| Summary: | 碩士 === 國立交通大學 === 光電工程研究所 === 102 === In the thesis, we use the polarization additive pulse mode-locking (P-APM) technique to mode-lock the laser. The laser cavity constitutes 4m Er-doped fiber and 6m SMF-28, with the pulse repetition rate of 20MHz. By adjusting the polarization controllers and the 980 nm LD pump power inside optical cavity, we can let laser operate under two very different operation states - soliton and chaotic pulse states. The optical spectrum under the chaotic state is smooth and the 3dB bandwidth is 12nm. In contrast, the optical spectrum under the soliton state has the symmetric Kelly sidebands and the 3dB bandwidth is 10nm. The output pulse-width is 300fs for both cases, but we can observe chaotic-like pulse amplitude variation under the chaotic state by using an oscilloscope. When the chaotic pulse train propagates through a section of SMF-28, we can observe a narrow center coherent spike in the auto-correlation trace, which width is almost not affected by the dispersion. We also compare the difference of propagation for the soliton case without and with Kelly sidebands. A band-pass filter can be used to filter out the Kelly sidebands. The result is that the soliton pulse without Kelly sidebands has shown obvious four-wave mixing effects after propagating through the dispersion-shifted fiber. In contrast, for the chaotic operation state, we can just use 24mW of the average power to produce a 120 nm relatively flat optical spectrum after propagating through the dispersion-shifted fiber. Finally we compare the pulse compression possibility of the two operation states. The shortest compressed pulse we can achieve is 223 fs for the soliton case. In comparison, the chaotic pulse cannot be compressed well.
|
|---|
