JP2016109559A - Test light cutoff filter and in-service testing method applying the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow an in-service test of a test object optical line to be performed by reducing an impact which test light has on communication light in the test object optical line.SOLUTION: An in-service testing method according to the present invention uses a test light cutoff filter 14 that gives loss to light with the wavelength of test light and lets light with the wavelength of communication light propagated by test object optical fiber penetrate. The test light cutoff filter 14 comprises: a mode conversion unit 31 that converts the mode of light with the wavelength of the test light that propagates in a fundamental mode in the test object optical fiber into a higher order mode; and a loss inflicting unit 32 that inflicts only little loss to the communication light propagating in the fundamental mode in the test object optical fiber and inflicts loss to the test light propagating in the higher mode in the test object optical fiber.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a test light blocking filter that transmits test light while causing loss to test light for an in-service test of an optical line, and an in-service test method using the same.

  Over 10 years have passed since the start of the FTTH (Fiber To The Home) service, and there is concern about the occurrence of failures due to deterioration of the working optical equipment over time. Among them, in an optical line, a bent portion or a connection portion of an optical fiber is a place where failure is likely to occur. In order to prevent failures before they occur, potential optical failure points such as optical fiber bends and connections are detected before the effects on the user become obvious by regularly testing the optical line, and countermeasures are taken. It is hoped to do. When testing an active optical line, it is necessary to perform the test without affecting user communication.

  In Non-Patent Document 1, as a technique capable of detecting with high sensitivity an abnormality in an optical line due to bending or connection of an optical fiber before the influence on the user becomes obvious, a cut in the optical fiber to be tested is performed. A technique for measuring a higher-order mode of backscattered light using a wavelength shorter than the off-wavelength is disclosed. However, there is no mention of a method in which the test light does not affect user communication.

  On the other hand, as a method for preventing the test light from affecting user communication, Non-Patent Document 2 describes a test in OTDR (Optical Time Domain Reflectometry) using test light having a wavelength band shorter than the cutoff wavelength of a single mode fiber. A technique for reducing the influence on communication by setting the wavelength of light outside the light receiving band of the transmission device is disclosed.

A. Nakamura, K. Okamoto, I. Ogushi, N. Hanzawa, K. Katayama and T. Manabe, "Highly Sensitive Detection of Fiber Bending Using 1-μm-band Mode-detection OTDR," OECC2014, TU6C4, 2014. Yoshida Yoko et al., “A Proposal for Determining Failure of Optical Splitter Using 0.65μm Band OTDR”, 2004 IEICE General Conference, B-13-33, pp. 581.

  As described above, in the technique disclosed in Non-Patent Document 2, the influence on communication is reduced by setting the wavelength of the test light outside the light receiving band of the transmission device. However, in this method, a short wavelength that is outside the light receiving band of the transmission device has a very large loss when propagating through the optical fiber, so that the distance that can be tested is significantly limited. There are challenges.

  The present invention has been made paying attention to the above circumstances. The first object of the present invention is to reduce the influence of test light on communication light in an optical line to be tested. It is to provide a test method that enables testing.

  A second object of the present invention is to provide a test light blocking filter that allows loss of test light while allowing communication light to pass therethrough in order to enable such a test method.

  In order to achieve the above object, a first aspect of the present invention includes the following components.

  That is, the first aspect of the present invention is an optical line testing method that is performed using test light having a wavelength that performs multimode operation. In this test method, a test light blocking filter that transmits light having a wavelength of communication light transmitted through an optical line while causing loss to light having a wavelength of test light is used. The test light blocking filter converts the light of the wavelength of the test light that propagates in the optical line in the fundamental mode into a higher-order mode, and causes little loss to the communication light that propagates in the fundamental mode in the optical line. Loss to the test light propagating in the higher order mode.

  Moreover, the 1st viewpoint of this invention is equipped with the following aspects.

  That is, the conversion to the higher order mode is performed by forming a long period grating for the optical fiber forming the optical line.

  A loss is given to the test light by forming a long-period grating in the optical fiber forming the optical line and further converting the light converted into the higher-order mode into the cladding mode.

  Alternatively, by utilizing the characteristics of the optical fiber that forms the optical line that the higher-order mode has a greater loss due to bending than the fundamental mode, the communication light propagated in the fundamental mode has little loss and is A bend is applied to the optical fiber that causes a loss in the test light propagated in the next mode. Thereby, almost no loss is given to the communication light, and the test light is given a loss.

  Moreover, the 2nd viewpoint of this invention is equipped with the following components.

  That is, the second aspect of the present invention is an optical line test method that is performed using test light having a wavelength for multimode operation. In this test method, a test light blocking filter that transmits light having a wavelength of communication light transmitted through an optical line while causing loss to light having a wavelength of test light is used. The test light blocking filter converts the light having the wavelength of the test light propagating through the optical line in the fundamental mode to the cladding mode by the first long-period grating, and converts the light in the optical line to the higher order by the second long-period grating. The light having the wavelength of the test light propagating in the mode is converted into the clad mode. As a result, the test light can be tested without affecting the communication.

