JP5990624B1 - Optical fiber sensor system, optical fiber sensor and measuring method - Google Patents

Abstract

An object of the present invention is to provide an optical fiber sensor system that uses an MMF having no hole structure and can easily grasp the relationship between an interference pattern observed at an output end and a propagation mode in the MMF. And An optical fiber sensor according to the present invention uses a number-mode optical fiber (FMF) in which the number of modes that can be propagated is limited to 2 to 4, and is observed at the output end of the optical fiber sensor. Clarify the relationship between the propagation mode and inter-mode interference. In the optical fiber sensor system of the present invention, the FMF uses a step-type refractive index distribution having no holes. [Selection] Figure 1

Description

  The present invention relates to optical sensing technology, and more particularly to temperature and tension optical sensing using inter-mode interference in an optical fiber.

  2. Description of the Related Art In recent years, an optical fiber sensor (hereinafter referred to as an SMS sensor) configured by connecting a single mode optical fiber (SMF) to both ends of a multimode optical fiber (MMF: Multi-mode fiber). (For example, refer nonpatent literature 1).

  The SMS sensor is easy to manufacture and has the feature that sensing can be realized by observing the light intensity change in the wavelength region. For example, in Non-Patent Document 2, the SMS sensor using MMF simultaneously detects temperature and tension. Has been reported to be possible. In Non-Patent Document 3, an SMS sensor with improved sensitivity to temperature is realized by using an optical fiber having a hole structure as an MMF medium and filling the hole region with a liquid having an appropriate refractive index. It has been reported that it can be done.

Q. Wang, and G.W. Farrell, “All-fiber multimode-interference-based refractometer sensor: proposal and design.” Opt. Lett. , Vol. 31, no. 3, pp. 317-319, 2006. J. et al. Zhou. C. Liao, Y .; Wang, G.G. Yin, X. Zhong, K.K. Yang, B.B. Sun, G.M. Wang, and Z.M. Li, “Simultaneous measurement of strain and temperature by embedding fiber Mach-Zehnder interferometer,” Opt. Express, vol. 22, no. 2, pp. 1680-1686, 2014. W. Lin, B.B. Song, Y .; Miao, H.M. Zhang, D.H. Yan, B.B. Liu, and Y.J. Liu, “Liquid-filled photonic-crystal-fiber-based multimodal interferometer for simulated measurement of temperature and force,” Appl. Opt. , Vol. 54, no. 6, pp. 1309-1313, 2015.

  However, when the core diameter of the MMF is several tens of μm or more, the number of modes propagating in the MMF increases, and it becomes difficult to control the mode propagating in the MMF, and the interference pattern observed at the output end and the MMF It becomes difficult to grasp the relationship between the propagation modes. For this reason, there has been a problem that the relative change amounts of a plurality of desired physical quantities cannot be calculated clearly. In addition, the optical fiber having a hole structure has a problem that it is difficult to manufacture the optical fiber itself, and the price of the sensor is generally high.

  Therefore, an object of the present invention is to provide an optical fiber sensor that is easy to manufacture an optical fiber and that can clearly calculate the relative change amounts of a plurality of desired physical quantities.

  The optical fiber sensor of the present invention uses a number mode optical fiber (FMF: Few-mode fiber) in which the number of modes that can be propagated is limited to 2 to 4, and the propagation mode observed at the output end of the optical fiber sensor This is a means to clarify the relationship of inter-mode interference.

Specifically, the optical fiber sensor of the present invention is
A sensor unit in which a single mode optical fiber capable of guiding one kind of propagation mode at the measurement wavelength is connected to both ends of a number mode optical fiber capable of guiding at least two kinds of propagation modes at a predetermined measurement wavelength. With
Of the wavelength dependence of the light intensity at the exit end of the sensor unit of the measurement light having the measurement wavelength,
A wavelength change amount corresponding to a wavelength change amount at which the wavelength-dependent light intensity is maximized or minimized; and
Using the light intensity change amount corresponding to the difference between the maximum value and the minimum value of the wavelength-dependent light intensity,
A relative change amount of temperature or tension in the sensor unit is detected.

Specifically, the optical fiber sensor of the present invention is
One type at the first measurement wavelength and the second measurement wavelength at both ends of the number mode optical fiber capable of guiding at least two types of propagation modes at a predetermined first measurement wavelength and second measurement wavelength. A sensor unit connected to a single mode optical fiber capable of guiding the propagation mode of
The first wavelength dependence of the first measurement light having the first measurement wavelength and the second measurement light having the second measurement wavelength indicating the wavelength dependence of the light intensity at the output end of the sensor unit. Of the second wavelength dependency indicating the wavelength dependency of the light intensity at the emission end of the sensor unit,
A first wavelength change amount corresponding to a wavelength change amount at which the first wavelength-dependent light intensity is maximized or minimized; and
Using a second wavelength change amount corresponding to a wavelength change amount at which the second wavelength-dependent light intensity is maximized or minimized,
A relative change amount of temperature or tension in the sensor unit is detected.

Specifically, the optical fiber sensor of the present invention is
One type at the first measurement wavelength and the second measurement wavelength at both ends of the number mode optical fiber capable of guiding at least two types of propagation modes at a predetermined first measurement wavelength and second measurement wavelength. A sensor unit connected to a single mode optical fiber capable of guiding the propagation mode of
The first wavelength dependence of the first measurement light having the first measurement wavelength and the second measurement light having the second measurement wavelength indicating the wavelength dependence of the light intensity at the output end of the sensor unit. Of the second wavelength dependency indicating the wavelength dependency of the light intensity at the emission end of the sensor unit,
A first wavelength change amount corresponding to a wavelength change amount at which the first wavelength-dependent light intensity is maximized or minimized;
A second wavelength change amount corresponding to a wavelength change amount at which the second wavelength-dependent light intensity is maximized or minimized; and
Using the light intensity change amount corresponding to the difference between the maximum value and the minimum value of the light intensity of the first wavelength dependency or the second wavelength dependency,
A relative change amount of any three types of physical quantities among temperature, tension, curvature, and lateral pressure in the sensor unit is detected.

