Superheterodyne amplification of electromagnetic waves of optical and terahertz bands in gallium nitride films

Superheterodyne amplification of electromagnetic waves of optical and terahertz bands in the case of three-wave interaction in n–GaN films with the space change wave of millimeter band amplified due to negative differential resistance is studied. It is shown that amplification of the space change wave in n–GaN films may be achieved on higher frequencies f ≤ 500 GHz than when using GaAs. The case of three-wave resonant interaction of two counter-propagating waves with the space charge wave is considered for the waveguide on based on GaN film on dielectric substrate. It is shown that gain of electromagnetic waves of optical band may reach 20–40 dB on the waveguide lengths of up to 100 μm

Propagation of centimeter and millimeter spin-dipolar waves in nonuniform magnetic fields

Propagation of exchangeless spin-dipolar waves (SDW) of centimeter (f ~ 3–20 GHz) and millimeter (f ~ 30–60 GHz) wavelength ranges in ferrite films into nonuniform magnetic fields was researched analytically and numerically. Applied magnetic field is directed along film plane and it is slightly nonuniform in this plane. Proposed SDW propagation in magnetic fields was researched with complex geometric optics. We have shown a possibility of SDW type transformation from superficial SDW into backward volume SDW along propagation trajectory in both centimeter and millimeter wavelength range. An influence of electromagnetic delay on SDW propagation in nonuniform magnetic fields is essential in millimeter wavelength range and it can modify wave trajectories

Integrated silicon p–i–n structures with highly doped p++, n++ regions for modulation in terahertz frequency band

Modulators of terahertz range on the base of silicon integrated p–i–n-structures are investigated theoretically. The generalization of the Fletcher boundary conditions at the injecting contacts has been put forward for the case of highly doped p++, n++ regions, where both forbidden gap narrowing and dependence of coefficients of diffusion on doping concentration are taken into account. The problem of double injection into i-region has been simulated in a two-dimensional case. The investigations of modulation properties of integrated p–i–n-structures in the terahertz range have demonstrated a possibility to use these structures up to the frequencies 8 THz

Self-action of intense millimeter waves in waveguides with integrated p-i-n structures

The nonlinear interaction of high power millimeter (mm) electromagnetic waves with silicon integral p-i-n structures placed in a metal waveguide is theoretically investigated. The level of double injection of charge carriers due to detection of high intensity millimeter wave electric field in p-i-n structures is estimated. A mathematical model of the mutual influence of electromagnetic waves and injected charge carriers in the active region of p-i-n structures is formulated. A numerical solution of the nonlinear Helmholtz equation supplemented by proper boundary conditions on the active region boundary is obtained. The effect of high-power electromagnetic waves leads to an excessive injection of carriers into the active region of the semiconductor between p+-i, n+-i injection junctions and redistribution of the electric field in the structure. The reflection and transmission coefficients vary rapidly with the change in the input amplitude of the electromagnetic wave. This leads to bistability of these coefficients. The bistability is more pronounced in the low-frequency part of the mm range

Modulation instability of transversely limited electromagnetic waves of terahertz range in strontium titanate paraelectric

In the framework of developed approximate phenomenological model we have performed the investigation of modulation instability of transversely limited electromagnetic waves of terahertz range in paraelectric crystals SrTiO3 at the temperatures of about 77 K. Cubic nonlinearity and frequency dispersion correspond to the existence of modulation instability of long input pulses. The results of numerical investigations of the modulation instability are presented. Transversal boundedness of the input pulses can stabilize the modulation instability. Modulation instability threshold is reduced in the presence of reflections from the crystal boundaries. In the case of development of the modulation instability it is possible to generate a sequence of short terahertz pulses at the output of the crystal. The focusing of input pulses reduces the threshold of modulation instability

Frequency multiplication of terahertz radiation in the crystals of strontium titanate paraelectric

In this article we have investigated frequency multiplication in the crystals of strontium titanate paraelectric at a temperature of 77 K. Frequency dispersion affects the process of harmonics generation. It has been shown that the efficiency of higher harmonics generation is high and it is equal to 30%. One can perform the selective extraction of certain harmonic by means of an optimal choice of the crystal length

Amplification and nonlinear interaction of space charge waves of microwave band in heterogeneous gallium nitride films

Theoretical study of amplification and nonlinear interaction of space charge waves caused by negative differential conductivity in gallium nitride n-GaN films placed over a semi-infinite substrate is presented. A general case of transversally heterogeneous films is considered. Hydrodynamic diffusion-drift equations for bulk electron concentration together with Poisson equation are used. Transversal heterogeneity leads to decreased electronic mobility near the film’s surface and to decreased space amplification increments of space charge waves. Heterogeneous alloying may compensate the influence of surfaces on space amplification increments. Amplification of space charge waves in n-GaN films of sub-micron thickness on higher frequencies f ≥ 100 GHz is possible in comparison to n-GaAs films. High output electric fields ~10 kV/cm can be obtained in the short-wave range of the millimeter band.Nonlinear interaction of space charge waves in n-GaN films is also considered using the diffusion-drift equation. The possibility of generating second and third multiples of input signal as well as amplification of combination frequencies is proven

Propagation of coupled Rayleigh-gravity waves on the ocean

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Active and tunable metamaterials

Metamaterial research is an extremely important global activity that promises to change our lives in many different ways. These include making objects invisible and the dramatic impact of metamaterials upon the energy and medical sectors of society. Behind all of the applications, however, lies the business of creating metamaterials that are not going to be crippled by the kind of loss that is naturally heralded by use of resonant responses in their construction. This review sets out some solutions to the management of loss and gain, coupled to controlled and nonlinear behavior, and discusses some critical consequences concerning stability. Under the general heading of active and tunable metamaterials, an international spectrum of authors collaborates here to present a set of solutions that addresses these issues in several directions. As will be appreciated, the range of possible solutions is really fascinating, and it is hoped that these discussions will act as a further stimulus to the field