A tunable high-efficiency optical switch based on graphene coupled photonic crystals structure



A plasmonic device for high-efficiency optical switch is proposed based on graphene coupled photonic crystals structure. The finite-difference time-domain simulation results show that the transmission and reflection ratio can be controlled by tuning the parameters of the graphene strip, such as chemical potential or width. And the corresponding contrast ratio can be 25 and 26.8 for a single and double graphene strips coupled photonic crystals structure, respectively. The results in this paper will have potential application in nanosensors and integrated photonic circuits.


Related paper: Fang Chen, BA tunable high-efficiency optical switch based on
graphene coupled photonic crystals structure, Journal of Modern Optics,Pages 1-7, (2017).


Band structure engineered layered metals for low-loss plasmonics




Plasmonics currently faces the problem of seemingly inevitable optical losses occurring in the metallic components that challenges the implementation of essentially any application. In this work, they show that Ohmic losses are reduced in certain layered metals, such as the transition metal dichalcogenide TaS2, due to an extraordinarily small density of states for scattering in the near-IR originating from their special electronic band structure. On the basis of this observation, they propose a new class of band structure engineered van der Waals layered metals composed of hexagonal transition metal chalcogenide-halide layers with greatly suppressed intrinsic losses. Using first-principles calculations, they show that the suppression of optical losses lead to improved performance for thin-film waveguiding and transformation optics.

Sources: https://www.nature.com/articles/ncomms15133
Related paper: Morten N. Gjerding et al., Band structure engineered layered metals for low-loss plasmonics, Nature Communications 8, Article number: 15133 (2017).

Congratulations on the acceptance of the paper “Optical detection of brain activity using plasmonic ellipsometry technique”





The paper entitled “Optical detection of brain activity using plasmonic ellipsometry technique” is written by Foozieh Sohrabi under the direct supervision of  Dr Seyedeh Mehri Hamidi and it is accepted in the journal of Sensors and Actuators B: Chemical. In this paper, a new method of optical detection of brain activity has been proposed.


The journal link will be available in near future.


Controllable design of super-oscillatory lenses with multiple sub-diffraction-limit foci


41598_2017_1492_Fig1_HTMLThe conventional multifocal optical elements cannot precisely control the focal number, spot size, as well as the energy distribution in between. Here, the binary amplitude-type super-oscillatory lens (SOL) is utilized, and a robust and universal optimization method based on the vectorial angular spectrum (VAS) theory and the genetic algorithm (GA) is proposed, aiming to achieve the required focusing performance with arbitrary number of foci in preset energy distribution. Several typical designs of multifocal SOLs are demonstrated. Verified by the finite-difference time-domain (FDTD) numerical simulation, the designed multifocal SOLs agree well with the specific requirements. Moreover, the full-width at half-maximum (FWHM) of the achieved focal spots is close to λ/3 for all the cases (λ being the operating wavelength), which successfully breaks the diffraction limit. In addition, the designed SOLs are partially insensitive to the incident polarization state, functioning very well for both the linear polarization and circular polarization. The optimization method presented provides a useful design strategy for realizing a multiple sub-diffraction-limit foci field of SOLs. This research can find its potentials in such fields as parallel particle trapping and high-resolution microscopy imaging.

Source: https://www.nature.com/articles/s41598-017-01492-y

Related paper:  Muyuan et al., Controllable design of super-oscillatory lenses with multiple sub-diffraction-limit foci, Scientific Reports 7, Article number: 1335 (2017).

Dynamic plasmonic colour display



Plasmonic colour printing based on engineered metasurfaces has revolutionized colour display science due to its unprecedented subwavelength resolution and high-density optical data storage. However, advanced plasmonic displays with novel functionalities including dynamic multicolour printing, animations, and highly secure encryption have remained in their infancy. Here they demonstrate a dynamic plasmonic colour display technique that enables all the aforementioned functionalities using catalytic magnesium metasurfaces. Controlled hydrogenation and dehydrogenation of the constituent magnesium nanoparticles, which serve as dynamic pixels, allow for plasmonic colour printing, tuning, erasing and restoration of colour. Different dynamic pixels feature distinct colour transformation kinetics, enabling plasmonic animations. Through smart material processing, information encoded on selected pixels, which are indiscernible to both optical and scanning electron microscopies, can only be read out using hydrogen as a decoding key, suggesting a new generation of information encryption and anti-counterfeiting applications.

Source: https://www.nature.com/articles/ncomms14606

Related paper:  Xiaoyang Duan et al., Dynamic plasmonic colour display, Nature Communications 8, Article number: 14606 (2017).


