JPH1079713A - Frequency division and multiplexing optical fiber sensor system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide more optical fibers in one system, to multiplex them and to reduce the cost by measuring a wide band signal such as a current signal at multiple points through the use of 9 plural optical fibers. SOLUTION: A side band inn an unwanted beat frequency generated in a part converted k an O/E converter 3 is removed in a reception gate 60. Since return components generated in the gate 60 are removed in band pass filters 4-1 and 4-2, noise components are not mixed in respective demodulation processors 5-1 and 5-2. The filters 4-1 and 4-2 operate as interpolation filters, and the pulse output signals of the gate 60 are interpulse-interpolated. Then, they are outputted as continuous signals. Thus, the respective side bands owing to the unnecessary beat components are prevented from leaking and they are prevented from affecting other optical fiber sensor signals as noise. Thus, the number of the optical fiber sensors of one system is increased axed much more multiplexing can be executed. Then, the number of systems required for measurement can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency division multiplexing type optical fiber sensor for measuring and detecting a wideband signal such as a current signal at multiple points using a plurality of optical fibers.

[0002]

2. Description of the Related Art Conventionally, as a technology of such a frequency division multiplexing type optical fiber sensor system, "Frequency-division
vision multiplexing of optical-fiber sensors using
a frequency-modulated source '', Optical and Qant
um Electronics Vol. 18, No. 4 (1986), I. Sakai.

FIG. 7 is a configuration diagram of a frequency division multiplexing (FDM) type optical fiber sensor based on the above-mentioned document. In the figure, reference numeral 1 denotes a light source, and LFM (Linear Fr)
It outputs a laser light signal that is modulated by a frequency modulation and the frequency of which is modulated to a sawtooth wave. 2
Denotes a sensor array, which includes a plurality of optical fiber sensors. FIG. 7 illustrates the first and second optical fiber sensors 2-0-1 and 2-0-2. A laser light signal output from the light source 1 is branched by an input coupler 2-1-1, one of which travels along an optical path to a first optical fiber sensor 2-0-1 and the other is a second optical fiber sensor. 2-0
Follow the light path to -2. First optical fiber sensor 2-0-
1, the power is equally divided by the sensor coupler 2-2-1, and one is divided into the sensing fiber 2 as the sensing light.
Pass through -3-1. The other passes through the reference fiber 2-4-1 as reference light. Sensing fiber 2-3-1 and reference fiber 2-4-
1 means that the optical path length changes according to the physical quantity measured by the magnetostriction effect or the like, which causes a phase change. Sensing fiber 2-3-1 and reference fiber 2-4-
The laser light signal that has passed through 1 is coupled to the sensor coupler 2-5.
1 and interfere with each other, and are combined with the signal passed through another optical fiber sensor by the output coupler 2-6-1 and output. This operation is similarly performed for other optical fiber sensors connected in parallel.

[0004] Reference numeral 3 denotes an O / E converter, which square-detects the laser light signal interfered by the optical sensor array 2 and converts it into a voltage. 4-1 and 4-2 are band pass filters (BP
F), and passes signals in the respective determined frequency bands. 5-1 and 5-2 are demodulation processors that demodulate and output signals that have passed through the band-pass filters 4-1 and 4-2, respectively.

A light source 1 outputs an LFM-modulated laser light signal having a repetition period T [sec] and a frequency sweep rate a [Hz / sec], and a sensing fiber 2-3 constituting a first optical fiber sensor. −1 and the reference fiber 2-4-1 are set to have an optical path difference ΔL ₁ . At this time, in the sensor coupler 2-5-1, the sensing light and the reference light have a propagation time difference τ ₁ (= optical path difference Δ).
L ₁ / velocity of light) to interfere with the (for LFM light interfere with the time difference tau _1), the signal output from the O / E converter 3, beats having a frequency of a × τ ₁ [Hz] Signal is included.

If the phase change Φ ₁ (t) corresponding to the physical quantity to be measured is generated between the sensing light and the reference light by utilizing the magnetostriction effect or the like, the O / E converter 3 Assuming that the amplitude value is A, the output signal includes Acos (2πaτ ₁ t + Φ) including the above-mentioned beat signal.
₁ (t)). This was passed through a band pass filter 4-1 center frequency Eitau ₁ a, F the demodulation processor 5-1
It performs demodulation as a current signal Φ ₁ by performing processing such as M detection,
Output.

In the second optical fiber sensor, a sensing fiber 2-3-2 and a reference fiber 2-4 are used.
The optical path difference from −2 is set to ΔL ₂ ＬΔL ₁ and the beat frequency at that time is set to a × τ ₂ [Hz]. O / E signal which has passed through the transducer 3, passed through the band-pass filter 4-2 center frequency Eitau _2, demodulates the current signal [Phi ₂ by the processing of FM detection such as the demodulation processor 5-2 ,Output.

The signals interfered by the respective optical fiber sensors are transmitted by carrier waves having different frequencies. That is, frequency multiplex transmission is performed. Usually, ΔL _n
= ΔL ₁ × n to change the optical path difference of each optical fiber sensor so that the beat frequency a × τ _n of the n-th optical fiber sensor becomes (a × τ ₁ ) × n.

