JP2009294100A - Fiber identification method and device using short-wavelength region - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fiber identification method and a fiber identification device solving the problem that a conventional fiber identification device does not cope with an optical fiber with improved bending loss, the problem that introduction of various kinds of optical fibers with different optical characteristics increases the variance of leakage light obtained by the fiber identification, and the problem that test light should be removed for performing in-service test because a light receiver for communication also detects the test light when the test is performed at a wavelength near communication light and the communication signal is adversely affected. <P>SOLUTION: The fiber identification device includes a test light source, a leakage light generation part causing the test light to leak from a fiber to be measured, and a light receiving part detecting the leaking light. A light wave having a wavelength not longer than 1.26 μm is incident from the test light source so that the fiber identification of the optical fiber is performed by causing the light to leak therefrom. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a light continuity test in an optical transmission system, and more particularly, to a method for contrasting a core and a device for contrasting using a short wavelength region.

  In the construction and operation of the optical line, it is necessary to find the desired optical fiber core at the work site in order to confirm the desired optical fiber core. For this reason, the core wire contrast device is widely used to take out a part of the light propagating through the optical fiber and confirm whether the optical fiber is a desired optical fiber. In order to extract a part of the propagating light in the optical fiber, a method of bending the optical fiber is generally used. For example, in Patent Document 1, the optical fiber contrast device forms a bent portion in an optical fiber and receives light leaking from the bent portion to determine whether or not light propagates through the optical fiber.

Japanese Patent No. 3407812

  However, for optical fibers with improved bending loss characteristics that have been attracting attention recently, there is almost no light leaking out even if a bent portion is formed. There was a problem that could not be handled. In addition, the introduction of various optical fibers having different optical characteristics has caused a problem that variations in leaked light obtained by contrast control of the cores are increased. In addition, when a test is performed at a wavelength close to that of communication light, the communication light receiver also detects the test light and affects the communication signal. Therefore, in order to perform the in-service test, it is necessary to remove the test light.

  In order to solve the above-mentioned problems, the core wire contrast method and the core wire contrast device according to the present invention leak the light wave having a wavelength of 1.26 μm or less to the optical fiber to be measured for performing the core wire contrast. It is characterized in that the core line is controlled.

  In addition, in the core line contrast method and the core line contrast device according to the present invention, the optical wave has a first higher-order mode or a higher-order propagation mode, and leaks the higher-order mode to cause the measured optical fiber to leak. It is good also as what performs a core line contrast.

  Further, the core wire contrast method and the core wire contrast device of the present invention form a long period grating by periodically applying stress along the longitudinal direction to the optical fiber to be measured, and set the propagation mode to a higher order mode. It is good also as what carries out a core line contrast by converting into (1) and detecting the leakage of the higher order mode which generate | occur | produced.

  The core wire contrast method and the core wire contrast device of the present invention may have a period in which the stress is applied is 0.53 mm or less.

  The core wire contrast method and the core wire contrast device of the present invention may be configured such that the leakage of the light wave is performed by bending the measured fiber, and the bending radius is 8.5 mm or more.

  The cord control method and the cord control device of the present invention have the effect that the cord control can be realized even in an optical fiber having improved bending loss characteristics. In addition, since the variation in the optical characteristics with respect to the structural change is smaller as the wavelength is shorter, it is possible to reduce the variation in the leaked light obtained by the control. Further, since the light receiving efficiency at a wavelength of 1.26 μm or less is low in a light receiver of a general communication device, there is an effect that the influence on communication light can be reduced.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, the first embodiment will be described.
FIG. 1 (a) is a diagram showing a measurement system 100 including an example of a cord control method and a cord control device according to the first embodiment of the present invention.
In FIG. 1, the measurement system 100 includes a light source 101, a non-measurement fiber 102, and a core wire contrast device 103, and the core wire contrast device 103 includes a leakage means 104 and a light receiver 105. The light source 101 makes a light wave having a wavelength of 1.26 μm or less incident on the measured fiber 102. Leakage means 104 leaks a light wave incident on fiber under measurement 102 by bending, grating, or the like, and receives the leaked light with light receiver 105, thereby performing a core contrast with respect to fiber under measurement 102. it can.

