Manufacturing method for multicore optical fiber gain equalization components, multicore optical fiber manufactured by the same manufacturing method, and multicore optical fiber gain equalization component manufacturing system

Abstract

To form a Bragg grating by which the optical characteristics of each core become uniform, in a multicore optical fiber.SOLUTION: A manufacturing method of a multicore optical fiber gain equalization component for forming a gain equalization filter in a multicore optical fiber having multiple cores includes the steps of: fixing a multicore optical fiber on a jig; installing a phase mask in parallel to an axial direction of the multicore optical fiber; passing the phase mask, radiating ultraviolet laser light, and forming a Bragg grating, in each core of the multicore optical fiber; rotating the multicore optical fiber by using a central axis of the multicore optical fiber as the center; and parallel-moving the multicore optical fiber in a central axis direction of the multicore optical fiber.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a multi-core optical fiber gain equalization component that forms a gain equalization filter on a multi-core fiber having a plurality of cores, a multi-core optical fiber manufactured by the manufacturing method, and a multi-core optical fiber gain equalization component manufacturing system.

Background Art

[0002] In recent years, as one of the technologies to break through the physical limit of the transmission capacity in single-mode optical fibers (SMF: Single-Mode Fiber), space-division multiplexing (SDM: Space-Division Multiplexing) communication technology has been researched and developed. Among SDM communication technologies, there is a multi-core optical fiber (MCF: Multi-Core Fiber) that provides a plurality of cores through which light propagates in an optical fiber.

[0003] Multi-core optical fibers are actively researched and developed as an enabling technology for increasing the transmission capacity. It has been studied to apply the technologies that have been used in conventional optical fiber communication using single-mode optical fibers to multi-core optical fibers as well.

[0004] In an optical fiber communication system, it is common to use an optical amplifier to extend the transmission distance. For the gain equalization filter used as a component for extending the transmission distance, there are a spatial type using a dielectric multilayer film (dielectric multilayer film filter) and a fiber type that directly forms a Bragg grading in the core of an optical fiber (Bragg grading filter). Non-Patent Document 1 discloses a technique of forming a Bragg grading in each core of a multi-core optical fiber and using it as a gain equalization filter for an amplifier.

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

[0006] A fiber-optic gain equalization filter is formed within a core by irradiating it with optical pulses and writing in a grading designed to equalize the gain. To minimize the refraction of the irradiated light when irradiating the core with optical pulses, the area around the optical fiber is filled with matched oil, and the irradiated light travels basically in a straight line through the optical fiber with little influence from the refractive index distribution of the fiber.

[0007] Therefore, by arranging multicore optical fibers so that multiple cores do not overlap in the direction of light pulse propagation and writing grading to each core, the difference in the light irradiation pattern in each core can be minimized, and as a result, the difference in optical characteristics between each core can be minimized. However, since the distance between each core and the light source that irradiates it with light pulses is different for each, it is difficult to completely eliminate the difference in optical characteristics between each core. Also, as the number of cores in a multicore optical fiber increases, it becomes easier for light to overlap with other cores during irradiation, making uniform light irradiation difficult. Non-patent document 1 does not consider the uniformity of optical characteristics between each core due to light irradiation.

[0008] This invention has been made in view of these circumstances, and aims to provide a method for manufacturing a multicore optical fiber gain equalization component that minimizes the difference in optical characteristics between each core of a multicore optical fiber, a multicore optical fiber manufactured by the same manufacturing method, and a multicore optical fiber gain equalization component manufacturing system. [Means for solving the problem]

[0009] (1) In order to achieve the above objective, the present invention employs the following means. That is, the method for manufacturing a multicore optical fiber gain equalization component of the present invention is a method for manufacturing a multicore optical fiber gain equalization component in which a gain equalization filter is formed on a multicore optical fiber having a plurality of cores, comprising the steps of fixing the multicore optical fiber to a jig and the axial direction of the multicore optical fiber flat The process involves setting a phase mask in a row, irradiating each core of the multicore optical fiber with ultraviolet laser light through the phase mask to form a Bragg grating, and rotating the multicore optical fiber around its central axis. Afterward, ultraviolet laser light is irradiated through the phase mask to form a Bragg grating. The process involves moving the multicore optical fiber in the direction of the central axis of the multicore optical fiber. flat Move row Afterward, ultraviolet laser light is irradiated through the phase mask to form a Bragg grating. The process comprises a step of rotating the multicore optical fiber, and the number of steps for rotating the multicore optical fiber and the angle at which the multicore optical fiber is rotated are calculated based on the number of cores or the arrangement position of the cores of the multicore optical fiber. flat The distance to be moved is characterized by being longer than the irradiation width of the ultraviolet laser light. [Effects of the Invention]

