R-3 Repository :: Browsing by Author "Zheng, Chuantao"

Browsing by Author "Zheng, Chuantao"

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A compact mid-infrared dual-gas CH4/C2H6 sensor using a single interband cascade laser and custom electronics
(SPIE, 2017) Ye, Weilin; Zheng, Chuantao; Tittel, Frank K.; Sanchez, Nancy P.; Gluszek, Aleksander K.; Hudzikowski, Arkadiusz J.; Lou, Minhan; Dong, Lei; Griffin, Robert J.
A compact mid-infrared (MIR) dual-gas sensor system was demonstrated for simultaneous detection of methane (CH4) and ethane (C2H6) using a single continuous-wave (CW) interband cascade laser (ICL) based on tunable laser absorption spectroscopy (TDLAS) and wavelength modulation spectroscopy (WMS). Ultracompact custom electronics were developed, including a laser current driver, a temperature controller and a lock-in amplifier. These custom electronics reduce the size and weight of the sensor system as compared with a previous version based on commercial electronics. A multipass gas cell with an effective optical length of 54.6 m was employed to enhance the absorption signal. A 3337 nm ICL was capable of targeting a C2H6 absorption line at 2996.88 cm-1 and a CH4 line at 2999.06 cm-1. Dual-gas detection was realized by scanning both the CH4 and C2H6 absorption lines. Based on an Allan deviation analysis, the 1 σ minimum detection limit (MDL) was 17.4 ppbv for CH4 and 2.4 ppbv for C2H6 with an integration time of 4.3 s. TDLAS based sensor measurements for both indoor and outdoor mixing ratios of CH4 and C2H6 were conducted. The reported single ICL based dual-gas sensor system has the advantages of reduced size and cost without influencing the midinfrared sensor detection sensitivity, selectivity and reliability.
A NDIR Mid-Infrared Methane Sensor with a Compact Pentahedron Gas-Cell
(MDPI, 2020) Ye, Weilin; Tu, Zihan; Xiao, Xupeng; Simeone, Alessandro; Yan, Jingwen; Wu, Tao; Wu, Fupei; Zheng, Chuantao; Tittel, Frank K.
In order to improve the performance of the large divergence angle mid-infrared source in gas sensing, this paper aims at developing a methane (CH4) sensor with non-dispersive infrared (NDIR) technology using a compact pentahedron gas-cell. A paraboloid concentrator, two biconvex lenses and five planar mirrors were used to set up the pentahedron structure. The gas cell is endowed with a 170 mm optical path length with a volume of 19.8 mL. The mathematical model of the cross-section and the three-dimension spiral structure of the pentahedron gas-cell were established. The gas-cell was integrated with a mid-infrared light source and a detector as the optical part of the sensor. Concerning the electrical part, a STM32F429 was employed as a microcontroller to generate the driving signal for the IR source, and the signal from the detector was sampled by an analog-to-digital converter. A static volumetric method was employed for the experimental setup, and 20 different concentration CH4 samples were prepared to study the sensor’s evaluation, which revealed a 1σ detection limit of 2.96 parts-per-million (ppm) with a 43 s averaging time.
A near-infrared gas sensor system based on tunable laser absorption spectroscopy and its application to CH4/C2H2 detection
(SPIE, 2017) He, Qixin; Zheng, Chuantao; Liu, Huifang; Wang, Yiding; Tittel, Frank K.
