The superlattice long-wavelength infrared focal plane detectors operate at low temperatures. The differences in the thermal expansion coefficients among the various material layers of the detectors can lead to deformation and generate thermal stress, which in turn affects the optoelectrical performance of the detector. This study designed two structural modules to achieve the regulation of stress in the superlattice detectors. The changes in the dark current and spectral response of InAs/GaSb type II superlattice long-wave infrared focal plane detectors under different stress conditions were explored. The research indicates that within the stress range of-10. 7 MPa to 131. 9 MPa, the variation in the opto- electrical performance of the detector is small. The detector was subjected to a temperature shock test, and it demon- strated high reliability. The research results provide guidance for the structural design of InAs/GaSb type II superlattice long-wave infrared focal plane detectors and offer a basis for their performance and reliability assessment.

Infrared detector has been widely applied in aerospace reconnaissance, electro-optical countermeasures, and space science. Currently, it is undergoing a critical transition from the "full development of the third generation" to the "exploration of the fourth generation. " Based on the pressing demands of current infrared detection applications, the pre- liminary definition and development considerations of the fourth-generation infrared detector was discussed. First, the developmental trajectory of infrared detectors was outlined. The evolution trend of the fourth-generation infrared detectors was explored from the perspectives of function integration, disciplinary advancement, and technology progression, and an initial definition for fourth-generation infrared detectors was proposed. Secondly, the preliminary contemplation on pivotal technological advancements for fourth-generation infrared detectors, encompassing the exploration of extreme detection performance, multidimensional light field information sensing, on-chip intelligence, and infrared micro- system chips, was delineated. Finally, an intelligent manufacturing ecosystem for infrared detectors was envisaged, which facilitates the transition of fourth-generation infrared detectors from conceptualization to practical application.

1/f noise is a critical parameter affecting the performance of infrared detectors. In this work, the 1/f noise in mid-wavelength InAs/GaSb type-II superlattice (T2SL) devices was investigated. The Hooge model was employed to extract the noise coefficients associated with different dark current components, including diffusion current (Idiff), generation-recombination current (Ig_ r), trap-assisted tunneling current (Itat), and shunt current (Ishunt). The noise coefficients alpha diff, alpha g_r, alpha shunt, alpha tat show little dependence on variations in temperature and bias voltage. Results from multiple devices reveal that alpha shunt and alpha tatare highly sensitive to the device's surface state and exhibit a wide distribution range while alpha diff and alpha g_r are nearly unaffected by surface conditions. Our work demonstrates the correlation between 1/f noise and dark current components, and further reveals the influencing factors of the noise coefficients, thereby advancing the understanding of 1/f noise. The results suggest that 1/f noise can be reduced by optimizing the device's surface state for InAs/GaSb T2SL detectors.

In order to investigate the electrical properties of InAs/GaSb type-II superlattices, a lattice-matched AlAsSb electrical isolation layer was grown between the GaSb substrate and the InAs/GaSb type-II superlattice epitaxial material to suppress the conductive effect of the substrate. Temperature-dependent Hall measurements revealed that the unintentionally doped superlattice exhibited N-type conductivity. As the P-type doping concentration increased, a carrier com- pensation was observed, with the conductivity type reversal occurring at 95 K and 230 K. Below the transition tempera- tures, P-type conductivity was exhibited, while above the transition temperatures, the material exhibited N-type conduc- tivity. The phenomenon was analyzed using the Fermi level model, and the results indicated that the transition tempera- ture for the conductivity type change increased with increasing doping concentration.

Metalenses, with their unique optical field modulation characteristics and remarkable advantages of high integration and miniaturization, have broad applications in the integrated imaging system of lightweight and small-sized op- toelectronic chips. In this paper, a metalens structure for pixel-level integrated infrared focal plane applications was designed. The preparation of the structure adopted a method combining stepper lithography technology and the Inductively Coupled Plasma (ICP) etching process. Through a systematic optimization of etching parameters, including gas flow rate, working pressure, and power, the loading effect was effectively suppressed and the standard deviation of the etching rate was decreased from 0. 205% to 0. 073%. Finally, a highly uniform metalens array was fabricated, with a pixel center distance of 30 pm, an array of 640 & times;512, and a maximum aspect ratio of 3.42 of Si pillars. The focusing distance for 4. 3 pm wavelength infrared light is 35 pm. The measured optical field convergence efficiencies, within radial ranges of 10 pm and 20 pm in the central area at the focal length, are 66. 4% and 84. 9%, respectively. The optical field en- ergy is increased by 5. 98 times and 1. 91 times, respectively, compared with that without the integrated metalens within the same area range. This study will provide the structural design and processing foundation for the integration of pixel-level metalens arrays with infrared chips.