In the optical fiber sensor of the present invention,
The several-mode optical fiber may have a step-type refractive index distribution, an LP11 mode cutoff wavelength of 1650 nm or more, and a normalized frequency V value of 2.9 or more and 3.8 or less.

In the optical fiber sensor of the present invention,
The number mode optical fiber has a step-type refractive index profile, an LP11 mode cutoff wavelength of 1650 nm or more, and a normalized frequency V value of 2.9 or more and 3.8 or less,
An interval Δλ between the center wavelength of the first measurement wavelength and the center wavelength of the second measurement wavelength may satisfy the formula (5) using the normalized frequency V.

In the optical fiber sensor of the present invention,
The number mode optical fiber may have a cladding outer diameter of 125 μm or less.

Specifically, the optical fiber sensor system of the present invention is
A sensor unit in which a single mode optical fiber capable of guiding one kind of propagation mode at the measurement wavelength is connected to both ends of a number mode optical fiber capable of guiding at least two kinds of propagation modes at a predetermined measurement wavelength. When,
A measurement light source which Ru is incident the measurement light to the sensor unit having the measuring wavelength,
Measuring the wavelength dependency of the light intensity at the output end of the sensor unit, before of the wavelength dependency of the light intensity at the output end of the sensor portion of Kihaka constant light, the wavelength dependence of the light intensity is maximum or minimum wavelength change amount corresponding to the amount of change of the wavelength at which, and the light intensity variation corresponding to the difference between the maximum value and the minimum value of the wavelength dependence of the light intensity, using a pre-Symbol temperature or tension in the sensor unit An analysis unit for detecting a relative change amount;
Is provided.

Specifically, the optical fiber sensor system of the present invention is
One type at the first measurement wavelength and the second measurement wavelength at both ends of the number mode optical fiber capable of guiding at least two types of propagation modes at a predetermined first measurement wavelength and second measurement wavelength. A sensor unit connected to a single mode optical fiber capable of guiding the propagation mode of
Said first first second measuring light source of the measuring light Ru is incident to the sensor unit having a measuring beam and the second measuring wavelength having a measurement wavelength,
Wavelength dependence of the light intensity in the first wavelength dependent and the exit end of the sensor portion of the front Stories second measuring beam of a wavelength dependence of the light intensity at the output end of the sensor portion of the front Symbol first measuring beam A first wavelength change amount corresponding to a wavelength change amount at which the light intensity of the first wavelength dependency is maximized or minimized, and the second wavelength dependency. An analysis unit for detecting a relative change in temperature or tension in the sensor unit using a second change in wavelength corresponding to a change in wavelength at which the light intensity of the light reaches a maximum or minimum;
Is provided.

Specifically, the optical fiber sensor system of the present invention is
One type at the first measurement wavelength and the second measurement wavelength at both ends of the number mode optical fiber capable of guiding at least two types of propagation modes at a predetermined first measurement wavelength and second measurement wavelength. A sensor unit connected to a single mode optical fiber capable of guiding the propagation mode of
Said first first second measuring light source of the measuring light Ru is incident to the sensor unit having a measuring beam and the second measuring wavelength having a measurement wavelength,
Wavelength dependence of the light intensity in the first wavelength dependent and the exit end of the sensor portion of the front Stories second measuring beam of a wavelength dependence of the light intensity at the output end of the sensor portion of the front Symbol first measuring beam Of the second wavelength dependency, the first wavelength change amount corresponding to the change amount of the wavelength at which the light intensity of the first wavelength dependency becomes maximum or minimum, and the second wavelength dependency the second wavelength variation of light intensity corresponding to the amount of change of the wavelength at which the maximum or the minimum, and, the maximum value and the minimum value of the first wavelength-dependent or the second wavelength dependence of the light intensity An analysis unit that detects a relative change amount of any three types of physical quantities among temperature, tension, curvature, and lateral pressure in the sensor unit using a light intensity change amount corresponding to the difference;
Is provided.

Specifically, the measurement method of the present invention is:
A sensor unit in which a single mode optical fiber capable of guiding one kind of propagation mode at the measurement wavelength is connected to both ends of a number mode optical fiber capable of guiding at least two kinds of propagation modes at a predetermined measurement wavelength. A measuring method using
A measurement procedure for measuring the wavelength dependence of the light intensity at the output end of the sensor unit of the measurement light having the measurement wavelength;
A wavelength change amount corresponding to a wavelength change amount at which the wavelength-dependent light intensity is maximized or minimized, and a light intensity change amount corresponding to a difference between the maximum value and the minimum value of the wavelength-dependent light intensity, Using an analysis procedure for detecting a relative change in temperature or tension in the sensor unit;
Have

Specifically, the measurement method of the present invention is:
One type at the first measurement wavelength and the second measurement wavelength at both ends of the number mode optical fiber capable of guiding at least two types of propagation modes at a predetermined first measurement wavelength and second measurement wavelength. A measurement method using a sensor unit connected to a single mode optical fiber capable of guiding a propagation mode of
The first wavelength dependence of the first measurement light having the first measurement wavelength and the second measurement light having the second measurement wavelength indicating the wavelength dependence of the light intensity at the output end of the sensor unit. A measurement procedure for measuring the second wavelength dependency indicating the wavelength dependency of the light intensity at the emission end of the sensor unit;
A first wavelength change amount corresponding to a wavelength change amount at which the first wavelength-dependent light intensity is maximized or minimized, and a wavelength at which the second wavelength-dependent light intensity is maximized or minimized. An analysis procedure for detecting a relative change in temperature or tension in the sensor unit using a second wavelength change corresponding to the change;
Have

Specifically, the measurement method of the present invention is:
One type at the first measurement wavelength and the second measurement wavelength at both ends of the number mode optical fiber capable of guiding at least two types of propagation modes at a predetermined first measurement wavelength and second measurement wavelength. A measurement method using a sensor unit connected to a single mode optical fiber capable of guiding a propagation mode of
The first wavelength dependence of the first measurement light having the first measurement wavelength and the second measurement light having the second measurement wavelength indicating the wavelength dependence of the light intensity at the output end of the sensor unit. A measurement procedure for measuring the second wavelength dependency indicating the wavelength dependency of the light intensity at the emission end of the sensor unit;
A first wavelength change amount corresponding to a wavelength change amount at which the first wavelength-dependent light intensity is maximized or minimized; and a wavelength change amount at which the second wavelength-dependent light intensity is maximized or minimized. And the second wavelength change amount corresponding to the first wavelength dependency or the light intensity change amount corresponding to the difference between the maximum value and the minimum value of the second wavelength dependency light intensity, An analysis procedure for detecting a relative change amount of any three kinds of physical quantities among temperature, tension, curvature and lateral pressure in the sensor unit;
Have

  The above inventions can be combined as much as possible.

