Mid-infrared Wavelengths Research Articles

Highly oriented as-grown beta-phase bismuth oxide for optical MEMS

AbstractReactive sputtering of bismuth has been used to form highly oriented beta-phase Bi2O3 thin films at 120 °C. Notably, the films consist of nearly vertical ~ 50 nm diameter nano-filaments of highly aligned β phase pure bismuth oxide. The optical characteristics of the films include a direct optical bandgap of 3.95 eV at 300 K and nearly negligible optical absorption in the wavelength range from 500 to 3000 nm. Nanoindentation experiments show that the mechanical characteristics of the films include reduced modulus and hardness values of 90 and 4.5 GPa, respectively. As fabricated, the films exhibit tensile stress which in combination with a relatively high refractive index value in the range of 2.4–2.5 makes the realized Bi2O3 films structurally and optically suitable for fabrication of optical microelectromechanical (MEMS) devices with applications in the visible to mid-infrared wavelength region, such as MEMS-based Fabry–Pérot microspectrometers, which is demonstrated through simulations. Graphical Abstract

Incorporating Er:YAP Microcrystals Into Tellurite Fiber Using Volumetric Interface Doping

AbstractIn this semi‐quantitative study, laser crystal microparticles which are potentially capable of generating mid‐infrared (MIR) light are incorporated into MIR transmitting optical fibers using a volumetric interface doping technique that combines interface doping with volumetric doping. Using confocal microscopy with a refractive index matching fluid, the Er:YAP microcrystals (MCs) inside the tellurite glass fiber are observed based on the detection of the green upconversion fluorescence emission of Er3+ ions, produced under excitation at 976 nm and localized at the central region within the fiber. The key outcome from this proof‐of‐concept study is that MC particles that are fused with the glass during the fiber drawing process survived heat treatment because the MC particles are exposed for a short time to a glass fluid with high viscosity of ≈105 Pa.s, which prevented the glass from exerting a dissolution effect. The survival of the MCs demonstrated the viability of the doping technique for fabricating fibers with exotic crystal‐glass combinations for applications including good refractive index matching across the pump and lasing bands of rare earth ions. This latter parameter provides significant particle size flexibility whilst minimizing additional loss from scattering especially at MIR wavelengths where the MC diameter‐to‐wavelength ratio becomes smaller.

Hole diffusion length and mobility of a long wavelength infrared InAs/InAsSb type-II superlattice nBn design

We demonstrated high-performance 8.9 μm cutoff wavelength nBn InAs/InAsSb type-II strained-layer superlattice (T2SL). These detectors exhibit a long minority carrier (hole) lifetime of 1.2 μs at 80 K, high quantum efficiency of 40% for back-side illuminated devices without antireflection coating, and low dark current density of 4.6 × 10−6 A/cm2 at 80 K. We measured absorption, minority carrier (hole) lifetime, quantum efficiency, and spectral response as a function of the temperature and applied bias. We investigated the temperature dependence of the hole diffusion length and mobility and found that their values increase with temperature from 1.3 μm and 6.5 cm2/Vs at 30 K to 6.5 μm and 36 cm2/Vs at T = 90 K. We compared the measured diffusion length and mobility of holes in long-wavelength infrared (LWIR) T2SL with these parameters of a high-performance mid-wavelength infrared (MWIR) T2SL. Unexpectedly, hole mobility in LWIR T2SL was found to be higher than in MWIR that is contrary to the theoretical predictions.

An Ultra-Wideband Metamaterial Absorber Ranging from Near-Infrared to Mid-Infrared

This study focused on designing an ultra-wideband metamaterial absorber, consisting of layers of Mn (manganese) and MoO3 (molybdenum trioxide) arranged in a planar interleaving pattern, with a matrix square-shaped Ti (titanium) on the top MoO3 layer. Key features of this research included the novel use of Mn and MoO3 in a planar interleaving configuration for designing an ultra-wideband absorber, which was rarely explored in previous studies. MoO3 thin film served as the fundamental material, leveraging its favorable optical properties and absorption capabilities in the infrared spectrum. Alternating layers of Mn and MoO3 were adjusted in thickness and order to optimize absorptivity across desired wavelength ranges. Another feature is that the Mn and MoO3 materials in the investigated absorber had a planar structure, which simplified the manufacturing of the absorber. Furthermore, the topmost layer of square-shaped Ti was strategically placed to enhance the absorber’s bandwidth and efficiency. When the investigated absorber lacked a Ti layer, its absorptivity and bandwidth significantly decreased. This structural design leveraged the optical properties of Mn, MoO3, and Ti to significantly expand the absorption range across an ultra-wideband spectrum. When the Ti height was 280 nm, the investigated absorber exhibited a bandwidth with absorptivity greater than 0.9, spanning from the near-infrared (0.80 μm) to the mid-infrared (9.07 μm). The average absorptivity in this range was 0.950 with a maximum absorptivity of 0.989. Additionally, three absorption peaks were observed at 1010, 2510, and 6580 nm. This broad absorption capability makes it suitable for a variety of optical applications, ranging from near-infrared to mid-infrared wavelengths, including thermal imaging and optical sensing.

