CN111595365A - Multi-wavelength laser for synchronously monitoring ocean temperature and pressure - Google Patents
Multi-wavelength laser for synchronously monitoring ocean temperature and pressure Download PDFInfo
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- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
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- H01S3/107—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity using electro-optic devices, e.g. exhibiting Pockels or Kerr effect
Abstract
The application provides a multi-wavelength laser for ocean temperature and pressure synchronization monitoring utilizes pulse controller to convert the wide spectrum laser of wide spectrum laser source output into wide spectrum pulse light, then, utilizes phase shift grating unit will demodulate out the pulse light of a plurality of different wavelengths from wide spectrum pulse light. The pulse light output by the laser is transmitted into the sensing optical fiber in the seawater through the wavelength division multiplexer, the scattered light returns to the control demodulation module through the wavelength division multiplexer, the control demodulation module demodulates the scattered light, and the dynamic pressure and the seawater temperature are analyzed according to the phase change of the optical signal, so that the two can be monitored simultaneously. According to the laser provided by the embodiment, the wide-spectrum laser source only needs to be a common wide-spectrum laser with low cost, meanwhile, demodulation of wide-spectrum laser is realized by utilizing the phase-shift grating, and due to the extremely narrow bandwidth, a high-quality pulse laser spectrum can be obtained.
Description
Technical Field
The application relates to the technical field of marine environment monitoring, in particular to a multi-wavelength laser for synchronously monitoring marine temperature and pressure.
Background
The ocean has wide area and is a very variable factor which influences natural disasters such as global climate, water, drought, typhoon and the like, so the ocean environment has great significance for weather forecast and disaster early warning. The measurement of the temperature and the pressure of the seawater is of great significance for researching oceanography, marine environment monitoring and the like, for example, in the fields of marine scientific investigation, military affairs and the like, a sea temperature profile and dynamic changes of the pressure need to be obtained in time.
At present, most of monitoring equipment for ocean temperature and pressure is electrical equipment, and most of the monitoring equipment has the problems of high price, large volume, difficulty in arrangement, easiness in electromagnetic interference and the like. In addition, the temperature and the pressure are mostly monitored and signal processed by adopting discrete electronic equipment, and a large number of sensor combination arrays are needed to realize large-scale monitoring of the sea area, so that the problems of huge investment, complex system, low reliability, difficult data compatibility and comprehensive processing and the like exist.
In view of this, in order to meet the ocean planning development requirements, ocean temperature and pressure monitoring equipment which has strong data compatibility, low cost and compact structure and meets the high-precision in-situ measurement requirements needs to be vigorously developed. The distributed optical fiber sensing technology can realize continuous sensing and measurement of measured physical quantity distributed along the length direction of the optical fiber, and can integrate sensing and transmission functions, thereby not only finishing continuous measurement of distributed environment parameter space and time multidimensional distribution state information on the whole optical fiber length, but also transmitting distributed measurement information to an information processing center in real time and in a lossless manner.
In a distributed optical fiber sensing system, a multi-wavelength laser source is a key device, while the price of the existing multi-wavelength laser source is high, which seriously affects the large-scale popularization of distributed optical fiber sensing, and a low-price and high-performance multi-wavelength laser source becomes a problem to be solved urgently by technical personnel in the field at present.
Disclosure of Invention
In view of the above problems, the embodiments of the present application provide a multi-wavelength laser for synchronously monitoring ocean temperature and pressure.
The multi-wavelength laser for ocean temperature and pressure synchronous monitoring provided by the embodiment of the application comprises:
the wide-spectrum laser source is used for outputting wide-spectrum laser;
the pulse controller is used for converting the wide-spectrum laser output by the wide-spectrum laser source into wide-spectrum pulse light;
the phase shift grating unit is used for demodulating a plurality of pulse lights with different wavelengths which are arranged according to a time sequence from the wide spectrum pulse light.
Optionally, the laser further comprises a first wavelength division multiplexer, wherein:
a first port of the first wavelength division multiplexer is connected with an output end of the pulse controller, a second port of the first wavelength division multiplexer is connected with the phase-shift grating unit, and a third port of the first wavelength division multiplexer is used for outputting the pulse light with different wavelengths arranged according to the time sequence;
the phase shift grating unit comprises an optical fiber, and a plurality of reflection type phase shift gratings with different central window wavelengths are arranged on the optical fiber.
