JP2004177947A - Optical communication device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical communication device which can maintain high performance even when an environmental change such as a change of mechanical conditions of vibration etc. occurs by performing highly accurate positioning processing relating to light from LD at all times. <P>SOLUTION: The optical communication device is provided with a light source, an optical fiber, a condenser lens, a moving means, a light receiving means and a control means. Therein, the optical fiber is composed of a core and a clad, has an incident end surface which is constituted so that the light reflected on the incident end surface has an optical intensity distribution in accordance with a reflection position, and transmits the light that is made incident to the core. The condenser lens is disposed between the light source and the optical fiber on an optical path and condenses the light so that the light forms a spot on the incident end surface. The moving means moves the spot on the incident end surface. The light receiving means has a light receiving surface that receives the reflected light and outputs a signal corresponding to the optical intensity distribution of the reflected light. The control means drives and controls the moving means so that the signal almost coincides with the signal corresponding to the standard distribution. <P>COPYRIGHT: (C)2004,JPO

Description

  The present invention relates to a configuration of an optical communication device that performs optical communication using light emitted from a semiconductor laser (hereinafter, referred to as an LD).

  An optical communication device is a device for transmitting light emitted from an LD and modulated by information to an optical fiber, and includes an LD, a lens for condensing light from the LD, and optical components such as an optical fiber. You. An optical communication module used as a line termination unit (ONU: Optical Network Unit) for drawing optical fiber communication into a subscriber's premises generally supports bidirectional communication in which transmission and reception are performed using a single optical fiber. The optical communication module further includes a light receiving element, a WDM (Wavelength Division Multiplex) filter for separating light of different wavelengths, and the like.

  In such an optical communication module, since the light from the LD is focused on the approximate center of the core of the optical fiber, the LD is positioned with high accuracy with respect to an optical fiber having a core diameter of several μm. Usually, these optical components are firmly fixed by welding or using an adhesive. A conventional positioning method is disclosed in, for example, Patent Document 1 below.

JP-A-6-94947

  According to the positioning method disclosed in Patent Document 1, the amount of light emitted from the optical fiber is detected, and it is determined that the light from the LD is incident on the approximate center of the core when the amount of light is the largest. I do.

  However, it is generally difficult to determine the boundary between the core and the clad on the fiber incident end face. Therefore, the relative positioning between the LD and the optical fiber must be repeated by trial and error until the amount of light emitted from the optical fiber is detected, which is troublesome.

  Furthermore, even if the optical communication module is configured by positioning and fixing the mutual positions of the components using an adhesive, the following problems remain. First, in the case where the optical communication module is manufactured as described above, since there is a possibility that the parts may be deformed or broken due to shrinkage of the adhesive or processing, the quality of the product can only be determined after bonding and drying. It is. It is also considered relatively difficult to achieve a high yield with such an optical communication module. Second, if there is a change in performance over time, it is impossible to correct it, and it is not possible to maintain high-accuracy positioning.

  In view of the above circumstances, the present invention always performs high-precision positioning processing on light from an LD to maintain high performance even when there is an environmental change such as a change in mechanical conditions such as vibration. It is an object of the present invention to provide an optical communication device capable of performing the following.

  In order to achieve the above object, an optical communication device according to the present invention includes a light source for irradiating light modulated by information, a core and a clad, and an end face on which light is incident, and light reflected on the end face. An optical fiber having an incident end face configured to have a light intensity distribution corresponding to the reflection position and transmitting light incident on the core; and an optical fiber disposed on the optical path of the light, between the light source and the optical fiber. A condensing lens for condensing the light so as to form a spot on the incident end face, a moving means for moving the spot on the incident end face, and a light receiving surface for receiving the reflected light; And light control means for driving and controlling the moving means so that the signal substantially matches the signal corresponding to the reference distribution.

  According to the first aspect of the present invention, the position of the core on the incident end face of the optical fiber can be detected in a short time and easily, and the positioning can be performed with high accuracy. Further, according to the above configuration, the negative feedback control is performed such that the position of the light from the light source at the optical fiber incident end face is directed toward the core center based on the signal output corresponding to the light intensity distribution of the reflected light that is constantly or periodically detected. Therefore, an optical communication device capable of maintaining high performance even when there is an environmental change or a temporal change is provided. Here, the reference distribution refers to a distribution obtained when light is incident on the center of the core of the optical fiber.

  Further, in the method disclosed in Patent Document 1, a high-precision stage for holding an expensive ultra-precision stage, a holder, and a photodetector provided on an emission side so that positioning with high accuracy is performed. Tools were needed. These stages and the like are also required when firmly fixing the above optical components so as not to be displaced. Therefore, the conventional configuration illustrated in Patent Literature 1 is expensive and complicated. However, according to the first aspect of the present invention, an ultra-precise stage or the like is not required, and a simple and inexpensive optical communication device is provided.

  Here, in order to form a brighter and clearer (ie clearer) diffraction pattern on the light receiving surface, it is preferable that the diameter of the spot formed on the incident end face be larger than the diameter of the core. However, if the spot diameter is larger than the diameter of the clad, that is, the entire diameter of the end face, useless light loss is caused, which is not preferable (claim 2).

