JP2003185984A - Optical variable attenuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical variable attenuator which is used in an optical communication field, and is compact and operated at higher speed than a conventional one, inexpensive and highly reliable. <P>SOLUTION: The optical variable attenuator which is arranged in an optical transmission line and changes the intensity of an input light and outputs the light, is characterized in that an optical deflector 15 which makes the optical axis of the output light different from that of the optical axis of the optical transmission line is used as a means which varies the intensity of the input light. <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 which is arranged in an optical transmission line and changes the intensity of input light to output the light. The optical variable attenuator is smaller than conventional ones and can operate at high speed. The present invention relates to an inexpensive and highly reliable variable optical attenuator.

[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.

An optical variable attenuator (hereinafter abbreviated as "EVOA") which controls an attenuation amount by an electric means has important characteristics such as an insertion loss and an attenuation variable range, but also an operating voltage and an operating speed. This is an important characteristic. Of course, small size, low price, and high reliability are also required.

As a conventional EVOA, there is an optical integrated circuit type using an Mach-Zehnder interferometer formed by an optical waveguide. This is one that directly uses the principles of optical integrated circuit type optical modulators and optical switches.
It is suitable for forming an array of elements and integration with other elements.

However, the optical integrated circuit type EVOA is very effective in making an array type device, but has a drawback that the manufacturing cost per channel becomes very high when the number of channels is small. Was there. Further, since the optical integrated circuit itself is relatively large and there are fiber input / output portions, it is difficult to reduce the size. Furthermore, depending on the operating principle, it is necessary to use a temperature control device to ensure stability,
Moreover, they have the drawbacks of being expensive and being large in size. Therefore, in a system having a relatively small number of channels, the in-line type EVOA shown below tends to be used.

On the other hand, the in-line type EVOA has a method of providing an attenuating part in the middle of an optical fiber without using an optical waveguide (for example, USP5966493) or a GR in the optical fiber.
This is a method of attenuating light by a method (for example, Japanese Patent Laid-Open No. 1994-51255) in which an attenuator is attached via a collimator such as an IN lens, and is characterized by being relatively small and inexpensive.

[0007]

However, in the in-line type EVOA, for example, in the method of providing the attenuating portion in the middle of the optical fiber, it is necessary to perform very fine processing on the optical fiber, so that the manufacturing efficiency is low. There are limits to price reduction.

Further, the one using the magneto-optical effect is difficult to miniaturize because the amount of attenuation is controlled by using an electromagnet, and further, high accuracy is required for mounting the element, and thus there is a limit to the cost reduction. It was

FIG. 17 shows an example of a conventional EVOA. In the figure, 161 is an input optical fiber, 162 is a collimating lens, 165 is an output optical fiber, and 166 is a mounting substrate. The main part of the EVOA is composed of a Faraday rotator 164 and a birefringent substrate 163.
Although not shown in the figure, the Faraday rotator 16
4 is equipped with an electromagnet for controlling the operation.

In order to operate this EVOA accurately, not only the optical system including the optical fiber and the lens is aligned, but also the optical axis thereof is accurately aligned with the optical axes of the Faraday rotator and the birefringent substrate. There is a need. Also,
Alignment with the electromagnet is also required. Due to the misalignment of these alignments, the insertion loss becomes large and the maximum attenuation becomes small, so that extremely high-precision component mounting work is required for manufacturing the EVOA. This is an EVOA
It was one of the factors that hindered the price reduction of. There is also a problem that a slight change in parts due to a change with time causes a characteristic deterioration of the EVOA.

Further, in the above-mentioned magneto-optical effect, electro-optical effect, or EVOA that operates on the principle of rotating the polarization direction of light using liquid crystal, or EVOA that utilizes light interference such as a Mach-Zehnder interferometer, It had the characteristic that the relationship between the applied voltage and the amount of attenuation was periodic. This relationship can be generally expressed by the following equation (1).

I ∝ (sin (aV)) ² (1) (where, I: output light power, a: proportional constant, V: applied voltage) Therefore, the attenuation amount (or transmission amount) is maximum. However, there is a drawback that the operating point changes greatly with a slight voltage deviation. Further, this has been a major cause of the wavelength dependence and reliability deterioration of the EVOA.