Optionally, the laser further comprises a first wavelength division multiplexer, wherein:
a first port of the first wavelength division multiplexer is connected with an output end of the pulse controller, a second port of the first wavelength division multiplexer is connected with the phase-shift grating unit, and a third port of the first wavelength division multiplexer is used for outputting the pulse light with different wavelengths arranged according to the time sequence;
the phase shift grating unit comprises a plurality of optical fibers, each optical fiber is provided with a reflective phase shift grating, and the central window wavelengths of the phase shift gratings on the optical fibers are different.
Optionally, the laser further includes a first wavelength division multiplexer, the phase shift grating unit includes a plurality of optical fibers, each of the optical fibers is provided with a transmissive phase shift grating, and the wavelengths of central windows of the phase shift gratings on the optical fibers are different;
and a first port of the first wavelength division multiplexer is connected with the output end of the pulse controller, and a second port of the first wavelength division multiplexer is connected with one end of each optical fiber.
Optionally, the laser further comprises a signal amplifier, wherein:
and the signal amplifier is used for amplifying the amplitudes of the pulse lights with different wavelengths and then outputting the amplified pulse lights.
Optionally, the signal amplifier is an erbium-doped fiber amplifier or an ytterbium-doped fiber amplifier.
Optionally, the pulse controller is an electro-optic modulator and/or an acousto-optic modulator.
As can be seen from the above embodiments, in the multi-wavelength laser for synchronously monitoring ocean temperature and pressure provided by this embodiment, the pulse controller is used to convert the broad-spectrum laser output by the broad-spectrum laser source into broad-spectrum pulsed light, and then the phase shift grating unit is used to demodulate a plurality of pulsed lights with different wavelengths from the broad-spectrum pulsed light. The pulse light output by the laser is transmitted into the sensing optical fiber in the seawater through the wavelength division multiplexer, the scattered light returns to the control demodulation module through the wavelength division multiplexer, the control demodulation module demodulates the scattered light, and the dynamic pressure and the seawater temperature are analyzed according to the phase change of the optical signal, so that the two can be monitored simultaneously. According to the laser provided by the embodiment, the wide-spectrum laser source only needs to be a common wide-spectrum laser with low cost, meanwhile, demodulation of wide-spectrum laser is realized by utilizing the phase-shift grating, and due to the extremely narrow bandwidth, a high-quality pulse laser spectrum can be obtained.
Drawings
In order to more clearly illustrate the technical solution of the present invention, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious to those skilled in the art that other drawings can be obtained according to the drawings without any inventive exercise.
Fig. 1 is a schematic diagram of a basic structure of a first multi-wavelength laser provided in an embodiment of the present application;
fig. 2 is a schematic diagram of a basic structure of a second multi-wavelength laser provided in an embodiment of the present application;
FIG. 3 is a schematic diagram of a basic structure of a third multi-wavelength laser provided in the embodiments of the present application;
FIG. 4 is a schematic diagram of a time-sequenced laser spectrum output by a multi-wavelength laser according to an embodiment of the present application;
FIG. 5 is a schematic diagram of a basic structure of a continuous spatial monitoring device for ocean temperature and pressure according to an embodiment of the present disclosure;
fig. 6 is a schematic diagram of a basic structure of a first control demodulation module according to an embodiment of the present disclosure;
fig. 7 is a schematic diagram of a basic structure of a second control demodulation module according to an embodiment of the present application;
fig. 8 is a schematic diagram of a basic structure of a third control demodulation module according to an embodiment of the present application.
Detailed Description
Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, like numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the invention, as detailed in the appended claims.
The multi-wavelength laser provided by the embodiment comprises a wide-spectrum laser source, a pulse controller and a phase-shift grating unit, wherein the pulse controller is used for converting the wide-spectrum laser output by the wide-spectrum laser source into wide-spectrum pulse light, and the phase-shift grating unit is used for demodulating a plurality of pulse light with different wavelengths from the wide-spectrum pulse light.
The Phase shift Grating (PSFBG) in the Phase shift Grating unit can realize the reflection or transmission of the laser light, and the bandwidth of the transmission spectrum and the reflection spectrum is very narrow. In the present embodiment, the above-mentioned phase shift grating pair and laser demodulation method are used to divide the grating fiber into a transmission type phase shift grating and a reflection type phase shift grating. Based on the above-mentioned type of phase-shift grating, the broad-spectrum laser source, the pulse controller and the phase-shift grating unit in the multiwavelength laser can have three different structural forms.
