Design of single TM-like mode photonic crystal fiber with an actinomorphic elliptical-hole lattice core

When human society entered the 21st century, the demand of high-speed and large-capacity optical communication systems is constantly increasing and at the same time photonic crystal fabrication techniques have also made great progress. Precisely because of this, optical devices for information and communication systems, which are designed by the concept of photonic crystal, have been studied attractively in the world. One important component of these devices is polarization or mode selective device, and single mode optical fibers [1–3] are advantageous over multi mode optical fibers in this component. Therefore, we design a novel photonic crystal fiber (PCF), which can achieve single TM-like mode transmission in this research. The cross section of the proposed PCF is shown in Fig. 1. It has a 5-rings actinomorphic elliptical-hole lattice core to destroy the isotropy between circumferential and radial directions of core, since the elliptical hole is effective to break the symmetry [3]. Meanwhile, we defect the center of core into a large air hole to make the HE11^x mode guided hardly. So birefringence between TM-like and HE11^x modes can be earned easily. We employ the vectorial finite element method (VFEM) [4] to discuss the properties of the proposed PCF. The H-field profiles of the TM-like mode and HE11^x mode are shown in Fig. 2 at the wavelength of 1.55 µm. We can observe that HE11^x mode is not guided, only TM-like mode can be guided in the proposed PCF. A bandwidth of 150nm (1.50 µm ∼ 1.65 µm), which covers C- and L-band of the optical communication wavelength bands, can be achieved for the single TM-like mode transmission.