JP2015108580A - Interference type optical fiber sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an interference type optical fiber sensor capable of relatively reducing a noise, while increasing the number of signals used after photoelectric conversion.SOLUTION: The interference type optical fiber sensor includes a light source 12, a detection part 13 including a plurality of sets of sensing interferometers configured so that an inputted pulse and a pulse obtained by delaying the inputted pulse, according to a measurement signal are superimposed and outputted, a photoelectric conversion part 170 photoelectrically converting a plurality of pulses from the detection part 13, and a processing part 17 processing an electrical signal supplied from the photoelectric conversion part 170, to demodulate the measurement signal. The detection part 13 includes a delay circuit configured so that the output pulses of the plurality of sets of sensing interferometers are delayed so as to be continuous and outputted to the photoelectric conversion part 170. The photoelectric conversion part 170 includes a filter 172 suppressing a non-demodulation component from the pulses from the detection part 13.

Description

  The present invention relates to an interference type optical fiber sensor, and in particular, in an interference type optical fiber sensor including a PMDI (Pass Matched differential Interferometer) configuration, a plurality of continuous pulses are continuously generated according to a repetition period of pulses output from a pulse light source. The present invention relates to an interference-type optical fiber sensor that multiplexes by delaying and suppresses components other than the demodulated component to increase the number of signals used after photoelectric conversion and relatively reduce noise.

  FIG. 12 is a diagram illustrating an example of a schematic configuration of the interference optical fiber sensor 1 in the related art. As shown in FIG. 12, the interference type optical fiber sensor 1 in the prior art includes, for example, a light source unit 11, a detection unit 13, an O / E (Optical / Electrical) converter 15, and a processing unit 17. The unit 11 includes an optical frequency shifter 25 and an optical frequency shifter 26. The interference-type optical fiber sensor 1 relatively reduces noise by using the correlation of signals to be superimposed (see, for example, Patent Document 1).

  FIG. 13 is a diagram illustrating an example of a schematic configuration of the interference optical fiber sensor 2 in the related art. As shown in FIG. 13, the interference type optical fiber sensor 2 in the prior art includes, for example, a light source unit 12, a detection unit 13, an O / E converter 15, a filter 16, and a processing unit 17, and in particular, the light source unit 12. The first feedback circuit 31 and the second feedback circuit 32 are included. The first feedback circuit 31 includes an optical pulse gate 35, an optical frequency shifter 25, a modulation signal generator 23, and the like. The second feedback circuit 32 includes an optical pulse gate 39, an optical frequency shifter 26, a modulation signal generator 24, and the like. The interference type optical fiber sensor 2 adjusts the timing of the output waveform of the optical frequency shifter 25 with the optical pulse gate 35 so that it can follow even when the frequency of the signal detected by the detection unit 13 is fast, and the optical pulse gate 39, the timing of the output waveform of the optical frequency shifter 26 is adjusted (see, for example, Patent Document 2).

Japanese Patent Application No. 2012-044549 Japanese Patent Application No. 2012-247555

  However, in the prior art, many signals are discarded after photoelectric conversion. Therefore, the signal used after photoelectric conversion has been limited. Further, the signal input to the processing unit 17 includes a non-demodulated component and a DC component in addition to the demodulated component. Therefore, the signal processed by the processing unit 17 includes a lot of noise components.

  In other words, the related art cannot relatively reduce noise while increasing the number of signals used after photoelectric conversion. Therefore, an interference type optical fiber sensor that can relatively reduce noise while increasing the number of signals used after photoelectric conversion has been desired.

  The interference type optical fiber sensor of the present invention includes a pulse light source that periodically generates a plurality of pulses, an output unit that superimposes and outputs a plurality of pulses having different light frequencies in each optical path, and A detection unit having two optical paths, and including a sensing interferometer that outputs the superimposed pulse and a pulse obtained by delaying the superimposed pulse according to a measurement signal, and a plurality of the detection units from the detection unit A photoelectric conversion unit that photoelectrically converts a pulse; and a processing unit that processes an electrical signal supplied from the photoelectric conversion unit and demodulates the measurement signal, wherein the photoelectric conversion unit is based on a pulse from the detection unit. A filter that suppresses non-demodulated components is provided.

  In the interference-type optical fiber sensor of the present invention, the detection unit includes a delay circuit that delays the output pulses of a plurality of sets of sensing interferometers so that the output pulses are continuous, and outputs the delay circuit to the photoelectric conversion unit. One delay fiber is provided, and the delay fiber delays the continuous interval of the output pulses at the same interval as the interval between the plurality of superimposed pulses from the output unit.

  In the interference type optical fiber sensor of the present invention, the output unit feeds back one pulse branched from the optical path a plurality of times, and changes the frequency of light in the feedback circuit.

  In the interference-type optical fiber sensor of the present invention, the photoelectric conversion unit includes a light receiving element that photoelectrically converts a plurality of pulses from the detection unit, and a DC component that outputs a suppression signal that suppresses a DC component among the electrical signals. A differential amplifier that outputs an output corresponding to a difference between the output of the suppression power supply, the output of the filter, and the output of the direct current component suppression power supply, and the differential amplifier suppresses the direct current component. The demodulated component is output to the processing unit.

  The present invention delays a plurality of consecutive pulses according to the repetition period of pulses output from a pulse light source, and suppresses other than the demodulated component, thereby increasing the number of signals used after photoelectric conversion and Therefore, the noise can be reduced.

It is a figure which shows an example of a structure of the interference type optical fiber sensor 1 used as the premise of Embodiment 1 of this invention. It is a figure which shows an example of the output waveform of the pulse light source 21 contained in the interference type optical fiber sensor 1 used as the premise of Embodiment 1 of this invention, the output optical frequency of the optical frequency shifter 25, and the output optical frequency of the optical frequency shifter 26. is there. It is a figure which shows an example of the output waveform of the pulse light source 21 contained in the interference type optical fiber sensor 1 used as the premise of Embodiment 1 of this invention, and the input-output waveform of the O / E converter 15. FIG. It is a figure explaining the output power spectrum of the A / D converter 111 contained in the interference type optical fiber sensor 1 used as the premise of Embodiment 1 of this invention. It is a figure which shows an example of a structure of the interference type optical fiber sensor 2 used as the premise of Embodiment 1 of this invention. The output waveform of the pulse light source 21, the output waveform of the optical pulse gate 35, the output waveform of the optical frequency shifter 25, and the O / E converter 15 included in the interference type optical fiber sensor 2 that is the premise of the first embodiment of the present invention. It is a figure which shows an example of the input / output waveform. It is a figure explaining the output power spectrum of the A / D converter 111 contained in the interference type optical fiber sensor 2 used as the premise of Embodiment 1 of this invention. It is a figure which shows an example of a structure of the interference type optical fiber sensor 3 in Embodiment 1 of this invention. It is a figure explaining the detail of the input / output signal of each structure inside the O / E conversion part 170 contained in the interference type optical fiber sensor 3 in Embodiment 1 of this invention. It is a figure which shows the operation example of the interference type optical fiber sensor 3 in Embodiment 1 of this invention. It is a figure which shows an example of the waveform when passing through each path | route included in the interference type optical fiber sensor 3 in Embodiment 1 of this invention. It is a figure which shows an example of schematic structure of the interference type optical fiber sensor 1 in a prior art. It is a figure which shows an example of schematic structure of the interference type optical fiber sensor 2 in a prior art.

