CN201083500Y - Automatic tuning F-P optical fiber sensor - Google Patents

Abstract

An automatic tuning F-P optical fiber sensor comprises a light source and a sensing head, wherein the light source comprises a laser with a temperature control circuit, the laser is connected with the first port of the coupler through an optical fiber, the third port of the coupler is connected with the sensing head through a single mode optical fiber, the fourth port of the coupler is connected with the active control unit through a second photoelectric detector, the second port of the coupler is connected with the input port of the first photoelectric detector, the output port of the first photoelectric detector 5 is respectively connected with the active control unit and the signal output unit, the output end of the active control unit is connected with the temperature control circuit, the sensing head comprises an F-P cavity, the two cavity surfaces of the F-P cavity are respectively connected with a silicon film and a light guide optical fiber, the silicon film, the F-P cavity and the light guide optical fiber are fixed by a quartz sleeve, and the other end of the light guide optical fiber is connected with the single mode optical fiber. The utility model has the characteristics of harmonious convenience, low in cost, sensitivity height and adaptation environmental change.

Description

Automatic tuning control F-P fiber optic sensor

Technical field

The utility model relates to Fibre Optical Sensor, is a kind of stable fiber optics displacement/vibration transducer in high sensitivity working point (abbreviating the Q point as) that utilizes optical fiber as the Fabry based on MEMS (micro electro mechanical system) (MEMS) technology-Paro resonator cavity (being designated hereinafter simply as the F-P chamber) of transmission light medium.Specially refer to the F-P chamber of using plated film and utilize certain chamber long, obtain having the striped maximum-contrast that low fineness is interfered, control the sensing system of tunable laser wavelength and then locking system Q value point by signal output feedback.The utility model is applicable to be measured the displacement in environment temperature or the unsettled place of extraneous medium, pressure, ultrasound wave etc.

Background technology

Up to date, pressure transducer, for example vibration transducer remains the structure based on condenser type or pressure resistance type.This structure has a lot of shortcomings, and for example sensitivity is low, and high bias voltage requires between each layer insulation, requires the consistance etc. between the membrane electrode, and above problem all will have very complicated solution.

Fibre-optical F-P sensor can solve the disturbed a lot of problems of capacitance type sensor, such as need not biasing and solenoid isolation.In addition, also to have many good qualities be that capacitance type sensor is incomparable to fibre-optical F-P sensor.For example highly sensitive, anti-electromagnetic interference (EMI), safe and reliable, volume is little, corrosion-resistant, can constitute optical fiber sensing network etc., thereby in industrial flaw detection, the material behavior analysis, sound sensor, the detection of partial discharge of transformer, the aspects such as mensuration of liquid level and hydraulic pressure have good application prospects.But at present, also have some problems to limit its widespread use: selecting for use of light source, require the light source live width can not be too narrow can not be too wide, and require highly stable; In the making of sensing head, the variation that conform, owing to be based on interfere type, the range of linearity that sensing head is operated in F-P interference spectum (sinusoidal pattern) has the linear transformation function, signal Processing is more convenient.So we generally select for use the point of slope maximum in the interference spectrum of F-P chamber (to see Bing Yu as the working point (the following Q value point that is called again) of sensing head, Anbo Wang, " Grating-assisted demodulation of interferometric optical sensors " Appl.Opt.42 6824-6829 (2003)), near the Q point, the light signal response of signal to external world is linear, and has maximum response sensitivity.The variation of environment is easy to make sensing head to depart from sensitivity maxima point and arrives nonlinear area.

Fibre-optical F-P sensor all has argumentation in a lot of papers, at problem some solutions have been proposed all also, such as document 1[John F.Dorighi, " Stabilization of an embedded fiber optic Fabry-Perot sensorfor ultrasound detection " IEEE Trans.Ultrason.Ferroelectr.Freq.Control 42,820-824 (1995)], select for use the method for outside cavity gas laser+FEEDBACK CONTROL wavelength to carry out tuning to the Q point and control, played purpose the stable control of Q value point of sensing head.Yet this method can run into that the narrow linewidth of outside cavity gas laser is brought because the noise (parasitic F-P effect) that external interference causes, and the outside cavity gas laser that this method is used can allow this system become heavy and expensive, and do not consider the variation of laser instrument light intensity and because the influence that the generation of signal brings interference, also to use oscillograph in this tuning process, the practicality of this method is restricted.

