JP2006330049A - Variable optical attenuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable optical attenuator which is manufactured at a low cost and performs accurate attenuation processing in which a predetermined optical attenuation is obtained. <P>SOLUTION: The variable optical attenuator comprises: a first optical member having an optical transmission path which emits signal light; a second optical member which condenses the light emitted form the first optical member; a third optical member having an optical transmission path to which the light condensed with the second optical member is made incident; a spot moving means which moves a spot formed by making the signal incident on the incident end face of the third optical member; a light source which radiates control light having a wavelength shorter than that of the signal light; a light guide means which guides the control light emitted from the light source to the incident end face via the second optical member; a light quantity detection means which detects the light quantity of the control light received on a light receiving face; and a control means which performs a negative feedback control on a deflection means so that the position of the spot on the incident end face satisfies a predetermined condition on the basis of the light quantity detected with the light quantity detection means. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is used as an attenuator for attenuating and adjusting light intensity in an optical communication system or the like, and more particularly to a variable optical attenuator used for flattening amplification characteristics of an optical amplifier.

  In general, in an optical communication system or an optical measurement system, an optical attenuator for adjusting an optical transmission level is necessary. As the optical attenuator, a variable optical attenuator and a semi-fixed optical attenuator are known. A variable optical attenuator is generally capable of continuously adjusting an attenuation of 30 dB or more, and is used as a measuring instrument for adjusting a level of a system transceiver or measuring characteristics of an optical device. The semi-fixed optical attenuator is mainly used for adjusting the section transmission loss of the optical transmission line.

  As a conventional example of a variable optical attenuator, there is a configuration in which the optical attenuation is adjusted by cutting an optical fiber and shifting the core of each cut end face, as in Patent Document 1 below.

JP-A-4-166803

  In the configuration of Patent Document 1, signal light attenuation processing is performed using the feature that the amount of optical attenuation also changes when the amount of deviation of the core core changes. Here, the shift amount of the core core can be said to be a shift amount between the beam spot formed by the signal light emitted from one cut end face (exit end face) and the core of the incident end face formed on the other cut end face (incident end face). . In the configuration of Patent Document 1, in order to realize highly accurate attenuation processing so that a predetermined light attenuation amount can be obtained, it is necessary to accurately detect the deviation amount of the core core. As a method for accurately detecting the deviation amount of the core core, for example, the position of the beam spot is always detected by receiving a part of the signal light incident on the incident end face with a light receiving element or the like. Then, based on the detection result, it is conceivable to feedback control the beam spot forming position on the incident end face.

  However, signal light generally used in an optical communication system or the like has an extremely long wavelength of 1300 nm or more. For this reason, the light receiving element capable of detecting the signal light from the incident end face has to be specially configured so as to be sensitive to the above-mentioned wavelength, and inevitably has to be expensive.

  In view of the above circumstances, an object of the present invention is to provide a variable optical attenuator that can be manufactured at low cost and can realize a highly accurate attenuation process capable of obtaining a predetermined optical attenuation.

  In order to solve the above-described problem, the variable optical attenuator according to claim 1 includes a first optical member having an optical transmission path through which the first light is emitted, and a first light emitted from the first optical member. A second optical member having an optical transmission path on which the first light is incident, a moving means for moving the position where the first light is incident on the incident end face of the second optical member, and a second light having a shorter wavelength than the first light. A light source for irradiating light, a first light guide means for guiding the second light emitted from the light source to the incident end face via the moving means, and a second light received via the second light guide means A light amount detecting means for detecting the light amount of the second light received by the light receiving surface, and the first light based on the light amount of the second light detected by the light amount detecting means. Control means for controlling the moving means so that the position on the incident end face is directed to a position satisfying a predetermined condition; Characterized in that it comprises a.

  According to the first aspect of the present invention, the control light having a shorter wavelength than the signal light emitted from the light source separate from the signal light is used for controlling the attenuation process. Accordingly, it is not necessary to use a special light receiving element having sensitivity to the wavelength of the signal light as the light amount detecting means, and therefore the variable optical attenuator according to the present invention can be configured very inexpensively. Currently, the price of a light receiving element having sensitivity to the wavelength of signal light in the distribution process is extremely high. Therefore, as in the first aspect of the invention, even if a light source for irradiating the control light or a light amount detecting means sensitive to the control light is added, the light receiving element having sensitivity to the wavelength of the signal light is used. An inexpensive variable optical attenuator can be provided.

  In addition, the amount of control light from the incident end face is actually detected, and the spot moving means is configured to perform negative feedback control based on the detection result. Is executed.

  Specifically, the light amount detecting means includes a plurality of light receiving areas in which the light receiving surface is divided by at least one boundary line, and the control means is based on a difference in light amount of the second light received in each light receiving area. It is comprised so that control may be performed (Claim 2).