  Hereinafter, Embodiment 1 of the present invention will be described in detail with reference to the drawings.

Embodiment 1 FIG.
<Overview>
As will be described later, the interference type optical fiber sensor 3 delays a plurality of consecutive pulses according to the repetition period of pulses output from the pulse light source 21 and suppresses components other than the demodulated component, thereby photoelectric conversion. The noise is relatively reduced while increasing the number of signals used later.

<Description of configuration>
First, by using FIGS. 1 to 7, a technology that is a premise of the configuration of the interference type optical fiber sensor 1 to be described later will be described with reference to FIGS. 8 to 11. FIG. 1 is a diagram showing an example of the configuration of an interference optical fiber sensor 1 that is a premise of Embodiment 1 of the present invention. The interference type optical fiber sensor 1 changes a signal to be detected into respective strains of the first sensing fiber 71, the second sensing fiber 81, and the third sensing fiber 91. By using such an operation, the interference type optical fiber sensor 1 includes a first sensing interferometer 41 having the first sensing fiber 71 as an arm, a second sensing interferometer 42 having the second sensing fiber 81 as an arm, And the 3rd sensing interferometer 43 which makes the 3rd sensing fiber 91 an arm is comprised, and a signal is detected.

  Many of such interference type optical fiber sensors 1 use pulsed light to form a time division multiplex transmission system. In the interference type optical fiber sensor 1 using pulsed light, noise increases due to aliasing usually in the process of sampling and demodulating pulsed light. Therefore, in the interference type optical fiber sensor 1, aliasing noise is reduced by generating a plurality of beats having different frequencies and increasing the number of samplings.

  The interference optical fiber sensor 1 includes a light source unit 11, a detection unit 13, and a processing unit 17, for example. The light source unit 11 branches the pulsed light output from the pulsed light source 21 into two by the optical coupler 22, one of the branched pulsed lights is frequency-modulated by the optical frequency shifter 25, and the other is the optical frequency shifter. 26 to modulate the frequency. Among these, the fiber to which the pulsed light output from the optical frequency shifter 26 is transmitted is delayed by the delay compensation fiber 27, coupled to one fiber by the optical coupler 28, amplified by the optical amplifier 29, and then the detection unit 13. Is sent out. Each of the optical frequency shifter 25 and the optical frequency shifter 26 shifts the frequency of light by using the acoustooptic effect.

  In the detection unit 13, the pulse light transmitted from the light source unit 11 is branched by the optical coupler 51 and the optical coupler 53, and the first sensing interferometer 41, the second sensing interferometer 42, and the third sensing interferometer 43 Sent to each. The pulsed light input to the first sensing interferometer 41 is branched by the optical coupler 73, one pulsed light is immediately reflected by the mirror 77, and the other pulsed light reciprocates through the first sensing fiber 71. . Next, each pulse light is coupled to one fiber by the optical coupler 73. Each of the second sensing interferometer 42 and the third sensing interferometer 43 operates in the same manner as the first sensing interferometer 41. Next, the pulse light output from each of the first sensing interferometer 41, the second sensing interferometer 42, and the third sensing interferometer 43 is delayed by the delay fiber 61 or the delay fiber 62, and then the light is transmitted. Coupled to one fiber by the coupler 52 and the optical coupler 54 and sent to an O / E converter (Optical / Electrical) 15 as a pulse train.

  The O / E converter 15 converts the pulse train output from the detection unit 13 into an electrical signal and sends the electrical signal to the processing unit 17. The processing unit 17 converts the pulse train output from the O / E converter 15 into a digital signal by the A / D converter 111, and the first sensing interferometer 41, the second sensing interferometer 42, and the third sensing interferometer. 43, reference signal generator 121 to reference signal generator 126, multiplier 131 to multiplier 136, and LPF (Low Pass Filter) 141 to LPF 146, which generate reference signals in accordance with the timing and frequency corresponding to the outputs of 43, respectively. The arc tangent calculator 151 to arc tangent calculator 153 and the discontinuous point compensation calculator 155 to the discontinuous point compensation calculator 157 are used for the first sensing fiber 71, the second sensing fiber 81, and the third sensing fiber 91. Each detected signal is demodulated.

  FIG. 2 shows an example of the output waveform of the pulse light source 21, the output optical frequency of the optical frequency shifter 25, and the output optical frequency of the optical frequency shifter 26 included in the interference optical fiber sensor 1 which is the premise of the first embodiment of the present invention. FIG. The light waveform such as the output waveform of the pulse light source 21 is a waveform of optical power that can be observed through the O / E converter 15. The numbers appended to the output waveform of the pulse light source 21 are numbers representing the order of the pulsed light output from the pulse light source 21. The interference type optical fiber sensor 1 generates a beat having a frequency difference between the optical frequencies of the interfered pulse lights by causing the pulse lights having different frequencies to interfere with each other and performing O / E conversion.

The timing at which pulsed light is output from the pulse light source 21, the shift frequency and timing of the optical frequency shifter 25, and the shift frequency and timing of the optical frequency shifter 26 interfere with each other and the frequency of the beat generated when O / E conversion occurs. f _f1 −f _b1 , f _f2 −f _b2 , and f _f3 −f _b3 are set to be repeated sequentially. Here, the shift frequencies “f _f1 ”, “f _b1 ”, “f _f2 ”, “f _b2 ”, “f _f3 ”, and “f _b3 ” are beat frequencies “f _f1 − − The ratio of f _b1 ”,“ f _f2 −f _b2 ”,“ f _f3 −f _b3 ”is set to 2n−1 (n = 1, 2, 3,..., that is, n is a natural number). In setting the pulse repetition period, it is necessary to consider that the response times of the optical frequency shifter 25 and the optical frequency shifter 26 fall within the time not passing through the pulse.

  FIG. 3 is a diagram illustrating an example of an output waveform of the pulse light source 21 and an input / output waveform of the O / E converter 15 included in the interference optical fiber sensor 1 which is a premise of the first embodiment of the present invention. As shown in FIG. 3, the fluctuation range is shown in the portion where the voltage fluctuates in the output waveform of the O / E converter 15. As shown in FIG. 1, the path of the input light used symbols A, B, C, D, E1, E2, E3, F1, F2, F3, and G, and arranged these symbols in the order of passage.

