环形光子晶体光纤中涡旋光的传输特性研究

Propagation properties of vortex beams in a ring photonic crystal fiber

由于涡旋光具有轨道角动量,将它应用于光纤通信领域可以有效提高信息传输速率.设计了一种环形光子晶体光纤,利用COMSOL Multiphysics软件对其涡旋光TE01,HE±21和TM01模式特性进行模拟计算,它们之间有效折射率差分别为4.59×10^(-4)和3.62×10^(-4);其中,TE01模式的涡旋光在入射光波长范围为1650—1950 nm时,色散值在44.18—45.83 ps·nm^(-1)·km^(-1)之间平坦;入射光波长在1550 nm时,TE01模式的涡旋光的非线性系数为1.37 W^(-1)·km^(-1).该结构的光子晶体光纤的涡旋光具有损耗小、色散平坦等特性,对光纤中传输涡旋光、将涡旋光应用于超连续谱等方面的研究具有重要意义.

In the last decade, the vortex beams have received lots of attention for their orbital angular momentum.When they are applied to optical fiber communication field,the data channels will increase and information propagation speed will be effectively improved. Recently, researchers have shown the capabilities of long length stably propagation, nonlinear frequency conversion and mode division multiplexing of vortex modes in a ring fiber. Due to the photonic crystal fiber（PCF） having very flexible design degrees of freedom, it will enable a wide range of propagation properties. In this paper, a Si O_2air-hole ring PCF is proposed for separation and propagation of optical vortex modes.By using COMSOL Multiphysics software,the vortex modes（TE01, HE±21and TM01） are simulated and calculated. The differences in effective refractive index between them are 4.59 × 10（-4）and 3.62 × 10（-4）respectively. One can analyze the propagation properties of vortex beams in the ring PCF by changing the size of first layer air hole radius and air hole pitch. When the incident light wavelength of TE01 mode ranges from 1650 nm to 1950 nm, this ring PCF can achieve a total dispersion variation between 44.18 to 45.83 ps·nm（-1）·km（-1）, which is tend to be flat. When incident light wavelength is 1550 nm, the nonlinear coefficient of TE01 mode vortex light is 1.37 W（-1）·km（-1）. Due to the fact that long wavelength light is easier to leakage through the cladding than the short wavelength light, the confinement loss increases with the wavelength. When incident light wavelength is 2000 nm, there is still an eight-orders-of-magnitude of the low confinement loss. Theoretically, flat dispersion and low loss vortex beams in this fiber can be beneficial to propagating stably, and the vortex modes lay the foundation for long distance propagation in the optical fiber. In the future, this ring PCF will be used in optical fiber communication field and applications in aspects such as continuous spectrum research, which can make it have immense advantage over traditional fibers.