Introduction to the Principle and Error Analysis of Optical Return Loss Testing: With the development of fiber optic communication, the widespread production and application of high-speed fiber optic transmission systems (such as SDH, high-power CATV, etc.) require high return loss. Due to its narrow line width, the output characteristics of DFB lasers are easily affected by return loss. This seriously affects the performance of the system, and even ordinary lasers are affected to varying degrees by the return loss. Therefore, the testing of the return loss of various fiber optic devices in the system has become increasingly important
Keywords: Return Loss Fresnel Reflection Rayleigh Scattering Polarization Sensitivity Matching Load
Return Loss Testing Basic Principle: When light is transmitted in a certain optical device, a portion of the light is always reflected back, and the return in the optical device is mainly caused by Fresnel reflection (due to refractive index changes), backward Rayleigh scattering (caused by impurity particles), and directionality.
Factors generated, The return loss RL of the device is: RL (dB)=-10lg (reflected light power/incident light power) (1) The testing method for return loss is based on OTDR (The full English name of OTDR is Optical Time Domain Reflectometer, which means Optical Time Domain Reflectometer in Chinese. OTDR is a precision optoelectronic integrated instrument made by utilizing the backscatter generated by Rayleigh scattering and Fresnel reflection when light is transmitted in optical fibers. It is widely used in the maintenance and construction of optical cable lines, and can measure the length of optical fibers, transmission attenuation of optical fibers, joint attenuation, and fault location.) Compared to optical power meter testing, the OTDR testing method has fast speed, intuitive display, and can obtain the spatial distribution of reflection points without the need for end matching (short fiber still needs to be matched). However, the cost is high, and it is important that it cannot be used in certain situations (such as echo loss testing of photodetectors), such as RIFOCS688 in the United States and AR-301 echo loss tester from NTT-AT in Japan. The optical power meter method mainly separates the light reflected by the tested device and guides it to the optical power meter. It is simple, practical, and has a wide range of applications, requiring end matching when used
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