CN105890759A - Fiber grating demodulation system utilizing micro-motion detector array to improve spectrum resolution - Google Patents

Abstract

The invention provides a fiber grating demodulation system that uses a micro-movement detector array to improve the spectral resolution of a line array image sensor. The demodulation system includes a pump source, a wavelength division multiplexer, a fiber Bragg grating, an aperture, A slit, a collimating mirror, a spectroscopic grating, an imaging mirror and a linear array detector, a piezoelectric actuator and a voltage control system, wherein the pump source, the wavelength division multiplexer and the fiber Bragg grating are connected in sequence, and the wavelength division The multiplexer is connected to the aperture at the same time, and the light emitted by the pump source enters the fiber Bragg grating after being coupled by the wavelength division multiplexer, and the reflection spectrum of the fiber Bragg grating enters the fiber Bragg grating demodulation system as injected light, and the injected light After passing through the slit, it passes through the reflection of the collimating mirror, the spectroscopic grating, and the imaging mirror in turn, and finally converges on the line array detector, wherein the line array detector moves left and right along its long axis for a small distance.

Description

Fiber Bragg Grating Demodulation System Using Micro-motion Detector Array to Improve Spectral Resolution

technical field

The invention relates to the field of optical fiber sensing, in particular to an optical fiber grating demodulation system and method for improving spectral resolution by using a micro-motion detector array.

Background technique

Fiber Bragg Grating is a new type of passive sensing element, which has many advantages such as high sensitivity, strong anti-electromagnetic interference, and corrosion resistance. Since it is used in sensing, it has achieved rapid and sustainable development. It has broad application prospects in security monitoring in other fields. Fiber Bragg grating demodulation system is the key part of the whole sensing system, realizing high precision, high resolution, combination of dynamic and static parameters, multi-point multiplexing detection and low cost is the development trend of fiber Bragg grating demodulation technology. There are many methods of optical fiber demodulation. The tuned F-P filter method can only be used to measure static strain. The cost of the tunable laser method is very high. The unbalanced M-Z interferometry is easily affected by the environment and is not conducive to engineering applications. With the rapid development of optical detectors in recent years, miniaturized fiber optic spectrometers have developed rapidly, and fiber demodulation technology based on spectral imaging has also developed. The fiber grating demodulator based on the spectral imaging method is small in size and highly integrated, and can be used to measure static and dynamic strains. It has outstanding advantages in many demodulation methods and is an important direction of demodulation system research. Among them, demodulation The performance of the optical system of the instrument directly affects the resolution of the system, which is a key to the demodulator.

There are many types of optical system structures for grating spectrometers. At present, the Czerny-Turner optical path structure is more commonly used, that is, two concave mirrors are used as the collimator and imaging mirror respectively, and the plane reflective grating is used as the dispersion element. On the one hand, this is due to the low difficulty of planar grating design, low replication cost, and high diffraction efficiency; on the other hand, due to the fact that the Czerny-Turner structure can be adjusted and arranged with more structural parameters, it can avoid secondary or multiple diffractions, and it is convenient to use photoelectric An array detector receives the spectrum. Common small Czerny-Turner spectrometers are mainly divided into two structures: cross type and M type. The M type is the classic structure of the Czerny-Turner spectrometer, and the representative product is the Avaspec series of small fiber optic spectrometers developed by Avantes in the Netherlands; the cross type is evolved from it, with a more compact structure and high space utilization. However, due to the limited number of pixels in line array image sensors, the spectral spatial resolution is limited.

Therefore, it is a technical problem to be solved urgently in this field whether it is possible to realize accurate demodulation of the wavelength of the high-resolution grating under the condition that the pixels of the line array sensor are limited.