  More specifically, the control means has information regarding the relationship between the difference in the amount of second light detected in each light receiving area and the intensity of the first light transmitted from the first optical member to the second optical member. Therefore, it is possible to control the position of the first light on the incident end face so as to go to a position where the set light attenuation amount can be obtained based on the information (claim 3).

  According to the fourth aspect of the present invention, the moving means moves the position of the first light on the incident end face in the first direction, and the light receiving surface of the light amount detecting means is a direction corresponding to the first direction. Have two light receiving areas arranged along the line.

  As another aspect, the moving means moves the position of the first light on the incident end face in a first direction and a second direction orthogonal to each other, and the light receiving surface of the light quantity detecting means is in the first direction. A configuration may be adopted in which the light receiving area is divided into four light receiving areas by two boundary lines extending in a corresponding third direction and a fourth direction corresponding to the second direction. . In this case, the control means can also perform control relating to the adjustment of the incident position of the second light on the light receiving surface based on the difference in the amount of light detected in each of the four light receiving areas. Thus, by enabling the movement of the spot in the two-dimensional direction and the detection of the light amount difference, the initial position adjustment of each constituent member can be easily performed.

  According to the variable optical attenuator of the seventh aspect, the first light guide means can be integrally formed with the first optical member. For example, the exit end face of the first optical member can be used as the first light guide means. In this case, the exit end surface reflects the second light emitted from the light source and guides it to the second optical member (claim 8). By using the exit end face as the first light guide means, it is not necessary to arrange a new member as the light guide means in the optical path of the control light, and an unnecessary increase in the number of members can be suppressed.

  When used as the first light guiding means on the exit end face of the first optical member, the incident position of the second light on the exit end face (in other words, the exit position of the first light) is relative to the second light. It is preferable that an optical film having a wavelength selectivity having a high reflectance and a high transmittance with respect to the first light is coated. As a result, when the light is reflected at the exit end face, the light loss of the control light can be minimized, so that the light amount detection means can detect the light amount more effectively.

  According to the variable optical attenuator of the tenth aspect, the first optical member is an optical fiber. According to the variable optical attenuator of the eleventh aspect, the first optical member can use an optical fiber having a fiber coupler as the first light guiding means.

  Specifically, in the relationship with the first optical member, the light source has the second light center line reflected by the emission end face parallel to the first light center line emitted from the emission end face. It is desirable to be positioned so as to be incident on the two optical members (claim 12).

  More preferably, in the relationship with the first optical member, the light source has a second line in which the center line of the second light reflected by the emission end face substantially coincides with the center line of the first light emitted from the emission end face. The optical member is positioned so as to be incident thereon (claim 13). Thereby, the burden concerning the attenuation process of the signal light based on the light quantity of the control light detected by the light quantity detection means can be reduced.

  According to the invention described in claim 14, the second optical member is an optical fiber, and the optical transmission line of the second optical member is a core of the optical fiber.

  According to invention of Claim 15, it has a 3rd optical member which condenses the light inject | emitted from the 1st optical member, and the 2nd optical member has the core in the incident end surface into which 2nd light injects, A step having a predetermined dimension is formed in the clad, and the third optical member is configured so that the second light forms a spot having a diameter larger than the core diameter and smaller than the clad diameter on the incident end face. To collect the light. If comprised in this way, a diffraction pattern will generate | occur | produce by the 2nd light which injected into the light-receiving surface of a light quantity detection means. Therefore, a minute change in the amount of light can be detected as compared with the case where no step is formed, and finer attenuation adjustment can be performed.

  The predetermined dimension of the step is a dimension that is likely to cause a diffraction phenomenon, specifically, a value smaller than about λ / (4n), where λ is the wavelength of the second light and n is the refractive index of the medium. (Claim 16). For example, the step is preferably approximately λ / (8n).

  According to the eighteenth aspect of the present invention, the incident end face is configured such that the end face of the core and the end face of the clad are substantially parallel.

  According to the nineteenth aspect of the present invention, the moving means may move the position of the first light on the incident end face by driving the third optical member. Further, the position of the first light on the incident end face may be moved by a galvanometer mirror or a vertex angle variable prism installed between the second optical member and the end face of the optical member.

  According to the invention described in claim 22, the second light guide means includes an optical path of the second light through which the second light passing through the second light guide means enters the second light guide means. And deflecting means for deflecting the second light through the second light guiding means in a direction deviating from the optical path and guiding it to the light quantity detecting means. Also good.

  For example, the deflecting unit may include a polarizing beam splitter and a quarter wavelength plate.

  As described above, according to the present invention, negative feedback control related to light attenuation adjustment is performed using second light (for example, control light) having a short wavelength different from that of first light (for example, signal light) having a long wavelength. It was configured to do. Thereby, it is possible to realize a highly accurate attenuation process that can obtain a predetermined light attenuation amount. Further, since the signal light is not used for the negative feedback control, it is not necessary to use a special and expensive light receiving element as the light amount detecting means. Therefore, the cost of the entire variable optical attenuator can be reduced.

