In order to avoid inﬂuence of topography varia- tions, we have studied local polarization conversion at the distance of about 5 lm from the surface using the constant-height scanning mode (Fig. 4). The polarized images reveal complex optical ﬁeld distri- butions which can be understood taking into ac- count the high number of interfering scattered beams which could be coupled into the SNOM probe. The nodes of the structure correspond to the Fresnel diﬀraction region intermediate between the near- and far-ﬁelds. However, the polarization dependencies associated with these distributions ex- hibit similar behaviour as in the near-ﬁeld. The local intensities in diﬀerent areas over the gammadion ar- ray follow the average intensity variations having minima and maxima at the same polarization angles. Nevertheless, the relative intensity changes are diﬀer- ent in diﬀerent areas. The area 1 which is a centro- symmetrical point of the chiral structure exhibits the smallest polarization conversion as well as small- est absolute intensity of the scattered light. At the same time, the area 5 which is mirror-symmetrical with a mirror plane in the direction of the incident light provides the strongest polarization conversion.
In this paper, we propose a new design of a double helical particle (as a meta-atom) with the optimal shape for realization of linear- to-circular polarization conversion. The optimal shape denotes that the double stranded helix has a particular pitch angle at witch a strong scattering of circularly polarized waves towards a perpendicular to helix axis direction takes place. We have calculated this pitch angle by considering in detail an electromagnetic response in every elementary resonant fragment of the double helix and then recreated the full scattering field formed by all resonant fragments. Importantly, the incident linear wave should propagate perpendicular to the helix axis and the plane of the E-vector oscillation should cross the ends of the helix. This theoretical approach distinguishes this work from a number of related ones. In the next sections we confirm the analytical predictions by computer modeling. We emphasize the importance of the double stranded configuration of the particle, however, if the narrow directivity of the scattering is not necessary, an additional pairs of helices can be added into the particle design for more omnidirectional scattering.
16 Read more
To obtain the capacity of switching between absorption and polarization conversion (PC) modes, the MFD includes two categories of metasurfaces as shown in Fig. 1. One type is absorbing metasurface (AM), and the other type is PC metasurface (PCM). A typical configuration of the MFD, as presented in Fig. 1, includes PCM structure, AM structure, metallic mirror, and insulators to separate them. It is supposed that, at the absorption mode, the AM dominates the impinging wave and dissipates the incident power, and the PCM is of no avail at this mode. At the PC mode, the AM should be neutralized and the PCM plays a leading role; therefore, the polarization state of the incident wave is converted. To attain the above claims, the key point is the
The reﬂection coeﬃcients of u -incident wave and v -incident wave and the phase diﬀerence between them are shown in Fig. 3. It can be seen that at 4.2 GHz, 8.8 GHz, and 15 GHz, the magnitude and phase diﬀerence between u -incident wave and v -incident wave fulﬁll Equation (3), which indicates that the incident polarized wave is fully converted into the orthogonal component, whereas in the rest of frequency range, only part of the incident polarized component is converted. In order to demonstrate the polarization conversion ratio (PCR) of the proposed meta-surface, the relative parameters are deﬁned as follows: r xy = |E x r /E y i | and r yy = |E y r /E y i | are the reﬂection ratio of y -to- x and y -to- y polarization conversion, in which E r and E i represent the reﬂected electric ﬁeld and incident electric ﬁeld, while E x and E y represent the x -polarized and y -polarized electric ﬁelds, respectively. As a result, the PCR can be expressed as PCR = |r xy | 2 / ( |r xy | 2 + |r yy | 2 ).
Recently, an alternative sensing approach based on magneto- optical polarization conversion induced in ferromagnetic plasmonic nanodisks and dimers was presented. 15, 16 The technique displayed high sensitivity to bulk refractive index changes, as well as to adsorption of thin molecular layers. 15 However, a recent theoretical study predicted that even higher sensitivity could be achieved using a polarization rotation sensing scheme applied to anisotropic gold particles. 17 This approach utilizes the high quality factor effects in gold compared to magnetic materials and it does not require an applied magnetic field. Here we experimentally demonstrate LSPR sensing based on polarization conversion in anisotropic gold nanostructures and show that the technique indeed provides an extremely powerful means for real-time analysis of refractive index changes induced by molecular adsorption.
