JPH1152294A - Optical isolator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce reflected and scattered light so as to improve optical characteristic and to realize miniaturization and economization. SOLUTION: Light in a forward direction from an optical waveguide 1 having TEC(terminal expanded core) structure is changed to parallel beams at a lens part 1a; the 1st half of the light is transmitted through a 1/2 wavelength plate 7 and a magnetic garnet 5 and made incident on a lens part 3a; and the 2nd half of the light is transmitted through the magnetic garnet 5 and a 1/2 wavelength plate 9, made incident on a lens part 3a, synthesized with the 1st half of the light and emitted through an optical waveguide 3. The transmitted light in a reverse direction from the waveguide 3 is changed to the parallel beams at the lens part 3a; the 1st half of the light is transmitted through the magnetic garnet 5 and the plate 7 and made incident on the lens part 1a; and the 2nd half of the light is transmitted through the plate 9 and the magnetic garnet 5, made incident on the lens part 1a and negated with the 1st half of the light each other so as not to be transmitted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical isolator that transmits only forward transmission light with low loss and blocks reverse return light, and more particularly, as an optical passive component, mainly for optical communication related optical signal transmission. The present invention relates to an optical isolator used for organizing paths.

[0002]

2. Description of the Related Art In an optical communication system, use of an optical fiber amplifier for directly amplifying an optical signal as it is without replacing the optical signal with an electric signal has been studied in recent years. In this case, an Er-doped optical fiber having a specific length is installed in the amplifier, and the amplified signal light and pumping light are transmitted therethrough to obtain amplified light. It is indispensable for an optical fiber amplifier to use an optical isolator that transmits only light transmitted in the forward direction with low loss and blocks return light in the reverse direction.

There are two types of optical isolators: a polarization-dependent type that transmits only a specific polarization component of the transmitted light in the forward direction, and a polarization-independent type that transmits all components of the transmitted light. Although both optical isolators are used in an optical communication system, the polarization-dependent type is often used in the vicinity of an optical communication laser, and the polarization-independent type is often used in the middle of an optical fiber through which signal light passes. Of these, a polarization-independent optical isolator having a relatively complicated structure is of the type using a parallel birefringent flat plate (Japanese Patent Laid-Open No. 54-159245) and the type using a tapered birefringent plate (Japanese Patent Publication No. 61-159). No. 58809) have been proposed.

[0004] An example of the polarization-independent optical isolator shown in FIG. 8 was proposed by Shintaku et al. (C-3-98 p283 new structure polarization-independent optical isolator, 1997-1997 IEICE General Conference). It has a magnetic garnet 101 as one Faraday rotator, two half-wave plates 102, and two lens mechanisms 103, and optical fibers 1 at both ends.
This is an optical isolator composed of the components 04a and 104b.
Reference numeral 105 denotes a magnet that applies a magnetic field to the magnetic garnet 101.

FIG. 9 shows another conventional polarization-independent optical isolator. In this conventional optical isolator, an optical element such as a birefringent parallel plate or a polarization splitting prism is used, and transmitted light is always orthogonal to each other. The operation of separating and synthesizing into polarized light was performed. In FIG. 9, reference numeral 91 denotes a birefringent element, 92 denotes a 45 ° optical rotation element, and 93 denotes a magnetic garnet.

Although the optical isolator of FIG. 8 separates transmitted light, it does not separate light components of the same intensity as mixed light components, but does not separate light components of orthogonal polarization as in the optical isolator of FIG. is there. The two types of separated light include the same amount of the same polarization component, respectively, and in the case of forward transmission light, they are combined again at the end face of the optical fiber 104b after passing through the exit lens. In this case, since the two separated lights to be combined are in a mutually reinforcing relationship, the transmitted light passes through the optical isolator without attenuation.
It is most desirable that the light transmitted through the magnetic garnet 101, which is a Faraday rotator between the two lenses, and the half-wave plate 102 be parallel light.

On the other hand, in the case of transmitted light in the opposite direction in this optical isolator, the lights separated at the end of the optical fiber 104b cancel each other when they are combined at the end of the optical fiber 104a on the output side. In a relationship. Therefore, the transmitted light in the backward direction does not pass through the optical fiber, which indicates that the optical device functions as an optical isolator.

[0008]

In the conventional polarization-independent optical isolator shown in FIG. 8, the two separated lights do not follow completely different paths in a state where they are separated from each other, but actually spread greatly. It is considered that each parallel light, or half of the transmitted light according to it, is half. 2 of transmitted light
Since the kind of light is transmitted into different optical elements and then combined into one light again, it is described that the light is separated into two. However, in practice, the boundary between the two separated lights is continuous. On the contrary, since this boundary is located at the center of the light transmission area, it is considered that the light intensity of the transmitted light is usually the maximum area. Such an optical element (1
/ 2 wavelength plate), it is conceivable that the light transmitted through the side portion of the optical element scatters or interferes with the irregular behavior. It is considered that the influence of such light becomes remarkable especially in the case of transmitted light in the reverse direction.

