The Research On Hundreds Of Milliwatts Super-continuum All-fiber Laser

In recent years, super-continuum laser source is drawing more and moreattention. With advantages such as wide-spectrum, high intensity and high degree ofspatial coherence, it has been used in laser radar, long-distance communications,medical imaging, optical metrology, and other areas. Super-continuum laser sourcewith power of hundreds of milli-watts, however, has its own unique applications invarious fields such as surface Plasmon, fiber grating test, laser radar, transientspectroscopy and optical coherence tomography technology. For Its wide-spectrum,low cost and small size, it serves a perfect substitute for complex multi-wavelengthlaser system, as well as for common wide spectrum optical sources like ASE, SLD,xenon lamp, etc. Through investigating the current situation of low-powersuper-continuum laser, its advantages and disadvantages are summarized. Based onthe requirements of the project supporting this research, experimental program ofhundreds milli-watts all-fiber super-continuum laser is identified.The main content of this thesis is as follows:Theoretical aspects:1, From the basic equations of pulse transmission, this thesisderives the nonlinear Schrodinger equation describing nonlinear transmissioncharacteristics of optical fiber, and briefly introduces several nonlinear effectsproducing super-continuum spectrum2, this thesis gives an overview of passivemode-locking technology, and mainly explains the working principle ofsemiconductor saturable absorber mirror (SESAM) as well as the generating processof dissipation mechanism.Experiment aspects.1. By cavity structure comparison experiment on lowrepetition frequency passively mode-locked fiber laser, it was decided that the cavitytype with maximum mode-locked range is the primary type for the followingexperiment.2. The experiment was made with two aspects to increase peak power:lowering repetition frequency and narrowing pulse width. Firstly, by increasinglaser’s cavity length to reduce repetition frequency, based on the order of Ramaneffects, it was confirmed when the repetition frequency is10.65MHz, the output peakpower is maximal. Secondly, the dissipative soliton mode-locking experiment wasintroduced with the purpose of narrowing the pulse width in order to improve pulse’s peak power.3. Experiments of simplifying the structure. By selecting the parametersof devices in the cavity to improve the output power of the oscillator stage, it wasrealized that the laser structure was simplified with removing a level of preamplifierand the output power of the oscillator stage is1.52mW with the repetition frequencyof10.65MHz.4. In the experiment of increasing cavity length, it was managed to getthe ultra-low repetition frequency mode-locked pulse. Finally, the frequency of156.8KHz was gotten.5. The experiment on low loss welding between different corediameter photonic crystal fibers and single mode fiber. Through adjusting thedifferent welding parameters, the low loss welding between0.3dB and0.35dB wasachieved.6. Super-continuum generation experiments on different zero-dispersionpoint photonic crystal fiber and cascaded photonic crystal fiber. The super-continuumoutput with average power of105mW, spectral range from550nm to1700nm, theflatness of less than10dB was gotten by the use of photonic crystal fiber zerodispersion point at1040nm. The super-continuum output with average power of76mW, spectral range from530nm to1700nm, the flatness of10dB was gotten withthe use of cascaded photonic crystal fiber.