Terahertz (THz) lenses have numerous applications in imaging and communication systems. Currently, the common THz lenses are still based on the traditional design of a circular convex lens. In this work, we present a method for the design of a 3D-printed multilevel THz lens, taking advantage of the benefits offered by 3D printing technology, including compact size, lightweight construction, and cost-effectiveness. The approach utilizes an inverse design methodology, employing optimization methods to promise accurate performance. To reduce simulation time, we employ the finite-difference time-domain method in cylindrical coordinates for near-field computation and couple it with the Rayleigh–Sommerfeld diffraction theory to address far-field calculations. This technology holds great potential for various applications in the field of THz imaging, sensing, and communications, offering a novel approach to the design and development of functional devices operating in the THz frequency range.THz lens 3D printing achromatic lens THz communication
Chinese Optics Letters
2023, 21(11): 110006
Chiral metasurfaces integrated with active materials can dynamically control the chirality of electromagnetic waves, making them highly significant in physics, chemistry, and biology. Herein, we theoretically proposed a general and feasible design scheme to develop a chiral metadevice based on a bilayer anisotropic metasurface and a monolayer liquid crystal (LC), which can construct and flexibly manipulate arbitrary terahertz (THz) chirality. When the twist angle between the anisotropic axes of two metasurfaces is not 0°, the spatial mirror symmetry of the chiral metadevice is broken, resulting in a strong THz chiral response. In addition, the introduction of anisotropic LCs not only enhances the chiral response of the metadevice but also induces the flipping modulation and frequency tunability of the chirality. More importantly, by optimizing the , we can flexibly design the arbitrary chiral response and the operating frequency of chirality, thereby promoting the emergence of various chiral manipulation devices. The experimental results show that the maximum circular dichroism can reach at 0.94 THz and flip to 28 dB at 0.69 THz by rotating the LC optical axis from the to axis, with the maximum operating frequency tunable range of . We expect this design strategy can create new possibilities for the advancement of active THz chiral devices and their applications, including chiral spectroscopy, molecular recognition, biosensing, and fingerprint detection.
2023, 11(11): 1880
The powerful wavefront manipulation capability of metasurfaces originates from their subwavelength or deep subwavelength elements with designable optical responses, especially phase responses. However, they usually suffer from performance degradation as the spatial phase gradient is large. To solve this issue, we propose an accurate and efficient nonlocal diffraction engineering mechanism to tailor an arbitrary large-gradient wavefront utilizing superwavelength-scale elements. The fast-varying phase profile is cut into segments according to zones rather than subwavelength discretization. Each phase segment is accurately implemented by precisely tailoring the diffraction pattern of the element, where diffraction angles, efficiencies, and phases are controlled simultaneously. As proof of the concept, high numerical aperture cylindrical metalenses are designed using this method and experimentally validated at the terahertz band. The cylindrical metalens is further extended to a full-space metalens, which enables high-quality subwavelength imaging with resolved details of . The proposed mechanism offers an efficient way to capture the fast-varying wavefront using relatively coarse geometries with new physical insights.
