JP4671842B2 - Optical fiber sensor device - Google Patents

Description

  The present invention relates to an optical fiber sensor device, and more particularly to an optical fiber sensor device that detects physical quantities such as strain, temperature, displacement, and pressure.

Conventionally, optical fiber sensors have high reliability with respect to electromagnetic induction and low-loss optical transmission, so long-distance and large-scale multipoint measurement is possible. Hydrophone “underwater acoustic sensor” (for example, non-patent document) 1) and seismometer “acceleration sensor” (see, for example, Non-Patent Document 2).
Optical fiber sensors that are currently in practical use include phase detection type sensors that use Michelson interference and Sagnac interference, intensity detection type sensors that use microbend loss (a slight bending loss of optical fiber), There is a wavelength detection type sensor using a Bragg reflection wavelength shift of FBG (Fiber Bragg Grating).
Ryo Sato et al., “Development of optical fiber hydrophone”, IEICE Technical Report OPE95-2, Vol.95, No.32, pp.2-12, 1995 Shingo Yuuji et al., “Observation of submarine earthquakes using optical fiber accelerometers”, Proceedings of the 32nd Lightwave Sensing Technology Study Group, LST32-13, pp.93-98, 2003

In such a conventional optical fiber sensor such as a phase detection sensor, an intensity detection sensor, and a wavelength detection sensor, a transmission method for each round-trip path in which the transmitted light and the signal light are transmitted through different optical fibers for long-distance transmission. However, although the influence of Rayleigh backscattered light is small, there is a problem that the number of optical fiber cores in the transmission path is increased and the cost is increased.
In addition , in order to avoid an increase in cost, when adopting a round trip common transmission method in which the outgoing light and the signal light are sent back and forth in the same optical fiber, if the repetition time of the outgoing pulse and the round trip propagation time of the light are not considered, As the transmission distance becomes longer, Rayleigh backscattered light generated from the transmission path accumulates, which becomes dominant noise and the accuracy deteriorates, so that there is a problem that transmission over a long distance becomes difficult .
Accordingly, the present invention has been made to solve such a problem, and an object of the present invention is to obtain a low-cost optical fiber sensor device capable of a long-distance transmission path even with a round-trip common transmission system.

An optical fiber sensor device according to the present invention includes a single transmission line fiber that is commonly used for reciprocation, a light source, an optical gate switch that pulses the light from the light source and outputs the light to the transmission line fiber, and a response mechanism for a physical quantity to be detected. An optical fiber sensor provided on the transmission line fiber, and detecting the physical quantity by receiving the signal light from the optical fiber sensor through the transmission line fiber and converting the signal light into an electrical signal. The optical fiber sensor is provided with a plurality of discrete types of the same method that branch to the transmission line fiber so as to be time-division multiplexed, and the return light from each of the optical fiber sensors. a delay fiber but which is inserted between the optical fiber sensor to allow time division multiplexing becomes a pulse train, the light source light of different oscillation wavelengths band The optical switch in place of the optical gate switch sends out pulsed light obtained by WDM-multiplexing light of multiple wavelengths of the multiple wavelength variable light source, and the detection unit has a wavelength filter. A wavelength detection unit that detects a wavelength, and the optical fiber sensor is a wavelength detection type optical fiber sensor, and WDM-multiplexed pulse signal light is separated at the front stage of the wavelength detection unit with a plurality of wavelength filters. A signal separator is provided, and the signals of λ1 to λ3 received by the respective wavelength detection type optical fiber sensors at the subsequent stage of the wavelength detection unit, λ1 is combined into one by λ1, λ2 is combined into one by λ2, and λ3 is provided with a post-processing unit that bring together at [lambda] 3, the light repetition time of the transmission pulse light in the gate switch is set larger than the round-trip propagation time of light, one-pulse heat transfer through the said transmission line fiber It is obtained by way.

