JP3141212B2 - Optical circulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Conventionally, a four-terminal optical circulator has been used mainly in the field of optical communication as a circuit element for separating and synthesizing optical signals. FIG. 7 is a top view schematically showing the configuration of such a conventional four-terminal optical circulator. In general, a four-terminal optical circulator has four input / output terminals a, b, c, and d on the side surface of the housing 101. In such an optical circulator, for example, all light incident on the first input / output terminal a is output to the third input / output terminal c, and is not output to other input / output terminals. In addition, all light input to the third input / output terminal c is output to the second input / output terminal b, and is not output to other input / output terminals.

Similarly, all light input to the second input / output terminal b is output to the fourth input / output terminal d, and is not output to the other input / output terminals. And a fourth input / output terminal d
Are all output to the first input / output terminal a,
It is not output to other input / output terminals.

As one of the methods for forming a four-terminal optical circulator, there is a case where a Faraday rotator which is a non-reciprocal element is used. The non-reciprocal element is an optical element that can rotate the direction of the polarization plane according to the traveling direction of light in the presence of an external magnetic field, and its rotation angle is 45 °,
In combination with the 45 ° optical rotation plate, the rotation angle of the polarization plane can be 90 ° in the forward direction and 0 ° in the reverse direction.

FIGS. 8 to 12 show a specific structure and operation of a conventional four-terminal optical circulator using a combination of such a Faraday rotator and a 45 ° optical rotation plate. FIG. 8A is a perspective view of an optical element portion of a four-terminal optical circulator, and FIG. 8B is an exploded top view showing components of the optical circulator. As shown, the Faraday rotator 71 and the 45 ° optical rotation plate 72 are arranged in contact with each other. 45 ° of Faraday rotator 71
A first polarization splitting prism 73 and a first total reflection prism 74 are joined and arranged on the surface opposite to the optical rotation plate 72. On the other hand, the Faraday rotator 71 of the 45 ° optical rotation plate 72
A second polarization splitting prism 75 and a second total reflection prism 76 are joined and disposed on the surface on the opposite side. An external magnetic field to be applied to the Faraday rotator 71 is generated in a direction indicated by an arrow 77 by a magnetic field applying unit, although not shown in the figure.

[0006] The first input / output terminal a is arranged so as to input light in one direction to one surface of the first polarization splitting prism 73. The second input / output terminal b is arranged so as to allow light to enter the adjacent surface of the first polarization splitting prism 73 in the vertical direction. The third input / output terminal c is arranged so as to input and output light from one surface of the second polarization separation prism 75 in the horizontal direction, and the fourth input / output terminal d is connected to the second polarization separation prism 75. They are arranged so that light is input to adjacent surfaces in the vertical direction. A solid line 78 with an arrow in FIG. 8 indicates an optical axis through which input and output light passes.

9 and 10 are top views showing the operation of the conventional four-terminal optical circulator shown in FIG. 8, and FIG. 9 shows a case where input light is incident from a first input / output terminal a.
Indicates a case where input light is incident from the third input / output terminal c. When incident from the first input / output terminal a, as shown in FIG. 9, the input light 81 is incident on one surface of the first polarization splitting prism 73 in the horizontal direction. Here, the input light 81
Contains a horizontal polarization component parallel to the paper surface and a vertical polarization component perpendicular to the paper surface. In the drawing, the former is represented by a vertical straight line 82,
The latter is indicated by a circle 83.

The input light 81 is supplied to a first polarization splitting prism 73.
As a result, the light is separated into horizontal polarized light 84 having only a horizontal polarized component and vertical polarized light 85 having only a vertical component with respect to the bottom surface. The horizontal polarized light 84 travels in the same direction as the input light 81 and passes through the Faraday rotator 71 and the 45 ° optical rotation plate 72, during which the polarization plane is rotated 90 ° and the vertical polarized light 8 is rotated.
4 ′, and enters the second total reflection prism 76 and the second polarization separation prism 75. On the other hand, vertical polarization 85
Is bent in the direction of 90 ° with respect to the input light 81 by the first polarization separation prism 73, and the first total reflection prism 7
At 4, the direction is further bent by 90 ° and the light travels in a direction parallel to the input light 81. Like the horizontal polarized light 84, the vertically polarized light 85 passes through the Faraday rotator 71 and the 45 ° optical rotation plate 72, during which the polarization plane is rotated by 90 ° and the horizontal polarized light 8 is rotated.
The light enters the second polarization splitting prism 75 as 5 ′.
The vertically polarized light 84 ′ and the horizontally polarized light 85 ′ are combined in the second polarization splitting prism 75 and sent out from the third input / output terminal c as output light 86 having both polarized components.