[0009]

However, in the method of generating a beat signal having the above frequency, the frequency of the light source 1 is swept at a repetition period T [sec], so that the sweep switching is performed as shown in the time chart of FIG. Sometimes a × τ [H
Unnecessary beat frequencies other than z] occur. for that reason,
In addition to the beat signal of a × τ [Hz], a sideband is generated at a portion separated from a × τ [Hz] by a sweep frequency (1 / T) [Hz], and leakage of a wide-range component of the sideband is generated. As a result, noise is added to the signal of another optical fiber sensor. In order to suppress the intensity of the sideband and not affect the signals of other optical fiber sensors, it is necessary to reduce the optical path difference ΔL and the frequency sweep rate a. At the time of multiplexing, a difference is provided in the optical path difference ΔL to generate a different beat frequency (the product of the optical path difference and the frequency sweep rate). Therefore, if there is a restriction on the increase in the optical path difference ΔL, multiplexing is inevitable. Numbers will be limited lower. Therefore, the number of measurement points is also limited, and in order to increase the number of measurement points, it is necessary to provide a plurality of such optical fiber sensor systems, and there has been a problem in that it is inconvenient in terms of equipment and cost.

Therefore, it has been desired to realize a frequency division multiplexing type optical fiber sensor which can be equipped with a larger number of optical fiber sensors in one system and can reduce the price.

[0011]

According to a first aspect of the present invention, there is provided a frequency division multiplexing type optical fiber sensor system comprising: a light source for outputting a laser beam in which the frequency of a laser light electric field is linearly frequency-modulated into a sawtooth waveform; A plurality of sets of two optical fibers whose optical path lengths change in accordance with physical quantities are provided. Each set is an integral multiple of a reference delay time difference, and each set has a different delay time difference. Optical fiber sensor means for transmitting laser light through an optical fiber to cause interference, optical-voltage conversion means for square-detecting the interfering laser light to convert it into a detection signal (voltage), and a detection signal of the interference laser light. , The reception gate that passes except for the part where the frequency of the detection signal changes, and the frequency based on the delay time difference of each pair of the detection signals that have passed through the reception gate is defined as the center frequency. Filters that pass detection signals of different frequency bands, and a plurality of phase demodulators that demodulate the detection signals that have passed through the plurality of bandpass filters and output demodulated signals having phase signals corresponding to physical quantities, respectively. Means. In the present invention, the light source outputs the laser light in which the frequency of the laser light electric field is linearly frequency-modulated in a sawtooth waveform. In the optical fiber sensor means, a change in the optical path length corresponding to the physical quantity of the object to be measured occurs in each set of optical fibers, so that the phase of the interference light of the laser light passing through each set of optical fibers changes. The laser light passes through each optical fiber such that each set has an integer multiple of the reference delay time difference and a different delay time difference from the other sets. The interfering laser light is square-detected by the light-to-voltage converter and converted into a voltage. In order to remove a sideband generated at a portion where the frequency of the interference light changes, the reception gate passes the detected detection signal obtained by converting the interfered laser light except for a portion where the frequency of the detection signal changes. The plurality of band-pass filters set the center frequency of the band to be passed to a frequency based on the delay time difference of each set. The pulse-like detection signal that has passed through the reception gate is passed through a predetermined band, and is interpolated to be passed as a continuous signal. The plurality of phase demodulation means demodulate the detection signal passed through the band-pass filter,
A demodulated signal having a phase signal corresponding to the physical quantity to be measured is output.

Further, a frequency division multiplexing type optical fiber sensor system according to a second aspect of the present invention provides a light source for outputting a laser beam in which the frequency of a laser light electric field is linearly frequency-modulated in a sawtooth waveform, Among them, there are a plurality of sets of a transmission gate that transmits laser light in a portion where the frequency of the laser light electric field changes linearly, and two sets of two optical fibers whose optical path length changes in accordance with the physical quantity to be measured. An optical fiber sensor means for causing the laser light to pass through and interfere with each set of optical fibers with an integer multiple of the reference delay time difference, and each set having a different delay time difference; Light-to-voltage conversion means for detecting and converting to voltage, and among the detection signals passing through the light-to-voltage conversion means, the frequency based on the delay time difference of each pair is defined as the center frequency. And a plurality of mobile demodulators that demodulate the respective detection signals that have passed through the plurality of band-pass filters and output demodulated signals having phase signals corresponding to physical quantities, respectively. Means. In the present invention, the light source outputs the laser light in which the frequency of the laser light electric field is linearly frequency-modulated in a sawtooth waveform. The transmission gate passes the laser light in a portion where the frequency of the laser light electric field changes linearly, so that the laser light passes through, except for the laser light at the time of frequency sweep, which causes unnecessary beat components. Output as modulated laser light. In the optical fiber sensor means, a change in the optical path length corresponding to the physical quantity of the object to be measured occurs in each set of optical fibers, so that the phase of the interference light of the laser light passing through each set of optical fibers changes. The laser light passes through each optical fiber such that each set has an integer multiple of the reference delay time difference and a different delay time difference from the other sets. The interfering laser light is square-detected by the light-to-voltage converter and converted into a voltage. The plurality of bandpass filters set the center frequency of the band to be passed to a frequency based on each set. The pulse-like signal that has passed through the reception gate is passed through a predetermined band, and is interpolated to be passed as a continuous signal. The plurality of phase demodulation units demodulate the detection signal that has passed through the band-pass filter, and output a demodulated signal having a phase signal corresponding to a physical quantity to be measured.

