High-extinction-ratio periodic pulse signal generation based on MZ modulator

High extinction ratio is needed in high precision Optical Time Domain Reflectometer (OTDR) to enlarge the dynamic range. By transmitting part of pulse signal modulated by a Mach-Zehnder (MZ) optical modulator back to the input of the modulator via a feedback circuit, the pulse signal can be multi-modulated by one MZ optical modulation. And this technique offers great enhancements in the performance of extinction ratio and peak power of the output pulse. This paper present a theoretical analysis of this system, give out a system-parameters-setting methods to make the result output from the system is falling in line with expectation. A simulation platform and computer simulation are done to validate the validity of the system.