JP2017102139A - Probe fiber and optical fiber side input/output device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a probe fiber capable of improving the incident coupling efficiency to a bending part of working fiber, and an optical fiber side input/output device.SOLUTION: A probe fiber 102 is configured to concentrate a ray of incident light onto a small image diameter by disposing a quartz column 11 which has a refraction index identical to that in the outside between a GRIN lens 12 and a fiber 13, or to concentrate a ray of incident light onto a small image diameter by TEC (thermally-diffused expanded core)-fusing a small diameter fiber 13 having a small core diameter and a single mode fiber 10. The optical fiber side input/output device achieves a side light incidence of a high coupling efficiency by using the probe fiber, while improving the light receiving efficiency by combining a wavelength multiplexer/demultiplexer and a small diameter fiber of a double clad structure.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a probe fiber for entering and exiting an optical signal from and to a side of a bent portion formed in an optical fiber, and an optical fiber side input / output device including the probe fiber.

  As a technology to input and output optical signals to and from the optical fiber without cutting the optical fiber, the existing working optical fiber (main optical fiber) is bent, and another optical fiber (probe fiber) is opposed to this bent part from the side. In addition, a technique has been studied in which an optical signal is incident from the distal end portion of the probe optical fiber and an optical signal leaked and emitted from the bent optical fiber on the input side is received by the distal end portion of the probe optical fiber (for example, (See Non-Patent Document 1.)

  For example, in the related art, for the purpose of forming a temporary coupler for forming a circuit path at the time of switching work, an active optical fiber is connected between a cylindrical block having a convex curved surface and a transparent block having a concave curved surface corresponding to the cylindrical block. The working optical fiber is bent by being sandwiched between the probe fiber and the probe fiber is inserted into the gap formed in the transparent block so that the tip of the optical fiber abuts against the bending part. A technique is described in which an optical signal radiated to the concave curved surface of a transparent block is received by the probe fiber (see, for example, Non-Patent Document 1).

  In related technology, in an optical fiber side input / output device for a temporary coupler, light leaked from a bent working fiber is received by a probe fiber of a single mode fiber with a lens installed at the tip and transmitted to an amplifier. The light from the laser light source is coupled to the bending portion of the working fiber by a lens (such as a gradient index lens) at the tip of the probe and transmitted to the line. In this case, a typical value of the coupling efficiency is -20 dB for both optical input and optical output.

  In the optical fiber side input / output device, the efficiency when recombining from the probe fiber to the working fiber bent, that is, the incident coupling efficiency is important. If the incident coupling efficiency is low, the optical signal is lost, which causes many problems such as deterioration of the S / N ratio. In the existing technology, the imaging diameter of the probe fiber forming the incident beam is large, and the loss when condensing on the probe fiber core (core diameter: φ9 μm) is large. For this reason, it is difficult to reliably capture incident light, and the improvement in incident coupling efficiency has reached its peak. In particular, in application to a short break switch or the like, there is a problem that sufficient light incident coupling efficiency cannot be obtained between the probe fiber and the working fiber. If the light coupling efficiency was low, the light was too weak to reach the minimum light receiving sensitivity of the photodiode, and communication was impossible.

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) Hamada et al., "Examination of coupling efficiency of optical line switching using local optical input / output technology", IEICE Society Conference, September 2013 B-10-17 Tanobe et al., “SM / MM Shared Dual Mode Optical Fiber” IEICE Technical Report IEICE Technical Report OCS 2007-37 (2007-8) Seikura et al., "Study on improvement of light reception efficiency of local optical input / output technology by using dual mode fiber probe", IEICE Society Conference, September 2015 Thorlabs product information, "https://www.thorlabs.co.jp/thorcat/TTN/DCF13-SpecSheet.pdf", retrieved October 16, 2015

  In the related art optical fiber side input / output device, it is desirable that the incident coupling efficiency is high. Even if the coupling efficiency does not change, it is possible to increase the light incident on the bent portion of the working fiber by several times by increasing the light source intensity. However, if the light source intensity is increased unnecessarily to exceed the regulation value due to laser safety, the safety measures become strict and the use procedure becomes complicated, and the equipment cost increases.

