JP6438372B2 - Optical fiber side input / output device and optical fiber side input / output method - Google Patents

Description

  The present invention relates to a technique for inputting and outputting light from the side of an optical fiber.

  Optical fiber side input / output technology enables the transmission and reception of optical signals between two optical fibers by a structure in which another optical fiber is abutted against the side of a bent portion of an optical fiber bent at an angle. Technology. The optical fiber side input / output technology is used for entering and exiting an optical signal from the side of a bent optical fiber, for example, in order to perform contrast control, signal monitoring, and line switching (for example, Non-Patent Document 1). And 2). Hereinafter, in this specification, the optical fiber that is bent is referred to as a main optical fiber, and the optical fiber that is abutted against the side surface of the bent optical fiber is referred to as a probe fiber. Application of the optical fiber side input / output technology to a leakage light monitor, test light incidence for controlling a core wire, or a short interruption switch for changing the route of an optical line is being studied.

  In an access network, it is common to use a tape fiber in which a plurality of single fibers are bundled. A tape fiber is formed by adhering a plurality of ordinary optical fibers adjacent to each other.

  FIG. 1 is a diagram illustrating a state in which communication light is incident and coupled to a bent portion of a tape fiber as a main optical fiber. This optical system is known as a confocal compound lens system with low aberration, and this optical system inputs / outputs light to / from a fiber tape from an input / output fiber array. It comprises four input / output optical fiber arrays, a plano-convex lens (lens 1) facing the input / output fiber, a plano-convex lens (lens 2) facing the bending fiber, and a bent tape fiber. In the tape fiber, the four optical fibers are juxtaposed vertically in the tape fiber bending plane. An input / output optical fiber array and a bending fiber are installed at the focal length of each plano-convex lens. The “bending plane” is a plane including the main optical fiber (any optical fiber in the case of a tape fiber) before and after bending.

FIG. 2 is a diagram showing a circular beam image (FIG. 2A) and a light intensity profile (FIG. 2B) incident on the bent portion of the main optical fiber by the confocal compound lens system of FIG. The diameter at which the intensity is 1 / e ² (= 0.135) of the peak value is defined as the beam waist diameter. The beam waist diameter is 17 μm, and the incident efficiency of coupling to the bent portion of the main optical fiber is 81%. Here, the incident efficiency is the efficiency of coupling of the light beam exiting the input / output fiber array to the bent fiber core.

Kiyokura et al., "Radiation simulation of small-diameter optical fiber for local optical input / output technology -Examination of coupling efficiency of optical line switching-", IEICE Communication Society, B-10-16 (September 2013) Hirota et al., "Study of optical line switching device using side input / output technology", IEICE Technical Report, IEICE Technical Report OFT 2013-50 (2014-01) Tanobe et al., SM / MM shared dual mode optical fiber, IEICE Technical Report OCS 2007-37 Thorlabs product information, "https://www.thorlabs.co.jp/thorcat/TTN/DCF13-SpecSheet.pdf", retrieved September 15, 2015 Kiyokura et al., “Study on improvement of light receiving efficiency of local optical input / output technology by using dual mode fiber probe”, IEICE Communication Society Conference, B-13-14 (September 2015)

  The interval between the fiber cores of the tape fiber is about 250 μm, but in reality, there is a fluctuation of about 20 μm, not equal intervals. If the beam diameter is narrowed as shown in FIG. 2 and the core is displaced by 20 μm as shown in FIG. 2A, the beam does not enter the core at all and optical signal input / output becomes very difficult. In other words, if the lens is optimally focused so as to focus on the bent portion of the main optical fiber, the position tolerance deteriorates, and there arises a problem that it is difficult to cope with fluctuations in the position of the fiber core.

  On the other hand, if the beam diameter is widened in order to widen the position tolerance of the core, the light intensity density is lowered and the coupling efficiency is lowered. When the coupling efficiency is lowered, it is impossible to secure a light intensity at a level for performing communication via the fiber coating, and it becomes difficult to achieve the purpose of communication using local light input / output. Thus, the conventional optical fiber side input / output device has a trade-off relationship between the core position tolerance and the coupling efficiency, and there is a problem that it is difficult to satisfy both.

