JP2004086191A - Variable optical attenuator and optical module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable optical attenuator and an optical module which can securely reduce polarization dependent loss with simple structure. <P>SOLUTION: The variable optical attenuator 1 has a plane waveguide 2, which is provided with an optical waveguide core 3 forming an input optical path A and an output optical path B. A cantilever beam 6 is provided on the top surface of the plane waveguide 2 and a movable mirror 8 which reflects light passing through the input optical path A toward the output optical path B is fixed to the tip part of the cantilever beam 6. Further, an electrode 9 is provided on the top surface of the plane waveguide 2. The cantilever beam 6 and the electrode 9 are connected together through a voltage source 11, which applies a voltage between the cantilever beam 6 and electrode 9 to generate an electrostatic force between the both, thereby making the tip part of the cantilever beam 6 flex toward the electrode 9. Consequently, the movable mirror 9 moves toward the electrode 9. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical variable attenuator and an optical module used in optical communication and the like.
[0002]
[Prior art]
As a conventional variable optical attenuator, for example, the one described in Non-Patent Document 1 is known. The variable optical attenuator described in this document controls two optical fibers to face each other, and puts a shutter in and out of the space therebetween to control the amount of light attenuation.
[0003]
[Non-patent document 1]
IEICE Technical Report PS2001-31
[0004]
[Problems to be solved by the invention]
In the prior art, two shutters are used to reduce polarization-dependent loss (attenuation wavelength dependence) caused by diffraction of a light beam at an edge of the shutter. However, in this case, since an actuator for individually driving the two shutters is required, the structure of the variable optical attenuator becomes complicated and large-scale.
[0005]
An object of the present invention is to provide an optical variable attenuator and an optical module that can reliably reduce polarization dependent loss with a simple structure.
[0006]
[Means for Solving the Problems]
An optical variable attenuator according to the present invention includes a base member having an input optical path for inputting an optical signal and an output optical path for outputting an optical signal, and reflects an optical signal passing on the input optical path toward the output optical path. It is characterized by comprising a movable mirror and driving means for moving the movable mirror.
[0007]
In such a variable optical attenuator, when the movable mirror is at a predetermined position, light from the input optical path is totally reflected by the movable mirror and guided to the output optical path, and as a result, the optical attenuation is the smallest. State. In this state, when the movable mirror is moved by the driving means, only a part of the light from the input optical path is reflected by the movable mirror, and as a result, the light attenuation increases. When the movable mirror reaches a position completely deviated from the input optical path and the output optical path, no light is reflected by the movable mirror, and the reflected light is not guided to the output optical path. As a result, the state becomes infinite. As described above, since the variable optical attenuator of the present invention utilizes the reflection of light by the movable mirror, it is not affected by the diffraction of light at the edge of the movable mirror. Further, unlike a case where a simple shutter is used as a member for changing the amount of light attenuation, only one movable mirror is required. Therefore, with a simple structure, the polarization-dependent loss caused by the light diffraction effect can be reliably reduced. At this time, the polarization-dependent loss at an optical attenuation of 10 dB can be made smaller than 0.2 dB.
[0008]
Preferably, the movable mirror is formed by micro-electro-mechanical system technology. As a result, the size of the movable mirror can be reduced, and the size of the variable optical attenuator can be reduced.
[0009]
Preferably, the base member is a planar waveguide having two optical waveguide cores forming an input optical path and an output optical path, and the planar waveguide has a groove portion connected to the input optical path and the output optical path. The movable mirror is provided so as to be movable while being inserted into the groove. By forming the base member having the input optical path and the output optical path with a planar waveguide in this manner, the base member can be easily manufactured using semiconductor manufacturing technology, and cost reduction can be achieved.
[0010]
In this case, preferably, the virtual intersection angle between the input optical path and the output optical path is 9 degrees or more. Here, the virtual intersection angle refers to the angle at which the input optical path and the output optical path intersect assuming that they are straightened as they are. By setting such a virtual intersection angle to 9 degrees or more, the amount of light that is reflected by the movable mirror and returns to the input optical path is reduced, so that the optical loss due to the return light can be reduced.
