Experimental demonstration of waveguiding in honeycomb and square-lattice silicon photonic crystal membranes

Sub-micron waveguides and cavities have been shown to produce the confinement of elastic and optical waves in the same devices in order to benefit from their interaction. It has been shown that square and honeycomb lattices are the most suitable to produce simultaneous photonic and phononic band gaps on suspended silicon slabs. The introduction of line defects on such "phoxonic" (or optomechanical) crystals should lead to an enhanced interaction between confined light and sound. In this work we report on the experimental measurements of light guiding through waveguides created in these kinds of two-dimensional photonic crystal membranes. The dimensions of the fabricated structures are chosen to provide a "phoxonic" bandgap with a photonic gap around 1550 nm. For both kinds of lattice, we observe a high-transmission band when introducing a linear defect, although it is observed for TM polarization in the honeycomb lattice and for TE in the square. Using the plane-wave expansion and the finite element methods we demonstrate that the guided modes are below the light line and, therefore, without additional losses beside fabrication imperfections. Our results lead us to conclude that waveguides implemented in honeycomb and square lattice "phoxonic" crystals are a very suitable platform to observe an enhanced interaction between propagating photons and phonons.