Silicon on sapphire and SOI photonic devices for mid-infrared and near-IR wavelengths

Conventional SOI waveguide technology, serving as the foundation of near-IR photonics, meets its limitation in mid-IR due to high loss associated with the buried oxide. Silicon-on-sapphire (SOS) waveguides are considered as a good mid-IR alternative, because the transparency window of sapphire is up to 6 μm and SOS waveguides are compatible with SOI technology. We show that properly-designed SOS waveguides can facilitate frequency band conversion between near-IR and mid-IR. An indirect mid-IR detection scheme is proposed and the mid-IR signal is down-converted to telecommunication wavelength (1.55 μm) through SOS waveguides and indirectly detected by near-IR detectors. The performance of the indirect mid-IR detection scheme is discussed. Particularly we model and compare the noise performance of the indirect detection with direct detection using state-of-the-art mid-IR detectors. In addition to advantages of room temperature and high-speed operation, the results show that the proposed indirect detection can improve the electrical signal-to-noise ratio up to 50dB, 23dB and 4dB, compared to direct detection by PbSe, HgCdTe and InSb detectors respectively. The improvement is even more pronounced in detection of weak MWIR signals. In order to further boost the performance, we also investigate mechanisms to increasing the conversion efficiency in SOS waveguide wavelength converters. The conversion efficiency can be improved by periodically cascading SOS waveguide sections with opposite dispersion characteristics to achieve quasi-phase-matching. Conversion efficiency enhancement over 30dB and the conversion bandwidth increased by 2 times are demonstrated, which may facilitate the fabrication of parametric oscillators that can improve the conversion efficiency by 50dB.