It is very difficult to reduce the scattered light to zero due to the structure of a conventional optical isolator. A factor that further increases such scattered light is that when the transmitted light between the two lenses is not parallel light, the transmitted light is incident on the end face of the optical element from an oblique direction. (Because the end face of the element is parallel, the amount of light reflected and scattered at the end face is very small.) Since the installation position of the half-wave plate is structurally different in the transmission path of the two separated lights, 2
In order to install an independent lens in the optical path, where the end faces of the optical element of the separated light are not aligned and the stepped area becomes a source of reflection / scattering, a certain amount of Precise positioning required for the adhesive fixing of the half-wave plate installed on the front and back of the Faraday rotator, because the volume is absolutely necessary in the optical path and the optical distance between the two optical fibers is long as a result. Is difficult,
Further, since both optical elements are half the size of the Faraday rotator, it is possible that a slight overflow of the bonding agent at the time of bonding scatters transmitted light.

[0010] The present invention has been made in view of the above,
It is an object of the present invention to provide an optical isolator having improved optical characteristics by reducing reflected / scattered light.

[0011]

According to a first aspect of the present invention, there is provided a first optical waveguide having a lens portion formed at one end and a lens portion of the first optical waveguide. A second optical waveguide having a lens portion formed at one end facing the first optical waveguide, a Faraday rotator disposed between the lens portions of the first and second optical waveguides, and a lens of the first optical waveguide The first half of the light from the section is transmitted and the second half of the light is transmitted directly through the Faraday rotator.
A first half-wave plate joined to a first half side of a first surface of the Faraday rotator facing a lens portion of the optical waveguide, and opposite to the first surface of the Faraday rotator The second half of the second surface of the Faraday rotator, and the second half of the light from the second half of the second surface of the Faraday rotator is transmitted through the second half of the second light guide. The first half light from the Faraday rotator is incident on the lens portion of the optical waveguide, and the second half is directly incident on the lens portion of the second optical waveguide.
The point is to have a wave plate and magnetic field applying means for applying a magnetic field to the Faraday rotator.

According to the first aspect of the present invention, the light transmitted in the forward direction from the first optical waveguide becomes parallel light in the lens portion, and the first half of the light is halved in the first half. The light passes through the wavelength plate and the lens portion of the second optical waveguide through the Faraday rotator, and the second half light is transmitted through the Faraday rotator and the second 1/1/2.
The light passes through the lens portion of the second optical waveguide via the two-wavelength plate, is combined with the first half of the light, passes through the second optical waveguide, emits the light, and reverses the light from the second optical waveguide. The first half light is transmitted through the Faraday rotator and the first half-wave plate through the lens portion of the first optical waveguide, and the second half light is transmitted through the lens portion. Half of the light passes through the lens portion of the first optical waveguide through the second half-wave plate and the Faraday rotator, cancels out the first half of the light, and cannot be transmitted.

[0013] The present invention described in claim 2 provides the present invention in claim 1.
In the invention described above, the first and second optical waveguides are optical waveguides having a TEC structure having an enlarged portion as the lens portion.

Further, the present invention according to claim 3 provides the invention according to claim 1.
In the invention described above, the first and second optical waveguides are optical waveguides having a spherical lens having a spherical lens as the lens portion.

According to a fourth aspect of the present invention, a first optical waveguide is connected to one end of one end of the first optical waveguide, and the light incident from the one side is split into two to form a pair. A first light combining / branching unit that emits light from the other side of the pair, combines light incident from the other side of the pair, and emits the light from the one side,
A pair of one ends are connected to the other side of the pair of first light combining / branching units, and a pair of other ends are connected to the pair of other ends to separately guide the first and second lights branched by the first light combining / branching unit. A first pair of optical waveguides each having a lens portion formed thereon, and a pair of lens portions respectively opposed to the pair of lens portions formed at a pair of other ends of the first pair of optical waveguides. A second pair of optical waveguides formed at one pair of ends, a pair of one sides are connected to a pair of other ends of the second optical waveguide, and a pair of the other ends of the second optical waveguide are connected to each other. A second light combining / branching unit that combines light incident on one side of the pair, emits the light from the other side, splits the light incident from the other side into two, and emits the light from the one side of the pair. And a second optical waveguide connected to the other side of the second optical coupling / branching means; and the first and second optical waveguides. Disposed between each pair of lens portions of the first optical waveguide, light from one of the pair of lens portions of the first pair of optical waveguides directly enters one surface, and A Faraday rotator in which light from one of the pair of lens portions of the optical waveguide is directly incident on the other surface, and one surface of the Faraday rotator and the other of the pair of lens portions of the first pair of optical waveguides; The first half disposed between
A wave plate, the other surface of the Faraday rotator and the second
And a magnetic field applying means for applying a magnetic field to the Faraday rotator, the second half wavelength plate being disposed between the other of the pair of lens portions of the optical waveguide.

