JP2003270597A - Optical variable attenuating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical variable attenuating device which is small-sized, can operate with a low voltage, has high reliability and is used for optical communications. <P>SOLUTION: The optical variable attenuating device is equipped with an optical varying means 10 constituted by arranging electrodes 4-1, 4-2, and 4-3 on a base body (comprising members 3-1 and 3-2) made of a material having electrooptic effect so that an electric field is locally converged in the base body. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical variable attenuator arranged in an optical transmission line and using an electro-optical effect, and more particularly to an optical variable attenuator capable of operating at a low voltage.

[0002]

2. Description of the Related Art An optical attenuator is known as one of passive components used in the field of optical communication. This optical attenuator includes a fixed optical attenuator having a fixed amount of attenuation and an optical variable attenuator capable of changing the amount of attenuation. Among them, the variable optical attenuator is divided into one that manually controls the amount of attenuation and one that is controlled by electrical means.

Various methods have been proposed for an optical variable attenuator that controls the amount of attenuation by electrical means.
There are a method of driving a micromachine, a method of utilizing a magneto-optical effect, a method of utilizing a thermo-optical effect, and a method of utilizing an electro-optical effect.

Among them, the method of driving a micromachine is anxious about its reliability because it has a mechanically movable part. For this reason, a method without a movable part is often preferred for use. However, in the method utilizing the magneto-optical effect or the thermo-optical effect, there is no mechanically movable part, but the former uses current and the latter uses heat to control the amount of attenuation, so there is a drawback that power consumption is large.

Therefore, an optical variable attenuator utilizing the electro-optic effect has been proposed. For example, Japanese Patent Laid-Open No. 2001-272
In the one disclosed in Japanese Patent No. 638, a birefringent crystal separates polarized light, each polarization component is rotated by an electro-optical element, and when the polarization components are recombined by the birefringent crystal, a part of light is combined. By not doing so, the light can be attenuated, and the polarization rotation angle is controlled by controlling the voltage applied to the electro-optical element. In this method, it is not necessary to pass a current, and thus low power consumption can be realized.

The inventors of the present invention also filed Japanese Patent Application No. 13-3850.
In No. 98, a member made of an electro-optical material is provided with an electrode having a shape capable of exhibiting a refraction effect by a prism, and a voltage is applied to the electrode to deflect incident light,
We proposed an optical variable attenuator based on the principle that light is not coupled to the outgoing optical transmission line.

[0007]

However, even if a good material is selected, the change in the refractive index due to the electro-optic effect is relatively small. Therefore, in order to obtain a large amount of attenuation, a high voltage is applied to increase the electric field strength, or a member made of a material having an electro-optical effect is formed thin and the distance between the electrodes is decreased to increase the electric field strength. Had to do. However, since the low voltage operation is desired in use, the former method should be avoided. In the latter method, it is necessary to secure a region to which a strong electric field is applied at least in a region equal to or larger than the spot diameter of light. Therefore, a large number of layers are laminated with members made of a material having a thin electro-optical effect sandwiching electrodes. Therefore, it is necessary to handle thin members and the process is difficult and complicated.

[0008]

DISCLOSURE OF THE INVENTION As a result of investigations made by the present inventors to improve the above-mentioned problems, it has been found that the following configuration is effective. That is, the variable optical attenuator of the present invention is (1) an optical variable attenuator comprising a base made of a material having an electro-optical effect and a plurality of electrodes arranged so that an electric field is locally concentrated inside the base. It is characterized by having means.

(2) The plurality of electrodes are arranged substantially parallel to the optical axis of the light input to the base.

Further, in the configuration of (3), (1) or (2), the plurality of electrodes are arranged substantially symmetrically with respect to the optical axis of the light input to the base.

In addition, in the constitutions of (4) and (3), the electrodes are arranged on the surfaces of the base body which are at the positions to be the back surfaces and / or inside the base body, and the electric field is concentrated inside the base body. It is characterized by doing so.

