Conventional infrared objectives typically rely on multiple refractive elements; however, their size, mass, and assembly complexity limit compact, cost constrained LWIR applications. Here we report a high-transmittance monolithic hybrid metalens singlet for broadband LWIR (8-12 mu m) imaging, in which a plano-convex refractive surface and a dispersion-engineered metalens are integrated on opposing optical surfaces. Using subwavelength meta-units selected by an RMS phase criterion evaluated at multiple wavelengths, the singlet simultaneously corrects chromatic and spherical aberrations, achieves near diffraction-limited focusing, maintains back focal length variation within +/- 40 mu m across 8-12 mu m, and delivers a broadband MTF close to the diffraction limit. FTIR and system tests show in-band average transmittance of 83.2% (metalens) and 74.8% (complete singlet). The device enables clear thermal imaging of real scenes from 0.8 to 50 m. Owing to its compact form factor and scalable fabrication potential, the monolithic singlet provides a cost-effective building block for lightweight LWIR modules and can be further combined with simple refractive correctors to realize systems with a wider field of view.

Non-dispersive infrared (NDIR) gas sensors commonly use thermal detectors to convert infrared absorption by target molecules into concentration-dependent electrical signals. To further enhance the sensitivity of NDIR sensors while retaining the advantage of uncooled operation, we propose an approach that exploits localized surface plasmon resonance (LSPR) in a metal-insulator-metal (MIM) micro–nano structure to increase the light absorption and conversion of a mid-infrared semiconducting photodetector. By numerically designing and experimentally optimizing the radius and thickness of metal disks, their array period, and the thickness of the dielectric space layer, we clarified the tuning relationship between the metasurface geometry and the peak response wavelength as well as bandwidth. The metasurface-enhanced mid-infrared lead selenide (PbSe) photodetector exhibited a pronounced detectivity enhancement across 3~4.5 μm, with the peak specific detectivity improving from 1.24×10^10 of the control sample to 2.16×10^10 Jones when operated at room temperature. In a comparative study of the NDIR sensor module, the detection limit for methane and carbon dioxide reached 136.99 ppm and 21.96 ppm respectively, and the corresponding relative improvement rates were 9.5% and 19.1% respectively. These results indicate that the metasurface-integrated photodetectors have a promising prospect in high sensitivity, miniaturization, and multi-component detection of NDIR gas sensors.

Infrared detectors are essential for military and civilian applications, yet high-performance mid-infrared (MIR) detection still predominantly relies on cryogenically cooled narrow-bandgap semiconductors, which severely limits portability and scalability, particularly for imaging applications. Although PbSe enables room-temperature operation and is fully compatible with silicon-based processing, the thin-film PbSe active layer suffers from insufficient optical absorption, which fundamentally constrains its achievable performance. Here, we propose and experimentally demonstrate a metasurface-integrated PbSe active layer that overcomes this bottleneck by engineering multi-modal hybridization to realize broadband, high-efficiency light trapping. The metasurface supercell simultaneously excites gap-surface plasmon (GSP), Fabry-Pérot (FP) cavity modes, localized surface plasmon (LSP), magnetic dipole (MD), and guided-mode resonance (GMR), forming a continuous coupled modal landscape that yields a ∼4.5-fold enhancement in PbSe-layer absorption over a bandwidth exceeding 2.5 μm and peak absorption in the PbSe layer approaching 90%. The device further exhibits polarization-insensitive performance (<1% variation from 0-360°) and angular robustness up to 15° incidence. Importantly, strong enhancement persists in compact pixels comprising only a 2×2 metasurface unit-cell footprint (∼9.2 μm), confirming pixel-level scalability compatible with realistic MIR FPAs. These results establish multi-modal metasurface hybridization as a powerful route to overcome fundamental absorption limitations in PbSe films and open a promising pathway toward next-generation high-performance uncooled MIR imaging systems.

We present a hybrid optical system with a 63 mm focal length, 3.7-4.8µm band, and 10.8° field of view, combining a metalens doublet and aspheric lens, achieving achromatic aberration and high performance imaging.