Synergic Effect of N and Se Facilitates Photoelectric Performance in Co-Hyperdoped Silicon.

Femtosecond-laser-fabricated black silicon has been widely used in the fields of solar cells, photodetectors, semiconductor devices, optical coatings, and quantum computing. However, the responsive spectral range limits its application in the near- to mid-infrared wavelengths. To further increase the optical responsivity in longer wavelengths, in this work, silicon (Si) was co-hyperdoped with nitrogen (N) and selenium (Se) through the deposition of Se films on Si followed by femtosecond (fs)-laser irradiation in an atmosphere of NF3. The optical and crystalline properties of the Si:N/Se were found to be influenced by the precursor Se film and laser fluence. The resulting photodetector, a product of this innovative approach, exhibited an impressive responsivity of 24.8 A/W at 840 nm and 19.8 A/W at 1060 nm, surpassing photodetectors made from Si:N, Si:S, and Si:S/Se (the latter two fabricated in SF6). These findings underscore the co-hyperdoping method's potential in significantly improving optoelectronic device performance.

Unveiling the HD 95086 system at mid-infrared wavelengths with JWST/MIRI

Context. Mid-infrared imaging of exoplanets and disks is now possible with the coronographs of the Mid-InfraRed Instrument (MIRI) on the James Webb Space Telescope (JWST). This wavelength range unveils new features of young directly imaged systems and allows us to obtain new constraints for characterizing the atmosphere of young giant exoplanets and associated disks. Aims. These observations aim to characterize the atmosphere of the planet HD 95086 b by adding mid-infrared information so that the various hypotheses about its atmospheric parameters values can be unraveled. Improved images of cirsumstellar disks are provided. Methods. We present the MIRI coronagraphic imaging of the system HD 95086 obtained with the F1065C, F1140, and F2300C filters at central wavelengths of 10.575 µm, 11.3 µm, and 23 µm, respectively. We explored the method for subtracting the stellar diffraction pattern in the particular case when bright dust emitting at short separation is present. Furthermore, we compared different methods for extracting the photometry of the planet. Using the atmospheric models Exo-REM and ATMO, we measured the atmospheric parameters of HD 95086 b. Results. The planet HD 95086 b is detected at the two shortest MIRI wavelengths F1065C and F1140C. The contribution from the inner disk of the system is also detected. It is similar to that in the HR 8799 system. The outer colder belt is imaged at 23 µm. Background objects are observed in all filters. The mid-infrared photometry provides better constraints on the atmospheric parameters. We evaluate a temperature of 800–1050 K, consistent with one previous hypothesis that only used near-infrared data. The radius measurement of 1.0–1.14 RJup is better aligned with evolutionary models, but still smaller than predicted. These observations allow us to refute the hypothesis of a warm circumplanetary disk. Conclusions. HD 95086 is one of the first exoplanetary systems to be revealed at mid-infrared wavelengths. This highlights the interests and challenges of observations at these wavelengths.

JWST Observations of Young protoStars (JOYS). HH211: Textbook case of a protostellar jet and outflow

