Research On The Multi-wavelength Mode-locked Polarization Maintaining Double Clad Er/Yb Fiber Laser

With the rapid development of the communication field in the recent years, multi-wavelength short pulse laser sources have become a research hotspot. These lasers have the advantages such as simple structure, low price and ease to access to the optical fiber connectors, and can thus be widely used in the fiber-optic sensing, optical measurement, spectral analysis, wavelength division multiplexing optical fiber communication systems and so on. With the narrow pulse width and high peak power, the short pulse fiber lasers are widely used in biochemistry, computer, communication systems, and fine processing fields. If the short pulse lasers have a multi-wavelength comb broadband spectrum, there will be a lot of potential applications such as fiber dispersion interrogation, wavelength division multiplexing technology, optical sensing and signal processing technology.In the thesis, we focused on the experimental research on multi-wavelength fiber laser and mode-locked fiber laser which are based on the Er/Yb co-doped double clad polarization maintaining fiber. The mode-locked fiber laser with MOPA structure was achieved in order to obtain relatively high output power by amplifying the developed mode-locked fiber laser seed.Firstly, numerical simulation analysis on the sagnac interference ring has been made to prove the principle and the feasibility of generating the multi-wavelength output in a sagnac interference ring. Based on this, the normal double-clad erbium-doped fiber and Er/Yb co-doped double cladding polarization maintaining fiber were tested experimentally. A stable multi-wavelength fiber laser with centre wavelength at 1612 nm and wavelength interval of 3.3nm (±0.2nm) was developed based on the figure-of-eight cavity.Then by adjusting the experimental setup of the multi-wavelength fiber laser mentioned above, a mode-locked fiber laser which can work both in Q-switching mode-locking and continuous mode-locking condition was developed. The repetition rate of the Q-switched mode-locking changed with the pump power and the orientation of the polarization controllers. The pulse width of the Q-switched mode-locking fiber laser decreases as the pump power increases. When the laser operates in the condition of the continuous mode-locking, different dispersion fibers have been used for different broadband spectrum. Multi-wavelength broadband mode-locking spectrum, which has the equal wavelength interval, could be obtained when we used the common single mode fiber. Broadband mode-locking spectrum could also be obtained when we used the dispersion shift fiber with the zero dispersion spot at 1600nm. Theshape of the pulse obtained by the experiment is rectangular with pulse width of nano-second level. The pulse width increased with the pump power. When the pump power increased to a fixed value, rectangular nano-second pulse bunch could be obtained. The number of the pulse in the bunch increased with the pump power. The time interval of the pulse could be equal or unequal.Finally, by using the Er/Yb co-doped double clad polarization maintaining fiber -based mode-locked fiber laser as the seed source, performance of the MOPA structured fiber laser was investigated. Using one or two stage amplifier, amplification to the rectangular pulse mode-locking and the rectangular pulse bunch mode-locking laser was realized respectively. Linearly polarized laser output with average output power of 592mW and 668mW were obtained respectively. It was found that the pulse shape and the pulse width remained unchanged after amplification.