The Drive Technology Of Fabry-perot Filter

Fiber Bragg grating(FBG) sensor encoded by wavelength can avoid the energy huntinginfluence of the light path, which has been used in many occasions because ofanti-electromagnetic interference, corrosion-resistant, safe, reliable, wide measurementrange and so on in recent years. However, the signal demodulation technology for fiberBragg grating is an important factor to limit the development of grating sensing, and it isalso a great chanllenge of the sensing field. At present, the main demodulation ways offiber Bragg grating consist of filtering method, interferometry and dispersion method etc.Among them, the filtering method is simple in principle and easy to be implemented. In thecase, tunable Fabry-Perot filter is used to scan the wavelength, which can scan severaltens of nanometers or even hundreds of nanometers. Moreover the bandwidth oftransmission peak is less than0.2nm, or even0.05nm and the resolution of the wavelengthcan reach picometer order of magnitude. The demodulation can implement the regulation totransmission wavelength according to electrostrictive effect of piezoelectric ceramic toadjust the length of the cavity, so it is necessary to design a high-precision and real-timeadjustable driver circuit to drive tunable Fabry-Perot filter.In this paper, the working principle of the tunable Fabry-Perot cavity is analyzed andthe idea that the combination of digital circuit and analog circuit is proposed, by which thedigital circuit generates sawtooth signal and the analog circuit amplifies power in order todrive the tunable Fabry-Perot filter.In the process of implementation, the sawtooth wave signal is gained by the family ofSTM32microprocessors, and the lager power is obtained by the push-pull amplifier madeup of the transistors TIP29C and TIP30C. Moreover, on the basis of the design of thehardware circuit, the embedded development tools-MDK and Keil C are used tocomplete the development and design of the software system. It includes serialcommunication circuit, by which data exchange can achieved between hostcomputer and microprocessor, and the communication circuit between themicrocontroller and the D/A converter chip AD560, by which the digital signal canbe changed to analog signal real-time.The development of the drive circuit can take out continuously adjustable voltage at0~30V, frequency from0~1KHz, offset from0~30V and duty cyclefrom0.006%~99.994%. The waveform is stable, high precision and the ripplerejection ratio is to0.0025%. For sampling and searching the signal and peak moreeasily, the applied voltage is rectified by using cubic fitting algorithm in a free spectralrange.It is showed from the experiment results that the standard error and the maximumerror of the tuning wavelength are reduced by62.7%and80.1%.When the frequency of the scanning voltage is5.8Hz, the voltage amplitude is11.4V~23.3V and the duty cycle is99.994%, sensing grating gains strain by Microplatform. After4hours repeatability test, the measurement accuracy is1.58pm andstability is4pm and repeatability is4.02pm at2micro-strain.