Analysis Of Characteristics Of Equivalent Double-cladding Photonic Crystal Fibers Using Effective-index Method

Because of the unique configuration and light guiding principle, advanced guiding properties and huge degree of freedom for design, photonic crystal fibers have became a research topic in optics and photoelectronic fields. Based on the concept of photonic crystal, the characters of photonic crystal are briefly summarized .By introducing the concept of photonic crystal fiber (PCF) , the structure and light guiding principle of photonic band gap PCF (PBG-PCF) and modified total internal reflection PCF (TIR-PCF) are respectively introduced. In addition, the properties and applications in communications, optic devices and optical signal processing of these two kinds of PCF are introduced. It is of great actual significance to study PCF.Using the effective-index method, the refractive index property of cladding material of PCF is investigated based on a scalar approximation. A PCF model with two different sizes of air holes in the fiber cladding is proposed, which is equalized as a double-cladding fiber by expanding effective-index method. The characteristic equations of double-cladding fiber are deduced. By adjusting the structure parameters, the influences of structure parameters on the dispersion and cut-off characteristics are investigated. The calculated results indicate that the dispersion can be normal or abnormal and the zero dispersion wavelength can be shifted flexibly under single mode operation. The potentialities for dispersion shift and dispersion flat are indicated. The results have some consultative value for designing PCF.