JP2004157360A - Optical fiber - Google Patents

Abstract

An optical device that is always suitable for a configuration of an optical communication device capable of maintaining a high performance even when there is an environmental change such as a change in a mechanical condition such as a vibration by executing a positioning process for light from an LD at all times. Providing fiber.
An optical fiber has a configuration in which at least a part of a clad at a predetermined end face is coated with a material having a higher reflectance than the clad. The optical fiber has a configuration in which a predetermined amount of step is formed between a core and a clad at a predetermined end face. .
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical fiber used for an optical communication device.
[0002]
[Prior art]
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) that brings optical fiber communication into a subscriber's home 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.
[0003]
In the optical communication module as described above, since the signal light from the LD is transmitted and received via the optical fiber, it is necessary to make the light enter the approximate center of the core. In other words, the LD must be positioned with high accuracy with respect to an optical fiber having a core diameter of several μm. The conventional positioning method detects the amount of light emitted from an optical fiber, and determines that light from the LD is incident on the approximate center of the core when the amount of light reaches a predetermined level or more. Usually, these optical components are firmly fixed by welding or using an adhesive after positioning.
[0004]
However, in the above-described conventional positioning method, when the amount of emitted light does not reach a predetermined level, it is determined in which direction and how much the incident position of the light from the LD is shifted with respect to the center of the core. I can't. Therefore, the relative position between the incident position of the light from the LD and the center of the core of the optical fiber must be repeated by trial and error until the light amount of the light emitted from the optical fiber reaches a predetermined level, which is extremely troublesome. It took a lot of time.
[0005]
Further, even if the optical communication module is configured by positioning and fixing the mutual positions of the components using an adhesive after the positioning is completed by the above-described positioning method, 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.
[0006]
In order to solve the above problem, it is desired to actually detect the incident position of the light from the LD on the optical fiber incident surface and to position the incident position so that the incident position coincides with the center of the core. Then, the optical communication module may be configured to always perform the positioning process regarding the light from the LD. For this purpose, the incident position of the light from the LD on the optical fiber incident surface can be detected with high accuracy, and the incident surface is processed so that the boundary between the core and the clad on the optical fiber incident surface can be clearly identified. Must.
[0007]
Here, conventionally, the contents disclosed in Patent Literature 1 and Patent Literature 2 below have been known as optical fibers with processed end faces.
[0008]
[Patent Document 1]
JP-A-5-107428 [Patent Document 2]
JP 2001-305382 A
The above Patent Documents 1 and 2 aim at improving the light propagation efficiency when optically connecting an optical fiber to another optical member such as an optical waveguide. Therefore, each of Patent Documents 1 and 2 discloses a processing method of forming a core end itself on one surface of an optical fiber into a convex shape, or forming a convex member (lens) near the core end. That is, the optical fiber processed by the processing method has a lens processed on the exit surface located opposite to another optical member.
[0010]
However, when the surface formed by processing the core itself into a convex shape is provided as the incident surface, light is scattered at the convex portion, and the incident position of the light from the LD cannot be detected with high accuracy. Further, in an optical fiber in which a convex member is formed in the vicinity of the core, it is impossible to clearly distinguish the boundary between the core and the clad. Therefore, the optical fibers described in Patent Documents 1 and 2 cannot achieve highly accurate position detection and positioning.
[0011]
[Problems to be solved by the invention]
In view of the above circumstances, the present invention always performs a positioning process for 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. An object of the present invention is to provide an optical fiber optimal for a configuration of a communication device.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, an optical fiber according to the present invention is characterized in that at least a part of a clad at a predetermined end face is coated with a material having a higher reflectance than the clad.
[0013]
According to the first aspect of the present invention, it is possible to provide an optical fiber in which the reflectance is increased only in a region other than the core without obstructing light incident on the core on the incident surface. Therefore, if the optical fiber is used, it is possible to perform negative feedback control based on the amount of light detected constantly or periodically so that the position on the incident surface (incident surface) of the light from the light source is directed toward the core center. An apparatus can be provided. Since such an optical communication device can always execute the positioning process, it can maintain high performance even when there is an environmental change or a change with time.