  In addition, the variable optical attenuator configured to perform negative feedback control regarding the optical attenuation processing as described above always obtains light intensity suitable for optical communication without being influenced by environmental changes or changes with time. Therefore, high performance can be maintained.

  FIG. 1 is a diagram showing a configuration of a variable optical attenuator 101 as a first embodiment of the present invention. The variable optical attenuator 101 is used as an attenuator that attenuates and adjusts the light intensity of signal light in an optical communication system or the like.

  The variable optical attenuator 101 of the first embodiment includes an LD, a first optical fiber 1, a first condenser lens 2, a second optical fiber 3, a photodetector 4, a controller 5, an actuator 6, and a second condenser lens 7. Is provided. FIG. 2 is an enlarged view of the vicinity of the incident end face 3 a of the second optical fiber 3. The incident end face 3a of the second optical fiber 3 includes a clad 3b and a core 3c. In the present specification, for convenience of explanation, it is assumed that the center of the core 3 c coincides with the center of the second optical fiber 3. The variable optical attenuator 101 uses control light used for processing for attenuating the intensity of the signal light in addition to the signal light used for optical communication. Control light having a shorter wavelength than that of signal light (for example, 1300 nm), for example, 650 to 820 nm is used.

  The signal light is irradiated from a light source (not shown) and enters the incident end surface 3 a of the second optical fiber 3 through the first optical fiber 1 and the first condenser lens 2. As shown in FIG. 2, only the component incident on the core 3c among the signal light incident on the incident end face 3a of the second optical fiber 3 is transmitted. Therefore, the light attenuation process is executed by adjusting how much signal light is incident on the core 3c.

  Here, under the control of the controller 5, the first condenser lens 2 is moved by the actuator 6 in one axial direction (X direction) in the plane orthogonal to the optical axis and in the Y direction orthogonal to the X direction. is there. The spot moves in the X ′ direction or the Y ′ direction on the incident end surface 3 a corresponding to the driving direction of the lens 2.

  In this specification, the positional relationship and direction in the variable optical attenuator 101 will be described with reference to the moving direction (X ′ direction, Y ′ direction) of the spot on the incident end face 3a. In the configuration of the present embodiment, when facing the incident end face 3a from the first optical fiber 1, the left direction is the X ′ (−) direction, the right direction is the X ′ (+) direction, and the upward direction with respect to the position of the core 3c. Is the Y ′ (+) direction, and the downward direction is the Y ′ (−) direction. Further, the driving direction of the first condenser lens 2 is the X (−) direction in the left direction, the X (+) direction in the right direction, and the upward direction when facing the first condenser lens 2 from the first optical fiber 1. Is the Y (+) direction, and the downward direction is the Y (−) direction.

  The control light emitted from the LD converges via the second condenser lens 7 and travels toward the core 1b of the end face (exit end face) 1a from which the signal light in the first optical fiber 1 is emitted. The control light is reflected by the core 1b. Here, in order to increase the reflection efficiency of the control light without decreasing the intensity of the signal light at the exit end face 1a, the core 1b of the exit end face 1a has a reflectance with respect to the wavelength of the control light and a transmittance with respect to the wavelength of the signal light. An optical film having a wavelength selectivity set high is coated.

  The control light reflected by the exit end face 1a enters the entrance end face 3a of the second optical fiber 3 in the same manner as the signal light. Here, as shown in FIG. 2, the first condenser lens 2 is controlled so that the diameter r1 of the spot formed by the control light incident on the incident end face 3a is slightly larger than the diameter r2 of the core 3c. Has the power to collect light. For example, in this embodiment, r1 is set to 11 μm and r2 is set to 10 μm. Therefore, even if the signal light is incident on the position with the highest optical transmission efficiency, that is, the center of the core 3c, the spot peripheral edge of the control light is incident on the clad 3b.

  As shown in FIG. 2, the incident end face 3a has a step formed by the core 3c protruding in a direction substantially orthogonal to the surface of the clad 3b (the optical axis direction of the second optical fiber 3). Further, the incident end face 3a is processed so that the protruding surface of the core 3c and the surface of the clad 3b are substantially parallel. In the present embodiment, the incident end face 3a is processed into the above shape by using a photolithography technique. The dimension of the step is set to a value smaller than λ / (4n), preferably λ / (8n) when light is incident on both the surface of the protruding core 3c and the surface of the clad 3b. Where λ is the wavelength of incident light (in this embodiment, the wavelength of control light), and n is the refractive index of the medium. When the step size is set as described above, a diffraction phenomenon occurs when the control light is incident on both the core 3c and the clad 3b on the incident end face 3a. In the present embodiment, the medium is assumed to be air, and the light intensity difference obtained by the light incident on the core 3c and reflected (zero-order light) and the light incident on the clad 3b and reflected (primary light). The predetermined dimension is set to approximately λ / 8 so that is maximized.