As described above, the present invention includes a single transmission path fiber common to both reciprocations, a light source, an optical gate switch that pulsates light from the light source and outputs the light to the transmission path fiber, and a response mechanism for a physical quantity to be detected. An optical fiber sensor provided in the transmission line fiber; and a detection unit that receives the signal light from the optical fiber sensor through the transmission line fiber, converts the signal light into an electrical signal, and detects a physical quantity; The optical fiber sensor is provided with a plurality of discrete types of the same system that branch to the transmission line fiber so as to be time-division multiplexed , and the return light from each optical fiber sensor is pulsed. train and become comprises a plurality of delay fiber inserted between the optical fiber sensor so that it can be time-division multiplexed delivery path in the optical gate switch The repetition time of the light is set to be larger than the round-trip propagation time of the light, and the one-pulse transmission is performed in the transmission line fiber, so that the Rayleigh backscattered light is not accumulated in the transmission line fiber, and the round-trip path Since Rayleigh backscattering noise can be suppressed with common transmission, long-distance transmission is possible, and there is an effect that a low-cost large-scale sensing system can be constructed.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing a configuration of an optical fiber sensor device according to Embodiment 1 of the present invention, and FIG. 2 is a waveform showing a transmission waveform and a detection waveform of a one-pulse transmission method and a conventional pulse transmission method of the optical fiber sensor device, respectively. FIG. 3 and FIG. 3 are graphs showing Rayleigh noise comparison between the one-pulse transmission method and the conventional pulse transmission method of the optical fiber sensor device.
As shown in FIG. 1, an optical fiber sensor device according to Embodiment 1 of the present invention includes a coherent light source 1 such as a DFB-LD (Distributed Feed Back-Laser Diode) or a fiber laser, and time-division multiplexing (TDM). Response to an optical gate switch 2 for performing division multiplexing, an optical circulator 3 for switching the light transmission direction, a single transmission line fiber 4 that is common to both reciprocations, and physical quantities to be detected (strain, temperature, displacement, pressure, etc.) A plurality of phase detection type optical fiber sensors 5a to 5n having a mechanism, a plurality of optical couplers 6a to 6c for branching outgoing light to each optical fiber sensor at an appropriate branching ratio, and return light from each optical fiber sensor Is converted into an electrical signal by a delay fiber 7a to 7n of an appropriate length inserted between optical fiber sensors and a PD (Photo Diode) so that the signal becomes a pulse train and can be time-division multiplexed. It comprises a phase detector 8 that performs demodulation processing and detects the phase.
Major examples of the phase detection sensors 5a to 5n include a Michelson interference type, a Mach-Zehnder interference type that uses two beams of interference light, a Fabry-Perot type that uses multipath interference light, and a Sagnac type.

In the optical fiber sensor device according to the first embodiment of the present invention, the transmitted pulsed light from the optical gate switch 2 is the next until all the optical signals from the respective optical fiber sensors are returned after the pulse is transmitted once. This is a method that does not send out the above-mentioned pulse, and since there is only one forward optical pulse in the transmission line fiber at the same time, it is hereinafter referred to as a “one-pulse transmission system”.
That is, as shown in FIG.
Set so that the repetition time of the transmitted pulse> the round-trip propagation time of the light.
Since the speed of light propagating through the optical fiber core of the transmission line fiber 4 is 2.04 × 10 ⁸ m / s, when the transmission distance is L [km], the relationship with the pulse repetition time T _rep [sec] is , The following formula

で与えられ、1kmで10μsecである。

And is 10 μsec at 1 km.

Next, the operation of the optical fiber sensor device according to the first embodiment of the present invention will be described.
The transmitted light from the coherent light source 1 is pulsed by the optical gate switch 2, passes through the optical circulator 3, and then passes through the transmission line fiber 4 and the optical couplers 6 a to 6 n, respectively, and a plurality of phase detection type optical fiber sensors 5 a to 5. Each is sent to 5n.
In the phase detection type optical fiber sensors 5a to 5n, the interference waveform corresponding to the magnitude of the measured physical quantity passes through the optical circulator 3 through the transmission line fiber 4 and then returns to the phase detection unit 8.
Appropriate delay fibers 7a to 7n are inserted between the respective phase detection type optical fiber sensors, and the signal from each phase detection type optical fiber sensor is transmitted to and from the round trip propagation time of the delay fibers 7a to 7n with respect to one transmission pulse. The pulse train deviates by a certain amount and returns to the phase detector 8.
In the one-pulse transmission method satisfying “repetition time of transmission pulse> round-trip propagation time of light”, the transmission waveform and the detection waveform have a relationship as shown in FIG.
The phase detection unit 8 calculates the measured physical quantity by performing phase demodulation processing of the interference signals from the phase detection type optical fiber sensors 5a to 5n.