According to the present invention, the transmitted light in the forward direction from the first optical waveguide is split by the first light splitting means, and the split first and second lights are separated by the first light splitting means. Through the first pair of optical waveguides, it becomes parallel light at its lens portion, and the first light is split into a first half-wave plate, a Faraday rotator, and a second
Through one of the lens portions of the pair of optical waveguides and one of the second pair of optical waveguides to reach the second optical coupling / branching means, where the second light is a Faraday rotator and a second half-wave plate. The other of the lens portions of the second pair of optical waveguides and the other of the second pair of optical waveguides, to the second optical coupling / branching means, and combined with the first light, from the second optical waveguide. The emitted light and the transmitted light in the opposite direction from the second optical waveguide are split by the second optical coupling / branching means, and the split first and second lights are transmitted through the second pair of optical waveguides. The light becomes parallel light at the lens portion, and the first light passes through the Faraday rotator, the first half-wave plate, one of the lens portions of the first pair of optical waveguides, and one of the first pair of optical waveguides. To the first light combining / branching means, and the second light
を wavelength plate, the Faraday rotator, the other of the lens units of the first pair of optical waveguides, and the other of the second pair of optical waveguides to reach the first optical coupling / branching unit, where the first light Cancel each other out and cannot be transmitted.

The present invention according to claim 5 provides the present invention according to claim 4.
In the invention described above, the gist is that the first and second pairs of optical waveguides are optical waveguides having a TEC structure having an enlarged portion as the lens portion.

Further, the present invention according to claim 6 provides the invention according to claim 4.
In the invention described above, the gist is that the first and second pairs of optical waveguides are an optical waveguide with a spherical lens having a spherical lens as the lens portion.

According to a seventh aspect of the present invention, there is provided a first optical waveguide having a PLC structure, and a second optical waveguide having a PLC structure having one end disposed opposite to one end of the first optical waveguide. A Faraday rotator disposed between opposed ends of the first and second optical waveguides; a first half of light from one end of the first optical waveguide is transmitted; Of the first Faraday rotator is connected to the first half of the first surface of the Faraday rotator facing one end of the first optical waveguide so that half of the light is directly transmitted through the Faraday rotator. A two-wave plate and a second half of the Faraday rotator joined to a second half of the Faraday rotator opposite to the first surface, the second half of the second surface of the Faraday rotator being The second half of the light is transmitted, enters the second optical waveguide, and is transmitted from the Faraday rotator. Serial first half light and a second half-wave plate incident to direct the second optical waveguide, and summarized in that and a magnetic field applying means for applying a magnetic field to the Faraday rotator.

According to a seventh aspect of the present invention, a PLC
The forward transmitted light from the first optical waveguide having the structure is separated into two lights by the PLC structure, and the first half light passes through the first half-wave plate and the Faraday rotator, The light reaches the second optical waveguide having the PLC structure, and the second half of the light passes through the Faraday rotator and the second half-wave plate, and
The light reaches the second optical waveguide having the C structure, is combined with the first half light, is emitted from the second optical waveguide, and the transmitted light in the opposite direction from the second optical waveguide is converted into two light beams by the PLC structure. And the first half of the light is split by the Faraday rotator, the first 1
The second half of the light passes through the half-wave plate and reaches the second optical waveguide, and the second half of the light passes through the second half-wave plate and the Faraday rotator to reach the second optical waveguide. When combined with the PLC structure of the second optical waveguide, the first half light cancels each other and cannot be transmitted.

The present invention according to claim 8 provides the present invention according to claim 1.
In the invention described in any one of the first to seventh aspects, the Faraday rotator includes first and second Faraday rotators that are divided into two, and the first Faraday rotator is configured to be the first 1/2. The second wavelength plate is integrally joined to the second wavelength plate,
Is integrally joined to the second half-wave plate, and the first integrated Faraday rotator and the second half-wave plate are integrally joined to the second half-wave plate. And the second integrated structure of the second Faraday rotator and the second half-wave plate, which are integrally joined, are continuous with each other so that there is no step in the light entrance / exit surface. The gist is that it is joined to

[0022]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a configuration of an optical isolator according to a first embodiment of the present invention. In the figure, 1
Numerals 3 and 3 denote optical waveguides having a TEC (Thermal Expanded Core) structure. At one end, lens portions 1a and 3a formed by enlarging the core portion by heating are provided. 5 is a magnetic garnet as a Faraday rotator, 7 and 9 are half-wave plates, 11
Is a magnet for applying a magnetic field to the magnetic garnet 5.

