Optical frequency conversion by ultra-fine waveguide and their application to phtonic integration

本课题研究材料中具有多维光子周期结构的光子晶体的特性。重点研究了光子晶体光纤的非线性特性。在单折射率导向光子晶体光纤（PCF）中，通过在可独立寻址的几个小芯处泵送140 fs脉冲来表征位相关的非线性光学特性。利用反射法原位观察PCF输入面相对于准直激光束固定焦点的波导结构，实现了泵浦点在PCF上的位置分配。泵浦采用波长在800nm左右的钛蓝宝石激光器。在这些小芯处的一系列输入峰值功率相关光谱表明，从红外到可见光再到紫外光产生了宽光谱相干光（超连续光谱光），并从芯尺寸变化的角度进行了讨论。在较小的核心处产生更多的离子主要是由于通过减小核心尺寸来增加反常色散的程度。设计了一种独特的测量装置来检测多芯型PCFs中光纤长度相关的能量转换。利用该系统观测到5m长的PCF产生的一些峰的光谱逐渐变化。这些峰值和它们的位移被认为是孤子和孤子的自频移。另一方面，较短波长的峰的起源既不是由孤子发射和捕获的色散波，也不是由四波混频或和频移产生的闲散波。在飞秒钛蓝宝石激光脉冲照射下，利用光谱条纹相机和超连续光测量了20毫米长的PCF的色散，确定了5m长PCF的波长色散曲线。利用光刻技术制备了一种空气包层型小芯波导结构，研究了PCF的较短长度限制。在硅脊结构的锐边上制备了35微米长的SiO2细线。在钛蓝宝石激光810nm光的泵浦作用下，该波导在795nm左右得到了波长转换的新光谱。这些结果对开发光子集成功能器件具有重要的指导意义。少

The research project concerns characteristics of photonic crystal that has multi-dimensional photonic periodic structures in the material. Especially, nonlinear properties of a photonic crystal fiber were investigated.Site dependent nonlinear optical properties are characterized by pumping 140 fs pulses at independently addressable several small cores formed in a single index-guiding photonic crystal fiber (PCF). The positional assignment of pumping site onto the PCF is achieved based on the reflection method to observe in situ the waveguiding structure of PCF input facet relative to the fixed focal point of the collimated laser beam. Pumping was done by Ti-sapphire laser with the wavelength around 800nm. A series of input peak power dependent spectra at these small cores demonstrate generation of a wide spectrum coherent light (supercontinuum light) from infra-red to visible light down to the violet, which were discussed from the viewpoint of core-size variation. Visible light generat … More ion at smaller core is principally due to an increase of the degree of anomalous dispersion by decreasing the core size.A unique measurement setup has been designed to examine the fiber-length-dependent energy conversion in multi-core-type PCFs. Gradual spectral change of some peaks generating through 5 m-long PCF has been observed by using this system. Those peaks and their shifts have been identified as solitons and soliton self-frequency shift. On the other hand, the origin of peaks in shorter-wavelength regime is neither dispersive waves which are emitted and trapped by solitons nor idler waves generated by four-wave mixing or sum-frequency shift. Wavelength dispersion profiles of 5m-long PCF have been determined by measuring chromatic dispersion using a spectroscopic streak camera and the supercontinuum light, which is generated from a 20-mm-long PCF under illumination of a femto-second Ti-sapphire laser pulse.An air-cladding type small core waveguide structures were fabricated to investigate the shorter length limit of PCF using photolithographic techniques. The 35 micrometer-long SiO2 thin wire on the sharp edge of the Si ridge structure was fabricated. A wavelength converted new spectrum around 795nm was observed with this waveguide under pumping with 810nm light from Ti-sapphire laser. These results are promising for developing photonic integrated functional devices. Less