[0011]
Preferably, a matching oil having a refractive index equivalent to that of the optical waveguide core is filled in the groove. Thereby, the insertion loss of light between the input optical path and the output optical path and the movable mirror can be reduced.
[0012]
Further preferably, the movable mirror is attached to a cantilever supported by a cantilever on a base member, and the driving means includes an electrode provided on the base member, and a movable member provided between the cantilever and the electrode. Means for generating an electrostatic force. Since the movable mirror is driven by using the electrostatic force as described above, current does not need to flow, so that power consumption can be reduced.
[0013]
In this case, preferably, the cantilever is provided with a plurality of first comb teeth, and the electrode is provided with a plurality of second comb teeth inserted between the first comb teeth. This increases the surface area of the cantilever and the electrode, so that a large electrostatic force can be generated between the cantilever and the electrode with a small applied voltage. Further, since the cantilever and the electrode come close to each other, the linearity of the moving amount of the movable mirror with respect to the applied voltage, that is, the linearity of the optical attenuation with respect to the applied voltage is improved. Therefore, the amount of light attenuation can be easily controlled.
[0014]
Preferably, the movable mirror, the cantilever, and the electrode are formed of conductive Si, and the surface of the movable mirror is coated with one of Au, Ag, and Al. By forming the movable mirror, the cantilever, and the electrode from Si having conductivity in this way, these structures can be manufactured at low cost. Further, by coating any one of Au, Ag, and Al on the surface of the movable mirror, a high-performance movable mirror having good reflectance can be obtained.
[0015]
Furthermore, preferably, the base member is provided so as to face the input optical path, and further has a monitoring optical path for monitoring the light amount of the optical signal, and the movable mirror is provided between the input optical path and the monitoring optical path. It is located between them. In such a configuration, of the optical signal from the input optical path, the light reflected by the movable mirror is incident on the output optical path, and the remaining light is transmitted without being reflected by the movable mirror and is incident on the monitor optical path. Will be. Therefore, by measuring the amount of transmitted light that has entered the optical path for monitoring, the amount of light of the attenuated optical signal can be confirmed. In this case, it is not necessary to branch a part of the attenuated optical signal using an optical directional coupler or the like, so that the amount of the attenuated optical signal can be monitored without increasing the optical loss. it can.
[0016]
An optical module according to the present invention includes the above-described variable optical attenuator. By providing the variable optical attenuator that adjusts the amount of light attenuation by using the reflection of light by the movable mirror in this manner, as described above, the polarization dependent loss due to the light diffraction effect can be reduced with a simple structure. It can be surely reduced.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of an optical variable attenuator and an optical module according to the present invention will be described with reference to the drawings.
[0018]
FIG. 1 is a plan view showing an embodiment of an optical variable attenuator according to the present invention, and FIG. 2 is a vertical sectional view of the optical variable attenuator. 1 and 2, the variable optical attenuator 1 of the present embodiment has a planar waveguide 2, and the planar waveguide 2 is provided with an optical waveguide core 3 forming optical paths A to D. Here, the optical path A constitutes an input optical path for inputting an optical signal, and the optical path B constitutes an output optical path for outputting an optical signal. The planar waveguide 2 is provided with a groove 4 extending in the width direction of the planar waveguide 2 and connected to the optical paths A to D.
[0019]
The input optical path A and the output optical path B are formed in a substantially V shape on the same side with respect to the groove 6. The optical path A and the optical path D are formed so as to oppose each other with the groove 4 interposed therebetween, and the optical path B and the optical path C are formed so as to oppose each other with the groove 4 interposed therebetween.
[0020]
The planar waveguide 2 having such optical paths A to D and the groove 4 is manufactured as follows. That is, first, a planar waveguide having two optical waveguide cores arranged in a cross is formed. Subsequently, the groove 4 is formed at the intersection of the two optical waveguide cores by using, for example, reactive ion etching (RIE). Thereby, optical paths A to D are formed.
