Polarization Of Incident Light Research Articles

Switching electromagnetically induced transparency in all-dielectric Si metamaterials with orthogonal double bright modes

Active control of electromagnetically induced transparency (EIT) in metamaterials promises tremendous potential applications. However, previously reported strategies most require sensitive materials as well as additional experimental apparatus, which are inconvenient for on-chip operation and restrain their implementations in fully integrated design. We propose a low-loss all-dielectric metamaterial with orthogonal double bright modes, which shows a narrowband transparency window at 950.05 nm with a high Q-factor of 2111. Just by varying the incident light polarization angle, an on-to-off in-situ EIT modulation without changing Q-factor is perfectly achieved, and the modulation depth can be up to 99.7%. Additionally, optical control of group delay with up to 36.22 ps is also demonstrated. This work provides a simple route to design chip-scale devices with optically dynamic controllability and finds fascinating applications in low-loss active slow light devices, optical switch and sensitive bio-sensing.

Linear optical properties of a linear chain of interacting gold nanoparticles

In a Drude-like model for the conduction electrons of metal nanoparticles (MNPs) in a periodic linear chain, considering dipole-dipole interactions of adjacent particles, an analytical expression is derived for each particle permittivity for two different polarizations of incident light: parallel with and perpendicular to the chain line. A numerical analysis is carried out for a chain including 10 identical gold nanoparticles (NPs) for two different sizes of NPs and two different host media: air and glass. It is shown that in the parallel case of polarization, interaction of NPs leads to a substantial increase in the extinction cross section and the redshift of the surface plasmon resonance (SPR) wavelength. In comparison with the linear properties of a single NP, the second and penultimate particles have the most increase in the extinction cross section and SPR wavelength displacement while the first and last particles experience the least variations due to the mutual interactions. For the perpendicular polarization, inversely, the dipolar coupling causes a decrease in extinction cross section of all particles and the blue-shift of SPR wavelength. For the parallel polarization, the absolute values of the real and imaginary parts of complex permittivity of each MNP decrease in comparison with the single particle case while they increase for the perpendicular state of polarization.

Impact of Fabrication and Operation Errors on Super-Focusing Performance of a Nanoslit-Based Metalens

Metasurfaces with optical manipulation at subwavelength resolution show promises for developing ultrathin and flat optical components, attracting great interest from the optical scientific community. In our recent work, a metalens has demonstrated a special capability of quasi-far-field super-resolution focusing, which comprised a metallic nanoslit array with the incidence of a transverse-electric (TE) polarized light. In this paper, in order to guide practical fabrication and operation of a device, we perform a study on the metalens to analyze the impact of many imperfections on the super-resolution focusing capability. We take fabrication and operation errors into account, including errors in nanoslit width, metal film thickness, operating wavelength, polarization and incident angle of incident light. Numerical results illustrate that the sensitivity of the metalens focusing performance to each error is different. To be specific, the focusing performance of the metalens is considerably susceptible to the error in the incidence angle. Therefore, we not only need to fabricate the metalens device precisely, but also need to ensure that the working conditions agree well with the design, so as to achieve the desired focusing performance. Our research offers a valuable guide for the realization of the super-resolution focusing technology in practice.

Anisotropic Two-Photon Absorption and Second Harmonic Generation in Single Crystals of Silver(I) Coordination Complexes.

Metal complexes have been gaining attention in recent times over the traditional inorganic materials such as nonlinear optical materials. Here, we report both two-photon absorption (2PA) and second harmonic generation (SHG) from single crystals of two Ag(I) complexes with considerable optical anisotropy. We demonstrate that by controlling the incident light polarization, the tunability between these two nonlinear optical processes can be achieved. The deff values of the observed SHG from one complex are determined to be one order of magnitude greater than β-BBO crystals.