  In a high-speed optical line used for a public line, a low loss 1.3 μm or 1.55 μm band is used, so InGaAs is used as the light receiver 105. The light receiver 105 using InGaAs has high light receiving sensitivity with respect to light waves in the 1.3 to 1.65 μm band. On the other hand, the cut-off wavelength of a single mode optical fiber used in a public line is defined as 1.26 μm or less. Here, FIG. 1B shows a distribution example 110 of the light reception bands of various light receivers used as the light receiver 105. As shown in FIG. 1B, if the test light is equal to or less than the cutoff wavelength, the light receiving sensitivity of the light receiver 105 is small, so that the test can be performed without affecting the communication signal. Hereinafter, a method of performing the contrast control by detecting leakage light caused by bending using a light wave having a wavelength of 1.26 μm or less will be described.

FIG. 2 is a characteristic diagram showing a characteristic example 200 of bending loss characteristics of a photonic crystal fiber (PCF) and a conventional single mode fiber (SMF).
In FIG. 2, a solid line shows PCF and a broken line shows conventional SMF. PCF has attracted attention as a next-generation optical communication medium because it has a structure having a plurality of holes in the longitudinal direction and has various characteristics that cannot be realized by conventional optical fibers. As shown in FIG. 2, the PCF has very good bending loss characteristics in the communication wavelength band as compared with the SMF. In SMF, the bending loss decreases as the wavelength becomes shorter, whereas in PCF, the bending loss increases rapidly in the short wavelength band. Accordingly, when the measured fiber 102 shown in FIG. 1A is a PCF, communication light is selected by selecting test light in a short wavelength band where bending loss increases and detecting leakage light due to bending at the wavelength. Efficient cord contrast can be performed while reducing the influence on light.

FIG. 3 is a characteristic diagram showing a characteristic example 300 of bending loss characteristics in the SMF propagation mode and the first higher-order mode.
In FIG. 3, a solid line and a broken line indicate bending losses in the fundamental mode (LP ₀₁ mode) and the first higher-order mode (LP ₁₁ mode) at a wavelength of 0.85 μm, and a two-dot chain line indicates a bending in the fundamental mode at a wavelength of 1.55 μm. Indicates loss. As shown in FIG. 2, in the SMF, since the bending loss of the propagation mode becomes smaller as the wavelength becomes shorter, it becomes difficult to detect the leakage light due to the bending of the propagation mode in the short wavelength band. However, as shown in FIG. 3, the bending loss of the higher order mode is several orders of magnitude larger than the propagation mode. Therefore, if the higher order mode is included in the incident light, the higher order mode leaks due to bending, so that the leaked light can be detected. Further, in SMF, since the first higher-order mode can be propagated at 1.26 μm or less, it is possible to propagate the incident light by including the higher-order mode component in advance. Here, it is necessary to reduce the influence on communication light when bending is applied. For example, in order to suppress loss at 180 ° bending to 3 dB or less at a wavelength of 1.55 μm used in communication, the bending radius is preferably 8.5 mm or more.

Next, a second embodiment of the present invention will be described.
FIG. 4 is a diagram showing a measurement system 400 using a mode conversion by a long-period grating, which is an example of the cardiac line contrast method and the cardiac line contrast device according to the second embodiment of the present invention.
In FIG. 4, the measurement system 400 includes a measured fiber 402, a stress applying unit 403, and a light receiver 405. First, a light wave having a wavelength of 1.26 μm or less is incident on the measured fiber 402. Here, when a periodic stress 403 is applied to the measured fiber 402, a long-period grating is formed, and incident light is converted into a higher-order mode by appropriately selecting this period. Since the higher-order mode has a large bending loss as shown in FIG. 3, it leaks in the subsequent stress applying section 403 and is detected by the light receiver 405, and the cord contrast is realized. At this time, the incident light only needs to include only the fundamental mode of the fiber to be measured 402. The fundamental mode is preferable because the transmission distance is small and the test distance can be increased.