In addition, in any one of (5), (1) to (4), a concave portion or a through hole parallel to the optical axis is provided in the base so that an electric field is concentrated inside the base. It is characterized by doing so. For example, at least two or more grooves or through holes that are parallel to the light propagation direction are provided.

Further, in the constitutions (6) and (5), a member having a dielectric constant smaller than that of the material having the electro-optical effect at the frequency of the electric field applied to the substrate is provided in the recess or the through hole. Characterize.

Further, in any one of (7), (1) to (6), as the material having the electro-optical effect,
It is characterized by using PLZT, BaTiO3, or SBN.

[0015]

[Operation] By adopting the configuration as described in (1),
It is possible to locally obtain a stronger electric field than the electric field generated when the flat plate-shaped electrodes are opposed to each other. Therefore, by propagating the light to this portion, the light is generated while the flat-plate-shaped electrodes are opposed to each other. Since a higher effect can be obtained with the same voltage as in the case of propagation, the operating voltage of the device can be lowered.

The electrodes for locally concentrating the electric field are
For example, as in (2), it can be realized by arranging it in parallel with the light propagation direction. However, by providing an electrode as in (2), a material having an electro-optical effect with respect to light that propagates is used. Since the effect derived from the electro-optic effect can be continuously applied until the light enters and exits the member, it is possible to obtain a great effect.

Further, by providing the electrodes as in (3), it is possible to obtain an electric field distribution having an axis of symmetry in the light spot, so that the design becomes simpler as compared with the case where no axis of symmetry is provided.

Further, the structure of (4) is effective for propagating light to the region where the electric field is concentrated.

Further, by adopting the configuration as described in (5),
The electric field can be concentrated more effectively.

Further, by adopting a configuration such as (6),
In addition to the effect of (5), the mechanical strength of the element can be secured.

Further, since the material such as (7) has a large electro-optic constant, it is possible to realize lower voltage operation and downsizing.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION An optical variable attenuator according to an embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a perspective view showing an example of the basic structure of the present invention. In FIG. 1, the variable optical attenuator of the present invention is
A plurality of electrodes 4-1, 4-2 and a plurality of electrodes 4-1 and 4-2 are arranged on a base body (a member 3-1 and a member 3-2) made of a material having an electro-optical effect so that an electric field is locally concentrated inside the base body. 4-
The light variable means 10 is provided by disposing the three. Also,
The plurality of electrodes are arranged substantially parallel to the optical axis of the light input to the base. Further, the plurality of electrodes are arranged substantially symmetrically with respect to the optical axis of the light input to the base. In this way, the electrodes are arranged on the surfaces of the base body at the positions which are the back surfaces of each other and / or on the inside of the base body,
The electric field is concentrated inside the substrate.

In the above structure, an optical transmission line (not shown)
The input light 1 propagating through the light enters the light variable means 10.
The light variable means 10 includes, for example, members 3-1 and 3-2 made of a material having an electro-optical effect, and electrodes 4-1 and 4-.
It consists of 2, 4-3. These electrodes are connected to an external control unit that controls the voltage (not shown), and the input light undergoes some change (for example, deflection or phase change) according to the voltage and is emitted as output light 2. It is incident on the optical transmission line on the output side (not shown).

FIG. 2A shows the light variable means 10 shown in FIG.
3 is a cut surface on a plane A (plane where the optical axis is the normal line) A indicated by the alternate long and short dash line. Here, a member made of a material having an electro-optical effect is composed of two parts 3-1 and 3-2, an electrode 4-3 is inserted between them, and further electrodes 4-1 and 4-2 are provided. Is provided. The input light 1 incident on the light varying means 10 passes through the region 5 near the center of FIG. 2A in the z direction. At this time, the electrodes 4-1 and
When a voltage is applied to 4-2 and 4-3, an electric field as shown by an electric force line 6 shown by a broken line is generated, and members 3-1 and 3-2 made of a material having an electro-optical effect are generated. A refractive index distribution is generated due to the electro-optic effect, and the input light 1 undergoes a change corresponding to this, but as shown in the figure, the electric field is concentrated in the vicinity of the region 5 indicated by the alternate long and short dash line, and the electric field concentration occurs. It can be seen that a large effect can be expected as compared with a structure having no structure (for example, a parallel plate). For example, deflection and phase change can be considered as the effect that the light receives.

