针对单层黑磷表面等离激元器件存在吸光效率低的难题，提出了一种基于石墨烯/黑磷异质结构的各向异性表面等离激元器件，系统研究了其共振光谱及红外传感特性。所设计的石墨烯/黑磷异质结构和非对称类法珀腔结构能够有效提高器件的吸光效率，通过优化器件中谐振腔的厚度将器件在x和y偏振方向上的吸光效率提高至95.54%和97.44%。此外，通过改变入射光的偏振方向动态调控器件的共振波长，实现了对8 nm厚聚环氧乙烷分子v（COC）_s和r（CH₂）_a振动模式的选择性探测，其最高增强倍数分别为88和155。该各向异性表面等离激元器件具有工作波段可调谐、增强倍数高等优点，在痕量物质分析中具有广阔的应用前景。

The polarization of a D-shaped fiber is modulated after immersing it in magnetic fluid (MF) and applying a magnetic field. Theoretical analysis predicts that magneto-optical dichroism of MF plays a key role in light polarization modulation. During light polarization modulation, the evanescent wave polarized parallel to the magnetic field has greater loss than its orthogonal component. Light polarization of a D-shaped fiber with a wide polished surface can be modulated easily. High concentration MF and a large magnetic field all have great ability to modulate light polarization.

We propose and experimentally demonstrate a wideband linear polarization converter in a reflection mode operating from 2.4 to 4.2 THz with conversion efficiency of more than 80%. Our device can expand the applications to a higher frequency band. A numerical simulation is performed for this metamaterial converter, which shows a good agreement with experimental results. Importantly, a concise and intuitive calculating model is proposed for the Fabry–Pérot cavity. The theoretical results indicate that the underlying reason for the enhanced polarization conversion is the additional phase difference induced by the resonance of the meta-structure and multiple reflections within the Fabry–Pérot cavity.

We have investigated the whole polarization-extinction-ratio (PER) spectrum and annealing properties of 45°-tilted fiber gratings (45°-TFGs). Experimental results show the PER spectrum of 45°-TFGs is a Gaussian-like profile and covers a 540 nm bandwidth from 1260 to 1800 nm, in which the bandwidth with PER greater than 10 dB is over 250 nm. The output polarization distribution of 45°-TFGs was analyzed by employing a bulk linear polarizer, and the results show a perfect figure “8”, which indicates that the 45°-TFG is a type of linear polarizer. Moreover, the annealing property of 45°-TFGs was measured up to 700°C, in which the PER of the grating started to decrease at 300°C and reached the minimum at 700°C. Based on these results, the 45°-TFGs can be used as an ultra-wide bandwidth in-fiber polarizing device.

New techniques for controlling the amplitudes of two orthogonal linearly polarized light are presented. One is based on adjusting the DC voltage into a Mach–Zehnder modulator (MZM) to alter the amplitude of the light traveling on the slow axis of a fiber into the modulator with little changes in the fast-axis light amplitude. Another is based on adjusting the input DC voltages of a dual-polarization MZM operating in the reverse direction, which enables independent control of the two input orthogonal linearly polarized light amplitudes. Experimental results demonstrate that more than 30 dB difference in slow- and fast-axis light power can be obtained by controlling an MZM input DC voltage, and over 24 dB independent power adjustment for light traveling on the slow and fast axes into a dual-polarization MZM.

Based on the traditional directional coupler, we proposed a scheme to design on-chip polarization beam splitters using an inverse design method. In our scheme, the coupling area of the designed devices are only 0.48 μm×6.4 μm. By manipulating the refractive index of the coupling region, the devices can work in C-band, L-band, O-band, or any other communication band. Different from conventional design methods, which need to adjust the design parameters artificially, if the initial conditions are determined, the proposed scheme can automatically adjust the design parameters of devices according to specific requirements. The simulation results show that the insertion losses of the designed polarization beam splitters can be less than 0.4 dB (0.35 dB) for TE (TM) mode at the wavelengths of 1310, 1550, and 1600 nm, and the extinction ratios are larger than 19.9 dB for the TE and TM modes at all three wavelengths. Besides, the extinction ratios of both polarization states are more than 14.5 dB within the wavelength range of 1286–1364 nm, 1497–1568 nm, and 1553–1634 nm. At the same time, the insertion losses are smaller than 0.46 dB.

We propose an ultra-broadband and fabrication-tolerant polarization rotator-splitter (PRS) based on a waveguide with an L-shaped cross section and a Y-junction. The proposed PRS is based on the 220 nm silicon-on-insulator platform, and it shows less than 0.27 dB insertion losses and larger than 14 dB polarization extinction ratios over a wavelength range from 1200 to 1700 nm. To the best of our knowledge, the PRS working in the whole optical communication band is proposed for the first time.