Ultra-compact on-chip slot Bragg grating structure for small electric field detection

In this paper, we present an ultra-compact 1D photonic crystal(Ph C) Bragg grating design on a thin film lithium niobate slot waveguide(SWG) via 2D-and 3D-FDTD simulations. 2D-FDTD simulations are employed to tune the photonic bandgap(PBG) size, PBG center, cavity resonance wavelength, and the whole size of Ph C. 3DFDTD simulations are carried out to model the real structure by varying different geometrical parameters such as SWG height and Ph C size. A moderate resonance quality factor Q of about 300 is achieved with a Ph C size of only 0.5 μm× 0.7 μm× 6 μm. The proposed slot Bragg grating structure is then exploited as an electric field(E-field) sensor. The sensitivity is analyzed by 3D-FDTD simulations with a minimum detectable E-field as small as 23 m V∕m. The possible fabrication process of the proposed structure is also discussed. The compact size of the proposed slot Bragg grating structure may have applications in on-chip E-field sensing, optical filtering, etc.

Experimental evidence of Bloch surface waves on photonic crystals with thin-film LiNbO_3 as a top layer

Strong nonlinear, electro-optical, and thermo-optical properties of lithium niobate(LN) have gained much attention. However, the implementation of LiNbO_3 in real devices is not a trivial task due to difficulties in manufacturing and handling thin-film LN. In this study, we investigate an optical device where the Bloch surface wave(BSW) propagates on the thin-film LN to unlock its properties. First, access to the LN film from air(or open space) is important to exploit its properties. Second, for sustaining the BSW, one-dimensional photonic crystal(1DPhC) is necessary to be fabricated under the thin-film LN. We consider two material platforms to realize such a device: bulk LN and commercial thin-film LN. Clear reflectance dips observed in far-field measurements demonstrate the propagation of BSWs on top of the LN surface of the designed 1DPhCs.