As an example, consider a case where light linearly polarized in the y-axis direction is incident on the light variable means 10. If the crystal axis direction and the electric field direction of the members 3-1 and 3-2 made of a material having an electro-optical effect are appropriately selected, the refractive index distribution formed according to the distribution of the electric field component in the y direction is affected. As it travels through the light varying means 10, the portion of the light in the region 5 that is incident on the member 3-1 made of a material having an electro-optical effect is the y-axis positive direction and the portion that is incident on 3-2 is y.
It can be deflected in the negative direction of the axis.

Of the light in the area 5, 3-1 and 3-2
Since there is no electric field component in the y-axis direction in the vicinity of the boundary of and the distance from the electrode 4-3, the light is transmitted without being deflected. Further, a phase distribution is generated in the light spot according to the refractive index distribution.

As described above, the light which has undergone different deflection and phase distribution change in each part by the light varying means 10 passes through the light varying means 10 and then enters the collimating optical system on the exit side and is joined to the collimating optical system. Coupled to the propagation mode of the optical transmission line. At this time, the light is changed by the light variable means 10 to a mode other than the mode propagated through the original optical transmission line. For this reason, the power calculated by the overlap integral is coupled to the propagation mode on the emission side, and the light whose power is attenuated with respect to the input light can be obtained. The distribution of the power of the light emitted from the light variable means 10 can be controlled by the voltage applied to the electrodes. That is, it is possible to control the coupling efficiency with the emitting side, and thus it is possible to realize the variable optical attenuator.

In FIG. 2A, the member made of the material having the electro-optical effect is composed of two parts 3-1 and 3-2, but as shown in FIG. The electrode 4-3 may be formed by forming a through hole in the above member and filling the through hole with a metal. Here, the through-hole can be formed with a laser with high precision in parallel to the optical axis.

Further, as shown in FIG. 3 (a), a recess parallel to the optical axis may be provided in the base so that the electric field is concentrated inside the base. That is, the electrode 4-
Groove 7- which is a recess for narrowing the distance between 1 and 4-2
1, 7-2 may be provided. This groove can be formed by dicing or etching. By providing the groove and narrowing the electrode interval, the effective electric field becomes stronger, and lower voltage operation can be expected.

Further, as shown in FIG. 3B, the grooves 7-3 and 7-4 may be provided on the surface where the electrodes are not provided. Since the permittivity of the groove portion is reduced by providing the groove, members 3-1 and 3-made of a material having an electro-optical effect in which the electric field has a high permittivity, such as the electric flux line 6 in FIG. 3B. Two
It is possible to expect lower voltage operation by concentrating inside. Groove 7-
Although nothing may be placed inside 3, 7-4 (the permittivity of air is smaller than the material having the electro-optical effect), the member 8-1 made of resin or the like having a permittivity smaller than the material having the electro-optical effect 8-1. , 8-2 may be filled, or such a bar may be bonded in the groove. By doing so, the mechanical strength of the light varying means 10 can be improved.

Further, as shown in FIG. 3C, in the light varying means 10, a groove having the above-mentioned effect may be formed on each surface parallel to the light propagation direction. . Although a rectangular groove is exemplified here, the shape of the recess is not particularly specified. Although the groove is mentioned here, the same effect can be obtained by forming the through hole. In addition, here, in FIG.
The case where a groove is formed in the example shown in FIG.
Of course, it may be formed as shown in FIG.