  ADVANTAGE OF THE INVENTION According to this invention, the optical fiber sensor which can manufacture the optical fiber easily and can calculate the relative variation | change_quantity of several desired physical quantities clearly can be provided.

1 is a schematic diagram illustrating an example of a configuration of an optical fiber sensor system in Embodiment 1. FIG. FIG. 6 is a conceptual diagram illustrating an example of an output waveform detected by a light receiving unit 20. 6 is a diagram illustrating an example of temperature dependency of a wavelength change amount δλ and a light intensity change amount δP in the first embodiment. 6 is a diagram illustrating an example of distortion amount dependency of a wavelength change amount δλ and a light intensity change amount δP in the first embodiment. It is drawing which shows an example of the measurement result in the light-receiving part in Embodiment 2. FIG. 6 is a diagram illustrating an example of temperature dependency of a wavelength change amount δλ in the second embodiment. 6 is a diagram illustrating an example of distortion amount dependency of a wavelength change amount δλ in the second embodiment. It is drawing shown about an example of the parameter of the core structure of FMF in Embodiment 3. FIG. 10 is a diagram illustrating an example of a relationship between a relative change amount of an effective refractive index difference and a wavelength change amount in Embodiment 3. It is drawing which shows an example of the temperature dependence of the relative variation | change_quantity of an effective refractive index difference in Embodiment 3, and the relationship of a wavelength. It is drawing which shows an example of the relationship between the temperature dependence of the relative variation | change_quantity of an effective refractive index difference, and the V value of FMF in Embodiment 3. FIG. It is drawing which shows an example of the relationship between the temperature dependence of the relative variation | change_quantity of the effective refractive index difference between two measurement wavelengths, and a measurement wavelength interval in Embodiment 3. FIG. It is drawing which shows an example of the relationship between the minimum wavelength interval of two measurement wavelength bands and V value of FMF in Embodiment 3.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to embodiment shown below. These embodiments are merely examples, and the present invention can be implemented in various modifications and improvements based on the knowledge of those skilled in the art. In the present specification and drawings, the same reference numerals denote the same components.

  The optical fiber sensor according to the present embodiment uses a number mode optical fiber (FMF) in which the number of modes that can be propagated is limited to 2 to 4, and clarifies the relationship between the propagation mode and inter-mode interference. As a means to do. The FMF used in the optical fiber sensor of the present invention is a means for realizing a simpler structure by using a step type refractive index distribution.

An optical fiber sensor system according to the present embodiment includes an optical fiber sensor in which a single mode optical fiber is connected to both ends of a few mode optical fiber, a broadband light source that receives broadband light from one end of the optical fiber sensor, and the light An optical spectrum analyzer that measures the wavelength dependence of the light intensity of light emitted from the other end of the fiber sensor, and calculates the relative change in temperature and tension of the optical fiber sensor based on the wavelength dependence of the measured light intensity. In an optical fiber sensor system including an analysis device, the analysis device executes any of the following processes.
The amount of change δλ1 from the reference value of the wavelength at which the light intensity in the first wavelength band is maximum (or minimum), the difference δP between the maximum value and the minimum value of the light intensity in the first wavelength band, and the second measurement wavelength The relative amount of change in temperature and tension of the optical fiber sensor using Equation (3) from any two values of the amount of change δλ2 from the reference value of the wavelength at which the light intensity in the band becomes maximum (or minimum) Is calculated.
The amount of change δλ1 from the reference value of the wavelength at which the light intensity in the first wavelength band is maximum (or minimum), the difference δP between the maximum value and the minimum value of the light intensity in the first wavelength band, and the second measurement wavelength Of the temperature, tension, curvature, and lateral pressure of the optical fiber sensor, using equation (4) from the three values of change δλ2 from the reference value of the wavelength at which the light intensity in the band is maximum (or minimum), Any three relative change amounts are calculated.

(Embodiment 1)
FIG. 1 is a schematic diagram showing a configuration of an optical fiber sensor system according to an embodiment of the present invention. The optical fiber sensor system of the present embodiment includes a measurement light source 10, a sensor unit 30, a light receiving unit 20, and an analysis unit 40.

  The measurement method according to the present embodiment is a measurement method using the sensor unit 30 and includes a measurement procedure and an analysis procedure in this order.

  In the measurement procedure, the measurement light source 10 emits measurement light having a predetermined measurement wavelength and inputs the measurement light to the sensor unit 30. As the measurement light source 10, for example, a broadband light source such as a super luminescent diode (SLD) can be used. The light receiving unit 20 receives the measurement light output from the sensor unit 30 and measures the wavelength spectrum indicating the wavelength dependence of the received light intensity. In addition, for example, an optical spectrum analyzer (OSA) can be used for the light receiving unit 20.

  The sensor unit 30 includes normal SMFs 31 a and 31 b and an FMF 32 capable of propagating 2 to 4 modes. The SMFs 31a and 31b are connected to both ends of the FMF 32. At this time, in order to improve the excitation efficiency of a plurality of propagation modes in the FMF 32, it is preferable that the input side of the FMF 32 is connected by setting an axial shift between the FMF 32 and one end of the SMF 31a. Here, it is more preferable to set the axial shift amount so that the excitation ratios of the plurality of propagation modes are the same because the interference between the propagation modes is maximized.

  In the analysis procedure, the analysis unit 40 calculates the relative change amount of the temperature change δT and the strain amount change δε in the sensor unit 30 using the waveform of the wavelength spectrum measured by the light receiving unit 20. The analysis unit 40 calculates the relative change amount of the tension applied to the sensor unit 30 from the strain amount change δε. A method of calculating the temperature change δT and the strain amount change δε will be described later.

