JP6658256B2 - Gas detection system - Google Patents

Description

  The present invention relates to a gas detection system, and more particularly to a gas detection method and a gas detection device that can compensate for fluctuations in measured gas concentration values due to environmental temperature.

  In recent years, natural gas, which emits less carbon dioxide as a factor of global warming than coal and oil, has attracted attention, and natural gas consumption in each country has been increasing. Accordingly, the importance of a gas detection system for detecting gas leakage in a distribution network of natural gas has been increasing.

Main component of natural gas is methane molecule (CH _4). Semiconductor sensors may be used for detecting methane molecules (hereinafter simply referred to as “methane”). The semiconductor sensor detects a change in resistance value generated when the metal oxide semiconductor comes into contact with the gas to be detected as a gas concentration. However, when a semiconductor sensor is used, it is necessary to heat the electrodes of the sensor, so that the sensor needs to have an explosion-proof structure. In addition, since the life of a semiconductor sensor is generally about several months, maintenance work such as calibration and replacement of the sensor is required. As a result, the gas detection system using the semiconductor sensor has a problem that the operation cost is high in addition to the high system construction cost.

  As an alternative to the method using a semiconductor sensor, a gas detection device using light absorption of gas is known. Patent Documents 1 and 2 disclose gas detection devices capable of measuring gas concentrations at multiple locations. Non-Patent Document 1 describes an optical fiber gas detection system that uses infrared absorption of methane molecules.

  Further, in connection with the present invention, Non-Patent Document 2 describes a wavelength conversion technique for shifting a carrier frequency of an optical signal input to an optical SSB (Single Side Band) modulator by a certain frequency. ing. Non-Patent Document 3 describes actually measured values of the relationship between frequency shift due to Brillouin scattering and temperature.

  In order to monitor leaks from long-length pipelines, such as national and regional trunk lines, and conduits running through plants, a power supply is required for sensors that detect gas from the viewpoint of power supply construction and explosion-proof measures. It is desirable not to do so. The gas detection systems described in Patent Literatures 1 and 2 and Non-Patent Literature 1 realize functions of sensors arranged in various places without power supply.

JP-A-6-148071 JP-A-9-043141

Ichimura et al., “Optical Fiber Gas Detection System”, Hitachi Cable, 25 pp. 23-28 (2006-1) Shimotsu et al., "Broadband Wavelength Conversion Using Optical SSB Modulator", IEICE Electronics Society Conference, C-3-73, Japan (2000) Sakairi et al., “Study on Measurement System for Separating Strain and Temperature Using BOTDR and OTDR”, IEICE Technical Report, OFT2002-57 (2002-11)

  The gas detection system using light absorption has a problem that the intensity of the absorption spectrum of gas molecules changes depending on the environmental temperature. Specifically, if the ambient temperature of the sensor differs by 10 ° C., the peak intensity of the absorption spectrum of methane molecules changes by about 10%. Therefore, in order to accurately measure the gas concentration in the atmosphere, it is necessary to measure the ambient temperature of each sensor and perform temperature compensation of the measured value for each sensor. At this time, it is preferable that information on the ambient temperature of each sensor can also be obtained without power supply so as not to impair the characteristics of the gas detection system that power is not supplied to the sensors.

  An optical fiber temperature sensor is known as a method of acquiring temperature information of a remote place without power supply. By using an optical fiber temperature sensor, the stress and temperature at various points in the optical fiber can be measured by measuring the frequency change and intensity change of the backscattered light generated by Brillouin scattering and Raman scattering generated in the optical fiber. Can be measured.

  In the technique described in Non-Patent Document 1, an absorption spectrum near a wavelength of 1650 nm is used to measure the concentration of methane gas in the atmosphere. The frequency shift of Brillouin scattering is about 10 GHz, whereas the frequency shift of Raman scattering is about 13 THz. That is, the wavelength band of the backscattered light due to the Raman scattering greatly deviates from the transmittable wavelength band of a general communication optical fiber. For this reason, Brillouin scattering is often used for optical fiber temperature sensors.

  FIG. 11 is a block diagram of a temperature measuring device 1210 realized by an OTDR (Brillouin Optical Time Domain Reflectometer: BOTDR) using Brillouin scattering. The temperature measuring device 1210 generates a pulsed probe light by a light source (LDgas) 1211 such as a laser diode, a driver (LDD) 1216 and a light intensity modulator (Pulse) 1212. The temperature measuring device 1210 sends the probe light to the optical fiber transmission line 1219 via the optical circulator 1213. At each point on the optical fiber transmission line 1219, Rayleigh backscattered light and Brillouin backscattered light are generated. The wavelength of the Rayleigh backscattered light is the same as the wavelength of the probe light, and the Brillouin backscattered light appears at a wavelength about 10 GHz away from the probe light due to the Brillouin frequency shift.

  The temperature measurement device 1210 measures the frequency shift amount of the Brillouin backscattered light by using a photodetector (PDgas) 1214 and a signal processing unit (Sig. Proc.) 1215. Then, the temperature at each point of the optical fiber transmission line 1219 can be obtained from the frequency shift amount. The frequency shift amount is obtained by heterodyne detection between the Brillouin backscattered light and the light source 1211. The frequency of Brillouin scattering also changes due to the stress applied to the optical fiber, but by laying the optical fiber with a degree of deflection that does not affect Brillouin scattering, only the temperature information can be obtained from the frequency shift amount. Obtainable.

  FIG. 12 is a diagram showing a simplified configuration of a gas detection system 901 obtained by combining the gas detection system described in Patent Document 1 and the temperature measuring device using BOTDR shown in FIG. The gas detection system 901 includes a control device 1220, a temperature measurement device 1230, a wavelength multiplexing / demultiplexing filter (WDM filter) 1250, and a sensor network 1260.

  In the gas detection system 901, the wavelength of the light source 1211 is modulated within a range including the absorption wavelength of the gas. In Patent Document 1, wavelength modulation is performed by changing an AC component of a driving current of a light source. In Non-Patent Document 1, wavelength modulation is performed by changing the DC component of the drive current of the light source. Such wavelength modulation broadens the spectrum of the light source.

  The wavelength-modulated light is transmitted through an optical circulator 1213 and a wavelength multiplexing / demultiplexing filter 1250 to an optical fiber transmission line 1270 to which a sensor network 1260 is connected. The sensor network 1260 includes a plurality of optical couplers and a gas sensor. The optical signal transmitted through the gas sensor is turned back to the wavelength multiplexing / demultiplexing filter 1250. The wavelength multiplexing / demultiplexing filter 1250 outputs, to the control device 1220, light of the same wavelength band as the light source 1211 among the optical signals received from the optical fiber transmission line 1270. The control device 1220 uses the photodetector 1217 and the signal processing unit 1218 to obtain the gas concentration detected by each sensor from the absorption amount of the wavelength of the light source.

  The wavelength multiplexing / demultiplexing filter 1250 outputs, to the temperature measuring device 1230, an optical signal in the wavelength band of the Brillouin backscattered light whose wavelength has been shifted. The temperature measuring device 1230 uses the photodetector 1214 and the signal processing unit 1215 to determine the temperature detected near each sensor from the Brillouin shift amount of the wavelength of the light source. By using the temperature obtained by the signal processing unit 1215, the temperature characteristics of the gas concentration obtained by the signal processing unit 1218 can be compensated.

  As described above, the gas detection system 901 can measure the temperature of the gas concentration monitoring point in a remote place without power supply, and can compensate the temperature characteristic of the intensity of the absorption spectrum of the gas molecule. However, the gas detection system 901 has the following problems.

