cylindrical torsion tuning optical fiber grating sensing demodulator

Technical field:

The invention relates to a demodulator fiber grating sensor, in particular to a cylindrical torsion tuning optical fiber grating sensing demodulator, used mainly in the optical fiber sensor, optical measurement, optical device the technical field of tuning the wavelength.

Background technology:

Optical fiber grating of the optical fiber is a kind of making narrow-band reflection characteristic of the optical filter. Because the elastic deformation of the quartz fiber, thermal expansion characteristic, and its thermo-optic, elastic optical effect, it has the characteristic of the stress and temperature sensitive. In a certain range in this sensitive characteristic is linear, comply with the following relations:

Δλ_ε / λ=ε (1-   )     (1)

Δλ_T / λ=(α+e) Δ T     (2) in the formula: for the optical fiber strain ε, of the material for the optical fiber γ ball light coefficient, α is the coefficient of thermal expansion fiber material, ΔT to the variable quantity of the temperature, e=1ndndTThe thermo-optical coefficient. through advantage according to the above-mentioned measuring the change of wavelength can be determined by the relationship between the sensed temperature and stress. Therefore, the optical fiber grating is used as the sensor, accurate, fast measurement and reads the Bragg wavelength become the key technology for practical application, the matched Bragg wavelength read-out device, in other words that known as the Bragg wavelength tuning demodulator become the key device of the sensing applications.

In the prior art, the optical fiber grating wavelength encoding the demodulation process, traditional means is to use the spectrometer, monochromator or spectral instrument and the like. Furthermore, it has been made a number of model the wavelength information of the programme of demodulation, such as Mach-Zehnder interferometer method, adjustable Fabry-Perot filter method, such as matching optical fiber grating filter method. To sum up, the demodulation of the reflection light wavelength of the fiber Bragg grating technology can be divided into the following types:

1, the sensing head to be detected is reflected back with a certain optical signal directly input to the spectrometer, monochromator or wavelength in idea , direct measurement of the fiber optic grating the wavelength position of the reflection signal. In the prior art such as: li Zhiguo, and the like, high-sensitivity optical fiber grating sensing characteristic tester research, photon Journal, 1999, 28 (2): 138-141. This demodulation mode is simple, the measuring precision is high, but these instruments expensive and not easy to carry. Only suitable for laboratory use, inconvenience in is applied to actual sensing system.

2, the tunable laser as testing the light source, in a certain wavelength of the laser output within the range of the continuous scanning, according to the optical signal in the position of the scanning cycle, the optical fiber grating to be measured can be obtained the change of wavelength of the reflected light, or with the reference measuring optical fiber grating reflection light wavelength of the fiber Bragg grating. In the prior art such as:   Hyun Soek   Yun, et   al. ,   Sensor   arrays with Interrogation   wavelength-swept   fiber   for   fiber   grating   laser, Optics   Letters, 1998, 23 (11): 843-845; and in the prior art, :, guan Baiou , a high resolution optical fiber grating sensing demodulation technique, optical Journal, 2000, 20 (11): 1509-1513. This kind of method has the advantages of high energy reflected light, and the optical power of the ordinary only charged to accept element, signal is easy to detect, with high resolution, the multiplexing is simple to realize. However, this kind of method is the light source of the difficulty of the design and manufacture of large, the cost is high.

3, as a test light source using broadband light source, utilizing a filter or tunable filter for sensing optical fiber grating demodulation element of the reflected light signal, the optical power of the optical signal detecting counts. This kind of method can be divided into two types of reflection and transmissive. The principle of the former are as follows: from sensing the reflected light of the FBG incident to the receiving end of the FBG, if the receiving end of the FBG wavelength reflected light, is reflected to the detector. FBG by performing fine adjustment on the drive receiving PZT, get sensing the peak wavelength of the FBG. The precision of this method by the light source and the stability limit of the external disturbance, the detection end high stability requirements of FBG spectrum. The prior technical: M.A.Davis, et   al. , Matched-filter   interrogation   technique for   Bragg   grating   fiber   arrays, Electronics   Letters, 1995, 31 (10): 822-823 transmission of the measurement scheme. The programme and the reflection type distinction lies in that: the photoelectric detector is not placed on the receiving end the position of the FBG reflected light, and the position of the transmitted light is positioned, by monitoring the presence or absence of light transmission to determine whether to match, so as to improve the detection sensitivity. This method requires the receiving end is close to the sensor FBG wavelength of the FBG, sensing and demodulation of the relatively small wavelength range.

