CN207991566U - A kind of double SLED optical fiber Fabry-Perot sensors demodulating equipments - Google Patents

Abstract

The utility model relates to a demodulation device of a dual SLED fiber optic sensor. The fiber optic sensor demodulation device consists of two SLED light sources, a wavelength division multiplexer, an optical fiber coupler, an optical fiber collimator, a column lens, and an optical wedge. , linear array CCD, AD conversion module and signal processing unit; two different band SLED light sources are connected to one end of the two incident ports of the fiber coupler through a wavelength division multiplexer, and the exit port is connected to the fiber optic sensor. The other incident port is connected to the fiber collimator. Behind the fiber collimator, a cylindrical lens, an optical wedge, and a linear array CCD are placed in sequence. The CCD outputs the detected optical signal as an electrical signal, and converts it into a digital signal through the AD conversion module. It is used for analysis and processing by the signal processing unit to obtain the cavity length value. The demodulation device uses two SLEDs with different wavelengths as light sources, which significantly improves the contrast of the relevant interference signal, and the signal waveform is more convenient for the extraction of the peak position of the relevant interference signal, thereby accurately calculating the cavity length.

Description

A demodulation device for dual SLED fiber optic F-P sensor

technical field

The utility model relates to the technical field of optical fiber sensing, in particular to a demodulation device for dual SLED optical fiber F-P sensor.

Background technique

Due to its light weight, small size, high sensitivity, large dynamic response range and strong anti-electromagnetic interference ability, the optical fiber sensor has become one of the important research directions in the field of optical fiber sensing, especially in the field of strong electromagnetic interference, high temperature and high pressure. Applications in harsh environments such as sensors have incomparable advantages over traditional sensors. Mainly manifested in bridge surface stress monitoring, turbine engine pressure monitoring and other fields. At present, there are mainly intensity demodulation and phase demodulation methods for the demodulation of fiber optic F-P sensor. The intensity demodulation method is simpler in the detection method and signal processing, but the measurement accuracy depends on the light intensity test accuracy and the stability of the optical path system. The disturbance of the light source and the loss of the optical path will cause fluctuations in the light intensity, resulting in low accuracy and poor stability. . The phase method is divided into spectral method and correlation method.

Among them, the correlation method is more widely used. Most of the existing non-scanning correlation demodulation systems using the correlation method use a single SLED (Super Luminescent Light Emitting Diode) as the light source input. At present, the bandwidth of the SLED light source on the market is mainly 20nm, the bandwidth is relatively narrow, and the contrast of the output related interference fringes is low. Cost equipment is extremely high.

Utility model content

Aiming at the problems faced by the non-scanning related demodulation technology of the fiber-optic F-P sensor, the utility model proposes a dual-SLED fiber-optic F-P sensor demodulation device, which uses two SLEDs of different bands as the light source input, and obtains conditions different from that of a single SLED light source. The correlation interference signal under the condition improves the fringe contrast, and the signal waveform is also more conducive to the extraction of the peak value of the correlation interference signal, realizing high-precision, high-resolution cavity length calculation, and greatly reducing the cost.

In order to achieve the above object, the technical scheme of the utility model is as follows:

A dual-SLED fiber optic F-P sensor demodulation device, including a fiber coupler, a fiber F-P sensor, a fiber collimator, a cylindrical lens or a cylindrical reflector, an optical wedge, a linear array CCD, an AD conversion module, and a signal processing unit, It also includes two SLED light sources of different bands and a wavelength division multiplexer, the two SLED light sources are respectively connected to the two input ports of the wavelength division multiplexer, and the output port of the wavelength division multiplexer is connected to two optical fiber couplers. One of the incident ports is connected, the exit port of the fiber coupler is connected with the fiber optic sensor, the other port of the two incident ports of the fiber coupler is connected with the fiber collimator, and a column lens or column is placed behind the fiber collimator. An optical wedge is installed behind the surface reflector, cylindrical lens or cylindrical reflector, and a linear array CCD is installed behind the optical wedge. The linear array CCD is connected to the signal processing unit after the AD conversion module, and the components are connected by single-mode optical fiber;

The 3dB bandwidth of the emission spectrum of the two SLED light sources is greater than or equal to 20nm, and the center wavelength interval is greater than or equal to 100nm;

The outer surface of the two surfaces of the optical wedge is coated with a two-color broadband antireflection film, and the inner surface is coated with a two-color broadband reflective film with a certain reflectivity. The antireflection band of the two-color broadband antireflection film and the reflection band of the broadband reflective film completely cover both The emission spectrum of an SLED light source.