The patent No. is among ZL200610024955's " fibre-optical acoustic sensor " (Cai Haiwen etc.), sonic transducer is selected the scheme of wideband light source+tunable optic filter for use, obtain the light source of live width about 1nm, if this method wave filter is reliable, can obtain the light source of stable suitable F-P sensing head, but the shortcoming of this method also is clearly, except tunable optic filter generally compares the costliness, and generally be more weak through the light behind broadband and the tunable optic filter, this will cause the decline of system sensitivity.

Summary of the invention

The technical problems to be solved in the utility model is to overcome above-mentioned the deficiencies in the prior art, a kind of automatic tuning control F-P fiber optic sensor is provided, and this sensor should have tuning convenience, cheap, highly sensitive and the variation of environment had extremely strong adaptive characteristics.

The main foundation of the utility model design comprises:

Canonical process analysis for the feedback effect of the distributed feed-back formula laser instrument (abbreviating DFB as) in the light source can be described with model Debao sieve equation (Van der Pol equation).The relation of external feedback and its live width can directly be represented with following examination:

$\∂f=\frac{{\∂f}_o}{{[1+\sqrt{1+{\mathrm{\α}}^2}{\mathrm{\κ\τ}}_e\cos ({\mathrm{\ω\τ}}_e+{\tan }^{-1}\mathrm{\α})]}^2}---\left(1\right)$

Wherein:  f _oThe live width of DFB when not feeding back, τ _eBe the time delay of external feedback, α is that live width is widened the factor, and the expression formula of k is:

$\mathrm{\κ}=\frac{1}{{\mathrm{\τ}}_s}\frac{1-R_s}{\sqrt{R_s}}\sqrt{R_e}---\left(2\right)$

τ _sBe the time of light in one week of distributed feedback laser semiconductor internal communication, R _sBe the power reflectance of the front end surface of laser, R _eBe the external energy feedback factor.

From formula 1 as can be seen, the distributed feedback laser live width widens by the factor

Decision, just energy back size and the feedback delay by the outside determines, in our system, the energy of external feedback is generally at negative tens dB, just in time be in our the live width widening range, record live width through experiment and widened about 1000 times, reach about 10GHz.

We also measure the influence of the output power of laser instrument external feedback, find that under the modulation of feedback signal at 5KHz, feedback is negligible to the influence of laser output power.

About sensing head, the formation of the utility model sensing head comprises the F-P chamber, and the two chamber faces in this F-P chamber connect silicon fiml and light-conductive optic fibre respectively, and described silicon fiml, F-P chamber and light-conductive optic fibre are fixed by a quartz sleeve, is the long selection foundation in chamber, F-P chamber below:

For the contrast maximum that obtains interfering, the chamber in F-P chamber length and silicon fiml reflectivity have following relation:

${\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="S2007200751773E00011.png"\; state="\{\{state\}\}">R</figure-callout>}}_2^2=\frac{\underset{0}{\overset{a}{\&Integral;}}\exp (-\frac{{2\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="S2007200751773E00011.png"\; state="\{\{state\}\}">r</figure-callout>}}^2}{{\mathrm{\&omega;}}_0^2})\&CenterDot;r\&CenterDot;2\mathrm{\&pi;}\&CenterDot;\mathrm{dr}}{\underset{0}{\overset{a}{\&Integral;}}\frac{{\mathrm{\&omega;}}_0^2}{{\mathrm{\&omega;}}_2^2}\exp (-\frac{{2\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="S2007200751773E00011.png"\; state="\{\{state\}\}">r</figure-callout>}}^2}{{\mathrm{\&omega;}}_2^2})\&CenterDot;r\&CenterDot;2\mathrm{\&pi;}\&CenterDot;\mathrm{dr}}\&CenterDot;\frac{{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="S2007200751773E00011.png"\; state="\{\{state\}\}">R</figure-callout>}}_1^2}{{\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="S2007200751773E00011.png"\; state="\{\{state\}\}">T</figure-callout>}}_1^4}---\left(3\right)$

