This study proposes a novel structure of index-guiding square photonic crystal fibers (SPCF) having simultaneously ultra-flattened chromatic dispersion characteristics and low confinement losses in a wide wavelength range. The finite difference method (FDM) with anisotropic perfectly matched layers (PMLs) is used to analyze the various properties of square PCF. The findings reveal that it is possible to design five-ring PCFs with a flattened negative chromatic dispersion of 0-1.5 ps/(nm.km) in a wavelength range of 1.27 µm to 1.7 µm and a flattened chromatic dispersion of 01.15 ps/(nm.km) in a wavelength range of 1.25 µm to 1.61 µm. Simultaneously it also exhibited that the confinement losses are less than 10-9 dB/m and 10-10 dB/m in the wavelength range of 1.25 µm to 1.7 µm.

In this paper, we describe detailed experimental demonstrations of blue/violet light generation by the injection of ultrashort optical pulses into photonic crystal fibers (PCFs). Two lightwaves appear one on each side of the injected pulses in the spectral domain. They simultaneously evolve in the PCFs, changing their center wavelengths so as to spectrally stand apart from each other. Such behaviors are explained on the basis of the theory of nonlinear optics. The final center-wavelength difference between the two lightwaves at the end of the PCFs, depending on the power density of the injected pulse, is increased up to a limit imposed by the PCFs. Owing to this increase, the shorter wavelength limit reaches approximately 400 nm, which shows that short-pulse injection in PCFs is a promising method of realizing simple blue/violet light sources.

Recent progress on photonic crystal fibers is reviewed aiming at their application to high performance networks. A photonic crystal fiber has an array of air holes surrounding the silica core region. Light is confined to the core by the refractive index difference between the core and the array of air holes. Photonic crystal fibers have special characteristics compared with conventional single mode fibers. One is that the dispersion characteristics can be designed. Another characteristic, that strong birefringence can be established by sizing and/or arranging the air holes, is expected to realize a polarization maintaining fiber with high birefringence of the order of 110-3. This paper will describe the characteristics of dispersion controlled PCFs and polarization maintaining PCFs that include supercontinuum generation and absolute single polarization characteristics for various types of optical devices in high performance network systems.