Terahertz polarization sensing,chirality enhancement,and specific binding based on metasurface sensors for biochemical detection:a review[Invited]

Specific and highly-sensitive biochemical detection technology is particularly important in global epidemics and has critical applications in life science,medical diagnosis,and pharmaceutics.As a newly developed technology,the THz metamaterialbased sensing method is a promising technique for extremely sensitive biomolecular detection.However,due to the significant resonant peaks generated by THz metamaterials,the characteristic absorption peaks of the analyte are usually masked,making it difficult to distinguish enantiomers and specifically identify target biomolecules.Recently,new ways to overcome this limitation have become possible thanks to the emergence of chiral metasurfaces and the polarization sensing method.Additionally,functionalized metasurfaces modified by antibodies or other nanomaterials are also expected to achieve specific sensing with high sensitivity.In this review,we summarize the main advances in THz metamaterials-based sensing from a historical perspective as well as application in chiral recognition and specific detection.Specifically,we introduce the basic theory and key technology of THz polarization spectrum and chiral sensing for biochemical detection,and immune sensing based on biomolecular interaction is also discussed.We mainly focus on chiral recognition and specific sensing using THz metasurface sensors to cover the most recent advances in the topic,which is expected to break through the limitations of traditional THz absorption spectroscopy and chiral spectroscopy in the visible-infrared band and develop into an irreplaceable method for the characterization of biochemical substances.

Highly sensitive and fast response strain sensor based on evanescently coupled micro/nanofibers

Flexible strain sensors play an important role in electronic skins,wearable medical devices,and advanced robots.Herein,a highly sensitive and fast response optical strain sensor with two evanescently coupled optical micro/nanofibers(MNFs)embedded in a polydimethylsiloxane(PDMS)film is proposed.The strain sensor exhibits a gauge factor as high as 64.5 for strain≤0.5%and a strain resolution of 0.0012%which corresponds to elongation of 120 nm on a 1 cm long device.As a proof-of-concept,highly sensitive fingertip pulse measurement is realized.The properties of fast temporal frequency response up to 30 kHz and a pressure sensitivity of 102 kPa^(−1) enable the sensor for sound detection.Such versatile sensor could be of great use in physiological signal monitoring,voice recognition and micro-displacement detection.

Mechanochemical transformation of fluorescent hydrogel based on dynamic lanthanide-terpyridine coordination

As a burgeoning research field, ultrasound-responsive materials have attracted intense interest in healthcare research. However, the basic mechanism of sonochemical effect in the quasi-solid state is far from being well understood than those in the solution. Herein, we showcase mechanochemical transformations of europium(Ⅲ) complexes in a supramolecular hydrogel matrix. With the combination of labile terpyridine-europium complexes(TPY-Eu^(3+)) as mechanochromic moieties and an ultrasound-responsive fluorogen(URF) as a molecular tweezer, the hydrogel produces a notable fluorescence change in response to ultrasound. The mechanochemical transformation was elucidated by molecular dynamics(MD) simulations, and fully probed and evidenced by electrochemical experiments, X-ray photoelectron spectroscopy(XPS), and attenuated total reflectance-Fourier transform infrared(ATR-FTIR) spectroscopy.

“以膜制膜”:三维聚吡咯纳米管阵列薄膜及其应用

导电聚合物具有良好的导电性和化学稳定性等优异特性,在各种应用领域被广泛研究.三维导电聚合物具有相互连接的网络结构,可提供超高比表面积,是极具潜力的高性能材料结构.尽管纳米制造技术已取得飞速进展,但制备有序导电聚合物超结构,如有序排列的纳米通道,仍极具挑战性.本研究提出了一种简便高效的模板合成法,可制备三维聚吡咯膜结构.以柔性径迹蚀刻聚碳酸酯膜为模板,通过化学聚合法,经去除模板即可获得具有垂直排列通道和连续连接层的三维纳米管阵列薄膜.膜结构中纳米通道长度、直径等微结构尺寸均可精细调控.这种“以膜制膜”的方法具通用性、成本低等特点.进一步,我们证明了该精密膜结构在毒害离子吸附、太阳能光热转换、毒害气体传感等方面应用的可能.该结构对六价铬离子表现出快速、优异的吸附性能;无需额外表面改性和基底结构辅助,可直接应用为界面太阳能光热转换材料;对毒害气体氨气展现出优异的传感响应.该工作不仅为聚比咯精细膜结构的制备提供了一种可行的方法,也极大地拓展了三维导电聚合物材料的应用.

