Optical fiber testing device and optical fiber testing method

Abstract

The purpose of the present invention is to provide an optical fiber testing device and a method therefor that enable stable measurement of crosstalk in an MCF and an MMF without being affected by noise.　An optical fiber testing device according to the present invention measures crosstalk of a space-division multiplexed optical fiber 50, and comprises: a light transmission unit 10 that causes modulated test light to enter one path of the space-division multiplexed optical fiber 50 from one end of the space-division multiplexed optical fiber 50; a light receiver 22 that receives transmitted light output from each path at the other end of the space-division multiplexed optical fiber 50 and outputs the transmitted light as a light reception signal; a signal processing unit 24 that demodulates each light reception signal and detects the light intensity of the respective transmitted light; and a calculation unit 30 that calculates crosstalk from the light intensity of the transmitted light.

Description

Optical Fiber Test Apparatus and Optical Fiber Test Method

[0001] The present disclosure relates to an optical fiber test apparatus and a method thereof for measuring the amount of crosstalk in space division multiplexed optical fibers such as multi-core optical fibers (MCFs) and multi-mode optical fibers (MMFs).

[0002] With the increase in communication traffic, an increase in the transmission capacity per optical fiber is required. However, existing single-mode optical fibers have a limit in transmission capacity, and space division multiplexing transmission technology has attracted attention as a technology for breaking through the transmission capacity limit per optical fiber. In space division multiplexing transmission, the transmission capacity is expanded by multiplexing cores or modes, and MCFs and MMFs are used.

[0003] In MCFs and MMFs, a phenomenon called crosstalk occurs in which optical power is coupled between cores or modes. Since crosstalk is a factor that limits the transmission distance, evaluating this is important for realizing a communication system (see, for example, Non-Patent Document 1).

[0004] Tetsuya Hayashi, Toshiki Taru, Osamu Shimakawa, Takashi Sasaki, and Eisuke Sasaoaka, Characterization of Crosstalk in Ultra-Low-Crosstalk Multi-Core Fiber, JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 30, NO. 4, FEBRUARY 15, 2012, 583-589

[0005] Crosstalk in MCFs and MMFs is defined by the intensity ratio of transmitted light between cores or modes as shown in FIG. 6. The following formula is the calculation formula for crosstalk. Here, P1 is the light intensity of the transmitted light of the core or mode into which the incident light is incident, and Pi is the light intensity of the transmitted light of the core or mode to be measured (into which the incident light is not incident). In this specification, cores and modes may be expressed as "paths".

[0006] Typically, crosstalk is measured from the intensity of transmitted light from each core or mode using a light source and a photodetector. However, because the intensity of the crosstalk component is small, noise introduced during measurement of the crosstalk component causes fluctuations in the measured intensity, resulting in fluctuations in the measured crosstalk value. In other words, there is a challenge in stably measuring crosstalk in MCF and MMF without being affected by noise.

[0007] Therefore, the present invention aims to provide an optical fiber testing apparatus and method that can stably measure crosstalk in MCF and MMF without being affected by noise, in order to solve the above problems.

[0008] To achieve the above objective, the optical fiber testing apparatus according to the present invention modulates the test light and demodulates the received light signal to reduce the influence of noise and measure the optical intensity of each core.

[0009] Specifically, the optical fiber testing apparatus according to the present invention is an optical fiber testing apparatus for measuring crosstalk of a spatial division multiplexed optical fiber, and is characterized by comprising: an optical transmission unit that injects modulated test light from one end of the spatial division multiplexed optical fiber into one path of the spatial division multiplexed optical fiber; an optical reception unit that receives transmitted light output from each of the paths at the other end of the spatial division multiplexed optical fiber and outputs each as a received signal; a signal processing unit that demodulates each of the received signals and detects the light intensity of each of the transmitted light; and a calculation unit that calculates the crosstalk from the light intensity of the transmitted light.

[0010] Furthermore, the optical fiber testing method according to the present invention is an optical fiber testing method for measuring the crosstalk of a spatially divided multiplexed optical fiber, comprising: injecting modulated test light into one path of the spatially divided multiplexed optical fiber from one end of the spatially divided multiplexed optical fiber; receiving transmitted light output from each of the paths at the other end of the spatially divided multiplexed optical fiber and outputting each as a received signal; demodulating each of the received signals and performing signal processing to detect the light intensity of each of the transmitted light; and calculating the crosstalk from the light intensity of the transmitted light.