  The variable light attenuator 101 is configured such that when the control light emitted from the first condenser lens 2 is reflected by the incident end face 3a, it is reflected in a direction different from the incident direction. Thereby, the light receiving surface 4a of the photodetector 4 can be arranged on the optical path of the control light reflected by the incident end surface 3a without interfering with the optical path of the signal light incident on the incident end surface 3a.

  In the present embodiment, a quadrant photodetector is used as the photodetector 4. FIG. 3 is a view showing the light receiving surface 4a of the photodetector 4 according to the first embodiment. FIG. 3 shows a state where the light receiving surface 4a is viewed from the back side for convenience of explanation. As shown in FIG. 3, the direction of the light receiving surface 4a is directed to the direction corresponding to the X ′ (+) direction, that is, the light detection areas A and D, with the center O as a reference when the light receiving surface 4a is viewed from the back side. The direction corresponding to the X ″ (+) direction and the direction corresponding to the X ′ (−) direction, that is, the direction toward the light detection areas B and C is defined as the X ″ (−) direction. Similarly, with respect to the center O, the direction corresponding to the Y ′ (+) direction, that is, the direction toward the light detection areas A and B is the Y ″ (+) direction, and the direction corresponding to the Y ′ (−) direction, that is, light detection. The direction toward areas C and D is defined as the Y ″ (−) direction.

  Specifically, as shown in FIG. 3, the light receiving surface 4a is divided into four lattice-like light detection areas A to D by two boundary lines 4b and 4c orthogonal to each other at the center O of the light receiving surface 4a. Has been. The photodetector 4 has a direction (X ″ direction, Y ″ direction) in which the extending direction of the two boundary lines 4b, 4c corresponds to the direction in which the first condenser lens 2 can move (X direction, Y direction). ) To substantially match. Further, the second optical fiber 3 and the photodetector 4 are fixed in a pre-positioned state so that the light beam reflected at the center of the core 3c of the incident end face 3a is incident on the center O on the light receiving surface 4a. . A predetermined optical system (not shown) is arranged between the incident end face 3a and the photodetector 4 so that the reflected light enters the four light detection areas A to D. The photodetector 4 outputs to the controller 5 a voltage signal corresponding to the amount of light received for each of the light detection areas A to D.

  In performing optical signal attenuation processing, the variable optical attenuator 101 performs the following initial adjustment. In the initial adjustment of the present embodiment, first, more specifically, the control light center line is reflected so that the optical path of the control light reflected by the exit end face 1a is the same as the optical path of the signal light emitted from the exit end face 1a. The optical path is adjusted so that the center lines of the signal light coincide. In the adjustment of the optical path, the exit end face 1a is set to the optical axis of the first optical fiber 1 so that the relative positioning between the members can be easily achieved so that the control light travels in substantially the same optical path as the signal light. It is formed to tilt. The LD and the second condensing lens 7 are converged by the core 1b of the emission end face 1a in relation to the first optical fiber 1, and the optical path of the signal light from which the reflected control light is emitted from the first optical fiber 1. Are arranged at positions that pass through substantially the same optical path.

  Next, the position of the spot is adjusted so that the spot formed on the incident end face 3a by the signal light is directed to the center of the core 3c. In this embodiment, the signal light and the control light travel on the same optical path. Therefore, here, the position of the spot is adjusted using the control light. Specifically, the controller 5 moves the first condenser lens 2 in the X direction and the Y direction so that a light beam incident on the center 3c of the incident end surface 3a in the control light enters the center O on the light receiving surface 4a. Drive control. Whether or not a light beam incident on the core 3c center of the incident end face 3a in the control light is incident on the center O on the light receiving surface 4a is determined by the amount of light detected in each of the light detection areas A to D of the photodetector 4 being 1: 1. : Judgment is made based on whether or not the ratio is 1: 1. The above is the initial adjustment.

  Next, the light attenuation process which is the main feature of the present invention will be described in detail. 4A to 4C show the incident position on the incident end face 3a of the control light and the respective light detection areas A when the control light is at each incident position in the state where the initial adjustment is performed. It is the figure which showed the light intensity distribution of the X "direction based on the output from D. The incident end surface 3a shown in each figure is X '(-) direction on the left side, and X' (+) direction on the right side. 4A shows a state in which the control light is incident in the X ′ (−) direction from the core 3c, and the light intensity distribution of the control light in this state, and FIG. 4A and 4B show the light intensity distribution of the control light in the state substantially matching the core 3c and the state in which the control light is incident in the X ′ (+) direction from the core 3c. The light intensity distribution of the control light in is shown.

