Optical fiber processing device

Abstract

An optical fiber processing device (10) is provided with: a roller (11) that has, on the outer periphery thereof, a recess (15) on which an optical fiber (1) is hung; and an irradiation part (12) that irradiates the optical fiber (1), while hanging on the recess (15), with an optical pulse (16). The optical axis (16a) of the optical pulse (16) intersects the deepest section (19) of the recess (15).

Description

Optical Fiber Processing Equipment

[0001] The present disclosure relates to optical fiber processing equipment.

[0002] To increase transmission capacity, research is being conducted into the technology of transmitting different information in each mode using few-mode optical fiber (hereinafter referred to as FMF). The delay time during transmission in FMF differs for each mode (see Non-Patent Document 1).

[0003] Each mode propagating through the FMF has a different propagation constant, with the exception of some mode combinations, resulting in different delay times during transmission. Signals propagating through each mode of the FMF are mixed at the receiving unit. Therefore, it is necessary to independently restore the mixed signals using multi-input multi-output (MIMO) technology. The larger the difference in delay times, the larger the decoding circuitry becomes (see Non-Patent Document 2).

[0004] Mode coupling is expected to reduce differential delay. Mode coupling can be promoted by using a long-period fiber grating (LPFG). The efficiency of mode coupling can be increased by setting the period of the LPFG to a value appropriate for the effective refractive index difference between each mode of the optical fiber (see Non-Patent Document 3).

[0005] Patent Document 1 discloses an optical fiber cable incorporating an LPFG for promoting mode coupling. This LPFG is formed in a sheet shape. Typically, the LPFG is in contact with the surface of the optical fiber coating. This results in little change in the refractive index of the core. Therefore, sufficient lateral pressure is required to generate mode coupling. Furthermore, applying a large lateral pressure causes optical loss due to mode coupling.

[0006] A method for identifying optical fiber cores by applying color at regular intervals along the length of the optical fiber core is already known (see Non-Patent Document 4). The timing of the discharge of paint or the like is controlled as the optical fiber is transported. This makes it possible to color the optical fiber cores at regular intervals. However, the coloring of the optical fiber cores is applied across the entire width of the core, and it is not possible to target specific parts of the optical fiber.

[0007] A method for changing the refractive index of a silica optical waveguide, such as an optical fiber or a planar optical circuit, by irradiating it with an optical pulse is known (Patent Document 2). For example, the configuration shown in Patent Document 2 allows the refractive index of a desired position in the optical fiber to be changed by irradiating the core of the optical fiber with an optical pulse. Furthermore, by appropriately sliding the stage, any processing can be performed in the longitudinal direction. Therefore, a periodic change in the refractive index can be generated along the longitudinal direction of the optical fiber.

[0008] JP 2018-036339 A JP 2005-257719 A

[0009] D. Soma et al., "10.16 Peta-bit / s Dense SDM / WDM transmission over Low-DMD 6-Mode 19-Core Fiber Across C+L Band," 2017 European Conference on Optical Communication (ECOC), 2017, pp. 1-3, doi: 10.1109 / ECOC.2017.8346082.PJ Winzer, H. Chen, R. Ryf, K. Guan and S. Randel, "Mode-dependent loss, gain, and noise in MIMO-SDM systems," 2014 The European Conference on Optical Communication (ECOC), 2014, pp. 1-3, doi: 10.1109 / ECOC.2014.6963888.H. Liu, H. Wen, R. Amezcua-Correa, P. Sillard and G. Li, “Reducing group delay spread in a 9-LP mode FMF using uniform long-period gratings," 2017 Optical Fiber Communications Conference and Exhibition (OFC), 2017, pp. 1-3.M. Isaji et al., "Ultra-High density wrapping tube optical fiber cable with 12-fiber spider web ribbon," the proceedings of 62nd International Wire and Connectivity Symposium, pp. 605-609, 2013.

[0010] As described above, the technique of Patent Document 2 can cause a periodic change in refractive index. However, since the operating range of the stage is limited, it is not possible to process the entire area of ​​a long optical fiber.

[0011] The present disclosure has been made in view of the above circumstances, and aims to provide an optical fiber processing device that can continuously impart a periodic refractive index change to a long optical fiber.

[0012] An optical fiber processing device according to an aspect of the present disclosure comprises a roller having a recess on its outer periphery in which an optical fiber is hung, and an irradiation unit that irradiates the optical fiber with a light pulse while it is hung in the recess, and the optical axis of the light pulse intersects with the deepest part of the recess.

[0013] According to the present disclosure, it is possible to provide an optical fiber processing device that can continuously impart a periodic refractive index change to a long optical fiber.

[0014] Fig. 1 is a configuration diagram of an optical fiber processing device according to this embodiment. Fig. 2 is a partial cross-sectional view of a roller according to this embodiment. Fig. 3 is a diagram showing an example of a focal point of a light pulse. Fig. 4 is a partial cross-sectional view of a roller according to a modified example of this embodiment.

