The paper investigates the resonances of reflection (transmission) of a structure consisting of two optically coupled subwavelength silicon rectangular diffraction gratings, separated by a layer of optically transparent dielectric. The considered structure combines gain, loss and optical coupling coefficient of the periodic structure to effectively operate in parity-time symmetry mode. The spectral characteristics of the resonant reflection (transmission) of the metastructure are analyzed both in PT-symmetry mode and when switching the system to broken PT-symmetry mode. The advantages and disadvantages of using optical parity-time symmetry to control resonant reflection (transmission) for TM- and TEpolarized light incidence are demonstrated. It is shown that changing the relative arrangement of the gain and loss gratings with respect to the incident signal field significantly affects the ratio of transmission and reflection coefficients. All results are obtained considering the dispersion of the materials used.
The purpose of this study is to develop an optical inclination angle sensor using a metasurface as a scale. We propose to use the dependence of the reflection or transmission spectrum of the metasurface on the direction of light incident on it to measure the inclination angle. The disadvantages of this approach when using the simplest completely passive metasurfaces are considered. In particular, the use of bulky devices to scan the spectrum of the structure. As an alternative, the possibility of using metasurfaces with parity-time-symmetry properties to measure the inclination angle is proposed and investigated. Then no spectrum scanning of the metasurface is required to perform inclination angle measurements. As an example, a metastructure formed by two optically coupled subwavelength diffraction gratings (one of which is characterized by losses, and the other by gain) with a rectangular stroke profile is considered. The study is based on computer modeling by the finite element method.
The use of metasurfaces as scales of optical rotation angle sensors (encoders) makes it possible to reduce their overall dimensions by several orders of magnitude. The paper briefly discusses one of the possible options for implementing a rotation angle sensor with a scale from a metasurface. As a scale it is proposed to use a metasurface – a dielectric onedimensional subwavelength array designed to operate in the infrared spectral range (at a wavelength of 1.5 microns). By the finite element method, a prototype of an optical angular scale from a metasurface has been developed by computer modeling. The results of an experimental study of a prototype of an optical angular scale from a metasurface are presented. The metasurface was made of tantalum oxide and deposited on a quartz glass substrate. For the convenience of the study, the size of the scales was set to 400 × 400 microns, but if necessary, it can be reduced by more than an order of magnitude. The dependences of the transmission spectra of the prototype scale on its rotation angle are experimentally investigated.
The article describes an optical response of metastructure consisted of two optically coupled resonant subwavelength rectangular - profile diffraction gratings, between which a layer of optically transparent dielectric was placed. The features of optical resonance transmittance and reflectance for optical PT-symmetry mode was numerical investigated and some advantages of using optical PT-symmetry for resonance transmittance (reflectance) improving was demonstrated. The spectral characteristics of the metastructure change when the pumping level changes and when the system switches from the optical parity-time-symmetry mode to the broken parity-time-symmetry mode were analyzed too.
The work is devoted to the analysis of the accuracy characteristics of rotation angle sensors using angular scales from nanostructured metasurfaces. The principle of their operation is based on the dependence of the frequency response of metasurfaces on the orientation of the incident light polarization plane. The influence of the noise characteristic of angle sensors on the measurement result is considered. It is shown that for the sensors considered in the work, it might be on the order of units of arc seconds. The influence on the accuracy characteristics of misalignments of the angular scale and thermal effects that the sensor may experience during operation is analyzed. Recommendations to reduce the influence of parasitic effects and further improve the accuracy characteristics are given.
The article presents a study of the dependence of the change in the shape of the resonance transmission line for optical thin dielectric gratings. The result of changing the duty cycle for high and low medium contrast while maintaining the amount of substance has been demonstrated. The results of the effect of the filling factor on the resonance transmission width and the frequency position in the normal TE wave drop are numerically investigated. Results for various options of a angles of the falling bunch at various coefficients of filling are presented. The effect of refractive index contrast of this structure on the width and shape of resonance lines was analyzed. In the first approximation, effective refractive indices and effective thicknesses for such structures were calculated. Conclusions are drawn about the conditions under which the structure can be considered optically thin.
We report the results of analysis of ways of application of nanostructured metasurfaces in rotation angle sensor (angle encoders). The dependence of optical properties of nanostructured metasurfaces upon their orientation relative to the incident optical radiation service as the basis of the study. The metasurfaces’ response to the incident radiation allows to judged on the mutual orientation of the radiation source and the metasurface. This allows to use metasurfaces as angle encoder scales. We discuss the possibility of using of amplitude and phase response of different types of metasurfaces. The main attention is paid to metasurfaces in the form of plasmonic nanorods, Pancharatnam–Berry elements and Cshaped antennas. The overall dimensions of the scales of angular encoders based on metasurfaces (width and length or diameter) can be tens of microns or less. Thus, the use of metasurfaces in angular encoders allows to reduce their size by orders of magnitude. Alongside, the use of metasurfaces should allow to realize non-contact measurements of the rotation angle (when only the scale based on the metasurface is placed on the controlled object or a part of an object itself acts as a scale) and to implement an absolute rotation angle sensor without significant increase of its size and manufacture complexity.
This article considers the use of holographic interferometer to overwrite the holograms for distortion correction. Each optical system contains some deviations of the beam path, called aberrations of the optical system. They are considered in the resulting interference figure as a distortion of the bands. While increasing the sensitivity of the interference pattern, new aberrations caused by re-registration of the installation in addition to the aberrations already presented on the interferogram caused by the initial record, also multiplied by N times, are introduced N times. In this experiment we decided to use a modified setup with spatially combined interferograms with use of reflective SLM (spatial light modulator) LETO and digital image handling of the interferograms recorded by CCD or CMOS camera.
The article considers the use of holographic interferometer to overwrite the holograms for distortion correction. Each optical system contains some deviations of the beam path, called aberrations of the optical system. They are considered in the resulting interference figure as a distortion of the bands. While increasing the sensitivity of the interference pattern, new aberrations caused by re-registration of the installation in addition to the aberrations already presented on the interferogram caused by the initial record, also multiplied by N times, are introduced N times. In this experiment we decided to use a modified setup with spatially combined interferograms with use of reflective SLM (spatial light modulator) LETO and digital image handling of the interferograms recorded by CCD or CMOS camera.
The method of amplification of hologram was applied to the so-called Rozhdestvenskiy hooks, that were obtained in the Rozhdestvenskiy interferometer (Michelson interferometer, combined with a grating spectrograph). In such a device the absorption lines reveal themselves as specific “hooks”, whose curvature provides the information about the atomic oscillator force. The holographic amplification “smoothes” the hooks and thus makes their analysis much simpler.
The method of amplification of hologram was applied to the so-called Rozhdestvenskiy hooks, that were obtained in the Rozhdestvenskiy interferometer (Michelson interferometer, combined with a grating spectrograph). In such a device the absorption lines reveal themselves as specific “hooks”, whose curvature provides the information about the atomic oscillator force. The holographic amplification “smoothes” the hooks and thus makes their analysis much simpler.
The paper considers the use of holographic interferometer for hologram recording of the wide spectrum from the comb – generator of the femtosecond laser was applied for illuminating of Michelson interferometer with atomic vapor. The behavior of spectral interference fringes on the exit slit of spectrograph reflects the behavior of nonlinear refractive index. The method of holographic interferometry with increasing sensitivity using phase modulator was applied for digital hologram processing.
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