Here, first, in the round-trip common transmission system in which the transmitted light and the signal light are reciprocally transmitted through the same optical fiber, the conventional configuration of “repetition time of transmitted pulse <reciprocal propagation time of light” (hereinafter referred to as “conventional system”). )), And will describe the troubles in the case of long distance transmission.
When pulse light having an incident power I _in is incident on a transmission path of L [km], the signal light power I _out returning to the phase detector 8 is a transmission loss α [dB / km] and a transmission distance L [km]. ], And can be expressed by the following equation using the branching ratio R [dB] of the coupler. (Because both fiber transmission loss and coupler branch loss are subject to double loss in round trips, the exponent is 2αL × 2R)

On the other hand, the total power I _RS of Rayleigh scattering returning from the entire transmission path to the light source unit can be expressed by the following equation using the duty ratio D of the transmitted pulse light and the Rayleigh backscattering coefficient S of the transmission path fiber.

Here, when the optical signal-to-noise ratio (OSNR) with respect to Rayleigh scattering noise is defined as OSNR _RS = Iout / I _RS , from the equations (1) and (2),

となる。

It becomes.

Next, the operation in the case of adopting the one-pulse transmission method satisfying “sending pulse repetition time> light round-trip propagation time” given by the equation (1) described in the first embodiment of the present invention will be described.
The signal light power I _out returning to the phase detector 8 is the same as that in the equation (2). Rayleigh backscattered light in the one-pulse transmission system is not accumulated in the transmission line fiber, but only Rayleigh scattered light in the vicinity of the pulsed light overlaps with the signal light.
Therefore, the total power I _RS of Rayleigh scattering can be expressed by the following equation when the pulse width is T, the speed of light is c, and the refractive index is n of the fiber.

となる。 At this time, OSNR _{RS with} respect to Rayleigh scattering noise is obtained from the equations (2) and (5).

It becomes.

Unlike Equation (4), OSNR _RS does not depend on the transmission distance L. Therefore, no matter how long the transmission distance is increased, the measurement accuracy is not degraded by Rayleigh noise.
Received signal power and Rayleigh light in conventional and one-pulse systems when using a general dispersion-shifted fiber (compliant with ITU-T G.653: α = 0.25 dB / km, S = 2.2 × 10 ⁻³ ) The calculation results are shown in FIG.
This is a relative calculation of the received light signal power and the Rayleigh backscatter noise power in each transmission method when the coupler branch ratio R = 0 dB, the duty ratio D = 0.1, and the pulse width T = 1 μs.
In the conventional method, Rayleigh scattered light converges to a substantially constant power at 10 km or more, and signal light deteriorates by the amount of transmission loss. As a result, OSNR _RS deteriorates rapidly with distance. On the other hand, in the one-pulse transmission system of the present invention, the slopes of the signal light and the Rayleigh scattered light are the same, and the distance dependency of OSNR _RS is lost.

  The optical fiber sensor device according to the first embodiment of the present invention uses the coherent light source 1 as a light source, uses phase type optical fiber sensors 5a to 5n as optical fiber sensors, uses a phase detection unit 8 as a detection unit, and transmits light. A one-pulse transmission system that satisfies the “repetition time of transmission pulse> round-trip propagation time of light” given by the above formula (1) is adopted as a common transmission system for round trip transmission of signal light through the same transmission line fiber. As a result, Rayleigh backscattering light is not accumulated in the transmission line fiber, and Rayleigh backscattering noise can be suppressed while using round-trip common transmission. There is an effect that can be.

Embodiment 2. FIG.
FIG. 4 is a block diagram showing the configuration of the optical fiber sensor device according to Embodiment 2 of the present invention.
As shown in FIG. 4, the optical fiber sensor device according to the second embodiment of the present invention includes a broadband light source 11 such as an LED (Light-Emitting Diode), an optical gate switch 2, an optical circulator 3, and a reciprocating common 1 A transmission line fiber 4, three intensity detection type optical fiber sensors 15a to 15n having a response mechanism for a physical quantity to be detected, optical couplers 6a to 6n, delay fibers 7a to 7n, and a PD It is comprised from the intensity | strength detection part 18 which detects this.
As the main sensors for detecting the intensity, there are sensors that use microbend loss (small bending loss of optical fiber), and others that use propagation loss of light between air gaps.
Similarly to the first embodiment, the optical fiber sensor device according to the second embodiment of the present invention also transmits the transmitted light by a one-pulse transmission method that satisfies “repetition time of transmitted pulse> round-trip propagation time of light”.

