JPH10253829A - Fiber type tunable filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fiber type tunable filter of high stability and high reliability having high tuning speed. SOLUTION: An actuator 14 is laid for applying a tensile force or a compressive force to a fiber diffraction grating 13 provided at the intermediate position of an optical fiber 11. Furthermore, incident light 15 having a plurality of types of wavelength has specific wavelength reflected with the diffraction grating 13 via an optical circulator 12, resulting in outgoing reflected light 16. When a tensile force is applied from the actuator 14 to the diffraction grating 13, the refractive index thereof changes, and light of another wavelength is emitted as the reflected light 16. The actuator 14 may be piezoelectric type, electromagnetic type, a micrometer or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength tunable filter, and more particularly to a fiber type wavelength tunable filter suitably used in fields such as optical communication, optical information processing, and optical measurement.

[0002]

2. Description of the Related Art In recent years, with the increase in the capacity of an optical fiber communication system, a system construction using a wavelength multiplexing method has been studied. However, when performing optical transmission using a plurality of wavelengths, a specific (desired) wavelength is required. An optical filter (optical tuner) for discriminating between the two is required.

A conventional tunable filter has a structure in which a reflection wavelength is variable by mechanically rotating or moving a grating or a dielectric multilayer film formed on flat glass, or a gap control by a fiber etalon piezo. Some of them change the reflection wavelength. In either case, it is necessary to once emit light from the optical fiber to free space, which has disadvantages such as an increase in insertion loss and a lack of mechanical stability.

A method for forming a diffraction grating in an optical fiber is disclosed in Japanese Patent Application Laid-Open No. Sho 62-500052. However, when a tension is applied to a processed fiber to give an elongation in the axial direction, the diffraction grating is formed. It has been reported that the reflection characteristic changes almost linearly with respect to the tension due to the change in pitch (Laser Research Vol. 23, No. 10, 68-77).
page).

Further, as a fiber type wavelength filter,
One disclosed in Japanese Patent Application Laid-Open No. Hei 5-188222 is known. FIG. 7 shows the configuration of this fiber type wavelength filter. The clad 72 is removed from a predetermined portion of the optical fiber 71, and the core 73 from which the clad 72 is removed.
Next, a diffraction grating 74 having a periodic structure is formed concentrically. Next, the diffraction grating 74 is covered with a coating material 76 that does not absorb light, and the portion of the clad 72 removed earlier is filled. At the same time, a cylindrical heater 75 is arranged concentrically around the coating material 76. By adjusting the heating by the heater 75, the center wavelength of the transmission blocking region of the wavelength filter can be changed.

[0006]

The center wavelength of the transmission stop band in a fiber-type wavelength filter [0005] In order to vary, it is necessary to the refractive index n _c of the period Λ or core portion of the diffraction grating in the variable, conventional In the method shown in the example, the refractive index changes with temperature. However, in the fiber type wavelength filter according to this method, since the refractive index is changed according to the temperature, the change speed is slow, a time until it is stabilized is required, and the cladding is removed when forming the diffraction grating. Therefore, there is a disadvantage that mechanical stability and reliability are lacking.

In view of the foregoing, it is an object of the present invention to provide a fiber type wavelength tunable filter having high stability, high reliability, and high tuning speed, which is used for optical communication.

[0008]

In order to achieve the above object, a fiber type wavelength tunable filter according to the present invention is provided on a diffraction grating provided in an optical fiber by a piezoelectric actuator, a micrometer, an electromagnetic actuator, or the like. A tension or a compressive force is applied, thereby realizing a fiber type tunable filter having a high stability, a high reliability, and a high tuning speed in which the period interval of the diffraction grating is variable.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention described in claim 1 is an optical fiber having a periodic structure of refractive index in a core or a clad and having a filter characteristic, and an optical fiber having the periodic structure having a refractive index distribution of an optical fiber. A fiber type wavelength tunable filter including means for controlling by applying tension or compression force to the fiber, and an input / output unit for light to the optical fiber, and among signal light having a plurality of wavelength components, It has the function of outputting only signal light having a wavelength component.