The relationship between the surface leakage and surface chemical state of InAs/GaSb type-II superlattices (T2SLs) infrared detectors was studied in this work. At first, a simple but effective method of wet-chemical treatment was used to modify surface oxides of T2SL. XPS and valence band spectra were used to characterize the chemical state and surface energy band. We found a direct and strong correlation between surface oxidation and surface band bending. As the surface oxidation increases, the band bending becomes more significant. InAs/ GaSb T2SL mid-wave detectors with a 100% cutoff wavelength of 4.5 mu m were also fabricated to characterize the electrical properties under different etchants. It's worth noting that the dark current results are highly consistent with the surface state and band bending, the device shows a poor performance while the oxide ratio is high. Among these etchants, HCl seems to be an effective way to remove surface oxides. The device under HCl-treated, which demonstrates minimal surface oxide and band bending, shows the best dark current density of 1.19 & times; 10-9 A/cm2 at -50 mV bias at 77 K. This work may provide a valuable insight to reduce leakage for InAs/GaSb T2SLs mesa-devices and high-performance focal plane arrays detectors.

Due to the close pixel size and working wavelength of the focal plane polarization integrated infrared detector, diffraction effects cause severe crosstalk between adjacent pixels with different polarized light. A single traditional metal grating structure cannot achieve high extinction ratio polarization detection chips. This article proposes and designs a metasurface lens stacked polarization integrated infrared detector structure, studies the optical field convergence ability of metalens for different wavelengths of infrared light waves, prepares metastructural lenses and submicron grating structures, and integrates them with infrared focal planes. The polarization extinction ratio of the device exceeds 15: 1, and dynamic and variable temperature objects are selected for polarization imaging experiments, demonstrating the imaging advantages of polarization integrated devices with focal planes.

InAs/GaSb type-II superlattice infrared detectors, with their advantages of tunable bandgap and high material uniformity, have become a preferred material for mid-infrared imaging detectors. Conventional superlattice infrared photodetectors predominantly employ mesa architectures. In contrast, planar junction configurations offer higher fill factors at reduced pixel dimensions while mitigating etch-induced leakage currents, rendering them promising alternatives. Nevertheless, research on such structures remains scarce in the literature. This study presents Si-implanted planar junction photodetectors based on InAs/GaSb type-II superlattices, achieved through optimised device design, fabrication, and systematic characterisation. X-ray diffraction (XRD) measurements indicate that the overall crystalline quality of the material remains intact mainly following post-implantation annealing, and spectral measurements verify the mid-wavelength infrared (MWIR, 3–5 μm) photoresponse. Performance tests further showed that the dark current of the device is related to the area of the implantation window, which decreases as the implantation window area increases. Subsequently, the LBIC laser-induced detection system was used to characterise the optical response distribution of the InAs/GaSb superlattice planar junction device at 77 K and to fit the signal decay curve outside the junction region. The findings indicate that the photosensitive region expanded by 5.4 ± 0.16 μm after implantation, demonstrating the presence of lateral carrier diffusion in the superlattice material. The results of this study show the feasibility of the planar junction design of the mid-infrared focal plane array.

Infrared spectroscopy covers the "fingerprint" region of molecular vibrations, offering non-destructive detection capabilities and excellent anti-interference performance, thereby providing robust technical support for material identification and target recognition. However, conventional infrared spectral imaging systems typically rely on complex wavelength separation or time-division filtering schemes, leading to challenges such as low energy utilization efficiency, inadequate system stability, and limited integration capabilities. Here, we present a dispersion-engineered metasurface with a quadratic phase profile, which maps spectral information directly onto spatial coordinates for single-shot spatial-spectral data acquisition. Additionally, we introduce a novel, to the best of our knowledge, wavelength-dependent focal position function that achieves broadband tunable focusing across the mid-wave infrared (MWIR) range. Based on this design, we demonstrate four-band detection capability in the MWIR range (3-5 μm), achieving peak efficiencies of 28%, 52%, 61%, and 49% at four distinct pixels, with an average efficiency of 54%. The broadband-efficient focusing capability effectively suppresses spectral crosstalk, yielding a maximum isolation of 48 between the four bands. This is the first demonstration of pixel-level-multiplexed spectral detection in the mid-infrared regime, offering a promising pathway toward compact, energy-efficient, and real-time multi-spectral infrared detection technologies.