Spatial shifts of the reflective light beam off the metasurface of hyperbolic crystals

We investigated Goos–Hänchen (GH) and Imbert–Fedorov (IF) shifts of the reflective beam from a uniaxial hyperbolic crystal (HC) with a metasurface (MS) that is a subwavelength rectangular-grating layer. Due to the optical axis of this MS normal to that of the HC, this structure is similar to a biaxial HC for the reflective beam. We obtained analytical expressions of reflective beam for any polarized incident light beam and then derived the GH and IF shifts of the relevant reflective beam. Based on the hexagonal boron nitride crystal (hBN), we numerically simulated shift spectra of the reflective beam for differently polarized incident beams. We compared the results obtained from this structure with those for the bulk hBN or MS layer with infinite thickness. We found that the shift spectra from this structure resemble neither those from the bulk hBN nor those from the MS layer so that they are much more complicated than those in the two extreme cases. The effect of the MS coupling with the hBN substrate is very remarkable. First, both the GH and IF shifts are evidently enlarged, especially the IF shift. Second, the shift spectra exhibit oscillation behavior and sharp shift peaks or dips. Finally, the MS brings out the nonreciprocity of the two shifts for the circularly polarized incident beams.

Computerized FDTD Method for Longitudinal Optical Phonon Energy on Semiconductor Hybrid Structure for High Power Devices Fabrication

The research problem in this study is the longitudinal optical phonon energy on metal/semiconductor interface for high performance semiconductor device. The research solution is to make the software model with finite difference time domain (FDTD) solution for transmission and reflection pulse between metal and semiconductor interface for carrier dynamics effects. The objective of this study is to find the quantum mechanics understanding on interface engineering for fabricating the high performance device for future semiconductor technology development. The analysis was carried out with the help of MATLAB. The quantum mechanical spatial field on metal-semiconductor stripe structure has been analyzed by FDTD techniques. This emission reveals a characteristic polar radiation distribution of electric dipoles and a wavelength independent of the structure size or the direction of emission; consequently, it is attributed to thermally generate electric dipoles resonating with the longitudinal optical phonon energy. Phonon energy occurs lattice vibration of material by the polarization of light, if the material has rigid structure reflect back the incident light. So, high reflective metal-semiconductor structure always use as photodectors devices in optical fiber communication. No lattice vibration material structure has no phonon effect, so this structure based devices can get high performance any other structure based devices. The transmission and reflection coefficient of metal-semiconductor GaN/Au layer structure compare with GaN/Ti and GaN/Pt structure. Parallel (P) and transverse (S) polarization of light incident on a metal-semiconductor nanolayer structure with IR wavelength. Efficient use of the layer by layer (LbL) method to fabricate nanofilms requires meeting certain conditions and limitations that were revealed in the course of research on model systems.

Polarization-maintaining terahertz anti-resonant fibers based on mode couplings between core and cladding

This study numerically investigated the index-induced mode coupling between the fundamental mode in core and the fundamental mode in cladding tubes in THz anti-resonant fibers (ARFs), and then, this index-induced mode coupling was applied for designing polarization-maintaining ARFs. Simulated results indicate that in the polarization-maintaining ARFs based on index-induced mode coupling, when the core diameter approaches the diameter of cladding tubes, ARFs can realize a birefringence which maintaining the polarization of incident light. Besides, the birefringence property which is realized by deforming the core boundary or categorizing the core boundary into two orthometric anti-resonant boundaries can be enhanced by the index-induced mode coupling. Based on the index-induced mode coupling, this paper proposed three compact polarization-maintaining ARFs, and the highest birefringence index exceeded 4 × 10−4.

Anisotropic optical properties in a square quantum well wire under different polarizations of intense laser fields

In this paper, the polarization angle of intense laser field and incident light effects on the intersubband optical absorption and refractive index change in the square quantum well wire are investigated theoretically by Kramers–Henneberger approximation. It is found that the polarization angle of the intense laser field can influence the energy gap and exchange electronic configuration by breaking symmetry. Hence, the incident light polarization angle should be considered. The variation of optical absorption and refractive index change are given with different polarization-intense laser fields and probe light, which provides the possibility of designing various polarization-sensitive devices.

