基于5 μm厚向列相液晶的高效圆极化相控阵系统的设计、校准和实验验证

This paper presents a systematic investigation and demonstration of a K-band circularly polarized liquidcrystal-based phased array(LCPA),including the design,over-the-air(OTA)in-array calibration,and experimental validation.The LCPA contains 16 phase-shifting radiating channels,each consisting of a circularly polarized stacked patch antenna and a liquid-crystal-based phase shifter(LCPS)based on a loaded differential line structure.Thanks to its slow-wave properties,the LCPS exhibits a maximum phase-shifting range of more than 360°with a figure of merit of 78.3(°)·dB^(-1)based on a liquid crystal layer with a thickness of only 5μm.Furthermore,an automatic OTA calibration based on a state ergodic method is proposed,which enables the extraction of the phase-voltage curve of every individual LCPA channel.The proposed LCPA is manufactured and characterized with a total profile of only 1.76 mm,experimentally demonstrating a scanned circularly polarized beam from-40°to+40°with a measured peak gain of 12.5 dBic and a scanning loss of less than 2.5 dB.The bandwidth of the LCPA,which satisfies the require-ments of port reflection(|S_(11)|)<-15 dB,an axial ratio(AR)<3 dB,beam squinting<3°,and a gain variation<2.2 dB,spans from 25.5 to 26.0 GHz.The total efficiency is about 34%,which represents a new state of the art.The use of the demonstrated low-profile LCPA to support circularly polarized scanning beams,along with the systematic design and calibration methodology,holds potential promise for a variety of millimeter-wave applications.

THE THEORY OF LIQUID-CRYSTAL BIOMEMBRANES

In 1992 the Overseas Chinese Physicists, Association (OCPA) established an Outstanding Young Researcher Award to promote research in physics.The Award is to recognize outstanding work done by young overseas Chinese physicists in Europe and America.The candidates are nominees from research institutions in both continents.In 1993 OCPA set up another award,the OCPA Achievement in Asia Award. to encourage research achievements that are being done by

Dynamic shaping of vectorial optical fields based on two-dimensional blazed holographic grating

We propose a vectorial optical field generation system based on two-dimensional blazed grating to high-efficiently generate structured optical fields with prescribed amplitude,phase,and polarization.In this system,an optimized blazed grating hologram is written on a spatial light modulator(SLM)and can diffract the majority of the incident light into the first-order diffractions of the x and y directions,which then serve as base vectors for synthesizing desired vector beams.Compared with the conventional cosine grating used in the previous work,the proposed two-dimensional,blazed grating has a much higher efficiency.Both computer simulation and optical experiment validate that a conversion efficiency up to 5 times that of the former work is achieved.Our method can facilitate applications of the optical field manipulation.

UV-Vis-NIR Light-deformable Shape-memory Polyurethane Doped with Liquid-crystal Mixture and GO towards Biomimetic Applications

Nature has been inspiring material researchers to fabricate biomimetic functional devices for various applications, and shape-memory polymer materials(SMPMs) have received tremendous attention since the promising intelligent materials possess more advantages over others for the fabrication of biomimetic functional devices. As is well-known, SMPMs can be stimulated by heat, electricity, magnetism, pH, solvent and light. From the viewpoint of practical applications, ultraviolet(UV)-visible(Vis)-near infrared(NIR) light-responsive SMPMs are undoubtedly more advantageous. However, up to now, UV-Vis-NIR light-deformable SMPMs by combining photothermal and photochemical effects are still rarely reported. Here we designed a UV-Vis-NIR light-deformable SMP composite film via incorporating a liquid crystal(LC) mixture and graphene oxide(GO) into a shape-memory polyurethane matrix. The elongated composite films exhibited interesting photomechanical bending deformations with different light-triggered mechanisms,(1) photochemically induced LC phase transition upon UV exposure,(2) photochemically and photothermally induced LC phase transition upon visible-light irradiation,(3) photothermally triggered LC phase transition and partial stress relaxation upon low-intensity NIR exposure. All the deformed objects could recover to their original shapes by high-intensity NIR irradiation.Moreover, the biomimetic circadian rhythms of acacia leaves and the biomimetic bending/spreading of fingers were successfully achieved, which could blaze a way in the field of biomimetic functional devices due to the excellent light-deformable and shape-memory properties of the SMP composite films.

Liquid-crystal Assembly of Semiflexible-coil/Homopolymer Blends: a Dissipative Particle Dynamics Study

The liquid-crystal assembly of semiflexible-coil diblock copolymers with coil or semiflexible homopolymers is studied by dissipative particle dynamics simulation. Phase diagrams of the blends and orientation ordering parameters among semiflexible blocks are constructed as a function of chain stiffness and homopolymer volume fraction. For semiflexible-coil/coil blends with varying stiffness of semiflexible blocks, we display the rich phase behaviors of the system transited from coil-coil/coil to rod-coil/coil blends. The disorder- lamellae or lamellae-liquid crystalline transition and ＂dry brush＂ phenomenon induced by coil homopolymers are observed. For semiflexible-coil/semiflexible blends, adding semiflexible homopolymers also leads to a disorder-order transition and even a transition between monolayer and bilayer smectic-A phase. The results demonstrate that blending homopolymers into semiflexible copolymers can induce liquid-crystal assembly and even improve the orientation ordering of semiflexible blocks effectively.

Entanglement-free determination of pretilt angles of twisted nematic liquid-crystal cells by phase measurement

Because of low cost, fast response time, and high light transmittance, thin-film-transistor （TFT） driven twisted nematic （TN） liquid-crystal displays （LCDs） have been widely used in calculators, computer screens, and cell phones. The pretilt angle of the TN medium within the TFT-TN panel affects not only its response times and view- ing angles but also the light-leakage positions of fringed- field-induced disclination lines within pixels of theTFT-TN panel.

Synthesis and Characterization of Planar Five-Ring-Fused Dithiophene-dione

A series of new organic semiconductors based on s-indaceno[1,2-b：5,6-b＇]dithiophene-4,9-dione was success fully synthesized and characterized. The electron withdrawing carbonyl group lowers the LUMO energy levels, leading to increased electronegativities, which is beneficial for high photo-stability in air. The n-alkyl substituted compounds, lc and ld, crystallize with the rigid coplanar systems packed into slipped face-to-face n-stacks. Inter- estingly, lc and ld also show liquid crystalline behaviors, which give highly ordered molecular packing over large area.

The engineered eyeball, a tunable imaging system using soft-matter micro-optics

We demonstrate a tunable imaging system based on the functionality of the mammalian eye using soft-matter micro-optical components.Inspired by the structure of the eye,as well as by the means through which nature tunes its optical behavior,we show that the technologies of microsystems engineering and micro-optics may be used to realize a technical imaging system whose biomimetic functionality is entirely distinct from that of conventional optics.The engineered eyeball integrates a deformable elastomeric refractive structure whose shape is mechanically controlled through application of strain using liquid crystal elastomer(LCE)actuators;two forms of tunable iris,one based on optofluidics and the other on LCEs with embedded heaters;a fixed lens arrangement;and a commercial imaging sensor chip.The complete microsystem,optimized to yield optical characteristics close to those of the human eye,represents the first fully functional,soft-matter-based tunable single-aperture eye-like imager.