Further, the fiber collimator is a combined lens type large-diameter fiber collimator.

Further, the optical wedge is close to the receiving surface of the linear array CCD, and the optical wedge and the receiving surface of the linear array CCD are located at the focal point of the cylindrical lens or the cylindrical reflector.

Compared with the prior art, the utility model has the advantages of:

1. The utility model adopts two SLED light sources of different bands as the light source input. Compared with a single SLED light source, due to the use of two different bands of light waves, multiple oscillations and multiple interference zeros appear in the relevant interference signals, making the signal contrast In addition, due to the existence of multiple interference zero points, it is also beneficial to obtain the peak position of the relevant interference signal, and realize high-precision and high-resolution cavity length calculation.

2. Low cost: In order to obtain higher fringe contrast, the bandwidth of a single SELD light source must be 150nm, and the price is about 130,000. However, the utility model uses two SLED light sources to improve the contrast, and the bandwidth of 20nm can meet the requirements, and the price At around 20,000, in comparison, the cost is significantly lower.

Description of drawings

Fig. 1 is the structural representation of the utility model embodiment;

Fig. 2 is when a single SLED light source 1 is input, the obtained light intensity distribution curves of the relevant interference signals corresponding to different positions on the optical wedge;

Figure 3 is the light intensity distribution curves of the related interference signals corresponding to different positions on the optical wedge obtained when dual SLEDs are used as the light source input;

In the figure, 1-SLED light source with a center wavelength of 850nm, 2-SLED light source with a center wavelength of 750nm, 3-wavelength division multiplexer, 4-fiber coupler, 5-fiber-optic sensor, 6-fiber collimator, 7 -cylindrical lens, 8-optical wedge, 9-linear array CCD, 10-AD conversion module, 11-signal processing unit.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present utility model clearer, the utility model will be further described in detail below in conjunction with the accompanying drawings. Obviously, the described embodiments are only some embodiments of the utility model, rather than all implementations example. Based on the embodiments of the present utility model, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the scope of protection of the present utility model.

The utility model will be described in detail in conjunction with the accompanying drawings and embodiments.

The basic principle of the demodulation method of the demodulation device of the dual-SLED optical fiber FAP sensor of the utility model is: when the external physical quantity acts on the optical fiber FAP sensor, the cavity length of the FAP cavity is changed to cause the change of the optical path difference. According to the principle of cavity length matching, the non-scanning element optical wedge is used to realize the spatial scanning of the optical path difference of the fiber optic FAP sensor. When the thickness of the optical wedge is equal to the cavity length of the FAP sensor, the output light intensity of the relevant interference signal is the largest. Therefore, it is only necessary to determine the maximum output light intensity point of the relevant interference signal, and the wedge thickness corresponding to this point is the cavity length value at this moment. The utility model adopts two SLEDs with different wave bands as the light source input, effectively improves the fringe contrast of the related interference signal, thereby easily obtaining the precise position of the peak value of the related interference signal. This double SLED demodulation method for optical fiber F-P sensor has the advantages of high measurement accuracy, large cavity length measurement range, and high demodulation rate.

As shown in Figure 1, the embodiment provides a fiber optic F-P sensor demodulation device and method, specifically: two SLED light source 1 and SLED light source 2 with center wavelengths of 850nm and 750nm and a bandwidth of 20nm respectively, through wavelength division The multiplexer 3 is connected to one incident port of the 2×1 fiber coupler 4 .

The exit port of the 2×1 fiber coupler 4 is connected to the pigtail fiber of the fiber optic sensor 5 through a single-mode fiber, and the other incident port of the 2×1 fiber coupler 4 is connected to the pigtail fiber of the fiber collimator 6 through a single-mode fiber connect. In this embodiment, the discrete optical fiber components are connected through flanges; however, in other embodiments, they can also be connected by fusion splicing.