  The moving means may be configured to move the spot in a first direction and a second direction that are non-parallel to each other on the incident end face (claim 3).

  Here, it is desirable that the signal used for the positioning process is a signal corresponding to the light intensity distribution in the first direction and the second direction, which are the moving directions of the spot. Thereby, the burden on the positioning process is reduced.

  According to the invention as set forth in claim 5, the light receiving means has a light receiving surface extending in at least one boundary line extending in the third direction and a fourth direction non-parallel to the third direction. It is preferable that the light receiving area is divided into N × M (where N and M are integers of 2 or more) lattice-shaped light receiving areas by at least one boundary line.

  Thus, even if the incident position of the reflected light from the incident end face on the light receiving unit changes due to a change with time or the like, the reflected light can be reliably received.

  Note that the above effect can be obtained by setting both N and M to 2, in other words, dividing the light receiving surface of the light receiving means into at least four light receiving areas (claim 6).

  Further, the optical communication device using the light receiving means having a plurality of light receiving areas as described above can have the following configuration. That is, according to the invention described in claim 7, the light receiving means detects the signal by converting the signal into an output of a predetermined number of light receiving areas that have received the reflected light, and the control means detects each output of the light receiving area. The optical communication apparatus can be configured to drive and control the moving means such that the ratio of the light receiving area and the ratio of each output of the light receiving area corresponding to the reference distribution substantially match. The output of the light receiving area corresponds to the amount of light received in each area.

  In the above configuration, in order to reduce the load on the positioning process, the control unit determines that the ratio of the output of the four light receiving areas adjacent to each other where the reflected light has entered and the ratio of each output of the light receiving area corresponding to the reference distribution. It is desirable to drive and control the moving means so that they substantially coincide with each other.

  In order to more easily and accurately perform the positioning with respect to the incident position of the light from the LD on the incident end face of the optical fiber, the light receiving unit has a third direction corresponding to the first direction and a fourth direction corresponding to the first direction. It is preferable to be provided so as to correspond to the second direction (claim 9). In a case where the light receiving means is provided as in claim 9, the control means includes two light receiving areas on one side based on a boundary line extending in the third direction among four adjacent light receiving areas. The driving means is driven and controlled to move the spot in the second direction so that the output ratio between the light receiving area and the two light receiving areas on the other side has a predetermined relationship. At the same time, the control means, based on the boundary line extending in the fourth direction, of the four light receiving areas, two light receiving areas on one side and two light receiving areas on the other side. The driving means is controlled to move the spot in the first direction so that the output ratio has a predetermined relationship. This makes it possible to make the light intensity distribution coincide with the reference distribution (claim 10).

  In this specification, the extension direction of each boundary line corresponds to the first direction and the second direction, which means that the optical path of the light emitted from the LD and reflected at the optical fiber incident end face is developed to be linear. It means that they match when it is assumed that they have been done.

  From another point of view, the light receiving means sets the angle between the movement trajectory of the spot in the first direction and the movement trajectory of the spot in the second direction in the third direction and the fourth direction, respectively. It is also possible to dispose them equally. In the case of the configuration according to claim 11, the control means determines that the output ratio of the two light receiving areas, which are diagonally arranged with respect to the sensor center where the two boundary lines intersect, among the four light receiving areas is a reference. The driving means is driven and controlled so as to have a predetermined relationship, and the spot on the incident end face is positioned. (Claim 12).

  The control means performs negative feedback control so that the output difference becomes zero when the reference distribution is symmetrical (claim 13). At this time, the light beam emitted from the light source and passing on the optical axis is reflected at the center of the incident end face of the optical fiber, and is received at the point where the above-mentioned specific four light receiving areas on the light receiving surface come into contact.

  It is desirable that the optical fiber constituting the optical communication device according to the present invention has the following configuration in detail. First, a step of a predetermined dimension is formed between the core and the clad on the incident end face (claim 14). The size of the step is set such that the reflected light is diffracted by the step (claim 15). Specifically, assuming that the wavelength of the light from the LD is λ and the refractive index of the medium is n, it is set to a value smaller than approximately λ / (4n). In a more preferred embodiment, the dimension is set to approximately λ / (8n) (claim 17). Further, the step may be formed by protruding the core from the clad (claim 18) or by denting the core from the clad (claim 19). Photolithography can be used to protrude or dent the core. In order to realize more accurate positioning, it is preferable to process the end surface of the core and the end surface of the clad so as to be substantially parallel (claim 20).

  According to the twenty-first aspect, the moving means can move the spot in the first direction or the second direction by driving the condenser lens.

  From another viewpoint, the moving means can move the spot position on the incident end face in the first direction or the second direction by driving the light source (claim 22). From another viewpoint, the moving means may be provided between the condenser lens and the fiber end face, and may have a transmission type deflecting member that deflects the incident light beam in the first direction and the second direction. (Claim 23). Examples of the transmission type deflection member include a variable apex angle prism and a set of wedge prisms.