In addition, since the in-line type EVOA utilizes the thermo-optical effect and the magneto-optical effect, it has a drawback that the operation speed is slow.

The present invention relates to an optical variable attenuator used in the field of optical communication, which is the conventional EV as described above.
An object of the present invention is to provide an optical variable attenuator that is improved in the drawbacks of OA, is smaller in size, can operate at high speed, and is inexpensive and highly reliable.

[0015]

DISCLOSURE OF THE INVENTION The present inventors have studied means for solving the above problems and realizing an optical variable attenuator that is smaller in size, can operate at high speed, is inexpensive, and has high reliability. As a result, the following inventions have been reached.

That is, the variable optical attenuator of the present invention is an optical variable attenuator which is arranged in an optical transmission line and changes the intensity of the input light to output it. An optical deflector is used which makes the optical axis of the optical axis different from the optical axis of the optical transmission line.

Further, in the above structure, at least one of the input light and the output light may be coupled to the optical deflector via a condensing means or a collimator. Further, at least one of the input light and the output light may be collimated by using a GRIN lens or a fiber collimator. Further, at least one of the input light and the output light may be collimated by using an optical fiber in which a GI fiber is coupled.

Further, in particular, the optical deflector also utilizes the refraction effect of the prism, which is formed by forming an electrode on a substrate having an electro-optic effect and using a difference in refractive index generated by applying a voltage to the electrode. Good. In this structure, PLZT (lead lanthanum zirconate titanate), BaTiO3, or SBN (strontium barium niobate; tungsten bronze) is preferably used as the substrate material having the electro-optical effect. Further, the optical deflector is
Substrates having an electro-optical effect and electrodes may be alternately laminated. Further, the light deflector may have electrodes arranged substantially symmetrically in a direction perpendicular to the optical axis of the input light to the light deflector. Further, the electrodes may be arranged in a prism shape and in an array shape. Further, the light deflector may be configured by connecting light deflectors for two different polarization directions in series and compensating for polarization dependency.

Further, in the above structure, light absorbing means for absorbing the light from the light deflector may be provided. Further, a means for monitoring a part of the output light or the light deflected by the optical deflector may be provided in the variable optical attenuator.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The variable optical attenuator of the present invention will be described below in detail with reference to the drawings. The same components will be denoted by the same reference numerals, and the description thereof will be omitted.

FIG. 1 is a perspective view for explaining an optical variable attenuator according to claims 1 and 2. In the figure, 11 and 12 are optical fibers for input and output which are respectively arranged in the optical transmission path, and 13 and 14 are lenses for condensing or collimating light. Further, 15 is an optical deflector, and 16 is a supporting substrate for mounting those components.

FIG. 2 shows the operating principle of the variable optical attenuator of FIG. The input light from the optical fiber 11 is collimated by the lens 13 and guided to the optical deflector 15. The light deflector 15 gives a certain deflection angle to the light and outputs the light to the optical fiber 12 through the lens 14. here,
By changing the deflection angle by the optical deflector 14,
The coupling degree of light to the output optical fiber 12 changes, and the intensity of output light can be continuously changed.

In FIG. 2, the light beam when the deflection angle is 0 ° (non-deflection) is shown by the solid line arrow, and the light beam when the maximum attenuation is obtained is shown by the dotted line arrow. Thus, the amount of attenuation is minimum (the amount of transmission is maximum) when there is no deflection, and the amount of attenuation is maximum (the amount of transmission is minimum) with sufficient deflection. Further, by shifting the optical axis of the output in advance, it is possible to use an attenuator having the inverse characteristic (the attenuation amount is maximum when there is no deflection). In the variable optical attenuator of the first aspect, the principle and structure of the optical deflector 15 are not particularly limited, but the one using the electro-optic effect of the dielectric is optimal in terms of operating speed.

As can be seen from FIG. 2, in the variable optical attenuator of the present invention, the maximum attenuation can be obtained if the deflection angle is made large enough not to couple the light to the optical fiber 12 that outputs the light. Even if it is made, the amount of attenuation becomes almost constant.
Therefore, the change in the output light intensity with respect to the applied voltage is as shown in FIG.
As shown in, it is not periodic.