The thermal characteristics of lenses play an essential role in the performance of optical systems, particularly infrared detection systems. Metalenses, composed of sub-wavelength nanostructured surfaces, have recently emerged as a promising technology to realize flat, lightweight, and mass-producible lenses. However, their thermal behavior remains largely unexplored. This study examines the impact of uniform temperature variations (both theoretically and experimentally) and laser heating (theoretically) on the performance of polarization-insensitive metalens (PIM) at a representative wavelength of 10.6 µm. We compare the thermal performance of PIMs with refractive and diffractive lenses, by a comprehensive structural, thermal, and optical performance (STOP) analysis through finite-element analysis (FEA) and finite-difference-time-domain (FDTD) simulations. A comprehensive analysis of various thermal aberration indicators reveals that the PIM exhibits smaller thermal aberrations than both the aspheric lens and the harmonic diffractive lens, and its performance is closer to that of a traditional diffractive optical element (DOE). We also find that the unique nanostructures of PIM make it highly sensitive to the refractive index change induced by temperature variations, allowing the PIM to achieve unique capabilities compared to other lenses. A typical example is that the PIM consistently demonstrates an opposite shift in focal length and depth of focus, contrary to conventional cases. We also experimentally verify the near-athermal properties of 5-centimeter-aperture metalens, confirming the advantages of large-aperture PIMs over refractive lenses in athermal infrared imaging applications. Additionally, our numerical analysis demonstrates that the broadband achromatic metalens notably outperforms the DOE in simultaneously achromatic (8 to 12 µm) and athermal (-60 to 80°C) performance. It is reasonable to speculate that the thermal diffraction efficiency of the achromatic metalens is likely superior to that of the achromatic multi-level diffractive lens (MDL). Our results confirm the strong potential of metalenses in athermal imaging applications.

Flat-top laser beams have significant applications in fields such as laser processing due to their uniform intensity distribution and clear boundaries. Since lasers typically emit Gaussian beams in the fundamental mode, devices that convert Gaussian beams into flat-top beams are essential. However, traditional beam shapers composed of refractive or diffractive optical elements need improvements in volume, weight, and cost. In this study, we propose a beam-shaping metalens to address these issues. We present an extended Gerchberg-Saxton (GS) algorithm to design two beam-shaping metalenses that convert Gaussian beams into 2D circular and square flat-top beams, respectively. We develop an analytical rapid simulation (ARS) method for simulating metalenses and verify its accuracy. Additionally, we consider the microloading effect in etching and compensate for the impact caused by etching depth inconsistencies. We experimentally fabricated and characterized two beam-shaping metalenses, achieving a circular flat-top beam with a conversion efficiency of 91.8% and an RMS value of 16.7%, and a square flat-top beam with a conversion efficiency of 89.7% and an RMS value of 24.0%. This method for designing beam-shaping metalenses that convert Gaussian beams into flat-top beams of arbitrary shapes provides a novel solution for laser beam shaping.

This study introduces what we believe is a novel approach to manipulating light in the mid-infrared spectrum through phonon-mediated metal-insulator-metal (MIM) cavities. Leveraging the unique interactions between resonantly excited electric and magnetic dipoles and phonons within silicon dioxide spacers, we have developed a technology different from traditional methods that rely on geometric modifications of nanostructures, offering a more versatile and effective means of tailoring light-matter interactions at the nanoscale. Our experimental results showcase the ability of these MIM cavities to perform multifunctional information encoding, display, and concealment with high precision. Notably, we encoded 13 distinct gray levels, surpassing previous capabilities in the long-wave infrared spectrum using metamaterial emitters. Furthermore, the incorporation of rotating nanorod structures enabled the encoding of grayscale patterns through polarization states, enhancing the potential for high-capacity information storage. The study also demonstrates the capability of these structures for subwavelength-resolution printing and near-diffraction-limit information encoding in the long-wave infrared band. We have successfully employed an innovative ink coating method, transparent in the long-wave infrared but opaque in the visible spectrum, to conceal encoded information, thereby adding a layer of security. In summary, the phonon-mediated infrared plasmonic metamaterial emitters presented in this work pave the way for future research in high-capacity information storage, anti-counterfeiting, and security technologies.

