Polarization beam splitter is an important part of integrated optical system to overcome the strong polarization dependence of silicon nanodevices, and has broad application prospects in optical fiber communication and polarization imaging. In this paper, a polarization beam splitter of metalens based on the fiber end face is designed. Through the planar light field control ability of metalens and the coordinated regulation of the geometric phase and propagation phase, the device adjusts the medium duty cycle in the meta-unit and the rotation angle of the nanoantenna to realize the polarization beam splitting and focusing simultaneously. In order to simplify the manufacturing process and achieve high focusing efficiency even further, Si with high transmittance in the near infrared band is selected as the nanoantenna, and SiO2 is used as the substrate. Since the substrate used the same material with fiber cladding, compared with the traditional polarization beam splitter, the structure can directly etch the nanofins periodically on the fiber end face, which is convenient for optical system integration. Theoretical design and numerical simulation results show that any polarized light in fiber cladding can realize polarization focusing through fiber end face.
In this paper, a polarization splitting square fiber is designed to make up for some defects of Dtype fiber in common fiber devices. Compared with D-type optical fiber, square-type optical fiber can be directly drawn by processing the optical fiber preform. Thereby eliminating the need to process the micron-level optical fiber, while maintain the original core-cladding structure. Most of the optical field energy is still limited to the core, which can greatly reduce the insertion loss of the devices. Using the finite element method, the half-length core distance (30 to 90 microns), radius of arc (1 to 9 microns), numerical aperture (0.18 to 0.24) and isolation thickness (0.1 to 2 microns) of the square fiber are optimized. Theoretical calculation results show that under the optimal parameters, the mode loss of our designed square fiber under X polarization is 0.0179dB/mm. And under Y polarization, the mode loss is 0.0454dB/mm. In addition, the mode mismatch loss is 7.506%. This value will reduce the mode loss by 100 times compared with D-type fiber and make full use of the advantages of good coupling to the allfiber system.
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