Contents of the invention

The object of the present invention is to provide a fiber grating demodulation system that uses a micro-motion detector array to improve the spectral resolution of a linear image sensor. The demodulation system includes a pump source, a wavelength division multiplexer, a fiber Bragg grating, an optical diaphragm, slit, collimating mirror, spectroscopic grating, imaging mirror and linear array detector, piezoelectric actuator and voltage control system, wherein the pumping source, wavelength division multiplexer and fiber Bragg grating are connected in sequence, and the The wavelength division multiplexer is connected to the diaphragm at the same time, the light emitted by the pump source enters the fiber Bragg grating after being coupled by the wavelength division multiplexer, and the reflection spectrum of the fiber Bragg grating enters the fiber Bragg grating demodulation system as injected light, After the injected light passes through the slit, it is sequentially reflected by the collimating mirror, the beam splitting grating, and the imaging mirror, and finally converges on the line array detector, wherein the line array detector moves left and right along its long axis for a small distance.

Preferably, the moving range of the linear array detector is between 0-1 cm.

Preferably, the linear array detector is adjusted at high speed through piezoelectric actuators.

Preferably, the method of moving a small distance is as follows:

a) The piezoelectric actuator is adjusted to the lowest end, and this voltage is the initial adjustment voltage;

b) Record the lowest end spectral data as the initial spectrum;

c) Adjust the piezoelectric actuator with a small step to calculate the current spectrum and the initial spectrum. The piezoelectric actuator is a position servo, and the linear array detector is controlled to move slightly by inputting a position command, and the spatial position of the incident light is adjusted. , finally determine the spectral imaging position;

d) The adjusted voltage at the first correlation peak value is recorded as the final adjusted voltage;

e) Divide the initial adjustment voltage and the final adjustment voltage into several levels, and measure each level for each demodulation to obtain higher spatial resolution.

Preferably, the specific process of the sub-step b) is as follows:

When there are 256 pixels, you can get 256 segmented integral values: {I0, I1, I2, ..... I255}, when the pixel scans slightly along a certain direction, you get another sequence : {I0', I1', I2', .....I255'}, put this sequence to the former, get: {I0'-I0, I1'-I1, I2'-I2, .. ....I255'-I255,}, that is, {G1-G0, G2-G1, G3-G2,...}; where G0 represents the true value of light intensity at position 0, and G1 represents the true value of light intensity at position 1 Light intensity value; sum this sequence to get {G1-G0, G2-G0, G3-G0,...G255-G0}, so that the new value after the first fine-tuning is obtained, and then is the new value after the second fine-tuning. If N times of fine-tuning is performed, N times of interpolation will be obtained.

It should be understood that both the foregoing general description and the following detailed description are exemplary illustrations and explanations, and should not be used as limitations on the claimed content of the present invention.

Description of drawings

With reference to the accompanying drawings, more objects, functions and advantages of the present invention will be clarified through the following description of the embodiments of the present invention, wherein:

Fig. 1 is the structure schematic diagram of the fiber grating demodulation system that improves the linear array image sensor spectral resolution according to the present invention;

Fig. 2 schematically shows a schematic structural diagram of a fiber grating demodulation system that uses slit translation to improve the spectral resolution of a line array image sensor;

Fig. 3 schematically shows the structure schematic diagram of the fiber grating demodulation system that adopts collimating mirror fine-tuning to improve the spectral resolution of the detector array;

Fig. 4 schematically shows a schematic structural view of a fiber grating demodulation system using a micro-movable grating to improve the spectral resolution of the detector array;

Fig. 5 schematically shows a schematic structural view of a fiber grating demodulation system that uses fine-tuning of an imaging mirror to improve the spectral resolution of a detector array;

Fig. 6 schematically shows a schematic structural view of a fiber grating demodulation system that uses linear array detector fine-tuning to improve the spectral resolution of the detector array;

Fig. 7 schematically shows a structural diagram of a fiber grating demodulation system for improving the spectral resolution of a detector array;

Fig. 8 schematically shows a flow chart of the feedback control method of the fiber grating demodulation system for improving the spectral resolution of the line array image sensor according to the present invention by micro-scanning the line array detector;

Fig. 9 (a) shows a light intensity in space and is a one-dimensional Gaussian curve distribution graph;

Figure 9(b) shows the interpolated result graph of multiple measurement results after scanning when the slit is not adjusted;

Fig. 9(c) shows the interpolation result graph of the multiple measurement results after scanning when the slit is adjusted.