Halide perovskites, considered a new generation of semiconductors, have demonstrated notable advancements in nuclear radiation detection, highlighting their cost-effectiveness in fabrication. However, great challenges can arise from crystal edge effects associated with imperfect surface status, likely resulting in high surface leakage currents and incomplete charge collections, which greatly impede the obtaining of excellent spectroscopic capability. In this work, a guard ring configuration for shielding edge effects was designed on a perovskite CsPbBr3 detector for spectral optimization and long-term stabilization. The implementation of a guard ring resulted in significantly decreased and stable leakage currents passing through the central collecting electrode. As a result, the bulk leakage current from the active region was reduced by approximately 80%. Consequently, the 122 and 136 keV photopeaks in Co-57 gamma-ray spectra were well resolved, with an energy resolution improvement from similar to 9.8 to 4.8% at 122 keV. Notably, the low energy tailing of the photopeak has been greatly weakened by reducing the edge effects.

The metasurface structure can effectively manipulate the direction of light propagation, making it highly promising for the development of high-performance photonic devices. GeSn alloy, which is compatible with CMOS processes, is a highly attractive infrared semiconductor. In this study, GeSn metasurface photodetectors (PDs) were fabricated and comprehensively investigated. Optical field distribution simulations at a 2 mu m wavelength revealed that the optimized metasurface structure significantly enhances the quantum efficiency (QE) of GeSn PDs by converting light propagation from the longitudinal to the transverse direction. The dark current of the fabricated GeSn metasurface PDs remained nearly unchanged, while the responsivity increased significantly. At a wavelength of 2000 nm, the room-temperature responsivity was improved from 0.10 to 0.34 A/W, and both temperature-dependent and incident light power-dependent responsivities were studied. The cutoff wavelength of the PD was extended from 2750 to 2950 nm due to the enhanced interaction between the light and the GeSn layer. In the tested photocurrent spectrum between 1600 and 2400 nm, the maximum response enhancement factor reached approximately 2 to 4. The significantly enhanced optoelectronic performance indicates that the proposed metasurface structure has great potential for fabricating GeSn PDs operating in the short-wave infrared (SWIR) region.

Existing mid-infrared thermographic cameras rely on a stack of refractive lenses, resulting in bulky and heavy imaging systems that restrict their broader utility. Here, we demonstrate a lightweight metalens-based thermographic camera (MTC) enabled by a single 0.5-mm-thick, 3.7-g-weight, flat, and mass-producible metalens. The large aperture size (5 cm) of our metalens, when combined with an uncooled focal plane array, enables thermal imaging at distances of tens of meters. By computationally removing the veiling glare, our MTC realizes the temperature mapping with an inaccuracy of less than ±0.7% within the range of 35° to 700°C and shows exceptional environmental adaptability. Furthermore, by using intelligent algorithms and spectral filtering, our uncooled MTC enables visualization and quantification of the SF 6 gas leakage at a long distance of 5 m, with a remarkable minimum detectable leak rate of 0.2 sccm. Our work opens the door to the lightweight and multifunctional intelligent thermal imaging systems.

We designed and fabricated an extra-large metalens doublet(EMD). Leveraging on the EMD, we developed a camera for broadband large field of view imaging in the long-wavelength infrared spectrum, and evaluated the performances of the meta-camera.