Fig. 1 is a schematic diagram of a basic structure of a first multi-wavelength laser according to an embodiment of the present application. As shown in fig. 1, the multiwavelength laser includes a broad spectrum laser source 101, a pulse controller 102, a first wavelength division multiplexer 103, and a phase shift grating unit 104.
The output end of the wide-spectrum laser source 101 is connected to the input end of the pulse controller 102, and is configured to output a wide-spectrum laser with a small coherence length, for example, a light with a line width of several hundred MHz or more, to the pulse controller 102. The pulse controller 102 may be an electro-optical modulator, an acousto-optical modulator, or a combination of the two, and the pulse controller 102 converts the wide-spectrum laser light into a wide-spectrum pulse light based on the received pulse control signal, for example, when the pulse control signal is at a low level, the pulse controller 102 does not output light, and when the pulse control signal is at a high level, the pulse controller 102 outputs light, thereby outputting the wide-spectrum pulse signal. The pulse control signal received by the pulse controller 102 may be controlled by the pulse control signal module. In the present embodiment, since the laser signal received by the pulse controller 102 is a broad-spectrum laser, the pulse signal output therefrom is referred to as a broad-spectrum pulse light.
The first port W1 of the first wavelength division multiplexer 103 is connected to the output terminal of the pulse controller 102, and the second port W2 is connected to the phase shift grating unit 104. The wide-spectrum pulse light output by the pulse controller 102 passes through the first port W1 and the second port W2 of the first wavelength division multiplexer 103, and the phase-shift grating unit includes an optical fiber on which a plurality of reflective phase-shift gratings with different central window wavelengths are disposed. For example, in this embodiment, n phase shift gratings are etched on an erbium-doped fiber, and the central window wavelengths are λ1、λ2、λ3、λ4、λ5、λ6……λn-1、λnThe broad spectrum pulse light output by the pulse controller 102 enters the optical fiber after passing through the first wavelength division multiplexer 103, and the wavelength λ is demodulated after passing through the PSFBG11Pulse of blood (II)The light is pulsed and returns to the third port W3 through the second port W2 of the first wavelength division multiplexer 103, the light with other wavelengths is transmitted to the PSFBG2 through the optical fiber (referred to as a delay fiber in this embodiment) between the PSFBG1 and the PSFBG2, and the wavelength λ is demodulated through the PSFBG22And the pulsed light returns to the third port W3 through the second port W2 of the first wavelength division multiplexer 103, and similarly, the pulsed light with other wavelengths is demodulated after the remaining PSFBGs, so as to obtain laser spectrums with different wavelengths arranged in time sequence, and the time interval between the pulsed light with each wavelength can be set by setting the length of the delay fiber between the PSFBGs.
Further, in order to amplify the optical signal output from the third port W3 of the first wavelength division multiplexer 103, as shown in fig. 2, the present embodiment is further provided with an erbium-doped fiber amplifier 105, wherein one end of the erbium-doped fiber amplifier 105 is connected to the third port W3 of the first wavelength division multiplexer 103, and is configured to amplify and output the plurality of pulse lights with different wavelengths output by the first wavelength division multiplexer 103, and of course, in other embodiments, the present embodiment may also be other types of optical signal amplifiers, such as an ytterbium-doped fiber amplifier.
Fig. 2 is a schematic diagram of a basic structure of a second multi-wavelength laser according to an embodiment of the present application. As shown in fig. 2, the main difference between this embodiment and the multi-wavelength laser is that the phase-shift grating unit 104 is composed of a plurality of optical fibers, each of the optical fibers is etched with a reflective phase-shift grating, and the central windows of the phase-shift gratings on the optical fibers have different wavelengths, and then the optical fibers are injected through the second port W2 of the first wavelength division multiplexer 103, so as to obtain pulsed light with different wavelengths, and by setting the lengths of the delay fibers in the optical fibers, laser spectra with different wavelengths arranged in time sequence are obtained.