In the optical isolator thus configured, the transmitted light in the forward direction from the optical waveguide 1 having the TEC structure is converted into parallel light by the lens portion 1a and the first
Half of the light passes through the half-wave plate 7 and the magnetic garnet 5 which is a Faraday rotator in order, and enters the lens portion 3a without passing through the half-wave plate 9, and The light does not pass through the half-wave plate 7 but passes through the magnetic garnet 5, which is a Faraday rotator, and the half-wave plate 9 in sequence, enters the lens unit 3a, and is combined with the first half light. Then, the light exits through the optical waveguide 1b.

The transmitted light in the opposite direction from the optical waveguide 3 having the TEC structure becomes parallel light at the lens portion 3a, and the first half of the light passes through the magnetic garnet 5 and the half-wave plate 7. Then, the second half light is transmitted through the half-wave plate 9 and the magnetic garnet 5 and is incident on the lens portion 1a to cancel out the first half light with each other. It cannot be transmitted.

The lens portions 1a and 3a have a function as a lens by expanding the diameter of the optical fibers constituting the optical waveguides 1 and 3 to several times by heating the core portions thereof. Among the optical waveguides 1 and 3 having the TEC structure, those using optical fibers are also called core-expanded fibers. Then, the light emitted from the optical waveguide 1 having the TEC structure becomes parallel light.

In this embodiment, the half-wave plates 7, 9
The magnetic garnet 5 and the magnetic garnet 5 constitute an optical element. Assuming that transmitted light in a communication wavelength band of 1.55 μm is assumed, the thickness of the magnetic garnet 5 is generally about 500 μm.
When the half-wave plates 7, 9 are made of quartz, their thickness is about 90 μm.

The optical isolator according to the present embodiment employs the optical waveguides 1 and 3 having the TEC structure with respect to the conventional optical isolator shown in FIG.
Since the optical fiber 3a is provided integrally with the optical fibers serving as the optical waveguides 1 and 3, the optical alignment work and optical adjustment at the time of assembly are easy, and the total length of the optical isolator is shortened, resulting in miniaturization. Accordingly, the area of the optical element used can be reduced, and the cost can be reduced. Assuming the above-mentioned transmitted light of 1.55 μm, the distance between the optical waveguides 1 and 3 on both sides can be set to 1 mm or less.

That is, in the optical isolator of this embodiment, the optical adjustment of the optical waveguide and the lens unit can be performed in advance by the optical waveguides 1 and 3 having the TEC structure integrally having the lens units 1a and 3a. It can facilitate the optical alignment work of the assembled type of isolator,
The configuration of the optical element can be reduced in size. Further, the transmitted light between the lens portions 1a and 3a of each optical waveguide is always maintained as a parallel light or a state close to the parallel light, so that the optical characteristics of the optical isolator can be improved. Since optical adjustment between the waveguides 1 and 3 is not required, adjustment after assembly is easy, and a structure for separately holding a lens portion is unnecessary. The total length of the isolator can be shortened. Furthermore, the area occupied by the optical element composed of the Faraday rotator and the half-wave plate required for one optical isolator structure can be reduced, and the cost can be reduced.

FIG. 2 is a perspective view showing the structure of an optical isolator according to a second embodiment of the present invention. The optical isolator shown in the figure uses the TEC fibers 21 and 23 as the optical waveguides 1 and 3 having the TEC structure in the first embodiment shown in FIG. 1, respectively.
One end of each of the C fibers 21 and 23 has a lens portion 2
1a and 23a are formed. The other configurations of the magnetic garnet 5 and the half-wave plates 7, 9 are the same as those of the optical isolator of FIG. In FIG. 2, a magnet for applying a magnetic field to the magnetic garnet is omitted.

In FIG. 2, 13 is a substrate,
Numeral 15 denotes a V-shaped groove formed in the substrate 13;
The TEC fibers 21 and 23 are disposed in the V-shaped groove 15. Reference numeral 17 denotes a vertical groove-shaped notch formed in the substrate 13, and an optical element including the magnetic garnet 5 and the half-wave plates 7 and 9 is provided in the notch 17.

The TEC fiber 2 is inserted into the V-shaped groove 15.
Since the lenses 1 and 23 can be disposed so that the lens portions 21a and 23a face each other accurately, the number of assembling steps is small, and the optical adjustment at that time is easy.