  If the condensing size can be reduced as a gradient index lens at the tip of the probe fiber, the coupling efficiency increases. FIG. 1A shows an example of a typical graded refractive index lens-attached fiber. An image of the fiber core 9 μm is condensed by the gradient index lens and formed 1313 μm ahead of the lens end face, but the image diameter is 18 μm and is obtained as an enlarged image of the fiber core. In this case, the coupling efficiency of the working fiber to the bent portion is calculated to be 37%. Here, if the diameter of the image can be reduced, the coupling efficiency is improved (see, for example, Non-Patent Document 2).

  For example, if the image of the light source can be formed without enlarging the gradient index lens, the diameter of the image can be made smaller than the above. Therefore, if the pitch of the gradient index lens is 0.50, the image of the light source on the front side of the gradient index lens (one end on the LD side of both ends of the gradient index lens) is not enlarged and the end face on the rear side The image is formed on (the other end). However, since the image is formed on the end face, the working distance cannot be taken and the bent portion of the working fiber cannot be approached. As described above, it is difficult to reduce the image of the fiber core with a single lens of a graded index lens that is normally used.

Note that the pitch represents the meandering cycle of light rays passing through the gradient index lens. Pitch 0.25 is the length at which an inverted real image of an object at infinity is formed on the exit end face. The pitch P is a dimensionless number and is expressed by the following equation.
[formula]
P = (1 / 2π) z√A
Here, z is the length of the lens, √A is the refractive index distribution constant, and the unit is the reciprocal of the length.

  In order to reduce the diameter of the image in the gradient index lens, if a small diameter fiber having a core diameter of about 4 μm is used as the probe fiber, the size of the light source for incidence is reduced, and the image diameter is also reduced as shown in FIG. . However, the coupling efficiency when the laser beam is coupled from the communication laser light source to the thin fiber having a core diameter of about 4 μm is reduced, and the amount of light incident on the bent portion of the working fiber is not increased.

  Although communication is performed in both directions, when a thin fiber is used as a probe fiber as shown in FIG. 3, the core diameter is 4 μm when receiving light leaking from the bent portion of the current fiber. There is a trade-off in that the coupling efficiency on the light receiving side is significantly reduced compared to the case of receiving light with the probe fiber (core diameter 8 μm).

  As described above, there is a problem that it is difficult to increase the coupling efficiency between the bending portion of the current fiber and the probe fiber. Accordingly, an object of the present invention is to provide a probe fiber and an optical fiber side input / output device capable of improving the incident coupling efficiency to the bent portion of the working fiber in order to solve the above-described problems.

  In order to achieve the above object, the present invention employs means for reducing the diameter of the image at the focal point of the gradient index lens without causing the above-described deterioration in workability and trade-off.

Specifically, the first probe fiber according to the present invention is:
A single mode fiber that is single mode at the wavelength of the propagating light;
A gradient index lens whose optical axis coincides with the optical axis of the single-mode fiber;
An optical body having a uniform refractive index distribution in a cross section and connecting the single mode fiber and the gradient index lens;
Is provided.

  This probe fiber does not have a gradient index lens directly installed at the tip of the single mode fiber, and is uniform between the gradient index lens and the single mode fiber. Install an optical body with a refractive index. Since the optical body can reduce the condensing diameter by removing aberration when an image is obtained by the gradient index lens, incident coupling efficiency can be increased. Since the focal point is at a position away from the gradient index lens, the working distance can be secured, and there is no trade-off as described above. And since incident coupling efficiency is high, the light which injects into the bending part of working fiber can be transmitted with working fiber even if it does not strengthen very much.

  Therefore, the present invention can provide a probe fiber that can improve the efficiency of incident coupling to the bent portion of the current fiber.

The second probe fiber according to the present invention is:
A single mode fiber that is single mode at the wavelength of the propagating light;
A gradient index lens whose optical axis coincides with the optical axis of the single-mode fiber;
The single mode fiber and TEC are fused together so that the core diameter is smaller than the single mode fiber and the optical axis coincides with the optical axis of the single mode fiber, and the single mode fiber and the gradient index lens are connected. Fine fiber,
Is provided.