According to a second aspect of the present invention, as a means for controlling the refractive index distribution of the optical fiber, there is provided a fiber type having a mechanism for applying a tension or a compressive force in the optical axis direction of the optical fiber by a cylindrical piezoelectric actuator. The wavelength tunable filter has a function of outputting only a signal light having a desired wavelength component among signal lights having a plurality of wavelength components, similarly to the first aspect of the present invention.

According to a third aspect of the present invention, as a means for controlling the refractive index distribution of the optical fiber, a cylindrical piezoelectric actuator that comes into contact with the periphery of the optical fiber is used to control the light in a direction perpendicular to the optical axis direction of the optical fiber. A fiber-type wavelength tunable filter having a mechanism for applying a compressive force from the periphery of the fiber toward the center, wherein a desired wavelength component of the signal light having a plurality of wavelength components is provided as in the invention described in claim 1. Has the effect of outputting only the signal light having

According to a fourth aspect of the present invention, as a means for controlling the refractive index distribution of the optical fiber, a cylindrical piezoelectric actuator having a concavo-convex structure having the same period as the pitch of the periodic structure of the refractive index is used to control the optical fiber. A fiber type wavelength tunable filter having a mechanism for applying a compressive force from the periphery to the center of an optical fiber in a direction perpendicular to an axial direction, and has a plurality of wavelength components as in the invention described in claim 1. It has an effect of outputting only signal light having a desired wavelength component among the signal lights.

According to a fifth aspect of the present invention, there is provided a fiber-type wavelength tunable filter having a structure in which both ends of the fiber are pulled by a fine movement mechanism using a micrometer or a linear actuator as means for controlling the refractive index distribution of the optical fiber. Yes, as in the first aspect of the present invention, it has an effect of outputting only signal light having a desired wavelength component out of signal light having a plurality of wavelength components.

According to a sixth aspect of the present invention, as a means for controlling the refractive index distribution of the optical fiber, the optical fiber is bonded to a ferrule having an electromagnet, and the optical fiber is pulled by a movable mechanism by electromagnetic induction. This is a fiber-type wavelength tunable filter provided with the function of outputting only the signal light having a desired wavelength component among the signal lights having a plurality of wavelength components, similarly to the first aspect of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. (Embodiment 1) FIG. 1 schematically shows the entire configuration of a fiber-type wavelength tunable filter according to a first embodiment of the present invention. In FIG. 1, reference numeral 11 denotes an optical fiber, and a fiber diffraction grating 13 is coupled to one terminal of an optical circulator 12 coupled to the optical fiber 11,
An actuator 14 is fixed to the fiber diffraction grating 13 so that tension can be applied. Let λ _B be the Bragg reflection wavelength of the fiber diffraction grating 13 before applying tension.

The incident light 15 having a plurality of wavelengths passes through the optical circulator 12 and enters the fiber diffraction grating 13. Both ends of the optical fiber on which the fiber diffraction grating 13 is formed are fixed to the actuator 14. The actuator 14 has a function of changing its shape so as to extend in the axial direction of the optical fiber 11. Of the plurality of incident lights 15, light passing through the fiber diffraction grating 13 becomes transmitted light 17, while light reflected by the fiber diffraction grating 13 becomes reflected light 16.

The light tuning operation of the above configuration will be described below. Multiple wavelengths (λ _{1 to} λ
_The incident light 15 having _n ) is guided to the optical circulator 12, exits again, and reaches the diffraction grating 13. When no tension is applied to the fiber diffraction grating 13, only light of the wavelength λ _B is reflected, returns to the optical circulator 12 again, and is emitted as reflected light 16. Here, when tension is applied to the fiber diffraction grating 13 by the actuator 14, a change in the refractive index occurs in the fiber diffraction grating 13, and the Bragg reflection wavelength changes from λ _B to λ _k (λ _k > λ _B ).
Then looks like the light of wavelength lambda _k instead of light of the wavelength lambda _B is reflected, returning to the optical circulator 12 again, and is emitted as reflected light 16. The wavelength components other than λ _k are emitted as transmitted light 17 as they are. Controlling the magnitude of the voltage applied to the actuator 14, by adjusting the tension applied, it is possible to continuously change the value of the Bragg reflection wavelength lambda _k.