[0021]
An actuator structure 5 formed using a micro electro mechanical system (MEMS) technology is provided on the planar waveguide 2. The actuator structure 5 has a cantilever 6 that is cantilevered on the upper surface of the planar waveguide 2, and the cantilever 6 extends from one end of the planar waveguide 2 to the position of the groove 4. A plurality of comb teeth 7 are provided on the tip side of the cantilever 6. The cantilever 6 is preferably made of conductive silicon (Si) from the viewpoint of cost reduction.
[0022]
A movable mirror 8 that reflects an optical signal passing through the input optical path A toward the output optical path B is fixed to the tip of the cantilever 6. The movable mirror 8 is configured to enter the groove 4 of the planar waveguide 2. The movable mirror 8 has dimensions of, for example, a thickness of 30 μm, a height of 50 μm, and a width of 50 μm.
[0023]
Here, when the optical path A and the optical path D are connected by a line and the optical path B and the optical path C are connected by a line, the angle at which these lines intersect (the virtual intersection angle between the input optical path A and the output optical path B). Is preferably 9 degrees or more (see FIG. 3). Thus, when the light from the input optical path A is reflected by the movable mirror 8, the reflected light hardly returns to the input optical path A, so that light loss (return loss) due to return light (leakage light) is reduced. Reduced. At this time, in order to reduce the dimension in the width direction of the planar waveguide 2 while securing a desired light reflectance, the virtual intersection angle θ between the input optical path A and the output optical path B is in the range of 9 to 20 degrees. It is more preferable to be within.
[0024]
The movable mirror 8 is formed of conductive Si similarly to the cantilever 6. The surface of the movable mirror 8 is coated with gold (Au), silver (Ag), aluminum (Al), or the like. This increases the reflectance with respect to light in the wavelength band for optical communication such as infrared light, so that insertion loss of light to the output optical path B can be reduced.
[0025]
The actuator structure 5 has an electrode 9 provided on the upper surface of the planar waveguide 2. The electrode 9 is provided with a plurality of comb teeth 10 inserted between the comb teeth 7 of the cantilever 6. Similarly to the cantilever 6, the electrode 9 is made of conductive Si.
[0026]
The actuator structure 5 including the cantilever 6, the movable mirror 8, and the electrode 9 is manufactured by, for example, inductively coupled plasma reactive ion etching (ICP-RIE).
[0027]
The above planar waveguide 2 and the actuator structure 5 are housed in a package (not shown) together with the fiber arrays (not shown) arranged on both ends of the planar waveguide 2. The package is filled with a matching oil (for example, silicone resin) having a refractive index equivalent to that of the optical waveguide core 3. Thus, the matching oil is filled in the groove 4 of the planar waveguide 2 as well. Therefore, since there is no discontinuous surface of the refractive index between the input optical path A and the output optical path B and the movable mirror 8, the insertion loss of light to the output optical path B can be reduced.
[0028]
Further, the cantilever 6 and the electrode 9 are connected via a voltage source 11, and when a voltage is applied between the cantilever 6 and the electrode 9 by the voltage source 11, an electrostatic force is applied between the both. Generate. The tip of the cantilever 6 is attracted to the electrode 9 and bent by the electrostatic force, and the movable mirror 8 moves toward the electrode 9 with the movable mirror 8 inserted into the groove 4 of the planar waveguide 2. (See FIG. 3). As described above, since the movable mirror 8 is driven by generating an electrostatic force between the cantilever 6 and the electrode 9, power saving can be achieved.
[0029]
At this time, since the comb teeth 7 are provided on the cantilever 6 and the comb teeth 10 are provided on the electrode 9, the surface area of the cantilever 6 and the electrode 9 is increased as a whole. Accordingly, the electrostatic force generated between the cantilever 6 and the electrode 9 is increased by that amount, so that the voltage applied between the cantilever 6 and the electrode 9 can be reduced.
