Characteristics of supercontinuum generation in birefringent optical fibers

Introduction Supercontinuum (SC) has attracted considerable attentions due to its versatility in many fields such as telecommunication [1], optical metrology [2] and medical science. The SC phenomenon originates from the third-order nonlinearity of the media. In nonlinear optical fibers, both chromatic dispersion and nonlinear effects determine the SC generation characteristics. Different dispersion characteristics will results in different SC spectra. Therefore SC generation in various fibers, such as the dispersion decreasing fiber (DDF), dispersion flattened fiber (DFF), high nonlinear DSF and photonic crystal fiber (PCF), has been investigated and demonstrated. Recently PCF has attracted our attention. As the dispersion and nonlinear properties of the PCF can be controlled by altering the size and arrangement of the air holes, unusual dispersion properties and the enlarged effective nonlinearities can be achieved in PCF. This makes photonic crystal fibers a promising tool for effective SC generation. Recently fully dispersion controlled PCF has been reported [3]. However nonlinear PCFs exhibit significant birefringence at only moderate asymmetries in the core region due to the small core and high index contrast, and the birefringent can be as high as 10. The advantage of the birefringent fiber is in the preservation of the state of polarization. The preserved polarization enhances the nonlinear interaction that is crucial in nonlinear applications. Further more, the interaction of the two orthogonal polarizations in the fiber allows for controlling and tuning the properties of the SC. Recently SC generation in birefringent fiber has been demonstrated and the polarization dependency of SC generation in birefringent fiber has been investigated experimentally [4][5]. In this paper, we investigated SC generation in birefringent fiber theoretically using a modified nonlinear-coupled Schrodinger equation. Based on the numerical model, the polarization dependent characteristics are investigated. Some results are presented and discussed.