JP2003131147A - Variable optical attenuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a miniaturized and reliable variable optical attenuator. SOLUTION: Light inputted to a GRIN lens 2 from an input optical fiber 1 propagates in the direction of the light axis of the GRIN lens 2. The GRIN lens 2 receives a stress from a stress-giving mechanism and the form of the lens and the condensing position of a light beam vary, thus the attenuation of the light which passes through the GRIN lens 2 varies according to the given stress. Specifically, the stress given to the GRIN lens 2 by a directly pushing movable part 7 is adjusted by operating a screw 6, and the attenuation of the light is available according to the given stress.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable optical attenuator used in the field of optical communication and capable of varying the attenuation amount of optical power.

[0002]

2. Description of the Related Art With the recent development of optical fiber amplifiers and high-density wavelength-division multiplexing communication systems, high-output light is controlled for the purpose of equalizing optical power between optical fiber amplifier stages and simultaneously attenuating multiple wavelengths. Therefore, the demand for variable optical attenuators is increasing. As this variable optical attenuator, there is one that realizes an optical attenuation effect by mechanical means, for example, by separating or aligning the end faces of an optical fiber, by microbending of an optical fiber, or by a stepping motor drive. There is a mechanical interference method of a light beam with a blade or a filter. However, the variable optical attenuator using these mechanical means has a problem that it is inferior in the speed of changing the optical attenuation amount.

On the other hand, thermo-optical effect type variable optical attenuators, electro-optical effect type variable optical attenuators, etc. have been developed as variable optical attenuators by non-mechanical means. An example of this thermo-optical effect type variable optical attenuator is shown in FIG. In FIG. 6, reference numeral 11 is an input optical fiber, and the input optical fiber 11 is connected to the input end of the substrate 13 on which the optical waveguide 12 is formed. Control electrodes 14 are provided on both sides of one branched optical waveguide 12a on the substrate 13, and an output optical fiber 15 is connected to an output end of the substrate 13. In this thermo-optical effect type variable optical attenuator, since the refractive index of the substrate 13 depends on temperature, the optical waveguide 12a heated by the control electrode 14 causes an optical path length difference with respect to one optical waveguide 12b, The output light power output to the output optical fiber 15 is attenuated depending on the temperature difference between these two optical waveguides. In this way, the light attenuation amount is adjusted by the temperature control by the control electrode 14.

Next, an example of the electro-optical effect type variable optical attenuator is shown in FIG. In FIG. 7, reference numeral 21 is an input optical fiber, and this input optical fiber 21 is connected to the input end of the input side collimator 22a. Reference numeral 22b is an output side collimator, and an output optical fiber 23 is connected to an output end of the output side collimator 22b. An electro-optical element 24 is arranged between the input side collimator 22a and the output collimator 22b with a space therebetween.
In this electro-optical effect type variable optical attenuator, the input light from the input optical fiber 21 is input side collimator 22a.
Is collimated as shown in FIG. 7 and enters the electro-optical element 24 as a parallel beam. By adjusting the electric field of the electro-optical element 24, the optical power transmitted through the electro-optical element 24 changes, and the transmitted light is focused via the output side collimator 22b and output to the output optical fiber 23. In this way, the amount of light attenuation is adjusted by controlling the electric field applied to the electro-optical element 24.

[0005]

However, the above-mentioned thermo-optical effect type variable optical attenuator requires a substrate for producing the thermo-optical effect, and therefore has a drawback that it is large in size due to its configuration. Further, the electro-optical effect type variable optical attenuator requires three independent parts, that is, the lens-element-lens to be fixed accurately and stably for a long period of time, resulting in high structure and construction cost. In addition, since the light beam propagates through the air when it is transmitted to the electro-optical element, the structure is such that dust, moisture, etc. do not enter the space, and it is costly to improve reliability. was there. The present invention has been made to solve such problems, and an object of the present invention is to provide a variable optical attenuator that can be miniaturized, has low cost, and has high reliability.

[0006]

In order to solve the above problems, the invention according to claim 1 is provided with a stress applying mechanism for applying stress to the GRIN lens, and the GRIN lens penetrates through the stress applying mechanism. It is a variable optical attenuator characterized by adjusting the amount of light. As a result, the focal position in the GRIN lens fluctuates sensitively and the light beam converging position changes, so that a variable optical attenuator capable of adjusting the optical attenuation amount according to the stress application amount can be realized. According to a second aspect of the present invention, in the variable optical attenuator according to the first aspect, the stress applying mechanism is means for operating a screw to press the GRIN lens.