A near-infrared (NIR) dual-channel differential gas sensor system was experimentally demonstrated based on tunable laser absorption spectroscopy (TLAS) and wavelength modulation spectroscopy (WMS). The sensor consists of four modules, including distributed feedback (DFB) lasers for the detection of targeted gases, a custom portable DFB driver compatible for butterfly-packaged DFB lasers, a 20cm-long open-reflective gas-sensing probe and a custom cost-effective lock-in amplifier for harmonic signal extraction. The optical and electrical modules were integrated into a standalone sensor system, which possesses advantages of user-friendly operation, good stability, small volume and low cost. With different DFB lasers, the sensor system can be used to detect different gases. Two DFB diode lasers with emission wavelengths of 1.65 μm and 1.53 μm were used to detect CH4 and C2H2, respectively. Standard CH4 and C2H2 samples were prepared and experiments were carried out to evaluate the performance of the two-gas TLAS sensor system. The relation between the second harmonic amplitudes (2f) and gas concentrations was obtained for the two gases by means of calibration. Both the detection error and the limit of detection (LoD) were determined experimentally. The sensor system will be useful in industrial trace gas monitoring due to its use of a low-loss optical fiber and an open-reflective gas-sensing probe.
Compact TDLAS based sensor design using interband cascade lasers for mid-IR trace gas sensing
(The Optical Society, 2016) Dong, Lei; Tittel, Frank K.; Li, Chunguang; Sanchez, Nancy P.; Wu, Hongpeng; Zheng, Chuantao; Yu, Yajun; Sampaolo, Angelo; Griffin, Robert J.
Two compact TDLAS sensor systems based on different structural optical cores were developed. The two optical cores combine two recent developments, gallium antimonide (GaSb)-based ICL and a compact multipass gas cell (MPGC) with the goal to create compact TDLAS based sensors for the mid-IR gas detection with high detection sensitivity and low power consumption. The sensors achieved minimum detection limits of ~5 ppbv and ~8 ppbv, respectively, for CH4 and C2H6 concentration measurements with a 3.7-W power consumption.
CW DFB-QCL and EC-QCL based sensor for simultaneous NO and NO2 measurements via frequency modulation multiplexing using multi-pass absorption spectroscopy
(SPIE, 2017) Yu, Yajun; Sanchez, Nancy P.; Lou, Minhan; Zheng, Chuantao; Wu, Hongpeng; Głuszek, Aleksander K.; Hudzikowski, Arkadiusz J.; Griffin, Robert J.; Tittel, Frank K.
Nitrogen oxides (NOx), including nitric oxide (NO) and nitrogen dioxide (NO2) play important roles in determining the photochemistry of the ambient atmosphere, controlling the production of tropospheric ozone, affecting the concentration levels of the hydroxyl radical, and forming acid precipitation. A sensor system capable of simultaneous measurements of NO and NO2 by using a commercial 76 m astigmatic multi-pass gas cell (MPGC) was developed in order to enable fast-response NOx detection. A continuous wave (CW), distributed-feedback (DFB) quantum cascade laser (QCL) and a CW external-cavity (EC) QCL were employed for targeting a NO absorption doublet at 1900.075 cm-1 and a NO2 absorption line at 1630.33 cm-1, respectively. Both laser beams were combined and transmitted through the MPGC in an identical optical path and subsequently detected by a single mid-infrared detector. A frequency modulation multiplexing scheme was implemented by modulating the DFB-QCL and EC-QCL at different frequencies and demodulating the detector signal with two Labview software based lock-in amplifiers to extract the corresponding second-harmonic (2f) components. Continuous monitoring of NO and NO2 concentration levels was achieved by locking the laser frequencies to the selected absorption lines utilizing a reference cell filled with high concentrations of NO and NO2. The experimental results indicate minor performance degradation associated with frequency modulation multiplexing and no cross talk between the two multiplexed detection channels. The performance of the reported sensor system was evaluated for real time, sensitive and precise detection of NO and NO2 simultaneously.
Development and Measurements of a Mid-Infrared Multi-Gas Sensor System for CO, CO2 and CH4 Detection
(MDPI, 2017) Dong, Ming; Zheng, Chuantao; Miao, Shuzhuo; Zhang, Yu; Du, Qiaoling; Wang, Yiding; Tittel, Frank K.