Fig. 3 is a schematic diagram of a basic structure of a third multi-wavelength laser according to an embodiment of the present application. As shown in fig. 3, the main difference between the present embodiment and the second multi-wavelength laser is that the phase-shift grating on the optical fiber is a transmissive phase-shift optical fiber, and further, in the present embodiment, the second port W2 of the first wavelength division multiplexer 103 is connected to one end of the phase-shift grating unit 104, and the other end is connected to the input port of the erbium-doped fiber amplifier 105.
Fig. 4 is a schematic diagram of a time-sequenced laser spectrum output by a multi-wavelength laser according to an embodiment of the present application. As shown in fig. 4, the optical pulses output from the multi-wavelength laser 10 output a wavelength sequence λ (λ 1, λ 2, … …, λ n-1, λ n) within a time sequence T (T1, T2, … …, tn-1, tn), and satisfy the following condition:
tn-tn-1＝Ln/vg(n≥2) (1)
tn-t1＝W (2)
wherein: ln is the length of the nth delay fiber, W is the pulse width of the pulse control signal, upsilongIs the speed of light transmission through the fiber medium.
It should be noted that, in other embodiments, the internal structure of the multi-wavelength laser 10 may also be a combined structure of any two or three of the above embodiments.
Based on the multi-wavelength laser, the embodiment also provides a continuous space monitoring device for ocean temperature and pressure. Fig. 5 is a schematic diagram of a basic structure of a continuous space monitoring device for ocean temperature and pressure according to an embodiment of the present disclosure. As shown in fig. 5, the apparatus includes a multi-wavelength laser 10, a second wavelength division multiplexer 20, a sensing fiber 30, and a control demodulation module 40. The pulse control signal received by the pulse controller in the multi-wavelength laser 10 may be output by the control demodulation module 40, or of course, another pulse control signal output module may be provided.
The pulse light of each wavelength output from the multi-wavelength laser 10 enters the sensing optical fiber 30 through the second wavelength division multiplexer 20. The sensing fiber 30 is disposed in the sea water, wherein the sensing fiber 30 may be routed vertically through the sea floor. The sensing fiber 30 is connected vertically to the deepwater anchored mooring on the seabed. The deepwater anchoring mooring device may use an anchor for mooring a ship, and the anchor may be directly connected to the lower end of the sensing optical fiber 30.
The sensing fiber 30 is vertically routed to the sea floor by a deep water anchoring mooring, and thus the temperature distribution and pressure at various points on the sensing fiber 30, i.e., the temperature field and pressure distribution of the sea vertically along the depth. The sensing optical fiber 30 has strong seawater corrosion resistance, seawater side pressure resistance and tensile resistance under the sea surface of tens of thousands of meters.
Further, the multi-wavelength laser 10 adopted in the present embodiment has a low coherence length of pulsed light output, and in order to implement interference modulation demodulation, the present embodiment abandons a conventional method of interference between backward rayleigh scattered light and laser local oscillation light, and implements signal demodulation by a method of backward rayleigh scattered light self-interference.
The thermal perturbation causes the non-uniformity of the fiber density and the non-uniformity of the fiber concentration (e.g., oxide with non-uniform concentration) are the main causes of the non-uniformity of the fiber refractive index, because the size of the non-uniform structure in the fiber is generally smaller than the wavelength of the incident light, so the rayleigh scattering phenomenon occurs when the incident light is transmitted in the sensing fiber 30.
Let the power of the pulse light incident into the optical fiber be P0The power P of the backward Rayleigh scattered light at the initial end L of the distance sensing fiber 30BSThe expression (L) is:
in equation (3): upsilon isgτ is the width of the pulse incident on the fiber, CRIs the Rayleigh back scattering coefficient, i.e. the ratio of the back Rayleigh scattering power to the total Rayleigh scattering power, αsThe rayleigh attenuation coefficient is α, the fiber attenuation coefficient, and L is the distance from the initial end of the fiber to the scattering point.
Formula (3) is the scattered power at different positions on the sensing fiber 30, and distributed measurement of the whole fiber, i.e. continuous spatial measurement of parameters, can be realized by monitoring the optical power.
When the temperature on the sensing optical fiber is not changed, the backward Rayleigh scattering curves measured at different moments are the same; when the temperature on the sensing optical fiber changes, the backward Rayleigh scattering curve before the temperature change can be restored by searching the incident light frequency.