Infrared polarization detection technology can distinguish the polarization characteristics from the intensity of infrared radiation, thereby revealing the material composition, surface morphology, and physicochemical properties of the measured scene. Division of focal plane (DoFP) polarization detection schemes offer high integration and real-time capabilities, attracting significant research interest. However, inter-pixel crosstalk reduces polarization extinction ratios, limiting its utility. This work proposes a cascaded polarization crosstalk suppression scheme for mid-infrared broadband polarization-integrated detectors, based on all-silicon dielectric full-Stokes polarization metalenses. Combining transmission and geometric phase, pixel-level full-Stokes polarization beam-splitting and filtering metalenses are designed on an all-silicon platform, enabling efficient polarization decoupling and detection in the 3.5-4.5 μm range. Furthermore, through the co-design of the integrated detector chip, a fourfold improvement in polarization extinction ratio (PER) over broadband is achieved compared to independent metasurface. This work lays the foundation for a coordinated optimization strategy between microstructures and detector devices, offering valuable insights into the design and integration for infrared polarization-integrated focal plane array (FPA) devices.

The sensitivity of the detector is the core technical indicator of the infrared detector. Short-wave infrared de- tector has low dark current and the sensitivity will be limited by the inherent read-out circuit noise of the detection sys- tem. Therefore, it is an effective way to further enhance the sensitivity by introducing internal gain into the detector. The heterogeneous phototransistor has advantages of high gain, low operating bias, and low excess noise, which pro- vides novel approach for high-sensitive detection. This paper mainly focuses on the simulation design of InGaAs/GaAs- Sb type-II superlattice short-wave infrared phototransistor, and studies the dependence of the device size on the optoelec- tronic characteristics. The results show that a higher gain, a lower dark current, and a faster response can be achieved by a smaller base size. Based on the optimization design of size structure, a noise equivalent photon lower than 10 can be achieved, which provides a new technical approach to achieve high-sensitive heterogeneous phototransistor detector.