  The analysis unit 40 may be realized by causing a computer to function as the analysis unit 40. In this case, each configuration is realized by a CPU (Central Processing Unit) (not shown) included in the analysis unit 40 executing a computer program stored in a storage unit (not shown). Here, the computer for realizing the analysis unit 40 may further include an arbitrary device controlled by the computer. Further, a program for realizing the analysis unit 40 can be recorded on a recording medium or provided through a network.

  FIG. 2 shows an example of the waveform of the wavelength spectrum measured by the light receiving unit 20. Wavelength spectra measured under different environments such as temperature and strain amount change as L2A and L2B. In L2A and L2B, the light intensity change amount δP in the wavelength spectrum changes and the peak wavelength shifts. In the present embodiment, the deviation between the maximum value and the minimum value of the light intensity in the same waveform of L2A or L2B in FIG. 2 is defined as the light intensity change amount δP. Further, a change amount of the maximum value or the minimum value of the light intensity detected between two different waveforms of L2A and L2B is defined as a wavelength change amount δλ. In FIG. 2, the wavelength change amount δλ is the change amount of the minimum value of L2A and L2B.

  Below, the optical fiber sensor system using FMF32 whose length L is 0.48 m is demonstrated. The FMF 32 provided in the sensor unit 30 used in the present embodiment has a step type refractive index distribution, the relative refractive index difference is 0.58%, and the core radius is 6.2 μm. The FMF 32 can propagate two modes, LP01 and LP11, at a wavelength longer than 1457 nm. Further, the FMF 32 can propagate four modes including LP01 and LP11 plus LP21 and LP02 at wavelengths shorter than 1457 nm. Incidentally, the cladding outer diameter of the FMF 32 used in the present embodiment is 100 μm.

  Here, when the tension applied to the optical fiber is constant, if the outer diameter of the cladding is reduced, the tension per unit cross-sectional area can be increased, and the sensitivity to the tension can be improved. Therefore, in the optical fiber sensor system of the present embodiment, it is preferable to set the cladding outer diameter of the FMF 32 as 125 μm, which is equivalent to that of a normal optical fiber, or less.

  In the optical fiber sensor system according to the present embodiment, the 1580 nm band is used for the first measurement wavelength, the wavelength change amount δλ that minimizes the received light intensity of the light receiving unit 20 in the wavelength band, and the maximum light intensity in the wavelength band. The temperature and tension of the sensor unit 30 can be evaluated using the light intensity change amount δP that is the difference between the minimum light intensity and the minimum light intensity. The wavelength sweep range and resolution of OSA were 20 nm and 0.01 nm, respectively.

  FIG. 3 shows the results of measuring the temperature dependence of the wavelength variation δλ and the light intensity variation δP. The sensor unit 30 was installed without tension, and the strain amount ε was 0%. As can be seen from FIG. 3, the wavelength variation δλ decreases in proportion to the temperature T as in L31, and the temperature coefficient is −0.042 nm / ° C. On the other hand, it can be seen that the dependence of the light intensity change amount δP on the temperature T is almost negligible as in L32. In FIG. 3, the vertical axis of the light intensity change amount δP is normalized with the value when the temperature T is 20 ° C.

  FIG. 4 shows the results of measuring the dependency of the wavelength variation δλ and the light intensity variation δP on the strain amount. Here, both ends of the sensor unit 30 are fixed so that the sensor unit 30 is linear on the fine movement table, and one of the fine movement tables is pulled in the propagation direction of the optical fiber, whereby the tension in the longitudinal direction of the sensor unit 30 is obtained. Was applied. The horizontal axis of FIG. 4 indicates the elongation strain amount ε of the sensor unit 30 at this time in% units, and the strain amount ε of 0.083% corresponds to a tensile amount of 400 μm. The external temperature T during measurement was constant at 24 ° C.

  From FIG. 4, the wavelength change amount δλ indicated by L41 decreased in proportion to the strain amount ε of the sensor unit 30, and the proportionality coefficient was −27.9 nm /%. In addition, the light intensity change amount δP indicated by L42 increases as the strain amount ε of the sensor unit 30 increases, and the proportionality coefficient is 27.1 dB /%. Therefore, the analysis unit 40 measures the change amount of the wavelength change amount δλ and the light intensity change amount δP, and substitutes δλ and δP into the following formulas (1) and (2), whereby the temperature T and the strain amount ε It is possible to detect a temperature change δT and a strain amount change δε, which are relative changes in the above. Further, the relative change amount of the tension applied to the sensor unit 30 can be detected from the strain amount change δε.

  For example, it is assumed that changes in δP in X (unit dB) and δλ1 in Y (unit nm) are observed. In this case, in Equation (1), the strain amount change δε (unit%) can be obtained by substituting X for δP and 27.1 (unit dB /%) for dP / dε. Further, in the formula (2), Y is set to δλ, the numerical value obtained from the formula (1) is set to δε, 27.1 (unit dB /%) is set to dP / dε, and −0.042 (unit is set to dλ / dT). By substituting (nm / ° C.), the temperature change δT (unit: ° C.) can be obtained.

  Here, when the strain amount ε is constant, the tension per unit cross-sectional area of the FMF 32 increases as the cladding outer diameter of the FMF 32 decreases. For this reason, the sensitivity with respect to the tension | tensile_strength of an optical fiber sensor system is controllable by reducing the clad outer diameter of FMF32 used for the sensor part 30. FIG.

  As described above, since the optical fiber sensor system according to the present embodiment can obtain the temperature change δT and the strain amount change δε in the sensor unit 30, it can simultaneously detect the temperature and the tension. As described above, according to the optical fiber sensor of the present invention, by applying the FMF capable of propagating 2 to 4 modes to the sensor unit, the relationship between the detected physical parameter and the inter-mode interference can be clarified, and the necessary measurement is performed. There is an effect that the conditions can be clearly derived.

  Further, by using a general-purpose step-type refractive index distribution for the FMF 32, there is an effect that FMF can be easily manufactured as in the case of a normal SMF. In addition, by using the step type FMF 32, it is possible to easily realize a core structure having good connectivity with a general-purpose SMF.

(Embodiment 2)
The optical fiber sensor system according to the second embodiment of the present invention measures the temperature change δT and the strain amount change δε by using measurement light having two measurement wavelengths.

