Pulse characteristics of long-cavity-length mode-locked Er-doped fiber laser in the anomalous dispersion regime

• Main Authors: Yang, Liang-Yu, 楊良愉
• Other Authors: Lai, Yinchieh
• Format: Others
• Language: en_US
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/97909080177226221233

碩士 === 國立交通大學 === 光電工程學系 === 100 === This thesis work mainly studies Er-doped passive mode-locked fiber laser configuration. The cavity length mainly consists of 400 meters-long single mode fiber and 1.65 meters long Er-doped gain fiber. We use the polarization additive pulse mode-locking (P-APM) technique to mode-lock the laser. An optical output coupler with the ratio of 30/70 (30% power back into the cavity) is used to extract the optical pulses and the pulse repetition rate is 500 kHz. By adjusting the polarization controller inside the cavity, we can produce different stable mode-locked states including the long square pulse state and the short pulse state. In the square pulse operation regime, a single pulse can reach the pulse energy of 142 nJ by increasing the pump power. The pulse-width increases proportionally without the pulse breaking. Dual-wavelength phenomenon is another interesting mode-locked state of the laser. It is a combination of two different pulse states: one is the short pulse state and the other is the square pulse state. We filter the optical spectrum to observe the changes of the pulse shape in the time domain to confirm their properties. We are also interested in the analysis of the spectral chirp characteristics in both the square pulse and short pulse regimes by sliding-filtering the pulses. We filter the spectra of the optical pulses in the two different mode-locked regimes and record the resulting pulses in the time domain. The spectral 2nd and 3rd order chirps are estimated based on the measurement results. In the meantime, we try to compress the filtered optical pulses by connecting a section of dispersion compensation fiber (DCF) and different lengths of single mode fiber (SMF). The optical pulse-width was measured by an autocorrelator and the minimum pulse-width can be below 160ps with proper lengths of the DCF and SMF fibers.