  In this probe fiber, a gradient index lens is not installed directly at the tip of the single mode fiber, but a thin fiber having a smaller core diameter than the single mode fiber is disposed between the gradient index lens and the single mode fiber. Since the diameter of the light source can be reduced in the small diameter fiber, the image diameter projected by the gradient index lens is reduced. However, since the thin fiber has a small core diameter, the coupling efficiency with the laser diode is lowered. In order to prevent this, an ordinary single mode fiber is connected to the laser diode to secure the light quantity. A small-diameter fiber is connected to a single mode fiber, and the connection is performed by TEC (Thermal-diffused Expanded Core) fusion. TEC fusion is a fusion of fibers with different MFDs while suppressing loss during fusion by thermally diffusing the distribution of Ge doped into the core of the optical fiber to widen the region of high refractive index. Technology. Since the single mode fiber core and the small diameter fiber core are smoothly connected by TEC fusion, the loss of the connection portion is suppressed to 0.5 dB or less. As a result, a small-diameter image obtained by projecting a thin fiber core with a gradient index lens can be obtained while suppressing a reduction in coupling efficiency from the laser diode to the probe fiber, and the incident coupling efficiency to the working fiber can be increased. .

  Therefore, the present invention can provide a probe fiber that can improve the efficiency of incident coupling to the bent portion of the current fiber.

The third probe fiber according to the present invention is:
A multimode fiber that is multimode at the wavelength of the first light to propagate;
A single mode fiber that is single mode at the wavelength of the second light propagating;
A small-diameter fiber having a core diameter smaller than that of the single-mode fiber and one end of which is TEC-fused with the single-mode fiber so that an optical axis coincides with the optical axis of the single-mode fiber;
A double-clad fiber having a two-stage profile of the refractive index of the core from the center toward the surface, the diameter of the core on the center side being equal to the diameter of the core of the thin fiber,
A gradient index lens connected to one end of the double-clad fiber such that the optical axis coincides with the optical axis of the double-clad fiber;
One end of the multimode fiber, the other end of the small-diameter fiber, and the other end of the double-clad fiber are connected to couple the second light from the small-diameter fiber to the central core of the double-clad fiber. A wavelength multiplexer / demultiplexer for coupling the first light propagating from the gradient index lens to the outer core of the double clad fiber to the multimode fiber;
Is provided.

  The above-described second probe fiber uses a small-diameter fiber to obtain a small core image, so that it is possible to improve the incident coupling efficiency. However, when the leaked light is received from the working optical fiber, the second probe fiber is coupled. Efficiency will decrease. Therefore, this probe fiber uses a double clad fiber (for example, see Non-Patent Documents 3, 4, and 5) in consideration of reception of leaked light. This probe fiber can receive the leaked light by a double-clad fiber with a large outer core and simultaneously improve the light receiving efficiency.

  Specifically, the thin fiber cladding is used as a multimode core by disposing a low refractive index F-doped quartz layer around the thin fiber cladding of the second probe fiber. Further, the refractive index distribution lens and the double clad fiber are fused, and the leakage light received by the gradient index lens is transmitted by a multimode core (outer core) of the double clad fiber. The leaked light propagated through the double clad fiber is coupled to the multimode fiber to which the light receiving element is connected by the wavelength multiplexer / demultiplexer.

  On the other hand, the light incident on the bending portion of the working fiber enters the wavelength multiplexer / demultiplexer from the transmission line in which the core of the single mode fiber and the core of the small diameter fiber are fused together, and the wavelength multiplexer / demultiplexer Coupled to the inner core. In the same manner as the second probe fiber, the bending portion of the working optical fiber is irradiated from the inner core of the double clad fiber through the gradient index lens. As described above, the present fiber probe can improve both the incident coupling efficiency to the bent portion of the working fiber and the light receiving coupling efficiency of the leaked light from the bent portion.

  Therefore, the present invention can provide a probe fiber that can improve the efficiency of incident coupling to the bent portion of the current fiber.

The fourth probe fiber according to the present invention is:
A multimode fiber that is multimode at the wavelength of the first light to propagate;
A single mode fiber that is single mode at the wavelength of the second light propagating;
A double-clad fiber having a two-stage profile of the refractive index of the core from the center toward the surface, the diameter of the center-side core being smaller than the diameter of the core of the single-mode fiber, and the center-side core being TEC processed at one end; ,
A gradient index lens connected to the other end of the double clad fiber so that the optical axis coincides with the optical axis of the double clad fiber;
One end of the multi-mode fiber, one end of the single-mode fiber, and one end of the double-clad fiber are connected to couple the second light from the single fiber to the central core of the double-clad fiber, and the refraction A wavelength multiplexer / demultiplexer for coupling the first light propagating from the rate distribution lens through the outer core of the double clad fiber to the multimode fiber;
Is provided.