Further, by making the variable optical attenuator have such a structure, the requirements for manufacturing precision and mounting precision of parts are greatly relaxed. For example, in the case of an optical variable attenuator that uses interference, even if the optical axes of the optical fiber and lens are perfectly aligned, even a slight manufacturing error or misalignment of the interfering components will prevent perfect interference, so the maximum attenuation Becomes smaller. In the case of an optical variable attenuator that uses polarization rotation,
Accurate operation cannot be performed unless the optical axes of the two birefringent crystal plates, the Faraday rotator, and the electromagnet are perfectly aligned.

On the other hand, in the variable optical attenuator of the present invention, the characteristic of the variable optical attenuator does not affect the characteristics of the variable optical attenuator even if the positional deviation occurs when the optical deflector 15 is mounted. Further, although the voltage value that causes the maximum attenuation slightly changes due to the deviation of the mounting angle of the optical deflector 15, it does not substantially affect the maximum attenuation amount. In general, the mounting angle shift is much smaller than the positional shift and is easy to control. Therefore, the optical variable attenuator of the present invention has a significantly reduced mounting precision and can be manufactured at low cost. Further, due to this feature, the device is highly resistant to positional deviation caused by environmental changes during use and changes over time, and has high reliability.

Since the variable optical attenuator of the present invention has the above characteristics, it can be used not only as a variable optical attenuator but also as a light intensity modulator, an optical switch, or an optical shutter. In the present invention, its use is not particularly limited.

In FIGS. 1 and 2, the operation principle has been described by taking the case where both the input and the output are optical fibers as an example.
Of course, it is not limited to this example. For example, the structure may be such that the input side shown in FIG. 1 is directly input from a laser diode or other optical component, or the output side may be directly output to the photodiode. In fact, integrating the variable optical attenuator of the present invention with a laser diode or a photodiode is effective in reducing the number of parts, lowering the cost, and improving the reliability.

FIG. 4 shows an example of the variable optical attenuator of claim 3. FIG. 5 shows an example of the variable optical attenuator of claim 4. In the figure, 31 and 32 are GRI
Collimators using N lenses, 41 and 42 are collimators using GI fibers. By using such a component integrated with the optical fiber, it is possible to manufacture a smaller, cheaper and highly reliable variable optical attenuator.

In particular, in the variable optical attenuator shown in FIG. 5, the optical system can be made extremely compact, and the alignment of the optical fiber and the collimator (GI fiber in this case) is unnecessary. Further, since the variable optical attenuator can be incorporated in a ferrule or the like, it is very effective for downsizing, cost reduction, and high reliability.

Next, the operating principle of the variable optical attenuator of claim 3 or 4 will be described in more detail with reference to FIG. FIG. 6 shows an optical deflector 15 which constitutes an optical variable attenuator.
3 is a detailed layout diagram of the output side collimator 32 (or 42) and the optical fiber 12. FIG. In FIG. 6, the deflection angle by the optical deflector 15 is θ, the distance between the optical deflector 15 and the collimator 32 (or 42) is L, and the collimator 32 is
The effective opening diameter of (or 42) is D. In this variable optical attenuator, when the condition of the following formula (2) is satisfied, the coupling of light to the collimator 32 (or 42) on the output side becomes almost zero.

Tan θ> D / L (2) That is, by changing the deflection angle of the optical deflector 15 from 0 ° to the value shown by the above equation, the minimum attenuation amount to the complete attenuation are continuously changed. Can be made. For example, in the collimating system using the GRIN lens in the variable optical attenuator of claim 3, generally D = 1 mm, L = 1.
It is about cm. In a collimating system using a GI fiber, D = 0.1 mm and L = 1 mm. In these cases, the deflection angle required to achieve the condition of the above equation is about 5.7 °, which is a value that can be sufficiently achieved by using the low operating voltage reducing method and the deflection angle amplifying method described later. Also, by increasing L, the required deflection angle can be reduced. In reality, since there are diffraction and scattering effects of collimated light, it is necessary to further increase the scattering angle in order to achieve complete attenuation.