A multi-gas sensor system was developed that uses a single broadband light source and multiple carbon monoxide (CO), carbon dioxide (CO2) and methane (CH4) pyroelectric detectors by use of the time division multiplexing (TDM) technique. A stepper motor-based rotating system and a single-reflection spherical optical mirror were designed and adopted to realize and enhance multi-gas detection. Detailed measurements under static detection mode (without rotation) and dynamic mode (with rotation) were performed to study the performance of the sensor system for the three gas species. Effects of the motor rotating period on sensor performances were also investigated and a rotation speed of 0.4π rad/s was required to obtain a stable sensing performance, corresponding to a detection period of ~10 s to realize one round of detection. Based on an Allan deviation analysis, the 1σ detection limits under static operation are 2.96, 4.54 and 2.84 parts per million in volume (ppmv) for CO, CO2 and CH4, respectively and the 1σ detection limits under dynamic operations are 8.83, 8.69 and 10.29 ppmv for the three gas species, respectively. The reported sensor has potential applications in various fields requiring CO, CO2 and CH4 detection such as in coal mines.
Double-range near-infrared acetylene detection using a dual spot-ring Herriott cell (DSR-HC)
(Optical Society of America, 2018) Dong, Ming; Zheng, Chuantao; Yao, Dan; Zhong, Guoqiang; Miao, Shuzhuo; Ye, Weilin; Wang, Yiding; Tittel, Frank K.
Design and fabrication of a dual spot-ring Herriott cell (DSR-HC) were proposed. The sealed Herriott cell with a dimensional size of 5.5 cm × 9.2 cm × 32.1 cm, possessed two input/output coupling holes leading to two absorption path lengths of ~20 m and ~6 m, respectively. An acetylene (C2H2) sensor system with a double-range was developed using the DSR-HC and wavelength modulation spectroscopy (WMS) technique. A near-infrared distributed feedback (DFB) laser was employed for targeting a C2H2 absorption line at 6521.2 cm-1. C2H2concentration measurements were carried out by modulating the laser at a 5 kHz frequency and demodulating the detector signal with LabVIEW software. An Allan-Werle deviation analysis indicated that the limit of detection (LoD) for the two absorption path lengths of 20 m and 6 m are 7.9 parts-per-million in volume (ppmv) and 4.0 ppmv, respectively. The DSR-HC concept can be used to fabricate similar cells for single-gas detection requiring two different detection ranges as well as for dual-gas detection requiring different absorption path lengths.
Dual-feedback mid-infrared cavity-enhanced absorption spectroscopy for H2CO detection using a radio-frequency electrically-modulated interband cascade laser
(The Optical Society, 2018) He, Qixin; Zheng, Chuantao; Lou, Minhan; Ye, Weilin; Wang, Yiding; Tittel, Frank K.
A mid-infrared cavity-enhanced sensor system was demonstrated for the detection of formaldehyde (H2CO) using a continuous-wave (cw) interband cascade laser (ICL) centered at 3599 nm. A compact Fabry-Perot (F-P) cavity with a physical size of 38 × 52 × 76 mm3 was developed consisting of two concave mirrors with a radius of curvature of 80 mm and a reflectivity of 99.8% at 3.6 μm. Different from the widely reported electro-optical (EO) external modulation based Pound-Drever-Hall (PDH) locking technique, a radio-frequency electrical internal modulation based PDH technique was used for locking the laser mode to the cavity mode. A dual-feedback control on the laser current and on the piezo transducer (PZT) displacement was utilized for further stabilizing mode locking. A 20 m effective optical path length was achieved with a cavity length of 2 cm and a finesse of 1572. The effectiveness and sensitivity of the sensor system were demonstrated by targeting an absorption line at 2778.5 cm−1 for H2CO measurements. A linear relation between the cavity transmitted signal amplitude and the H2CO concentration was obtained within the range of 0−5 ppm. A 1σ detection limit of 25 parts-per-billion (ppb) was achieved with an averaging time of 1 s based on Allan-Werle variance analysis. The reported dual-feedback RF modulation based PDH technique led to a method for gas detection using a similar experimental setup and measurement scheme.