4, edge filtering method, with the line width relatively large, leads to assume linear change through the filter, and the sensing of the reflection wave length FBG convolution, with the resulting signal is proportional to the position of the peak wavelength of the FBG, can be derived from the signal magnitude of the FBG wavelength location, such as in the prior art,: A.D.Kersey A   review   of   recent   developments   in   technology   sensor   fiber   optic,   Fiber Technology Optical, 1996, 2,291-317. This method requires the demodulation filter good linearity, requests the system each component parameter is stable. Therefore the use of harsh conditions.

Because the defects of the above-mentioned method, optical fiber grating sensing system in demodulation technology of this sensing technology promotion application of one of the major obstacles.

The content of the invention is:

The invention aims to solve the technical problem of overcoming the defects of the above-mentioned in the prior art, provides a cylindrical torsion tuning optical fiber grating sensing demodulator.

The basic principle of this invention is to utilize the strain tuning characteristic of the fiber grating, the optical fiber grating spectral characteristic of the sensing head for scanning, demodulation.

Technical solutions of this invention are as follows:

A cylindrical torsion tuning optical fiber grating sensing demodulator, is characterized in that it is formed of: the optical fiber section containing optical fiber grating with a certain angle in a stuck on the outer surface of cylindrical-shaped, one end of the cylindrical-shaped fixed on the fixture, the cylindrical-shaped this one end of the cap, the cylindrical shaped neck portion of the other end of the rotary installation of the bearing bracket, the end of the cylindrical-shaped transverse to the movement of the connecting rod is provided with a wrench, the wrench connecting rod and a motor connected to form a driving relationship, the clamp, bearing bracket, a motor fixed on a casing.

On the cylindrical-shaped with an angle is substantially parallel to respectively having different peak wavelengths of a plurality of optical fiber grating.

The cylindrical rod is a hollow cylindrical-shaped rod.

The advantage of this invention is:

(1) the present invention adopts the tunable fiber Bragg grating as a sensing wavelength signal read-out device. With a spectrometer, monochromator, wavelength meter the method relatively, more low-cost, convenient for popularization and application.

(2) signal demodulating apparatus of the invention, all the optical fiber and optical fiber component, is a kind of the whole optical fiber system. Between the device and element, optical fiber heat sealing machine can be completely used for welding, to form a whole. Therefore, stable and reliable use, it is easy to realize instrumented.

(3) the invention utilizes the optical fiber grating scan strain sensitive characteristic, measuring strain measurement can be at the same time of the sensing head and the temperature of the peak wavelength of the fiber Bragg grating. As long as the two kinds of sensing optical fiber grating spectrum are not overlapped with each other, and are connected in series on the other a reference optical fiber grating, can be respectively measured by temperature and strain.

(4) demodulation method of the present invention is a kind of spectral scanning method, capable of reading the position of peak value of the fiber Bragg grating, with a number of the method and the fixed filters compared with the method of the interference principle, has the advantage of large measuring range.

(5) the invention is a method for the direct measurement of the wavelength, rather than from the light intensity indirect projections, data reliability is high. One of the advantages of the optical fiber grating sensor, can be as a distributed measurement system, can be remote sensing-multipoint strain and temperature information, has wide application. Modem optical fiber grating tuning of this invention as a sensing system for measuring the key device of the essential, its use value is fully reflected, has a good cost performance ratio, is expected to have very good market prospects.