  As described above, according to the present invention, it is possible to position the signal light for transmission on the incident end face of the optical fiber with high accuracy so as to coincide with the center of the core. Further, according to the present invention, it is possible to perform negative feedback control so that the position of the light from the light source on the incident end face of the optical fiber becomes the center of the core at all times. The optical communication device configured to perform the negative feedback control as described above can maintain high performance without being affected by environmental changes, temporal changes, and the like.

  FIG. 1 is a diagram illustrating a configuration of an optical communication module 10 according to an embodiment of the present invention. The optical communication module 10 is used as an ONU that brings optical fiber communication into a subscriber's house. For example, the optical communication module 10 is configured to transmit a wavelength of 1.3 μm as an upstream signal and receive a signal of 1.5 μm as a downstream signal using one optical fiber, and the optical communication module 10 supports bidirectional WDM transmission. It is a communication module. The optical communication module 10 according to the present embodiment includes an LD, a condenser lens 2, an optical fiber 3, a photodetector 4, a controller 5, and an actuator 6. In the optical communication module actually used, the angle of incidence of the light beam output from the LD and entering the optical fiber 3 via the condenser lens 2 is extremely small. However, in FIG. 1, the incident angle is shown larger than the actual angle for convenience of explanation.

  FIG. 2 is an enlarged view of the optical fiber 3 in the vicinity of a surface (incident end surface) 3a on which light from the LD enters. The incident end face 3a of the optical fiber 3 includes a clad 3b and a core 3c. In this specification, for convenience of explanation, the center of the core 3c is assumed to coincide with the center of the optical fiber 3.

  The light emitted by the LD enters the incident end face 3 a of the optical fiber 3 via the condenser lens 2. Here, the condenser lens 2 is movable by an actuator 6 in one axial direction (X ′ direction) in a plane perpendicular to the optical axis and in a Y ′ direction orthogonal to the X ′ direction under the control of the controller 5. In state. That is, the spot moves on the incident end face 3a according to the driving direction of the lens 2. Hereinafter, of the spot movement directions, directions corresponding to the movement of the condenser lens 2 in the X 'direction and the Y' direction are referred to as the X direction and the Y direction, respectively.

  In this specification, the positional relationship and the direction will be described with reference to the driving direction (X direction, Y direction) of the spot. In the configuration of the present embodiment, when the incident end face 3a is viewed from the LD side, the left direction of the position of the core 3c is the X (+) direction, and the right direction is the X (-) direction. The upward direction of the position of the core 3c is defined as a Y (+) direction, and the downward direction is defined as a Y (-) direction.

  Further, as shown in FIG. 2, a step is formed in the incident end face 3 a by the core 3 c protruding in a direction substantially orthogonal to the surface of the clad 3 b (the optical axis direction of the optical fiber 3). The incident end face 3a is processed so that the surface of the protruding 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 the photolithography technique. The size of the step is set to a value smaller than λ / (4n). Here, λ is the wavelength of the incident light, and n is the refractive index of the medium. By setting the size of the step in this way, when a light beam condensed so that the spot diameter r1 is slightly larger than the core diameter r2 is incident on both the protruding core 3c surface and the clad 3b surface, In this embodiment, where the diffraction phenomenon occurs, the medium is assumed to be air. Therefore, in the present embodiment, the predetermined dimension is set to approximately λ / 8.

  The optical communication module 10 guides light reflected on the incident end face 3 a to the photodetector 4. Therefore, the optical communication module 10 is configured such that light from the LD is incident on the incident end face 3a at an incident angle other than 0 °. Thus, the optical path of the light reflected on the incident end face 3a is different from the optical path of the light incident on the incident end face 3a. The light reflected by the incident end face 3a of the optical fiber 3 is incident on the photodetector 4 and forms a diffraction pattern.

Here, in general, the spot size of the light emitted from the LD is defined as a range having an intensity of 1 / e ² (where e is the base of natural logarithm) or more of the maximum intensity in the intensity distribution of the light. You. It is also known that diffraction patterns are formed more remarkably by light having higher intensity. However, a diffraction pattern can be formed on the light receiving surface 4a even in a portion of the incident light beam having an intensity smaller than 1 / e ² of the maximum intensity.

  In other words, as the spot diameter formed on the incident end face 3a increases, the amount of reflected light increases, and the diffraction pattern clearly appears on the light receiving surface 4a, but the amount of light incident on the optical fiber 3 decreases. The coupling efficiency between the LD and the optical fiber 3 deteriorates. Conversely, the smaller the diameter of the spot formed on the incident end face 3a, the more the diffraction pattern on the light receiving surface 4a becomes blurred, but the higher the coupling efficiency can be.

  In view of the above circumstances, in order to balance the clarity of the diffraction pattern and the effectiveness of the coupling efficiency, in the present embodiment, as shown in FIG. 2, the diameter r1 of the spot formed on the incident end face 3a is set to the end face. Is designed to be slightly larger than the diameter r2 of the core at. Therefore, even if the light is incident on the incident end face 3a at the position where the light transmission efficiency is highest, that is, when the light is incident on the core 3c, the spot periphery of the light is incident on the clad 3b. Specifically, in the present embodiment, r1 = 11 μm and r2 = 10 μm.

