Pablo Bianucci

Backscattering in surface nanoscale axial photonic resonators (SNAPRs) fabricated using flame heating is investigated as a consequence of fabrication-induced asymmetry. Forward and backward spectrograms are recorded using an amplified detection scheme, revealing measurable backscattering across the measured spectral window and mode-dependent coupling among the observed mode groups. A relative quantitative metric based on the integrated forward and backward signals is introduced to compare the strength of counter-propagating mode coupling. By varying the angular symmetry of the heating process, we show that the backscattering metrics are reduced by a factor of 2 – 3 while preserving well-defined forward axial confinement. Additional measurements under modified fabrication and measurement conditions support the reproducibility of this trend. These results establish fabrication symmetry as a robust and controllable parameter for tuning the coupling between counter-propagating modes in flame-fabricated SNAPRs.

Optical frequency combs were generated for the first time in surface nanoscale axial photonic microresonators (SNAPRs) using continuous-wave light pumping. These SNAPRs were created in silica optical fibers through a localized heating process. The frequency combs created from fibers with different diameters (220 µm, 440 µm, and 660 µm) exhibited consistent spectral spacing that was in agreement with the theoretical spacing for untreated fibers of their respective sizes, without the need for fine-tuning the fabrication recipe.

2D materials, including transition metal dichalcogenides, are attractive for a variety of applications in electronics as well as photonics and have recently been envisioned as an appealing platform for phonon polaritonics. However, their direct characterization in the terahertz spectral region, of interest for retrieving, e.g., their phonon response, represents a major challenge, due to the limited sensitivity of typical terahertz spectroscopic tools and the weak interaction of such long‐wavelength radiation with sub‐nanometer systems. In this work, by exploiting an ad‐hoc engineered metallic surface enabling a ten‐thousand‐fold local absorption boost, enhanced terahertz spectroscopy of a monolayer transition metal dichalcogenide (tungsten diselenide) is performed and its dipole‐active phonon resonance features are extracted. In addition, these data are used to obtain the monolayer effective permittivity around its phonon resonance. Via the direct terahertz characterization of the phonon response of such 2D systems, this method opens the path to the rational design of phonon polariton devices exploiting monolayer transition metal dichalcogenides.

Microresonator dispersion plays a crucial role in shaping the nonlinear dynamics of microcavity solitons. Here, we introduce and validate a method for dispersion engineering through modulating a portion of the inner edge of ring waveguides. We demonstrate that such partial modulation has a broadband effect on the dispersion profile, whereas modulation on the entire resonator’s inner circumference leads to mode splitting primarily affecting one optical mode. The impact of spatial modulation amplitude, period, and number of modulations on the mode splitting profile is also investigated. Through the integration of four modulated sections with different modulation amplitudes and periods, we achieve mode splitting across more than 50 modes over a spectral range exceeding 100 nm in silicon nitride resonators. These results highlight both the simplicity and efficacy of our method in achieving flatter dispersion profiles.

We report on the experimental detection of optically excited axial longitudinal elastic modes in an optical cavity formed in an optical fiber acting as a long uniform glass cylinder.

The implementation of physical models with topological features in optical systems has garnered much attention in recent times. In particular, on-chip integrated photonics platforms are promising platforms enabling us to take advantage of the promise of topologically robust modes against inevitable fabrication defects. Here, we propose to study the SSH model superimposed in an optical ring resonator in a quantitative way using electromagnetic simulations. We are interested in the localized states that appear when a topological phase transition is introduced into the ring. In particular, we examine the extent to which topologically protected modes maintain their properties in the presence of random deformations in the surrounding lattice. We find that the modes maintain their properties when small amounts of disorder are introduced into the system. We also study loss mechanisms in the localized states, distinguishing between losses to the adjacent waveguide and to radiation, finding that the topological protection only applies to the former.

We present a systematic investigation of the different parameters involved in the fabrication of surface nanoscale axial photonics resonators from optical fibers using a flame, and how they affect the resulting resonant mode structure.

Photonic topological systems are enticing alternatives to realize multifunctional optical circuits with minimum distortions due to their unique insulating features. Among them, expanded honeycomb structures give rise to topological phases without involving any external field or gyromagnetic materials. Unlike atoms in crystals, the morphology of the repeating element in photonic systems can be tailored, allowing to tune the different interelement couplings. In this regard, traditional circular rods are replaced in honeycomb lattices with teardrop‐shaped pillars to push the “center of mass” outward, thus heightening the intercell interaction. This teardrop honeycomb lattice can provide a broader nontrivial bandgap and better edge‐state confinement compared with a circular rod lattice with the same material‐to‐void filling factor. The approach proposes a novel method to tailor the performance of topological systems by engineering the individual pillars and results in better‐confining waveguides that can be building blocks for designing more compact optical circuits under the same platform.

Long cylinders, such as optical fibers, are some of the most widely used photonic devices. The radius and refractive index of these fibers are therefore fundamentally important parameters in determining their performance. We have developed a method to determine the absolute radius, refractive index, and chromatic dispersion of a long cylinder using only the resonance wavelengths of the whispering gallery modes around its circumference for two different polarizations. Since this method only requires the measurement of resonance wavelengths, it is non-destructive and it can be performed using standard equipment. As a proof-of-concept, we demonstrate the method on a 125µm optical fiber and an 80µm borosilicate capillary fiber with thick walls, obtaining values for the diameter and the refractive index with an accuracy of 2 nm and 2 × 10⁻⁵, respectively.

We introduce a formalism, inspired on the perturbation theory for nearly free electrons in a solid-state crystal, to describe the resonances in optical ring resonators subjected to a perturbation in their dielectric profile. We find that, for small perturbations, degenerate resonant modes are split with the splitting proportional to one specific coefficient of the Fourier expansion of the perturbation. We also find an expected asymmetry in the linewidths (and Q factors) of the split modes. Experimental transmission spectra from rings with specially designed perturbations show a qualitative match with the formalism predictions.