Abstract

Wideband radar signal processing technology meets the demand of large bandwidth and high speed data transmission in short distance. Pulse compression, a common way to process wideband signal, is the core technology to process radar signal. Because it can solve the contradiction between spatial resolution and detection range. However, there exists huge loss during long distance transmission in microwave transmission medium. Meanwhile, processing signals in electrical domain is limited by frequency band and sampling frequency, which affects the processing speed and accuracy. In this thesis, we theoretically demonstrate pulse compression processing based on all-optical Brillouin dynamic grating (BDG) and its application in wideband radar signal processing technology.

​

We build a system to study the coupling mode and output signal of BDG through mathematical modeling and numerical simulation. In a birefringent medium like a polarization maintaining fiber (PMF), acoustic waves is generated by the coupling between chirp signal as pump lightwave and pulse signal as probe lightwave. The acoustic wave inheriting the amplitude and phase information of pump lightwave plays as a reflection grating for orthogonally-polarized chirp signal as pump wave at a different wavelength. We can thus obtain a pulse compression signal of pump lightwave in two orthogonal directions of the output probe signals. When there exists time delay and frequency shift between two orthogonally-polarized chirp signals, we can calculate time delay and frequency shift through analyzing the output probe signals. In radar systems, continuous chirp wave is electro-optically modulated onto the pump lightwave that is launched into one end of the fiber. By calculating time delay and frequency shift, we can obtain the speed and position information of targets.

Key words: Brillouin dynamic grating, wideband radar signal processing technology, pulse compression, Brillouin scattering, polarization maintaining fiber