Assuming that the temperature at the initial time a on the sensing fiber 30 is 25 ℃, the backward rayleigh scattered light power Pa (v, z) on the sensing fiber is obtained by the incident frequency v of the multi-wavelength laser 10. The backward rayleigh scattered light power Pb (v, z) was measured in the same manner at time b. Pb (v, z) is the same as Pa (v, z) if there is no change in temperature on the sensing fiber at time a and time b; if the temperature or strain changes, Pb (v + Δ v, z) is the same as Pa (v, z) when the incident frequency reaches v + Δ v. Δ v represents the amount of frequency change in the incident frequency, related to the temperature change on the sensing fiber, which means that temperature or strain changes on the sensing fiber cause the backward rayleigh scattered light power Pb (v, z) to move in the frequency domain.
As described above, the backward rayleigh scattered light powers Pa (v, z) and Pb (v, z) generated at the timings a and b are correlated, and the correlation function takes the maximum value according to the amount of change in the incident light frequency. Therefore, the distribution information of the temperature on the sensing fiber 30 can be obtained by calculating the peak frequency of the spectrum of the correlation function. That is, the control/demodulation module 40 can obtain the temperature distribution information on the sensing fiber 30 and further obtain the temperature field of the ocean along the depth distribution according to the power change of the backward rayleigh scattered light of the pulse light of each wavelength caused by the temperature change of each point on the sensing fiber 30.
Meanwhile, the backward rayleigh scattered light wavelength sequence enters the control demodulation module 40, and the phase of the fixed wavelength in the backward rayleigh scattered light is demodulated, so that the dynamic pressure of the seawater can be analyzed. In this embodiment, a PGC (Phase Generated Carrier) or a 3 × 3 coupler Phase demodulation scheme is adopted according to different forms of control demodulation modules to demodulate the Phase of the backward rayleigh scattered light self-interference.
Fig. 6 is a schematic diagram of a basic structure of a first control demodulation module according to an embodiment of the present application. As shown in fig. 6, the present embodiment adopts a PGC demodulation method based on a michelson interferometer, and the module mainly includes a coupler 411, a first interference arm 412, a second interference arm 413, a faraday rotator 414/415, a photodetector 416, and an acquisition processing unit 417, where:
a first terminal of the coupler 411 and a second wavelength division multiplexer 20The second port is connected to the first end of the first interference arm 412 and the second interference arm 413, and the second end of the first interference arm 412 and the second interference arm 413 are connected to the faraday rotator 414 and 415, respectively. Further, the phase modulator 4121 is provided in the first interference arm 412, the phase matching loop 4131 is provided in the second interference arm 413, and the length L of the phase matching loop 4131 satisfies the following condition: l is less than or equal to Lo/2, LoIt is the coherence length of the pulsed light, and of course, the phase matching loop 4131 may be provided on the first interference arm 412.
The photodetector 416 is connected to the third end of the coupler 411, and is configured to receive the backward rayleigh scattered interference light returned by the first interference arm 412 and the second interference arm 413, and generate a corresponding electrical signal according to the backward rayleigh scattered interference light. The acquisition processing unit 417 is connected to the photodetector 416, and is configured to process the electrical signal output by the photodetector 416, and demodulate a phase change of pulsed light of one wavelength caused by a disturbance signal in the sensing optical fiber, so as to implement monitoring of the seawater pressure; in addition, the seawater temperature is monitored according to the power change of backward Rayleigh scattering light of pulse light with each wavelength caused by temperature change.
Specifically, for phase demodulation, according to the coherent principle of light, the light intensity I on the photodetector 416 can be expressed as:
I＝A+BcosΦ(t) (4)
in formula (4): a is the average optical power output by the interferometer, B is the interference signal amplitude, B is kA, and kO is the interference fringe visibility. Φ (t) is the phase difference of the interferometer. Is provided with
Then equation (2) can be written as:
ccos omega in formula (5)0t is the phase carrier, C is the amplitude, ω0Is the carrier frequency;
Dcosωst is the phase change caused by the disturbing signal of the sensing fiber 30, D is the amplitude, omegasIs the sound field signal frequency, Ψ (t) is a slow change in initial phase caused by environmental disturbances and the like. Equation (5) is developed using the Bessel function:
in the formula (6), JnAnd (m) is an n-order Bessel function value under the m modulation depth, and k is respectively equal to 0 and 1, so that an extreme signal and a double frequency signal can be obtained.
