CN100432655C

CN100432655C - Gas concentration detection method and equipment based on optical fiber laser intracavity sensitivity

Info

Publication number: CN100432655C
Application number: CNB2005100970032A
Authority: CN
Inventors: 管祖光; 陈达如; 何赛灵
Original assignee: Zhejiang University ZJU
Current assignee: Zhejiang University ZJU
Priority date: 2005-12-31
Filing date: 2005-12-31
Publication date: 2008-11-12
Anticipated expiration: 2025-12-31
Also published as: CN1793849A

Abstract

The present invention relates to a sensitive gas concentration detecting method and a device based on a linearising cavity optical fiber laser inner cavity. The present invention uses 980 nm laser as a pumping source. A feedback cavity is composed of an optical fiber Bragg grating pair. Light energy travelling in a tapered optical fiber is formed into an evanescent field trail in outside air. The loss of the light energy has sensitivity to some gas concentration. The output light power of the linearising cavity optical fiber laser is measured to obtain gas concentration. The present invention is suitable for measuring the gas concentration of different kinds. Because signal light vibrates forwards and backwards in a laser cavity, an effective light range for sensing is increased. The present invention greatly improves the measuring accuracy of the gas concentration. Meanwhile, the power of the signal light is amplified by the laser, and the present invention is favourable for long-distance signal transmission.

Description

Gas concentration detection method and equipment based on optical fiber laser intracavity sensitivity

Technical field

The invention belongs to technical field of optical fiber sensing, particularly a kind of gas concentration detection method and equipment based on the linear cavity fiber laser intracavity sensitivity.

Background technology

Along with progress of science and technology and industrialized development, the pollution of human habitat is also in continuous increase, wherein atmospheric pollution is one of very serious problem, exist various harmful poisonous, inflammable and explosive gases in people's the living environment, the various harmful gases that discharge from the family expenses inflammable gas to industry, transportation, and even frequently cause the former fierce methane of explosion of coal mines, all need high-precision gas sensor to measure.

Fiber gas sensor has following advantage than other gas sensors: (1) is suitable for the on-line measurement of long distance; (2) be suitable for measuring flammable explosion hazard gases or work in Flammable atmosphere and under strong electromagnetic interference environment, measure; (3) sensing unit is simple in structure, and is reliable and stable; (4) be easy to form optical fiber sensing network.Therefore, recent two decades comes Fibre Optical Sensor to emerge a lot of application schemes aspect gas sensing, as utilizes the fiber spectrum absorption process of Lambert-Beer law and improved fast travelling waves of optical fibre loss method on this principle.Said method often needs to utilize the method for geometrical optics to increase the stroke of light in gas to be measured to improve measuring accuracy, and this is integrated very unfavorable with encapsulation to sensor.

Summary of the invention

The present invention is directed to the deficiencies in the prior art, proposed a kind of be easy to gas concentration detection method and equipment based on the linear cavity fiber laser intracavity sensitivity integrated and encapsulation.

Method of the present invention may further comprise the steps:

1, determine the spectral absorption peak position of gas to be measured at 1525～1565 nanometer optical communication wave bands, according to this absorption peak position, the design Fiber Bragg Grating FBG makes it this gas absorption peak of reflection peak position alignment, and reflectivity is more than or equal to 99%.

2, the Fiber Bragg Grating FBG of two identical parameters is distinguished the end of welding at two sections Er-doped fibers, the other end of two sections Er-doped fibers connects by tapered fiber light, and Fiber Bragg Grating FBG, tapered fiber and Er-doped fiber constitute reaction cavity; With wavelength is that 980 nanometer pump lights carry out pumping by resonator cavity one end to this resonator cavity through one-way isolator, and the resonator cavity other end is as laser output.

3, will place the air chamber that is full of gas to be measured as the tapered fiber of sensing unit, when linear cavity fiber laser is worked, flashlight is concussion back and forth in resonator cavity, during through tapered fiber, the evanescent wave hangover is exposed in the gas to be measured, because signal light wavelength just in time drops on the gas absorption peak, luminous energy is by gas absorption loss to be measured, and the loss equation satisfies the Lambert-Beer law:

I＝I ₀exp(-αrnL)，(1)

Wherein, I is output light light intensity, I ₀Be the incident light light intensity, α is an absorption coefficient, and r is that the evanescent wave hangover accounts for total luminous energy ratio, and n is a gas concentration, and L is effective light path of flashlight process in gas to be measured.From formula (1) as can be seen, laser chamber internal loss and gas concentration exponent function relation.Because it is relevant with the laser chamber damage that laser instrument goes out luminous power, so the luminous power size has reflected the gas concentration size.

4, in air chamber, charge into the sample gas under study of variable concentrations, detect corresponding laser output intensity, determine concentration and laser output intensity relation; Consider the light concentration gas that is of measurement, can think that gas concentration and laser output intensity are linear:

I＝An+B，(2)

Wherein, I is a laser output intensity, and n is a gas concentration.

