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eSNR improvement in indirect detection of mid-IR signals by wavelength conversion in SOS waveguides

With a transparency window up to 6 μm, sapphire can serve as a platform to support silicon photonic integrated circuit in MWIR. Planar waveguide devices based on silicon-on-sapphire (SOS) are emerging as a bridge between MWIR and SWIR through frequency band conversion process. While these devices are widely proposed to amplify MWIR signals and generate MWIR source, it can also be inversely utilized to achieve MWIR light detection. Here MWIR signals are down-converted to telecommunication wavelength (1.55 μm) through SOS waveguides and indirectly detected by SWIR detectors. Since detectors at telecommunication wavelengths exhibit superior performances in terms of speed, noise and sensitivity, the indirect detection scheme can be a promising candidate to improve the detection performance. In this report, we analyze performance of the indirect detection of MWIR signals by wavelength conversion in SOS waveguides. Particularly we modeled and compared the noise performance of the indirect detection with direct detection using state-of-the-art MWIR detectors. We show that, in addition to advantages of room temperature and high speed operation, 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 more pronounced in detection of weak MWIR signals.