  The measurement method according to the present embodiment is a measurement method using the sensor unit 30 and includes a measurement procedure and an analysis procedure in this order.

  In the measurement procedure, the measurement light source 10 inputs the first measurement light using the 1580 nm band as the first measurement wavelength and the second measurement light using the 1430 nm band as the second measurement wavelength to the sensor unit 30. . The light receiving unit 20 receives the first measurement light output from the sensor unit 30 and measures the first wavelength spectrum. In addition, the light receiving unit 20 receives the second measurement light output from the sensor unit 30 and measures the second wavelength spectrum.

  In the analysis procedure, the analysis unit 40 uses the wavelength change amount δλ1 in the first wavelength spectrum waveform and the second wavelength spectrum waveform as the change amount of the wavelength at which the light receiving intensity of the light receiving unit 20 is minimum in each measurement wavelength band. Is used to calculate a temperature change δT and a strain amount change δε, which are relative changes in the temperature T and the strain amount ε of the sensor unit 30. The wavelength sweep range and resolution of the OSA included in the light receiving unit 20 were 20 nm and 0.01 nm, respectively.

  FIG. 5 shows an example of the second wavelength spectrum. The FMF 32 used in this embodiment can guide four LP modes LP01, LP11, LP21, and LP02 in the 1430 nm band. Therefore, a plurality of interference patterns are observed in the second wavelength spectrum waveform, and there are at least two interference patterns of L5δλ1 that is inter-mode interference with a period of about 4 nm and L5δλ2 with a period of about 0.5 nm. Recognize.

  In this embodiment, the analysis unit 40 extracts the waveform corresponding to each period from the measured wavelength spectrum waveform by inverse Fourier transform, thereby evaluating the wavelength variation δλ associated with the two types of inter-mode interference. For example, when the wavelength spectrum of FIG. 5 is subjected to inverse Fourier transform, periods T1 and T2 corresponding to L5δλ1 and L5δλ2 can be extracted. Here, by subtracting the light intensity change of the period T2 from the wavelength spectrum of FIG. 5, the wavelength dependence of the light intensity corresponding to L5δλ1 can be extracted. Similarly, by subtracting the light intensity change of the period T1 from the wavelength spectrum of FIG. 5, the wavelength dependence of the light intensity corresponding to L5δλ2 can be extracted. In the measurement waveform, a plurality of inter-mode interferences are mixed, so that it is considered that the detection accuracy of the light intensity change amount δP by the analysis unit 40 deteriorates in the wavelength band in which the four modes propagate.

  FIG. 6 shows the temperature dependence of the wavelength change amount δλ2 in the second wavelength spectrum waveform. L61 and L62 show the evaluation results for the interference patterns with periods of 4 nm and 0.5 nm, respectively. In L61 with an interference pattern having a period of 4 nm, the wavelength variation δλ2 in the second wavelength spectrum waveform decreases in proportion to the temperature, and the proportionality factor is −0.028 nm / ° C. Further, comparing L61 with L31 in FIG. 3, it can be seen that there is a sufficient significant difference in the proportionality coefficient between the 1580 nm band and the 1430 nm band. On the other hand, for L62 having an interference pattern with a period of 0.5 nm, no clear temperature dependence of the wavelength variation δλ2 in the second wavelength spectrum waveform was observed.

  FIG. 7 shows the distortion amount dependency of the wavelength change amount δλ2 in the second wavelength spectrum waveform. L71 and L72 show the evaluation results for the interference patterns with periods of 4 nm and 0.5 nm, respectively. L71 decreases in proportion to the amount of strain, and the proportionality coefficient is −21.8 nm /%. Further, comparing L71 with L41 in FIG. 4, it can be seen that there is a sufficient significant difference in the proportionality coefficient between the 1580 nm band and the 1430 nm band. On the other hand, no dependency on the amount of strain was observed for L72.

  Therefore, the analysis unit 40 measures the wavelength change amounts δλ1 and δλ2 in two wavelength bands of the 1580 nm band that is the first measurement wavelength and the 1430 nm band that is the second measurement wavelength, respectively, and the following equation (3) By substituting into the relational expression shown as, it is possible to calculate the temperature change δT and the strain amount change δε, which are relative changes between the temperature T of the FMF 32 and the strain amount ε. The analysis unit 40 extracts interference patterns between lower modes by extracting interference patterns between lower-order modes even in the 4LP mode region in which the four LP modes LP01, LP11, LP21, and LP02 propagate. It can be seen that the temperature and strain amount ε can be extracted without being affected by the above.

  For example, when δλ1 of X (unit nm) is observed in the wavelength 1580 nm band and δλ2 of Y (unit nm) is observed in the wavelength 1430 nm band, the analysis unit 40 substitutes X and Y described above into Expression (3). . Specifically, the analysis unit 40 calculates −0.042 (unit: nm / ° C.) and −27.9 (units) for dλ1 / dT, dλ1 / dε, dλ2 / dT, and dλ2 / dε in Equation (3), respectively. nm /%), -0.028 (unit nm / ° C), -21.8 (unit nm /%) are substituted, and δT (unit ° C) and δε (unit%) are obtained by solving simultaneous equations. Is possible.

  Here, in the light receiving unit 20 according to the present embodiment, the 2LP mode in which the two LP modes of the wavelength change amounts δλ1 and δλ2 and LP01 and LP11 of the measurement light output from the sensor unit 30 are propagated. Since a maximum of three types of changes in the light intensity change amount δP in the region can be measured, the temperature coefficient or the strain amount depending on the side pressure F or the curvature R in addition to the temperature T and the strain amount ε of the sensor unit 30. Knowing the coefficients makes it possible to evaluate changes in up to three environmental parameters simultaneously. For example, the wavelength shift amount δλ3 is measured in a desired wavelength band when the temperature T applied to the sensor unit 30 and the strain amount ε due to tension are constant and the side pressure F, which is the pressing force applied to the side surface of the FMF 32, is changed. Thus, the analysis unit 40 can calculate a coefficient (dδλ3 / dF) with respect to the pressing force of the sensor unit 30.