Significance Infrared polarization detection technology,beyond mere intensity detection,enables the extraction of the polarization characteristics of infrared radiation from targets.These characteristics reveal the material properties,surface morphology,and physicochemical traits of the target and its surroundings,making this technology essential for military,civilian,and medical applications.In particular,focal plane array-based infrared polarization detectors have garnered significant attention from researchers owing to their high level of integration and real-time imaging capabilities.However,as the pixel size of infrared focal plane arrays continues to shrink,approaching the scale of the characteristic wavelength,there is an increasing demand for efficient polarization decoupling at the pixel level using microstructures.Furthermore,polarization structures must be vertically integrated at the pixel level with the pixel arrays to ensure accurate and efficient transmission of polarization components to the absorption region.These requirements place stringent demands on the design and integration of polarization micro-and nano-structures. Progress It is a significant challenge for traditional imaging systems to capture the polarization information of a target's light field,which typically requires bulky optical components and time-domain multiplexing.Conventional polarization-detection technologies,such as time-division,amplitude-division,and aperture-division schemes,suffer from drawbacks such as large size,system complexity,and low stability.In response to the demand for lightweight,highly integrated,stable,and real-time full-polarization infrared detection,pixel-level polarization-sensitive structures in infrared focal-plane array polarization detectors have become a key development direction for next-generation infrared detection technologies.Emerging technologies have driven significant advances in polarization filter devices with innovations such as metal wire grids,photonic crystals,and metasurfaces,enabled by nanofabrication technologies.These micro-and nano-structures,with immense potential for optical field manipulation,have become mainstream technologies in polarization detection devices.Currently,relatively mature polarization-integrated focal-plane arrays typically rely on subwavelength metal wire grids to achieve strong polarization sensitivity.These grids offer advantages such as high polarization selectivity,customizable broad operational bandwidth,miniaturization,high stability,and ease of integration.However,when the operational wavelength extends into the infrared range,the extinction ratio of the integrated polarization devices declines significantly compared to that of standalone wire grid arrays.Several researchers have analyzed the impact of key parameters such as pixel size,pixel pitch,distance between the polarizer and the photosensitive area,and alignment errors in integration on the polarization extinction ratio.All conclusions indicate that optical crosstalk between adjacent pixels becomes particularly severe in the infrared wavelength range,where the operational wavelength is comparable to the pixel size,resulting in diffraction effects that severely limit the extinction ratio of focal-plane infrared polarization devices. To address this issue,researchers have begun incorporating directional light field focusing into pixel-level micro and-nano-structures to reduce crosstalk between adjacent pixels.They are also advancing polarization multiplexing techniques to enhance energy utilization efficiency in weak-light infrared detection.These efforts are aimed at accelerating the practical applications of infrared polarization imaging devices.This paper reviews a series of notable works on polarization filtering/multiplexing and the implementation of pixel-level light field focusing(see Table 1),comparing key metrics such as operational wavelength range,energy utilization efficiency,number of polarization-encoded channels,unit cell size,and focal length.Given the impact of pixel-level discretized phase control and micro-nano fabrication errors,there is significant interest in ensuring the extinction ratio and other performance parameters of focal-plane array polarization detectors.New approaches,including the inverse design of novel microstructures,the integration of microstructures with pixel arrays,and the correction and reconstruction of readout signals,are being explored.These methods hold promise for driving efficient device optimization and achieving performance improvements beyond the limitations imposed by design and fabrication errors. Conclusions and Prospects This study reviews research progress on focal-plane array integrated infrared polarization detectors based on polarization-sensitive microstructures.It focuses on key issues such as improving energy utilization,reducing crosstalk between adjacent pixels,increasing the number of multiplexing channels,and enhancing structural design efficiency.This review discusses various design approaches and advancements in pixel-level polarization-sensitive microstructures.Additionally,from the perspective of integrated polarization devices,this study analyzes the key technologies related to polarization decoupling and reconstruction that affect polarization detection capabilities.The proposal and optimization of these design methods have facilitated a series of concept-level experimental validations of on-chip polarization imaging,thereby accelerating the development of application-grade integrated devices. Advancing the development of on-chip infrared polarization imaging devices based on micro-and nano-structures is of significant importance.Future research and applications should focus on several key innovations:AI-driven design of micropolarizers,designing pixel-level microstructures and key parameters of pixel arrays from an integrated device perspective,and establishing comprehensive polarization component transmission models for polarization calibration and reconstruction.By aligning with practical requirements and integrating multidisciplinary design approaches,this field offers new technological pathways for the development and application of miniature optical imaging systems in infrared polarization and spectroscopy.

Spectral integrated detection is one of important branch anticipated for the next generation infrared FPA, which includes so-called multi-dimensional detection capabilities with function diversity. Such enhancement of the current state-of-the-art FPA technologies allow real-time tuning of spectral information to be gathered from multiple narrow wavelength bands, getting data-cube to meet the requirements of clear target recognition in complex noisy scenarios. In order to provide a reduced size, weight and power (SWaP) solution, micro- electromechanical systems (MEMS) based electrically tunable filter technology has been developed. This adopted approach is capable of delivering on-chip spectral detector by obtaining narrow-band spectral sensitivity utilizing tunable MEMS optical filter directly integrated on FPA chips. Especially for integration with cooled infrared FPA, it is necessary to meet the reliability and stability challenges of large-sized filters matching FPA chip area under low-temperature vacuum environment. In this paper, a multi physics field coupling analysis work was also dug out for understanding the stability performance of electromechanical characteristics. Then we produced MEMS based tunable FP filters, which demonstrated a transmission of 45 % with a well uniformity within the filter area of 3 mm radius, and maximum tuning wavelength range of 0.7 mu m (from 5.3 to 4.6 mu m) under voltage bias. We integrated the tuning filter with InAs/GaSb Type-II superlattice infrared detector and tested the performance of tunable photo-responsivity at liquid nitrogen temperature. All the work laid the foundation for integration with cooled FPA in our next step work.

