Multiplexed rectangular dielectric gratings with multiple narrow-band refractive index filtering and sensing.

We propose a low-loss compound structure consisting of a multiplexed rectangular dielectric grating and a waveguide layer, which can function as multi-band optical filters and sensors in TE and TM polarization by utilizing the resonant mode of the waveguide (WG) and the hybrid SP, respectively. By manipulating the parameters and subsequently constraining the local density of multi-resonant modes to several distinct resonant wavelengths, we propose a novel category of highly sensitive refractive index sensing platforms. Spectral shifts ranging from 110 to 131 nm/RIU with FOM of (22, 26.2)/RIU under TE polarization and 80 to 114 nm/RIU with FOM of (5.7, 8.1)/RIU under TM polarization can be accurately discerned for multiple individual analytes across a broad spectral range. The proposed structures offer enhanced flexibility in the design of structures across a wide spectral range, catering to various potential applications in multi-band optical filters, sensors, and photodetectors.

Narrower-band multiplet resonances of surface plasmons on periodically phase-shifted metal gratings.

In this Letter, we report properties of surface plasmon resonances (SPRs) on metal gratings with periodic phase shifts, in which high-order SPR modes corresponding to the long-pitch (a few to tens of wavelengths, λ) phase shifts are excited, instead of those corresponding to the short-pitch (∼λ) gratings. In particular, it is shown that, for quarter-phase shifts, spectral features of doublet SPR modes with narrower bandwidths are notably present when the underlying first-order short-pitch SPR mode is designed to be located between an arbitrarily chosen pair of neighboring high-order long-pitch SPR modes. Also, the positions and interspacing of the doublet SPR modes can be arbitrarily tuned by adjusting the pitch values. Resonance characteristics of this phenomenon are numerically investigated, and an analytical formulation based on coupled-wave theory is developed to elucidate the resonance conditions. Characteristics of the narrower-band doublet SPR modes may find application in the resonant control of light-matter interactions involving photons of multiple frequencies, and in high-precision SPR sensing with multi-probing channels.

Multiplet independent resonance modes in multiplexed gratings.

Resonance modes in usual optical resonators are orthogonal, but correlated and their resonance properties cannot be independently controlled. Multiplexed gratings, consisting of multiple harmonic grating features, show multiplet resonance modes that can be independently adjusted. This offers flexibility in designing resonance characteristics for various potential applications in nonlinear optics and controlling/enhancement of light-matter interactions, e.g., to resonantly enhance the local densities of photonic modes of both the excitation and emission light in photoluminescence, which cannot be intentionally achieved with conventional resonators. Here we report the design, characteristics and experimental implementation of the multiplexed metal gratings that have doublet or triplet resonance modes. Based on numerical simulations, we investigated dependences of the resonance modes, field distributions and local field enhancements on structure features of the gratings. In implementation, we elaborated the experimental considerations, and demonstrated the consistency in structure features and their resonance characteristics for designed and as-fabricated multiplexed grating resonators.