The cylindrical lens 7 used in this embodiment is arranged behind the fiber collimator 6, and the cylindrical lens 7 is a plano-convex cylindrical lens with a focal length of 50 mm and a side width of 35×35×2 mm.

The optical wedge 8 is set near the focal position of the cylindrical lens 7, and is constructed by two pieces of flat glass, and the outer surface is coated with a broadband anti-reflection film, and the inner surface is coated with a 50% broadband reflective film. The reflection band of the film completely covers the emission spectrum of the two SLED light sources at the same time.

The linear array CCD 9 is arranged behind the optical wedge 8 to detect the related interference optical signal and output it as an electrical signal.

The AD conversion module 10 is arranged behind the line array CCD 9 for signal acquisition and conversion.

The signal processing unit 11 is arranged behind the AD conversion module 10 to analyze and process the converted digital signal to obtain the cavity length value at this moment.

The two SLED light sources 1 and 2 output two groups of broadband lights of different wavelength bands, and are combined and coupled into an input port of a 2×1 fiber coupler 4 through the wavelength division multiplexer 3, and the combined broadband light is composed of 2×1 The output port of the fiber coupler 4 enters the fiber optic F-P sensor 5, and multi-beam interference occurs, and part of the broadband light carrying the cavity length information is reflected and returned along the original optical path. After passing through the 2×1 fiber coupler 4, part of the light is coupled to the The fiber collimator 6 is collimated by the fiber collimator 6 and converted into a large-size parallel beam of a certain width. The parallel beam is focused by the cylindrical lens 7 and converted into a linear spot. The linear spot passes through the optical wedge 8. Due to the reflection of the two reflective surfaces before and after the optical wedge 8, multi-beam interference occurs again. After passing through the optical wedge 8, the light intensity of the linear spot is modulated, and the modulated light is received by the linear array CCD 9, and then passes through the AD conversion module 10 After being converted into a digital signal, it is finally analyzed and processed by the signal processing unit 11 to obtain the cavity length value at the moment.

Assuming that a single SLED light source 1 is used as input, since a broadband light source is used, and the light source has a Gaussian distribution in space and spectrum, the output light intensity detected on the CCD is:

In the formula, the first term is the Gaussian distribution of the SLED light source 1 in space, the second term is the reflection output term of the fiber optic sensor, the third term is the transmission output term of the optical wedge, and the fourth term is the spectrum of the SLED light source 1. Gaussian distribution on . Among them, R ₁ and R ₂ are the end face reflectivity of the near end face and the far end face of the air cavity respectively; L is the cavity length of the Fappel cavity, R ₃ is the reflectance of the inner surface of the optical wedge; x is the short side of the optical wedge θ is the angle between the two planes of the optical wedge; I ₀₁ is the constant of the light intensity of SLED light source _{1 distributed with λ 1} ; λ _P1 is the central wavelength of the spectrum of SLED light source 1; B _λ1 is the spectral bandwidth of SLED light source 1 The half-height width of the Gaussian function determined; x _p1 is the center position of the SLED light source 1; B _x1 is the half-height width of the Gaussian function determined by the spatial bandwidth of the SLED light source 1.

From a mathematical point of view, the above formula is very similar to the formula of the cross-correlation function. When the thickness of the optical wedge is equal to the length of the Fab cavity, that is: when xtanθ=L, the maximum intensity of the correlation interference signal will appear at the position of the optical wedge x value. Then, during demodulation, it is only necessary to index the wedge thickness corresponding to the maximum light intensity of the correlation interference signal, and the cavity length value L at that moment can be obtained, realizing non-scanning correlation demodulation.

For this formula, Matlab is used for simulation. As shown in Figure 2, assuming that the reflectivity of the end face of the fiber optic Fab sensor Fab cavity is 4%, the cavity length L=80μm, and the thickness of one end of the optical wedge is 0 and the other end is 125μm, the center wavelength of the SLED light source 1 is 850nm, and the bandwidth is 20nm , the light intensity distribution curves of the related interference signals corresponding to different positions on the optical wedge are obtained.

