JP2005234078A - Manufacturing method of optical fiber depolarizer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the manufacturing method of an optical fiber depolarizer capable of converting polarized light into non-polarized light by releasing the polarized state of light easily while performing depolarization to entire polarized states of incident light in an optical fiber whose length is short. <P>SOLUTION: In this manufacturing method, polarized light is made incident on the optical fiber from one end of the optical fiber and ion implantation is performed to the core part of the optical fiber with respect to a plurality of prescribed positions from a plurality of prescribed directions respectively so that depolarization effects become the largest while observing the polarization degree of outgoing light from the other end of the optical fiber. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method of manufacturing an optical fiber depolarizer that converts polarized light into non-polarized light.

  A depolarizer is an element that converts polarized light into non-polarized light, and is used to remove the polarization dependence of an optical device. Since there are many optical communication devices and sensors using optical fibers whose characteristics depend on the polarization of light propagating in the optical fiber, it is necessary to control the polarization state. For example, in an optical fiber Raman amplifier, its operating characteristics depend on the polarization state of pumping light. Therefore, the excitation light is depolarized by the depolarizer and then incident on the optical fiber Raman amplifier.

  A conventional optical fiber depolarizer is a Riot depolarizer that connects two polarization-maintaining optical fibers of length L and 2L so that the birefringence directions of the polarization-maintaining optical fibers are inclined by 45 degrees. . However, the length L in this depolarizer is about several tens of meters, and there is a problem that the storage space becomes large. In addition, a depolarizer using a birefringent crystal has been devised for a Fabry-Perot laser diode, but this depolarizer is effective only for a Fabry-Perot laser diode and has low versatility.

Therefore, we invented and disclosed a method for fabricating a depolarizer by implanting ions into the core of the optical fiber from the outside of the optical fiber. However, in the optical fiber type depolarizer manufactured by this method, the depolarization characteristic (depolarization characteristic) depends largely on the polarization state of the incident light, and corresponds to all the polarization states of the incident light. There is a problem that it cannot be converted into non-polarized light.
Japanese Patent Laid-Open No. 2004-12538

  In view of the above problems, the problem of the present invention is that light in a short length of optical fiber can be easily canceled with respect to all polarization states of incident light and converted to non-polarized light. It is to provide a method of manufacturing a fiber depolarizer.

  In the present invention, in order to solve the above problems, in the method according to claim 1, polarized light is incident on one end of an optical fiber ion-implanted into a core portion, and the other end of the optical fiber and the core The second optical fiber is rotated while contacting one end of the second optical fiber ion-implanted into the portion and observing the degree of polarization of the outgoing light from the other end of the second optical fiber, This is a method of manufacturing an optical fiber depolarizer in which both optical fibers are fused where the depolarization effect is greatest. With this manufacturing method, it is possible to manufacture an optical fiber depolarizer that can easily obtain substantially unpolarized outgoing light with respect to all polarization states of incident light.

  Further, the method according to claim 2 is a method of manufacturing an optical fiber depolarizer in which the above-described method is sequentially repeated and three or more optical fibers are fused. By this manufacturing method, the depolarization characteristic is further improved, and an optical fiber depolarizer capable of effectively obtaining the non-polarized outgoing light with respect to all the polarization states of the incident light can be manufactured.

  Further, in the method according to the third aspect, the condition is such that the ions stop at least at the core portion from a plurality of predetermined directions at a plurality of predetermined positions of the optical fiber, instead of fusing the optical fibers. Is a method of manufacturing an optical fiber depolarizer that performs ion implantation. With this manufacturing method, an optical fiber depolarizer that obtains output light that is substantially non-polarized with respect to all the polarization states of incident light can be manufactured more easily.

  In the method according to claim 4, the polarized light is incident from one end of the optical fiber, and the depolarization effect is maximized while observing the degree of polarization of the outgoing light from the other end of the optical fiber. This is a method for manufacturing an optical fiber depolarizer in which ions are implanted into a core portion of an optical fiber from a plurality of predetermined directions respectively at a plurality of predetermined positions. By this manufacturing method, the depolarization characteristic is further improved, and an optical fiber depolarizer that can effectively obtain the output light in the non-polarized state with respect to all the polarization states of the incident light can be easily manufactured.

