KR100952053B1 - Opical Fiber Bragg Grating Sensing System Using Spectral Tag - Google Patents

Abstract

An optical fiber Bragg grating portion comprising a plurality of sensors each comprising at least two Bragg wavelengths at Bragg wavelengths of λ ₁ to λ _N (N is a natural number of two or more) connected to a light source, and an optical fiber Bragg grating An optical data analysis unit detects and analyzes an optical signal output from the unit, and includes a plurality of windows by dividing a communication band into windows that are wavelength bands that an optical fiber grating can have, and each window includes at least two different wavelengths. The optical fiber grating Bragg sensor system is assigned a Bragg wavelength of.

Optical fiber, Bragg grating, spectrum tracking, spectrum code

Description

Optical Fiber Bragg Grating Sensing System Using Spectral Tag}

The present invention relates to a multi-channel Bragg grating sensor system using a spectral tracking method, and more particularly, having an optical fiber Bragg grating portion formed by separating a plurality of sensor groups, free of one fiber grating A Bragg grating sensor system for dividing a given wavelength band with windows up to the threshold of the spectral region (FSR) and assigning Bragg grating wavelengths to each window.

Fiber Bragg gratings induce periodic cyclic refractive index changes in the fiber core. The optical fiber grating reflects light of a narrow line width (typically 0.1 to 1 nm) at the center of the Bragg wavelength that satisfies the Bragg conditions and passes the light of the remaining wavelengths. This Bragg wavelength is changed when the temperature of the fiber Bragg grating is changed or when stress is applied. Therefore, many fiber Bragg grating sensors have been developed that use this property to measure temperature, strain and pressure.

The advantage of this fiber Bragg grating sensor is that it can measure the absolute values of physical quantities such as temperature and strain. In addition, since the optical fiber material is a silica (SiO ₂ ) system, which is not affected by electromagnetic waves, it is an electrical insulator, and its small size and light weight allow it to be installed and inserted without affecting the function of the structure to be measured. It can be transmitted over long distances without the need for telemetry.

Another great advantage of the fiber Bragg grating sensor is the ease of multiplexing by arranging a number of grating sensors in multiple places within the fiber, arranged in line along one strand of fiber. That is, each optical fiber grating can be easily applied to a wavelength division multiplexing scheme in which the wavelengths are designed to have different reflection wavelengths so that the wavelengths do not overlap each other when measured. By applying this method, it is possible to perform the function of a quasi-distributed sensor by placing each sensor in an arbitrary place several mm to several tens of kilometers away.

1 is a diagram illustrating an example of an optical fiber Bragg grating 10 used in a multiplexer according to the prior art for convenience of description. Referring to FIG. 1, it can be seen that Bragg gratings are sequentially formed in an optical fiber according to Bragg wavelengths between λ ₁ and λ _N.

However, according to the related art, for example, in order to form 10 channels, an optical fiber Bragg grating having 10 different Bragg wavelengths must be formed. As the number of channels increases, the number of wavelengths of the Fiber Bragg grating must also increase. Therefore, a light source in a wide wavelength range is required. Therefore, a broad wavelength light source and numerous Bragg grating wavelengths are required to improve the wavelength multiplexing capability, which makes it difficult to realize the sensor at low cost while improving the multiplexing capability within a certain wavelength band.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to improve the detection capability of many channels having at least two Bragg wavelengths (spectral codes) in a wavelength division scheme (WDM) within an existing communication wavelength band. It is to provide a multi-channel Bragg grating sensor system using a spectral tracking method that can handle the sensor.

As a technical means for solving the above problems, the first aspect of the present invention is a light source; An optical fiber Bragg grating portion connected to the light source and including a plurality of sensors each consisting of at least two Bragg wavelengths at Bragg wavelengths of λ ₁ to λ _N (N is a natural number of two or more); And an optical data analyzer for detecting and analyzing an optical signal output from the optical fiber Bragg grating unit,

The present invention provides a fiber grating Bragg sensor system in which a communication band is divided into windows that are wavelength bands that an optical fiber grating can have, and each window is assigned Bragg wavelengths of at least two different wavelengths.

Preferably, the Bragg wavelengths may be assigned to different wavelength intervals to prevent multiple sensors from operating and overlapping or malfunctioning, and the maximum number of the plurality of sensors is _N C _M (M = N / 2). Can be.

On the other hand, the window is a free spectral region of the optical fiber grating, the free spectral region means the maximum wavelength moving distance that can be moved before being broken or broken by its physical properties.

Preferably, at least one Bragg wavelength of the plurality of sensors is assigned to different windows. The constant communication band may be C, L, and S-band, respectively.

