Design and Analysis of Ultra-Wideband Highly-Birefringent Bragg Layered Photonic Bandgap Fiber With Concave-Index Cladding

A ultra-wideband highly-birefringent Bragg layered photonic bandgap fiber (BL-PBGF) with concave-index cladding is proposed and demonstrated, by incorporating PBG effect with Bragg multilayers for the first time to the best of our knowledge. The proposed BL-PBGF contains honeycomb capillary cladding and elliptical core with horizontal asymmetry for birefringence. By innovatively introducing three modified silica capillary layers with different refractive indices, the cladding with concave-convex refractive index distribution is combined, providing superior characteristics for optical polarization implementation, such as confinement loss, bending loss and birefringence. Results show that the confinement loss stays around 2 dB/km level within ultrawide 180 nm wavelength range, basically 3 times wider than conventional PBGF. The birefringence maintains at the order of 10
⁻³
across the entire bandwidth and the maximum value reaches 2.5 × 10
⁻³
. The bending loss at 1550 nm is significantly reduced to below one third of the conventional uniform index PBGF when the bending radius is less than 3.5 mm, and maintains below 1 dB/km level when the bending radius is beyond 10 mm. The proposed universal BL-PBGF has great potential in minimized freestanding fiber coil and small footprint fiber optical gyroscope applications.