Output waveforms I _A , I _B , and I _C are pulses sampled by the A / D converter 111. The _f f2 _-f b2, _{I C} of _f f3 _{-f b3} of _f f1 _-f b1, _{I B} of I _A contained only the first signal detected by the first sensing fiber 71, these A / D converter The first signal is demodulated from the output of the device 111. Strictly speaking, noise and the like input from the delay compensation fiber 27 are included in addition to the first signal, but are detected by other than the first sensing fiber 71 such as the second sensing fiber 81 and the third sensing fiber 91. In the following description, it is assumed that only the first signal is included.

Similarly, the _f f1 _-f b1, _{I C} of _f f2 _{-f b2} of _f f3 _-f b3, _{I B} of _{I A} and contains only the second signal. Similarly, the _f f3 _-f b3, _{I C} of _f f1 _{-f b1} of _f f2 _-f b2, _{I B} of _{I A} contain only third signal. Each of the first signal, the second signal, and the third signal is demodulated by the processing unit 17.

FIG. 4 is a diagram for explaining the output power spectrum of the A / D converter 111 included in the interference optical fiber sensor 1 which is the premise of the first embodiment of the present invention. In FIG. 4, the output power spectrum of the A / D converter 111 is divided into three parts, I _A , I _B , and I _C. Any one of the first sensing fiber 71, the second sensing fiber 81, and the third sensing fiber 91 is included in each of the three frequency bands of f _f1 -f _b1 , f _f2 -f _b2 , and f _f3 -f _b3. A beat containing only the detected signal is generated.

Beats including noise input from another fiber to be sensed, beat sidebands including noise input from another fiber to be sensed, beats generated by folding, beats generated by folding _These sidebands are generated in higher frequency bands than the three frequency bands demodulated by f _f1 -f _b1 , f _f2 -f _b2 , and f _f3 -f _b3 . Thereby, since the interference type optical fiber sensor 1 can distinguish a demodulation component and a non-demodulation component by a frequency, it can demodulate a 1st signal, a 2nd signal, and a 3rd signal.

  FIG. 5 is a diagram showing an example of the configuration of the interference optical fiber sensor 2 which is a premise of the first embodiment of the present invention. The pulsed light output from the pulse light source 21 is branched by the optical coupler 22, one pulsed light is input to the optical frequency shifter 25 via the optical coupler 36, and the other pulsed light is transmitted via the optical coupler 40. To the optical frequency shifter 26.

  The output of the optical frequency shifter 25 is branched by the optical coupler 33. The light source unit 12 includes a first feedback circuit 31 in which one output of the optical coupler 33 passes through the delay adjustment fiber 34, the optical pulse gate 35, and the optical coupler 36 and is fed back to the optical frequency shifter 25. The light source unit 12 is configured such that the other output of the optical coupler 33 is input to the optical coupler 28.

  The output of the optical frequency shifter 26 is branched by the optical coupler 37. The light source unit 12 includes a second feedback circuit 32 in which one output of the optical coupler 37 passes through the delay adjustment fiber 38, the optical pulse gate 39, and the optical coupler 40 and is fed back to the optical frequency shifter 26. The light source unit 12 is configured such that the other output of the optical coupler 37 is input to the optical coupler 28 via the delay compensation fiber 27.

A modulation signal generator 23 is connected to the optical frequency shifter 25. The modulation signal generator 23 sends a signal whose frequency is constant at f _f and constant in amplitude to the optical frequency shifter 25. A modulation signal generator 24 is connected to the optical frequency shifter 26. The modulation signal generator 24 sends a signal whose frequency is constant at f _b and constant in amplitude to the optical frequency shifter 26. The output of the optical coupler 28 is amplified by the optical amplifier 29 and sent to the detection unit 13. As described above, the detection unit 13 outputs a pulse train and sends it to the O / E converter 15. The O / E converter 15 converts the pulse train into a voltage, limits the band by the filter 16, and sends the band to the processing unit 17.

  FIG. 6 shows an output waveform of the pulse light source 21 included in the interference optical fiber sensor 2 which is a premise of the first embodiment of the present invention, an output waveform of the optical pulse gate 35, an output waveform of the optical frequency shifter 25, and an O / It is a figure which shows an example of the input-output waveform of E converter. The setting of the pulse timing will be described with reference to FIG.

  In the first embodiment, it is assumed that the time for the pulsed light to make one round in each of the first feedback circuit 31 and the second feedback circuit 32 is set to 3τ, and the repetition period of the pulses output from the pulse light source 21 is set to 9τ. Here, τ is a time for reciprocating the first sensing fiber 71. Further, τ is a time for reciprocating the second sensing fiber 81. τ is the time for reciprocating the third sensing fiber 91.

  The optical pulse gate 35 is set so as to pass through the first feedback circuit 31 and pass the pulse light until it passes through the optical frequency shifter 25 three times, and to block the pulse light that passes four times. The optical pulse gate 39 is set so as to pass through the second feedback circuit 32 and pass the pulse light until it passes through the optical frequency shifter 26 three times and to block the pulse light that passes four times.

With the above setting, the output of the optical frequency shifter 25 becomes a pulse train having a repetition period of 3τ, and the optical frequency of the pulse becomes repetition of ν + f _f , ν + 2f _f , and ν + 3f _f . The output of the optical frequency shifter 26 is a pulse train having a repetition period 3τ, and the optical frequency of the pulse is a repetition of ν + f _f , ν + 2f _f , and ν + 3f _f . Note that the number of beat frequencies used for demodulation is changed by changing the number of times the optical frequency shifter 25 is allowed to pass through the pulsed light and the repetition period 3τ of the pulsed light output from the pulsed light source 21. Further, the number of beat frequencies used for demodulation is changed by changing the number of times the optical frequency shifter 26 is passed through the pulsed light and the repetition period 3τ of the pulsed light output from the pulsed light source 21.

  In FIG. 6, symbols indicating the respective paths correspond to A, B, C, D, E1, E2, E3, F1, F2, F3, and G shown in FIG. Note that routes unnecessary for the description are omitted.

  The pulsed light that has passed through the ABDE 1G is input to the O / E converter 15 earliest. Then, each of the first sensing fiber 71 and the delay compensation fiber 27 is set so that the pulsed light passing through the ABDF 1G and the pulsed light passing through the ACDE 1G are input to the O / E converter 15 with a delay of τ. The length of is set.

