JP-7856149-B2 - Brillouin gain analyzer and Brillouin gain analyzer

Inventors

• 石丸 貴大
• 高橋 央
• 脇坂 佳史
• 飯田 大輔
• 古敷谷 優介

Assignees

• ＮＴＴ株式会社

Dates

Publication Date

20260511

Application Date

20220623

Claims (4)

1. A laser that outputs continuous light of a single frequency, An ASE (Amplified Spontaneous Emission) light source generates continuous light with a broader bandwidth of frequency components than the frequency of the continuous light output by the aforementioned laser, and directly incidents it onto one end of the optical fiber to be measured as probe light, A pulse generator that pulses the continuous light from the laser and injects it into the other end of the optical fiber as pump light, A modulator that generates local light obtained by shifting the frequency of the continuous light from the laser by an arbitrary frequency, A detector that performs heterodyne detection of the Brillouin scattered light generated in the optical fiber and the local light, A Brillouin gain analyzer equipped with the following features.
2. The Brillouin gain analysis apparatus according to claim 1, further comprising a signal processing unit that performs a Fourier transform on the signal heterodyne detected by the detector to detect the Brillouin gain spectrum (BGS), and acquires the vibration distribution of the optical fiber from the time-series change of the peak of the BGS.
3. The method involves directly injecting ASE (Amplified Spontaneous Emission) continuous light, which has a broader frequency band than single-frequency laser light, into one end of the optical fiber being measured as probe light. The laser light is pulsed and incident as pump light at the other end of the optical fiber. A Brillouin gain analysis method characterized by shifting the frequency of the laser light by an arbitrary frequency to generate local light, and heterodyne detecting the Brillouin scattered light generated in the optical fiber and the local light.
4. The Brillouin gain analysis method according to claim 3, further characterized by performing a Fourier transform on the heterodyne detected signal to detect the Brillouin gain spectrum (BGS), and obtaining the vibration distribution of the optical fiber from the time-series change of the peak of the BGS.

Description

This disclosure relates to reflectance measurement, which performs sensing by measuring the scattered light of light incident on an optical fiber. As an optical fiber sensing technology, there is a measurement method called BOTDA (Brillouin Optical Time Domain Analysis) as shown in Figure 1. This method acquires a Brillouin Gain Spectrum (BGS) as shown in Figure 2 to measure the strain and temperature of the optical fiber 50. The strain and temperature of the optical fiber can be obtained distributedly by the change in the peak 21 of the BGS. In order to capture the Brillouin Frequency Shift (BFS), which is the amount of shift in the change in the peak 21 of the BGS, it is necessary to perform a frequency sweep of the probe light Lpr. When a single pulsed pump light Lpn is injected into the optical fiber 50, the frequency of the probe light Lpr is fixed. Therefore, in order to measure the entire BGS, it is necessary to change the frequency of the probe light Lpr and inject the pulsed pump light Lpn multiple times. Hiroshi Takahashi, Chihiro Kitou, Kunihiro Toge, and Tetsuya Manabe, "Measurement Method of Brillouin Loss Using Broadband Probe Light," Proceedings of the 2014 IEICE Society Conference, B-13-21, 2014.Kikuchi, Kazuro. “Fundamentals of coherent optical fiber communications”, Journal of lightwave technology, vol. 34, Issues. 1, pp. 157-179, 2015. This is a diagram explaining BOTDA.This is a diagram explaining the measurement principle of BOTDA.This is a diagram illustrating an example of BOTDA's application.This is a diagram illustrating the Brillouin gain analyzer according to the present invention.This diagram illustrates the comparison of probe light.This is a diagram illustrating the configuration of a detector.This diagram illustrates the measurement principle of the Brillouin gain analyzer according to the present invention.This is a diagram illustrating the Brillouin gain analysis method according to the present invention.This diagram illustrates an experimental system for acquiring Brillouin scattered light using ASE light.This figure illustrates the experimental results of acquiring Brillouin scattered light using ASE light. 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. Figure 4 is a diagram illustrating the Brillouin gain analyzer 301 of this embodiment. The Brillouin gain analyzer 301 is A laser 11 that outputs continuous light of a single frequency, An ASE (Amplified Spontaneous Emission) light source 13 generates continuous light with a broader bandwidth of frequency components than the frequency of the continuous light output by the laser 11 and incidents it onto one end of the optical fiber 50 to be measured. A pulse generator 12 pulses the continuous light from the laser 11 and injects it into the other end of the optical fiber 50, A modulator 14 generates local light obtained by shifting the frequency of the continuous light from the laser 11 by an arbitrary frequency, A detector 15 that performs heterodyne detection of the Brillouin scattered light generated in the optical fiber and the local light, It is equipped with. The Brillouin gain analyzer 301 includes a scattered light generation unit 41 and a scattered light acquisition unit 42. The scattered light generation unit 41 generates two types of light, pump light Lpn and probe light Lpr, and propagates them in opposite directions through the optical fiber 50 under test. Pump light Lpn is generated by pulsed single-frequency continuous light output by laser 11 through intensity modulation by AOM in pulse generator 12. The power of pump light Lpn is amplified by EDFA 61. On the other hand, probe light Lpr is generated by amplified broadband light generated using ASE light source 13 by EDFA 62. Figure 5 is a comparison of probe light Lpr of Brillouin gain analyzer 300 (Figure 5(A)) and probe light Lpr of Brillouin gain analyzer 301 (Figure 5(B)). The pump light Lpn and the probe light Lpr interact within the optical fiber 50 under test. Due to this interaction, the light in which the Brillouin scattered light from the pump light Lpn is superimposed on the probe light Lpr is sent to the scattered light acquisition unit 42 by the circulator 63. The scattered light acquisition unit 42 converts the light sent from the scattered light generation unit 41 into an electrical signal. First, the Rayleigh scattered light component is removed by the BPF 64, resulting in a signal light Lsig consisting only of Brillouin scattered light. In addition, the scattered light acquisition unit 42 also receives a continuous beam of single-frequency light branched from the laser 11. The SSB modulator 14 modulates this continuous beam of light to near the