JP6306922B2 - Optical frequency domain reflection measurement method, optical frequency domain reflection measurement apparatus, and apparatus for measuring position or shape using the same - Google Patents

Description

  The present invention relates to a technique for measuring the strain distribution of an optical fiber to be measured, and in particular, inputs two orthogonally polarized lights to the optical fiber to be measured, and two orthogonal light beams reflected from the optical fiber to be measured in each. The present invention relates to a technique for measuring the polarized component and correcting birefringence.

  Conventionally, strain measurement of an optical fiber using an optical frequency domain reflectometry (OFDR) has been performed.

  FIG. 24 shows a basic configuration of an optical frequency domain reflection measuring apparatus (hereinafter simply referred to as a measuring apparatus) 200. In FIG. 24, the wavelength sweep light source 1 includes a semiconductor laser, and outputs a wavelength sweep light P0 in which the frequency of light linearly changes with respect to time.

  The wavelength swept light P0 is inputted to the branching means 3 made of an optical coupler or the like and branched into two, and one of the branched lights P1 is measured as an optical fiber to be measured via the directional coupling means 31 made of an optical circulator or the like as the measurement light Pmes. It is led to one end side of 38.

  The reflected light Pret that is reflected inside the optical fiber to be measured 38 and returns to one end side is input to the multiplexing means 41 including an optical coupler via the directional coupling means 31. The other light P2 (= reference light Pr) branched by the branching means 3 is also input to the multiplexing means 41, and the reflected light Pret and the reference light Pr interfere with each other.

  The two lights Psum (+) and Psum (−) output from the multiplexing means 41 have phases of light that interfere with each other. Two lights Psum (+) and Psum (-) output from the multiplexing means 41 are input to the balance light receiver 55 to detect a beat signal due to interference between the reflected light Pret from the measured optical fiber 38 and the reference light Pr. To do.

  An analog electric signal A output from the balance light receiver 55 is converted into a digital signal D by an A / D converter 65, and a Fourier transform process or the like is performed in a signal processing unit 90.

  Here, as shown in FIG. 25A, assuming that the measurement optical fiber 38 has three reflection points, point a, point b, and point c, and the distance from the near end o of the measurement optical fiber 38. Are La, Lb, and Lc.

  Further, if the optical path length from the branching means 3 to the multiplexing means 41 at the near end o of the measured optical fiber 38 and the optical path length from the branching means 3 through which the reference light Pr propagates to the multiplexing means 41 are made equal. The light Preta reflected at point a of the optical fiber 38 to be measured is multiplexed by the multiplexing means 41 with a time delay of ta = 2 nLa / c compared to the reference light Pr. Here, n is the refractive index of the optical fiber 38 to be measured, and c is the speed of light. Similarly, the light Pretb and Prec reflected at the points b and c are delayed by tb = 2nLb / c and tc = 2nLc / c.

  Therefore, the optical frequency νr of the reference light Pr, the optical frequency νa of the reflected light from the point a, the optical frequency νb of the reflected light from the point b, and the optical frequency νc of the reflected light from the point c are shown in FIG. As described above, the change characteristic of the optical frequency with respect to the time of the reference light Pr (in this case, a straight line having a constant slope) appears with a delay from the above-described times ta to tc.

If the amount of change in the optical frequency per unit time of the swept wavelength P0 is S, the beat frequency due to the interference between the reflected light Preta from the point a and the reference light Pr is
fa = | νa−νr | = S · ta = (2nS / c) La (1)
It becomes. Similarly, the beat frequency due to interference between the reflected light from point b and point c and the reference light is
fb = | νb−νr | = S · tb = (2 nS / c) Lb (2)
fc = | νc−νr | = S · tc = (2 nS / c) Lc (3)
It becomes.

  Therefore, when the digital signal D is Fourier-transformed in the signal processing unit 90, the frequencies proportional to the distances La, Lb, and Lc from one end of the measured optical fiber 38 to the respective reflection points as shown in FIG. Beat signals of fa, fb, and fc are observed. It is assumed that the reflectance at each point is sufficiently small, and multiple reflections are ignored.

  As described above, the longitudinal distribution of reflection from the optical fiber to be measured can be measured by the optical frequency domain reflectometry.

  Further, when light is continuously reflected in the longitudinal direction due to Rayleigh scattering of the optical fiber to be measured, and distortion is applied in the longitudinal direction of the optical fiber to be measured, the phase of the reflected light due to Rayleigh scattering changes.

  Therefore, by observing the phase of the beat signal obtained by the optical frequency domain reflection measurement method, it is possible to measure the longitudinal distribution of minute distortions of the optical fiber to be measured.

  Patent Document 1 discloses a method of measuring the position or shape of the optical frequency domain reflection measurement method applied to a multi-core fiber having a plurality of cores.

  In the configuration example of FIG. 24 described above, the polarization of light is not taken into consideration. However, the polarization of light is not maintained in a normal single mode fiber, and the polarization changes due to bending of the fiber. When the reflected light from the beam and the polarization of the reference light are orthogonal, there is a problem that a beat signal due to interference cannot be obtained. In addition, when the optical fiber is bent, birefringence having a different refractive index is generated depending on the polarization state of light, which affects phase measurement by the optical frequency domain reflectometry.

  In order to solve these problems, two orthogonal polarization states of light are switched for each sweep and incident on the optical fiber, and for each polarization state, the two orthogonal polarizations of the reflected light from the optical fiber are changed. A polarization diversity system that separates and measures the wave components is used.

  FIG. 26 shows a configuration example of a measurement apparatus 210 using a conventional polarization diversity method. In this measuring apparatus 210, the wavelength swept light P0 output from the wavelength swept light source 1 is branched into two by the branching means 3, as in the measuring apparatus 200 shown in FIG. 25, and one of the branched lights P1 is polarized. Input to the controller 15. The polarization controller 15 is for switching the polarization state of the emitted light between the first polarization state and the second polarization state orthogonal to the first polarization state. Each time the wavelength sweep is performed, the two polarization states are switched.

  The output light P1 'of the polarization controller 15 is input as the measurement light Pmes to the measured optical fiber 38 through the directional coupling means 31 as described above, and the reflected light Pret from the measured optical fiber 38 with respect to the measurement light Pmes. Is input to the multiplexing unit 41 via the directional coupling unit 31.

  The other light P <b> 2 branched by the branching unit 3 is input to the polarization controller 25. The polarization controller 25 is for adjusting the intensity of the reference light branched into two by the polarization separation means 45 and 46, which will be described later, so that the polarization state of the wavelength swept light P0 is previously set. However, this is not necessary when the reference light beams branched into two by the polarization separation means 45 and 46 are set to have substantially the same intensity.

  P2 ′ output from the polarization controller 25 is input as the reference light Pr together with the reflected light Pret from the optical fiber to be measured 38 to the combining means 41 and combined, and the reflected light Pret and the reference light Pr interfere with each other. As described above, the two lights Psum (+) and Psum (−) output from the multiplexing means 41 have the phases of the interfering lights opposite to each other, and one of the lights Psum (+) is the polarization beam splitter. The signal is input to the polarization separation means 45 composed of (PBS) or the like, and is branched into two orthogonal polarization components s (+) and p (+). The other light Psum (−) is also input to the polarization separating means 46 made of PBS or the like and branched into two orthogonal polarization components s (−) and p (−).

  The separated polarization components s (+) and s (−) are input to the balance light receiver 55, and an electric signal As proportional to the difference in light intensity between the polarization components s (+) and s (−) is output. The A / D converter 65 converts the signal into a digital signal Ds. Similarly, the separated polarization components p (+) and p (−) are input to the balance light receiver 56, and an electric signal Ap proportional to the difference in light intensity between the p (+) and p (−) is output. Then, the A / D converter 66 converts it into a digital signal Dp.

  These digital signals Ds and Dp are input to a signal processing unit 91 composed of a CPU or the like, and are respectively subjected to Fourier transform processing.

  In Patent Literature 1, the Fourier transform results of digital signals Ds and Dp obtained when the polarization controller 15 is set to the first polarization state and swept in the measurement apparatus 210 having the above configuration are respectively a, b, The Fourier transform results of the digital signals Ds and Dp obtained when the polarization controller 15 is set to the second polarization state and swept are denoted as c and d, respectively. These four types of Fourier transform results a, b, c, From d, a technique for correcting the birefringence of the optical fiber 38 to be measured is disclosed.

  FIG. 27 shows a configuration example of another measurement apparatus 220 using a conventional polarization diversity method. In this measuring apparatus 220, the output light P0 from the wavelength sweep light source 1 is given to the polarization controller 15 before branching by the branching means 3, and the polarization state of the output light is changed to the first polarization state for each wavelength sweep. It switches to the 2nd polarization state orthogonal to it.

  Then, the reflected light Pret from the optical fiber to be measured 38 and the reference light Pr are combined by the combining means 41, and the combined light Psum is input to the polarization controller 25. As described above, the polarization controller 25 is adjusted so that the intensities of the reference light branched into two by the subsequent polarization separation means 45 are substantially equal.

  The output light Psum ′ of the polarization controller 25 is separated into light in the polarization states s and p by the polarization separation means 45.

  In FIG. 27, single-ended light receivers 57 and 58 are used instead of the balance light receivers 55 and 56 of FIG. The digital signal Ds is obtained from the light in the polarization state s, and the digital signal Dp is obtained from the light in the polarization state p. As described with reference to FIG. 26, the polarization state of the output light from the polarization controller 15 is the first. Fourier transform results a and b obtained when the wavelength is swept in the polarization state and the Fourier transform obtained when the wavelength sweep is performed with the polarization state of the output light of the polarization controller 15 in the second polarization state. From the results c and d, the birefringence of the measured optical fiber 38 can be corrected by the method described in Patent Document 1.

  FIG. 28 shows a configuration of a measuring apparatus 230 that measures a three-dimensional position or shape using a multi-core fiber 39, with FIG. 27 as a basic configuration.

  In this measuring device 230, the output light P0 from the wavelength swept light source 1 is branched by the branching means 2, and one of the branched lights P1 is input to the polarization controller 15 as described above, and the other branched light P2 is monitored. Input to the unit 70.

  As shown in FIG. 29, the monitoring unit 70 divides the input light P2 into two by the branching means 71, supplies one of them to a hydrogen cyanide (HCN) gas cell 72, and the power of the light that has passed through the gas cell 72 Is measured by the light receiver 73 and the A / D converter 74 and output to the signal processing unit 92. The signal processing unit 92 calibrates the absolute wavelength of the wavelength swept light source 1 according to the gas absorption wavelength.

  The other light branched by the branching unit 71 is given to a delay interferometer including an optical coupler 81, a delay fiber 82, and Faraday rotator type mirrors 83 and 84. The output of the delay interferometer is measured by the light receiver 85 and the A / D converter 86. From the output of the delay interferometer, a sine wave having a beat frequency corresponding to the optical frequency change of the wavelength swept light source 1 is obtained. Since the actual wavelength-swept light source 1 often has a change in optical frequency with respect to time that is not completely linear, the signal processing unit 92 performs correction processing for nonlinearity of wavelength sweep using the output of the delay interferometer.