  However, the present invention can be implemented even if r1 <r2 is set, that is, a configuration in which the spot falls within the core 3c at the incident end face.

  In the present embodiment, a four-segment photodetector is used as the photodetector 4. Specifically, as shown in FIG. 3, the light receiving surface 4a is divided into four lattice light receiving 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. Have been. The photodetector 4 sets the extending directions of the two boundary lines 4b and 4c to the X ″ direction and the Y ″ direction, respectively. In the present embodiment, the direction in which the intensity distribution of the pattern appearing on the photodetector 4 fluctuates due to the movement of the spot formed on the incident end face 3a in the X direction and the Y direction coincides with the X ″ direction and the Y ″ direction. The photodetector 4 is arranged so that 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 receiving 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 receiving areas A to D.

  As shown in FIG. 3, the light receiving areas A and D are in the X "(+) direction, and the light receiving areas B and C are X" on the basis of the boundary line 4b extending in the Y "direction through the center O on the light receiving surface 4a. Similarly, the light receiving areas A and B are in the Y "(+) direction, and the light receiving areas C and D are in the Y direction with reference to a boundary line 4c extending in the X" direction through the center O on the light receiving surface 4a. "It is called the (-) direction.

  The controller 5 drives the condenser lens 2 via the actuator 6 so as to eliminate a deviation between the position of the spot formed by the light from the LD on the incident end face 3a and the position of the core 3c based on the principle described in detail below. By controlling, the position of the spot is made to coincide with the position of the core 3c.

  First, the principle of the positioning process performed by the controller 5 will be described. 4A to 4C are diagrams showing incident positions of light from the LD on the incident end face 3a and light intensity distributions in the X direction when the light from the LD is at each incident position. In the incident end face 3a shown in each figure, the left side of the drawing is the X (-) direction, and the right side is the X (+) direction. FIG. 4A shows a state in which light from the LD is incident on the core 3c in the X (-) direction, and a light intensity distribution of light from the LD in this state. FIG. 3B shows a state in which light from the LD is incident on the core 3c in the X (+) direction and a light intensity distribution of light from the LD in this state. FIG. 3C shows a state in which the incident position of the light from the LD substantially coincides with the core 3c and a light intensity distribution of the light from the LD in this state.

  As shown in FIGS. 4A to 4C, the light intensity distribution differs depending on the position of the spot on the incident end face 3a. That is, the light intensity distribution changes according to the displacement between the spot and the core 3c. Therefore, by using the light intensity distribution when the position of the spot coincides with the position of the core 3c as a reference distribution, the position of the spot formed on the incident end face 3a is moved so that the light intensity distribution coincides with the reference distribution. Positioning processing is performed. Here, the signal output of each of the sensors A to D (that is, the amount of received light in each of the sensors A to D) is proportional to the integrated value of the light intensity distribution. Therefore, the position of the spot formed on the incident end face 3a is moved so that the signal output of each of the sensors A to D actually matches the signal output of each of the sensors A to D corresponding to the reference distribution acquired in advance. The position of the spot on the incident end face 3a can also be determined by the method.

  Hereinafter, an example of a specific positioning process will be described in detail with reference to FIG.

  As shown in FIG. 4A, when the incident position of the light from the LD is shifted from the core in the X (−) direction, the sum of the outputs of the light detection sensors A and D (hereinafter referred to as the output in the X ″ (+) direction). ), The sum of the outputs of the light detection sensors B and C (hereinafter referred to as the output in the X ″ (−) direction) is larger. Since the output of each of the sensors A to D (that is, the amount of light received by each of the sensors A to D) is proportional to the integral value of the light intensity distribution, the incident position of the light from the LD is shifted from the core in the X (-) direction. In this case, the light intensity distribution is higher in the X ″ (−) direction. Conversely, as shown in FIG. 4C, the incident position of the light from the LD is shifted in the X (+) direction relative to the core 3c. In this case, the output in the X "(+) direction is larger than the output in the X" (-) direction. Therefore, the light intensity distribution is higher in the X "(+) direction.

  When the incident position of the light from the LD substantially coincides with the core 3c as shown in FIG. 4B, the light ray passing through the optical axis of the light from the LD is reflected at the center of the optical fiber 3 and then detected by the photodetector. 4 is incident on the light receiving surface 4a. Therefore, the outputs of the light detection sensors A to D are substantially equal, and the light intensity distribution is also substantially symmetric on the left and right. When the light intensity distribution is converted into the output of each of the light detection sensors A to D, each output is substantially equal. That is, each output ratio is 1: 1: 1: 1.

  The controller 5 determines whether the current light intensity distribution created based on the output from each of the light detection sensors A to D is such that the incident position of the light from the LD on the incident end face 3a matches the position of the core 3c. Negative feedback control regarding the positioning of the spot on the incident end face 3a is performed so as to substantially match an intensity distribution (hereinafter, referred to as a reference distribution). In the present embodiment, the reference distribution corresponds to the distribution shown in FIG. 4B.

