Design of taper coupler type polarization splitter with single-polarization photonic crystal fiber

Abstract

In recent years, with the rapid development of the information society, the demand for a high-speed large-capacity optical communication system is further increased. Since the multiplexing communication systems are widely used to improve the transmission capacity, studies on the key devices for the multiplexing systems have attracted lot of attentions. Among them, designs of high-performance optical device based on special fibers have been extensively studied. Photonic crystal fibers (PCFs), which consists of single material with periodic array of air holes around the fiber core, have attracted a lot of attention in the last two decades due to their flexible structure and the special properties. Moreover, elliptical-hole core circular-hole holey fiber (EC-CHF), a novel PCF with the core filled with elliptical air holes, has been proposed for achieving the single-polarization transmission easily in recent years [1]. A crosstalk-free polarization splitter (PS) based on single-polarized EC-CHFs has been proposed, and its structural tolerance has also been discussed in detail [2]. However, the investigation result shows that the PS has a low tolerance, especially for the elliptical holes in the core. In this research, in order to improve the structural tolerance of the crosstalk-free PS in Ref. [2], we consider a three-core PS with tapered structure. The following figure illustrates the schematic of our proposed tapered PS structure, referring Ref. [2], when the incident light is launched into the polarization independent waveguide in the middle, with the light propagation, y- and x-polarized components will only couple into the single-polarized waveguides at top and bottom, respectively. All of the air hole sizes in each waveguide varies along the transmission direction with the same scale, and the light wave transmission through these slightly varied waveguides has no propagation loss. In the coupling region, strong mode coupling occurs by satisfying the phase matching condition between two adjacent waveguides. This may leads to a high tolerance for the entire structure.