UC Santa Barbara

The mid-infrared spectral region, ~2–20 µm, is of interest for numerous sensing, medical, industrial, and military applications. The rovibrational transition energies of many important molecules fall within this region, making mid-infrared light particularly suitable for gas-sensing or material identification. Mid-infrared chemical bond spectroscopy of the earth’s atmosphere and planetary bodies helps improve our understanding of greenhouse gases, pollutants, and biochemical compositions. Defense technologies, including scene illumination and infrared counter-measures, benefit from high-power mid-infrared light sources. The atmospheric transmission windows in the ~3–5 µm and ~8–13 µm ranges can extend infrared technologies to longer distances for remote explosive detection, thermal imaging, and free-space communications.

Silicon photonic integration promises to address many of these applications on an integrated, low-cost platform. For example, a diverse portfolio of photonic sensors can potentially be integrated on a single silicon chip. Resonators, multiplexers, modulators, phase shifters, frequency combs, detectors, and various other optical devices operating at wavelengths throughout the mid-infrared have already been demonstrated on silicon photonic waveguiding platforms. Heterogeneous integration, where III-V material layers are transferred above silicon waveguides by wafer- or die-bonding, has previously been applied to construct near-infrared lasers on silicon, however, prior to 2014 no mid-infrared laser source integrated on silicon had been reported.

This thesis presents the heterogeneous silicon/III-V integration of mid-infrared InP-based type-I diode lasers for λ ≈ 2.0 µm, InP-based quantum cascade lasers (QCLs) for λ ≈ 4.8 µm, and GaSb-based interband cascade lasers (ICLs) for λ ≈ 3.7 µm. These Fabry-Perot and distributed feedback (DFB) lasers function above room temperature, are integrated on silicon substrates, and couple mid-infrared light into silicon waveguides. The design considerations, fabrication processes, and performance of each set of lasers are discussed in detail.