The main approaches to the construction of optical gyroscopes based on passive ring resonators are analyzed and reviewed. The history of the development of the first prototypes of such gyroscopes, which were in the focus of attention in the late 70s as a part of trials of vanishing the lock-in zone of laser gyroscopes, is considered. Modern studies of optical gyroscopes based on passive ring resonators are performed due to the trend towards the miniaturization of optical gyroscopes. The main disadvantages and problems of such gyroscopes as well as possible solutions are described. In particular, the results of research performed by the authors of the article are presented. The main types of gyroscope sensitive elements and their achievable characteristics are considered
A new type of optical resonator gyroscopes based on systems with parity-time-symmetry properties is considered. A system with parity-time-symmetry properties is composed of two direct coupled waveguides, one of which is characterized by losses, and the second one – by amplification, and a passive ring resonator connected to them. The influence of the characteristics of the parity-time-symmetry system on the optical resonator gyroscope parameters is investigated. Attention is paid to the influence of the gain, losses and coupling coefficients of the waveguides that make up the system with the parity-time-symmetry properties. The influence of the gain coefficient instability caused by a change in the pumping power on the angular velocity measurement results is also considered. The advantages and disadvantages of this approach are compared with a conventional optical resonator gyroscope. The main advantage of using systems with parity-timesymmetry properties is the increase of accuracy of registration of passive ring resonator eigenfrequencies by several orders of magnitude and, as a result, the maximum sensitivity to angular velocity.
In the optical parity-time-symmetry systems, at certain values of their parameters, a phase transition from real eigenvalues of the Hamiltonian to the complex ones is observed. This phase transition, which can be directly or indirectly caused by a change in the measured physical quantity, leads to a sharp change in the optical properties of the system. This can be used to improve the accuracy of various optical sensors, in particular, angular rate sensors. Present communication is devoted to the analysis of previously announced and newly developed by the authors methods for measuring angular rates based on the use of the optical parity-time-symmetry systems. In particular, various variations of laser gyroscopes based on the systems of two identical coupled ring resonators that differ from each other only in the level of losses and gain are considered. We propose a new method for measuring the angular rate, based on the use of a parity-time-symmetry system of two straight coupled waveguides with a passive ring resonator connected to it.
To date, many works devoted to the influence of grazing angle on the spectral properties of nanostructured metasurfaces have been published. In this case, the dependence of the spectrum on grazing angle was previously considered within the framework of solving filtering problems, for example: constructing tunable optical filters based on metasurfaces; development of a bandpass filter with characteristics that are minimally dependent on the angle of incidence of light (angular tolerant color filter), etc. We propose to use the described property of nanostructured metasurfaces for solution of an inverse problem – determination of light incidence angle from the change in the metasurface spectral response. It will provide no-contact determination of an inclination angle of an object, on which the metasurface is installed; it is a step towards creating a miniature and accurate angle sensor. We consider the idea of using metasurfaces to measure inclination angles of objects on the basis of dielectric subwavelength gratings using computer simulation. We also analyze the possibility of simultaneous measurement of rotations (inclination angles) along two orthogonal axes using the same nanostructured metasurface.
In recent decades a noticeable surge in research on nanostructured materials and their interactions with light has been observed. This is explained not only by basic interest, but also by the potential of miniaturization of devices and the expansion of their functional capabilities through the use of metasurfaces. On the other hand, in the last decade a pronounced tendency towards miniaturization of position control and navigation systems can be observed either. A need of positioning and navigation of small-sized mobile objects arises frequently. At the same time, the size of controlled objects is constantly decreasing, and the development of sensors for micro- and nanoscale objects is already required nowadays. Therefore, the use of nanostructured metasurfaces in position control and navigation systems seems to be extremely promising. We focus on the use of nanostructured metasurfaces for rotation angle determination. We discuss a new rotation angle measurement method where metasurface amplitude response is used, its main advantages and disadvantages are demonstrated, a variant of its improvement is proposed.
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.
Systems, based on aqueous suspensions of single walled carbon nanotubes, stabilized by surfactants, and having supramolecular ordering are studied by spectroscopy and polarized microscopy. Nonlinear optical behavior of the suspensions has been checked. A correlation between sizes of aggregate in suspension and nonlinear optical limiting parameters has been found. A nematic meso-phase based on suspension of carbon nanotubes has been obtained.
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