2022, 10(4): 04000896
太赫兹(Terahertz，THz)波具有相干性好、信噪比高、辐射能量低等性质，在传感领域有着广泛应用。此外，THz传感还具有实时、非接触、无标记、非电离等优点，在生化传感特别是生物活性物质的传感中有着重要应用。但THz传感也存在着灵敏度低、水的吸收强、检测信息有限、适用性差等缺陷。介绍在THz时域偏振光谱传感技术方面的系列工作，采用微结构器件作为传感器，使用透射或反射传感方法分别检测了细胞、氨基酸和脱氧核糖核酸(DNA)几种生化样品。实验结果表明：与传统的谐振传感方法相比，偏振传感方法的品质因数和传感灵敏度均有着显著提高；反射式传感有效避免了水对THz的吸收，实现了液体环境下活性生化样品的传感；使用具有手性的微结构器件作为传感器，或利用手性THz波作为激发场，可以增强样品的偏振响应，提高传感灵敏度，实现手性分子的传感。太赫兹传感 偏振 手性 微结构传感器 生化样品 terahertz sensing polarization chirality microstructure sensor biochemical samples
2021, 19(6): 951
糖类是典型的手性物质，其在太赫兹波段的手性光谱尚未得到充分研究。本文研究了乳糖、半乳糖、葡萄糖3种糖类在低温和常温下的折射率和吸收谱，并通过太赫兹时域偏振光谱检测，获得了这些样品的手性光谱。实验结果显示，糖类吸收会随着温度降低而减弱，低温下有利于获得样品的手性特征；在80 K温度下，葡萄糖在1.3~1.5 THz频段表现出很强的圆二色性(CD)，在1.39 THz处CD谱峰值达到44.97%；在1.6~1.8 THz频段内，3种糖类都具有特定的手性特征峰，CD值均超过20%。研究结果对进一步认识手性生化样品在太赫兹波段的手性光谱及其内在机制具有重要参考价值。太赫兹光谱 手性光谱 糖类 温度 terahertz spectroscopy chiral spectra saccharides temperature
2021, 19(5): 819
Compared with traditional optical elements, metasurfaces have shown unique advantages in multifunctionality encoded in different frequencies, polarization states, and orbital angular momentums. However, the study of metasurfaces with well-controlled functions under different incident angles is still in its infancy. Here we propose a general method to tailor the angular dispersion over the simplest binary dielectric grating in the transmission mode. We demonstrate that the angular response is strongly related to the number of waveguide modes inside the grating, so one can intentionally reduce or enhance the angular dispersion by controlling the number of waveguide modes. Independent phase manipulation over incident angles is experimentally demonstrated by a metalens with angle-dependent focus. The angular dispersion in orthogonal polarization states is further utilized to demonstrate angle-insensitive and angle-multiplexed wave plates. These devices with simple configuration and clear physics offer a general platform to expand the scope of beam manipulation over metasurfaces.
2021, 9(11): 11002190
We experimentally investigate the linear polarization conversion for terahertz (THz) waves in liquid crystal (LC) integrated metamaterials, which consist of an LC layer sandwiched by two orthogonally arranged sub-wavelength metal gratings. A Fabry–Perot-like cavity is well constructed by the front and rear gratings, and it shows a strong local resonance mechanism, which greatly enhances the polarization conversion efficiency. Most importantly, the Fabry–Perot-like resonance can be actively tuned by modulating the refractive index of the middle LC layer under the external field. As a result, the integrated metamaterial achieves multi-band tunable linear polarization conversion.terahertz liquid crystals metamaterial polarization conversion
Chinese Optics Letters
2021, 19(9): 093701
由于超材料和超表面的亚波长结构单元的形状和尺寸具有很大的设计自由度,可对电磁波的振幅、相位、波前和方向等进行复杂而精确的调控,同时随着结构参数数量的增加,结构设计的时间往往呈指数增长。提出了一种基于反向传播(BP)神经网络快速优化超表面结构的方法,实现了兼具高衍射效率、宽带宽和高角色散等优势的太赫兹介质超光栅。利用有限次数的严格耦合波分析建立的数据集来训练BP神经网络,可准确预测任意结构参数的超光栅衍射光谱,并通过遍历所有结构参数快速筛选出具有最高衍射效率且宽带宽的超光栅,相比传统的遍历计算方法速度提高了一万倍,证明了基于BP神经网络的超表面优化方法的高效性以及精准性,同时为太赫兹波段提供了一种性能优异的衍射元件。光栅 深度学习 BP神经网络 超光栅 优化 gratings deep learning BP neural network metagrating optimization
2020, 40(23): 2305001
Subtractive imaging is used to suppress the axial sidelobes and improve the axial resolution of 4pi microscopy with a higher-order radially polarized (RP) Laguerre–Gaussian (LG) beam. A solid-shaped point spread function (PSF) and a doughnut-shaped PSF with a dark spot along the optical axis are generated by tightly focusing a higher-order RP-LG beam and a modulated circularly polarized beam, respectively. By subtracting the two images obtained with those two different PSFs, the axial sidelobes of the subtracted PSF are reduced from 37% to about 10% of the main lobe, and the axial resolution is increased from 0.21 to 0.15.110.0180 Microscopy 100.6640 Superresolution 170.0180 Microscopy 180.6900 Three-dimensional microscopy
Chinese Optics Letters
2019, 17(12): 121103