As described above, according to the first embodiment, the tuning operation of the wavelength can be performed by applying tension to the fiber diffraction grating 13 by the actuator 14, and the tuning speed for changing the periodic interval of the diffraction grating is high. A fiber-type wavelength tunable filter can be realized, and characteristics such as high stability and high reliability can be improved as compared with the temperature control method shown in the conventional example.

(Embodiment 2) FIG. 2 shows an overall configuration of a fiber-type wavelength tunable filter according to a second embodiment of the present invention. In FIG. 2, reference numeral 21 denotes an optical fiber, and one terminal No. of a three-terminal optical circulator 22 coupled to the optical fiber 21. 2 is coupled to a fiber diffraction grating 23 formed in an optical fiber. Each optical fiber 21 is connected via a connector 24. The fiber grating 23 includes a fiber grating 23
The piezoelectric actuator 25 is coupled to apply a tension to the fiber grating 23, and the Bragg reflection wavelength of the fiber diffraction grating 23 before the tension is applied is λ _B.

The incident light 26 having a plurality of wavelengths, which is introduced into the optical fiber 21 serving as the light input / output portion, is output from the optical circulator 22 at the No. 2 position. No. 1 terminal. The light enters the fiber diffraction grating 23 from two terminals via the connector 24.
Now, both ends of the optical fiber 21 on which the fiber diffraction grating 23 is formed are fixed to both ends of the piezoelectric actuator 25, respectively. The piezoelectric actuator 25 has a cylindrical hollow shape,
It is assumed that when a voltage is applied, the shape changes so as to extend in the axial direction of the optical fiber. The light that has passed through the fiber grating 23 becomes the transmitted light 28 while the fiber grating 2
The light reflected by No. 3 is the optical circulator 22 No. 3. The reflected light 2 from the three terminals via the optical fiber 21 and the connector 24
It becomes 7.

The light tuning operation of the above configuration will be described below. Multiple wavelengths (λ ₁ to
λ _n ) through the optical fiber 21. It is led from one terminal to the optical circulator 22 and N
o. The light exits from two terminals and reaches the fiber diffraction grating 23 from the connector 24 via the optical fiber 21. In a state where no tension is applied to the fiber diffraction grating 23, only the light of the wavelength λ _B is reflected. Returning from the second terminal to the optical circulator 22 again, Light reflected from three terminals 27
Is emitted. Here, when a voltage is applied to the piezoelectric actuator 25 and tension is applied to the fiber diffraction grating 23, a change in the refractive index occurs in the fiber diffraction grating, and the Bragg reflection wavelength changes from λ _B to λ _k (λ _k > λ _B ). I do. Thus the incident light 26 is reflected light of wavelength lambda _k instead of light of the wavelength lambda _B, No. Returning from the second terminal to the optical circulator 22 again, The reflected light 27 is emitted from the three terminals via the optical fiber 21 from the connector 24 via the optical fiber 21. The wavelength components other than λ _k are emitted as transmitted light 28 as they are. By controlling the magnitude of the voltage applied to the piezoelectric actuator 25 and adjusting the applied tension, the value of the Bragg reflection wavelength λ _k can be continuously changed.

As described above, according to the second embodiment, by applying a voltage to the piezoelectric actuator 25 and applying a tension to the fiber diffraction grating 23, a wavelength tuning operation can be performed, and the periodic interval of the diffraction grating can be varied. Thus, a fiber-type wavelength tunable filter having a high tuning speed can be realized, and the characteristics of high stability and high reliability can be improved as compared with the temperature control method shown in the conventional example.

The configuration of the cylindrical hollow piezoelectric actuator 25 may be a configuration in which a plurality of cylindrical piezoelectric actuators are connected in series.

(Embodiment 3) FIG. 3 shows a configuration of a section for applying a compressive force to a fiber diffraction grating of a fiber type tunable filter according to a third embodiment of the present invention. FIG. 3 (a)
The optical fiber core 31 and the optical fiber clad 3
A fiber diffraction grating 33
Are formed. Around the optical fiber 30, there is disposed a cylindrical piezoelectric actuator 34 which contacts the periphery of the optical fiber 30 and applies a compressive force from the periphery of the optical fiber 30 to the center in a direction perpendicular to the optical axis direction. I have. Also, in FIG. 3B, a cylindrical piezoelectric actuator 34 is shown.
The portion of the optical fiber clad 32 that comes into contact with the optical fiber is shaved to form an optical fiber clad removing portion 35, and the diameter of the entire optical fiber is reduced.

