Fiber Ring Laser And Applications Of Photonic Crystal Fiber In Active Devices

The research work in this dissertation covers both fiber ring laser and applications of photonic crystal fiber in active devices. For fiber ring laser, dual-pump mode-locked erbium-doped fiber ring laser, as well as compressing optical pulse by using Sagnca interferometer, is demenstrated. Also, a switchable multiwavelength fiber ring laser with Sagnac interferometer has been developed. As far as photonic crystal fiber is concerned, it is the fiber with a periodic microstrucure in air-glass. Compared with conventional single-mode fiber, PCF has some unique characteristics such as controllable dispersion and high nonlineatity. It can support endlessly single mode over a broad spectral range, as well as the zero-dispersion wavelength can vary from 800nm to 1600nm. PCF has high level of nonlinieatity due to the small core diameter, and values as high asγ=240W^-1. km^-1 at 850nm have been reported. Since the first PCF is invented in 1996, it has gained intense attention. For the expensive price and high loss compared with conventional single-mode fiber, it is impossible for long distance transmission in take place of conventional fiber. However, active devices based on PCF can expect a series of new applications in optical communication such as broadband dispersion compensation, optical pulse compression, wavelength conversion, supercontinuum generation and optical amplification. Based on the analysis of characteristics of PCF, applications of PCF in pulse compression, supercontinuum generation and parametric amplification are investigated in detail. The research works in the dissertation are summerized as follows:10GHz dual-pump mode-locked erbium-doped fiber ring laser is demonstrated. The schemes of ultrashort pulse compression are reviewed and summarized briefly. Pulse compression using Sagnac interferometer has been experimentally studied. According to the switching characteristics of Sagnac interferometer, the noise with low energy can be reflected by the Sagnac interferometer. Thus, it is helpful to eliminate the nosie and improve the qulity of pulse. For switchable multiwavelength fiber ring laser, the laser can be designed to operate in dual-wavelength or triple-wavelength mode and the lasing mode can be controlled by a polarization controller. Dual-wavelength operation at 1557.78nm and 1559.02nm can been obtained. The corresponding 3dB bandwidth is 0.018nm and 0.019nm. Also, triple-wavelength operation at 1558.61nm, 1558.76nm and 1559.03nm can be observed. And the corresponding 3dB bandwidth is 0.02nm, 0.016nm and 0.026nm. Moreover, it is found that the lasing is less stable when the numbers of lasing lines increase.Several prominent merits of PCF, such as property of single mode transmission, high nonlinearity, controllable dispersion and birefringence are systematically reviewed. Also, applications of PCF in active devices and potential advantages are introduced.For fiber ring laser based on PCF, it can largely improve the pump efficiency for same pump power compared with convential fiber and reduce the fiber length because PCF has high level of nonlinieatity due to the small core diameter. It is helpful to meet the practical and commertical demands. In our research work, PCF with dispersion parameter of 164ps/(nm. km) and nonlinear parameter of 36W^-1. km^-1 are introduced into the fiber laser and narrow pulse trains with broad spectrum can be obtained by soliton compression effects. Also, the output pulse is estimated as fundmental soliton.Several factors contributing to supercontinuum generation (SC), such as self-phase modulation (SPM), four-wave mixing (FWM) and stimulated Raman scattering (SRS), are analyzed in detail. By using 50MHz mode-locking fiber ring laser, SC can be obtained from dispersion-flattened PCF. The bandwidth of 237nm (at 20dB level) is achieved by launching 1.6ps pulses into a section of PCF. Moreover, the processes underlying spectral broadening are analyzed.By using passively mode-locking fiber ring laser, SC can be obtained from dispersion-flattened PCF. The results show that bandwidth of 439nm (at 20dB level) can be achieved by launching 689fs pulses into a section of PCFs. SC at different wavelength can be obtained by tuning the pump wavelength of the passively mode-locked fiber ring laser.The gain characteristics and bandwidth of optical parametric amplifiber (OPA) based on PCF are addressed theoretically. The relationship between the properties of PCF, such as nonlinearity and dispersion, and characteristics of OPA are analyzed. The modal is based on coupled equations derived from transmission equations of lightwave. Then, we propose an OPA based on PCF. The results show that maximum conversion efficiency is about -26dB.