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- 摘要
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Evanescent field ratio enhancement of a modified ridge waveguide structure for methane gas sensing application
摘要： We presented a significant improvement of the evanescent field ratio in a ridge waveguide modified into a dual hybrid plasmonic waveguide by tapering the middle section of the waveguide and placing a gold layer on both sides with a sub-wavelength gap. The waveguide geometry is optimized at 3.392 μm which is an absorption line of methane gas. The proposed waveguide scheme provides a large waveguide cross-section which facilitates a light with an enhanced evanescent field in the middle. To validate the study, the evanescent field ratio, propagation loss, confinement factor and electric field distribution of the waveguide is studied via the finite element method. Additionally, the device is also proposed. An elevated evanescent field ratio of 0.74 is obtained with a propagation loss of ~0.7 dB/μm. The sensitivity of 0.0715 (mW/gas conc.) is obtained for the proposed waveguide scheme by calculating the decay in transmission power due to absorption by the gas in the medium.
关键词： Evanescent field absorption gas sensor,3.392 μm,methane,mid-infrared,Lambert-Beer law
更新于2025-09-23 15:21:01
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Nonlinear Optics
摘要： The mid-infrared atmospheric window of 3–5.5 μm holds valuable information regarding molecular composition and function for fundamental and applied spectroscopy. Using a robust, mode-locked fiber-laser source of < 11 fs pulses in the near infrared, we explore quadratic (χe2T) nonlinear optical processes leading to frequency comb generation across this entire mid-infrared atmospheric window. With experiments and modeling, we demonstrate intrapulse difference frequency generation that yields few-cycle mid-infrared pulses in a single pass through periodically poled lithium niobate. Harmonic and cascaded χe2T nonlinearities further provide direct access to the carrier-envelope offset frequency of the near infrared driving pulse train. The high frequency stability of the mid-infrared frequency comb is exploited for spectroscopy of acetone and carbonyl sulfide with simultaneous bandwidths exceeding 11 THz and with spectral resolution as high as 0.003 cm?1. The combination of low noise and broad spectral coverage enables detection of trace gases with concentrations in the part-per-billion range.
关键词： few-cycle pulses,mid-infrared,frequency comb,spectroscopy,nonlinear optics
更新于2025-09-23 15:21:01
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Ultrahigh-Speed Mid-Infrared Photodetectors With 2-D Electron Gas in a CdTe/PbTe Heterojunction
摘要： A CdTe/PbTe heterojunction (HJ) yields two-dimensional electron gas (2DEG) with a high electron density and mobility. Ultrahigh-speed and room-temperature operating mid-infrared photodetectors are developed with the 2DEG. The photoresponse of the detectors originates from the intrinsic response of PbTe by virtue of the conduction-band and valence-band alignment of the HJ. The extremely short rise and decay photoresponse time demonstrate a major advantage of the 2DEG. At λ = 3.0 μm and a bias voltage of 100 mV, the responsivity and detectivity reach 0.94 A/W and 2 × 1010 Jones, respectively. The excellent performance of the detectors renders promising applications in novel mid-infrared frequency detection systems.
关键词： two-dimensional electron gas (2DEG),room-temperature (RT) operation,ultrahigh-speed response,Detectivity,mid-infrared detector
更新于2025-09-23 15:21:01
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Mid-infrared dual-comb spectroscopy with room-temperature bi-functional interband cascade lasers and detectors
摘要： Interband cascade (IC) laser structures offer attractive potential for operation at room temperature as both broadband coherent sources of mid-infrared light and fast photodetectors. This makes the realization of extremely compact spectrometers on a monolithic platform possible, and even dual-comb spectroscopy (DCS) configurations. IC comb devices are perfect candidates for this configuration, since they develop near-THz-wide optical frequency comb spectra from a millimeter-sized cavity, using a multi-stage structure that can also function as a very fast photodetector. In this work, we leverage IC photodetectors with a gigahertz bandwidth to demonstrate a self-contained, free-running, room-temperature DCS system in the mid-infrared. The DCS system used detection by the same bi-functional IC device structure to measure 1,1-difluoroethane over (cid:2)600 GHz of optical coverage around 3.6 mm. These results show that the IC platform is suitable for full integration as a broadband, high-resolution on-chip spectrometer in a future chemical sensing system.
