JP5883730B2 - Optical line monitoring device - Google Patents

Description

  The present invention relates to an optical line monitoring apparatus, and more particularly, to an optical line monitoring apparatus that monitors a break position, distortion around an optical line, and temperature change existing in an optical line constituted by optical fibers.

  Until now, OTDR (Optical time domain Reflectometer) has been used in order to detect a loss and a break point generated in an optical line (Patent Document 1). The method disclosed in Patent Document 1 is a method in which an optical pulse is output into an optical line, the reflected return light intensity generated at a break point or a connection point and the propagation time are measured, and the reflection position is observed.

  An outline of a conventional general-purpose pulse OTDR is shown in FIG. The output light pulse output from the pulsed OTDR 100 propagates through the monitored optical line 200, is reflected at the reflection points P1 and P2, propagates backward, and enters the OTDR 100 as return light. The distances between the OTDR 100 and the reflection point P1 and between the OTDR 100 and the reflection point P2 are calculated from the time until the output light pulse is output from the OTDR 100 and incident on the OTDR 100 as the return light, and the effective refractive index of the monitored optical line 200 Is done.

  In such an optical pulse method (FIG. 7), the spatial resolution depends on the pulse width and the influence of backscattered light, and there are a plurality of reflection points in the optical line, and the distance between these reflection points and the pulse source. When the difference is small, it is difficult to identify the reflection position with high accuracy. In order to measure the reflection position with high accuracy, a method has been proposed in which the frequency spectrum of the resonance mode existing between the reflection points is measured and the distance between the reflection points is calculated therefrom.

Japanese Patent Laid-Open No. 07-174666

  The reflection position is measured with high accuracy from the resonance frequency spectrum in the optical line, and in the optical line whose reflection position is known, strain and temperature change generated at the corresponding position are measured from the frequency spectrum.

In order to achieve the above object, the optical line monitoring apparatus of the present invention calculates one or a plurality of predetermined positions in the monitored optical line, and generates strains and temperature changes generated at the one or more predetermined positions. An optical line monitoring apparatus for measuring, a semiconductor laser capable of selecting an arbitrary oscillation wavelength, a first optical line for propagating output light of the semiconductor laser, a second optical line, and a third optical line, The propagation light of the first optical line is demultiplexed into the monitored optical line and the second optical line, and the propagation light of the monitored optical line is demultiplexed into the first optical line and the third optical line. Optical demultiplexer, first optical line and monitored optical line, polarization controller provided at an arbitrary position in the optical path connecting these, and the propagation light of the second optical line is converted into an electrical signal Receiver, an electrical spectrum analyzer that outputs the frequency spectrum of the electrical signal, and a third optical line And an optical spectrum analyzer that outputs a frequency spectrum of the carried light, wherein a periodic refractive index change is formed at predetermined intervals in each of one or more predetermined positions of the monitored optical line. And

  As described above, the optical line monitoring apparatus of the present invention measures the reflection position with high accuracy from the resonance frequency spectrum in the optical line, and in the optical line whose reflection position is known, the frequency spectrum is changed to the corresponding position. Strain and temperature changes that occur can be measured.

It is a block diagram of the optical path monitoring apparatus concerning this invention. It is a figure which shows the principle of a fiber Bragg grating (FBG). It is a graph which shows the relationship between a Bragg wavelength and a grating period. It is a graph which shows the relationship between a FBG reflection bandwidth and a refractive index change. It is a figure which shows the grating structural example of a to-be-monitored optical path. It is a graph which shows the example of a FBG reflection spectrum. It is the schematic of pulse type OTDR which is the conventional optical-line monitoring apparatus.

[Example]
FIG. 1 shows an optical line monitoring apparatus according to this embodiment of the present invention. The optical line monitoring apparatus of the present invention includes a semiconductor laser 1, a polarization controller 2, an optical demultiplexer 3, a light receiver 5, an electric spectrum analyzer (ESA) 6, an optical spectrum analyzer (OSA) that can select an arbitrary oscillation wavelength. ) 7 and fiber Bragg gratings (FBG1, FBG2) 8 and 9. In this embodiment, a wavelength tunable semiconductor laser diode (TLD) 1 is used as a semiconductor laser, an optical coupler 3 is used as an optical demultiplexer, and a PIN-photodiode (PD) 5 is used as a light receiver. The optical components are connected by a single mode fiber, and the electrical components are connected by a coaxial line. The optical coupler 3 has an input / output demultiplexing ratio of 1: 1, the port 1 is connected to the polarization controller 2, the port 2 is connected to the OSA 7, the port 3 is connected to the PD 5, and the port 4 is connected to the monitored optical line 4. The fiber Bragg gratings 8 and 9 are formed at predetermined positions of the monitored optical line 4.