[0030]
In the variable optical attenuator 1 as described above, when the supply voltage from the voltage source 11 is off, the cantilever 6 extends straight as shown in FIG. In this state, the light emitted from the input optical path A is totally reflected by the movable mirror 8 and is incident on the output optical path B, so that a minimum optical attenuation is obtained as an optical attenuator.
[0031]
When a voltage is applied between the cantilever 6 and the electrode 9 by the voltage source 11 from such an initial state, the movable mirror 8 is moved toward the electrode 9 by an electrostatic force generated between the cantilever 6 and the electrode 9. Moving. In this state, only a part of the light emitted from the input optical path A is reflected by the movable mirror 8 and is incident on the output optical path B, and the remaining light is incident on the optical path D. growing.
[0032]
When the voltage applied between the cantilever 6 and the electrode 9 is further increased, the movable mirror 8 is completely removed from the input optical path A and the output optical path B as shown in FIG. In this state, all light emitted from the input optical path A is incident on the optical path D without being reflected by the movable mirror 8, so that the amount of light attenuation becomes infinite (a so-called shutter state).
[0033]
As described above, in the variable optical attenuator 1, the amount of light reflected by the movable mirror 8 is varied by changing the voltage applied between the cantilever 6 and the electrode 9, thereby adjusting the amount of light attenuation. . At this time, the comb teeth 7 are provided on the cantilever 6, and the comb teeth 10 are provided on the electrode 9, and the tip side portion of the cantilever 6 is close to the electrode 9. For this reason, the linearity of the optical attenuation with respect to the applied voltage is improved, so that the optical attenuation can be easily controlled.
[0034]
As described above, in the variable optical attenuator 1 of the present embodiment, since the configuration is such that the reflected light from the movable mirror 8 is used, there is no influence from the diffraction of light generated at the edge of the movable mirror 8. . Therefore, the polarization dependent loss (PDL) caused by such a light diffraction effect can be reduced. Further, since it is not necessary to make the edge portion of the movable mirror 8 sufficiently thin (for example, 1 μm or less) to reduce light diffraction, the movable mirror 8 can be easily manufactured. Furthermore, since one movable mirror 8 is used, only one set of actuator for driving the movable mirror 8 is required, and the structure of the variable optical attenuator is simplified.
[0035]
FIG. 4 is actual measurement data showing the correlation between the insertion loss (optical attenuation) and PDL in the above-described variable optical attenuator. The horizontal axis of the measured data indicates the voltage supplied between the cantilever and the electrode, the left vertical axis of the measured data indicates insertion loss, and the right vertical axis of the measured data indicates PDL. As can be seen from the figure, the PDL at the time of 10 dB attenuation is as extremely small as about 0.15 dB.
[0036]
FIG. 5 is a plan view showing another embodiment of the variable optical attenuator according to the present invention. In the drawing, the same reference numerals are given to the same or equivalent members as those in the above-described embodiment, and the description thereof is omitted.
[0037]
In FIG. 5, the variable optical attenuator 1A of the present embodiment has an actuator structure 5A equivalent to the actuator structure 5 described above. The actuator structure 5A is configured such that the movable mirror 8 completely deviates from the input optical path A and the output optical path B in the initial state. In this state, since the light from the input optical path A is not reflected at all by the movable mirror 8, the amount of light attenuation is infinite.
[0038]
When a voltage is applied between the cantilever 6 and the electrode 9 by the voltage source 11 from such an initial state, the movable mirror 8 moves to the electrode 9 due to an electrostatic force generated between the two. In this state, a part of the light from the input optical path A is reflected by the movable mirror 8 and guided to the output optical path B, so that the optical attenuation is reduced. When the movable mirror 8 reaches the position shown in FIG. 6, the light from the input optical path A is totally reflected by the movable mirror 8 and guided to the output optical path B, so that the optical attenuation is minimized.
[0039]
FIG. 7 shows an example of an optical module including the above-described variable optical attenuator 1. In FIG. 1, an optical module 12 is an optical add / drop multiplexer (OADM) having a function of adding / dropping a signal of an arbitrary wavelength from wavelength-multiplexed signals.