FIG. 5 is a characteristic diagram showing a characteristic example 500 of a grating period necessary for converting the basic mode (LP ₀₁ mode) to the first higher-order mode (LP ₁₁ mode).
In FIG. 5, a solid line indicates SMF, and a broken line and a two-dot chain line indicate trench type and hole assist type optical fibers having improved bending loss characteristics. In the wavelength range (0.8 to 1.3 μm) in the figure, conversion to the first higher-order mode can be performed by setting the grating period to 460 to 530 μm. In general, the higher the mode, the shorter the required grating period, so that mode conversion can be performed using a shorter period. Also, as the wavelength becomes shorter, the required grating period value between the SMF and the optical fiber with improved bending characteristics becomes closer, so a single element can handle more types of optical fibers. In addition, although an example in the SMF is shown here, the same effect can be obtained by appropriately designing the grating period in an optical fiber having different optical characteristics such as a dispersion shift fiber and a cutoff shift fiber.

  The present invention can be used for specifying an optical fiber during construction, maintenance, and operation of an optical line.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram for explaining a method and a device for contrasting cores according to the present invention, and FIG. FIG. 1B is a diagram showing a system 100, and FIG. 1B is a diagram showing distribution examples 110 of light reception bands of various light receivers used as the light receiver 105. FIG. It is a characteristic view which shows the characteristic example 200 of the bending loss characteristic of the photonic crystal fiber (PCF) and the conventional single mode fiber (SMF) used for the core line contrast method and the core line contrast apparatus of this invention. It is a characteristic view which shows the characteristic example 300 of the bending loss characteristic of the single mode fiber used for the core line contrast method and core line contrast apparatus of this invention. It is an example of the core line contrast method and the core line contrast device according to the second embodiment of the present invention, and is a diagram showing a measurement system 400 using mode conversion by a long period grating. It is a characteristic view which shows the characteristic example 500 of the grating period required in order to convert the fundamental mode in connection with the core line contrast method and the core line contrast device of the present invention to the first higher-order mode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Light source 102 Fiber to be measured 103 Core line contrast apparatus 104 Leak means 105 Light receiver 402 Fiber to be measured 403 Stress application section 404 Stress 405 Light receiver

Claims (10)

  A method of contrasting a core, comprising performing a contrast of the optical fiber by leaking a light wave having a wavelength of 1.26 μm or less to the optical fiber to be measured.   2. The optical fiber has a first higher-order mode or a higher-order propagation mode, and the optical fiber to be measured is contrasted by leaking the higher-order mode. The core contrast method.   By forming a long-period grating by periodically applying stress along the longitudinal direction to the optical fiber to be measured, converting the propagation mode to a higher-order mode, and detecting leakage of the higher-order mode that has occurred 3. The method of contrasting cores according to claim 1 or 2, wherein the cores are contrasted.   The core wire contrast method according to claim 3, wherein a period in which the stress is applied is 0.53 mm or less.   5. The method according to claim 1, wherein the leakage of the light wave is performed by bending the fiber to be measured, and the bending radius is 8.5 mm or more.   A test light source; a leakage light generating unit that leaks test light to the fiber to be measured; and a light receiving unit that detects the leaked light; and a light wave having a wavelength of 1.26 μm or less is incident from the test light source Then, the optical fiber contrast device performs the optical fiber core contrast by leaking the optical fiber.   7. The optical fiber has a first higher-order mode or a higher-order propagation mode, and the optical fiber to be measured is contrasted by leaking the higher-order mode. Core wire contrast device.   The leakage light generating part has a stress applying part that applies periodic stress along the longitudinal direction of the fiber to be measured, and forms a long-period grating by periodically applying stress, and the propagation mode is higher order. The cord contrast device according to claim 6 or 7, wherein the cord contrast is performed by converting into a mode and detecting leakage of a higher-order mode that has occurred.   The core wire contrast device according to claim 8, wherein a period in which the stress is applied is 0.53 mm or less.   The core according to any one of claims 6 to 9, wherein the leakage light generation part has a structure that bends the fiber to be measured, and a bending radius of the bending part is 8.5 mm or more. Line contrast device.

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