The problem of the gas detection system 901 arises by using an optical signal (wavelength λ _gas ) for measuring the absorption spectrum of gas molecules also for temperature measurement. FIG. 13 is a diagram illustrating a spectrum of an optical signal of each unit of the gas detection system 901. The vertical axis in FIG. 13 indicates the intensity of the optical signal, and the horizontal axis indicates the wavelength.

The wavelengths of the transmitted optical signals are indicated by optical signals 31 and 32 in FIG. The wavelength of the light source 1211 before the wavelength modulation is λ _gas (optical signal 31), and the output of the controller 1220 is expanded to include the absorption wavelength of the gas (optical signal 32) by controlling the drive signal of the light source 1211. The optical signal 32 is an output signal transmitted to the sensor network 1260 as probe light. Of the return light from the sensor network 1260, the optical signal and the Rayleigh backscattered light reflected by the sensor of the optical signal 32 are shown in the optical signal 33, and the Brillouin backscattered light of the optical signal 32 is shown in the optical signals 34 and 35. It is. The optical signal returned by the optical signal sensor 32 is used for detecting the gas concentration.

  Since the spectrum of the optical signal 32 is broadened, the wavelength of the optical signal 33 is close to the wavelength of the Brillouin backscattered light (optical signals 34 and 35). Therefore, high performance is required for the wavelength multiplexing / demultiplexing filter 1250 in order to separate the optical signal 33 from the Brillouin backscattered light. Further, when the spectrum of the optical signal 32 is further broadened, it may be impossible to separate the Rayleigh backscattered light and the Brillouin backscattered light. That is, the gas detection system 901 has a problem that it is difficult to accurately detect the temperature information by separating only the Brillouin backscattered light from the return light from the sensor network 1260.

The second problem is that the temperature detection is performed using an optical signal (wavelength _λth ) different from the optical signal (wavelength _λgas ) used in the gas detection system in order to avoid the first problem. Occurs. FIG. 14 is a diagram showing a simplified configuration of the gas detection system 902 in this case. FIG. 15 is a diagram illustrating a spectrum of an optical signal of each unit of the gas detection system 902.

The gas detection system 902 shown in FIG. 14 uses a light source 1211 (wavelength λ _gas ) and a light source 1241 (wavelength λ _th ) having different wavelengths for measuring the gas concentration and measuring the temperature around the sensor. As shown in FIG. 15C, the spectrum of the Brillouin backscattered light 44 from the sensor network 1260 is sufficiently separated from the optical signal 42 that is the Rayleigh backscattered light of the optical signal 41. Therefore, since the wavelength multiplexing / demultiplexing filter 1250 can relatively easily separate the Brillouin backscattered light 44, the temperature measuring device 1240 determines the temperature of each part of the sensor network 1260 based on the Brillouin backscattered light 44 of the optical signal 41. Can be measured.

  However, the gas detection system 902 requires two light sources (1211 and 1241), two light source drivers (1216 and 1246), two light intensity modulators (1212 and 1242), and two light circulators (1213 and 1243). As a result, the gas detection system 902 has a problem of high cost.

  Further problems of the technology described in Patent Documents 1 and 2 will be described below. The multipoint gas concentration measurement device described in Patent Literature 1 includes a configuration in which one optical fiber is branched by a plurality of branching coupling units. In the device described in Patent Literature 1, a pulsed optical signal is used so that reflected lights from a plurality of measurement points do not overlap during reception. However, the device described in Patent Document 1 has a problem that the distance between measurement points cannot be reduced. The reason is as follows. The device described in Patent Literature 1 changes a drive current or a temperature of a light source (laser) to perform wavelength modulation. In order to cover the absorption spectrum of methane, it is necessary to change the wavelength by about 5 GHz. It takes several μs (microseconds) to obtain this wavelength change by changing the drive current of the laser. As a result, the pulse light transmitted to the gas cell has a width of several μs or more. However, since this width corresponds to a propagation distance of several km on the optical fiber, the device described in Patent Document 1 requires a distance of several km between each of the measurement points so that reflected light does not overlap during reception. It is necessary to separate more. That is, the device described in Patent Document 1 cannot realize a multipoint gas concentration monitoring system with high distance resolution.

  In the device described in Patent Literature 1, the distance between the measurement points can be increased by arranging the optical fibers by spooling them between the optical branching and joining means. However, in this case, the distance over which the gas concentration can be monitored is greatly limited by the propagation loss caused by the spooled optical fiber. For example, the propagation loss of a single mode fiber (Single Mode Fiber, SMF) at 1.65 μm where the absorption spectrum of a methane molecule exists is about 0.4 dB / km. Therefore, if a 1 km spool optical fiber is arranged between each measurement point, a system having 25 measurement points causes an excessive loss of up to 20 dB in a round trip. As a result, the gas detection accuracy is significantly degraded, and the extension of the propagation distance and the increase in the number of measurement points are greatly restricted.

  The gas detection device described in Patent Literature 2 requires a light source that generates high-output and broad-spectrum pulsed light in order to measure gas absorption using an optical signal having a wide spectrum width. However, when pulsed light with a wide spectrum propagates through an optical fiber, the pulse width is widened due to chromatic dispersion, and when the return light pulses from multiple measurement points return to the gas detection device, they overlap temporally, and the gas concentration is measured. Cannot be performed. Further, the gas detection device described in Patent Literature 2 includes a wavelength selective separator and a pulsed optical delay device on the receiving side in order to separate a wavelength component that absorbs gas molecules from a wavelength component that does not. As a result, the optical circuit on the receiving side becomes complicated. Thus, the gas detection device described in Patent Document 2 has a problem that the configuration is complicated and the cost is high.

(Object of the invention)
An object of the present invention is to realize a gas detection system capable of accurately measuring both gas concentration and temperature using a single light source and compensating for temperature dependency during gas concentration measurement with a simple configuration.

The gas detection system according to the present invention includes a first optical signal that has been subjected to the first modulation in a first time zone with respect to the wavelength of the pulse light, and a second optical zone in which the first modulation has been performed with respect to the wavelength of the pulse light. Transmitting means for generating a second optical signal subjected to the second modulation by an optical wavelength modulation means, and outputting the first optical signal and the second optical signal to an optical fiber transmission line;
A plurality of sensor heads for transmitting the first optical signal in the atmosphere and outputting the first optical signal propagated in the atmosphere as a third optical signal;
A third optical signal is received and converted into a first electrical signal, and a predetermined type of gas contained in the atmosphere is detected for each sensor head based on a temporal change in the amplitude of the first electrical signal. And a fourth optical signal, which is scattered light of the second optical signal, is received and converted into a second electrical signal, and the sensor head calculated based on the second electrical signal is transmitted to the sensor head. Receiving means for compensating a gas detection result calculated from the first electric signal based on the corresponding temperature;
The optical fiber transmission line is branched, the transmitting unit and the sensor head are connected via the branched optical fiber transmission line, and the sensor head and the receiving unit are connected via the branched optical fiber transmission line. Branching means;
Is provided.

The gas detection method according to the present invention generates a first optical signal that is subjected to a first modulation in a first time zone with respect to a wavelength of a pulse light,
Generating a second optical signal that is subjected to a second modulation in a second time zone with respect to the wavelength of the pulse light;
Outputting the first optical signal and the second optical signal to an optical fiber transmission line;
In the sensor head, the first optical signal is propagated in the atmosphere, the first optical signal propagated in the atmosphere is received as a third optical signal, converted into a first electrical signal, and the first electrical signal is transmitted. A predetermined type of gas contained in the atmosphere is detected for each sensor head based on a temporal change in amplitude of the sensor head, and a detection result of the gas is generated,
A fourth light signal, which is scattered light of the second light signal, is received and converted into a second electric signal, and based on the temperature corresponding to the sensor head calculated based on the second electric signal, Compensating the gas detection result calculated from the electric signal of (1),
It is characterized by the following.

