Distributed Optical Fiber Micro- Seismic Signal Modulation System Based on Linear Frequency Modulation

Based on the traditional distributed optical fiber sensing technology that uses back Rayleigh scattering, a linear sweep pulse modulation method for micro-seismic detection is proposed. The rectangular pulse in the modulation system is first transformed into a linear sweep pulse, and long- distance and high-spatial- resolution sensing is realized by compressing the pulse and matching filtering. Through simulation and experimental verifications, a narrow line-width laser with a line width of approximately 10 kHz is selected as the light source. Electro- optical and acousto- optical modulations determine the frequency scanning range and time as 5. 6. 5. 8 GHz and 2 mu s, respectively. Linear sweep signal modulation obtains a sensing distance of 10 km, and the intensity range of the received back Rayleigh scattering signal is -60 similar to- 50 dBm.