JP2004070054A - Optical attenuator and optical attenuator array - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small-sized optical attenuator with superior mass-productivity which is used for an optical multiplex communication system etc. <P>SOLUTION: On a base 2, optical fibers 11 and 23, a cylindrical lens 4, and an MEMS substrate 5 are arranged. A tilt mirror of a mirror unit 21 on the MEMS substrate 5 is tilted from the angle at which light from the optical fiber 11 is made incident on the optical fiber 12. Consequently, the quantity of light incident on the optical fiber 12 varies with the angle of the tilt mirror, so the attenuation quantity is continuously varied. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical attenuator and an optical attenuator array for adjusting the level of an optical signal used in a branch node or the like of an optical network system.
[0002]
[Prior art]
2. Description of the Related Art In an optical communication system, various and flexible optical transmission systems are required with the progress of optical wavelength division multiplexing and transmission technology. 2. Description of the Related Art In an optical transmission system, it is required to adjust the level of an optical signal wavelength-multiplexed at an arbitrary node or to equalize the optical level of wavelength-multiplexed light. An optical attenuator whose attenuation factor can be varied is used for such an application. As a conventional optical attenuator, for example, as shown in US Pat. No. 6,137,941, a light guide for light projection and a light guide for light reception are held toward a lens, and the angle of a mirror provided at a focal position thereof is set. Is known in which the optical axis of the projected light applied to the light receiving light guide is changed to change the attenuation factor.
[0003]
As another conventional optical attenuator, an optical attenuator using a distributed ND filter is known. The distributed ND filter is formed by depositing a metal film having a large light absorption such as chromium or inconel on a transparent glass substrate with distribution in a longitudinal direction. This optical attenuator arranges an ND filter substantially perpendicular to the optical axis, moves the ND filter in the distribution direction, and changes the light transmittance by changing the thickness of the metal film through which light passes, thereby changing the attenuation rate. Like that.
[0004]
[Problems to be solved by the invention]
Information transmitted through an optical fiber along with recent advances in wavelength division multiplexing technology is distributed (cross-connected) as a signal of each wavelength, or selected, or a new signal is added / dropped to a necessary path. It is transmitted. In such a node, optical components such as a multiplexer / demultiplexer, an optical switch, and an optical attenuator are used. These components are required to have extremely low loss. In addition, there is a demand for an inexpensive optical component that is small in size and can easily be multi-channeled.
[0005]
However, according to the conventional method of adjusting the attenuation rate by shifting the optical axis to adjust the coupling rate, it is difficult to manufacture a small optical attenuator. Further, there is a disadvantage that it is difficult to configure an optical attenuator array in which a large number of optical attenuators are arranged. In the case of an optical attenuator in which an attenuation factor is changed by sliding an ND filter having a metal film distributed in the distribution direction, the size of the element is limited by the size of the ND filter and a motor for driving the ND filter, and the size is reduced. There was a disadvantage that it was difficult. In addition, there is a drawback that the variable speed is limited because the motor is moved using a motor.
[0006]
The present invention has been made in view of such conventional problems, and has as its object to provide an optical attenuator and an optical attenuator array which are small and excellent in mass productivity.
[0007]
[Means for Solving the Problems]
The optical switch according to claim 1 of the present application includes an incident part and an exit part which are arranged adjacent to each other in parallel with each other, a cylindrical lens which focuses light of each optical axis of the incident part and the exit part, and a focal point of the cylindrical lens. A mirror unit including a tilt mirror that is disposed at a position and is rotatable along a rotation axis perpendicular to a plane formed by the optical axes, and a tilt mirror that continuously changes a reflection angle of the tilt mirror of the mirror unit And a control unit.
[0008]
According to a second aspect of the present invention, in the optical attenuator according to the first aspect, the mirror unit is configured such that a part of a movable part having a reflection surface formed on an upper surface is connected to a base substrate at a hinge part, and the mirror is centered on the hinge. The tilt mirror is rotated by applying a voltage between the tilt mirror that rotates and the electrode formed on the substrate.
[0009]
An optical attenuator according to a third aspect of the present invention is an optical attenuator, which is disposed adjacent to and parallel to each other, a cylindrical lens that focuses light of each optical axis of the incident unit and the output unit, and a focal point of the cylindrical lens. A mirror unit including a shift mirror arranged near the position and changing a distance between the cylindrical lens and the cylindrical lens; and a distance between the shift mirror of the mirror unit and the cylindrical lens being continuously set in an optical axis direction of the incident portion and the output portion. And a shift mirror control unit that changes the value to
[0010]
According to a fourth aspect of the present invention, in the optical attenuator according to the third aspect, the mirror unit has a diaphragm structure in which an outer peripheral portion of a movable portion having a reflection surface formed on an upper surface is vertically movably held on a base substrate. The present invention is characterized in that the shift mirror is moved up and down by applying a voltage between a certain shift mirror and an electrode formed on a substrate.
