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In this paper, an asymmetric large-mode-area photonic crystal fiber (LMA-PCF) with low bending loss at a smaller bending radius is designed. The finite-element method with a perfectly matched layer boundary is used to analyze the performance of the PCF. To achieve LMA-PCF with low bending loss, the air holes with double lattice constants and different sizes at the core are designed. Numerical results show that this structure can achieve low bending loss and LMA with a smaller bending radius at the wavelength of 1.55 μm. The effective mode area of the fundamental mode is larger than 1000 μm2 when the bending radius is ≥10 cm. The bending loss of the fundamental mode is just 0.0113 dB/m, and the difference between the fundamental and high-order modes of the bending loss is larger than 103 when the bending radius is 10 cm. Simulation results show this novel PCF can achieve LMA and have effective single-mode operation when the bending orientation angle ranges in ±110°. This novel photonic crystal has potential application in high-power fiber lasers.

In this work, a novel design of a high birefringence photonic crystal fiber (HB-PCF) with multimode and low confinement loss is proposed. To achieve high birefringence, the core is designed as an elliptical region, which is enclosed by twelve small holes. Based on this design, replacing the two circular holes at the top and bottom of the core region with two elliptical holes can further improve the birefringence. At the wavelength of 1.55 μm, the birefringence of the fundamental mode (LP01) and the second-order mode (LP11) are 1.70×10−2 and 1.85×10−2, respectively. Meanwhile, the confinement losses maintain on orders of 1×10−5 dB/km (LP01) and 1×10−1 dB/km (LP11). After the effective refractive indices of two types of the proposed HB-PCF are calculated by the finite element method, the birefringence, confinement loss, bending loss, dispersion, and nonlinear coefficient are studied. These results reveal that the HB-PCF might be applied for polarization-maintaining and nonlinear optics.