According to a third aspect of the present invention, in the variable optical attenuator according to the first aspect, the stress applying mechanism is means for applying stress to the GRIN lens by a piezo element. According to a fourth aspect of the present invention, in the variable optical attenuator according to the first aspect, the stress applying mechanism is means for applying a stress due to thermal expansion to the GRIN lens by changing the temperature of the stress applying substance. Characterize.

According to a fifth aspect of the present invention, in the variable optical attenuator of the fourth aspect, the temperature change is made by a heater or a Peltier element. Claim 6
The described invention is the variable optical attenuator according to claim 1, 2, 3, 4 or 5, wherein the GRI is adjusted according to the magnitude of optical attenuation.
It is characterized in that the amount of stress applied to the N lens is controlled so that an optimum amount of light attenuation can be obtained.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
FIG. 1 shows the configuration of a first example of the variable optical attenuator of the present invention. In FIG. 1, reference numeral 1 is an input optical fiber, and this input optical fiber 1 is connected to the input end of a GRIN lens 2. An output optical fiber 3 is connected to the output end of the GRIN lens 2. As the GRIN lens 2, a GRIN lens having a diameter of 125 μm to 1000 μm and a thickness almost equal to the optical fiber diameter is used. The GRIN lens 2 and the input optical fiber 1 and the output optical fiber 3 are bonded or fused by adjusting the positions of the input optical fiber 1 and the output optical fiber 3 so that the optical coupling rate is maximized. It is fixed by.

The GRIN lens 2 is supported by two supports 4, and the bottom of the support 4 has the GRIN lens 2
Is fixed to the case 5 for accommodating the. Reference numeral 6 denotes a screw provided on the upper surface side of the GRIN lens 2, and in this example, the screw 6 is driven by a motor or manually operated to directly move the GRIN lens 2 by the movable portion 7. The upper surface of is pressed. That is, in this example, a stress applying mechanism for applying stress such as bending and compressive stress to the GRIN lens 2 is constituted by the screw 6 and the direct-pressing movable portion 7.

Next, the operation of the variable optical attenuator of this example will be described. Input optical fiber 1 to GRIN lens 2
The light input to is propagated in the optical axis direction of the GRIN lens 2. Since the GRIN lens 2 is stressed by the stress applying mechanism and its shape and the light beam condensing position are changed, the attenuation amount of the light transmitted through the GRIN lens 2 is changed according to the stress applying amount. Here, the amount of stress applied to the GRIN lens 2 from the direct-press movable portion 7 is adjusted by operating the screw 6. In this example,
It is preferable to use a GRIN lens having a length that is half the optical path pitch in the GRIN lens 2, that is, an integral multiple of 0.5 pitch. The light incident on the GRIN lens 2 is G
It spreads in the RIN lens 2 and the light beam diameter becomes maximum at the position of 0.25 pitch. The light is then focused, focused at 0.5 pitch, and output to the output optical fiber 3.

The reason why the GRIN lens whose length is an integral multiple of 0.5 pitch is used is as follows. In the case of an optical component using a normal GRIN lens, a 0.25 pitch lens is used, which means that when the pitch length of the GRIN lens is 0.25 pitch, GR
This is because the light incident on the IN lens becomes parallel light, and the loss increase is small even if the optical functional element is sandwiched between the lenses. However, in the case of the variable optical attenuator of this example, the GRIN lens itself is provided with the variable optical attenuating function instead of sandwiching the optical functional element between the GRIN lenses, and therefore the pitch length of the GRIN lens is 0.5. By using an integral multiple of the pitch, the focused light can be output to the output optical fiber. When the GRIN lens 2 is not stressed, the insertion loss is ideally 0.
It becomes dB. However, in actuality, due to factors such as loss due to scattering and absorption in the GRIN lens 2 and misalignment when connecting the optical fiber and the GRIN lens 2, 0.2
Insertion loss of about dB is generated.

On the other hand, when the GRIN lens 2 is stressed, the light is attenuated in the GRIN lens 2. The reason for this will be described below. An optical fiber is known as an example in which the amount of optical attenuation changes due to stress such as bending. In the case of an optical fiber, since it has an optical waveguide structure, light is confined in the waveguide and travels while undergoing total reflection at the boundary surface with the core, but if bending occurs, it will not satisfy the condition for total reflection of light. Therefore, light loss occurs. Even in the case of a GRIN lens, when stress is applied, its shape changes, which causes a focus position change and changes the light beam focusing position. Therefore, the output end of the GRIN lens 2 changes according to the amount of stress applied. The amount of light output from the output optical fiber 3 changes. Also, stress G
When added to the RIN lens 2, the refractive index distribution inside the lens is disturbed, resulting in an increase in loss due to the collapse of the light beam shape at the condensing end and a change in the light amount.