때문에 센서의 멀티플렉싱 능력을 확대시켜 한정한 파장 대역 내에서도 여러 개의 센서를 설치하여 감시할 수 있는 장점이 있다.According to the present invention, by assigning several codes (maximum: N / 2, N is the number of wavelengths) for each sensor group, the number of channels that can be multiplexed in a limited bandwidth (C, L, S-band) is greatly increased.

As a result, the multiplexing capability of the sensor can be expanded to monitor and install multiple sensors within a limited wavelength band.

In addition, in order to eliminate untraceability when all of the multiple fiber grating sensors are operated, the maximum free spectral region that one fiber grating can have a certain communication band is divided into windows and the Bragg grating wavelength is assigned to each window. Avoid the number of cases. In order to increase the number of sensors in a limited wavelength band, it is possible to assign Bragg gratings having different wavelength intervals to each window.

In addition, it is possible to perform the sensing function according to the environmental change even when each wavelength is overlapped within a limited wavelength band than the conventional multiplexing method which needs to use only other wavelengths of broadband, and it has a much faster response time and additional signal processing. Since the algorithm is much simpler than other interrogation methods, cost savings can be expected.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the technical idea of the present invention. do. The present invention is not limited to the embodiments disclosed below, but can be implemented in various different forms, only the embodiments of the present invention to make the disclosure of the present invention complete and complete the scope of the invention to those skilled in the art. It is provided to inform you.

2 is a schematic diagram of an optical fiber Bragg grating sensor system according to a preferred embodiment of the present invention.

Referring to FIG. 2, the optical fiber Bragg grating sensor system includes a light source 110, an optical circulator 120, an optical fiber Bragg grating unit 130, and an optical data analyzer 140.

The optical fiber Bragg grating unit 130 is formed by separating the grating into a plurality of sensors consisting of at least two Bragg wavelengths in Bragg wavelengths of λ ₁ to λ _N. That is, 2, 3, 4... Which can be distinguished from each sensor. If M (M is a natural number of 2 or more) Bragg gratings (codes) are provided, it is possible to distinguish signals that change according to external environmental changes. Preferably, the number M of codes each sensor can have may be at most N / 2.

On the other hand, in the method of assigning the Bragg wavelength to the sensor, the free spectral region that one optical fiber grating can have a constant communication band (for example, S- / C- / L-band) is divided into windows. Then, at least two Bragg wavelengths are assigned to each window. In addition, at least one Bragg wavelength of the plurality of sensors is preferably assigned to different windows. The free spectral region refers to the maximum wavelength moving distance that can be moved before it is broken or broken by its physical properties. The value may vary depending on the optical fiber, but it is generally less than about 10 nm, and may be as small as about 8 nm. have. Therefore, the range of the window is preferably 8 to 10 nm. Thus, each band has a structure having a plurality of windows.

According to the optical fiber Bragg grating 130, the portion (change) due to the temperature or strain disappears due to the change in the overlapping amplitude, the code (wavelength) of the portion disappears and the size of the wavelength (code) of the moved region is Increased above the position of the superimposed amplitude so that it is easy to distinguish. In this case, in the case where the multiple sensors manufactured in the limited wavelength range (bandwidth) have no external change, the sum of the original reflection peaks, that is, the sum of all codes (wavelengths), allows the size of the received signal to be kept constant. The reflectivity can be immediately known by making constant (preferably less than 5%) and coding the amplitude change in detail according to the external environment change.

The optical data analyzer 140 detects and analyzes an optical signal output from the optical fiber Bragg grating 130. That is, the optical fiber Bragg grating sensors (sensor 1, sensor 2, ..., sensor _N C _M ) can determine whether there is a change in the external environment by changing the waveform of each Bragg wavelength of the optical signal. The detailed method will be described later.

On the other hand, in order to eliminate untraceability when all of the multiple fiber grating sensors are operated, the maximum free spectral region that one fiber grating can have a certain communication band is divided into windows, and the Bragg grating wavelength is assigned to each window. Eliminate the number of cases. In addition, in order to increase the number of sensors in a limited wavelength band, it is possible to assign a Bragg grating (spectral code) of different wavelength intervals in each window.

FIG. 3 shows the case where two distinctive codes are assigned to each optical fiber Bragg grating sensor. The Bragg grating has eight wavelengths, the number of sensors is ₈ C ₂ , and the number of codes M is two.

번째 광섬유 격자 센서(sensor #n)는 λ_N-1(λ₇)_, λ_N(λ₈)의 파장을 갖는 브래그 격자를 갖는 것을 의미한다.Referring to FIG. 3, the first optical fiber grating sensor (sensor # 1) is a Bragg grating having wavelengths of λ ₁ and λ ₂ , and the second optical fiber grating sensor (sensor # 2) has a wavelength of λ ₁ and λ ₃ . The grid, the last one

The first optical fiber grating sensor (sensor #n) means having a Bragg grating having wavelengths of λ _N-1 (λ ₇ ) _and λ _N (λ ₈ ).