  This probe fiber is similar in configuration to the third probe fiber, but does not place a thin fiber on the path from the light source to the wavelength multiplexer / demultiplexer. This probe fiber prevents the coupling efficiency of the light from the light source from decreasing between the wavelength multiplexer / demultiplexer and the double clad fiber by TEC fusion between the wavelength multiplexer / demultiplexer and the inner core of the double clad fiber. To do. This probe fiber has the further advantage that the operation | work which fuse | melts a single mode fiber and a small diameter fiber is unnecessary compared with a 3rd probe fiber.

An optical fiber side input / output device according to the present invention includes a first or second probe fiber,
Light is incident on the bent portion through an end surface of the gradient index lens on the side opposite to the single mode fiber close to the bent portion obtained by bending the main optical fiber.

An optical fiber side input / output device according to the present invention includes a third or fourth probe fiber,
The second light leaking from the bent portion is received through the end surface on the opposite side of the double-clad fiber of the gradient index lens close to the bent portion where the main optical fiber is bent, and then to the bent portion. The first light is incident.

  This optical fiber side input / output device includes first to fourth probe fibers. Therefore, the present invention can provide an optical fiber side input / output device capable of improving the incident coupling efficiency to the bent portion of the current fiber.

  INDUSTRIAL APPLICABILITY The present invention can provide a probe fiber and an optical fiber side input / output device that can improve the incident coupling efficiency to the bent portion of the working fiber.

It is a figure for demonstrating the related technique of this invention. (A) explains the incident light rate when a working distance of 1310 μm is taken. (B) demonstrates the case where the pitch of a gradient index lens is 0.5. By using a gradient index lens with a pitch of 0.50, light can be collected without image enlargement, but the working distance becomes zero, and it cannot be placed close to the bent portion of the working fiber. It is a figure for demonstrating the related technique of this invention. By using a thin fiber having a small core diameter of 4 μm as the probe fiber instead of the single mode fiber, the diameter of the light source can be reduced and the image diameter can be reduced, and the incident coupling efficiency is improved. However, when the light from the LD is condensed and coupled to the end face of the thin fiber, the core diameter is small, so that the coupling efficiency is lowered and the amount of light incident on the working fiber bending portion cannot be improved. It is a figure for demonstrating the related technique of this invention. By using a thin fiber having a small core diameter of 4 μm as the probe fiber instead of the single mode fiber, the diameter of the light source can be reduced and the image diameter can be reduced, and the incident coupling efficiency is improved. However, when light leakage from the bent portion of the working optical fiber is received, the light receiving coupling efficiency to the core 4 μm thin fiber is reduced. It is a figure explaining the probe fiber which concerns on this invention. In (A) and (B), a glass rod having a refractive index equivalent to that of the outside world is installed between the gradient index lens and the single mode fiber, and aberration is reduced as a one-to-one arrangement capable of projecting an image equivalent to a light source. This is an example in which the enlargement of the diameter of the image is suppressed. (C) is a reference example. It is a figure explaining the probe fiber which concerns on this invention. (A) By using a thin fiber having a small core diameter, the diameter of the light source can be reduced, and the image diameter can be reduced. For this reason, incident coupling efficiency improves. As for the loss when connecting to the light source, the loss of fusion between the SMF and the thin fiber (4 um / 80 um) can be suppressed to 0.2 dB by the TEC fusion technique. The connection loss between the SMF and the light source does not decrease as usual. (B) and (C) are diagrams for explaining the effect of the probe fiber according to the present invention. It is a figure explaining the probe fiber which concerns on this invention. It is a refractive index profile explaining the double clad fiber with which the probe fiber which concerns on this invention is provided. It is a figure explaining the probe fiber which concerns on this invention. It is a figure explaining the optical fiber side input / output apparatus which concerns on this invention. It is a figure explaining the optical fiber side input / output apparatus which concerns on this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to embodiment shown below. These implementation examples are merely illustrative,
The present invention can be implemented in various modifications and improvements based on the knowledge of those skilled in the art. In the present specification and drawings, the same reference numerals denote the same components.