[0014]
The region coated with a material having a high reflectivity may be the entire region of the clad, or may be a donut-shaped region near the core and surrounding the core. Further, as a material having a high reflectance, a metal material such as Al and Cr is preferable (claim 3).
[0015]
An optical fiber according to a fourth aspect is characterized in that a predetermined amount of step is formed between the core and the clad at a predetermined end face. Specifically, the end face may be processed so that the core protrudes in a direction perpendicular to the predetermined end face from the clad (claim 5), or the core may extend in a direction perpendicular to the predetermined end face than the clad. It may be processed so as to be depressed (claim 6). Such a step can be formed on the first end face by a photolithography technique or a coating technique.
[0016]
According to the optical fiber of the fourth aspect, it is possible to provide an optical fiber in which the intensity distribution of the first-order diffracted light of the reflected light generated by the step of the incident surface is clearly shown. Therefore, if the optical fiber is used, the negative feedback is performed so that the position of the light from the light source on the incident surface (incident surface) is directed toward the center of the core based on the light intensity distribution of the reflected light that is constantly or periodically detected. An optical communication device that can be controlled is provided. Since such an optical communication device can always execute the positioning process, it can maintain high performance even when there is an environmental change or a change with time.
[0017]
In order to make it possible to detect the light intensity distribution with higher accuracy, it is preferable that the core surface and the clad surface have a substantially parallel relationship at a predetermined end surface (claim 7).
[0018]
The predetermined amount defining the step has a value smaller than λ / (4n), where λ is the wavelength of light from the light source of the optical communication device and the refractive index of the medium is (claim 8). More preferably, the intensity distribution of the first-order diffracted light used for the control is set to λ / (8n) where the diffracted light (reflected light from the incident surface) maintains a constant light intensity for detection and the intensity distribution of the first-order diffracted light is easily detected ( Claim 9).
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows an optical fiber 3A of the first embodiment. As shown in FIG. 1, the optical fiber 3 </ b> A according to the first embodiment includes a clad 32 and a core 33 and has an end face 31. The optical fiber 3A is incorporated in the optical communication device so that the light emitted from the LD enters the end face 31. Therefore, in the following text, the end surface 31 is described as the incident surface 31. The same applies to the optical fiber 3B shown in the second embodiment described below and the optical fiber 3C shown in the third embodiment.
[0020]
On the incident surface 31 of the optical fiber 3A, a mirror surface m is vapor-deposited on substantially the entire area of the clad 32. As a method of forming the mirror surface m only on the clad 32, a metal material such as Cr, Au, or Al is deposited while the core 33 is covered with the resist, and then the remaining resist is deposited on the resist. The core 33 may be exposed by peeling off the entrance surface 31 together with the mirror surface.
[0021]
If the optical fiber 3A processed in this way is used, it is possible to increase the reflectance of the incident surface 31 as compared with a conventional optical fiber in which no processing is performed on the clad 32. Therefore, if the optical fiber 3A is arranged in the optical communication module with the incident surface 31 as the incident surface of the light from the LD, it is possible to detect the amount of light incident on and reflected by the mirror surface m (cladding 32). Become. If the incident position of the light on the incident surface (incident surface 31) is subjected to negative feedback control based on the detected light amount, the incident position can be accurately aligned with the center of the core 33.
[0022]
The above is the optical fiber 3A of the first embodiment. Note that, depending on the specifications of the optical communication device incorporating the processed optical fiber, more specifically, the specifications of the position detection system in the device, the mirror surface m does not necessarily need to be provided over the entire area of the core 33, and may be provided near the core 33. In some cases, it is sufficient that only the information be given. In such a case, if the core 33 is covered with the resist and Cr or the like is vapor-deposited only in the core and the vicinity thereof, only the clad 32 near the core 33 as shown in FIG. An optical fiber 3A ′ having a donut-shaped mirror surface region surrounding the core 33 can be provided.
