Blazed fiber bragg grating demodulation-based micro-displacement sensor and detection method

A blazed fiber grating and micro-displacement sensor technology, which is applied in light demodulation, optics, instruments, etc., can solve the problems that strain signal and temperature signal cannot be separated and detected, fiber grating sensor is cross-sensitive, and the system stability is not high. Achieve the effect of solving the problem of cross-sensitivity, low cost, and simple instrument structure

Inactive Publication Date: 2010-09-08
NORTHEASTERN UNIV
3 Cites 17 Cited by

AI-Extracted Technical Summary

Problems solved by technology

Because there are moving parts in the detection process of this method, piezoelectric ceramics have a hysteresis phenomenon, so the stability of the system is not high, and the cost of this method is relatively high, generally more than 100,000 yuan
[0003] In addition, due to the cross-sensitivity of strain and temperature of fiber grating itself, the sensor desi...
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Abstract

The invention relates to a blazed fiber bragg gating demodulation-based micro-displacement sensor and a detection method and belongs to the technical field of photoelectric detection. The sensor consists of a wideband light source 1, an optical circulator 2, optical fiber links (31, 32, 33), fiber bragg gating 4 used for sensing, a double-arched beam 5, a base 6, a helix millesimal screw 7, a blazed fiber bragg gating 8 used for demodulation, a refractive index matching liquid groove 9, a columnar lens 10, an optical fiber array 11, a CCD photoelectricity prober 12, a signal processing unit 13 and a computer 14. The sensor is characterized in that a reflective spectrum signal of the fiber bragg gating 4 used for sensing is broadened under the action of the detected micro-displacement; the signal is sent to the optical fiber array 11 by the blazed fiber bragg gating 8 used for demodulation with a certain beam angle and is transmitted to the CCD photoelectricity prober 12; the error of the measurement caused by light intensity wave, optical fiber transmission loss and the like is avoided on the basis of a gauss fitting algorithm and by identifying the detected displacement corresponding to the facula size received by the CCD photoelectricity prober 12.

Application Domain

Using optical meansMitigation of undesired influences +1

Technology Topic

Beam angleLight source +12

Image

  • Blazed fiber bragg grating demodulation-based micro-displacement sensor and detection method
  • Blazed fiber bragg grating demodulation-based micro-displacement sensor and detection method
  • Blazed fiber bragg grating demodulation-based micro-displacement sensor and detection method

Examples

  • Experimental program(1)

Example Embodiment

[0017] The specific structure, principle and measurement process of the present invention will be further explained below in conjunction with the drawings.
[0018] figure 1 It is a schematic diagram of the overall principle structure of the micro-displacement sensor based on blazed fiber grating demodulation provided by the present invention. The light emitted by the broadband light source is sent to the sensing fiber grating through the fiber circulator, and the fiber grating is pasted between one end of the double arched beam and the center point. The measured micro-displacement is provided by the spiral micrometer screw. When the micro-displacement is applied to the upper surface of the double-arched beam, the beam will be deformed, so that the fiber grating pasted on it will be strained. The reflection spectrum signal of the fiber grating for sensing is modulated by micro-displacement and reflected, and then sent to the demodulation blazed fiber grating through the fiber circulator. The blazed fiber grating radiates the signal light to the cylindrical prism at a certain angle, and then is concentrated by the fiber The array receives and then transmits to the CCD photodetector. After the photoelectric conversion of the CCD, the signal processing circuit and the computer system will collect and process.
[0019] The measured micro-displacement causes the deformation of the double-arched beam. The length of the beam is 130mm. The strain distribution generated by the displacement (force) of the beam is analyzed by the finite element analysis method, and the result is as follows figure 2 Shown. by figure 2 It can be seen that the strain distribution on the upper surface of the beam can be divided into three regions, two of which are the positive strain zone (the DC section and the AB section), and one is the negative strain zone (the CA section). From figure 2 (b) It can be seen that within the range of 2cm to 3cm from the center of the upper surface of the beam, the strain changes linearly with the position. And in the range of 2cm to 2.5cm from the center, the beam is subjected to negative strain; while in the range of 2.5cm to 3.0cm from the center, the beam is subjected to positive strain. In this way, if the length of the fiber grating for sensing is less than 10mm and it is symmetrically pasted in the positive and negative strain area, half of the fiber grating is subjected to negative strain and the other half is subjected to positive strain. At this time, the fiber grating will become chirp Grating, causing its reflection spectrum to broaden. Such as image 3 As shown, as the measured displacement increases, the width of the fiber grating reflection spectrum continues to increase. In other words, as the measured micro-displacement increases, the reflection spectrum of the fiber grating for sensing will accommodate more wavelengths of optical signals.
[0020] According to the volume current analysis method, the following relationship exists between the wavelength of the optical signal incident on the blazed fiber grating and the radiation angle:
[0021] cos ξ ( λ ) = n eff ( λ ) - λ Λ g cos θ n 0 - - - ( 1 )
[0022] Where, Λ g Is the period of the blazed fiber grating, λ is the light wavelength of the incident light, ξ is the radiation angle of the blazed fiber grating when the incident wavelength is λ, θ is the tilt angle of the blazed fiber grating, n 0 Is the initial refractive index of the fiber core, n eff (λ) is the effective refractive index of the guided mode in the fiber.
[0023] It can be seen from formula (1) that if the optical signal incident on the blazed fiber grating contains only one wavelength, then there will be only one angle of radiation emitted, so that the light spot received on the CCD photodetector is very small; however, If the light signal incident on the blazed fiber grating has multiple wavelengths, the radiation angle will have a certain range, that is to say, the size of the spot received on the CCD photodetector will become larger. The larger the wavelength range of the light incident on the blazed fiber grating, the larger the spot size received by the CCD photodetector, which corresponds to a larger measured displacement.
[0024] In order to verify the above principles and methods, experimental tests were carried out. In the experiment, the thickness of the double arched beam is 3mm and the length is 130mm. The Bragg reflection wavelength of fiber grating for sensing is λ B = 1550.01 nm. The spectral range of ASE light source is from 1523nm to 1568nm. The fiber array is composed of 24 multimode fibers. The core diameter of the multimode fiber is 62.5μm, the cladding diameter is 125μm, and the distance between each fiber is 250μm; the tilt angle of the demodulated blazed fiber grating grid is 2° ; The CCD photodetector uses the Sony ILX511 model, which contains 2048 pixels with a size of 14μm.
[0025] according to figure 1 The principle structure shown builds an experimental system, Figure 4 Shows the change of the spot size received by the CCD photodetector during the process of increasing the measured micro-displacement, and Figure 5 The relationship curve of the final recorded spot size with the measured micro-displacement is given. It can be seen that by recording the spot size, the value of the measured micro-displacement can be obtained.
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PUM

PropertyMeasurementUnit
Center wavelength1523.0 ~ 1568.0nm
Thickness3.0mm
Length130.0mm
tensileMPa
Particle sizePa
strength10

Description & Claims & Application Information

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