The method comprises the steps of multiplying a fundamental frequency signal (amplitude is G) and a double frequency signal (amplitude is H) by using an interferometer output detector signal I expanded by a Bessel function, carrying out Differential Cross Multiplication (DCM) on two paths of signals in order to overcome the phenomenon that the signals are blanked and distorted along with the fluctuation of external interference signals, and converting the signals subjected to differential cross multiplication into signals subjected to differential amplification and integral operation processing
Will be provided with
By substituting formula (5), one can obtain:
B2GHJ1(C)J2(C)[Dcosωst+Ψ(t)](8)
it can be obtained that the signal obtained after integration contains the signal to be measured Dcos omegast and the external environment information, the latter is usually a slowly varying signal, and the amplitude can be very large, and can be filtered out by a high-pass filter, and the final output is:
B2GHJ1(C)J2(C)Dcosωst (9)
the phase change Dcos omega caused by the disturbance signal of the sensing fiber 30 can be solved by the equation (9)sAnd (e) t signal.
Fig. 7 is a schematic diagram of a basic structure of a second control demodulation module according to an embodiment of the present application. As shown in fig. 7, the present embodiment adopts a 3 × 3 coupler phase demodulation method based on a michelson interferometer, and the module mainly includes a coupler 424, a first interference arm 425, a second interference arm 426, a faraday rotator 427/428, a first photodetector 421, a second photodetector 422, a third photodetector 423, a second wavelength division multiplexer, and an acquisition processing unit 429.
The coupler 424 has a first end connected to the third port of the second wavelength division multiplexer 20, a second end connected to one end of the first interference arm 425 and one end of the second interference arm 426, respectively, and the other end of the first interference arm 425 and the other end of the second interference arm 426 are connected to one faraday rotator 427/428, respectively. In addition, a phase matching ring 4261 is provided on the second interference arm 426, and the length L of the phase matching ring 4261 satisfies the following condition: l is less than or equal to Lo/2, LoIt is the coherence length of the pulsed light, and it is needless to say that the phase matching ring 4261 may be provided on the first interference arm 425.
The first photodetector 421, the second photodetector 422, and the third photodetector 423 are connected to the coupler 424, and are configured to receive the backward rayleigh scattered interference light returned by the first interference arm 425 and the second interference arm 426, and generate corresponding electrical signals according to the backward rayleigh scattered interference light.
The backward rayleigh scattered light enters a port 2 of the coupler 424 through the circulator 20, and is split into two optical signals by the port 2 of the coupler 424, one optical signal enters a port 4 of the coupler 424, returns to the port 4 of the coupler 424 through the first interference arm 425 and the faraday rotating mirror 427, the other optical signal enters a port 6 of the coupler 424, returns to the port 6 of the coupler 424 through the second interference arm 426 and the faraday rotating mirror 428, the two optical signals are combined and interfered at the coupler 424, the backward rayleigh scattered interference light enters the first photodetector 421 and the third photodetector 423 through the ports 1 and 3 of the coupler 424, and the backward rayleigh scattered interference light enters the second photodetector 422 through the second wavelength division multiplexer 20 after passing through the port 2 of the coupler 424.
Wherein, the light intensity expression formula that three detectors obtained is:
Ip＝D+I0cos[φ(t)-(p-1)×(2π/3)]，p＝1,2,3(10)
in formula (10), Φ (t) ═ Φ (t) + ψ (t); d is the direct current component of the interference signal; i is0Is the amplitude of the alternating current component of the interference signal; p is the serial number of the light signal received by the detector, and p is 1, 2 and 3; phi (t) is a phase difference signal, rad, caused by the disturbance signal; ψ (t) is a phase difference signal, rad, caused by environmental noise.
Then, the acquisition processing unit 429 is used for carrying out phase demodulation on the optical signals received by the three detectors, so as to obtain the phase change of the pulse light with one wavelength caused by the disturbance signal in the sensing optical fiber 30; the acquisition processing unit 429 is also used for changing the power of the backward rayleigh scattered light of the pulsed light of each wavelength due to a temperature change.
Fig. 8 is a schematic diagram of a basic structure of a third control demodulation module according to an embodiment of the present application. As shown in fig. 8, the present embodiment adopts a PGC phase demodulation method based on a mach-zehnder interferometer, and the module mainly includes a first interference arm 431, a second interference arm 432, a photodetector 433, and an acquisition processing unit 434.
