Bridging the mid-infrared-to-telecom gap with silicon nanophotonic spectral translation

Extending beyond traditional telecom-band applications to optical interconnects(1), the silicon nanophotonic integrated circuit platform also has notable advantages for use in high-performance mid-infrared optical systems operating in the 2-8 mu m spectral range(2,3). Such systems could find applications in industrial and environmental monitoring(4), threat detection(5), medical diagnostics(6) and free-space communication(7). Nevertheless, the advancement of chip-scale systems is impeded by the narrow-bandgap semiconductors traditionally used to detect mid-infrared photons. The cryogenic or multistage thermo-electric cooling required to suppress dark-current noise(8), which is exponentially dependent on E-g/kT, can restrict the development of compact, low-power integrated mid-infrared systems. However, if the mid-infrared signals were spectrally translated to shorter wavelengths, wide-bandgap photodetectors could be used to eliminate prohibitive cooling requirements. Furthermore, such detectors typically have larger detectivity and bandwidth than their mid-infrared counterparts(8). Here, we use efficient four-wave mixing in silicon nanophotonic wires(9-12) to facilitate spectral translation of a signal at 2,440 nm to the telecom band at 1,620 nm, across a span of 62 THz. Furthermore, a simultaneous parametric translation gain of 19 dB can significantly boost sensitivity to weak mid-infrared signals.