Experimental Study On Optical Finer Sensing Using Laser Active Mode Locking

With the continuous improvement of optical fiber communication technology,the development of various new optical fiber devices has attracted researchers' attention.Optical fiber sensor networks based on optical fiber devices are developing rapidly.Optical fiber lasers and optical fiber sensors play a key role in optical fiber sensor networks and have been widely used in the field of optical fiber communication.In the research and development of fiber laser,the first is based on the research of semiconductor laser as the prototype,the fiber technology is fused in the semiconductor laser,combined with the characteristics of external cavity semiconductor laser and fiber grating sensing,making the research of fiber laser more meaningful.At present,most researchers propose mode-locking technology in pursuit of narrower line-width laser output.Under the current research background,it will be very meaningful to realize the sensing of fiber grating in mode-locking technology by combining fiber laser with fiber grating as sensing element.Fiber laser realized by mode locking technology can not only provide compatible ultra-narrow pulse light source for fiber communication system,but also lay the foundation for some applications of fiber system.Based on the research of mode-locking technology,the wavelength tunable fiber laser developed into a new type of fiber laser which is widely used in WDM fiber communication system.Tunable fiber lasers are attractive because their emission wavelengths can be systematically tuned within a certain spectral range.The use of wavelength tunable light sources facilitates applications in a wide variety of disciplines,including telecommunications,material processing,microscopy,medicine,and imaging.The technique of wide tuning mechanism in laser cavity has many applications.Wavelength tunable fiber laser can effectively reduce the cost of communication system,increase communication capacity,communication system is made more compact.Due to the transmission medium of optical fiber,the signal is transmitted in the fiber core in the form of total reflection,with significant advantages such as large transmission capacity,low loss,light structure quality of the system and good anti-interference ability,etc.,which ensures efficient rate and reliability of performance in the transmission of information.Was proposed in this paper using a laser to the realization of actively mode-locked fiber optic sensing experiment device,which combines the method of in Fabry-Perot laser(F-P LD)and fiber Bragg grating,the formation of the structure of compound cavity,using filter characteristic of the fiber Bragg grating,and the signal generation directly outside the cloth fabry-perot in regulating the frequency of the cavity on laser,in the large dispersion cavity of actively mode-locked fiber laser optical fiber sensing system.Different from traditional sensors,optical fiber sensors of this kind have advantages of compact structure,anti-electromagnetic interference,low cost,high sensitivity and corrosion resistance.Moreover,laser beat frequency detection is used to simplify demodulation system and increase sensing nodes.Before realizing the sensing,the active mode locking mechanism is used to output multiple wavelengths in the range of fabry-perot laser,and the tunability of fiber laser is realized.Relative to other types of sensor network system,it can provide multiple wavelength of laser light source itself,at the same time in fiber Bragg grating(FBG)sensor for sensing and demodulation,namely when the strain effect on FBG,the center of the FBG wavelength shift will happen,in the presence of the dispersion of the cavity,different wavelength of laser will have different time delay.In this paper,the demodulation of the sensor signal USES the laser beat frequency technology to convert the sensor signal into frequency signal,that is,convert the change of wavelength into the change of frequency.The frequency signal can be directly collected by the spectrum analyzer and converted to the corresponding change of the sensor signal.In this optical fiber sensing system,the use of light source is reduced and the difficulty of direct optical signal processing is reduced.To a certain extent,the cost of the system is reduced,the structure of the system is simplified,and the noise interference of the circuit sensor itself is avoided.