The pulsed light passing through the ACDF 1G is input to the O / E converter 15 with a delay of 2τ from the pulsed light passing through the ABDE 1G. Pulse light propagated through the pulsed light and ACDE1G via the ABDF1G the beat frequency _"f f -f _b" to _{I A} beat frequency _{"2 (f f -f b)} " to _{I B,} frequency _{I C} Each beat of “3 (f _f −f _b )” is generated. These beats of pulsed light contain only the first signal detected by the first sensing fiber 71. In the processing unit 17, I _A , I _B , and I _C are sampled, and the first signal is demodulated from the beat of each pulse light including only the first signal.

Each of the second sensing fiber 81 and the delay fiber 61 is such that the pulse light passing through the ABDF 2G and the pulse light passing through the ACDE 2G are input to the O / E converter 15 with a delay of 3τ from the pulse light passing through the ABDF 1G. The length of is set. Thus, O / E converters 15 _{I A} to the frequency _{"3 (f f -f b)} " of the output of the beat, the beat frequency _"f f -f _b" to _{I B,} frequency _{I C} "2 ( f _f −f _b ) ”beats occur.

These beats of pulsed light include only the second signal detected by the second sensing fiber 81. In the processing unit 17, I _A , I _B , and I _C are sampled, and the second signal is demodulated from the beat of each pulse light including only the second signal. The lengths of the third sensing fiber 91 and the delay fiber 62 are set so that the pulse light passing through the ABDF 3G and the pulse light passing through the ACDE 3G are input to the O / E converter 15 with a delay of 6τ from the pulse light passing through the ABDF 1G. Is set.

Thus, O / E beats converter 15 the output of _{I A} to the frequency _{"2 (f f -f b)} ", the beat frequency _{"3 (f f -f b)} " to _{I B,} frequency _{I C} Each of the beats “f _f −f _b ” is generated. These beats of pulsed light include only the third signal detected by the third sensing fiber 91. In the processing unit 17, I _A , I _B , and I _C are sampled, and the third signal is demodulated from the beat of each pulse light including only the third signal.

FIG. 7 is a diagram for explaining the output power spectrum of the A / D converter 111 included in the interference optical fiber sensor 2 which is the premise of the first embodiment of the present invention. Assuming that f _f −f _b is set to 1/7 of 1 / 9τ which is the sampling frequency of each of I _A , I _B and I _C , the width of the sideband of the demodulated beat is It becomes the maximum in form 1. When the number of beat frequencies used for demodulation is changed, f _f −f is set so that the beat and sideband having the highest frequency used for demodulation are adjacent to the beat and sideband having the lowest frequency generated by folding. _By setting _b, the width of the sideband of the beat to be demodulated is maximized.

The output frequency “f _f ” of the modulation signal generator 23 and the output frequency “f _b ” of the modulation signal generator 24 are caused by interference of pulsed light having a different number of passes through the modulation signal generator 23 or the modulation signal generator 24. The generated beats and sidebands are set to frequencies that do not overlap with the beat and sideband frequency bands used for demodulation.

For example, simply, the f _f and f _b by leaving higher than high cutoff frequency of the filter 16, the number of occurrences that passed through the modulator signal generator 23 or the modulation signal generator 24 was different pulse light interference The beats to be attenuated will not overlap the beats and sidebands used for demodulation. Further, when f _f and f _b are set to a frequency higher than the pass band of the O / E converter 15, beats are not generated in pulses having different numbers of passes through the modulation signal generator 23 or the modulation signal generator 24.

  In the interference type optical fiber sensor 2, the change width of the light shift frequency is limited to the range of the shift frequency variable width of each of the optical frequency shifter 25 and the optical frequency shifter 26. Therefore, beats including signals other than those detected by the sensed fiber are lower than the respective shift frequencies of the optical frequency shifter 25 and the optical frequency shifter 26. The beat including other than the signal detected by the fiber sensed by the interference type optical fiber sensor 1 is caused by interference with light having different numbers of times of the first feedback circuit 31 and the second feedback circuit 32.

  Here, the frequency when a beat including a signal other than the signal detected by the fiber where sensing is performed is a frequency higher than the shift frequency of each of the optical frequency shifter 25 and the optical frequency shifter 26. Since the shift frequency of each of the optical frequency shifter 25 and the optical frequency shifter 26 can be higher than the sampling frequency 1 / 9τ, it is attenuated by the filter 16 before sampling by the processing unit 17, and the first feedback circuit 31 and When the difference in the number of times of each of the second feedback circuits 32 becomes large and becomes higher than the upper limit of the frequency band in which the O / E converter 15 operates, no beat is generated. Accordingly, the interference type optical fiber sensor 2 secures a band unnecessary for the demodulation process of the interference type optical fiber sensor 1, thereby eliminating the problem of narrowing the band necessary for the demodulation process.

  FIG. 8 is a diagram illustrating an example of the configuration of the interference optical fiber sensor 3 according to Embodiment 1 of the present invention. The interference type optical fiber sensor 3 includes a PMDI (Pass Matched differential Interface) configuration. PMDI has a configuration in which the optical path is known twice, and the optical path difference is adjusted, that is, the optical path difference is compensated. In the interference type optical fiber sensor 3, the number of signals to be time-division multiplexed and the number of beat frequencies used for demodulation can be set as necessary. In the first embodiment, an example is shown in which the number of time-division multiplexed signals is set to 3 and the number of beat frequencies used for demodulation is set to 3.

  FIG. 8 shows the configuration of the interference optical fiber sensor 3 according to the first embodiment. Components having the same functions as those of the interference type optical fiber sensor 1 shown in FIG. 1 and the interference type optical fiber sensor 2 shown in FIG. A component different from the others in the interference type optical fiber sensor 3 is an O / E converter 170, which includes a light receiving element 171, a filter 172, a DC component suppressing power source 173, and a differential amplifier 174. It has.

  The pulse light output from the pulse light source 21 is branched by the optical coupler 22, one is input to the optical frequency shifter 25 via the optical coupler 36, and the other is input to the optical frequency shifter 26 via the optical coupler 40. Configured.

The output of the optical frequency shifter 25 is branched by the optical coupler 33, and one output of the optical coupler 33 passes through the delay adjustment fiber 34, the optical pulse gate 35, and the optical coupler 36 and is fed back to the optical frequency shifter 25. The circuit 31 is configured, and the other output of the optical coupler 33 is configured to be input to the optical coupler 28. A modulation signal generator 23 is connected to the optical frequency shifter 25, and a signal having a constant frequency f _f and a constant amplitude is sent to the optical frequency shifter 25.

The output of the optical frequency shifter 26 is branched by the optical coupler 37, and one output of the optical coupler 37 passes through the delay adjustment fiber 38, the optical pulse gate 39, and the optical coupler 40, and returns to the optical frequency shifter 26. A feedback circuit 32 is configured, and the other output of the optical coupler 37 is configured to be input to the optical coupler 28 via the delay compensation fiber 27. To optical frequency shifter 26 is connected to modulation signal generator 24, the frequency is constant at f _b, the amplitude also sent a constant signal to the optical frequency shifter 26.

