A vectorial finite element method(VFEM) is adopted to investigate the novel single-polarization single-mode(SPSM) photonic crystal fiber(PCF) coupler which has asymmetric dual-core and two lines of enlarged air holes.It is demonstrated that the SPSM region of the designed fiber can be more than 250 nm wide with a set of optimized air-hole parameters and the width of the SPSM region could change slightly by fine adjustment of the inner large air holes.The coupling length between the odd and even x-polarization modes is also investigated through fine-tuning the large and small air-hole diameters.
We propose a new structure of broadband nearly-zero flattened dispersion highly nonlinear photonic crystal fiber （PCF）. Through optimizing the diameters of the first two inner rings of air-holes and the GeO2 doping concentration of the core, the nonlinear coefficient is up to 47 W^-1.km^-1 at the wavelength of 1.55 um and nearly-zero flattened dispersion of ±0.5 ps/（nm·km） is achieved in the telecommunication window （1460 - 1625 nm）. Due to the use of GeO2-doped core, this innovative structure can offer not only a large nonlinear coefficient and broadband nearly-zero flattened dispersion but also low leakage losses.
The switchable dual-wavelength erbium-doped fiber laser(EDFL) with a two-mode photonic crystal fiber(PCF) loop mirror and a chirped fiber Bragg grating(CFBG) at room temperature is proposed and experimentally demonstrated.The two-mode PCF loop mirror is formed by inserting a piece of two-mode PCF into a Sagnac loop mirror,with the air-holes of the PCF intentionally collapsing at the splices.By adjusting the state of the polarization controller(PC) appropriately,the laser can be switched between the stable single-and dual-wavelength operations by means of the polarization hole burning(PHB) and spectral hole burning(SHB) effects.
