Tellurite Subwavelength Core Photonic Crystal Fiber And Characteristics Research

The subwavelength core photonic crystal fibers (SCPCF) have a series of unique optical characteristics, which can not be achieved in the conventional photonic crystal fiber (PCF). The SCPCF can be extensively applied on the high nonlinear optic fibers, optical fiber communication, all-optical devices, and so on. Moreover, tellurite glass has a much higher nonlinear refractive index and a wider optical propagation band width than silica glass. By introducing the tellurite glass into SCPCF, we can design the fiber structure with a good flexibility and achieve more unique optical characteristics.In this paper, the structure and optical characteristics of the SCPCF based on the high refractive index tellurite glass core are been investigated theoretically. The main works and innovative fruits are as follows:(1)We design a SCPCF with the tellurite glass core. And by using finite element method(FEM),we get the fundamental mode field characteristics、group velocity dispersion(GVD) and Kerr nonlinearity coefficient. Taking into account the vector natures of electromagnetic field and the frequency dependence of the fundamental mode in the SCPCF, we improve the conventional generalized nonlinear Schrodinger equation (GNLSE) and obtain a new equation to describe the pulse propagation. A kind of new nonlinear, geometrical nonlinearity, emerges. The fiber absorption and the third-order dispersion coefficient are taken into account to accurately show the evolution of short pulse inside the SCPCF.(2) By adjusting the cladding structure and decreasing the core size, we can make the maximum of the geometrical nonlinear coefficient located inside the region of anomalous dispersion and the geometrical nonlinearity can happen to compete with the Raman effect in a specific wavelength range. The suppression of geometrical nonlinearity on the Raman soliton self-frequency shift (RSSFS) is demonstrated based on the new propagation equation. At different pulse power, pulse temporal width, and transmission distance, the suppression degree of RSSFS is different.(3) Based on tellurite ellipse core and V-shape distribution air holes, we design a new SCPCF with high birefringence and nonlinearity coefficient. By adjusting the size of tellurite ellipse core (when long axis radius is0.5μm, and the short axis radius is0.25μm), the birefringence of7.66×10-2and nonlinearity coefficient of3400W-1·km-1at the wavelength of1550nm can be obtained. In addition, by adjusting the size of tellurite ellipse core, the fiber can get two zero dispersion wavelengths and the second zero dispersion wavelength can be achieved at different wavelength region. This SCPCF structure can find extensive applications in the optical communication and sensor system.(4) We design a new dual-cladding SCPCF based on the tellurite core, and analyze the optical properties of SCPCFs. Compared with the big air holes in the outer-cladding, the small air holes in the inner-cladding have a greater impact on the waveguide dispersion and can tailor the dispersion more effectively. In addition, the small air holes have a greater flexibility in the control of dispersion slope and the zero dispersion wavelength (ZDW). By adjusting the diameter and pitch of the inner-cladding air holes, a very low dispersion slope can be obtained. Meanwhile, the ZDW can be moved to the long wavelength range. Moreover, the designed fiber proves a higher nonlinear coefficient than the silica glass by at least one order of magnitude. This SCPCF structure provides a new way to optimize dispersion propertie and get high nonlinear coefficient for extensive applications in four-wave mixing (FWM) and supercontinuum (SC).