Ultra-broadband simple hexagonal dual core photonic crystal fiber mid-infrared polarization beam splitter based on surface plasmon resonance

In this paper, an ultra-broadband simple hexagonal dual core photonic crystal fiber mid-infrared polarization beam splitter (SH-DC-PCF MIR-PBS) based on surface plasmon resonance (SPR) is proposed. Based on the SPR and DC-PCF coupled-mode theories, the polarization splitting performance can be achieved by utilizing the different mode coupling characteristics between the X-polarization (X-P) and Y-polarization (Y-P) odd modes and even modes, and 2nd-order surface plasmon polariton modes. The change rules of coupling lengths of the X-P and Y-P and the coupling length ratio with different structural parameters are summarized. The change rules of the extinction ratio (ERs) of the cores A and B with wavelength when the splitting length (L_S) is between 172–184 μm are discussed. The simulation results indicate that the fianl L_S is 179 μm, the splitting bandwidth of the cores A and B are 864 nm (3.397–4.261 μm) and 727 nm (3.447–4.174 μm), and the maximum insertion losses of the cores A and B are 0.17 and 0.015 dB, respectively. When the Λ changes ± 1 % or t changes ± 3 %, the proposed SH-DC-PCF MIR-PBS has good fabrication error-tolerant rate. The proposed SH-DC-PCF MIR-PBS not only achieves ultra-wide splitting bandwidth of the cores A and B, but also has ultra-low insertion loss, ultra-short L_S, and a easy to fabricate simple structure, so it is expected to have important application value in MIR spectroscopy related fields such as biomedicine imaging, fiber sensing, and environmental monitoring.