In the GRIN lens, the light beam diameter is expanded and focused due to the refractive index distribution of the GRIN lens. At this time, the larger the light beam diameter, the larger the fluctuation in the focal position due to the bending angle. Figure 2 shows two opposing GRINs
FIG. 3 shows the calculation result of the optical loss in the case of causing the angle bending between the lenses, and FIG. 3 shows the calculation of the optical loss in the case of causing the angle bending between the optical fiber and the GRIN lens. The results are shown for a mode field diameter of 10 μm.
From these calculation results, if the angle bending amount is 0.1 degree,
When the light beam diameter is 420 μm, the loss increase is 6 dB, whereas when the light beam diameter is 10 μm, the loss increase is only 0.00028 dB.

As described above, when an angle fold is generated between two opposing lenses, the larger the light beam diameter, the larger the loss increase amount. Therefore, stress is applied to one continuous GRIN lens to bend it. By causing the angle, the wave front of the beam expanding portion in the GRIN lens also becomes angled, so that the loss increase amount increases. Therefore, G
In the RIN lens 2, in the region where the light beam diameter is expanded, the loss increase amount with respect to the bending angle is large, and it is possible to greatly attenuate the light with a slight angle change.

Next, a second example of the variable optical attenuator of the present invention will be described. FIG. 4 shows a second variable optical attenuator of the present invention.
The structure of the example of is shown. The variable optical attenuator of this example is a GRI in which an input optical fiber 1 and an output optical fiber 3 are connected.
The N lens 2 is supported by the two supports 4 and housed in the case 5 as in the first example, but the structure of the stress applying mechanism is different from that in the first example. Reference numeral 6 is a screw, and when the screw 6 is operated, the slide type movable portion 8 presses the substantially central portion of the upper surface of the GRIN lens 2. That is, in this example, the screw 6
The slide type movable portion 7 constitutes a stress applying mechanism. Also in this example, a GR having a diameter approximately the same as the optical fiber diameter and having a length that is an integral multiple of 0.5 pitch
It is preferable to use an IN lens. In this example, by operating the screw 6, the G
The amount of stress applied to the RIN lens 2 is adjusted.
The GRIN lens 2 is stressed by the stress applying mechanism at its central portion, and its shape and light beam condensing position are changed.
The amount of attenuation of light transmitted through the lens 2 changes.

Next, a third example of the variable optical attenuator of the present invention will be described. FIG. 5 shows a third variable optical attenuator of the present invention.
The structure of the example of is shown. The variable optical attenuator of this example is a GRI in which an input optical fiber 1 and an output optical fiber 3 are connected.
The N lens 2 is supported by the support 4 and is housed in the case 5, and the stress applying mechanism is composed of the screw 6 and the slide type movable portion 8 as in the second example. The position where the means for supporting the lens 2 and the slide type movable portion 8 are provided is different from that of the second example. In this example, the support tool 4 supports only one end of the lower surface of the GRIN lens 2. Further, the slide type movable portion 8 is GR
By pressing the other end of the upper surface of the IN lens 2,
Functions as a stress applying mechanism. Also in this example,
It is preferable to use a GRIN lens having a diameter substantially equal to the diameter of the optical fiber and having a length that is an integral multiple of 0.5 pitch. In this example, the amount of stress applied to the GRIN lens 2 from the slide type movable portion 8 is adjusted by operating the screw 6. The GRIN lens 2 is subjected to stress on the side near the input end by a stress applying mechanism, and its shape and light beam condensing position change. Therefore, the amount of attenuation of light transmitted through the GRIN lens 2 is changed according to the amount of stress applied. Changes.

As the stress applying mechanism for applying stress to the GRIN lens 2, the following examples can be used in addition to the examples described above. One of them is a means for applying stress using a piezo element, and stress can be applied to the GRIN lens 2 by applying an electric field to the piezo element. The other one is GRI
A material having a large coefficient of thermal expansion such as metal is used as a stress applying material for applying stress to the N lens 2, and the temperature of this material is changed by using a heater or a Peltier element to generate stress due to thermal expansion. is there. Also, other means may be used as long as the stress can be applied to the GRIN lens 2 by means other than those described above. Further, the information about the light attenuation amount is fed back, and G is adjusted according to the magnitude of the light attenuation amount.
It is also possible to control the amount of stress applied to the RIN lens 2 so as to obtain the optimum light attenuation amount.