[0023]
In the optical fiber 3A of the first embodiment, the reflectance of the incident surface 31 is increased by forming the mirror surface m. However, instead of depositing a metal such as Cr on the optical fiber 3A, it is also possible to increase the reflectance of the incident surface 31 by coating a material having a higher reflectance than at least the cladding.
[0024]
FIG. 3 shows an optical fiber 3B of the second embodiment. As shown in FIG. 3, in the optical fiber 3B, the core 33 protrudes by a predetermined amount in the optical axis direction of the optical fiber with respect to the surface of the cladding 32 on the incident surface 31, and the protruding surface of the core 33 and the surface of the cladding 32 Are processed using the photolithography technology so that the light beams are substantially parallel to each other. The predetermined amount is set to a value smaller than λ / (4n) so that a diffraction phenomenon occurs when light enters both the protruding surface of the core 33 and the surface of the cladding 32. Here, λ is the wavelength of the incident light, and n is the refractive index of the medium. In the present embodiment, the predetermined amount is set to λ / 8 in order to assume that the medium is air.
[0025]
The optical fiber 3B having the incident surface 31 having the above-described shape is disposed in the optical communication module in a state where the incident surface 31 is an incident surface of light from the LD. Then, when light from the LD is made incident on the incident surface 31, reflected diffracted light having different intensities, such as zero-order light and primary light, is obtained. If the incident position is subjected to negative feedback control based on the light intensity distribution obtained by detecting the reflected light, the incident position of the light on the incident surface 31 can be adjusted to the center of the core 33 with high accuracy.
[0026]
The position detection based on the light intensity distribution of the light on the incident surface as described above cannot be executed by an optical communication module using a conventional optical fiber without any processing. Further, in an optical fiber in which a lens is integrally formed by the processing methods of Patent Documents 1 and 2, the core (near the core) on the processed surface (exit surface) has a convex lens shape. For this reason, even if the processed surface is provided in the optical communication module as the incident surface, the above-described diffraction effect cannot be effectively obtained, so that highly accurate position detection and positioning based on the light intensity distribution of light are also performed. Can not do it. More specifically, since the optical fiber disclosed in Patent Literature 1 is manufactured using the difference in melting between the clad and the core, the core that should not be melted is also melted. Therefore, the optical fiber has poor optical transmission efficiency and is not suitable for ordinary optical communication. In addition, the optical fiber disclosed in Patent Literature 2 not only adds cost to the manufacturing method, but also has a disadvantage that the yield is poor.
[0027]
The above is the description of the optical fiber 3B of the second embodiment. FIG. 4 shows an optical fiber 3C according to the third embodiment. As shown in FIG. 4, the optical fiber 3 </ b> C has a configuration in which a core 33 is recessed by a predetermined amount in the optical axis direction of the optical fiber with respect to the surface of the clad 32 on the incident surface 31. It is processed using a photolithography technique so that the surface is substantially parallel. The predetermined amount is preferably set to a value smaller than λ / 4, as in the second embodiment. The optical fiber 3C of the present embodiment is set to λ / 8 similarly to the optical fiber 3B.
[0028]
The optical fiber 3B of the second embodiment and the optical fiber 3C of the third embodiment form a step between the core 33 and the clad 32 by etching. However, a step can be formed even in a step other than the etching step. For example, in the case of the optical fiber 3B that has undergone the exposure / development step, the region from which the resist has been removed, that is, the clad 32 is coated with a material having a relatively high reflectance such as the metal material used in the first embodiment. Steps can also be formed. In the case of the optical fiber 3C which has been subjected to the exposure / development step, the area where the resist is removed, that is, the core 33 is coated with the same material as the core 33 or a material having a refractive index substantially the same as that of the area. By doing so, it is also possible to form a step. The coating thickness is a step difference, that is, λ / 8. Then, by stripping the resist (lift-off technique), it is possible to provide the optical fibers 3B and 3C having steps between the core 33 and the clad 32 as shown in FIG. 3 or FIG.