A frequency division multiplexing optical fiber sensor system according to a third aspect of the present invention provides a light source for outputting laser light whose frequency of a laser light electric field is modulated into a sine wave shape and a physical quantity to be measured. A plurality of sets of two optical fibers having different optical path lengths are provided, each set having an integral multiple of a reference delay time difference, and each set having a different delay time difference. Fiber-optic sensor means for transmitting and causing interference, light-to-voltage conversion means for square-detecting the interfering laser light and converting it to voltage, and the instantaneous frequency of the detection signal output from the light-to-voltage conversion means is substantially constant A reception gate that passes an output signal of a predetermined width centered on a detection signal portion to be detected, and a frequency centered on a delay time difference of each pair among signals that have passed through the reception gate. A plurality of band-pass filters for passing signals in a frequency band having a wave number; and a plurality of phase demodulators for demodulating respective signals passing through the plurality of band-pass filters and outputting demodulated signals having phase signals corresponding to physical quantities, respectively. Means. In the present invention, the light source outputs a laser beam obtained by frequency-modulating the frequency of the laser beam electric field into a sine wave shape. In the optical fiber sensor means, since the optical path length of each set of optical fibers changes according to the physical quantity to be measured, the phase of the interference light of the laser light passing through each set of optical fibers changes. The laser light passes through each optical fiber such that each set has an integer multiple of the reference delay time difference and a different delay time difference from the other sets. The interfering laser light is square-detected by the light-to-voltage converter and converted into a voltage. The reception gate allows the signal to pass through a predetermined width around a portion where the instantaneous frequency of the detected signal is substantially constant. Therefore, it can be considered that the beat frequency of the passing signal is constant. The plurality of bandpass filters set the center frequency of the band to be passed as a frequency based on the delay time difference of each set. The pulse-like signal that has passed through the reception gate is passed through a predetermined band, and is interpolated to be passed as a continuous signal. The plurality of phase demodulation units demodulate the detection signal that has passed through the band-pass filter, and output a demodulated signal having a phase signal corresponding to a physical quantity to be measured.

Further, a frequency division multiplexing type optical fiber sensor system according to a fourth aspect of the present invention provides a light source for outputting laser light whose frequency of a laser light electric field is modulated into a sine wave shape, and A transmission gate for passing a laser beam of a predetermined width centered on a portion where the instantaneous frequency change is linear, and a plurality of sets of two optical fibers whose optical path length changes in accordance with a physical quantity to be measured. An optical fiber sensor means for causing each set to have an integer multiple of the reference delay time difference, and each set having a different delay time difference, transmitting the laser light through each set of optical fibers and causing interference; and And a plurality of band-pass filters that transmit a frequency band centered on a frequency based on the delay time difference between each pair. A filter, and a plurality of phase demodulating means for demodulating each of the detection signal passing through the plurality of the band-pass filter, and outputs the demodulated signal with a phase signal corresponding to the physical quantity. In the present invention,
A light source outputs a laser light whose frequency of a laser light electric field is frequency-modulated into a sine wave shape. The transmission gate allows the laser light to pass through a predetermined width around a portion where the instantaneous frequency change of the laser light is linear. Therefore, the transmitted laser light can be regarded as a linear pulsed laser light,
It can be handled in the same way as linear frequency modulated laser light. In the optical fiber sensor means, since the optical path length of each set of optical fibers changes according to the physical quantity to be measured, the phase of the interference light of the laser light passing through each set of optical fibers changes. The laser light passes through each optical fiber such that each set has an integer multiple of the reference delay time difference and a different delay time difference from the other sets. The interfering laser light signal is square-detected by the light-to-voltage converter and converted into a voltage. The plurality of bandpass filters set the center frequency of the band to be passed as a frequency based on the delay time difference of each set. The pulse-like signal that has passed through the reception gate is passed through a predetermined band, and is interpolated to be passed as a continuous signal. The plurality of phase demodulation units demodulate the detection signal that has passed through the band-pass filter, and output a demodulated signal having a phase signal corresponding to a physical quantity to be measured.

Further, the optical fiber sensor means of the frequency division multiplexing type optical fiber sensor system according to the fifth invention comprises:
The optical path length is set so that the optical path distance from each set of light sources to the light-to-voltage conversion means is equal. Therefore, portions where the frequency of the laser light interfering with each set of optical fibers changes are input to the optical-to-voltage converter at substantially the same timing. Therefore, the setting of the gate width of the reception gate when removing the detection signal in the portion where the frequency of the laser beam changes is simplified.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. FIG. 1 is a diagram showing an F-mode according to a first embodiment of the present invention.
3A and 3B are a configuration diagram of a DM optical fiber sensor system, a frequency of a laser light signal, and a time chart of a reception gate 60. In FIG. 1A, reference numeral 1 denotes a light source, and LFM (L
inner Frequency Modulatio
n) outputting a modulated laser light signal whose frequency is modulated into a sawtooth waveform; Reference numeral 2 denotes a sensor array, which is configured by an optical fiber sensor using a plurality of Mach-Zehnder interferometer interferometers. Each optical fiber sensor has an input coupler,
It is composed of an output coupler, a sensing fiber, a reference fiber, and two sensor couplers. FIG.
Then, the first and second optical fiber sensors 2-0-1 and 2-0
-0-2 is shown. The laser light signal output from the light source 1 is split by the input coupler 2-1-1, one of which travels along the optical path to the first optical fiber sensor 2-0-1 and the other of which is the second optical fiber sensor 2-0-1. It travels along the optical path to the optical fiber sensor 2-0-2. In the first optical fiber sensor 2-0-1, the laser light signal is equally divided in power by the sensor coupler 2-2-1, and one of them passes through the sensing fiber 2-3-1 as sensing light. The other passes through the reference fiber 2-4-1 as reference light. Since the optical path length of the sensing fiber 2-3-1 changes according to the physical quantity measured by the magnetostriction effect or the like,
A phase change corresponding to the physical quantity occurs. The laser light signals that have passed through the sensing fiber 2-3-1 and the reference fiber 2-4-1 are coupled by the sensor coupler 2-5-1 and interfere with each other, and output by the output coupler 2-6-1. It is combined with the signal that has passed through the fiber sensor and output. Such an operation is similarly performed in another optical fiber sensor connected in parallel. Reference numeral 3 denotes an O / E converter, which square-detects the laser light signal interfered by the optical sensor array 2 and converts it into a voltage. 4-1 and 4-2 are band-pass filters (B
PF), and passes signals of respective fixed frequency bands. Reference numerals 5-1 and 5-2 denote demodulation processors, each of which is a bandpass filter 4-1 or a bandpass filter 4-1.
2, and demodulates and outputs the signal.

