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Breath analysis enables rapid, noninvasive diagnosis of human health by identifying and quantifying exhaled biomarker. Here, we demonstrated an exhaled breath sensing method using the near-infrared laser spectroscopy, and sub parts-per-million (ppm) level ammonia detection inside the exhaled gas was achieved employing a distributed feedback laser centered at 1512 nm and Kalman filtering algorithm. Integration of the ammonia sensor was realized for exhaled breath analysis of kidney patients, and a dual operation mechanism with static and dynamic modes was proposed to make this method applicable for real-time and comprehensive pre-diagnosis of kidney disease.
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Amônia , Testes Respiratórios , Espectroscopia de Luz Próxima ao Infravermelho , Testes Respiratórios/métodos , Testes Respiratórios/instrumentação , Humanos , Amônia/análise , Espectroscopia de Luz Próxima ao Infravermelho/métodos , Nefropatias/diagnóstico , Expiração/fisiologiaRESUMO
Cavity-enhanced direct frequency comb spectroscopy (CE-DFCS) is widely used as a highly sensitive gas sensing technology in various gas detection fields. For the on-axis coupling incidence scheme, the detection accuracy and stability are seriously affected by the cavity-mode noise, and therefore, stable operation inevitably requires external electronic mode-locking and sweeping devices, substantially increasing system complexity. To address this issue, we propose off-axis cavity-enhanced optical frequency comb spectroscopy from both theoretical and experimental aspects, which is applied to the detection of single- and dual-gas of carbon monoxide (CO) and carbon dioxide (CO2) in the near-infrared. An erbium-doped fiber frequency comb with a repetition frequency of â¼41.709 MHz is coupled into a resonant cavity with a length of â¼360 mm in an off-axis manner, exciting numerous high-order modes to effectively suppress cavity-mode noise. The performance of multiple machine learning models is compared for the inversion of a single/dual gas concentration. A few absorbance spectra are collected to build a sample data set, which is then utilized for model training and learning. The results demonstrate that the Particle Swarm Optimization Support Vector Machine (PSO-SVM) model achieves the highest predictive accuracy for gas concentration and is ultimately applied to the detection system. Based on Allan deviation, the detection limit for CO in single-gas detection can reach 8.247 parts per million by volume (ppmv) by averaging 87 spectra. Meanwhile, for simultaneous CO2/CO measurement with highly overlapping absorbance spectra, the LoD can be reduced to 13.196 and 4.658 ppmv, respectively. The proposed optical gas sensing technique indicates the potential for the development of a field-deployable and intelligent sensor system capable of simultaneous detection of multiple gases.
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Dióxido de Carbono , Gases , Monóxido de Carbono , Aprendizado de Máquina , Análise EspectralRESUMO
Compared to the most commonly used on-chip direct absorption spectroscopy (DAS) gas detection technique, the second harmonic (2f) based on-chip wavelength modulation spectroscopy (WMS) proposed by our group has the faculty to suppress noise and improve performance, but the accuracy of 2f WMS is easily affected by optical power variation. A mid-infrared auto-correction on-chip gas sensor based on 2f/1f WMS was proposed for decreasing the influence of the variation of optical power. The limit of detection of methane (CH4) obtained by a chalcogenide waveguide with a length of 10â mm is 0.031%. Compared with the 2f WMS, the maximum relative concentration error of the auto-correction on-chip gas sensor was decreased by â¼5.6 times. The measurement error is ≤2% in a temperature variation range of 30°C. This auto-correction sensor without a complicated manual calibration is helpful to the high accuracy measurement for on-chip integrated gas sensing.
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Folded-optics-based quartz-enhanced photoacoustic and photothermal hybrid spectroscopy (FO-QEPA-PTS) is reported for the first time. In FO-QEPA-PTS, the detection of the photoacoustic and photothermal hybrid signal is achieved through the use of a custom quartz tuning fork (QTF), thereby mitigating the issue of resonant frequency mismatch typically encountered in quartz-enhanced photoacoustic-photothermal spectroscopy employing multiple QTFs. A multi-laser beam, created by a multi-pass cell (MPC) with a designed single-line spot pattern, partially strikes the inner edge of the QTF and partially passes through the prong of the QTF, thereby generating photoacoustic and photothermal hybrid signals. To assess the performance of FO-QEPA-PTS, 1 % acetylene is selected as the analyte gas and the 2f signals produced by the photoacoustic, the photothermal, and their hybrid effects are measured. Comparative analysis against QEPAS and QEPTS reveals signal gain factors of â¼ 79 and â¼ 14, respectively, when these laser beams created by MPC excite the QTF operating at fundamental resonance mode in phase. In the FO-QEPA-PTS signal, the proportions of the photoacoustic and the photothermal effects induced by the multiple beams are â¼7 % and 93 %, respectively.
