JPH05323233A - Optical circulator - Google Patents

Abstract

PURPOSE:To realize cost reduction and to improve a yield by using birefringent parallel plates. CONSTITUTION:Birefringent parallel plates 21 and 22, Faraday rotators 24, a 45 degree azimuth rotator 25 and a birefringent parallel plate 23 are arranged along the prescribed direction, a light incident terminal 11a and a light transmitting terminal 11b confront the birefringent parallel plates 21 and 22, respectively, and an optical input/output terminal 11c faces the birefringent parallel plate 23. A magnetic field applying means for generating Faraday rotation is arranged in the proximity of the Faraday rotator 24. A total reflection surface for totally reflecting transmitted beam thereof on the prescribed surfaces of the birefringent parallel plates 21 and 22, an incident light from an optical input terminal is outputted as an output light at the optical input/output terminal 11c and an incident light from the optical input/output terminal 11c is outputted as an output light at the optical output terminal. Thus, since the birefringent parallel plate is utilized, a man-hour for adjustment such as positioning in the cource of assembling is reduced, the yield is improved and cost reduction is attained.

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 optical communication and optical measurement.

[0002]

2. Description of the Related Art Generally, an optical circulator having three optical input / output terminals is known, and an optical circulator of this type is called a three-terminal optical circulator. This three-terminal optical circulator is known to be used for separating transmitted light and received light from each other in optical communication and optical measurement.
That is, when one optical fiber is used for transmitting and receiving an optical signal, it is used as a passive optical path changing device for guiding all received light to the light receiving element side without giving it to the transmitting laser element side.

A conventional three-terminal optical circulator (hereinafter simply referred to as an optical circulator) will be briefly described with reference to FIG.

The illustrated optical circulator 11 has a terminal 11a.
To 11c, a transmission light source (not shown) is arranged on the terminal 11a side, and a reception light section (not shown) is arranged on the terminal 11b side. On the other hand, an optical fiber is connected to the terminal 11c, and this optical fiber is connected to another optical system.

The optical circulator 11 has a terminal 11a.
All the optical signals incident from the terminal 11c are emitted to the terminal 11c, and all the optical signals incident from the terminal 11c are detected at the terminal 1c.
The light signal is emitted to the terminal 1b, and no optical signal is emitted from the terminal 11a. Although it is not normally considered that an optical signal is incident from the terminal 11b, if it is incident, the optical signal is absorbed by the attenuation inside the optical circulator, and the optical signal is emitted from any of the terminals 11a to 11c. It is desirable that no signal be emitted.

As described above, this optical circulator 11
With, it is possible to completely separate the input and output of the optical signal with respect to the transmission light source and the reception light section, and it is possible to perform bidirectional optical communication with one optical fiber.

By the way, when constructing the optical circulator 11 as described above, a Faraday rotator which is a non-reciprocal element is generally used. The Faraday rotator has the function of rotating the direction of polarized light that is transmitted in the presence of an external magnetic field, but the direction of rotation of the polarization plane is different if the transmission direction of polarized light is different. Then, when a non-reciprocal element whose rotation amount is 45 degrees is used, by combining this non-reciprocal element with a 45-degree illuminating plate, the rotation angle of the polarization plane of the transmitted polarized light is 90 degrees in the case of forward transmission and reverse. In the case of directional transmission, it can be 0 degree. Therefore, an optical circulator can be constructed by combining a polarization splitting prism and a total reflection prism with both optical elements.

A specific example of the optical circulator will be outlined with reference to FIG.

As shown in FIGS. 5A and 5B, the polarization separation prism 12 is arranged corresponding to the terminals 11a and 11b, and the polarization separation prism 13 is arranged corresponding to the terminal 11c. Then, the total reflection prism 14 is arranged in close contact with the lower surface of the polarization separation prism 12, and the total reflection prism 15 is arranged in close contact with the upper surface of the polarization separation prism 13 (FIG. 5B). These total reflection prisms 1
Reference numerals 4 and 15 are prisms for forming a reflection film of metal aluminum or the like on the hypotenuse of the triangular prism to reflect all transmitted light in the right angle direction. Furthermore, these polarization separation prisms 12
Faraday rotators 16 and 45-degree optical rotators 17 are sandwiched between and and 13 and total reflection prisms 14 and 15.

