Investigated Result of Flattened dispersion on silica based PCF of Hexagonal lattice
Abstract
During this work, I focused on understanding and analyzing the model behaviour of micro-structured fiber. Micro-structured fibers with a complex dielectric topology offer a number of novel possibilities, compared to standard optical fiber. This paper presents a new design of photonic crystal fiber with flattened dispersion using elliptical hybrid cladding PCF with different dimension of air holes. The simulation result can be achieved using finite difference time domain (FDTD) numerical approach. In this paper, I investigate the method of chromatic dispersion of 4 proposed PCFs, among which design-3 provides the flattened and nearby zero dispersion at 1.55 µm wavelength. The basic difference among the 4 designs is based on the diameter of air holes. In all design pitch and number of rings are same to achieve the desired PCF structure.
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Introduction
During the last decade the scientific and technological interest of fiber optics research area has been focused on a special type of optical fiber, which is microstructured optical fiber or photonic crystal fiber (PCF)[1], with very interesting guiding properties. Photonic crystal fibers (PCFs) plays a vital role in optical communication system because of their various properties including endlessly single-mode[4], high nonlinearity , broadband negative chromatic dispersion and high birefringence [10] , which clearly surpass those of conventional optical fiber[3].
In conventional optical fiber When light is directed into an optical fiber the effectiveness of the wire depends on its ability to transmit the light ray in long distance applications, with little scattering or little absorption of the light as possible. These scattering or absorption losses can be reduced when the light ray must exhibit total internal reflection within the wire. Thus when considering the propagation of light for an optical fiber, one must know the refractive index of the dielectric medium. The typical fibers today are made out of glass or plastic since it is possible to make them thin and long. The fiber is constructed with a core of a high index surrounded by a layer of cladding of lower index.
Many PCF designs have been proposed to achieve ultra-flattened chromatic dispersion. Such as hexagonal PCFs (H-PCF), square PCFs(S-PCF), circular PCFs(C-PCF), triangular PCFs. H-PCFs are the most conventional type of PCF structures and are the most widely used [2]. Controllability of chromatic dispersion in PCFs is very important for realistic applications. In particular, ultra flattened dispersion PCFs are indispensable for optical data transmission systems over a broadband wavelength range because of the reduction of the accumulated dispersion difference in telecommunication bands without any zero-dispersion wavelength. Conversely, research is still going on to make it more enhanced by limiting dispersion and all other losses. The finite difference time domain method [4] and the TBC boundary condition is used for the simulation boundaries [2]. Internal structure and basic view of PCF structure is shown in fig 1 and fig 2.
PCF has number of properties which makes it very useful in optical communication system. The very important feature is to achieve zero dispersion and flattened dispersion over a wide wavelength range. This zero dispersion is achieved by varying the design parameters of PCF structure. These design parameters of PCF are hole pitch (˄), hole diameter, number of rings, radius of major and minor axis of elliptical air holes. By varying these design parameters, and carefully designing the hybrid cladding micro structured PCF, the desired PCF features (i.e. low dispersion) can be achieved.
Conclusion
In this paper I investigated the four different designs of PCF by altering the dimensions of air holes. It is observed dispersion is affected by changing the dimensions of inner rings, not by changing the dimensions of outer rings. I observed that Flattened dispersion in design-3 is achieved at the wavelength range of 1µm to 2µm. Design 3 provides the very low dispersion which is equal to -1.17 ps/(nm-km) at 1.5μm, 1.75 ps/(nm-km) at 1.6μm and is zero in 1.55μm wavelength when the pitch is 2.0 μm of the circular and elliptical air holes. With this flat dispersion characteristics design-3 can be used in optical wideband transmission system, and can resolve the issue of inter symbol interference (ISI) at the receiver side.