阅读说明：本技术 激光等离子体光纤光栅压电解调多气体传感系统及方法 (Laser plasma fiber grating piezoelectric demodulation multi-gas sensing system and method ) 是由 王寅 李连庆 岳建会 于 2021-07-20 设计创作，主要内容包括：本发明公开了一种激光等离子体光纤光栅压电解调多气体传感系统及方法,所述系统包括：电光开关与光纤耦合镜组相对设置,光纤耦合镜组连接光纤分束器,光纤分束器的输出端分别连接光纤延时器和由不同气体组分特征吸收谱线扫描单元的串联支路；每一个气体组分特征吸收谱线扫描单元包括：第一光纤环形器分别连接第一光纤光栅和第二光纤环形器,第二光纤环形器连接第二光纤光栅；第一光纤光栅和第二光纤光栅设置在同一个压电陶瓷片上；每一个气体组分特征吸收谱线扫描单元的光纤环形器分别连接光开关的一个支路。本发明实现了以激光诱导等离子体为光源的气体组分吸收光谱的有效获取,可以对多组分气体同时进行高精度在线监测传感。(The invention discloses a laser plasma fiber grating piezoelectric demodulation multi-gas sensing system and a method, wherein the system comprises: the electro-optical switch is arranged opposite to the optical fiber coupling lens group, the optical fiber coupling lens group is connected with the optical fiber beam splitter, and the output end of the optical fiber beam splitter is respectively connected with the optical fiber time delay unit and the serial branch of the scanning unit of the characteristic absorption spectrum line of different gas components; each gas component characteristic absorption line scanning unit comprises: the first optical fiber circulator is respectively connected with the first optical fiber grating and the second optical fiber circulator, and the second optical fiber circulator is connected with the second optical fiber grating; the first fiber grating and the second fiber grating are arranged on the same piezoelectric ceramic chip; the optical fiber circulator of each gas component characteristic absorption spectrum line scanning unit is respectively connected with one branch of the optical switch. The invention realizes the effective acquisition of the gas component absorption spectrum by taking the laser-induced plasma as the light source, and can simultaneously carry out high-precision on-line monitoring and sensing on multi-component gas.)

1. A laser plasma fiber grating piezoelectric demodulation multi-gas sensing system is characterized by comprising: the electro-optical switch is used for collecting laser-induced plasma, the electro-optical switch is arranged opposite to the optical fiber coupling mirror group, the optical fiber coupling mirror group is connected with the optical fiber beam splitter, and the output end of the optical fiber beam splitter is respectively connected with the optical fiber time delay unit and the serial branch of the scanning unit of the characteristic absorption spectrum line of different gas components;

each gas component characteristic absorption line scanning unit comprises: the first optical fiber circulator is respectively connected with the first optical fiber grating and the second optical fiber circulator, and the second optical fiber circulator is connected with the second optical fiber grating; the first fiber grating and the second fiber grating are arranged on the same piezoelectric ceramic chip; the optical fiber circulator of each gas component characteristic absorption spectrum line scanning unit is respectively connected with one branch of the optical switch;

the output end of the optical switch is sequentially connected with the gas absorption cell, the photoelectric detector, the pre-amplification circuit, the A/D sampling circuit and the microcontroller in series.

2. The laser plasma fiber grating piezoelectric demodulation multi-gas sensing system of claim 1, wherein the means for forming the laser induced plasma comprises: the Q-switched trigger circuit and the pulse laser are connected in series, and the position of a light outlet of the pulse laser and the position of the total reflector are fixed according to a set position, so that the total reflector can perform set angle turning on an emergent light beam of the pulse laser; the converging lens and the total reflection mirror are fixed according to the set position so as to realize the convergence of the converging lens on the turning light beam.

3. The laser plasma fiber grating piezoelectric demodulation multi-gas sensing system as claimed in claim 1, wherein the characteristic wavelengths of the fiber gratings in the different gas component characteristic absorption line scanning units are different and correspond to the characteristic absorption peak wavelengths of the corresponding gas components to be measured.

4. The laser plasma fiber grating piezoelectric demodulation multi-gas sensing system of claim 1, wherein each piezoceramic wafer is connected with a piezoceramic wafer control circuit; the piezoelectric ceramic control circuit can drive each piezoelectric ceramic piece to periodically stretch and deform to drive the fiber grating on the piezoelectric ceramic piece to periodically stretch and contract, so that the characteristic wavelength of the fiber grating is linearly changed.

5. The laser plasma fiber grating piezoelectric demodulation multi-gas sensing system as claimed in claim 1, wherein the reflection spectral bands of the first fiber grating and the second fiber grating in the same gas component characteristic absorption line scanning unit are different, but both correspond to the same gas component, and there is a cross at the edge of the reflection spectral band to form a cross narrow band of common reflection.

6. The laser plasma fiber grating piezoelectric demodulation multi-gas sensing system according to claim 5, wherein the piezoelectric ceramic piece is deformed to drive all the fiber gratings to deform, when a light beam passes through the first gas component characteristic absorption line scanning unit, the first fiber grating reflects and transmits a light beam of a characteristic spectrum segment corresponding to the deformation at the time to the second fiber grating, the second fiber grating reflects a cross narrow band on the basis of the reflection characteristic spectrum segment of the first fiber grating, and the cross narrow band light beam is transmitted to the optical switch;

and the light beam which is not reflected by the first fiber bragg grating enters a next gas component characteristic absorption line scanning unit, and the process is repeated until the characteristic absorption line scanning of all the gas components is finished.