[0040]
The OADM 12 includes an optical switch array 14 having a plurality of 2 × 2 optical switches 13 and an optical variable attenuator array 15 having a plurality of optical variable attenuators 1. Each optical switch 13 and each optical variable attenuator 1 are connected via a main waveguide 16 (corresponding to the input optical path A described above).
[0041]
Each optical switch 13 is connected to a duplexer 18 via a main waveguide 17. The demultiplexer 18 demultiplexes a plurality of optical signals having different wavelengths transmitted through one optical fiber 19 for each wavelength. Further, an add waveguide 24 and a drop waveguide 25 are connected to each optical switch 13.
[0042]
Each variable optical attenuator 1 is connected to a multiplexer 21 via a main waveguide 20 (corresponding to the above-described output optical path B). The multiplexer 21 multiplexes optical signals of each wavelength and guides the multiplexed optical signal to one optical fiber 22.
[0043]
Each main waveguide 20 is provided with an optical monitor 23 for detecting the power (light amount) of the optical signal attenuated by the variable optical attenuator 1. The optical monitor 23 includes an optical directional coupler 27 for branching a part of the optical signal attenuated by the optical variable attenuator 1 and a light receiver 28 for receiving the light branched by the optical directional coupler 27. Have. The light receiver 28 is, for example, a photodiode (PD).
[0044]
Each optical switch 13, each variable optical attenuator 1, and each optical monitor 23 are connected to a controller 26. The controller 26 has a plurality of voltage sources for supplying a voltage to each optical switch 13 and a plurality of voltage sources (corresponding to the above-described voltage source 11) for supplying a voltage to each optical variable attenuator 1. . The controller 26 sends a voltage signal to the variable optical attenuator 1 based on the detection value of the optical monitor 23 so that the output light amount (light attenuation amount) becomes a desired value. Further, the controller 26 sends a voltage signal to the optical switch 13 to switch the optical paths of the waveguides 16, 17, 24, and 25.
[0045]
FIG. 8 is a plan view showing still another embodiment of the variable optical attenuator according to the present invention. In the drawing, the same reference numerals are given to the same or equivalent members as those in the above-described embodiment, and the description thereof is omitted.
[0046]
8, the variable optical attenuator 50 of the present embodiment has the same structure as the variable optical attenuator 1 described above. An optical path D facing the input optical path A with the groove 4 interposed therebetween constitutes a monitoring optical path for monitoring the light amount of the optical signal, and a light receiver 51 such as a PD is connected to the monitoring optical path D. Is done.
[0047]
Of the optical signal emitted from the input optical path A, the light not reflected by the movable mirror 10 passes through the groove 4 and enters the monitor optical path D. Therefore, by measuring the intensity (light amount) of light incident on the monitoring optical path D by the light receiver 51, the light amount of the attenuated optical signal reflected by the movable mirror 10 can be confirmed.
[0048]
FIG. 9 illustrates an example of an OADM including the above-described variable optical attenuator 50. In the figure, the same members as those of the OADM shown in FIG. 7 are denoted by the same reference numerals, and description thereof will be omitted.
[0049]
9, the OADM 60 has an optical variable attenuator 50 as shown in FIG. 8, instead of the optical variable attenuator 1 shown in FIG. A light receiver 51 is connected to the monitoring optical path D of each variable optical attenuator 50. With such a configuration, even if the optical directional coupler is connected to each main waveguide 20 as shown in FIG. Can be monitored. Therefore, it is possible to suppress an optical loss caused by branching a part of the optical signal. Further, the number of components of the optical module can be reduced, and the size of the optical module can be reduced.
[0050]
Note that the present invention is not limited to the above embodiment. For example, in the above embodiment, the electrostatic actuator that drives the movable mirror 8 by the electrostatic force generated between the cantilever 6 and the electrode 9 is used, but the electromagnetic actuator that drives the movable mirror 8 by using the electromagnetic force is used. Etc. may be used.