The gas detection device according to the present invention includes a first optical signal that has been subjected to the first modulation in a first time zone with respect to the wavelength of the pulse light, and a second optical zone with respect to the wavelength of the pulse light. Transmitting means for generating a second optical signal subjected to the second modulation by an optical wavelength modulation means, and outputting the first optical signal and the second optical signal to an optical fiber transmission line;
A first optical signal is propagated in the atmosphere, and the third optical signal is received from a sensor head that outputs the first optical signal propagated in the atmosphere as a third optical signal, and is converted into a first electrical signal. A predetermined type of gas contained in the atmosphere is detected for each sensor head based on a temporal change in the amplitude of the first electric signal to generate a gas detection result, and the scattered light of the second optical signal is generated. Is converted into a second electric signal by receiving the fourth optical signal, and the gas calculated from the first electric signal based on the temperature corresponding to the sensor head calculated based on the second electric signal. Receiving means for compensating the detection result of
Is provided.

  ADVANTAGE OF THE INVENTION The gas detection system, the gas detection device, and the gas detection method of this invention make it possible to perform gas concentration measurement accurately and at low cost with a simple configuration.

FIG. 1 is a block diagram illustrating a configuration example of a gas detection system 1 according to a first embodiment. FIG. 3 is a block diagram illustrating a configuration example of an optical wavelength modulator 114. FIG. 3 is a diagram illustrating an example of generating an optical signal in a control device 110. FIG. 3 is a diagram illustrating an example of a spectrum of an optical signal of each unit of the gas detection system 1. FIG. 4 is a diagram conceptually illustrating a waveform example of an optical signal received by a photodetector 116. FIG. 4 is a diagram conceptually illustrating a waveform example of an optical signal received by a photodetector 116. FIG. 3 is a diagram conceptually illustrating a waveform example of an optical signal received by a photodetector 211 of a temperature measuring device 210. It is a block diagram showing an example of composition of gas detection system 2 of a 2nd embodiment. It is a block diagram showing the example of composition of gas sensing device 800 of a 3rd embodiment. 6 is a flowchart illustrating an example of an operation procedure of the gas detection device 800. It is a block diagram of temperature measuring device 1210 realized by BOTDR. FIG. 2 is a diagram schematically illustrating a configuration of a gas detection system 901. FIG. 4 is a diagram illustrating a spectrum of an optical signal of each unit of the gas detection system 901. FIG. 2 is a diagram showing a simplified configuration of a gas detection system 902. FIG. 4 is a diagram illustrating a spectrum of an optical signal of each unit of the gas detection system 902.

(First embodiment)
A first embodiment of the present invention will be described. FIG. 1 is a block diagram illustrating a configuration example of a gas detection system 1 according to the first embodiment of the present invention. The gas detection system 1 includes a control device 110, a temperature measurement device 210, a wavelength multiplexing / demultiplexing filter 220, optical fibers 120-1 to 120-n, optical couplers 121-1 to 121-m, and sensor heads 130-1 to 130-. n. n is an integer of 2 or more, and m = n-1.

  Hereinafter, the optical fibers 120-1 to 120-n are collectively referred to as an optical fiber 120. Similarly, the optical couplers 121-1 to 121-m and the sensor heads 130-1 to 130-n are collectively referred to as the optical coupler 121 and the sensor head 130.

  The control device 110 and the sensor head 130 are connected by an optical fiber 120 that is a transmission path. The control device 110 includes a laser diode (LD) 111, a laser diode driver (LDD) 112, a light intensity modulator (Pulse) 113, and a light wavelength modulator (λ mod) 114. The control device 110 further includes an optical circulator 115, a photodetector (Photo Detector, PD) 116, a signal processing unit (Sig. Proc.) 117, and a time control unit (Time) 118.

  The temperature measuring device 210 includes a photodetector 211 and a signal processing unit 212. The control device 110 and the temperature measurement device 210 are connected to the optical fiber 120-1 via a wavelength multiplexing / demultiplexing filter (WDM filter) 220.

  On the optical fiber 120, optical couplers 121-1 to 121-m are arranged in series. One of the branches of the p-th (1 ≦ p ≦ m−1) optical coupler 121-p is connected to the sensor head 130-p. The other branch of the optical coupler 121-p is connected to the optical fiber 120-q (q = p + 1). For example, one branch of the optical coupler 121-1 is connected to the sensor head 130-1. The other branch of the optical coupler 121-1 is connected to the optical fiber 120-2. However, the optical coupler 121-m farthest from the control device 110 is connected to the sensor head 130-m and the optical fiber 120-n. The optical fiber 120-n is connected to the sensor head 130-n.

  The sensor head 130 is a sensor used to measure the concentration of methane contained in the surrounding atmosphere. The sensor head 130 includes a lens 131 and a mirror 132. Since the lens 131 and the mirror 132 are common to the sensor heads 130-1 to 130-n, they are simply described as the lens 131 and the mirror 132 in FIG. The space between the lens 131 and the mirror 132 is exposed to the atmosphere around the sensor head 130.

  FIG. 2 is a block diagram illustrating a configuration example of the optical wavelength modulator 114. The variable oscillator (OSC) 201 is an electric signal oscillator whose output frequency is variable. The electric signal output from the variable oscillator 201 is branched into four by a coupler (CPL) 202. The phase of each branched signal is adjusted by phase shifters (PS) 203-1 to 203-4. The four signals output from the phase shifters 203-1 to 203-4 are input to four ports of an optical SSB (single side band) modulator 204, respectively. The variable oscillator 201 and the phase shifter 203 are controlled by a control unit (CONT) 205. Pulse light is input to the OPTin of the optical SSB modulator 204 from the light intensity modulator 113. The optical SSB modulator 204 wavelength-modulates the pulse light and outputs the modulated light from OPTout. OPTout is connected to optical circulator 115.

(Operation of gas detection system 1)
The drive current and temperature of the laser diode 111 are controlled by the laser diode driver 112. The laser diode 111 outputs continuous light having a wavelength of 1.65 μm. This wavelength is known as a wavelength at which absorption by methane is large. The outputted continuous light having a wavelength of 1.65 μm is pulse-modulated by the light intensity modulator 113 to become pulse light at a predetermined interval. The pulse light is wavelength-modulated by the optical wavelength modulator 114.

  The optical wavelength modulator 114 performs different wavelength modulation on the pulse light depending on the time zone. By the wavelength modulation, an optical signal subjected to wavelength modulation for use in gas concentration measurement and an optical signal subjected to wavelength modulation for use in temperature measurement are generated in a time division manner. Details of each wavelength modulation will be described later.

  The wavelength-modulated pulse light is transmitted to the optical fiber 120-1 via the optical circulator 115 and the wavelength multiplexing / demultiplexing filter 220. The optical signal propagating through the optical fiber 120 is split into two every time it passes through the optical coupler 121. One of the two branched optical signals is input to the sensor head 130, and the other is continuously transmitted by the optical fiber 120.

  The n sensor heads 130 are distributed and installed at locations where detection of gas leakage is required. The sensor head 130 emits an optical signal input from the optical coupler 121 from the end face of the optical fiber, and converts the emitted optical signal into a parallel light by the lens 131. The parallel light beam propagates in the atmosphere where the sensor head 130 is installed, and is reflected by the mirror 132 toward the lens 131. The lens 131 focuses the reflected parallel light beam on the optical fiber that has emitted the optical signal. The optical signal collected on the optical fiber propagates in the opposite direction through the optical coupler 121 and the optical fiber 120 and returns to the wavelength multiplexing / demultiplexing filter 220. The optical signal propagating in the opposite direction through the optical fiber 120 is split by the wavelength multiplexing / demultiplexing filter 220 according to the wavelength. The wavelength multiplexing / demultiplexing filter 220 outputs an optical signal that has been subjected to wavelength modulation for use in gas concentration measurement to the control device 110. In this way, the optical signal transmitted from the control device 110 is turned back by the sensor head 130 and received by the control device 110.