The light tuning operation of the above configuration will be described below. FIG. 3 (a), (b)
The operations are the same in both cases, and will be described here with reference to FIG. When a voltage is applied to the piezoelectric actuator 34 to apply a compressive force from the periphery of the optical fiber 30 to the center in a direction perpendicular to the optical axis direction, stress is applied to the optical fiber 30 in the axial direction, and the fiber diffraction grating 33 Changes the refractive index of the Bragg reflection wavelength from λ _B to λ _k
(Λ _k > λ _B ). Therefore, of the incident light, is as light of wavelength lambda _k is reflected instead of light of the wavelength lambda _B, by controlling the magnitude of the voltage applied to the piezoelectric actuator 34, by adjusting the compressive force applied, the value of the Bragg reflection wavelength lambda _k it is possible to continuously change.

As described above, according to the third embodiment, by applying a voltage to the piezoelectric actuator 34 and applying a tension to the fiber diffraction grating 33 in a direction perpendicular to the optical axis direction toward the center, A wavelength tuning operation can be performed, and a fiber-type wavelength tunable filter with a fast tuning speed that makes the period interval of the diffraction grating variable can be realized, and has higher stability and higher reliability than the temperature control method shown in the conventional example. Characteristics can be improved.

Even if the diameter of the entire optical fiber is reduced as shown in FIG. 3B, a fiber-type wavelength tunable filter having a high tuning speed and a variable periodic interval of the diffraction grating can be obtained by the above-described configuration. Can be realized.

(Embodiment 4) FIG. 4 shows a configuration of a section for applying a compressive force to an optical fiber of a fiber type wavelength tunable filter according to a fourth embodiment of the present invention. In FIG. 4A, around the optical fiber 40 including the optical fiber core 41 and the optical fiber clad 42, the optical fiber 40 is brought into contact with the periphery of the optical fiber 40 and in a direction perpendicular to the optical axis direction.
And a cylindrical piezoelectric actuator 43 for applying a compressive force from the periphery to the center. The piezoelectric actuator 43 has a concavo-convex structure with a period Λ on the contact surface with the optical fiber 40. If the design reflects light having a wavelength of about 1.55 μm, the refractive index of the optical fiber core 41 is 1.47.
Therefore, the period Λ of the uneven structure is set to 0.53 μm. Further, in FIG. 4B, the uneven structure of the piezoelectric actuator 44 is configured to have a sawtooth shape as illustrated.
In FIG. 4C, the optical fiber clad 42 in contact with the piezoelectric actuator 43 is shaved to reduce the diameter of the entire optical fiber.

The light tuning operation of the above configuration will be described below. FIG. 4 (a)
The operations of (b) and (c) are the same, and here, FIG.
This will be described with reference to FIG. A voltage is applied to the piezoelectric actuator 43 so that the optical fiber 4 is perpendicular to the optical axis direction.
When a compressive force is applied from the periphery of 0 to the center, the refractive index changes in the optical fiber core 41, and the Bragg reflection wavelength becomes λ.
A fiber grating, _B , is formed. When a voltage is further applied to increase the compressive force, the optical fiber 40 expands, and the Bragg reflection wavelength changes from λ _B to λ _k (λ _k > λ _B ).
I do. Therefore, by controlling the magnitude of the voltage applied to the piezoelectric actuator 43 and adjusting the applied compressive force, it is possible to continuously form the diffraction grating and change the value of its Bragg reflection wavelength λ _k .

As described above, according to the fourth embodiment, the voltage is applied to the piezoelectric actuator
By applying tension toward the center in the direction perpendicular to the optical axis direction, the wavelength tuning operation can be performed, and a fiber type wavelength tunable filter with a high tuning speed that can change the period interval of the diffraction grating can be realized. As a result, the characteristics of high stability and high reliability can be improved as compared with the temperature control method shown in the conventional example.

Even if the piezoelectric actuator 44 has the saw-toothed structure shown in FIG. 4 (b), the same structure as described above can be used to change the period interval of the diffraction grating and to increase the tuning speed of the fiber. Type tunable filter can be realized.