[0011]
According to a fifth aspect of the present invention, in the optical attenuator according to the third aspect, the mirror unit is disposed above the substrate and held between the shift mirror and the substrate, the shift mirror having a reflective surface on the upper surface. And a piezoelectric actuator for moving the shift mirror up and down, wherein the shift mirror control unit moves the shift mirror up and down in parallel with its surface by applying a voltage to the piezoelectric actuator. It is assumed that.
[0012]
According to a sixth aspect of the present invention, in the optical attenuator according to any one of the first to fifth aspects, the input section and the output section are each provided with an optical fiber and collimated light emitted from the optical fiber provided at an end thereof. The lens unit is characterized in that:
[0013]
According to a seventh aspect of the present invention, in the optical attenuator according to the sixth aspect, the lens portion is a ball lens, and is attached to a tip of each of the optical fibers.
[0014]
According to an eighth aspect of the present invention, in the optical attenuator according to the sixth aspect, the incident portion and the emission portion are held by a block that stores the optical fiber in a V-shaped groove. .
[0015]
According to a ninth aspect of the present invention, in the optical attenuator according to any one of the first to fifth aspects, the incidence unit and the emission unit, the mirror unit, and the cylindrical lens are arranged on a base, The base has a positioning mechanism for positioning them.
[0016]
According to a tenth aspect of the present invention, in the optical attenuator according to any one of the first to fifth aspects, the incidence unit and the emission unit, the mirror unit, and the cylindrical lens are arranged on a base, The cylindrical lens is formed integrally with the base.
[0017]
An optical attenuator array according to claim 11 of the present application is characterized in that a plurality of the optical attenuators according to any one of claims 1 to 10 are arranged in parallel.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a perspective view showing an assembled state of an optical attenuator according to Embodiment 1 of the present invention, FIG. 2 is a perspective view showing an assembled state, and FIGS. 3 and 4 are sectional views taken from different directions. It is. As shown in these drawings, an optical attenuator 1 according to the present embodiment fixes a block 3, a cylindrical lens 4, and a MEMS (microelectromechanical system) substrate 5 holding a later-described tilt mirror at a predetermined position on a base 2. It is composed. The base 2 is marked in advance for arranging each component as shown by a broken line in FIG. 1, and is accurately placed at that position. A groove for disposing the MEMS substrate 5 is provided at an end of the base 2. In order to accurately position the block 3 and the cylindrical lens 4, as shown in FIG. 5, a positioning mechanism such as guide protrusions 2a to 2h, pins, and depressions may be provided on the surface of the base 2.
[0019]
As shown in the sectional view of FIG. 3, the block 3 has two V-shaped grooves parallel to the upper surface formed in parallel in the X-axis direction. The V-shaped grooves 6, 7 of the block 3 are formed on a plane parallel to the XY plane. Optical fibers 11 and 12 whose heights exactly match the grooves are arranged in parallel, and collimating lenses 13 and 14 are integrally formed at the distal ends thereof. The optical fiber 11 and the collimating lens 13 at the tip constitute an incident portion, and the optical fiber 12 and the collimating lens 14 at the tip constitute an emitting portion. The optical axis is L1 at the entrance and the optical axis L2 is at the exit. These optical axes are parallel to the X axis. By inserting the optical fiber of the entrance / exit portion into the V-shaped groove of the block 3 and fixing it, the optical axis can be accurately positioned.
[0020]
On the base 2, a cylindrical lens 4, which is a convex lens having a flat surface on the side of the collimator lens and having the other end curved, is fixed. The lower surface and the upper surface of the cylindrical lens 4 are formed in a planar shape, and the lower surface is arranged at a predetermined position on the base 2. The optical axis of the cylindrical lens 4 is parallel to the X axis. The cylindrical lens 4 focuses on the MEMS substrate 5, and a mirror unit to be described later is formed at this position.