In addition, it divides into four windows (FSR maximum) having a constant wavelength bandwidth, and assigns two wavelengths to each fiber Bragg grating sensor, and the whole shows the case of using eight wavelengths.

Referring to FIG. 3, at least two Bragg wavelengths are arranged in each sensor, and a communication wavelength bandwidth set by an optical communication (ITU-T) standard to eliminate an indistinguishable case when multiple sensors are operated. By applying the wavelength division method (WDM) in (S-band, C-band, L-band, etc), it is based on the Free Spectral Range (FSR) limit where one optical fiber grating can move to the maximum. The communication wavelength bandwidth is divided and two or more Bragg wavelengths are assigned to each divided window. In addition, the number of sensors is increased by arranging Bragg gratings having different wavelength intervals in each window.

That is, multiple fiber Bragg gratings that can provide a large number of channels simply by using a window that effectively divides the communication wavelength bandwidth by the FSR maximum of the Bragg grating and assigning two or more Bragg gratings to one sensor. Provide a sensor system.

FIG. 4 shows a case where three codes (wavelengths) distinguishable to each optical fiber Bragg grating sensor are assigned (manufactured). Bragg grating wavelength is 12. In determining the number of the plurality of sensors, the number M of codes assigned is 3.

번째 광섬유 격자 센서(sensor #n)는 λ_N-2(λ₁₀)_, λ_N-1(λ₁₁)_, λ_N(λ₁₂)의 파장을 갖는 브래그 격자를 갖는 센서를 의미한다.Referring to FIG. 4, the first optical fiber grating sensor (sensor # 1) is Bragg grating sensor having λ ₁ , λ ₂ , and λ ₃ , and the second optical fiber grating sensor (sensor # 1) is λ ₁ , λ ₃ and λ _4. Bragg grating with a wavelength of the last,

The first optical fiber grating sensor (sensor #n) refers to a sensor having a Bragg grating having wavelengths of λ _N-2 (λ ₁₀ ) _, λ _N-1 (λ ₁₁ ) _{, and} λ _N (λ ₁₂ ).

In addition, the constant wavelength bandwidth is divided into four windows (FSR maximum value), three wavelengths are allocated to each window, and the case where 12 wavelengths are used is illustrated.

Referring to FIG. 4, the three wavelengths assigned to each window are different from each other, thereby eliminating the overlap between the optical fiber grating sensors. As shown in FIGS. 3 and 4, the Bragg wavelengths in the respective optical fiber Bragg grating sensors (sensor1, sensor2, ..., sensor _N C _M ) may be various numbers which are not particularly limited.

When the optical fiber Bragg grating sensor is formed in this manner, it is possible to overcome the prior art, which had limitations in forming many channels using a constant communication wavelength band. For example, when a fiber Bragg grating sensor is configured using six Bragg grating wavelengths, in the present embodiment, six Bragg grating wavelengths have two codes (each code) in each group. ID, tag) allows the formation of ₆ C ₂ (Combination) channels (i.e. 15), and the number of codes can be reduced to half of the wavelength (M = N / using 6 Bragg grating wavelengths). 2 = 3) When extended to form three codes assigned to the fiber Bragg grating sensor, up to ₆ C ₃ (Combination) channels (ie 20) can be formed.

5A to 5D are diagrams illustrating an example of a case in which the number of Bragg wavelengths in each optical fiber Bragg grating sensor (sensor1, sensor2, ..., sensor _N C _M ) is changed and coded.

FIG. 5A illustrates a case in which two Bragg wavelengths (codes) are formed on each sensor using four different Bragg wavelengths, and a maximum obtainable sensor is manufactured by allowing each wavelength to overlap three times. FIG. 5B is a diagram illustrating the maximum number of sensors that can be obtained by combining two Bragg wavelengths using six different Bragg wavelengths to form a sensor to overlap one wavelength five times. FIG. 5C is a diagram illustrating the maximum number of groups (sensors) obtained by forming two sensors by combining eight Bragg wavelengths and forming a sensor to overlap one wavelength seven times.

FIG. 5D shows N wavelengths according to an embodiment of the present invention, and one wavelength is N-1 times for each M Bragg wavelength included in each optical fiber Bragg grating group, that is, M number of codes. The figure shows the result of generalizing the maximum number obtained by overlapping. In this case, the maximum number of sensors is N! / [M! * (N-M)!] (Where M = N / 2), and the number of overlapping wavelengths is N-1.

FIG. 6 shows the number of Bragg wavelengths, i.e., codes included in each optical fiber Bragg grating group, when the number of wavelengths increases to 4, 5, 6, ..., N according to an embodiment of the present invention. To 2,3,4,... The figure shows the maximum value of a sensor that can be obtained according to the number of wavelengths and the number of codes while increasing to M (= N / 2). Generalizing the number of sensors is as follows.

