Parts-per-million level detection of carbon monoxide using grating array waveguides in InP/InGaAs at [lambda] = 4.6μm

Gas sensing based on infrared absorption spectroscopy has attracted considerable attention owing to the rovibrational signatures of compounds of interest in the molecular fingerprint region. On-chip spectrometers are promising devices that unlike their on-chip commercially available counterparts offer sensing in portable applications. Carbon monoxide as one of the major air pollutants is dangerous even at very low concentrations. For real-time and precise detection of trace amounts of this gas we need a compact highly sensitive and selective sensor. In this paper, we design a grating array device in the InP/InGaAs platform for trace detection of carbon monoxide. The passive device consists of an InGaAs strip waveguide with InP as cladding, split-cascaded into an equally spaced array of 32 separate optical paths by y-junctions. At the output of each waveguide shallow etched subwavelength emitter gratings couple the light out. Light-analyte interaction occurs on top of the gratings as well as in free space. The device is optimized to operate at mid-IR wavelength of λ=4.6μm where the absorption peak of carbon monoxide is located. Using this structure, gas sensing is experimentally demonstrated down to a concentration of 10ppm. Feasibility of achieving lower limit of detection will be shown by design modifications. This device, can be simply integrated with QCL/QCD and be used for portable high sensitivity gas sensors.