Optical Micro/Nano Fibers Enabled Smart Textiles for Human-Machine Interface

Wearable human-machine interface(HMI)is an advanced technology that has a wide range of applications from robotics to augmented/virtual reality(AR/VR).In this study,an optically driven wearable human-interactive smart textile is proposed by integrating a polydimethylsiloxane(PDMS)patch embedded with optical micro/nanofibers(MNF)array with a piece of textiles.Enabled by the highly sensitive pressure dependent bending loss of MNF,the smart textile shows high sensitivity(65.5 kPa^(−1))and fast response(25 ms)for touch sensing.Benefiting from the warp and weft structure of the textile,the optical smart textile can feel slight finger slip along the MNF.Furthermore,machine learning is utilized to classify the touch manners,achieving a recognition accuracy as high as 98.1%.As a proof-of-concept,a remote-control robotic hand and a smart interactive doll are demonstrated based on the optical smart textile.This optical smart textile represents an ideal HMI for AR/VR and robotics applications.

A three-dimensional measurement method for binocular endoscopes based on deep learning

In the practice of clinical endoscopy,the precise estimation of the lesion size is quite significant for diagnosis.In this paper,we propose a three-dimensional(3D)measurement method for binocular endoscopes based on deep learning,which can overcome the poor robustness of the traditional binocular matching algorithm in texture-less areas.A simulated binocular image dataset is created from the target 3D data obtained by a 3D scanner and the binocular camera is simulated by 3D rendering software to train a disparity estimation model for 3D measurement.The experimental results demonstrate that,compared with the traditional binocular matching algorithm,the proposed method improves the accuracy and disparity map generation speed by 48.9%and 90.5%,respectively.This can provide more accurate and reliable lesion size and improve the efficiency of endoscopic diagnosis.

High-power continuous-wave optical waveguiding in a silica micro/nanofibre

As miniature fibre-optic platforms,micro/nanofibres(MNFs)taper-drawn from silica fibres have been widely studied for applications from optical sensing,nonlinear optics to optomechanics and atom optics.While continuous-wave(CW)optical waveguiding is frequently adopted,so far almost all MNFs are operated in low-power region(e.g.,<0.1 W).Here,we demonstrate high-power low-loss CW optical waveguiding in MNFs around 1550-nm wavelength.We show that a pristine MNF,even with a diameter down to 410 nm,can waveguide an optical power higher than 10 W,which is about 30 times higher than demonstrated previously.Also,we predict an optical damage threshold of 70 W.In highpower CW waveguiding MNFs,we demonstrate high-speed optomechanical driving of microparticles in air,and second harmonic generation efficiency higher than those pumped by short pulses.Our results may pave a way towards high-power MNF optics,for both scientific research and technological applications.

基于稀疏随机矩阵光场调制的高分辨高速多模光纤三维压缩感知成像

多模光纤内窥镜能在如发丝般纤细的探头上容纳数千个模式,在低侵入和高分辨在体成像方面具有广阔的应用前景.传统的点扫描成像方式速度受限,而基于散斑采样的压缩感知方法只能对二维稀疏样品成像.本文提出了一种在多模光纤中生成具有高正交性的分区域稀疏随机压缩感知采样矩阵的方法,在提升8倍采样速度的同时可对复杂样品进行高对比度成像.分区域采样方法的引入赋予了在各目标区域内对成像参数进行灵活调节的能力,既可以保证图像强度的均匀分布,又能提高图像的局部分辨率.结合并行计算,整个重构速度比传统方法提高了约10倍.基于三维稀疏随机采样和体重构算法,首次实现了对分布在100μm×100μm×200μm体积中的荧光颗粒的高保真度压缩感知成像,可以有效去除离焦面噪声的干扰.此方法为多模光纤内窥镜以微创或无创的方式对狭窄空间内动态过程的高速在体三维成像奠定了基础.

