JP2007057415A - Connection loss determination method of optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a determination method of optical fiber connection loss monitorable even after starting communication use with a simple structure. <P>SOLUTION: A first clad light intensity detecting means 101 for detecting the intensity of the light propagating in the clad of a first optical fiber 11 is disposed near a connection end face of the first optical fiber 11. While a light source 100 of light travelling from a second optical fiber 12 to the first optical fiber through a connection point is connected to the second optical fiber side, it is determined whether the connection loss exceeds a predetermined reference value based on the light intensity detected by the first clad light intensity detecting means 101. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for measuring and determining a loss at an optical fiber connection point when or after an optical fiber communication network is constructed.

  Conventionally, the connection loss measurement / determination of the connection portion of the optical fiber is a method of directly measuring the connection loss (see Non-Patent Document 1) or a method of enlarging the optical fiber of the connection portion and estimating it from its core shape, etc. (See Non-Patent Document 2).

  An example of the former method is shown in FIG. In the figure, 1 is an optical fiber connection portion, 11 and 12 are optical fibers, 100 is a light source, 201 is an end face light receiving element that receives light intensity emitted from the end face of the optical fiber, and 202 is light received by the end face light receiving element 201. It is a display part which calculates and displays the intensity | strength of light as optical power. In the connection loss measurement method, first, the outgoing optical power Pin from the optical fiber 12 is measured before the optical fiber connection work, and the outgoing optical power Pout from the optical fiber 11 is measured after the connection work. And connection loss is calculated | required from the difference Pin-Pout of both measured values.

The latter method is widely used for fusion splicing, and the fused optical fiber is enlarged with a microscope or the like, and irregularities such as core displacement and deformation in the optical fibers 11 and 12 are measured. The connection loss is calculated from In this method, since the optical fiber core needs to be enlarged and displayed, the material of the optical fiber connecting portion 1 needs to be transparent. For this reason, in the connection method (hereinafter referred to as “butt connection”) that butt-fixes optical fibers such as mechanical splices that are widely used at present, colored plastic (for example, black) plastic or metal is used as the splice material. Therefore, this method cannot be applied.
T. Tanifuji and Y. Kato, "Realization of a Low Loss Splice for Single-Mode Fibers in the Field Using an Automatic Arc-Fusion Splicing Machine", in Proceedings, Optical Fiber Communication, Feb. 1983, paper MG3 T. Haibara, M. Matsumoto, T. Tanifuji and M. Tokuda, "Monitoring Method for Axis Alignment of Single-Mode Optical Fiber and Splice-Loss Estimation", Opt. Lett. 8. 502 1983

  However, the above-described method for directly measuring connection loss (Non-Patent Document 1) is premised on operation other than the connection work place. That is, there is a problem that it is necessary to dispatch a worker to a point where Pout is measured, such as when the optical fiber 11 is long, and it is necessary to cut and create an end face of the optical fiber 11 for Pout measurement.

  Moreover, although the method estimated from a core shape etc. (nonpatent literature 2) does not require operation other than a connection work place, there exists a possibility that there exists a difference in the estimated value of connection loss, and actual connection loss. Moreover, there exists a subject that it is difficult to apply except melt | fusion.

  Furthermore, monitoring the changes over time and long-term of connection loss after completing the connection work, installing transmission devices at both ends of the optical fiber transmission line, and starting communication use However, in the conventional method, in addition to the above-described reason, there is a problem that it is extremely difficult in consideration of the possibility of affecting the transmission path and communication.

  Therefore, the present invention has been proposed in view of the above-described problems, and is limited to the operation only at the connection work site, eliminates the need for cutting an optical fiber and creating an end face, and without using a means such as a microscope. To provide a simple optical fiber connection loss determination method that can monitor the change over time of connection loss at a connection point in a transmission line, regardless of the material of the fiber connection part, even after the start of communication use. With the goal.