In this optical circulator, incident light is temporarily converted into 2
The polarized light components of the seed are orthogonally separated and then combined again. As a result, the optical path of the incident light incident from the terminal 11a and the optical path of the incident light incident from the terminal 11c are made different from each other. This allows forward transmitted light (terminal 1
1a) and the reverse transmitted light (incident from the terminal 11c) have different emission terminals.

In the illustrated optical circulator, an external magnetic field applying device (not shown) is arranged in the vicinity of the Faraday rotator 16, whereby the external magnetic field is applied in the direction indicated by the thick arrow 18 in FIGS. 5 (a) and 5 (b). Is given, which gives
Faraday rotation occurs in the Faraday rotator 16.

Now, referring to FIG. 6A, the terminal 11
When light (elliptically polarized light including components horizontal / vertical to the paper surface, hereinafter referred to as elliptically polarized light) is incident from a (forward incidence), the elliptically polarized light is reflected by the polarization separation prism 12 and a part of it is reflected. The light is transmitted and emitted as linearly polarized light having only a component perpendicular to the paper surface (hereinafter referred to as vertical linearly polarized light) and linearly polarized light having only a component horizontal to the paper surface (hereinafter referred to as horizontal linearly polarized light). Then, the horizontal linearly polarized light is immediately given to the Faraday rotator 16, and the vertical linearly polarized light is totally reflected by the total reflection prism 14 and given to the Faraday rotator 16. The directions of the planes of polarization of the vertical and horizontal linearly polarized light are changed by the Faraday rotator 16 which is a non-reciprocal element, and the polarization planes of the vertical and horizontal linearly polarized light are rotated by 45 degrees. Further, due to the presence of the 45-degree optical rotator 17, these separated polarized lights become horizontal and vertical linearly polarized lights, respectively.
Is incident on. On the other hand, vertical linearly polarized light is a total reflection prism 1.
The light is totally reflected at 5 and is incident on the polarization separation prism 13.
As a result, basically the same elliptically polarized light as the incident light is emitted from the polarization splitting prism 13 and given to the terminal 11c.

On the other hand, as shown in FIG. 6B, the terminal 11c
When the elliptically polarized light is incident from (reverse incidence), the elliptically polarized light is emitted from the terminal 11b in the same manner as described above.

In this way, due to the existence of the Faraday rotator 16, the polarization planes of the light incident from the forward direction and the reverse direction change non-reciprocally, and the 90-degree polarization plane shifts midway. As a result, the forward incidence and the backward incidence will eventually follow different paths (optical paths).

When light is incident from the terminal 11b, no light is emitted from any of the terminals 11a to 11c and is absorbed inside the optical circulator.

[0016]

By the way, in the conventional optical circulator, two pairs of the polarization splitting prism and the total reflection prism are arranged and fixed on the Faraday rotator and the 45-degree optical rotator. In the prism, it is necessary to perform accurate alignment and adhesive fixing so that the optical path does not shift.

Therefore, when performing the above-mentioned alignment,
The external magnetic field application device is actually arranged near the Faraday rotator, and the transmitted light in each component of the optical circulator is observed using the measuring laser light to align the prisms.

In such a conventional optical circulator, delicate prism positioning and bonding steps are required a plurality of times, which makes the optical circulator assembling step extremely troublesome. Therefore, there is a problem that it is difficult to reduce the working time in the assembly process, the cost cannot be reduced, and the yield is reduced.

An object of the present invention is to provide an optical circulator which can realize cost reduction and has a high yield rate.