7. The laser plasma fiber grating piezoelectric demodulation multi-gas sensing system as claimed in claim 1, wherein the light beam entering the optical fiber is divided into two paths by the optical fiber beam splitter according to a set proportion, wherein one path is transmitted to the optical fiber time delay unit, and the other path is output and enters the gas component characteristic absorption line scanning unit for characteristic absorption line scanning;

and the light beam entering the optical fiber delayer enters the optical fiber beam splitter again after being delayed for a set time, is divided into two paths according to a set proportion, and the process is repeated.

8. The laser plasma fiber grating piezoelectric demodulation multi-gas sensing system as claimed in claim 1, wherein the optical switch comprises a plurality of branches, each branch corresponding to a gas component to be measured; keeping one branch open and the other branches closed within a certain set time; each light beam containing the corresponding wave band is output to enter the gas absorption cell for multiple reflection through a certain branch of the optical switch in sequence so as to be fully absorbed by the corresponding gas component.

9. A laser plasma fiber grating piezoelectric demodulation multi-gas sensing method is characterized by comprising the following steps:

controlling a pulse laser to emit pulse laser, wherein the pulse laser is bent and focused, and air is broken down at a focus to generate plasma;

the electro-optical switch is continuously switched on for a set time t1, and the plasma radiation beam in the time period is coupled into the optical fiber; the light beam entering the optical fiber is divided into two paths by the optical fiber beam splitter according to a set proportion, wherein one path is transmitted to the optical fiber time delay unit, and the other path is output and enters the gas component characteristic absorption spectrum line scanning unit for characteristic absorption spectrum line scanning; the light beam entering the optical fiber delayer enters the optical fiber beam splitter again after being delayed for a set time t2, is divided into two paths according to a set proportion, and the process is repeated; so that at set intervals of time t2, a light beam of the relevant wavelength band having a duration of t1 is input from the corresponding branch of the optical switch;

keeping one branch of the optical switch open and the other branches closed within a certain set time; each light beam containing corresponding wave band is output to enter the gas absorption cell for multiple reflection through a certain branch of the optical switch in sequence so as to be fully absorbed by corresponding gas components;

and then the light beam causes the photoelectric detector to respond to the light-emitting current, the light current is subjected to prepositive amplification and A/D sampling in sequence, and continuous gas absorption characteristic spectral lines are obtained through weighted correction and splicing of all scanning spectral bands, so that the concentration of related gas components is inverted.

10. The laser plasma fiber grating piezoelectric demodulation multi-gas sensing method according to claim 9, wherein the process of performing characteristic absorption line scanning on the entering gas component characteristic absorption line scanning unit specifically comprises:

reflection spectral bands of a first fiber grating and a second fiber grating in the same gas component characteristic absorption spectral line scanning unit are different, but correspond to the same gas component, and the edges of the reflection spectral bands are crossed to form a common reflection crossed narrow band;

the piezoelectric ceramic piece deforms to drive all the fiber gratings to deform, when a light beam passes through the first gas component characteristic absorption spectral line scanning unit, the first fiber grating reflects and transmits a characteristic spectral band light beam corresponding to the deformation at the moment to the second fiber grating, the second fiber grating reflects a cross narrow band on the basis of the first fiber grating reflection characteristic spectral band, and the cross narrow band light beam is transmitted to the optical switch;

and the light beam which is not reflected by the first fiber bragg grating enters a next gas component characteristic absorption line scanning unit, and the process is repeated until the characteristic absorption line scanning of all the gas components is finished.

Technical Field

The invention relates to the technical field of optical fiber multi-component gas sensing, in particular to a laser plasma optical fiber grating piezoelectric demodulation multi-gas sensing system and a method.

Background

The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.

At present, the demand of high-precision online monitoring and sensing of multi-component gas in the industrial fields of coal mining, petrochemical industry, oil and gas storage and transportation and the like is widely existed. In the prior art, the absorption spectrum technology of a tunable semiconductor laser is a main technical means for carrying out high-precision online monitoring and sensing on gas. The technical means uses a narrow-linewidth tunable semiconductor laser as a light source, and performs wavelength scanning near the wave band of the gas molecular absorption characteristic spectrum, so as to obtain a fine gas absorption spectrum.

However, in industrial applications, the technical need for simultaneous detection of multi-component gases is most common. For the simultaneous detection of multi-component gases, the prior art approach has significant drawbacks: the wavelength scanning range of the light source of the tunable semiconductor laser is narrow, and the light source cannot cover the absorption characteristic peak of a plurality of gas components, so that each tunable semiconductor laser light source can only obtain the characteristic absorption peak of a certain single gas component, and the light source does not have the capability of simultaneously detecting a plurality of gases.

Although the prior art means is usually to add corresponding tunable semiconductor lasers for various target gases to be detected, the power consumption and the volume of the device are accumulated, and the cost is also increased accumulatively (especially, the cost of the tunable semiconductor laser with the output center wavelength of more than 2 microns in the middle-infrared band is higher), so that the number of the types of the gas components which can be detected by the device is greatly limited.

The laser induced plasma generated by air breakdown of high-power laser pulses radiates wide-band light energy from an ultraviolet band to a band above a mid-infrared band in the evolution process of the laser induced plasma, can cover characteristic absorption spectral lines of most target gas components to be detected in the industrial field, is high in plasma radiation light intensity, and has great potential to become an ultra-wide-band spectral light source suitable for simultaneous detection of industrial multiple gas components. In view of this advantage, relevant documents have been reported. In these documents, it has been proposed to use laser-induced plasma as a light source in combination with gas absorption spectroscopy for detecting the corresponding gas component to be measured in the atmosphere. However, the evolution duration of the laser-induced plasma is short (usually about 10 microseconds), the radiation spectrum changes greatly during the plasma evolution process, and the spectral resolution of the current fast spectrometer equipment is generally lower than the fineness of the gas absorption line, so that the gas component absorption spectrum using the laser-induced plasma as the light source is difficult to be effectively acquired. No effective spectral acquisition scheme has been proposed in the prior relevant literature reports.