  According to the method of manufacturing an optical fiber depolarizer according to the present invention, in a short length of optical fiber, the polarization state of light is easily canceled with respect to all polarization states of incident light and converted to non-polarized light. There exists an effect which can manufacture an optical fiber depolarizer by a simple method.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view of an optical fiber showing a state in which ions are implanted into the core portion of the optical fiber from one direction. In FIG. 1, 1 is a part called a core, which is a part through which light passes. 2 is called a clad, and protects the core 1 and at the same time plays a role of confining light passing through the core in the core made of a material having a refractive index smaller than that of the core 1 portion. For example, when ion implantation is performed from above on an optical fiber having such a structure, the position where the implanted ions 3 stop is an arc as shown in FIG. For example, when light polarized in an oblique direction is incident on such an optical fiber, outgoing light in a non-polarized state can be obtained. However, if light polarized in a horizontal direction or light polarized in a vertical direction is incident, there is no light. There is a phenomenon that outgoing light in a polarized state cannot be obtained.

Experimental data for the above phenomenon is shown below. The depolarization effect was measured using a light source of a 1480 nm superluminescent diode with respect to an optical fiber having a length of 50 cm in which hydrogen ions of 1 × 10 ¹⁵ ions / cm ² were implanted into the core. Here, the degree of polarization (DOP) of the incident light is 100%. At this time, the degree of polarization of the light transmitted through the ion-implanted optical fiber depends on the polarization state of the incident light. When the most depolarization effect is observed, the DOP decreases to 2.4%, but there is no depolarization effect. So DOP was 95%, which was almost ineffective. Hereinafter, the polarization degree in the state where the depolarization effect is most seen is called MinDOP, and the polarization degree in the state where the depolarization effect is hardly seen is called MaxDOP.

  A preferred first embodiment for the present invention is shown in FIG. As shown in FIG. 2, prepare two optical fibers 10 and 11 having a length of 50 cm, which are ion-implanted under the same conditions as described above, and set these two in a rotary fusion machine. While rotating with respect to one optical fiber, light was incident from one optical fiber, and the two optical fibers were fused at an angle at which MaxDOP of the emitted light was the smallest. As a result, a depolarizer with MinDOP = 0.29% and MaxDOP = 29% could be obtained. In this way, an optical fiber depolarizer is obtained that has a length of only 1 m and obtains substantially unpolarized outgoing light by fusing two optical fibers having a length of 50 cm where the depolarization effect is greatest. I was able to.

  Furthermore, another ion-implanted optical fiber was fused to this depolarizer in the same process as described above, whereby a depolarizer with MinDOP = 0.56% and MaxDOP = 8.58% could be obtained. In this case, the length of the depolarizer was 1.5 m, and a depolarizer having almost the same effect could be obtained with a length of 1/10 or less of the conventional riot depolarizer. In this way, if the number of optical fibers is increased, a higher-performance depolarizer can be easily manufactured.

  Here, the optical fibers 10 and 11 do not need to be ion-implanted throughout the length of the optical fiber. A depolarizer is manufactured in the same process as described above, using an optical fiber with a total length of 70 cm, ion-implanted only in the central part 50 cm under the same conditions as above, but not ion-implanted in the 10 cm ends. I tried to get the exact same result.

  Furthermore, a preferred second embodiment of the present invention is shown in FIG. In the first embodiment, a depolarizer is obtained by fusing a plurality of ion-implanted optical fibers while observing the emitted light with respect to the incident light so as to have an optimum angle. In the second preferred embodiment, a method of manufacturing a depolarizer more easily without the step of fusing is described.

  In the ion implantation method, as shown in FIG. 3, the ion implantation direction can be changed during ion implantation. Actually, the injection direction is changed by rotating an optical fiber which is an injection target. Therefore, a depolarizer equivalent to the depolarizer obtained by fusing the above three ion-implanted optical fibers can be formed in one optical fiber by changing the ion implantation direction.