  Therefore, in order to solve the above-described problems, the present invention provides an optical fiber side input / output device and an optical fiber side input that can increase the position tolerance of the core of the main optical fiber while maintaining the coupling efficiency with the main optical fiber. An object is to provide an output method.

  The optical fiber side input / output device according to the present invention is a confocal compound lens system in which the focused beam is an ellipse whose diameter is enlarged only in the direction where position tolerance is required, and the optical coupling efficiency is reduced due to the misalignment of the core. In the direction where it is not necessary to take into account the misalignment of the core, the diameter of the beam is reduced, and the optical coupling efficiency is ensured by suppressing the decrease in the light intensity of the beam.

Specifically, an optical fiber side input / output device according to the present invention is an optical fiber side input / output device that inputs / outputs light to / from a main optical fiber formed with a bent portion. And
An input / output optical fiber that has a tip close to the bent portion, allows incident light to enter the bent portion through the tip, and can receive leaked light leaking from the bent portion at the tip;
The beam of incident light and the leaked light is provided between the bent portion and the tip, and is perpendicular to the tangential direction of the main optical fiber in the bent portion and the optical axis of the incident light and the leaked light. An optical system that expands the diameter;
Is provided.

Specifically, the optical fiber side input / output method according to the present invention is an optical fiber side input / output method for inputting / outputting light to / from a main optical fiber formed with a bend through the bend. And
When the distal end of the input / output optical fiber is brought close to the bent portion, incident light is incident on the bent portion through the distal end, and leaked light leaking from the bent portion is received at the distal end.
An optical system is provided between the bent portion and the tip, and the incident light and the leaked light are perpendicular to the tangential direction of the main optical fiber at the bent portion and the optical axis of the incident light and the leaked light. The beam diameter is expanded.

  The fluctuation of the tape fiber core position is only in the direction perpendicular to the bending plane, and the fluctuation in the bending plane can be ignored. Therefore, an elliptical image (beam) is formed that is wide in the direction of the core position fluctuation and narrow in the direction in which the core position does not fluctuate. By expanding the beam to the minimum necessary range, it is possible to increase the tolerance for misalignment of the core and to suppress a reduction in coupling efficiency due to a decrease in light intensity.

  Therefore, the present invention provides an optical fiber side input / output device and an optical fiber side input / output method capable of increasing the position tolerance of the core of the main optical fiber while maintaining the coupling efficiency with the main optical fiber. it can.

The optical system is
Two lenses that image the incident light emitted from the tip at the bent portion;
A concave lens having a concave surface at a point where the focal points of the respective lenses coincide between the two lenses;
It is characterized by having.

  In order to form an elliptical beam, the concave lens is preferably a cylindrical lens. That is, an optical system that is not cylindrically symmetric with respect to the optical axis is used. Using such a cylindrical lens, it is possible to collect light only in a direction that requires light collection, and to reduce light collection in an unnecessary direction.

The main optical fiber is a tape fiber in which a plurality of optical fiber core wires are arranged in parallel,
The input / output optical fibers may be a fiber array arranged in parallel corresponding to the optical fiber core wires.

  The input / output optical fiber preferably has a profile in which the refractive index of the core is stepped from the center toward the surface. Using the input / output optical fiber whose refractive index of the core is a stepped profile from the center to the surface, the incident light to the bent portion is propagated in a single mode, and the leakage from the received bent portion By propagating light in multimode, the light receiving efficiency of the input / output optical fiber receiving light leaked from the bent portion of the main optical fiber can be increased.

When the refractive index of the core is a stepped profile from the center toward the surface of the input / output optical fiber, the optical fiber side light input / output device according to the present invention separates incident light and leakage light,
An optical receiver that receives the leaked light propagated through the input / output optical fiber in a multimode via a multimode fiber;
A laser light source connected to a single mode fiber and emitting the incident light to the single mode fiber;
A wavelength multiplexing / demultiplexing unit that couples the incident light from the laser light source to the input / output optical fiber so as to propagate in a single mode, and couples the leakage light from the input / output optical fiber to the multimode fiber. When,
Is further provided.