Due to the high visual extinction and lack of sensitive mid-infrared (MIR) telescopes, the origin and properties of outflows and jets from embedded Class\,0 protostars are still poorly constrained. We aim to characterise the physical, kinematic, and dynamical properties of the HH\,211 jet and outflow, one of the youngest protostellar flows. We used the James Webb Space Telescope (JWST) and its Mid-InfraRed Instrument (MIRI) in the 5--28 mu m range to study the embedded HH\,211 flow. We mapped a 0farcm 95times 0farcm 22 region, covering the full extent of the blueshifted lobe, the central protostellar region, and a small portion of the redshifted lobe. We extracted spectra along the jet and outflow and constructed line and excitation maps of both atomic and molecular lines. Additional JWST NIRCam H$_2$ narrow-band images (at 2.122 and 3.235\,mu m) provide a visual-extinction map of the whole flow, and are used to deredden our data. The jet-driving source is not detected even at the longest MIR wavelengths. The overall morphology of the flow consists of a highly collimated jet, which is mostly molecular (H$_2$, HD) with an inner atomic ( structure. The jet shocks the ambient medium, producing several large bow shocks (BSs) that are rich in forbidden atomic ( and molecular lines (H$_2$, HD, CO, OH, H$_2$O, CO$_2$, HCO$^+$), and is driving an H$_2$ molecular outflow that is mostly traced by low-$J$, $v=0$ transitions. Moreover, H$_2$ 0-0\,S(1) uncollimated emission is also detected down to 2arcsec --3arcsec (sim 650--1000\,au) from the source, tracing a cold ($T$=200--400\,K), less dense, and poorly collimated molecular wind. Two H$_2$ components (warm, $T$=300--1000\,K, and hot, $T$=1000--3500\,K) are detected along the jet and outflow. The atomic jet ( at 26\,mu m) is detected down to sim 130\,au from the source, whereas the lack of H$_2$ emission (at 17\,mu m) close to the source is likely due to the large visual extinction ( Dust-continuum emission is detected at the terminal BSs and in the blue- and redshifted jet, and is likely attributable to dust lifted from the disc. The jet shows an onion-like structure, with layers of different size, velocity, temperature, and chemical composition. Moreover, moving from the inner jet to the outer BSs, different physical, kinematic, and excitation conditions for both molecular and atomic gas are observed. The mass-flux rate and momentum of the jet, as well as the momentum flux of the warm H$_2$ component, are up to one order of magnitude higher than those inferred from the atomic jet component. Our findings indicate that the warm H$_2$ red component is the main driver of the outflow, that is to say it is the most significant dynamical component of the jet, in contrast to jets from more evolved YSOs, where the atomic component is dominant.

Extending mid-infrared wavelength to 6.84 μm in oxide nonlinear optical crystal via birefringence dispersion management.

Extending lasing wavelengths to the mid-infrared (MIR) spectrum is vital for both civilian and military applications; however, it remains challenging when employing oxide nonlinear optical crystals. In this study, we report the generation of MIR nanosecond pulses via difference frequency generation (DFG) with a near-IR pump using a newly designed langasite (LGS) crystal, La3(Nb0.6Ta0.4)0.5Ga5.5O14 (LGNT0.4), which incorporates birefringence dispersion management techniques with La3Ga5.5Nb0.5O14 (LGN) as a template. Due to the improved effective nonlinear coefficients and the maintained IR cutoff relative to LGN, the tunable DFG laser in LGNT0.4 extended from 4.24 to 6.84 μm, delivering a maximum pulse energy of 16.3 μJ at 5.02 μm. To the best of our knowledge, this is the first known oxide material capable of generating tunable nanosecond pulsed lasers beyond 6 μm at μJ-level energies, demonstrating promising potential for high-intensity MIR laser systems owing to its high laser damage threshold.

The Challenge of Detecting Remote Spectroscopic Signatures from Radionuclides

The characterization of exoplanetary atmospheres through transit spectra is becoming increasingly feasible, and technology for direct detection remains ongoing. The possibility of detecting spectral features could enable quantitative constraints on atmospheric composition or even serve as a potential biosignature, with the sensitivity of the instrument and observation time as key limiting factors. This paper discusses the possibility that future remote observations could detect the presence of radioactive elements in the atmospheres of exoplanets. Such radionuclides could arise from cosmogenic or geologic sources, as well as from industrial sources, all of which occur on Earth. The detection of radionuclides in an exoplanetary atmosphere could reveal important properties about the planet’s geology or space environment and potentially could serve as a technosignature. However, many radionuclides, including those from industrial sources, attach to aerosol or other particles that cannot be remotely characterized. Limited experimental and theoretical spectral data exist for long-lived radionuclides, but the sensitivity required to detect the spectral features of some known radionuclides would be at least several orders of magnitude greater than required to detect the spectral features of molecular oxygen. Present-day remote spectroscopic observing mission concepts at ultraviolet to mid-infrared wavelengths are not sensitive to discern the presence of radionuclides in exoplanetary atmospheres. Interplanetary fly-by or probe missions may be more likely to provide such data in the future.

