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.
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Monolithic integration of quantum cascade laser, quantum cascade detector, and subwavelength waveguides for mid-infrared integrated gas sensing
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 require bulky and expensive optical elements and, furthermore, are very sensitive to beam alignment and have significant size and 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 required to enable a compact trace gas sensing system that is robust to vibrations and physical stress. Since the most efficient quantum cascade lasers (QCLs) demonstrated are in the InP platform, the choice of InGaAs-InP for passive photonics eliminates the need for costly wafer bonding versus silicon, germanium of GaAs, that would require optically absorbing bonding interfaces. The InGaAs-InP material platform can potentially cover the entire λ=3-15μm molecular fingerprint region. 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 transverse magnetic polarized QCL emission is efficiently coupled into an underlying InGaAs suspended membrane subwavelength waveguide. In addition to low-loss compact waveguide bends, the suspended membrane architecture offers a high analyte overlap integral with the analyte. The propagating light is absorbed at the peak absorbance wavelength of the selected analyte gas and the transduced signal is detected by the integrated QCD. Gas sensing will be demonstrated
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- Award ID(s):
- 1711824
- NSF-PAR ID:
- 10090867
- Date Published:
- Journal Name:
- Proceedings of the SPIE
- Page Range / eLocation ID:
- 64
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Chemicals are best recognized by their unique wavelength specific optical absorption signatures in the molecular fingerprint region from λ=3-15μm. In recent years, photonic devices on chips are increasingly being used for chemical and biological sensing. Silicon has been the material of choice of the photonics industry over the last decade due to its easy integration with silicon electronics as well as its optical transparency in the near-infrared telecom wavelengths. Silicon is optically transparent from 1.1 μm to 8 μm with research from several groups in the mid-IR. However, intrinsic material losses in silicon exceed 2dB/cm after λ~7μm (~0.25dB/cm at λ=6μm). In addition to the waveguiding core, an appropriate transparent cladding is also required. Available core-cladding choices such as Ge-GaAs, GaAs-AlGaAs, InGaAs-InP would need suspended membrane photonic crystal waveguide geometries. However, since the most efficient QCLs demonstrated are in the InP platform, the choice of InGaAs-InP eliminates need for wafer bonding versus other choices. The InGaAs-InP material platform can also potentially cover the entire molecular fingerprint region from λ=3-15μm. At long wavelengths, in monolithic architectures integrating lasers, detectors and passive sensor photonic components without wafer bonding, compact passive photonic integrated circuit (PIC) components are desirable to reduce expensive epi material loss in passive PIC etched areas. In this paper, we consider miniaturization of waveguide bends and polarization rotators. We experimentally demonstrate suspended membrane subwavelength waveguide bends with compact sub-50μm bend radius and compact sub-300μm long polarization rotators in the InGaAs/InP material system. Measurements are centered at λ=6.15μm for sensing ammoniamore » « less
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Abstract Thanks to the unique molecular fingerprints in the mid-infrared spectral region, absorption spectroscopy in this regime has attracted widespread attention in recent years. Contrary to commercially available infrared spectrometers, which are limited by being bulky and cost-intensive, laboratory-on-chip infrared spectrometers can offer sensor advancements including raw sensing performance in addition to utilization such as enhanced portability. Several platforms have been proposed in the past for on-chip ethanol detection. However, selective sensing with high sensitivity at room temperature has remained a challenge. Here, we experimentally demonstrate an on-chip ethyl alcohol sensor based on a holey photonic crystal waveguide on silicon on insulator-based photonics sensing platform offering an enhanced photoabsorption thus improving sensitivity. This is achieved by designing and engineering an optical slow-light mode with a high group-index of
n g = 73 and a strong localization of the modal power in analyte, enabled by the photonic crystal waveguide structure. This approach includes a codesign paradigm that uniquely features an increased effective path length traversed by the guided wave through the to-be-sensed gas analyte. This PIC-based lab-on-chip sensor is exemplary, spectrally designed to operate at the center wavelength of 3.4 μm to match the peak absorbance for ethanol. However, the slow-light enhancement concept is universal offering to cover a wide design-window and spectral ranges towards sensing a plurality of gas species. Using the holey photonic crystal waveguide, we demonstrate the capability of achieving parts per billion levels of gas detection precision. High sensitivity combined with tailorable spectral range along with a compact form-factor enables a new class of portable photonic sensor platforms when integrated with quantum cascade laser and detectors. -
This study presents the growth and characterization of an 8.1 μm-emitting, InGaAs/AlInAs/InP-based quantum cascade laser (QCL) formed on an InP-on-Si composite template by metalorganic chemical vapor deposition (MOCVD). First, for the composite-template formation, a GaAs buffer layer was grown by solid-source molecular-beam epitaxy on a commercial (001) GaP/Si substrate, thus forming a GaAs/GaP/Si template. Next, an InP metamorphic buffer layer (MBL) structure was grown atop the GaAs/GaP/Si template by MOCVD, followed by the MOCVD growth of the full QCL structure. The top-surface morphology of the GaAs/GaP/Si template before and after the InP MBL growth was assessed via atomic force microscopy, over a 100 μm2 area, and no antiphase domains were found. The average threading dislocation density (TDD) for the GaAs/GaP/Si template was found to be ∼1 × 109 cm−2, with a slightly lower defect density of ∼7.9 × 108 cm−2 after the InP MBL growth. The lasing performance of the QCL structure grown on Si was compared to that of its counterpart grown on InP native substrate and found to be quite similar. That is, the threshold-current density of the QCL on Si, for deep-etched ridge-guide devices with uncoated facets, is somewhat lower than that for its counterpart on native InP substrate, 1.50 vs 1.92 kA/cm2, while the maximum output power per facet is 1.64 vs 1.47 W. These results further demonstrate the resilience of QCLs to relatively high residual TDD values.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1117/12.2508873