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SU8 is a cost-effective polymer material that is highly suitable for large-scale fabrication of waveguides. However, it has not been employed for on-chip gas measurement utilizing infrared absorption spectroscopy. In this study, we propose a near-infrared on-chip acetylene (C2H2) sensor using SU8 polymer spiral waveguides for the first time to our knowledge. The performance of the sensor based on wavelength modulation spectroscopy (WMS) was experimentally validated. By incorporating the proposed Euler-S bend and Archimedean spiral SU8 waveguide, we achieved a reduction in the sensor's size by over fifty percent. Leveraging the WMS technique, we evaluated the C2H2 sensing performance at 1532.83 nm for SU8 waveguides of lengths 7.4 cm and 13 cm. The limit of detection (LoD) values were 2197.1 ppm (parts per million) and 425.5 ppm, respectively, with an averaging time of 0.2 s. Furthermore, the experimentally obtained optical power confinement factor (PCF) closely approximated the simulated value, with a value of 0.0172 compared to the simulated value of 0.016. The waveguide loss is measured to be 3 dB/cm. The rise time and fall time were approximately 2.05 s and 3.27 s, respectively. This study concludes that the SU8 waveguide exhibits significant potential for high-performance on-chip gas sensing in the near-infrared wavelength range.
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On-chip waveguide sensors are potential candidates for deep-space exploration because of their high integration and low power consumption. Since the fundamental absorption of most gas molecules exists in the mid-infrared (e.g., 3-12 µm), it is of great significance to fabricate wideband mid-infrared sensors with high external confinement factor (ECF). To overcome the limited transparency window and strong waveguide dispersion, a chalcogenide suspended nanorib waveguide sensor was proposed for ultra-wideband mid-infrared gas sensing, and three waveguide sensors (WG1-WG3) with optimized dimensions exhibit a wide waveband of 3.2-5.6 µm, 5.4-8.2 µm, and 8.1-11.5 µm with exceptionally high ECFs of 107-116%, 107-116%, and 116-128%, respectively. The waveguide sensors were fabricated by a two-step lift-off method without dry etching to reduce the process complexity. Experimental ECFs of 112%, 110%, and 110% were obtained at 3.291 µm, 4.319 µm, and 7.625 µm, respectively, through methane (CH4) and carbon dioxide (CO2) measurements. A limit of detection of 5.9 ppm was achieved for an averaging time of 64.2 s through the Allan deviation analysis of CH4 at 3.291 µm, leading to a comparable noise equivalent absorption sensitivity of 2.3 × 10-5 cm-1 Hz-1/2 as compared to the hollow-core fiber and on-chip gas sensors.
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To realize early fire identification in cotton harvesting operations, a mid-infrared carbon monoxide (CO) sensor system was developed. To match the broadband light source with a 15° divergence angle, a multipass gas cell (MPGC) with an effective path length of 180 cm was designed to improve sensor sensitivity, leading to a limit of detection (LoD) of 0.83 parts-per-million by volume (ppmv). A damping module with springs at the bottom and front/back sides was fabricated, which can effectively reduce the vibration intensity by >80%. The sensor system can operate normally from -40 °C to 85 °C by stabilizing the temperature of the optical module through heating or cooling as well as using automotive electronic components. An adaptive early fire identification algorithm based on a dual-parameter threshold alarming method was proposed to avoid false and missing alarms. Field deployments on a harvester verified the good practicability of the sensor system.
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Monóxido de Carbono , Temperatura Baixa , Temperatura , Limite de DetecçãoRESUMO
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.