detailed description

Fig. 1 is a schematic structural diagram of a fiber grating demodulation system for improving the spectral resolution of a line array image sensor according to the present invention; a fiber grating demodulation system for improving the spectral resolution of a line array image sensor by micro-movement of a line array detector provided by the present invention Modulation system 100 is shown in Figure 1, and described fiber Bragg grating demodulation system 100 comprises pump source (LD) 101, wavelength division multiplexer (WDM) 102, fiber Bragg grating (FBG) 103, diaphragm 104, slit 105 , a spectroscopic grating 106 , a collimating mirror 107 , an imaging mirror 108 and a line array detector (CCD) 109 . The pump source 101 , the wavelength division multiplexer 102 and the fiber Bragg grating 103 are connected in sequence, and the wavelength division multiplexer 102 is connected to the aperture 104 at the same time. The light emitted by the pump source 101 enters the fiber Bragg grating 103 after being coupled by the wavelength division multiplexer 102, and the reflection spectrum of the fiber Bragg grating 103 enters the fiber Bragg grating demodulation system as injected light. After the injected light passes through the slit 105 , it is sequentially reflected by the collimating mirror 106 , the beam splitting grating 107 , and the imaging mirror 108 , and finally converges on the linear array detector (CCD) 109 .

Firstly, the pumping source 101, the wavelength division multiplexer 102, and the fiber Bragg grating 103 are fused in the manner shown in FIG. 1, wherein the fiber Bragg grating 103 should have a higher reflectivity and a narrower line width. According to the embodiment of the present invention, the parameters of the wavelength division multiplexer (WDM) 102 and the fiber Bragg grating (FBG) 103 need to be matched with the parameters of the pump wavelength and laser emission wavelength. The specific parameters are shown in Table 1.

Table 1 according to the reflection spectrum light source parameter of demodulation system of the present invention

In the embodiment, if an erbium-doped fiber with a core diameter of 10/125 μm is selected as the gain medium, the pump source LD pigtail and the wavelength division multiplexer WDM need to select the same type of core diameter. The output wavelength of the pump source LD is 976nm, the working wavelength of the wavelength division multiplexer WDM is 976/1550nm, and the selection range of the fiber Bragg grating FBG is 1530nm-1560nm, and the laser output can be obtained within this range. In the experiment, if the ytterbium-doped fiber with a core diameter of 10/125 μm is selected as the gain medium, the pump source LD pigtail and the wavelength division multiplexer WDM need to select the same type of core diameter. The pump source LD is 915nm single-mode output, the wavelength division multiplexer WDM works at 915/1064nm, and the fiber Bragg grating FBG is selected around 1064nm, and the laser output can be obtained within this range.

The reflected light of the fiber Bragg grating 103 is used as the incident light a through the diaphragm 104 to the collimating mirror 106 to maintain the collimation of the beam, and then the collimated light is irradiated to the beam splitting grating 107 for diffraction and splitting. array detector 109 .

Spectroscopic grating 107 can be represented by formula (1)

nλ=d(sinα±sinβ) (1)

Among them, n is the spectral level, n=0, ±1, ±2...; α is the incident angle; β is the reflection angle; θ is the blaze angle; d is the grating constant.

n=0 is the zero-order spectrum, at this time, β has nothing to do with λ, that is, there is no spectroscopic effect; n=±1, ±2 corresponds to the first-order spectrum and the second-order spectrum, and the first-order spectrum has strong energy and can be used to realize spectroscopy. The resolution of the grating has nothing to do with the wavelength. The separated spectrum belongs to the homogeneous spectrum. The theoretical resolution of the grating is the product of the number of grating lines and the order of the spectrum, which can be expressed by formula (2)

R=nN (2)

For a grating with a width of 50 mm and a number of scribed lines of 1200 lines/mm, the resolution of the primary spectrum is 6×104.