  First, the controller 5 obtains a value obtained by subtracting the output in the X "(-) direction from the output in the X" (+) direction (hereinafter referred to as the output difference in the X "direction. 7 is a graph showing the relationship between the incident position on the incident end face 3a and the shift amount in the X direction with respect to the core 3c. As shown in FIG. 5, the shift amount of the spot formed on the incident end face 3a in the X direction changes in an S-shape with respect to the output difference in the X ″ direction. Therefore, the output difference in the X ″ direction is obtained. For example, the shift amount in the X direction is uniquely determined within a predetermined range ((A) to (C)). The controller 5 of the present embodiment drives the condenser lens 2 in the X ′ direction via the actuator 6 so as to eliminate the output difference in the X ″ direction, that is, to reduce the amount of displacement in the X direction to 0, and 3a is moved in the X direction.The state in which the shift amount in the X direction is 0 means that the detected light intensity distribution substantially matches the reference distribution, that is, in this embodiment, X In this state, the ratio between the output in the “(+) direction and the output in the X” (−) direction (hereinafter referred to as the output ratio in the X ″ direction) is 1: 1.

  For example, when the incident position on the incident end face 3a is at the position shown in FIG. 4A, the position of the spot is shifted in the X (-) direction from the position of the core 3c, as shown at A in FIG. Accordingly, the controller 5 moves the incident position on the incident end face 3a in the X (+) direction so that the output difference in the X ″ direction becomes 0. In addition, the incident position on the incident end face 3a is shifted to the position shown in FIG. In some cases, the position of the spot is shifted from the position of the core 3c in the X (+) direction as shown by C in Fig. 5. Therefore, the controller 5 controls the X (X) so that the output difference in the X "direction becomes zero. The incident position on the incident end face 3a is moved in the −) direction. If the incident position is at the position shown in FIG. 4B, that is, if the light intensity distribution matches the reference distribution, there is no output difference in the X ″ direction as shown in B in FIG. 5. Therefore, in this case, the controller 5 Since the incident position on the incident end face 3a is located at the core 3c, the optical transmission efficiency is determined to be the best, and the condenser lens 2 is not driven in the X direction.

  By performing the negative feedback control so that the output difference in the X ″ direction is eliminated by the controller 5 as described above, highly accurate positioning can be performed so that light from the LD enters the center of the core 3c at the incident end face 3a. it can.

  The above is the description of the positioning process in the X direction performed by the controller 5. Since the positioning process in the Y direction is performed according to the same principle, the detailed description is omitted here. However, in the positioning process in the Y direction, the amount of displacement of the spot on the incident end face 3a in the Y direction is determined by the sum of the outputs of the light detection sensors A and B (hereinafter referred to as the output in the Y ″ (+) direction). It is determined based on the output difference in the Y ″ direction calculated by subtracting the sum of the outputs of the sensors C and D (hereinafter referred to as the output in the Y ″ (−) direction). The drive control of the condenser lens 2 in the Y ′ direction is performed so that the output difference is eliminated.

  FIG. 6 is a table showing the light intensity distribution in each of X ″ and Y ″ detected by the photodetector 4 for each incident position on the incident end face 3a. If the incident position (spot) of the light from the LD on the incident end face 3a is shifted from the core 3c in one or both of the X direction and the Y direction, the outputs from the light detection sensors A to D are different. , The light intensity distribution is not symmetrical in the + and-directions. Therefore, by performing the above-described positioning processing, the output difference becomes zero in both the X ″ direction and the Y ″ direction. That is, both the light intensity distribution in the X ″ direction and the light intensity distribution in the Y ″ direction match the reference distribution.

  When the light intensity distribution in the X ″ direction and the light intensity distribution in the Y ″ direction match the reference distribution by the above positioning processing, the controller 5 determines that the incident position of the light from the LD is at the core 3c position. Note that the above-described positioning processing is performed not only during initial adjustment at the time of manufacturing the optical communication module 10 but also during optical communication after the power of the optical communication module 10 is turned on. That is, even if the incident position of the light from the LD is shifted from the core 3c during the optical communication, the controller 5 can correct the position shift based on the output from the photodetector 4.

  In the above description, the positioning process in the X direction and the positioning process in the Y direction are described separately for convenience. However, in the actual optical communication module 10, the positioning process in the X direction and the positioning process in the Y direction are performed simultaneously. The positioning process in the optical communication module 10 has been described above.

  In the above embodiment, the X direction and the Y direction, which indicate the moving direction of the spot formed on the incident end face 3a, have been described as being orthogonal to each other, but this is only for convenience of description and is not limited to this. In the optical communication device according to the present invention, the X direction and the Y direction may be non-parallel. In the present invention, the extending directions of the boundary lines 4b and 4c are not necessarily orthogonal.

