Photonic Crystal Fiber Lasers And Supercontinuum Light Source

Photonic crystal fibers, also known as microstructured or holey fibers, have recently generated great interest in the scientific community thanks to the new ways provided to control and guide light. Among the varieties of novel PCF-based apparatus, Rare-Earth Doped fiber laser and supercontinuum light source are relatively representative. In this dissertation, applications of PCF to the above mentioned fields are theoretically and experimentally investigated. Firstly, new occurrence on rare-earth doped fiber laser and SC generation are summarized with the focus mainly on photonic crystal fibers. Properties of birefringence in large mode area PCF are studied with a finite element method. As for PCF laser apparatus, Er3+ doped Bragg fiber based amplifier and Yb3+ PCFL are demonstrated. The last part of our work is concentrated on the propagation of quasi-continuous/continuous wave in PCF with high nonlinearity, which including both theoretical and experimental researches. The details are described as follows:1. The basic idea and analyzing process of finite element method are discussed. By means of this method, birefringence in PCF with a large mode area is studied and two fiber designs are proposed to realize form-induced birefringence: (1) A design of microstructure fiber containing small circular air holes in the center of the solid core is proposed, and it can have structure-induced birefringence with an order of ~10-4 whilst a large mode area of 100μm2. (2) By introducing two big air holes in the fiber cladding region and a small elliptical hole in the fiber core region at the same time, the cross section of the fiber shows twofold symmetry and group birefringence of ~10-4 can be achieved. These fibers can be applied to generation and propagation of high power laser.2. Modal properties and dispersion properties of high-index core Bragg fiber are theoretically investigated. Its application on rare-earth doped fiber laser apparatus is also discussed. Using the actual Er3+-doped Bragg fiber, we demonstrated a fiber amplifier and investigated its properties of gain. Result shows it have potential application in automatic gain control.3. A high power cladding pumped Yb3+ PCFL has been demonstrated using Fabry-Perot cavity configuration. The highest output power and the slope efficiency are 11.69W and 87%, respectively. In the latter experiment, a GaAs crystal was inserted into the cavity acting as a saturable absorber. Passive Q-switched Yb3+ PCFL was achieved with a pulse width less than 90ns.4. The fundamental properties of fiber nonlinearity are theoretically investigated with finite element method. Compared with the conventional fiber, the enhancement of the nonlinear coefficient in PCF can be considered from two aspects. One is the decreased mode area benefit from the large index difference between silica and air. However, the mode area can not be reduced unlimitedly and the energy will penetrate into the air holes when the diameter of the core is sufficiently small. Thus another way for nonlinearity enhancement is discussed, and PCF with Ge-doped core is studied in details.5. Based on the NLSE and Split-step Fourier Transform Method, the propagation of long pulse in PCF with low peak power is simulated, which shows that the modulation instability derived from SPM dominates the spectrum broadening. In the anomalous dispersion region, white noise can be introduced as the MI probe for speeding up the break of the long pulse. Thus unorderly ultra-short pulses come into being and its further propagation in PCF result in SC generation. The affection of peak power, fiber nonlinear coefficient and pulse width on SC spectrum are also investigated respectively.6. Pumping 70m long PCF with an 80ps pulse output, SC generation covering communication windows is demonstrated. In the experiment, two orders of amplifier are used as the noise source and MI is observed. It is in good agreement with the simulation results. In another experiment, the continuous wave from a Raman fiber laser is used to pump the same PCF, SC generation with high average power is acquired within a wavelength range of 1450-1650nm.7. The output of an Nd3+ doped Q-switched laser with high peak power is lunched into a 20m PCF for SC generation. Properties of SC both in frequency domain and time domain are measured and analyzed. By use of the ultra wide SC light source, we measured the band gap map of an all-solid PBG fiber. And it can also be used for providing multi-wavelength signals by means of filtering.