posted on 2020-03-16, 19:45authored byKyoung
Min Yoo, Jason Midkiff, Ali Rostamian, Chi-jui Chung, Hamed Dalir, Ray T. Chen
Mid-infrared
(mid-IR) absorption spectroscopy based on integrated
photonic circuits has shown great promise in trace-gas sensing applications
in which the mid-IR radiation directly interacts with the targeted
analyte. In this paper, considering monolithic integrated circuits
with quantum cascade lasers (QCLs) and quantum cascade detectors (QCDs),
the InGaAs–InP platform is chosen to fabricate passive waveguide
gas sensing devices. Fully suspended InGaAs waveguide devices with
holey photonic crystal waveguides (HPCWs) and subwavelength grating
cladding waveguides (SWWs) are designed and fabricated for mid-infrared
sensing at λ = 6.15 μm in the low-index contrast InGaAs–InP
platform. We experimentally detect 5 ppm ammonia with a 1 mm long
suspended HPCW and separately with a 3 mm long suspended SWW, with
propagation losses of 39.1 and 4.1 dB/cm, respectively. Furthermore,
based on the Beer–Lambert infrared absorption law and the experimental
results of discrete components, we estimated the minimum detectable
gas concentration of 84 ppb from a QCL/QCD integrated SWW sensor.
To the best of our knowledge, this is the first demonstration of suspended
InGaAs membrane waveguides in the InGaAs–InP platform at such
a long wavelength with gas sensing results. Also, this result emphasizes
the advantage of SWWs to reduce the total transmission loss and the
size of the fully integrated device’s footprint by virtue of
its low propagation loss and TM mode compatibility in comparison to
HPCWs. This study enables the possibility of monolithic integration
of quantum cascade devices with TM polarized characteristics and passive
waveguide sensing devices for on-chip mid-IR absorption spectroscopy.