  The optical circulator 115 sends the optical signal output from the optical wavelength modulator 114 to the optical fiber 120-1 and guides the optical signal received from the optical fiber 120-1 to the photodetector 116. The photodetector 116 converts the received optical signal into an electric signal. The signal processing unit 117 obtains the concentration of methane contained in the air at each point where the sensor head 130 is installed by processing the electric signal output from the photodetector 116.

  On the other hand, the wavelength-modulated optical signal used for temperature measurement is guided from the wavelength multiplexing / demultiplexing filter 220 to the temperature measuring device 210. The optical signal received by the temperature measuring device 210 is converted into an electric signal by the photodetector 211. The signal processing unit 212 calculates an ambient temperature of each of the sensor heads 130-1 to 130-n by processing the electric signal output from the photodetector 211. The obtained ambient temperature is notified from the signal processing unit 212 to the signal processing unit 117. The signal processing unit 117 corrects the determined methane concentration for each measurement value in the sensor heads 130-1 to 130-n based on the ambient temperature notified from the signal processing unit 212.

  FIG. 3 is a diagram illustrating an example of generating an optical signal in the control device 110. (1) to (3) of FIG. 3 show the time change of the intensity of the optical signal with the light intensity on the vertical axis and the time on the horizontal axis. (4) to (6) of FIG. 3 show the time change of the wavelength of the optical signal generated by the control device 110 with the wavelength of the optical signal as the vertical axis and the time as the horizontal axis. Light intensity, wavelength, and time are all arbitrary. In (5) and (6) of FIG. 3, the wavelength at the time when there is no optical signal is not shown.

The light intensity and the wavelength λ ₀ of the optical signal immediately after being output from the laser diode 111 are both constant ((1) and (4) in FIG. 3). The light intensity modulator 113 modulates an optical signal output from the laser diode 111 to generate pulse light having a length T1 and an interval T2. The period T of the pulse light is T1 + T2. The light intensity modulator 113 modulates the light intensity of the optical signal into a pulse, but the wavelength λ _{0 of the} optical signal remains constant ((2) and (5) in FIG. 3).

The optical wavelength modulator 114 modulates the optical wavelength of the pulse light output from the optical intensity modulator 113. In the present embodiment, the optical wavelength modulator 114 sweeps the wavelength in the longer wavelength direction (λ ₀ → λ ₁ ) within one pulse in the time zone 1, and converts the obtained optical signal into the sensor head 130-1. It is used for the measurement of the peripheral gas concentration in the range from 130 to n. In the time period 2, the optical wavelength modulator 114 shifts the wavelength of the pulsed light in the short wavelength direction and fixed to the wavelength lambda _2, the resulting ambient temperature of the optical signal sensor heads 130-1 to 130-n Used for measurement ((6) in FIG. 3). In the time zone 1, the wavelength of the pulse light is modulated so as to be unique with respect to the elapsed time from emission of one pulse light to extinction.

  The time control unit 118 manages the modulation operation of the optical wavelength modulator 114 for each of time zone 1 and time zone 2 so as to obtain the wavelength modulation waveform of (6) in FIG. FIG. 3 shows an example in which three pulse lights exist in time zone 1 and two pulse lights exist in time zone 2. However, the number of pulse lights included in each time zone is not limited to the description in FIG.

  FIG. 4 is a diagram illustrating an example of a spectrum of an optical signal of each unit of the gas detection system 1. The vertical axis indicates the intensity of the optical signal, and the horizontal axis indicates the wavelength. The wavelength of the laser diode 111 is λ0 (optical signal 21). The output of the optical wavelength modulator 114, that is, the wavelength of the optical signal output from the control device 110 to the optical fiber 120-1, is between λ0 and λ1 in the time zone 1 as shown in (6) of FIG. Yes (optical signal 22), λ2 in time zone 2 (optical signal 23).

  The spectrum of the return light signal from the sensor head 130 is shown as light signals 24-28 in FIG. Optical signals 24 and 25 are the reflected light and Rayleigh backscattered light of optical signals 22 and 23 from sensor head 130, respectively. Optical signals 26 and 27 are Brillouin backscattered light of optical signal 22. The optical signal 28 is Brillouin backscattered light (anti-Stokes light) of the optical signal 23. The spectrum of the optical signal 27 may overlap with the spectrum of the Brillouin backscattered light (Stokes light) of the optical signal 23 in some cases.

  Since the wavelength of the optical signal 28 is sufficiently far from the wavelength of the adjacent optical signal 25, the wavelength multiplexing / demultiplexing filter 220 easily separates only the Brillouin scattered light (optical signal 28) to the temperature measuring device 210. Can output.

  The wavelength modulation of the pulse light by the optical wavelength modulator 114 may be performed with reference to a wavelength conversion technique described in Non-Patent Document 2. According to the wavelength conversion technique described in Non-Patent Document 1, the optical SSB modulator 204 shifts the carrier frequency of an input optical signal by a constant frequency by a sine wave of a constant frequency output from an oscillator.

  However, since simple wavelength conversion can be performed only by simply applying the method of Non-Patent Document 2, in the optical wavelength modulator 114 of the present embodiment, the variable oscillator 201 is used to perform wavelength sweep. The control unit 205 changes the output frequency of the variable oscillator 201 in accordance with the time zones 1 and 2, the pulse light period T, and the light emission period T1. As a result, in the time zone 1, a modulated waveform whose wavelength is swept from λ0 to λ1 within the light emission period T1 of the pulse light as shown in (6) of FIG. 3 is obtained. Since the wavelength sweep is not performed in the time zone 2, the output frequency of the variable oscillator 201 is controlled so that the output wavelength is constant at λ2. The control unit 205 may further control the phase shifter 203 so that pulsed light having desired characteristics is obtained.

  Instead of the variable oscillator 201, an arbitrary waveform generator (Arbitrary Waveform Generator, AWG) may be used. For example, by using an AWG of 10 G (giga) samples / second and increasing the frequency by 0.1 GHz every 10 sampling points, it is possible to perform a frequency sweep of 5.0 GHz within a time of 50 ns (nano second). it can. Since the absorption spectrum width of methane is about 3.0 GHz, a frequency sweep that can sufficiently cover this absorption spectrum is realized in a short time. Further, since the pulse width of 50 ns corresponds to a fiber length of about 10 m, even if the sensor heads are arranged at relatively short intervals of 10 m, the return light from each sensor head is temporally distinguished. In other words, if the distance between the installation points of the sensor heads is about 10 m apart, gas can be detected at each point without being affected by signals from other sensor heads.

  FIGS. 5 and 6 are diagrams conceptually illustrating waveform examples of the optical signal received by the photodetector 116. FIG. FIG. 5 shows an example in which there is no gas leakage at any point where the sensor head 130 is arranged.

  FIGS. 5 and 6 show that an optical signal including a plurality of peaks is received from the sensor head 130 for one pulse included in the optical signal. The position of each peak on the time axis is determined by the round trip time of the optical signal, that is, the distance between the control device 110 and the sensor head 130 of the optical signal. In the present embodiment, each of the sensor heads 130 is arranged at regular intervals and at different distances from the control device 110. For this reason, the peaks in FIGS. 5 and 6 are also equally spaced.