Polarization dependent structural colors from tilted metalo-dielectric nanopillars

The structural color from self-assembled metalo-dielectric (In/InP) nanopillars is shown to be polarization sensitive when the axial symmetry is broken. The characteristic dip in the reflection spectra due to resonant absorption is shifted by 90 nm as the polarization of incident light is altered from TE to TM at an incidence angle of 40°. We also show wafer-scale, mask-less fabrication of pillars that are tilted with respect to the substrate, a fast and cost effective method of creating the asymmetrical structures required for polarization sensitivity at normal incidence. A dip shift of 100 nm is observed for 40° tilted nanopillars of average height 380 nm, resulting in a smooth range of colors with changing polarization. FDTD simulations confirm the polarization dependent dip-shift in the resonant absorption wavelength. Furthermore, the field and intensity profiles obtained from the simulations indicate that the resonant absorption dips are due to HE1m-like modal excitations and their shift with respect to the incident angle and polarization leads to the change in perceived color from the tilted nanopillar system.

Raman spectroscopy provides insight into carbonate rock fabric based on calcite and dolomite crystal orientation.

Carbonate rocks record the oldest forms of life on Earth, and their geologic reconstruction requires multiple methods to determine physical and chemical processes before conclusions of ancient biosignatures are made. Since crystal orientation within rock fabric may be used to infer geologic settings, we present here a complementary Raman method to study the orientation of calcite (CaCO3) and dolomite [CaMg (CO3)2] minerals. The relative peak intensity ratio of the carbonate lattice Eg modes T and L reveals the crystallographic orientation of calcite and dolomite with respect to the incident light polarization. Our results for calcite show that when the incident laser light propagates down the crystallographic a/b axis: (1) the L mode is always greater in intensity than the T mode (I T < I L), and (2) the spectra are most intense at 45° and least intense at 90° polarization angles measured from around the c axis. Our results for dolomite show that (1) I T > I L when the incident light propagation is down the crystallographic c axis and (2) I T < I L when the incident light propagation is down the crystallographic a/b axis. This study reveals mineral orientation variation related to deposition and paragenesis within limestone and dolostone samples. The method presented yields information related to growth and deformation during diagenetic and metamorphic alteration and may be used in research seeking to identify the fabric parameters of any calcite or dolomite containing rock. The compositional and structural data obtained from Raman mapping is useful in structural geology, materials science, and biosignature research.

Grayscale image for broadband linear polarization measurement by an ultracompact metasurface.

The polarization of light, the vector nature of electromagnetic waves, is one of the fundamental parameters. Finding a direct and efficient method to measure the state of polarized light is extremely urgent for nano-optical applications. Based on Malus's law, we design an ultracompact metasurface composed of silver nanorods, which is demonstrated to directly measure the state of linear polarization by a grayscale image. Using an ultrathin metasurface, we generate grayscale images with gradient grayscale levels which are linked directly to the polarization state of the incident light. The direction of the linear polarization of incident light can be conveniently and efficiently obtained through extracting the angle of the brightest area of the grayscale image. The ultrathin metasurface operates in the broadband 750-1100 nm spectral range. It is a novel and significant method to analyze the linear polarization state of light, which provides opportunities for various applications, such as polarimetric multispectral imaging and miniaturized polarimeter.

Resonant Optical Nonlinearity and Fluorescence Enhancement in Electrically Tuned Plasmonic Nanosuspensions

Controlled orientation and alignment of rod‐shaped plasmonic nanoparticles are of great interest for many applications. Herein, it is demonstrated that the nonlinear optical response of gold nanorod suspensions is dynamically controlled by electric field‐induced orientation. Merely by switching incident light polarization, the longitudinal and transverse surface plasmon resonance (SPR) absorption peaks are modulated with opposite trends, and the resulting optical nonlinearity is revealed from self‐trapping of plasmonic resonant solitons. Moreover, even with a very low concentration of fluorescent molecules, a significant increase in the fluorescent signal is observed with a transmittance‐type volume detection scheme. Such an enhancement is attributed to a combined action of optical force‐induced nonlinearity and electric field‐induced nanorod orientation, as explained by the theoretical analyses. Herein, new possibilities for engineering nonlinear plasmonic soft matter and detecting low‐concentration (yet a large total number of moleculesas needed) fluorescent samples are brought out.

