Study On Signal Modulation Using Fiber Bragg Grating With Ultrasonic Wave Driving

Fiber bragg grating(FBG) has great applications in optical communictions for its good filtering and selective reflection properties. Such as optical switching, wavelength division multiplexer, add-drop multiplexer, optical cross-connect equipment and all-fiber filter and so on. Especially in recent years, the optic devices based on tunable filter characteristics of FBG are becoming focus of study. The modulator using FBG with ultrasonic wave driving can easily tunes filtering proterties of the devices by changing the acoustic parameter, to realize dynamic tuning to FBG. So it is of great important to study on signal modulation using fiber bragg grating with ultrasonic wave driving.This thesis is devoted to design and validate the ultrasonic drive system and FBG reflection spectrum characteristics, including theoretical analysis and experimental research. And the main contents and achievements of this thesis are listed as follows:1.A PZT drive system is presented and designed in FBG modulation system, incluing a linear amplification circuit based on PA119operational amplifier. We complete the PZT power amplifiction drive circuit with good dynamic high-frequency response. And this drive circuit can almost distortion-free real-time amplify the continuous adjustable input signal of100KHz-1MHz,0-5V to the required voltage to drive PZT.2.According to the acousto-optic interaction principle, based on the FBG mode coupling theory, we draw that there are three kinds of coupling modes in FBG subjected to transverse vibration. In terms of phase-matching conditions, the reflection spectrum characteristics are theoretically analyzed, In addition, we also introduce the reflection spectrum characteristics of FBG subjected to longitudinal vibration based on the theory of acousto-optic interaction superlattice theory. Analysis show, new sidebands only appear at the short wavelength direction of the center wavelength when FBG induced by transverse vibration, and the reflection rate of various wavelengthes change with the change of voltage; but when FBG induced by longitudinal vibration, new sidebands appear at the both sides of the center wavelength.3.Experiment demonstrates the FBG transverse vibration reflection spectrum characteristics when induced by ultrasonic wave. Expeiment results show, new sidebands appear at the both sides of the center wavelength when transverse vibration is generated in FBG by specific frequency of ultrasonic wave driving. With the increase of voltage, the reflection rate of center wavelength gradually decreases, meanwhile, the first-order sidebnds gradually increase, and more higer order sidebands appear if the voltage continues to increase. The location and intensity of reflection spectrum are changed by changing the frequency and amplitude of input signal. But in theory, new sidebands only appear at the short wavelength direction of the center wavelength, the gap between them is the problem we need to solve.