The third port of the second wavelength division multiplexer 20 is connected to one end of the first interference arm 431 and one end of the second interference arm 432, and the other end of the first interference arm 431 and the other end of the second interference arm 432 are connected to the photodetector 433. In addition, a phase matching loop 4321 is provided on the second interference arm 432, and the length L of the phase matching loop 4321 satisfies the following condition: l is less than or equal to L0，LoIt is a coherence length of the pulsed light, and of course, the phase matching loop 4321 may be provided on the first interference arm 431.
The photodetector 433 is configured to receive the backward rayleigh scattering interference light output by the first interference arm 431 and the second interference arm 432, and generate a corresponding electrical signal according to the backward rayleigh scattering interference light. The collecting and processing unit 434 is connected to the photodetector 433 and configured to process the electrical signal output by the photodetector, and demodulate a phase change of the pulsed light with one wavelength caused by the disturbing signal in the sensing fiber and a backward rayleigh scattered light power change of the pulsed light with each wavelength caused by a temperature change.
The embodiments in the present specification are described in a progressive manner, and the same and similar parts among the embodiments are referred to each other, and each embodiment focuses on the differences from the other embodiments.
Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
It will be understood that the invention is not limited to the precise arrangements described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the invention is limited only by the appended claims.
Claims (7)
1. A multi-wavelength laser for synchronously monitoring ocean temperature and pressure is characterized by comprising a wide-spectrum laser source, a pulse controller and a phase-shift grating unit, wherein:
the wide-spectrum laser source is used for outputting wide-spectrum laser;
the pulse controller is used for converting the wide-spectrum laser output by the wide-spectrum laser source into wide-spectrum pulse light;
the phase shift grating unit is used for demodulating a plurality of pulse lights with different wavelengths which are arranged according to a time sequence from the wide spectrum pulse light.
2. The multiwavelength laser for simultaneous monitoring of ocean temperature and pressure according to claim 1, wherein the laser further comprises a first wavelength division multiplexer, wherein:
a first port of the first wavelength division multiplexer is connected with an output end of the pulse controller, a second port of the first wavelength division multiplexer is connected with the phase-shift grating unit, and a third port of the first wavelength division multiplexer is used for outputting the pulse light with different wavelengths arranged according to the time sequence;
the phase shift grating unit comprises an optical fiber, and a plurality of reflection type phase shift gratings with different central window wavelengths are arranged on the optical fiber.
3. The multiwavelength laser for simultaneous monitoring of ocean temperature and pressure according to claim 1, wherein the laser further comprises a first wavelength division multiplexer, wherein:
a first port of the first wavelength division multiplexer is connected with an output end of the pulse controller, a second port of the first wavelength division multiplexer is connected with the phase-shift grating unit, and a third port of the first wavelength division multiplexer is used for outputting the pulse light with different wavelengths arranged according to the time sequence;
the phase shift grating unit comprises a plurality of optical fibers, each optical fiber is provided with a reflective phase shift grating, and the central window wavelengths of the phase shift gratings on the optical fibers are different.
4. The multiwavelength laser for synchronously monitoring ocean temperature and pressure according to claim 1, wherein the laser further comprises a first wavelength division multiplexer, the phase-shift grating unit comprises a plurality of optical fibers, each of the optical fibers is provided with a transmissive phase-shift grating, and the central window wavelengths of the phase-shift gratings on the optical fibers are different;
and a first port of the first wavelength division multiplexer is connected with the output end of the pulse controller, and a second port of the first wavelength division multiplexer is connected with one end of each optical fiber.
5. The multiwavelength laser for simultaneous monitoring of ocean temperature and pressure as in any of claims 1 to 4, further comprising a signal amplifier, wherein:
and the signal amplifier is used for amplifying the amplitudes of the pulse lights with different wavelengths and then outputting the amplified pulse lights.
6. The multiwavelength laser for simultaneous monitoring of ocean temperature and pressure as claimed in claim 5, wherein the signal amplifier is an erbium doped fiber amplifier or an ytterbium doped fiber amplifier.
7. The multiwavelength laser for simultaneous monitoring of ocean temperature and pressure according to claim 1, wherein the pulse controller is an electro-optic modulator and/or an acousto-optic modulator.
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