Wherein: R ₁And T ₁Be the reflectivity and the transmitance of light-conductive optic fibre end face, R ₂Be the reflectivity of silicon fiml inboard, z ₀Be the characteristic parameter in chamber, ω ₀Be the inside radius of fiber core, ω ₂For light propagates into the spot radius at silicon fiml place, λ is an optical maser wavelength, the long z in chamber ₂Be expressed as:

$z_2=z_0\sqrt{1-\frac{{\mathrm{\&omega;}}_2^2}{{\mathrm{\&omega;}}_0^2}}---\left(4\right)$

$z_0=\frac{\mathrm{\&pi;}{\mathrm{\&omega;}}_0^2}{\mathrm{\&lambda;}}---\left(5\right)$

Owing to be subjected to the wavelength tuning restriction of general semiconductor Distributed Feedback Laser, our F-P chamber length is generally selection greater than 200um, consider the reflection of avoiding two faces of silicon, the reflectivity that we select the silicon fiml plated film should be greater than 70%, so the long selection in chamber is the coefficient result of each factor.

Technical solution of the present utility model is as follows:

A kind of automatic tuning control F-P fiber optic sensor, comprise light source and sensing head, be characterized in that this light source comprises a laser instrument and corresponding driving circuit and temperature control circuit, this laser instrument links to each other with first port of coupling mechanism through optical fiber, the 3rd port of this coupling mechanism connects described sensing head through single-mode fiber, the 4th port of described coupling mechanism connects the ACTIVE CONTROL unit through second photodetector, second port of this coupling mechanism connects the input port of first photodetector, this first photodetector output port connects described ACTIVE CONTROL unit and signal output unit respectively, the described temperature control circuit of output termination of described ACTIVE CONTROL unit, the formation of described sensing head comprises the F-P chamber, the two chamber faces in this F-P chamber connect silicon fiml and light-conductive optic fibre respectively, described silicon fiml, F-P chamber and light-conductive optic fibre are fixed by a quartz sleeve, the described single-mode fiber of another termination of described light-conductive optic fibre.

Long 〉=200 μ m in the chamber of described F-P.

Described coupling mechanism is a three-dB coupler.

The laser instrument of described light source is a distributed feed-back single mode semiconductor laser, and the output terminal of this distributed feed-back single mode semiconductor laser has the light feedback.

The medial surface of described silicon fiml is coated with reflectance coating, and the range of choice of reflectivity is 70%～100%.Owing to can have certain degree of difficulty and randomness at the light-conductive optic fibre end face coating, we do not carry out coating film treatment to the end face of light-conductive optic fibre, and the power reflectance of light-conductive optic fibre end face approximately is exactly 3.5% like this,

All lines all adopt single-mode fiber to connect, and joint generally all adopts angled flexible jumper (APC joint) as far as possible, disturb to reduce extra F-P.

Technique effect of the present utility model:

(1) the utility model adopts the chamber progress row design to the F-P chamber of sensing head, adopts the long sensing head in long F-P chamber, to reduce the requirement to the laser wavelength tuning range;

(2) medial surface of the silicon fiml of the utility model sensing head is coated with reflectance coating, avoided two reflecting surface reflected light of silicon fiml to produce interference to received signal, make the contrast of F-P interference fringe big as much as possible,, greatly improved the sensitivity of system generally greater than 30dB;

(3) ACTIVE CONTROL of the present utility model unit receives the temperature control of Distributed Feedback Laser of the electric signal active adjustment light source of first photodetector, in time the working point of FEEDBACK CONTROL sensing head is in the Q point position in F-P chamber, the sensitivity and the dynamic range of system have been improved, avoided when system calibration, using big spectrometer and oscillographic problem, greatly simplified the structure of system.