  The optical communication device according to the present invention can be positioned with high accuracy by processes other than the above embodiment. For example, in the above embodiment, as an optimal embodiment for simplifying and speeding up the positioning process, the extending direction of the boundary line 4c matches the moving direction X of the spot formed on the incident end face 3a, and The photodetector 4 is arranged so that the extending direction of the boundary line 4b matches the moving direction Y of the spot formed on the incident end face 3a. In the optical communication device of the present invention, the extending direction of each boundary line and the moving direction (X direction, Y direction) of the spot formed by the incident end face 3a do not necessarily need to match. For example, as shown in FIG. 7, the photodetector 4 may be arranged to be rotated 45 degrees from the position shown in FIG. In this case, the controller 5 performs the positioning process using two sensors located symmetrically with respect to the center O. Specifically, a process of adjusting the spot position in the X direction based on the outputs of the light receiving areas A and C located diagonally is performed, and the spot position in the Y direction is adjusted based on the outputs of the light receiving areas B and D. Perform processing. That is, in this modified example, when the spot moves in the X direction, the outputs of the light receiving areas A and C change, and when the spot moves in the Y direction, the outputs of the light receiving areas B and D change.

  Further, the above-described positioning process can be executed even in a configuration other than the optical communication module 10. FIGS. 8 to 11 show optical communication modules 11 to 14 having a different configuration from the optical communication module 10 but capable of executing the same positioning processing as described above. FIG. 8 shows an optical communication module 11 using an optical fiber 3 ′ cut at a plane other than a plane orthogonal to the fiber extending direction. In the optical communication module 11, each member is arranged and configured such that light from the LD is incident on the incident end face 3a at an incident angle other than 0 °. Therefore, there is a feature that the coupling efficiency of the fiber is higher than that of the optical communication module 10 and the manufacturing is easy. In the optical communication module 11, the optical fiber 3 ′ is disposed so that the optical axis of the fiber is inclined at a predetermined angle with respect to the optical axis of the condenser lens 2 in consideration of the refraction phenomenon at the incident end face 3 a. ing.

  FIG. 9 shows an optical communication module 12 in which the LD, the condenser lens 2 and the optical fiber 3 are arranged on a common optical axis. In the optical communication module 12, the reflected light from the incident end face 3a passes through the same optical path as the incident optical path. Therefore, a deflecting means including a quarter-wave plate 7 and a polarizing beam splitter 8 is arranged between the condenser lens 2 and the optical fiber 3 to deflect the reflected light and guide the reflected light to the photodetector 4. . According to the optical communication module 12, since the reflected light is in a linear polarization state orthogonal to the incident light by the quarter-wave plate 7 and the polarizing beam splitter 8, almost totally reflected light is detected without returning the reflected light to the LD. Incident on the vessel 4. Therefore, efficient light detection becomes possible. The optical communication module 13 shown in FIG. 10 has almost the same configuration as the optical communication module 12 described above. However, the optical communication module 13 differs from the optical communication module 12 in that the quarter-wave plate 7 and the polarizing beam splitter 8 are arranged between the LD and the condenser lens 2. Further, as in an optical communication module 14 shown in FIG. 11, a collimator lens 9 can be disposed between the LD and the deflecting means 7 and 8. It is to be noted that the spot is positioned by controlling the driving of the condenser lens 2 based on the detection result as in the above embodiment.

  Further, in the above embodiment, since the light from the LD incident on the incident end face 3a of the optical fiber 3 is diffracted, the core 3c is projected more than the clad 3b on the incident end face 3a. The same effect can be obtained by a configuration other than the above, for example, a configuration in which the core 3c is recessed by λ / 8 from the cladding.

  In the above embodiment, for convenience, the reference distribution is defined as a distribution in a state where the incident position of the light from the LD substantially coincides with the position of the core 3c. The reference distribution is such that the output ratio in each direction of X ″ and Y ″ is 1: 1 (FIG. 2B). However, the actual reference distribution does not always have the distribution shown in FIG. 4B due to individual differences between the optical communication devices and the like, and the intensity may be biased in either the + direction or the − direction. That is, the reference distribution itself may already have a predetermined output difference, in other words, the output ratio in each direction of X ″ and Y ″ corresponding to the reference distribution may not be 1: 1. In this case, the positioning process may be performed so that the output ratio in each of the directions X ″ and Y ″ obtained based on the output from each of the optical output sensors A to D matches the output ratio corresponding to the reference distribution. .

  Further, in the above embodiment, a four-segment photodetector is used as the photodetector 4, but the photodetector 4 is not limited to this. For example, a multi-segmented photodetector having a plurality of light receiving areas divided into N × M (where N and M are integers of 2 or more) lattices may be used. If the multi-segment photodetector is used, the position of the reflected light incident on the light receiving surface 4a may change due to the aging of the optical system disposed from the incident end surface 3a to the light receiving surface 4a. Also, the positioning process can be performed based on the outputs from the four adjacent light receiving areas that have newly received the reflected light.

  In the above-described embodiment, the configuration has been described in which the spot formed by the light from the LD on the incident end face 3a is moved to position the spot on the core 3c by driving the condenser lens 2. The spot moving means may have a configuration other than the above configuration. FIG. 12 is a diagram illustrating a schematic configuration of an optical communication module 10 ′ which is a modification of the optical communication module 10. The optical communication module 10 'has a deflection member K. In the optical communication module 10 ', the spot on the incident end face 3a is moved by controlling the driving of the deflecting member K without driving the condenser lens 2. As the deflecting member K, an apex angle variable prism shown in FIG.