In summary, the prior art means is difficult to satisfy the requirement of high-precision online monitoring and sensing for multi-component gas in the industrial application field. Although the multi-gas detection scheme using laser-induced plasma as a light source and combining gas absorption spectroscopy has potential application, an effective method for obtaining relevant absorption spectroscopy is still lacking.

Disclosure of Invention

In order to solve the problems, the invention provides a laser plasma fiber grating piezoelectric demodulation multi-gas sensing system and a method, wherein laser-induced plasma is used as an active detection light source, and the scanning of gas component absorption spectrum is realized based on a fiber grating piezoelectric tuning technical means, so that the technical problems of short evolution duration of the laser-induced plasma, large change of radiation spectrum in the plasma evolution process, insufficient analysis precision of the gas component absorption spectrum and the like are solved, and the effective acquisition of the gas component absorption spectrum with the laser-induced plasma as the light source is realized, thereby simultaneously carrying out high-precision online monitoring and sensing on multi-component gas.

In order to achieve the above purpose, in some embodiments, the following technical solutions are adopted:

a laser plasma fiber grating piezoelectric demodulation multi-gas sensing system comprises: the electro-optical switch is used for collecting laser-induced plasma, the electro-optical switch is arranged opposite to the optical fiber coupling mirror group, the optical fiber coupling mirror group is connected with the optical fiber beam splitter, and the output end of the optical fiber beam splitter is respectively connected with the optical fiber time delay unit and the serial branch of the scanning unit of the characteristic absorption spectrum line of different gas components;

each gas component characteristic absorption line scanning unit comprises: the first optical fiber circulator is respectively connected with the first optical fiber grating and the second optical fiber circulator, and the second optical fiber circulator is connected with the second optical fiber grating; the first fiber grating and the second fiber grating are arranged on the same piezoelectric ceramic chip; the optical fiber circulator of each gas component characteristic absorption spectrum line scanning unit is respectively connected with one branch of the optical switch;

the output end of the optical switch is sequentially connected with the gas absorption cell, the photoelectric detector, the pre-amplification circuit, the A/D sampling circuit and the microcontroller in series.

The reflection spectrum sections of the first fiber grating and the second fiber grating in the same gas component characteristic absorption spectrum line scanning unit are different, but correspond to the same gas component, and the edges of the reflection spectrum sections are crossed to form a crossed narrow band of common reflection.

The piezoelectric ceramic piece deforms to drive all the fiber gratings to deform, when a light beam passes through the first gas component characteristic absorption spectral line scanning unit, the first fiber grating reflects and transmits a characteristic spectral band light beam corresponding to the deformation at the moment to the second fiber grating, the second fiber grating reflects a cross narrow band on the basis of the first fiber grating reflection characteristic spectral band, and the cross narrow band light beam is transmitted to the optical switch;

and the light beam which is not reflected by the first fiber bragg grating enters a next gas component characteristic absorption line scanning unit, and the process is repeated until the characteristic absorption line scanning of all the gas components is finished.

In other embodiments, the following technical solutions are adopted:

a laser plasma fiber grating piezoelectric demodulation multi-gas sensing method comprises the following steps:

controlling a pulse laser to emit pulse laser, wherein the pulse laser is bent and focused, and air is broken down at a focus to generate plasma;

the electro-optical switch is continuously switched on for a set time t1, and the plasma radiation beam in the time period is coupled into the optical fiber; the light beam entering the optical fiber is divided into two paths by the optical fiber beam splitter according to a set proportion, wherein one path is transmitted to the optical fiber time delay unit, and the other path is output and enters the gas component characteristic absorption spectrum line scanning unit for characteristic absorption spectrum line scanning; the light beam entering the optical fiber delayer enters the optical fiber beam splitter again after being delayed for a set time t2, is divided into two paths according to a set proportion, and the process is repeated; so that at set intervals of time t2, a light beam of the relevant wavelength band having a duration of t1 is input from the corresponding branch of the optical switch;

keeping one branch of the optical switch open and the other branches closed within a certain set time; each light beam containing corresponding wave band is output to enter the gas absorption cell for multiple reflection through a certain branch of the optical switch in sequence so as to be fully absorbed by corresponding gas components;

and then the light beam causes the photoelectric detector to respond to the light-emitting current, the light current is subjected to prepositive amplification and A/D sampling in sequence, and continuous gas absorption characteristic spectral lines are obtained through weighted correction and splicing of all scanning spectral bands, so that the concentration of related gas components is inverted.

The process of scanning the characteristic absorption spectrum line of the entering gas component characteristic absorption spectrum line scanning unit specifically comprises the following steps:

reflection spectral bands of a first fiber grating and a second fiber grating in the same gas component characteristic absorption spectral line scanning unit are different, but correspond to the same gas component, and the edges of the reflection spectral bands are crossed to form a common reflection crossed narrow band;

the piezoelectric ceramic piece deforms to drive all the fiber gratings to deform, when a light beam passes through the first gas component characteristic absorption spectral line scanning unit, the first fiber grating reflects and transmits a characteristic spectral band light beam corresponding to the deformation at the moment to the second fiber grating, the second fiber grating reflects a cross narrow band on the basis of the first fiber grating reflection characteristic spectral band, and the cross narrow band light beam is transmitted to the optical switch;

and the light beam which is not reflected by the first fiber bragg grating enters a next gas component characteristic absorption line scanning unit, and the process is repeated until the characteristic absorption line scanning of all the gas components is finished.