The light reflected by the fiber Bragg grating 103 is used as the injection light source, which reduces the spectral width of the incident light, and under the condition that the resolution of the grating is determined, interference fringes with finer intervals can be obtained. At this time, adjust the slit, aperture, spectroscopic grating, collimating mirror, imaging mirror and line array detector, and control the micro-movement of the slit or control the spectroscopic grating, collimating mirror, imaging mirror and line array by inputting position commands The micro-rotation of the detector adjusts the spatial position of the incident light, the light path incident to the imaging mirror changes, and the fringes converged on the line array detector also change accordingly, finally determining the spectral imaging position.

Specifically, it is described in detail by the following examples.

Example 1

(a) of FIG. 2 schematically shows a schematic structural diagram of a fiber grating demodulation system that uses slit translation to improve the spectral resolution of a line array image sensor. As shown in (a) of FIG. 2 , the slit 105 is adjusted so that the slit moves in the direction of the arrow b shown in the figure. The slit movement step is 0.1 micron, and the adjustment range is between 0-1 cm. The slit 105 is adjusted at high speed by a piezoelectric actuator. The piezoelectric actuator is controlled by a voltage control system, so that the spectral imaging position on the line image sensor can be moved within the minimum pixel interval. In this way, the light path incident on the imaging mirror 108 will change, and the fringes converging on the line array detector 109 will also change accordingly. The schematic diagram of the light path change is shown in (b) in FIG. By adjusting the width of the incident slit of the fiber, the slight movement of the stripes can be realized, thereby improving the test accuracy.

Example 2

Fig. 3 schematically shows the structure diagram of a fiber grating demodulation system for improving the spectral resolution of a detector array by fine-tuning a collimating mirror. As shown in FIG. 3 , the collimating mirror 106 is adjusted so that the collimating mirror rotates in the direction of arrow c in the figure, and the rotation angle is 10°-30° counterclockwise or clockwise. The collimating mirror 106 is adjusted at high speed by piezoelectric actuators. The piezoelectric actuator is controlled by a voltage control system, so that the spectral imaging position on the line image sensor can be moved within the minimum pixel interval. In this way, the light path incident on the imaging mirror 108 will change, and the fringes converged on the line array detector 109 will also change accordingly. By adjusting the rotation angle of the collimating mirror, the slight movement of the stripes can be realized, thereby achieving the effect of improving the test accuracy.

Example 3

Fig. 4 schematically shows the structure diagram of a fiber grating demodulation system using a micro grating to improve the spectral resolution of a detector array. As shown in FIG. 4 , the spectroscopic grating 107 is adjusted so that the spectroscopic grating rotates in the direction of arrow d in the figure, and the rotation angle is 10°-30° counterclockwise or clockwise. The split grating 107 is adjusted at high speed by piezoelectric actuators. The piezoelectric actuator is controlled by a voltage control system, so that the spectral imaging position on the line image sensor can be moved within the minimum pixel interval. In this way, the light path incident on the imaging mirror 108 will change, and the fringes converged on the line array detector 109 will also change accordingly. By adjusting the rotation angle of the spectroscopic grating, the slight movement of the fringe can be realized, thereby achieving the effect of improving the test accuracy.

Example 4

Fig. 5 schematically shows the structural diagram of a fiber grating demodulation system that uses imaging mirror fine-tuning to improve the spectral resolution of the detector array. As shown in FIG. 5 , the imaging mirror 108 is adjusted so that the spectroscopic grating rotates in the direction of arrow e in the figure, and the rotation angle is 10°-30° counterclockwise or clockwise. The imaging mirror 108 is adjusted at high speed by piezoelectric actuators. The piezoelectric actuator is controlled by the voltage control system, so that the spectral imaging position on the line array image sensor moves within the minimum pixel interval range, and the fringes converged on the line array detector 109 also change accordingly. By adjusting the rotation angle of the imaging mirror, the small movement of the stripes can be realized, thereby achieving the effect of improving the test accuracy.