[0016] According to the present invention, a Bragg grating can be formed in a multicore optical fiber in which the optical properties of each core are uniform. [Brief explanation of the drawing]

[0017] [Figure 1] This figure shows a schematic configuration of a manufacturing system for gain equalization components of multicore optical fibers. [Figure 2] (a) and (b) are cross-sectional views of a multicore optical fiber 1 showing the irradiation of ultraviolet laser light onto the multicore optical fiber. [Figure 3] This flowchart shows the manufacturing procedure for gain equalization components in each core of a multicore optical fiber in Example 1. [Figure 4]This flowchart shows the manufacturing procedure for gain equalization components in each core of the multicore optical fiber in Example 2. [Figure 5] This diagram shows the process of forming a Bragg grating on each core of a multicore optical fiber. [Figure 6] This diagram shows the process of forming a Bragg grating on each core of a multicore optical fiber. [Modes for carrying out the invention]

[0018] The inventors focused on the fact that when writing grading to each core of a multicore fiber, the inability to irradiate each core with uniform light results in differences in the optical characteristics between each core, leading to a decrease in transmission quality. They then discovered a method for manufacturing a multicore optical fiber gain equalization component that minimizes the differences in optical characteristics between each core, leading to the present invention.

[0019] In other words, the present invention provides a method for manufacturing a multicore optical fiber gain equalization component, which involves forming a gain equalization filter on a multicore optical fiber having multiple cores, and is characterized by comprising the steps of: fixing the multicore optical fiber to a jig; setting a phase mask parallel to the axial direction of the multicore optical fiber; irradiating each core of the multicore optical fiber with ultraviolet laser light through the phase mask to form a Bragg grating; rotating the multicore optical fiber about its central axis; and moving the multicore optical fiber in parallel along the central axis direction of the multicore optical fiber.

[0020] Hereinafter, each embodiment of the present invention will be described in detail with reference to the drawings. In order to facilitate understanding of the description, the same reference numerals will be used for the same components in the drawings of each embodiment, and redundant explanations will be omitted.

[0021] The multi-core optical fiber (MCF) used in the embodiments of this specification is an optical fiber in which a plurality of cores through which light propagates are arranged in one cladding. Further, in the embodiments of this specification, an example using a 4-core fiber (4CF) will be described as an example, but it is not limited thereto. It may be a 2CF or may have a larger number of cores.

[0022] [Multi-Core Optical Fiber Gain Equalization Component Manufacturing System] FIG. 1 is a diagram showing a schematic configuration of a multi-core optical fiber gain equalization component manufacturing system 100. The multi-core optical fiber gain equalization component manufacturing system 100 (hereinafter, also simply referred to as the gain equalization component manufacturing system) includes at least an irradiation unit 11, a phase mask 13, a support unit 15, a rotation unit 17, a slide unit 19, and a control unit (not shown).

[0023] The irradiation unit 11 irradiates the multi-core optical fiber with ultraviolet laser light, which is pulsed light, from a light source. The phase mask 13 diffracts the ultraviolet laser light irradiated from the irradiation unit 11 and generates interference fringes with the diffracted diffracted light. As shown in FIG. 1, the phase mask 13 is provided so as to be parallel to the axial direction of the multi-core optical fiber 1.

[0024] The support unit 15 arranges the multi-core optical fiber 1 at the irradiation position of the ultraviolet laser light and fixes the multi-core optical fiber 1 so that the multi-core optical fiber 1 does not move when irradiating the ultraviolet laser light. The rotation unit 17 rotates the multi-core optical fiber 1 at an arbitrary angle about the central axis of the multi-core optical fiber 1. The direction of rotation can be not only in either the clockwise or counterclockwise direction but also in both directions. The slide unit 19 slides the multi-core optical fiber 1 in the axial direction of the multi-core optical fiber 1 by an arbitrary distance. The direction of sliding can be in the front and back in the axial direction.

[0025] The control unit irradiates the multicore optical fiber 1 with ultraviolet laser light, then transmits light from the light source to the multicore optical fiber and measures the output optical power and the irradiation position of the ultraviolet laser light. The control unit also calculates the rotation angle, number of rotations, and slide distance of the multicore optical fiber and controls the rotation angle, number of rotations, and slide distance of the multicore optical fiber.

