Integrated Metallic Hollow Waveguides with Terahertz Quantum Cascade Lasers

Abstract Scaling down the size of terahertz optical systems is a challenging task because of the long wavelengths involved. We have addressed the problem with on-chip integration of terahertz quantum cascade laser (THz QCL) devices with subwavelength metallic hollow waveguides. The application of flip-chip bonding allows for alignment of the waveguide to the emitting facet of the THz QCL with micrometer precision. This eliminates the need for lenses or other beam-forming optics, providing a robust platform for THz QCL–based integrated photonic circuits. In these circuits, quantum cascade devices can be used interchangeably as a light source or detector to monitor the power of embedded lasers. Measurements on the fabricated demonstrator waveguide yield an insertion loss of 7.2 dB compared to the free THz QCL emitting facet and a responsivity of the embedded quantum cascade detector of up to 48 mA/W.