The operation of the optical isolator of FIG. 2 thus configured is the same as that of the optical isolator of FIG.
The transmitted light in the forward direction from the fiber 21 is
1a, the light becomes parallel light, and the first half of the light passes through the half-wave plate 7 and the magnetic garnet 5 in that order, and the lens portion 23
a, and the second half of the light is
The light passes through the half-wave plate 9 in order, enters the lens portion 23 a, is combined with the first half light, and exits from the TEC fiber 23.

The light transmitted in the opposite direction from the TEC fiber 23 is converted into parallel light by the lens portion 23a, and the first half of the light passes through the magnetic garnet 5 and the half-wave plate 7 and passes through the lens portion 23a. The second half light is transmitted through the half-wave plate 9 and the magnetic garnet 5 and is incident on the lens portion 21a, and is canceled by the first half light and cannot be transmitted.

FIG. 3 is a diagram showing a configuration of an optical isolator according to a third embodiment of the present invention. The optical isolator shown in the figure is different from the optical isolator of the first embodiment shown in FIG. 1 in that optical waveguides 31 and 33 with spherical lenses are used instead of the optical waveguides 1 and 3 having the TEC structure. The other configuration, operation, and effects are the same as those of the optical isolator of the embodiment shown in FIG. In addition, the opposing ends of the optical waveguides 31 and 33 with the spherical lenses are provided at the ends shown in FIG.
Lens part 3 in the same manner as the lens part of the optical waveguide having the TEC structure
1a and 33a are provided.

The optical waveguides 31 and 33 with spherical lenses have a structure in which spherical lens portions 31a and 33a having a diameter of several tens to several hundreds of micrometers are bonded or fused to the tip of the core portion of an optical waveguide such as an optical fiber. If properly designed, the emitted light can be made into parallel light.

FIG. 4 is a diagram showing a configuration of an optical isolator according to a fourth embodiment of the present invention. In the optical isolator shown in FIG. 5, the magnetic garnet 5 constituting the Faraday rotator in the optical isolator of the embodiment shown in FIG. 1 is divided into upper and lower parts, and first and second magnetic garnets 5a and 5b are provided.
And the other configuration, operation, and effects are the same as those of the optical isolator of the first embodiment described above.

The half-wave plates 7 and 9 and the magnetic garnet 5 used in the optical isolator of the fourth embodiment.
The optical element composed of a and 5b is manufactured by dividing the optical element into upper and lower halves. As shown in FIG. The two-wavelength plate 53 is attached, cut into two or more pieces as shown in the figure, and then, as shown in FIG.
5b and the half-wave plates 7, 9 are taken out and combined. The magnetic garnets 5a and 5b and the half-wave plates 7 and 9 are desirably elements cut out from the same block. In this case, the magnetic garnets 5a and 5b and the half-wave plates 7 and 9 are used. The thickness of the optical elements is equal, the Faraday rotation angle and 1
The directions of the optical axes of the half-wave plates are also equal to each other.

By using the optical element configured as described above, the step at the connection point between the two optical elements can be made almost zero. One of the causes of scattering and refraction of the light transmitted through the connection point is the presence of the step. By eliminating the step, optical characteristics such as insertion loss and isolation of the optical isolator can be improved. . As in the case of the above-described first to third embodiments,
Assuming 1.55 μm transmitted light in the communication wavelength band,
The thickness of the magnetic garnets 5a and 5b is generally about 500 μm.
In the case where the half-wave plates 7 and 9 are made of quartz, their thicknesses are about 90 μm, respectively. Therefore, the thickness of the optical element at the center is about 600 μm in the present embodiment. The length is slightly shorter than that of the embodiment by 100 μm. In addition,
In the upper and lower two-stage optical elements, the optical axes of the half-wave plates 7 and 9 need to have an angle of 45 ° or 135 °. As shown in FIG. 5, in the case where the optical element is formed of elements cut out from the same optical element block, since the optical axis is oriented symmetrically with respect to the surface of the connection point, the inclination of the optical axis is ± 22 with respect to the surface of the connection point. 0.5 ° or ± 67.5 ° (= ± 22.5 ° + ± 45 °).

FIG. 6 is a diagram showing a configuration of an optical isolator according to a fifth embodiment of the present invention. The optical isolator according to the fifth embodiment shown in the same drawing is different from the optical isolator according to the fourth embodiment shown in FIG. 4 in that the first and second optical couplers 65 and 65 are respectively provided in the optical waveguide having the TEC structure.
67, and the branch output terminals of the optical couplers 65, 67 and the magnetic garnets 5a, 5a,
A pair of optical waveguides 61 and 62 having a TEC structure are provided between the optical element 5b and the optical element including the half-wave plates 7 and 9, respectively.
And 63 and 64, and are different in that lens portions 61a and 62a are formed at the ends of the pair of optical waveguides on the optical element side, respectively.