[0020]

According to the present invention, an optical input terminal, an optical output terminal, and an optical input / output terminal are provided, and first, second, and third birefringent parallel plates, a Faraday rotator, And a 45-degree optical rotation plate, and along a predetermined direction, the first birefringent parallel flat plate, the second birefringent parallel flat plate, the Faraday rotator, the 45-degree optical rotation plate, and the third birefringent parallel plate. The birefringent parallel plates are sequentially arranged, and the first
Of the birefringent parallel flat plate includes a light emitting surface and a contact surface that faces the light emitting surface and is in close contact with the second birefringent parallel flat plate. 1
Of the birefringent parallel flat plate and a light-incident region in close contact with the close-contact face of the birefringent parallel plate, the third birefringent parallel flat plate has a light incident / exiting face, and the input terminal faces the light incident region.
The light output terminal faces the light output surface, the light input / output terminal faces the light input / output surface, and a magnetic field is applied near the Faraday rotator to generate Faraday rotation in the Faraday rotator. Means are provided for reflecting the transmitted light beams passing through the first and second birefringent parallel plates on the predetermined surfaces of the first and second birefringent parallel plates, respectively. A total reflection surface is formed, the incident light from the optical input terminal is emitted to the optical input / output terminal as outgoing light, and the incident light from the optical input / output terminal is emitted to the optical output terminal as outgoing light. An optical circulator characterized by doing so is obtained.

[0021]

In the present invention, since the birefringent parallel flat plate is used, optical alignment and the like can be easily performed in the assembling process. As a result, the assembling process can be simplified, the yield rate can be improved, and the cost can be reduced. Furthermore, when a plurality of circulators are created, optical alignment can be collectively performed in a large amount.

[0022]

EXAMPLES The present invention will be described below with reference to examples.

Referring to FIG. 1A, the illustrated optical circulator includes birefringent parallel flat plates 21, 22, and 23, a Faraday rotator 24, and a 45-degree optical rotation plate 25.
Further, the Faraday rotator 24 is provided with an external magnetic field applying device (not shown) for applying an external magnetic field in the direction indicated by the thick arrow 24a. A uniaxial optical crystal is generally used as the birefringent parallel plates 21 to 23, and a rutile parallel plate is used here. Birefringent parallel plates 21 to 2
3 has a crystal axis indicated by a thick arrow 26 in FIG. 1B, and this crystal axis represents the axial direction (C-axis direction) of the optical crystal. Further, total reflection surfaces 21a and 22a are formed on one surface of each of the birefringent parallel plates 21 and 22 (in FIG. 1A, the bottom surface of the birefringent parallel plate 21 and the top surface of the birefringent parallel plate 22 are respectively formed. Total reflection surface 21a
And 22a are formed). Further, here, a magnetic garnet film is used as the Faraday rotator 24, and
A SiO ₂ single crystal plate is used as the optical rotation plate 25. Since the magnetic garnet film is a ferromagnetic substance, it is sufficient for the external magnetism applying device to obtain a magnetic flux sufficient to magnetically saturate the magnetic garnet film. For example, SmCo,
A permanent magnet such as Nd-Fe-B may be used.

Next, the assembly of the optical circulator according to the present invention will be described with reference to FIG.

First, referring to FIG. 2A, two birefringent parallel plates 30 and 31 are prepared in a large plate state, and a Faraday rotator 32 and a 45-degree optical rotation plate 33 are arranged in a large plate state. prepare. The birefringent parallel plate 30, the Faraday rotator 32, the 45-degree optical rotation plate 33, and the birefringent parallel plate 31 are arranged in this order (the thick arrow 34 indicates the crystal axis (C
(Axis) represents the polarization component in the plane). Then, the external magnetic field applying device 35 is installed as illustrated. Next, the optical adjustment light is incident from the direction (forward direction) indicated by the one-dot chain line arrow,
By the transmitted light, the Faraday rotator 32 obtains a condition for giving a predetermined Faraday rotation angle to the transmitted light, and the optical adjustment of the rotation direction (indicated by an arrow 34a in the figure) is performed for each optical element, that is, the alignment is performed. While performing the above, each optical element is fixed to each other with an adhesive to obtain an optical circulator body.