When two SLEDs are used as light source input, similarly, the output light intensity detected on the CCD is:

In the formula, I ₀₂ is the constant of the light intensity of SLED light source 2 distributed with λ ₁ ; λ _P2 is the center wavelength of the spectrum of SLED light source 2; B _λ2 is the half-height width of the Gaussian function determined by the spectral bandwidth of SLED light source 2; x _p2 is the SLED The center position of the light source 2; B _x2 is the half-height width of the Gaussian function determined by the spatial bandwidth of the SLED light source 2. The remaining parameters are consistent with the parameters expressed in the above formula.

Similarly, for this formula, Matlab is used for simulation to keep the conditions consistent with the above formula, and the light intensity distribution curves of the relevant interference signals corresponding to different positions of the optical wedge are obtained, as shown in Figure 3.

It can be seen from the two figures that when other conditions remain unchanged, two SLEDs with different wavelength bands are used as the light source input, and the related interference signal is different from the result when a single SLED light source is input, and multiple interference zeros appear in the related interference signal ( Subtracting the base signal), the contrast of the fringe is significantly enhanced, and the peak position of the relevant interference signal is easier to obtain. In addition, this waveform is also conducive to adopting a new calculation method to accurately obtain the peak position of the relevant interference signal, thereby accurately solving the optical fiber method. The cavity length value of the Perco sensor.

It should be noted that, in this embodiment, the fiber coupler 4 is a 2×1 coupler, and in other embodiments, a 2×2 fiber coupler may also be used. The fiber optic Fab sensor 5 can be a diaphragm-type extrinsic fiber optic Fab sensor, or an extrinsic and intrinsic fiber optic Fab sensor with other structural forms. The fiber collimator 6 uses a combination lens type large diameter fiber collimator. The optical wedge 8 that realizes the cross-correlation calculation is built with two pieces of flat glass, the outer surface is coated with a broadband anti-reflection film, and the inner surface is coated with a 50% broadband reflective film. The angle and thickness of the optical wedge 8 can be changed, and it can also be realized by using a wedge .

The above uses specific examples to illustrate the utility model, which is only used to help understand the utility model, and is not intended to limit the utility model. For those skilled in the technical field to which the utility model belongs, some simple deduction, deformation or replacement can also be made according to the idea of the utility model.

Claims (3)

1. A dual SLED fiber optic F-P sensor demodulation device, comprising a fiber coupler (4), a fiber F-P sensor (5), an optical fiber collimator (6), a cylindrical lens (7) or a cylindrical reflector, an optical Wedge (8), linear array CCD (9), AD conversion module (10) and signal processing unit (11), are characterized in that, also comprise the SLED light source of two different bands and wavelength division multiplexer (3), so The two SLED light sources are respectively connected to two input ports of the wavelength division multiplexer (3), and the output port of the wavelength division multiplexer (3) is connected to one of the two incident ports of the fiber coupler (4), The output port of the fiber coupler (4) is connected with the fiber optic Fab sensor (5), and the other port in the two incident ports of the fiber coupler (4) is connected with the fiber collimator (6), and the fiber collimator (6 ) is placed behind the cylindrical lens (7) or cylindrical reflector, the optical wedge (8) is set behind the cylindrical lens (7) or the cylindrical reflector, the linear array CCD (9) is arranged behind the optical wedge (8), and the linear array CCD ( 9) The signal processing unit (11) is connected after the AD conversion module (10), and the components are all connected by single-mode optical fiber; The 3dB bandwidth of the emission spectrum of the two SLED light sources is greater than or equal to 20nm, and the center wavelength interval is greater than or equal to 100nm; The outer surface of the two surfaces of the optical wedge (8) is coated with a two-color broadband antireflection film, the inner surface is coated with a two-color broadband reflective film with a certain reflectivity, and the antireflection band of the two-color broadband antireflection film and the reflection band of the broadband reflective film are simultaneously Complete coverage of the emission spectrum of the two SLED light sources. 2. The demodulation device of double SLED optical fiber F-Per sensor according to claim 1, characterized in that, the described optical fiber collimator (6) is a combined lens type large-diameter optical fiber collimator. 3. The demodulation device of double SLED optical fiber Falper sensor according to claim 1, characterized in that, the optical wedge (8) is close to the receiving surface of the linear array CCD (9), and the optical wedge (8) and the linear array CCD (9) The receiving surface is located at the focal point of the cylindrical lens (7) or the cylindrical reflector.