Thesis or Dissertation Single-frequency ber laser sources based on the gain control by photonic bandgap waveguide

陳, 明晨  ,  Chen, Mingchen

pp.1 - 155 , 2015-03-25 , The University of Electro-Communications
For the applications at the yellow-orange color region, such as laser guide star, laser coagulation, and spectroscopy,fiber laser sources at the wavelength range of 1150 nm-1200 nm are alternatively investigated because of no gain medium at the visible region. Ytterbium fiber laser and amplifier have shown excellent performances in high output power and efficiency at 1μm. Since the gain peak of an Yb fiber is around 1030 nm, in the case of the long wavelength operation, the Yb fiber laser/amplifier suffers from strong amplified spontaneous emission (ASE) and parasitic lasing at unwonted wavelengths near the gain peak. In this thesis the development of the high-power, single-frequency fiber sources at 1178 nm is presented. The gain peak of Yb3+ is modified by use of the photonic bandgap fiber (PBGF). At the high gain region, large propagation loss was applied by the spectral filtering property of the PBGF core. The single-frequency source is based on the master-oscillator power amplifier configuration and composed of one oscillator and two amplifiers. The seed was in-house external cavity laser diode. Fiber Raman amplifier (FRA) was developed as the preamplifier in order to obtain highly efficient amplification at the PBGF amplifier. Because the power limitation by the nonlinear effect, stimulated Brillouin scattering (SBS), is the main obstacle in the case of the narrow linewidth, mitigation techniques of SBS are investigated for the power scaling. Three different SBS mitigation techniques were experimentally tested in the FRA. Eventually the SBS mitigation at both FRA and PBGF amplifier were achieved by the spectral linewidth broadening using electro-optical phase modulator. Besides the experiments, several numerical studies were introduced to predict the suitable PBGF and amplifier designs. The higher ASE suppression was founded in the case of that the fiber bending radius is orthogonal to the PBGF's boron axis. For the further power scaling large mode area PBGFs have been developed and experimentally tested in the amplifier.

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