Reference numeral 60 denotes a receiving gate having a gate width of T _g [sec] and a cycle of T _s [sec]. Reception gate 60
Are set so as to take a gate timing such that the laser light signal at the time of the sweep switching interferes and the signal of the portion converted by the O / E converter 3 does not pass.

Next, a specific operation of the optical fiber sensor system will be described. The light source 1 has a repetition period T _s [s
ec] and LFM of frequency sweep rate a [Hz / sec]
Transmits a laser light signal. Sensing fiber 2-3
1 and the optical path difference between the reference fiber 2-4-1 are ΔL
_If it is set to ₁ , the beat frequency at the output of the O / E converter 3 is a × τ ₁ [Hz]. Where τ ₁ represents the delay difference,
τ ₁ = (ΔL ₁ / speed of light). Since the cycle of the reception gate 60 is T _s [sec], noise due to the aliasing component is generated at a frequency interval of 1 / T _s [Hz]. It is necessary to prevent this noise from affecting the demodulation.

The receiving gate 60 has a function of (1 / T _g ) [Hz].
Has a frequency characteristic where the response is lost at the frequency interval of. Therefore, the beat frequency output from each optical fiber sensor is set to, for example, a × τ _{1 in} the first optical fiber 2-0-1.
= 1 / T when _g keep an integral multiple of 1 / T _g as aliasing noise, the response is zero at an integer multiple of the frequency of the beat frequency by the frequency characteristic, for example, the second
Does not affect the signal of the beat frequency a × τ ₂ = 2 / T _g generated by interference by the optical fiber sensor 2-0-2.

At this time, each band-pass filter sets the center frequency to an integral multiple of a × τ ₁ = 1 / T _g [Hz] (the beat frequency of the interference light output from each optical fiber sensor).
The pass band is 1 / T _s [Hz]. Since each bandpass filter cannot remove a sideband due to an unnecessary beat frequency, it can be removed by the reception gate 60, and the aliasing component generated by providing the reception gate 60 can be removed. As a result, noise components are not mixed in each demodulation processor by removing with a pass filter.

Each band-pass filter also serves as an interpolation filter. Therefore, when a signal output as a pulse from the reception gate 60 passes through each band-pass filter, the interval between pulses is interpolated and a continuous signal is output. If the amplitude value of the signal at this time is B, for example, the signal passing through the band-pass filter 4-1 is Bcos (2πaτ ₁ t + Φ).
₁ (t)). The signal subjected to demodulation processing by the FM detector, and outputs a current signal [Phi _1. This current signal [Phi ₁ is a representation of the physical quantity sensed by the first optical fiber sensor 2-0-1.

Similarly, the second optical fiber sensor 2-0
In -2, the signal passed through the reception gate 60 is set so that the beat frequency becomes a × τ ₂ = (a × τ ₁ ) × 2 [Hz], and the pass band is set at the center frequency a × τ ₂ [Hz]. Is 1 /
T _s is passed through a band pass filter 4-2 [Hz], and demodulates the current signal [Phi ₂ performs processing by FM detection, etc. in the demodulation processor 5-1. Do this with other demodulators,
Measure the physical quantity.

In the first embodiment, the receiving gate 60 does not need to generate unnecessary laser light signals at the portion where the laser light signal interfered with the laser light signal at the time of the sweep switching is converted by the O / E converter 3. Since the sideband generated from the beat component is prevented from passing, each sideband due to the unnecessary beat component does not leak and does not affect the signal of the other optical fiber sensor as noise. Since the number of optical fiber sensors can be increased and more multiplexing can be performed, the number of systems required for measurement can be reduced, equipment can be more convenient, and costs can be reduced. . In the first embodiment, the interval between the sensors is reduced in multi-point measurement (for example, when the signal is 10K).
When the band is limited by Hz, several km or the like), the delay difference due to the difference in the optical path distance between the optical fiber sensors is reduced,
Since the difference between the portions where the laser light signals interfere with each other at the time of the sweep switching by each optical fiber sensor is reduced and the reception gate 60 is used in common, the number of components can be reduced.

Embodiment 2 FIG. FIG. 2 is a configuration diagram of an FDM optical fiber sensor system according to a second embodiment of the present invention, a frequency of a laser light signal, and a time chart of a reception gate 60. In FIG. 2A, light source 1, O / E
Converter 3, band-pass filter (BPF) 4-1 and 4
-2, demodulation processors 5-1 and 5-2 and reception gate 6
0 performs the same operation as that of FIG.