When the input light is incident from the third input / output terminal c, as shown in FIG. 10, the input light 81 is transmitted from the third input / output terminal c to one surface of the second polarization splitting prism 75 in the horizontal direction. Incident on. The input light 81 is split into a horizontally polarized light 84 and a vertically polarized light 85 by the second polarization splitting prism 75. The horizontal polarized light 84 travels in the same direction as the input light 81 and
The light passes through the 5 ° optical rotation plate 72 and the Faraday rotator 71. However, during that time, the rotation angle of the polarization plane is zero, so that the light enters the first polarization splitting prism 73 via the first total reflection prism 74 as horizontal polarized light 84.

On the other hand, the direction of the vertically polarized light 85 is bent by 90 ° by the second total reflection prism 76 and travels in a direction parallel to the input light 81. Like the horizontally polarized light 84, the vertically polarized light 85 passes through the 45 ° optical rotation plate 72 and the Faraday rotator 71, but the polarization plane enters the first polarization splitting prism 73 as the vertically polarized light 85 without being rotated. Is done. The horizontally polarized light 84 and the vertically polarized light 85 are combined in the first polarization splitting prism 73 and sent out from the second input / output terminal b as output light 86 having both polarized components. As described above, the direction of the plane of polarization of the incident light in the forward and reverse directions is irreversibly changed by the presence of the Faraday rotator, which is a non-reciprocal element, and thus follows different paths in the four-terminal optical circulator. Will be.

FIG. 11 shows a case where input light enters from the second input / output terminal b and is output to the fourth input / output terminal d. FIG. 12 shows a case where input light enters from the fourth input / output terminal d. Each case is shown in which the light is incident and output to the first input / output terminal a. In these cases, since light is transmitted by substantially the same operation as in FIGS. 9 and 10, corresponding parts are denoted by the same reference numerals and detailed description thereof will be omitted.

[0012]

In such a conventional four-terminal optical circulator, since a polarization separating prism and a total reflection prism are arranged on both sides of a Faraday rotator and a 45 ° optical rotation plate, it is very difficult to assemble the same. There is a problem that many man-hours are required. In other words, each optical element is aligned with each other by irradiating a laser beam for measurement to the optical element with an external magnetic field applied and measuring the optical characteristics of each optical element with an optical power meter, etc. It is moved and aligned, and finally the adhesive is fixed. Such a delicate operation needs to be performed for each of the four light transmission methods at the time of assembling the optical circulator, which increases the number of assembling steps and limits the improvement of the product yield.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a four-terminal optical circulator having a new structure which solves the above-mentioned problems in assembling the conventional optical circulator.

[0014]