Exploratory study of atmospheric methane enhancements derived from natural gas use in the Houston urban area
(Elsevier, 2018) Sanchez, Nancy P.; Zheng, Chuantao; Ye, Weilin; Czader, Beata; Cohan, Daniel S.; Tittel, Frank K.; Griffin, Robert J.
The extensive use of natural gas (NG) in urban areas for heating and cooking and as a vehicular fuel is associated with potentially significant emissions of methane (CH4) to the atmosphere. Methane, a potent greenhouse gas that influences the chemistry of the atmosphere, can be emitted from different sources including leakage from NG infrastructure, transportation activities, end-use uncombusted NG, landfills and livestock. Although significant CH4 leakage associated with aging local NG distribution systems in the U.S. has been reported, further investigation is required to study the role of this infrastructure component and other NG-related sources in atmospheric CH4 enhancements in urban centers. In this study, neighborhood-scale mobile-based monitoring of potential CH4emissions associated with NG in the Greater Houston area (GHA) is reported. A novel dual-gas 3.337 μm interband cascade laser-based sensor system was developed and mobile-mode deployed for simultaneous CH4 and ethane (C2H6) monitoring during a period of over 14 days, corresponding to ∼ 90 h of effective data collection during summer 2016. The sampling campaign covered ∼250 exclusive road miles and was primarily concentrated on eight residential zones with distinct infrastructure age and NG usage levels. A moderate number of elevated CH4 concentration events (37 episodes) with mixing ratios not exceeding 3.60 ppmv and associated with atmospheric background enhancements below 1.21 ppmv were observed during the field campaign. Source discrimination analyses based on the covariance between CH4 and C2H6 levels indicated the predominance of thermogenic sources (e.g., NG) in the elevated CH4 concentration episodes. The volumetric fraction of C2H6 in the sources associated with the thermogenic CH4 spikes varied between 2.7 and 5.9%, concurring with the C2H6 content in NG distributed in the GHA. Isolated CH4 peak events with significantly higher C2H6 enhancements (∼11%) were observed at industrial areas and locations with high density of petroleum and gas pipelines in the GHA, indicating potential variability in Houston's thermogenic CH4 sources.
ICL-based mid-infrared carbon dioxide sensor system for deep-sea natural gas hydrate exploration
(Optical Society of America, 2019) Liu, Zhiwei; Zheng, Chuantao; Chen, Chen; Li, Yafei; Xie, Hongtao; Ren, Qiang; Wang, Yiding; Tittel, Frank K.
For deep-sea natural gas hydrate exploration, highly sensitive detection of the dissolved gas in seawater near the seabed is significant because it requires the sensor system to be small in size, low in power consumption, and high in sensitivity. A mid-infrared sensor system was developed to detect dissolved carbon dioxide (CO2) in sea-water, while employing a 4319 nm continuous-wave interband cascade laser (ICL) and a multi-pass gas cell (MPGC) with a 29.8 m optical path length. A compact rectilinear optical structure was proposed by using the free-space-emitting ICL and tunable laser absorption spectroscopy (TLAS). This leads to a minimized sensor size and a simple optical alignment for deep-sea operation. A strong CO2 absorption line, located at 2315.19 cm−1 and a weak 2315.28 cm−1 line and at a low pressure of 40 Torr, was targeted for low- and high-concentration CO2 detection within a concentration range of 0-1000 parts per billion by volume (ppbv) and 0-40 parts per million by volume (ppmv), respectively. The limit of detection (LoD) was assessed to be 0.72 ppbv at an averaging time of 2 s, and the response time was measured to be ~30 s at a flow rate of ~180 standard cubic centimeters per minute (sccm). Deployment of the CO2 sensor combined with a gas-liquid separator was carried out for the CO2 detection in the gas extracted from water, which validated the reported sensor system’s potential application for deep-sea natural gas hydrate exploration.