  In the first and second aspects of the present invention, the long-period grating is provided by applying a periodic stress in the longitudinal direction of the optical fiber forming the optical line.

  Furthermore, the 3rd viewpoint of this invention is equipped with the following components.

  That is, a third aspect of the present invention is a test light blocking filter applied to an optical line test performed using test light having a wavelength capable of multimode operation. This test light blocking filter gives little loss to communication light propagating in the fundamental mode through mode conversion means for converting the light of the wavelength of the test light propagating in the fundamental mode in the optical line to the higher order mode. And loss providing means for giving a loss to the test light propagating in the higher-order mode in the optical line.

  Furthermore, the 4th viewpoint of this invention is equipped with the following components.

  That is, the fourth aspect of the present invention is a test light blocking filter applied to an optical line test performed using test light having a wavelength that performs multimode operation. The test light blocking filter includes a first long-period grating that converts light having a wavelength of test light propagating in an optical line in a fundamental mode into a cladding mode, and the test light propagating in a higher-order mode in the optical line. A second long-period grating that converts light of a wavelength into the cladding mode. This makes it possible to transmit light having the wavelength of communication light propagated through the optical line while losing light having the wavelength of the test light.

  That is, according to the present invention, it is possible to provide a test method capable of reducing the influence of test light on communication light in an optical line to be tested, thereby enabling in-service testing of the optical line. it can.

  In addition, in order to enable such a test method, a test light blocking filter that transmits the communication light while causing loss to the test light can be provided.

FIG. 1 is a configuration example of a network for explaining an in-service test method according to an embodiment of the present invention. FIG. 2 is a diagram for explaining a first example of a test light blocking filter. FIG. 3 is a functional block diagram illustrating a second example of the test light blocking filter. FIG. 4 is a diagram for explaining the function of the mode conversion unit. FIG. 5 is a diagram for explaining the function of the loss providing unit. FIG. 6 is a functional block diagram showing a third example of the test light blocking filter.

  Embodiments according to the present invention will be described below with reference to the drawings. The embodiment described below is an example of the present invention, and the present invention is not limited to the following embodiment.

  FIG. 1 is a configuration example of a network 100 for explaining an in-service test method according to an embodiment of the present invention. The test method is executed using test light having a wavelength capable of multimode operation with respect to the optical fiber 10 to be tested which is an optical line to be tested.

  As shown in FIG. 1, the in-service test performed on the optical fiber under test 10 includes a transmission apparatus 11, a test apparatus 12 for testing the optical fiber under test 10, and communication light and test light. This is implemented by a coupler 13 that performs the test, a test light blocking filter 14 that gives a loss to the test light propagating through the optical fiber 10 to be tested, and a subscriber terminal 15 that is a transmission device on the user side.

  The test apparatus 12 is an apparatus that performs light reflection measurement such as OTDR, for example, and can analyze the intensity distribution with respect to the distance of the return light from the optical fiber under test 10 to obtain the characteristics of the optical fiber under test 10. it can.

  The communication light output from the transmission device 11 enters the optical fiber 10 to be tested, passes through the test light blocking filter 14, and is received by the subscriber terminal 15.

  On the other hand, the test light output from the test apparatus 12 is incident on the optical fiber 10 to be tested, and then a large loss is given by the test light blocking filter 14 and is blocked before the subscriber terminal 15.

  Hereinafter, the test light blocking filter 14 applied to this in-service test will be described in detail.

(First example of test light blocking filter 14)
FIG. 2 is a diagram for explaining a first example of the test light blocking filter 14. A first example of the test light blocking filter 14 is a wavelength filter 21. The wavelength filter 21 has a wavelength filtering function that transmits the wavelength of the communication light and blocks the wavelength of the test light.

(Second example of test light blocking filter 14)
FIG. 3 is a functional block diagram showing a second example of the test light blocking filter 14. In the second example, the test light blocking filter 14 includes a mode conversion unit 31 and a loss imparting unit 32.

  FIG. 4 is a diagram for explaining the function of the mode conversion unit 31.

  As shown in FIG. 4A, when communication light is incident on the mode converter 31 in the LP01 mode, the mode converter 31 does not perform mode conversion of the communication light, and the communication light in the LP01 mode is lost. The mode conversion unit 31 is transmitted without being received.

  On the other hand, as shown in FIG. 4B, when test light is incident on the mode converter 31 in the LP01 mode, the mode converter 31 converts the test light from the LP01 mode to the LP11 mode, LP11 mode test light is output from the converter 31.

  The mode converter 31 having such a function is, for example, a long-period grating that periodically changes the refractive index in the longitudinal direction of the optical fiber. Such a long-period grating changes the refractive index by applying periodic stress in the longitudinal direction of the optical fiber, irradiating the optical fiber with ultrasonic waves, or irradiating the optical fiber with ultraviolet rays or a CO2 laser. And so on.

  The long-period grating formed in this manner can generate mode coupling in light that satisfies the phase matching condition for the period. Therefore, by designing the period of the long-period grating to an appropriate value, light of a desired wavelength can be converted into a higher order mode, for example, from the LP01 mode to the LP11 mode, or the LP01 mode or the LP11 mode. Can be lost to light of a desired wavelength, for example, by coupling to a cladding mode.