Next, the operation of the optical fiber sensor device according to the second embodiment of the present invention will be described.
The transmitted light from the broadband light source 11 is pulsed by the optical gate switch 2, passes through the optical circulator 3, and then passes through the transmission line fiber 4 and the optical couplers 6 a to 6 n, respectively. To 15n.
The optical signal component attenuated by the measured physical quantity in the intensity detection type optical fiber sensors 15a to 15n returns to the intensity detection unit 18 after passing through the optical circulator 3 through the transmission line fiber 4 as well.
Appropriate delay fibers 7a to 7n are inserted between the respective intensity detection type optical fiber sensors, and the signal from each intensity detection type optical fiber sensor is the round-trip propagation time of the delay fibers 7a to 7n with respect to one pulse to be transmitted. The pulse train deviates by a certain amount and returns to the intensity detector 18.

In the one-pulse transmission method satisfying “repetition time of transmission pulse> round-trip propagation time of light”, the transmission waveform and the detection waveform have a relationship as shown in FIG.
The intensity detector 18 calculates a measured physical quantity from the received light power corresponding to each of the intensity detection type optical fiber sensors 15a to 15n.
As in the first embodiment, by adopting a one-pulse transmission method that satisfies “repetition time of transmission pulse> round-trip propagation time of light”, Rayleigh scattering noise in round-trip common transmission can be suppressed.
The effect of improving the OSNR _RS with respect to Rayleigh backscattered light is also the same as that of the first embodiment.

  The optical fiber sensor device according to the second embodiment of the present invention uses the broadband light source 11 as the light source, the intensity detection type optical fiber sensors 15a to 15n as the optical fiber sensor, and the intensity detection unit 18 as the detection unit. And a single-pulse transmission method that satisfies the “repetition time of the transmitted pulse> the round-trip propagation time of the light” given by the above equation (1). As a result, Rayleigh backscattering light is not accumulated in the transmission line fiber, and Rayleigh backscattering noise can be suppressed while using round-trip common transmission, thus constructing a low-cost large-scale sensing system. There is an effect that can be.

Embodiment 3 FIG.
FIG. 5 is a block diagram showing the configuration of the optical fiber sensor device according to Embodiment 3 of the present invention.
As shown in FIG. 5, the optical fiber sensor device according to the third embodiment of the present invention includes a wavelength variable light source 21 that outputs light whose wavelength changes periodically, an optical gate switch 2, an optical circulator 3, and a reciprocating common 1 The transmission line fiber 4 includes three wavelength detection type optical fiber sensors 25a to 25n equipped with a response mechanism for a physical quantity to be detected, optical couplers 6a to 6n, delay fibers 7a to 7n, a wavelength filter, and a PD. And a wavelength detector 28 for detecting the wavelength.
As the wavelength detection type sensors, there are those that use the Bragg reflection wavelength of the FBG and those that use the resonance frequency of the Fabry-Perot resonator.
Similarly to the first embodiment, the optical fiber sensor device according to the third embodiment of the present invention also transmits the transmitted light by a one-pulse transmission method that satisfies “repetition time of transmitted pulse> round-trip propagation time of light”.

Next, the operation of the optical fiber sensor device according to Embodiment 3 of the present invention will be described.
The transmitted light from the wavelength tunable light source 21 is pulsed by the optical gate switch 2, passes through the optical circulator 3, and then passes through the transmission line fiber 4 and the optical couplers 6a to 6n, respectively, and a plurality of wavelength detection type optical fiber sensors 25a. To 25n respectively.
In the wavelength detection type optical fiber sensors 25a to 25n, only the signal wavelength component corresponding to the magnitude of the measured physical quantity returns to the wavelength detection unit 28 after passing through the optical circulator 3 through the transmission line fiber 4 as well.
Appropriate delay fibers 7a to 7n are inserted between the respective wavelength detection type optical fiber sensors, and a signal from each optical wavelength detection type fiber sensor is transmitted to and from the round trip propagation time of the delay fibers 7a to 7n with respect to one transmission pulse. The pulse train deviates by a certain amount and returns to the wavelength detector 28.
In the one-pulse transmission method satisfying “repetition time of transmission pulse> round-trip propagation time of light”, the transmission waveform and the detection waveform have a relationship as shown in FIG.
The wavelength detection unit 28 includes a wavelength filter and a PD, and the transmission spectrum of the wavelength filter has a wavelength characteristic within the band of each wavelength detection type optical fiber sensor 25a to 25n. Therefore, each wavelength detection type optical fiber sensor 25a to 25n. The optical power corresponding to the reflected wavelength is transmitted. Therefore, the wavelength detector 28 can calculate the measured physical quantity from the optical power detected by the PD.

