Optical Fiber Fault Characteristic Detection Based On Broadband Boolean Chaos

Optical time domain reflectometer is a professional equipment used to detect optical fiber failure and loss of optical fiber connection points.Due to its advantages of high detection accuracy,long measurement distance and non-damage detection,it has been widely used in optical fiber link detection and maintenance in broadband Internet.The basic working principle^[1-2]of optical time domain reflection technology is to rely on the analysis of the relationship between the back Rayleigh scattering signal and Fresnel reflection signal received by the optical fiber injection end and the transmission time to detect optical fiber failure characteristics,such as the connection point,fusion point,bends,fracture,optical fiber loss,etc.At present,pulsed optical time domain reflectance is the most commonly used optical fiber detection technology in the world,but this technology has the technical flaw in principle,that is,it has the contradiction of principle that dynamic range and spatial resolution cannot be improved simultaneously.In the case of the measurement range larger than 100 kilometers,the maximum deviation of pulsed optical time domain reflectance is up to tens of meters,which cannot meet the requirements for long-distance,high-precision(centimeter-level)detection of optical fiber links in applications such as Fiber To The Home(FTTH)and big data centers.In order to expand the dynamic range,the optical time domain reflection technology based on photon counting increases the bandwidth of the laser pulse,thus reducing the spatial resolution.Moreover,it requires a longer measurement time and the correction of the test data,as a result,it has limitations in practical application.The optical time domain reflection technology using random code modulation can enlarge the dynamic range by increasing the code length without decreasing the spatial resolution.However,due to the need for an expensive electric random code modulator to modulate the laser to generate a random code sequence,and electric random code modulator encounters technical bottlenecks when generating random codes with an excessively long period,which limits the significant improvement of dynamic range and spatial resolution.With the rapid development of optical fiber communication technology and fiber to the home technology,it is urgent to develop an optical time domain reflectometer with high precision,reliable performance and low cost for optical fiber fault detection.In this thesis,an optical time domain reflectometer based on direct modulation technology is proposed.The broadband Boolean chaotic signal is utilized used as the signal source,and the distributed feedback laser is directly modulated by this signal,which contributes that the broadband chaotic laser can be generated to detect the fault of the optical fiber.The experimental results show that the proposed optical time domain reflectometer can achieve the spatial resolution of14 cm independent of the detection distance within the measurement range of about 70 km,and achieve the desired effect.The optical time domain reflectometer proposed in this thesis can solve the problem that the dynamic range and spatial resolution cannot be improved at the same time in optical fiber link and it is expected to be applied in practical engineering.In this thesis,the method of optical fiber fault detection based on broadband Boolean chaos is systematically studied.The main work includes:(1)A method of directly modulating a semiconductor laser with a broadband Boolean chaos electric signal is proposed to generate chaotic laser.(2)The broadband Boolean chaotic electric signal is generated in the simulation,and this electric signal is used as the signal source.According to the rate equation of the semiconductor laser,the chaotic laser is generated in the simulation.(3)The broadband Boolean chaotic electric signal and chaotic laser meeting the system requirements are generated in the experimental environment.(4)According to the scheme design,the experimental device is built to detect different types of faults on the optical fiber.