Example 5

Fig. 6 schematically shows the structural diagram of a fiber grating demodulation system that adopts linear array detector fine-tuning to improve the spectral resolution of the detector array. As shown in FIG. 5 , the linear array detector 109 is adjusted so that the spectroscopic grating moves left and right along the direction of the arrow f shown in the figure. The slit movement step is 0.1 micron, and the adjustment range is between 0-1 cm. The linear detector 109 is adjusted at high speed by piezoelectric actuators. The piezoelectric actuator is controlled by a voltage control system, so that the position of the spectral image on the line image sensor can be moved within the minimum pixel interval. By adjusting the rotation angle of the line array detector, the slight movement of the stripes can be realized, thereby achieving the effect of improving the test accuracy.

Example 6

Fig. 7 schematically shows a schematic structural diagram of a fiber Bragg grating demodulation system for improving the spectral resolution of a detector array. As shown in Figure 7, at least two of the slit, aperture, splitting grating, collimating mirror, imaging mirror and line array detector are fine-tuned, and the slit, diaphragm, splitting grating, collimating mirror, Imaging mirrors and line array detectors are adjusted at high speed by piezoelectric actuators. The piezoelectric actuator is controlled by a voltage control system, so that the spectral imaging position on the line image sensor can be moved within the minimum pixel interval. By adjusting the rotation angles of slits, diaphragms, splitting gratings, collimating mirrors, imaging mirrors and line array detectors, the test accuracy can be improved.

Fig. 8 schematically shows a flow chart of a feedback control method of a fiber grating demodulation system for improving the spectral resolution of a line array image sensor according to the present invention. The specific control method is as follows:

First, in step 801, the piezoelectric actuator is adjusted to the lowest end, and this voltage is the initial adjustment voltage;

Step 802, record the lowest end spectrum data as the initial spectrum;

Step 803, adjust the piezoelectric element with a small step. The piezoelectric element is a position servo. By inputting a position command, adjust the slit, spectroscopic grating, collimating mirror, imaging mirror or linear array detector respectively, and calculate the current spectrum and the initial spectrum. When the moving distance of the Gaussian image on the CCD is adjusted to reach one pixel width, one scan is completed, and each measurement data of one scan is interpolated separately to form a smoother curve. The processing process is like this, the pixel output is the segmental integration of the light intensity curve, when there are 256 pixels, you can get 256 segmental integral values: {I0, I1, I2,... ..I255}, when the pixel scans slightly along a certain direction, another sequence is obtained: {I0', I1', I2', .....I255'}, and this sequence is forwarded to the former, Get: {I0'-I0, I1'-I1, I2'-I2, ... I255'-I255,}, namely {G1-G0, G2-G1, G3-G2,..... .}. Among them, G0 represents the true value of light intensity at position 0 (note that it is position 0, not the integral of light intensity within the pixel scale), and G1 represents the value of light intensity at position 1. Sum this sequence to get {G1-G0, G2-G0, G3-G0,...G255-G0}, so that you get the new value after the first fine-tuning, and then the second The new value after fine-tuning, if it is fine-tuned N times, it will get N times of interpolation.

Step 804, the adjusted voltage at the first correlation peak value is recorded as the final adjusted voltage;

Step 805, divide the initial adjustment voltage and the final adjustment voltage into several levels, and determine the moving distance of the slit or the rotation angle of the spectroscopic grating, collimating mirror, imaging mirror or line array detector according to each level.

Step 806 , return to step 803 , measure each level for each demodulation to obtain higher spatial resolution.