Infrared polarization imaging holds significant promise for enhancing target recognition in both civil and defense applications. The Division of Focal Plane (DoFP) scheme has emerged as a leading technology in the field of infrared polarization imaging due to its compact design and absence of moving parts. However, traditional DoFP solutions primarily rely on micro-polarizer arrays, necessitating precise alignment with the focal plane array and leading to challenges in alignment and the introduction of optical crosstalk. Recent research has sought to augment the performance of infrared detectors and enable polarization and spectral selection by integrating metamaterial absorbers with the pixels of the detector. Nevertheless, the results reported so far exhibit shortcomings, including low polarization absorption rates and inadequate polarization extinction ratios. Furthermore, there is a need for a comprehensive figure of merit to systematically assess the performance of polarization-selective thermal detectors. In this study, we employ the particle swarm optimization algorithm to present a multilayer, multi-sized metamaterial absorber capable of achieving a remarkable polarization-selective absorption rate of up to 87.2% across the 8–14 μm spectral range. Moreover, we attain a polarization extinction ratio of 38.51. To elucidate and predict the resonant wavelengths of the structure, we propose a modified equivalent circuit model. Our analysis employs optical impedance matching to unveil the underlying mechanisms responsible for the high absorption. We also introduce a comprehensive figure of merit to assess the efficacy of infrared polarization detection through the integration of metamaterials with microbolometers. Finally, drawing on the proposed figure of merit, we suggest future directions for improving integrated metamaterial absorber designs, with the potential to advance practical mid-infrared polarization imaging technologies.

Mitigating the optical reflection of aluminum alloy over a broad spectral range from 0.45 μ m to 15 μ m is vital for many applications. This can be realized by introducing efficient light-absorbing textured surfaces via femtosecond laser surface processing. However, a clear analysis of antireflection performance has not been reported yet. This paper proposes a numerical model of anti-reflective structures is proposed based on SEM and EDS characterization. Multiple anti-reflective mechanisms were revealed intuitively through FDTD simulation.

Vanadium oxide (VOx) microbolometers enable the construction of high-performance yet low-cost and uncooled imaging detectors in the mid-infrared spectrum. Typical micro-bolometers are broadband sensors with no polarization selectivity. Thus, imaging detectors based on microbolometers have to use separate spectral and polarization filters to select the target spectral bands and polarization states, and the resulting systems are complicated and bulky. Here we demonstrate that by using metamaterial absorbers (MAs), which are arrays of optical resonators with sub-wavelength dimensions and spacing, we simultaneously tailor the VOx microbolometers' spectral and polarization responses, the need for separate spectral filters and polarizers can be mitigated. The MAs selectively absorb the TM polarization component of the incident light in a spectral band with tunable central wavelength and bandwidth while rejecting the TE polarization component. Two MAs with average TM absorption of 0.8322 in the 5.150 µm - 6.422 µm band and 0.7720 in the 5.867 µm - 7.467 µm band are fabricated, and the polarization extinction ratio (PER) are 42.24 and 42.65, respectively. The MAs are applied to VOx micro-bolometers, and the measured detector responses agree well with the absorption spectra of the MAs. The achieved peak responsivities of two fabricated detectors are 1.0 V/W at 6.0 µm and 1.46 V/W at 6.8 µm, respectively. And the two detectors achieve a D* of 6.94×105 cm·Hz1/2W-1 at 11Hz and 9.95×105 cm·Hz1/2W-1 at 36Hz, respectively. Our work paved the way towards large format room temperature multi-spectral infrared polarization imaging detector.

We designed and fabricated a metamaterial-integrated vanadium oxide microbolometer for dualband infrared polarization detection. The experimental spectral and polarization responses agree with the design. Our work paved the way towards multi-spectral infrared polarization imaging detector.

We present a lightweight long-wave infrared camera via a single 5cm-aperture, 0.5mm-thick, and 3.7g-weight metalens fabricated by standard semiconductor technology. Imaging experiments with an uncooled FPA are conducted to evaluate the performances of the metalens.