According to the present invention, a first birefringent parallel plate, a second birefringent parallel plate, a Faraday rotator for rotating a plane of polarization of incident light by 45 °, a 45 ° optical rotation plate, A joined body in which a third birefringent parallel plate and a fourth birefringent parallel plate are joined in this order, and a magnetic field is applied to the Faraday rotator of the joined body to cause the Faraday rotation of the angle. A first and a second input / output port provided at positions separated from each other and opposite to end faces of the first and second birefringent parallel plates; And third and fourth input / output ports provided at positions spaced apart from each other and opposite to the end surface of the fourth birefringent parallel plate, wherein the first birefringent parallel plate is provided with the second birefringent plate. Make the light incident surface smaller than the parallel plate, The incident light from the first input / output port directly enters the end surface of the second birefringent parallel plate without passing through the first birefringent parallel plate, and the incident light from the second input / output port. After being incident on the end face of the first birefringent parallel plate, one of the polarized lights separated by the first birefringent parallel plate is totally reflected by one surface of the first birefringent parallel plate, and And the second birefringent parallel plate is configured to be totally reflected on one surface of the second birefringent parallel plate and to be incident on the Faraday rotator.
The fourth birefringent parallel plate makes the light incident surface smaller than that of the third birefringent parallel plate, and the incident light from the third input / output port passes through the fourth birefringent parallel plate. The light is directly incident on the end face of the third birefringent parallel plate without passing through, and the incident light from the fourth input / output port is incident on the end face of the fourth birefringent parallel plate. One of the polarized lights separated by the refraction parallel plate is totally reflected by one surface of the fourth birefringence parallel plate and is incident on the third birefringence parallel plate, and one surface of the third birefringence parallel plate. The optical circulator is configured to be totally reflected by the optical circulator and to enter the 45 ° optical rotation plate.

Further, in the optical circulator of the present invention, the first birefringent parallel plate has a light incident surface substantially half of a lower side with respect to the light incident surface of the second birefringent parallel plate. The first birefringent parallel plate is arranged such that the separated one polarized light is totally reflected on the lower surface thereof, and the second birefringent parallel plate is totally reflected on the upper surface thereof. And the fourth birefringent parallel plate is arranged such that its light incident surface occupies approximately one half of the upper side with respect to the light incident surface of the third birefringent parallel plate. The fourth birefringent parallel plate is configured such that the separated one polarized light is totally reflected on its upper surface, and the third birefringent parallel plate is totally reflected on its lower surface.

Further, according to the present invention, the first to fourth embodiments
The upper or lower surface of the birefringent parallel plate is a smooth surface,
If necessary, a reflective film is further formed to generate total reflection.

The first birefringent parallel plate and the second birefringent parallel plate, and the third birefringent parallel plate and the fourth birefringent parallel plate are each integrally formed in advance. May be.

[0018]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1A is a perspective view of a four-terminal optical circulator of the present invention, and FIG. 1B is an exploded perspective view showing components of the optical circulator shown in FIG. 1A. The Faraday rotator 11 and the 45 ° optical rotation plate 12 are arranged adjacent to each other. 45 ° optical rotation plate 12 of Faraday rotator 11
A first birefringent parallel flat plate 13 and a second birefringent parallel flat plate 14 are sequentially arranged in contact with each other on the surface on the opposite side. On the other hand, a third birefringent parallel flat plate 15 and a second birefringent parallel flat plate 16 are sequentially contacted and arranged on the surface of the 45 ° optical rotation plate 12 opposite to the Faraday rotator 11.

An external magnetic field to be applied to the Faraday rotator 11 is generated in a direction indicated by an arrow 17 by magnetic field applying means (not shown). The first birefringent parallel plate 1
3 makes the light incident end face 18 smaller than that of the second birefringent parallel plate 14 so that the incident light from the first input / output terminal a does not pass through the first birefringent parallel plate 13. The second birefringent parallel plate 14 is configured so as to be directly incident on the end face 19 thereof. On the lower surface of the first birefringent parallel plate 13, a total reflection surface 20 is formed. For this reason, the incident light from the second input / output terminal b is incident on the end face 18 of the first birefringent parallel plate 13, and then is reflected by one of the polarization components separated by the first birefringent parallel plate 13. A certain horizontal polarized light is totally reflected on the lower surface of the first birefringent parallel plate 13 and is incident on the second birefringent parallel plate 14.

A total reflection surface 21 is also formed on the upper surface of the second birefringent parallel flat plate 14. The total reflection surface 21 is totally reflected by the lower surface of the first birefringent parallel flat plate 13, and the second birefringent parallel flat plate 14 is formed.
Is totally reflected by the total reflection surface 21 and is incident on the Faraday rotator. Similarly, the fourth birefringent parallel plate 16 has a light incident end face 23 smaller than that of the third birefringent parallel plate 15 so that the incident light from the third input / output terminal c is The third birefringent parallel plate 15 is configured to directly enter the end face 22 without passing through the fourth birefringent parallel plate 16.