FIG. 7 illustrates the change in the external environment when there are 120 optical fiber Bragg grating sensors by using 16 Bragg wavelengths and assigning M = 2 codes in each optical fiber Bragg grating sensor according to an embodiment of the present invention. It is a conceptual diagram for explaining the sensing according.

In FIG. 7, 16 Bragg wavelengths are divided into four windows to display each window. The optical fiber Bragg grating reflects light with a narrow line width (typically 0.1 to 1 nm) at the center of the Bragg wavelength that satisfies the Bragg conditions and passes the light of the remaining wavelengths. When an external environment, that is, a temperature or stress, is applied, the Bragg wavelength of the optical fiber Bragg grating changes accordingly. Therefore, this property can be used to measure temperature, strain, pressure, etc. It is possible to find out which fiber Bragg grating sensor is affected by detecting the change of Bragg wavelength changed by external environmental change in the whole band band. Can be.

Referring to FIG. 7, the change in the waveform of each Bragg wavelength is identified by the change in the waveform disappeared at that position and the change in the waveform at the shifted position, and the physical quantity is displayed by adding or subtracting from the reference point (red line). You can find out if you have received it. That is, 100 με, 500 με, 1000 με, 3000 με, 5000 με, and 7000 με, indicating that the optical fiber Bragg grating sensor is affected when there is a change in the external environment.

Specifically, the spectral code of each fabricated optical fiber grating sensor is memorized and set as a standard template when there is no external environmental change, and when any sensor detects a change due to external fluctuations. At the initial position of the sensors (assigned spectral code), they are reduced by the reflectance of the codes included in the changed sensors, and at the shifted position (any wavelength), they are increased by the amplitude of the reflectivity of the sensors. Determine whether it is affected (sensor location) and how much change (temperature, strain variation).

On the other hand, the reflectance of the individual spectral tracking code is set to 1 (coded size), and arbitrary sensors detect the change by external fluctuations so that the reduced reflectance "-1" and the shifted position (at the initial position (assigned spectral code)) It is also possible to determine the operating performance of the sensor by digitizing the increased reflectivity " + 1 "

1 is a diagram illustrating an example of an optical fiber Bragg grating used for a multiplexer according to the prior art for convenience of description.

2 is a schematic diagram of an optical fiber Bragg grating sensor system according to a preferred embodiment of the present invention.

FIG. 3 shows the case where two distinctive codes are assigned to each optical fiber Bragg grating sensor.

FIG. 4 shows a case where three codes (wavelengths) distinguishable to each optical fiber Bragg grating sensor are assigned (manufactured).

5A to 5D are diagrams illustrating an example of a case in which the number of Bragg wavelengths in each optical fiber Bragg grating sensor is changed and coded.

FIG. 6 is a diagram illustrating an optical fiber Bragg grating wavelength and each Bragg wavelength included in each sensor according to an embodiment of the present invention. In the case of, M (= N / 2), the figure shows the maximum number of sensors.

FIG. 7 is a conceptual diagram illustrating characteristics when one sensor operates due to an external environment change among the sensors of the first window in an arbitrary wavelength bandwidth according to an exemplary embodiment of the present invention.

Claims (8)

Light source; An optical fiber Bragg grating portion connected to the light source and including a plurality of sensors each consisting of at least two Bragg wavelengths at Bragg wavelengths of λ ₁ to λ _N (N is a natural number of two or more); And An optical data analysis unit for detecting and analyzing the optical signal output from the optical fiber Bragg grating unit, The communication band is divided into windows, which are wavelength bands that an optical fiber grating may have, and provided with a plurality of windows. And each window is assigned a Bragg wavelength of at least two different wavelengths. According to claim 1, The Bragg wavelengths are optical fiber grating Bragg sensor system is arranged to have a different wavelength interval to prevent the various sensors to operate to overlap or malfunction. According to claim 1, And the maximum number of the plurality of sensors is _N C _M individual (M = N / 2). According to claim 1, And the optical data analyzer determines which of the plurality of sensors has a change in the external environment through a change in the waveform of each Bragg wavelength of the optical signal. According to claim 1, And the window is a free spectral region of the optical fiber grating. According to claim 1, The communication band is a fiber grating Bragg sensor system capable of C, L, S-band respectively. According to claim 1, The optical data analyzer sets a reference point when there is no external environmental change, and when specific sensors sense a change due to external fluctuation, the Bragg grating wavelength included in the changed sensors at the initial Bragg grating wavelength of the specific sensors is determined. An optical fiber grating Bragg sensor system that decreases by reflectance and increases by the amplitude of the reflectance of the sensors at the wavelength of the shifted location, measuring the affected sensor and the amount of change affected. According to claim 1, And at least one Bragg wavelength of the plurality of sensors is assigned to different windows.

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