Reference numeral 2a denotes a sensor array, which is slightly different from the sensor array 2 of the first embodiment. The sensor array 2a is also configured by an optical fiber sensor using a plurality of Mach-Zehnder interferometer interferometers. Each optical fiber sensor is composed of an input coupler, an output coupler, a sensing fiber, a reference fiber, and two sensor couplers as in the first embodiment.
FIG. 2 shows the first and second optical fiber sensors 2-0-1a.
And 2-0-2a are illustrated. The laser light signal output from the light source 1 is branched by the input coupler 2-1-1.
One travels along the optical path to the first optical fiber sensor 2-0-1a, and the other travels along the optical path 2-0-2a to the subsequent second optical fiber sensor. First optical fiber sensor 2
In −0-1a, the laser light signal is output from the sensor coupler 2-2.
The power is equally divided by −1, and one passes through the sensing fiber 2-3-1 as sensing light. The other is a reference fiber 2-4-
Pass 1 The optical fiber length of the sensing fiber 2-3-1 changes according to the physical quantity measured by the magnetostriction effect or the like, and a phase change corresponding to the physical quantity occurs. The laser light signals passing through the sensing fiber 2-3-1 and the reference fiber 2-4-1 are coupled by the sensor coupler 2-5-1 and interfere with each other. This is similarly performed for other optical fiber sensors connected in parallel. Further, as in the first embodiment, each optical fiber sensor has a 1 / T so that a × τ ₁ = 1 / T _{g in} the first optical fiber, for example.
Set as an integer multiple of _g .

The interfered laser light signal passing through the output coupler 2-6-1a is transmitted to the second optical fiber sensor 2-0.
-2a toward the output coupler 2-6-2a. The laser light signal interfered by another optical fiber sensor is also sent to the output coupler of the subsequent optical fiber sensor, and is combined with the laser light signal interfered by the final optical fiber sensor. Output to the E converter 3. Therefore, the propagation time (optical path distance) of the laser light signal from the light source 1 to the interference and input to the O / E converter 3
Are substantially the same regardless of the measurement distance interval between the optical fiber sensors.

In the second embodiment, the optical path distances of the optical fiber sensors of the sensor array 2a are substantially the same, and the interference light of the laser light signal output from each optical fiber sensor at the time of the sweep switching is O. Since the time input to the / E converter 3 is almost the same, the time during which the reception gate 60 does not pass a signal may be set in that time zone. and it is not necessary to set the gate width T _g of the reception gate 60.

Embodiment 3 FIG. 3 is a configuration diagram of an FDM optical fiber sensor system according to a third embodiment of the present invention, a frequency chart of a laser light signal, and a time chart of a transmission gate 70. In FIG. 3A, a light source 1, a sensor array 2, an O / E converter 3, band-pass filters 4-1 and 4-2, and demodulation processors 5-1 and 5-2 correspond to those of the first embodiment. The same operation as that of FIG.

In FIG. 3, reference numeral 70 denotes a transmission gate,
The laser light signal output from the light source 1 is gated with a gate width T _g and a period T _s . Therefore, the signal width T _g and the period T _s
Is input to the sensor array 2. The output signal of the transmission gate 70 also has a frequency characteristic in which no response occurs at a frequency interval of the gate width (1 / T _g ), similarly to the reception gate 60. Therefore, the beat frequency output from each optical fiber sensor is set to 1 such as a × τ ₁ = 1 / T _{g in} the first optical fiber.
/ T _g , the return of the aliasing noise that occurs simultaneously with the beat frequency a × τ ₁ becomes zero at a frequency that is an integral multiple of the beat frequency due to the frequency characteristics. Sensor beat frequency a
It does not affect the signal of × τ ₂ = 2 / T _g . In the sensor array 2, a pulsed laser light signal passing through the sensing fiber 2-3-1 and the reference fiber 2-4-1 interferes. The interfering laser light signal also becomes a pulse signal.

The interfered laser light signal is supplied to an O / E converter 3
, And is converted into a voltage. The converted signal is input to each band pass filter. Since each band-pass filter also serves as an interpolation filter, a signal output in a pulse form from the O / E converter 3 is represented as a continuous signal when passing through each band-pass filter. If the amplitude value is B at this time, for example, a signal passing through the band-pass filter 4-1 is represented by Bcos (2πaτ ₁ t + Φ ₁ (t)). Output current signals [Phi ₁ this signal by performing demodulation processing by the FM detector and the like. This current signal [Phi ₁ is a representation of the physical quantity sensed by the first optical fiber sensor 2-0-1.

Similarly, the second optical fiber sensor 2-0
In -2, the signal passed through the reception gate 60 is set so that the beat frequency becomes a × τ ₂ = (a × τ ₁ ) × 2 [Hz], and the pass band is set at the center frequency a × τ ₂ [Hz]. Is 1 /
T _s is passed through a band pass filter 4-2 [Hz], and demodulates the current signal [Phi ₂ performs processing by FM detection, etc. in the demodulation processor 5-1. Do this with other demodulators,
Measure the physical quantity.

In the third embodiment, since the transmission gate 70 outputs to the sensor array 2 a pulse-like laser light signal in which the laser light signal at the time of the sweep switching is cut off in advance, each sideband due to unnecessary beat components is output. Does not give a noise signal to the signal of the other optical fiber sensor due to the leakage of the optical fiber sensor, the number of optical fiber sensors in one system can be increased, and more multiplexing can be performed.
The number of systems required for measurement can be reduced, which is convenient in terms of equipment and can reduce costs.
Further, in the third embodiment, the transmission gate 70
It is not necessary to set a distance interval and the gate interval T _g of the optical fiber sensor in consideration of the optical path length as the receiving gate 60.