  The present invention can provide an optical fiber side input / output device and an optical fiber side input / output method capable of increasing the position tolerance of the core of the main optical fiber while maintaining the coupling efficiency with the main optical fiber.

It is a block diagram explaining the conventional optical fiber side light input / output device. A confocal compound lens system that enters a bent portion of a four-core tape fiber (main optical fiber) is provided. (A) is the figure seen from the direction (z direction) parallel to a fiber bending plane. (B) is the figure seen from the direction (y direction) perpendicular | vertical to a fiber bending plane. It is a figure explaining the beam shape in the condensing position by the side of the main optical fiber by the confocal compound lens system of the conventional optical fiber side light input / output device. (A) is an image of a beam incident on the core of the bent portion, and (b) is a light intensity profile thereof. It is a block diagram explaining the optical fiber side light input / output device which concerns on this invention. A confocal compound lens system that enters a bent portion of a four-core tape fiber (main optical fiber) is provided. The confocal compound lens system includes a concave lens. (A) is the figure seen from the direction (z direction) parallel to a fiber bending plane. (B) is the figure seen from the direction (y direction) perpendicular | vertical to a fiber bending plane. It is a figure explaining the elliptical beam shape in the condensing position by the side of the main optical fiber by the confocal compound lens system of the optical fiber side light input / output device which concerns on this invention. (A) is an image of the beam incident on the core of the bent portion, and (b) and (c) are the light intensity profiles thereof. It is a figure explaining the leak light which the optical fiber for input / output of the optical fiber side light input / output device which concerns on this invention light-receives. (A) is a general view, and (b) is an enlarged view of a tip portion of an input / output optical fiber. It is a figure explaining the elliptical beam shape in the condensing position by the side of the optical fiber for input / output by the confocal compound lens system of the optical fiber side light input / output device which concerns on this invention. (A) is an image of the beam incident on the core of the bent portion, and (b) and (c) are the light intensity profiles thereof. It is a figure explaining the refractive index profile of a dual mode fiber. It is a figure explaining the wavelength multiplexing / demultiplexing part with which the optical fiber side light input / output device according to the present invention separates incident light and leakage light.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are embodiments of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

(Embodiment 1)
FIG. 3 is a diagram illustrating the optical fiber side light input / output device 301 of the present embodiment. The optical fiber side light input / output device 301 is an optical fiber side light input / output device that inputs / outputs light to / from the main optical fiber 101 formed with the bent portion 11 via the bent portion 11,
An input / output optical fiber 102 in which the tip 12 is brought close to the bending portion 11, incident light is incident on the bending portion 11 through the tip 12, and leakage light leaking from the bending portion 11 can be received by the tip 12; ,
The beam of incident light and the leaked light is provided between the bent portion 11 and the tip 12 and is perpendicular to the tangential direction of the main optical fiber 101 in the bent portion 11 and the optical axis of the incident light and the leaked light. An optical system 103 for expanding the diameter;
Is provided.

  Here, the main optical fiber 101 is a tape fiber in which a plurality of optical fiber cores are arranged in parallel, and the input / output optical fiber 102 is a fiber array arranged in parallel corresponding to each of the optical fiber cores.

  The optical system 103 has a concave surface in which the focal points of the two lenses (31, 32) for forming the incident light emitted from the tip 12 at the bending portion 11 and the lenses 31 and 32 coincide with each other. And a concave lens 33. In the present embodiment, the concave lens 33 is a cylindrical lens. The optical system 103 is a confocal compound lens system including a concave lens.

  The optical fiber side light input / output device 301 inputs / outputs light to / from the fiber tape (main optical fiber 101) from the probe fiber array (input / output optical fiber 102). The optical fiber side light input / output device 301 includes four input / output optical fibers 102, a plano-convex lens (lens 31) facing the input / output fiber 102, and a flat surface facing the bent portion 11 of the main optical fiber 101. It is composed of a convex lens (lens 32) and a plano-concave cylindrical lens (lens 33).

