CN201083500Y - Auto-tuning F-P fiber optic sensor - Google Patents

Abstract

An automatic tuning F-P optical fiber sensor includes a light source and a sensor head. The light source includes a laser with a temperature control circuit. The laser is connected to the first port of a coupler via an optical fiber. The third port of the coupler is connected to the sensor head via a single-mode optical fiber. The fourth port of the coupler is connected to an active control unit via a second photodetector. The second port of the coupler is connected to the input port of the first photodetector. The output port of the first photodetector is respectively connected to the active control unit and the signal output unit. The output end of the active control unit is connected to the temperature control circuit. The sensor head includes an F-P cavity. The two cavity surfaces of the F-P cavity are respectively connected to a silicon film and a light-guiding optical fiber. The silicon film, the F-P cavity and the light-guiding optical fiber are fixed by a quartz sleeve. The other end of the light-guiding optical fiber is connected to the single-mode optical fiber. The utility model has the characteristics of convenient tuning, low cost, high sensitivity and adaptability to environmental changes.

Description

Auto-tuning F-P fiber optic sensor

technical field

The utility model relates to optical fiber sensing, which is a high-sensitivity working point of a Fabry-Perot resonator (hereinafter referred to as F-P cavity) based on micro-electromechanical system (MEMS) technology using optical fiber as a transmission light medium (referred to as Q point) stable fiber optic displacement/vibration sensor. In particular, it involves the use of a coated F-P cavity and a sensor system that uses a certain cavity length to obtain the maximum contrast of fringes with low-precision interference, controls the wavelength of the tunable laser through signal output feedback, and then locks the Q value point of the system. The utility model is suitable for measuring the displacement, pressure, ultrasonic wave, etc. of places where the ambient temperature or the external medium is unstable.

Background technique

Until recently, pressure sensors, such as vibration sensors, were based on capacitive or piezoresistive structures. This structure has many disadvantages, such as low sensitivity, high bias voltage, insulation between layers, consistency between membrane electrodes, etc., all of which require complex solutions.

Fiber-optic F-P sensors can solve many problems that capacitive sensors suffer from, such as no bias and electromagnetic isolation. In addition, fiber optic F-P sensors have many advantages that capacitive sensors cannot match. For example, high sensitivity, anti-electromagnetic interference, safe and reliable, small size, corrosion resistance, and can form an optical fiber sensor network, etc., so it is widely used in industrial flaw detection, material characteristic analysis, sound sensing, transformer partial discharge detection, liquid level and water pressure detection. It has a good application prospect in measurement and so on. But at present, there are still some problems that limit its wide application: in the selection of the light source, it is required that the line width of the light source should not be too narrow or too wide, and it must be very stable; in the production of the sensor head, it must adapt to changes in the environment , because it is based on the interference type, the sensor head works in the linear region of the F-P interference spectrum (sinusoidal type) and has a linear transfer function, and the signal processing is more convenient. Therefore, we generally choose the point with the largest slope in the F-P cavity interference spectrum line as the working point of the sensor head (hereinafter referred to as the Q value point) (see Bing Yu, Anbo Wang, "Grating-assisted demodulation of interferometric optical sensors" Appl. Opt.42 6824-6829(2003)), near the Q point, the response of the optical signal to the external signal is linear, and has the maximum response sensitivity. Changes in the environment can easily cause the sensor head to deviate from the maximum sensitivity point and reach the nonlinear region.

Fiber optic F-P sensors have been discussed in many papers, and some solutions have been proposed for the problems, such as literature 1 [John F. Dorigi, "Stabilization of an embedded fiber optic Fabry-Perot sensor for ultrasound detection" IEEE Trans.Ultrason. Ferroelectr.Freq.Control 42, 820-824(1995)], the Q point is tuned and controlled by the method of external cavity laser + feedback control wavelength, which has achieved the purpose of stabilizing the Q value point of the sensor head. However, this method will encounter noise caused by external interference (parasitic F-P effect) brought by the narrow linewidth of the external cavity laser, and the external cavity laser used in this method will make the system bulky and expensive, and does not consider the laser Due to the change of light intensity and the influence of signal generation on interference, an oscilloscope is also used in this tuning process, which limits the practicality of this method.

In the "Fiber Optic Acoustic Sensor" (Cai Haiwen, etc.) whose patent number is ZL200610024955, the acoustic sensor adopts the solution of broadband light source + tunable filter to obtain a light source with a line width of about 1nm. If the filter is reliable in this method, stable It is suitable for the light source of F-P sensor head, but the disadvantage of this method is also obvious, except that the tunable filter is generally more expensive, and the light after the broadband and tunable filter is generally relatively weak, which will cause A drop in system sensitivity.