  The first peak (A0) shown in FIG. 5 indicates that the optical signal transmitted from the optical wavelength modulator 114 is detected by the photodetector 116 due to the imperfect directivity of the optical circulator 115. It occurs because it is received directly. The second and subsequent peaks (A1 to An) are peaks corresponding to the pulsed light returned from the sensor heads 130-1 to 130-n, respectively. The correspondence between the received peaks A1 to An and the sensor heads 130-1 to 130-n is known by previously connecting the sensor heads 130 one by one and measuring the timing at which the corresponding peaks A1 to An occur. be able to. The width of the peak is equal to the pulse light emission period T1, and the interval between the peaks is determined by the difference in response time of the optical signal from the sensor head 130 in the control device 110. Further, the period T of the pulse light is set longer than the time from the peak A0 to the peak An.

  In FIGS. 5 and 6, the dotted line and the curve indicating the period without pulsed light as “Rayleigh backscattering” show the intensity of the received light due to Rayleigh backscattering of the optical fiber. As the distance from the control device 110 to the sensor head increases, the intensity of Rayleigh backscattering decreases due to the transmission loss of the optical fiber 120 and the branch loss of the optical coupler 121. When there is no gas leakage at all points where the sensor heads 130 are installed, as shown in FIG. 5, the peaks of the pulse light turned back from the sensor heads 130 each show a gentle intensity change. The temporal change in signal intensity due to Rayleigh backscattering shown in FIGS. 5 and 6 is an example illustrating the concept, and the intensity of Rayleigh backscattering differs depending on the number of optical couplers 121 and the optical characteristics of optical fiber 120.

  On the other hand, FIG. 6 shows an example in which the methane gas concentration in the atmosphere is high as a result of gas leakage at the point where the i-th (1 ≦ i ≦ n) sensor head is installed. In this case, unlike FIG. 5, a dip due to the absorption of the optical signal by the methane gas is observed at the peak of the return pulse light (Ai) from the i-th sensor head. By detecting the amount of the dip in the photodetector 116 and the signal processing unit 117, the concentration of methane gas around the i-th sensor head can be known. The photodetector 116 outputs an electric signal having an amplitude proportional to the light intensity to the signal processing unit 117. The signal processing unit 117 monitors a temporal intensity change of the electric signal at the peak of the pulse light for each peak, and detects a dip due to gas absorption.

  The following is an example of the operation procedure of the signal processing unit 117. The signal processing unit 117 detects the depth of the dip of the i-th peak (that is, the amplitude change). When the change in amplitude is larger than the predetermined threshold, it is determined that gas is leaking around the sensor head 130-i, and an alarm is output to the outside of the control device 110. Alternatively, the signal processing unit 117 calculates the gas concentration around the sensor head 130-i based on the dip depth of the i-th peak, and outputs the calculated gas concentration to the outside of the control device 110. In general, the higher the gas concentration, the greater the light absorption by the gas and the deeper the dip. Therefore, by measuring the relationship between the gas concentration and the dip depth in advance, the gas concentration can be determined from the dip depth.

  FIG. 7 is a diagram conceptually showing a waveform example of the optical signal received by the photodetector 211 of the temperature measuring device 210 in correspondence with the waveform example of the optical signal shown in FIG. FIG. 7A illustrates an example of a signal waveform observed by the photodetector 116. FIG. 7A is displayed side by side on a common time axis to explain an example of the signal waveform of the temperature measurement receiver 122 shown in FIG. The photodetector 211 performs heterodyne detection using the optical signal (the optical signal 24 in FIG. 2) separated by the wavelength multiplexing / demultiplexing filter 220 and the output of the laser diode 111. Therefore, information corresponding to the frequency shift of the optical signal 24 can be obtained from the output of the photodetector 211.

  In (1) of FIG. 7, the Brillouin frequency shift is large in the time domain of the position described as “the return pulse from the i-th sensor head”. That is, it is understood that the temperature near the i-th sensor head is high. An actual measured value of the relationship between the Brillouin frequency shift and the temperature is disclosed in Non-Patent Document 3, for example. Therefore, the temperature around the sensor head can be calculated from the measured value of the frequency shift, and the measured value of the gas concentration sensor can be corrected.

(Effect of First Embodiment)
The gas detection system 1 according to the first embodiment has the following effects.

  The first effect is that the measurement accuracy of the gas concentration can be improved while maintaining the feature of no power supply. The reason is that the gas detection system 1 can measure the ambient temperature in each sensor unit by temperature sensing using an optical fiber.

  A second effect is that the cost for improving the measurement accuracy of the gas detection system can be reduced. The reason is that the wavelength of the optical signal output from one light source is modulated differently for each time zone, and the light source and peripheral circuits are changed by using optical signals of different wavelengths for gas detection and temperature measurement. Gas concentration measurement and temperature measurement can be shared. By using optical signals of different wavelengths for gas detection and temperature measurement, Brillouin backscattered light can be separated at low cost.

  The gas detection system 1 also has the following effects. That is, the gas detection system 1 can easily and inexpensively perform gas detection at multiple points. The first reason is that the wavelength of the output light of the single-wavelength light source is changed using the optical wavelength modulator 114, so that a light source that generates high-output and broad-spectrum pulse light is not required. It is. The second reason is that the folded optical signal is processed only by the photodetector 116 and the signal processing unit 117, so that a complicated optical circuit is not required on the receiving side.

  Furthermore, the gas detection system 1 of the first embodiment can realize a gas detection system with high distance resolution. The reason is that the wavelength of the short pulse output from the single-wavelength light source is changed using the optical wavelength modulator 114. With such a configuration, the pulse width of the optical signal can be reduced as compared with the case where pulsed light having a wide spectrum is used, and the pulse width is shorter than when wavelength modulation is performed by the laser drive current or temperature. , A desired wavelength change can be obtained. As a result, even when the distance between the sensor heads 130 is small, it is possible to avoid returning light pulses from a plurality of measurement points to overlap in time in the control device 110, and to obtain a high distance resolution. The gas detection system 1 according to the first embodiment does not need to dispose an optical fiber spool on the optical fiber 120 in order to obtain the above effects.

  Further, the gas detection system 1 of the first embodiment can reduce the operation cost of the gas detection system. The reason is that the gas detection system 1 can detect gas at many points by inserting an optical coupler into one fiber as compared with the case where an optical fiber is laid from the control device 110 for each sensor head. It is. The configuration in which the optical coupler is inserted into one fiber facilitates the construction and maintenance of the system, and also facilitates the introduction of the gas detection system into an area where the existing optical fiber network has few empty cores.

(Modification of First Embodiment)
Hereinafter, a modified example that provides the same effect as the gas detection system 1 according to the first embodiment will be described.

  In the first embodiment, an optical SSB modulator is used as an optical wavelength modulator. However, wavelength modulation may be realized by using an IQ modulator (In-phase / Quadrature modulator) used in a large-capacity optical communication technology instead of the optical SSB modulator. Wavelength modulation can also be realized by using a large-amplitude modulator driver and changing the applied voltage of an optical phase modulator (optical phase modulator) in the time direction.

  Further, an optical amplifier may be inserted between one or both of the laser diode 111 and the optical circulator 115 and between the optical circulator 115 and the photodetector 116. By using the optical amplifier, the signal-to-noise ratio of the optical signal received from the sensor head 130 can be improved.

  Further, the sensor head 130 according to the first embodiment reflects the optical signal once using the mirror 132 when spatially propagating the optical signal. However, the propagation path of the optical signal in space may be lengthened by reflecting the optical signal a plurality of times using a plurality of mirrors. By using the sensor head having such a configuration, absorption of an optical signal by a gas is increased, and a gas with a lower concentration can be detected.

  FIG. 3 shows an example in which the wavelength of the optical signal changes linearly within each pulse. However, the gas concentration may be calculated by wavelength modulation spectroscopy (WMS) by superimposing a sine wave on the change in wavelength. By using the WMS method, it is possible to measure the gas concentration with higher sensitivity. At this time, the linear wavelength modulation and the sinusoidal wavelength modulation may be performed by separate optical wavelength modulators.

