Abstract
A photonic crystal slab structure with one-dimensional periodicity, obtained by preferential etching of a silicon-on-insulator wafer, is numerically investigated in 3-D. The etched grooves are considered to be filled either with an isotropic or with a Nematic Liquid Crystal (NLC) material. The molecular director is calculated using a consistent model of NLC reorientation under an external voltage. Different structures together with a broad range of voltage values are numerically simulated by means of a three-dimensional finite-difference timedomain method. The shifting of the photonic bandgap induced by the applied voltage, as well as its sensitivity in terms of refractometric applications, are discussed for a range of different structure geometries. [DOI: 10.2971/jeos.2009.09017]
Highlights
Photonic Crystals (PhCs) are periodic optical structures in one, two or three dimensions and due to their property of prohibiting light transmission inside a certain range of wavelengths they have attracted continually growing attention in the field of sensing systems and communications [1]
Based on this principle the design and fabrication of micro-metre scale optical devices filled with polymers and Liquid Crystals (LCs) is presented in [15] and the experimental characterisation of the nematic liquid crystal channel waveguide is reported in [16]
The reference dashed curve corresponds to a structure of infinite W1 and W2, similar to the case of the two dimensional structures studied in [18] and here it has been calculated by artificially imposing periodic conditions along the x-axis in the 3D simulation
Summary
Photonic Crystals (PhCs) are periodic optical structures in one, two or three dimensions and due to their property of prohibiting light transmission inside a certain range of wavelengths they have attracted continually growing attention in the field of sensing systems and communications [1]. Our approach consists in exploiting the very high selectivity of anisotropic etching on monocrystalline silicon, which is a process that naturally leads to very smooth sidewalls and well-controlled geometries Based on this principle the design and fabrication of micro-metre scale optical devices filled with polymers and Liquid Crystals (LCs) is presented in [15] and the experimental characterisation of the nematic liquid crystal channel waveguide is reported in [16]. The transmission spectra are acquired by performing an FFT at the exit of the grating region, before the taper transition (cross-section AA’, Figure 1) and are normalized with respect to the transmission of a single mode un-patterned silicon rib waveguide of constant width W1 = W2 = 450 nm and equal length. The optical structure analysis is initially focused on the case where the etched area is filled with an isotropic material invariant to any external tuning and further when the grooves are infiltrated with a highly birefringent NLC under the application of the external electrical field
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