  The delay compensation fiber 27 compensates for different optical path differences between the pulse train output from the first feedback circuit 31 to the detection unit 13 and the pulse train output from the second feedback circuit 32 to the detection unit 13.

  The details will be described later with reference to FIG. 11. For example, when the pulsed light output from the pulse light source 21 passes through the path of the ABDF 1G, the light is delayed by the amount passing through the first sensing fiber 71. On the other hand, when the pulsed light output from the pulsed light source 21 passes through the ACDE1G path, the phase difference between the pulsed light passing through the ACDE1G path and the pulsed light passing through the ABDF1G path is compensated by the delay compensation fiber 27. As a result, the pulse light passing through the path ABDF1G and the pulse light passing through the path ACDE1G have the same phase, and a beat is generated. That is, the delay compensation fiber 27 compensates for the delay of the first sensing fiber 71.

  Similarly, for example, when the pulsed light output from the pulse light source 21 passes through the path of the ABDF 2G, it is delayed by the amount that passes through the second sensing fiber 81. On the other hand, when the pulsed light output from the pulse light source 21 passes through the ACDE2G path, the phase difference between the pulsed light passing through the ACDE2G path and the pulsed light passing through the ABDF2G path is compensated by the delay compensation fiber 27. As a result, the pulse light passing through the ABDF2G path and the pulse light passing through the ACDE2G path have the same phase, and a beat is generated. That is, the delay compensation fiber 27 compensates for the delay of the second sensing fiber 81.

  Similarly, for example, when the pulsed light output from the pulsed light source 21 passes through the path of ABDF3G, it is delayed by the amount that passes through the third sensing fiber 91. On the other hand, when the pulsed light output from the pulsed light source 21 passes through the ACDE3G path, the delay compensation fiber 27 compensates for the phase difference between the pulsed light passing through the ACDE3G path and the pulsed light passing through the ABDF3G path. As a result, the pulsed light passing through the ABDF3G path and the pulsed light passing through the ACDE3G path have the same phase, and a beat is generated. That is, the delay compensation fiber 27 compensates for the delay of the third sensing fiber 91.

  The output of the optical coupler 28 is amplified by the optical amplifier 29 and sent to the detection unit 13, and the pulse train output from the detection unit 13 is converted into a current by the light receiving element 171, and after being band-limited by the filter 172, the differential amplifier 174 Configure to be entered. A DC component suppressing power source 173 is connected to the other input of the differential amplifier 174 so that the DC component of the interfered pulsed light output from the differential amplifier 174 is canceled. The detection unit 13 and the processing unit 17 are configured similarly to the detection unit 13 and the processing unit 17 illustrated in FIGS. 1 and 5.

  The delay fiber 61 and the delay fiber 62 included in the detection unit 13 correspond to the delay circuit in the present invention. The O / E conversion unit 170 corresponds to the photoelectric conversion unit in the present invention.

  FIG. 9 is a diagram for explaining the details of input / output signals of respective components inside the O / E conversion unit 170 included in the interference optical fiber sensor 3 according to Embodiment 1 of the present invention. As shown in FIG. 9, in the O / E converter 170, the output of the light receiving element 171 is supplied to the filter 172, and the output of the filter 172 and the output of the DC component suppression power source 173 are supplied to the differential amplifier 174. Is done.

  Specifically, the light receiving element 171 outputs the intensity of the pulse to the filter 172 when a pulse train is input. The intensity of the pulse includes a DC component, a demodulated component, and a non-demodulated component. The filter 172 suppresses the non-demodulated component in the intensity of the pulse supplied from the light receiving element 171 and outputs it to the differential amplifier 174. On the other hand, the DC component suppression power source 173 outputs a DC component suppression signal to the differential amplifier 174. The differential amplifier 174 obtains the difference between the output of the filter 172 and the output of the DC component suppression power source 173 and outputs the result. As a result, the differential amplifier 174 outputs a demodulated component as the intensity of the pulse.

  The DC component suppressing power source 173 corresponds to the DC component suppressing power source in the present invention.

  More specifically, the intensity of the interfered pulse output from the light receiving element 171 is expressed by one of the following formulas (1) to (3) except for the first two pulses.

  Here, the first subscripts a, b, and c of I are types of pulse combinations. The second subscript “i” (i = 1, 2, 3) is a number corresponding to each of the first sensing interferometer 41, the second sensing interferometer 42, and the third sensing interferometer 43. . E is the electric field amplitude of light. Φ is the phase of light. The first subscript “f” of φ is the symbol of the optical frequency shifter 25 that has passed. The first subscript “b” of φ is a symbol of the passed optical frequency shifter 26. The number of the second subscript of φ is the number of passes through the optical frequency shifter 25 or the optical frequency shifter 26.

  The third subscript “i” (i = 1, 2, 3) of φ and “j” (j = 1, 2, 3) are identification numbers of the sensing interferometer, and i ≠ j. . For example, when “i” = 1 or “j” = 1, the first sensing interferometer 41 corresponds, and when “i” = 2 or “j” = 2, the second sensing interferometer 42 corresponds, When “i” = 3 or “j” = 3, the third sensing interferometer 43 corresponds.

  The fourth subscripts E and F are symbols of passing points given to the mirror 75 and the mirror 77 included in the first sensing interferometer 41, respectively. Further, the fourth subscripts E and F are symbols of passing points assigned to the mirror 85 and the mirror 87 included in the second sensing interferometer 42, respectively. The fourth subscripts E and F are symbols of passing points given to the mirror 95 and the mirror 97 included in the third sensing interferometer 43, respectively. “<” And “>” are time averages for optical frequencies that cannot pass through the light receiving element 171.

  The filter 172 is configured so that a high-frequency beat not demodulated output from the light receiving element 171 is attenuated. Thereby, the pulse output from the filter 172 is expressed by any one of the following formulas (4) to (6) except for the first two pulses.

  By substituting equation (5) into equation (4), the following equation (6) is derived.

  The differential amplifier 174 removes a DC component from the output of the filter 172 and amplifies the beat used for demodulation. Thereby, the pulse output from the differential amplifier 174 is expressed by any of the following formulas (7) to (9) except for the first two pulses.

  Here, G is the gain of the differential amplifier 174. As can be seen from the equations (7) to (9), the pulses output from the differential amplifier 174 include only beats used for demodulation, and beats and DC components not used for demodulation are suppressed.