Even if the diameter of the entire optical fiber is reduced as shown in FIG. 4 (c), a fiber type wavelength tunable filter having a high tuning speed and a variable periodic interval of the diffraction grating can be provided by the above configuration. Can be realized.

(Embodiment 5) FIG. 5 shows a configuration of a tension applying section for a fiber diffraction grating of a fiber type wavelength tunable filter according to a fifth embodiment of the present invention. In FIG. 5, a fiber diffraction grating 53 is formed on an optical fiber 50 including an optical fiber core 51 and an optical fiber clad 52. Ferrules 54 are fixed at both ends of the optical fiber clad 52 on which the fiber diffraction grating 53 is formed with an adhesive 55. A guide A56 is fixed to one ferrule 54, and the other ferrule 5
A guide B57 is fixed to 4 and a micrometer 58 for applying a force to the guide A56 is attached to the guide B57.

The light tuning operation of the above configuration will be described below. Micrometer 5
When the guide A 57 is pushed by the number 8, the two ferrules 54
Is applied to the optical fiber 50, tension is applied to the optical fiber 50, the optical fiber 50 expands in the axial direction, a refractive index change occurs in the fiber diffraction grating 53, and the Bragg reflection wavelength becomes λ compared to that before expansion.
_It changes from _B to λ _k (λ _k > λ _B ). Therefore, the light of the wavelength λ _k is reflected instead of the light of the wavelength λ _B of the incident light, and the tension is changed by controlling the size of the scale of the micrometer 58 and adjusting the applied force. , The value of the Bragg reflection wavelength λ _k can be changed continuously. The ferrule 54 and the adhesive 55 are for applying a tension to the fiber diffraction grating 53, and do not deform to the extent that the fiber itself is stretched.

As described above, according to the fifth embodiment, the optical fiber 5 is moved by the fine movement mechanism using the micrometer 58.
By applying tension to the fiber diffraction grating 53 by pulling both ends of the fiber grating 0, a tuning operation of the wavelength can be performed, and a fiber type wavelength tunable filter having a high tuning speed to change the period interval of the diffraction grating can be realized. Compared to the method using temperature control shown in the example, the characteristics of high stability and high reliability can be improved.

(Embodiment 6) FIG. 6 shows a portion for applying tension to a fiber diffraction grating of a fiber type wavelength tunable filter according to a sixth embodiment of the present invention. In FIG. 6, a fiber diffraction grating 63 is formed on an optical fiber 60 including an optical fiber core 61 and an optical fiber clad 62.
Ferrules 64 are fixed at both ends of the optical fiber clad 62 on which the fiber diffraction grating 63 is formed by an adhesive 65. A guide magnet A66 is fixed to one ferrule 64, a guide magnet B67 is fixed to the other ferrule 64, and guide magnets A66 and B6 are fixed.
7 is provided with an iron core 69 wound with a coil 68 for applying tension thereto by electromagnetic induction.
A power supply 70 is connected to 8.

The light tuning operation of the above configuration will be described below. An electric current is applied to the coil 68 using the power supply 70 to generate a magnetic field. The magnet poles of the guide magnet A66 and the guide magnet B67 are arranged such that repulsive force is generated. Guide magnet A by repulsion
When the 67 is pressed, a force is applied to each ferrule 64, and tension is applied to the optical fiber 60. As a result, the optical fiber 60 expands in the axial direction, the refractive index of the fiber diffraction grating 63 changes, and the Bragg reflection wavelength changes from λ _B to λ _k (λ _k > λ _B ) before expansion. Therefore, the light of the wavelength λ _k is reflected instead of the light of the wavelength λ _B of the incident light, the magnitude of the current flowing to the coil 68 is controlled, and the tension is changed by adjusting the repulsive force. the value of the Bragg reflection wavelength lambda _k it is possible to continuously change. The ferrule 64 and the adhesive 65 are for applying a tension to the fiber diffraction grating 63, and do not deform to the extent that the fiber itself is stretched.

As described above, according to the sixth embodiment, the wavelength tuning operation can be performed by applying tension to the fiber diffraction grating 63 by pulling both ends of the optical fiber 6 by the movable mechanism by electromagnetic induction of the electromagnet, It is possible to realize a fiber-type wavelength tunable filter with a high tuning speed for changing the period interval of the diffraction grating, and to improve characteristics such as high stability and high reliability as compared with the temperature control method shown in the conventional example.