  On the other hand, the polarization controller 15 outputs the light P 1 ′ whose polarization state is switched for each sweep and sweep as described above, and is branched into four by the branching unit 30. The four branched lights P3 to P6 are respectively input to the branching means 3A to 3D and branched to the measuring lights Pmes1 to Pmes4 and the reference lights Pr1 to Pr4, and the four measuring lights Pmes1 to Pmes4 are directionally coupled. The signals are input to the multi-core fiber fan-out 35 through the means 31 </ b> A to 31 </ b> D, and input to each core of the single multi-core fiber 39 to be measured.

  Reflected lights Pret1 to Pret4 from the respective cores of the measured multicore fiber 39 are input to the multiplexing means 41A to 41D via the multicore fiber fan-out 35 and the directional coupling means 31A to 31D, respectively.

  Reference light Pr1 to Pr4 are also input to the multiplexing means 41A to 41D, respectively, and the reflected light from each core of the multicore fiber 39 to be measured and the reference light are multiplexed, as in the configuration of FIG. The output is separated into two polarization components (s1, p1) to (s4, p4) by the polarization separation means 45A to 45D, and converted into electric signals by the light receivers 57A to 57D and 58A to 58D, respectively. Then, the signals are converted into digital signals (Ds1, Dp1) to (Ds4, Dp4) by the A / D converters 65A to 65D and 66A to 66D and input to the signal processing unit 92. Similarly to the above, the polarization controllers 25A to 25D are adjusted so that the intensities of the reference lights branched into two by the subsequent polarization separation means 45A to 45D are substantially equal.

  With this configuration, it is possible to correct the birefringence and measure the strain distribution of each core of the multi-core fiber 39 to be measured, as in FIG. Further, it is possible to calculate the position or shape of the measured multi-core fiber 39 from the strain distribution of each core.

  Patent Document 2 discloses a method using a fiber Bragg diffraction grating (FBG) as an optical fiber to be measured. Since the reflectivity of the FBG is higher than the reflectivity of Rayleigh scattering, the influence of reflection at the end of the optical fiber to be measured, optical connector, directional coupling means (optical circulator), etc., and crosstalk of the multicore fiber to be measured and fan-out It has the feature that can be reduced. In addition, by using FBG with a chirped reflection wavelength, reflected light can be obtained over a wide wavelength sweep range, and the dynamic range of the light receiver can be suppressed.

Special table 2013-505441 International publication WO-2013136247

  In the optical frequency domain reflection measurement apparatus using the conventional polarization diversity method, the two wavelengths when the polarization controller 15 is set to the first polarization state and the second polarization state are set. Since sweeping is necessary, it takes a measurement time for two sweeps, and there is a problem that an error occurs if the strain of the optical fiber to be measured changes between the first sweep and the second sweep.

  The present invention solves the above-described problem, and an optical frequency domain reflection measuring apparatus that can input two orthogonally polarized light beams into a measured optical fiber in a single wavelength sweep and can detect a change in distortion in a short time. And it aims at providing the apparatus which measures a position or a shape using the same.

In order to achieve the object, an optical frequency domain reflection measurement method according to claim 1 of the present invention comprises:
Wavelength swept light whose wavelength is continuously swept within a predetermined range is split into a plurality of light beams to generate measurement light and reference light. )
The reflected light from the optical fiber to be measured with respect to the measurement light is received, the reflected light and the reference light are combined and input to a light receiver, and a beat generated by interference between the reflected light and the reference light is electrically generated. Outputting as a signal;
In the optical frequency domain reflection measurement method, including the step of converting the electrical signal into a digital signal and performing a Fourier transform process,
As the measurement light, the first polarization state light and the second polarization state light having the same wavelength sweep characteristics as the wavelength sweep light and whose polarizations are orthogonal to each other pass through the fiber Bragg diffraction grating. And using polarization multiplexed light combined with a predetermined time difference shorter than the time for the round trip,
A Fourier transform process is performed on the digital signal obtained when the wavelength swept light is swept once, and interference between the reflected light from the measured optical fiber and the reference light with respect to the light in the first polarization state is performed. The beat frequency generated by the second polarization state and the beat frequency generated by the interference between the reflected light from the measured optical fiber and the reference light with respect to the light in the second polarization state are divided into a plurality of periods, By combining the Fourier transform results obtained for a plurality of periods on the distance axis, each of the reflected light of the measured optical fiber with respect to the light in the first polarization state and the light in the second polarization state The measurement result is obtained.

The optical frequency domain reflectometry method of claim 2 of the present invention is the optical frequency domain reflectometry method of claim 1,
In the step of outputting the beat as an electric signal, the reflected light and the reference light are separated into s-polarization components and p-polarization components orthogonal to each other, and the reflected light and the s-polarization components of the reference light are received. And inputting the p-polarized component of the reflected light and the reference light to a light receiver and outputting the electric signal Ap.
The step of converting the electrical signal into a digital signal and performing a Fourier transform process converts the electrical signal As into a digital signal Ds, and reflects the reflected light from the optical fiber under measurement with respect to the light in the first polarization state. The beat frequency generated by the interference between the s-polarization component and the s-polarization component of the reference light, the s-polarization component of the reflected light from the measured optical fiber with respect to the light in the second polarization state, and the reference light Performing a Fourier transform process by dividing the beat frequency generated by the interference with the s-polarized wave component into a plurality of periods, and converting the electric signal Ap into a digital signal Dp so that the first polarization state is obtained. The beat frequency generated by the interference between the p-polarized component of the reflected light from the optical fiber to be measured and the p-polarized component of the reference light, and the light with respect to the second polarized light And a step of performing a Fourier transform process in a plurality of periods beat frequency do not overlap caused by interference between the p polarization component of the p-polarized component of the reflected light and the reference light from the measurement optical fiber,
Obtaining the measurement results of the s-polarized component and the p-polarized component of the reflected light of the optical fiber under measurement for the light in the first polarization state and the light in the second polarization state, respectively. It is characterized by.

An optical frequency domain reflection measuring apparatus according to claim 3 of the present invention is
A wavelength swept light source (1) for outputting a wavelength swept light whose wavelength is swept continuously within a predetermined range;
Branching means (3) for receiving the wavelength swept light via a first optical path and branching into a plurality of branches;
The first branch light output from the branch means via the second optical path is received and output as measurement light to a measured optical fiber (37) having a fiber Bragg diffraction grating with a chirped grating interval. wherein a directional binding means for receiving the reflected light from the measured optical fiber (31) for,
Receiving a second branched light which is output through the third optical path from said branching means based light, reflected light and the multiplexing multiplexes means from said measured optical fiber output from the directional binding means (41)
A light receiver (55, 56, 57, 58) that receives the output light of the multiplexing means and outputs a beat generated by interference between the reflected light and the reference light as an electrical signal;
An A / D converter (65, 66) for converting the electrical signal into a digital signal;
In an optical frequency domain reflection measurement apparatus having a signal processing unit (101 to 104) for performing a Fourier transform process on the digital signal,
The wavelength swept light or its branched light that is inserted into one of the first optical path, the second optical path, or both the second optical path and the third optical path is orthogonal to each other. The light is divided into light in the first polarization state and light in the second polarization state, and is combined with a predetermined time difference shorter than the time for light to reciprocate through the fiber Bragg diffraction grating. A polarization multiplexing unit (10, 10A, 10B) that outputs the polarization multiplexed light, and uses the polarization multiplexed light as the measurement light for at least the optical fiber to be measured;
The signal processing unit performs a Fourier transform process on the digital signal obtained by the wavelength swept light source performing one wavelength sweep, and reflects the light in the first polarization state from the measured optical fiber. A plurality of beat frequencies generated by interference between light and the reference light, and beat frequencies generated by interference between the reflected light from the measured optical fiber and the reference light with respect to the light in the second polarization state Dividing into periods, and by combining the Fourier transform results obtained for the plurality of periods on the distance axis, the coverage with respect to the light in the first polarization state and the light in the second polarization state is obtained. Each measurement result of the reflected light of the measurement optical fiber is obtained.

An optical frequency domain reflectometry apparatus according to claim 4 of the present invention is the optical frequency domain reflectometry apparatus according to claim 3,
Polarization separation means (45, 46) for separating the reflected light and the reference light into s-polarization components and p-polarization components orthogonal to each other;
A light receiver (55, 57) that receives the s polarized component of the reflected light and the reference light and outputs a beat generated by interference as an electric signal As;
A light receiver (56, 58) that receives the p-polarized component of the reflected light and the reference light and outputs a beat generated by interference as an electric signal Ap;
An A / D converter (65) for converting the electrical signal As into a digital signal Ds; and an A / D converter (66) for converting the electrical signal Ap into a digital signal Dp;
The signal processing unit
Fourier transform processing is performed on the digital signal Ds obtained by the wavelength swept light source performing one wavelength sweep, and the s-polarized light of the reflected light from the measured optical fiber with respect to the light in the first polarization state The beat frequency generated by the interference between the component and the s-polarization component of the reference light, the s-polarization component of the reflected light from the optical fiber under measurement with respect to the light in the second polarization state, and the s-bias of the reference light Dividing into a plurality of periods that do not overlap with the beat frequency generated by interference with the wave component, synthesizing the Fourier transform results for the digital signal Ds obtained for the plurality of periods on the distance axis, and scanning the wavelength The measured optical fiber for the light in the first polarization state is subjected to Fourier transform processing on the digital signal Dp obtained by the light source performing one wavelength sweep. The beat frequency generated by the interference between the p-polarized component of the reflected light from the reference light and the p-polarized component of the reference light, and the p-polarized light of the reflected light from the measured optical fiber with respect to the light in the second polarization state performed in a plurality of periods beat frequency do not overlap caused by interference between the p polarization component of the component and the reference light, a distance axis Fourier transform result of the digital signal D p obtained for a period of plurality of By combining the above, the s-polarized component and the p-polarized component of the reflected light of the optical fiber under measurement for each of the light in the first polarization state and the light in the second polarization state Each measurement result is obtained.

An optical frequency domain reflectometry apparatus according to claim 5 of the present invention is the optical frequency domain reflectometry apparatus according to claim 3 or claim 4,
The polarization multiplexing unit is inserted only in the second optical path.

An optical frequency domain reflectometry apparatus according to claim 6 of the present invention is the optical frequency domain reflectometry apparatus according to claim 3 or claim 4,
The polarization multiplexing unit is inserted into the first optical path, and the polarization multiplexed light output from the polarization multiplexing unit is branched and output as the measurement light and the reference light.

An optical frequency domain reflectometry apparatus according to claim 7 of the present invention is the optical frequency domain reflectometry apparatus according to claim 3,
The polarization multiplexing unit includes a first polarization multiplexing unit (10A) inserted in the second optical path and a second polarization multiplexing unit (10B) inserted in the third optical path,
A first predetermined time difference given to the polarization multiplexed light in the first polarization multiplexing unit and a second predetermined time difference given to the polarization multiplexed light in the second polarization multiplexing unit. , Are set to different values.