A total reflection surface 24 is formed on the upper surface of the fourth birefringent parallel plate 16. For this reason, the incident light from the fourth input / output terminal d is incident on the end face 23 of the fourth birefringent parallel plate 16 and then the horizontal polarized light separated by the fourth birefringent parallel plate 16 is applied to the upper surface thereof. The light is totally reflected at 24 and enters the third birefringent parallel plate. A total reflection surface 25 is also formed on the lower surface of the third birefringent parallel plate 15, and is totally reflected on the upper surface of the fourth birefringent parallel plate 16 and enters the third birefringent parallel plate 15. The horizontal polarization is totally reflected by the total reflection surface 25 and is incident on the 45 ° optical rotation plate 12. As for the total reflection surface on the upper surface or the lower surface of the first to fourth birefringent parallel plates, the side surface of the birefringent parallel plate is polished to form a smooth surface, or a reflection film or a reflection thin plate is formed on the side surface. Thus, it is configured that total reflection occurs.

The double-headed arrow 26 in FIG. 1B indicates the direction of the crystal axis of the first to fourth birefringent parallel flat plates. In the embodiment of the present invention, a magnetic garnet film is used as the Faraday rotator 11, and a 45 ° optical rotation plate 12 is made of Si.
An O ₂ single crystal plate was used, and rutile polarizing plates were used as the first to fourth birefringent parallel flat plates 13, 14, 15, and 16, respectively. The rutile polarizing plate is obtained by cutting a titanium oxide (TiO 2) single crystal, which is a birefringent crystal, along a plane that forms an angle of about 43 ° with respect to the crystal axis. Since the crystal thus cut out has a different refractive index of light between the plane including the crystal axis and the plane perpendicular to the crystal axis, this property is used to separate the incident light into horizontal polarized light and vertical polarized light having polarization planes orthogonal to each other. can do.

FIGS. 2 to 5 are views showing the operation of the four-terminal optical circulator of the present invention shown in FIG. 1, in which (a) is a top view and (b) is a broken line in FIG. A,
The position of the light flux and the direction of the polarization plane when each element is viewed from the terminal a to the direction c on the cut planes indicated by B, C, D, and E are shown. FIG. 2A shows that the input light is transmitted to the first input / output terminal a.
, And the input light 31 is horizontally incident on the end face 19 of the second birefringent parallel plate 14. Here, the input light 31 includes a horizontal component 32 parallel to the paper surface and a vertical component 33 perpendicular to the paper surface. The input light 31 is separated into a horizontal polarized light 34 and a vertical polarized light 35 by the second birefringent parallel plate 14. .

The vertically polarized light 35 travels in the same direction as the input light 31 and passes through the Faraday rotator 11 and the 45 ° optical rotation plate 12, and during the passage, as shown by arrows 38 and 37 in FIG. The plane of polarization is rotated by 90 ° to become horizontally polarized light 35 ′, and enters the third birefringent parallel plate 15. On the other hand, the horizontal polarized light 34 is polarized and separated by the second birefringent parallel plate 14 in a predetermined angle direction in the horizontal plane with respect to the input light 31, and is refracted again by the opposite end face to be parallel to the input light 31. proceed. The horizontal polarized light 34, like the vertical polarized light 35, is composed of the Faraday rotator 11 and the 45 ° optical rotation plate 12.
, The polarization plane is rotated by 90 ° to become vertically polarized light 34 ′, and enters the third birefringent parallel plate 15. The horizontal polarized light 35 ′ is polarized and separated in the third birefringent parallel plate 15 in a predetermined angle direction in the horizontal plane with respect to the input light 31 direction, and is combined with the vertical polarized light 34 ′ at the opposite end face, and has an output having both components. The light 36 is sent out from the third input / output terminal c.

FIG. 3A shows a case where the input light 31 is inputted from the third input / output terminal c. As shown in the figure, the input light 31 enters the end face 22 of the third birefringent parallel plate 15 from the third input / output terminal c. The input light 31 is the third
Are split into horizontal polarized light 34 and vertical polarized light 35 by the birefringent parallel plate 15. The vertically polarized light 35 travels in the same direction as the input light 31 and passes through the 45 ° optical rotation plate 12 and the Faraday rotator 11, during which the plane of polarization is not rotated and is converted into the vertically polarized light 35 as the second birefringent parallel light. The light enters the flat plate 14.