Mid-infrared waveguide photodetectors, offering advantages such as high bandwidth, low power consumption, and ease of integration, are highly suitable for applications in spectral detection and molecular fingerprint recognition. To enhance the sensitivity and signal-to-noise ratio of waveguide photodetectors, this paper demonstrates the structural design of a mid-infrared waveguide photodetector integrated with an ultra-short waveguide taper. The proposed structure compresses the fiber-coupled optical field to subwavelength dimensions, effectively decreasing the area of the integrated absorber while maintaining quantum efficiency, thus achieving low dark current noise. The total length of the ultra-short waveguide taper has been reduced by an order of magnitude compared to the conventional waveguide taper. Simulation results indicate a one-order-of-magnitude reduction in dark current and a 68.2

With the advancement of mathematical tools, computational spectrometers have gained new vitality by shifting the challenge of fine spectral detection to computing power and algorithms. This approach addresses the limitations of traditional spectrometers, including the need for precise dispersion elements, complex optical paths, and challenges in miniaturization. The traditional strategy of using static filter arrays with fixed spectral channels cannot flexibly or dynamically select spectral ranges based on the spectral characteristics of different targets. In this study, we present a computational spectrometer based on a mid-infrared photodetector integrated with a MEMS-FP tunable filter for dynamic encoding, enhancing reconstruction accuracy and flexibility compared with conventional static encoding approaches. In addition, we conducted in-depth research on reconstruction algorithms. Using the Enhanced Inverse Spectral Reconstruction algorithm, we optimize the selection of encoding channel numbers and the full width at half maximum of encoding curves. This balance ensures high reconstruction fidelity while preventing performance saturation, as an excessive number of encoding channels offers diminishing returns on reconstruction quality. Our system achieves a spectral fidelity as high as 99.8% with an encoding efficiency of 200%, ensuring a spectral resolution of 5 nm. Through our experiments, we successfully reconstructed the absorption spectra of aspirin and acetaminophen aqueous solutions within the 3–5 μm range, underscoring the spectrometer's potential in the pharmaceutical industry.

The thermal stress, significantly impacting the performance of infrared detectors, is typically caused by the thermal mismatch between adjacent materials. This presents a complex physical picture for InAs/GaSb type-II superlattice focal plane arrays, as it requires an analysis across multiple scales, from millimeter-scale device structures to micron-scale mesa-structured pixels. In this paper, an innovative multi-scale finite element model for InAs/GaSb type-II superlattice infrared focal plane array detectors has been developed, revealing the equivalent stress and its distribution along the mesa sidewall for the first time. Based on the specific boundary displacement method, an InAs/GaSb type-II superlattice infrared detector with 320 × 256 micro-mesa arrays is built, and the impact of various structural parameters, including pixel sizes, channel widths, indium bump diameters, and mechanical properties of underfill, on the pixel stresses is investigated. Simulation results indicate that, for the same pixel, the equivalent stress of the sidewall is higher and more sensitive to structural parameters compared to that of the planar surface. Our research offers a novel approach for the accurate and efficient simulation of thermal stresses in infrared detectors with mesa structures and provides valuable guidance for analyzing failure mechanisms and optimizing low-stress designs in InAs/GaSb type-II superlattice focal plane infrared detectors.

Class II superlattice infrared detectors generally detect infrared radiation through mesa junction, while transverse PN junction is realized through ion implantation. On the one hand, the material epitaxy process is simple, and at the same time, the advantages of superlattice material that the transverse diffusion length is far higher than the longitudinal can be used to improve the transport of photogenerated current carriers, and it is easy to make high-density planar arrays. In this paper, the effects of Si ion implantation with different energies and annealing on the properties of InAs/ GaSb type II superlattice materials were studied by using a variety of material characterization techniques. Through Si ion implantation, the epitaxial material changes from P type to N type, and the vertical tensile strain is generated in the superlattice material. The lattice constant becomes larger, and the mismatch increases with the increase of implantation energy. The mismatch before implantation is-0. 012%. When the implantation energy reaches 200 keV, the mismatch reaches 0. 072%, and the superlattice partially relaxes, with the relaxation degree of 14%. After annealing at 300 degrees C for 60 s, the superlattice returns to the fully strained state, and the lattice constant becomes smaller, This tensile strain is caused by the diffusion of Ga-In caused by annealing and lattice shrinkage caused by Si substitution.