[0026] In the gain equalization component manufacturing system 100 configured in this way, interference fringes generated by the phase mask 13 are irradiated onto each core 3 of the multicore optical fiber 1 supported by the support portion 15 (hereinafter also referred to simply as irradiating the multicore optical fiber with ultraviolet laser light), thereby forming a Bragg grating, which is a gain equalization component, on the core 3 of the multicore optical fiber 1.

[0027] Furthermore, when irradiating each core with ultraviolet laser light, matched oil is filled around the optical fiber to minimize the refraction of the irradiated light. As a result, the irradiated ultraviolet laser light travels essentially in a straight line through the optical fiber, with little influence from the refractive index distribution of the optical fiber.

[0028] Figures 2(a) and 2(b) are cross-sectional views of the multicore optical fiber 1 showing the irradiation of ultraviolet laser light onto the multicore optical fiber 1. After irradiating the multicore optical fiber 1 with ultraviolet laser light at the core arrangement shown in Figure 2(a), the multicore optical fiber 1 is rotated by an arbitrary angle in the direction of arrow A in the figure, and the irradiation of the multicore optical fiber 1 with ultraviolet laser light at the core arrangement shown in Figure 2(b) is shown.

[0029] In multicore optical fibers, multiple cores are arranged within a single cladding. Ideally, the multicore optical fibers should be positioned so that the cores do not overlap in the direction of ultraviolet laser light propagation, and then irradiated with ultraviolet laser light. However, depending on the arrangement and number of cores, overlapping may occur when irradiating with ultraviolet laser light, resulting in the formation of an identical Bragg grating on each core. Furthermore, differences in the distance between each core and the light source may also result in the formation of an identical Bragg grating on each core. In addition, depending on the type of phase mask, the diffracted light may change. As a result, the optical properties of each core may differ, affecting the transmission loss of the multicore optical fiber.

[0030] However, in the multicore optical fiber gain equalization component manufacturing system 100 according to this embodiment, as shown in Figures 2(a) and (b), a Bragg grating with uniform optical properties can be formed on each core by rotating and / or translating the multicore optical fiber 1 and irradiating it with ultraviolet laser light multiple times from different directions and / or different positions. Figures 2(a) and (b) show how the multicore optical fibers are arranged so that multiple cores do not overlap with respect to the direction of propagation of the ultraviolet laser light, but it is acceptable if the cores overlap.

[0031] Thus, in the gain equalization component manufacturing system 100 according to this embodiment, by irradiating the multicore optical fiber 1 with ultraviolet laser light multiple times from different directions and / or different positions, a Bragg grating with uniform optical properties is formed on each core, regardless of the arrangement of cores in the cladding, the number of cores, or the diffracted light irradiated from the phase mask, thereby achieving uniformity of optical properties between cores. As a result, the transmission loss of the multicore optical fiber can be kept low.

[0032] [Manufacturing method for gain equalization components of multicore optical fibers] Next, we will explain the manufacturing method for gain equalization components for each core of a multicore optical fiber.

[0033] [1] Example 1 Figure 3 is a flowchart showing the manufacturing procedure for gain equalization components for each core of a multicore optical fiber in Example 1. Example 1 describes a method for manufacturing gain equalization components for each core of a multicore optical fiber when the number of cores and the placement positions of the cores have been confirmed in advance.

[0034] First, the phase mask and the multicore optical fiber are positioned parallel to the axial direction of the multicore optical fiber (Step S1). Next, ultraviolet laser light emitted from the light source is irradiated onto the core of the multicore optical fiber through the phase mask (Step S2). Then, light is transmitted to the multicore optical fiber and the output optical power is measured (Step S3).

[0035] Step S4 determines whether the sum of the rotation angles obtained after positioning the multicore optical fiber is 360 degrees or more. If the sum of the rotation angles is less than 360 degrees, the multicore optical fiber is slid by an arbitrary distance in the direction of its central axis, and the multicore optical fiber is rotated by an arbitrary angle around its central axis (Step S5), and the process returns to Step S2.

[0036] On the other hand, if the sum of the rotation angles in step S4 exceeds 360 degrees, the process is terminated. Details on how to determine the arbitrary rotation angle, number of rotations, and arbitrary distance to slide the multicore optical fiber will be described later.

[0037] (Method for determining rotation angle and rotation speed) We will examine the arbitrary angle and number of rotations for the multicore optical fiber in Example 1. By reducing the rotation angle of the multicore optical fiber and increasing the number of rotations, it is possible to form a Bragg grating in which the optical characteristics of each core become more uniform. However, if the axis of rotation is misaligned when rotating the multicore optical fiber, it is not possible to write a grading that results in uniform optical characteristics for each core. Furthermore, repeatedly writing grading in the same location is undesirable because it disrupts the grating. In addition, there is a limit to the number of times grading can be written to a core.