Interband cascade laser based mid-infrared methane sensor system using a novel electrical-domain self-adaptive direct laser absorption spectroscopy (SA-DLAS)
(Optical Society of America, 2017) Song, Fang; Zheng, Chuantao; Yan, Wanhong; Ye, Weilin; Wang, Yiding; Tittel, Frank K.
To suppress sensor noise with unknown statistical properties, a novel self-adaptive direct laser absorption spectroscopy (SA-DLAS) technique was proposed by incorporating a recursive, least square (RLS) self-adaptive denoising (SAD) algorithm and a 3291 nm interband cascade laser (ICL) for methane (CH4) detection. Background noise was suppressed by introducing an electrical-domain noise-channel and an expectation-known-based RLS SAD algorithm. Numerical simulations and measurements were carried out to validate the function of the SA-DLAS technique by imposing low-frequency, high-frequency, White-Gaussian and hybrid noise on the ICL scan signal. Sensor calibration, stability test and dynamic response measurement were performed for the SA-DLAS sensor using standard or diluted CH4ﾠsamples. With the intrinsic sensor noise considered only, an Allan deviation of ~43.9 ppbv with a ~6 s averaging time was obtained and it was further decreased to 6.3 ppbv with a ~240 s averaging time, through the use of self-adaptive filtering (SAF). The reported SA-DLAS technique shows enhanced sensitivity compared to a DLAS sensor using a traditional sensing architecture and filtering method. Indoor and outdoor atmospheric CH4measurements were conducted to validate the normal operation of the reported SA-DLAS technique.
Light-induced off-axis cavity-enhanced thermoelastic spectroscopy in the near-infrared for trace gas sensing
(Optical Society of Americ, 2021) Zheng, Kaiyuan; Zheng, Chuantao; Zheng, Chuantao; Hu, Lien; Guan, Gangyun; Ma, Yanming; Song, Fang; Zhang, Yu; Zhang, Yu; Wang, Yiding; Tittel, Frank K.
A trace gas sensing technique of light-induced off-axis cavity-enhanced thermoelastic spectroscopy (OA-CETES) in the near-infrared was demonstrated by combing a high-finesse off-axis integrated cavity and a high Q-factor resonant quartz tuning fork (QTF). Sensor parameters of the cavity and QTF were optimized numerically and experimentally. As a proof-of-principle, we employed the OA-CETES for water vapor (H2O) detection using a QTF (Q-factor ∼12000 in atmospheric pressure) and a 10cm-long Fabry-Perot cavity (finesse ∼ 482). By probing a H2O line at 7306.75 cm-1, the developed OA-CETES sensor achieved a minimum detection limit (MDL) of 8.7 parts per million (ppm) for a 300 ms integration time and a normalized noise equivalent absorption (NNEA) coefficient of 4.12 × 10−9cm-1 WHz-1/2. Continuous monitoring of indoor and outdoor atmospheric H2O concentration levels was performed for verifying the sensing applicability. The realization of the proposed OA-CETES technique with compact QTF and long effective path cavity allows a class of optical sensors with low cost, high sensitivity and potential for long-distance and multi-point sensing.
Long-distance in-situ methane detection using near-infrared light-induced thermo-elastic spectroscopy
(Elsevier, 2021) Hu, Lien; Zheng, Chuantao; Zhang, Minghui; Zheng, Kaiyuan; Zheng, Jie; Song, Zhanwei; Li, Xiuying; Zhang, Yu; Wang, Yiding; Tittel, Frank K.