[0029]
The optical fiber 3B and the optical fiber 3C both have the incident surface 31 orthogonal to the optical axis direction of the optical fiber. Therefore, the projecting direction of the core 33 shown in FIG. 3 and the concave direction of the core 33 shown in FIG. However, the optical fiber 3B can also be formed so that the incident surface 31 is not orthogonal to the optical axis direction in relation to the other components of the optical communication module on which the optical fiber 3B is mounted. FIG. 5 is an enlarged view of the vicinity of the incident surface 31 of the optical fiber 3D having the incident surface 31 inclined obliquely to the optical axis direction. As shown in FIG. 5, in the case of an optical fiber 3D having an incident surface 31 inclined obliquely to the optical axis direction, a direction perpendicular to the incident surface 31 (broken line in FIG. 5) and an optical axis direction (dashed line in FIG. 5) ) Does not match. As described above, in each of the above embodiments, in the optical fiber having the steps such as the optical fibers 3B and 3C, the direction in which the core 33 projects (the direction in which the core 33 protrudes) is the optical axis direction.
[0030]
By mounting the optical fibers 3A, 3B, and 3C processed as described above on, for example, an optical communication module as described below, the optical communication module changes the incident position of the light from the LD on the incident surface 31 to the core 33. , It is possible to always execute the positioning process for adjusting to the center of the image with high accuracy.
[0031]
FIG. 6 is a diagram illustrating a configuration of the optical communication module 10 including the optical fiber 3A. 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 fiber 3A shown in FIG. 6 has an incident surface 31 inclined obliquely to the optical axis direction, similarly to the optical fiber 3D shown in FIG.
[0032]
The laser LD, which is the light source of the signal light for transmission, is a surface emitting laser and is configured to be modulated by information for transmission. The laser LD, the first condenser lens 2, and the optical fiber 3A are arranged on a common optical axis. The optical fiber 3 </ b> A is disposed such that the incident surface 31 faces the first condenser lens 2. That is, the incident surface 31 corresponds to a surface on which light from the LD is incident. The transmission light having a wavelength of 1.3 μm emitted from the laser LD is collected by the first condenser lens 2 toward the incident surface (incident surface) 31 of the optical fiber 3. The collected transmission light is transmitted to an optical communication module (not shown) on the receiving side via an optical fiber.
[0033]
Hereinafter, the positioning process of the signal light for transmission incident on the incident surface 31 of the optical fiber 3A in the optical communication module 10 will be outlined. The optical communication module 10 according to the present embodiment includes the laser LD, the first condenser lens 2 and the optical fiber 3A, the second condenser lens 4, the photodetector 5, the controller 6, and the actuator 7.
[0034]
As described above, the light emitted by the laser LD enters the incident surface 31 of the optical fiber 3A via the first condenser lens 2. The light reflected by the incident surface 31 enters the second condenser lens 4. The second condenser lens 4 condenses the reflected light and guides the reflected light to the photodetector 5. The photodetector 5 is provided at a position conjugate with the incident surface 31. That is, the reflected light reflected at the center of the optical fiber is incident on substantially the center of the light receiving surface of the photodetector 5.
[0035]
The photodetector 5 is a four-division photodiode in which the light receiving surface is divided into four areas by two boundary lines extending orthogonally to each other at the center of the light receiving surface. The photodetector 5 transmits a change in the amount of incident light to the controller 6 as light amount data for each area.
[0036]
Strictly speaking, the reflectance of the core 33 is lower than the reflectance of the cladding 32 (mirror surface m). Therefore, the amount of light received by the light reflected by the core 33 may be too small to be accurately detected. Therefore, the photodetector 5 of the present embodiment increases the sensitivity of the light receiving surface in a region where the light reflected by the core 33 is incident so that the amount of light reflected by the core 33 can be detected with high accuracy.