5, will need the gas to be measured of detectable concentration to charge into air chamber,, determine gas concentration to be measured by measuring laser output intensity according to formula (2).

The equipment of realizing such scheme comprises: one to place air chamber interior diameter D be that 1～3 micron, length L are 5～15 centimetres tapered fiber, and the two ends of tapered fiber are connected with Er-doped fiber light respectively, and the other end of Er-doped fiber is respectively equipped with Fiber Bragg Grating FBG.The pumping source of 980 nano wave lengths is connected with a Fiber Bragg Grating FBG light by one-way isolator, and photodiode is connected with another Fiber Bragg Grating FBG light.

The present invention mainly is applicable to the high-acruracy survey that low concentration (volume ratio 1～5%) gas at spectral absorption peak is arranged at optical communication spectral coverage (1525～1565 nanometer).Because the resonance effect in the laser chamber increases the effective cavity length of sensing greatly, thereby has greatly improved measuring accuracy.Because laser instrument to the amplification of flashlight, is strengthened the ability of light signal long-distance transmissions, very be suitable for the application scenario of remote recording again.Simultaneously, the present invention also with anti-electromagnetic interference (EMI), be suitable for distributed schemes, simple for structurely be easy to advantages such as integrated.

Description of drawings

Fig. 1 is an one-piece construction synoptic diagram of the present invention;

Fig. 2 is the partial enlarged drawing of Fig. 1.

Embodiment

To detect gas concentration lwevel is example, and selected carbon dioxide is changed to 1538 nanometers in the spectral absorption peak position of optical communication wave band, and designing and make two reflection peak positions is that 1538 nanometers, reflectivity are 99% Fiber Bragg Grating FBG.

As illustrated in fig. 1 and 2, one to place air chamber 6 interior diameters be that 2 microns, length are 10 centimetres tapered fiber 5, the two ends of tapered fiber 5 are connected with 7 light with Er-doped fiber 4 respectively, the Er-doped fiber 4 and 7 the other end are respectively equipped with Fiber Bragg Grating FBG 3 and 8, the pumping source 1 of 980 nano wave lengths is connected with a Fiber Bragg Grating FBG 3 light by one-way isolator 2, and photodiode 9 is connected with another Fiber Bragg Grating FBG 8 light.

The Distributed Feedback Laser work of 980 nano wave lengths, linear cavity fiber laser begins bright dipping.In air chamber, charge into the sample gas under study of variable concentrations, detect corresponding laser output intensity, determine concentration and laser output intensity relation; Consider measurement for light concentration gas, can think the linear of gas concentration and Output optical power:

I＝An+B，(2)

Wherein, I is a laser output power, and n is a gas concentration.

Sensor is installed in mine, tunnel, gas station etc. measures the place, ambient atmos is charged into air chamber, measure optical power value, utilize formula (2) to obtain the gas concentration in tested area with photodiode.

This programme has the measuring accuracy height, is fit to remote recording, anti-electromagnetic interference (EMI) and advantage such as simple for structure.

Claims

1,, it is characterized in that this method may further comprise the steps based on the gas concentration detection method of linear cavity fiber laser intracavity sensitivity:

(1), determines the spectral absorption peak position of this gas at 1525～1565 nanometer optical communication wave bands according to gas to be measured; According to this absorption peak position, the design Fiber Bragg Grating FBG makes it this gas absorption peak of reflection peak position alignment, and reflectivity is more than or equal to 99%;

(2) Fiber Bragg Grating FBG of two identical parameters is distinguished the end of welding at two sections Er-doped fibers, the other end of two sections Er-doped fibers connects by tapered fiber light, and Fiber Bragg Grating FBG, tapered fiber and Er-doped fiber constitute reaction cavity; With wavelength is that 980 nanometer pump lights carry out pumping by resonator cavity one end to this resonator cavity through one-way isolator, and the resonator cavity other end is as laser output;

(3) will place air chamber as the tapered fiber of sensing unit, in air chamber, charge into the sample gas under study of variable concentrations, detect corresponding laser output intensity, determine concentration and laser output intensity relation; Described sample gas under study is a light concentration gas, and gas concentration and laser output intensity are linear: I=An+B, and wherein, I is that laser output intensity, n are gas concentration;

(4) will need the gas to be measured of detectable concentration to charge into air chamber,, determine gas concentration to be measured by the mensuration laser output intensity according to the gas concentration and the relation of laser output intensity that (3) are determined.

2, adopt the employed equipment of claim 1 method, it is characterized in that this equipment comprises that one places the tapered fiber in the air chamber, the two ends of tapered fiber are connected with Er-doped fiber light respectively, the other end of Er-doped fiber is respectively equipped with Fiber Bragg Grating FBG, the pumping source of 980 nano wave lengths is connected with a Fiber Bragg Grating FBG light by one-way isolator, and photodiode is connected with another Fiber Bragg Grating FBG light; Described tapered fiber diameter is that 1～3 micron, length are 5～15 centimetres.