[0051]
In the above embodiment, the movable mirror 8 is driven in the width direction of the planar waveguide 2 that crosses the input optical path A and the output optical path B. However, the movable mirror 8 may be driven in the vertical direction or the like. Good.
[0052]
Further, in the above embodiment, the input optical path and the output optical path are configured by the optical waveguide cores. However, the present invention is also applicable to a configuration in which the input optical path and the output optical path are configured by optical fibers.
[0053]
【The invention's effect】
According to the present invention, since the movable mirror that reflects the optical signal passing through the input optical path toward the output optical path and the driving unit that moves the movable mirror are provided, the light diffraction can be performed with a simple structure. Can be reliably reduced.
[Brief description of the drawings]
FIG. 1 is a plan view showing an embodiment of a variable optical attenuator according to the present invention.
FIG. 2 is a vertical sectional view of the variable optical attenuator shown in FIG.
FIG. 3 is a plan view showing an operation state of the actuator structure shown in FIG. 1;
4 is measured data showing a correlation between an insertion loss and a polarization-dependent loss in the optical variable attenuator shown in FIG.
FIG. 5 is a plan view showing another embodiment of the variable optical attenuator according to the present invention.
6 is a plan view showing an operation state of the actuator structure shown in FIG.
FIG. 7 is a diagram showing an example of an optical module including the variable optical attenuator shown in FIG.
FIG. 8 is a plan view showing still another embodiment of the variable optical attenuator according to the present invention.
FIG. 9 is a diagram illustrating an example of an optical module including the variable optical attenuator illustrated in FIG. 8;
[Explanation of symbols]
1, 1A: Variable optical attenuator, 2: planar waveguide (base member), 3: optical waveguide core, 4: groove, 6: cantilever, 7: comb tooth (first comb tooth), 8: movable mirror , 9 ... electrodes (drive means), 10 ... comb teeth (second comb teeth), 11 ... voltage source (drive means), 12 ... optical module, 50 ... variable attenuator, 60 ... optical module, A ... input Optical path, B: output optical path, D: monitor optical path.

Claims (11)

A base member having an input optical path for inputting an optical signal and an output optical path for outputting the optical signal,
A movable mirror that reflects an optical signal passing on the input optical path toward the output optical path,
And a drive unit for moving the movable mirror. The variable optical attenuator according to claim 1, wherein the movable mirror is formed by a micro electro mechanical system technology. The base member is a planar waveguide having two optical waveguide cores constituting the input optical path and the output optical path,
The planar waveguide is provided with a groove connected to the input optical path and the output optical path,
The variable optical attenuator according to claim 1, wherein the movable mirror is provided so as to be movable while being inserted into the groove. The variable optical attenuator according to claim 3, wherein a virtual intersection angle between the input optical path and the output optical path is 9 degrees or more. 5. The variable optical attenuator according to claim 3, wherein the groove is filled with a matching oil having a refractive index equivalent to that of the optical waveguide core. The movable mirror is attached to a cantilever supported on the base member,
The device according to claim 1, wherein the driving unit includes an electrode provided on the base member, and a unit configured to generate an electrostatic force between the cantilever and the electrode. Item 3. The variable optical attenuator according to the above. The cantilever is provided with a plurality of first comb teeth,
7. The variable optical attenuator according to claim 6, wherein the electrode is provided with a plurality of second comb teeth inserted between the first comb teeth. The movable mirror, the cantilever and the electrode are formed of conductive Si,
The variable optical attenuator according to claim 6, wherein a surface of the movable mirror is coated with one of Au, Ag, and Al. 9. The optical variable attenuator according to claim 1, wherein a polarization dependent loss at an optical attenuation of 10 dB is smaller than 0.2 dB. The base member is provided so as to face the input optical path, and further includes a monitoring optical path for monitoring the light amount of the optical signal,
The variable optical attenuator according to any one of claims 1 to 9, wherein the movable mirror is disposed between the input optical path and the monitor optical path. An optical module comprising the variable optical attenuator according to claim 1.

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