[0021]
On the side surface of the MEMS substrate 5, a mirror unit 21 is arranged at a center position of the optical axis within a plane defined by the optical axes L1 and L2. Hereinafter, the peripheral portion of the mirror unit 21 will be described with reference to FIG. The mirror unit 21 has first and second electrodes 22a and 22b formed symmetrically on the upper surface of the MEMS substrate 5 as shown in the drawing. The third and fourth electrodes 24a and 24b are disposed on the sides of the tilt mirror 26 via spacers 23a and 23b, and the tilt mirror 26 is rotatably held from the center of the electrode via a hinge 25. A line passing through the hinge 25 and the tilt mirror 26 is a rotation axis, and the first and second electrodes 22a and 22b of the MEMS substrate 5 are separated along the rotation axis. The tilt mirror 26 is a circular or polygonal member whose diameter is slightly larger than the beam size of the incident light, and its surface is a mirror and also serves as an electrode. As shown in FIG. 7, an arbitrary voltage can be applied between the electrodes 24a and 24b electrically connected to the tilt mirror 26 and one of the electrodes 22a and 22b via the variable voltage source 27. Be composed.
[0022]
FIG. 7A shows a state where no voltage is applied, and FIG. 7B shows a state where a certain voltage is applied. By applying a voltage as shown in FIG. 7B, electrostatic force acts between the tilt mirror 26a and one of the electrodes 22a, and the tilt mirror 26 can be rotated along the hinge 25. By changing this voltage, the tilt angle can be changed. Here, the variable voltage source 27 constitutes a tilt mirror control unit that continuously changes the reflection angle of the tilt mirror. The rotation axis of the tilt mirror is an axis parallel to the Z axis, and the rotation angle is φ.
[0023]
As the rotatable mirror unit 21 used here, for example, SERIES8001 manufactured by MEMS Optical may be used.
[0024]
Next, the operation of the present embodiment will be described with reference to FIGS. First, it is assumed that the reflection surface of the tilt mirror 26 is aligned with the YZ plane on the optical axis of the cylindrical lens as shown in FIG. At this time, when light is incident from the input optical fiber 11, the light is collimated by the collimator lens 13, passes through the cylindrical lens 4, and is incident on the tilt mirror 26 at the focal position. Then, the light is reflected by the tilt mirror 26 at the same angle and is applied to the collimator lens 14 and is applied to the optical fiber 12. If the positions of the optical fibers 11 and 12 are set to predetermined positions in advance, light is transmitted from the optical fiber 11 to the optical fiber 12 with almost no attenuation.
[0025]
Next, as shown in FIG. 9, the tilt mirror 26 is rotated by an angle φ. At this time, when light is incident from the optical fiber 11, the light is collimated by the collimator lens 13, passes through the cylindrical lens 4, and is incident on the tilt mirror 26 at the focal position. Then, the light is reflected by the tilt mirror 26 at the same angle, is added to the collimator lens 14, and is incident on the optical fiber 12. At this time, since the tilt mirror 26 is slightly inclined, the amount of light incident on the optical fiber 12 decreases. Therefore, the attenuation rate can be changed by continuously changing the tilt angle φ of the tilt mirror. FIG. 10 shows that the diameter of the incoming / outgoing beam of the collimating lens is 70 μm, the focal length of the cylindrical lens is 2 mm, and the fiber interval is 0.2 mm. It is a graph which shows the change of the attenuation rate with respect to the tilt angle (phi) when it is set to 5 mm.
[0026]
Here, as shown in FIG. 8, the focal position of the cylindrical lens 4 is set to about 1 to 2 mm. The interval from the collimating lens 13 to the collimating lens 14 is 5 mm or less when a line parallel to the X-axis is not taken into consideration, and the working distance between the collimating lenses can be extremely reduced. Therefore, a lens fiber, a ball lens fiber, or the like can be employed, and the insertion loss can be reduced. Therefore, a small mirror having a small diameter can be used as the tilt mirror. If the tilt mirror is small, it can be rotated at high speed with low voltage driving, so that the speed of adjusting the amount of attenuation can be increased.
[0027]
Next, a second embodiment of the present invention will be described. In this embodiment, a shift mirror is attached to the side wall of the MEMS substrate 5 instead of the tilt mirror as shown in FIG. 11, and the other configuration is the same as that of the above-described first embodiment. Description is omitted. In this embodiment, a mirror unit 40 is arranged at a position where the mirror unit 21 of the first embodiment is arranged. The mirror unit 40 changes the distance between a later-described shift mirror 46 and the cylindrical lens 4 in the X-axis direction, and the shift amount can be controlled by an external voltage. As shown in FIG. 11, if the shift amount of the mirror unit 40 can be changed, the position of the reflected light shifts parallel to the reference position, and the optical axis of the light incident on the collimator lens 14 changes.