Ultra-broadband selective tailoring of infrared spectral features for the application of compatible infrared and laser stealth

With the rapid development of detection technology, aircraft face growing threats from various detectors covering visible to infrared light. Therefore, aircraft must be equipped with the ability of compatible stealth. The emergency of the metasurface provides a promising method to realize this purpose. On this basis, in this work, a composite periodic metasurface is proposed by employing the type of metal-insulator-metal (MIM) structure for compatible infrared and laser stealth. In one unit cell, different dimensions of patterns are used to give rise to magnetic polaritons (MPs) at specific wavelengths. Through overall optimization of parameters of single periodic structures and the internal mechanisms in composite structures, appropriate parameters and arrangements are selected to obtain the required spectral features from laser to mid-infrared wavelengths. The simulated results demonstrate that the absorption at 1.06 μm can be over 70% and the absorption peaks in the region of 5∼8 μm are over 74%. High absorption at 1.06 μm is suitable for laser stealth, and the ability of high-performance infrared stealth comes with the advantages of low emissivity at the atmosphere windows and radiative cooling at the non-atmosphere window. This design is easy to fabricate and has a promising perspective for various compatible stealth and many other applications.

Imaging with an inverse-designed 50 mm-diameter f/1 MWIR flat lens with enhanced field of view and depth of focus.

We utilize inverse design and grayscale optical lithography to create a flat lens with a diameter and focal length of 50 mm, operating in the mid-wavelength infrared (MWIR) band. This lens demonstrates an extended depth of focus (DOF ≥±100μm), a field of view (FOV ≥20°), and an angular resolution of 300μrad. We characterize the lens's performance and use it as the primary optic in a hybrid refractive-diffractive telescope, which increases the angular resolution to 160μrad. Using this telescope, we perform video imaging of aircraft and vehicles. Our experiments were constrained by the higher f-number of the focal plane array. Nonetheless, through rigorous simulations, we demonstrate that the inverse-designed flat lens surpasses the performance of a conventional Fresnel zone plate (FZP) in DOF and in FOV, even under these limitations. The flat lens, weighing approximately 20g, is significantly lighter than its refractive counterparts, confirming the feasibility of high-resolution, lightweight MWIR imaging systems.

Resolving Twin Jets and Twin Disks with JWST and ALMA: The Young WL 20 Multiple System

We report the discovery of jets emanating from pre-main-sequence objects exclusively at mid-infrared wavelengths, enabled by the superb sensitivity of JWST’s Mid-Infrared Instrument Medium-Resolution Spectrometer. These jets are observed only in lines of [Ni ii], [Fe ii], [Ar ii], and [Ne ii]. The H2 emission, imaged in eight distinct transitions, has a completely different morphology, exhibiting a wide-angled, biconical shape, symmetrically distributed about the jet axes. Synergistic high-resolution Atacama Large Millimeter/submillimeter Array (ALMA) observations resolve a pair of side-by-side edge-on accretion disks lying at the origin of the twin mid-infrared jets. Assuming coevality of the components of the young multiple system under investigation, the system age is at least (2–2.5) × 106 yr, despite the discrepantly younger age inferred from the spectral energy distribution of the combined edge-on disk sources. The later system evolutionary stage is corroborated by ALMA observations of CO(2−1), 13CO(2−1), and C18O(2−1), which show no traces of molecular outflows or remnant cavity walls. Consequently, the observed H2 structures must have their origins in wide-angled disk winds, in the absence of any ambient, swept-up gas. In the context of recent studies of protostars, we propose an outflow evolutionary scenario in which the molecular gas component dominates in the youngest sources, whereas the fast, ionized jets dominate in the oldest sources, as is the case for the twin jets discovered in the WL 20 system.

Developing a robust sensor for infrared imaging bolometers.

A new type of large area sensor for infrared imaging bolometers has been developed. It replaces the thin and fragile free-standing metal foils, which typically have been used, with a multi-layer coated sapphire (or diamond) substrate. Sapphire is transparent to mid-infrared wavelengths, is robust against transients, and can be thick enough to even be the vacuum window. The primary radiation absorber is still a thin deposited metal layer, but now it is partially insulated from the supporting sapphire substrate by a black (carbon-based) layer, which also acts as a blackbody remitter. Test results indicate 6× more noise equivalent power density (estimated NEPD = 23 W/m2 at 5ms camera exposure time, foil temperature decay time 60ms) for a 2μm gold-coated sapphire disk compared to estimated NEP = 4 W/m2 at 1.8ms exposure time, with foil decay time 420ms, for a nominal 2.5μm thick platinum-free-standing foil.