<Description of operation>
FIG. 10 is a diagram illustrating an operation example of the interference optical fiber sensor 3 according to Embodiment 1 of the present invention. Note that the processing in step S11 and step S12 corresponds to the process of the light source unit 12. Further, the process of step S13 corresponds to the process of the detection unit 13. Further, the processing of step S14 to step S16 corresponds to the process of the O / E conversion unit 170. Further, the processing of step S17 to step S22 corresponds to the process of the processing unit 17.

(Process of the light source unit 12)
(Step S11)
The interference type optical fiber sensor 3 includes a circuit including the optical frequency shifter 25 and the optical pulse gate 35 and a circuit including the optical frequency shifter 26 and the optical pulse gate 39 that are connected at intervals of time τ. Generate multiple pulses. The plurality of consecutive pulses are, for example, triple pulses as will be described later with reference to FIG.

(Step S12)
The interference-type optical fiber sensor 3 outputs a plurality of pulses that are continuous according to the repetition period of the pulses output from the pulse light source 21 while matching the optical path difference with the delay compensation fiber 27. It is assumed that the matching of the optical path difference here means that the optical path difference is compensated.

(Process of the detection unit 13)
(Step S13)
The interference optical fiber sensor 3 multiplexes a plurality of continuous pulses using the delay fiber 61 or the delay fiber 62.

(Process of O / E converter 170)
(Step S14)
The interference type optical fiber sensor 3 performs photoelectric conversion.

(Step S15)
The interference type optical fiber sensor 3 suppresses non-demodulation components.

(Step S16)
The interference type optical fiber sensor 3 suppresses the DC component.

(Process of processing part 17)
(Step S17)
The interference type optical fiber sensor 3 encodes the demodulated component.

(Step S18)
The interference type optical fiber sensor 3 generates a reference signal.

(Step S19)
The interference type optical fiber sensor 3 multiplies the encoded demodulated component and the reference signal.

(Step S20)
The interference type optical fiber sensor 3 suppresses noise components.

(Step S21)
The interference type optical fiber sensor 3 determines the phase.

(Step S22)
The interference type optical fiber sensor 3 compensates for the discontinuity and ends the process.

<Explanation of operation results>
FIG. 11 is a diagram illustrating an example of a waveform when passing through each path included in the interference type optical fiber sensor 3 according to Embodiment 1 of the present invention. FIG. 11 shows the waveform of an optical pulse that passes through A, B, C, and G in FIG. 8 and the output waveform of the light receiving element 171. Each optical pulse has the number of passes through the optical frequency shifter 25 or the optical frequency shifter 26 added to the first digit, and a number indicating the order of the pulses output from the pulse light source 21 added to the second digit.

  The setting of the pulse timing, which is the main part of the first embodiment, will be described with reference to FIG. In the case of the first embodiment, the time required for the pulse to make one round of the first feedback circuit 31 including the optical frequency shifter 25 and the optical pulse gate 35 or the second feedback circuit 32 including the optical frequency shifter 26 and the optical pulse gate 39. Is set to τ. Further, it is assumed that the repetition period of pulses output from the pulse light source 21 is set to 9τ. Here, τ is a round-trip propagation time common to the first sensing fiber 71, the second sensing fiber 81, and the third sensing fiber 91.

  It is assumed that the optical pulse gate 35 is set so that it passes through the circuit including the optical frequency shifter 25 and passes through the optical frequency shifter 25 up to a pulse that passes three times and blocks a pulse that passes four times. Similarly to the optical pulse gate 35, the optical pulse gate 39 is assumed to pass through the optical frequency shifter 26 up to three passes and to block the four passes.

With the above setting, the output of the optical frequency shifter 25 becomes a triple pulse in which a pulse of the optical frequency ν + f _f, a pulse of the optical frequency ν + 2f _f , and a pulse of the optical frequency ν + 3f _f are connected at a time difference τ. Becomes a pulse train repeated at a repetition period corresponding to the number of multiplexing. Similarly, the output of the optical frequency shifter 26 is a triple pulse in which a pulse with an optical frequency ν + f _b, a pulse with an optical frequency ν + 2f _b , and a pulse with an optical frequency ν + 3f _b are connected with a time difference τ. Becomes a pulse train repeated at a repetition period corresponding to the number of multiplexing. Note that the number of signals to be multiplexed can be changed by changing the repetition period of pulses output from the pulse light source 21.

  A point G in FIG. 11 shows a waveform of a pulse input from the output of the pulse light source 21 to the light receiving element 171 for each path. As the path symbols, A, B, C, D, E1, E2, E3, F1, F2, F3, and G shown in FIG. 8 were used. The pulse that has passed through the ABDE 1G is input to the light receiving element 171 earliest.

  Next, the first sensing fiber 71, the second sensing fiber 81, and the third sensing fiber 91 so that the pulse passing through the ABDF 1 G and the pulse passing through the ACDE 1 G are input to the light receiving element 171 with a delay of the time difference τ. , And the length of the delay compensation fiber 27 is set.

  The pulse passing through the ACDF 1G is input to the light receiving element 171 with a delay of 2τ from the pulse passing through the ABDE 1G. The length of the delay fiber 61 is set so that the pulse passing through the ABDE2G is input to the light receiving element 171 with a delay of 3τ from the pulse passing through the ABDE1G. The pulse passing through the ABDE3G The length of the delay fiber 62 is set so that the light is input to the light receiving element 171 with a delay of 6τ.

Specifically, between a pulse via ABDE1G and a pulse via ABDE2G, a pulse of optical frequency “ν + 3f _f ” via ABDE1G and a pulse of optical frequency “ν + f _f ” via ABDE2G Is inserted with a delay of the time difference τ. The time difference τ is, for example, between a pulse having an optical frequency “ν + f _f ” via ABDE1G, a pulse having an optical frequency “ν + 2f _f ” passing through ABDE1G, and a pulse having an optical frequency “ν + 3f _f ” passing through ABDE1G. Respectively, which is the same as the delay of the time difference τ.

  That is, the output pulse of the first sensing interferometer 41 and the output pulse of the second sensing interferometer 42 are delayed so as to be continuous with a time difference τ. Thereby, at least the signal generated from the beat generated by the first sensing interferometer 41 and the signal generated from the beat generated by the second sensing interferometer 42 are wasted. Therefore, the number of signals used after photoelectric conversion can be increased.

Similarly, between a pulse passing through ABDE2G and a pulse passing through ABDE3G, a pulse having optical frequency “ν + 3f _f ” passing through ABDE2G and a pulse having optical frequency “ν + f _f ” passing through ABDE3G are between A delay of time difference τ is inserted. The time difference τ is, for example, between a pulse of optical frequency “ν + f _f ” via ABDE2G, a pulse of optical frequency “ν + 2f _f ” via ABDE32, and a pulse of optical frequency “ν + 3f _f ” via ABDE2G. Respectively, which is the same as the delay of the time difference τ.

