Design Of Swept-frequency Laser Source

Swept-frequency laser source is the key technology of the distributed fiber optic sensor based on stimulated Brillouin scattering(SBS).In this paper,we studied the process of generating a swept-frequency laser source by external modulation,including the circuit design and the method to improve its performance.To achieve a laser with stable frequency and power output is the key point of this paper since the temperature,current and other external factors will directly affect the stability of the semiconductor laser.The hardware circuit includes the power module,the DFB-LD drive control module,bias control module of LiNb03 and the RF module.The low-dropout linear voltage regulator chip and a series of filter circuits are used in the power supply module.The temperature control module is designed to drive Peltier cooler,which is controlled by PID algorithm to achieve real-time temperature adjusting.The current control module uses a high-current op amp to drive the laser with constant operating current.A microwave broadband synthesizer with integrated VCO is used in the frequency synthesizing module.The integrated phase-locked loop(PLL)could generate a high-accurate-frequency signal with an external frequency reference.Mach-Zehnder LiNb03 modulator is used as the electro-optic modulator and an automatic bias control circuit is designed to stabilize the working state of the modulator.In this dissertation,we combine the frequency-controllable microwave broadband synthesizers,a stable output DFB laser and an external modulator together to produce frequency swept laser signal.The detailed schematic design and PCB layout are discussed and accomplished.