Ultra-wideband flat anomalous dispersion in nanostructured silicon membrane waveguides (Conference Presentation)

The Si transparency (1.1 μm – 8 μm wavelength) contains the strongest absorption features of a wide range of chemical and biological substances. However, the use of SOI in the mid-IR is hampered by the large absorption of the buried oxide (BOX) for wavelengths above 4 μm. Silicon membranes have garnered great interest for their unique capability to overcome the BOX limitation while leveraging the advantages of Si photonics. On the other hand, silicon is uniquely poised for the implementation of wideband mid-IR sources based on nonlinear frequency generation. Promising supercontinuum and frequency comb generation have already been demonstrated in Si. Still, current implementations have a limited flexibility in the engineering of phase-matching conditions and dispersion, which complicates the shaping of the nonlinear spectrum. Patterning Si with features smaller than half of the wavelength (well within the capabilities of standard large-volume fabrication processes) has proven to be a simple and powerful tool to implement metamaterials with optimally engineered properties. Here, we present the design of nanostructured silicon membrane waveguides with ultra-wideband flat anomalous dispersion in a wavelength span exceeding 5 µm. Our three-dimensional finite difference time domain (FDTD) calculations predict flat anomalous dispersion near 50 ps/km⋅nm between 2.5 µm and 8 µm wavelength. These results illustrate the potential of subwavelength metamaterial engineering to control chromatic dispersion in Si membrane waveguides. This is a promising step towards the implementation of wideband nonlinear sources in the mid-IR for silicon photonics.