Antimonide superlattice interband cascade infrared photodetectors (ICIPs) are novel semiconductor devices that enable the directional transport of photogenerated carriers within multi-stage absorbers formed through phonon-assisted tunneling, allowing for higher operating temperatures. The dark current of infrared detectors has been the main factor limiting their performance. ICIPs have complex interfaces characterized by multi-layer heterostructures. Interfacial intermixing leads to band misalignment in the actual device structure, affecting both photocurrent transport and the dark current mechanism. Based on previous research on interfacial intermixing and the computational results from the $\mathbf{k}\cdot \mathbf{p}$ model, this paper explores the impact of interfacial intermixing on dark current and establishes a dark current model for ICIP at high operating temperatures. The calculation results are compared and analyzed against experimental results, partially validating its accuracy and providing a theoretical foundation for subsequent research.

Scenting is an important process for the formation of aroma quality in floral Longjing tea. There are differences in the aroma quality of osmanthus Longjing teas processed by different scenting processes. The efficient isolated scenting method was employed to process a new product of osmanthus Longjing tea in this study, and this was compared with the traditional scenting method. The volatile compounds of osmanthus Longjing tea were analyzed by a GC-MS instrument. In addition, the effects of scenting time and osmanthus consumption on the aroma quality of Longjing tea were studied. The results indicated that there were 67 kinds of volatile compounds in the osmanthus Longjing tea produced by the isolated scenting process (O-ISP), osmanthus Longjing tea produced by the traditional scenting process (O-TSP), and raw Longjing tea embryo (R), including alcohols, ketones, esters, aldehydes, olefins, acids, furans, and other aroma compounds. The proportions of alcohol compounds, ester compounds, aldehyde compounds, and ketone compounds in O-ISP were higher than in O-TSP and R. When the osmanthus consumption was increased, the relative contents of volatile aroma compounds gradually increased, which included the contents of trans-3,7-linalool oxide II, dehydrolinalool, linalool oxide III (furan type), linalool oxide IV (furan type), 2,6-Dimethyl cyclohexanol, isophytol, geraniol, 1-octene-3-alcohol, cis-2-pentenol, trans-3-hexenol, β-violet alcohol, 1-pentanol, benzyl alcohol, trans-p-2-menthene-1-alcohol, nerol, hexanol, terpineol, 6-epoxy-β-ionone, 4,2-butanone, 2,3-octanedione, methyl stearate, cis-3-hexenyl wasobutyrate, and dihydroanemone lactone. When the scenting time was increased, the relative contents of aroma compounds gradually increased, which included the contents of 2-phenylethanol, trans-3,7-linalool oxide I, trans-3,7-linalool oxide II, dehydrolinalool, isophytol, geraniol, trans-3-hexenol, β-ionol, benzyl alcohol, trans-p-2-menthene-1-ol, nerol, hexanol, terpineol, dihydroβ-ionone, α-ionone, and β-ionone,6,10. The isolated scenting process could achieve better aroma quality in terms of the floral fragrance, refreshing fragrance, and tender fragrance than the traditional scenting process. The isolated scenting process was suitable for processing osmanthus Longjing tea with high aroma quality. This study was hoped to provide a theoretical base for the formation mechanism and control of quality of osmanthus Longjing tea.

: In this paper, , we report research results of 1 280x1 024 dual-color mid-wavelength infrared InAs/GaSb super- lattice focal plane arrays. The detector structure is PN-NP epitaxial multilayer and the signal is read out by sequential mode. The superlattice structure was grown on GaSb substrate using molecular beam epitaxy (MBE ) technology. The respective structures of each absorption region are Mid-Wavelength 1(MW1): (MW1 ): 6 ML (InAs ) /7 ML (GaSb ) and Mid- Wavelength 2 (MW2 ): 9 ML (InAs ) /7 ML (GaSb ). The pixel center distance of the detector is 12 mu m. At 80 K mea- surements, , the detector has spectral response wavelength of 3-4 mu m and 3. 8-5. 2 mu m respectively. The MW1 detector has a peak detectivity of 6. 32x10(11) cmHz(1/2)W(-1). The MW2 detector has a peak detectivity of 2. 84x10(11) cmHz(1/2)W(-1). In- frared images of both wavebands have been taken using infrared imaging test by adjusting the device voltage bias. It's 's the first time that a 1 280 x 1 024 InAs/GaSb Type II superlattice mid-wave length two-color infrared focal plane detec- tor has been in China.