Take a normally x -polarized incident wave as an example. The incident wave E i can be decomposed into two perpendicular components along u - and v -axes, respectively. Then, the incident EM wave can be expressed as E i = u E iu + v E iv , and the reﬂected wave as E r = u E ru + v E rv . In the symmetric mode, the proposed structure behaves as a PEC because of the electric resonance, leading to the opposite phase between E iv and E rv . In the antisymmetric mode, the function can be considered as high impedance surface because of the magnetic resonance, which makes E iu in-phase with E ru . Hence, the synthetic ﬁelds for E ru and E rv will be along the y -axes, as demonstrated in Fig. 3(a). Likewise, the polarization conversion can be realized by the mirror unit cell in Fig. 3(b).
Abstract—Polarization converters based on metamaterial have broad application in imaging, sensing and communication from microwave to optical frequency. However, its performance is limited by single function and narrowband. In this paper, a new type of polarization converter based on square loop shaped metamaterial has been presented. It works in the reﬂection mode to achieve broadband polarization conversion for both circular and x/y linear polarization waves. The incident linearly polarized wave will be converted to its cross-polarized state with a polarization conversion ratio (PCR) lager than 0.9 in two distinct broad frequency ranges; on the other hand, circularly polarized wave will be reﬂected to its co-polarized state eﬃciently in the same spectrum regimes. Good agreements have been observed for both simulation and measurement results. This work oﬀers a further step in developing high performance multi-function microwave or optical devices.
phenomena of trapped magnetic mode resonance and high Q-factors are modulated by inserting graphene between silicon and silica. This results in a broader transmission wavelength in comparison to the all-dielectric structure without graphene. The birefringence tunability is based on the dimensions of silicon and the Fermi energy of graphene. Consequently, a linear-to-circular polarization conversion is achieved at a high degree of 96%, in the near-infrared. Moreover, the polarization state of the scattered light is switchable between right and left hand circular polarizations, based on an external gate biasing voltage. Unlike in plasmonic metasurfaces, these achievements demonstrate an efficient structure that is free from radiative and ohmic losses. Furthermore, the ultrathin thickness and the compactness of the structure are demonstrated as key components in realizing integrable and CMOS compatible photonic sensors.
Abstract. Map the sky polarization mode is an important feature of remote sensing observation sky effect, describes the polarization signal distribution in the whole sky. The observer instrument design of polarization image acquisition all sky in this paper is used to analyze the distribution of polarized light in the sky, the sky a preliminary determination of polarization distribution around several polarization neutral zone has ring distribution. Firstly, according to the atmosphere the polarization characteristics of information analysis, to determine the basic requirements of remote sensing polarization array design; secondly, gives the design idea of instrument all the components of the system; finally, to obtain the atmospheric observation chart like data processing, access to high quality space atmospheric polarization diagram. Basically meet the request of space atmospheric polarization observations.
The camera (Fig.4) is a linear Stokes division of time imaging polarimeter. It uses standard CCD, standard F mount lenses, and the proprietary patented fast polarization modulator with 4 states of linear polarization. It goes up to 35 frames per seconds in full resolution and up to 111 frames per second in half resolution. The camera is compact (4”x4”x6”) and robust. The acquisition and image processing software run on a standard computer. The interface between the camera and the computer is IEEE-1394 connection (FireWire) and USB. The camera presented is integrated and can be calibrated with Red, Green, or Blue filters.
The pitting corrosion of atmospheric storage tank (AST) bottom steel specimens was studied by combined using acoustic emission (AE) and electrochemical polarization techniques in acidic NaCl solution. The AE signal characteristic parameters including amplitude, energy, hits, duration time and rise time varied over time, and the relationship between them were analyzed in each stage of pitting corrosion process. The AE parameters and electrochemical polarization curve in time domain were also compared. The result shows that the AE activity is consistent with that of potentiodynamic polarization. The AE signal features are remarkably different in oxidized film rupture, pits propagation and corrosion products movement of the pitting stage. Extracting these AE signal features will be of great help for diagnosing the corrosion severity and identifying the corrosion type of the AE on-line storage tank bottom inspection, and further to assess the corrosion degree of the whole storage tank bottom.