  As shown in FIGS. 4A to 4C, the light intensity distribution generated based on the output from the photodetector 4 differs depending on the position of the spot on the incident end face 3a. That is, the light intensity distribution changes corresponding to the deviation between the spot on the incident end face 3a and the core 3c. Here, the amount of light received by each of the sensors A to D is proportional to the integral value of the generated light intensity distribution. Therefore, the change in the light intensity distribution refers to the sum of the outputs of the light detection sensors A and D (hereinafter referred to as output in the X ″ (+) direction) and the sum of the outputs of the light detection sensors B and C (hereinafter referred to as X ″). It can also be said to be a change in the difference (hereinafter referred to as the output difference in the X ″ direction). FIG. 5 shows the difference in the output in the X ″ direction and the X of the control light spot relative to the core of the incident end face 3a. It is a graph showing the relationship with the amount of deviation | shift in 'direction. As shown in FIG. 5, the displacement amount in the X ′ direction changes in an S shape with respect to the output difference in the X ″ direction. Therefore, if the output difference in the X ″ direction is obtained, the displacement amount in the X ′ direction is Determine uniquely.

  In addition, the amount of signal light transmitted through the core 3c decreases as the spot position on the incident end face 3a increases from the center of the core 3c, in other words, the amount of optical attenuation increases. FIG. 6 is a graph showing the relationship between the light attenuation amount of the signal light and the shift amount of the signal light spot on the incident end face 3a in the X ′ direction with respect to the core 3c. As shown in FIG. 6, the amount of optical attenuation of the signal light is uniquely determined if the amount of deviation of the signal light spot from the core 3c in the X 'direction is obtained.

  Here, by the initial adjustment, in the variable optical attenuator 101, the signal light and the control light travel on the same optical path and form a spot at the same position on the incident end face 3a. That is, the deviation amount shown in FIG. 5 and the deviation amount shown in FIG. 6 have the same value. Therefore, if the characteristic information shown in FIGS. 5 and 6 is given to the controller 5 in advance, the controller 5 can execute the light attenuation process as follows. That is, when the light attenuation amount for the signal light is set, the controller 5 calculates the output difference in the X ″ direction of the control light based on the output from the photodetector 4. While referring to the characteristic information, The first condenser lens 2 is driven and controlled in the X direction via the actuator 6 so that the calculation result matches the output difference in the X ″ direction of the control light necessary to obtain the light attenuation amount. Thereby, the intensity of light used for optical communication is adjusted, in other words, an optical attenuation process is performed.

  During the light attenuation process, the first condenser lens 2 is held so as not to be driven in the Y direction. That is, in the present embodiment, drive control of the first condenser lens 2 in the Y direction is performed only at the time of initial adjustment.

  Further, the photodetector 4 has a sensitivity only with respect to the wavelength of the control light. Therefore, even if a partial component of the signal light reflected by the incident end face 3a is incident on the photodetector 4, the photodetector 4 does not reduce the accuracy of light amount detection due to the partial component. Furthermore, there is a possibility that the control light is transmitted through the core 3c of the second optical fiber 3, but the control light is set to a wavelength much shorter than that of the signal light, so that optical communication is not hindered.

  The above is the description of the variable optical attenuator 101 according to the first embodiment of the present invention. 7-12 is a figure showing the structure of the variable optical attenuators 102-107 of 2nd-7th embodiment of this invention. The variable optical attenuators 102 to 107 of the second to seventh embodiments are different from the variable optical attenuator 101 of the first embodiment in that some constituent members are added, replaced, or deformed. Although different, the other configurations and the specific contents of the optical attenuation processing are the same as those of the variable optical attenuator 101 of the first embodiment. Accordingly, in FIGS. 7 to 12, members common to the variable optical attenuator 101 of the first embodiment are denoted by the same reference numerals. Only the features that are different from the variable optical attenuator 101 of the first embodiment will be described below.

  The variable optical attenuator 102 of the second embodiment shown in FIG. 7 is configured such that the incident end face 3 a of the second optical fiber 3 is inclined with respect to the optical axis of the second optical fiber 3. Therefore, the optical path between the first condenser lens 2 and the incident end face 3a and the optical path between the incident end face 3a and the photodetector 4 can be substantially orthogonal. As described above, the variable optical attenuator according to the present invention can arbitrarily change the optical path so as not to disturb the degree of freedom related to the arrangement of other components in the optical communication system.

  The variable optical attenuator 103 of the third embodiment shown in FIG. 8 is provided with a polarizing beam splitter 8 and a quarter wavelength plate 9 as deflection means between the first condenser lens 2 and the incident end face 3a. In the variable light attenuator 103, the control light emitted from the first condenser lens 2 is incident on the incident end face 3a through the polarization beam splitter 8 and the quarter wavelength plate 9 at an approximately right angle (with an incident angle of 0 °). To do. Therefore, the control light reflected by the incident end face 3a returns on the same optical path as when incident on the incident end face 3a. The control light reflected by the incident end face 3 a enters the polarization beam splitter 8 through the quarter wavelength plate 9. Here, the control light is transmitted through the quarter-wave plate 9 twice, so that the phase is in a polarization state whose phase is shifted by half. Therefore, the control light reflected by the incident end face 3 a is reflected by the polarization beam splitter 8 and guided to the photodetector 4.