An optical frequency domain reflectometry apparatus according to claim 8 of the present invention is the optical frequency domain reflectometry apparatus according to any one of claims 3 to 7,
The optical fiber to be measured is divided into a plurality of regions in the longitudinal direction, and the plurality of regions have fiber Bragg diffraction gratings each chirped with a lattice spacing;
The signal processing unit performs Fourier transform processing on the digital signal obtained when the wavelength swept light source performs one wavelength sweep, the plurality of optical fibers to be measured with respect to light in the first polarization state. Interference between the reflected light from the plurality of regions of the measured optical fiber and the reference light with respect to the beat frequency generated by the interference between the reflected light from the region and the reference light, and the light in the second polarization state By dividing into a plurality of periods that do not overlap with the beat frequency generated by the above and synthesizing the Fourier transform results obtained for the plurality of periods on the distance axis, so that the light in the first polarization state and the first Each measurement result of reflected light from the plurality of regions of the optical fiber to be measured with respect to light having two polarization states is obtained.

An optical frequency domain reflectometry apparatus according to claim 9 of the present invention is the optical frequency domain reflectometry apparatus according to claim 8,
The predetermined time difference of the polarization multiplexing unit is set to be shorter than the time for light to reciprocate in one of the regions of the optical fiber to be measured.

An optical frequency domain reflectometry apparatus according to claim 10 of the present invention is the optical frequency domain reflectometry apparatus according to claim 8 or 9,
It is formed so that a part of the reflection wavelength range of the plurality of regions of the optical fiber to be measured overlaps,
The wavelength sweep range of the wavelength swept light source reaches the overlapping portion of the wavelength sweep range of the optical fiber to be measured.

Moreover, the optical frequency domain reflection measuring apparatus of Claim 11 of this invention is an optical frequency domain reflection measuring apparatus in any one of Claims 3-10,
The optical fiber to be measured is a multi-core fiber (36) having a plurality of M or more cores,
The directional coupling means for providing the measurement light to a plurality of M cores of the multi-core fiber core and obtaining a beat signal obtained by interference between the reflected light from the plurality of M cores and the reference light. A plurality of M sets of the multiplexing means, the light receiver and the A / D converter are provided.

Moreover, the optical frequency domain reflection measuring apparatus of Claim 12 of this invention is an optical frequency domain reflection measuring apparatus in any one of Claims 3-10,
The optical fiber to be measured is a multi-core fiber (36) having a plurality of M or more cores,
The directional coupling means is provided in the plurality of M sets to provide the measurement light to a plurality of M cores of the core of the multi-core fiber, and to receive the reflected light from the plurality of cores with respect to the measurement light, respectively.
Reflected light multiplexing means (48) for multiplexing reflected light from the plurality of M cores via the directional coupling means;
Means (51A-51D) for providing a delay time difference so that the reflected light from the plurality of M cores is multiplexed with a different delay time for each core in the reflected light multiplexing means;
Processing on the output of the reflected light multiplexing means is performed by a set of the multiplexing means, the light receiver and the A / D converter.

An optical frequency domain reflectometry apparatus according to claim 13 of the present invention is the optical frequency domain reflectometry apparatus according to claim 11 or claim 12,
The plurality M is four.

An apparatus for measuring a position or shape according to claim 14 of the present invention comprises:
A position or a shape of an object to be measured to which the optical fiber to be measured is fixed is measured by using the optical frequency domain reflection measuring apparatus according to any one of claims 3 to 13.

An apparatus for measuring position or shape according to claim 15 of the present invention is the apparatus for measuring position or shape according to claim 14,
The object to be measured is a medical catheter, a medical inspection probe, a medical sensor, a building inspection sensor, a seabed sensor, or a geological sensor.

  As described above, in the present invention, as the measurement light subjected to wavelength sweeping to be provided to the optical fiber to be measured having the fiber Bragg diffraction grating having the chirped grating interval, the first polarization state light and the first polarization state whose polarizations are orthogonal to each other are used. This is obtained when the polarization-multiplexed light in which the polarization-polarized light of 2 is combined with a predetermined time difference shorter than the time for which the light reciprocates through the fiber Bragg grating is used and the wavelength-swept light is swept once. Fourier transform processing is performed on the digital signal, the beat frequency generated by the interference between the reflected light from the measured optical fiber with respect to the light in the first polarization state and the reference light, and the measured light with respect to the light in the second polarization state Fourier obtained by dividing into multiple periods where the beat frequency generated by the interference between the reflected light from the fiber and the reference light does not overlap, and obtained for the multiple periods By combining the conversion result on the distance axis, to obtain a respective measurement result of the reflected light of the optical fiber to be measured for the first light of the light and a second polarization state of the polarization state.

  Therefore, unlike the conventional apparatus, it is not necessary to switch and measure the polarization of the measurement light for each wavelength sweep, and the light in the first polarization state and the light in the second polarization state can be obtained by one wavelength sweep. The characteristic of the reflected light of the optical fiber to be measured with respect to can be obtained, the measurement can be performed in a short time, and even if a change in distortion applied to the optical fiber to be measured occurs in the stage time, it can be measured without overlooking it.

  Further, as in claim 6, the polarization multiplexing unit is inserted into the first optical path, and the polarization multiplexed light output from the polarization multiplexing unit is branched and output as measurement light and reference light. In this case, in the multiplexing means, the two orthogonal polarization components of the reference light and the two orthogonal polarization components of the reflected light are combined, and the orthogonal polarization components of the reflected light with respect to the reference light are combined. Separation can be performed by a single polarization separation unit, the configuration after the multiplexing unit can be simplified, and the configuration of the apparatus is simplified when a multi-core fiber is a measurement target.

  Further, when two polarization multiplexing units having different multiplexing time differences are inserted into the second optical path and the third optical path as in claim 7, two orthogonal polarization components of the reference light and reflected light are combined in the multiplexing means. The two orthogonal polarization components are combined with each other being shifted by the difference of their respective multiplex time differences, and the two orthogonal polarization components of the reflected light are combined and output. Thus, the signal can be input to a single light receiver without going through the polarization separating means, the structure after the combining means can be further simplified, and the structure of the apparatus is further simplified when a multi-core fiber is used as a measurement object.

Configuration diagram of embodiment using polarization multiplexed light only for measurement light The figure which shows the structural example of the principal part of embodiment of this invention. The figure which shows the example which comprised the principal part of embodiment of this invention with the free space optical system. Diagram showing an example of the structure of the optical fiber to be measured Diagram showing the relationship between the reflected wavelength characteristics of the optical fiber to be measured and the sweep wavelength The figure which shows the structural example of the signal processing part of embodiment of this invention. Operation explanatory diagram when performing Fourier transform of the embodiment of the present invention divided into two periods Operation explanatory diagram when performing Fourier transform of the embodiment of the present invention divided into three periods Operation explanatory diagram when performing Fourier transform after window function processing of the embodiment of the present invention Another configuration diagram of the embodiment of the present invention The figure which shows the example which comprised the principal part of embodiment of this invention with the free space optical system. The figure which shows the example which comprised the principal part of embodiment of this invention with the free space optical system. Another configuration diagram of the embodiment of the present invention Configuration diagram of an embodiment in which polarization multiplexed light is branched and used as measurement light and reference light FIG. 14 is a diagram for explaining the operation of the component device shown in FIG. Configuration diagram of an embodiment in which the outputs of two polarization multiplexing units having different multiplexing time differences are used as measurement light and reference light, respectively. Operation explanatory diagram of the component device shown in FIG. Diagram showing the relationship between the reflected wavelength characteristics and sweep wavelength of optical fibers with overlapping chirp regions Diagram showing the relationship between the reflected wavelength characteristics and sweep wavelength of optical fibers with overlapping chirp regions Configuration diagram of an embodiment corresponding to a multi-core fiber Diagram showing an example of multi-core fiber structure Another block diagram of the embodiment corresponding to the multi-core fiber Another block diagram of the embodiment corresponding to the multi-core fiber Basic configuration of conventional equipment Diagram for explaining the basic principle of optical frequency domain reflectometry Configuration diagram of conventional equipment considering polarization Another configuration diagram of conventional equipment considering polarization Another block diagram of a conventional device that supports multi-core fibers The figure which shows the structural example of the principal part of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First configuration)
FIG. 1 shows a configuration example of an optical frequency domain reflection measuring apparatus (hereinafter simply referred to as a measuring apparatus) 100 to which the present invention is applied. In the following configuration example, the same reference numerals are given to the same components as those of the conventional device described above.

  In FIG. 1, the wavelength swept light source 1 of the measuring apparatus 100 outputs light (wavelength swept light) P <b> 0 that has been swept in a specified wavelength range and sweep speed. The wavelength swept light source 1 can be realized, for example, in an external resonator laser using a diffraction grating by sweeping the oscillation wavelength by changing the resonance wavelength by changing the angle of the diffraction grating or the mirror.

  In general, in optical frequency domain reflection measurement, a sweep in which the frequency of light changes linearly with respect to time is ideal, but this is not a limitation, and the wavelength of light changes linearly with respect to time. It may be a sweep or a sweep in which the wavelength of light changes sinusoidally. In addition, when the wavelength sweep width is sufficiently small with respect to the center wavelength, in the sweep in which the wavelength changes linearly, the optical frequency changes almost linearly. In the case of a sinusoidal sweep, it can be regarded as a sweep that is close to a straight line by using only a region of the sine wave that is relatively close to a straight line. Further, as will be described later, the non-linearity of the sweep can be corrected using a delay interferometer.

  The output light P0 of the wavelength swept light source 1 is input to the branching means 3 made of an optical coupler or the like via a predetermined optical path (first optical path) and branched into two, and one of the branched lights P1 is directed from the branching means 3. The light is input to the polarization multiplexing unit 10 inserted between the optical paths (second optical path) to the coupling means 31, and the other branched light P2 is inserted into the optical path (third optical path) between the multiplexing means 41. Is input to the polarization controller 25 for adjusting the polarization of the reference light.

  Here, the light input to the polarization multiplexing unit 10 is a single polarized wave, and may be any of a linearly polarized wave, a circularly polarized wave, and an elliptically polarized wave.

  The polarization multiplexing unit 10 divides the input wavelength swept light into light in the first polarization state and light in the second polarization state where the polarizations are orthogonal to each other, and the two lights are separated by a predetermined time difference ( (Multiple time difference) ΔT1 is multiplexed and output as polarization multiplexed light. Basically, polarization orthogonality imparting means 12 is provided between the lights P1a and P1b bifurcated by the branching means 11. Thus, polarization orthogonality in which the polarizations are orthogonal to each other is imparted, and a delay time difference imparting unit 13 imparts a predetermined time difference ΔT1 to the two lights whose polarizations are orthogonal to each other and outputs the combined signal. Note that this time difference ΔT1 is shorter than the time required for light to reciprocate in a fiber Bragg diffraction grating, which will be described later, or the time required for light to reciprocate in one region of the measured optical fiber. The polarization orthogonality providing unit 12 and the delay time difference providing unit 13 may be in the reverse order.

Here, the orthogonal polarization means that the first polarization state E1 and the second polarization state E2 represented by the Jones vector have a relationship of E1 · E2 ^* = 0 (where the symbol is an inner product, The symbol ^* represents a complex conjugate), or the point indicating the first polarization state on the Poincare sphere is the point where the second polarization state is symmetric with respect to the center of the Poincare sphere. .

  For example, when the polarization of one light is a linear polarization, a linear polarization having an angle different from that of the linear polarization by 90 degrees is generated as the other light, and the two lights are combined with a predetermined time difference. When the polarization of one of the lights is a circular polarization, a circularly polarized wave having the opposite rotation direction is generated as the other light, and the two lights are combined with a predetermined time difference. Furthermore, when the polarization of one light is elliptical polarization, the elliptical long axis angle is different by 90 degrees, the ellipticity is the same and the rotation direction is reversed, and the other light is generated as the other light. And combine.

