Group IV photonics for the mid infrared

This paper outlines the challenges and benefits of applying silicon-based photonic techniques in the 2 to 5 mu m mid-infrared (MIR) wavelength range for chem.-bio-physical sensing, medical diagnostics, industrial process control, environmental monitoring, secure communications, Ladar, active imaging, and high-speed communications at 2 mu m. On-chip passive and active components, mostly waveguided, will enable opto-electronic CMOS or BiCMOS integrated circuits for system-on-a-chip applications such as spectroscopy and lab-on-a-chip. Volume manufacture in a silicon foundry is expected to yield low-cost (or even disposable) chips with benefits in size-weight-power and ruggedness. This is long-wavelength optoelectronic integration on silicon which we call LIOS. Room temperature operation appears feasible, albeit with performance compromises at 4 to 5 mu m. In addition to the electronics layer (which may include RF wireless), a 3-D LIOS chip can include several inter-communicating layers utilizing the photonic, plasmonic, photonic-crystal and opto-electro-mechanical technologies. The LIOS challenge can be met by (1) discovering new physics, (2) employing new IV and III-V alloys, (3) scaling-up and modifying telecom components, and (4) applying nonlinear-optical wavelength conversion in some cases. This paper presents proposals for MIR chip spectrometers employing frequency-comb and Ge blackbody sources. Active heterostructures employing Si, Ge, SiGe, GeSn and SiGeSn are key for laser diodes, photodetectors, LEDs, switches, amplifiers, and modulators that provide totally monolithic foundry integration, while numerous III-V semiconductor MIR devices within the InGaAsSb and InGaAsP families offer practical hybrid integration on Si PICs. Interband cascade and quantum cascade lasers on Ge waveguides are important in this context.