That is, the vertically polarized light 35 (D in FIG. 3B) separated by the third birefringent parallel plate 15 becomes 45
The polarization plane is rotated by 45 ° in the rotation direction indicated by the arrow 37 of C in FIG. 3B by the optical rotation plate 12, and the Faraday rotator 11 is indicated by the arrow 38 in B of FIG. Is rotated in the opposite direction as described above and the second polarization
Is supplied to the birefringent parallel flat plate 14. On the other hand, horizontal polarized light 34
Is polarized and separated in the horizontal plane by a predetermined angle direction with respect to the input light 31 in the third birefringent parallel flat plate 15, and travels again in a direction parallel to the input light 31 at the opposite end face. The horizontal polarized light 34 is, similarly to the vertically polarized light 35, a 45 ° optical rotation plate 1.
2 and the Faraday rotator 11, but the polarization plane is not rotated during that time and is supplied to the second birefringent parallel plate 14 as horizontal polarized light 34.

The horizontally polarized light 34 incident on the second birefringent parallel plate 14 refracts and proceeds in a predetermined angle direction in a horizontal plane due to the difference in the refractive index, and the total reflection surface on the upper surface of the second birefringent parallel plate 14. And the first birefringent parallel plate 13
Go straight in. The reflection angle of the horizontally polarized light 34 is very large in the design of the optical circulator (when a rutile polarizing plate is used as a birefringent parallel plate, the refractive index is about 5.7 °,
Since the refraction angle is about 84.3 °), total reflection can normally be performed by mirror-finishing the upper surface of the second birefringent parallel plate 14. However, if necessary, a metal film may be applied to the reflection surface to form a reflection surface. The horizontal polarized light 34 traveling straight in the first birefringent parallel flat plate 13 is reflected again by the total reflection surface 20 on the lower surface of the first birefringent parallel flat plate 13, and passes through the second birefringent parallel flat plate 14. It becomes parallel to the vertical polarized light 35 supplied into the birefringent parallel plate 13 and is synthesized therewith, as output light 36 having both polarized components.
Output to the second input / output terminal b.

FIG. 4A shows that the input light is supplied to the second input / output terminal b.
FIG. The input light 31 enters the end face 18 of the first birefringent parallel plate 13 in the horizontal direction. Here, the input light 31 is split into a horizontally polarized light 34 and a vertically polarized light 35. The vertically polarized light 35 travels in the same direction as the input light 31 and travels through the second birefringent parallel plate 14 to the Faraday rotator 1.
4 through the 1 and 45 ° optical rotatory plates 12 during the passage.
As shown in (b), the polarization plane is rotated by 90 ° to become horizontal polarized light 35 ′, and enters the third birefringent parallel plate 15.

On the other hand, the horizontal polarized light 34 refracts and proceeds in a predetermined angle direction in the horizontal plane, is reflected by the total reflection surface 20 on the lower surface of the first birefringent parallel plate 13, and is reflected in the second birefringent parallel plate 14. Go straight to. The horizontally polarized light 34 traveling straight in the second birefringent parallel plate 14 is reflected again by the total reflection surface 21 on the upper surface of the second birefringent parallel plate 14, is refracted and output from the other end surface, and is parallel to the vertically polarized light 35. Faraday rotator 1
The light passes through the 1 and 45 ° optical rotation plates 12. During this time, FIG.
As shown in (b), the plane of polarization is rotated by 90 ° to become vertically polarized light 34 ′, and is incident on the third birefringent parallel plate 15. The vertically polarized light 34 ′ travels straight through the third birefringent parallel plate 15, and further travels straight inside the fourth birefringent parallel plate 16.