Second-harmonic generation in nonlinear plasmonic lattices enhanced by quantum emitter gain medium.

We report on a theoretical study of second-harmonic generation (SHG) in plasmonic nanostructures interacting with two-level quantum emitters (QEs) under incoherent energy pump. We generalize the driven-dissipative Tavis-Cummings model by introducing the anharmonic surface plasmon-polariton (SPP) mode coupled to QEs and examine physical properties of corresponding SPP-QE polariton states. Our calculations of the SHG efficiency for strong QE-SPP coupling demonstrate orders of magnitude enhancement facilitated by the polariton gain. We further discuss time-domain numerical simulations of SHG in a square lattice comprising Ag nanopillars coupled to QEs utilizing a fully vectorial nonperturbative nonlinear hydrodynamic model for conduction electrons coupled to Maxwell-Bloch equations for QEs. The simulations support the idea of gain enhanced SHG and show orders of magnitude increase in the SHG efficiency as the QEs are tuned in resonance with the lattice plasmon mode and brought above the population inversion threshold by incoherent pumping. By varying pump frequency and tuning QEs to a localized plasmon mode, we demonstrate further enhancement of the SHG efficiency facilitated by strong local electric fields. The incident light polarization dependence of the SHG is examined and related to the symmetries of participating plasmon modes.

Generation of a polarization insensitive Airy beam using an all-dielectric metasurface

The Airy beam possesses some unusual properties, which are non-diffraction, self-healing, and a unique self-bending behavior. Previous works about metasurfaces have used geometric phase or plasma resonance to produce the Airy beam. However, the former requires a circular polarized light incident, while the latter has a large optical loss. In this paper, a polarization insensitive metasuface is designed to generate the Airy beam. It works in 635 nm, which is the working wavelength of the commonly used semiconductor laser. The nature of all-dielectric eliminates the ohmic loss improving the working efficiency of the metasurface. The efficiency of generating the Airy beam is approximately 58 %. Most important of all, the square nanopillar is easier to be realized in processing. The square structure can have a smooth side as in the case of processing equipment accuracy is not very high.

Polarization singularities in light scattering by small particles

Using full-wave numerical simulations and analytical multipole expansions we investigated the properties of real-space polarization singularities that emerge in light scattering by subwavelength particles. We considered spherical and torus particles made of dielectric or perfect-electric-conductor material. We determined the topological indices and the trajectories of electric-field polarization singularities in both the near-field and far-field regions. In the far-field region, a total of four singularities are identified and the sum of their polarization topological indices is two, independent of the particle's geometric shape. In the near-field region, the polarization singularities strongly depend on the particle's shape and the polarization of incident light, and their index sum is not governed by the Poincar\'e-Hopf theorem anymore due to the non-transverse nature of the fields. From near field to far field, a flipping of sign can happen to the polarization topological indices of the C lines. The far-field properties of the singularities can be well explained by the interference of the excited multipoles, but their near-field properties can be strongly affected by the evanescent fields that are not captured by the multipole expansions. Our work uncovers the important relationship between particles' geometric properties and the polarization singularities of their scattering field. The results can be applied to manipulate polarization singularities in nanophotonic systems and could generate novel applications in optical sensing.

Heliconical cholesteric liquid crystals as electrically tunable optical filters in notch and bandpass configurations

ABSTRACT Heliconical cholesteric liquid crystals are a recently proposed novel class of liquid crystalline materials in which the chiral pitch can be tuned by an external electric field acting parallel to the helical axis. Here we show that these materials can be used as tunable optical filters of a simple architecture. The spectral properties of transmitted light can be tuned within the whole visible range. In particular, the bandpass wavelength can be shifted from 405 nm to 637 nm by changing the applied field from 2.7 to 1.7 V/µm. The electric field can also switch the filters on and off, within 1 s or less. Moreover, the filters work with both polarised and unpolarised light and can be switched from a notch to a bandpass configuration by changing the polarisation of incident light. An optical switch among three different laser lines is also reported as an additional possible application.