Figures 9(a)-9(c) show the principle of the present invention to improve spectral spatial resolution by adjusting slits, spectroscopic gratings, collimating mirrors, imaging mirrors or linear array detectors. FIG. 9( a ) shows a distribution graph of light intensity in space as a one-dimensional Gaussian curve. A light beam whose light intensity is distributed in a one-dimensional Gaussian curve in space is irradiated on a CCD sensor. The pixels of the CCD are closely arranged, and each pixel is equivalent to a vertical grid. As shown in Figure 9(a), the output of the pixel is actually Integral of the total amount of light intensity falling on a pixel. Due to the excessive discretization, the resolution of the image is low. In order to increase the number of sampling points of the curve, the Gaussian curve on the CCD sensor can be changed by adjusting the slit, spectroscopic grating, collimating mirror, imaging mirror or linear array detector. The position is equivalent to moving the CCD sensor to collect different positions of the curve. The fine-tuning of slits, beam-splitting gratings, collimating mirrors, imaging mirrors, or linear array detectors is equivalent to fine-tuning the position of the sensor, so that a more delicate description of the curve can be obtained. Fig. 9(b) is an interpolation result diagram of multiple measurement results after scanning without adjusting the slit, spectroscopic grating, collimating mirror, imaging mirror or linear array detector. Fig. 9(c) is a result diagram after interpolation of multiple measurement results after scanning when adjusting the slit, spectroscopic grating, collimating mirror, imaging mirror or linear array detector. It can be seen from Figures 9(b) and 9(c) that when the moving distance of the Gaussian image on the CCD reaches one pixel width by adjusting the slit, splitting grating, collimating mirror, imaging mirror or line array detector, it is completed once Scanning, interpolating each measurement data of one scanning to form a smoother curve.

Other embodiments of the invention will be apparent to and understood by those skilled in the art from consideration of the specification and practice of the invention disclosed herein. The description and examples are considered exemplary only, with the true scope and spirit of the invention defined by the claims.

Claims (5)

1. one kind uses the optical fiber light that fine motion detector array improves line scan image sensor spectral resolution Grid demodulating system, described demodulating system includes pumping source, wavelength division multiplexer, bragg grating, light Door screen, slit, collimating mirror, spectro-grating, imaging lens and linear array detector, piezoelectric-actuator and voltage Control system,

Wherein said pumping source, wavelength division multiplexer and bragg grating are sequentially connected with, and described wavelength-division is multiple It is simultaneously connected with diaphragm with device,

The light that described pumping source sends is by entering bragg grating, institute after the coupling of wavelength division multiplexer The reflectance spectrum stating bragg grating enters optical fiber grating regulating system as injecting light,

Inject light by, after slit, passing sequentially through the reflection of collimating mirror, spectro-grating, imaging lens, finally Converge on linear array detector,

Wherein said linear array detector moves left and right slight distance along its long axis direction.

2. optical fiber grating regulating system as claimed in claim 1, wherein said linear array detector moves Scope is between 0-1 centimetre.

3. optical fiber grating regulating system as claimed in claim 2, wherein said linear array detector passes through Piezoelectric-actuator adjusts at a high speed.

4. optical fiber grating regulating system as claimed in claim 1, wherein said mobile slight distance Method is as follows:

A) piezoelectric-actuator regulates to least significant end, and this voltage is initial adjustment voltage；

B) record least significant end spectroscopic data is initial spectrum；

C) half step distance regulation piezoelectric-actuator, calculates current light spectrum and initial spectrum, and described piezoelectricity performs Element is position servo, instructs control line array detector by input position and carries out micro-movement, to incidence The locus of light is adjusted, and finally determines light spectrum image-forming position；

D) first degree of association peak value time regulation voltage be recorded as eventually adjusting voltage；

E) between voltage, initial adjustment voltage and whole tune being divided into some grades, each grade is all carried out by demodulation every time Measure, to obtain higher spatial resolution.

5. optical fiber grating regulating system as claimed in claim 4, the tool of wherein said sub-step b) Body processing procedure is as follows:

When there being 256 pixels, then can obtain 256 subsection integral values: I0, I1, I2 ... ..I255}, when pixel scans along a direction fine motion, obtain another ordered series of numbers: I0 ', I1 ', I2 ' ... ..I255 ' }, before this ordered series of numbers, go the former, obtain: I0 '-I0, I1 '-I1, I2 '-I2 ... I255 '-I255, i.e. G1-G0, G2-G1, G3-G2 ... }；Wherein G0 represents The light intensity true value of the 0th position, G1 represents the light intensity value of 1 position；This ordered series of numbers is sued for peace, obtains G1-G0, G2-G0, G3-G0 ... G255-G0}, so obtain is new after for the first time fine setting New value after value, followed by second time fine setting, if having finely tuned n times, just obtains the interpolation of n times.