Lithium niobate microring with ultra-high Q factor above 10^(8)

We demonstrate integrated lithium niobate(LN) microring resonators with Q factors close to the intrinsic material absorption limit of LN.The microrings are fabricated on pristine LN thin-film wafers thinned from LN bulk via chemo-mechanical etching without ion slicing and ion etching.A record-high Q factor up to 10^(8)at the wavelength of 1550 nm is achieved because of the ultra-smooth interface of the microrings and the absence of ion-induced lattice damage,indicating an ultra-low waveguide propagation loss of ~0.0034 dB/cm.The ultra-high Q microrings will pave the way for integrated quantum light source,frequency comb generation,and nonlinear optical processes.

Electro-optic tuning of a single-frequencyultranarrow linewidth microdisk laser

Single-frequency ultranarrow linewidth on-chip microlasers with a fast wavelength tunability play a game-changing role in a broad spectrum of applications ranging from coherent communication,light detection and ranging,to metrology and sensing.Design and fabrication of such light sources remain a challenge due to the difficulties in making a laser cavity that has an ultrahigh optical quality(Q)factor and supports only a single lasing frequency simultaneously.Here,we demonstrate a unique single-frequency ultranarrow linewidth lasing mechanism on an erbium ion-doped lithium niobate(LN)microdisk through simultaneous excitation of high-Q polygon modes at both pump and laser wavelengths.As the polygon modes are sparse within the optical gain bandwidth compared with the whispering gallery mode counterpart,while their Q factors(above 10 million)are even higher due to the significantly reduced scattering on their propagation paths,single-frequency lasing with a linewidth as narrow as 322 Hz is observed.The measured linewidth is three orders of magnitude narrower than the previous record in on-chip LN microlasers.Finally,enabled by the strong linear electro-optic effect of LN,real-time electro-optical tuning of the microlaser with a high tuning efficiency of∼50 pm∕100 V is demonstrated.

Revealing complex optical phenomena through vectorial metrics

Advances in vectorial polarization-resolved imaging are bringing new capabilities to applications ranging from fundamental physics through to clinical diagnosis.Imaging polarimetry requires determination of the Mueller matrix(MM)at every point,providing a complete description of an object’s vectorial properties.Despite forming a comprehensive representation,the MM does not usually provide easily interpretable information about the object’s internal structure.Certain simpler vectorial metrics are derived from subsets of the MM elements.These metrics permit extraction of signatures that provide direct indicators of hidden optical properties of complex systems,while featuring an intriguing asymmetry about what information can or cannot be inferred via these metrics.We harness such characteristics to reveal the spin Hall effect of light,infer microscopic structure within laser-written photonic waveguides,and conduct rapid pathological diagnosis through analysis of healthy and cancerous tissue.This provides new insight for the broader usage of such asymmetric inferred vectorial information.

多模光纤成像:迅速发展的新领域

Multimode fibers(MMFs)are low-cost,mode-division multiplexing waveguide mediums that can support the propagation of thousands of spatial modes within an ultra-compact footprint(~100μm).Despite these advantages,the spatial degree of freedom in MMFs is often not fully utilized due to mode coupling.

Sub-diffraction dark spot localization microscopy

Single molecular localization microscopy(SMLM)is a useful tool in biological observation with sub-10-nm resolution.However,SMLM is incapable of discerning two molecules within the diffraction-limited region unless with the help of a stochastic on–off switching scheme which yet entails time-consuming processes.Here,we produce a novel kind of focal spot pattern,called sub-diffraction dark spot(SDS),to localize molecules within the sub-diffraction region of interest.In our proposed technique nominated as sub-diffracted dark spot localization microscopy(SDLM),multiple molecules within the diffraction-limited region could be distinguished without the requirement of stochastic fluorescent switches.We have numerically investigated some related impacts of SDLM,such as detection circle diameter,collected photon number,background noise,and SDS size.Simulative localization framework has been implemented on randomly distributed and specifically structured samples.In either two-or three-dimensional case,SDLM is evidenced to have2 nm localization accuracy.