[First Embodiment]
FIG. 4A and FIG. 4B are diagrams for explaining the probe fiber 101 of this embodiment. FIG. 4C is a comparative example. The probe fiber 101 includes a single mode fiber 10 that becomes a single mode at a wavelength of propagating light, a refractive index distribution type lens 12 whose optical axis coincides with the optical axis of the single mode fiber 10, and a uniform refractive index distribution in a cross section. And an optical body 11 that connects the single mode fiber 10 and the gradient index lens 12 to each other.

The probe fiber of Non-Patent Document 2 (FIGS. 1A and 4C) was focused by arranging a gradient index lens 12 directly at the tip of the single mode fiber 10. In the probe fiber 101, the refractive index distribution type lens 12 is not directly arranged at the tip of the single mode fiber 10, but the refraction of the outside world (for example, air) between the single mode fiber 10 and the refractive index distribution type lens 12. An optical body 11 having a uniform refractive index equivalent to the refractive index is installed. The optical body 11 is
For example, a transparent glass rod. The transparent glass rod has a refractive index equivalent to that of the external refractive index medium. For example, when the refractive index of an external refractive index matching agent is about 1.44, a quartz glass rod is used.

  By the arrangement of the optical body 11, the positions of the image point and the object point are targeted, and an image having the same diameter as the core of the single fiber 10 can be obtained with a constant working distance. FIGS. 4A and 4B show the cases where the gradient index lens 12 has a diameter of 125 μm and 250 μm in parallel. In both cases, an image having a core diameter is obtained, but it can be seen that the refractive index distribution type lens 12 having a diameter of 250 μm has a larger numerical aperture and a smaller image diameter. The smaller the image diameter, the better the coupling efficiency. For this reason, the incident efficiency of the probe fiber of Non-Patent Document 2 was 37% (FIG. 4C), and the image diameter of the probe fiber 101 of FIGS. The incident coupling efficiency is improved to 54% and 61%, respectively, by reducing to 3 μm and 9.9 μm. These image diameters are about the same as 9 μm, which is the diameter of the single mode fiber core.

  By arranging the optical body 11, it is possible to remove the aberration when an image is obtained by the gradient index lens 12, reduce the condensing diameter, and increase the incident coupling efficiency. This eliminates the need to greatly increase the light incident on the bent portion of the working fiber (increase the output of the LD). That is, the light from the probe fiber 101 is received by the bent portion of the working fiber, so that it can be amplified and transmitted.

[Second Embodiment]
FIG. 5A is a diagram illustrating the probe fiber 102 of the present embodiment. The probe fiber 102 includes a single mode fiber 10 that is a single mode at the wavelength of propagating light, a gradient index lens 12 whose optical axis matches the optical axis of the single mode fiber 10, and a core diameter that is greater than that of the single mode fiber 10. A small diameter fiber 13 which is small and is TEC-fused with the single mode fiber 10 so that the optical axis coincides with the optical axis of the single mode fiber 10, and connects the single mode fiber 10 and the gradient index lens 12. .

  The probe fiber 102 uses a thin fiber 13 having a smaller core diameter than the single mode fiber for optical communication. Since the diameter of the light source can be reduced by using the small diameter fiber 13, the image diameter projected by the gradient index lens 12 is reduced. However, since the thin fiber 13 has a small core diameter (4 μm), the coupling efficiency with the laser diode is lowered. In order to prevent a reduction in coupling efficiency, an ordinary optical communication single mode fiber 10 is connected to the laser diode to ensure the light quantity.

  When the thin fiber 13 is connected to the single mode fiber 10, the connection is TEC fusion. Since the core of the single-mode fiber 10 and the core of the small-diameter fiber 13 are smoothly connected by TEC fusion, the loss of the connection portion is suppressed to less than 0.5 dB (less than 11%). The probe fiber 102 obtains a small-diameter image obtained by projecting the core of the small-diameter fiber 13 with the gradient index lens 12 while suppressing the reduction in coupling efficiency from the laser diode to the small-diameter fiber 13 by TEC fusion. Incidence coupling efficiency to the bent portion of the working fiber can be increased. For example, when the gradient index lens 12 used in FIG. 4C is used, as shown in FIG. 5B, the diameter is about 8 μm, which is about twice the core diameter 4 μm of the thin fiber 13. An image is obtained at the image point.