In FIGS. 2, 4, 5 and 6, the optical deflector 15 utilizing the refraction effect of the prism is illustrated, but of course, in the variable optical attenuator of the present invention, another type of optical deflector is used. May be used.

The basic form of the variable optical attenuator of claim 5 is the same as that shown in FIGS. FIG. 10 shows claim 5.
FIG. 3 is a view of an optical deflector 15 and an output collimator 103 that form the variable optical attenuator of FIG. In the figure,
Reference numeral 101 is a substrate having an electro-optical effect, and 102 is an electrode. The same shape of the electrode 102 is formed on the back surface of the substrate 101, and by applying a voltage to the electrode 102, the refractive index of the same shape as the electrode 102 in the substrate 101 changes due to the electro-optical effect. The part which was done is induced.
That is, it operates as a prism as a whole. In general, the electro-optical effect is an effect of decreasing the refractive index when a voltage is applied, and therefore the light incident on the optical deflector 15 is bent upward in the drawing as shown in the figure. The light bent by the prism is further refracted at the interface of the substrate 101 and output from the optical deflector 15 at a larger angle. In this optical deflector 15, since the difference in the refractive index between the prism and the substrate 101 induced in the substrate 101 can be changed by changing the applied voltage, the deflection angle can be continuously changed. . That is, the collimator 103
The amount of light coupled to the can be continuously changed by the applied voltage to operate as a variable optical attenuator.

In the actual manufacturing process of the variable optical attenuator, the mounting accuracy of the optical deflector is limited. For this reason, it is necessary to optimize the operation by actually performing alignment while transmitting light. However, in the optical variable attenuator of the present invention, the optical deflector 1
By making 5 slightly wider than the actual light beam width, it is said that theoretically no influence is exerted on the characteristics of the variable optical attenuator even if the mounting deviation occurs in the vertical direction and front-back direction of the paper surface of FIG. It has features. In addition, the optical deflector 15
With respect to the mounting angle and deviation in the horizontal direction of the paper, only the applied voltage that achieves the specified attenuation changes, but it does not affect the characteristics such as insertion loss and maximum attenuation of the optical attenuator. . Therefore, the accuracy at the time of mounting is greatly relaxed, and the variable optical attenuator can be manufactured in large quantities at low cost.

According to the present invention, with the structure as described above,
Although a variable optical attenuator having high speed and low cost and high reliability can be configured, the operating voltage may be a problem in actual use. In optical / electronic components, a voltage of about 3 to 20 V is generally used as an operating voltage, and therefore the variable optical attenuator must often operate at such a voltage. However, since the change in the refractive index due to the electro-optic effect is very small, an extremely high voltage may be required for operation. For example, Journal of Light
ve Technology, Vol. 12, No.
8, the optical deflector shown in p1401 requires a voltage of 600 V to obtain a deflection angle of 0.23 °.

On the other hand, in the variable optical attenuator of the present invention, since the size of the optical deflector is small and the applied effective electric field strength can be increased, the operating voltage is considerably low, but the operating voltage is still lower. The device is very effective industrially.

The optical deflector 15 using a prism can obtain a larger deflection effect as the difference in the refractive index between the prism and the substrate 101 induced by the voltage is larger and the apex angle α of the prism is larger. Prism and substrate 10
Since the difference in refractive index between 1 and 1 depends on the magnitude of the applied voltage, it is possible to operate at a lower voltage by increasing the apex angle α of the prism. However, in this case, there is a problem that the length of the optical deflector becomes long. Since the change in the refractive index induced by the electro-optic effect is very small, the deflection angle of the prism is almost proportional to the apex angle α. Further, since the length of the optical deflector 15, that is, the length of the base of the prism in FIG. 10 is also substantially proportional to the apex angle α, the deflection angle per unit length of the optical deflector 15 does not depend on the apex angle α. It becomes almost constant. Therefore, increase the apex angle α,
The method of arranging many electro-optic effect prisms in series is not very effective for low voltage operation and miniaturization.

The variable optical attenuator of claim 6 is the optical deflector 1.
As the substrate 101 having an electro-optical effect in 5, a single crystal or a ceramic such as PLZT (lead lanthanum zirconate titanate), BaTiO3, SBN (strontium barium niobate; tungsten bronze) having a particularly high electro-optical effect, or By using the film, a high refractive index difference can be induced even with the same applied voltage.
Therefore, it is possible to realize a smaller optical variable attenuator that operates at a low voltage.