  FIG. 13 is a cross-sectional view illustrating an example of the apex angle variable prism 20. The apex angle variable prism 20 has two parallel glass plates 21 and 22 and an elastic bellows cover 23 sealed by the two glass plates 21 and 22. The inside of the cover 23 is filled with a liquid such as silicone oil. The glass plates 21 and 22 are held by glass holding units 24a to 24d. The glass holding section 24a is movably held by the vertical angle adjusting section 27. Specifically, the glass holding portion 24a is screwed to a lead screw 26 which is rotatable by a motor portion 25. Therefore, with the rotation of the lead screw 26, the glass holding portion 24a moves forward and backward in the α direction (the direction in which the lead screw 26 extends) in the figure. As a result, the apex angle θ between the glass plates 21 and 22 changes, and the optical path of the light passing through the apex angle variable prism 20 can be moved (from the broken line to the solid line in the figure). Therefore, by arranging the two apex angle variable prisms 20 so that the moving direction of the optical path corresponds to the X ′ direction and the Y ′ direction, it is possible to move the spot without driving the first condenser lens 2. Can be. Thus, the modification in which the deflecting member K is provided is very suitable for a configuration in which the condenser lens itself cannot be driven, such as a module using an LD in which the condenser lens is integrally formed.

  In addition, as the deflection member K, the following configurations can be exemplified. For example, the apex angle variable prism 20 shown in FIG. 9 has been described assuming a so-called uniaxial variable type that can move the optical path only in one predetermined direction, but a so-called biaxial variable type that can move the optical path in two different directions. It is also effective to use types. Further, a set of two wedge-shaped prisms may be used as the deflection member K. In this case, the light can be deflected by tilting or rotating each wedge-shaped prism to change the respective arrangement positions. Further, by driving the LD itself in the X 'direction or the Y' direction, it is also possible to move the position of the spot on the incident end face 3a. Furthermore, the spot can be moved using both the first condenser lens 2 and the deflection member K.

It is a figure showing the schematic structure of the optical communication module of the embodiment of the present invention. FIG. 3 is an enlarged view of the vicinity of an incident end face in the optical fiber according to the embodiment of the present invention. FIG. 3 is a diagram illustrating a light receiving surface of the photodetector according to the embodiment of the present invention. FIG. 3 is a diagram illustrating an incident position of light from an LD on an incident end face, and a light intensity distribution in an X ″ direction based on an output from each light receiving area. 11 is a graph showing a relationship between an output difference in the X ″ direction and a shift amount in the X direction with respect to the core at the incident position on the incident end face. The relationship between the incident position of the reflected light on the light receiving surface and the light intensity distribution in each of X ″ and Y ″ directions is shown. 5 shows another arrangement example of the light receiving surface of the photodetector. 5 shows a modification of the optical communication module according to the embodiment of the present invention. 5 shows a modification of the optical communication module according to the embodiment of the present invention. 5 shows a modification of the optical communication module according to the embodiment of the present invention. 5 shows a modification of the optical communication module according to the embodiment of the present invention. 5 shows a modification of the optical communication module according to the embodiment of the present invention. 5 shows a modification of the moving means in the optical communication module according to the embodiment of the present invention.

Explanation of reference numerals

2 Condensing lens 3 Optical fiber 3a Incident end face 3b Cladding 3c Core 4 Photodetector 5 Controller 10, 11, 12, 13, 14 Optical communication module

Claims (30)

