Two Novel Mechanisms for Suppressing Higher-Order Radial Modes in Dual-Ring Core Hollow-Core Fibers for OAM Transmission

Using orbital angular momentum (OAM) modes can effectively enhance the information capacity of communication systems. To achieve high-performance OAM transmission characteristics in optical fiber waveguides, it is essential to minimally excite higher-order radial OAM modes in the optical fiber waveguide. Here, we propose two novel mechanisms to suppress the guidance of second-order radial OAM modes in the newly designed dual-core hollow-core fiber, while ensuring the support of a larger number of OAM modes. A detailed analysis process is also performed. The first method obtains the mode patterns and conducts a mathematical analysis based on the cutoff conditions for vector modes. The designed fiber structure is capable of supporting 10 and 30 OAM modes in the outer and inner rings, respectively, within the frequency band of 0.13–0.16 THz. The second approach leverages the coupling effect between two ring cores to achieve the inhibition of high-order radial OAM modes in the core area. This fiber structure supports the transmission of 42 (in) + 74 (out) OAM modes over the span of 0.25–0.35 THz. At the same time, a comparative analysis is conducted on the waveguide dispersion, effective mode field area, confinement loss, mode purity, effective refractive index, and isolation parameters of the two fiber structures. The two methods proposed in this study for suppressing higher-order radial modes can be applied to OAM multiplexing in fiber waveguides under different conditions, which will further increasing the communication capacity of the communication system, this will and also enhance the stability of OAM mode transmission.