Contents of the invention

The technical problem to be solved by the utility model is to overcome the deficiencies of the above-mentioned prior art and provide an automatic tuning F-P optical fiber sensor. The sensor should have the advantages of convenient tuning, low cost, high sensitivity and strong adaptability to environmental changes. features.

The main basis of the utility model design comprises:

The typical process analysis of the feedback effect of the distributed feedback laser (referred to as DFB) in the light source can be described by the Van der Paul equation. The relationship between external feedback and its line width can be expressed directly by the following test:

$<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; =</span>\frac{{<span\; class="notranslate">\; \&PartialD;</span>\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}{{<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\sqrt{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; \&kappa;\&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;\&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; the\; tan</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Among them: f _o is the line width of DFB when there is no feedback, τ _e is the delay time of external feedback, α is the line width widening factor, and the expression of k is:

$\mathrm{<span\; class="notranslate">\; \&kappa;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}\frac{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{\sqrt{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}}\sqrt{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

τ _s is the time for light to propagate in the semiconductor of the distributed feedback laser for one week, R _s is the power reflectivity of the front surface of the laser, and _Re is the external energy feedback factor.

决定，也就是由外部的能量反馈大小和反馈延迟决定，在我们的系统中，外部反馈的能量一般在负十几个dB，正好处在我们的线宽加宽范围内，经实验测得线宽加宽了大约1000倍，达到10GHz左右。From Equation 1, it can be seen that the broadening of the linewidth of a distributed feedback laser is given by the factor

It is determined by the external energy feedback and feedback delay. In our system, the energy of external feedback is generally in the range of minus ten dB, which is just within the widening range of our line width. The bandwidth has been widened by about 1000 times, reaching about 10GHz.

We also measured the influence of external feedback on the output power of the laser, and found that the influence of feedback on the output power of the laser can be ignored under the modulation of the feedback signal at 5KHz.

Regarding the sensing head, the composition of the sensing head of the present utility model includes an F-P cavity, and the two cavity surfaces of the F-P cavity are respectively connected to a silicon film and a light-guiding optical fiber, and the silicon film, the F-P cavity and the light-guiding optical fiber are fixed by a quartz sleeve , the following is the selection basis for the F-P cavity length:

In order to obtain the maximum contrast of the interference, the cavity length of the F-P cavity and the reflectivity of the silicon film have the following relationship:

${\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="R"\; filenames="S2007200751773E00011.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\underset{\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; a</span>}}{<span\; class="notranslate">\; \&Integral;</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="r"\; filenames="S2007200751773E00011.png"\; state="\{\{state\}\}">r</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; dr</span>}}{\underset{\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; a</span>}}{<span\; class="notranslate">\; \&Integral;</span>}}\frac{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="r"\; filenames="S2007200751773E00011.png"\; state="\{\{state\}\}">r</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; dr</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="T"\; filenames="S2007200751773E00011.png"\; state="\{\{state\}\}">T</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; 4</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Among them: R ₁ and T ₁ are the reflectivity and transmittance of the end face of the light-guiding fiber, R ₂ is the reflectivity inside the silicon film, z ₀ is the characteristic parameter of the cavity, ω ₀ is the inner radius of the fiber core, ω ₂ is the spot radius where the light propagates to the silicon film, λ is the laser wavelength, and the cavity length z ₂ is expressed as:

${\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\sqrt{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

Due to the wavelength tuning limitation of ordinary semiconductor DFB lasers, our F-P cavity length is generally selected to be greater than 200um. Considering the avoidance of reflections on both sides of silicon, the reflectivity of our silicon film coating should be greater than 70%, so the cavity length Selection is the result of the joint action of various factors.

The technical solution of the utility model is as follows:

An automatic tuning F-P fiber optic sensor, including a light source and a sensor head, is characterized in that the light source includes a laser and a corresponding drive circuit and temperature control circuit, the laser is connected to the first port of the coupler through an optical fiber, and the coupler's The third port is connected to the sensing head through a single-mode optical fiber, the fourth port of the coupler is connected to the active control unit through the second photodetector, and the second port of the coupler is connected to the input of the first photodetector port, the output port of the first photodetector is respectively connected to the active control unit and the signal output unit, the output terminal of the active control unit is connected to the temperature control circuit, and the composition of the sensing head includes F-P cavity, the two cavity surfaces of the F-P cavity are respectively connected to the silicon film and the light-guiding fiber, the silicon film, the F-P cavity and the light-guiding fiber are fixed by a quartz sleeve, and the other end of the light-guiding fiber is connected to the single mode fiber.