  In order to achieve the above object, the present application is a method for measuring a connection loss at a connection point of a pair of optical fibers, and propagates the cladding of the first optical fiber in the vicinity of the connection end face of the first optical fiber. A first clad light intensity detecting means for detecting the light intensity is provided, and a light source of light traveling from the second optical fiber to the first optical fiber through the connection point is connected to the second optical fiber side. Therefore, it is proposed to determine whether or not the connection loss exceeds a predetermined reference value based on the light intensity detected by the first clad light intensity detecting means.

  Generally, when the connection loss of an optical fiber exceeds a predetermined reference value, light often leaks into the cladding of the optical fiber due to an optical axis shift or the like. Therefore, in the present invention, first clad light intensity detection means for detecting the intensity of light propagating through the cladding of the first optical fiber is provided in the vicinity of the connection end face of the first optical fiber, and the intensity of light propagating through the cladding is provided. Based on the above, it is determined whether or not the connection loss exceeds a predetermined reference value. As a result, only the connection work site needs to be operated. In addition, there is no need to cut or create an end face of the optical fiber, and since no means such as a microscope is used, when using fusion splicing, mechanical splices, or various optical connectors, regardless of the material of the optical fiber connection part Even so, connection loss can be determined. In addition, it is possible to monitor the change with time of the connection loss at the connection point in the transmission path even after the start of communication use.

  Further, as an example of a preferred aspect of the above invention, the connection loss is determined based on the change in the light intensity detected by the first cladding light intensity detecting means during the connection work of the first optical fiber and the second optical fiber. What is characterized by determining whether it exceeds a predetermined reference value is proposed.

  In general, if the connection work is performed properly, the light intensity detected by the first cladding light intensity detection means after the connection work will be sufficiently lower than during the work, while the connection work is performed properly. If not, the light intensity detected by the first clad light intensity detecting means after the connection work is slightly lower or higher than that during the work. In the present invention, since the connection loss is determined based on such a change in the clad light intensity during the operation, a reliable determination operation is possible.

  Further, as an example of a preferred aspect of the above invention, a second clad light intensity detecting means for detecting the intensity of light propagating through the clad of the second optical fiber is provided in the vicinity of the connection end face of the second optical fiber, It is characterized in that it is determined whether or not the connection loss exceeds a predetermined reference value based on the light intensity detected by the first cladding light intensity detection means and the light intensity detected by the second cladding light intensity detection means. Suggest a thing.

  In the present invention, a more accurate determination can be made by comparing and comparing the clad propagation light intensity of the second optical fiber on the light source side with respect to the connection end face and the clad propagation light intensity of the first optical fiber.

  As an example of a preferable aspect of the above clad light intensity detecting means, a fixing member that detachably fixes an optical fiber with a predetermined curvature, and an intensity of leaked light from a predetermined portion of the optical fiber bent by the fixing member And a light receiving element that detects the light emission. With this clad light intensity detection means, it is not necessary to cut the optical fiber, and the clad light intensity can be detected without affecting the communication light propagating through the core by appropriately adjusting the curvature and lateral pressure conditions. It becomes. This makes it possible to determine the connection loss at any time even during communication after the construction of the optical fiber communication network. Therefore, it is possible to grasp the change with time of the connection loss.

  According to the method for measuring an optical fiber connection loss of the present invention, since light propagating through the cladding is detected at the connection work place, the operation and the optical fiber cutting work required for the measurement of Pout can be made unnecessary. it can. Further, the material of the optical fiber connecting portion may be arbitrary, and it becomes possible to determine the splicing connection, mechanical splice, and connection loss in various optical connectors. In addition, the light propagating through the cladding leaks from the optical fiber and the skin film due to slight bending and lateral pressure, and the optical power can be detected from the side of the optical fiber. If the bending and side pressure conditions at that time are adjusted appropriately, the communication light propagating through the core will not be affected, so a transmission path is constructed, and the optical fiber connection loss changes over time even during communication. It becomes possible to judge.

  An optical fiber connection loss determination method according to an embodiment of the present invention will be described with reference to the drawings. First, the outline of the optical fiber connection portion 1 will be described by taking a butt connection represented by a mechanical splice as an example.

