【作者】 季玲玲；

【导师】 陆培祥；

【作者基本信息】 华中科技大学 ， 物理电子学， 2008， 博士

【摘要】 光子晶体光纤可具有超宽带单模传输性、增强的模式限制特性、色散可调控等优点,在光通讯、光谱学、传感器等领域被广泛应用。光子晶体光纤中的非线性光学效应在近十年内成为研究热点,且促进了其他研究领域的发展。例如,光子晶体光纤中超连续光谱产生在光相干层析技术、高精密光学测量等领域有很重要应用价值。其他非线性频率转换过程如四波混频过程在纠缠光子对制备、光参量放大和振荡器方面有应用潜力;光子晶体光纤中的三次谐波过程可用以产生紫外光源。另外,光子晶体光纤中的部分非线性光学过程产生的物理机制并不十分清晰,有关这些问题的探究将丰富非线性光学的内容,具有很大的科学价值。本文采用掺钛蓝宝石飞秒激光系统,开展了飞秒激光脉冲在光子晶体光纤中的传输特性的实验研究。主要关注光子晶体光纤中的非线性光学效应,包括超连续光谱产生、四波混频过程、色散波产生,并探索其潜在的应用价值。全文的主要研究内容、结论与创新性如下:（1）利用有限元方法设计了具有高折射率复合纤芯的Bragg光纤,其零色散点在1.55μm附近,最大非线性系数可达40 W^-1Km^-1。（2）在双折射光子晶体光纤中实现了基于高阶孤子分裂的超连续光谱产生。经计算用脉冲俘获条件较合理地解释了高阶孤子分裂过程中产生的色散波和红移光孤子的波长关系,该工作对于研究孤子分裂及色散波产生的物理机制有一定价值。（3）在大占空比的光子晶体光纤的多个具有不同色散特性的次芯中实现了多重频率转换过程,所用次芯的尺寸比早期文献中的报道大并首次关注次芯的双折射特性。揭示了空气孔随机分布的多孔微结构光纤在频率调谐器、传感器的应用潜力。（4）利用亚纳焦量级的飞秒激光脉冲在光子晶体光纤中获得接近倍频的蓝光,经分析蓝光是参量四波混频过程产生的信号光,蓝光的转换效率高达15%。伴随信号光产生的闲置光可以处于太赫兹波段,实验也预示了通过四波混频过程在光纤内产生太赫兹波的可能性。（5）在实验上详细研究了光子晶体光纤次芯中的三种偏振调控的蓝移非孤子辐射产生。蓝移辐射的波长可在一定范围内调节,且具有优于早期报道的特性,如窄线宽性（小于10 nm）或具有空心光束模式等,在可调谐光源研制、光镊技术等领域有应用潜力。更多还原

【Abstract】 Phontonic crystal fibers （PCFs） can have excelent properties shuc as single-mode propagation over broad wavelength ranges, enhanced modal confinement and the ability to engineer theirgroup velocity dispersion. Therefore, they were used generally in optical communication, sepectrscopy and sensors. Supercontinuum generation in PCFs has subsequently been widely applied in interdisciplinary fields such as optical coherence tomography and optical frequency metrology. Other nonlinear frequency conversion processes such as four-wave-mixing have applications in generation of correlated photon pairs, optical parametric amplifiers and oscillators. Another interesting class of nonlinearity reported in experiments involves multimode phase-matched harmonic generation. This has been applied to the case of UV generation. In addition, understanding the physics under some nonlinear optical process in PCFs will undoubtedly present many opportunities to discover even more surprises.Experimental investigations of femtosecond laser pulses propagation in PCFs were performed. Nonlinear optical effectes such as surpercontinuum spectrum generation, parametric four-wave mixing process, and blueshifted nonsolitonic radiation of femtosecond laser pulses in multiple PCFs were studied. The potential applications were discussed. The main contents, research conclusions and contributions to innovation are summarized as following:（1） A all-solid Bragg fiber with compound cores having high- refractive index was designed theoretically. The zero dispersion wavelengthλ₀ near 1.55μm can be obtained in the Bragg fiber, and the nonlinear coefficientγis about 40 W^-1km^-1.（2） Super-continuum generation based high-order solitons fission was performend in a in a bi-refringent photonic crystal fiber in experiments. Pulse trapping condition explains well the relations between the solitons and dispersive waves in the experimental results.（3） Multiplex frequency conversion of sub-nanojoule Ti: sapphire femtosecondlaser pulses were performed in the trefoil and quatrefoil secondary cores in a holey fiber with high air fration. This suggests the holey fiber with random structure and large air-filling fraction can serve as an efficient multiplex frequency converter and sensor.（4） Efficient blue light with central wavelength near 0.4μm was obtained by Ti: Saphire femtosecond laser pules in a high-delta microstructure fiber. The blue light can take 15% of output power. The mechanisms for its generation is analyzed to be a degenerate parametric process, where frequency of the signal light is near twice the pump frequency and frequency of the idler light can lies in terahertz region. Our experiments may give the first demonstration of terahertz-wave generation in optical fibervia a FWM proces.（5） Three scenes of polarization-dependent blue-shifted emissions of femtosecond Ti:sapphire laser pulses were carried out in secondary cores of photonic crystal fibers. The blue-shifted emissions can be narrower than 10 nm or can lie in a hollow beam, and have potential use in design of tunable optical sources and optical tweezers.更多还原