[0015] An optical fiber processing device 10 according to an embodiment of the present disclosure will be described below with reference to the drawings. In the drawings, identical parts are designated by the same reference numerals and will not be described again. For ease of explanation, mutually orthogonal X, Y, and Z directions are defined. The X direction is the width direction of the roller 11 and the extension direction of the rotation axis 13 of the roller 11. The Y direction coincides with the radial direction of the roller 11.

[0016] The optical fiber processing device 10 according to this embodiment irradiates an optical fiber 1 with a light pulse 16, periodically changing the refractive index of the core 2. The optical fiber 1 applied to this embodiment is not limited in length. That is, the refractive index of the core 2 can be periodically changed for a long optical fiber 1. The optical fiber 1 irradiated with the light pulse 16 is, for example, a few-mode optical fiber. By imparting a periodic refractive index change to the core of a few-mode optical fiber, an optical fiber with improved mode coupling efficiency can be obtained.

[0017] 1 is a configuration diagram of an optical fiber processing device 10 according to this embodiment. For ease of explanation, the optical fiber processing device 10 will be referred to as the processing device 10 hereinafter. As shown in FIG. 1 , the processing device 10 includes a roller 11 that can rotate around a rotation axis 13, and an irradiation unit 12 that irradiates the roller 11 with a light pulse 16.

[0018] The roller 11 is a disk centered on a rotation axis 13, and is rotated by a drive unit 14 such as a motor. The roller 11 has a recess 15 on its outer periphery. The recess 15 is recessed toward the rotation axis 13 of the roller 11. The optical fiber 1 is hung in the recess 15.

[0019] The irradiation unit 12 is a so-called femtosecond laser device, and irradiates the optical fiber 1, which is hung in the recess 15, with a light pulse 16 having a pulse width of about femtoseconds. The light pulse 16 emitted from the irradiation unit 12 is focused by a lens (not shown). As will be described later, a focusing point 17 of the light pulse 16 is located somewhere within the core 2 (see FIG. 2 ) of the optical fiber 1. The light pulse 16 has an intensity that changes the refractive index of the core 2 of the optical fiber 1.

[0020] The control unit 18 is a so-called computer, and controls the drive unit 14 and the irradiation unit 12. With respect to the drive unit 14, the control unit 18 controls the rotation speed of the roller 11, in other words, the transport amount of the optical fiber 1 caused by the rotation of the roller 11. Based on this transport amount, the control unit 18 controls (adjusts) the generation timing of the light pulses 16, and imparts a refractive index change of a desired period to the core 2 of the optical fiber 1.

[0021] The driving unit 14 may include a moving mechanism such as a movable stage that controls the position of the roller 11. In this case, the control unit 18 controls the driving unit 14 to adjust the position of the roller 11.

[0022] FIG. 2 is a partial cross-sectional view of the roller 11, showing the recess 15. The cross-section shown in FIG. 2 includes the central axis of the rotation shaft 13. That is, this cross-section is perpendicular to the rotation direction of the roller 11. As shown in FIG. 2, the contour 15a of the recess 15 may be formed by a curve or by multiple straight lines. In the latter case, for example, the recess 15 may have a V-shaped cross-section. In either case, a deepest portion 19 is formed at or near the center of the width direction (X direction) of the recess 15. The deepest portion 19 is the deepest part of the recess 15 in the radial direction (Y direction). The optical fiber 1 hung in the recess 15 is positioned closest to the deepest portion 19 due to the tension of the optical fiber 1. For example, in the example shown in FIG. 2, the optical fiber 1 is positioned within the recess 15 with its outer circumferential surface 1a in contact with the deepest portion 19.

[0023] Optical axis 16a of light pulse 16 intersects with deepest part 19 of recess 15. Optical axis 16a is also perpendicular to rotation axis 13 of roller 11 and is located on a plane that includes deepest part 19. Optical axis 16a is the central axis of the beam bundle formed by light pulse 16.

[0024] As described above, the optical fiber 1 is located closest to the deepest part 19. Therefore, as shown in FIG. 2 , the center of the core 2 and the deepest part 19 are both located on the optical axis 16 a. In this case, by focusing the light pulse 16 at the center of the core 2, a distribution of refractive index changes centered on the center of the core 2 can be obtained. Furthermore, by repeatedly irradiating the light pulse 16 in accordance with the rotation of the roller 11 to transport the optical fiber 1, it is possible to periodically impart (form) portions of the core 2 where the refractive index has changed along the longitudinal direction of the optical fiber 1. Note that, as will be described later, the position of the focusing point 17 of the light pulse 16 is not limited to the center of the core 2.