As in the first embodiment, by adopting a one-pulse transmission method that satisfies “repetition time of transmission pulse> round-trip propagation time of light”, Rayleigh scattering noise in round-trip common transmission can be suppressed.
The effect of improving the OSNR _RS with respect to Rayleigh backscattered light is also the same as that of the first embodiment.

  The optical fiber sensor device according to the third embodiment of the present invention uses the wavelength variable light source 21 as a light source, uses wavelength detection type optical fiber sensors 25a to 25n as optical fiber sensors, and uses a wavelength detection unit 28 as a detection unit. A one-pulse transmission method that satisfies the “repetition time of transmission pulse> round-trip propagation time of light” given by the above equation (1) is adopted as a round-trip common transmission method in which light and signal light are transmitted back and forth in the same transmission line fiber. Because Rayleigh backscattered light is not accumulated in the transmission line fiber and Rayleigh backscattering noise can be suppressed while using round-trip common transmission, a low-cost large-scale sensing system is constructed. There is an effect that can be done.

FIG. 6 is a block diagram showing the configuration of the optical fiber sensor device according to the fourth embodiment of the present invention, and FIG. 7 shows the transmission waveform of the one-pulse transmission method of the optical fiber sensor device according to the first to third embodiments and the fourth embodiment. FIG. 8 is a graph showing the relationship between the transmission distance and the sampling frequency in the one-pulse transmission method.
As shown in FIG. 6, the optical fiber sensor device according to the fourth embodiment of the present invention includes wavelength tunable light sources 21A to 21C that output three lights having different oscillation wavelength bands, and oscillation wavelengths from the wavelength tunable light sources 21A to 21C. Wavelength Division Multiplexing (WDM: Light Division Multiplexing) of three different bandwidths, pulsed and transmitted optical switch 22, optical circulator 3, single transmission line fiber 4 common to round trip, response mechanism for physical quantity to be detected A plurality of wavelength detection type optical fiber sensors 25a to 25n, optical couplers 6a to 6n, delay fibers 7a to 7n, and a signal separator that separates WDM multiplexed signal light with three wavelength filters (DEMUX: Demultiplexer) 29, a wavelength detection unit 28 that detects a wavelength from a separated signal having a wavelength filter and a PD, Is Karakara configured as a post-treatment 30 joining the WDM signal.
As the wavelength detection type sensor, a Fabry-Perot type sensor having a periodic wavelength characteristic is desirable.

Next, the operation of the optical fiber sensor device according to the fourth embodiment of the present invention will be described.
Light from the three wavelength variable light sources 21A to 21C is wavelength-division multiplexed by the optical switch 2 (with a time difference for each different wavelength) and transmitted. The transmitted light passes through the optical circulator 3, and then is transmitted to the plurality of wavelength detection type optical fiber sensors 25a to 25n through the transmission line fiber 4 and the optical couplers 6a to 6n, respectively.
In the wavelength detection type optical fiber sensors 25a to 25n, the signal wavelength component corresponding to the magnitude of the measured physical quantity passes through the optical circulator 3 through the transmission line fiber 4 and is then wavelength-separated by the signal separator 29 to be a wavelength detector. Return to 28.