In the optical isolator thus configured, the transmitted light in the forward direction from the optical waveguide 68 is split by the first optical splitter 65 into two lights of the same intensity, phase and degree of polarization. The first and second light beams are independently transmitted to a pair of optical waveguides 61, 6 having a TEC structure.
2, the first light is transmitted through the half-wave plate 7 and the magnetic garnet 5a constituting the Faraday rotator, and the second light is transmitted through the magnetic garnet 5b. The light passes through the half-wave plate 9. Then, the first and second lights are further transmitted to the lens unit 63, respectively.
a, 64a, and a pair of optical waveguides 63, 64, pass through to a second optical coupler / demultiplexer 67, where the first and second lights are combined and output from the optical waveguide 69. Is done. Further, the transmitted light in the opposite direction from the optical waveguide 69 is split by the second optical splitter 67, and the split first light is split.
The second light is converted into parallel light at the lens portions 63a and 64a through the pair of optical waveguides 63 and 64, and the first light is emitted from the magnetic garnet 5a, the half-wave plate 7, the lens portion 62a,
The light passes through the optical waveguide 62 to reach the first optical coupler / splitter 65,
The second light passes through the half-wave plate 9, the magnetic garnet 5b, the lens portion 61a, and the optical waveguide 61, reaches the first optical coupler / branch 65, cancels out the first light, and cannot transmit.

In the optical isolator of the fifth embodiment shown in FIG. 6, optical waveguides 61 to 64 having a TEC structure are provided.
However, instead of this, an optical waveguide with a spherical lens and other components may be used.

As described above, the first and second optical couplers 6
In the embodiment using 5,67, the two separated lights are independently guided to the optical element, so that the light transmitted near the surface of the connection point between the upper and lower optical elements becomes almost zero, which is caused by the presence of this surface. The effects of reflection and scattering can be almost completely eliminated. Therefore, an optical isolator that is more excellent in optical characteristics than the above-described embodiments can be configured. In this case, it is necessary to accurately control the optical path lengths of the two separated lights including the two optical waveguides 61 to 64 having the TEC structure. This is two TEs at the time of assembly
This can be implemented by optically adjusting the distance between the end faces of the optical waveguide having the C structure. However, compared to the above-described embodiment, the total length of the optical isolator is reduced by the presence of the two optical couplers 65 and 67. It is inevitable that it will be slightly longer. However, if the optical waveguide is formed on a PLC structure in which the optical waveguide is formed on a glass substrate, and the optical coupler is included on the PLC, the size can be reduced.

FIG. 7 is a perspective view showing the structure of an optical isolator according to the sixth embodiment of the present invention. The optical isolator of the embodiment shown in FIG. 1 is configured such that an optical waveguide having a PLC (Planar Lightwave Circuit) structure is formed on a glass substrate as described above, and the function of an optical coupler is achieved by the optical waveguide. It is. In FIG. 7, 7,
Reference numerals 9 and 5a and 5b denote magnetic garnets constituting the above-described half-wave plate and Faraday rotator, respectively, and reference numerals 71 and 73 denote optical waveguides having a PLC structure.
75 is a substrate.

In the optical isolator thus configured, the transmitted light in the forward direction from the optical waveguide 71 having the PLC structure on the left is split into two lights in the region of the PLC structure. The light passes through the 5b and the half-wave plates 7 and 9 and is incident on the optical waveguide 73 having the PLC structure on the right side, is synthesized by the PLC structure, and is emitted from the optical waveguide 73. When the transmitted light is separated by the PLC structure of the left optical waveguide 71, the phases thereof are shifted by 90 °. This is because when the transmitted light is recombined by the PLC structure of the right optical waveguide 73. The same phase shift cancels out and does not affect the result.

Also, the transmitted light in the opposite direction, which is incident from the right optical waveguide 73, is synthesized by the PLC structure of the optical waveguide 73, is separated into two lights, and is independently independent of the magnetic garnets 5a, 5b and 1/2 wavelength. After passing through the plates 7 and 9 and entering the optical waveguide 71 having the PLC structure on the left side,
When they are recombined in the LC structure, they cancel each other out and cannot pass through the inside of the optical isolator.

In the embodiment shown in FIG. 7, the magnetic garnets 5a and 5b constituting the Faraday rotator use elements having a shape divided into two parts. Instead, as shown in FIGS. A magnetic garnet, which is an integral Faraday rotator, may be used. Note that the optical waveguides that enter and exit the optical element are not located at the junction between the magnetic garnet, which is a Faraday rotator, and the half-wave plate, but are located at slightly shifted positions. Therefore, care must be taken when arranging the optical elements.