  The probe fiber 101 of FIG. 4 employs a transparent glass rod having a refractive index comparable to the refractive index of the outside as the optical body 11, and a single mode fiber that is a light source by making the positions of the image point and the object point symmetrical. An image with a diameter comparable to the core diameter of 10 was obtained. As shown in FIG. 5C, the probe fiber 102 of the present embodiment uses a transparent glass rod and a GRIN lens, and further adopts a thin fiber 13 as the optical body 11 so that the core diameter of the thin fiber 13 is 4 μm. An image having a diameter of the same level as the above is obtained, and the incident coupling efficiency is further improved.

[Third Embodiment]
FIG. 6 is a diagram for explaining the probe fiber 103 of the present embodiment. The probe fiber 103 is
A multimode fiber 15 that is multimode at the wavelength of the first light to propagate;
A single mode fiber 10 that is single mode at the wavelength of the second light to propagate;
A small-diameter fiber 13 having a core diameter smaller than that of the single-mode fiber 10 and one end of which is TEC-fused with the single-mode fiber 10 so that the optical axis coincides with the optical axis of the single-mode fiber 10;
A double-clad fiber 16 having a two-stage profile of the refractive index of the core from the center toward the surface, the diameter of the center-side core being equal to the diameter of the core of the thin fiber 13;
A gradient index lens 12 connected to one end of the double clad fiber 16 so that its optical axis coincides with the optical axis of the double clad fiber 16;
One end of the multimode fiber 15, the other end of the small diameter fiber 13, and the other end of the double clad fiber 16 are connected to couple the second light from the small diameter fiber 13 to the central core of the double clad fiber 16. A wavelength multiplexer / demultiplexer 14 for coupling the first light propagating from the gradient index lens 12 to the outer core of the double clad fiber 16 to the multimode fiber 15;
Is provided.

  The probe fiber 102 of FIG. 5 can improve the incident coupling efficiency because a small core image is obtained, but the core of the small-diameter fiber 13 is used when receiving leaked light from the bent portion of the working optical fiber. Since it is smaller than the single mode fiber for normal optical communication at 4 μm, the light receiving coupling efficiency is lowered.

  In order to receive the leaked light from the bent portion of the working optical fiber, the probe fiber 103 has a larger core diameter and increases the light receiving coupling efficiency like the multimode fiber. Specifically, the probe fiber 103 has a two-stage refractive index distribution structure (double clad structure) as shown in FIG. 7 by forming an ultraviolet curable resin having a low refractive index around the clad of the thin fiber. A double clad fiber 16 is employed. It is composed of a core made of quartz doped with Ge at the center (center core), a cladding made of undoped quartz on the outside (outer core), and a cladding made of F-doped quartz on the outside (Non-Patent Documents 3, 4, 5). See).

  The probe fiber 103 transmits light incident on the working optical fiber through the central core (4 μm diameter) of the bull clad fiber 16 and transmits leaked light received from the working fiber using the 80 μm cladding (outer core) as a multimode core. be able to. By adopting the double clad fiber 16, the probe fiber 103 can improve the incident coupling efficiency and also improve the light receiving coupling efficiency.

  The wavelength multiplexer / demultiplexer 14 has three ports, to which a double clad fiber 16, a multimode fiber 15, and a single mode fiber 10 and a small diameter fiber 13 fused with TEC are connected. The wavelength multiplexer / demultiplexer 14 includes a wavelength filter 21, which couples the leaked light having the wavelength λ 1 from the double clad fiber 16 to the multimode fiber 15, and incident light having the wavelength λ 2 from the small diameter fiber 13. Can be coupled to the double clad fiber 16.

  Specifically, the wavelength multiplexer / demultiplexer 14 couples the leaked light propagated in the multimode through the outer core of the double clad fiber 16 to the multimode fiber 15 and causes the optical receiver (APD) to receive the light. On the other hand, the wavelength multiplexer / demultiplexer 14 is connected to the small-diameter fiber 13, and the incident light from the laser light source (LD) via the single-mode fiber 10 and the small-diameter fiber 13 is transmitted to the center-side core of the double-clad fiber 16. And is emitted to the bent portion of the working optical fiber.