  Here, one of the two types of light combined with a predetermined time difference in the polarization multiplexing unit 10 is referred to as light in the first polarization state, and the other is referred to as light in the second polarization state.

  FIG. 2 shows a more specific configuration example of the polarization multiplexing unit 10. In FIG. 2A, one of the lights P 1 a branched by the branching unit 11 is changed to the polarization orthogonal conversion unit 12. The light P1a ′ (light in the first polarization state) whose polarization is orthogonal to the input light is generated. The polarization orthogonal conversion unit 12 can be constituted by, for example, a polarization controller obtained by winding a fiber into a circular shape a predetermined number of times, or a polarization controller combining a half-wave plate or a quarter-wave plate. Further, the other light P1b branched by the branching means 11 is delayed by a predetermined time ΔT1 by a delay means 13 such as a delay fiber, and the delayed light P1b ′ (light in the second polarization state) and the polarization are orthogonal to each other. The converted light P <b> 1 a ′ is multiplexed by the multiplexing means 14. FIG. 2 shows an example in which the polarization of the input light is linearly polarized.

  When an optical fiber having a refractive index n and a length ΔL1 is used as the delay means 13, the time difference ΔT1 is nΔL1 / c. Here, c is the speed of light.

Actually, if the other of the output optical paths of the branching means 11 is made of a fiber that does not maintain polarization, the polarization of the other light in the output optical path from the branching means 11 changes, so that the multiplexing means 14 composed of an optical coupler. When the two lights are combined, the polarization states of the two lights are orthogonal to each other (Jones vector has a relationship of E1 · E2 ^* = 0, or a point symmetrical with respect to the center on the Poincare sphere. As described above, it is desirable to use a polarization controller capable of adjusting the polarization state as the polarization orthogonal conversion means 12.

  In addition, since the polarization orthogonal conversion means 12 such as a polarization controller also has a certain delay time, when the two lights are multiplexed by the multiplexing means 14, the delay time difference between the two lights becomes ΔT1. The delay time (fiber length etc.) of the delay means 13 is set.

  In FIG. 2A, the polarization orthogonal conversion unit 12 is arranged at one of the outputs of the branching unit 11, and the delay unit 13 is arranged at the other. However, as shown in FIG. Both the polarization orthogonal conversion unit 12 and the delay unit 13 may be arranged, and the order of the polarization orthogonal conversion unit 12 and the delay unit 13 may be reversed. In other words, when the two lights are multiplexed by the multiplexing means 14, the time difference may be a predetermined value ΔT1 with the polarizations orthogonal to each other, and either of the two lights may have a larger delay time.

  Since the polarization multiplexing unit 10 only needs to multiplex two lights whose polarizations are orthogonal to each other and have a delay time difference, configurations other than (a) and (b) are possible. For example, a polarization beam splitter (PBS) may be used as the multiplexing means 14 as shown in FIG. In this case, it is necessary to match the polarization of the two lights with the PBS, and two polarization adjustment units 12a and 12b including a polarization controller or the like are necessary as the polarization orthogonality imparting unit. Since there is no 3 dB loss at the time of multiplexing by the multiplexing means, there is a feature of low loss.

  Further, as shown in FIG. 2D, either one of the two polarization adjusting units 12 a and 12 b can be arranged in front of the branching unit 11.

  Further, the polarization multiplexing unit 10 can also be configured by a free space optical system as shown in FIG. 3 (a) uses half mirrors 11 and 14 as branching and combining means, two mirrors 13a and 13b as delay means, and a half-wave plate 12 with adjustable rotation angle as orthogonal transform means. FIG. 3B shows an example in which the delay means includes the orthogonal movable mirror 13c so that the delay time difference can be adjusted. FIG. 3 (c) uses polarization beam splitters 11 and 14 as branching means and combining means, and combines a fiber-type polarization adjusting means 12b and a free-space half-wave plate 12a as orthogonal converting means. In addition, fiber type and free space type elements can be arbitrarily combined.

  The output light (polarization multiplexed light) of the polarization multiplexing unit 10 is input to the measured optical fiber 37 via the directional coupling means 31 as the measurement light Pmes.

  Here, the optical fiber 37 to be measured is an optical fiber including a fiber Bragg diffraction grating (FBG) in which the interval Λ of the diffraction grating 37c in the core 37a is chirped (changed in the longitudinal direction) as shown in FIG. Yes, the reflection wavelength λ of the FBG is expressed as λ = 2nΛ. n is the refractive index of the core.

  Therefore, the reflection wavelength of the chirp FBG varies depending on the distance, as shown in FIG. Although it is desirable that the reflected light frequency changes linearly with respect to the distance, it is not always necessary to be a straight line, and the reflected wavelength may change linearly with respect to the distance.

  4 and 5 schematically show three regions, the number of regions may be one or more. Since a chirped FBG having a region length of about centimeters can be easily manufactured, an optical fiber to be measured having a total length of about meters may be divided into about 100 regions.

  4 and 5, the change in the diffraction grating spacing is exaggerated. However, in an actual chirped FBG, for example, the center of the reflection wavelength is 1550 nm, and the change width of the reflection wavelength is about several tens of nm. is there. FIG. 5A shows an example of chirping from a long wavelength to a short wavelength as viewed from the left side of the figure, but conversely, chirping from a short wavelength to a long wavelength may be performed.

  When light that is swept in wavelength as shown in FIG. 5B is input to the measured optical fiber 37 having such reflection wavelength characteristics, the position reflected by the FBG varies with time. When the reflectivity of the FBG is small, the multiple reflection by the FBG in a plurality of regions can be ignored, and the light is reflected from the FBG region and returned from the measured optical fiber 37.

  In the optical frequency domain reflection measurement method, the reflected light Pret from the optical fiber 37 to be measured and the reference light Pr interfere to generate a beat signal, but the beat frequency corresponds to the distance of the optical fiber to be measured. For the wavelength-swept light, the beat spectrum peaks as many as the FBG regions as shown in FIG. 5C, and the peak frequency changes with time.

  Here, in order to obtain a continuous measurement result in the longitudinal direction of the optical fiber to be measured, each region of the FBG must be arranged without a gap, and the wavelength sweep range λ1 to λ2 must be greater than or equal to the reflection wavelength range of the FBG ( FIG. 5 shows an example in which the wavelength sweep ranges λ1 to λ2 and the reflection wavelength range of the FBG match. FIG. 5 shows an example in which one wavelength swept light is incident on the chirped FBG. Actually, two wavelength swept light whose polarizations are orthogonal to each other are multiplexed with a predetermined time difference ΔT1. The polarization multiplexed light is input as the measurement light, and the operation will be described later.

  The reflected light Pret from the above-described chirped FBG optical fiber 37 to be measured is input to the multiplexing means 41 via the directional coupling means 31. The directional coupling means 31 can also be constituted by an optical circulator, an optical fiber coupler, or a half mirror. Further, the multiplexing means 41 can be composed of an optical fiber coupler or a half mirror, and considering the use of a balanced type as a light receiver, two systems of combined phase in which the phase relationship of the combined light is inverted. Although it is desirable that it can output wave light, it can also be used with one system output as described later.

  On the other hand, the other light P <b> 2 branched by the branching unit 3 is input to the polarization controller 25. The polarization controller 25 outputs light P2 ′ (= reference light) so that the intensity of the reference light component branched into two by polarization separation means 45 and 46, which will be described later, is approximately equal to the input light P2. This is for adjusting the polarization state of the light Pr). As described above, the polarization state of the output light of the wavelength swept light source 1 is previously split into two by the polarization separation means 45, 46. If the strengths of the components are set to be approximately equal, they can be omitted.

  Usually, the intensity of the reflected light Pret from the optical fiber 37 to be measured is smaller than the intensity of the reference light Pr, so that the intensity of all the light branched into two by the polarization separation means 45 and 46 is substantially equal. The polarization controller 25 may be adjusted.

  One light Psum (+) output from the multiplexing means 41 is input to a polarization separating means 45 such as PBS and branched into two orthogonally polarized light s (+) and p (+). The other light Psum (−) is also input to the polarization separation means 46 such as PBS, and is branched into two orthogonally polarized light s (−) and p (−).

  The light s (+) and s (−) are input to the balance light receiver 55, and an electric signal As proportional to the difference in light intensity between the input light s (+) and s (−) is output from the balance light receiver 55. The A / D converter 65 converts the digital signal Ds. The balance light receiver has a structure in which two light receiving elements (for example, photodiodes) that receive input light independently are connected in series and a signal is taken out from the connection point, or is composed of two light receiving elements and a differential amplifier. It has been done.

  Similarly, the light p (+) and p (−) are input to the balance light receiver 56, and the electric signal Ap proportional to the difference in light intensity between the input light p (+) and p (−) from the balance light receiver 56. Is output and converted to a digital signal Dp by the A / D converter 66.

  As described above, the light s (+) and s (−) and the light p (+) and p (−) have beat phases that are opposite to each other. The beat signal amplitude is doubled. Then, noise due to intensity fluctuation of the wavelength swept light source 1 is canceled, and random noise has an amplitude of √2 times, so that the signal-to-noise ratio is improved.

  Digital signals Ds and Dp output from the A / D converters 65 and 66 are input to the signal processing unit 101.

  For example, as shown in FIG. 6, the signal processing unit 101 is a buffer memory 101a that temporarily stores a digital signal, a Fourier transform unit 101b that performs Fourier transform on the temporarily stored digital signal, and obtained on the frequency axis by Fourier transform. The distance conversion unit 101c converts the result into information on the distance of the optical fiber to be measured, the correction unit 101d that performs birefringence correction processing, and the control unit 101e that controls these.

  The control unit 101e receives the wavelength sweep information such as the sweep wavelength range, the information on the multiplex time difference (ΔT) in the polarization multiplexing unit, and the information on the measured fiber 37 while taking sweep synchronization with the wavelength sweep light source 1. The necessary parameters are set and controlled with respect to the digital signal, but especially in the time domain of the digital signal obtained by one wavelength sweep, a plurality of beat frequencies that do not overlap due to the use of polarization multiplexed light as measurement light are generated. And is designated to the Fourier transform unit 101b.

  The Fourier transform unit 101b performs Fourier transform on the digital signal divided into periods specified by the control unit 101d. Note that the arithmetic processing by the correction unit 101d is equivalent to the processing described in Patent Document 1, and will not be described in detail here.

(Explanation of measurement principle)
Next, a description will be given of the principle by which the measurement apparatus 100 having the above configuration can separate and detect responses when polarized lights orthogonal to each other enter the optical fiber 37 to be measured.

  As described above, the FBG reflects light with high efficiency when twice the spacing of the diffraction grating is equal to an integer multiple of the wavelength of light in the fiber. This is because the lights reflected by the diffraction gratings are in phase and strengthen each other. Further, since the chirped FBG has the diffraction grating interval changed depending on the position in the longitudinal direction of the optical fiber, the position in the longitudinal direction to be reflected differs depending on the wavelength of light. When a plurality of chirps exist at a predetermined period in the longitudinal direction of the optical fiber, light is reflected at a plurality of positions in the longitudinal direction of the optical fiber.