Optical analog computing for salient object detection in complex scenes via dielectric metasurface

Optical analog computing overcomes the throughput and computational speed limitations of traditional digital computing, facilitating salient object detection on platforms that rapidly process massive image data, such as optical remote sensing. Further device miniaturization and integration can be achieved by replacing filters in optical analog computing with metasurface. Based on the combination of optical analog computing and dielectric metasurface, we proposed an optical analog cross-correlation operation operating in the mid-infrared wavelength band to achieve the real-time and compact salient object detection. Even in extremely complex scenes, this cross-correlation operation can be used to identify and segment target patterns based on several target features accurately. The proposed optical analog cross-correlation operation may find applications in object tracking, medical image segmentation, and person re-identification.

Advanced visualisation of biomass charcoal combustion dynamics using MWIR hyperspectral and LWIR thermal imaging under varied airflow conditions

Biomass charcoal combustion is a complex process, significantly influenced by various operating parameters. Among these parameters, air supply emerges as a critical factor affecting combustion efficiency, gas emissions, and thermal dynamics. In this study, we explored these complex interdependencies using a novel combination of mid-wavelength infrared (MWIR) hyperspectral imaging and long-wavelength infrared (LWIR) thermal imaging, under different airflow rates. Our findings demonstrated that while increased airflow accelerated the overall combustion rate, it simultaneously decreased combustion efficiency. Specifically, the thermal profiles showed an increased surface temperature at a low flowrate (0.5 L/min) while decreasing in temperature with higher flowrates. The decreased system temperature led to a lower combustion efficiency because of the reduced conversion rate from combustible gases (CH4 and CO) into CO2 and H2O. Additionally, the results also demonstrated that cooling effects of the high flowrates primarily impeded the solid-phase combustion stage. This is further corroborated by the temporal and spatial variation in the emissions of key gas species (H2O vapor, CH4, CO, and CO2) observed through hyperspectral imaging. The emission evolution of these gases displayed the different stages of the gas-phase and solid-phase combustion. The spatial distribution of the trace gases showed a decreased distribution radius due to the enhanced diffusion to the fuel surface when the airflow increases, aligning well with the two-film model established in the literature. Furthermore, we utilised spectral radiance ratios (CO/CO2, CH4/CO2, H2O/CO2) to gain additional insights into the combustion dynamics. These ratios evidenced the decrease in combustion efficiency at high airflow rates. Finally, the increased H2O/CO2 ratio further demonstrated the impeded char combustion and a shift towards pyrolysis at higher airflow rates because of the decreased thermal equilibrium of the system. The findings from this study provide critical insights into the dynamics of biomass charcoal combustion and illuminates the path for optimising energy efficiency and assessing the environmental implications from burning biomass fuels.

The impact of anodic mesh density and halogen anions on the optical characteristics of gradient refractive index microlens arrays fabricated in chalcohalide glass via microthermal poling

Gradient refractive index microlens arrays (GRIN MLAs), covering the visible to mid-infrared wavelength range, are imprinted in GeS2-Ga2S3-CsX (X = Cl, Br, and I) chalcohalide glasses by an efficient and economical microthermal poling process. This study investigates the impact of anodic mesh number (ranging from 400 to 2000 mesh) and halogen anions on the optical properties, including focal length, resolution, and aberration. Findings reveal that as the mesh number decreases, the focal length and aberration of GRIN MLAs increase. Optimal resolution is achieved with the 500 mesh sample, which also shows the best phase difference performance. The migration depth of Cs+ ions, influenced by halogen anions (from Cl to I), results in contrasting optical properties between lower mesh (400–750) and higher mesh (1000–2000) samples. Notably, the Cl-500 GRIN MLAs demonstrate a focal length of 615.0 μm, a maximum resolution of 6.35 lp/mm, and minimal aberration of −0.0591. These changes are attributed to the predominant transverse and longitudinal migration of Cs+ ions in mesh square areas. This research highlights the relationship between microthermal poling conditions, ion migration, and optical performance, providing valuable insights for the application of GRIN MLAs in advanced optical systems.

High-power hollow-core fiber gas laser at 3.1 µm with a linear-cavity structure.