Further, in the variable optical attenuator of the seventh aspect, as the optical deflector 15, a structure in which the electrodes 102 and the substrate 101 having the electro-optical effect as shown in FIG. 15 are alternately laminated is used. In this case, the effective electric field strength applied to the substrate 101 can be increased, and a more compact and variable optical attenuator that operates at a low voltage can be realized.

The variable optical attenuator of claim 8 is the optical deflector 1.
As shown in FIG.
Is arranged substantially symmetrically with respect to the optical axis of the input light. In this case, as can be easily understood from FIG. 11, the required deflection angle is about half and the length of the optical deflector 15 is longer than that in the case of using the normal prismatic electrode shown in FIG. Can be halved.
That is, if the optical deflectors have the same length, the required refractive index difference is about 1/4. This is very effective for low voltage operation and miniaturization of the variable optical attenuator.

As described above, the method of arranging the electro-optic effect prisms in series is not very effective for low voltage operation and miniaturization. However, by arranging the electro-optic effect prisms in parallel, it is possible to realize an optical deflector having the same length but a larger deflection angle. An example of the electrode configuration of the optical deflector used in the variable optical attenuator of claim 9 shown in FIG. 12 is shown. In the case of the optical deflector 15 of FIG. 12, although the length is the same as that of the optical deflector shown in FIG. 11, the apex angle of the prism is about double. Therefore, the required refractive index difference is about 1/2 of the case of the optical deflector of FIG. 11 and about 1/8 of the case of the optical deflector of FIG. 10, which contributes to low voltage operation and miniaturization of the variable optical attenuator. It has a great effect.

When the device length can be increased, increasing the apex angle α of the prism has a great effect on low-voltage operation, but increasing α too much is not a good idea because it increases the diffraction of light. Therefore, FIG. 11 and FIG.
It is actually an effective method to connect the electrode structures shown in 1 above in series.

13 and 14 show examples of the optical deflector used in the variable optical attenuator of claim 10. In this variable optical attenuator, an optical deflector 15 for two different polarization directions is used.
Polarization dependence is compensated by using A and 15B connected in series.

In many cases, the variable optical attenuator is required not to change the attenuation amount even if the polarization direction of the input light changes. However, as the refractive index changing means of the optical deflector, for example, when a first-order lateral electro-optical effect is used,
Only the refractive index in the direction of the applied electric field will change. That is, it does not operate as an optical deflector for light having a polarization direction inclined by 90 ° from that direction.

In order to solve this problem, as shown in FIGS. 13 and 14, the optical deflector 1 corresponding to each deflection direction.
By constructing a device by connecting 5A and 15B in series, a variable optical attenuator that does not depend on the polarization direction can be obtained. Here, the case of FIG. 13 is an example of the case where two types of electrode structures capable of applying electric fields in different directions are formed on the same plane. In the case of FIG. 14, two optical deflectors 15A and 15B having the same electrode structure are connected in series. In an actual variable optical attenuator, it is necessary to precisely adjust the lengths of the two optical deflectors in order to secure the same amount of attenuation for lights of different polarization directions. .

FIG. 7 shows an optical deflector, an output collimator, and a light absorbing portion for absorbing light, which constitute the variable optical attenuator of claim 11. In the figure, 71 is a light absorbing portion formed on the side surface of the optical deflector, and 72 is a light absorbing portion provided in the variable optical attenuator. A portion of the light deflected by the optical deflector 15 that is not output through the output collimator 32 (or 42), that is, an unnecessary portion, is reflected inside the package, for example, and returns to the input side to deteriorate the reflection loss. Or, it may enter the output side and become noise. Further, when absorbed in a part of the variable optical attenuator, that part is heated, which causes characteristic deterioration due to thermal strain and device failure. Furthermore, when an unnecessary portion of light enters the clad portion of the optical fiber, a clad mode is generated and becomes noise. In order to prevent such a problem, it is effective to previously provide a portion for absorbing unnecessary light in the variable optical attenuator.

