A circular photonic crystal fiber supporting 26 OAM modes

• A new design of a circular photonic crystal fiber (C-PCF), which can support 26 OAM modes, is proposed.
• The new C-PCF needs no doping and has lots of adjustable parameters compared with ring fibers.
• The fiber has low confinement loss, flatten chromatic dispersion and small nonlinear coefficient.
• The influence of some parameters on the properties of the fiber have been discussed.
• Most of higher order modes have a small birefringence when the deformation is not very large.

A new design of a circular photonic crystal fiber, which can support 26 OAM modes, is proposed. The numerical analysis shows that the proposed fiber possesses very good values of the fiber parameters, such as low confinement loss which is lower than 0.003 dB/m at wavelength of 1.55 μm, flat chromatic dispersion whose dispersion variation for the OAM modes with the order number |l|⩽4|l|⩽4 is within 39.84 ps/nm/km over a 750 nm bandwidth from 1.25 to 2 μm, and small nonlinear coefficient which is less than 2.08 W−1/km for all modes at 1.55 μm. In addition, the influence of geometric deformation on the modal birefringence of the proposed fiber has also been discussed. It is proved that the modal birefringence caused by the geometric deformation is different for different vector modes, and most of the higher order modes have a smaller modal birefringence than the lower order modes when the ellipticity is less than 1.08.