The Double Wavelength Fiber Laser Dry Involves Dynamic Demodulation Technology

Multi-wavelength fiber laser can be used to provide the required light source for multiple channel simultaneously, making the transmitter design more compact and economical, and thus has a very important application in the dense wavelength division multiplexing system. At the same time, the excellent performance of the multiple wavelength light source also has great application value in the laser rangefinder, spectrum analysis, the distributed sensing and other fields. If the multi-wavelength fiber laser is combined with self mixing interference (SMI), introducing feedback to it, the fiber laser active sensing will be realized and be more widely used in the optical fiber sensing field. SMI signal in fiber ring lasers has many advantages such as high power, high signal-to-noise ratio (SNR) and the potential for long distance transmission and multiplexing. SMI can be easily combined with fiber technology, performing noncontact and remote measurement for velocity, vibration and displacement, and form a new fiber active sensing system based on optical feedback.In this paper, the dual-wavelength fiber ring laser of serial topology and its active sensing are researched. On the basis of dual-wavelength output from the fiber ring laser with fiber Bragg grating (FBG) in series, the wavelength multiplexing and active sensing by extracting single wavelength and adding feedback to the system are achieved. The principle of dual-wavelength fiber laser with gain competition among the applied channels and the output power with optical feedback are theoretically analyzed. The experimental results show that this system is feasible for the measurement of the movement of multiple channel vibrational targets. And by investigating the output signals under different feedback conditions, it can be concluded that this system has the same sensitivity as self mixing interference, the direction of the movement can be distinguished from the inclination of the fringes and we can get information of the feedback targets from the output signals.In addition, the strain sensing system of FBG based on array waveguide grating (AWG) light source is researched in this paper. Considering that the AWG narrowband light source has its linear region and FBG wavelength is linear to the strain loaded to it, it is obvious that we can get the measurement results of FBG strain from the detection of output power. The basic structure and principle of fiber Bragg grating strain measuring system is introduced, experimental system is built and the influence of different parameters on the system output is discussed. This system has the advantages of simple structure, compact, requiring less device compared with conventional demodulation method, and the measuring result is better. Further more, because of the multiple channel of AWG, this scheme is expected to achieve the real-time measurement of multiplex FBG strain at the same time.