  In addition, the optical frequency domain reflection measurement method is such that the light of a swept light source whose light frequency changes at a constant rate in time is incident on the optical fiber to be measured, and the interference between the reflected light from the optical fiber to be measured and the reference light. It measures beats. In this case, since the frequency of the light changes at a substantially constant rate in time, a difference in optical frequency is generated between the reflected light and the reference light in proportion to the delay time difference between them, and both of them are caused by interference between the reflected light and the reference light. A beat with a frequency corresponding to the difference in optical frequency occurs. Since the delay time of the reflected light differs depending on the position where the light is reflected by the measured optical fiber, the beat frequency varies depending on the reflection position.

  Therefore, as shown in FIG. 5, when the chirp FBG is measured by the optical frequency domain reflectometry, beat spectrum peaks are generated by the number of chirp periods, and the peak frequency changes at a constant rate with time.

  As shown in FIG. 4, the optical fiber 37 to be measured is a chirp with a short lattice distance on the far end side from the near end side and a chirp period (region) of 3 periods, as shown in FIG. When the sweep is in the direction in which the frequency of light increases with time, the optical path length of the reference light Pr from the branching unit 3 to the multiplexing unit 41 is reflected from the branching unit 3 at the near end of the optical fiber 37 to be measured. When it is shorter than the optical path length reaching the multiplexing means 41, the beat signal obtained by the interference between the light in the first polarization state included in the measurement light output from the polarization multiplexing unit 10 and the reference light, As shown by the solid line in FIG. 7A, three beat spectrum peaks B1a to B3a whose frequencies increase with time are obtained.

  In addition, since the light in the second polarization state included in the measurement light output from the polarization multiplexing unit 10 is delayed by the time ΔT1 relative to the light in the first polarization state, the second polarization state The beat signal obtained by the interference between the state light and the reference light has a higher frequency than the beat spectrum peak corresponding to the light in the first polarization state.

  For example, when the optical path length difference ΔL1 of the polarization multiplexing unit 10 is set to ½ of the optical path length for the round trip of the FBG chirp period, the light in the first polarization state as shown by the broken line in FIG. The beat spectrum peaks B1b to B3b corresponding to the light in the second polarization state are generated in the middle of the beat spectrum peaks corresponding to.

  Here, when looking at the entire time range t1 to t2 in which the wavelength is swept, the frequency range taken by the peak represented by the solid line and the frequency range taken by the peak represented by the adjacent broken line overlap almost half of the frequency range, Even if Fourier transform is performed including the overlapping range of the frequencies, the distribution of strain in the longitudinal direction of the optical fiber 37 to be measured cannot be obtained correctly.

  Therefore, in the measurement apparatus 100 of the embodiment, as shown in FIG. 7B, the time domain is divided into a plurality of (in this example, two) periods so that the frequency ranges of the peaks do not overlap, and the division is performed. For each period, Fourier transform (for example, fast Fourier transform (FFT) using CPU or FPGA) is performed.

  FIG. 7C shows the result of the Fourier transform process performed for two periods. In the Fourier transform process in period 1, the result of Fourier transform in period 1 of each peak B1a to B3a and B1b to B3b ( B1aL) to (B3aL), (B1bL) to (B3bL) are obtained separately, and in the Fourier transform process in period 2, the Fourier transform results (B1aH) to (B1aH) to (B1aH) in period 2 of each peak B1a to B3a and B1b to B3b are obtained. B3aH) and (B1bH) to (B3bH) are obtained separately.

  When the result obtained in FIG. 7C is converted into the distance on the optical fiber 37 to be measured, the conversion results [B1bL] to [B3bL] and [B1bH corresponding to the second incident polarization state are converted. ] To [B3bH] are corrected to the near end side by ½ of the optical path length difference ΔL1 of the polarization multiplexing unit 10, and the first incident polarization state is obtained over the entire distance range as shown in FIG. The corresponding results [B1aL] to [B3aL] and [B1aH] to [B3aH] are separated from the results [B1bL] to [B3bL] and [B1bH] to [B3bH] corresponding to the second incident polarization state. And a distribution over the entire distance range of the FBG.

  In this way, only the beat spectrum corresponding to the first polarization state is obtained by overlapping the beat spectrum corresponding to the first polarization state and the beat spectrum corresponding to the second polarization state within the entire measurement time. Compared to the case of measuring the frequency, the entire measurement time is divided into multiple areas and Fourier transformed without significantly increasing the bandwidth of the receiver and A / D converter and the sampling frequency after the A / D converter. Thus, both the beat spectrum corresponding to the first polarization state and the beat spectrum corresponding to the second polarization state can be obtained by one wavelength sweep.

  When a large strain is partially applied to the optical fiber 37 to be measured, the lattice spacing of the FBG changes due to the strain, and the peak of the beat spectrum in FIG. Due to an error in the optical path length difference ΔL1, the broken line in FIG. 7A may deviate from the middle of the solid line. In addition, it is desirable to continuously measure the distortion without any defect in the longitudinal direction of the optical fiber 37 to be measured. However, since it is difficult to arrange the chirp FBG completely without a gap, the chirp FBG is partially overlapped. (The structure will be described later). Since it is difficult to set the wavelength sweep range so that the beat spectrum peaks are aligned completely without a gap, it is desirable to set the wavelength sweep range so that a part of the beat spectrum peaks overlap.

  For these reasons, in the two-part Fourier transform described above, the beat signal frequency for light in the first incident polarization state overlaps with the frequency of the beat signal for light in the second incident polarization state, and complete separation is possible. There is a risk of disappearing. In this case, duplication can be avoided by increasing the number of divisions on the time axis.

  FIG. 8A shows an example in which beat spectrum peaks B2a and B2b are not straight lines, the optical path length difference ΔL1 has an error, and beat spectrum peaks overlap.

  In this case, by dividing into periods 1 to 3 on the time axis as shown in (b) of FIG. 8, duplication of beat frequencies is avoided, and in periods 1 to 3 as shown in (c) of FIG. 8. Fourier transform results (B1aL) to (B3aL), (B1aM) to (B3aM), (B1aH) to (B3aH) in the first incident polarization state, and Fourier transforms of the second incident polarization state in periods 1 to 3 When the results (B1bL) to (B3bL), (B1bM) to (B3bM), and (B1bH) to (B3bH) are obtained separately and the horizontal axis is converted into the distance on the optical fiber 37 to be measured, (d) in FIG. Thus, the results corresponding to the first incident polarization state and the second incident polarization state can be obtained separately over the entire distance range.

  Note that, as shown in the Fourier transform result of FIG. 8C, the variation range of the beat frequency in each period may be different, but both ends of the frequency can be detected by the amplitude (intensity) of the Fourier transform result.

  In addition, in order to reduce the side lobe of the spectrum at the time of Fourier transform, it is also possible to perform Fourier transform after applying a window function. However, if the time function is divided into two and the window function is applied as shown in FIG. 7B, there arises a problem that beat spectra at positions corresponding to both ends of the window function cannot be obtained. In this case, the chirp FBG partially overlaps (that is, the solid line portions and the broken line portions overlap) as shown in FIG. 9A, and the window function partially overlaps as shown in FIG. 9B. Then, when performing Fourier transform of three divisions, although both ends of the beat spectrum of the first incident polarization state and the beat spectrum of the second incident polarization state partially overlap as shown in FIG. By correcting the optical path length difference ΔL1 as shown in FIG. 9D and not using the overlapping portions at both ends of the beat spectrum, the first incident polarization is obtained over the entire distance range as shown in regions 1 to 3. The results corresponding to the state and the second incident polarization state can be obtained separately.

  Note that the chirp direction, the number of chirp cycles, the light source sweep direction, and the optical path length difference of the polarization multiplexing section are not limited to the above example. Even under other conditions, the same effect can be obtained although the number of beat spectrum peaks, the direction of time gradient, and the number of Fourier transform divisions are different.

  Therefore, the measurement apparatus 100 having the configuration shown in FIG. 1 can obtain both the result corresponding to the first incident polarization state and the result corresponding to the second incident polarization state by one wavelength sweep, and the sweep. There is no need to switch the polarization of the polarization controller 15 every time.

  As described above, the signal processing unit 101 performs the above-described Fourier transform processing for each period on the digital signals Ds and Dp obtained by one wavelength sweep, so that the first incident polarization state And a result corresponding to the second incident polarization state. Thus, the Fourier transform results a and b of the digital signals Ds and Dp corresponding to the first polarization state, and the Fourier transform results c and d of the digital signals Ds and Dp corresponding to the second polarization state are obtained. From the four Fourier transform results a, b, c, and d, the birefringence of the optical fiber 37 to be measured can be corrected by the method described in Patent Document 1.

  The configuration of the measuring apparatus 100 in FIG. 1 is an example, and various modifications can be made. For example, a polarization controller 25 for adjusting the polarization state of the reference light with respect to the polarization separation unit 45 may be disposed in front of the branching unit 3 as in the measurement apparatus 110 in FIG. Also in this case, the polarization controller 25 is adjusted so that the reference light components branched into two by the polarization separation means 45 and 46 or the intensities of all the lights are substantially equal to those in the measurement apparatus 100 of FIG. deep.

  Further, when an optical fiber coupler using a normal single mode fiber is used as the multiplexing means 41, the light Psum (+) input to the polarization separation means 45 and the light input to the polarization separation means 46 The polarization of Psum (−) may be different. In that case, a polarization controller is inserted in front of at least one polarization separation means to adjust the polarization, or, as shown in FIG. It is desirable to use a free space optical system using PBS as the separating means 45 and 46.

  Further, as shown in FIG. 12, the reflected light Pret and the reference light Pr are polarized and separated by polarization separating means 45 'and 46' made of PBS, respectively, and then two half mirrors 41 and 41 as multiplexing means are used. The polarization separation components of the reflected light and the reference light may be combined by '.

  Further, as in the measurement apparatus 120 shown in FIG. 13, it is also possible to perform single-end light reception using the multiplexing means 41, the polarization separation means 45 such as PBS, and the light receivers 57 and 58. In this configuration, the polarization controller 25 can be disposed after the multiplexing means 41 (it can be omitted for the reason described above). Further, in the case of this configuration, there is no problem that the polarizations of the light input to the two polarization separation means are different, and therefore, it can be configured by either an optical fiber optical system or a free space optical system.

  Usually, the intensity of the reflected light Pret from the optical fiber 37 to be measured is smaller than the intensity of the reference light Pr, so that the intensity of all the light branched into two by the polarization separation means 45 is substantially equal, that is, The polarization controller 25 may be automatically adjusted so that the DC component of the output of the light receiver 57 and the DC component of the output of the light receiver 58 are equal.

  Furthermore, a configuration in which the polarization multiplexing unit 10 is inserted into the optical path (first optical path) from the wavelength swept light source 1 to the branching unit 3 is also possible as in the measurement apparatus 130 shown in FIG. In this case, the polarization controller 25 is positioned between the wavelength sweeping light source 1 and the polarization multiplexing unit 10, between the polarization multiplexing unit 10 and the branching unit 3, and between the branching unit 3 and the multiplexing unit 41. Any of the path, the multiplexing means 41 and the polarization separating means 45 may be used. In this configuration, since the reference light also becomes polarization multiplexed light, there is a feature that correction including birefringence in the path of the reference light can be made.

