[en] The propagation of space-charge waves through a coaxial waveguide containing an annular plasma in an axial magnetic field is investigated. Both plasma and cyclotron types of waves are analyzed in the electrostatic approximation. Equations for the determination of the dispersion relations are derived from the Poisson equation and the electron continuity and momentum transfer equations. A numerical study of the dispersion curves for azimuthally symmetrical waves is presented. A significant departure from the dispersion characteristics of a cylindrical plasma waveguide are found to occur unless the inner radius of the waveguide is small compared to the outer radius. copyright 1998 American Institute of Physics

[en] The tapered quantum cascade lasers operating at about 9.0 μm are reported. In contrast to the common ridge waveguide laser, tapered devices give rather small horizontal beam divergence. Performances of devices with identical 11 μm ridge waveguide sections and different tapered gain sections are comparatively studied. The optimal taper angle of 3^o leads to a relative high output power and a very small horizontal beam divergence of 7.1^o. (semiconductor integrated circuits)

[en] A reactor-heating concept utilizing a wave-guide-launched ion-Bernstein wave in the ion-cyclotron range of frequencies is presented. Details of wave-launching transformation, propagation and absorption, together with low-power experimental results from the ACT-1 toroidal device, are summarized. (author)

No abstract available

[en] A theoretical study of parametric amplification in magnetoinductive waveguides comprising metamaterial elements is presented. It is shown that phase-matching conditions can be satisfied in coupled waveguides by tailoring the dispersion characteristic of magnetoinductive waves. The corresponding formulation for parametric amplification is developed ab initio and analysed for a number of special cases. The problem of loss compensation in metamaterials by means of parametric amplification of magnetoinductive waves is studied in more detail

[en] A possibility of transferring of light energy between coupled plasmon waveguide channels is considered. These channels are formed on the basis of a metal-dielectric-metal structure in which the dielectric gap has two closely located minima along the thickness. Dependences of the light energy pumping speed on the minimum gap thickness and distance between channels are found

[en] Silk fibroin is an abundant natural polymer, which in the last years has been proposed as an attractive material for high-technological applications, offering also new opportunities for photonics and optoelectronics. In this context, the design of optical waveguides based on silk fibroin is of great interest because of their ability to direct light in a controlled manner. In this work, we demonstrate the use of femtosecond direct laser writing (fs-DLW) to fabricate silk fibroin waveguides. Such waveguides were characterized by coupling 632.8 nm light from a He–Ne laser. Our findings demonstrate the potential of fs-DLW as a novel approach for the fabrication of silk fibroin waveguides, which provides a versatile platform for optical and biomedical applications.

[en] A pseudo-Hermitian (PH) system made up of three coupled waveguides (trimer) with an overall balanced gain and loss is investigated in a parity time (PT)-symmetric-like regime. Remarkably, the pseudo hermiticity parameter controls the asymmetric spatial field modulation between left and right propagating waves whereby, a complex coupling arises that induces an additional source of non-Hermiticity, which in the system acts as a relative gain/loss Hellmann-Feynman correction. In this situation, we show that, transmissionless backscatterings are observed for the PH-trimer in the non PT broken phase. Interestingly, the scattering properties of PH-trimer result in multiple lasing states with different mechanisms. In particular, we show that in the PT-symmetric case, the lasing modes associated to the coherent perfect-absorption (CPA), occur from the spectral singularity induced by the Hermitian chain coupling and give rise to unidirectional invisibility in the direction of incident wave. On the contrary, additional emerging lasing modes in a PH regime result from the scattering maxima resonance. We demonstrate that this specific cases suppress the CPA-laser phenomenon and rather exhibit exceptional points characterized by reflectionless but also the points of transmissionless. Numerical beam propagations realized to emphasize the results are in good agreement with the scattering investigation until gain/loss parameter is around it’s value giving resonance. (paper)

[en] GaAs/AlGaAs quantum-wire (QWR) gain-coupled distributed-feedback (GC-DFB) lasers were fabricated and characterized. Interestingly, as the shape of the active grating was varied, the lasing characteristics changed greatly; for example, one laser with sharp gratings lased at a threshold current of 13 mA while another one with dull gratings lased at 230 mA. This may be due to a change in the gain coupling coefficient with the shape of the QWR active grating. Little observation of the stopband and the wavelength consistency between the lasing and the photoluminescence peaks of the QWRs also provided evidence for lasing via GC-DFB effects in these devices

[en] Highlights: • The fluorescent microwires of ADPI were prepared by a facile solution process. • These microwires displayed the excellent waveguide and polarization performance. • The ADPI molecules in the microwires are the uniaxially oriented packing. The well-defined single-crystalline microwires of a solid-emissive organic functional molecule, 2-(anthracen-9-yl)-4, 5-diphenyl-1H-imidozole (ADPI) were successfully prepared by a facile solution process without the use of surfactant or additional templates. In addition, the optical loss coefficient is as low as 0.1 dB μm⁻¹ for the as-prepared ADPI microwires, which is lower than most previous reported organic optical waveguides. Meanwhile, these microwires also show optically uniaxial properties as demonstrated by the linearly polarized emission, providing potentially orientation-sensitive applications as optical waveguides with low optical loss.