[0037]
When receiving the light amount data of each area, the controller 6 performs negative feedback control based on each light amount data so that the light from the LD enters the center of the core 33. Specifically, the controller 6 drives the first condenser lens 2 via the actuator 7 until the light amount difference of the light incident on each area disappears, and the incident position of the light from the light source on the incident surface 31. To move. When there is no difference in the amount of light incident on each area, the light from the LD is incident on the center position of the core 33.
[0038]
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, since the photodetector 5 always receives the light from the LD during the optical communication, the controller 6 performs the positioning processing based on the light amount data constantly transmitted from the photodetector 5 so that the light amount difference in each area is eliminated. Can be performed.
[0039]
The above is the description of the positioning process of the optical communication module 10 equipped with the optical fiber 3A. In addition, the configuration of the optical communication module 10 can execute the same positioning processing as described above by mounting an optical fiber 3B or an optical fiber 3C instead of the optical fiber 3A. However, when the optical fiber 3B or the optical fiber 3C is used, the controller 6 does not perform the negative feedback control so as to eliminate the light quantity difference in each area on the light receiving surface. The controller 6 performs negative feedback control such that the light intensity distribution of the light reflected on the incident surface 31 matches a predetermined distribution obtained when light from the LD enters the center of the core 33. When the optical fiber 3B or the optical fiber 3C is used, the photodetector 5 is far from being disposed at a position conjugate with the incident surface 31.
[0040]
【The invention's effect】
As described above, according to the present invention, when mounted on an optical communication device, the surface on the side where light from the LD is incident is processed to enable highly accurate positioning processing regarding the incident position of the light. An optical fiber is provided. In other words, according to the present invention, by performing the positioning process for the light from the LD at all times, an optical fiber optimal for the configuration of an optical communication device capable of maintaining high performance even when there is an environmental change or a temporal change is provided. Can be provided.
[Brief description of the drawings]
FIG. 1 shows an optical fiber according to a first embodiment.
FIG. 2 shows an optical fiber according to a second embodiment.
FIG. 3 shows an optical fiber according to a third embodiment.
FIG. 4 shows an optical fiber according to a fourth embodiment.
FIG. 5 shows an optical fiber according to a fourth embodiment.
FIG. 6 is a diagram illustrating a configuration of an optical communication module equipped with an optical fiber processed by the processing method of the first embodiment.
[Explanation of symbols]
3A, 3B, 3C, 3D Optical fiber 31 Incident surface 32 Cladding 33 Core m Mirror surface 10 Optical communication module

Claims (9)

An optical fiber, wherein at least a part of the cladding at a predetermined end face is coated with a material having a higher reflectance than the cladding. The optical fiber according to claim 1,
The optical fiber according to claim 1, wherein the at least a partial region is a donut-shaped region near the core and surrounding the core. In the optical fiber according to claim 1 or claim 2,
The optical fiber, wherein the material is a metal material. An optical fiber, wherein a predetermined amount of step is formed between a core and a clad at a predetermined end face. The optical fiber according to claim 4,
The optical fiber, wherein the core protrudes from the predetermined end face in the optical axis direction of the optical fiber from the clad. The optical fiber according to claim 4,
The optical fiber, wherein the core is recessed from the predetermined end face in the optical axis direction of the optical fiber with respect to the clad. In the optical fiber according to any one of claims 4 to 6,
An optical fiber, wherein the surface of the core and the surface of the clad are substantially parallel to each other. 5. The predetermined amount is set to a value smaller than approximately λ / (4n), where λ is the wavelength of light used in the device into which the optical fiber is incorporated, and n is the refractive index of the medium. Item 8. An optical fiber according to any one of Items 7. The optical fiber according to claim 8, wherein the predetermined amount is set to approximately λ / (8n).

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