We report photon–phonon atomic coherence (cascade- and nested-dressing) interaction from the various phase transitions of Eu³⁺: BiPO₄ crystal. Such atomic coherence spectral interaction evolves from out-of-phase fluorescence to in-phase spontaneous four-wave mixing (SFWM) by changing the time gate. The dressing dip switch and three dressing dips of SFWM result from the strong photon–phonon destructive cross- and self-interaction for the hexagonal phase, respectively. More phonon dressing results in the destructive interaction, while less phonon dressing results in the constructive interaction of the atomic coherences. The experimental measurements of the photon–phonon interaction agree with the theoretical simulations. Based on our results, we proposed a model for an optical transistor (as an amplifier and switch).

We report a plasmonic–dielectric metasurface that offers dynamic control over chiroptical properties, adjustable Q-factors, and inter-band chirality manipulation through multiple symmetry-breaking mechanisms. By controlling chiral quasi-bound states in the continuum (BIC) modes and Fano resonances, we enable hybridized and independently tunable spectral responses, offering precise control over resonance amplitude, polarization sensitivity, and refractive index sensing with high flexibility. Chirality is induced by rotating silicon nanofins on a dielectric spacer with a gold backplate, enabling tunable chiroptical responses with controllable spectral linewidth and independent or simultaneous dual-wavelength band excitation. We report a novel phenomenon of controlling interplay of chirality between two closely positioned wavelength bands to tailor symmetry breaking for a specific resonant mode (chiral) while preserving symmetry for the other mode (achiral). Additionally, we report the phase-sensitive evolution of Fano resonance from pure reflectance dip when controlled by dielectric spacer height and further demonstrated phase-insensitive control of Fano resonance amplitude. We divided Fano resonance into a distinct spectral peak and dip to improve light manipulation within the metasurface. Our proposed sensor demonstrates sensitivity and a quality factor of about 435 nm/RIU and 3888, respectively. Furthermore, we compared different phenomena (chiral selectivity, quasi-BIC, Fano) and sensing parameter values for different metasurface configurations (including single nanofin and absence of a spacer) and observed that the configuration without a spacer achieved the highest sensitivity of approximately 640 nm/RIU.

The ultra-wideband polarization converters have been of interest to researcher due to their demand in satellite communication and navigation systems. This paper presents an ultra-wideband reflective cross-polarization converter comprising a stair-shaped metasurface. By observation, the alleged structure allows the conversion of linearly polarized waves to orthogonal components, having a polarization conversion ratio of greater than 90% spread across the large frequency range of 12.94 to 16.54 GHz and 17.54 to 26 GHz. A highly efficient, ultra-high frequency polarization conversion is achieved by the utilization of strong electromagnetic resonance coupling between the upper and lower layers of the metasurface. Further, it is depicted that the polarization converter has a wide obliquity of incidence wave. Moreover, the simulation and measured results show a good match. The linear polarization converter is simple in design but is of high performance, and therefore, might be useful in satellite communication, imaging systems, and navigation systems.

We report non-Hermitian energy level alignment via photon–phonon dressing quantization. We propose a spectral homogenizer based on four types of alignment, revealing that the reverse dressing effect induces this alignment.

In this paper, we explore the asymmetry observed between the effects of photon–phonon coupling (nested-dressing) and a crystal field (CF) on the fine structure of fluorescence (FL) and spontaneous four-wave mixing (SFWM) in Eu³⁺: BiPO₄ and Eu³⁺: NaYF₄. The competition between the CF and the strong photon–phonon dressing leads to dynamic splitting in two directions. The CF leads to static splitting in one direction under weak phonon dressing. The evolution from strong dressing to weak dressing results in spectral asymmetry. This spectral asymmetry includes out-of-phase FL and in-phase SFWM. Further, the large ratio between the dressing Rabi frequency and the de-phase rate leads to strong FL and SFWM asymmetry due to photon–phonon constructive dressing. Moreover, the experimental results suggest the analogy of a spectra asymmetry router with a channel equalization ratio of 96.6%.

Optical hybrid communication is one of the key fields of quantum communications, where scientists are focusing to integrate classical and quantum system as single hybrid system. In this regard, we realized optical hybrid switch using second-order fluorescence (FL) and spontaneous parametric four-wave mixing (SPFWM). The hybrid signal contains Stokes and the FL signal which can be distinguished using power of incident beam. In addition, we investigate the resonant and off-resonant excitation spectrum of negatively charged Nitrogen-vacancy (NV ⁻ ) center in diamond. The hybrid switch is realized by results obtained in time domain and intensity noise correlation. The optical hybrid switch can be controlled by power of incident beams. The hybrid index and temporal width contrast of the hybrid switch are about 4 and 90%, respectively.