Next, after removing the external magnetic field applying device 35, the optical circulator body is vertically and horizontally cut to obtain a plurality of optical circulator elements 36 as shown in FIG. 2B. As a result, a plurality of optical circulator elements having the birefringent parallel plates 22 and 23, the Faraday rotator 24, and the 45-degree optical rotation plate 25 are obtained.

After that, a predetermined surface of each optical circulator element is polished, and a metal film is formed if necessary to form a total reflection surface as described above. Further, an external magnetic field applying device (not shown) such as a permanent magnet is adhered and fixed to each optical circulator element 36, and in the presence of transmitted light for optical adjustment from the opposite direction, the birefringent parallel plate 21 (FIG. 1).
While aligning, bond and fix. Then, after the structure is housed in a housing (not shown), the terminals 11a, 11b,
And 11c form an optical circulator.

As described above, after the optical circulator body is obtained, the optical circulator body is cut to obtain a plurality of optical circulator elements. Therefore, the substantial alignment step is performed by a large number of optical circulator elements. However, as a result, it is possible to greatly simplify the assembly process as a result (it is necessary to align the first birefringent parallel plate with each optical circulator element). However, this does not complicate the assembly process because this alignment is relatively easy).

Next, the operation of the optical circulator according to the present invention will be described with reference to FIGS. 3 and 4.

First, referring to FIGS. 3 (a) and 3 (b),
FIG. 3A shows transmitted light when light is incident in the forward direction, that is, when signal light by a laser or the like (elliptical polarized light including components horizontal / vertical to the paper surface) is incident from the terminal 11a. 3B, and FIG. 3B shows polarization planes of transmitted light at positions A to E in FIG. 3A.

The signal light is separated by the birefringent parallel plate 22 into linearly polarized light containing only a component perpendicular to the paper surface and linearly polarized light containing only a component parallel to the paper surface, and the Faraday rotator 24
Given to. In the Faraday rotator 24, the directions of the polarization planes change non-reciprocally, and the polarization planes of the vertical and horizontal linearly polarized lights rotate, respectively. 45 degree optical rotation plate 2
Due to the presence of 5, the separated signal lights become horizontal and vertical linearly polarized lights, respectively, and enter the birefringent parallel plate 23. In the birefringent parallel plate 23, the horizontal linearly polarized light is bent as shown in the figure, and as a result, the horizontal and vertical linearly polarized light are combined and emitted from the terminal 11c as elliptically polarized light.

Next, referring to FIGS. 4A and 4B,
FIG. 4A shows an optical path of transmitted light when light is incident in the opposite direction, that is, when signal light (elliptically polarized light) is incident from the terminal 11c, and FIG. 4A shows polarization planes of transmitted light at positions A to E of FIG.

The signal light is separated by the birefringent parallel plate 23 into a linearly polarized light containing only a component perpendicular to the paper surface and a linearly polarized light containing only a component parallel to the paper surface and given to the 45-degree optical rotation plate 25. In the 45-degree optical rotation plate 25, the planes of polarization of the horizontal and vertical linearly polarized light are respectively rotated, and subsequently, the signal lights separated by the Faraday rotator 24 become the linearly and vertically linearly polarized light, respectively, and are incident on the birefringent parallel plate 22. It In the birefringent parallel plate 22, horizontal linearly polarized light is bent as shown in the drawing, and is totally reflected by the total reflection surface. Then, the horizontal and vertical linearly polarized lights are incident on the birefringent parallel plate 21, and the horizontal linearly polarized lights are totally reflected by the total reflection surface and combined with the vertical linearly polarized lights to be emitted from the terminal 11b as elliptically polarized lights.

The above-mentioned polarized light has a very small reflection angle (when a rutile parallel plate is used, the reflection angle is about 5.
Therefore, the total reflection surface can be formed only by forming a mirror surface, but a metal film or the like may be further formed on the reflection surface to form the total reflection surface, if necessary. The light emitted from the terminal 11b can be made parallel to the light incident from the terminal 11c by performing total reflection twice as described above.

