A minitype optical fiber acceleration sensor based on the cantilever is investigated. The sensor mainly makes up of the cantilever and the distributed feedback (DFB) fiber laser. The beam is deformed when the vibration due to the acoustic field applied on the beam. The DFB fiber laser is stuck on the surface of the cantilever beam. It leads to the frequency shift of the output of the fiber laser. By measuring the frequency shift, the acceleration of the vibration can be realized. The center element of the sensor is the cantilever beam and fiber laser, so the mass and volume of the sensor are greatly reduced. The largest dimension of the cantilever beam in this work is just 30mm. And then the cantilevers are taken into simulations and experiments. The experimental results are coincident with the simulations. The experiments of the sensors shows that the acceleration sensitivity is flat and can reach 108Hz/g below 80Hz. And the highest sensitivity is 2.02×109Hz/g. Compared with existing acceleration sensors, this cantilever acceleration sensor can obtain high sensitivity in small scale and light weight.
A minitype optical fiber acceleration sensor based on the cantilever is investigated. The sensor mainly makes up of the cantilever and the distributed feedback (DFB) fiber laser. The beam is deformed when the vibration due to the acoustic field applied on the beam. The DFB fiber laser is stuck on the surface of the cantilever beam. It leads to the frequency shift of the output of the fiber laser. By measuring the frequency shift, the acceleration of the vibration can be realized. The center element of the sensor is the cantilever beam and fiber laser, so the mass and volume of the sensor are greatly reduced. The largest dimension of the cantilever beam in this work is just 30mm. And then the cantilevers are taken into simulations and experiments. The experimental results are coincident with the simulations. The experiments of the sensors shows that the acceleration sensitivity is flat and can reach 108Hz/g below 80Hz. And the highest sensitivity is 2.02×109Hz/g. Compared with existing acceleration sensors, this cantilever acceleration sensor can obtain high sensitivity in small scale and light weight.
The photoelectric signal detection technology based on the 3×3 coupler is widely used in various interferometric sensing systems. In practice, the three-way asymmetry of the 3×3 coupler seriously affects the demodulation of the interferometric optical fiber sensing system. Therefore, the accurate and stable calibration of the demodulation parameters in the 3×3 demodulation, such as the DC quantity, the AC quantity, and the phase difference between the couplers, is of vital importance to the 3×3 demodulation. In the process of studying the ellipse fitting calibration parameters based on optical frequency modulation, it is found that the laser's associated amplitude modulation fluctuation has a greater impact on the demodulation. Based on this, this paper conducts an in-depth study on the impact of the associated amplitude modulation through simulation and experiments and propose a method to eliminate the associated amplitude modulation, that is, the three-channel interference signal is proportionally divided by the laser output signal to eliminate the laser associated amplitude modulation fluctuation caused by optical frequency modulation. The experimental results show that this method can eliminate the associated amplitude modulation well. The influence of amplitude modulation improves the calibration accuracy of 3×3 demodulation parameters, realizes the stable coefficients calibration of the interferometric optical fiber sensing system, and greatly improves the stability and reliability of the system.
A kind of fiber optic particle velocity sensor based on planar cantilever beam is studied. The fiber laser is attached to the surface of a cantilever. The cantilever beam is deformed by the acoustic field in the vertical direction of the surface, and the frequency of the output of the fiber laser is modulated, so as to realize the acoustic vector sensor. In particular, in viscous fluids, the cantilever is driven by an additional force proportional to the velocity of fluid particle. By selecting the appropriate liquid, the fluid viscous force will become the main driving force of the cantilever beam, making the sensor respond directly to the velocity of water particle, thus having a flat sound pressure sensitivity response curve. According to the cantilever beam equation in fluid, the theoretical simulation of the frequency response of the sensor shows that the acoustic pressure sensitivity is 104Hz/Pa and the acceleration sensitivity is 108Hz/g from 10Hz to 60Hz. The acoustic pressure sensitivity and acceleration sensitivity of the sensor in air and water are studied by experiment, and the results are consistent with the theoretical simulation. Compared with the traditional fiber optic accelerometer, the sensor of this structure has the advantages of small size, simple structure and high sensitivity, which is of great significance for application of vector hydrophone in low frequencies and is beneficial to constitute large scale hydrophone array.
The photoelectric detecting technology bas-ed on the 3×3 coupler is widely used in interferometric fiber optic hydrophone systems. Parameters such as DC and AC amplitude and phase difference of the couplers have a crucial influence on the accuracy and stability of demodulation. In this paper, an ellipse fitting algorithm based on light source modulation is used to achieve real-time, accurate measurement and correction of the detection parameters, eliminating the impact of the 3×3 coupler asymmetry on the system. The signal detecting accuracy is improved with the effectively suppressed system noise, realizing the stable signal detecting for the fiber optic hydrophone. Compared with the traditional ellipse fitting algorithm based on external large signal modulation, the proposed algorithm presents higher reliability and practicability. Furthermore, in view of the characteristics of large-scale array data processing and high real-time requirements, this paper adopts a heterogeneous design of ARM+FPGA, using the SDSoc platform to carry out software and hardware collaborative development of the 3×3 coupling demodulation algorithm based on light source modulation. ARM implements task allocation and scheduling functions, and FPGA implements specific function calculation modules. this design greatly reduces the pressure of computer data processing, and ensures that the optical fiber hydrophone system can complete automatic parameter calibration while real-time demodulation. The demodulation efficiency of the 3×3 algorithm is improved, coupled with the high integration and easy expansion of the system itself, provides the possibility for future large-scale arrays of 3×3 detection schemes in fiber optic hydrophone systems.
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