That is, in this embodiment, both the left and right optical waveguides 71 and 73 on the substrate 75 are １ ／ wavelength plates 7 and 9.
The transmitted light is linearly incident on the side, and the magnetic garnet 5a,
5b (Faraday rotator) is incident so as to wrap around. By appropriately designing the shape and area of the optical waveguide, incident light can be divided into two separated lights having the same light intensity, and can be separately incident on the half-wave plate and the Faraday rotator, respectively. is there. However, the phase of the separated light on the Faraday rotator side is delayed by 90 °.
By forming such an optical waveguide on a substrate, an optical coupler can be easily formed.

[0049]

As described above, according to the present invention,
First and second optical waveguides each having a lens portion formed at one end are disposed so that the respective lens portions face each other, and an optical element including a Faraday rotator and a half-wave plate is provided between the facing lens portions. Is arranged, and the optical isolator is configured, so that the optical waveguide and the lens unit can be optically adjusted in advance and integrated, and the transmitted light between the lens units can be always parallel light or close thereto. The optical characteristics of the optical isolator can be improved, and the optical adjustment between the optical waveguide and the lens unit is not required at the time of assembling, so that the adjustment after assembling becomes easy. Further, a structure for separately holding the lens portion is not required, so that the size can be reduced, and the size of the optical element can be reduced, so that the economy and the optical characteristics can be improved.

Further, according to the present invention, the first and second pairs of optical waveguides each having a lens portion formed at one end are disposed so that the respective lens portions face each other, and between the facing lens portions. In addition to disposing an optical element composed of a Faraday rotator and a half-wave plate, a light combining / branching unit is provided in the middle of each of the first and second optical waveguides to perform light branching and combining. Since the transmitted light is separated and separated separately from each other by the optical coupling / branching means, there is no need to consider reflection and scattering due to the step structure at the end of the optical element, and an array-type optical isolator having excellent optical characteristics can be provided. Can be configured.

Further, according to the present invention, the first and second optical waveguides having the PLC structure are disposed so as to face each other, and the Faraday rotator and the 1 /
Since an optical element composed of a two-wavelength plate is provided, it is possible to branch and combine transmitted light with a PLC structure without providing an independent light combining / branching means, which enables downsizing and excellent optical characteristics. Obtainable.

According to the present invention, the Faraday rotator is composed of the first and second Faraday rotators divided into two, and the Faraday rotators are respectively divided into the first and second Faraday rotators.
Is integrally joined to the half-wave plate, so that it is joined continuously so that there is no step on the light entrance / exit surface by this integrally joined structure, so that light scattering and refraction can be reduced. ,
The insertion loss and optical characteristics of the optical isolator can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an optical isolator according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of an optical isolator according to a second embodiment of the present invention.

FIG. 3 is a diagram illustrating a configuration of an optical isolator according to a third embodiment of the present invention.

FIG. 4 is a diagram illustrating a configuration of an optical isolator according to a fourth embodiment of the present invention.

FIG. 5 is a diagram illustrating a method of manufacturing an optical element including a Faraday rotator and a half-wave plate used in the optical isolator illustrated in FIG.

FIG. 6 is a diagram illustrating a configuration of an optical isolator according to a fifth embodiment of the present invention.

FIG. 7 is a perspective view illustrating a configuration of an optical isolator according to a sixth embodiment of the present invention.

FIG. 8 is a diagram showing a configuration of a conventional optical isolator.

FIG. 9 is a diagram showing another configuration of a conventional optical isolator.

[Explanation of symbols]

 1,3 Optical waveguide having TEC structure 1a, 3a, 31a, 33a Lens unit 5,5a, 5b Magnetic garnet (Faraday rotator) 7,9 1/2 wave plate 11 Magnet 21,23 TEC fiber 31,33 Top ball Optical waveguide with lens 65, 67 Optical coupler / branch 71, 73 Optical waveguide having PLC structure

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Akiyuki Tate 3-19-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Japan Telegraph and Telephone Corporation (72) Inventor Makoto Shimokozono 3-19 Nishishinjuku, Shinjuku-ku, Tokyo No. 2 Nippon Telegraph and Telephone Co., Ltd. (72) Inventor Hiroshi Honma 6-7-1, Koriyama, Taishiro-ku, Sendai, Miyagi Prefecture Tokin Co., Ltd. (72) Haruhiko Tsuchiya 6-7, Koriyama, Tashiro-ku, Sendai, Miyagi No. 1 Tokin Co., Ltd. (72) Inventor Kazuho Yamada 6-7-1, Koriyama, Taishiro-ku, Sendai, Miyagi Prefecture Tokin Co., Ltd.

