JP2000231080A - Optical circulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compacter optical circulator without increasing the number of component even when it is made into the multi-port one. SOLUTION: A double refraction member 3, a 1st phase member 4, a polarization rotator 5 and a composite double refraction member 6 are arranged between an arraying body 2 where at least, three or more optical fibers 2b are arrayed and a lens 7 in this optical circulator. A 2nd phase member 8 and a reflector 9 are arranged on an opposite side to the members 3, 4, 5 and 6 with respect to the lens 7.

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 the field of optical communication systems and optical measurement.

[0002]

2. Description of the Related Art An optical circulator is one of important non-reciprocal optical circuit elements in fields such as optical communication and optical measurement. The optical circulator has two optical circulators, one on the input side and the other on the output side.
In contrast to the port type, it has at least three or more ports, for example, if it has three ports represented by numbers 1, 2, and 3, in the forward direction, 1 → 2, 2 → 3, 3 → 1 The light traveling in the direction of (1) has low loss, and the light traveling in the opposite direction of 1 → 3, 3 → 2, 2 → 1 is transmitted as a high loss output.

As such an optical circulator, for example, an optical circulator disclosed in International Publication No. WO97 / 22034 is known.

[0004]

By the way, the optical circulator has a structure in which light is transmitted from one optical waveguide array arranged along the optical axis to the other optical waveguide array, and the number of components is large. Therefore, there is a problem that the size is increased. In addition, when the number of ports is to be increased, the number of components increases accordingly, and there is a problem that it is difficult to increase the number of ports and increase the number of ports.

The present invention has been made in view of the above points, and the number of components does not increase even if the number of ports is increased.
It is an object of the present invention to provide an optical circulator that is smaller than a conventional product.

[0006]

In order to achieve the above object, in an optical circulator of the present invention, a birefringent member, a first birefringent member, and a first birefringent member are provided between an array of at least three or more optical fibers and a lens. A phase member, a polarization rotator, and a complex birefringent member are arranged, and a second phase member and a reflector are arranged on the opposite side of these members with respect to the lens.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the optical circulator of the present invention will be described below in detail with reference to FIGS. As shown in FIG. 1, the optical circulator 1 includes a birefringent member 3, a first phase member 4, a polarization rotator 5, and a composite between an array 2 in which four optical fibers are arrayed and a lens 7. A birefringent member 6 is arranged, and a second phase member 8 and a reflector 9 are arranged on the opposite side of the lenses 7 of the constituent members 3 to 6. Birefringent member 3 to second phase member 8
It is desirable to use a material in which an anti-reflection coating such as SiO2 / TiO2 is applied to the light entrance / exit surfaces, respectively.

Here, FIGS. 3A and 3B show the arrangement from the birefringent member 3 to the reflector 9 and the traveling direction of light on the Z axis.
It shows the polarization state of light when the horizontal direction is the X axis and the vertical direction is the Y axis in a plane orthogonal to the Z axis. These X axis to Z axis are the same in other drawings attached to this specification. In the array 2, optical fibers 2b are arranged and fixed in four V-grooves (not shown) formed at equal intervals and in parallel (within a degree of parallelism of 3 degrees) on the surface of the substrate 2a. Here, the four optical fibers 2b are referred to as ports P1 to P4, respectively, as shown in FIG. 1 for convenience of distinction in the following description. At this time, the array 2 has the optical fiber 2b (port P1) closest to the central axis AcX of the lens 7.
Is a, and the width separated by the complex birefringent member 6 is d.
Then, the distance wn from the first optical fiber 2b to the n-th optical fiber 2b is defined as wn = Lf × n =
2 {a + 2 (n-1) d} + d (n = 1, 2, 3,...)
………). However, Lf is determined by taking into consideration the back focus of the lens 7 and the crystal length of the members constituting the optical circulator 1 and the relationship between the crystal length and the separation width, which is 126 μm in the present embodiment.
Set to.

