Generation Of Supercontinua With Picosecond And Nanosecond Laser Pulses

Supercontinuum has been the hot topic of research owe to its broad application in optical coherence tomography, future high-speed dense wavelength-division-multiplexing optical networks, spectroscopy, optical metrology and so on. In the past, obvious supercontinuum was obtained by femtosecond pulses because it was difficult to find a media with high nonlinear coefficient. With the emergence of photonic crystal fiber, which has high nonlinear coefficient and controllable zero dispersion wavelength, supercontinuum can be generated using the picosecond and nanosecond pulses even continuous lasers. Since a mountain of work about femtosecond supercontinuum have done in the laboratory, we mainly focus on the research of picosecond and nanosecond supercontina. Main works in this thesis are summarized as follows:1. The development, application and theory of supercontinuum are introduced.2. The concept, basic principle of light-transfering, classification, kinds of characteristic, analytical methods and application prospect of photonic crystal fiber were summarized.3. In the condition of picosecond pulses, a supercontinuum source with output power up to 1.7 W and spectral width of 1700 nm(500-2200 nm) was obtained, the 5 dB spectral width is about 1100 nm(1100-2200 nm). The influence of parameters of the photonic crystal fiber such as fiber length, zero dispersion wavelength and dispersion characteristics to supercontinuum was analyzed. High efficiency supercontinuum generation needs suitable fiber length. The center wavelength of pump pulse must be matched with the zero dispersion wavelength of fiber. Suitable dispersion characteristic can also affect the spectral width and flatness of supercontinuum.4. In the condition of nanosecond pulses, the influence of repetition rate and pulse width of pump pluse to supercontinuum was analyzed. The peak power of pulse is increasing with the decreasing of repetition frequency. When the duration of pulse is very short, we can obtain obvious spectrum broadened only using a photonic crystal fiber with the length of a few centimeters. In contrast, we need a very long photonic crystal fiber to generate supercontinuum when the pulse width is broad.