That is, by providing the light absorbing portions 71 and 72 on the path of the unnecessary light from the optical deflector 15 as in the variable optical attenuator of the eleventh aspect, the problem of the unnecessary light can be solved. As the light absorbing means in the light absorbing parts 71, 72, a metal plate having a carbon film, a knife edge, or the like can be used, but the light absorbing means is not particularly limited thereto, and any means capable of effectively absorbing light can be used. Good.

FIG. 8 shows an example of arrangement of an optical deflector, an output collimator, an output monitor branch mirror, and a photodetector, which constitute the variable optical attenuator of claim 12. In the figure, 81 is a branching mirror for branching the output light, and 82 is a photodetector. As shown in FIG. 8, a part of the output light from the optical deflector 15 is branched and introduced into the photodetector 82, whereby the intensity of the output light can be directly monitored.

FIG. 9 shows an example of the arrangement of an optical deflector, an output collimator, and a photodetector for monitoring the attenuation amount, which constitutes another variable optical attenuator of claim 12. In the figure, reference numeral 91 indicates a photo detector for a monitor. As shown in FIG. 9, out of the light deflected by the optical deflector 15, by monitoring a part of unnecessary light that does not enter the collimator 32 (or 42), the output light intensity or the attenuation amount can be indirectly measured. Can be monitored. Since this configuration monitors unnecessary light, it has an advantage that the insertion loss of the variable optical attenuator can be improved.

In any case, According to the variable optical attenuator of claim 12, by monitoring the output light, it is not necessary to provide a coupler or a photodetector as a separate component outside the variable optical attenuator. It can contribute to cost reduction and price reduction.

[0052]

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. First, 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. A connector is attached to the end of the optical fiber that is not fused to the GI fiber so that it can be connected to the evaluation system. This optical system is designed so that input light propagating in a single mode fiber can be collimated to a spot size of about 0.1 mm, and by inserting a refractive index matching resin into the cut portion, It has been confirmed that the loss is 1 dB or less. Further, a carbon-containing resin was applied to the side surface of the GI fiber on the output side so that unnecessary light could be absorbed.

The optical deflector was manufactured by laminating three layers on a 0.05 mm thick PLZT substrate on which gold electrodes having the shapes shown in FIGS. Of an optical variable attenuator manufactured by using
OA1, EVOA2, and EVOA3).

The thickness of all the gold electrodes described above is 0.3 μm.
It was confirmed that there was almost no effect on the light transmission characteristics. The length of the optical deflector was 1 mm for all devices. In this configuration, considering the refraction between the optical deflector and the refractive index matching resin, the applied voltage is about 60 V in the shape of EVOA1, about 29 V in the shape of EVOA2, and about 21 V in the shape of EVOA3, and the attenuation is about 10 dB. Can be In addition, a carbon film was vapor-deposited on the side surface of each light deflector to absorb unnecessary light.

The optical deflector was mounted at a predetermined position of the optical system, the electrodes were taken out by wire bonding, and then a refractive index matching resin was filled to obtain a variable optical attenuator. The table below shows the relationship between the amount of attenuation and the voltage of this variable optical attenuator.

[0057]

[Table 1]

FIG. 16 shows the numerical simulation results of the characteristics of the above EVOA1 to EVOA3 and the experimental results.
In the figure, each curve shows the simulation result, and the marker points show the measured values. In FIG. 16, the fact that the attenuation amount of the experimental result is smaller than that of the simulation result is considered to be due to the influence of diffraction of light, which is not considered in the simulation. In this way, it was proved that a practically sufficient attenuation amount can be obtained at a realistic operating voltage.

Using the EVOA3, the characteristics for the input of the digital wave oscillating between the voltages 0 V and 15 V at 1 MHz were observed. As a result, it was confirmed that the variable optical attenuator of the present invention works well as an optical modulator.

[0060]

As described above, according to the variable optical attenuator of the first aspect, the optical deflector for deflecting the optical axis of the output light is used as the means for changing the light intensity.
It is possible to change the coupling amount of the output light, and it is not necessary to have high mounting accuracy like the optical variable attenuator that uses polarization rotation and interference, and it is possible to realize a low cost and highly reliable one.
Moreover, since the relationship between the applied voltage and the attenuation amount is not periodic, the attenuation amount can be easily controlled.