Further, the plurality of optical fibers 2b heat the birefringent member 3 side to form a core of a TEC (thermal expanded corona).
e) process the mode field diameter (MFD)
MFD with reduced divergence angle by expanding
It has an enlarged portion 2c. As the MFD expansion unit 2c, the T
The optical fiber is not limited to the EC-treated optical fiber, but may be a distributed index fiber or a microlens. On the other hand, if the arrangement body 2 can arrange three or more optical fibers at equal intervals and in parallel, it is needless to say that the number of optical fibers may be as many as four or more. For example, various types such as a ferrule made of ceramics or SUS for a multi-core connector, a type in which a plurality of optical fibers are fixed to a V-groove array, or a type in which a plurality of optical fibers are molded with a synthetic resin can be used. .

The birefringent member 3 separates the light emitted from the optical fiber 2b into an ordinary ray and an extraordinary ray, and combines the reflected light reflected by the reflector 9 and returns. It is made to match the separation width that separates the light into extraordinary rays. As the birefringent member 3, a birefringent crystal plate or a uniaxial optical crystal (polarizer) is used. For example, rutile (TiO2), calcite (CaCO3), yttrium osovanadate (YVO)
4) There are crystals such as alpha barium bodate (αBaB2O4). The birefringent member 3 has an optical axis processed to about 42 to 50 degrees with respect to incident light so as to have a minimum crystal length, and rutile is preferable in consideration of availability and reliability of the crystal itself. The birefringent member 3 sets the crystal length t to a relationship of Lf = about 0.1 t with respect to the distance Lf between the optical fibers 2b, and in the present embodiment, an optical axis of 2 mm square and about 1.3 mm thick. The polarization splitter cut at 45 was used.

The first phase member 4 rotates the plane of polarization of the polarized light transmitted through the birefringent member 3 by 45 degrees. For example, a composite reciprocal polarization rotator or a composite half-wave plate is used.
Garnets such as TBIG and GBIG, and crystals are available. The composite reciprocal polarization rotator is desirably as thin as possible, such as a zero-order single plate or a first-order single plate. If a higher-order wave plate is used, wavelength characteristics and temperature characteristics are deteriorated. When the composite half-wave plate is used, the first phase member 4
As shown in (a), the optical axis AOP1 is -2 with respect to the Y axis.
The half-wave plate 4a tilted by 2.5 degrees and the half-wave plate 4b whose optical axis AOP2 is tilted by +22.5 degrees with respect to the Y axis are joined to each other at the joint surface 4.
The layers are overlapped in the Y-axis direction by c, and are bonded and used with an optical adhesive such as an ultraviolet curing type. The first phase member 4 takes care that the adhesive used does not protrude from the bonding surface 4c to the light input / output surface.

In this embodiment, as the first phase member 4,
A zero-order single-plate quartz wave plate having an inclination of the optical axis AOP1 of -22.5 degrees and an inclination of the optical axis AOP2 of +22.5 degrees is adjusted so that the chipping of the bonding surface 4c with a dicing saw has an accuracy of 0.02 mm or less. Was used. The polarization rotator 5 is a non-reciprocal polarization rotator that rotates the polarization plane of the polarized light transmitted through the first phase member 4, and has an optical rotation angle of 45 in the used wavelength band.
Use something as thin as possible. Polarization rotator 5
For example, garnet, TBIG (terbium bismuth iron garnet), GBIG (gadolinium bismuth iron garnet), or the like can be used. In the present embodiment, the garnet clockwise with respect to the traveling direction of light is used. However, when the garnet clockwise is used, the first phase member 4 has an optical axis AOP1 of +22.5 degrees and an optical axis AOP2 of The inclination may be -22.5 degrees.