Further, the shape of the electrodes mentioned here is an example, and all the electrode shapes and arrangements in which a plurality of electrodes are provided substantially symmetrically with respect to the light propagation direction (optical axis) are within the scope of the present invention. is there. Even if a plurality of electrodes are not provided substantially symmetrically with respect to the plane including the axis including the propagation direction of light, there are shapes that can expect the effect of electric field concentration, but information about the polarization of the incident light is also output. If you want to save it, the design becomes complicated, which is not desirable.

FIG. 4 shows an example of the arrangement of electrodes. Figure 4
(A) is a member 3-3 made of a material having an electro-optical effect
In this structure, a wide electrode 4-4 is provided on one of the surfaces facing each other and a narrow electrode 4-5 is provided on the remaining one. As indicated by the broken line of electric force 6, the electric field is concentrated immediately below the narrow electrode 4-5, and this portion can be used. In this figure, the electrode 4-5 has a rectangular cross section, but if a groove having a Δ cross section is provided in the member 3-3 made of a material having an electro-optical effect, and an electrode is formed in this groove, the electric field can be more concentrated. it can. In the structure shown in FIG. 1 and FIG. 2, since the electrode 4-3 exists in the light spot (electrode 4-
The size of 3 can be made sufficiently small for the spot of light. For example, the electrode 4-3 has a spot size of 300 μmφ for a width of 1 μm and a height of 20 nm. ), The insertion loss increases to some extent, but with the shape of FIG. 4A, the insertion loss can be reduced and the power resistance can be improved because there is no electrode in the light spot. You can

As shown in FIG. 4B, a cylindrical member 3-6 made of a material having an electro-optical effect may be used. When a through hole is formed in the center with a laser, an electrode 4-9 is provided in the through hole, and an electrode 4-8 is provided also on the outer circumference of the cylinder, an electric field is concentrated near the center, which can be used.

It is desirable that the input light be collimated. Although not shown in the description up to this point, a GRIN lens, a GI fiber, a flat lens made in a waveguide, a bulk lens, a fiber with a lens, or the like can be used for the collimating optical system. In particular, when the structure of FIG. 4A is used, it is desirable to use a GI fiber or a fiber with a lens that can reduce the spot size of light in order to pass the light directly under the electrode 4-5 where a great effect can be expected. Further, in the case of using the structure in which the electrode exists in the light spot as shown in FIGS. 1 to 3 and 4B, the larger the light spot size, the smaller the influence of the electrode in the spot. Therefore, it is desirable to use a GRIN lens or a bulk lens.

As the optical transmission line, a single mode optical fiber, a multimode optical fiber, or a waveguide built in a substrate can be used. Since the attenuation of light is controlled by the coupled state of the modes, the number of modes that can propagate in the optical transmission line is also a design matter.

Further, a polarizer may be inserted in at least one of the front and rear of the light variable means 10. A plurality of light variable means 10 may be connected in series. By using these means, a variable optical attenuator having no polarization dependence can be manufactured.

Further, a structure may be provided in the optical transmission line on the output side to remove an unnecessary clad mode in which the propagation mode is not coupled. For example, place a member with a larger refractive index than the cladding on the outside of the cladding of the output fiber,
A structure is conceivable in which a notch that does not reach the core is placed in the clad, and a member that absorbs light is arranged in the notch. Clad mode light can also be used for monitoring.

As described above, it is possible to realize a variable optical attenuator which uses the electro-optical effect, has low power consumption, has high reliability because it has no mechanical moving parts, and has a low driving voltage. In addition, low voltage operation can be realized without complicated lamination even in the manufacturing process and without thinning a member made of a material having an electro-optical effect to be unwieldy.

[0041]

EXAMPLES Examples in which the variable optical attenuator of the present invention is embodied will be described below.

A variable optical attenuator was manufactured as follows.