[0028]
Next, an example of the mirror unit 40 using a micro electro mechanical system (MEMS) will be described with reference to FIGS. In the mirror unit 40, an electrode 42 is formed at the center position of the upper surface of the mirror substrate 41. Hinge 45 is held by spacers 43a and 43c at the four corners on the sides. The electrode 42 described above is formed below the mirror 46 formed at the center position. The shift mirror is a circular or polygonal member whose diameter is slightly larger than the beam size of the incident light, and its surface is a mirror and also serves as an electrode. As shown in FIG. 13, a voltage is applied between the shift mirror 46 and the electrode 42 on the substrate via the variable voltage source 47. Here, by applying a voltage, the shift mirror 46 at the center moves up and down in parallel with the substrate according to the voltage. Assuming that the shift amount in the X-axis direction is Δ, the amount of incidence on the optical fiber 12 changes according to the shift amount Δ as shown by the broken line in FIG. If the shift amount Δ is changed in accordance with the voltage, the axis shift amount of the optical axis also changes, and the attenuation amount can be changed continuously. FIG. 14 shows the change in the amount of attenuation with respect to the amount of shift Δ of the mirror unit when the optical configuration has the same dimensions as FIG. Thus, by changing the shift amount Δ by the voltage, the attenuation amount can be continuously changed.
[0029]
Instead of the MEMS mirror, a piezoelectric actuator may be provided on a mirror substrate, and a shift mirror may be provided above the piezoelectric actuator. Also in this case, the mirror surface can be moved in the X-axis direction by changing the voltage applied to the piezoelectric actuator. Therefore, the attenuation can be changed by changing the shift amount by the applied voltage.
[0030]
Next, a third embodiment of the present invention will be described. In the first and second embodiments described above, a one-channel optical attenuator has been described, but the present embodiment is an optical attenuator array in which many such optical attenuators are arranged in parallel. FIG. 15 is a perspective view schematically showing the third embodiment. Since each optical attenuator is the same as in the first embodiment, detailed description will be omitted. In this embodiment, as shown in FIG. 15, two optical fiber pairs 51 to 54 are arranged on a base 50 in parallel in the horizontal direction. Then, similarly to the first embodiment, cylindrical lenses 45 to 48 for focusing the optical axes of the optical fibers of each pair are arranged at positions facing the respective optical fiber pairs. In this case, a block provided with 4 × 2 V-grooves may be used, or a cylindrical lens in which a plurality of cylindrical lenses are connected and integrated may be used. Further, a MEMS substrate 59 having mirror units 60 to 63 is provided at the focal position of each cylindrical lens. Each mirror unit has a tilt mirror as in the case described above. The operation of the tilt mirror is the same as in the first embodiment. The shift mirror described in Embodiment 2 may be used instead of the tilt mirror. In this case, the optical attenuator array can be easily assembled simply by arranging these optical components and the MEMS substrate on the base 50. If the optical attenuator array is configured as described above, the light amount of four channels can be reduced in parallel by changing the angle of each tilt mirror or the position of each shift mirror.
[0031]
Further, if an arbitrary natural number is not limited to four channels and n is an arbitrary natural number, an n-channel attenuator can be realized by arranging n × 2 optical fibers in parallel to form an optical attenuator array. In this case, multiple channels can be arranged on the substrate and assembled, and a small-sized optical attenuator array can be realized.
[0032]
In the above-described embodiment, as shown in FIG. 16, a small ball lens is attached to the tip of each optical fiber as a collimating lens. Instead of this, a collimator in which each optical fiber is connected to a normal aspheric lens, GRIN lens, or microlens array as a collimating lens may be employed.
[0033]
The cylindrical lens can be formed integrally with the bases 2 and 50, or can be formed simultaneously with the base using photolithography or etching technology. In this case, there is no need to dispose it on the base, and it is possible to improve the positioning accuracy and simplify the manufacturing process.
[0034]
【The invention's effect】
As described above in detail, according to the first to eleventh aspects of the present invention, input and output light can be coupled in a short distance, and a small and inexpensive optical attenuator can be realized. Further, an optical attenuator which can be easily aligned and has high reliability can be obtained. Further, by holding the input / output unit in a block having a V-shaped groove, the positioning of the input / output unit can be easily performed. By forming the optical attenuator in an array, an n-channel optical attenuator array can be easily realized.
[Brief description of the drawings]
FIG. 1 is an assembly configuration diagram of an optical attenuator according to a first embodiment of the present invention.
FIG. 2 is a perspective view showing an overall configuration of the optical attenuator according to the first embodiment of the present invention.
FIG. 3 is a cross-sectional view showing a block according to the present embodiment and an optical fiber disposed thereon.
FIG. 4 is a sectional view showing a configuration of a main part of the optical attenuator according to the first embodiment of the present invention.
FIG. 5 is an assembly configuration diagram showing a modification of the first embodiment.
