Multifunctional dual-core liquid crystal photonic crystal fiber

We designed and numerically analyzed a multifunctional dual-core photonic crystal fiber (DC-PCF). The right core, in the proposed structure, is fully infiltrated with a nematic liquid crystal (NLC), whereas the left core has a hole filled with NLC and surrounded by a layer of BK7 glass. The suggested design can control the coupling between the two cores via the NLC temperature. At a temperature of 25°C and a wavelength of 1.3 μm, the refractive index of the BK7 and the ordinary index (no) of the NLC are approximately equal; therefore, the two cores are identical with a strong coupling among them. However, away from 25°C, the two cores are asymmetric, and the coupling is weak at wavelength λ=1.3 μm. Moreover, the reported DC-PCF can work as a switchable polarization splitter between the transverse electric (TE) and transverse magnetic (TM) modes by varying the NLC rotation angle (φ) between 0 and 90 deg. It is noteworthy that at temperatures different from 25°C, strong coupling between the two cores can occur at other wavelengths rather than 1.3 μm, which ensures the thermal tunability of the suggested splitter. The analysis of the splitter’s characteristics is performed using the full vectorial finite difference method showing a crosstalk better than −20 dB in both TE (at φ=90 deg) and TM (at φ=0 deg) polarizations with bandwidths of 22 and 35 nm, respectively, and an average device length of 1529 μm.