A wavelength-locked light-induced thermo-elastic spectroscopy (WL-LITES) gas sensor system was proposed for long-distance in-situ methane (CH4) detection using a fiber-coupled sensing probe. The wavelength-locked scheme was used to speed the sensor response without scanning the laser wavelength across the CH4 absorption line. A small-size piezoelectric quartz tuning fork (QTF) with a wide spectral response range was adopted to enhance the photo-thermal signal. The optical excitation parameters of the QTF were optimized based on experiment and simulation for improving the signal-to-noise ratio of the LITES technique. An Allan deviation analysis was employed to evaluate the limit of detection of the proposed sensor system. With a 0.3 s lock-in integration time and a ∼ 100 m optical fiber, the WL-LITES gas sensor system demonstrates a minimum detection limit (MDL) of ∼ 11 ppm in volume (ppmv) for CH4 detection, and the MDL can be further reduced to ∼ 1 ppmv with an averaging time of ∼ 35 s. A real-time in-situ monitoring of CH4 leakage reveals that the proposed sensor system can realize a fast response (< 12 s) for field application.
Mid-infrared chalcogenide slot waveguide plasmonic resonator sensor embedded with Au nanorods for surface-enhanced infrared absorption spectroscopy
(Elsevier, 2022) Pi, Mingquan; Zhao, Huan; Li, Chunguang; Min, Yuting; Peng, Zihang; Ji, Jialin; Huang, Yijun; Song, Fang; Liang, Lei; Zhang, Yu; Wang, Yiding; Tittel, Frank K.; Zheng, Chuantao
The problem of a traditional waveguide plasmonic resonator sensor is that part of the near-field intensity enhanced area is confined in the waveguide dielectric layer, which decreases the interaction effect between light and analyte. In order to solve this problem, a novel mid-infrared (MIR) chalcogenide (ChG) slot waveguide plasmonic resonator (SWGPR) sensor embedded with Au nanorods was proposed, where Au nanorods were used as antenna for enhancing mode coupling with the waveguide through resonance at the absorption wavelength of the analyte. The antenna parameters were optimized to make the resonance wavelength align with the absorption wavelength of the analyte. The proposed waveguide structure provides a sufficient sensing area and increases the electric field enhancement factor to > 6400. Polymethyl methacrylate (PMMA) and styrene were adopted as the analyte for sensing performance evaluation. The normalized absorption reaches 23.31 when the maximum extinction coefficient of PMMA is 0.08, which is at least 7 times higher than other silicon-on-insulator (SOI) waveguide plasmonic resonator sensors. The proposed waveguide structure provides a new idea for the design of other waveguide plasmonic resonator sensors with high sensing performance and has the potential for biochemical sensing.
Mid-infrared dual-gas sensor for simultaneous detection of methane and ethane using a single continuous-wave interband cascade laser
(The Optical Society, 2016) Ye, Weilin; Li, Chunguang; Zheng, Chuantao; Sanchez, Nancy P.; Gluszek, Aleksander K.; Hudzikowski, Arkadiusz J.; Dong, Lei; Griffin, Robert J.; Tittel, Frank K.
A continuous-wave (CW) interband cascade laser (ICL) based mid-infrared sensor system was demonstrated for simultaneous detection of atmospheric methane (CH4) and ethane (C2H6). A 3.337 µm CW ICL with an emitting wavenumber range of 2996.0−3001.5 cm−1 was used to simultaneously target two absorption lines, C2H6 at 2996.88 cm−1 and CH4 at 2999.06 cm−1, respectively. The sensor performance was first evaluated for single-gas detection by only targeting the absorption line of one gas species. Allan deviations of 11.2 parts per billion in volume (ppbv) for CH4 and 1.86 ppbv for C2H6 with an averaging time of 3.4 s were achieved for the detection of these two gases. Dual-gas detection was realized by using a long-term scan signal to target both CH4 and C2H6 lines. The Allan deviations increased slightly to 17.4 ppbv for CH4 and 2.4 ppbv for C2H6 with an averaging time of 4.6 s due to laser temperature and power drift caused by long-term wavelength scanning. Measurements for both indoor and outdoor concentration changes of CH4 and C2H6 were conducted. The reported single ICL based dual-gas sensor system has the advantages of reduced size and cost compared to two separate sensor systems.
