A new type of device consisting of a lithium niobate film coupled with a distributed Bragg reflector (DBR) was theoretically proposed to explore and release Bloch surface waves for applications in sensing and detection. The film and grating made of lithium niobate (LiNbO3) were placed on both sides of the DBR and a concentrated electromagnetic field was formed at the film layer. By adjusting the spatial incidence angle of the incident light, two detection and analysis modes were obtained, including surface diffraction detection and guided Bloch detection. Surface diffraction detection was used to detect the gas molecule concentrations, while guided Bloch detection was applied for the concentration detection of biomolecule-modulated biological solutions. According to the drift of the Fano curve, the average sensor sensitivities from the analysis of the two modes were 1560 °/RIU and 1161 °/RIU, and the maximum detection sensitivity reached 2320 °/RIU and 2200 °/RIU, respectively. This study revealed the potential application of LiNbO3 as a tunable material when combined with DBR to construct a new type of biosensor, which offered broad application prospects in Bloch surface wave biosensors.
A compact and broadband polarization beam splitter (PBS) is proposed based on an asymmetric directional coupler consisting of a hybrid plasmonic waveguide and a ridge waveguide on lithium-niobate-on-insulator. Due to the surface plasma polariton (SPP) effect, the phase-matching condition is satisfied for transverse electric polarization, whereas the transverse magnetic polarization has a significant phase mismatch by choosing reasonable widths of both waveguides. A short (∼28 μm long) PBS is designed while the gap width is chosen to be 200 nm to make it easy to fabricate. Numerical simulations show that the designed PBS has a broad bandwidth (>130 nm) for an extinction ratio of >15 dB and a large fabrication tolerance for the variation of the waveguide width (over AE50 nm).
A polarization beam splitter (PBS) is proposed based on an asymmetric directional coupler consisting of a silicon nitride assisted waveguide and two ridge waveguides on a lithium niobate on insulator. Due to the silicon nitride buffer layer, the phase-matching condition is satisfied for TE polarization, whereas TM polarization has a significant phase mismatch by choosing reasonable widths of three waveguides. A 112.2-μm-long PBS is designed, and the gap width is chosen to be 300 nm to make it easy to fabricate. Numerical simulations show that the designed PBS has a broad bandwidth (>80 nm) for an extinction ratio of >15 dB and an ultralow insertion loss (<0.35 dB).
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