Example 1 First, as a light input / output system, a single-mode optical fiber having a GRIN lens adhered thereto was faced with the optical axis adjusted, and the optical axis was adhered to a substrate. In addition, an electrode pattern for connecting the alignment marker and the electrode of the light varying means 10 to an external control unit was formed on the substrate. Attach a connector to the end of the optical fiber that is not bonded to the GRIN lens,
Enabled to connect to the evaluation system. This optical system is capable of inputting about 0.3 mm of input light propagating in a single mode optical fiber.
It was designed to be able to collimate to different spot sizes. Further, a resin having a refractive index larger than that of the cladding of the single mode optical fiber is applied to the side surface of the output single mode optical fiber so that unnecessary light can be absorbed.

Next, the light variable means 10 was made to have the structure shown in FIG. A PLZT substrate (thickness 300 μm) was used as a member made of a material having an electro-optical effect. First, an electrode 4-3 (Au having a thickness of 20 nm and a width of 1 μm) was formed on one PLZT substrate by a normal wafer process, and was bonded to another PLZT substrate using an epoxy adhesive. After that, the groove 7-
1, 7-2 (depth 100 μm, width 500 μm) were prepared, and electrodes A and A were formed on electrodes 4-1 and 4-2 (Ti (thickness 20 nm)).
u (thickness 200 nm)) was formed by vapor deposition. After that, the substrate is separated by dicing, and the light variable means 1
0 was singulated (width 1 mm x length 1 mm x thickness 0.6 m
m). Then, the end surface where light is input and output is polished and AR coating is performed. Then, the grooves 8-1 and 8-2 are formed by dicing (width 300 μm, depth 300 μm).
m), the groove was filled with an epoxy resin having a dielectric constant lower than that of PLZT and thermally cured. This individualized light variable means 10 is mounted at a predetermined position on the above-mentioned substrate, and the electrode pattern of the board and the electrodes of the light variable means 10 are connected and fixed by soldering to form a light variable attenuator.

Applied voltage of this optical variable attenuator (vertical axis)-
The relationship of the output light intensity (horizontal axis) is shown in FIG. However, the output light intensity on the vertical axis represents a value normalized by the output light intensity when the voltage is zero. As shown in FIG. 5, the output light could be almost extinguished with an applied voltage of 10 V, and the operation of the variable optical attenuator could be confirmed. Using this variable optical attenuator, the characteristics with respect to the input of a digital wave that oscillates at a voltage of 0 V and 10 V at 1 MHz were observed. As a result, it was confirmed that the variable optical attenuator of the present invention also works sufficiently as an optical modulator.

<Embodiment 2> As a light input / output system, a GI fiber was fused between two single mode optical fibers, adhered to a substrate, and then cut near the center of the GI fiber with a width of 3 mm. Was produced. A connector was attached to the end of the optical fiber which was not fused to the GI fiber so that it could be connected to the evaluation system. This optical system allows input light propagating in a single mode optical fiber to be about 0.1
It was designed to be able to collimate to a spot size of mm, and it was confirmed that the insertion loss becomes 1 dB or less by filling the cut portion with a refractive index matching resin. Further, the side surface of the output single mode optical fiber is coated with a resin having a refractive index larger than that of the cladding of the single mode optical fiber so that unnecessary light can be absorbed.

The light variable means was produced in the structure of FIG. As a member made of a material having an electro-optical effect, P
An LZT substrate (thickness 300 μm) was used. First, an electrode 4-4 (Au (thickness: 200 nm) on Ti (thickness: 20 nm)) is formed on the entire one surface of this substrate by vapor deposition, and then an electrode 4-5 (Ti (( Au (thickness: 200 nm, width: 1 μm) stripe) was formed on the thickness (20 nm). After that, the substrate is separated by dicing, and the light variable means 10 is divided into individual pieces (width 1 mm).
X length 1 mm x thickness 0.6 mm). Then, the end surface where light is input and output is polished and AR coating is performed. Next, the individualized light variable means 10 is placed and fixed at a predetermined position in the groove formed between the GI fibers, and the electrodes 4-4 and 4-5.
And an external control unit were connected. Finally, the light variable means 10
A variable index attenuator was prepared by filling a refractive index matching resin between the end surface of the GI fiber and the end surface of the GI fiber and thermosetting.