  The main optical fiber 101 is a tape fiber in which four optical fibers are juxtaposed in a vertical direction within a fiber bending plane. The curvature direction of the plano-concave cylindrical lens (lens 33) is also arranged to be perpendicular to the fiber bending plane. The plano-convex lens (lens 31) is arranged at the position of the focal length of the plano-convex lens with respect to the four light input / output fiber arrays, that is, the position serving as a collimator. The plano-convex lens (lens 32) is disposed at the focal length position of the plano-convex lens (lens 32) with respect to the bent tape fiber, that is, the collimator. The position of the curved surface of the plano-concave lens (lens 33) is arranged at the position of the focal length of the lens 31 to the lens 31 and the position of the focal length of the lens 32 to the lens 32.

  In this embodiment, the bent fiber tape (main optical fiber 101) is in a refractive index medium such as a refractive index matching agent or an ultraviolet curable adhesive, and each lens (31, 32, 33) is in the air.

The effects according to this embodiment will be described.
The input / output fibers 102 are also connected to individual communication laser light sources and light receiving photodiodes (not shown). Communication light from the laser light source for communication exits from the core of the optical fiber (diameter of about 9 μm) into the air and enters the lens 31 and enters the lens 33 as collimated light. The direction of the communication light in the lens 33 is not affected by the lens 33, and the communication light is slightly diverged only by the influence of the concave lens in the direction perpendicular to the bending plane. Thereafter, the communication light enters the lens 32 and is condensed at the core position of the bent portion 11 of the main optical fiber 101. That is, the optical system 103 inherently relaxes light condensing only in one direction by adding an optical element (concave lens 33) that loosens light condensing to the system that optimally condenses light.

FIG. 4 is a diagram for explaining the beam shape (FIG. 4A) and the light intensity profile (FIGS. 4B and 4C) at the condensing position near the bent portion 11 of the main optical fiber 101. FIG. FIG. 4A is a diagram showing the formed image, which is clearly an elliptical beam. Specifically, the beam diameter in the vertical direction is focused on the beam waist diameter 2ω0 = 18.5 μm, but the beam diameter in the horizontal direction is expanded about four times as compared with the conventional one, and the beam waist diameter 2ω ₀ = 72 μm. Condensation is relaxed compared to the vertical direction.

  The optical fiber side light input / output device 301 condenses communication light into an elliptical beam by the optical system 103, thereby wide tolerance (in a direction perpendicular to the bending plane in which the core position of the main optical fiber 101 fluctuates). (Fig. 4 (a)). On the other hand, since the tolerance in the bending plane direction, which is the direction in which the core position of the main optical fiber 101 does not fluctuate, may be narrow, the optical fiber side light input / output device 301 collects the communication light in this direction. Thus, the light intensity is increased to prevent a decrease in coupling efficiency (FIG. 4C). As a result of the specific ray tracing calculation, the incidence efficiency is 16.5%, and the beam width is 3.9 times (major axis / minor axis), so that the reduction in incidence efficiency is suppressed while maintaining the position tolerance.

(Embodiment 2)
In the first embodiment, the effect of relaxing the position tolerance when the signal light is incident on the main optical fiber 101 has been described. In the present embodiment, a case where the input / output fiber 102 receives signal light will be described with reference to FIG.

  FIG. 5B is a diagram illustrating the state of light rays in the vicinity of the distal end 12 of the input / output fiber 102. Since the optical system works in both directions, the leaked light emitted from the bent portion 11 of the main optical fiber 101 reaches the elliptical beam that spreads in one direction in the optical system 103. FIG. 6 is a diagram for explaining the beam shape (FIG. 6A) and the light intensity profile (FIGS. 6B and 6C) at the end face of the input / output fiber 102. The input / output fiber 102 has a diameter of 125 μm.

  The beam shape has a beam width of 12.3 μm, which is about the same as that of the fiber core in the bending plane, but the beam width expands to 47.5 μm in the direction perpendicular to the bending plane. Since the position of the core of the main optical fiber 101 fluctuates by about 20 μm, it fluctuates by about 20 μm even on the end face 12 of the input / output fiber 102. It can be seen that the optical fiber side light input / output device 301 also has tolerance on the input / output fiber 102 side due to the core position fluctuation of the main optical fiber 101. When the core of the input / output fiber 102 is 10 μm, the light receiving efficiency is 7.4%. However, when the input / output fiber 102 is replaced with a large-diameter 50 μm core multimode fiber, the light receiving efficiency is 45.3%. improves. Thereby, both the core position fluctuation tolerance and the light receiving efficiency of the main optical fiber 101 can be improved.