On the other hand, the horizontally polarized light 35 'incident on the third birefringent parallel flat plate 15 is refracted and
5 travels in the horizontal plane at a predetermined angle direction, is reflected by the total reflection surface 25 on the lower surface of the third birefringent parallel plate 15, and
Into the birefringent parallel flat plate 16. The vertically polarized light 34 ′ that has traveled straight in the fourth birefringent parallel plate 16 is reflected again by the total reflection surface 24 on the upper surface of the fourth birefringent parallel plate 16,
The light is refracted from the other end face. The refracted and output vertical polarized light 34 ′ becomes parallel to the horizontal polarized light 35 ′ supplied into the fourth birefringent parallel flat plate 16 via the third birefringent parallel flat plate 15, and is synthesized therewith. Output light 36 having
Is output to the fourth input / output terminal d.

FIG. 5A shows a case where the input light 31 is input from the fourth input / output terminal d. As shown in the figure, the input light 31 enters the end face 23 of the fourth birefringent parallel plate 16 from the fourth input / output terminal d. The input light 31 is the fourth
Is split into horizontal polarized light 34 and vertical polarized light 35 by the birefringent parallel plate 16. The vertically polarized light 35 travels in the same direction as the input light 31 and passes through the 45 ° optical rotation plate 12 and the Faraday rotator 11, during which the plane of polarization is not rotated and is converted into the vertically polarized light 35 as the second birefringent parallel light. The light enters the flat plate 14. That is, the vertically polarized light 35 (D in FIG. 3B) separated by the second birefringent parallel plate 16 is rotated by the 45 ° optical rotation plate 12 in the rotation direction indicated by the arrow 37 in C of FIG. Although its polarization plane is rotated by 45 °, it is rotated in the Faraday rotator 11 in the opposite direction as shown by the arrow 38 in FIG. 3B and supplied to the second birefringent parallel plate 14 as vertical polarized light 35. Is done.

On the other hand, the horizontal polarized light 34 travels in the fourth birefringent parallel plate 16 in a predetermined angle direction in the horizontal plane with respect to the input light 31, and a total reflection surface on the upper surface of the fourth birefringent parallel plate 16. 24, the third birefringent parallel plate 1
Go straight into 5. The horizontal polarized light 34 traveling straight in the third birefringent parallel plate 13 is reflected again by the total reflection surface 25 on the lower surface of the third birefringent parallel plate 15, and is parallel to the vertical polarized light 35 from the third birefringent parallel plate 15. Direction is output.

The horizontal polarized light 34 passes through the 45 ° optical rotation plate 12 and the Faraday rotator 11 in the same manner as the vertical polarized light 35, but the plane of polarization is not rotated during that time, and becomes the horizontal polarized light 34 as a second birefringent parallel light. It is supplied to the flat plate 14. The horizontal polarized light 34 incident on the second birefringent parallel plate 14 refracts and proceeds in a predetermined angle direction in a horizontal plane due to a difference in refractive index, and is supplied to the second birefringent parallel plate 14 and travels straight.
5, and as output light 36 having both polarization components,
The signal is output from the end face 19 of the second birefringent parallel plate 14 to the first input / output terminal a.

A method for manufacturing the four-terminal optical circulator of the present invention having the above-described structure will be described with reference to FIG. A large plate-like Faraday rotator 11 'and a 45 ° optical rotation plate 12' having the same thickness as the optical element constituting the four-terminal optical circulator but having a surface area several times to several hundred times are laminated and arranged. Further, a second birefringent parallel flat plate 14 'and a third birefringent parallel flat plate 15' are stacked and arranged above and below.

The Faraday rotator 11 'is made of a magnetic garnet film. To magnetically saturate the Faraday rotator 11', the ring-shaped permanent magnet 61 is
It is arranged so that it surrounds. Second birefringent parallel flat plate 1
The 4 'and the third birefringent parallel flat plate 15' are obtained by dividing the same rutile polarizing plate, whereby the optical characteristics of the two can be matched.