  In the configuration of FIG. 14, the polarization multiplexing unit 10 multiplexes the light in the first polarization state and the light in the second polarization state, and the output light P0 ′ from the polarization multiplexing unit 10 is branched into two. One of them P1 enters the measured optical fiber 37 as the measurement light Pmes, and the other P2 becomes the reference light Pr.

  For this reason, the beat signal Ba generated by the interference between the light Pret1 incident on the optical fiber 37 to be measured and reflected by the first polarization state light and the reference light Pr1 in the first polarization state, and the second polarization Wave signal Bb generated by the interference between the light Pret2 incident on the optical fiber 37 to be measured and the reference light Pr2 in the second polarization state, and the light in the second polarization state to be measured Beat signal Bc generated by interference between the light incident on the optical fiber and reflected by the reference light Pr1 in the first polarization state, and the light reflected by the first polarization light incident on the optical fiber to be measured And a beat signal Bd generated by interference between the reference light Pr2 in the second polarization state.

  The former two Ba and Bb have the same beat frequency because the relationship between the delay time of the reflected light from the measured optical fiber 37 and the reference light is equal. Since the reflected light from the optical fiber 37 to be measured is delayed by the time ΔT1, the third person Bc has a higher beat frequency than the former two persons Ba and Bb. The fourth person Bd has a lower beat frequency than the former two persons Ba and Bb because the reference light is delayed by the time ΔT1.

  Therefore, for example, if the optical path length difference ΔL1 of the polarization multiplexing unit 10 is set to 1/3 of the optical path length for the round trip of the FBG chirp period, three types of beat spectra Bn + and Bnc as shown in FIG. , Bnd appear at equal intervals for three periods (n is the period value of FBG, Bn + is the beat spectrum of Ba and Bb having the same frequency).

  As shown in (b) of FIG. 15, Fourier transform is performed by equally dividing the period into three periods 1 to 3 in the time axis direction so that the beat frequencies do not overlap, as shown in (c) of FIG. 15. Fourier transform results (B1 + L) to (B3 + L), (B1 + M) to (B3 + M), (B1 + H) to (B3 + H), and Fourier transform results (B1cL) corresponding to the third party Bc. ~ (B3cL), (B1cM) ~ (B3cM), (B1cH) ~ (B3cH) and Fourier transform results (B1dL) ~ (B3dL), (B1dM) ~ (B3dM), (B1dH) corresponding to the fourth person Bd To (B3dH) are obtained separately.

  When the horizontal axis in FIG. 15C is converted into the distance on the optical fiber 37 to be measured, the third party is corrected to the near end side by 1/2 of the optical path difference ΔL1 of the polarization multiplexing unit 10, and The four parties are corrected to the far end side by 1/2 of the optical path length difference ΔL1 of the polarization multiplexing unit 10, and as shown in FIG. 15 (d), over the entire distance range from the third party Bc and the fourth party Bd. Both a result corresponding to the first incident polarization state and a result corresponding to the second incident polarization state are obtained. The third party Bc and the fourth party Bd are different in the polarization state of the reference light. However, since the polarization states of the reference light are orthogonal to each other, either the third party Bc or the fourth party Bd is used. In the case of reference light in the same polarization state, one of the digital signals Ds and Dp obtained by separation by the polarization separation means 45 is exchanged, or one of the digital signals Ds and Dp is reversed in phase. Can be converted.

  Even in the case of this measuring apparatus 130, the beat spectrum peak deviates from a straight line due to distortion of the optical fiber 37 to be measured, the beat spectrum peak interval deviates due to an error in the optical path length difference ΔL1, or the chirp FBG is over. In the case of wrapping, duplication of beat spectra can be avoided by increasing the number of divisions on the time axis from three divisions. In addition, when Fourier transform is performed after the window function is applied in the same manner as described above, the number of divisions on the time axis is increased from 3 divisions and a part of the window function is overlapped, so that all the overlapped portions are not used. Results can be obtained over a range of distances.

  FIG. 16 shows another modification of the measuring apparatus 140 to which the present invention is applied. In this measuring apparatus 140, two polarization multiplexing units 10A and 10B are used, and the polarization multiplexing unit 10A is inserted into the optical path (second optical path) from the branching unit 3 to the directional coupling unit 31 and one branch is made. The light P1 is given, the output is given as the measurement light Pmes to the measured optical fiber 37, the reflected light Pret of the measured optical fiber 37 is input to the multiplexing means 41, and the optical path from the branching means 3 to the multiplexing means 41 ( The other branched light P2 is given to the polarization multiplexing unit 10B inserted in the third optical path), and the output thereof is input to the multiplexing means 41 as the reference light Pr.

  The configuration of the two polarization multiplexing units 10A and 10B is the same as that of the polarization multiplexing unit 10, but the time differences ΔT1 and ΔT2 of the multiplexed light are set to different values.

  The two lights Psum (+) output from the multiplexing means 41 are input to the balance light receiver 55 and converted into an electric signal A, and converted into a digital signal D by an A / D converter 61. Is done. Note that a single-ended light receiver may be used instead of the balance light receiver 55.

  In this measuring apparatus 140, as described above, the frequency of the light is temporally swept with respect to the optical fiber 37 to be measured having a chirp with a short lattice distance on the far end side from the near end side and a chirp period of 3 periods. In the increasing direction, the optical path length of the reference light from the branching means 3 to the multiplexing means 41 is shorter than the optical path length reflected from the branching means 3 at the near end of the measured optical fiber 37 and reaching the multiplexing means 41 think of.

  In the case of the measuring apparatus 140 configured as described above, the measurement light Pmes is multiplexed with the light in the first polarization state and the light in the second polarization state, and the reference light Pr is the reference light in the s-polarization state. Prs and p-polarized reference light Prp are multiplexed.

  For this reason, when the reflected light Pret from the measured optical fiber 37 and the reference light Pr are combined by the combining means 41, the s-polarized component Prets and s-polarized light of the reflected light with respect to the first incident polarization state The beat signal Bas is generated by the interference with the reference light Prs in the state, and the beat signal Bap is generated by the interference between the p polarization component Pretp of the reflected light for the first incident polarization state and the reference light Prp in the p polarization state. The beat signal Bbs is generated by interference between the s-polarization component Prets' of the reflected light with respect to the second incident polarization state and the reference light Prs in the s-polarization state, and the reflected light with respect to the second incident polarization state. The p-polarized component Pretp 'and the reference light Prp in the p-polarized state interfere with each other to generate a beat signal Bbp.

  Here, since the light in the second incident polarization state is delayed by the time ΔT1 compared to the light in the first incident polarization state, the peak of the beat spectrum corresponding to the second incident polarization state is the first. The frequency is higher than the peak of the beat spectrum corresponding to one incident polarization state. Further, since the reference light Prp in the p-polarized state is delayed by the time ΔT2 from the reference light Prs in the s-polarized state, the peak of the beat spectrum corresponding to the p-polarized components Pretp and Pretp ′ of the reflected light is The frequency becomes lower than the peak of the beat spectrum corresponding to the s-polarized components Prets and Prets ′ of the reflected light.

  For example, the optical path length difference ΔL1 of the polarization multiplexing unit 10A is set to ½ of the optical path length for the round trip of the FBG chirp period, and the optical path length difference ΔL2 of the polarization multiplexing unit 10B is set to the round trip of the FBG chirp period. When the optical path length is set to ¼, the beat spectrum peak (solid line) Bas1, Bas2, and Bas3 of the s-polarized component of the reflected light with respect to the first incident polarization state as shown in FIG. Beat spectrum peaks (broken lines) Bbs1, Bbs2, and Bbs3 of the s-polarized component of the reflected light with respect to the second incident polarization state are generated, and p of the reflected light with respect to the first incident polarization state is between the broken line and the solid line. Beat spectrum peaks of the polarization component (dashed lines) Bap1, Bap2, Bap3 are generated, and the beat spectrum peaks of the p polarization component of the reflected light with respect to the second incident polarization state (two points) between the solid line and the broken line Chain line) Bbp1, Bbp2, Bbp3 are generated

  Conversely, the optical path length difference ΔL1 of the polarization multiplexing unit 10A is set to ¼ of the optical path length corresponding to the round trip of the FBG chirp cycle, and the optical path length difference ΔL2 of the polarization multiplexing unit 10B is set to the round trip of the FBG chirp cycle. A similar result can be obtained even when the optical path length is set to ½.

  When Fourier transform (for example, fast Fourier transform (FFT) using a CPU or FPGA) is performed by equally dividing the period into four periods 1 to 4 in the time axis direction as shown in FIG. 17B, (c) in FIG. ), Fourier transform results (Bas11) to (Bas31), (Bas12) to (Bas32), and (Bas13) corresponding to the s-polarization component of the reflected light with respect to the first incident polarization state for each period. (Bas33), (Bas14) to (Bas34), Fourier transform results (Bap11) to (Bap31), (Bap12) to (Bap12) to (Bap34) corresponding to the p polarization component of the reflected light with respect to the first incident polarization state for each period. Bap32), (Bap13) to (Bap33), (Bap14) to (Bap34), Fourier transform results (Bbs11) to (Bbs31) corresponding to the s-polarized component of the reflected light with respect to the second incident polarization state for each period ), (Bbs12) to (Bbs32), (Bbs13) to (Bbs33), (Bbs14 ) To (Bbs34), Fourier transform results (Bbp11) to (Bbp31), (Bbp12) to (Bbp32), (Bbp13) corresponding to the p polarization component of the reflected light with respect to the second incident polarization state for each period To (Bbp33) and (Bbp14) to (Bbp34) are obtained separately.

  Similarly to the above, when the horizontal axis in FIG. 17C is converted into the distance on the optical fiber 37 to be measured, the Fourier transform result corresponding to the second incident polarization state is the optical path length difference of the polarization multiplexer 10A. The correction result is corrected to the near end side by 1/2 of ΔL1, and the Fourier transform result corresponding to the p polarization component of the reflected light is corrected to the far end side by 1/2 of the optical path length difference ΔL2 of the polarization multiplexer 10B. The result corresponding to the s-polarization component of the reflected light with respect to the first incident polarization state and the s-polarization component of the reflected light with respect to the second incident polarization state over the entire distance range as in (d) of 17 And a result corresponding to the p-polarized component of the reflected light with respect to the first incident polarization state and a result corresponding to the p-polarized component of the reflected light with respect to the second incident polarization state. In FIG. 17, the Fourier transform result is distinguished by an underline, and the distance converted result is distinguished by an upper line.

  As described above, the beat spectrum corresponding to the s-polarization component of the reflected light with respect to the first incident polarization state and the beat spectrum corresponding to the s-polarization component of the reflected light with respect to the first incident polarization state within the entire measurement time. And the beat spectrum corresponding to the p-polarization component of the reflected light for the second incident polarization state and the beat spectrum corresponding to the p-polarization component of the reflected light for the second incident polarization state are overlapped. Compared to the case of measuring only the beat spectrum corresponding to the s-polarization component of the reflected light with respect to the incident polarization state, the band of the light receiver and the A / D converter and the sampling frequency after the A / D converter are greatly increased. By dividing the total measurement time into four or more regions and performing Fourier transform without increasing, the first incident polarization state with one set of light receiver and A / D converter can be obtained with one sweep. Anti Corresponds to the beat spectrum corresponding to the s-polarization component of the light and the beat spectrum corresponding to the s-polarization component of the reflected light for the second incident polarization state and the p-polarization component of the reflected light to the first incident polarization state And the beat spectrum corresponding to the p polarization component of the reflected light with respect to the second incident polarization state can be obtained separately.

