arXiv subjects
Publications and source records attributed to Nelson Castro.
We experimentally demonstrate dual-line coherent detection using an optical frequency comb local oscillator, enabling large frequency offset tolerance with minimal additional signal processing. The proposed method achieves 200 GHz offset tolerance for 400 Gbit/s signals with low penalty, supporting uncooled, low-cost coherent transceivers.
The properties of a degenerate band-edge (DBE) oscillator based on the synchronous interaction between a linear electron beam synchronized with four degenerate electromagnetic modes are presented. The DBE in the cold slow-wave structure is implemented in a rectangular waveguide with a staggered double corrugation in it. At the DBE, four modes coalesce into a single degenerate mode, forming a very flat dispersion diagram with vanishing or very small group velocity. The DBE oscillator frequency is robust to variations in electron beam current, electrons' velocity, and cavity length. The DBE oscillator concept provided here is expected to be extendable to several other geometries as long as the slow wave structure supports a DBE.
We explore the use of glide symmetry (GS) and electromagnetic bandgap (EBG) technology in a glide-symmetric double corrugated gap waveguide (GSDC-GW) slow wave structure (SWS) for traveling wave tube (TWT) applications. Notably, this GS structure provides the advantage of wide-band operation and the EBG eliminates the need for a conductive connection between the top and bottom waveguide plates. The TWT performance is evaluated via particle-in-cell simulations that reveal a 3-dB bandwidth of approximately 12 GHz spanning from 54.5 GHz to 66.3 GHz, accompanied by a maximum gain of 23 dB. Because of GS, the backward wave in the first spatial harmonic is not longitudinally polarized, leading to a low risk of backward wave oscillations in the TWT. This work places the GSDC-EBG structure within the arena of potential SWS topologies for TWTs operating under similar conditions.
We propose a novel MIMO-WDM Volterra-based nonlinear-equalisation scheme with adaptive time-domain nonlinear stages enhanced by filtering in both the power and optical signal waveforms. This approach efficiently captures the interplay between dispersion and non-linearity in each step, leading to $46\%$ complexity reduction for $9\times 9$-MIMO operation.
Focusing on traveling wave tube (TWT) applications, the interaction impedance between an electron beam and electromagnetic modes in three distinct, but related, corrugated waveguides that operate at millimeter waves is investigated together with the role of glide symmetry. Two waveguide structures have glide symmetry, and the irreducible Brillouin zone is related to half of the period, leading to a wide band linearity, i.e., nondispersive, property of the dispersion diagram. The investigation on the modes with longitudinal electric field that can be excited shows that the bottom-top glide (BT Glide) symmetric corrugated waveguide has a wide band interaction impedance, hence it is a good candidate for millimeter wave TWT amplifiers. Furthermore, the backward electromagnetic mode in such BT Glide slow wave structure is not $z$ polarized, eliminating the {risk} of backward wave oscillations.
Network representations of the nervous system have been useful for the understanding of brain phenomena such as perception, motor coordination, and memory. Although brains are composed of both neurons and glial cells, neuron-glial networks have been little studied so far. Given the emergent role of glial cells in information transmission in the brain, we developed a mathematical representation for neuron-glial networks ($\Upsilon$-graph). We also defined the concepts of isomorphisms, unnested form (multidigraph) and matrix equation for $\Upsilon$-graphs. Although we found several network motives where the isomorphism between unnested forms does not guarantees the isomorphism between their respective $\Upsilon$-graphs, we found that if the matrix equations satisfy some conditions, the unnested forms isomorphism guarantees the isomorphism between $\Upsilon$-graphs. Finally, we introduced a novel approach to modeling the network shape. Our work presents a mathematical framework for working with neuron-glia networks.