  Further, in the variable optical attenuator 104 of the fourth embodiment shown in FIG. 9, the deflecting means including the polarization beam splitter 8 and the quarter wavelength plate 9 is provided between the exit end face 1a and the first condenser lens 2. Yes. Further, the variable optical attenuator 105 of the fifth embodiment shown in FIG. 10 is provided with a collimating lens 10, a polarizing beam splitter 8, and a quarter wavelength plate 9 in order from the exit end face 1a side. In the variable optical attenuators 103 to 105 of the third to fifth embodiments, as shown in FIGS. 8 to 10, the control light is deflected at substantially right angles by the exit end face 1 a and the polarization beam splitter 8 and is incident. It is configured to retroreflect at the end face 3a. Therefore, there exists an advantage that the positioning between each structural member becomes easy.

  Further, in each of the above-described embodiments, the spot formed by the signal light and the control light on the incident end surface 3a is moved by driving the first condenser lens 2. The spot moving means may have another configuration. For example, the position of the spot on the incident end surface 3a can be moved by driving the first optical fiber 1 itself in the X direction or the Y direction.

  In addition, for example, a variable vertex angle prism having a structure described below can be arranged as a spot moving means. FIG. 11 is a cross-sectional view showing an example of the variable apex angle prism 20. The variable apex angle prism 20 has two parallel glass plates 21 and 22 and an elastic bellows-like cover 23 sealed by the two glass plates 21 and 22. The cover 23 is filled with a liquid such as silicone oil. Each glass plate 21 and 22 is hold | maintained by glass holding | maintenance part 24a-24d. The glass holding portion 24 a is screwed to a lead screw 26 that is rotatable by the motor portion 25. Therefore, as the lead screw 26 rotates, the glass holding portion 24a moves forward and backward in the α direction (the extending direction of the lead screw 26) in the drawing. Thereby, the magnitude | size of the vertex angle (theta) made by each glass plate 21 and 22 changes, and the optical axis of the light which permeate | transmits the vertex angle variable prism 20 can be moved (from a broken line to a continuous line in the figure). Accordingly, the apex angle adjusting unit 27 including the motor unit 25 and the lead screw 26 is disposed so that the moving direction of the optical axis corresponds to the X direction and the Y direction, so that the apex angle variable prism 20 is spot-moved. It can be used as a means.

  Further, the variable optical attenuator 106 of the sixth embodiment shown in FIG. 12 moves the position of the spot on the incident end face 3a by disposing the galvanometer mirror 11 on the optical path of the signal light and control light from the exit end face 1a. . In the variable optical attenuator 106, the signal light and the control light are transmitted by the second condenser lens 2, reflected by the galvano mirror 11, and enter the incident end face 3 a of the second optical fiber 3. The galvanometer mirror 11 is configured to be swung in the X and Y directions indicated by white arrow lines in FIG. 12 under the control of the controller 5.

  A variable optical attenuator 107 of the seventh embodiment shown in FIG. 13 uses a first optical fiber 1 ′ that includes a fiber coupler FC. The control light emitted from the LD is emitted from the emission end face 1a of the first optical fiber 1 'through the fiber coupler FC. That is, in the case of the variable optical attenuator 107 of the present embodiment, the control light and the signal light emitted from the emission end face 1a are configured to travel on the same optical path by the fiber coupler. That is, in the seventh embodiment, the exit end face 1a is not used as a light guide means for guiding the control light to the same optical path as the signal light.

  The above is the embodiment of the present invention. The variable optical attenuator according to the present invention is not limited to each of the above-described embodiments, and the same effects as those of the above-described embodiments can be obtained even when the following modifications are performed.

  For example, in the said embodiment, the 1st optical fiber 1 is used as an optical member in which the signal light which injects into the 2nd optical fiber 3 through the 1st condensing lens 2 is inject | emitted. Here, the optical member that can be used in the variable optical attenuator according to the present invention is not limited to the optical fiber such as the first optical fiber 1 but may be an optical waveguide.

  In the above description, during the light attenuation process, the first condenser lens 2 is driven and controlled only in the X direction, but is driven and controlled only in the Y direction and is held so as not to be driven in the X direction. It may be.

  Furthermore, the spot moving means including the first condenser lens 2 only needs to be configured to be driven only in either the X direction or the Y direction required for the light attenuation process. In this case, the photodetector 4 may have a light receiving surface that is perpendicular to a direction corresponding to the moving direction of the spot moving means and is divided into two by a boundary line passing through the center O. For example, in the variable optical attenuator 107 of the seventh embodiment, the first condenser lens 2 is configured to be driven only in the X direction, and the light receiving surface 4a extends in the Y ″ direction and is separated by a boundary line passing through the center O. A divided photodetector 4 may be used.