Mid-infrared hollow-core fiber (HCF) gas lasers based on a population inversion regime of gas molecules have made advanced development in recent years, but mostly with single-pass cavity-free structures. Here, we demonstrated a 3.1 µm high-power acetylene-filled HCF continuous wave (CW) laser and a self-Q-switched pulse laser with a linear-cavity structure. This configuration not only facilitates the transformation of amplified spontaneous emission into the laser output but also enhances the coherence of the light source and imparts distinct cavity mode characteristics. Harnessing a homemade high-power 1535 nm single-frequency fiber laser that served as the pump source, a CW laser output of 8.23 W at 3.1 µm was achieved, which is over three orders of magnitude higher than those in reported works so far. The corresponding slope efficiency of 31.8% and beam quality of Mx 2 = 1.18 and My 2 = 1.15 were characterized. When the gas pressure was up to 50 mbar, the laser generated a 3.1 µm self-Q-switched pulse with an output power of 1.98 W as well as a pulse width of 45 ns under the repetition rate of 4.59 MHz. To the best of our knowledge, this is the first time that an HCF gas laser achieves a self-Q-switched pulse. Future studies will aim to further optimize the experimental setup, potentially enabling the direct generation of picosecond pulses in the mid-infrared wavelength band.

Optimization of the inverted "T"-shaped double-layer subwavelength grating design integrated on an InSb detector

Polarization detectors have significant applications in fields such as target background contrast enhancement and free-space optical communication. While the technology for polarization detection using polarizers and waveplates added to detector lenses is well-established, there is still limited research on on-chip integrated polarization detection based on hypersurface technology. In this paper, we present a novel inverted "T"-shaped double-layer subwavelength grating structure, integrated into an InSb detector for polarization detection in the mid-infrared wavelength region (3–5 μm). This structure primarily consists of a high refractive index dielectric layer and a subwavelength grating layer, which together improve the grating's transmittance and extinction ratio. Using the finite-difference time-domain (FDTD) method, we simulate and optimize the effects of various grating parameters on polarization performance. The results show that the optimized grating achieves a TM wave transmittance of nearly 80% within the 3–5 μm wavelength range, with an extinction ratio exceeding 45 dB, and is suitable for a wide range of incidence angles from 0° to 70°.

High-performance uncooled PbSe/CdSe nanostructured mid-infrared photodetector with tunable cutoff wavelength

Room-temperature (RT) high-performance mid-wavelength infrared (MWIR) Lead Selenide (PbSe)/Cadmium Selenide (CdSe) heterostructure nanocrystal photoconductors are designed and fabricated on commercial silicon dioxide on silicon (SiO2/Si) wafer via vapor phase deposition. Tunable absorption edges at 3.75 and 4.0 μm are demonstrated with different sizes of the nanostructure. The devices are annealed in oxygen to make the thin film much more sensitive to MWIR light. The detectors are etched by the reactive ion etching method to define an active area of 17.5 × 20 μm2. All devices exhibit external quantum efficiencies exceeding 100%, a clear indication of photoconductive gain. 1/f noise is the dominating noise source, and it follows Hooge's empirical relation for a homogeneous semiconductor. RT peak specific detectivity (D*) of 2.17 × 1010 and 1.61 × 1010 Jones is achieved for pixels with absorption edge at 3.75 and 4 μm, respectively.

Development of Photonic In-Sensor Computing Based on a Mid-Infrared Silicon Waveguide Platform.

Neuromorphic in-sensor computing has provided an energy-efficient solution to smart sensor design and on-chip data processing. In recent years, various free-space-configured optoelectronic chips have been demonstrated for on-chip neuromorphic vision processing. However, on-chip waveguide-based in-sensor computing with different data modalities is still lacking. Here, by integrating a responsivity-tunable graphene photodetector onto the silicon waveguide, an on-chip waveguide-based in-sensor processing unit is realized in the mid-infrared wavelength range. The weighting operation is achieved by dynamically tuning the bias of the photodetector, which could reach 4 bit weighting precision. Three different neural network tasks are performed to demonstrate the capabilities of our device. First, image preprocessing is performed for handwritten digits and fashion product classification as a general task. Next, resistive-type glove sensor signals are reversed and applied to the photodetector as an input for gesture recognition. Finally, spectroscopic data processing for binary gas mixture classification is demonstrated by utilizing the broadband performance of the device from 3.65 to 3.8 μm. By extending the wavelength from near-infrared to mid-infrared, our work shows the capability of a waveguide-integrated tunable graphene photodetector as a viable weighting solution for photonic in-sensor computing. Furthermore, such a solution could be used for large-scale neuromorphic in-sensor computing in photonic integrated circuits at the edge.