The cavity length of the F-P is ≥200 μm.

The coupler is a 3dB coupler.

The laser of the light source is a distributed feedback single-mode semiconductor laser, and the output end of the distributed feedback single-mode semiconductor laser has optical feedback.

The inner surface of the silicon film is coated with a reflective film, and the selectable range of reflectivity is 70%-100%. Due to the difficulty and randomness of coating the end face of the light guide fiber, we do not coat the end face of the light guide fiber, so that the power reflectivity of the end face of the light guide fiber is about 3.5%.

All connections are connected by single-mode optical fiber, and the joints generally try to use angled active connectors (APC joints) to reduce additional F-P interference.

Technical effect of the present utility model:

(1) The utility model adopts the design of the cavity length of the F-P cavity of the sensor head, and adopts a sensor head with a long F-P cavity length to reduce the requirements for the wavelength tuning range of the laser;

(2) The inner surface of the silicon film of the sensor head of the utility model is coated with a reflective film, which prevents the reflected light from the two reflective surfaces of the silicon film from interfering with the received signal, and makes the contrast of the F-P interference fringes as large as possible, generally greater than 30dB , greatly improving the sensitivity of the system;

(3) The active control unit of the present utility model receives the electric signal of the first photodetector and actively adjusts the temperature control of the DFB laser of the light source, and timely feedbacks and controls the operating point of the sensing head to be at the Q point position of the F-P cavity, which improves the system performance. Sensitivity and dynamic range avoid the problem of using large spectrometers and oscilloscopes during system calibration, which greatly simplifies the structure of the system.

(4) A distributed feedback single-mode semiconductor laser is used as the light source, which solves the problem of sensitivity to the outside world caused by the narrow bandwidth laser, and makes the energy utilization rate of the light source high, the output energy is high, and the sensitivity of the system is improved. Become compact and reduce the size of the system;

Description of drawings

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

Detailed ways

First please refer to Fig. 1, Fig. 1 is the structural representation of the automatic tuning F-P fiber optic sensor of the present invention, also is the structural representation of the utility model embodiment, as can be seen from the figure, the present embodiment automatic tuning F-P fiber optic sensor, comprises light source 1 and sensor Head 4, the light source 1 is a distributed feedback single-mode semiconductor laser with a temperature control circuit, the laser is connected to the first port 201 of the coupler 2 through an optical fiber, and the third port 203 of the coupler 2 is connected through a single-mode optical fiber 3 The sensor head 4, the fourth port 204 of the coupler 2 is connected to the active control unit 7 through the second photodetector 6, and the second port 202 of the coupler 2 is connected to the input of the first photodetector 5 port, the output end of the first photodetector 5 is respectively connected to the active control unit 7 and the signal output unit 8, the output end of the active control unit 7 is connected to the temperature control circuit of the light source 1, and the The composition of the sensing head 4 includes an F-P cavity 402, and the two cavity surfaces of the F-P cavity 402 are respectively connected to a silicon film 401 and a light-guiding fiber 404, and the silicon film 401, the F-P cavity 402 and the light-guiding fiber 404 are formed by a quartz sleeve 403 is fixed, and the other end of the light-guiding fiber 404 is connected to the single-mode fiber 3 .

The coupler 2 described in this embodiment is a 3dB coupler. The inner surface of the silicon film 401 is coated with a high reflection film. All connections are connected by single-mode optical fiber, and the joints are generally connected by angled movable connectors to reduce additional F-P interference.

The first photodetector 5 and the second photodetector 6 are selected as photodetectors near 1550nm.

The working conditions of this embodiment are as follows:

The light starts from the light source 1, enters through the first port of the coupler 2, and outputs in two ways from the third port 203 and the fourth port 204, and one way is output from the fourth port 204 and is detected by the second photodetector 6, and converted into electrical The signal, called beam electrical signal G, enters the active control unit 7, and the other route is output through the third port 203 and enters the sensing head 4 through the single-mode optical fiber 3. The sensing head 4 is composed of a silicon membrane 401, an F-P cavity 402, and a quartz sleeve 403. It is composed of a light-guiding fiber 404, the end face of the fiber is not coated, the reflectivity is 3.5%, the inner side of the silicon film is gold-plated, the reflectivity is 100%, the cavity length is 362um, and the measurement shows that the interference contrast of the F-P cavity 402 reaches 22.88dB. When the light beam enters the sensing head 4, there is a part of reflection at the end face of the light guiding fiber 404, and a part enters the F-P cavity 402 and is reflected by the silicon film 401 and then interferes at the end face of the light guiding fiber 404, which belongs to low-precision F-P interference. And because the line width of the light source 1 is relatively wide, generally only one reflection interference result needs to be considered. The inner surface of the silicon film 401 is coated with a high reflection film, and an F-P cavity 402 is formed with the end surface of the light guiding fiber 404 . External vibrations cause the silicon membrane 401 to vibrate, thereby changing the cavity length of the F-P cavity 402, so that the interference fringes on the end face of the light guiding fiber 404 will modulate the intensity of the light. The modulated light is called signal light, which is input from the third port 203 of the coupler 2 through the single-mode fiber 3, and output from the first port 201 and the second port 202 of the coupler 2, and the signal light output from the second port 202 Detected by the first photodetector 5, it is converted into an electrical signal, which is called a signal photoelectric signal. The main part of the signal photoelectric signal X1 is output through the output unit 8 for use, and the other part of the signal photoelectric signal X2 enters the active control unit 7. In control unit 7:

(1) The signal photoelectric signal X2 and the beam electrical signal G are averaged (filtered) and then divided by a divider to obtain a X2/G control signal relative to the light source. The purpose of this is to remove the influence of light source power drift and obtain a A control signal that has nothing to do with light source power drift, that is, a relative value that reflects the laser reflection output level of the sensing head 4;

(2) Compare the result with the magnitude of a parameter that is only related to the properties of the sensing head itself.

(3) The comparison result adjusts and controls the temperature control circuit in the light source 1 through a proportional integral circuit, so as to ensure that the wavelength of the laser in the light source 1 always makes the sensor head 4 work near the Q value point.

In addition, as a very important point of the utility model, the output end of the laser of the utility model does not add an isolator. According to the theory, after adding a small amount of feedback to the distributed feedback semiconductor laser, the output line width of the laser will be sharply increased by about 15-18dB. Widening, the measurement results show that the output linewidth of the laser changes from a few MHz to about 10GHz after the feedback is introduced, which is just within the range we measured.

The signal output unit 8 can be pre-amplified by the signal, filtered, and then connected to the oscilloscope or display system after the post-amplification; or connected to the computer by the data acquisition card after the pre-amplification, so as to process the signal and obtain detection Physical quantities of a signal such as frequency, intensity, speed of sound, azimuth, etc.

Tests show that the sensor of the utility model has the characteristics of convenient tuning, low cost, high sensitivity and strong adaptability to environmental changes.

Claims (6)

1. an automatic tuning F-P fiber optic sensor, comprising a light source (1) and a sensing head (4), is characterized in that the light source (1) includes a laser with a temperature control circuit, and the laser directly passes through the optical fiber and the coupler ( 2) connected to the first port (201), the third port (203) of the coupler (2) is connected to the sensor head (4) via a single-mode optical fiber (3), and the coupler (2) The fourth port (204) of the coupler (2) is connected to the input port of the first photodetector (5) through the second photodetector (6) to the active control unit (7), and the second port (202) of the coupler (2) is connected to the input port of the first photodetector (5), The output ports of the first photodetector (5) are respectively connected to the active control unit (7) and the signal output unit (8), and the output terminal of the active control unit (7) is connected to the temperature control circuit , the composition of the sensing head (4) includes an F-P cavity (402), and the two cavity surfaces of the F-P cavity (402) are respectively connected to a silicon film (401) and a light-guiding optical fiber (404), and the silicon film ( 401), the F-P cavity (402) and the light-guiding fiber (404) are fixed by a quartz sleeve (403), and the other end of the light-guiding fiber (404) is connected to the single-mode fiber (3). 2. The auto-tuning F-P fiber sensor according to claim 1, characterized in that the cavity length of the F-P cavity (402) is ≥ 200 μm. 3. The automatic tuning F-P fiber optic sensor according to claim 1, characterized in that said coupler (2) is a 3dB coupler. 4. The automatic tuning F-P fiber sensor according to claim 1, characterized in that the laser of the light source (1) is a distributed feedback single-mode semiconductor laser, and the output of the laser has optical feedback. 5. The self-tuning F-P fiber optic sensor according to claim 1, characterized in that the inner surface of the silicon film (401) is coated with a reflective film, and the reflectivity ranges from 70% to 100%. 6. The automatic tuning F-P fiber optic sensor according to claim 1, characterized in that all connections are connected by single-mode optical fibers, and all joints are angled movable connectors.

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