  Therefore, the optical receiver (APD) can receive the leaked light having the wavelength λ1 propagating in the multimode through the outer core of the double clad fiber 16 via the multimode fiber 15 connected to the wavelength multiplexer / demultiplexer 14. On the other hand, the laser light source (LD) can enter the wavelength λ2 into the small-diameter fiber 13 that is TEC-fused with the single-mode fiber 10 and can be coupled to the central core of the double-clad fiber 16 with a small core diameter.

  The probe fiber 103 of the present embodiment employs the double clad fiber 16 and the wavelength multiplexer / demultiplexer 14 to increase the incident coupling efficiency to the bent portion of the working optical fiber and the light receiving coupling efficiency of the leaked light from the bent portion. Both can be improved.

[Fourth Embodiment]
FIG. 8 is a diagram for explaining the probe fiber 104 of the present embodiment. The probe fiber 104 is
A multimode fiber 15 that is multimode at the wavelength of the first light to propagate;
A single mode fiber 10 that is single mode at the wavelength of the second light to propagate;
A double-clad fiber 16 in which the refractive index of the core is a two-stage profile from the center to the surface, the diameter of the center-side core is smaller than the diameter of the core of the single mode fiber 10, and the center-side core is TEC processed at one end. When,
A gradient index lens 12 connected to the other end of the double clad fiber 16 so that its optical axis coincides with the optical axis of the double clad fiber 16;
One end of the multimode fiber 15, one end of the single mode fiber 10, and one end of the double clad fiber 16 are connected to couple the second light from the single fiber 10 to the central core of the double clad fiber 16, and the refractive index. A wavelength multiplexer / demultiplexer 14 for coupling the first light propagating from the distributed lens 12 to the outer core of the double clad fiber 16 to the multimode fiber 15;
Is provided.

  The probe fiber 103 of FIG. 6 has a mode field diameter reduced by TEC-fusion of the single mode fiber 10 and the small diameter fiber 13 between the LD light source and the wavelength multiplexer / demultiplexer 14. The probe fiber 104 is an example in which TEC processing is applied to the core on the center side of the double clad fiber 16 at the connecting portion between the wavelength multiplexer / demultiplexer 14 and the double clad fiber 16.

  The probe fiber 104 is optically coupled via the wavelength multiplexer / demultiplexer 14 from the single mode fiber 10 to the center side core of the TEC-processed double clad fiber 16. The probe fiber 104 has the same effect as the probe fiber 103 in FIG. 6, but has the advantage that the fusion work between the single mode fiber 10 and the small-diameter fiber 13 that is necessary for the probe fiber 103 is unnecessary. is there.

[Fifth Embodiment]
FIG. 9 is a diagram illustrating the optical fiber side input / output device 301 of the present embodiment. The optical fiber side input / output device 301 includes probe fibers (101, 102), and is close to a bent portion 110 where the main optical fiber 100 is bent, on the side opposite to the single mode fiber 10 of the gradient index lens 12. Light is incident on the bent portion 110 through the end face. The main optical fiber 100 is a working optical fiber that connects between the transceivers (160, 170).

  As described in the first and second embodiments, the probe fiber (101, 102) employs the optical body 11 and the small-diameter fiber 13 to reduce the image diameter and increase the incident coupling efficiency. Therefore, the optical fiber side input / output device 301 can enter light into the working optical fiber 100 without having to increase the output of the LD. Therefore, the optical fiber side input / output device 301 can be used as a repeater for coupling a signal transmitted from another to the working optical fiber 100.

[Sixth Embodiment]
FIG. 10 is a diagram illustrating the optical fiber side input / output device 302 of the present embodiment. The optical fiber side input / output device 302 includes probe fibers (103, 104), and is located near the bent portion 110 where the main optical fiber 100 is bent, on the side opposite to the double clad fiber 16 of the gradient index lens 12. The second light leaking from the bent portion 110 is received through the end face, and the first light is incident on the bent portion 110. The main optical fiber 100 is a working optical fiber that connects between the transceivers (160, 170).