关键词： mid-infrared,photodetectors,dual-comb spectroscopy,interband cascade lasers,room-temperature
更新于2025-09-23 15:21:01
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Volume Fabrication of Quantum Cascade Lasers on 200 mm-CMOS pilot line
摘要： The manufacturing cost of quantum cascade lasers is still a major bottleneck for the adoption of this technology for chemical sensing. The integration of Mid-Infrared sources on Si substrate based on CMOS technology paves the way for high-volume low-cost fabrication. Furthermore, the use of Si-based fabrication platform opens the way to the co-integration of QCL Mid-InfraRed sources with SiGe-based waveguides, enabling realization of optical sensors fully integrated on planar substrate. We report here the fabrication and the characterization of DFB-QCL sources using top metal grating approach working at 7.4 μm fully implemented on our 200 mm CMOS pilot line. These QCL featured threshold current density of 2.5 kA/cm2 and a linewidth of 0.16 cm?1 with a high fabrication yield. This approach paves the way toward a Mid-InfraRed spectrometer at the silicon chip level.
关键词： Mid-Infrared sources,DFB-QCL sources,Si substrate,CMOS technology,Quantum Cascade Lasers
更新于2025-09-23 15:21:01
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Enhanced 2???μm Mida??Infrared Laser Output from Tm <sup>3+</sup> a??Activated Glass Ceramic Microcavities
摘要： Transparent glass ceramics (GCs) consisting of an homogeneous glass phase and a well-dispersed crystal phase are considered as ideal optical gain materials potentially applied in optoelectronic devices due to the combination of facile processability of glass and the intense crystal ?eld of nanocrystals. Here, a heat-induced nanocrystal-in-glass method is employed to integrate the active ions Tm3+ into Bi2Te4O11 nanocrystals with an intense crystal ?eld to realize an enhanced microlaser output. This strategy endows the e?cient tellurate GC microcavity laser operating at ≈2 μm. Compared with the laser properties of as-prepared glass microcavities, the pump threshold (260 μW) is as low as less than a quarter and the slope e?ciency (0.0296%) is 5.5 times higher. Furthermore, by carefully engineering the heat treatment temperature and duration, the crystal size and distribution can be precisely controlled. Thus, the Rayleigh scattering loss that is detrimental to quality (Q) factor is e?ectively suppressed and the GC microcavities with high Q factors up to 105 are successfully obtained. This work provides useful insight on the development of optical functional materials and expands the practical applications of GC microcavities in various optoelectronic ?elds.
关键词： mid-infrared lasers,glass-ceramic microspheres,microcavities,whispering gallery mode
更新于2025-09-23 15:21:01
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Tunable graphene-on-insulator band-stop filter at the mid-infrared region
摘要： This paper presents a novel graphene-on-insulator (GOI) band-stop filter in the mid-infrared region. The finite-difference time-domain method is used to model our GOI basic and advanced filters and calculate their transmission spectra for different graphene layers at every gate-source voltage. The numerical results reveal the resonance wavelength, modulation depth, and bandwidth of the advanced filter can be tuned in the range of 11.5 to 30 μm, ?57 to ?60 dB, and 2 to 4 μm, respectively. These results are obtained by variation of the physical parameters, such as the number of overlapped filters, the number of graphene layers, and the applied chemical potential. Our results indicate that the proposed advanced band-stop filter is an excellent device to be used in an ultra-fast active graphene-based plasmonic systems for THz applications.
关键词： Finite-difference time-domain,Graphene-on-insulator,Transmission,Mid-infrared,Band-stop filter
更新于2025-09-23 15:21:01
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Higha??Responsivity Mida??Infrared Black Phosphorus Slow Light Waveguide Photodetector
摘要： Black phosphorus (BP) offers unique opportunities for mid-infrared (MIR) waveguide photodetectors due to its narrow direct bandgap and layered lattice structure. Further miniaturization of the photodetector will improve operation speed, signal-to-noise ratio, and internal quantum efficiency. However, it is challenging to maintain high responsivities in miniaturized BP waveguide photodetectors because of reduced light–matter interaction lengths. To address this issue, a method utilizing the slow light effect in photonic crystal waveguides (PhCWGs) is proposed and experimentally demonstrated. A shared-BP photonic system is proposed and utilized to fairly and precisely characterize the slow light enhancement. Close to the band edge around 3.8 μm, the responsivity is enhanced by more than tenfold in the BP photodetector on a 10 μm long PhCWG as compared with the counterpart on a subwavelength grating waveguide. At a 0.5 V bias, the BP PhCWG photodetector achieves a 11.31 A W?1 responsivity and a 0.012 nW Hz?1/2 noise equivalent power. The trap-induced photoconductive gain is validated as both the dominant photoresponse mechanism and the major limiting factor of the response speed. The BP slow light waveguide photodetector is envisioned to realize miniaturized high-performance on-chip MIR systems for widespread applications including environmental monitoring, industrial process control, and medical diagnostics.