Embodiment 4 FIG. FIG. 4 is a configuration diagram of an FDM optical fiber sensor system according to a fourth embodiment of the present invention, a frequency of a laser light signal, and a time chart of a reception gate 61. In FIG. 4A, the sensor array 2
a, O / E converter 3, band-pass filters 4-1 and 4
-2 and the demodulation processors 5-1 and 5-2 perform the same operations as those denoted by the same reference numerals in FIG. 1a in Fig. 4 denotes a light source, and outputs a laser light signal that is FM modulated sinusoidal period T _s.

[0034] When the optical path difference between the sensing fiber 2-3-1 and the reference fiber 2-4-1 and [Delta] L _1,
The interference output I (t) output from the O / E converter 3 is roughly expressed by the following equation (1) when the DC component is omitted. I (t) = Acos (2πf d τ 1 cos2πf 0 t + Φ) ... (1) where f ₀ and f _d denotes the modulation frequency and the maximum frequency deviation of FM modulation. A is a constant and indicates an amplitude value. τ ₁ represents the propagation delay difference as in the first embodiment, and τ ₁ = (ΔL
₁ / speed of light).

The receiving gate 61 sets the gate width Tg sufficiently smaller than the sine wave cycle 1 / f ₀ (= T _s ), and sets the gate cycle to 1 / f ₀ (or an integral multiple thereof). When the center timing of the gate of the reception gate 61 is adjusted to the zero cross point of the sine wave of the interference light, I (t) passing through the reception gate 61 is limited to a region where the sine wave can be regarded as linear. Equation (2) can be approximated. I (t) = Acos (( 2πf d τ 1) 2πf 0 t + Φ i) ... (2) where (1), it is assumed that represents the time waveform of only the pulse width with (2). Note that Φ _i is a constant indicating the initial phase.

Therefore, the signal passing through the reception gate 61 has a repetition period T _s (= 1 / f ₀ ), a pulse width T _g ,
The beat frequency 2πf _d f ₀ τ ₁ of the beat signal. The signal that has passed through the reception gate 61 is passed through a predetermined frequency band by each band-pass filter, is subjected to interpolation processing, is converted into a continuous signal, and is converted into a current signal by a demodulation processor connected to each band-pass filter. Is demodulated. In this case an integral multiple of the band-pass filter beat frequency _{2πf d f 0 τ 1 [Hz} ] and the center frequency, the passband (1 /
T _s ) [Hz].

In the fourth embodiment, a laser light signal FM-modulated into a sine wave is output from the light source 1a, and only a portion of the sine wave that can be regarded as linear is demodulated to extract a phase change. Since unnecessary sidebands due to unnecessary beat signal components do not occur and do not affect the signals of other optical fiber sensors as noise, the number of optical fiber sensors in one system can be increased to achieve more multiplexing. This makes it possible to reduce the number of systems required for measurement, to make equipment more convenient, and to reduce costs.

The optical path distances of the respective optical fiber sensors of the sensor array 2a are substantially the same, and the interference light at the time of the sweep switching of the laser light signal output from each optical fiber sensor is input to the O / E converter 3. Since the time taken is almost the same, the time during which the reception gate 61 does not pass a signal may be set in that time zone, and there is no need to set the interval between the optical fiber sensors in consideration of the optical path distance difference.

Embodiment 5 FIG. FIG. 5 is a configuration diagram of an FDM optical fiber sensor system according to a fifth embodiment of the present invention, a frequency chart of a laser light signal, and a time chart of a transmission gate 71. In FIG. 5A, the sensor array 2, the O / E converter 3, the band-pass filters 4-1 and 4
-2 and the demodulators 5-1 and 5-2 perform the same operation as that of the third embodiment having the same reference number in FIG. In FIG. 5, reference numeral 1a denotes a light source, which outputs an FM-modulated laser light signal as in FIG. 4 of the fourth embodiment.

The transmission gate 71 sets the gate width T _g to be sufficiently smaller than the period 1 / f ₀ (= T _s ) of the sine wave, and sets the gate interval to 1 / f ₀ (or an integral multiple thereof) to set the center timing of the gate. Is set at the point where the instantaneous frequency of the FM-modulated laser light signal crosses the center frequency, and the sine wave is allowed to pass through a region that can be regarded as linear.

Sensing fiber 2-3-1 of optical fiber sensor 2-0-1 and reference fiber 2-4-1
Assuming that the optical path difference is ΔL ₁ , the interference output I (t) of the O / E converter can be expressed as in the above equation (1) if the DC component is omitted.

Since the sine wave interferes with a portion that can be regarded as linear, the interference output I (t) of the O / E converter 3
Is approximated by the above equation (2). However, (1),
Equation (2) is assumed to represent a time waveform only within the pulse width. The signal output from the O / E converter 3 is a signal having a repetition period T _s (= 1 / f ₀ ), a pulse width of approximately T _g , and a beat frequency of 2πf _d f ₀ τ ₁ .
This signal is passed through a predetermined frequency band by each band-pass filter, is subjected to interpolation processing, is converted into a continuous signal, and a current signal is demodulated by a demodulation processor connected to each band-pass filter. At this time, each band pass filter sets the center frequency to the beat frequency 2πf _d f ₀ τ ₁ [H
z], and the pass band is set to (1 / T _s ) [Hz].

