Zero-index metamaterials (ZIMs) offer exotic optical properties such as uniform spatial phase and infinite wavelength, as well as photonic applications including super-coupling and omnidirectional phase matching in nonlinear optics.
Here we present an on-chip ZIM consisting of a square array of air-holes in a 220-nm-thick silicon-on-insulator (SOI) wafer. This design enables mass production of ZIM-based photonic devices at low cost and high fidelity using standard CMOS fabrication technology.
To transition from the high-aspect ratio inverse case of silicon pillars under transverse magnetic (TM) polarization, our design is instead intended for a transverse electric (TE) polarization because of TE modes are, in general, better confined than TM modes for a given thin film. Furthermore, the larger volume fraction of silicon provided by the air-holes structure improves the confinement as compared with the silicon-pillars structure. We optimized the design to obtain a zero index corresponding to a finite impedance of 0.8 at 1550 nm. The bandstructure of the metamaterial shows a Dirac-cone dispersion at the center of the Brillouin zone at 1550 nm. These results indicate that this metamaterial possesses an impedance-matched, isotropic zero index at 1550 nm.
To experimentally verify that the metamaterial has a zero index, we fabricated a right-triangular prism measuring twenty unit cells across. The measured effective index of this prism crosses zero linearly at 1630 nm and shows positive and negative indices at short and longer wavelengths, respectively, indicating a Dirac-cone induced zero index. This measurement is in excellent agreement with the result of full-wave simulation.
Recent progress on Si-based optical components for advanced optical communication systems has been demonstrated. The polarization beam splitter with extinction ratio of more than 20 dB and the optical 90-deg hybrid having phase deviation within ±5-deg were obtained using multimode interference structures. The 12 Gb/s modulators and the 20 GHz photodetectors were measured. Benefiting from the unique properties of silicon modulator, an error-free 80 Km transmission of the signals generated by our silicon carrier-depletion Mach-Zehnder modulator was also demonstrated at 10 Gb/s and the power penalty was as low as 1.15 dB. These results show that silicon photonics has a great potential in advanced optical communication systems.
In this paper, we demonstrated recent progress on Si based optical components for advanced optical communication systems. The polarization beam splitter with extinction ratio of more than 20dB and the optical 90° hybrid having phase deviation within ±5° were obtained using MMI structures. The 12Gb/s modulators and the 20GHz photodetectors were measured. Benefiting from the unique properties of silicon modulator, an error-free 80Km transmission of the signals generated by our silicon carrier-depletion Mach-Zehnder modulator was also demonstrated at 10Gb/s and the power penalty was as low as 1.15dB. These results show that silicon photonics has a great potential in advanced optical communication systems.
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