  Non-Patent Document 2 shows that higher-order sidebands are generated by wavelength conversion. In order to suppress such higher-order sidebands, an optical band-pass filter may be arranged downstream of the optical wavelength modulator 114. Noise is suppressed by adding an optical bandpass filter that removes higher-order sidebands, so that more accurate measurement is possible.

  Further, an optical bandpass filter may be provided between the wavelength multiplexing / demultiplexing filter 220 and the sensor head 130. Brillouin scattering in the optical fiber 120 occurs not only at the rear but also at the front. When the scattered light propagating forward is reflected by the sensor head 130 and returns to the temperature measuring device 210, accurate temperature measurement becomes difficult. Therefore, an optical bandpass filter having a wavelength characteristic for removing forward scattered light may be used.

  In the first embodiment, the optical wavelength modulator 114 modulates the wavelength of the optical signal to the longer wavelength side during the time zone for measuring the gas concentration (time zone 1), and modulates the light in the time zone for the temperature measurement (time zone 2). The example in which the wavelength of the signal is modulated to the short wavelength side has been described. However, conversely, the wavelength of the optical signal is modulated to the short and long wavelength side in the time zone for measuring the gas concentration (time zone 1), and the wavelength of the optical signal is shifted to the long wavelength side in the time zone for the temperature measurement (time zone 2). May be modulated. In this case, the temperature can be measured using the Stokes component (scattered light on the long wavelength side) of the Brillouin backscattered light.

  In the present embodiment, an example in which methane is detected using an optical signal having a wavelength of 1.65 μm has been described. As the wavelength of the optical signal, a wavelength corresponding to another absorption spectrum of methane may be used. Alternatively, an absorption spectrum of a gas molecule different from methane may be monitored at a wavelength other than 1.65 μm to detect a gas other than methane. Further, a plurality of different types of gases may be detected using optical signals of a plurality of wavelengths.

(Second embodiment)
FIG. 8 is a block diagram illustrating a configuration example of the gas detection system 2 according to the second embodiment of the present invention. In the first embodiment, two photodetectors 116 and 212 for gas concentration measurement and temperature measurement are used. In the second embodiment, one photodetector performs gas concentration measurement and temperature measurement. In the following description, the same elements and reference numerals as those described above are denoted by the same reference numerals, and redundant description will be omitted.

(Configuration of the embodiment)
8, the gas detection system 2 includes a control device 1110, optical fibers 120-1 to 120-n, optical couplers 121-1 to 121-m, and sensor heads 130-1 to 130-n. n is an integer of 2 or more, and m = n-1.

  The control device 1110 includes a laser diode 111, a laser diode driver 112, a light intensity modulator 113, and a light wavelength modulator 114. The control device 110 further includes an optical circulator 115, a photodetector 116, a signal processing unit 117, and a time control unit 118.

(Operation of Second Embodiment)
The process of generating an optical signal in the control device 1110 and the modulation operation by the optical wavelength modulator 114 are the same as in the first embodiment, and a description thereof will be omitted in this embodiment. In the present embodiment, all the optical signals returned from the optical fiber 120-1 are converted into electric signals by the photodetector 116, and the electric signals are processed by the signal processing unit 117. Here, the operations of the photodetector 116 and the signal processing unit 117 are managed by the time control unit 118. That is, the time control unit 118 determines the operation of the photodetector 116 and the signal processing unit 117 when the return light of the optical signal generated in the time zone 1 is received and when the return of the optical signal generated in the time zone 2 is received. Switch between receiving and receiving light.

  Specifically, in a time zone in which the return light of the optical signal generated in the time zone 1 of FIG. 3 is received, the time control unit 118 sets the photodetector 116 and the signal processing unit 117 as the light intensity receiver. Make it work. In this case, based on the time change of the intensity of the optical signal input to the photodetector 116, as described with reference to FIGS. 5 and 6 of the first embodiment, the gas concentration around each sensor head 130 is reduced. Measured.

  On the other hand, in the time zone in which the return light of the optical signal generated in the time zone 2 in FIG. 3 is received, the time control unit 118 controls the photodetector 116 and the signal processing unit 117 in the first embodiment. The temperature detector 210 is operated as the light detector 211 and the signal processor 212. At this time, the photodetector 116 may operate as a wavelength detector that performs heterodyne reception using the output of the laser diode 111, for example. In the time zone 2, since the photodetector 116 outputs a signal having a frequency corresponding to the Brillouin shift amount of the optical signal, the controller 1110 can use this signal to measure the ambient temperature of the sensor head 130. Then, the control device 1110 uses the information of the ambient temperature measured by the optical signal transmitted and received during the time period 2 to determine the temperature dependence of the gas concentration measurement value measured by the optical signal transmitted in the time period 1. Gender correction can be performed.

(Effect of Second Embodiment)
The gas detection system 2 of the present embodiment can measure the gas concentration and the ambient temperature at a remote point by using one photodetector and a signal processing unit. For this reason, in addition to the effect of the gas detection system 1 of the first embodiment, the gas detection system 2 can further reduce the system cost.

  The contents of the second embodiment are not limited to the form described above. As in the first embodiment, the second embodiment also includes configurations that use different modulators, optical amplifiers, spectral methods, wavelengths, and the like, within the scope of the present invention.

  In the first and second embodiments, one optical fiber transmission line is branched into two, a sensor head is connected to one branch, and return light from the sensor head is transmitted using the same optical fiber transmission line. Was explained. However, the arrangement of the sensor head to which the present invention can be applied is not limited to this. For example, the present invention can be applied to a configuration described in Patent Document 2 in which different optical fiber transmission lines are used for the forward path and the return path. Further, the present invention is also applicable to a configuration in which a sensor head is connected to an optical fiber transmission line branched using an optical star coupler.

(Third embodiment)
FIG. 9 is a block diagram illustrating a configuration example of a gas detection device 800 according to the third embodiment. FIG. 10 is a flowchart illustrating an example of an operation procedure of the gas detection device 800. The control device 1110 described in the second embodiment can also be called a gas detection device 800 having the following configuration. That is, the gas detection device 800 includes a transmission unit 801 and a reception unit 802. The transmitting unit 801 includes the optical wavelength modulator 114 of FIG. The transmitting unit 801 may further include the laser diode 111, the laser diode driver 112, and the light intensity modulator 113 of FIG. The receiving unit 802 may include the photodetector 116 and the signal processing unit 117 of FIG.

  The transmitting unit 801 generates a first optical signal that has been subjected to the first modulation in the time zone 1 with respect to the wavelength of the pulse light, and has generated the second optical signal that has been subjected to the second modulation in the time zone 2. Is generated (step S01 in FIG. 10). The first and second modulations are performed in an optical wavelength modulator. The transmitting unit 801 outputs the first optical signal and the second optical signal to a transmission path connected to the sensor head (Step S02). Here, the sensor head outputs the first optical signal propagated in the atmosphere as a third optical signal.

  The receiving unit 802 receives the third optical signal (Step S03) and converts it into a first electric signal (Step S04). Then, the receiving unit 802 detects a predetermined type of gas contained in the atmosphere for each sensor head based on a temporal change in the amplitude of the first electric signal (step S05), and determines the result of the gas detection. It is generated (step S06).

  The receiving unit 802 further receives the fourth optical signal, which is the scattered light of the second optical signal (Step S07), and converts it into a second electric signal (Step S08). Then, the receiving unit 802 calculates the temperature corresponding to the sensor head based on the second electric signal (Step S09). The receiving unit 802 compensates the detection result of the gas generated in step S06 based on the calculated temperature, and outputs the compensated detection result (step S10).

  The gas detection device 800 according to the third embodiment has the following effects.

