We numerically analyzed Q-switched erbium-doped fiber lasers (QEFLs) using a traveling-wave analytical model that allows axial nonuniformity in the population inversion density and light intensity within the QEFLs. The model enabled us to calculate complicated output pulse shapes from the QEFLs such as those with a multipeak structure. The calculated and measured pulse shapes agreed well. We found a guide for designing QEFLs through repeated calculations. We designed a QEFL to generate output pulses suitable for constructing optical time domain reflectometers (OTDRs) of high performance. We developed an OTDR by using a QEFL with a dynamic range of 35 dB and a spatial resolution of less than 100 m. This result represents an increase of more than 5 dB in the dynamic range over current standard OTDRs.
Shoji Adachi and Yahei Koyamada, "Analysis and Design of Q-Switched Erbium-Doped Fiber Lasers and Their Application to OTDR," J. Lightwave Technol. 20, 1506- (2002)