Development Of High Precision Optical Time Domain Reflectometer

Optical time domain reflectometer is the main instrument for the fault detection of optical fiber and optical cable line. The instrument generally uses the pulse laser as the probe signal, by detecting the backward Rayleigh scattering in the optical fiber and the Fresnel reflection signal at the fault point, the attenuation information and the location information of the fault point are obtained. However, the measurement method has the principle contradiction that the range resolution and dynamic range cannot be improved at the same time, that is, with the increase of measurement distance, the range resolution will be reduced. At present, the typical spatial resolution of commercial OTDR of pulse laser is usually in the order of several to tens of meters, unable to realize the accurate measurement of optical fiber and cable line intensive fault events. With the rapid development of fiber optical communication and fiber to the home, it has become an urgent problem to be solved in the field of optical fiber fault detection to design an optical time domain reflectometer with large dynamic range, high-resolution and low cost for fiber fault detection. In this paper, we propose and demonstrate experimentally and numerically an optical time domain reflectometer using a laser modulated by Boolean chaos to realize the fiber fault detection with high precision. The technology using chaos random signal combined with correlation measurement method, overcome the contradiction that traditional pulsed optical time-domain reflectometer dynamic range and spatial resolution cannot be improved at the same time, realizing the high precision optical fiber fault measurement with independent of measuring distance. In addition, the technology based on chaotic optical time domain reflectometer measurement has been integrated into the pulse optical time domain reflectometer technology. Through the optimization design of the two kinds of optical fiber fault detection methods, a new optical time domain reflectometer system is obtained which can measure the optical fiber attenuation information and realize the high precision positioning of the optical fiber fault. Experimental results show that the system can detect various types of reflection(optical fiber failure) events in the fiber, such as mismatch connector and fiber breakpoint. A detection range of approximately 123 km and a range-independent spatial resolution of 24 cm are achieved. At the same time, the system also realizes the accurate measurement of the attenuation of the optical fiber.The types of optical fiber fault and its detection principle are described. The contrast and analysis of the traditional pulse optical time domain reflection technique and chaotic optical time domain reflection technique are carried out, and point out their problems. A novel optical time domain reflection technique is proposed for the combination of chaotic light and pulse light, realizing the high precision positioning of the optical fiber fault independent of distance and the measurement of the optical fiber attenuation. We have completed the design of the novel optical time domain reflectometer system and the development of each module in the system, including the laser driver module, signal modulation module, chaotic signal generation module and a pulse signal generating module etc. We use the novel optical time domain reflectometer system to measure the single mode optical fiber which is made up of many sections. The performance of the system is analyzed and evaluated from two aspects of the distance resolution and the farthest distance measurement(dynamic range),and the methods to improve the measurement performance are also pointed out.