  In FIG. 3, in the next process B in which ion implantation is performed under the condition that ions are stopped at the part of the core 1 at a predetermined position (a) in the process A, the optical fiber is moved to a predetermined length in the length direction ( In this embodiment, it is slid and rotated to a position (b) by a predetermined angle, and ions are implanted under the condition that the ions stop at the core 1 portion. Further, in step C, the optical fiber is slid again in the length direction by a predetermined length (in this embodiment, 50 cm) and rotated to a position (c) by a predetermined angle, so that the ions enter the core 1 portion. Ions are implanted under conditions to stop. Here, the angle change in the ion implantation direction can be set to an appropriate value obtained from the first embodiment. Of course, the predetermined position and the predetermined angle can be more than three and a plurality of positions. Also, the predetermined length can be freely changed. In FIG. 3, the predetermined positions (a), (b), and (c) are drawn close to each other, but these predetermined positions (a), (b), (b), and ( It may be separated during c).

  Here, any ions may be implanted. The ions to be implanted may be, for example, hydrogen ions, single helium ion ions, molecular ions, or cluster ions. However, since it is necessary for the implanted ions to pass through the clad 2 and reach the core 1 to stop, the practical level of the applied voltage for acceleration and the depth of penetration of ions into the material can be reduced. In consideration, hydrogen ions and helium ions are suitable. Further, the acceleration voltage is practically 10 MeV or less. Further, in FIG. 1, the ions 3 are implanted almost at the center of the core 1, but this may be within the core 1 portion and is not necessarily at the center of the core 1. In the first embodiment, a plurality of optical fibers into which ions are implanted are used. In each optical fiber, the position of ions 3 implanted in the core 1 portion, that is, the depth at which ions are implanted. Similarly, in Example 2, ion implantation is performed at a plurality of locations, but at this time, the positions of the ions 3 implanted within the core 1 are different at each location. May be.

  The length of the ion-implanted portion is determined by the relationship with the ion implantation density. Generally, to obtain the same effect, the larger the ion implantation density, the shorter the length of the ion-implanted portion. There is a good relationship.

  A preferred third embodiment is a method of controlling the ion implantation density while observing outgoing light with respect to incident light in the second embodiment. In this specific method, as shown in FIG. 3, predetermined positions (a), (b), (c) and a predetermined angle are determined in advance, and the ion implantation density is observed while observing the outgoing light with respect to the incident light. This is a method for optimally controlling. Of course, in this case as well, as in the second embodiment, the predetermined position and the predetermined angle can be more than three and a plurality of positions. Also, the predetermined length can be freely changed.

  The present invention should not be limited to this embodiment, and those that can achieve equivalent effects by replacement or modification by those skilled in the art based on substantially equivalent ideas shall also fall within the scope of the present invention.

Sectional view of an ion-implanted optical fiber. The figure explaining the 1st Example by this invention. The figure explaining the 2nd Example by this invention.

Explanation of symbols

1 core 2 clad 3 implanted ions
10 ion-implanted first optical fiber
11 Ion-implanted second optical fiber

Claims (4)

  Polarized light is incident on one end of the optical fiber ion-implanted into the core portion, the other end of the optical fiber is brought into contact with one end of the second optical fiber ion-implanted into the core portion, The second optical fiber is rotated while observing the degree of polarization of the outgoing light from the other end of the optical fiber of No. 2, and the two optical fibers are fused at the place where the depolarization effect is greatest. An optical fiber depolarizer manufacturing method.   An optical fiber characterized in that three or more optical fibers ion-implanted into a core portion are used, and the method according to claim 1 is sequentially repeated to fuse the three or more optical fibers. A method of manufacturing a depolarizer.   A method of manufacturing an optical fiber depolarizer, characterized in that ion implantation is performed at a plurality of predetermined positions of an optical fiber from a plurality of predetermined directions under such conditions that ions stop at least in a core portion. 4. The method according to claim 3, wherein polarized light is incident from one end of the optical fiber and the depolarization effect is maximized while observing the degree of polarization of the outgoing light from the other end of the optical fiber. A method of manufacturing an optical fiber depolarizer, characterized by performing ion implantation on a fiber.

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