  For example, when the analysis unit 40 observes the change of δP of X (unit dB) at 1580 nm, δλ1 of Y (unit nm), and δλ2 of Z (unit nm) in the 1430 nm band, By substituting X for the light intensity change amount δP in 1) and 27.1 (unit dB /%) for dP / dε, δε (unit%) can be obtained. Further, the analysis unit 40 obtains Y for the wavelength change amount δλ1 in the first measurement light of Equation (4), Z for the wavelength change amount δλ2 in the second measurement light, and δε from Equation (1). By substituting δε (unit%) and using the coefficients of the respective wavelength bands for T, ε, and F, δT (unit ° C) and δF (unit N) can be obtained.

  Similarly, by measuring the wavelength shift amount δλ3 when the temperature and tension applied to the sensor unit 30 are constant and changing the curvature R of the sensor unit 30 in a desired wavelength band, The coefficient (dδλ3 / dR) with respect to the curvature R can be known, and the relative change in the curvature R can be detected by replacing either the temperature T or the side pressure F in the equation (4) with the curvature R.

(Embodiment 3)
In the present embodiment, the relationship between the structural conditions suitable for the FMF 32 and the sensing conditions will be described.

  FIG. 8 shows the relationship between the core radius and the relative refractive index difference in the step type FMF 32. L81 and L82 represent cutoff wavelength conditions. L82 represents a structural boundary where the cutoff wavelength of the LP11 mode of the FMF 32 is 1650 nm, and the two modes LP01 and LP11 can propagate in the region above L82. On the other hand, L81 represents a structural condition in which the cutoff wavelength of the LP21 and LP02 modes of the FMF 32 is 1500 nm, and the four modes LP01, LP11, LP21, and LP02 can propagate in the region above L81.

  As shown in the second embodiment, the optical fiber sensor according to the present embodiment can be applied in the 4LP mode region in which the four LP modes LP01, LP11, LP21, and LP02 propagate. In order to eliminate the influence of the interference, it is desirable to use in the 2LP mode region where the two LP modes LP01 and LP11 propagate. Therefore, when setting the measurement wavelength in the 1500 nm band, it is desirable to set the core radius and the relative refractive index difference in the region surrounded by L81 and L82 in FIG.

  L83 and L84 shown in FIG. 8 indicate structural boundaries. L84 indicates a structure boundary where the mode field diameter (MFD) of the LP01 mode at a wavelength of 1310 nm is 8.6 μm. L83 indicates a structure boundary where the mode field diameter of the LP01 mode at a wavelength of 1310 nm is 9.5 μm.

  Here, a typical value of MFD at a wavelength of 1310 nm of general-purpose SMF is 8.6 μm to 9.5 μm. Therefore, by setting the core radius and the relative refractive index difference in the region surrounded by L83 and L84 in the figure, the FMF 32 can realize an MFD equivalent to a normal SMF in the FMF 32. When configuring the sensor unit 30, it is possible to reduce the connection loss between the FMF 32 and the SMFs 31a and 31b. Therefore, by setting the core radius and relative refractive index difference of FMF32 in the region surrounded by L81 and L82 and L83 and L84 shown in FIG. 8, it has a two-mode region in the 1500 nm band of wavelengths from 1500 nm to 1650 nm, It is possible to configure the sensor unit 30 having high consistency with a normal SMF MFD.

In the relative refractive index difference (four points of about 0.42%, 0.52%, 0.62%, and 0.73%) at which L81 and L82 intersect with L83 and L84 shown in FIG. Focusing on the core radius of .6 μm or 9.5 μm, the relationship between the effective refractive index and the temperature dependence of the refractive index in each core structure was examined. Here, the normalized frequency V value in the combination of the relative refractive index difference and the core radius becomes three levels of about 2.9, 3.3, and 3.8. In the following examination, the temperature dependence of the refractive index of quartz glass was 8.75 × 10 ⁻⁷ / ° C.

9, the effective refractive index difference change amount indicating the relative amount of change in the effective refractive index difference .DELTA.n _eff delta and (.DELTA.n _eff) indicating the relationship between the wavelength change amount [delta] [lambda]. The effective refractive index difference change amount Δ (δn _eff ) shown in FIG. 9 indicates the relative change amount of the effective refractive index difference δn _eff between the LP01 mode and the LP11 mode. In general, it is known that the wavelength change amount δλ in the SMS sensor changes in proportion to the effective refractive index difference between the two corresponding modes (see, for example, Non-Patent Document 3). Assuming that the minimum value of the wavelength sweep resolution of the light receiving unit 20 is 0.01 nm, if Δ (δn _eff ) of 1.9 × 10 ⁻⁸ or more is generated from FIG. 9, the sensor unit 30 of the present embodiment. It can be seen that detection becomes possible.

FIG. 10 shows the relationship between the temperature dependence of the effective refractive index difference variation Δ (δn _eff ) and the wavelength. The vertical axis represents dΔ (δn _eff ) / dT, which is the amount of change in Δ (δn _eff ) with respect to temperature change, and the unit is (10 ⁻⁷ / ° C.). As described above, the temperature dependence of the refractive index of quartz glass is 8.75 × 10 ⁻⁷ / ° C.

  L101a and L101b in FIG. 10 show the calculation results for the core structure with the normalized frequency V value of 2.9, L102a and L102b show the calculation results for the core structure with the normalized frequency V value of 3.3, L103a and L103b indicate calculation results for the core structure in which the normalized frequency V value is 3.8. L101a, L102a, and L103a show the calculation results for the core structure with an MFD of 8.6 μm, and L101b, L102b, and L103b show the calculation results for the core structure with an MFD of 9.5 μm.

As shown in FIG. 10, if the normalized frequency V value is constant, the wavelength dependency of Δ (δn _eff ) is equivalent as in L101a and L101b. Further, the absolute value of the temperature coefficient of Δ (δn _eff ) increases as the normalized frequency V value is smaller and the longer wavelength side.

FIG. 11 shows the effective refractive index difference variation Δ (δn _eff ) at the measurement wavelength of 1550 nm in the optical fiber sensor according to the present embodiment as a function of the normalized frequency V value. The vertical axis represents dΔ (δn _eff ) / dT, which is the amount of change in Δ (δn _eff ) with respect to temperature change, and the unit is (10 ⁻⁷ / ° C.). As described above, the temperature dependence of the refractive index of quartz glass is 8.75 × 10 ⁻⁷ / ° C.