In the fourth embodiment, pulse light multiplexed by WDM is transmitted by the optical switch 22, but the wavelength detection type optical fiber sensors 25a to 25n are branched by the optical couplers 6a to 6n. Respond.
Accordingly, when light from the three wavelength variable light sources 21A to 21C is wavelength division multiplexed by the optical switch 22 and, for example, three wavelength WDM light sources are used, the three wavelength detection type optical fiber sensors 25a to 25n are used. Three signal lights are returned.
These signals are separated by the signal separator 29 and connected by the post-processing unit 30 after wavelength detection by the wavelength detection unit 28, whereby the sampling frequency of the one-pulse transmission method can be tripled, which is a disadvantage of the one-pulse transmission method. A decrease in sampling frequency can be improved (see FIG. 7B).
Here, the linking by the post-processing unit 30 means that λ1 to λ3, which are WDM channel signals, are received with a slight timing shift, so signals are received by the same number of A / D boards as the number of channels. After that, rearrange the data so as to sweep the data of each channel, that is, λ1 to λ3 signals received by each wavelength detection type optical fiber sensor, λ1 is combined into λ1, and λ2 is combined into λ2. In summary, λ3 means that λ3 is combined into one. By this joining process, the time interval can be shortened to 1/3 (high sampling).

In the one-pulse transmission systems of the first to third embodiments, the measurement sampling time becomes longer as the transmission distance becomes longer. This is because “sampling time> light round-trip propagation time” is limited. Sampling time is about 100μsec at 10km transmission distance (sampling frequency 10kHz). FIG. 8 shows the relationship between the transmission distance and the maximum sampling frequency in the one-pulse transmission system.
In order to increase the sampling frequency, it is only necessary to narrow the pulse interval so that a plurality of pulses exist on the transmission line at the same time. However, Rayleigh backscattered light from other pulses becomes noise.
Therefore, in the fourth embodiment, a pseudo one-pulse transmission system is adopted by transmitting a plurality of transmission lights with different wavelengths for each wavelength.

Since each wavelength is one-pulse transmission in which only one pulse exists on the transmission line, it can be called a pseudo one-pulse transmission system.
In this case, Rayleigh scattered light having different wavelengths can be separated by the wavelength filter of the signal separator 29. By connecting the WDM signals demodulated after wavelength demodulation, the sampling frequency can be increased while suppressing Rayleigh backscattered light, and by performing n-wavelength pseudo WDM, the sampling frequency is increased by n times. (See FIG. 7B).

  In the one-pulse transmission method of the first to third embodiments, since the transmission pulse cannot be transmitted until the transmission pulse light returns, the sampling time of the sensor signal is delayed as the long-distance transmission is performed. In such a case, the optical fiber sensor device of the fourth embodiment can increase the sampling frequency by n times while suppressing Rayleigh backscattered light by using an n-wave pseudo WDM light source. .

Description of (Usage Mode) In Embodiments 1 to 3, the configuration of a multiple sensor that receives outgoing light by a plurality of optical fiber sensors is described because the transmission loss is one digit less than that of a coaxial cable. However, even one optical fiber sensor without multiplexing has the effect of suppressing Rayleigh noise by adopting the one-pulse transmission method.
In all the embodiments, the configuration based on long-distance transmission has been described. Even if the transmission distance is short (<1 km), the system noise level is very low, and Rayleigh backscattered light is dominant noise. It works effectively in such a system.
In all the embodiments, even in a configuration used in combination with other multiplexing schemes such as spatial division multiplexing (SDM) and frequency division multiplexing (FDM), it functions effectively.

In all the embodiments, the same effect can be obtained even if the optical circulator immediately after the light source is changed to an optical coupler. However, since there are effects of insertion loss and multiple reflection of the optical coupler, it is desirable to insert an optical isolator at an appropriate position when replacing the optical coupler.
In all the embodiments, the optical amplifier is omitted. However, in the case of high multiplexing by long-distance transmission, optical amplification by an erbium-doped fiber amplifier (EDFA) or a Raman amplifier is used. Is essential. In addition, the transmission system of each embodiment functions effectively for both the booster amplifier that amplifies immediately before transmission and the preamplifier that amplifies immediately before the light receiving unit.
In all the embodiments, the multiplexing type of the branch type optical fiber sensor using the optical coupler or the optical multiplexer / demultiplexer (optical circulator) has been described. However, the in-line type optical fiber sensor using the FBG or the dielectric multilayer film is used. The same effect can be obtained even when a non-branching multiplex configuration is used.