  Here, the input / output optical fiber 102 preferably has a step-like profile in which the refractive index of the core extends from the center toward the surface. For example, as the input / output fiber 102, a dual-mode fiber (see Non-Patent Document 3) or a double-clad fiber (see Non-Patent Document 4) in which a single-mode core and a multi-mode core are coaxial and doubled is used. Can be used. These fibers have a stepwise refractive index profile in the diametrical direction as shown in FIG. 7, and have both the properties of a single mode fiber and a multimode fiber. For this reason, if the incident light is propagated through the single mode core and output from the single mode core, the incident coupling efficiency to the bent portion 11 of the main optical fiber 101 can be maintained. On the other hand, if the leakage light emitted from the bent portion 11 of the main optical fiber 101 is received by the multi-mode core, the light receiving efficiency can be improved (see Non-Patent Document 5).

FIG. 8 is a diagram illustrating the wavelength multiplexing / demultiplexing unit 104 connected to the input / output optical fiber 102 when the input / output optical fiber 102 is a dual mode fiber or a double clad fiber. The wavelength multiplexing / demultiplexing unit 104 is
An optical receiver 28 that receives the leaked light propagated through the input / output optical fiber 102 in multimode via the multimode fiber 24;
A laser light source 27 connected to the single mode fiber 21 and emitting incident light to the single mode fiber 21;
Wavelength multiplexing / demultiplexing for coupling incident light from a laser light source (LD) 27 to the input / output optical fiber 102 so as to propagate in a single mode and coupling leakage light from the input / output optical fiber 102 to the multimode fiber 24. Vessel 29;
Is further provided.

  The wavelength multiplexer / demultiplexer 29 has three ports, to which the input / output optical fiber 102, the multimode fiber 24, and the single mode fiber 21 are connected. The wavelength multiplexer / demultiplexer 29 includes a reflection filter 26, which couples the leakage light having the wavelength λ 1 from the input / output optical fiber 102 to the multimode fiber 24, and has the wavelength λ 2 from the single mode fiber 21. Incident light can be coupled to the input / output optical fiber 102.

  For this reason, the leaked light of wavelength λ1 propagating in the multimode through the large-diameter core of the input / output optical fiber 102 passes through the multimode fiber 24 connected to the wavelength multiplexer / demultiplexer 29 and has almost no loss, and is an avalanche. Light can be received by the photodiode 28 (APD). On the other hand, the wavelength λ 2 enters the single mode fiber 21 from the LD 27 and can be sent to the input / output optical fiber 102 with a small core diameter.

  By including the wavelength multiplexing / demultiplexing unit 104, the fiber side optical input / output device 301 can amplify and shape the signal after the avalanche photodiode (APD) 28 and transmit it to the other. It can be used as a repeater that amplifies and shapes the signal and transmits it from the LD 27 to the input / output optical fiber 102.

[Appendix]
The following describes the optical fiber side light input / output device of the present embodiment.
(the purpose)
The conventional optical fiber side light input / output device has a trade-off relationship that the light intensity decreases and the coupling efficiency decreases when the beam diameter is widened and the position tolerance is widened in order to cope with the misalignment of the core of the tape fiber. It was in. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an optical fiber side light input / output device that can cope with the positional deviation of the core of the tape fiber while eliminating the trade-off and maintaining the coupling efficiency.

(1): In a system that collects light using an optical system with respect to an optical fiber and inputs / outputs light, the position of the optical fiber fluctuates in one direction, and there is no fluctuation in a direction orthogonal to that direction. In this case, the light input / output is characterized in that the light collection diameter in the direction with fluctuation is about the same as the width of the fluctuation, and the light collection diameter in the direction without fluctuation is about the same as the optical fiber core diameter. Optical system.

(2): In the optical input / output optical system, by adding a concave lens in the optical system that forms an image from the light emitting point of the optical input / output optical system to the condensing position, by reducing the condensing in the direction of fluctuation The optical input / output optical system according to (1), wherein an elliptical beam is formed and the positional tolerance is relaxed.