  Next, the loss imparting unit 32 will be described.

  FIG. 5 is a diagram for explaining the function of the loss providing unit 32. As shown in FIG. 5, when communication light is incident on the loss imparting unit 32 in the LP01 mode, the communication light passes through the loss imparting unit 32 with almost no loss. On the other hand, when the test light is incident on the loss applying unit 32 in the LP11 mode, the loss applying unit 32 gives a loss to the test light. As a result, the test light does not pass through the loss imparting unit 32.

  The loss imparting unit 32 having such a function is realized by, for example, imparting a bending to the optical fiber that does not give a loss to the long-period grating described above or the LP01 mode but gives a large loss to the LP11 mode. Is done.

(Third example of test light blocking filter 14)
FIG. 6 is a functional block diagram showing a third example of the test light blocking filter 14. A third example of the test light blocking filter 14 includes a long-period grating 61 and a long-period grating 62 that are continuously arranged.

  The long period grating 61 has a function of blocking the test light propagated in the LP01 mode by converting the test light propagated in the LP01 mode into a clad mode and giving a loss.

  The long period grating 62 has a function of blocking the test light propagated in the LP11 mode by converting the test light propagated in the LP11 mode into a cladding mode and giving a loss.

  Therefore, by arranging the long-period grating 61 and the long-period grating 62 continuously, it becomes possible to block both the test light propagated in the LP01 mode and the LP11 mode. Note that the order of arranging the long-period grating 61 and the long-period grating 62 may be reversed.

  As described above, according to the test light blocking filter 14 described with reference to FIGS. 2 to 6, only the test light is lost, while the communication light is transmitted.

  Therefore, by arranging such a test light blocking filter 14 in the middle of the optical fiber under test 10 as shown in FIG. 1, the in-service test method according to the present embodiment allows the optical fiber under test 10 to Since the influence of the test light on the communication light can be reduced, the in-service test of the optical fiber 10 to be tested can be realized.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible in the range which does not deviate from the summary of this invention.

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

DESCRIPTION OF SYMBOLS 10 Optical fiber 11 to be tested 11 Transmission apparatus 12 Test apparatus 13 Coupler 14 Test light cutoff filter 15 Subscriber terminal 21 Wavelength filter 31 Mode conversion part 32 Loss imparting part 61 Long period grating 62 Long period grating 100 Network

Claims (8)

In a test method of an optical line executed using test light having a wavelength that operates in a multimode,
While providing a loss to the light of the wavelength of the test light, a test light blocking filter that transmits the light of the wavelength of the communication light propagated by the optical line is installed,
The test light blocking filter converts light having a wavelength of the test light propagating in the fundamental mode in the optical line to a higher order mode, and almost loses the communication light propagating in the fundamental mode in the optical line. An in-service test method that gives a loss to test light propagating in the higher-order mode in the optical line.   The in-service test method according to claim 1, wherein the conversion to the higher-order mode is performed by forming a long-period grating for the optical fiber forming the optical line.   The loss to the test light is performed by forming a long-period grating in an optical fiber forming the optical line and further converting the light converted into the higher-order mode into a cladding mode. The in-service test method described in 1.   By utilizing the characteristic of the optical fiber forming the optical line that the higher-order mode has a greater loss due to bending than the fundamental mode, the communication light propagated in the fundamental mode is hardly lost. The optical fiber is given a bend that gives a loss to the test light propagated in the higher-order mode, so that the communication light is hardly given a loss and the test light is given a loss. The in-service test method described. In a test method of an optical line executed using test light having a wavelength that operates in a multimode,
While providing a loss to the light of the wavelength of the test light, a test light blocking filter that transmits the light of the wavelength of the communication light propagated by the optical line is installed,
The test light blocking filter converts light having a wavelength of the test light propagating through the optical line in a fundamental mode into a clad mode by using a first long-period grating, and converts the light into the optical line by using a second long-period grating. An in-service test method that enables the test light to perform a test without affecting communication by converting the light having the wavelength of the test light propagating in a high-order mode into the clad mode. .   The in-service test according to any one of claims 2, 3, and 5, wherein the long-period grating is formed by applying a periodic stress in a longitudinal direction of an optical fiber forming the optical line. Method. A test light blocking filter applied to a test of an optical line performed using a test light having a wavelength for multimode operation,
Mode conversion means for converting light of the wavelength of the test light propagating in the fundamental mode in the optical line into a higher-order mode;
A test light blocking filter comprising: loss imparting means that imparts a loss to test light propagating in the higher-order mode in the optical line, while causing little loss to communication light propagating in the fundamental mode in the optical line. A test light blocking filter applied to a test of an optical line performed using a test light having a wavelength for multimode operation,
A first long-period grating that converts light of the wavelength of the test light propagating in the fundamental mode in the optical line into a cladding mode;
A second long-period grating that converts light of the wavelength of the test light propagating in the optical line in a higher-order mode into the cladding mode, thereby giving a loss to the light of the wavelength of the test light, A test light blocking filter capable of transmitting light having a wavelength of communication light propagated through the optical line.

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