Claims (8)

[Claims] A first optical waveguide having a lens portion formed at one end; a second optical waveguide having a lens portion formed at one end opposite to the lens portion of the first optical waveguide; A Faraday rotator disposed between the lens portions of the first and second optical waveguides; a first half of light from the lens portion of the first optical waveguide is transmitted; A first half-wave plate joined to a first half of a first surface of the Faraday rotator facing a lens portion of the first optical waveguide so as to directly transmit the Faraday rotator; A second half of the second surface of the Faraday rotator which is opposite to the first surface of the Faraday rotator, and the second half of the second surface of the Faraday rotator from a second half of the second surface of the Faraday rotator. Half of the light is transmitted, enters the lens portion of the second optical waveguide, and is transmitted from the Faraday rotator. The serial of the first half of the light is directly the second
An optical isolator comprising: a second half-wave plate incident on a lens portion of the optical waveguide of (1); and magnetic field applying means for applying a magnetic field to the Faraday rotator. 2. The optical isolator according to claim 1, wherein said first and second optical waveguides are optical waveguides having a TEC structure having an enlarged portion as said lens portion. 3. The optical isolator according to claim 1, wherein each of the first and second optical waveguides is an optical waveguide with a spherical lens having a spherical lens as the lens unit. 4. A first optical waveguide, and one end is connected to one end of the first optical waveguide, and light incident from the one side is branched into two and emitted from a pair of the other sides. A first light combining / branching unit that combines light incident from the other side of the pair and emits light from the one side, and separates the first and second lights branched by the first light combining / branching unit. A first pair of optical waveguides each having a pair of one ends connected to the pair of other sides of the first optical coupling / branching unit and a pair of lens portions formed at the pair of other ends, respectively, A second pair of optical waveguides each having a pair of lens portions formed at one end thereof opposite to the pair of lens portions formed at a pair of other ends of the pair of optical waveguides; One side is connected to a pair of other ends of the optical waveguide, and a pair of other ends of the second optical waveguide A second light combining and branching device combines light incident on one side of the pair, emits the light from the other side, splits the light incident from the other side into two, and emits the light from the one side of the pair. Means, a second optical waveguide connected to the other side of the second optical coupling / branching means, and disposed between a pair of lens portions of each of the first and second pairs of optical waveguides; Light from one of the pair of lens portions of the first pair of optical waveguides directly enters one surface,
A Faraday rotator in which light from one of the pair of lens portions of the second pair of optical waveguides is directly incident on the other surface; and a pair of one surface of the Faraday rotator and the first pair of optical waveguides. The first lens unit disposed between the other lens unit
A second half-wave plate disposed between the other surface of the Faraday rotator and the other of the pair of lens portions of the second optical waveguide; An optical isolator comprising: a magnetic field application unit that applies a magnetic field to the Faraday rotator. 5. The first and second pairs of optical waveguides,
5. The optical isolator according to claim 4, wherein the optical isolator is an optical waveguide having a TEC structure having an enlarged portion as the lens portion. 6. The first and second pairs of optical waveguides,
5. The optical isolator according to claim 4, wherein the lens portion is an optical waveguide with a spherical lens having a spherical lens. 7. A first optical waveguide having a PLC structure, and a P having one end disposed opposite to one end of the first optical waveguide.
A second optical waveguide having an LC structure; a Faraday rotator disposed between opposed ends of the first and second optical waveguides; and a second optical waveguide from one end of the first optical waveguide. The first half of the first surface of the Faraday rotator facing one end of the first optical waveguide such that one half of the light is transmitted and the second half of the light is transmitted directly through the Faraday rotator. A first half-wave plate joined to the second half of the Faraday rotator, the second half of the Faraday rotator being joined to a second half of the Faraday rotator opposite to the first surface. The second half of the light from the second half of the surface is transmitted and impinges on the second optical waveguide, and the first half of the light from the Faraday rotator is directly transmitted to the second half of the surface. A second half-wave plate incident on the optical waveguide; and a magnetic field applying means for applying a magnetic field to the Faraday rotator. An optical isolator having a step. 8. The Faraday rotator includes a first and a second Faraday rotator divided into two parts, and the first Faraday rotator is integrated with the first half-wave plate. And the second Faraday rotator part is integrally joined to the second half-wave plate, and the integrally joined first Faraday rotator and second half-wavelength A first integral structure with the plate and a second Faraday rotator integrally joined with the second half-wave plate.
9. The integrated structure of claim 1, wherein the light-in / out surface is continuously joined so that there is no step.
An optical isolator according to any one of the above.