(3) The optical input / output optical system according to (1) or (2), wherein the concave lens is a cylindrical lens.

(4) The optical input / output optical system according to (1) to (3) above, wherein the optical fiber is a tape fiber in which a plurality of fibers are bundled.

(5): The above-mentioned (1) to (4), wherein a fiber core and a core having a larger diameter are formed coaxially as an optical input / output fiber, and a single mode and a multimode can be propagated simultaneously. ) The optical input / output optical system.

(effect)
According to the present invention, the following operational effects are exhibited.
By making the focused beam elliptical, it expands only in the direction where position tolerance is required to prevent the optical coupling efficiency from being lowered, and it does not occur in a direction where position tolerance does not occur and position tolerance is not required. Optical coupling efficiency can be ensured. That is, according to each aspect of the present invention, it is possible to provide a side light input / output device that can maintain high optical coupling efficiency with a probe.

  The present invention can be applied to the information communication industry.

11: bending portion 12: tip 21: single mode fiber 24: multimode fiber 26: reflection filter 27: LD
28: APD
29: Wavelength multiplexer / demultiplexer 31, 32: Plano-convex lens 33: Plano-concave lens 101: Main optical fiber 102: Input / output fiber 103: Optical system 104: Wavelength multiplexer / demultiplexer 301: Optical fiber side light input / output device

Claims (7)

An optical fiber side input / output device that inputs and outputs light through the bent portion with respect to a main optical fiber formed with a bent portion,
An input / output optical fiber that has a tip close to the bent portion, enters incident light into the bent portion through the tip, and receives leaked light leaking from the bent portion at the tip;
The beam of incident light and the leaked light is provided between the bent portion and the tip, and is perpendicular to the tangential direction of the main optical fiber in the bent portion and the optical axis of the incident light and the leaked light. An optical system that expands the diameter;
Equipped with a,
The main optical fiber is a tape fiber in which a plurality of optical fiber core wires are arranged in parallel,
The input-output optical fibers, said optical fiber to correspondingly optical fiber side light output device according to claim fiber array der Rukoto in parallel, respectively. The optical system is
Two lenses that image the incident light emitted from the tip at the bent portion;
A concave lens having a concave surface at a point where the focal points of the respective lenses coincide between the two lenses;
The optical fiber side light input / output device according to claim 1, comprising:   The optical fiber side light input / output device according to claim 2, wherein the concave lens is a cylindrical lens. The optical fiber side light input / output device according to any one of claims 1 to 3 , wherein the input / output optical fiber has a stepped profile with a refractive index of the core from the center toward the surface. An optical receiver that receives the leaked light propagated through the input / output optical fiber in a multimode via a multimode fiber;
A laser light source connected to a single mode fiber and emitting the incident light to the single mode fiber;
A wavelength multiplexer / demultiplexer that couples the incident light from the laser light source to the input / output optical fiber so as to propagate in a single mode, and couples the leakage light from the input / output optical fiber to the multimode fiber. When,
The optical fiber side light input / output device according to claim 4 , further comprising: An optical fiber side input / output method for inputting / outputting light to / from a main optical fiber formed with a bent portion through the bent portion,
When the distal end of the input / output optical fiber is brought close to the bent portion, incident light is incident on the bent portion through the distal end, and leaked light leaking from the bent portion is received at the distal end.
An optical system is provided between the bent portion and the tip, and the incident light and the leaked light are perpendicular to the tangential direction of the main optical fiber at the bent portion and the optical axis of the incident light and the leaked light. The beam diameter of
The main optical fiber is a tape fiber in which a plurality of optical fiber cores are arranged in parallel,
An optical fiber side input / output method, wherein the input / output optical fibers are fiber arrays arranged in parallel corresponding to the optical fiber core wires, respectively . Using the input / output optical fiber whose refractive index of the core is a stepped profile from the center to the surface, the incident light to the bent portion is propagated in a single mode, and the leakage from the received bent portion The optical fiber side input / output method according to claim 6 , wherein the light is propagated in a multimode.