  A first effect is that the measurement accuracy of the gas concentration can be improved while maintaining the feature of no power supply. The reason is that the gas detection device 800 can measure the ambient temperature at each sensor head based on the signal generated from the scattered light of the optical fiber.

  A second effect is that the cost for improving the measurement accuracy of the gas detection system can be reduced. The reason is that by modulating the wavelength of the pulsed light for each time zone using one optical wavelength modulator, the light source and peripheral circuits can be shared between the gas concentration measurement and the temperature measurement.

  The functions and procedures described in the above embodiments may be realized by a central processing unit (Central Processing Unit, CPU) included in the control device 110 or 1110 or the temperature measurement device 210 executing a program. The program is recorded on a fixed, non-transitory recording medium. As the recording medium, a semiconductor memory or a fixed magnetic disk device is used, but is not limited thereto. The CPU may be, for example, a computer provided in at least one of the signal processing units 117 and 212, but is not limited thereto.

  The embodiments of the present invention can be described as the following supplementary notes, but are not limited thereto.

(Appendix 1)
A first optical signal that has been subjected to a first modulation in a first time zone with respect to the wavelength of the pulse light, and a second optical signal that has been subjected to a second modulation in a second time zone with respect to the wavelength of the pulse light Transmitting means for generating the second optical signal by an optical wavelength modulation means, and outputting the first optical signal and the second optical signal to an optical fiber transmission line;
A plurality of sensor heads for transmitting the first optical signal in the atmosphere and outputting the first optical signal propagated in the atmosphere as a third optical signal;
The third optical signal is received and converted into a first electrical signal, and a predetermined type of gas contained in the atmosphere is detected for each of the sensor heads based on a temporal change in the amplitude of the first electrical signal. And generates a detection result of the gas, receives a fourth optical signal that is scattered light of the second optical signal, converts the fourth optical signal into a second electrical signal, and generates a second electrical signal based on the second electrical signal. Receiving means for compensating the detection result of the gas calculated from the first electric signal based on the temperature corresponding to the sensor head calculated in the above manner;
Branching the optical fiber transmission line, connecting the transmitting means and the sensor head via the branched optical fiber transmission line, and further, the sensor head and the sensor head via the branched optical fiber transmission line Branching means for connecting the receiving means,
Gas detection system comprising:

(Appendix 2)
The receiving means generates the second electric signal having information of a frequency shift amount of the fourth optical signal with respect to the second optical signal by optical heterodyne detection, and the second electric signal is calculated based on the frequency shift amount. 2. The gas detection system according to claim 1, wherein the detection result of the gas calculated from the first electric signal is compensated based on the temperature.

(Appendix 3)
A first light detection unit and a second light detection unit provided in the reception unit;
The third and fourth lights connected so that the third light signal is received by the first light detection means and the fourth light signal is received by the second light detection means. 3. The gas detection system according to claim 1, further comprising a wavelength multiplexing / demultiplexing filter that separates signals.

(Appendix 4)
The transmitting unit controls the optical wavelength modulation unit so as to generate the first optical signal in the first time zone and generate the second optical signal in the second time zone. Equipped with time control means,
The receiving means includes third light detecting means for receiving the third and fourth optical signals,
A gas detection system according to claim 1 or 2.

(Appendix 5)
The time control means causes the reception means to output the detection result based on the first electric signal when receiving the third optical signal, and to output the detection result when receiving the fourth optical signal. The gas detection system according to claim 4, wherein the control is performed such that a temperature corresponding to the sensor head is calculated based on the second electric signal.

(Appendix 6)
The first modulation monotonously changes the wavelength of the pulse light with the passage of time, and the second modulation shifts the wavelength of the pulse light in a direction opposite to the change in the wavelength of the first optical signal. , The gas detection system according to any one of supplementary notes 1 to 5.

(Appendix 7)
Generating a first optical signal in which a first modulation is performed in a first time zone with respect to a wavelength of the pulse light;
Generating a second optical signal that is subjected to a second modulation in a second time zone with respect to the wavelength of the pulse light;
Outputting the first optical signal and the second optical signal to an optical fiber transmission line;
In the sensor head, the first optical signal is propagated in the atmosphere, the first optical signal propagated in the air is received as a third optical signal, and converted into a first electric signal. A predetermined type of gas contained in the atmosphere is detected for each of the sensor heads based on a temporal change in the amplitude of the electric signal to generate a detection result of the gas,
A fourth light signal, which is scattered light of the second light signal, is received and converted into a second electric signal, and based on a temperature corresponding to the sensor head calculated based on the second electric signal. And compensating the detection result of the gas calculated from the first electric signal,
Gas detection method.

(Appendix 8)
Generating the second electric signal having information on a frequency shift amount of the fourth optical signal with respect to the second optical signal by optical heterodyne detection;
Compensating the detection result of the gas calculated from the first electric signal based on the temperature calculated based on the frequency shift amount,
A gas detection method according to attachment 7.

(Appendix 9)
Separating the third and fourth optical signals,
Receiving the third light signal by first light detection means;
Receiving the fourth optical signal by second optical detection means;
A gas detection method described in Supplementary Note 7 or 8.

(Appendix 10)
By the time control means, the first optical signal is generated in the first time zone,
Generating the second optical signal in the second time period;
A gas detection method described in Supplementary Note 7 or 8.

(Appendix 11)
The time control means outputs the detection result based on the first electric signal when receiving the third optical signal, and outputs the second detection signal when receiving the fourth optical signal. Calculating a temperature corresponding to the sensor head based on the electric signal,
A gas detection method described in Supplementary Note 10.

(Appendix 12)
The first modulation monotonously changes the wavelength of the pulse light with the passage of time, and the second modulation shifts the wavelength of the pulse light in a direction opposite to the change in the wavelength of the first optical signal. , The control method of the gas detection device according to any one of supplementary notes 7 to 11.

(Appendix 13)
The computer equipped with the gas detection system
Generating a first optical signal that is subjected to a first modulation in a first time zone with respect to a wavelength of the pulse light;
Generating a second optical signal in which a second modulation is performed in a second time zone with respect to the wavelength of the pulse light;
Outputting the first optical signal and the second optical signal to an optical fiber transmission line,
A step of, in the sensor head, transmitting the first optical signal in the atmosphere, receiving the first optical signal propagated in the atmosphere as a third optical signal, and converting the third optical signal into a first electrical signal;
A step of detecting a predetermined type of gas contained in the atmosphere for each of the sensor heads based on a temporal change in the amplitude of the first electric signal and generating a detection result of the gas;
Receiving a fourth optical signal, which is scattered light of the second optical signal, and converting the fourth optical signal into a second electrical signal;
A step of compensating the detection result of the gas calculated from the first electric signal based on a temperature corresponding to the sensor head calculated based on the second electric signal;
Control program of the gas detection system to execute the program.

(Appendix 14)
Generating the second electric signal having information on the amount of frequency shift of the fourth optical signal with respect to the second optical signal by optical heterodyne detection;
A step of compensating the detection result of the gas calculated from the first electric signal based on the temperature calculated based on the frequency shift amount;
The control program of the gas detection system according to supplementary note 13, further causing the program to execute.

(Appendix 15)
Separating the third and fourth optical signals;
Receiving the third optical signal by first optical detection means;
Receiving the fourth light signal by a second light detection means;
14. The control program for a gas detection system according to claim 13 or 14, further causing

(Appendix 16)
further,
A time controlling means for generating the first optical signal in the first time zone and generating the second optical signal in the second time zone;
The control program of the gas detection system according to Supplementary Note 13 or 14, which executes

(Appendix 17)
The time control means includes a step of outputting the detection result based on the first electric signal when receiving the third optical signal, and a step of outputting the second detection signal when receiving the fourth optical signal. Calculating a temperature corresponding to the sensor head based on the electrical signal of
The control program of the gas detection system according to supplementary note 16, further causing the computer to execute.