[0025] FIG. 3 is a diagram showing an example of a focal point 17 of the light pulse 16. In this embodiment, the relative position of the core 2 with respect to the deepest part 19 is stable. Therefore, by three-dimensionally adjusting the position of the roller 11 using the driving unit 14, a portion where the refractive index changes can be accurately formed at any position within the core 2. For example, as shown in FIG. 3, the focal point 17 of the light pulse 16 may be located at a position where a maximum value of the overlap component between the propagation modes occurs in the optical fiber 1 while it is hung on the recess 15. The position where a maximum value of the overlap component occurs refers to the position where the overlap between the electric field intensities E of the different propagation modes is greatest in the electric field intensity distributions of the different propagation modes. In other words, it can be said to be the position where the intensity ratio of the electric field intensities E of the different propagation modes is smallest.

[0026] FIG. 3 shows the LP ０１ Mode and LP １１ This shows the electric field intensity distribution of the modes. Mode coupling occurs when the electric field energy transfers at the point where the propagation constants match. １１ Higher-order modes such as the 1000-2000 mode do not necessarily have a maximum electric field distribution at the center of the core 2. Therefore, the focusing point 17 of the optical pulse 16 is positioned at a position where the overlap component between the propagation modes has a maximum value, and the refractive index in that area is locally changed. This makes it possible to improve the coupling efficiency between different modes.

[0027] The position where the maximum value is generated varies depending on the combination of modes to be combined. Therefore, the processing device 10 may include a plurality of irradiation units 12, each having a focal point 17 set at a different position.

[0028] When the processing device 10 is used to impart a refractive index change to the optical fiber 1, the optical fiber 1 hung in the recess 15 is irradiated with a light pulse 16 that is focused within the core 2. Next, the optical fiber 1 is transported by the rollers 11 by a length corresponding to the period of the refractive index change, and the optical fiber 1 is again irradiated with the light pulse 16. By repeating these steps, it is possible to impart a periodic refractive index change to the optical fiber 1 that will result in mode coupling.

[0029] In this embodiment, the optical fiber 1 to be irradiated with the light pulse 16 is transported by rollers 11, and the optical fiber 1 is irradiated with the light pulse 16 on the rollers 11. Therefore, the length of the optical fiber 1 is not limited. That is, a periodic refractive index change can be continuously imparted to a long optical fiber 1. Furthermore, the optical fiber 1 is stably positioned at a position closest to the deepest part 19 of the recess 15 due to its own tension. Therefore, a refractive index change can be stably imparted to a desired position in the width direction of the optical fiber 1, for example.

[0030] Fig. 4 is a partial cross-sectional view of roller 11 according to a modified example of this embodiment. As shown in Fig. 4, recess 15 may have a slit 20 in its deepest part 19. Slit 20 extends in the extension direction of recess 15 (i.e., the rotation direction of roller 11). The width of slit 20 along the X direction is smaller than the diameter of optical fiber 1 and larger than the beam diameter of light pulse 16 at deepest part 19. Note that slit 20 may be formed as a groove with a bottom recessed radially inward.

[0031] The deepest part 19 is also the part that is irradiated with the light pulse 16 whose refractive index has been changed. Therefore, the deepest part 19 is easily deteriorated by repeated irradiation with the light pulse 16. By forming the slit 20, the roller 11 is irradiated with the light pulse 16 whose intensity density has been reduced. In other words, damage to the roller 11 is mitigated, and the progress of wear of the roller 11 can be suppressed.

[0032] Furthermore, if a cavity 21 is formed inside the roller 11, the slit 20 may extend all the way through the cavity 21. In this case, the optical axis 16a is positioned so as to pass through the slit 20. Therefore, the irradiation unit 12 may be positioned radially outward from the outer periphery of the roller 11 as shown by the solid line in FIG. 4, or may be positioned radially inward from the outer periphery of the roller 11 as shown by the dotted line in FIG. 4. In the latter case, the irradiation unit 12 is installed inside the roller 11 (e.g., in the cavity 21), and the light pulse 16 that passes through the slit 20 and the optical fiber 1 does not hit any part of the roller 11. Therefore, the progress of wear of the roller 11 can be further suppressed.

[0033] REFERENCE SIGNS LIST 1 Optical fiber 2 Core 10 Optical fiber processing device (processing device) 11 Roller 12 Irradiation unit 15 Recess 16 Light pulse 16a Optical axis 17 Focusing point 19 Deepest part 20 Slit

Claims

1. An optical fiber processing device comprising: a roller having a recess on its outer periphery in which an optical fiber is hung; and an irradiation unit that irradiates the optical fiber with a light pulse while it is hung in the recess, wherein the optical axis of the light pulse intersects with the deepest part of the recess.

2. The optical fiber processing device according to claim 1, wherein the recess has a slit at the deepest part thereof that extends in the extension direction of the recess.

3. The optical fiber processing device according to claim 1 or 2, wherein the focal point of the optical pulse is located at a position where a maximum value of overlapping components between propagation modes occurs in the optical fiber when it is hung on the recess.

Images