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.