If the amplitude value of the signal at this time is B, for example, the signal passing through the first band-pass filter 4-1 is B
represented by _{cos (2πf d f 0 τ 1} t + Φ 1 (t)). The signal subjected to demodulation processing by the FM detector, and outputs a current signal [Phi _1. This current signal [Phi ₁ is a representation of the physical quantity sensed by the first optical fiber sensor 2-0-1.

Similarly, the second optical fiber sensor 2-0
In -2, the beat frequency of the signal passed through the O / E converter 3 is _{2πf d f 0 τ 2 = (} 2πf d f 0 τ 1) × 2 [H
z], and the center frequency is 2πf _d f ₀ τ ₂
[Hz] is passed through a band pass filter 4-2 passbands 1 / T _s [Hz] at demodulates the current signal [Phi ₂ performs processing by FM detection, etc. in the demodulation processor 5-1. This is also performed by another demodulator to measure the physical quantity.

In the fifth embodiment, a laser light signal FM-modulated sinusoidally is output from the light source 1a, and the transmission gate 71 passes only a portion where the instantaneous frequency of the FM-modulated light can be regarded as linear. Interference, demodulation in each demodulation processor, and phase change are taken out, so that sidebands due to unnecessary beat signal components do not occur, and do not affect other optical fiber sensor signals as noise,
Since the number of optical fiber sensors in one system can be increased to perform more multiplexing, the number of systems required for measurement can be reduced and the cost can be reduced.

In the first, second and fifth embodiments,
The reception gates 60 and 61 are common without being set for each beat frequency. However, the present invention is not limited to this, and may be set individually according to the time delay due to the optical path distance of each optical fiber sensor. Good.

In the first to fifth embodiments, an optical fiber sensor system provided with the reception gate 60 or 61 and the transmission gate 70 or 71 at the same time may be used.

In the first to fifth embodiments, the optical fiber sensors of the sensor arrays 2 and 2a are described in the Mach-Zehnder system. It is also possible to use a Michelson sensor array 2b, and instead of the sensor array 2a, use a Michelson sensor array 2c in which the optical path distances are almost the same as shown in FIG. 6B. . The sensor arrays 2b and 2c are provided with sensing fibers 2-3-1 and 2-3-2, and the reference fibers 2-4-1 and 2-4-2 are provided with a reflector 2-.
7-11, 2-7-21, 2-7-12 or 2-7-2
2, but with a reflector (Faraday Rotator Mirro) attached with a magnetic element.
r) may be used. Further, instead of the Mach-Zehnder method or the Michelson method, a Fabry-Perot sensor array may be used. In the present invention, the reception gates 60 and 61, the transmission gates 70 and 71, and the sensor array 2
And 2a may not be a problem.

In the first to fifth embodiments, the reference fiber is separated from the object to be measured and has a structure in which the propagation time does not change. However, the present invention is not limited to this, and the sensing fiber and the reference The phase change may be caused by the differential operation with the fiber.

In the first embodiment, each optical fiber sensor has a different optical path distance. However, an extra length fiber is used between the input coupler and the output coupler to reduce the optical path distance of each optical fiber. The adjustment of the optical path distance may be performed so as to be almost the same.

In the present invention, an amplification optical amplifier may be connected on the transmission path of the laser light signal through the optical fiber.

[0052]

As described above, according to the present invention, the reception gate cuts and transmits a portion where the frequency of the detection signal is changed in the detection signal obtained by converting the interfering laser light by the light-to-voltage converter. Therefore, a sideband generated from an unnecessary beat component generated in a portion where the frequency changes does not pass, and this sideband leaks into a high frequency component and gives a noise signal to a signal of another optical fiber sensor. However, since the number of optical fiber sensors in one system can be increased and more multiplexing can be performed, the number of systems required for measurement can be reduced, which is convenient in terms of equipment. Costs can be reduced.

Further, according to the present invention, by the transmission gate,
In order to output a pulsed laser beam to the optical fiber sensor from which the laser beam causing unnecessary beat components has been removed in advance, leakage of high-frequency components in each sideband due to unnecessary beat components causes other optical fiber No noise signal is added to the sensor signal, and the number of optical fiber sensors in one system can be increased to perform more multiplexing, so that the number of systems required for measurement can be reduced, and Costs can be reduced. Further, since it is not necessary to use a receiving gate, it is not necessary to set the distance interval and the gate interval of the optical fiber sensor in consideration of the optical path distance.

According to the present invention, a laser beam which is sinusoidally FM-modulated is output from a light source, and only a specific portion of the sinusoidal wave is passed through a reception gate to demodulate the phase. Multiplexing by increasing the number of optical fiber sensors in one system without generating sidebands due to As a result, the number of systems required for the measurement can be reduced, and the cost can be reduced.

Further, according to the present invention, a sinusoidally FM-modulated laser beam is output from the light source, and only a specific portion of the sinusoidal wave passes through the transmission gate to cause interference and demodulate the phase. No sideband is generated due to the beat signal component, and the signal of the other set of optical fibers is not affected as noise, and the number of optical fiber sensors in one system is increased to allow more multiplexing. As a result, the number of systems required for the measurement can be reduced, and the cost can be reduced.

Further, according to the present invention, since the optical path distances of the laser beams passing through the respective optical fibers of the sensor array are substantially the same, the interference light at the time of the sweep switching of the laser beams output from the respective optical fibers is reduced. -The time input to the voltage converter becomes almost the same, and the time during which the reception gate does not pass a signal may be set in that time zone, and the measurement distance interval and reception gate of each optical fiber are considered in consideration of the optical path distance difference. There is no need to set the gate width.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an FDM optical fiber sensor system according to a first embodiment of the present invention, a frequency of a laser light signal, and a time chart of a reception gate 60.