The absolute value of the temperature coefficient of Δ (δn _eff ) increases on the low V value side. In the region where the normalized frequency V value is 3.12 or less, the absolute value of Δ (δn _eff ) is 1.9 × 10 ⁻⁷ or more, and a temperature resolution of about 0.1 ° C. is more preferable.

FIG. 12 shows the relationship between the difference in dΔ (δn _eff ) / dT and the wavelength interval between two measured wavelengths. The vertical axis represents the difference in dΔ (δn _eff ) / dT between the two measurement wavelengths, and the unit is (10 ⁻⁸ / ° C.). L121, L122, and L123 in the figure represent calculation results for the core structure having normalized frequency V values of 2.9, 3.3, and 3.8, respectively. As described above, the temperature dependence of the refractive index of quartz glass is 8.75 × 10 ⁻⁷ / ° C.

From FIG. 12, the absolute value of the difference in dΔ (δn _eff ) / dT between the two wavelengths increases with the wavelength interval. Here, L124 in the figure represents a level at which the absolute value of Δ (δn _eff ) is 1.9 × 10 ⁻⁸ . Therefore, as shown in FIG. 9, by setting the interval between the two measurement wavelengths to be equal to or greater than the wavelength interval at which the solid lines L121 to L123 of each normalized frequency V value intersect with the broken line L124, the first wavelength at the two measurement wavelengths It is possible to cause a deviation of 0.01 nm or more between the change amount δλ1 and the second wavelength change amount δλ2. For this reason, by setting the wavelength sweep resolution of the light receiving unit 20 to 0.01 nm, a relative change in the temperature T is obtained from the equation (3) using the difference between the first wavelength change amount δλ1 and the second wavelength change amount δλ2. It is possible to obtain a strain amount change δε which is a relative change between the temperature change δT and the strain amount ε.

FIG. 13 shows the relationship between the minimum wavelength interval at which the absolute value of Δ (δn _eff ) in the optical fiber sensor according to this embodiment is 1.9 × 10 ⁻⁸ or more and the normalized frequency V value. As shown in FIG. 13, the minimum wavelength interval increases with the normalized frequency V value. When the normalized frequency V value is 3.8, a wavelength interval of about 120 nm is required. Therefore, as shown in FIGS. 8 and 13, the sensor unit 30 is configured using the FMF 32 whose normalized frequency V value is in the range of 2.9 to 3.8, and the wavelength range of 1500 nm to 1650 nm is used. Thus, temperature evaluation can be performed with a resolution of 1 ° C. or less. Here, the relationship between the minimum wavelength interval Δλ and the V value shown in FIG. 13 can be approximated by the following equation (5).

  Therefore, in the sensor unit 30 provided in the optical fiber sensor of the present invention, it is possible to realize an efficient temperature sensor by setting the normalized frequency V value and Δλ so as to satisfy the relationship of Expression (5). Become.

  The present invention can be applied to the information communication industry.

10: Measurement light source 20: Light receiving unit 30: Sensor unit 31a: SMF
31b: SMF
32: FMF
40: Analysis unit

Claims (12)