Controllable transport of nanoparticles along waveguides by spin-orbit coupling of light.

Waveguide optical tweezers can capture and transport nanoparticles, and have important applications in biology, physics, and materials science. However, traditional waveguide optical tweezers need to couple incident light into one end of the waveguide, which causes problems such as difficulty in alignment and low efficiency. Here, we propose a new type of waveguide optical tweezers based on spin-orbit coupling of light. Under the effect of spin-orbit coupling between the waveguide and nearby particles illuminated by a circularly polarized light, the particles experience a lateral recoil force and a strong optical gradient force, which make particles in a large area to be trapped near the waveguide and then transmitted along the waveguide, avoiding the coupling of light into one end of the waveguide. We further demonstrate that the particles can be transmitted along a curved waveguide and even rotated along a ring-shaped waveguide, and its transmission direction can be simply switched by adjusting the spin polarization of incident light. This work has significance in the research of optical on-chip nano-tweezers.

Ultrabroadband metamaterial absorbers from ultraviolet to near-infrared based on multiple resonances for harvesting solar energy.

In this paper, a metal-dielectric metamaterial absorber is proposed to achieve ultrabroadband absorption at frequencies from ultraviolet to near-infrared. Based on finite element method solutions, the average absorption of the absorber is 97.75% from 382 nm to 1100 nm, with a maximum of 99.92%, resulting from multiple resonance coupling. The influences of geometric parameters and incident conditions on absorption are investigated. Broadband and narrowband absorption changes are realized by changing incident light polarization. Polarization-independent properties can be realized by changing the dielectric structure to centrosymmetric. The average absorption of the polarization-independent structure is 97.11% from 250 nm to 1115 nm, with a maximum of 99.98%. The proposed absorber structure has wide optical applications including solar energy harvesting and light-emitting devices.

Hot-electron photocurrent detection of near-infrared light based on ZnO

We demonstrate an unconventional near-infrared photodetector fabricated from a ZnO chip with a metallic subwavelength grating structure as a contact and optical window, which harvests hot electrons generated by plasmonic resonances introduced by incident light. The grating structure has a strong selection of the polarization of incident light, meaning that the detector is naturally polarization-sensitive. In our device, the polarization extinction ratio is as high as 64:1, much higher than that relying on crystal orientations. Since the photoresponse is introduced by plasmonic resonance, a narrow photoresponse spectrum with a linewidth of 32.1 nm at 1.201 μm is obtained. By simply changing the grating period, the spectral position can be tailored freely within the near-infrared region, i.e., wavelength-selective. Such a spectral response is not likely to be realized with conventional semiconductor photodetectors, which depend on the band edge absorption. We propose a modified Fowler's model, which well explains the line shape of photoresponse spectra of such devices.

Patterned Photoalignment in Thin Films: Physics and Applications

Photoalignment of liquid crystals by using azo dye molecules is a commonly proposed alternative to traditional rubbing alignment methods. Photoalignment mechanism can be well described in terms of rotational diffusion of azo dye molecules exposed by ultraviolet polarized light. A specific feature of the irradiated light is the intensity dependent change of azimuthal anchoring of liquid crystals. While there are various mechanisms of azo dye photoalignment, photo-reorientation occurs when dye molecules orient themselves perpendicular to the polarization of incident light. In this review, we describe both recent achievements in applications of photoaligned liquid crystal cells and its simulation. A variety of display and photonic devices with azo dye aligned nematic and ferroelectric liquid crystals are presented: q-plates, optically rewritable flexible e-paper (monochromatic and color), and Dammann gratings. Some theoretical aspects of the alignment process and display simulation are also considered.