Compared with the prior art, the invention has the beneficial effects that:

(1) the laser induced plasma is used as a radiation light source, the radiation spectrum of the plasma is wide, the characteristic absorption spectrum lines of most industrial gas components to be detected are covered, a large amount of light energy is radiated in a short time, the power is high, signals are easy to detect, and the laser induced plasma is suitable for simultaneously detecting multiple gas components;

(2) the invention adopts a mode that one output branch and one input branch of a 2 multiplied by 2 optical fiber beam splitter are connected with an optical fiber time delay device in series, and the light energy radiated by laser plasma in a short time (100ns) is prolonged to more than 2 mu s in the time domain. The scheme realizes time domain extension of instantaneous signals and is beneficial to the subsequent fiber grating piezoelectric demodulation aiming at gas fine absorption spectral lines. Moreover, based on the technical means, only instantaneous radiant light (within 100ns) of the plasma in a short time is required to be acquired, and adverse factors of the radiant spectrum changing along with time in the plasma evolution process are avoided as much as possible;

(3) the invention adopts a scheme of edge crossing of double fiber bragg grating reflection spectrum bands, realizes fine scanning of gas absorption spectrum lines based on a crossed narrow band obtained by edge crossing, and has high spectral resolution. Moreover, because the device directly scans the gas fine absorption spectrum line, the inversion of the gas component concentration is based on the relative height of the absorption peak relative to the spectrum line base line, and the adverse effect caused by the optical energy loss of the system can be effectively overcome;

(4) most of core elements acquired by the spectrum are optical fiber devices, and optical fibers are thin like hair and can be highly integrated with piezoelectric ceramic pieces to form a chip module; when the demand of the gas component to be detected is increased, the quantity of the fiber bragg grating and the quantity of the piezoelectric ceramic pieces are increased. Because the optical fiber device and the piezoelectric ceramic piece are beneficial to integration and low in cost, when the detection requirement is improved, the volume and the manufacturing cost of the system can be effectively controlled, and the popularization of the system in various industrial application fields is facilitated.

Additional features and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

Drawings

FIG. 1 is a schematic diagram of a multi-gas sensing system based on laser plasma wide-spectrum radiation fiber grating piezoelectric demodulation in an embodiment of the invention;

FIGS. 2(a) - (e) are schematic control timing diagrams of various components of the system according to the embodiment of the present invention;

FIG. 3 is a schematic diagram of a gas composition characteristic absorption line scanned using a dual fiber grating in an embodiment of the present invention.

Detailed Description

It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

Example one

According to an embodiment of the present invention, an embodiment of a laser plasma fiber grating piezoelectric demodulation multi-gas sensing system is disclosed, which comprises: the electro-optical switch is used for collecting laser-induced plasma, the electro-optical switch is arranged opposite to the optical fiber coupling mirror group, the optical fiber coupling mirror group is connected with the optical fiber beam splitter, and the output end of the optical fiber beam splitter is respectively connected with the optical fiber time delay unit and the serial branch of the scanning unit of the characteristic absorption spectrum line of different gas components;

each gas component characteristic absorption line scanning unit comprises: the first optical fiber circulator is respectively connected with the first optical fiber grating and the second optical fiber circulator, and the second optical fiber circulator is connected with the second optical fiber grating; the first fiber grating and the second fiber grating are arranged on the same piezoelectric ceramic chip; the optical fiber circulator of each gas component characteristic absorption spectrum line scanning unit is respectively connected with one branch of the optical switch;

the output end of the optical switch is sequentially connected with the gas absorption cell, the photoelectric detector, the pre-amplification circuit, the A/D sampling circuit and the microcontroller in series.

Specifically, referring to fig. 1, the optical fiber coupling mirror group is fixedly connected with the optical fiber jumper FC/APC connector through a threaded structure; the 2 x 2 optical fiber beam splitter is provided with 2 input branches and 2 output branches; the other end of the optical fiber jumper is fusion-welded with 1 input branch of the 2 x 2 optical fiber beam splitter; 1 output branch of the 2 x 2 optical fiber beam splitter is connected with an optical fiber of the optical fiber delayer, and the other 1 output branch is connected with an optical fiber circulator 11; the other end of the optical fiber delayer is connected with the other 1 input branch optical fiber of the 2 multiplied by 2 optical fiber beam splitter.

In this embodiment, the optical fiber delay is formed by coiling a section of optical fiber, the total length of the optical fiber delay is 20m, and the transmission time of the light beam in the delay can be calculated to be 200ns based on the transmission theory of the light beam in the single-mode optical fiber.