A sensor unit in which a single mode optical fiber capable of guiding one kind of propagation mode at the measurement wavelength is connected to both ends of a number mode optical fiber capable of guiding at least two kinds of propagation modes at a predetermined measurement wavelength. With
Of the wavelength dependence of the light intensity at the exit end of the sensor unit of the measurement light having the measurement wavelength,
A wavelength change amount corresponding to a wavelength change amount at which the wavelength-dependent light intensity is maximized or minimized; and
Using the light intensity change amount corresponding to the difference between the maximum value and the minimum value of the wavelength-dependent light intensity,
Detecting a relative change in temperature or tension in the sensor unit;
Optical fiber sensor. One type at the first measurement wavelength and the second measurement wavelength at both ends of the number mode optical fiber capable of guiding at least two types of propagation modes at a predetermined first measurement wavelength and second measurement wavelength. A sensor unit connected to a single mode optical fiber capable of guiding the propagation mode of
The first wavelength dependence of the first measurement light having the first measurement wavelength and the second measurement light having the second measurement wavelength indicating the wavelength dependence of the light intensity at the output end of the sensor unit. Of the second wavelength dependency indicating the wavelength dependency of the light intensity at the emission end of the sensor unit,
A first wavelength change amount corresponding to a wavelength change amount at which the first wavelength-dependent light intensity is maximized or minimized; and
Using a second wavelength change amount corresponding to a wavelength change amount at which the second wavelength-dependent light intensity is maximized or minimized,
Detecting a relative change in temperature or tension in the sensor unit;
Optical fiber sensor. One type at the first measurement wavelength and the second measurement wavelength at both ends of the number mode optical fiber capable of guiding at least two types of propagation modes at a predetermined first measurement wavelength and second measurement wavelength. A sensor unit connected to a single mode optical fiber capable of guiding the propagation mode of
The first wavelength dependence of the first measurement light having the first measurement wavelength and the second measurement light having the second measurement wavelength indicating the wavelength dependence of the light intensity at the output end of the sensor unit. Of the second wavelength dependency indicating the wavelength dependency of the light intensity at the emission end of the sensor unit,
A first wavelength change amount corresponding to a wavelength change amount at which the first wavelength-dependent light intensity is maximized or minimized;
A second wavelength change amount corresponding to a wavelength change amount at which the second wavelength-dependent light intensity is maximized or minimized; and
Using the light intensity change amount corresponding to the difference between the maximum value and the minimum value of the light intensity of the first wavelength dependency or the second wavelength dependency,
Detecting a relative change amount of any three kinds of physical quantities among temperature, tension, curvature and lateral pressure in the sensor unit;
Optical fiber sensor. The number mode optical fiber has a step-type refractive index distribution, the cutoff wavelength of the LP11 mode is 1650 nm or more, and the normalized frequency V value is 2.9 or more and 3.8 or less.
The optical fiber sensor in any one of Claim 1 to 3. The number mode optical fiber has a step-type refractive index profile, an LP11 mode cutoff wavelength of 1650 nm or more, and a normalized frequency V value of 2.9 or more and 3.8 or less,
An interval Δλ between the center wavelength of the first measurement wavelength and the center wavelength of the second measurement wavelength satisfies the following relational expression using the normalized frequency V.
The optical fiber sensor according to claim 2 or 3.
(Equation 1)
Δλ ≧ 464-334V + 64V ² The number mode optical fiber has a cladding outer diameter of 125 μm or less.
The optical fiber sensor in any one of Claim 1 to 5. A sensor unit in which a single mode optical fiber capable of guiding one kind of propagation mode at the measurement wavelength is connected to both ends of a number mode optical fiber capable of guiding at least two kinds of propagation modes at a predetermined measurement wavelength. When,
A measurement light source which Ru is incident the measurement light to the sensor unit having the measuring wavelength,
Measuring the wavelength dependency of the light intensity at the output end of the sensor unit, before of the wavelength dependency of the light intensity at the output end of the sensor portion of Kihaka constant light, the wavelength dependence of the light intensity is maximum or minimum wavelength change amount corresponding to the amount of change of the wavelength at which, and the light intensity variation corresponding to the difference between the maximum value and the minimum value of the wavelength dependence of the light intensity, using a pre-Symbol temperature or tension in the sensor unit An analysis unit for detecting a relative change amount;
An optical fiber sensor system comprising: One type at the first measurement wavelength and the second measurement wavelength at both ends of the number mode optical fiber capable of guiding at least two types of propagation modes at a predetermined first measurement wavelength and second measurement wavelength. A sensor unit connected to a single mode optical fiber capable of guiding the propagation mode of
Said first first second measuring light source of the measuring light Ru is incident to the sensor unit having a measuring beam and the second measuring wavelength having a measurement wavelength,
Wavelength dependence of the light intensity in the first wavelength dependent and the exit end of the sensor portion of the front Stories second measuring beam of a wavelength dependence of the light intensity at the output end of the sensor portion of the front Symbol first measuring beam A first wavelength change amount corresponding to a wavelength change amount at which the light intensity of the first wavelength dependency is maximized or minimized, and the second wavelength dependency. An analysis unit for detecting a relative change in temperature or tension in the sensor unit using a second change in wavelength corresponding to a change in wavelength at which the light intensity of the light reaches a maximum or minimum;
An optical fiber sensor system comprising: One type at the first measurement wavelength and the second measurement wavelength at both ends of the number mode optical fiber capable of guiding at least two types of propagation modes at a predetermined first measurement wavelength and second measurement wavelength. A sensor unit connected to a single mode optical fiber capable of guiding the propagation mode of
Said first first second measuring light source of the measuring light Ru is incident to the sensor unit having a measuring beam and the second measuring wavelength having a measurement wavelength,
Wavelength dependence of the light intensity in the first wavelength dependent and the exit end of the sensor portion of the front Stories second measuring beam of a wavelength dependence of the light intensity at the output end of the sensor portion of the front Symbol first measuring beam Of the second wavelength dependency, the first wavelength change amount corresponding to the change amount of the wavelength at which the light intensity of the first wavelength dependency becomes maximum or minimum, and the second wavelength dependency the second wavelength variation of light intensity corresponding to the amount of change of the wavelength at which the maximum or the minimum, and, the maximum value and the minimum value of the first wavelength-dependent or the second wavelength dependence of the light intensity An analysis unit that detects a relative change amount of any three types of physical quantities among temperature, tension, curvature, and lateral pressure in the sensor unit using a light intensity change amount corresponding to the difference;
An optical fiber sensor system comprising: A sensor unit in which a single mode optical fiber capable of guiding one kind of propagation mode at the measurement wavelength is connected to both ends of a number mode optical fiber capable of guiding at least two kinds of propagation modes at a predetermined measurement wavelength. A measuring method using
A measurement procedure for measuring the wavelength dependence of the light intensity at the output end of the sensor unit of the measurement light having the measurement wavelength;
A wavelength change amount corresponding to a wavelength change amount at which the wavelength-dependent light intensity is maximized or minimized, and a light intensity change amount corresponding to a difference between the maximum value and the minimum value of the wavelength-dependent light intensity, Using an analysis procedure for detecting a relative change in temperature or tension in the sensor unit;
Measuring method. One type at the first measurement wavelength and the second measurement wavelength at both ends of the number mode optical fiber capable of guiding at least two types of propagation modes at a predetermined first measurement wavelength and second measurement wavelength. A measurement method using a sensor unit connected to a single mode optical fiber capable of guiding a propagation mode of
The first wavelength dependence of the first measurement light having the first measurement wavelength and the second measurement light having the second measurement wavelength indicating the wavelength dependence of the light intensity at the output end of the sensor unit. A measurement procedure for measuring the second wavelength dependency indicating the wavelength dependency of the light intensity at the emission end of the sensor unit;
A first wavelength change amount corresponding to a wavelength change amount at which the first wavelength-dependent light intensity is maximized or minimized, and a wavelength at which the second wavelength-dependent light intensity is maximized or minimized. An analysis procedure for detecting a relative change in temperature or tension in the sensor unit using a second wavelength change corresponding to the change;
Measuring method. One type at the first measurement wavelength and the second measurement wavelength at both ends of the number mode optical fiber capable of guiding at least two types of propagation modes at a predetermined first measurement wavelength and second measurement wavelength. A measurement method using a sensor unit connected to a single mode optical fiber capable of guiding a propagation mode of
The first wavelength dependence of the first measurement light having the first measurement wavelength and the second measurement light having the second measurement wavelength indicating the wavelength dependence of the light intensity at the output end of the sensor unit. A measurement procedure for measuring the second wavelength dependency indicating the wavelength dependency of the light intensity at the emission end of the sensor unit;
A first wavelength change amount corresponding to a wavelength change amount at which the first wavelength-dependent light intensity is maximized or minimized; and a wavelength change amount at which the second wavelength-dependent light intensity is maximized or minimized. And the second wavelength change amount corresponding to the first wavelength dependency or the light intensity change amount corresponding to the difference between the maximum value and the minimum value of the second wavelength dependency light intensity, An analysis procedure for detecting a relative change amount of any three kinds of physical quantities among temperature, tension, curvature and lateral pressure in the sensor unit;
Measuring method.

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