  That is, the output pulse of the second sensing interferometer 42 and the output pulse of the third sensing interferometer 43 are delayed so as to be continuous with a time difference τ. As a result, at least the signal generated from the beat generated by the second sensing interferometer 42 and the signal generated from the beat generated by the third sensing interferometer 43 are wasted. Therefore, the number of signals used after photoelectric conversion can be increased.

  Therefore, it is generated from the signal generated from the beat generated by the first sensing interferometer 41, the signal generated from the beat generated by the second sensing interferometer 42, and the beat generated by the third sensing interferometer 43. Since signals are not wasted between signals, the number of signals used after photoelectric conversion can be increased.

  For example, the output period of the pulse light source 21 is 9τ, and the output of the first feedback circuit 31 and the output of the second feedback circuit 32 are a plurality of continuous pulses, for example, a triple pulse with an interval of time difference τ. Thus, by making the output timing of the optical pulse gate 35, the output timing of the optical pulse gate 39, the delay amount of the delay fiber 61, and the delay amount of the delay fiber 62 the same, the output waveform of the light receiving element 171 is changed. The output timing becomes the time difference τ, and the number of signals used after photoelectric conversion can be increased.

  That is, the output pulses of the first feedback circuit 31 are made to be three consecutive with a time difference τ and the output pulses of the second feedback circuit 32 are made to be three consecutive with a time difference τ, and then the respective outputs of the optical pulse gate 35 and the optical pulse gate 39. By setting the timing and the respective delay amounts of the delay fiber 61 and the delay fiber 62 to the same time difference τ, it is possible to generate a beat of a signal without providing a wasteful time for signal multiplexing. Thereby, the number of signals used after photoelectric conversion can be increased.

  Note that the three continuous output pulses described above are merely examples, and the present invention is not particularly limited to this. By inserting delay amounts into various pulses with a time difference τ, signals used after photoelectric conversion Any pulse configuration that increases the number may be used.

  The A / D converter 111 of the processing unit 17 samples all pulses output from the differential amplifier 174. The reference signal generator 121 to the reference signal generator 126 correspond to Iai ″, Ibi ″, Ici ″ (i = 1, 2, 3) including signals detected by the sensing interferometer “i” to be demodulated. A reference signal is output, and the multiplier 131 to the multiplier 136, the LPF 141 to the LPF 146, the arc tangent calculator 151 to the arc tangent calculator 153, and the discontinuous point compensation calculator 155 to the discontinuous point compensation calculator 157 are interference type light. It operates in the same manner as the fiber sensor 1 and the interference type optical fiber sensor 2 and demodulates the signal detected by the sensing interferometer “i”.

<Description of effects>
As described above, the interference type optical fiber sensor 3 multiplexes the plurality of consecutive pulses by delaying them in succession according to the repetition period of the pulses output from the pulse light source 21 and suppresses components other than the demodulated components. Thus, it is possible to relatively reduce noise while increasing the number of signals used after photoelectric conversion.

  The interference type optical fiber sensor 3 has three beats corresponding to the demodulated component and three beats corresponding to the demodulated component, as is apparent from FIG. 11 and equations (1) to (9) described above. The signal can be demodulated from each of the sidebands.

  In the conventional technique, the signals detected by the first sensing interferometer 41, the second sensing interferometer 42, and the third sensing interferometer 43 are demodulated using beats of a plurality of frequencies, and are generated in the optical amplifier 29 and the like. Although there is an effect of suppressing noise, when the dynamic range of the O / E converter 15 is narrow, the level of light input to the O / E converter 15 is suppressed, so the S / N ratio of the beat signal is reduced. The noise of demodulated output increased. In the first embodiment, in the process of O / E conversion from the light receiving element 171 to the differential amplifier 174, a high-frequency beat not used for demodulation and a direct current component are attenuated, so that The signal can be demodulated with low noise by effectively using the dynamic range of the component. If the noise becomes low, a signal with a lower level can be detected accordingly.

  In other words, a pulse that has not been used in the prior art is also used for demodulation, so that more pulses can be sampled and demodulated than in the prior art. As a result, the number of samples of the demodulated signal is also increased, and an effect of reducing random noise can be obtained, so that a low level signal can be detected accordingly.

  As described above, the first embodiment includes the pulse light source 21 that periodically generates a plurality of pulses and the two optical paths, and superimposes and outputs a plurality of pulses having different light frequencies in each optical path. An output unit, a detection unit 13 having two optical paths, and having a sensing interferometer that outputs a superimposed pulse and a pulse obtained by delaying the superimposed pulse according to the measurement signal; An O / E converter 170 that photoelectrically converts a plurality of pulses; and a processor 17 that processes an electrical signal supplied from the O / E converter 170 and demodulates a measurement signal. The interference type optical fiber sensor 3 including the filter 172 that suppresses the non-demodulated component from the pulse from the detection unit 13 is configured.

  As a result, the interference type optical fiber sensor 3 delays a plurality of consecutive pulses according to the repetition period of the pulses output from the pulse light source 21 so as to be continuous, and suppresses other than the demodulated component, so that it is used after photoelectric conversion. The noise can be reduced relatively while increasing the number of signals to be generated.

  Further, in the first embodiment, the detection unit 13 includes a delay circuit that delays the output pulses of a plurality of sets of sensing interferometers so as to be continuous and outputs them to the O / E conversion unit 170, and the delay circuit includes at least One delay fiber 61 is provided, and the delay fiber 61 delays a continuous interval of output pulses at the same interval as the interval between a plurality of superimposed pulses from the output unit.

  Thereby, the interference type optical fiber sensor 3 can generate a plurality of beats over a wide range of frequencies, such as a beat including a low frequency component to a beat including a high frequency component.

  In the first embodiment, the output unit feeds back one pulse branched from the optical path a plurality of times, and changes the frequency of light in the feedback circuit (first feedback circuit or second feedback circuit 32). is there.

  Thereby, the interference type optical fiber sensor 3 generates a plurality of beats having different frequencies. Therefore, the interference type optical fiber sensor 3 can generate a signal including a DC component and a demodulation component.

  Further, in the first embodiment, the O / E conversion unit 170 outputs a suppression signal that suppresses a direct current component among the light receiving element 171 that photoelectrically converts a plurality of pulses from the detection unit 13 and an electrical signal. And a differential amplifier 174 that outputs an output corresponding to the difference between the output of the component suppression power supply 173, the output of the filter 172, and the output of the DC component suppression power supply 173. The differential amplifier 174 It suppresses and outputs the demodulated component to the processing unit 17.

  Thereby, the interference type optical fiber sensor 3 suppresses the direct current component corresponding to the bias. Therefore, the interference type optical fiber sensor 3 can relatively reduce noise.