Near-infrared acetylene sensor system using off-axis integrated-cavity output spectroscopy and two measurement schemes
(Optical Society of America, 2018) Zheng, Kaiyuan; Zheng, Chuantao; He, Qixin; Yao, Dan; Hu, Lien; Zhang, Yu; Wang, Yiding; Tittel, Frank K.
For highly sensitive and accurate acetylene (C2H2) detection, a near-infrared (NIR) off-axis integrated-cavity output spectroscopy (OA-ICOS) sensor system based on an ultra-compact cage-based absorption cell was proposed. The absorption cell with dimensions of 10 cm × 8 cm × 6 cm realized a dense-pattern and an easily-aligned stable optical system. The OA-ICOS sensor system employed a 6cm-long optical cavity that was formed by two mirrors with a reflectivity of 99.35% and provided an effective absorption path length of ∼9.28 m. The performance of the C2H2 sensor system based on two measurement schemes, i.e. laser direct absorption spectroscopy (LDAS) and wavelength modulation spectroscopy (WMS) is reported. A NIR distributed feedback (DFB) laser was employed for targeting a C2H2 absorption line at 6523.88 cm−1. An Allan deviation analysis yielded a detection sensitivity of 760 parts-per-billion in volume (ppbv) for an averaging time of 304 s using the LDAS-based OA-ICOS. A detection sensitivity of 85 ppbv for an averaging time of 250 s was obtained using the WMS-based OA-ICOS, which was further improved by a factor of ~9 compared to the result obtained with the LDAS method. The proposed sensor system has the advantages of reduced size and cost with acceptable detection sensitivity, which is suitable for applications in trace gas sensing in harsh environments and weight-limited balloon-embedded observations.
Near-Infrared Dual-Gas Sensor System for Methane and Ethane Detection Using a Compact Multipass Cell
(Frontiers Media S.A., 2022) Xi, Zhenhai; Zheng, Kaiyuan; Zheng, Chuantao; Zhang, Haipeng; Song, Fang; Li, Chunguang; Ye, Weilin; Zhang, Yu; Wang, Yiding; Tittel, Frank K.
In this invited paper, a compact dense-pattern multipass cell-based near-infrared sensor system was demonstrated for detection of parts-per-billion in volume (ppbv)-level methane (CH4) and ethane (C2H6). The dimension size of the fabricated gas cell is 18.5 × 8 × 9 cm3 with an absorption path length of 9.39 m. CH4 measurement was realized within a spectral range of 6,046–6,048 cm−1 and an absorption line of 6,046.95 cm−1. The spectral range for C2H6 detection is 5,951–5,953 cm−1 with an absorption line of 5,951.73 cm−1. Allan deviation analysis was used for evaluating the dual-gas sensing performance, and a detection limit of 78 ppbv for CH4 and 190 ppbv for C2H6 were achieved, respectively, with an averaging time of 0.8 s. Furthermore, CH4 measurement in the indoor and outdoor atmosphere was both performed to verify the field sensing capability of the sensor system. Compared with two separate sensor systems for CH4/C2H6 sensing, the proposed dual-gas sensor system using two near-infrared lasers and one multipass cell has the advantages of low-cost, compact-size without decreasing the selectivity and sensitivity.
On-chip mid-infrared silicon-on-insulator waveguide methane sensor using two measurement schemes at 3.291 μm
(Frontiers Media S.A., 2022) Zhao, Huan; Zheng, Chuantao; Pi, Mingquan; Liang, Lei; Song, Fang; Zhang, Yu; Wang, Yiding; Tittel, Frank K.