FIG. 6 is a perspective view showing a structure of a mirror unit according to the present embodiment.
FIG. 7 is a cross-sectional view showing a state in which a voltage is not applied to the mirror unit according to the present embodiment, and a rotation in a state where the voltage is applied.
FIG. 8 is a diagram showing a reflection surface and a light path when the tilt mirror according to the first embodiment is not rotated.
FIG. 9 is a diagram illustrating a reflection surface and a light path when the tilt mirror according to the first embodiment is rotated.
FIG. 10 is a graph showing a change in an attenuation rate with respect to a tilt angle φ.
FIG. 11 is a diagram showing movement of a shift mirror and a light path thereof according to a second embodiment of the present invention.
FIG. 12 is a perspective view showing a structure of a mirror unit according to the present embodiment.
FIG. 13 is a sectional view showing the structure of the mirror unit according to the present embodiment.
FIG. 14 is a graph showing a change in an attenuation rate with respect to a shift amount Δ according to the present embodiment.
FIG. 15 is a perspective view showing an optical attenuator array according to a second embodiment of the present invention.
FIG. 16 is a diagram showing an optical fiber and a collimating lens provided at the tip thereof.
[Explanation of symbols]
Reference Signs List 1 optical attenuator 2 base 3 block 4 cylindrical lens 5 MEMS substrate 6, 7 V-shaped groove 11, 12 optical fiber 13, 14 collimator lens 21, 30, 40 mirror unit 22a, 22b, 24a, 24b, 23a to 23d electrode 23a, 23b Spacer 25 Hinge 26 Tilt mirror 27, 47 Variable voltage source 41 Mirror substrate 46 Shift mirror 51-54 Optical fiber pair 55-58 Cylindrical lens 59 MEMS substrate 60-63 Mirror unit 71, 72 Collimator

Claims (11)

An entrance section and an exit section arranged adjacent to each other in parallel with each other,
A cylindrical lens that converges light of each optical axis of the incident part and the exit part,
A mirror unit that is disposed at a focal position of the cylindrical lens and includes a tilt mirror that is rotatable along a rotation axis perpendicular to a plane formed by the optical axes;
An optical attenuator comprising: a tilt mirror control unit that continuously changes a reflection angle of a tilt mirror of the mirror unit. The mirror unit,
By applying a voltage between the tilt mirror that rotates around the hinge and the electrode formed on the substrate, a part of the movable part with the reflective surface formed on the upper surface is connected to the base substrate at the hinge part. 2. The optical attenuator according to claim 1, wherein the tilt mirror is rotated. An entrance section and an exit section arranged adjacent to each other in parallel with each other,
A cylindrical lens that converges light of each optical axis of the incident part and the exit part,
A mirror unit that is disposed near the focal position of the cylindrical lens and includes a shift mirror that changes an interval between the cylindrical lens and
An optical attenuator comprising: a shift mirror control unit that continuously changes an interval between a shift mirror of the mirror unit and the cylindrical lens in an optical axis direction of the incident unit and the exit unit. The mirror unit,
By applying a voltage between a shift mirror having a diaphragm structure in which an outer peripheral portion of a movable portion having a reflection surface formed on an upper surface thereof is vertically movable and held on a base substrate, and applying a voltage between electrodes formed on the substrate, 4. The optical attenuator according to claim 3, wherein the shift attenuator moves up and down. The mirror unit,
A shift mirror disposed on the top of the substrate and having a reflective surface on the upper surface,
A piezoelectric actuator that is held between the shift mirror and the substrate and moves the shift mirror up and down,
The shift mirror control unit includes:
4. The optical attenuator according to claim 3, wherein a voltage is applied to said piezoelectric actuator to move said shift mirror up and down in parallel with its surface. The optical attenuator according to any one of claims 1 to 5, wherein the incident part and the emission part are an optical fiber and a lens unit provided at a tip thereof and collimating light emitted from the optical fiber. . The optical attenuator according to claim 6, wherein the lens unit is a ball lens, and is attached to a tip of each of the optical fibers. The optical attenuator according to claim 6, wherein the incident part and the emission part are held by a block that stores the optical fiber in a V-shaped groove. The entrance and exit sections, the mirror unit and the cylindrical lens are arranged on a base,
The optical attenuator according to any one of claims 1 to 5, wherein the base has a positioning mechanism for positioning them. The entrance and exit sections, the mirror unit and the cylindrical lens are arranged on a base,
The optical attenuator according to claim 1, wherein the cylindrical lens is formed integrally with the base. An optical attenuator array comprising a plurality of the optical attenuators according to claim 1 arranged in parallel.

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