Recently, in collaboration with Professor Jiang Weixiang, academician of Cui Tiejun, Southeast University, and Professor Zhang Shuang, University of Birmingham, UK, Professor Cao's team of Dalian University of technology proposed an innovative method of enhancing hand optical signal based on the super surface of the fabry-p é rot cavity (FP cavity). Theoretical and experimental results show that the circularly polarized FP resonator can significantly improve the optical activity of chiral molecules. Relevant achievements were published on research under the title of "chirality enhancement using Fabry – P é rot like cavity" (research, 2020 doi: 10.34133 / 2020 / 7873581).
01
Research background
Chirality, which refers to the asymmetry between an object and its mirror image, plays an important role in the fields of chemistry and biomedicine. Not only do the macromolecules that make up life, such as protein and DNA, have chirality, it also determines the combination of drugs, additives, pesticides or agricultural chemicals. However, because the size of chiral molecules is far smaller than the wavelength of electromagnetic wave, the response of chiral optical signal of natural chiral molecules is very low, so it needs a high concentration to study them qualitatively and quantitatively. Therefore, it is of great significance to enhance the chiral optical signal of molecules.
Local changes in the distribution of electromagnetic fields can enhance the chirality of chiral molecules, but this method depends on the precise positioning of these nanoparticles. The circularly polarized FP cavity is an effective way to detect a single molecule, because the resonant cycle of the beam in the cavity enables the light to sample the molecule many times, which can be widely used to enhance the interaction between light and matter. Compared with local resonance, FP resonator has the advantages of insensitive position and easy operation.
Traditional isotropic mirrors can reverse the polarization state of circularly polarized reflected light, so the FP resonator can not be directly used to enhance the chiral optical signal. Metamaterial is a kind of artificial material, aiming to achieve a large number of new functions and phenomena, which are often impossible to achieve by natural materials. Metamaterials are usually arranged in a periodic pattern, and their proportion is much smaller than the wavelength of interest. Hypersurface is a special form of two-dimensional metamaterials. The latest development in this field shows that hypersurface can realize the free regulation of electromagnetic waves. Especially through the proper design of the super surface structure, the circularly polarized light reflected by it can keep the chirality unchanged.
02
innovation research
In this work, the researchers designed a hypersurface structure as a mirror of a circularly polarized FP resonator, so that the circularly polarized light reflected by the hypersurface can still maintain the polarization state when it is incident. A circularly polarized FP cavity is composed of a pair of orthogonal super surface mirrors, which can reflect circularly the circularly polarized light in the cavity and enhance the chiral optical signal of the chiral molecules in the cavity.
(a) Schematic diagram of chiral metamaterials, (b) schematic diagram of circularly polarized FP cavity formed by placing chiral metamaterials on two hypersurfaces, (c) schematic diagram of unit structure design of chiral molecules and (d) Hypersurfaces
Figure 1 design of super surface structure
In a specific demonstration example, the researchers use a super material composed of two-layer cross line structure to replace the chiral molecule, which has a very weak chiral optical signal response in the microwave frequency band. Each super surface reflector is composed of a metal / dielectric / metal sandwich artificial structure. Two artificial super surfaces, which are used as circularly polarized FP cavity mirrors, are placed vertically on the left and right sides of the dielectric layer of the circuit board. The super surface mirror can make the reflected light keep its polarization state and accumulate the chirality response at the same time. The two copper metal grids can reflect most of the electromagnetic waves propagating in the circularly biased FP resonator, and transmit some of them to the circularly biased FP resonator at the same time.
(a) Schematic diagram of general FP cavity (b) schematic diagram of circular maintaining and eccentric FP cavity
Fig. 2 Schematic diagram of FP cavity
By comparing the transmission coefficients of homopolarization and cross polarization of the chiral metamaterials in free space and circularly polarized FP resonators, it can be found that the new circularly polarized FP resonators greatly improve the optical activity of the chiral metamaterials, so that their chirality is correspondingly increased by an order of magnitude. Experimental results and numerical simulation results verify the feasibility of the technology.
(a) , (b) CST software simulation results
(c) , (d) experimental measurement results
Fig. 3 transmission coefficients of chiral metamaterials and those placed in FP cavity
(a) (b) optical activity of chiral metamaterials and those placed in FP cavity
(c) (d) ellipticity of chiral metamaterials and those placed in FP cavity
Figure 4 optical activity and ellipticity of chiral metamaterials and those placed in FP cavity
It is worth mentioning that this new strategy can be directly extended to other higher frequencies, such as visible light, infrared and terahertz. This research provides a new idea for the detection of low concentration chiral molecules, will effectively promote the development of rapid and accurate recognition and separation technology of biomolecular chirality, and provide a new technical scheme for the rapid detection of viruses and the development of corresponding therapeutic drugs in the future.
03
About the author
Professor Cao Huang is now working in the College of Optoelectronic Engineering and Instrument Science, Dalian University of technology. Professor Cao Huang's team has been committed to the research of micro nano components and their applications for a long time, and has accumulated some experience in the theoretical research, nano processing and technical application of nano components such as super materials and photonic crystals, etc.
Jiang Weixiang, researcher and doctoral director of School of information science and engineering, Southeast University, senior member of China Electronics Society and member of young scientists club, is currently engaged in theoretical, experimental and application research related to new artificial electromagnetic materials in millimeter wave State Key Laboratory of Southeast University, in new electromagnetic control devices, high-performance antennas and radomes, high-resolution imaging, etc It has made important achievements and has been selected as "research highlight" by international academic journals for several times and reported by domestic and foreign scientific and technological media.
Zhang Shuang, Professor, Department of physics and astronomy, University of Birmingham, UK. Research interests include: nanophotonics, metamaterials and surface plasmon, nonlinear optics, etc. Elected member of the American Optical Society in 2016.
04
Previous review
The application of metamaterials is expected to reduce the cost of wireless communication. Cui Tiejun team of Southeast University proposes a simplified digital wireless communication system scheme
Twenty-nine
03-2019
Metamaterials make it possible for "private customization" of high-order harmonics. Zhou Ji team of Tsinghua University first proposed a new mechanism of artificial generation of high-order harmonics
Ten
03-2020
Liang Bin, Nanjing University and Johan & nbsp; Christensen, University of Carlos III, Madrid, Spain
Research is a large-scale OA science and technology journal co founded by China Association for science and technology and American Association for the promotion of Science in 2018, which is characterized by internationalization, high influence, world-class level, comprehensiveness, and is the first cooperative Journal of science since it was founded in 1880. It mainly publishes eight breakthrough research results in eight hot cross fields with great development potential, including life science, new material research, new energy, artificial intelligence, micro nano science, environmental science, mechanical science, robot and advanced manufacturing. At present, 93 editorial boards with international influence and 50% of domestic and foreign members have been established. The chief editor (China) is Huang Wei, executive vice president of Northwestern Polytechnic University and academician of the Chinese Academy of Sciences. The chief editor (International) is Cui Tianhong, an outstanding professor of McCart at the University of Minnesota. It has been included in CAS, CSCD, DOAJ, esci, inspec, PMC and Scopus databases.
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