  Even in the case of this embodiment, when the beat spectrum peak deviates from a complete straight line, when there are errors in the optical path length differences ΔL1 and ΔL2, and when the chirp FBG overlaps, a part of the beat spectrum peak is In the case of overlap, each component overlaps and cannot be separated by four-part Fourier transform. In that case, as described above, by increasing the number of divisions on the time axis, duplication can be avoided and four results can be obtained separately over the entire distance range.

  Also, when performing Fourier transform by applying a window function, as explained in FIG. 9, by partially overlapping the chirp FBG and increasing the number of divisions on the time axis, the window function is partially overlapped. The four results can be obtained separately over the entire distance range.

  Note that the chirp direction, the number of chirp cycles, the light source sweep direction, and the optical path length difference of the polarization multiplexing section are not limited to the above example. Even under other conditions, the same effect can be obtained although the number of beat spectrum peaks, the direction of time gradient, and the number of Fourier transform divisions are different.

  Therefore, the measurement apparatus 140 having the configuration shown in FIG. 16 obtains four results with one wavelength sweep and one set of light receiver and A / D converter. There is no need to switch waves or use two sets of light receivers and A / D converters, and the polarization is adjusted so that the intensity of the reference light branched into two by the polarization separation means 45 is approximately equal. There is an advantage that it is not necessary.

  Also in this measuring apparatus 140, the signal processing unit 102 performs the Fourier transform process for each period in the same manner as described above, and from the obtained four results a, b, c, and d, the method described in Patent Document 1 is used. Although the birefringence of the optical fiber 37 to be measured can be corrected, in this configuration, the reference light is also polarization-multiplexed light. Therefore, there is an advantage that the birefringence of the path of the reference light can be corrected. is there.

  Next, an example in which the chirped FBG regions adjacent in the longitudinal direction of the optical fiber 37 to be measured partially overlap will be described with reference to FIG. As described above, since it is difficult to arrange the FBGs of a plurality of regions without any gaps, a part of each of the regions 1 to 3 may overlap. In the overlapping portion, there are two diffraction gratings having different grating intervals, and they are reflected at two wavelengths. For this reason, as shown in FIG. 18B, there is an overlapping portion of the relationship between the distance and the reflected wavelength. Note that the number of overlapping portions may be increased so that three or more regions overlap. By performing the limited wavelength sweep as shown in FIG. 18C with respect to the characteristic shown in FIG. 18B, the peaks of the beat spectrum do not overlap as shown in FIG. , Can be arranged without gaps.

  FIG. 19 shows an example in which the chirp FBG regions overlap and the beat spectrum peaks also overlap. For the characteristic shown in FIG. 19B, the wavelength sweep range is set slightly narrower than the reflected wavelength range of the chirped FBG as shown in FIG. 19C, and the beat frequency is changed as shown in FIG. Duplication is occurring. The wavelength sweep range of the wavelength swept light source 1 may be set equal to or wider than the reflection wavelength range of the chirped FBG. In this way, the position accuracy of arranging the chirp FBG is relaxed by overlapping the chirp FBG region, and the setting accuracy of the wavelength sweep range of the wavelength sweep light source 1 is relaxed by overlapping the peaks of the beat spectrum. Becomes easier.

  In each of the above embodiments, an example in which the optical fiber to be measured 37 is a single core has been described. FIG. 20 shows an example of the configuration of a measuring apparatus 150 in which the optical fiber to be measured is a multicore fiber.

  This measuring apparatus 150 has a configuration in which the measuring apparatus 130 having the configuration shown in FIG. 14 is expanded to measure the 4-core optical multicore fiber 36 to be measured.

  That is, the light P0 output from the wavelength swept light source 1 is branched into two by the branching means 2, one of which is supplied to the polarization multiplexing unit 10, and the output light P1 'is branched into four by the branching means 30, and the branching is performed. The lights P3 to P6 are given to the branching means 3A to 3D. The branching means 2 and the branching means 3A to 3D can be constituted by one branching means having 8 branches. Further, it can be constituted by one branching means of two branches and two branching means of four branches following it.

  One light branched by each of the branching means 3A to 3D is supplied as measurement light Pmes1 to Pmes4 to each core of one multicore fiber 36 to be measured via the directional coupling means 31A to 31D and the multicore fiber fan-out 35. Led.

  The measured multicore fiber 36 is used for spatially multiplexed optical fiber transmission, and has a plurality of cores in one clad.

  FIG. 21A shows an example of a multi-core fiber having a chirped FBG. Three cores 36b to 36d are arranged around a central core 36a, and a chirped FBG is formed in each of the cores 36a to 36d.

  In order to measure the three-dimensional position or shape of the optical fiber to be measured, it is necessary to measure the three-dimensional distortion of bending and twisting in two directions of the fiber. Furthermore, it is necessary to compensate the temperature of the optical fiber to be measured, and a total of four cores are required. If a two-dimensional position or shape is measured, three cores may be used, and if a one-dimensional position or shape is measured, two cores may be used. In FIG. 21A, all the cores 36a to 36d are drawn in a straight line. However, in order to measure the torsion of the optical fiber under measurement, in FIG. As in b), the other cores need to be spirally twisted around the central core. In addition, in a spatial multiplexing optical fiber transmission application, a 7-core fiber in which six cores 2 to 7 are disposed around a central core 1 as shown in FIG. 21C is used. Only the central core 1 and the three surrounding cores can be used for three-dimensional position or shape measurement.

  The configuration after the branching means 3A to 3D is provided with four sets of the measuring apparatus 130 having the configuration shown in FIG. 14, and each of the cores is provided by the directional coupling means 31A to 31D and the multi-core fiber fan-out 35. Measurement lights Pmes1 to Pmes4 are provided, and the reflected lights Pret1 to Pret4 from the respective cores are input to the multiplexing means 41A to 41D, respectively, and are combined with the reference lights Pr1 to Pr4 branched by the branching means 3A to 3D. Further, the outputs of the multiplexing means 41A to 41D are respectively supplied to the polarization controllers 25A to 25D, the polarization of the reference light is adjusted and input to the polarization separation means 45A to 45D, and the polarization separated light s1 to s1 s4 and p1 to p4 are input to the light receivers 57A to 57D and 58A to 58D, respectively, and their outputs are converted into digital signals Ds1 to Ds4 and Dp1 to Dp4 by A / D converters 65A to 65D and 66A to 66D, respectively. This is given to the processing unit 103.

  Further, the other light P <b> 2 branched by the branching unit 2 is input to the monitoring unit 70. The configuration and function of the monitoring unit 70 are the same as those shown in FIG.

  The measuring apparatus 150 having this configuration can perform the same measurement as described above for each core of the multicore fiber 36 to be measured, and accurately measures the distortion of each core of the multicore fiber 36 to be measured from the state of the plurality of cores. The position or shape of the multicore fiber 36 to be measured can be measured by the method described in Patent Document 1.

  FIG. 22 shows a measurement apparatus 160 that realizes measurement of a multi-core fiber with a simpler configuration. This measuring device 160 is an extension of the measuring device 140 shown in FIG. 16 so as to correspond to the multi-core fiber 36, and inputs the lights P3 and P4 branched by the branching means 3 to the polarization multiplexing units 10A and 10B. Then, the output of the polarization multiplexing section 10A is branched into four by the branching means 30A, and the measured light Pmes1 to Pmes4 are respectively measured as directional coupling means 31A to 31D and the multi-core fiber fan-out 35 of the multicore fiber 36 to be measured. Input to each core. The reflected lights Pret1 to Pret4 from the respective cores are given to the multiplexing means 41A to 41D via the multi-core fiber fan-out 35 and the directional coupling means 31A to 31D.

  Further, the output of the polarization multiplexing unit 10B is branched into four by the branching unit 30B, and each is supplied to the multiplexing units 41A to 41D as the reference lights Pr1 to Pr4.

  The outputs of the multiplexing means 41A to 41D are input to the balance light receivers 55A to 55D, and the outputs are converted into digital signals by the A / D converters 65A to 65D and supplied to the signal processing unit 103.

  Also in the case of this measuring apparatus 160, the operation for each core is the same as that of the measuring apparatus 140 shown in FIG. 16, and the measurement for each core can be performed with a very simple configuration.

  In this configuration, a single-ended light receiver may be used instead of the balance light receivers 55A to 55D.

  Thereby, the distortion of each core of the multicore fiber to be measured 36 can be accurately measured, and the position or shape of the multicore fiber 36 to be measured can be measured by the method described in Patent Document 1.

  FIG. 23 shows a configuration example of the measuring device 170 that is further simplified. The measuring device 170 gives different delay times to the reflected lights Pret1 to Prte4 from the respective cores of the measuring device 160 of FIG. It is multiplexed. In FIG. 23, the delay means 51A to 51D are inserted between the directional coupling means 31A to 31D and the multiplexing means 48, but between the branching means 30 and the directional coupling means 31A to 31D, or the directional coupling means. Delay means 51A to 51D may be provided between 31A to 31D and the multi-core fiber fan-out 35.

  The output light from the multiplexing means 48 and the output light (reference light) Pr from the polarization multiplexing unit 10B are given to the multiplexing means 41, and the output lights Psum (+) and Psum (-) are input to the balance light receiver 55. The output signal A is converted into a digital signal D by the A / D converter 65 and supplied to the signal processing unit 104. In this case, a single-ended light receiver can be used instead of the balance light receiver 55.

  In the case of this measuring apparatus 170, the delay time of the reflected light from the four cores of the multicore fiber 36 to be measured and the delay times of the polarization multiplexing unit 10A and the polarization multiplexing unit 10B are, for example, 0, 1, 2, 3, By setting the ratio of 4 and 8 and performing Fourier transform by dividing into 16 or more regions on the time axis, each of the four cores of the multicore fiber to be measured 36 is measured in the same manner as shown in FIG. Fourier transform result corresponding to the s-polarization component of the reflected light for the first incident polarization state, Fourier transform result corresponding to the s-polarization component of the reflected light for the second incident polarization state, and the first incident polarization The 16 signals of the Fourier transform result corresponding to the p polarization component of the reflected light with respect to the state and the Fourier transform result corresponding to the p polarization component of the reflected light with respect to the second incident polarization state can be separated.

  The configuration for measuring the multi-core fiber 36 is not limited to the above configuration example, but may be a configuration in which the measurement device 100 in FIG. 1, the measurement device 110 in FIG. 10, and the measurement device 120 in FIG. realizable.

  Further, the configuration of the signal processing units 102 to 104 shown in the above embodiment is the same as that of the signal processing unit 101 shown in FIG. 6 although the number of input digital signal sequences is different. .

  The embodiment of the optical frequency domain reflectometry apparatus of the present invention has been described above. As described in the above embodiment, the object on which the optical fiber is fixed based on the information of the optical fiber obtained by the above-described embodiment apparatus. Can be applied to an apparatus for measuring each position or shape.

  As a specific example in that case, a medical catheter, a medical inspection probe, a medical sensor, a building inspection sensor, a seabed sensor, or a geological sensor can be realized as the object to be fixed to the optical fiber.