FIG. 2 is a configuration diagram of an FDM optical fiber sensor system according to a second embodiment of the present invention, a frequency of a laser light signal, and a time chart of a reception gate 60;

FIG. 3 is a configuration diagram of an FDM optical fiber sensor system according to a third embodiment of the present invention, a frequency of a laser light signal, and a time chart of a transmission gate 70;

FIG. 4 is a configuration diagram of an FDM optical fiber sensor system according to a fourth embodiment of the present invention, a frequency of a laser light signal, and a time chart of a reception gate 61;

FIG. 5 is a configuration diagram of an FDM optical fiber sensor system according to a fifth embodiment of the present invention, a frequency of a laser light signal, and a time chart of a transmission gate 71.

FIG. 6 is a configuration diagram of a Michelson type sensor array 2b, 2c.

FIG. 7 is a configuration diagram of a conventional FDM optical fiber sensor system and a time chart of the frequency of a laser light signal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 1a Light source 2, 2a Sensor array 3 O / E converter 4-1 and 4-2 Bandpass filter 5-1 and 5-2 Demodulator 60 and 61 Reception gate 70 and 71 Transmission gate

Claims (5)

[Claims] 1. A plurality of sets of a light source for outputting a laser beam in which the frequency of a laser light electric field is linearly frequency-modulated in a sawtooth waveform, and two optical fibers whose optical path lengths change according to a physical quantity to be measured. An optical fiber sensor means in which each set is an integral multiple of the reference delay time difference, and each set has a different delay time difference, and transmits and interferes with the laser light in the optical fiber of each set, A light-voltage conversion unit that square-detects the interfering laser light and converts it into a voltage, and a reception gate that passes through the detection signal obtained by converting the interfering laser light except for a portion where the frequency of the detection signal changes. A plurality of band-pass filters for passing a detection signal in a frequency band whose center frequency is a frequency based on the respective delay time differences among the detection signals passing through the reception gate. And a plurality of phase demodulating means for demodulating each of the detection signals passed through the plurality of band-pass filters and outputting a demodulated signal having a phase signal corresponding to the physical quantity. Division multiplex optical fiber sensor system. 2. A light source for outputting a laser beam in which the frequency of a laser beam electric field is linearly frequency-modulated in a sawtooth waveform, and a portion of the laser beam outputted by the light source, in which the frequency of the laser beam electric field changes linearly. And a plurality of sets of two optical fibers whose optical path lengths change according to the physical quantity to be measured, each set being an integral multiple of a reference delay time difference, and An optical fiber sensor means for causing the laser light to pass through the respective sets of optical fibers and causing interference with the respective sets of optical fibers, and a light-to-voltage conversion for square-detecting the interfered laser light and converting it into a voltage. A plurality of means for passing a detection signal in a frequency band having a center frequency of a frequency based on the delay time difference between the respective sets of the detection signals having passed through the light-to-voltage conversion means. A band-pass filter, and a plurality of mobile demodulation means for demodulating each detection signal passed through the plurality of band-pass filters and outputting a demodulated signal having a phase signal corresponding to the physical quantity. Frequency division multiplexing optical fiber sensor system. 3. A plurality of sets of a light source for outputting a laser beam in which the frequency of a laser light electric field is frequency-modulated in a sine wave shape, and two optical fibers whose optical path lengths change according to a physical quantity to be measured. Optical fiber sensor means for causing the laser light to pass through and interfere with the optical fibers of the respective sets so that each set has an integer multiple of the reference delay time difference, and each set has a different delay time difference; and Light-to-voltage conversion means for square-detecting the converted laser light and converting it to a voltage, and the detection signal having a predetermined width centered on a portion where the instantaneous frequency is substantially constant among the detection signals output from the light-to-voltage conversion means. A reception gate through which the signal passes; and a detection signal in a frequency band having a frequency centered on a frequency based on the delay time difference between the respective sets among the detection signals passing through the reception gate. A plurality of band-pass filters, and a plurality of phase demodulation means for demodulating each detection signal passed through the plurality of band-pass filters and outputting a demodulated signal having a phase signal corresponding to the physical quantity. Characteristic frequency division multiplexing optical fiber sensor system. 4. A light source for outputting a laser beam in which the frequency of a laser light electric field is frequency-modulated into a sine wave shape, and a laser beam output from the light source having a predetermined width centered on a portion where the instantaneous frequency is linear. A transmission gate for passing the laser light, and a plurality of sets of two optical fibers whose optical path lengths change in accordance with the physical quantity to be measured, each set being an integral multiple of a reference delay time difference, and each set being An optical fiber sensor means for causing the laser light to pass through the respective sets of optical fibers and causing interference with the respective sets of optical fibers, and a light-to-voltage conversion for square-detecting the interfered laser light and converting it into a voltage. Means, a plurality of band-pass filters transmitting a detection signal in a frequency band having a frequency based on the delay time difference between the respective sets as a center frequency, and the plurality of band-pass filters. Spent and the respective detection signal demodulated frequency division multiplexing optical fiber sensor system is characterized in that a plurality of phase demodulating means and outputs the demodulated signal with a phase signal corresponding to the physical quantity. 5. The optical fiber sensor device according to claim 1, wherein an optical path length is set such that an optical path distance from each set of said light sources to said light-to-voltage converter is equal. 5. The frequency division multiplexing type optical fiber sensor system according to item 3 or 4.