  As shown in the block diagram of FIG. 1, the optical fiber connector 1 includes a V-groove substrate 2 in which a groove 2a having a V-shaped cross section is formed in a straight line, and a pair of optical fibers inserted along the V-groove 2a. And a presser plate 3 that presses 11 and 12 in between. The depth of the groove 2a is deep at both ends, the center where the end faces of the optical fibers abut each other is formed shallow, and the connection between the both ends and the center is smoothly connected so that no step is generated. . In the figure, Y and Y 'represent directions in which the opposing optical fibers 11 and 12 are inserted.

  A procedure for performing the butt connection in the optical fiber connection unit 1 will be described with reference to FIGS. FIG. 2 is a diagram for explaining the configuration of the optical fiber connection portion during connection work, and FIG. 3 is a diagram schematically showing the states of the optical fibers 11 and 12 during connection work.

  As shown in FIG. 2, in this embodiment, a wedge 4 is used between the V-groove substrate 2 and the holding plate 3 in order to create a gap necessary for inserting the optical fibers 11 and 12. By inserting the wedge 4 between the V-groove substrate 2 and the pressing plate 3, a gap is created between them. In this state, the optical fibers 11 and 12 are inserted along the V-groove 2a, and each optical fiber 11 is inserted. , 12 face each other. Then, by pulling out the wedge 4, the optical fibers 11 and 12 are fixed with the axes aligned along the V groove 2 a.

  Such a butt connection operation can be understood as a state transition as follows. State 1: Inserted state of mechanical splice (FIG. 3A) State 2: Abutment of fiber end face inside mechanical prize (FIG. 3B) State 3: Removal of wedge from mechanical price (FIG. 3) 3 (c)). In state 1, the end face spacing of the optical fiber decreases. In state 2, the distance between the fiber end faces is minimized with the axis of the center of the opposing optical fiber shifted in the radial direction. In state 3, the optical fiber center axes are aligned while the fiber end face spacing is minimal.

  A method of determining the connection loss in such a butt connection will be described with reference to the configuration diagram of FIG. In the figure, 100 is a light source, 101 is a clad light receiving unit that is attached to the optical fiber 11 and receives light propagating through the clad of the optical fiber 11, and 102 is the intensity of light received by the clad light receiving unit 101. It is a display unit that calculates and displays power.

  As described above, the axes of the facing optical fibers 11 and 12 are shifted in the state 1 at the time of butt connection. For this reason, most of the light emitted from the optical fiber 12 is not coupled to the core of the optical fiber 11, but is scattered or attenuated between both fiber end faces, or is coupled to the cladding of the optical fiber 11 and propagates. As the distance between the end faces decreases, the light that is coupled to and propagates through the cladding of the optical fiber 11 increases, and the power of the light that propagates through the cladding in state 2 is stabilized. When the wedge 4 is pulled out 3 and the axes of the two optical fibers coincide with each other, that is, in the case of a good connection, the light previously coupled to the cladding is coupled to the core and propagates through the cladding. The light to be suddenly decreased. FIG. 5 shows changes in the optical power propagating through the cladding in each of the above states.

  On the other hand, when the wedges 4 are pulled out and the axes of the two optical fibers do not coincide with each other or the deviation further increases, as shown in FIG. 6, the light propagating through the cladding is not sufficiently reduced or increased. To do.

  That is, measuring the transition of the clad propagation light intensity over the states 1 to 3 is suitable for determining the connection loss of the optical fiber connection portion 1. Specifically, the suitability of the connection is determined based on whether the clad propagation light intensity (optical power) in the state 3 exceeds a predetermined reference value. In addition, not only the mechanical splice of this example but also various optical connectors and fusion splicing, the state at the time of completion of the connection work is set to the state 3, and the transition of the optical power after that is measured. This is suitable for determining the temporal change in connection loss.

  A modification of the present invention will be described with reference to the block diagram of FIG. In the figure, reference numeral 101 ′ denotes a clad light receiving portion that is attached to the optical fiber 12 and receives the clad propagation light of the optical fiber 12. The clad light receiving unit 101 ′ is the same as the clad light receiving unit 101 attached to the optical fiber 11. In the optical fiber 12, the intensity of light propagating through the cladding is extremely small and hardly changes between the states 1 to 3. FIG. 8 shows changes in the optical power of the clad propagation light of the optical fiber 12 and the optical power of the clad propagation light of the optical fiber 11. In FIG. 8, the solid line represents the optical power of the clad propagation light of the optical fiber 11, and the alternate long and short dash line represents the optical power of the clad propagation light of the optical fiber 12.

