Abstract
Waveguide gratings are used for applications such as guided-mode resonance filters and fiber-to-chip couplers. A waveguide grating typically consists of a stack of a single-mode slab waveguide and a grating. The filling factor of the grating with respect to the mode intensity profile can be altered via changing the waveguide’s refractive index. As a result, the propagation length of the mode is slightly sensitive to refractive index changes. Here, we theoretically investigate whether this sensitivity can be increased by using alternative waveguide grating geometries. Using rigorous coupled-wave analysis (RCWA), the filling factors of the modes of waveguide gratings supporting more than one mode are simulated. It is observed that both long propagation lengths and large sensitivities with respect to refractive index changes can be achieved by using the intensity nodes of higher-order modes.
Highlights
We theoretically investigate whether this sensitivity can be increased by using alternative waveguide grating geometries
Passive and low-loss planar optical waveguides can transport light over large areas [1–4]. When they are combined with optical elements such as diffraction gratings, they can be used for applications such as optical filters [5–10] and sensors [11–17] via exploiting guided mode resonances
The results presented in this study show a way to drastically increase both the propagation length and sensitivity of waveguide grating by using the TE1 mode, as long as the grating thickness is small, compared with the waveguide grating thickness
Summary
Passive and low-loss planar optical waveguides can transport light over large areas [1–4]. Only the spectral positions of resonance are sensitive to refractive index changes, while the corresponding propagation length Lprop remains almost constant. This circumstance indicates the necessity of spectrometers for such devices based on waveguide gratings. It has been shown that intensity nodes of TE modes (s-polarized modes with a transversal electric field node) can be used to maximize the propagation length [23–25] by placing a lossy, diffractive, or scattering structure at the node position This way, spectrally narrow resonances can be obtained [26]. It has been estimated that such node modes should provide high sensitivities, Optics 2022, 3 structure at the node position
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