[0011] By modulating the test light with a predetermined signal, the influence of noise can be significantly reduced. Therefore, the present invention provides an optical fiber testing apparatus and method that can stably measure crosstalk in MCF and MMF without being affected by noise.

[0012] The signal processing unit of the optical fiber testing apparatus according to the present invention preferably performs synchronous detection.

[0013] Furthermore, the above inventions can be combined as much as possible.

[0014] The present invention provides an optical fiber testing apparatus and method that can stably measure crosstalk in MCF and MMF without being affected by noise.

[0015] This is a diagram illustrating the configuration of the optical fiber testing apparatus according to the present invention. This is a diagram illustrating the optical fiber testing method according to the present invention. This is a diagram illustrating the configuration of the optical fiber testing apparatus according to the present invention. This is a diagram illustrating the signal processing unit of the optical fiber testing apparatus according to the present invention. This is a diagram illustrating the effects of the present invention. This is a diagram illustrating spatial division multiplexing transmission.

[0016] Embodiments of the present invention will be described with reference to the attached drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to these embodiments. In this specification and in the drawings, components with the same reference numerals refer to the same components.

[0017] Figure 1 is a diagram illustrating the configuration of the optical fiber testing apparatus of this embodiment. The optical fiber testing apparatus comprises an optical transmitting unit 10, an optical multiplexer / demultiplexer 15, an optical receiving unit 20, and a calculation unit 30. Specifically, the optical fiber testing apparatus is an optical fiber testing apparatus for measuring the crosstalk of a spatial division multiplexed optical fiber 50, and comprises: an optical transmitting unit 10 that incidents modulated test light from one end of the spatial division multiplexed optical fiber 50 into one path of the spatial division multiplexed optical fiber 50; a photodetector 22 that receives transmitted light output from each of the aforementioned paths at the other end of the spatial division multiplexed optical fiber 50 and outputs each as a received signal; a signal processing unit 24 that demodulates each of the received signals and detects the light intensity of each of the transmitted light; and a calculation unit 30 that calculates the crosstalk from the light intensity of the transmitted light.

[0018] The optical transmission unit 10 comprises a light source 11, a signal generator 12, and a modulator 13. The light source 11 outputs continuous light. The signal generator 12 outputs an electrical signal of an arbitrary waveform. The modulator 13 modulates the continuous light with the electrical signal and outputs test light. The optical multiplexer 15 injects the test light into one of the paths of the spatial division multiplex optical fiber 50.

[0019] The optical receiving unit 20 includes an optical multiplexer / demultiplexer 21, a photodetector 22, a signal generator 23, and a signal processing unit 24. The optical multiplexer / demultiplexer 21 separates the transmitted light that has propagated through each path of the spatial division multiplex optical fiber 50 and inputs it to the photodetector 22. The photodetector 22 independently receives the transmitted light from each path and outputs a corresponding received signal (electrical). The signal processing unit 24 demodulates the received signals using the electrical signals generated by the signal generator 23 and measures the light intensity of the transmitted light from each path. Preferably, the signal generator 23 outputs an electrical signal with the same waveform as the electrical signal generated by the signal generator 12.

[0020] Figure 1 shows a configuration in which the optical receiving unit 20 has a photodetector 22#1 and a photodetector 22#i. In other words, the optical receiving unit 20 includes a photodetector 22#1 that measures the transmitted light of the path into which the test light was incident, and a photodetector 22#i that measures the transmitted light of other paths. The minimum number of photodetectors 22 is two. In this case, the photodetector 22#i sequentially receives the transmitted light of paths other than the path into which the test light was incident. Note that the optical receiving unit 20 may also have as many photodetectors 22 as there are paths.

[0021] The calculation unit 30 calculates the crosstalk using equation (1).

[0022] Figure 2 is a flowchart illustrating the method for measuring crosstalk with this optical fiber test apparatus (when there are two photodetectors 22). Step S01: First, two paths of the spatially divided multiplexed optical fiber 50 to be measured are set to the optical multiplexer 15 and optical multiplexer 21. Specifically, the path into which the test light is incident is set to the optical multiplexer 15, and the path into which the test light is incident and one other path are set to the optical multiplexer 21. Step S02: Test light is incident on the spatially divided multiplexed optical fiber 50 from the optical transmitter 10. Step S03: The transmitted light emitted from the spatially divided multiplexed optical fiber 50 is received by each photodetector 22. Step S04: The signal processing unit 24 demodulates the received signals from each photodetector 22 using the electrical signal from the signal generator 23 and measures the light intensity of the transmitted light for each. Step S05: Steps S01 to S04 are repeated until the light intensity of the transmitted light has been measured for all combinations of two paths of the spatially divided multiplexed optical fiber 50. Step S06: The calculation unit 30 calculates the crosstalk between each path. The calculation result may be output to the display unit or storage unit.

