High-sensitivity Detection Technology Of Optical Fiber Faults Based On Feedback Time Delay Signal Of Semiconductor Lasers

At present,the widespread deployment of optical access networks has brought great convenience to our lives.In the optical access network,the most commonly used is the time division multiplexing passive optical network(TDM-PON).The large attenuation introduced by the power splitter(PS)in the TDM-PON will cause the echo power to be lower than the sensitivity of the detection method when the fault point of the fiber occurs,so that the fault point in the TDM-PON cannot be detected.In order to detect the fault point in TDM-PON,a high-sensitivity optical fiber fault detection method is urgently needed.In addition,in order to distinguish each branch in the optical network,the spatial resolution of the optical fiber fault detection method cannot be too low.Researchers have proposed a variety of optical fiber fault detection technologies,but there are certain limitations in principle.For example,The sensitivity of the pulse flight method and the correlation method is limited by the sensitivity of the detector.Although the single-photon detector can improve the sensitivity,the high cost is not conducive to large-scale applications;The coherent method utilizes the coherent properties of lasers to achieve highly sensitive fault detection,but its detection distance is limited by the coherence length,so it cannot be used in long-distance optical networks;The sensitivity of the fault detection method using the timedelay signal of the optical feedback semiconductor laser is not limited by the sensitivity of the detector,and its detection distance is not limited by the coherence length of the laser light source,which has the potential of high-sensitivity fiber fault detection.However,the existing methods for extracting time delay signal have certain limitations,that is,the laser is required to be in a chaotic state.This paper also uses the optical feedback semiconductor laser time delay signal for fiber fault detection.On this basis,we propose a new method to extract the time delay signal,which is not limited by the state of the laser.Based on the resonance phenomenon between the modulated signal and the external cavity,we extract the feedback delay signal from the modulation response curve of the semiconductor laser by means of inverse Fourier transform(IFT).Finally,we use the extracted time delay signal to locate the fiber fault point.Based on the above content,the related work carried out in this paper is as follows:(1)Based on the Lang-Kobayashi rate equation,the modulation response characteristics of the laser and the corresponding IFT detection results are theoretically simulated.The results show that the detection sensitivity and spatial resolution of this method can reach-84 d B and7.1 cm,respectively.In addition,we also investigated the influence of the laser bias current and modulation parameters(modulation depth,modulation sweep range,and stepping)on the detection results.(2)We experimentally built an optical fiber fault detection system based on modulation resonance method and detected optical fiber faults.The results show that the detection sensitivity and spatial resolution of the method can reach-70 d B and 5.2 cm,respectively,and the influence of the laser bias current and modulation parameters on the detection results is consistent with the simulation law.In addition,we use 1×64 PS to build an optical network with 64 branches.We compare the detection results of the modulated resonance method with those of OTDR products.The results show that this method can not only achieve the detection of 64 branches,but also the spatial resolution can be significantly improved.