The optical fiber circulator 11 is respectively connected with the optical fiber grating 11 and the optical fiber circulator 12, and the optical fiber circulator 12 is connected with the optical fiber grating 12; the other end of the fiber grating 11 is in optical fiber connection with a fiber circulator 21, the fiber circulator 21 is in optical fiber connection with the fiber grating 21 and a fiber circulator 22 respectively, and the fiber circulator 22 is in optical fiber connection with the fiber grating 22; the connection modes are analogized in sequence until the similar optical fiber connection modes are arranged among the optical fiber circulator n1, the optical fiber circulator n2, the fiber grating n1 and the fiber grating n 2;

the fiber grating 11 and the fiber grating 12 are bonded on the same piezoelectric ceramic sheet, the fiber grating 21 and the fiber grating 22 are bonded on the same piezoelectric ceramic sheet, and the rest is done in sequence until the fiber grating n1 and the fiber grating n2 are bonded on the same piezoelectric ceramic sheet; all the piezoelectric ceramic pieces are electrically connected with the piezoelectric ceramic control circuit; the optical fiber circulator 12, the optical fiber circulators 22 and … … and the optical fiber circulator n2 are respectively connected with corresponding branch optical fibers of the optical switch;

the output end of the optical switch is connected with the gas absorption cell through an optical fiber, and the other end of the gas absorption cell is connected with the photoelectric detector through an optical fiber; the photoelectric detector is electrically connected with the preamplification circuit; the pre-amplification circuit is electrically connected with the A/D sampling circuit; and the Microcontroller (MCU) is electrically connected with the A/D sampling circuit, the electro-optical switch, the Q-switching trigger circuit, the piezoelectric ceramic control circuit and the storage display module.

In the embodiment, the Q-switching trigger circuit is electrically connected with the pulse laser; the position of a light outlet of the pulse laser and the position of the total reflector are fixed according to a certain relative position, so that the total reflector can perform 90-degree turning on the light beam emitted by the pulse laser; the converging lens and the total reflector are fixed according to a certain relative position, so that the converging lens is ensured to converge the turning light beam; the electro-optical switch is arranged in front of the optical fiber coupling mirror group and is used for collecting the radiant light of the laser-induced plasma.

The pulse laser is a Q-switched pulse laser (such as Nd:: YAG Q-switched laser), and emits high-power pulse laser with nanosecond duration under the trigger of a Q-switched signal.

The gas absorption cell is provided with a gas inlet and a gas outlet, can be combined with a pumping system, and sucks in the gas to be detected on site and detects the gas.

Each fiber grating is adhered to the corresponding piezoelectric ceramic sheet; the characteristic wavelengths of the fiber gratings are different and correspond to the characteristic absorption peak wavelengths of the corresponding gas components to be detected. The piezoelectric ceramic control circuit drives each piezoelectric ceramic piece to periodically stretch and deform, and simultaneously drives the fiber grating adhered to the piezoelectric ceramic piece to periodically stretch and contract, so that the characteristic wavelength of the fiber grating is linearly changed. Due to the limitation of the current fiber grating manufacturing process, the characteristic peak broadening of the fiber grating is usually several times of the characteristic peak broadening of the gas absorption, and if the gas absorption peak is directly scanned by using a single fiber grating, only an integral spectrum can be obtained, which brings difficulty for further analysis of subsequent spectrum data. Therefore, the present embodiment further proposes a scheme of dual fiber grating scanning, which specifically includes:

referring to fig. 3, the characteristic reflection spectrum of each of the dual fiber gratings is wide, but the specific reflection spectrum of the dual fiber gratings is different and has an intersection. Moreover, the two reflection spectral bands are crossed only at the edges, forming a narrow cross band of common reflection. The two fiber gratings correspond to the same gas component, although the characteristic reflection spectrum bands are different. The double fiber gratings are adhered on the same piezoelectric ceramic chip, and the characteristic reflection spectrum sections of the two fiber gratings are scanned simultaneously along with the deformation of the piezoelectric ceramic chip. Accordingly, the narrow crossed bands will then be scanned. Because the characteristic spectrum section of the double fiber bragg gratings corresponds to the related gas components to be detected, the scanning of the characteristic absorption spectrum line of the related gas components to be detected is realized during the cross narrow-band scanning, so that the effective acquisition of the fine characteristic absorption spectrum line of the gas components is realized.

The specific working process of the laser plasma fiber grating piezoelectric demodulation multi-gas sensing system of the embodiment is as follows:

the microcontroller sends a command to the Q-switching trigger circuit, and the Q-switching trigger circuit sends a trigger signal to the pulse laser so that the pulse laser emits pulse laser. The pulse laser is bent by the total reflection mirror for 90 degrees and is focused at the focus of the pulse laser after passing through the converging lens. The air at the focus is broken down by the high power laser and a plasma is generated. The plasma will radiate a broad band beam during its evolution. Each time spectral data is acquired, the microcontroller will send a command to the electro-optical switch so that it is turned on for about 100ns, during which time the plasma evolves within 100ns and radiates a broad-band beam that passes through the electro-optical switch and is collected by the fiber coupling optics and coupled into the fiber. The design choice of the electro-optical switch can ensure high transmittance of the required spectrum when the electro-optical switch is opened. The optical fiber coupling mirror group is achromatic, and can ensure that light beams in a required spectrum band are coupled into the optical fiber with higher efficiency.

The light beam entering the optical fiber is transmitted to the 2 x 2 optical fiber beam splitter and enters from 1 input branch thereof. A 2 x 2 fiber splitter splits the beam in an intensity ratio of 5: 95. And 95% of the light beams are output by 1 of the output branches and transmitted to the optical fiber delayer along the optical fiber. The light beam is transmitted by 20 meters in the optical fiber delayer, is delayed by 200ns, is output by the other end of the optical fiber delayer and enters the 2 x 2 optical fiber beam splitter again through the other input branch of the 2 x 2 optical fiber beam splitter. Wherein the ratio of the light beam I is 5%⁽¹⁾Is output by another output branch and goes toUp to the fiber circulator 11.