The position of the polarization rotator 5 may be replaced with the position of the first phase member 4 in FIG. With this arrangement, the polarization rotator 5 can be used where the beam diameter of the light is small because the spread angle of the transmitted light is constant. Therefore, in the optical circulator 1, when the polarization rotator 5 is arranged in this manner, the possibility of beam kick due to an assembly error or a processing error of a component is reduced.

The complex birefringent member 6 switches an ordinary ray into an extraordinary ray and an extraordinary ray into an ordinary ray.
A half of the interval between the optical fibers 2b is made equal to the separation width for separating the ordinary ray and the extraordinary ray. As the composite birefringent member 6, a composite birefringent crystal plate or a composite uniaxial optical crystal (polarizer) is used. There are crystals such as (αBaB2O4). For example, as shown in FIG. 4A, the complex birefringent member 6 includes a crystal plate 6a in which the optical axis AOP1 is inclined by about θ1 = −42 to −50 degrees with respect to the Z axis and the optical axis AOP2 is in On the other hand, θ2 = about +4
The crystal plate 6b inclined by 2 to +50 degrees is overlapped in the X direction at the joint surface 6c, and is used by bonding with an optical adhesive. The complex birefringent member 6 is arranged so that the crystal axis is orthogonal to the crystal axis of the birefringent member 3.

At this time, care should be taken so that the adhesive of the composite birefringent member 6 does not protrude from the joining surface 6c to the light entrance / exit surface. The composite birefringent member 6 is obtained by cutting the crystal plates 6a and 6b with a dicing saw so that the chipping has an accuracy of 0.1 mm or less, and the adhesive is made as thin as possible to reduce the pyramidal error. (Pyramidal
error). In this embodiment, two Savart plates having a thickness of about 0.63 mm, in which the optical axes AOP1 and AOP2 are cut at ± 45 degrees with respect to the Z axis, are inverted, and rutile is bonded at the bonding surface 6c as shown in FIG. Was used.

Here, the composite birefringent member 6 is shown in FIG.
As shown in FIG. 4, on the contrary to the case of FIG.
1 is the crystal plate 6a inclined at θ1 = about +42 to +50 degrees with respect to the Z axis, and the optical axis AOP2 is at θ2 = about −42 to −5 with respect to the Z axis.
The crystal plate 6b inclined at 0 degrees is overlapped in the X direction at the joint surface 6c,
You may bond with an optical adhesive. In this case, the four optical fibers 2b are ports P3 and P4 near the central axis Ac of the lens 7, and ports P1 and P2 are far optical fibers 2b, contrary to the case shown in FIG. .

The lens 7 cancels and collimates the polarization mode dispersion of incident light, and may be an aspherical lens, a ball lens, a plano-convex lens, a distributed refraction lens, or the like. However, as the lens 7, a lens having a back focus in which the constituent members 3 to 6 can be arranged between the lens and the array 2 is used. In this embodiment,
An aspheric lens having a focal length f = 1.8 mm was used.

The second phase member 8 is a retardation plate such as a quarter-wave plate, and a 0th-order single plate or a 0th-order 2-plate quartz plate is appropriate. And the temperature characteristics deteriorate. The second phase member 8 may use a non-reciprocal polarization rotator of 45-degree optical rotation, for example, a garnet such as GBIG. In the present embodiment, the optical axis A is used as the second phase member 8.
A quarter-wave plate in which the OP was set at 45 degrees with respect to the polarization direction was used.

The reflector 9 is a reflecting mirror for reflecting the light passing through the second phase member 8, and in the present embodiment, for example, a reflecting mirror in which the surface of a base 9a is coated with SiO2 / TiO2 is used. As described above, the optical circulator 1 of the present invention comprises the birefringent member 3, the first phase member 4, the polarization rotator 5 between the lens 7 and the array 2 in which the four optical fibers 2b are arrayed. And the complex birefringent member 6 is disposed,
It is characterized in that the second phase member 8 and the reflector 9 are arranged on the opposite side to the lenses 7 to 6. That is, the optical circulator 1 has a structure in which light incident from any one of the optical fibers 2b of the array 2 is reflected by the reflector 9 to be folded.