[0039]

As described above, according to the present invention, a high stability, a high reliability and a variable period interval of a fiber diffraction grating can be achieved.
Further, a fiber-type wavelength tunable filter having a high tuning speed can be realized. Therefore, it is possible to provide an optical tuner that enables high-speed, long-distance, and large-capacity optical fiber communication systems, and has a large practical effect.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an overall configuration of a fiber-type wavelength tunable filter according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram showing an entire configuration of a fiber-type wavelength tunable filter according to a second embodiment of the present invention.

FIG. 3 is a schematic sectional view of a fiber type tunable filter according to a third embodiment of the present invention.

FIG. 4 is a schematic sectional view of a fiber-type tunable filter according to a fourth embodiment of the present invention.

FIG. 5 is a schematic sectional view of a fiber-type wavelength tunable filter according to a fifth embodiment of the present invention.

FIG. 6 is a schematic sectional view of a fiber-type wavelength tunable filter according to a sixth embodiment of the present invention.

FIG. 7 is a schematic cross-sectional view of a fiber type wavelength tunable filter in a conventional example.

[Explanation of symbols]

 Reference Signs List 11 optical fiber 12 optical circulator 13 fiber diffraction grating 14 actuator 15 incident light 16 reflected light 17 transmitted light 21 optical fiber 22 optical circulator 23 fiber diffraction grating 24 connector 25 piezoelectric actuator 26 incident light 27 reflected light 28 transmitted light 30 optical fiber 31 light Fiber core 32 Optical fiber clad 33 Fiber diffraction grating 34 Piezoelectric actuator 35 Optical fiber clad remover 40 Optical fiber 41 Optical fiber core 42 Optical fiber clad 43 Piezoelectric actuator 44 Piezoelectric actuator 45 Optical fiber clad remover 50 Optical fiber 51 Optical fiber core 52 Optical fiber clad 53 Fiber diffraction grating 54 Ferrule 55 Adhesive 56 Guide A 57 Guide B 58 Micrometer 60 Optical fiber Fiber 61 Optical fiber core 62 Optical fiber clad 63 Fiber diffraction grating 64 Ferrule 65 Adhesive 66 Guide magnet A 67 Guide magnet B 68 Coil 69 Iron core 70 Power supply

Claims (6)

[Claims] An optical fiber having a periodic structure of a refractive index in a core or a clad and having a filter characteristic, and a refractive index distribution of the optical fiber having the periodic structure are controlled by applying a tension or a compressive force to the optical fiber. And a unit for inputting and outputting light to and from the optical fiber. 2. The fiber-type wavelength tunable device according to claim 1, further comprising a mechanism for applying a tension or a compressive force in the optical axis direction of the optical fiber by a cylindrical piezoelectric actuator as means for controlling the refractive index distribution of the optical fiber. filter. 3. As means for controlling the refractive index distribution of the optical fiber, a cylindrical piezoelectric actuator in contact with the periphery of the optical fiber is used to move from the periphery of the optical fiber to the center in a direction perpendicular to the optical axis direction of the optical fiber. The fiber type tunable filter according to claim 1, further comprising a mechanism for applying a compressive force. 4. As means for controlling the refractive index distribution of the optical fiber, a cylindrical piezoelectric actuator having a concavo-convex structure having the same period as the pitch of the periodic structure of the refractive index is provided in a direction perpendicular to the optical axis direction of the optical fiber. 2. The fiber-type wavelength tunable filter according to claim 1, further comprising a mechanism for applying a compressive force from the periphery to the center of the optical fiber. 5. The fiber-type tunable filter according to claim 1, wherein the means for controlling the refractive index distribution of the optical fiber has a structure in which both ends of the fiber are pulled by a fine movement mechanism using a micrometer or a linear actuator. 6. The structure according to claim 1, wherein the means for controlling the refractive index distribution of the optical fiber includes a structure in which the optical fiber is bonded to a ferrule having an electromagnet and the ferrule is pulled by a movable mechanism by electromagnetic induction. Fiber type tunable filter.