Portable or even on-chip detection of methane (CH4) is significant for environmental protection and production safety. However, optical sensing systems are usually based on discrete optical elements, which makes them unsuitable for the occasions with high portability requirement. In this work, we report on-chip silicon-on-insulator (SOI) waveguide CH4 sensors at 3.291 μm based on two measurement schemes including direct absorption spectroscopy (DAS) and wavelength modulation spectroscopy (WMS). In order to suppress noise, Kalman filter was adopted in signal processing. By optimizing the waveguide cross-section structure, an etch depth of 220 nm was selected with an experimentally high power confinement factor (PCF) of 23% and a low loss of only 0.71 dB/cm. A limit of detection (LoD) of 155 parts-per-million (ppm) by DAS and 78 ppm by WMS at an averaging time of 0.2 s were obtained for a 2 cm-long waveguide sensor. Compared to the chalcogenide (ChG) waveguide CH4 sensors at the same wavelength, the reported sensor reveals the minimum waveguide loss and the lowest LoD. Therefore the SOI waveguide sensor has the potential of on-chip gas sensing in the mid-infrared (MIR) waveband.
Performance Enhancement of Methane Detection Using a Novel Self-Adaptive Mid-Infrared Absorption Spectroscopy Technique
(IEEE, 2018) Song, Fang; Zheng, Chuantao; Yan, Wanhong; Ye, Wei Lin; Zhang, Yu; Wang, Yiding; Tittel, Frank K.
An electrical-domain self-adaptive mid-infrared absorption spectroscopy for methane detection based on an interband cascade laser was demonstrated. By adding noise into the laser drive signal, denoising and sensing performances were evaluated for the technique. Experiments were made to study the effects of noise level/type on sensor stability, characterized by Allan deviation. High- and low-frequency noise levels have the same functional variation trend on Allan deviation, which differs from white Gaussian noise. Within a noise level range of 0-125 mV for low- and high-frequency noise and 0-62.5 mV for white Gaussian noise in the mercury-cadmium-telluride detector's output (with a pure signal amplitude of ~300 mV), the sensor stability using self-adaptive denoising was enhanced by a factor of 1.05-20, 1.32-6.25, and 1.15-3.33 times compared to that using no filtering, for the three kinds of noise, respectively. The reported self-adaptive methane sensor system shows enhanced stability compared to the direct laser absorption spectroscopy sensor using traditional sensing architecture and classic filtering method. The sensor was further evaluated through outdoor atmospheric methane measurements using such technique. A second-order self-adaptive direct laser absorption spectroscopy technique was also proposed for noise suppression in both optical and electrical domain as an outlook of the concept of this paper.
Ppbv-Level Ethane Detection Using Quartz-Enhanced Photoacoustic Spectroscopy with a Continuous-Wave, Room Temperature Interband Cascade Laser
(MDPI, 2018) Li, Chunguang; Dong, Lei; Zheng, Chuantao; Lin, Jun; Wang, Yiding; Tittel, Frank K.
A ppbv-level quartz-enhanced photoacoustic spectroscopy (QEPAS)-based ethane (C2H6) sensor was demonstrated by using a 3.3 μm continuous-wave (CW), distributed feedback (DFB) interband cascade laser (ICL). The ICL was employed for targeting a strong C2H6 absorption line located at 2996.88 cm−1 in its fundamental absorption band. Wavelength modulation spectroscopy (WMS) combined with the second harmonic (2f) detection technique was utilized to increase the signal-to-noise ratio (SNR) and simplify data acquisition and processing. Gas pressure and laser frequency modulation depth were optimized to be 100 Torr and 0.106 cm−1, respectively, for maximizing the 2f signal amplitude. Performance of the QEPAS sensor was evaluated using specially prepared C2H6 samples. A detection limit of 11 parts per billion in volume (ppbv) was obtained with a 1-s integration time based on an Allan-Werle variance analysis, and the detection precision can be further improved to ~1.5 ppbv by increasing the integration time up to 230 s.

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