12 Read more
Specific paths connecting the smallest + 共 R3c 兲 polarization value with the smallest − 共 R3c 兲 value have yet to be deter- mined. One approach to finding such a path would be to identify a centrosymmetric reference structure with zero po- larization 共 modulo a quantum 兲 , the path then being the atomic displacements from R3c to this structure. To get a zero 共 or integer-quantum 兲 polarization from only a small dis- tortion of the perovskite structure would require a somewhat drastic rearrangement of the centers of the Wannier func- tions. In the present case this may be facilitated by the known multiple valences possible for Bi and Fe. For ex- ample, if the Bi ions were to acquire an average formal charge of +4 共 likely if a disproportionation to Bi 3+ and Bi 5+
POL-neurones are polarization-opponent interneurones that receive input from two analyzer channels with orthogonal orientations of maximal sensitivity to the e-vector (Labhart, 1988). In the dark or with unpolarized light, they show spontaneous spike activity (Fig. 2; Labhart, 1988). Stimulated with the rotating e-vector of polarized light, they respond with a strong 180 ° periodic modulation of spike frequency around the spontaneous activity level (Fig. 3A; Labhart, 1988). The sharp responses to the varying e-vector and the high maximal spike frequencies of approximately 100 Hz and above indicate that all recordings were from the ‘classical’ (type I) POL- neurones described by Labhart and Petzold (1993; compare Petzold et al. 1995; J. Petzold, personal communication). In the present experiments, we used periods of polarized light during which the polarizer rotated twice from 0 ° to 360 ° and back to 0 ° (the four 360 ° rotations are designated 1–4; see Fig. 2A). Originally, the stimulation periods were separated by dark
In contrast to cultured neurons, the polarization processes of neurons in vivo have different properties depending on brain region and developmental stage. For example, vertebrate retinal ganglion cells and retinal bipolar cells inherit their polarity (Barnes and Polleux, 2009). When born, they possess a neuroepithelium-like morphology, with apical and basal processes that eventually develop into a dendrite and an axon, respectively (Barnes and Polleux, 2009). By contrast, cortical and hippocampal pyramidal neurons, and cerebellar granule neurons establish their polarity during differentiation (Noctor et al., 2004; Solecki et al., 2006; Funahashi et al., 2014). Cortical pyramidal neurons are generated in the ventricular zone (VZ) and migrate through the subventricular zone towards the intermediate zone (IZ) (Miyata et al., 2004; Noctor et al., 2004). They extend multiple minor neurites and are called multipolar (MP) cells (Miyata et al., 2004; Noctor et al., 2004). One of the minor neurites grows rapidly to become a trailing process, and another develops into a leading process, which finally develop into an axon and a dendrite, respectively (Miyata et al., 2004; Noctor et al., 2004). The remaining minor neurites are retracted and MP cells subsequently transform into bipolar (BP) cells in the IZ. BP cells are completely polarized and migrate towards the cortical plate (CP). Although neuronal polarization can occur in parallel with neuronal migration, how these two processes are coordinated remains elusive. Polarization of neurons in the cerebral cortex serves as a well-studied model for polarity establishment in vivo (Funahashi et al., 2014), and the processes regulating it are discussed in detail below.
For instance, a polarization sensitive microring resonator could be employed for optical signal processing like filtering or add-drop multiplexing. At the output section, a symmetrical configuration, including one polarization splitter (i.e., PS2) and one polarization rotator (i.e., PR2) will be implemented to combine both polarizations without any interference. In conclusion, it is also possible to use spot size converters (SSC) at both output and input sections for coupling the optical signal from the input fibre to the circuit and vice versa. Finally, the schematic in Figure.1.1 represents that it is possible to design a reciprocal configuration in which the functional device operates with only TM polarized optical signals. These polarization diverse components are also very useful for various applications such as coherent optical communications, which attract a lot of attention for long-haul optical fibre communications. The reason is that it improves the spectral efficiency in a great deal . Similar coherent technology can be also very efficient in the future network-on-chip for optical interconnects. In this case, it is better to implement the polarization diversity components which are very small. Recently the polarization-handling technology also plays an important role for realizing integrated photonic quantum circuits . Furthermore, the polarization-diversity technology is considered as a general solution to eliminate the polarization-sensitivity of photonic integrated devices based on SOI nanowires and at the end enables polarization transparent silicon nano-PICs , , which play an important role in the fibre-fed cases. There are usually numerous elements integrated monolithically for these applications, and consequently obtaining ultrasmall elements consisting of polarization diversity components is desired, which can be realized by using the giant birefringence of SOI nanowires.