The light beam passes through the fiber circulator 11 and then reaches the fiber grating 11. The microcontroller sends a command to the piezoelectric ceramic control circuit, so that the piezoelectric ceramic control circuit drives all the piezoelectric ceramic pieces to deform, and all the fiber bragg gratings are driven to deform.

The fiber grating 11 deforms the characteristic spectrum light beam corresponding to the deformationReflected, and transmitted to the fiber circulator 12 after passing through the fiber circulator 11 again. The light beam is transmitted to the fiber grating 12 after passing through the fiber circulator 12. The fiber grating 12 and the fiber grating 11 are adhered to the same piezoelectric ceramic plate, and the two are deformed together. The fiber grating 12 reflects the characteristic spectrum band corresponding to the deformation at that time. Since the fiber grating 11 crosses the narrow band of the characteristic reflection spectrum of the fiber grating 12, the fiber grating 12 will reflect the said narrow band of the reflection cross on the basis of the reflection characteristic spectrum of the fiber grating 11. The narrow-band light beamAgain through the fiber optic circulator 12 and then to the optical switch.

Because the characteristic reflection wave bands of the fiber bragg gratings 11 and the fiber bragg gratings 12 correspond to the gas component 1, the crossed narrow bands can realize scanning of the characteristic absorption spectrum line of the gas component 1 along with the deformation of the two fiber bragg gratings.

The light beam that is not reflected by the fiber grating 11 will be transmitted through the fiber grating 11 to the fiber circulator 21. Similar to the incident beam demodulation process of the fiber bragg gratings 11 and 12, the fiber bragg gratings 21 and 22 are adhered to the same piezoelectric ceramic plate, the two are used for scanning the characteristic absorption spectrum line of the gas component 2, and the corresponding light beamsWill be transmitted to the optical switch via the fiber optic circulator 22. The light beam that is not reflected by the fiber grating 21 will continue to be transmitted through the fiber grating 21. The similar process is repeated until the fiber grating n1 and the fiber grating n2 are obtainedEffecting a scanning of the characteristic absorption lines of the gas component n, the associated beamTransmitted to the optical switch via the fiber circulator n 2.

95% of the light beam passes through the optical fiber delayer and returns to the 2X 2 optical fiber beam splitter again and is split according to the intensity ratio of 5:95 again, wherein 5% of the light beam I⁽²⁾The light beams are respectively obtained after the analysis of the fiber bragg grating 11, the fiber bragg grating 12, the fiber bragg grating 21, the fiber bragg gratings 22 and … …, the fiber bragg grating n1 and the fiber bragg grating n2The light beams are transmitted to the optical switch through each branch of the optical switch in sequence; and the other 95 percent of light beams enter the 2X 2 optical fiber beam splitter again after being delayed by the optical fiber delayer and are split again according to the intensity ratio of 5: 95. The process is repeated so that every about 200ns there will be a beam of the relevant wavelength band having a duration of about 100nsFrom the corresponding branch j of the optical switch.

The optical switch keeps one branch open for a certain period of time, while the rest branches are closed, and the period of time reaches more than 10 times of 200 ns. During the opening of a branch of the optical switch, a plurality of light beams with corresponding wave bands, the duration of the light beams is about 100ns and the interval of the light beams is about 200nsAnd the light enters the gas absorption cell through the output end of the optical switch in sequence to be reflected for multiple times so as to be fully absorbed by corresponding gas components.

The multiple light beams are absorbed and then sequentially emitted from the gas absorption cell and irradiated onto a photosensitive surface of the photoelectric detector, so that multiple pulse photocurrent signals are responded in a time domain. The pulse photoelectric current signals are sequentially subjected to trans-impedance amplification of a preamplifier circuit and acquisition of an A/D sampling circuit and then sent to a microcontroller. The plurality of light beamsAre obtained by using 2 x 2 fiber beam splitters to split light with different ratios, therefore, if only the light intensity loss factor caused by the splitting ratio is considered, the light beam intensities should satisfy the following conditions:

so that the intensity of the responding photoelectric signal also satisfies the quantitative relation described in formula (1).

The microcontroller completes the calculation work of analysis of original spectrum data, inversion of the concentration of each gas component to be measured and the like, and sends the original spectrum data, the calculated result and the like to the storage display module for storage and real-time display of the monitoring result.

In this embodiment, the control timing sequence of each component of the system refers to fig. 2(a) - (e), and only one branch of the optical switch is in an open state and the other branches are closed in a certain period of time. The high level voltage signal in fig. 2(a) indicates that a branch of the optical switch is in an open state for a certain period of time, wherein the rising and falling edges of the sloped voltage indicate that the action time of opening and closing the branch of the optical switch is significantly longer than that of the remaining signals. During the time period when a certain branch of the optical switch is open, the Q-switched trigger circuit will inject a Q-switched signal into the pulsed laser, as shown in fig. 2 (b). The rising edge of the voltage immediately triggers the pulsed laser to emit a laser pulse. At the same time the electro-optical switch is opened triggered by the rising edge of the voltage at the same time and is held for about 100ns, after which the falling edge of the voltage signal arrives, the electro-optical switch is immediately closed, as shown in fig. 2 (c). The laser-induced plasma is generated by breaking down air with laser pulses and radiates a wide-spectrum light beam. The above timing control method makes the electro-optical switch continuously collect the wide-band light beam radiated by the plasma for 100ns after the plasma is generated, and then immediately stop. When the electro-optical switch is turned on, the piezoelectric ceramic piece driving circuit starts to inject a linearly increasing voltage signal into the piezoelectric ceramic piece and drives the piezoelectric ceramic piece to start to deform, as shown in fig. 2 (d). The a/D sampling circuit starts to be in both the on and standby states periodically while the electro-optical switch is turned on, as shown in fig. 2 (e).

