Dielectric Hollow Waveguide Research Articles

Compact and sensitive heterodyne receiver at 2.7 THz exploiting a quasi-optical HEB-QCL coupling scheme

We demonstrate a sensitive and compact terahertz heterodyne detection system based on a quantum cascade laser (QCL) as a local oscillator and a hot electron bolometer (HEB) as a mixer. It relies on an original optical coupling scheme where the terahertz (THz) signal to be detected and the local oscillator (LO) signal are coupled to the HEB from both sides of the integrated lens/antenna mixer. The THz signal of interest impinges on the front side through the silicon lens while the LO onto the rear (air) side. This concept allows us to remove the beam splitter usually employed in terahertz heterodyne receivers. The mixer consists of a Niobium Nitride HEB with a log-spiral planar antenna mounted on the flat side of a hyperhemispherical silicon lens. The local oscillator of the heterodyne detector is a low power consumption and low beam divergence 3rd-order distributed feedback laser with single mode emission at the target frequency of 2.7 THz. The coupling between the QCL and the HEB has been further optimized, using a dielectric hollow waveguide that reliably increases the laser beam directivity and permits us to pump the HEB into its most sensitive state through the air side of the planar antenna. We have measured a noncorrected double sideband receiver noise temperature of 880 K at 2.7 THz.

Modal Expansion Approach for Electromagnetic Propagation in Street Canyons

We present a simple and efficient model to compute electromagnetic (EM) propagation in urban street canyons, when transmitting and receiving antennas are located below the rooftop level. A parallel-plate dielectric hollow waveguide model of the street canyon is proposed, and propagation is analyzed by using the modal expansion approach. Obtained results for the case of line-of-sight (LoS) propagation are substantially equivalent to those obtained with the ray-optics method, but, with respect to the latter, our method presents important advantages: it is more efficient from a computational viewpoint, it allows deriving a very simple and reasonably accurate formulation of the average received signal strength, and it provides a fairly simple way to compute coupling at cross-junctions, exploited to obtain an analogous formulation for the non-LoS case. Obtained results are compared with simulations of a ray-tracing-based EM solver and with experimental measurements available in the literature.

Generation of sub-5 fs pulses in vacuum ultraviolet using four-wave frequency mixing in hollow waveguides

We investigate the potential of four-wave mixing in dielectric hollow waveguides for vacuum ultraviolet pulse generation with unprecedented short durations. Taking into account higher-order transverse modes and plasma effects we predict the generation of a 2.5 fs pulse at 160 nm using an intense 10 fs, 800 nm pulse and its weaker third harmonic at 267 nm, both coupled to the fundamental transverse mode. Excitation of higher transverse modes allows an increase of the signal energy (up to by a factor of 20) but with a pulse duration of 13 fs (compressible to 7.7 fs).

Nonlinear TE waves in asymmetric dielectric hollow waveguides with a self-focusing Kerr-like nonlinear film

A treatment of the behaviour of TE nonlinear waves guiding in asymmetric dielectric hollow waveguides with a self-focusing Kerr-like nonlinear film is given. The mathematical results are derived by introducing the physical parameter which depends upon both the optical power density at the peak of the electric field profile and the dielectric constant difference between the film and the substrate, and relating the field amplitudes at the film boundaries to the wave number in the film. For three TE0 waves, the dispersion curves, the electric field profiles, the cut-off frequency, the wave index and the guided power are illustrated and discussed. In addition, the effects of the waveguide asymmetry on the wave index for three TE0 waves are discussed.

Wave Propagation and Attenuation in the General Class of Circular Hollow Waveguides with Uniform Curvature

A general method has been developed to evaluate the propagation constant in oversized circular hollow-core waveguides characterized by a surface impedance and admittance due to a uniform bend. Completely different formulas are obtained for the attenuation constants of the modes in metallic or dielectric hollow waveguides from those obtained by Marcatili and Schmeltzer. Electric-field lines are also presented for several lower order modes in bent waveguides.