Monolithic integration of quantum cascade laser, quantum cascade detector, and subwavelength waveguides for mid-infrared integrated gas sensing

摘要

Mid-infrared trace gas sensing is a rapidly developing field with wide range of applications. Although CRDS, TDLAS,FTIR and others, can provide parts per billion and in some cases, parts per trillion sensitivities, these systems requirebulky and expensive optical elements and, furthermore, are very sensitive to beam alignment and have significant sizeand weight that place constrains on their applications in the field, particularly for airborne or handheld platforms.Monolithic integration of light sources and detectors with an optically transparent passive photonics platform is requiredto enable a compact trace gas sensing system that is robust to vibrations and physical stress. Since the most efficientquantum cascade lasers (QCLs) demonstrated are in the InP platform, the choice of InGaAs-InP for passive photonicseliminates the need for costly wafer bonding versus silicon, germanium of GaAs, that would require optically absorbingbonding interfaces. The InGaAs-InP material platform can potentially cover the entire λ=3-15μm molecular fingerprintregion. In this paper, we experimentally demonstrate monolithic integration of QCL, quantum cascade detector (QCD)and suspended membrane sub-wavelength waveguides in a fully monolithic InGaAs/InP material system. The transversemagnetic polarized QCL emission is efficiently coupled into an underlying InGaAs suspended membrane subwavelengthwaveguide. In addition to low-loss compact waveguide bends, the suspended membrane architecture offers a highanalyte overlap integral with the analyte. The propagating light is absorbed at the peak absorbance wavelength of theselected analyte gas and the transduced signal is detected by the integrated QCD. Gas sensing will be demonstrated.