According to the variable optical attenuator of the second to fourth aspects, at least one of the input light and the output light is coupled to the optical deflector via a condensing means or a collimator, and further, GRIN. Since the lens, the fiber collimator, or the GI fiber is used, the alignment of the apparatus can be further facilitated, and a low-cost and highly reliable device can be realized.

According to the variable optical attenuator of the fifth aspect, as an optical deflector, an electrode is formed on a substrate having an electro-optical effect, and a difference in refractive index generated by applying a voltage to the electrode is used. The one utilizing the refraction effect of the prism was used. Therefore, the optical deflector is
Since it can be manufactured by a process of forming electrodes on a substrate and processing it into a predetermined size, it is possible to provide a variable optical attenuator having high mass productivity and low cost, and further utilizing the electro-optical effect. As a result, a device that operates at extremely high speed can be realized.

According to the variable optical attenuator of claim 6, PLZT, Ba are used as the substrate having the electro-optical effect.
TiO3 or SBN was used. As a result, it has a higher electro-optical effect than lithium niobate, which is a common material for optical devices, and thus contributes to a drastic downsizing of the device.

According to the variable optical attenuator of the seventh aspect, the optical deflector is formed by alternately laminating substrates having an electro-optical effect and electrodes. Thereby, the effective electric field strength applied to the material having the electro-optical effect can be increased, and the operating voltage can be reduced. In addition, the device can be made smaller when the same operating voltage is used.

According to the eighth aspect of the variable optical attenuator, the optical deflector is characterized in that the electrodes are arranged substantially symmetrically with respect to the optical axis of the input light to the optical deflector. The optical attenuator, unlike a simple optical deflector whose purpose is to change the direction of light, is intended to change the intensity of light. According to this variable optical attenuator, there is no problem in which direction the light deflected by the optical deflector is emitted unless it is coupled to the output. Therefore, by making the electrode arrangement of the optical deflector substantially symmetrical in the direction perpendicular to the optical axis and dividing the light into left and right or up and down, the same effect can be obtained with a smaller deflection angle. Become. By configuring an optical variable attenuator using such an optical deflector, the operating voltage can be reduced. In addition, the device can be made smaller when the same operating voltage is used.

According to the variable optical attenuator of the ninth aspect, the electrodes are arranged in a prism shape and in an array shape. By configuring an optical variable attenuator using such an optical deflector, the refraction effect of the electro-optic prism can be amplified and the operating voltage can be reduced. In addition, the device can be made smaller when the same operating voltage is used.

According to the optical variable attenuator of the tenth aspect, the optical deflector is formed by connecting the optical deflectors for two different polarization directions in series, and compensates the polarization dependence. To do. Optical variable attenuators often require that the amount of attenuation does not change even if the polarization direction of input light changes. However, when a first-order lateral electro-optic effect is used as the refractive index changing means of the optical deflector, only the refractive index in the direction of the applied electric field changes. That is, it does not operate as an optical deflector for light having a polarization direction inclined by 90 ° from that direction. To solve this problem, an optical variable attenuator that does not depend on the polarization direction can be obtained by connecting optical deflectors corresponding to the respective polarization directions in series to form a device.

Further, according to the variable optical attenuator of the eleventh aspect, the light absorbing means for absorbing the output light from the optical deflector is provided. For example, the light absorbing means may be provided on the side surface of the light deflector or inside the device. By using the variable optical attenuator having such a structure, it is possible to prevent unnecessary diffused reflection of the deflected light and generation of the cladding mode in the optical fiber, and realize a variable optical attenuator having a good SN ratio. be able to.

According to the twelfth aspect of the variable optical attenuator, a means for monitoring a part of the output light or the light deflected by the optical deflector is provided. For example, means can be incorporated into the device to split and monitor a portion of the output light to the output fiber.
It is also possible to incorporate in the device means for monitoring the light deflected by the light deflector. With such a structure, a coupler and a photodiode for an output monitor are not required outside the device, which can contribute to reduction of the number of parts of the entire device, downsizing, and cost reduction.