  In the drawings of the first embodiment, the relationship between the sizes of the constituent members may be different from the actual one. In the drawings of the first embodiment, the same reference numerals are added to the same or corresponding parts, and this is common throughout the entire specification. Furthermore, the form of the component described in the whole specification is merely an example, and is not limited to these descriptions.

  Further, the step of describing the program for performing the operation of the first embodiment is a process performed in time series in the order described, but even if not necessarily processed in time series, it is performed in parallel or individually. Processing to be executed may also be included.

<Description of usage pattern>
In the first embodiment, an example in which the configuration from the optical coupler 22 to the optical coupler 28 is provided before the detection unit 13 has been described. However, the configuration may be provided between the detection unit 13 and the O / E conversion unit 170. Good. In this case, the order of steps until the pulse output from the pulse light source 21 is input to the O / E converter 170 is switched, but after the input of the O / E converter 170, the operation is the same as in the first embodiment. The same effect can be obtained.
In the first embodiment, the interference-type optical fiber sensor 3 detects signals detected by the three sensing fibers, such as the first sensing fiber 71, the second sensing fiber 81, and the third sensing fiber 91. An example of time-division multiplexing and demodulating a signal from three beats and respective sidebands of the three beats has been described, but the number of signals to be time-division multiplexed is not particularly limited, and time division The number of signals to be multiplexed can be changed.

  In the first embodiment, the first feedback circuit 31 including the optical frequency shifter 25 and the optical pulse gate 35, the second feedback circuit 32 including the optical frequency shifter 26 and the optical pulse gate 39, Although an example in which a part having a function corresponding to the optical amplifier 29 is not provided in each of the above has been described, the present invention is not particularly limited thereto. For example, depending on the amount of pulse attenuation in each of the first feedback circuit 31 and the second feedback circuit 32, the optical amplifier 29 is provided in each of the first feedback circuit 31 and the second feedback circuit 32. A component having a corresponding function may be provided.

In the first embodiment, an example in which the filter 172 is provided after the light receiving element 171 has been described. However, the present invention is not particularly limited thereto. For example, when the shift frequency such as the frequency “f _f ” and the frequency “f _b ” is higher than the pass band of the differential amplifier 174 in each of the optical frequency shifter 25 and the optical frequency shifter 26, the high frequency component is different. The filter 172 may not be provided in the interference optical fiber sensor 3 because it does not pass through the dynamic amplifier 174.

  In the first embodiment, an example in which the DC component is suppressed by the DC component suppressing power source 173 and the differential amplifier 174 has been described. However, the present invention is not particularly limited thereto. For example, the interference optical fiber sensor 3 may block the direct current component by using a high pass filter (HPF) or a band pass filter (BPF). Further, the interference type optical fiber sensor 3 may be provided with a bias tee so as to branch the DC component and the AC component and cancel the DC component.

  In the first embodiment, the interference type optical fiber sensor 3 constitutes a Michelson interferometer such as the first sensing interferometer 41 including the first sensing fiber 71, the optical coupler 73, the mirror 75, and the mirror 77. However, the present invention is not particularly limited to this. For example, the interference type optical fiber sensor 3 may be configured with a Mach-Zehnder interferometer as an interferometer. Further, the interference type optical fiber sensor 3 may constitute an interferometer provided with an FBG (Fiber Bragg Grating) instead of the mirror 75 or the like.

  In the first embodiment, the interference type optical fiber sensor 3 shows an example in which a pulse is branched by the optical coupler 22 or the like, but the present invention is not particularly limited thereto. For example, the interference type optical fiber sensor 3 can branch the pulse by a partially reflecting mirror or FBG. In addition, the interference type optical fiber sensor 3 may be provided with a component in which the configuration of the optical coupler 22 for pulse branching is changed, and is used in combination with a configuration for realizing other multiplexing methods such as wavelength branch multiplexing. Things may be provided.

  1, 2, 3 Interferometric optical fiber sensor, 11, 12 Light source unit, 13 Detector unit, 15 O / E converter, 16, 172 Filter, 17 Processing unit, 21 Pulse light source, 22, 28, 33, 36, 37 , 40, 51, 52, 53, 54, 73, 83, 93 Optical coupler, 23, 24 Modulation signal generator, 25, 26 Optical frequency shifter, 27 Delay compensation fiber, 29 Optical amplifier, 31 First feedback circuit, 32 Second feedback circuit, 35, 39 Optical pulse gate, 34, 38 Delay adjustment fiber, 41 First sensing interferometer, 42 Second sensing interferometer, 43 Third sensing interferometer, 61, 62 Delay fiber, 71 First sensing Fiber, 75, 77, 85, 87, 95, 97 Mirror, 81 Second sensing fiber, 91 Third sensing fiber, 111 A D converter, 121, 122, 123, 124, 125, 126 Reference signal generator, 131, 132, 133, 134, 135, 136 Multiplier, 141, 142, 143, 144, 145, 146 LPF, 151, 152 153, arc tangent calculator, 155, 156, 157 discontinuous point compensation calculator, 170 O / E converter, 171 light receiving element, 173 DC component suppressing power source, 174 differential amplifier.

Claims (4)

A pulse light source that periodically generates a plurality of pulses;
An output unit that includes two optical paths and superimposes and outputs a plurality of pulses having different light frequencies in each optical path;
A detection unit having a sensing interferometer that includes two optical paths and outputs the superimposed pulse and a pulse obtained by delaying the superimposed pulse according to a measurement signal;
A photoelectric conversion unit that photoelectrically converts a plurality of pulses from the detection unit;
A processing unit that processes an electrical signal supplied from the photoelectric conversion unit and demodulates the measurement signal,
The photoelectric converter is
An interference type optical fiber sensor comprising a filter that suppresses a non-demodulated component from a pulse from the detection unit. The detector is
A delay circuit that delays the output pulses of a plurality of sets of sensing interferometers to be continuous and outputs them to the photoelectric conversion unit,
The delay circuit is
Comprising at least one delay fiber;
The delay fiber is
The interference type optical fiber sensor according to claim 1, wherein the continuous interval of the output pulses is delayed by the same interval as the interval between a plurality of superimposed pulses from the output unit. The output unit is
The interference type optical fiber sensor according to claim 2, wherein one pulse branched from the optical path is fed back a plurality of times, and the frequency of light is changed in the feedback circuit. The photoelectric converter is
A light receiving element that photoelectrically converts a plurality of pulses from the detection unit;
Among the electrical signals, a DC component suppression power source that outputs a suppression signal that suppresses a DC component;
A differential amplifier that outputs in accordance with the difference between the output of the filter and the output of the DC component suppressing power supply;
The differential amplifier is
The interference type optical fiber sensor according to claim 3, wherein the direct current component is suppressed and a demodulated component is output to the processing unit.

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