Compact, lightweight, high-power beam-steering devices operating in the
mid-infrared atmospheric window
λ
=
3
−
5
µ
m
are attractive for aerial-based
applications such as long-range lidar and countermeasures. In the
near-infrared spectral region, optical phased arrays (OPAs) have
emerged as the dominant nonmechanical on-chip beam-steering
technology, with a preponderance in silicon-based platforms.
Extensions to the mid-infrared spectral region are scarce. Further,
considering that the requirements for high performance in this region
will likely demand monolithic integration with quantum cascade lasers,
development of the photonic technology on a native III–V platform is
advantageous. To this end, at
λ
=
4.6
µ
m
, on an InGaAs/InP platform, we
experimentally demonstrate the operation of a 32-channel OPA with
thermo-optic tuning for azimuthal (lateral) steering. With a waveguide
spacing of
2.5
λ
, we steer the beam to the maximum
uninfringed field of view at
±
11.5
∘
.
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.
We design and experimentally demonstrate the propagation loss of waveguides and the operation of a single-step etched polarization rotator-splitter (PRS) in low index contrast InGaAs-InP material system at 6.15 μm. Propagation losses 4.19 dB/cm for TM mode and 3.25 dB/cm for TE mode are measured. The designed PRS can achieve near 100% conversion efficiency. This study enables the possibility of monolithic integration of quantum cascade devices with TM-polarized characteristics and TE-guiding two-dimensional slotted photonic crystal waveguide gas sensors for on-chip monolithic absorption spectroscopy.
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