Abstract
We study disorder-induced propagation losses of guided modes in photonic crystal slabs with line-defects. These losses are treated within a theoretical model of size disorder for the etched holes in the otherwise periodic photonic lattice. Comparisons are provided with state-of-the-art experimental data, both in membrane and Silicon-on-Insulator (SOI) structures, in which propagation losses are mainly attributed to fabrication imperfections. The dependence of the losses on the photon group velocity and the useful bandwidth for low-loss propagation are analyzed and discussed for membrane and asymmetric as well as symmetric SOI systems. New designs for further improving device performances are proposed, which employ waveguides with varying channel widths. It is shown that losses in photonic crystal waveguides could be reduced by almost an order of magnitude with respect to latest experimental results. Propagation losses lower than 0.1 dB/mm are predicted for suitably designed structures, by assuming state-of-the-art fabrication accuracy.
Highlights
Photonic crystals (PhC) exploit the periodicity of the refractive index as a mean to artificially manipulate the confinement and propagation characteristics of light in three dimensions [1, 2, 3]
According to the suggestions given in Ref. [22], we show in Fig. 5 the defect mode dispersion and the related propagation losses for reduced-width PhC waveguides, in which the structure parameters are slightly modified with respect to Fig. 3
It has been shown that very low propagation losses may be achieved in Siliconbased photonic crystal waveguides by the combined use of highly developed fabrication technology and properly designed guided mode dispersion
Summary
Photonic crystals (PhC) exploit the periodicity of the refractive index as a mean to artificially manipulate the confinement and propagation characteristics of light in three dimensions [1, 2, 3]. Owing to the difficulties in fabricating fully three-dimensional periodic systems with controlled defects at optical wavelengths, two-dimensional photonic crystals embedded in planar waveguides are emerging as important candidates for prospective applications to integrated optics [4, 5, 6] In such systems, called PhC slabs, the in-plane confinement of light provided by the spatial periodicity of an etched dielectric material is added to the usual dielectric guiding mechanism along the vertical direction. It has become of crucial importance to understand the out-of-plane scattering of light, leading to attenuation and losses in photonic integrated waveguides and resonators realized in PhC slabs.
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