According to the variable optical attenuator of this example, GRIN
By providing a stress applying mechanism for applying stress to the lens 2 and applying stress to the GRIN lens 2 having a diameter approximately the same as the optical fiber diameter, the GRIN
Since the focal position in the lens 2 sensitively changes and the light beam condensing position changes, a variable optical attenuator capable of adjusting the optical attenuation amount according to the stress application amount can be realized. Further, since the GRIN lens 2 having a diameter approximately equal to the diameter of the optical fiber is used, it is possible to realize a variable optical attenuator which can be downsized and can be manufactured at low cost. Moreover, since the light beam does not propagate in the air, a highly reliable variable optical attenuator can be realized. Furthermore, since the amount of light attenuation can be adjusted sensitively to the applied stress, it is possible to realize light attenuation with a small amount of stress, and to use power such as electric power to control the stress applying part. It is possible to realize a variable optical attenuator in which the desired amount of optical attenuation can be obtained by reducing the amount.

[0020]

As described above, according to the present invention,
A GRI lens having a stress applying mechanism for applying stress to the GRIN lens and having a diameter about the same as the optical fiber diameter
By applying stress to the N lens, GR
Since the focus position in the IN lens fluctuates sensitively and the light beam condensing position changes, it is possible to realize a variable optical attenuator capable of adjusting the optical attenuation amount according to the stress application amount. In addition, GRIN having a diameter similar to the optical fiber diameter
Since the lens is used, it is possible to realize a variable optical attenuator that can be downsized and that is low in cost. Further, since the light beam does not propagate in the air and the number of components can be reduced, a highly reliable variable optical attenuator can be realized. Furthermore, since the amount of light attenuation can be adjusted sensitively to the applied stress, it is possible to realize light attenuation with a small amount of stress, and to use power such as electric power to control the stress applying part. It is possible to realize a variable optical attenuator in which the desired amount of optical attenuation can be obtained by reducing the amount.

[Brief description of drawings]

FIG. 1 is a diagram showing a first example of a variable optical attenuator of the present invention.

FIG. 2 is a diagram showing light loss due to angular bending between GRIN lenses.

FIG. 3 is a diagram showing optical loss due to angle bending between an optical fiber and a GRIN lens.

FIG. 4 is a diagram showing a second example of the variable optical attenuator of the present invention.

FIG. 5 is a diagram showing a third example of the variable optical attenuator of the present invention.

FIG. 6 is a diagram showing an example of a conventional variable optical attenuator.

FIG. 7 is a diagram showing another example of a conventional variable optical attenuator.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Input optical fiber, 2 ... GRIN lens, 3 ... Output optical fiber, 4 ... Support tool, 5 ... Case, 6 ... Screw, 7
… Directly moving part, 8… Sliding type moving part

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Katsutoshi Komoto             Fuji Co., Ltd. 1440 Rokuzaki, Sakura City, Chiba Prefecture             Kura Sakura Office (72) Inventor Yoichi Kurumiya             Fuji Co., Ltd. 1440 Rokuzaki, Sakura City, Chiba Prefecture             Kura Sakura Office (72) Inventor Hideyuki Hosoya             Fuji Co., Ltd. 1440 Rokuzaki, Sakura City, Chiba Prefecture             Kura Sakura Office (72) Inventor Makiko Yokoyama             Fuji Co., Ltd. 1440 Rokuzaki, Sakura City, Chiba Prefecture             Kura Sakura Office F-term (reference) 2H038 AA21 AA35 BA23 BA30                 2H041 AA02 AB24 AC01 AC07 AZ02                       AZ05

Claims (6)

[Claims] 1. A variable optical attenuator comprising a stress applying mechanism for applying stress to a GRIN lens, and adjusting the amount of light transmitted through the GRIN lens by applying the stress. 2. The variable optical attenuator according to claim 1, wherein the stress applying mechanism is means for operating a screw to press the GRIN lens. 3. The variable optical attenuator according to claim 1, wherein the stress applying mechanism is means for applying stress to the GRIN lens by a piezo element. 4. The stress applying mechanism changes the temperature of a stress applying substance to apply stress due to thermal expansion to the G
The variable optical attenuator according to claim 1, which is a means for applying the RIN lens. 5. The variable optical attenuator according to claim 4, wherein the temperature change is performed by a heater or a Peltier element. 6. The amount of stress applied to the GRIN lens is controlled according to the magnitude of light attenuation so that an optimum light attenuation can be obtained.
The variable optical attenuator according to 3, 4, or 5.