[0023] (Example) An example of the optical fiber test apparatus described above will be explained. The spatial division multiplexed optical fiber 50 is a two-core optical fiber. Equation (1) is used to calculate the crosstalk. As shown in Figure 3, independent noise was added to the transmitted light from each core. Figure 4 is a diagram illustrating the configuration of the signal processing unit 24. The signal processing unit 24 has a multiplier 41 and a low-pass filter 42 for each photodetector 22. The multiplier 41 multiplies the received signal from the photodetector 22 by the electrical signal from the signal generator 23 (the same signal as the signal applied to the modulator). The low-pass filter 42 extracts the DC component from the received signal multiplied by the electrical signal.

[0024] The details of the calculation process in Figures 3 and 4 are explained below. Assume that a test beam is incident on core #1 of the spatial division multiplexed optical fiber 50, and the light intensity of the transmitted light emitted from core #2 is calculated. The light intensity of the test beam output by modulator 13 can be expressed as follows. However, A is the light intensity of the continuous light output by the light source 11 before modulation, and f is the modulation frequency.

[0025] If T is the degree of coupling of light intensity from core #1 to core #2 due to crosstalk, and N is the noise component mixed in, then the light intensity of the transmitted light output from core #2 is as follows.

[0026] In the synchronous detection process performed by the signal processing unit 24 as shown in Figure 4, the received signal, multiplied by the modulated signal, is expressed as follows. By using a low-pass filter to extract only the DC component from this received light signal, it is possible to detect the light intensity of the transmitted light (i.e., AT / 2) which is unaffected by noise.

[0027] Figure 5 compares the crosstalk calculation results in this embodiment with the crosstalk calculation results in a comparative example where synchronous detection is not performed. The black line represents the crosstalk of the comparative example, and the white dashed line represents the crosstalk of this embodiment. In the comparative example where synchronous detection is not performed, the measured crosstalk values ​​vary greatly due to noise. On the other hand, in this embodiment, the effect of noise is reduced by synchronous detection, and a constant crosstalk value can be measured.

[0028] As described above, the present invention reduces the influence of noise during optical intensity measurement of each core and enables stable crosstalk measurement by modulating the test light and demodulating the received signal in the measurement of crosstalk in spatially divided multiplexed optical fibers.

[0029] 10: Optical transmitter 11: Light source 12: Signal generator 13: Modulator 15: Optical multiplexer / demultiplexer 20: Optical receiver 21: Optical multiplexer / demultiplexer 22, 22#1, 22#2, 22#i: Photodetectors 23: Signal generator 24: Signal processing unit 30: Calculation unit 50: Spatial division multiplex optical fiber

Claims

1. An optical fiber test apparatus for measuring crosstalk of a spatially divided multiplexed optical fiber, comprising: an optical transmitting unit that incident modulated test light from one end of the spatially divided multiplexed optical fiber into one path of the spatially divided multiplexed optical fiber; an optical receiving unit that receives transmitted light output from each of the paths at the other end of the spatially divided multiplexed optical fiber and outputs each as a received signal; a signal processing unit that demodulates each of the received signals and detects the light intensity of each of the transmitted light; and a calculation unit that calculates the crosstalk from the light intensity of the transmitted light.

2. The optical fiber testing apparatus according to claim 1, characterized in that the signal processing unit performs synchronous detection.

3. An optical fiber test method for measuring crosstalk of a spatially divided multiplexed optical fiber, comprising: injecting modulated test light into one path of the spatially divided multiplexed optical fiber from one end of the spatially divided multiplexed optical fiber; receiving transmitted light output from each of the paths at the other end of the spatially divided multiplexed optical fiber and outputting each as a received signal; demodulating each of the received signals and performing signal processing to detect the light intensity of each of the transmitted light; and calculating the crosstalk from the light intensity of the transmitted light.

4. The optical fiber testing method according to claim 3, characterized in that the signal processing is synchronous detection.

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