  As shown in the figure, when the optical power in the clad light receiving unit 101 is sufficiently larger than the optical power in the clad light receiving unit 101 ′, there is a lot of light in the clad of the optical fiber 11, It can be seen that there is light that is not coupled to the core at the connection point, that is, connection loss occurs. In state 3, it can be seen that the optical power in the clad light receiving unit 101 and the optical power in the clad light receiving unit 101 'are approximate. From the above, comparing and comparing the two optical powers is suitable for determining the connection loss of the optical fiber connection unit 1.

  Although FIG. 7 shows a structure in which the light intensity of the clad propagation light is simultaneously measured using the clad light receiving parts 101 and 101 ′, the same connection loss determination is performed with only one clad light receiving part. be able to. In this case, before the connection, the optical fiber 12 is measured by the clad light receiving unit 101, and then the optical power is transferred to the optical fiber 11 to propagate the clad in the states 1 to 3 during the connection work. Can be measured. Since this method can measure the clad propagation light in the optical fiber before and after the optical fiber connecting portion even with a limited number of the clad light receiving portions, it is suitable for determining the connection loss with higher accuracy.

  Further, if the cladding light receiving unit 101 ′ is removed after the measurement in the configuration of FIG. 7 and the transition of the optical power thereafter is measured by the configuration shown in FIG. It is suitable for determination of a typical change.

  Next, the structure of the clad light receiving part 101 will be described with reference to FIG. As shown in FIG. 9, the clad light receiving unit 101 includes a holder 101 a that detachably fixes and holds the optical fiber 11 and a light receiving element 101 b that receives light leaking from the curved optical fiber 11. . The holder 101a is formed with a groove (not shown) that is curved with a predetermined radius of curvature r and a waveguide port 101c that opens from a substantially middle point of the groove to the light receiving element 101b.

  Actually, when an experiment was performed on a 1.3 μm zero-dispersion single mode optical fiber, when a light source having a wavelength of 1.3 μm was used as the light source 100, it was difficult to sufficiently receive the clad propagation when the curvature radius r was 10 mm or more. It has been found that less than 10 mm is desirable.

  On the other hand, when a light source having a wavelength of 1.5 μm or longer is used as the light source 100 for the 1.3 μm zero-dispersion single mode optical fiber, the clad propagation light can be received even if the curvature radius r is 10 mm. However, since the core propagation light partially leaks due to bending and is received by the light receiving element 101b, there is a risk that the connection loss is determined to be small.

  In the case of a dispersion-shifted optical fiber, the light source 100 and the clad light receiving unit 101 having a wavelength of 1.5 μm or longer and the radius of curvature r of 10 mm do not receive the core propagation light, but only the clad propagation light. It was found that light can be received and the present invention is applicable.

  In the case of the present embodiment, a dedicated light source for determination can be used as the light source 100 in a situation before the start of communication. Further, if the curvature radius r is appropriately set so that the bending loss at the communication light wavelength propagating through the core is sufficiently small, the light source 100 is a communication light source (wavelength 1) of a transmission apparatus installed in a user's house or station. .3 μm band or 1.55 μm wavelength band) can also be used. Further, when a test / monitoring light cutoff filter having a wavelength of 1.65 μm is installed in front of the user's transmission device, the light source 100 is used as a light source for determination in the wavelength of 1.65 μm to monitor the station side. Light can be incident on the transmission path from the optical input port. By these methods, it is possible to determine a change with time in the connection loss of the optical fiber in a situation during communication. The appropriate setting of the radius of curvature r is easier in the case of a dispersion-shifted optical fiber that is less prone to loss due to bending of the core propagation light, but for a 1.3 μm zero-dispersion single-mode optical fiber, For example, as described in “Yamamoto et al.,“ Examination of core contrast device that enables determination of upper and lower parts of optical line ”, Society Conference of the Institute of Electronics, Information and Communication Engineers, B-10-10” is sufficiently possible. is there.

