High Precision OTDR Event Analysis And PC Software Design And Implementation

With the rapid development of communication technology,all kinds of information transmission medium emerge in endlessly.Optical fiber has the advantages of wide transmission band,large transmission capacity,light weight and so on,coupled with its low production cost,it has become the mainstream in today's information carrier,and is applied to major communication trunk lines.The optical fiber to the home is a great invention in the history of communication.Fiber optic communication technology is not only widely used in the field of civil communication,but also in the military field,especially in avionics network,the traditional copper bus of avionics system is gradually replaced by fiber optic bus.OTDR(Optical Time Domain Reflectometer)is a major instrument of fault detection in the field of optical fiber,and there are many products on the market,but mostly for thousands of meters or dozens of kilometers of optical fiber detection.The optical fiber in the airborne avionics network is only a few tens of meters in length.So for the daily inspection and maintenance of avionics optical network equipment,we demand higher accuracy,further optimization of event analysis performance,and more convenient visualization.The high-precision OTDR designed in this thesis adopts the OTDR system technology scheme based on time-dependent photon counting,which can solve the contradiction between the positioning accuracy and detection sensitivity faced by traditional OTDR.It can achieve detection sensitivity and positioning accuracy of centimeter level,so as to meet the needs of optical fiber fault detection in avionics optical network.The main work of this thesis is as follows:1.Based on the principle of OTDR optical fiber detection,this thesis analyzes the index parameters that affect OTDR test,and combines the requirements of high precision index to build a high precision OTDR system based on time-dependent single photon count.The core components of the system are analyzed and selected.The optical gating processing technology is applied to deal with single photon detector counting saturation caused by strong reflection peak.2.Wavelet transform and other methods are used to analyze the OTDR curve,so as to detect the reflected events and non-reflected events reflected on the curve.Firstly,the principle of wavelet analysis and its advantages in OTDR signal analysis are explained.Then the wavelet transform is used for signal denoising.Several common wavelet denoising methods and threshold processing methods are compared.Finally,the wavelet transform method and the slope method are used to detect the reflection and nonreflection events.3.A convenient upper computer software is designed by using VS and Qt platform,which is suitable for the high-precision OTDR in this thesis.The functions of the application mainly include test parameter setting,data receiving and processing,graph display and operation,automatic curve analysis and test result output,etc.4.The performance and functions of the high-precision OTDR system in this thesis were verified.The performance test(such as blind area,dynamic range,distance accuracy and loss accuracy)and the functional test(such as adjustment of test time and optical fiber fault detection)were carried out.The results were analyzed and explained.