Directional luminescence of the diamond NV center via Bloch surface waves in one-dimensional photonic crystals

In this work, we numerically study the luminescence of nanodiamonds with NV centres embedded in a polymer layer on the surface of one-dimensional photonic crystal. The interaction of NV center spontaneous emission with the Bloch surface wave (BSW) is demonstrated. The presence of a photonic crystal leads to a change in the angular distribution of the emitter radiation due to the coupling of luminescence to BSW. We show that the best coupling efficiency of 71% is observed when NV centres are located in the close proximity to the BSW field maximum.

High-Q two-groove resonator for all-dielectric Bloch surface wave platform

We propose a simple integrated resonant structure for the Bloch surface wave platform, which consists of two subwavelength grooves patterned on the surface of a one-dimensional dielectric photonic crystal. We demonstrate that the investigated structure can operate in a parasitic-scattering-free regime and, in this case, provide unity transmittance and zero reflectance at resonance conditions associated with the excitation of a leaky mode of the structure localized at the central ridge formed by the grooves. The proposed structure may find application in integrated photonic devices for optical filtering and analog optical computing.

Theoretical Model for a Highly Sensitive Near Infrared Biosensor Based on Bloch Surface Wave with Dirac Semimetal

In this work, we present a theoretical model of a near-infrared sensitive refractive index biosensor based on the truncate 1D photonic crystal (1D PC) structure with Dirac semimetal. This highly sensitive near-infrared biosensor originates from the sharp reflectance peak caused by the excitation of Bloch surface wave (BSW) at the interface between the Dirac semimetal and 1D PC. The sensitivity of the biosensor model is sensitive to the Fermi energy of Dirac semimetal, the thickness of the truncate layer and the refractive index of the sensing medium. By optimizing the structural parameters, the maximum refractive index sensitivity of the biosensor model can surpass 17.4 × 103/RIU, which achieves a certain competitiveness compared to conventional surface plasmon resonance (SPR) or BSW sensors. Considering that bulk materials are easier to handle than two-dimensional materials in manufacturing facilities, we judge that 3D Dirac semimetal and its related devices will provide a strong competitor and alternative to graphene-based devices.

Sensitive THz sensing based on Fano resonance in all-polymeric Bloch surface wave structure

Simultaneous realization of high quality factor (Q), sensitivity, and figure of merit (FOM) play a pivotal role in building the THz sensor. For such purpose, we propose an all-polymeric Bloch surface wave (BSW) structure that supports a bright BSW mode and a dark surface Fano state that is embedded in the continuum, both of which coupled to the same radiation channels. The existence of the sharp dip with a maximum depth of Fano line could be interpreted with the physics of Friedrich–Wintgen bound states in the continuum (FW-BICs), because of the destructive interference between bright BSW and dark surface Fano modes. A strong angular- and frequency-dependent Q was found. Related influential factors to Q value may also include an asymmetric arrangement of top and grating layers, together with the weak coupling provided by photonic crystals. One numerically optimized design shows a quality factor Q of the Fano mode as 23,670, which is almost two orders higher than that in conventional metallic-metamaterial-based designs. The optimized sensitivity can numerically reach 4.34 THz/RIU in the frequency domain, which is one order higher than that reported in all-dielectric metasurfaces. We infer the high sensitivity is related to the phase-matching condition provided by near-subwavelength gratings. The associated FOM can reach 8857/RIU. Besides, the proposed design also numerically demonstrates high sensitivity in the angular domain ∼125.5°/RIU. Considering it poses no specific requirement for materials that own high contrast of permittivity in the THz regime, large interfacing area, the mechanical and chemical robustness offered by polymers and low cost in fabrication, such all-polymeric BSW structure that supports novel Fano resonance in THz window may give access to rich applications in hazardous gas detection and label-free bio-sensing.

Integrated diffraction gratings on the Bloch surface wave platform supporting bound states in the continuum

We propose and theoretically and numerically investigate integrated diffraction gratings for the Bloch surface wave (BSW) platform, which have subwavelength or near-subwavelength period. We demonstrate that, in the oblique incidence geometry of a transverse-electric polarized BSW and with a properly chosen band gap configuration of the photonic crystal supporting the surface waves, the proposed structures operate in the scattering-free regime, when the energy of the incident BSW is divided between the reflected and transmitted BSWs with the same polarization corresponding to the propagating diffraction orders of the grating, and not scattered away from the propagation surface. In this regime, the studied integrated gratings support high-Q resonances and bound states in the continuum not only in the subwavelength case when only the specular (zeroth) diffraction orders propagate, but also in the case when non-evanescent zeroth and −1st diffraction orders satisfy the so-called Littrow mounting condition. The proposed integrated gratings on the BSW platform can be used as efficient narrowband spatial or spectral filters operating in reflection, or as BSW beam splitters or deflectors operating in transmission. The obtained results may find application in two-dimensional photonic circuits for steering the BSW propagation.

Unidirectional propagation of the Bloch surface wave excited by the spinning magnetic dipole in two-dimensional photonic crystal slab

The photonic spin Hall effect (PSHE) can be realized in a photonic crystal (PC) slab, that is, the unidirectional Bloch surface wave can propagate along the surface of the PC slab under the excitation of elliptical polarized magnetic dipole. It is further proved that PSHE is caused by the interference of the component surface waves excited by the different components of the incident light, which is the so called component wave interference (CWI) theory. In addition, we also find that the spin of the surface wave oscillates periodically in space, and the oscillation period is a unit cell. In a unit cell, the average spin keeps the spin orbit locked. The results show that the spin separation can also be modulated by the position and the polarization state of the magnetic dipole.