The principle of measuring strain and temperature change occurring at a predetermined position in the monitored optical line will be described. The monitored optical line is a fiber in which a periodic refractive index change is formed at a predetermined interval. In this embodiment, the case where the refractive index change is given by a fiber Bragg grating (FBG) will be described. FIG. 2 shows the principle of FBG. Assume that the grating period is Δ, the effective refractive index of the fiber is neff, and the grating length is Lg. FBG has a property of reflecting only a specific wavelength called a Bragg wavelength proportional to Δ with respect to incident light. The Bragg wavelength λ _b is generally expressed by the formula 1.1. Figure 3 is a graph showing a relationship between lambda _b and Δ (neff = 1.45).

The bandwidth Δλ _b of the FBG reflection spectrum depends on the increments Δn and Lg from the fiber core refractive index. Δλ _b is generally expressed by Expression 1.2 (n: fiber core refractive index, α: propagation light ratio coefficient).

FIG. 4 shows the relationship between Δλ _b and Δn (Lg = 3.5, λ _b = 1.55, neff = 1.45, α = 1.0).

Δ, Lg, and Δn vary according to the stress and temperature around the grating. That is, λ _b depending on Δ and Δλ _b depending on Δ, Lg, and Δn vary depending on the stress and temperature around the grating. By analyzing the change in the lambda _b of the shift amount and [Delta] [lambda] _b, it is possible to measure the strain and temperature changes in ambient grating.

FIG. 5 shows a grating configuration example of the monitored optical line. On the monitored optical line, a plurality of FBGs having a determined grating period are formed at predetermined positions. In the example shown in FIG. 5, the distances between the TLD and the FBG are L1 and L2, the grating periods are Δ1 and Δ2, respectively, and the TLD can selectively oscillate at the Bragg wavelengths λ _b 1 and λ _b 2. It is assumed that the relationship between Δλ _b and the strain or temperature change of the fiber is already known. When the oscillation wavelength of the TLD is λ _b 1, the FBG reflected light spectrum from the position L1 is observed by OSA. FIG. 6 shows an example of the FBG reflected light spectrum. By analyzing the FBG reflection spectrum change, distortion and temperature change around the position L1 can be measured. The position L2 can be measured in the same way if the oscillation wavelength of the TLD is λ _b 2.

  A resonator is formed between the FBG and the TLD reflection end, and the resonance spectrum can be observed by ESA. From the frequency interval of the spectrum, the resonator length, that is, the length between the FBG and the TLD reflection end can be calculated. The relational expression is generally represented by Expression 1.3. (Δf: frequency interval of resonance spectrum, L: resonator length, neff: effective refractive index of monitored optical line, c: speed of light in vacuum)

The resonance spectrum intensity is adjusted by the polarization controller.

DESCRIPTION OF SYMBOLS 1 Wavelength variable semiconductor laser 2 Polarization controller 3 Optical coupler 4,200 Monitored optical line 5 PIN-photodiode 6 Electric spectrum analyzer 7 Optical spectrum analyzer 8, 9 Fiber Bragg grating 100 Pulse type OTDR

Claims (4)

An optical line monitoring device that calculates one or a plurality of predetermined positions in a monitored optical line, and measures strain or temperature change that occurs at the one or more predetermined positions,
A semiconductor laser capable of selecting an arbitrary oscillation wavelength; and
A first optical line for propagating output light of the semiconductor laser;
A second optical line,
A third optical line,
The propagation light of the first optical line is split into the monitored optical line and the second optical line, and the propagation light of the monitored optical line is divided into the first optical line and the third light beam. An optical demultiplexer that demultiplexes the road,
A polarization controller provided at an arbitrary position in the optical path connecting the first optical line and the monitored optical line;
A light receiver that converts the propagation light of the second optical line into an electrical signal;
An electrical spectrum analyzer that outputs the frequency spectrum of the electrical signal;
An optical spectrum analyzer that outputs a frequency spectrum of the propagation light of the third optical line, and each of the one or more predetermined positions of the monitored optical line has a periodic refractive index at predetermined intervals. An optical line monitoring device characterized in that a change is formed.   The optical line monitoring apparatus according to claim 1, wherein the refractive index change is given by a fiber Bragg grating (FBG). A monitoring method for a monitored optical line that calculates h predetermined positions in the monitored optical line, and measures strain and temperature changes generated at the h predetermined positions,
Forming a periodic refractive index change at a predetermined interval Δ _i (1 ≦ i ≦ h) in each of the h predetermined positions of the monitored optical line;
A step of inputting an input light having a wavelength λ _i from a semiconductor laser capable of selecting an arbitrary oscillation wavelength into the monitored optical line, wherein the wavelength λ _i satisfies λ _i = 2neff · Δ _i (neff Is the effective refractive index of the monitored optical line) step;
The frequency interval Δf _i of the resonance spectrum of the resonator formed between the semiconductor laser and the i th predetermined position is measured, and the relationship between Δf _i and the resonator length L _i is measured.

Calculating the i th predetermined position from
The bandwidth Δλ _i of the reflection spectrum from the i th predetermined position is measured, and the surrounding stress change and / or temperature change at the i th predetermined position is calculated from the change in Δλ _i. A monitoring method for a monitored optical line, comprising the steps of:   The monitoring method for a monitored optical line according to claim 3, wherein the refractive index change is given by a fiber Bragg grating (FBG).

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