Single-polarization dual-hollow-core anti-resonant fiber coupler by polarized mode filtered method

A single-polarization (SP) coupler based on a dual-hollow-core anti-resonant fiber (DHC-ARF) by polarized mode filtered method is proposed. The DHC-ARF is composed of ten cladding tubes with each core surrounded by five cladding tubes. By introducing cladding tubes with two different thicknesses along the two orthogonal directions, one polarized mode can be filtered out due to its high confinement loss caused by the mode coupling with the dielectric mode in the cladding wall, while another polarized mode with a low confinement loss can be maintained. By optimizing the structural parameters of the DHC-ARF, the confinement loss of the high-loss polarized mode is 50.44 dB/cm and that of the low-loss polarized mode is only 0.24 dB/cm at a wavelength of 1550 nm. By using a 1.52 cm long DHC-ARF, the SP coupler can be implemented with an operational bandwidth of 11 nm spanning the wavelength range between 1545 nm and 1556 nm, in which the polarization extinction ratio (PER) is less than -20 dB, the coupling ratio (CR) stabilizes to 50 +/- 0.6 %, and the loss of the coupler is less than 0.44 dB. At the wavelength of 1550 nm, the lowest PER of -91.7 dB is achieved, while the CR and loss are 50 % and 0.37 dB, respectively. Furthermore, empirical formulas are derived for the structural parameters and wavelength, making it possible to predict the structural parameters of a DHC-ARF in the development of SP couplers for the expected wavelength. High-performance hollow-core SP coupler is significantly important to develop highprecision resonant HCF gyroscopes.