Arbitrary Polarization Conversion with a Photonic Crystal Slab

Abstract

Our structure consists of a photonic crystal slab patterned with a square array of air holes introduced into the dielectric slab and a mirror underneath, as illustrated in Figure 1. We choose the periodicity of the structure such that within the wavelength It is shown that a simple photonic crystal slab structure provides a powerful mechanism for the control of the polarization properties of light. For a lossless system, for a given incident light with any fixed polarization, one can generate arbitrary polarization in the reflected light, as one varies the direction of the incident light. In the lossy system, the capability for arbitrary polarization generation is still preserved for s-or p-polarized incident light. This capability for arbitrary polarization generation closely relates to the nontrivial topological properties of the reflection matrix of the structure and exists over a wide range of frequencies.

Circularly Polarized States Spawning from Bound States in the Continuum

“…In recent years, great attention has been paid to modulate polarization of light with compact structures such as metasurfaces [4][5][6][7] instead of classical wave plates and polarizers, which are more applicable in on-chip devices. On the other hand, application of another kind of structure, photonic crystal (PhC) slab, in modulating polarization, is capturing interest nowadays [8][9][10][11]. Their simplicity in fabrication, designable band structures, and complex polarization features in the momentum space which are topologically linked with bound states in the continuum [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] are favorable for polarization modulation.…”

“…On the other hand, application of another kind of structure, photonic crystal (PhC) slab, in modulating polarization, is capturing interest nowadays [8][9][10][11]. Their simplicity in fabrication, designable band structures, and complex polarization features in the momentum space which are topologically linked with bound states in the continuum [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] are favorable for polarization modulation. However, the reported PhC slabs only support nearly linearly polarized resonances which only cover a small area on the Poincaré sphere.…”

Topological scattering singularities and embedded eigenstates for polarization control and sensing applications

“…The topological nature of EEs has spun-off several research efforts, exploring the merging of EE charges to produce even more confined resonances in realistic systems [26] and unidirectional guided modes within the continuum [27]. The topological properties of EEs have been especially useful for polarization control, as it was shown that topologically protected polarization conversion is possible [28][29][30], and circularly polarized states can arise from BICs by breaking spatial symmetries [31][32][33]. Recently, the generation of vortex beams through EEs [34] and efficient topological vortex laser generation [35] were demonstrated, showing the potential of topological phenomena in radiative and scattering processes.…”

On-Chip Ultra-Small Arbitrary-Elliptical-Polarization Converters

“…In order to achieve high-density and multi-function on-chip integration, optical devices are required to expand their functions while further reducing their size. It is an alternative way to use elliptical polarization in order to increase information capacity [22,26]. However, existing elliptical polarization converters take advantage of transmission or reflection of metasurfaces, and convert light in free space, which are not easy to be compatible with on-chip integration [22].…”