A light source for emitting light modulated by information;
An end face comprising a core and a clad, the end face on which the light is incident, the light reflected on the end face having an incident end face configured to have a light intensity distribution corresponding to a reflection position, and the light incident on the core. An optical fiber that transmits light,
A condensing lens disposed on the optical path of the light, between the light source and the optical fiber, and condensing the light so that the light forms a spot on the incident end face;
Moving means for moving the spot on the incident end face;
A light receiving unit having a light receiving surface for receiving the reflected light, and outputting a signal corresponding to a light intensity distribution of the reflected light,
Control means for driving and controlling the moving means so that the signal substantially matches a signal corresponding to a reference distribution. The optical communication device according to claim 1,
The optical communication device according to claim 1, wherein the spot has a diameter larger than a diameter of the core and smaller than a diameter of the clad. The optical communication device according to claim 1 or 2,
The optical communication device, wherein the moving means moves the spot in a first direction and a second direction that are not parallel to each other on the incident end face. The optical communication device according to claim 3,
The optical communication device, wherein the signal is a signal corresponding to a light intensity distribution in the first direction and the second direction. In the optical communication device according to claim 3 or 4,
The light receiving means, the light receiving surface, by at least one boundary line extending in a third direction and at least one boundary line extending in a fourth direction non-parallel to the third direction, An optical communication device, wherein the optical communication device is divided into N × M (where N and M are integers of 2 or more) lattice-shaped light receiving areas. The optical communication device according to claim 5,
The optical communication device, wherein both N and M are 2. The optical communication device according to claim 6,
The light receiving unit outputs the signal for each of a predetermined number of the light receiving areas that have received the reflected light,
The optical communication system, wherein the control unit controls the driving of the moving unit so that a ratio of each output of the light receiving area is substantially equal to a ratio of each output of the light receiving area corresponding to the reference distribution. apparatus. The optical communication device according to claim 7,
The control means drives and controls the moving means such that the output of the four light receiving areas adjacent to each other on which the reflected light has entered and the ratio of each output of the light receiving areas corresponding to the reference distribution substantially match. An optical communication device, comprising: The optical communication device according to claim 8,
The optical communication device according to claim 1, wherein the light receiving unit is provided such that the third direction corresponds to the first direction, and the fourth direction corresponds to the second direction. The optical communication device according to claim 9, wherein the control unit includes:
The output ratio between the two light receiving areas on one side and the two light receiving areas on the other side has a predetermined relationship based on a boundary line extending in the third direction among the four light receiving areas. While driving the moving means to move the spot in the second direction so as to have,
The output ratio between the two light receiving areas on one side and the two light receiving areas on the other side of the four light receiving areas is based on a boundary extending in the fourth direction. An optical communication device, wherein the light intensity distribution is made to coincide with the reference distribution by driving and controlling the moving means to move the spot in the first direction. The optical communication device according to claim 8,
The light-receiving means may be configured such that the third direction and the fourth direction each have an angle substantially equal to the angle between the movement locus of the spot in the first direction and the movement locus of the spot in the second direction. An optical communication device, wherein the optical communication device is arranged so as to be separated. The optical communication device according to claim 11, wherein the control unit includes:
Driving control of the moving means so that an output ratio of two light receiving areas arranged diagonally with respect to a sensor center where the two boundary lines intersect has a predetermined relationship among the four light receiving areas. Moving the spot in the first direction and the second direction to match the light intensity distribution with the reference distribution. In the optical communication device according to claim 10 or 12,
In the optical communication device, the predetermined relationship is that the output difference is zero. The optical communication device according to any one of claims 1 to 13,
The optical communication device according to claim 1, wherein a step of a predetermined dimension is formed between the core and the clad at the incident end face. The optical communication device according to claim 14,
The optical communication device according to claim 1, wherein the predetermined dimension is such that the reflected light is diffracted by the step.   The optical communication device according to claim 15, wherein the predetermined dimension is set to a value smaller than approximately λ / (4n), where λ is the wavelength of the light and n is the refractive index of the medium.   The optical communication device according to claim 16, wherein the predetermined dimension is set to approximately λ / (8n). The optical communication device according to any one of claims 14 to 17, wherein the incident end face is:
The optical communication device, wherein the core protrudes from the clad. The optical communication device according to any one of claims 14 to 17, wherein the incident end face is:
The optical communication device, wherein the core is recessed from the clad. In the optical communication device according to claim 18 or 19, the incident end face is:
An optical communication device, wherein an end surface of the core and an end surface of the clad are in a substantially parallel relationship. The optical communication device according to any one of claims 1 to 20, wherein the moving means comprises:
An optical communication device, wherein the spot is moved in the first direction and the second direction by driving the condenser lens. The optical communication device according to any one of claims 1 to 20, wherein the moving means comprises:
An optical communication device, wherein the spot is moved in the first direction and the second direction by driving the light source. The optical communication device according to any one of claims 1 to 20, wherein the moving means comprises:
An optical communication device, comprising: a transmission-type deflecting member disposed between a condenser lens and an end face of a fiber and deflecting an incident light beam in the first direction and the second direction.   24. The optical communication device according to claim 23, wherein the transmission type deflection member is a vertex angle variable prism that can change a vertex angle. The optical communication device according to any one of claims 1 to 24,
The light source, the condenser lens, and the optical fiber are arranged on a common optical axis,
An optical communication device, further comprising an optical path branching unit that deflects the reflected light returning on the same optical path as the optical path from the light source toward the incident end face in a direction deviating from the optical path and guides the reflected light to the light receiving unit. The optical communication device according to claim 25,
The optical communication device, wherein the optical path branching unit has a polarization beam splitter and a quarter-wave plate. A light source for emitting light modulated by information;
An optical fiber in which a step of a predetermined dimension is formed in a core and a clad on an incident end face where the light is incident,
Moving means for moving the spot formed on the incident end face by the light on the incident end face;
Light receiving means for receiving reflected light from the incident end face,
An optical communication device, comprising: a control unit that drives and controls the moving unit based on the light received by the light receiving unit such that an incident position of the light on the incident end surface coincides with a predetermined position.   28. The optical communication device according to claim 27, wherein the predetermined dimension is such that the light incident on the incident end face is diffracted by the step. In the optical communication device according to claim 27 or claim 28,
The light receiving unit outputs a signal corresponding to a light intensity distribution of the reflected light to the control unit,
The optical communication device according to claim 1, wherein the control unit drives and controls the moving unit so that the signal substantially matches a signal corresponding to a light intensity distribution when the light is incident on a predetermined position. The optical communication device according to any one of claims 27 to 29,
The optical communication device according to claim 1, wherein the spot has a diameter larger than a diameter of the core and smaller than a diameter of the clad.

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