[0038] Therefore, in Example 1, the number of cores and the arrangement of the cores are measured in advance, and the multicore optical fiber is irradiated with ultraviolet laser light by rotating it in increments of 360 degrees / number of cores until the total rotation angle reaches 360 degrees (or 360 degrees or more) from the position where the ultraviolet laser light is first irradiated, thereby forming a Bragg grating. This allows for the formation of a Bragg grating in which the number of irradiations is kept to a suitable number and the optical properties of each core are uniform. It is preferable to use the number of rotations as the number of cores and the rotation angle as the angle calculated by (360 degrees / number of cores), but depending on the number of cores and the arrangement of the cores, the number of rotations may be (number of cores × n (n: an integer of 2 or more)) and the rotation angle may be calculated as 360 degrees / (number of cores × n) or 360 degrees / (number of cores × (1 / n)), etc.

[0039] In this embodiment, a multicore optical fiber with four cores arranged in a square grid with each core offset by 90 degrees in the circumferential direction is used. By rotating the multicore optical fiber by 90 degrees (calculated as 360 degrees / 4 (number of cores)) and irradiating it with ultraviolet laser light, Bragg grading can be formed in which the optical properties of each core are uniform. In addition to 90 degrees, the rotation angle may also be, for example, 45 degrees or 180 degrees.

[0040] Furthermore, the irradiation position can be adjusted by changing the rotation direction and angle of the multicore optical fiber as appropriate, depending on the number of cores, the arrangement of the cores, and the measured output optical power value. For example, it is possible to irradiate with ultraviolet laser light by rotating the optical fiber 180 degrees to the right and then rotating it 90 degrees to the left and irradiating with ultraviolet laser light again.

[0041] (Method for determining slide distance) In Example 1, we will consider an arbitrary distance for sliding the multicore optical fiber. Since repeatedly writing the grading to the same location will cause the grading to become distorted, which is undesirable, the sliding distance should be longer than the irradiation width of the ultraviolet laser light. The irradiation width of the ultraviolet laser light may be measured by the control unit or measured in advance.

[0042] As described above, in Example 1, in step S5, the steps of sliding the multicore optical fiber in the axial direction of the multicore optical fiber by an arbitrary distance, rotating the multicore optical fiber by an arbitrary angle around the central axis of the multicore optical fiber, and irradiating the multicore optical fiber with ultraviolet laser light are repeatedly performed to form a Bragg grating in which the optical properties of each core are uniform. However, the steps of rotating the multicore optical fiber by an arbitrary angle around the central axis of the multicore optical fiber and irradiating it with ultraviolet laser light may also be repeated without sliding the multicore optical fiber in the axial direction to form a Bragg grating in which the optical properties of each core are uniform.

[0043] [2] Example 2 Figure 4 is a flowchart showing the manufacturing procedure for gain equalization components for each core of a multicore optical fiber in Example 2. Example 2 describes a method for manufacturing gain equalization components for each core of a multicore optical fiber when the number of cores and the arrangement positions of the cores have not been confirmed.

[0044] First, the phase mask and the multicore optical fiber are positioned parallel to the axial direction of the multicore optical fiber (Step T1). Next, ultraviolet laser light emitted from the light source is passed through the phase mask and irradiated onto the cores of the multicore optical fiber (Step T2). Then, light is transmitted to the multicore optical fiber and the output optical power of each core is measured (Step T3). Here, the difference in optical power between the cores is calculated.

[0045] Step T4 determines whether the difference in optical power between each core is within an acceptable range. If the difference in optical power between each core is not within an acceptable range, the multicore optical fiber is slid in the axial direction of the multicore optical fiber and rotated by an arbitrary angle around the central axis of the multicore optical fiber (Step T5), and the process returns to Step T2.

[0046] On the other hand, the process also terminates in step T4 if the difference in optical power between each core falls within an acceptable range. In Example 2, since the multicore optical fiber is rotated and / or parallel-moved after irradiation with ultraviolet laser light until the difference in optical power between each core falls within an acceptable range, it is not necessary to measure or know the number of cores or their positions in advance. The acceptable range for the difference in optical power between each core can be determined arbitrarily. For example, it is preferable that the difference in optical power between each core is within approximately 0.5 dB. Details on how to determine the arbitrary rotation angle, number of rotations, and arbitrary distance for sliding the multicore optical fiber will be described later.