The birefringent parallel plates 21 and 22 are fixed to each other by using an adhesive having the same refractive index as that of the birefringent parallel plates 21 or 22, or an AR coating is applied to each of the adhesives used for the contact surfaces of both. It is necessary to prevent reflection scattering, refraction, etc. of the transmitted light on the contact surface by such a method.

Although the birefringent parallel plates 21 and 22 are fixed with an adhesive in the above-mentioned embodiment, the birefringent parallel plates 21 and 22 are integrated instead of using the birefringent parallel plates 21 and 22. It is also possible to use a birefringent parallel plate having a different shape (integrated birefringent parallel plate). In this case, in producing the optical circulator, as described above, first, the Faraday rotator 24 and the 45-degree optical rotation plate 2 are used.
After obtaining a plurality of optical elements in which only 5 and the birefringent parallel plate 23 are fixed with an adhesive, the integrated birefringent parallel plate is aligned and bonded to each optical element.

[0037]

As described above, according to the present invention, by using a plurality of birefringent parallel flat plates, the step of aligning the optical elements in a large number of optical circulators can be performed once, and the alignment of each optical element can be fixed. You can simplify the work,
As a result, not only the yield rate is improved, but also the cost can be reduced.

[Brief description of drawings]

FIG. 1A is a perspective view showing an embodiment of an optical circulator according to the present invention, and FIG. 1B is a perspective view showing the optical circulator shown in FIG.

FIG. 2 is a diagram for explaining the production of the optical circulator according to the present invention.

3A is a diagram showing a path of forward transmitted light in the optical circulator shown in FIG. 1A, and FIG. 3B is a diagram for explaining a polarization plane of the transmitted light.

4A is a diagram showing a path of transmitted light in a reverse direction in the optical circulator shown in FIG. 1A, and FIG. 4B is a diagram for explaining a polarization plane of the transmitted light.

5A is a perspective view showing an example of a conventional optical circulator, and FIG. 5B is a view showing an optical path.

6A is a diagram showing a path of transmitted light in the forward direction in the optical circulator shown in FIG. 5A, and FIG. 6B is a diagram showing a path of transmitted light in the reverse direction.

FIG. 7 is a diagram showing an appearance of a three-terminal optical circulator.

[Explanation of symbols]

 21 birefringent parallel plate 22 birefringent parallel plate 23 birefringent parallel plate 24 Faraday rotator 25 45 degree optical rotation plate

Claims (4)

[Claims] 1. A light input terminal, a light output terminal, and a light input / output terminal, and a first, a second, and a third birefringent parallel flat plate, a Faraday rotator, and a 45-degree optical rotation plate.
The first birefringent parallel flat plate, the second birefringent parallel flat plate, the Faraday rotator, the 45-degree optical rotation plate, and the third birefringent parallel flat plate are sequentially arranged along a predetermined direction. The first birefringent parallel flat plate has a light exit surface and a contact surface that faces the light exit surface and is in close contact with the second birefringent parallel flat plate. One surface includes a close area that is in close contact with the close surface of the first birefringent parallel flat plate and a light incident area, the third birefringent parallel flat plate includes a light incident / exit surface, and the input terminal is the optical terminal. Facing the incident area, the light emitting terminal faces the light emitting surface, and the light input / output terminal faces the light incident and emitting surface. Faraday rotation is generated in the Faraday rotator near the Faraday rotator. Magnetic field applying means for Wherein and each of the predefined surface of the second birefringent parallel plate first and the second
Has a total reflection surface for totally reflecting transmitted light passing through the birefringent parallel flat plate, and the incident light from the optical input terminal is emitted to the optical input / output terminal as outgoing light, An optical circulator characterized in that incident light from a terminal is emitted to the optical output terminal as outgoing light. 2. The optical circulator according to claim 1, wherein the first and second birefringent parallel flat plates are integrated. 3. The optical circulator according to claim 1, wherein the total reflection surface is formed by making the predetermined surface a smooth surface. 4. The optical circulator according to claim 1 or 2, wherein the total reflection surface is formed by forming the reflection film on the smooth surface as the smooth surface. And optical circulator.