(4) adopted the distributed feed-back single mode semiconductor laser to make light source, solved the sensitive issue to external world that the narrow bandwidth laser instrument is brought, and made the capacity usage ratio height of light source, output energy height, improved the sensitivity of system, and light source becomes small and exquisite, dwindled the volume of system;

Description of drawings

Fig. 1 is the structural representation of the utility model automatic tuning control F-P fiber optic sensor

Embodiment

See also Fig. 1 earlier, Fig. 1 is the structural representation of the utility model automatic tuning control F-P fiber optic sensor, it also is the structural representation of the utility model embodiment, as seen from the figure, the present embodiment automatic tuning control F-P fiber optic sensor, comprise light source 1 and sensing head 4, this light source 1 is the distributed feed-back single mode semiconductor laser of a band temperature control circuit, this laser instrument links to each other with first port 201 of coupling mechanism 2 through optical fiber, the 3rd port 203 of this coupling mechanism 2 connects described sensing head 4 through single-mode fiber 3, the 4th port 204 of described coupling mechanism 2 connects ACTIVE CONTROL unit 7 through second photodetector 6, second port 202 of this coupling mechanism 2 connects the input port of first photodetector 5, the output terminal of this first photodetector 5 connects described ACTIVE CONTROL unit 7 and signal output unit 8 respectively, the temperature control circuit of the described light source 1 of output termination of described ACTIVE CONTROL unit 7, the formation of described sensing head 4 comprises F-P chamber 402, the two chamber faces in this F-P chamber 402 connect silicon fiml 401 and light-conductive optic fibre 404 respectively, described silicon fiml 401, F-P chamber 402 and light-conductive optic fibre 404 are fixing by a quartz sleeve 403, the described single-mode fiber 3 of another termination of described light-conductive optic fibre 404.

Described in the present embodiment coupling mechanism 2 is a three-dB coupler.The medial surface of described silicon fiml 401 is coated with highly reflecting films.All lines all adopt single-mode fiber to connect, and joint generally all adopts angled flexible jumper to connect as far as possible, disturb to reduce extra F-P.

Described first photodetector 5 and second photodetector 6 are elected near the photodetector the 1550nm as.

The working condition of present embodiment is as follows:

Light is from light source 1, first port through coupling mechanism 2 advances, from the 3rd port 203, the two-way output in 204 fens of the 4th port, one the road is surveyed by second photodetector 6 from the output of the 4th port 204, change electric signal into, be called light beam electric signal G, enter ACTIVE CONTROL unit 7, another route the 3rd port 203 outputs enter sensing head 4 through single-mode fiber 3, and sensing head 4 is by silicon fiml 401, F-P chamber 402, quartz sleeve 403 and light-conductive optic fibre 404 constitute, at fiber end face plated film not, reflectivity is 3.5%, and the silicon fiml inboard is gold-plated, reflectivity 100%, the long 362um in chamber shows that through measurement the interference contrast in this F-P chamber 402 reaches 22.88dB.When light beam enters sensing head 4, in some reflection of light-conductive optic fibre 404 end faces, a part enters 402 backs, F-P chamber and is produced interference by silicon fiml 401 reflection backs in the end of light-conductive optic fibre 404, the F-P that belongs to low fineness interferes, again since the live width of light source 1 than broad, so the general result of interference that only needs to consider primary event.The inner face of silicon fiml 401 is coated with highly reflecting films, with F-P chamber 402 of end face formation of light-conductive optic fibre 404.External shock produces silicon fiml 401 and is forced to vibrations, and then the chamber in change F-P chamber 402 is long, will modulate light intensity in the interference fringe of light-conductive optic fibre 404 end faces like this.Modulated light is called flashlight, import from coupling mechanism 2 the 3rd port 203 through single-mode fiber 3 again, first port 201 and 202 outputs of second port by coupling mechanism 2, surveyed by first photodetector 5 from the flashlight of second port, 202 outputs, change electric signal into, be called the flashlight electric signal, this flashlight electric signal major part X1 exports for using through output unit 8, this flashlight electric signal another part X2 enters ACTIVE CONTROL unit 7, in ACTIVE CONTROL unit 7:

(1) flashlight electric signal X2 and light beam electric signal G being averaged (filtering) back is divided by by divider, obtain the X2/G control signal of a relative light source, the purpose of doing like this is to remove the light source power influence that floats, obtain one with the light source power irrelevant control signal that floats, also promptly reflect the relative value of sensing head 4 laser-bounce output levels;

(2) this result is compared with the size of one parameter relevant with the character of sensing head itself.

(3) Bi Jiao result regulates the temperature control circuit of controlling in the light source 1 by a proportional integral circuit, thereby the wavelength that guarantees the laser instrument in the light source 1 makes sensing head 4 be operated near the Q value point all the time.

In addition, as the utility model the very important point, laser output of the present utility model is not add isolator, according to theory, after a small amount of feedback of distributed feedback semiconductor laser adding, about 15～18dB, the output linewidth of laser instrument can sharply be widened, measurement result shows that the output linewidth of introducing feedback back laser instrument has changed to about 10GHz by several MHz, is in just in the scope of our measurement.

Signal output unit 8 can be as required by the preposition amplification of signal, and filtering is received on the oscillograph after back level is amplified or on the display system; Perhaps before put the back and be connected on the computer by data collecting card, so that signal is handled, with obtain detectable signal such as frequency, intensity, the velocity of sound, physical quantitys such as orientation.

Test shows, the utility model sensor has tuning convenience, cheap, highly sensitive and the variation of environment had extremely strong adaptive characteristics.

Claims (6)

1. automatic tuning control F-P fiber optic sensor, comprise light source (1) and sensing head (4), it is characterized in that this light source (1) comprises a laser instrument that has temperature control circuit, this laser instrument directly links to each other with first port (201) of coupling mechanism (2) through optical fiber, the 3rd port (203) of this coupling mechanism (2) connects described sensing head (4) through single-mode fiber (3), the 4th port (204) of described coupling mechanism (2) connects ACTIVE CONTROL unit (7) through second photodetector (6), second port (202) of this coupling mechanism (2) connects the input port of first photodetector (5), the output port of this first photodetector (5) connects described ACTIVE CONTROL unit (7) and signal output unit (8) respectively, the described temperature control circuit of output termination of described ACTIVE CONTROL unit (7), the formation of described sensing head (4) comprises F-P chamber (402), the two chamber faces in this F-P chamber (402) connect silicon fiml (401) and light-conductive optic fibre (404) respectively, described silicon fiml (401), F-P chamber (402) and light-conductive optic fibre (404) are fixing by a quartz sleeve (403), the described single-mode fiber of another termination (3) of described light-conductive optic fibre (404).

2. automatic tuning control F-P fiber optic sensor according to claim 1 is characterized in that 〉=200 μ m are grown in the chamber in described F-P chamber (402).

3. automatic tuning control F-P fiber optic sensor according to claim 1 is characterized in that described coupling mechanism (2) is a three-dB coupler.

4. automatic tuning control F-P fiber optic sensor according to claim 1, the laser instrument that it is characterized in that described light source (1) is the distributed feed-back single mode semiconductor laser, the output terminal of this laser instrument has the light feedback.

5. automatic tuning control F-P fiber optic sensor according to claim 1 is characterized in that the medial surface of described silicon fiml (401) is coated with reflectance coating, and the range of choice of reflectivity is 70%～100%.

6. automatic tuning control F-P fiber optic sensor according to claim 1 is characterized in that all lines all adopt single-mode fiber to connect, and all joints adopt angled flexible jumper.

Images