arXiv subjects

Josep Martínez-Romeu

Publications and source records attributed to Josep Martínez-Romeu.

4 recordsLinked to original sources

arXiv2026

On-Chip Chiroptical Sensor based on Directional Deflection of Light: A Stern-Gerlach Integrated Optical Analog

Chiroptical techniques for detecting and characterizing the chirality of matter and artificial nanostructures are traditionally based on their interaction with chiral light, typically circularly-polarized fields propagating in free space. More recently, these approaches have been extended to integrated photonic platforms, offering significant practical advantages. However, the generation of chiral guided light is challenging, it requires degeneracy of the fundamental modes of the integrated waveguide, which occurs at a single wavelength and limits broadband characterization. Here, we introduce and simulate numerically a new alternative integrated optical configuration inspired by the Stern-Gerlach experiment, in which a chiral sample is illuminated by a linearly polarized light beam. Such a beam exits from a dielectric waveguide that propagates the fundamental TE mode, thereby eliminating the need for circularly polarized excitation. On this basis, enantio-discrimination is achieved through a spatially resolved scheme using a symmetric arrangement of optical antennas on either side of the propagation axis. Our simulation results suggest that the selective scattering and absorption of the circular polarization component matching the chirality of the sample induces an imbalance of (spin) angular momentum of the optical field, resulting in a transverse deflection of the beam toward the corresponding side. This on-chip platform then provides a direct route to chiroptical functionalities under linearly-polarized illumination, enabling compact implementations of chiral sensing, spectroscopy, optical computing, and communication schemes.

physics.optics↗

arXiv2025

Chiral optical forces in a slot waveguide for separation of molecules in gas

Chiral optical forces present an exciting avenue into the separation of enantiomers in an all-optical fashion. In this work, we explore via numerical simulations and analytical calculations the feasibility of the separation of chiral molecules by using guided light in a dielectric slot waveguide. Our results suggest that it is possible to separate [6]helicene enantiomers suspended in gas within several hours when applying optical powers of 100 mW.

physics.optics↗

arXiv2024

Longitudinal chiral forces in photonic integrated waveguides to separate particles with realistically small chirality

Chiral optical forces exhibit opposite signs for the two enantiomeric versions of a chiral molecule or particle. If large enough, these forces might be able to separate enantiomers all optically, which would find numerous applications in different fields, from pharmacology to chemistry. Longitudinal chiral forces are especially promising for tackling the challenging scenario of separating particles of realistically small chiralities. In this work, we study the longitudinal chiral forces arising in dielectric integrated waveguides when the quasi-TE and quasi-TM modes are combined as well as their application to separate absorbing and non-absorbing chiral particles. We show that chiral gradient forces dominate in the scenario of beating of non-denegerate TE and TM modes when considering non-absorbing particles. For absorbing particles, the superposition of degenerate TE and TM modes can lead to chiral forces that are kept along the whole waveguide length. We accompany the calculations of the forces with particle tracking simulations for specific radii and chirality parameters. We show that longitudinal forces can separate non-absorbing chiral nanoparticles in water even for relatively low values of the particle chirality and absorbing particles with arbitrarily low values of chirality can be effectively separated after enough interaction time.

physics.optics↗

arXiv2023

Chiral forces in longitudinally invariant dielectric photonic waveguides

Optical forces can be chiral when they exhibit opposite signs for the two enantiomeric versions of a chiral molecule or particle. Such forces could be eventually used to separate enantiomers, which could find application in numerous disciplines. Here, we analyze numerically the optical chiral forces arising in the basic element of photonic integrated circuitry: a dielectric waveguide with rectangular cross-section. Such waveguides are inherently lossless thus generating chiral forces that are invariant in the longitudinal direction and therefore enable enantiomeric separation over long (cm-scale) distances. Assuming Brownian motion in a liquid environment, we calculate first the force strength and time span needed to perform the separation of chiral nanoparticles as a function of the radii. Then we analyze the chiral forces produced by the fundamental quasi-TE guided mode in a silicon nitride waveguide and show that it can lead to enantiomeric separation via the transverse spin at short wavelengths (405 nm). At longer wavelengths (1310 nm), the proper combination of degenerate quasi-TE and quasi-TM modes would result in a quasi-circularly polarized mode with intrinsic chirality (helicity), leading to chiral gradient forces that also enable the enantiomeric separation of smaller nanoparticles. We report particle tracking simulations where the optical force field produced by a quasi-TE and a quasi-circular mode proved to separate enantiomers under a time span of two seconds. Our results suggest the viability of enantiomeric separation using simple photonic integrated circuits, though different wavelength windows should be selected according to the nanoparticle size.

physics.optics↗