The A/D sampling circuit firstly enters into an operating state, and the duration is the same as the opening holding time of the electro-optical switch. And in the working state, the A/D sampling circuit samples the analog photovoltage signal at a high speed according to the sampling rate. After that, the A/D sampling circuit enters a waiting state, and the waiting duration is slightly longer than the holding time of the working state according to the optical path of the gas absorption cell. After that, the light beam with 95% intensity split by the 2 × 2 beam splitter is delayed by the optical fiber delay device and returned to the 2 × 2 fiber beam splitter again, and the corresponding light beam with 5% intensity is continuously split. The beam will again respond to a photo signal of duration 100 ns. At the same time, the A/D sampling circuit just enters the working state again and starts high-speed sampling. Each time the a/D sampling circuit enters an operating state, it corresponds to a light beam of 100ns duration and its corresponding photo-electric signal. And each time the A/D sampling circuit enters a working state, the driving voltage signal of the piezoelectric ceramic piece is linearly changed in the period, and the piezoelectric ceramic piece is driven to drive the fiber bragg grating to deform, so that the characteristic absorption peak of the gas component is scanned. In different working periods of the A/D sampling circuit, the deformation processes of the fiber bragg gratings are different, so that the double fiber bragg gratings scan the gas characteristic absorption spectral lines section by section. Each beam of 100ns duration corresponds to a period of operation of the a/D sampling circuit and also to a segment of the gas characteristic absorption line.

Formula (1) shows that, for the jth group of characteristic line scanning units, the intensity value of each acquired gas characteristic absorption line is self-weighted with loss due to the light splitting effect of the 2 × 2 fiber beam splitter. In order to eliminate the influence of the weighted loss, weighted correction needs to be performed on each section of the gas characteristic absorption line obtained by scanning.

Assuming that a co-scan obtains m-section gas characteristic absorption linesAfter weighted correction, obtainThen:

for each discrete spectral line segment obtained after correction And splicing to obtain the characteristic absorption spectrum line of the corresponding gas component j.

Although the obtained multi-section gas characteristic absorption spectrum lines are discrete, the frequency of the piezoelectric ceramic piece driving voltage signal is far lower than the frequency of the A/D sampling circuit sampling control signal, the multi-section gas characteristic absorption spectrum lines are approximately continuous when spliced, and finally the quasi-continuous gas characteristic absorption spectrum lines can be effectively obtained. Based on the obtained gas absorption characteristic spectral line, the concentration of related gas components can be inverted according to a built-in quantitative analysis model.

In this embodiment, each branch of the optical switch is opened in turn, each branch corresponds to a gas component to be measured, and the above process is repeatedly performed when each branch is opened, so that high-precision online monitoring and sensing of various gas components are realized.

Example two

According to the embodiment of the invention, an embodiment of a laser plasma fiber grating piezoelectric demodulation multi-gas sensing method is disclosed, and the method is based on the laser plasma fiber grating piezoelectric demodulation multi-gas sensing system described in the first embodiment, and specifically comprises the following processes:

firstly, extracting gas to be detected into a gas absorption cell for detection; a calibrated quantitative analysis model is built in the microcontroller, and when the height of the absorption characteristic spectral line peak value of the gas to be measured relative to the spectral line baseline is obtained through analysis, the concentration value of the gas component can be accurately obtained through inversion by the model.

Under the control of the microcontroller, all the branches of the optical switch are sequentially opened and kept for a period of time, only one branch is kept opened in the same period of time, and the rest branches are in a closed state. And detecting corresponding gas components in a certain time period when one branch of the optical switch is opened and the other branches are closed. And the microcontroller simultaneously sends commands to the Q-switching trigger circuit, the electro-optical switch, the piezoelectric ceramic control circuit and the A/D sampling circuit.

After receiving the command of the microcontroller, the Q-switching trigger circuit sends a Q-switching trigger signal to the pulse laser, and the pulse laser immediately emits pulse laser with the duration of nanosecond. The pulse laser is bent by 90 degrees through the total reflector, then is focused at the focal point of the pulse laser through the converging lens and breaks through air to generate plasma. The plasma randomly evolves and radiates a broad spectrum beam.

The electro-optical switch opens upon receiving a microcontroller command and remains open for 100 ns. The electro-optical switch allows the plasma to radiate light through for the 100ns period and is turned off immediately after 100 ns. Plasma radiation light with a duration of 100ns is coupled into the optical fiber by an achromatic optical fiber coupling mirror group.

The light beam enters the optical fiber and is transmitted to a 2X 2 optical fiber coupler, and is separated according to the intensity ratio of 5: 95. And 95% of the light beams are output by 1 of the output branches and transmitted to the optical fiber delayer along the optical fiber. The light beam is transmitted by 20 meters in the optical fiber delayer, is delayed by 200ns, is output from the other end of the optical fiber delayer and enters the 2 x 2 optical fiber beam splitter through the other input branch of the 2 x 2 optical fiber beam splitter. Of which 5% is output by the other output branch and reaches the fiber circulator 11. The light beam passes through the fiber circulator 11 and then is transmitted to the fiber grating 11.