Although the fourth embodiment has described the configuration in which the three wavelength variable light sources 21A to 21C are applied to the wavelength detection type system of the third embodiment, the three wavelength variable light sources 21A to 21C are applied to the first and second embodiments. However, the same effect can be obtained.
Although the configuration using the coherent light source in the first embodiment, the broadband light source in the second embodiment, and the wavelength tunable light source in the third embodiment has been described, these are light sources used in a general configuration. Similar effects can be obtained by replacing with other light sources, such as a system using a low-coherent light source for the phase detection type of Embodiment 1 and a system using a broadband light source for wavelength detection of Embodiment 3.
In all the embodiments, the configuration in which the long-distance transmission line fiber is inserted between the light source and the frontmost optical fiber sensor has been described. However, the long-distance transmission line fiber is inserted between the sensors. The same effect can be obtained with respect to the configuration.
In the first to third embodiments, the individual configurations of the phase / intensity / wavelength detection type optical fiber sensors are described. However, when the number of cores of the transmission line fiber is limited, the system uses both wavelength detection and intensity detection. Even in a multi-sensor system that combines a wavelength detection type optical fiber sensor and an intensity detection type optical fiber to the same transmission line fiber, the effects of all the embodiments function effectively. To do.

In the fourth embodiment, the configuration using the signal separator 29 and the parallel wavelength detector 28 has been described. However, since there are time differences in the three returning wavelengths, this time difference is used instead of the signal separator. The same effect can be obtained even if the system is replaced with a single wavelength detection unit using a variable wavelength filter synchronized with a transmission pulse distributed by an optical switch synchronized with this.
In the fourth embodiment, the pseudo-WDM of three wavelengths has been described. However, the present invention is not limited to the three wavelengths, and the same effect can be obtained in the pseudo-WDM of a plurality of wavelengths.

The block diagram which shows the structure of the optical fiber sensor apparatus of Embodiment 1 of this invention. The wave form diagram which respectively shows the transmission waveform and detection waveform of the one pulse transmission system of the same optical fiber sensor apparatus, and the conventional pulse transmission system. The graph which shows the Rayleigh noise comparison of the one pulse transmission system of the same optical fiber sensor apparatus, and the conventional pulse transmission system. The block diagram which shows the structure of the optical fiber sensor apparatus of Embodiment 2 of this invention. The block diagram which shows the structure of the optical fiber sensor apparatus of Embodiment 3 of this invention. The block diagram which shows the structure of the optical fiber sensor apparatus of Embodiment 4 of this invention. The wave form diagram which shows the transmission waveform and detection waveform of the one pulse transmission system of the optical fiber sensor apparatus of Embodiment 1-3 and Embodiment 4, respectively. The graph which shows the relationship between the transmission distance and sampling frequency in a one pulse transmission system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Coherent light source, 2 optical gate switch, 3 optical circulator, 4 transmission line fiber, 5a-5n phase type optical sensor, 6a-6n optical coupler, 7a-7n delay fiber, 8 phase detection part.

Claims (1)

One transmission line fiber common to both round trips;
A light source;
An optical gate switch for pulsing the light from the light source and outputting it to the transmission line fiber;
A response mechanism for a physical quantity to be detected; an optical fiber sensor provided in the transmission line fiber;
An optical fiber sensor device comprising: a detection unit that receives signal light from the optical fiber sensor through the transmission line fiber, converts the signal light into an electrical signal, and detects a physical quantity;
The optical fiber sensor is provided with a plurality of discrete types of the same method branching to the transmission line fiber so as to be time-division multiplexed,
A delay fiber inserted between the optical fiber sensors so that the return light from each optical fiber sensor becomes a pulse train and can be time-division multiplexed;
The light source is a plurality of wavelength tunable light sources that output light having different oscillation wavelength bands, and the optical switch in place of the optical gate switch sends out a pulsed light in which light of a plurality of wavelengths of a plurality of wavelength tunable light sources is WDM multiplexed, The detection unit is a wavelength detection unit that has a wavelength filter to detect a wavelength, the optical fiber sensor is a wavelength detection type optical fiber sensor, and a plurality of pulse signal lights multiplexed in the WDM before the wavelength detection unit. A signal separator is provided to separate the signals of λ1 to λ3 received by each of the wavelength detection type optical fiber sensors at the subsequent stage of the wavelength detection unit, λ1 is combined into λ1, and λ2 Is provided with a post-processing unit that combines λ2 into one and λ3 into one with λ3,
In the optical gate switch, the repetition time of the transmitted pulse light is set to be longer than the round-trip propagation time of light, and one-pulse transmission is performed in the transmission line fiber.

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