关键词： waveguides,slow light,photodetectors,mid-infrared,black phosphorus
更新于2025-09-23 15:21:01
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Mid-infrared saturated absorption spectroscopy inside a hollow glass waveguide
摘要： We report the saturation spectroscopy of carbon dioxide inside a hollow glass waveguide (GW) using a tunable mid-infrared difference frequency generation (DFG) source. This DFG source was generated in a periodically poled lithium niobate crystal with a tuning range from 3.97 to 4.71 μm. Saturated spectroscopy was performed on the R(60) transition of CO20001 ← 0000 band at 4.2 μm inside a hollow GW of diameter 300 μm and length 1 m. The saturation dip signal was found with a pump power as low as 0.18 mW inside the hollow GW. The linewidth of the dip was determined to be 4.40 MHz.
关键词： Nonlinear optical interaction,Mid-infrared,Saturation spectroscopy,Hollow glass waveguide
更新于2025-09-23 15:21:01
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EXPRESS: Comparison of Individual and Integrated Inline Raman, Near-Infrared, and Mid-Infrared Spectroscopic Models to Predict the Viscosity of Micellar Liquids
摘要： In many industries, viscosity is an important quality parameter which significantly affects consumer satisfaction and process efficiency. In the personal care industry, this applies to products like shampoo and shower gels whose complex structures are built up of micellar liquids. Measuring viscosity offline is well established using benchtop rheometers and viscometers. The difficulty lies in measuring this property directly in the process via on or inline technologies. Therefore, the aim of this work is to investigate whether proxy measurements using in-line vibrational spectroscopy, e.g., near infrared (NIR), mid-infrared (MIR), and Raman, can be used to predict the viscosity of micellar liquids. As optical techniques, they are non-destructive and easily implementable process analytical tools where each type of spectroscopy detects different molecular functionalities. Inline fiber optic coupled probes were employed; a transmission probe for NIR measurements, an attenuated total reflectance (ATR) probe for MIR and a backscattering probe for Raman. Models were developed using forward interval partial least squares (iPLS) variable selection and log viscosity was used. For each technique combinations of pre-processing techniques were trialed including detrending, Whittaker filters, standard normal variate (SNV) and multiple scatter correction (MSC). The results indicate that all three techniques could be applied individually to predict the viscosity of micellar liquids all showing comparable errors of prediction: NIR: 1.75 Pa s; MIR: 1.73 Pa s; and Raman: 1.57 Pa s. The Raman model showed the highest relative prediction deviation (RPD) value of 5.07, with the NIR and MIR models showing slightly lower values of 4.57 and 4.61, respectively. Data fusion was also explored to determine whether employing information from more than one dataset improved the model quality. Trials involved weighting datasets based on their signal to noise ratio and weighting based on transmission curves (IR datasets only). The signal to noise weighted NIR-MIR-Raman model showed the best performance compared with both combined and individual models with a RMSECV of 0.75 Pa s and an RPD of 10.62. This comparative study provides a good initial assessment of the three prospective process analytical technologies for the measurement of micellar liquid viscosity but also provides a good basis for general measurements of inline viscosity using commercially available process analytical technology. With these techniques typically being employed for compositional analysis, this work presents their capability in the measurement of viscosity–an important physical parameter, extending the applicability of these spectroscopic techniques.
关键词： MIR,viscosity,near-infrared,micellar liquids,spectroscopy,partial least squares,Raman,mid-infrared,NIR,PLS,Inline
更新于2025-09-23 15:19:57