  As described above, by appropriately selecting the wavelength of the light source 100 and the radius of curvature r of the clad light receiving portion 101, the light intensity of the clad propagation light can be reliably detected for various single mode optical fibers and the connection loss can be determined. Is possible.

  In addition, according to the present embodiment, the cladding light receiving unit 101 and the display unit 102 are continuously mounted even after the connection work is completed, or after being removed, the cladding light receiving unit 101 and the display unit 102 are mounted again as necessary, so Change can be judged. In order to fix the measurement conditions, when the light receiving unit 101 is mounted again, it is desirable to mount it at a fixed position as much as possible.

  Causes of changes in connection loss include environmental factors such as temperature and humidity, and mechanical factors such as tensile tension and vibration, but the loss of core propagation light at connection 1 is coupled to 100% cladding. FIG. 11 shows theoretical values calculated on the assumption. The horizontal axis represents the change amount of the connection loss, the vertical axis represents the change amount of the optical power propagating through the cladding, and the connection loss of 0.1 dB is represented as an initial reference value. When the connection loss increases from near 0.1 dB to 0.5 to 1 d or more, the optical power propagating through the cladding is expected to increase by about 5 to 10 dB.

  From the above, in the present invention, by measuring the optical power propagating through the clad, the connection loss over time, for example, the change over time in the unit of months or years after the construction of the optical fiber communication network is improved. It is possible to determine with accuracy.

  Although the embodiment of the present invention has been described in detail above, the present invention is not limited to this. For example, in the above embodiment, the end face butt connection using a mechanical splice as the optical fiber connection portion 1 has been described, but the present invention can also be applied to various connection forms such as fusion connection.

Configuration diagram of optical fiber connection Diagram explaining optical fiber connection work Schematic diagram of optical fiber explaining state transition during optical fiber connection work System configuration diagram used in connection loss judgment method Diagram explaining the transition of clad propagation optical power during connection work Diagram explaining the transition of clad propagation optical power during connection work System configuration diagram used in connection loss judgment method Diagram explaining the transition of clad propagation optical power during connection work Configuration diagram of clad light detector Correlation diagram of clad propagation optical power change and splice loss change The figure explaining the conventional connection loss judgment method

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Optical fiber connection part, 2 ... V groove board | substrate, 2a ... V groove, 3 ... Holding plate, 4 ... Wedge, 11, 12 ... Optical fiber, 100 ... Light source, 101, 101 '... Cladding light-receiving part, 101a ... Holder, 101b ... light receiving element, 101c ... waveguide opening, 102 ... display unit

Claims (4)

A method of measuring connection loss at a connection point of a pair of optical fibers,
Providing a first cladding light intensity detection means for detecting the intensity of light propagating through the cladding of the first optical fiber in the vicinity of the connection end face of the first optical fiber,
Detected by the first clad light intensity detecting means in a situation where a light source of light traveling from the second optical fiber through the connection point to the first optical fiber is connected to the second optical fiber side A method for determining an optical fiber connection loss, comprising: determining whether the connection loss exceeds a predetermined reference value based on light intensity. During connection work of the first optical fiber and the second optical fiber, it is determined whether or not the connection loss exceeds a predetermined reference value based on the change in the light intensity detected by the first cladding light intensity detection means. The optical fiber splice loss determination method according to claim 1. Providing a second cladding light intensity detection means for detecting the intensity of light propagating through the cladding of the second optical fiber in the vicinity of the connection end face of the second optical fiber,
Determining whether or not the connection loss exceeds a predetermined reference value based on the light intensity detected by the first cladding light intensity detection means and the light intensity detected by the second cladding light intensity detection means; The optical fiber connection loss determination method according to claim 1 or 2. The clad light intensity detecting means includes a fixing member that detachably fixes the optical fiber with a predetermined curvature, and a light receiving element that detects the intensity of leaked light from a predetermined portion of the optical fiber bent by the fixing member. The optical fiber connection loss determination method according to any one of claims 1 to 3, wherein the connection loss is determined.

Images