Creating large bandwidth line defects by embedding dielectric waveguides into photonic crystal slabs

Abstract

We introduce a general designing procedure that allows us, for any given photonic crystal slab, to create an appropriate line defect structure that possesses single-mode bands with large bandwidth and low dispersion within the photonic band-gap region below the light line. This procedure involves designing a high index dielectric waveguide that is phase matched with the gap of the photonic crystal slab, and embedding the dielectric waveguide as a line defect into a crystal in a specific configuration that is free of edge states within the guiding bandwidth. As an example, we show a single mode line defect waveguide with a bandwidth approaching 13% of the center-band frequency, and with a linear dispersion relation throughout most of the bandwidth.

Mode mixing in asymmetric double-trench photonic crystal waveguides

“…At the same time the mode is guided by the photonic band gap and correspondingly, radiation losses at sharp bends might be significantly suppressed. This idea has been extended further 6,7 to the case of a triangular lattice of holes in high-refractive index slab which is believed to be a more fabrication-friendly design. It has been proposed to replace the line defect in a PhC slab with low-index oxide 7 or high-index strip waveguide 6 , thus producing single-mode gap guiding with bandwidth spanning over 60% of the photonic band gap width.…”

“…It has been proposed to replace the line defect in a PhC slab with low-index oxide 7 or high-index strip waveguide 6 , thus producing single-mode gap guiding with bandwidth spanning over 60% of the photonic band gap width. Consideration of the truncation of the PhC lattice has been shown to be important to eliminate the influence of surface states on the waveguiding mode 6,8 .…”

“…At the same time group velocity dispersion is large owing to lattice-induced distributed feedback along the propagation direction 4 . Recently another waveguide design has attracted much attention, where the conventional single-mode strip waveguide is embedded into a PhC slab 6 (also known as the double-trench waveguide). It combines the best features of PhC slabs, such as strong localization of the waveguiding mode with the potential to suppress radiation losses at bends, with a broad bandwidth and linear dispersion characteristic of strip waveguides.…”

“…Two-dimensional slab-type silicon photonic crystals (PhC) are seen as a possible platform for dense integration of photonic integrated circuits (IC) on a chip-scale level 1,2,3,4,5,6,7,8,9 . Single-mode PhC waveguides are typically defined by introducing a line defect in an otherwise perfect periodic lattice, for example omitting one row of holes creates the so-called W1 waveguide 1,2,3,4,5,9 .…”

Coupling techniques between dielectric waveguides and planar photonic crystals.

“…In figure 2.12(c), the central row of columns is shifted up to be aligned with the adjacent rows [Yam02]. Finally, in figure 2.1.2(d), the row of columns is replaced by a dielectric waveguide to create the waveguide [Lau02]. One important point for any waveguide design is trying to maintain the periodicity of the lattice, which is only achieved in the above examples for the cases shown in figures 2.11, 2.12(b) and 2.12(d).…”