151 Read more
In this paper, we discuss a potential multiple access and modulation scheme based on polarized states (PS) of electromagnetic (EM) waves for line-of-sight (LOS) communications. The proposed scheme is theoretic different from the existing polar modulation for EDGE and WCDMA systems. We propose the detailed bit representation (modulation) and multiple access scheme using PS. Because of the inflexibility of polarization information in the time and frequency domains, as well as independence of frequency and space, the polarization information can be used independently for wireless communications, i.e., another independent resource domain that can be utilized. Due to the independence between the PS and the specific features of signals (such as waveform, bandwidth and data rate), the discussed polarization division multiple access (PDMA) and polarization modulation (PM) are expected to improve the spectrum utilization effectively. It is proved that the polarization filtering technique can be adopted in the PDMA-PM wireless communications to separate the multiuser signals and demodulate the bit information representing by PS for desired user. Some theoretical analysis is done to demonstrate the feasibility of the proposed scheme, and the simulation results are made to evaluate the performance of the suggested system.
Pressuromodulation of the cell results in changes in intracellular pressure that are transduced to the nuclear membrane by the way of cytoplasmic microtubular net- work . These alterations in cell pressure align genes (gene loci) horizontally for transcription , open cell membrane (CM) channels, and depolarize cells for exocytosis [1, 2]. Positive pressuromodulation increases intracellular pressure [synergistic CM, endocytic, CM R- to-CM R-mediated polarization, CM receptor (R)-medi- ated polarization, and short duration CM R-adjusted for receptor number-mediated]; whereas, mixed pressuro- modulation decreases intracellular pressure via mito- chondrial branching/oxidative challenge (long duration CM R-adjusted for receptor number-mediated), and negative pressuromodulation decreases intracellular pressure via CM perturbation (transient duration).
19 Read more
The instrument will change after launch. Experience with other missions indicates that some change and degradation is bound to happen. In the case of HMI, a likely change from a polarization point of view is an increase in the front-window absorptivity, as seen on the Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory. The effect of this is that the window will absorb more energy, heat up, and cause the center- to-edge gradient to change. As discussed in Section 6.2.2, this has significant consequences and it is desirable to keep the gradient low by adjusting the setpoint of the window heaters. There are various ways that this degradation can be tracked.
29 Read more
Abstract—Unlike ellipsometry using light, ellipsometry using microwaves can be subject to significant standing wave effects resulting from reflection of the received wave back to the source. This paper examines these effects on the apparent homogeneity of circular polarization. These effects are examined experimentally using an ellipsometer with no sample and compared with calculated results for a single order of reflection. Good agreement is obtained. That the peak- to-peak variations in the observed irradiance are on the order of four times the amplitude reflectance is observed. The angular dependencies of these effects are path length dependent.
Figure 2 displays the impedance evolution of electrogalvanised steel samples, either without or with passivation treatments, after potential stabilization in ae- rated 0.05 mol/L NaCl solution. Two time constants were indicated in the im- pedance spectra of the untreated electrogalvanised sample, the one at the higher frequencies (HF) likely due to the presence of zinc corrosion products, and the one at the lower frequencies associated to charging of the electrochemical double layer in parallel with the charge transfer processes at the zinc/solution interface. The HF time constant dislocated into lower frequencies with the immersion time, due to the slowing down of the dissolution processes as result of the in- creasing zinc corrosion products formed on the electrogalvanised surface. Simi- lar effects were obtained for ZCe or ZCeD samples, however, for these last sam- ples types, the second time constant at lower frequencies are not well defined. Besides, the electrochemical response of a Ce conversion layer, usually seen at high frequencies was not identified on neither of the two types of the tested Ce surface coatings.
23 Read more