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A vehicle-deployed parts-per-billion in volume (ppbv)-level off-axis integrated cavity output spectroscopic (OA-ICOS) CH4/C2H6 sensor system was experimentally presented for mobile inspection of natural gas leakage in urban areas. For the time-division-multiplexing-based dual-gas sensor system, an antivibration 35-cm-long optical cavity with an effective path length of â¼2510 m was fabricated with a high-stability temperature and pressure control design. An Allan deviation analysis yielded a minimum detection limit of 0.2 ppbv for CH4 detection and 10 ppbv for C2H6 detection for a 1 s averaging time. A natural gas leakage source location algorithm was proposed using an improved hybrid Nelder-Mead simplex search method and a particle swarm optimization (NM-PSO) algorithm. For field industrial application, the accuracy of the sensor system and leakage source location algorithm was confirmed through a CH4/C2H6 cylinder leakage experiment on the campus. Furthermore, through natural gas pipeline network inspection measurements in urban areas, three types of leakage sources, including natural gas, biogas, and possible leakage source were respectively located and confirmed using the global positioning system and wind speed and direction measurement system, verifying the reliability and potential application of the vehicle-deployed inspection system for future natural gas pipeline leakage monitoring.
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Metano , Gás Natural , Metano/análise , Gás Natural/análise , Reprodutibilidade dos Testes , Análise EspectralRESUMO
In order to realize early fire detection and location, a mid-infrared carbon monoxide (CO) and carbon dioxide (CO2) dual-gas sensor system was developed, which mainly includes a gas pretreatment module, a CO2 sensor module, a CO sensor module, and a laptop monitoring platform. CO2 and CO absorption lines located at 4.26 µm and 4.66 µm, respectively, were selected to ensure good selectivity of the sensor system. A series of experiments were carried out to evaluate the sensor performance. The 10-90% response time of the CO and CO2 sensor modules was measured to be â¼ 30 s at a flow rate of 1 L/min, and the limits of detection (LoD) of CO2 and CO were assessed to be 5.66 parts per million by volume (ppmv) and 0.94 ppmv, respectively, when the averaging time was 0.25 s. According to the correlation between CO2 and CO concentration in the early fire stage, a method of early fire detection was studied and proposed using the normalized concentration ratio between CO and CO2 (C(CO)/C(CO2)) as the key alarm parameter. Based on gas turbulent diffusion (GTD) model combined with particle swarm optimization (PSO) algorithm, a mobile early fire location method was presented. Correlative experiment results verified that the reported sensor system has a good performance for early fire detection and location.
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Dióxido de Carbono , Monóxido de CarbonoRESUMO
In SF6 insulated high-voltage gas power systems, H2O is the most problematic impurity which not only decreases insulation performance but also creates an acidic atmosphere that promotes corrosion. Corrosion damages electrical equipment and leads to leaks, which pose serious safety hazards to people and the environment. A QEPAS-based sensor system for the sub-ppm level H2O detection in SF6 buffer gas was developed by use of a near-infrared commercial DFB diode laser. Since the specific physical constants of SF6 are strongly different from that of N2 or air, the resonant frequency and Q-factor of the bare quartz tuning fork (QTF) had changed to 32,763 Hz and 4173, respectively. The optimal vertical detection position was 1.2 mm far from the QTF opening. After the experimental optimization of acoustic micro-resonator (AmR) parameters, gas pressures, and modulation depths, a detection limit of 0.49 ppm was achieved for an averaging time of 1 s, which provided a powerful prevention tool for the safety monitoring in power systems.
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This publisher's note contains corrections to Opt. Lett.46, 4797 (2021)OPLEDP0146-959210.1364/OL.440361.
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A ppb-level H2S and CO photoacoustic spectroscopy (PAS) gas sensor was developed by using a two-stage commercial optical fiber amplifier with a full output power of 10 W. Two near-infrared diode lasers with the central wavenumbers of 6320.6â cm-1 and 6377.4â cm-1 were employed as the excitation laser source. A time-division multiplexing method was used to simultaneously detect CO and H2S with an optical switch. A dual-resonator structural photoacoustic cell (PAC) was theoretically simulated and designed with a finite element analysis. A µV level background noise was achieved with the differential and symmetrical PAC. The performance of the multi-component sensor was evaluated after the optimization of frequency, pressure and modulation depth. The minimum detection limits of 31.7 ppb and 342.7 ppb were obtained for H2S and CO at atmospheric pressure.