  Moreover, in said embodiment, since the light from the 1st optical fiber 1 which injected into the incident end surface 3a of the 2nd optical fiber 3 diffracts, the structure which makes the core 3c protrude rather than the clad 3b in this incident end surface 3a However, the same effect can be obtained even in other configurations, for example, a configuration in which the core 3c is recessed by λ / 8 from the cladding. Further, the diameter of the region divided by the step (that is, r2 shown in FIG. 2) can be set slightly larger than the diameter of the core.

  In each of the above embodiments, by obtaining the characteristics shown in FIG. 5, even if the change in the deviation between the spot and the core is minute, it can be detected reliably by the change in the output difference. The diffraction phenomenon occurs in 3a. Therefore, when mounted in an optical communication system that does not require highly accurate optical attenuation processing, the variable optical attenuator according to the present invention may be configured not to actively use the diffraction phenomenon. For example, the spot diameter r1 shown in FIG. 2 may be set smaller than the core diameter r2, that is, the spot may be accommodated in the core 3c on the incident end face 3a. Furthermore, in the variable optical attenuator according to the present invention, it is possible to execute the optical attenuation process of the signal light based on the light amount difference of the control light without providing a step on the incident end face 3a and utilizing the diffraction phenomenon. If it is the structure which does not form a level | step difference in the incident end surface 3a, a further cost reduction can be aimed at.

  In the above embodiment, it has been described that the control light and the signal light travel on the same optical path by adjusting the optical path (the center lines of the control light and the signal light coincide), but the optical path adjustment is performed at least with the signal light and the control light. The two optical paths may be adjusted so that the optical path (center line) between the light exit end face 1a and the first condenser lens 2 is parallel. However, in this case, the amount of deviation of the control light spot from the center of the core 3c does not coincide with the amount of deviation of the signal light spot from the center of the core 3c at the incident end face 3a. Therefore, even if the characteristic information shown in FIGS. 5 and 6 is given to the control unit 5, it is not always possible to perform negative feedback control so that a set light attenuation amount can be obtained. Therefore, when the optical paths are adjusted so that the optical paths of the signal light and the control light are parallel, the intensity of the signal light transmitted through the core 3c and the spot position of the control light on the incident end face 3a (in other words, the light detection) The characteristic of the output difference in the device 4 is determined from the measurement result, and the controller 5 is configured to perform negative feedback control based on the information about the characteristic.

It is a figure showing schematic structure of the variable optical attenuator of 1st embodiment of this invention. It is an enlarged view of the incident end face vicinity in the 2nd optical fiber of 1st embodiment of this invention. It is the figure which showed the light-receiving surface of the photodetector of 1st embodiment of this invention. It is the figure which showed the light intensity distribution of the X "direction based on the incident position in the incident end surface of control light, and the output from each photon detection area. It is a graph showing the relationship between the output difference in the X ″ direction and the shift amount in the X ′ direction with respect to the core of the spot of the control light at the incident end face. The relationship between the amount of optical attenuation of the signal light and the amount of deviation of the spot of the signal light on the incident end surface in the X ′ direction from the core is represented. It is a figure showing the structure of the variable optical attenuator of 2nd embodiment of this invention. It is a figure showing the structure of the variable optical attenuator of 3rd embodiment of this invention. It is a figure showing the structure of the variable optical attenuator of 4th embodiment of this invention. It is a figure showing the structure of the variable optical attenuator of 5th embodiment of this invention. It is a figure showing the structure of the variable optical attenuator of 6th embodiment of this invention. It is a figure showing the structure of the variable optical attenuator of 7th embodiment of this invention. The modification of the spot moving means in the variable optical attenuator of embodiment of this invention is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st optical fiber 2 1st condensing lens 3 2nd optical fiber 3a Incident end surface 3b Clad 3c Core 4 Photodetector 5 Controller 8 Polarizing beam splitter 9 1/4 wavelength plate 11 Galvano mirrors 101-102 Variable optical attenuator 20 Vertical angle variable prism

Claims (23)