[0047] (Method for determining rotation angle and rotation speed) We will examine the arbitrary angles and number of rotations for rotating the multicore optical fiber in Example 2. In Example 2, the rotation angle is approximately the golden angle (222.5 degrees or 137.5 degrees). By rotating the multicore optical fiber by 222.5 degrees or 137.5 degrees from the initial irradiation position, and irradiating the multicore optical fiber with ultraviolet laser light, it is possible to form a grading that results in uniform optical characteristics for each core.

[0048] Furthermore, in Example 2, in step T5, the multicore optical fiber is slid axially by an arbitrary distance, rotated by an arbitrary angle around the central axis of the multicore optical fiber, and then irradiated with ultraviolet laser light. However, a Bragg grating in which the optical properties of each core are uniform may be formed by repeatedly rotating the multicore optical fiber by an arbitrary angle around the central axis of the multicore optical fiber and irradiating it with ultraviolet laser light, without sliding the multicore optical fiber axially.

[0049] Figures 5 and 6 illustrate the procedure for forming Bragg gratings on each core of a multicore optical fiber. First, as shown in Figure 5, ultraviolet laser light is irradiated onto core 3 of the multicore optical fiber 1 through a phase mask 13 to form a Bragg grating, and the multicore optical fiber 1 is rotated and translated. Then, as shown in Figure 6, after rotating and translating the multicore optical fiber 1, ultraviolet laser light is irradiated onto core 3 of the multicore optical fiber 1 through a phase mask at a different position on each core to form a Bragg grating. By repeating the steps shown in Figures 5 and 6 until the multicore optical fiber 1 is rotated 360 degrees, or until the difference in optical power between each core is within an acceptable range, a Bragg grating with uniform optical properties can be formed on each core 3.

[0050] As explained above, a Bragg grating with uniform optical properties is formed on each core, thereby achieving uniformity in optical properties between cores. As a result, the transmission loss of the multicore optical fiber can be kept low. [Explanation of Symbols]

[0051] 100 Multicore Optical Fiber Gain Equalization Component Manufacturing System 1 Multicore optical fiber 3 cores 11 Irradiation area 13 Phase Mask 15 Support part 17 Rotating part 19. Slide section

Claims

1. A method for manufacturing a multicore optical fiber gain equalization component, which forms a gain equalization filter on a multicore optical fiber having multiple cores, The process of fixing the multicore optical fiber to the jig, A step of setting a phase mask parallel to the axial direction of the multicore optical fiber, The process involves irradiating each core of the multicore optical fiber with ultraviolet laser light through the phase mask to form a Bragg grating, The process involves rotating the multicore optical fiber around its central axis, then irradiating it with ultraviolet laser light through the phase mask to form a Bragg grating. The process includes the steps of: moving the multicore optical fiber in parallel along the central axis direction of the multicore optical fiber, and then irradiating it with ultraviolet laser light through the phase mask to form a Bragg grating, The number of steps for rotating the multicore optical fiber and the angle at which the multicore optical fiber is rotated are calculated based on the number of cores or the arrangement of the cores in the multicore optical fiber. A method for manufacturing a multicore optical fiber gain equalization component, characterized in that the distance over which the multicore optical fiber is moved in parallel is longer than the irradiation width of the ultraviolet laser light.

2. The method for manufacturing a multicore optical fiber gain equalization component according to claim 1, characterized in that the angle at which the multicore optical fiber is rotated at once is the angle obtained by dividing 360 degrees by the number of cores.

3. A multicore optical fiber gain equalization component manufacturing system for forming a gain equalization filter in a multicore optical fiber having multiple cores, A support section for fixing the multicore optical fiber, An irradiation unit that emits ultraviolet laser light from a light source, A phase mask that diffracts ultraviolet laser light irradiated from the irradiation unit and forms a Bragg grating on the core of the multicore optical fiber, A rotating part that rotates the multicore optical fiber about the central axis of the multicore optical fiber, The system includes a sliding section that moves the multicore optical fiber in parallel along the central axis direction of the multicore optical fiber, The number of steps for rotating the multicore optical fiber and the angle at which the multicore optical fiber is rotated are calculated based on the number of cores or the position of the cores. The distance over which the multicore optical fiber is moved in parallel is longer than the irradiation width of the ultraviolet laser light. A multicore optical fiber gain equalization component manufacturing system characterized in that the same phase mask is used to form the Bragg grating before and after rotating the multicore optical fiber, and before and after translating the multicore optical fiber.

Images