  As described in the third and fourth embodiments, the probe fiber (103, 104) employs the double clad fiber 16, reduces the image diameter, increases the incident coupling efficiency, widens the light receiving area, and bends. Increasing the light receiving coupling efficiency of leaked light from Therefore, the optical fiber side input / output device 301 can enter light into the working optical fiber 100 without increasing the output of the LD, and can receive the leaked light from the working optical fiber 100 without error. Therefore, the optical fiber side input / output device 302 can amplify and shape the signal after the APD and transmit it to the other, and amplify and shape the signal transmitted from the other and transmit it from the LD to the working optical fiber 100. Can be used as a repeater.

[Other Embodiments]
In the third and fourth embodiments, the double clad fiber 16 is exemplified by fibers of Ge-doped quartz, undoped quartz, and F-doped quartz from the center. A fiber coated with a low refractive index coating may be used.

In short, the present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. Moreover, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above embodiments. For example, some components may be deleted from all the components shown in each embodiment. further,
You may combine suitably the component covering different embodiment.

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

10: single mode fiber 11: optical body 12: gradient index lens (GRIN lens)
13: Fine fiber 14: Wavelength multiplexer / demultiplexer 15: Multimode fiber 16: Double clad fiber 21: Wavelength filter 100: Main optical fiber (current optical fiber)
101, 102, 103, 104: probe fiber 110: bending section 160, 170: transceiver 301, 302: optical fiber side input / output device

Claims (6)

A single mode fiber that is single mode at the wavelength of the propagating light;
A gradient index lens whose optical axis coincides with the optical axis of the single-mode fiber;
An optical body having a uniform refractive index distribution in a cross section and connecting the single mode fiber and the gradient index lens;
A probe fiber comprising: A single mode fiber that is single mode at the wavelength of the propagating light;
A gradient index lens whose optical axis coincides with the optical axis of the single-mode fiber;
The single mode fiber and TEC are fused together so that the core diameter is smaller than the single mode fiber and the optical axis coincides with the optical axis of the single mode fiber, and the single mode fiber and the gradient index lens are connected. Fine fiber,
A probe fiber comprising: A multimode fiber that is multimode at the wavelength of the first light to propagate;
A single mode fiber that is single mode at the wavelength of the second light propagating;
A small-diameter fiber having a core diameter smaller than that of the single-mode fiber and one end of which is TEC-fused with the single-mode fiber so that an optical axis coincides with the optical axis of the single-mode fiber;
A double-clad fiber having a two-stage profile of the refractive index of the core from the center toward the surface, the diameter of the core on the center side being equal to the diameter of the core of the thin fiber,
A gradient index lens connected to one end of the double-clad fiber such that the optical axis coincides with the optical axis of the double-clad fiber;
One end of the multimode fiber, the other end of the small-diameter fiber, and the other end of the double-clad fiber are connected to couple the second light from the small-diameter fiber to the central core of the double-clad fiber. A wavelength multiplexer / demultiplexer for coupling the first light propagating from the gradient index lens to the outer core of the double clad fiber to the multimode fiber;
A probe fiber comprising: A multimode fiber that is multimode at the wavelength of the first light to propagate;
A single mode fiber that is single mode at the wavelength of the second light propagating;
A double-clad fiber having a two-stage profile of the refractive index of the core from the center toward the surface, the diameter of the center-side core being smaller than the diameter of the core of the single-mode fiber, and the center-side core being TEC processed at one end; ,
A gradient index lens connected to the other end of the double clad fiber so that the optical axis coincides with the optical axis of the double clad fiber;
One end of the multi-mode fiber, one end of the single-mode fiber, and one end of the double-clad fiber are connected to couple the second light from the single fiber to the central core of the double-clad fiber, and the refraction A wavelength multiplexer / demultiplexer for coupling the first light propagating from the rate distribution lens through the outer core of the double clad fiber to the multimode fiber;
A probe fiber comprising: A probe fiber according to claim 1 or 2,
The optical fiber side entrance is characterized in that light is incident on the bent portion through an end surface opposite to the single mode fiber of the gradient index lens adjacent to the bent portion where the main optical fiber is bent. Output device. A probe fiber according to claim 3 or 4,
The second light leaking from the bent portion is received through the end surface on the opposite side of the double-clad fiber of the gradient index lens close to the bent portion where the main optical fiber is bent, and then to the bent portion. An optical fiber side input / output device, wherein the first light is incident.

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