Toward Chiral Sensing and Spectroscopy Enabled by All‐Dielectric Integrated Photonic Waveguides

Abstract

Chiral spectroscopy is a powerful technique enabling to identify optically the chirality of matter. So far, most experiments to check the chirality of matter or nanostructures have been performed through arrangements wherein both the optical excitation and detection are realized via circularly polarized light propagating in free space. However, for the sake of miniaturization, it would be desirable to perform chiral spectroscopy in photonic integrated platforms, with the additional benefit of massive parallel detection, low‐cost production, repeatability, and portability. Here it is shown that all‐dielectric photonic waveguides can support chiral modes under proper combination of fundamental eigenmodes. Two mainstream configurations are investigated: a dielectric wire with square cross section and a slotted waveguide. Three different scenarios in which such waveguides could be used for chiral detection are numerically analyzed: waveguides as near‐field probes, evanescent‐induced chiral fields, and chiroptical interaction in void slots. In all the cases, a metallic nanohelix is considered as a chiral probe, though all the approaches can be extended to other kinds of chiral nanostructures as well as matter. These results establish that chiral applications such as sensing and spectroscopy could be realized in standard integrated optics, in particular, with silicon‐based technology.

Collimating the growth of twisted crystals of achiral compounds

“…Optical fibers conventionally transmit linear polarization as transverse electric (TE) and transverse magnetic (TM) modes 41 . Waveguiding with circularly polarized modes is attractive for a variety of applications 50 and can be achieved with a chiral medium 51–53 . Though likely only marginally relevant to spherulitic growth of molecular crystals, helically twisted photonic bundles of silica fibers exploit their dissymmetry to control the orbital angular momentum of light 54 …”

“…Photoluminescence can also be measured using a laser light source above the waveguide. Source : Modeled from Vázquez‐Lozano and Martínez 50 …”

Surface-Enhanced Circular Dichroism Spectroscopy on Periodic Dual Nanostructures

“…Since the seminal contributions of Y. Tang and A. E. Cohen, several nanophotonic platforms have been proposed to augment the sensitivity of CD experiments through the local and global enhancement of C ( r ), the local density of electromagnetic chirality. To mention a few, high refractive index nanoparticles, − plasmonic chiral , and nonchiral nanoantennas, − optical waveguides, and metasurfaces − have been explored as enablers of surface-enhanced circular dichroism and other chiral spectroscopy techniques.…”

Elliptical Birefringent Rib‐Channel Chirowaveguides for Quasicircularly Polarized Light Applications in Integrated Photonics

“…[10,11] The simplest idea to allow CPL propagation in PICs without loss of polarization is to suppress the linear birefringence LB with zero-birefringence (ZBR) waveguides. ZBR in channel waveguides is reached for some exact given geometries, such as square-shape buried channels, [12,13] rib channels, [14] strip-loaded channels, [15] and ridge channels. [16] In all these examples, the fabrication constraints are tedious and the slightest deviation from the ideal-channel geometry leads to nonzero LB.…”