30-01-2016, 12:04 PM
Abstract
A photonic crystal fiber (PCF) with circular air holes in the fiber cladding and elliptical air holes in the fiber core is proposed. According to calculation, both ultrahigh birefringence (larger than 0.01) and ultralow confinement loss (less than 0.001 dB/km) can be achieved simultaneously over a large wavelength range for a PCF with only four rings of circular air holes in the fiber cladding. The confinement loss in this PCF can be effectively reduced while the birefringence almost remains the same. The proposed design of the PCF is a solution to the tradeoff between the birefringence and the confinement loss for the originally reported highly birefringent elliptical-hole PCF. Moreover, an approach to modify the effective index of fiber core is also suggested in this letter.
INTRODUCTION
P HOTONIC crystal fibers (PCFs) have attracted increasing interest over the past decade because of their ability to provide extra degrees of freedom in manipulating the optical properties of light [1]–[3]. Based on the design flexibility and the large index contrast, high birefringence can be easily realized in PCFs. So far, several designs of highly birefringent PCFs have been reported [3]–[6], among which, high birefringence exceeding has been demonstrated [3]. Simulation has also indicated that the birefringence of the PCF can be further improved by employing elliptical air holes in the fiber cladding [6]. For the PCFs of this category, high birefringence is achieved when the bulk of the mode energy is in the fiber cladding; thus, the high birefringence is often accompanied with poor energy confinement. In this letter, an ultrahigh birefringent PCF with ultralow confinement loss is proposed by employing elliptical air holes in the fiber core (to induce the birefringence) but circular air holes in the fiber cladding (to reduce the confinement loss). We will show that such a design is able to offer a perfect solution to the tradeoff between the high birefringence and the confinement loss in elliptical-hole PCFs.