(Appendix 18)
The first modulation changes the wavelength of the pulse light monotonically with time, and the second modulation changes the wavelength of the pulse light in a direction opposite to the change in the wavelength of the first optical signal. 18. The control program for a gas detection system according to any one of supplementary notes 13 to 17, wherein

(Appendix 19)
A first optical signal that has been subjected to a first modulation in a first time zone with respect to the wavelength of the pulse light, and a second optical signal that has been subjected to a second modulation in a second time zone with respect to the wavelength of the pulse light Transmitting means for generating the second optical signal by an optical wavelength modulation means, and outputting the first optical signal and the second optical signal to an optical fiber transmission line;
Receiving the third optical signal from a sensor head that propagates the first optical signal in the atmosphere and outputs the first optical signal propagated in the atmosphere as a third optical signal; Converting the signal into a signal, detecting a predetermined type of gas contained in the atmosphere for each of the sensor heads based on a temporal change in the amplitude of the first electric signal, and generating a detection result of the gas, A fourth light signal, which is scattered light of the second light signal, is received and converted into a second electric signal, and based on a temperature corresponding to the sensor head calculated based on the second electric signal. Receiving means for compensating the gas detection result calculated from the first electric signal,
A gas detection device comprising:

(Appendix 20)
The receiving means generates the second electric signal having information of a frequency shift amount of the fourth optical signal with respect to the second optical signal by optical heterodyne detection, and the second electric signal is calculated based on the frequency shift amount. 20. The gas detection device according to claim 19, wherein the gas detection device compensates the detection result of the gas calculated from the first electric signal based on the temperature.

  Although the present invention has been described with reference to the exemplary embodiments, the present invention is not limited to the above exemplary embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention. The components of each embodiment can be combined as long as there is no contradiction.

  The present invention is applicable to a gas concentration measurement system. In particular, the present invention can be applied to a system that remotely measures gas concentration information at multiple points in a wide area.

1, 2 Gas detection system 21 to 28, 31 to 34, 41, 42, 44 Optical signal 110, 1110, 1220 Controller 111 Laser diode 112 Laser diode driver 113, 1212, 1242 Optical intensity modulator 114 Optical wavelength modulator 115 , 1213, 1243 Optical circulator 116, 211, 1214, 1217 Photodetector 117, 212, 1215, 1218 Signal processing unit 118 Time control unit 120, 120-1 to 120-n Optical fiber 121, 121-1 to 120-m Optical coupler 122 Temperature measuring receiver 130, 130-1 to 130-n Sensor head 131 Lens 132 Mirror 201 Variable oscillator 203 Phase shifter 204 Optical SSB modulator 205 Controller 210, 1210, 1230, 1240 Temperature measuring device 2 0,1250 WDM filter 800 gas detector 801 transmitting unit 802 receiving unit 901 Gas detection systems 1211,1241 source 1219,1270 optical fiber transmission line 1260 Sensor Networks

Claims (10)

A first optical signal that has been subjected to a first modulation in a first time zone with respect to the wavelength of the pulse light, and a second optical signal that has been subjected to a second modulation in a second time zone with respect to the wavelength of the pulse light Transmitting means for generating the second optical signal by an optical wavelength modulation means, and outputting the first optical signal and the second optical signal to an optical fiber transmission line;
A plurality of sensor heads for transmitting the first optical signal in the atmosphere and outputting the first optical signal propagated in the atmosphere as a third optical signal;
The third optical signal is received and converted into a first electric signal, and a predetermined type of gas contained in the atmosphere is detected for each of the sensor heads based on a temporal change in the amplitude of the first electric signal. And generates a detection result of the gas, receives a fourth optical signal that is scattered light of the second optical signal, converts the fourth optical signal into a second electrical signal, and generates a second electrical signal based on the second electrical signal. Receiving means for compensating the detection result of the gas calculated from the first electric signal based on the temperature corresponding to the sensor head calculated in the above manner;
Branching the optical fiber transmission line, connecting the transmitting means and the sensor head via the branched optical fiber transmission line, and further, the sensor head and the sensor head via the branched optical fiber transmission line Branching means for connecting the receiving means,
Gas detection system comprising:   The receiving means generates the second electric signal having information of a frequency shift amount of the fourth optical signal with respect to the second optical signal by optical heterodyne detection, and the second electric signal is calculated based on the frequency shift amount. The gas detection system according to claim 1, wherein the detection result of the gas calculated from the first electric signal is compensated based on a temperature. A first light detection unit and a second light detection unit provided in the reception unit;
The third and fourth lights connected so that the third light signal is received by the first light detection means and the fourth light signal is received by the second light detection means. The gas detection system according to claim 1, further comprising a wavelength multiplexing / demultiplexing filter that separates a signal. The transmitting unit controls the optical wavelength modulation unit so as to generate the first optical signal in the first time zone and generate the second optical signal in the second time zone. Equipped with time control means,
The receiving means includes third light detecting means for receiving the third and fourth optical signals,
The gas detection system according to claim 1.   The time control means causes the reception means to output the detection result based on the first electric signal when receiving the third optical signal, and to output the detection result when receiving the fourth optical signal. 5. The gas detection system according to claim 4, wherein the controller controls the temperature corresponding to the sensor head to be calculated based on the second electric signal. 6.   The first modulation monotonously changes the wavelength of the pulse light with the passage of time, and the second modulation shifts the wavelength of the pulse light in a direction opposite to the change in the wavelength of the first optical signal. The gas detection system according to any one of claims 1 to 5. Generating a first optical signal in which a first modulation is performed in a first time zone with respect to a wavelength of the pulse light;
Generating a second optical signal that is subjected to a second modulation in a second time zone with respect to the wavelength of the pulse light;
Outputting the first optical signal and the second optical signal to an optical fiber transmission line;
In the sensor head, the first optical signal is propagated in the atmosphere, the first optical signal propagated in the atmosphere is received as a third optical signal, and converted into a first electrical signal. A predetermined type of gas contained in the atmosphere is detected for each of the sensor heads based on a temporal change in the amplitude of the electric signal to generate a detection result of the gas,
A fourth light signal, which is scattered light of the second light signal, is received and converted into a second electric signal, and based on a temperature corresponding to the sensor head calculated based on the second electric signal. And compensating the detection result of the gas calculated from the first electric signal,
Gas detection method. Generating the second electric signal having information on a frequency shift amount of the fourth optical signal with respect to the second optical signal by optical heterodyne detection;
Compensating the detection result of the gas calculated from the first electric signal based on the temperature calculated based on the frequency shift amount,
A gas detection method according to claim 7. Separating the third and fourth optical signals,
Receiving the third light signal by first light detection means;
Receiving the fourth optical signal by second optical detection means;
The gas detection method according to claim 7. A first optical signal that has been subjected to a first modulation in a first time zone with respect to the wavelength of the pulse light, and a second optical signal that has been subjected to a second modulation in a second time zone with respect to the wavelength of the pulse light Transmitting means for generating the second optical signal by an optical wavelength modulation means, and outputting the first optical signal and the second optical signal to an optical fiber transmission line;
Receiving the third optical signal from a sensor head that propagates the first optical signal in the atmosphere and outputs the first optical signal propagated in the atmosphere as a third optical signal; Converting the signal into a signal, detecting a predetermined type of gas contained in the atmosphere for each of the sensor heads based on a temporal change in the amplitude of the first electric signal, and generating a detection result of the gas, A fourth light signal, which is scattered light of the second light signal, is received and converted into a second electric signal, and based on a temperature corresponding to the sensor head calculated based on the second electric signal. Receiving means for compensating the gas detection result calculated from the first electric signal,
A gas detection device comprising:

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