A first optical member having an optical transmission path through which the first light is emitted;
A second optical member having an optical transmission path on which the first light emitted from the first optical member is incident;
Moving means for moving the position at which the first light is incident on the incident end face of the second optical member;
A light source that emits second light having a shorter wavelength than the first light;
First light guiding means for guiding the second light emitted from the light source to the incident end face via the moving means;
A light amount detecting means for detecting the light amount of the second light received by the light receiving surface, the light receiving surface receiving the second light via a second light guide means;
Based on the light quantity of the second light detected by the light quantity detection means, the moving means is controlled so that the position of the first light on the incident end face is directed to a position that satisfies a predetermined condition. A variable optical attenuator. The variable optical attenuator according to claim 1, wherein
The light amount detecting means includes a plurality of light receiving areas in which a light receiving surface is divided by at least one boundary line,
The variable optical attenuator, wherein the control unit performs the control based on a difference in light amount of the second light received in each light receiving area. The variable optical attenuator according to claim 2, wherein
The control means has information relating to a relationship between a difference in the amount of the second light detected in each light receiving area and the intensity of the first light transmitted from the first optical member to the second optical member. The variable optical attenuator is controlled so that the position of the first light on the incident end face is directed to a position where a set light attenuation amount can be obtained based on the information. The variable optical attenuator according to claim 2 or 3,
The moving means moves the position of the first light on the incident end face in a first direction,
The variable light attenuator, wherein the light receiving surface of the light amount detecting means has two light receiving areas arranged along a direction corresponding to the first direction. The variable optical attenuator according to claim 2 or 3,
The moving means moves the position of the first light on the incident end surface in a first direction and a second direction orthogonal to each other,
The light receiving surface of the light amount detecting means includes four light receiving areas by two boundary lines extending in a third direction corresponding to the first direction and a fourth direction corresponding to the second direction. A variable optical attenuator characterized by being divided into two. The variable optical attenuator according to claim 5, wherein
The control means also performs control related to adjustment of an incident position of the second light on the light receiving surface based on a difference in light amount detected in each of the four light receiving areas. . The variable optical attenuator according to any one of claims 1 to 6,
The variable optical attenuator, wherein the first light guide means is integrally formed with the first optical member. The variable optical attenuator according to claim 7,
The first light guide means is an emission end face of the first optical member,
The emission end face reflects the second light emitted from the light source and guides it to a second optical member. The variable optical attenuator according to claim 8,
An optical film having a wavelength selectivity having a high reflectance with respect to the second light and a high transmittance with respect to the first light at the incident position of the second light on the exit end face. Is a variable optical attenuator. The variable optical attenuator according to any one of claims 1 to 9,
The variable optical attenuator, wherein the first optical member is an optical fiber. The variable optical attenuator according to claim 7,
The variable optical attenuator, wherein the first optical member is an optical fiber having a fiber coupler as the first light guiding means. The variable optical attenuator according to any one of claims 7 to 11,
In the relationship with the first optical member, the light source has a center line of the second light reflected by the emission end face parallel to the center line of the first light emitted from the emission end face. A variable optical attenuator that is positioned so as to be incident on a second optical member. The variable optical attenuator according to any one of claims 7 to 12,
In the relationship with the first optical member, the light source has a center line of the second light reflected by the emission end face substantially coincident with a center line of the first light emitted from the emission end face. A variable optical attenuator that is positioned so as to be incident on a second optical member. The variable optical attenuator according to any one of claims 1 to 13,
The second optical member is an optical fiber;
The variable optical attenuator, wherein the optical transmission line of the second optical member is a core of the optical fiber. The variable optical attenuator according to claim 14, further comprising:
A third optical member for condensing the light emitted from the first optical member;
In the second optical member, a step having a predetermined dimension is formed on the core and the clad on the incident end face on which the second light is incident.
The third optical member condenses the second light so that the second light forms a spot having a diameter larger than the diameter of the core and smaller than the diameter of the clad on the incident end face. A variable optical attenuator. The variable optical attenuator according to claim 15,
The variable optical attenuator is characterized in that the predetermined dimension is set to a value smaller than about λ / (4n) where λ is the wavelength of the second light and n is the refractive index of the medium. The variable optical attenuator according to claim 16, wherein
The variable optical attenuator is characterized in that the predetermined dimension is set to approximately λ / (8n). The variable optical attenuator according to any one of claims 15 to 17,
In the variable optical attenuator, the end face of the core is substantially parallel to the end face of the clad. The variable optical attenuator according to any one of claims 15 to 18,
The variable optical attenuator, wherein the moving means moves the position of the first light on the incident end face by driving the third optical member. The variable optical attenuator according to any one of claims 1 to 18,
The variable optical attenuator, wherein the moving means includes a galvanometer mirror installed between the first optical member and the second optical member. The variable optical attenuator according to any one of claims 1 to 18,
The variable optical attenuator is characterized in that the moving means includes a vertex angle variable prism which is installed between the first optical member and the second optical member and can freely change the vertex angle. The variable optical attenuator according to any one of claims 1 to 21,
The second light guiding means is configured such that the second light passing through the second light guiding means returns on the same optical path as the second light incident on the second light guiding means. Has been
A variable optical attenuator further comprising a deflecting unit that deflects the second light through the second light guiding unit in a direction deviating from the optical path and guides the light to the light amount detecting unit. The variable optical attenuator according to claim 22,
The variable optical attenuator, wherein the deflecting means includes a polarizing beam splitter and a quarter wave plate.

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