A novel bend-resistant large-mode-area photonic crystal fiber

A novel bend-resistant large-mode-area silica photonic crystal fiber (PCF) is proposed and fabricated. With the advantage of flexible design on the PCF configuration, the properties of large-mode-area, single mode propagation and low bend loss can be simultaneously achieved by intentionally designing the position of defect and the size of air holes. Modal properties and bending loss of the actual PCF can be evaluated with previous model for assessing the properties of the actual fiber. Numerical results demonstrate that this fiber has an extremely large mode area of 2812 mu m(2), low confine loss of 0.00024 dB/m of the fundamental mode and high confine loss of over 1.248 dB/m of higher order mode at a wavelength of 1064 nm when the optical fibre is kept straight. The large difference in propagation loss levels between fundamental mode and higher order modes ensures the efficient single-mode propagation in the fiber core. Furthermore, the effects of bend radius and bend direction angle on bend loss are investigated when the fiber is bent. Even if bend radius is as small as 5 cm, bend loss of this fiber is still below 10(-3) dB/m. It is found that the proposed fiber has the negligible bending loss at a bending radius of 30 cm with the bending angle ranging from -60 degrees to 60 degrees. These results illustrate that the fabricated fiber possesses the better bend resistant properties and can overcome the sensitivity to bend direction angle caused by the asymmetric structure. The fabricated fiber will play an important role in developing high power fiber laser, fiber amplifier and high power delivery application.