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

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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