optical isolator.

[Explanation of symbols]

 11, 14, 17, 31, 41 Permanent magnet 12, 15, 18, 32, 42 Faraday rotator 13, 16, 19 Cross-sectional shape of transmitted light beam 21a, 21b, 25a, 25b Polarizer holder 22a, 22b Depression 26a , 26b Groove 24, 28 Aperture hole 33a, 43a First polarizer 33b, 43b Second polarizer 34, 44 Holder

Claims (9)

[Claims] 1. An optical isolator comprising a first polarizer, a Faraday rotator, a second polarizer, and a permanent magnet disposed outside the Faraday rotator, which are sequentially arranged in a light transmission direction. The permanent magnet has a columnar outer shape and a shape having a polygonal through hole, and is capable of transmitting through the optical isolator, and has a direction of a major axis or a minor axis of a light beam having an elliptical or elliptical cross-sectional shape. An optical isolator characterized by having a display that can be easily recognized from the appearance. 2. An optical surface of the Faraday rotator has a square shape, and a direction of a diagonal line of the optical surface is displayed as a direction of a major axis of a light beam that can be transmitted so as to be easily understood from the appearance. The optical isolator according to claim 1, wherein: 3. The optical isolator according to claim 1, wherein the material of the permanent magnet is a samarium-cobalt magnet. 4. The optical isolator according to claim 1, wherein the material of the permanent magnet is a neodymium / iron / boron magnet. 5. The optical isolator according to claim 1, wherein said Faraday rotator is a paramagnetic material. 6. The Faraday rotator is compounded with Mn.
Cd consisting of_1-xMn _xTe (0 <x <1) single crystal or
Is a magneto-optical element made of polycrystal
The optical isolator according to claim 5. 7. The Faraday rotator is compounded with Hg.
Hg_1-yMn _yTe (0 <y <1) single crystal or
Is a magneto-optical element made of polycrystal
The optical isolator according to claim 5. 8. The Faraday rotator is compounded with Hg.
Hg_1-zCd _zTe (0 <z <1) single crystal or
Is a magneto-optical element made of polycrystal
The optical isolator according to claim 5. 9. The Faraday rotator includes Mn and Hg.
Cd composed _1-uvMn_uHg_vTe (0 <u
<1,0 <u + v <1) consisting of single crystal or polycrystal
6. The light according to claim 5, wherein the light is a magneto-optical element.
Isolator.