Optical tunable multifunctional slow light device based on double monolayer graphene grating-like metamaterial

A very simple optical tunable device, which can realize multiple functions of frequency selection, reflection and slow light, is presented at the investigation. The proposed device is constructed by a periodic grating-like structure. There are two dielectrics (graphene and silicon) in a period of the equivalent grating. The incident light will strongly resonate with the graphene of electrostatic doping, forming an evanescent wave propagating along the surface of graphene, and this phenomenon is the surface plasmon. Under constructive interference of the polaritons, a unique plasmonic induced transparency phenomenon will be achieved. The induced transparency produced by this device can be well theoretically fitted by the bright and dark mode of optical equivalent cavity which can be called coupled mode theory (CMT). This theory can well analyze the influence of various modes and various losses between the function of this device. The device can use gate voltages for electrostatic doping in order to change the graphene carrier concentration and tune the optical performance of the device. Moreover, the length of the device in y-direction is will be much larger than the length of single cycle, providing some basis for realizing the fast tunable function and laying a foundation for the integration. Through a simulation and calculation, we can find that the group index and group delay of this device are as high as 515 and 0.257 picoseconds (ps) respectively, so it can provide a good construction idea for the slow light device. The proposed grating-like metamaterial structure can provide certain simulation and theoretical help for the optical tunable reflectors, absorbers, and slow light devices.

Simulation of an Adaptive Method of Improving the Accuracy and Extending the Range of Frequency Signal Processing in a Frequency-to-Code Converter

The article discusses the modification of one of the basic methods of converting successive periods of a variable frequency signal into numerical values representing them. The method performs the adaptive frequency selection of the clock signal in the system processing the consecutive periods of input signal. The signal processing error is analyzed on an ongoing basis, and the frequency change factor is selected. Algorithms describing the operation of the method are included. The program of the simulator of the measurement channel operation with a frequency carrier of information is described, which allows for the verification of the proposed method. Examples of the simulation results are included.

AN ANTENNA BASED ON A HYBRID METAL–DIELECTRIC STRUCTURE

Purpose: Nowadays, in the millimeter frequency range, the dielectric waveguides of various modifications have certain advantages over the standard metal waveguides, primarily due to the possibility of creating functional units based on them. This is due to the relative simplicity and low cost of manufacturing the dielectric waveguides and functional units using them, the high degree of their integration with active elements, the use in their manufacture of different dielectrics and polymers with a wide range of material constants and a variety of mechanical properties (in particular, some materials have a significant flexibility). After making a series of physical experiments we have found the possibility of implementing the frequency selection and radiation into free space of electromagnetic waves by a hybrid metal-dielectric structure. Design/methodology/approach: The studied electrodynamic structure belongs to the class of hybrid metal-dielectric structures. It includes a modified inverted dielectric waveguide with a periodic sequence on the dielectric plate of fifteen dielectric rods with metallized coating on one of the faces placed outwards. The structure efficiency was estimated by the voltage standing-wave ratio (VSWR) values and power attenuation in the duct. The measurements were made with the reflectometer method. To estimate the degree of electromagnetic field concentration near the rod inhomogeneities in the near zone, the mobile probe method was used. The field structures were visualized with the method of isolines. Findings: The results of a series of experimental investigations showed the possibility of matching the structure with the external waveguides in the frequency range of 26.5-32.5 GHz with the voltage standing-wave ratio (VSWR) less than 1.8. The frequency dependence of attenuation is oscillatory with clearly expressed frequency ranges with small and large attenuation values. Moreover, the dependence is almost periodic, which is typical of periodic structures. The frequency response slope in the transition zones can be quite high and reach values of 41.26 dB/GHz. The degree of concentration of the electric field near the waveguide dielectric rod and the degree of excitation of the dielectric inhomogeneities was found by directly measured electric field strength in the near zone. Measurements of energy characteristics made under the short-circuit conditions for the main guide and in the mode of matched load of the main guide showed both the ability to control the polarization characteristics and the ability to change the appearance of the pattern and its orientation in space. Conclusions: It has been experimentally proven that a hybrid metal-dielectric structure, being a modified inverted dielectric waveguide with a periodic sequence on the dielectric plate of fifteen dielectric rods with metalized coating on one of the faces placed outwards, can be effectively integrated into a standard transmission line. It is found that this structure can be matched with the external circuits in a fairly wide frequency range. It is also found that in different frequency ranges this hybrid metal-dielectric structure shows the possibility of both efficient frequency selection and radiation in free space. Antenna measurements have shown the beam pattern shape controllability. Key words: inverted dielectric waveguide, periodic sequence, voltage standing-wave ratio (VSWR), attenuation, reflectometer method, mobile probe method, directivity pattern

Y-Shaped Demultiplexer Photonic Circuits Based on Detuned Stubs: Application to Radiofrequency Domain

We present a theoretical and experimental study of photonic demultiplexers based on detuned stubs. The demultiplexers consist of Y-shaped structures with one input line and two output lines. Two different types of structures are proposed to achieve a selective transfer of a single mode in one output line without disturbing the second one. (i) In the first platform each output contains two different stubs attached at two different sites (U-shaped resonators). We derive in closed form the geometrical parameters of the stubs to achieve a selected frequency in each line while keeping the other line unaffected. The frequency selection can be made on the basis of two different mechanisms, namely a Fano or an electromagnetic induced transparency (EIT) resonance. Consequently, different demultiplexing schemes can be designed by a combination of the two mechanisms, such as Fano-Fano, Fano-EIT or EIT-EIT. In particular, the width of the Fano or EIT resonances can become zero for an appropriate choice of the stubs’ lengths, giving rise to trapped modes also called bound in continuum states (BICs) with infinite quality factors. We also show that the crosstalk between the two outputs can reach minimum values around −45 dB. (ii) In the second platform, each output line contains a photonic comb with a defect stub. The latter is appropriately designed to filter one or a few frequencies in the bandgap of the photonic comb. The analytical calculations are performed with the help of the Green’s function method which enables us to derive the transmission and reflection coefficients as well as the density of states (DOS). These results are confirmed by experimental measurements using coaxial cables in the radio frequency domain.

Development of Parameters towards Voice Bifurcations

Pathological vocal folds are known to exhibit multiple oscillation patterns, depending on tissue imbalance, subglottal pressure level, and other factors. This includes mid-phonation changes due to bifurcations in the underlying voice source system. Knowledge of when changes in oscillation patterns occur is helpful in the assessments of voice disorders, and the knowledge could be transformed into useful objective measures. Mid-phonation bifurcations can occur in rapid succession; hence, a fast classification of oscillation pattern is critical to minimize the averaging of data across bifurcations. This paper proposes frequency-ratio based short-term measures, named harmonic disturbance factor (HDF) and biphonic index (BI), towards the detection of the bifurcations. For the evaluation of HDF and BI, a frequency selection algorithm for glottal source signals is devised, and its efficacy is demonstrated with the glottal area waveforms of four cases, representing the wide range of oscillatory behaviors. The HDF and BI exhibit clear transitions when the voice bifurcations are apparent in the spectrograms. The presented proof-of-concept experiment’s outcomes warrant a larger scale study to formalize the parameters of the frequency selection algorithm.