Therefore, in the optical circulator 1, for example, the light that has entered the ports 1 of the four optical fibers 2b, on a plane including the X and Y axes, as shown in FIG. The light propagates to the second phase member 8, is reflected by the reflector 9, and is emitted to the ports 2 of the four optical fibers 2b with low loss as shown in FIG. At this time, in FIGS. 2 (a) and 2 (b), circles indicate polarized light that oscillates in the Z-axis direction perpendicular to the paper with respect to the traveling direction of light, and arrows indicate X parallel to the paper with respect to the traveling direction of light. A polarized light that vibrates in the axial direction.

However, the light that has entered the port 4 of the four optical fibers 2b has a large loss, so that it does not travel in the reverse direction and exit to the port 1. Similarly, the optical fiber 2b
Is emitted from port 2 → port 3, port 3 → port 4, but does not travel in the opposite direction. Thus, the optical circulator 1 has non-reciprocal characteristics with respect to the light propagation direction.

At this time, as defined in FIGS. 3A and 3B, the traveling direction of the light is defined as the Z axis, the horizontal direction in a plane orthogonal to the Z axis is defined as the X axis, and the vertical direction is defined as the Y axis. , Reflector 9
When viewed from the side, the horizontal direction is the X axis, the vertical direction is the Y axis,
For convenience of description, the horizontal direction is divided into 13 and the vertical direction is divided into 1 to 13 and the vertical direction is divided into 5 and represented by a to e.
Is "6d" as shown in FIG. 5A when viewed in a matrix. This relationship is the same in FIGS. 5B to 6G below. The symbol AcY is the central axis of the lens 7 in the Y-axis direction, and the symbol AcX is the central axis of the lens 7 in the X-axis direction.

Accordingly, for example, the light incident on the port 1 propagates through the optical fiber 2b and is emitted to the birefringent member 3, and as shown in FIG. It is split into orthogonal ordinary rays and extraordinarily parallel extraordinary rays. Next, in the first phase member 4, the optical axis AOP1 is -22.5 degrees with respect to the Y axis, and the optical axis AOP2 is +22.
Since they are tilted by 5 degrees, the separated ordinary ray and extraordinary ray pass through the first phase member 4, and as shown in FIG. In the same direction. Here, in the drawing, reference numeral 4c is a joining surface of the two zero-order single-plate quartz wave plates.

Next, these lights pass through the polarization rotator 5 and are rotated counterclockwise as shown in FIG. 5D, so that they are polarized to be parallel to the crystal axis of the birefringent member 3. Can be Thereafter, these lights enter the complex birefringent member 6. At this time, since the crystal axis of the composite birefringent member 6 is orthogonal to the crystal axis of the birefringent member 3, as shown in FIG. Passes as an ordinary ray.

Next, the light that has passed through the complex birefringent member 6 is refracted at a predetermined angle by the lens 7, but the polarization state does not change as shown in FIG. The refraction angle at this time is determined from the central axes AcX and AcY of the lens 7 by the central position of light and the focal length f of the lens 7. Next, the light that has passed through the lens 7 enters the second phase member 8. The second phase member 8
Since the optical axis AOP is set at 45 degrees with respect to the polarization direction, the light passing therethrough becomes right circularly polarized light as shown in FIG.

The right circularly polarized light is reflected by the reflector 9
In FIG. 6, the phase changes due to reflection on the side opposite to the incident angle.
The left circularly polarized light shown in FIG. Thus, in the optical circulator 1, light is reflected by the reflector 9,
The overall optical path length is reduced. Next, the reflected left-handed circularly polarized light passes through the second phase member 8 again, and as shown in FIG.
As shown in FIG. 5, the light is polarized in the horizontal direction orthogonal to the light passing through the lens 7 (see FIG. 5F).