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A novel, to the best of our knowledge, mid-infrared chalcogenide (ChG) on magnesium fluoride (MgF2) waveguide gas sensor was fabricated by using the lift-off method. MgF2 was used as a lower cladding layer to increase the external confinement factor for enhancing light-gas interaction. Wavelength modulation spectroscopy (WMS) was used in carbon dioxide (CO2) detection at the wavelength of 4319 nm (2315.2cm-1). The limit of detection for the 1-cm-long sensing waveguide based on WMS is â¼0.3%, which is >8 times lower than the same sensor using direct absorption spectroscopy (DAS). The combination of WMS with the waveguide gas sensor provides a new measurement scheme for the performance improvement of on-chip gas detection.
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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 â¼12000 in atmospheric pressure) and a 10cm-long Fabry-Perot cavity (finesse â¼ 482). By probing a H2O line at 7306.75â cm-1, the developed OA-CETES sensor achieved a minimum detection limit (MDL) of 8.7 parts per million (ppm) for a 300â 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.
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Radial-cavity quartz-enhanced photoacoustic spectroscopy (RC-QEPAS) was proposed for trace gas analysis. A radial cavity with (0,0,1) resonance mode was coupled with the quartz tuning fork (QTF) to greatly enhance the QEPAS signal and facilitate the optical alignment. The coupled resonance enhancement effects of the radial cavity and QTF were analyzed theoretically and researched experimentally. With an optimized radial cavity, the detection sensitivity of QEPAS was enhanced by >1 order of magnitude. The RC-QEPAS makes the acoustic detection module more compact and optical alignment comparable with a bare QFT, benefiting the usage of light sources with poor beam quality.
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A surface-enhanced infrared absorption spectroscopic chalcogenide waveguide sensor based on the silver island film was proposed for the first time to enhance the sensing performance in both liquid and gas phases. The chalcogenide waveguide sensor was fabricated by the lift-off and oblique angle deposition methods. The surface morphology of the silver island film with different thicknesses was characterized. The absorption of ethanol (liquid) at a wavelength of 1654 nm and that of methane (gas) at 3291 nm were measured using the fabricated chalcogenide waveguide sensor. The chalcogenide waveguide sensor integrated with the 1.8 nm-thick silver island film revealed the best sensing performance. With an acceptable increased waveguide loss resulting from the fabrication of the film, the absorbance enhancement factors for ethanol and methane were experimentally obtained to be >1.5 and >2.3, respectively. The 1σ limit of detection of methane for the sensor integrated with the 1.8 nm-thick silver island film was â¼4.11% for an averaging time of 0.2 s. The mathematic relation between the absorbance enhancement factor and the waveguide loss was derived for sensing performance improvement. Also, the proposed rectangular waveguide sensor provides an idea for the design of a sensor-on-a-chip instead of other waveguide sensors with a high requirement of fabrication accuracy, for example, a slot waveguide or a photonic crystal waveguide.
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We demonstrated a novel multi-input multi-output (MIMO) laser-to-cavity coupling scheme in off-axis integrated cavity output spectroscopy (OA-ICOS) for cavity mode noise suppression. Theoretical investigation was performed to explore the relation between the number of splitting beams and the MIMO parameters. Mode distribution and propagation inside the cavity was simulated. The noise suppression factor of the MIMO scheme and the noise level and dominated noise in the cavity were studied based on cavity mode simulation. Methane measurements were carried out using a dual-input dual-output (DIDO, N = 2) sensor system to validate the presented scheme, and good agreement was found between simulation and experiment.
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A multi-pass quartz-enhanced photoacoustic spectroscopy (MP-QEPAS)-based trace gas sensor is reported. In MP-QEPAS, a multi-pass laser beam pattern through the prong spacing of a quartz tuning fork (QTF) is obtained by means of two right-angle prisms. A large QTF with the prong length of 17 mm and prong spacing of 0.8 mm was employed to increase the passage of multi-pass time and ease the alignment of the beam reflection pattern through the QTF. This multi-pass configuration allows the laser beam to pass through the QTF prong spacing six times. Water vapor (H2O) was chosen as target gas to investigate the performance of the MP-QEPAS sensor. Compared to a conventional QEPAS measurement, the MP-QEPAS technique provided an enhancement of signal level of â¼3.2 times.