  DESCRIPTION OF SYMBOLS 1 ... Wavelength sweep light source, 2, 3, 30A, 30B ... Branch means 10, 10A, 10B ... Polarization multiplexing part, 25 ... Polarization controller, 31, 31A-31D ... Directional coupling means, 41, 41A to 41D: multiplexing means, 45, 46 ... polarization separation means, 55, 55A to 55D, 56, 56A to 56D ... balance light receivers, 65, 65A to 65D, 66, 66A to 66D ... ... A / D converter, 70 ... monitoring unit, 100, 110, 120, 130, 140, 150, 160, 170 ... optical frequency domain reflection measuring apparatus, 101-104 ... signal processing unit

Claims (15)

Wavelength swept light whose wavelength is continuously swept within a predetermined range is split into a plurality of light beams to generate measurement light and reference light. )
The reflected light from the optical fiber to be measured with respect to the measurement light is received, the reflected light and the reference light are combined and input to a light receiver, and a beat generated by interference between the reflected light and the reference light is electrically generated. Outputting as a signal;
In the optical frequency domain reflection measurement method, including the step of converting the electrical signal into a digital signal and performing a Fourier transform process,
As the measurement light, the first polarization state light and the second polarization state light having the same wavelength sweep characteristics as the wavelength sweep light and whose polarizations are orthogonal to each other pass through the fiber Bragg diffraction grating. And using polarization multiplexed light combined with a predetermined time difference shorter than the time for the round trip,
A Fourier transform process is performed on the digital signal obtained when the wavelength swept light is swept once, and interference between the reflected light from the measured optical fiber and the reference light with respect to the light in the first polarization state is performed. The beat frequency generated by the second polarization state and the beat frequency generated by the interference between the reflected light from the measured optical fiber and the reference light with respect to the light in the second polarization state are divided into a plurality of periods, By combining the Fourier transform results obtained for a plurality of periods on the distance axis, each of the reflected light of the measured optical fiber with respect to the light in the first polarization state and the light in the second polarization state An optical frequency domain reflection measurement method characterized by: In the step of outputting the beat as an electric signal, the reflected light and the reference light are separated into s-polarization components and p-polarization components orthogonal to each other, and the reflected light and the s-polarization components of the reference light are received. And inputting the p-polarized component of the reflected light and the reference light to a light receiver and outputting the electric signal Ap.
The step of converting the electrical signal into a digital signal and performing a Fourier transform process converts the electrical signal As into a digital signal Ds, and reflects the reflected light from the optical fiber under measurement with respect to the light in the first polarization state. The beat frequency generated by the interference between the s-polarization component and the s-polarization component of the reference light, the s-polarization component of the reflected light from the measured optical fiber with respect to the light in the second polarization state, and the reference light Performing a Fourier transform process by dividing the beat frequency generated by the interference with the s-polarized wave component into a plurality of periods, and converting the electric signal Ap into a digital signal Dp so that the first polarization state is obtained. The beat frequency generated by the interference between the p-polarized component of the reflected light from the optical fiber to be measured and the p-polarized component of the reference light, and the light with respect to the second polarized light And a step of performing a Fourier transform process in a plurality of periods beat frequency do not overlap caused by interference between the p polarization component of the p-polarized component of the reflected light and the reference light from the measurement optical fiber,
Obtaining the measurement results of the s-polarized component and the p-polarized component of the reflected light of the optical fiber under measurement for the light in the first polarization state and the light in the second polarization state, respectively. The optical frequency domain reflection measurement method according to claim 1. A wavelength swept light source (1) for outputting a wavelength swept light whose wavelength is swept continuously within a predetermined range;
Branching means (3) for receiving the wavelength swept light via a first optical path and branching into a plurality of branches;
The first branch light output from the branch means via the second optical path is received and output as measurement light to a measured optical fiber (37) having a fiber Bragg diffraction grating with a chirped grating interval. wherein a directional binding means for receiving the reflected light from the measured optical fiber (31) for,
Receiving a second branched light which is output through the third optical path from said branching means based light, reflected light and the multiplexing multiplexes means from said measured optical fiber output from the directional binding means (41)
A light receiver (55, 56, 57, 58) that receives the output light of the multiplexing means and outputs a beat generated by interference between the reflected light and the reference light as an electrical signal;
An A / D converter (65, 66) for converting the electrical signal into a digital signal;
In an optical frequency domain reflection measurement apparatus having a signal processing unit (101 to 104) for performing a Fourier transform process on the digital signal,
The wavelength swept light or its branched light that is inserted into one of the first optical path, the second optical path, or both the second optical path and the third optical path is orthogonal to each other. The light is divided into light in the first polarization state and light in the second polarization state, and is combined with a predetermined time difference shorter than the time for light to reciprocate through the fiber Bragg diffraction grating. A polarization multiplexing unit (10, 10A, 10B) that outputs the polarization multiplexed light, and uses the polarization multiplexed light as the measurement light for at least the optical fiber to be measured;
The signal processing unit performs a Fourier transform process on the digital signal obtained by the wavelength swept light source performing one wavelength sweep, and reflects the light in the first polarization state from the measured optical fiber. A plurality of beat frequencies generated by interference between light and the reference light, and beat frequencies generated by interference between the reflected light from the measured optical fiber and the reference light with respect to the light in the second polarization state Dividing into periods, and by combining the Fourier transform results obtained for the plurality of periods on the distance axis, the coverage with respect to the light in the first polarization state and the light in the second polarization state is obtained. An optical frequency domain reflection measurement apparatus characterized in that the measurement result of each reflected light of a measurement optical fiber is obtained. Polarization separation means (45, 46) for separating the reflected light and the reference light into s-polarization components and p-polarization components orthogonal to each other;
A light receiver (55, 57) that receives the s polarized component of the reflected light and the reference light and outputs a beat generated by interference as an electric signal As;
A light receiver (56, 58) that receives the p-polarized component of the reflected light and the reference light and outputs a beat generated by interference as an electric signal Ap;
An A / D converter (65) for converting the electrical signal As into a digital signal Ds; and an A / D converter (66) for converting the electrical signal Ap into a digital signal Dp;
The signal processing unit
Fourier transform processing is performed on the digital signal Ds obtained by the wavelength swept light source performing one wavelength sweep, and the s-polarized light of the reflected light from the measured optical fiber with respect to the light in the first polarization state The beat frequency generated by the interference between the component and the s-polarization component of the reference light, the s-polarization component of the reflected light from the optical fiber under measurement with respect to the light in the second polarization state, and the s-bias of the reference light Dividing into a plurality of periods that do not overlap with the beat frequency generated by interference with the wave component, synthesizing the Fourier transform results for the digital signal Ds obtained for the plurality of periods on the distance axis, and scanning the wavelength The measured optical fiber for the light in the first polarization state is subjected to Fourier transform processing on the digital signal Dp obtained by the light source performing one wavelength sweep. The beat frequency generated by the interference between the p-polarized component of the reflected light from the reference light and the p-polarized component of the reference light, and the p-polarized light of the reflected light from the measured optical fiber with respect to the light in the second polarization state performed in a plurality of periods beat frequency do not overlap caused by interference between the p polarization component of the component and the reference light, a distance axis Fourier transform result of the digital signal D p obtained for a period of plurality of By combining the above, the s-polarized component and the p-polarized component of the reflected light of the optical fiber under measurement for each of the light in the first polarization state and the light in the second polarization state 4. The optical frequency domain reflection measurement apparatus according to claim 3, wherein each measurement result is obtained.   The optical frequency domain reflectometry apparatus according to claim 3 or 4, wherein the polarization multiplexing unit is inserted only in the second optical path.   The polarization multiplexing unit is inserted into the first optical path, and polarization multiplexed light output from the polarization multiplexing unit is branched and output as the measurement light and the reference light. The optical frequency domain reflection measuring apparatus according to claim 3 or 5. The polarization multiplexing unit includes a first polarization multiplexing unit (10A) inserted in the second optical path and a second polarization multiplexing unit (10B) inserted in the third optical path,
A first predetermined time difference given to the polarization multiplexed light in the first polarization multiplexing unit and a second predetermined time difference given to the polarization multiplexed light in the second polarization multiplexing unit. 4. The optical frequency domain reflectometry apparatus according to claim 3, wherein different values are set. The optical fiber to be measured is divided into a plurality of regions in the longitudinal direction, and the plurality of regions have fiber Bragg diffraction gratings each chirped with a lattice spacing;
The signal processing unit performs Fourier transform processing on the digital signal obtained when the wavelength swept light source performs one wavelength sweep, the plurality of optical fibers to be measured with respect to light in the first polarization state. Interference between the reflected light from the plurality of regions of the measured optical fiber and the reference light with respect to the beat frequency generated by the interference between the reflected light from the region and the reference light, and the light in the second polarization state By dividing into a plurality of periods that do not overlap with the beat frequency generated by the above and synthesizing the Fourier transform results obtained for the plurality of periods on the distance axis, so that the light in the first polarization state and the first 8. The optical frequency according to claim 3, wherein each measurement result of reflected light from the plurality of regions of the optical fiber to be measured with respect to light having two polarization states is obtained. Domain reflectometry apparatus.   9. The optical frequency domain reflectometry apparatus according to claim 8, wherein a predetermined time difference of the polarization multiplexing unit is set to be shorter than a time required for light to reciprocate in one of the regions of the optical fiber to be measured. . It is formed so that a part of the reflection wavelength range of the plurality of regions of the optical fiber to be measured overlaps,
The optical frequency domain reflectometry apparatus according to claim 8 or 9, wherein a wavelength sweep range of the wavelength swept light source reaches a portion where the wavelength sweep range of the optical fiber to be measured overlaps. The optical fiber to be measured is a multi-core fiber (36) having a plurality of M or more cores,
The directional coupling means for providing the measurement light to a plurality of M cores of the multi-core fiber core and obtaining a beat signal obtained by interference between the reflected light from the plurality of M cores and the reference light. The optical frequency domain reflectometry apparatus according to claim 3, wherein a plurality of M sets of the multiplexing unit, the light receiver, and the A / D converter are provided. The optical fiber to be measured is a multi-core fiber (36) having a plurality of M or more cores,
The directional coupling means is provided in the plurality of M sets to provide the measurement light to a plurality of M cores of the core of the multi-core fiber, and to receive the reflected light from the plurality of cores with respect to the measurement light, respectively.
Reflected light multiplexing means (48) for multiplexing reflected light from the plurality of M cores via the directional coupling means;
Means (51A-51D) for providing a delay time difference so that the reflected light from the plurality of M cores is multiplexed with a different delay time for each core in the reflected light multiplexing means;
The optical frequency domain reflection according to any one of claims 3 to 10, wherein the processing on the output of the reflected light multiplexing means is performed by one set of the multiplexing means, the light receiver and the A / D converter. measuring device.   The optical frequency domain reflectometry apparatus according to claim 11 or 12, wherein the plurality M is four.   A position or shape is measured by measuring the position or shape of an object to which the optical fiber to be measured is fixed, using the optical frequency domain reflectometry apparatus according to any one of claims 3 to 13. Device to do.   The apparatus for measuring position or shape according to claim 14, wherein the object to be measured is a medical catheter, a medical inspection probe, a medical sensor, a building inspection sensor, a seabed sensor, or a geological sensor.

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