Next, the polarized light in the horizontal direction is again transmitted to the lens 7.
As shown in FIG. 6 (c), the light is emitted at a position symmetrical to the center axis AcY of the lens 7 as shown in FIG. 5 (f). At this time, the polarization state does not change before and after passing through the lens 7. After that, the polarized light that has passed through the lens 7 passes through the complex birefringent member 6, and the beam position shifts to the right in the horizontal direction as an extraordinary ray, as shown in FIG.

Next, after passing through the polarization rotator 5, these polarized lights are rotated to the left by 45 degrees as shown in FIG. This state is the same as the polarization state after passing through the first phase member 4 from the birefringent member 3 side, as shown in FIG. Then, when these lights pass through the first phase member 4, as shown in FIG.
And the polarization direction becomes the orthogonal direction.

After that, these lights pass through the birefringent member 3 to be multiplexed as ordinary rays and extraordinary rays, respectively, and correspond to “9d” as shown in FIG. 6 (g). The light enters the optical fiber 2b of the port 2. Here, in the figure, “1d”, “4d”, “6d”, and “11d”
The circles with d "indicate positions corresponding to the other ports.

Hereinafter, also for the other ports 2, 3, and 4,
The light is propagated between the birefringent member 3 and the reflector 9 as described above. As described above, in the optical circulator 1, the birefringent member 3, the first phase member 4, the polarization rotator 5, and the complex birefringent member 6 are arranged between the array 2 and the lens 7,
The second embodiment is characterized in that a second phase member 8 and a reflector 9 are arranged on the opposite side of the lens 7 of the constituent members 3 to 6. For this reason, the optical circulator 1 can be reduced in size by halving the number of components compared to a structure that does not reflect light, even if the number of optical fibers, and thus the number of ports, is large. Further, the light reflected on the surfaces of the constituent members 3 to 6 diverges at twice the reflection angle, so that it is difficult to enter the optical fiber 2b. For this reason, the optical circulator 1 does not need to take measures against return loss.

[0031]

According to the first aspect of the present invention, even if the number of ports is increased, the number of components does not increase, and an optical circulator smaller than conventional products can be provided.

[Brief description of the drawings]

FIG. 1 is a plan view showing a configuration of an optical circulator of the present invention.

2A is a cross-sectional view illustrating a polarization state of incident light in a cross section along a port of a plurality of optical fibers, and FIG. 2B is a cross-sectional view illustrating a polarization state of reflected light returning from a reflector. FIG.

FIG. 3 shows the arrangement from the birefringent member to the reflector in the optical circulator of FIG. 1, the direction of light propagation as the Z axis, the horizontal direction in a plane perpendicular to the Z axis as the X axis, and the vertical direction as the Y axis.
FIG. 3 is a perspective view showing a polarization state of light when the axis is divided into a first half (a) and a second half (b).

FIG. 4 is a perspective view showing a first arrangement of optical axes of two crystal plates constituting a complex birefringent member in the optical circulator of FIG. 1, and FIG. 4B is a perspective view showing a second arrangement; It is.

FIG. 5 is an explanatory diagram showing a first half of a state of light after passing through each constituent member in the optical circulator of FIG. 1;

FIG. 6 is an explanatory view showing the latter half of the state of light after passing through each component in the optical circulator of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical circulator 2 Array 2b Optical fiber 2c MFD expansion part 3 Birefringent member 4 First phase member 5 Polarization rotator 6 Composite birefringent member 7 Lens 8 Second phase member 9 Reflector AcX, AcY Central axis (of lens ) AOP optical axis AOP1, AOP2 optical axis P1 ~ P4 port

Claims (1)

[Claims] 1. A birefringent member, a first phase member, a polarization rotator, and a compound birefringent member are arranged between an array in which at least three or more optical fibers are arranged and a lens. An optical circulator, wherein a second phase member and a reflector are arranged on a side of the member opposite to the lens.