The laminated body 62 is irradiated with transmitted light 63 for optical adjustment such as a laser beam for measurement so as to transmit the laminated body 62, and while measuring the amount of transmitted light, the Faraday rotator 11
', 45 ° optical rotation plate 12', second birefringent parallel plate 14 '
And the third birefringent parallel flat plate 15 ′ is rotated in the direction of the arrow 64 to adjust the mutual angular position. After the relative positions of the laminated boards are adjusted in this way, they are bonded and fixed to each other. At this time, measures such as applying an AR coating on the surface of the optical element in advance are required so that light scattering and reflection do not occur on the bonding surface. As shown in FIG. 6B, the large-sized laminate 62 bonded and fixed as described above is cut by a cut surface 65 in a vertical and horizontal matrix.

The four-terminal optical circulator main body is formed by the individual laminated bodies 66 cut in this manner. Thereafter, a total reflection surface is formed on the required side surface of the laminate 66 by polishing or vapor deposition of a reflection film. These laminates 66
The first and fourth birefringent parallel flat plates (not shown) manufactured separately from the above are aligned in the presence of transmitted light for optical adjustment, and then adhesively fixed. Further, first to fourth input / output terminals a, b, c and d are provided, and an external magnetic field applying means is further provided.

By the way, the first and second birefringent parallel flat plates 13, 14 are so arranged that the reflection, scattering or refraction of transmitted light does not occur on the bonding surface between the first and second birefringent parallel flat plates 13, 14. Bonding using an adhesive having the same refractive index as that of the first and second birefringent parallel plates 13,
A corresponding to the adhesive to be used for both of the 14 adhesive surfaces
It is necessary to take measures such as applying R coating.

This is also necessary between the third and fourth birefringent parallel flat plates 15 and 16. Other means of such a measure are the first and second birefringent parallel flat plates 1.
3, 14 or third and fourth birefringent parallel flat plates 1
5 and 16 are integrally formed from the beginning. That is, the above problem can be solved by using a key-type birefringent parallel flat plate having a step on one surface. In this case, it is structurally difficult to apply the manufacturing method as shown in FIG. 6 as a whole, but it is difficult to apply the manufacturing method as shown in FIG. , The second birefringent parallel plate 14 ′ and the third
The manufacturing method as shown in FIG. 6 can be used for a laminate to which either one of the birefringent parallel flat plates 15 ′ is added. In this case, as shown in FIG. 6B, after a key-shaped birefringent parallel flat plate is positioned on one or both end surfaces of the cut-out laminate in the presence of transmitted light for optical adjustment,
What is necessary is just to adhere and fix.

[0040]

As described above, according to the present invention, since the optical circulator can be constructed by laminating and bonding all plate-shaped optical elements, the assembling process is extremely easy as compared with the conventional optical circulator. Become. further,
The optical circulator of the present invention is suitable for mass production because of its structure, and by using the manufacturing method of the present invention, an optical circulator having uniform characteristics can be manufactured with high yield.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining an embodiment of the present invention, and FIG.
1 is a perspective view of a four-terminal optical circulator of the present invention, FIG.
FIG. 2B is an exploded top view showing components of the optical circulator shown in FIG.

FIGS. 2A and 2B are diagrams showing the operation of the four-terminal optical circulator of the present invention shown in FIG. 1, wherein FIG.
And (b) shows a change in the polarization plane of the input light.

FIGS. 3A and 3B are diagrams showing the operation of the four-terminal optical circulator of the present invention shown in FIG. 1, wherein FIG.
And (b) shows a change in the polarization plane of the input light.

4A and 4B are diagrams showing the operation of the four-terminal optical circulator of the present invention shown in FIG. 1, wherein FIG.
And (b) shows a change in the polarization plane of the input light.

5A and 5B are diagrams showing the operation of the four-terminal optical circulator of the present invention shown in FIG. 1, wherein FIG.
And (b) shows a change in the polarization plane of the input light.

6A and 6B are views for explaining a method for manufacturing a four-terminal optical circulator of the present invention, wherein FIG. 6A is a perspective view showing a step of forming a laminate made of a large laminated plate, and FIG. 6B is a perspective view showing a cutting step. FIG.

FIG. 7 is a top view showing a configuration of a conventionally known four-terminal optical circulator.

8A and 8B are schematic structural views showing the configuration of a conventionally known four-terminal optical circulator, in which FIG. 8A is a perspective view, and FIG. 8B is an exploded top view showing an optical element constituting the optical circulator.