As a result of measuring the applied voltage and the output light intensity of this variable optical attenuator, the same results as the characteristics shown in FIG. 5 were obtained in this example.

[0049]

As described above, according to the first aspect of the present invention, a member made of a material having an electro-optical effect having a plurality of electrodes is used as the light varying means, and the plurality of electrodes are locally subjected to an electric field. By arranging and arranging so as to concentrate, it is possible to locally obtain an electric field stronger than the electric field generated when the electrodes are opposed to each other in a flat plate shape, and therefore, it is possible to propagate light to this portion. Since a higher effect can be obtained with the same voltage as when light is propagated while the flat plate-shaped electrodes are opposed to each other, the operating voltage of the device can be lowered.

According to the second aspect, the effect derived from the electro-optical effect can be continuously applied until the light enters and exits the member made of the material having the electro-optical effect. The effect can be obtained.

According to the third aspect, since the electric field distribution having the symmetry axis can be obtained in the light spot, the design becomes simple as compared with the case where the symmetry axis is not provided.

The structure of claim 4 is effective for propagating light to the region where the electric field is concentrated.

Further, with the structure according to claim 5, the electric field can be more effectively concentrated.

In addition, with the structure of claim 6, mechanical strength can be secured.

Further, by using the materials recited in claim 7, it is possible to realize lower voltage operation and miniaturization.

[Brief description of drawings]

FIG. 1 is a perspective view schematically explaining an embodiment of a variable optical attenuator according to the present invention.

2A is a cross-sectional view schematically illustrating a state of being cut along a plane A (a plane whose optical axis is a normal line) shown in FIG. 1;
(B) is sectional drawing which illustrates other embodiment of this invention typically.

3 (a) to 3 (c) are cross-sectional views each schematically illustrating a further embodiment of the present invention cut along a plane A of FIG.

4 (a) and 4 (b) are cross-sectional views each schematically illustrating a further embodiment of the present invention cut along a plane A in FIG.

FIG. 5 is a diagram showing applied voltage-normalized output light intensity characteristics of the variable optical attenuator according to the first embodiment of the present invention.

[Explanation of symbols]

Reference numeral 1 ... Input light 2 ... Output light 3-1, 3-2, 3-3, 3-6 ... Members 4-1, 4-2, 4-3 made of a material having an electro-optical effect , 4-4, 4-5, 4-8, 4
-9 ... Electrode 5 ... Light-transmitting area 6 ... Electric force lines 7-1, 7-2, 7-3, 7-4 ... Grooves 8-1, 8-2 ... .Member 10 having a lower refractive index than a material having an electro-optical effect ... Optical variable means

Claims (7)

[Claims] 1. A light varying means comprising a base made of a material having an electro-optical effect and a plurality of electrodes arranged so that an electric field is locally concentrated inside the base. Optical variable attenuator. 2. The variable optical attenuator according to claim 1, wherein the plurality of electrodes are arranged substantially parallel to an optical axis of light input to the base. 3. The variable optical attenuator according to claim 1, wherein the plurality of electrodes are arranged substantially symmetrically with respect to the optical axis of the light input to the base. 4. The electric field is concentrated inside the base by arranging the electrodes on the surfaces of the base that are located at the back sides of each other and / or on the inside of the base. Item 5. The variable optical attenuator according to Item 3. 5. The base body is provided with a recess or a through hole parallel to the optical axis so that an electric field is concentrated inside the base body. The variable optical attenuator according to. 6. The light according to claim 5, wherein the recess or the through hole is provided with a member having a dielectric constant smaller than that of the material having the electro-optical effect at a frequency of an electric field applied to the substrate. Variable damping device. 7. A material having the electro-optical effect,
7. The variable optical attenuator according to claim 1, wherein PLZT, BaTiO3, or SBN is used.