arXiv subjects

Paula Nuño Ruano

Publications and source records attributed to Paula Nuño Ruano.

6 recordsLinked to original sources

arXiv2026

Topological photonic cavities based on dissimilar Bragg gratings

Topological photonic cavities offer a powerful route to robust optical confinement and enhanced light-matter interactions. Interface states that emerge at the boundary between one-dimensional periodic structures with distinct topological phases, enable cavities with ultra-small mode volumes and intrinsic protection against disorder. Existing implementations typically create the trivial and topological phases by redefining the unit cell on either side of the cavity, so that both periodic structures share the same band structure. This constraint limits design flexibility and the range of accessible devices. Here we introduce a fundamentally different strategy for realizing topological cavities based on combining periodic waveguides with distinct band structures. By exploiting bandgap closing and band inversion in Bragg gratings, we independently control the topological phase and bandgap width of each structure. We experimentally realize silicon topological cavities formed by two different Bragg gratings without period shifting, and observe topological modes despite significant differences between the two gratings. Our results establish a new route to topological photonic cavity design, demonstrating that band inversion between dissimilar Bragg gratings enables cavity formation beyond symmetric constraints and provides a mechanism to engineer optical confinement via mirror asymmetry.

physics.optics↗

arXiv2026

Boundary-dominated optomechanics in silicon metamaterial membranes

Stimulated Brillouin scattering in integrated photonic waveguides enables coherent coupling between optical photons and gigahertz acoustic phonons, providing a powerful mechanism for on-chip microwave photonics and opto-acoustic signal processing. Despite theoretical predictions of ultra-strong Brillouin interactions arising from enhanced light-sound coupling at device boundaries, most state-of-the-art integrated demonstrations remain governed by bulk photoelastic effects. This limitation stems from trade-offs between optical loss, interaction with waveguide boundaries and accessible phonon frequencies associated with the use of transverse-electric optical modes coupled to horizontally breathing mechanical modes. Here we demonstrate a new approach based on transverse-magnetic optical modes coupled to vertically breathing mechanical modes in suspended silicon membranes engineered with subwavelength metamaterial claddings. In this geometry, the interaction is dominated by the moving-boundary effect occurring at smooth top and bottom interfaces, while the phonon frequency is set primarily by the membrane thickness rather than its width. We observe forward Brillouin interactions at a record frequency of 12 GHz with a gain of 7200 W$^{-1}$ m$^{-1}$ and a mechanical quality factor of 620, yielding the highest Brillouin gain-to-quality-factor ratio reported in silicon waveguides. The devices exhibit net Brillouin amplification in millimeter-scale waveguides with pump powers below 15 mW, establishing a scalable platform for high-frequency integrated opto-acoustic signal processing.

physics.optics↗

arXiv2025

Stimulated Forward Brillouin Scattering in Subwavelength Silicon Membranes

Brillouin scattering enables efficient and coherent conversion between optical photons and gigahertz-frequency phonons. Integrated circuits that harness this nonlinear interaction have immense potential for signal processing, quantum transduction, and sensing applications. However, achieving strong overlap and tight confinement of optical and mechanical modes in silicon nanophotonic waveguides remains a significant challenge. Here, we propose and demonstrate a novel strategy that enables independent control of optical and mechanical modes in periodically segmented silicon waveguides. Our approach combines two distinct periodic lattices: one with a period shorter than half of the optical wavelength, providing light guiding by metamaterial-induced index contrast, and another that creates a complete phononic bandgap confining acoustic modes. This dual-lattice strategy opens new degrees of freedom to optimize optomechanical confinement and coupling simultaneously. Based on this approach, we experimentally demonstrate remarkably high Brillouin gain of $G_\mathrm{B}=2673$ W$^{-1}$m$^{-1}$, resulting in a Stokes gain of 3 dB and an anti-Stokes loss of 4 dB with 6.4 MHz mechanical linewidth. These results illustrate the potential of subwavelength silicon metamaterials for engineering on-chip optomechanical interactions.

physics.optics↗

arXiv2023

Genetic optimization of Brillouin scattering gain in subwavelength-structured silicon membrane waveguides

On-chip Brillouin optomechanics has great potential for applications in communications, sensing, and quantum technologies. Tight confinement of near-infrared photons and gigahertz phonons in integrated waveguides remains a key challenge to achieving strong on-chip Brillouin gain. Here, we propose a new strategy to harness Brillouin gain in silicon waveguides, based on the combination of genetic algorithm optimization and periodic subwavelength structuration to engineer photonic and phononic modes simultaneously. The proposed geometry is composed of a waveguide core and a lattice of anchoring arms with a subwavelength period requiring a single etch step. The waveguide geometry is optimized to maximize the Brillouin gain using a multi-physics genetic algorithm. Our simulation results predict a remarkable Brillouin gain exceeding 3300 1/(W m), for a mechanical frequency near 15 GHz.

physics.optics↗

arXiv2022

Spatial and polarization division multiplexing harnessing on-chip optical beam forming

On-chip spatial and polarization multiplexing have emerged as a powerful strategy to boost the bandwidth of integrated optical transceivers. State-of-the-art multiplexers require accurate control of the relative phase or the spatial distribution among different guided optical modes, seriously compromising the bandwidth and performance of the devices. To overcome this limitation, we propose a new approach based on the coupling between guided modes in integrated waveguides and optical beams free-propagating on the chip plane. The engineering of the evanescent coupling between the guided modes and free-propagating beams allows spatial and polarization multiplexing with state-of-the-art performance. To demonstrate the potential and versatility of this approach, we have developed a two-polarization multiplexed link and a three-mode multiplexed link using standard 220-nm-thick silicon-on-insulator technology. The two-polarization link shows a measured -35 dB crosstalk bandwidth of 180 nm, while the three-mode link exhibits a -20 dB crosstalk bandwidth of 195 nm. These bandwidths cover the S, C, L, and U communication bands. We used these links to demonstrate error-free transmission (bit-error-rate < 10-9) of two and three non-return-to-zero signals at 40 Gbps each, with power penalties below 0.08 dB and 1.5 dB for the two-polarization and three-mode links respectively. The approach demonstrated here for two polarizations and three modes is also applicable to future implementation of more complex multiplexing schemes.

physics.optics↗

arXiv2020

Localized waves carrying orbital angular momentum in optical fibers

We consider the effect of orbital angular momentum (OAM) on localized waves in optical fibers using theory and numerical simulations, focusing on splash pulses and focus wave modes. For splash pulses, our results show that they may carry OAM only up to a certain maximal value. We also examine how one can optically excite these OAM-carrying modes, and discuss potential applications in communications, sensing, and signal filtering.

physics.optics↗