[Brief description of drawings]

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

FIG. 2 is a plan view schematically illustrating an embodiment of a variable optical attenuator according to the present invention.

FIG. 3 is a voltage-attenuation amount curve of the variable optical attenuator according to the present invention.

FIG. 4 is a plan view schematically explaining another embodiment of the variable optical attenuator according to the present invention.

FIG. 5 is a plan view schematically explaining another embodiment of the variable optical attenuator according to the present invention.

FIG. 6 is a plan view schematically explaining the operation principle of another variable optical attenuator according to the present invention.

FIG. 7 is a plan view schematically illustrating another variable optical attenuator according to the present invention.

FIG. 8 is a plan view schematically illustrating another variable optical attenuator according to the present invention.

FIG. 9 is a plan view schematically illustrating another variable optical attenuator according to the present invention.

FIG. 10 is a plan view schematically explaining another variable optical attenuator according to the present invention.

FIG. 11 is a plan view schematically explaining another variable optical attenuator according to the present invention.

FIG. 12 is a plan view schematically illustrating another variable optical attenuator according to the present invention.

FIG. 13 is a perspective view schematically illustrating an example of an optical deflector according to the present invention.

FIG. 14 is a perspective view schematically illustrating an example of an optical deflector according to the present invention.

FIG. 15 is a perspective view schematically illustrating an example of an optical deflector according to the present invention.

FIG. 16 is a diagram showing a simulation and actual measurement result of voltage-attenuation amount characteristics of the variable optical attenuator of the present invention.

FIG. 17 is a perspective view showing an example of a conventional variable optical attenuator.

[Explanation of symbols]

11: Input optical fiber 12: Output optical fiber 13: Input side focusing / collimating lens 14: Output side focusing / collimating lens 15: Optical deflector 16: Substrate 31: Input GRIN lens 32: output GRIN lens 41: input GI fiber collimator 42: output GI fiber collimator 71: light absorbing means 7 attached to the side surface of the optical deflector
2: Light absorbing means 81 mounted in the device: Optical branching device 82: Photodetector for monitor 91: Photodetector for monitor 101: Substrate 102 having electro-optical effect: Electrode 103 for voltage application: Collision for output Meter 161: Input optical fiber 162: Condensing / collimating lens 163: Birefringent crystal 164: Faraday rotator 165: Output optical fiber 166: Substrate

Claims (12)

[Claims] 1. An optical variable attenuator which is arranged in an optical transmission line and changes the intensity of input light to output the light, wherein the optical axis of the output light is the optical axis of the optical transmission line as means for changing the intensity of the input light. An optical variable attenuator characterized by using an optical deflector that is different from the optical axis. 2. The variable optical attenuation according to claim 1, wherein at least one of the input light and the output light is coupled to the optical deflector via a condensing unit or a collimator. vessel. 3. The variable optical attenuator according to claim 2, wherein the condenser or the collimator is a GRIN lens or a fiber collimator. 4. The variable optical attenuator according to claim 2, wherein the condensing unit or the collimator is a GI fiber. 5. The optical deflector is characterized in that an electrode is formed on a substrate having an electro-optical effect, and a refraction effect of a prism using a refractive index difference generated by applying a voltage to the electrode is utilized. The variable optical attenuator according to claim 1. 6. The variable optical attenuator according to claim 5, wherein PLZT, BaTiO 3, or SBN is used as the substrate material having the electro-optical effect. 7. The variable optical attenuator according to claim 5, wherein the optical deflector is formed by alternately laminating substrates and electrodes having an electro-optical effect. 8. The variable optical attenuator according to claim 5, wherein the optical deflector has electrodes arranged substantially symmetrically in a direction perpendicular to an optical axis of input light to the optical deflector. 9. The variable optical attenuator according to claim 5, wherein the electrodes are prism-shaped and arranged in an array. 10. The variable optical attenuator according to claim 5, wherein the optical deflector is formed by connecting optical deflectors for two different polarization directions in series and compensating for polarization dependence. . 11. The variable optical attenuator according to claim 1, further comprising a light absorbing unit that absorbs light from the light deflector. 12. The variable optical attenuation according to claim 1, further comprising means for monitoring a part of the output light or a light deflected by an optical deflector. apparatus.