In this work, a photonic device integration platform capable of integration of active-passive InP-based photonic devices without the use of material regrowth is introduced. The platform makes use of an adiabatic active-layer waveguide connection (ALWC) to move an optical beam between active and passive devices. The performance of this platform is analyzed using an example made up of four main sections: (1) a fiber coupling section for enabling vertical beam coupling from optical fiber into the photonic chip using a mode-matched surface grating with apodized duty cycles; (2) a transparent waveguide section for realizing passive photonic devices; (3) an adiabatic mode connection structure for moving the optical beam between passive and active device sections; and (4) an active device section for realizing active photonic devices. It is shown that the coupled surface grating, when added with a bottom gold reflector, can achieve a high chip-to-fiber coupling efficiency (CE) of 88.3% at 1550 nm. The adiabatic active-layer mode connection structure has an optical loss of lower than 1% (CE > 99%). The active device section can achieve an optical gain of 20 dB/mm with the use of only 3 quantum wells. The optimized structural parameters of the entire waveguide module are analyzed and discussed.

Photodetectors are the essential building blocks of a wide range of optical systems. Typical photodetectors only convert the intensity of light electrical output signals, leaving other electromagnetic parameters, such as the frequencies, phases, and polarization states unresolved. Metasurfaces are arrays of subwavelength structures that can manipulate the amplitude, phase, frequency, and polarization state of light. When combined with photodetectors, metasurfaces can enhance the light-matter interaction at the pixel level and also enable the detector pixels to resolve more electromagnetic parameters. In this paper, we review recent research efforts in merging metasurfaces with photodetectors towards improved detection performances and advanced detection schemes. The impacts of merging metasurfaces with photodetectors, on the architecture of optical systems, and potential applications are also discussed.

A fully numerical method for designing efficient adiabatic mode evolution structure (AMES) (referred to as NAMES) is introduced, which can be applied to adiabatic taper, coupler, splitter, mode converter, and a wide range of AMES based devices. The method can compute efficient adiabatic waveguiding shapes for these devices, including those with complex waveguiding geometries involving 2D/3D mode connections. We introduce two algorithms for the NAMES, referred to as “maximal mode-power loss at top algorithm” and “mode-power loss at initial slope algorithm”. Both are based on keeping the mode-connection power exchange constant. We use the simple case of a waveguide taper to explain the algorithms, and then apply it to a more complex case of an adiabatic waveguide coupler to show how it can readily generate a waveguiding shape that can give the same mode-connection power transfer with a much shorter length than that based on a linear shape. In the coupler case, we show the device efficiency is equal to that based on an optimized analytical approach developed for a simple geometry, but the NAMES can address many different device types and complex device geometries all with a single numerical approach that would also enable design automation. The algorithms utilize Eigenmode Expansion (EME) simulator for field propagation with functionalities that are particularly efficient for the algorithms. We cross-checked the EME simulator results using finite-difference time-domain method. With sufficiently fine division of the structure, the waveguiding shape generated converges to basically the same shape for both algorithms and the shape is quite insensitive to the starting parameters. Thus, the NAMES given is robust, convergent, efficient, and general (not restricted to a particular device type). The NAMES would have wide applications to designing AMES based devices with complex geometries for photonic integrated circuits.

Metalenses enable the multifunctional control of light beams with an optically thin layer of nanoantennas. Efficient on-chip voltage tuning of the focal length is the crucial step toward the integration of metalenses into dynamically tunable optical systems. We propose and numerically investigate the on-chip electrical tuning of a reflective metalens via an optomechanic cavity. Light is focused by an array of silicon nanopillar antennas separated from a deformable metallic reflector by a small air gap. A transparent electrode is inserted into the optomechanic cavity to electrostatically deform the reflector and rearrange the reflection phase profile, resulting in a shift in the focal point. Two modes of voltage tuning via the relative curvature change of the reflector are analyzed. In mode 1, the size of the air gap is modified through the nearly parallel shift of the reflector, whereas in mode 2, the distribution of the air-gap size is tailored by the curvature change of the reflector. With the designed working wavelength of 3.8 µm and the initial focal length of 80.35 µm, the focal length is shifted by 20.3 µm in mode 1 and 7.25 µm in mode 2. Such a device can be used as a free space coupler between quantum cascade lasers and mid-infrared fibers with variable coupling efficiency.