After receiving the command sent by the microcontroller, the piezoelectric ceramic control circuit drives all the piezoelectric ceramic pieces to deform, so that all the fiber bragg gratings are driven to deform. The fiber grating 11 reflects the characteristic spectrum band corresponding to the deformation, and the reflected characteristic spectrum band passes through the fiber circulator 11 again and is transmitted to the fiber circulator 12. The light beam is transmitted to the fiber grating 12 after passing through the fiber circulator 12. The fiber grating 12 and the fiber grating 11 are adhered to the same piezoelectric ceramic plate, and the two are deformed together. The fiber grating 12 reflects the characteristic spectrum band corresponding to the deformation at that time. Since the fiber grating 11 crosses the narrow band of the characteristic reflection spectrum of the fiber grating 12, the fiber grating 12 will reflect the said narrow band of the reflection cross on the basis of the reflection characteristic spectrum of the fiber grating 11. The narrow-band light beam is transmitted to the optical switch again after passing through the fiber circulator 12. Because the characteristic reflection wave bands of the fiber bragg gratings 11 and the fiber bragg gratings 12 correspond to the gas component 1, the crossed narrow bands can realize scanning of the characteristic absorption spectrum line of the gas component 1 along with the deformation of the two fiber bragg gratings.

The light beam that is not reflected by the fiber grating 11 will be transmitted through the fiber grating 11 to the fiber circulator 21. Similar to the demodulation process of the fiber bragg grating 11 and the fiber bragg grating 12 on the incident light beams, the fiber bragg grating 21 and the fiber bragg grating 22 are adhered to the same piezoelectric ceramic plate, the two devices can scan the characteristic absorption spectrum line of the gas component 2, and the corresponding light beams are transmitted to the optical switch through the fiber circulator 12. The light beam that is not reflected by the fiber grating 21 will continue to be transmitted through the fiber grating 21. This similar process will be repeated until the fiber grating n1 and the fiber grating n2 effect a scan of the characteristic absorption lines of the gas component n, the associated light beam being transmitted to the optical switch via the fiber circulator n 2.

Returning 95% of the light beams to the 2 × 2 fiber beam splitter again after passing through the fiber delay unit, and splitting the light beams again according to the intensity ratio of 5:95, wherein 5% of the light beams are transmitted to the optical switch through each branch of the optical switch in sequence after passing through the resolving action of the fiber grating 11, the fiber grating 12, the fiber grating 21, the fiber gratings 22, … …, the fiber grating n1 and the fiber grating n2 again; and the other 95 percent of light beams enter the 2X 2 optical fiber beam splitter again after being delayed by the optical fiber delayer and are split again according to the intensity ratio of 5: 95. The process is repeated so that every about 200ns a light beam of the relevant wavelength band having a duration of about 100ns is input from the corresponding branch of the optical switch.

In the same time period, only one branch of the optical switch is in an open state, and the other branches are closed. And the light beam of the wave band corresponding to the opened branch enters the gas absorption cell through the optical switch and is fully absorbed by the gas component to be detected in the gas absorption cell. The light beam then causes the photodetector to respond with an optical photocurrent. And the photocurrent is amplified by the pre-amplification circuit in a trans-resistance mode and then is sent to an A/D sampling circuit for collection. After receiving the command of the microcontroller, the A/D sampling circuit starts to be in a working state and a waiting state periodically. The A/D sampling circuit firstly enters into an operating state, and the duration is the same as the opening holding time of the electro-optical switch. And in the working state, the A/D sampling circuit samples the analog photovoltage signal at a high speed according to the sampling rate. After that, the A/D sampling circuit enters a waiting state, and the waiting duration is more than or equal to the sum of the holding time and the transmission time of the light beam in the gas absorption cell.

The light beam with 95% strength separated by the 2X 2 optical fiber beam splitter returns to the 2X 2 optical fiber beam splitter after being delayed by the optical fiber time delay device, and the light beam with 5% strength is separated continuously. The beam will again respond to a photo signal of duration 100 ns. At the same time, the A/D sampling circuit just enters the working state again and starts high-speed sampling.

Each time the a/D sampling circuit enters an operating state, it corresponds to a light beam of 100ns duration and its corresponding photo-electric signal. And each time the A/D sampling circuit enters a working state, the driving voltage signal of the piezoelectric ceramic piece is linearly changed in the period, and the piezoelectric ceramic piece is driven to drive the fiber bragg grating to deform, so that the characteristic absorption peak of the gas component is scanned.

In different working periods of the A/D sampling circuit, the deformation processes of the fiber bragg gratings are different, so that the double fiber bragg gratings scan the gas characteristic absorption spectral lines section by section. Each beam of 100ns duration corresponds to a period of operation of the a/D sampling circuit and also to a segment of the gas characteristic absorption line. When a branch of the optical switch is opened, after the fiber grating scanning process is completed, weighting correction is carried out on each obtained scanning spectral band, then the corrected discrete spectral band segments are spliced, and finally the quasi-continuous gas characteristic absorption spectral line can be effectively obtained.

Based on the obtained gas absorption characteristic spectral line, the relative height of the absorption peak value relative to the spectral line base line is calculated, and the concentration of the related gas components can be inverted according to the built-in quantitative analysis model. And the information such as the original spectrum data, the gas component concentration and the like is sent to a storage display module by the microcontroller for storage and real-time display.

The implementation process is continuously carried out, and high-precision online monitoring and sensing of the multi-component gas in different concentration ranges are simultaneously carried out.

It should be noted that specific implementation manners of the above processes, such as a method for performing weighted correction on each scanning spectrum, a timing control method of each component, and the like, have been described in detail in the first embodiment, and are not described herein again.

Although the embodiments of the present invention have been described with reference to the accompanying drawings, it is not intended to limit the scope of the present invention, and it should be understood by those skilled in the art that various modifications and variations can be made without inventive efforts by those skilled in the art based on the technical solution of the present invention.