Fano resonance with high local field enhancement under azimuthally polarized excitation



Being an enabling technology for applications such as ultrasensitive biosensing and surface enhanced spectroscopy, enormous research interests have been focused on further boosting the local field enhancement at Fano resonance. Here, they demonstrate a plasmonic Fano resonance resulting from the interference between a narrow magnetic dipole mode and a broad electric dipole mode in a split-ring resonator (SRR) coupled to a nanoarc structure. Strikingly, when subjected to an azimuthally polarized beam (APB) excitation, the intensity enhancement becomes more than 60 times larger than that for a linearly polarized beam (LPB). We attribute this intensity enhancement to the improved conversion efficiency between the excitation and magnetic dipole mode along with improved near-field coupling. The APB excited Fano structure is further used as a nanoruler and beam misalignment sensor, due to the high sensitivity of intensity enhancement and scattering spectra to structure irregularities and excitation beam misalignment. Interestingly, they find that, regardless of the presence of structural translations, the proposed structure still maintains over 60 times better intensity enhancement under APB excitation compared to LPB excitation. Moreover, even if the APB excitation is somewhat misaligned, their Fano structure still manages to give a larger intensity enhancement than its counterpart excited by LPB.

Source: https://www.nature.com/articles/s41598-017-00785-6

Related paper:  Wuyun Shang et al.,Fano resonance with high local field enhancement under azimuthally polarized excitation, Scientific Reports 7, Article number: 1049 (2017).


Clathrate colloidal crystals



DNA-programmable assembly has been used to deliberately synthesize hundreds of
different colloidal crystals spanning dozens of symmetries, but the complexity of the
achieved structures has so far been limited to small unit cells.They assembled DNA-modified triangular bipyramids (~250-nanometer long edge, 177-nanometer short edge) into clathrate architectures. Electron microscopy images revealed that at least three
different structures form as large single-domain architectures or as multidomain
materials. Ordered assemblies, isostructural to clathrates, were identified with the help
of molecular simulations and geometric analysis. These structures are the most
sophisticated architectures made via programmable assembly, and their formation
can be understood based on the shape of the nanoparticle building blocks and mode of
DNA functionalization.

Source: http://science.sciencemag.org/content/355/6328/931

Related paper: Haixin Lin et al.,Clathrate colloidal crystals,Science 355, 931–935 (2017).

Ultrasensitive detection of HIV-1 p24 antigen by a hybrid nanomechanical-optoplasmonic platform with potential for detecting HIV-1 at first week after infection




Early detection of HIV infection is the best way to prevent spread of the disease and to improve the efficiency of the antiretroviral therapy. Nucleic acid amplification tests (NAAT) have become the gold-standard for detecting low-concentrations of the virus in blood. However, these methods are technically demanding and cost-prohibitive in developing countries. Immunoassays are more affordable and can be more easily adapted for point-of-care diagnosis. However, the sensitivity so far of these methods has been too low. They here report the development of a sandwich immunoassay that combines nanomechanical and optoplasmonic transduction methods for detecting the HIV-1 capsid antigen p24 in human serum. The immunoreactions take place on the surface of a compliant microcantilever where gold nanoparticles are used as both mechanical and plasmonic labels. The microcantilever acts as both a mechanical resonator and an optical cavity for the transduction of the mechanical and plasmonic signals. The limit of detection of the immunoassay is 10−17 g/mL that is equivalent to one virion in 10 mL of plasma. This is 5 orders of magnitude better than last generation of approved immunoassays and 2 orders of magnitude better than NAAT. This technology meets the demands to be produced en masse at low cost and the capability for miniaturization to be used at the point-of-care.


Source: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0171899

Related paper: Priscila M. Kosaka et al.,Ultrasensitive detection of HIV-1 p24 antigen by a hybrid nanomechanical-optoplasmonic platform with potential for detecting HIV-1 at first week after infection,  PLoS ONE 12(2): e0171899. doi:10.1371/journal.pone.0171899 (2017)

Coherent Terahertz Radiation from Multiple Electron Beams Excitation within a Plasmonic Crystal-like structure



Coherent terahertz radiation from multiple electron beams excitation within a plasmonic crystal-like structure (a three-dimensional holes array) which is composed of multiple stacked layers with 3 × 3 subwavelength holes array has been proposed in this paper. It has been found that in the structure the electromagnetic fields in each hole can be coupled with one another to construct a composite mode with strong field intensity. Therefore, the multiple electron beams injection can excite and efficiently interact with such mode. Meanwhile, the coupling among the electron beams is taken place during the interaction so that a very strong coherent terahertz radiation with high electron conversion efficiency can be generated. Furthermore, due to the coupling, the starting current density of this mechanism is much lower than that of traditional electron beam-driven terahertz sources. This multi-beam radiation system may provide a favorable way to combine photonics structure with electronics excitation to generate middle, high power terahertz radiation.

Source: http://www.nature.com/articles/srep41116

Related paper:  Yaxin Zhang et al.,Coherent Terahertz Radiation from Multiple Electron Beams Excitation within a Plasmonic Crystal-like structure, Scientific Reports 7, Article number: 41116 (2017).