FIG. 9 is a top view showing the operation of the conventional four-terminal optical circulator shown in FIG. 8, showing a case where input light is incident from a first input / output terminal a.

FIG. 10 is a top view showing the operation of the conventional four-terminal optical circulator shown in FIG. 8, showing a case where input light is incident from a third input / output terminal c.

11 is a top view showing the operation of the four-terminal optical circulator of the present invention shown in FIG. 8, showing a case where input light is incident from a second input / output terminal b.

FIG. 12 is a top view showing the operation of the four-terminal optical circulator of the present invention shown in FIG. 8, showing a case where input light is incident from a fourth input / output terminal d.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Faraday rotator 12 45 degree optical rotation plate 13-16 1st-4th birefringent parallel flat plate a-d 1st-4th input / output terminal

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-61001 (JP, A) JP-A-5-34633 (JP, A) JP-A-5-19207 (JP, A) 103519 (JP, A) Proceedings of the 1991 Autumn Meeting of the Institute of Electronics, Information and Communication Engineers, Pt. 4 (September 1991) p. 4-127 (58) Field surveyed (Int. Cl. ⁷ , DB name) G02B 27/28

Claims (4)

(57) [Claims] A first birefringent parallel plate, a second birefringent parallel plate, a Faraday rotator for rotating the plane of polarization of incident light by 45 °, a 45 ° optical rotation plate, a third birefringent parallel plate, and a second birefringent parallel plate. And a magnetic field applying means provided to apply a magnetic field for causing Faraday rotation to the Faraday rotator of the bonded body. The first and second birefringent parallel plates have first and second birefringent plates provided at positions separated from each other and opposed to end surfaces thereof.
And a second input / output port, and third and fourth input / output ports provided at positions spaced apart from each other and opposite to the end faces of the third and fourth birefringent parallel flat plates. The birefringent parallel plate has a light incident surface smaller than that of the second birefringent parallel plate, and the incident light from the first input / output port does not pass through the first birefringent parallel plate. The light is directly incident on the end face of the second birefringent parallel plate, and the incident light from the second input / output port is incident on the end face of the first birefringent parallel plate. Is totally reflected on one surface of the first birefringent parallel plate and is incident on the second birefringent parallel plate, and is totally reflected on one surface of the second birefringent parallel plate. And incident on the Faraday rotator. The birefringent parallel plate makes the light incident surface smaller than that of the third birefringent parallel plate, and the incident light from the third input / output port does not pass through the fourth birefringent parallel plate. The light is directly incident on the end face of the third birefringent parallel plate, and the incident light from the fourth input / output port is incident on the end face of the fourth birefringent parallel plate. One of the separated polarized lights is totally reflected on one surface of the fourth birefringent parallel plate and is incident on the third birefringent parallel plate, and is also totally reflected on one surface of the third birefringent parallel plate. An optical circulator configured to be incident on the 45 ° optical rotation plate. 2. The first birefringent parallel plate is arranged such that its light incident surface occupies approximately one half of the lower side with respect to the light incident surface of the second birefringent parallel plate. The first birefringent parallel plate is configured such that the separated one polarized light is totally reflected on a lower surface thereof, and the second birefringent parallel plate is totally reflected on an upper surface thereof; The fourth birefringent parallel plate is disposed such that its light incident surface occupies approximately one half of the upper side with respect to the light incident surface of the third birefringent parallel plate. 2. The light according to claim 1, wherein the flat plate is configured such that the one polarized light beam is totally reflected on an upper surface thereof, and the third birefringent parallel flat plate is totally reflected on a lower surface thereof. Circulator. 3. An apparatus according to claim 2, wherein said first to fourth birefringent parallel flat plates have a smooth surface or a reflection film formed on an upper surface or a lower surface thereof so that total reflection occurs. Light circulator. 4. The first birefringent parallel flat plate and the second birefringent parallel flat plate, and the third birefringent parallel flat plate and the fourth birefringent parallel flat plate are integrally formed in advance. The optical circulator according to claim 1, wherein: