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Liquid metal-based printing techniques are emerging as an exemplary platform for harvesting non-layered 2D materials with a thickness down to a few nanometres, leading to an ultra-large surface-area-to-volume ratio that is ideal for sensing applications. In this work, the synthesis of 2D tin dioxide (SnO2) by exfoliating the surface oxide of molten tin is reported which highlights the enhanced sensing capability of the obtained materials to ammonia (NH3) gas is reported. It is demonstrated that amperometric gas sensors based on liquid metal-derived 2D SnO2 nanosheets can achieve excellent NH3 sensing performance at low temperature (150 °C) with and without UV light assistance. Detection over a wide range of NH3 concentrations (5–500 ppm) is observed, revealing a limit of detection at the parts per billion (ppb) level. The 2D SnO2 nanosheets also feature excellent cross-interference performance toward different organic and inorganic gas species, showcasing a high selectivity. Further, ab initio DFT calculations reveal the NH3 adsorption mechanism is dominated by chemisorption with a charge transfer into 2D SnO2 nanosheets. In addition, a proof of concept for prototype flexible ammonia sensors is demonstrated by depositing 2D SnO2 on a polyimide substrate, signifying the high potential of employing liquid metal printed SnO2 for realizing wearable gas sensors.

A single photodetector capable of switching its peak spectral photoresponse between two wavelength bands is highly useful, particularly for the infrared (IR) bands in applications such as remote sensing, object identification, and chemical sensing. Technologies exist for achieving dual-band IR detection with bulk III-V and II-VI materials, but the high cost and complexity as well as the necessity for active cooling associated with some of these technologies preclude their widespread adoption. In this study, we leverage the advantages of low-dimensional materials to demonstrate a bias-selectable dual-band IR detector that operates at room temperature by using lead sulfide colloidal quantum dots and black phosphorus nanosheets. By switching between zero and forward bias, these detectors switch peak photosensitive ranges between the mid- and short-wave IR bands with room temperature detectivities of 5 × 109 and 1.6 × 1011 cm Hz1/2 W-1, respectively. To the best of our knowledge, these are the highest reported room temperature values for low-dimensional material dual-band IR detectors to date. Unlike conventional bias-selectable detectors, which utilize a set of back-to-back photodiodes, we demonstrate that under zero/forward bias conditions the device's operation mode instead changes between a photodiode and a phototransistor, allowing additional functionalities that the conventional structure cannot provide.

Flexible optoelectronics is a rapidly growing field, with a wide range of potential applications. From wearable sensors to bendable solar cells, curved displays, and curved focal plane arrays, the possibilities are endless. The criticality of flexible photodetectors for many of these applications is acknowledged, however, devices that are demonstrated thus far are limited in their spectral range. In this study, flexible photodetectors are demonstrated using a VOx nanoparticle ink, with an extremely broad operating wavelength range of 0.4 to 20 µm. This ink is synthesized using a simple and scalable wet‐chemical process. These photodetectors operate at room temperature and exhibit minimal variance in performance even when bent at angles of up to 100 ° at a bend radius of 6.4 mm. In addition, rigorous strain testing of 100 bend and release cycles revealed a photoresponse with a standard deviation of only 0.55%. This combination of mechanical flexibility, wide spectral response, and ease of fabrication makes these devices highly desirable for a wide range of applications, including low‐cost wearable sensors and hyperspectral imaging systems.

Semiconductor lasers play critical roles in many different systems, ranging from optical communications to absorption spectroscopy for environmental monitoring. Despite numerous applications, many semiconductor lasers have problems such as significant beam divergence and polarization instability. External optical elements like objective lenses and polarizers are usually needed to address these issues. This Review will discuss how these issues have recently been dealt with by instead integrating metasurfaces into semiconductor lasers. This necessitates the development of innovative fabrication methods; these will also be the topic of this Review. Metasurfaces can be integrated on the emitting facet of a laser. This can help select the lasing mode or can be used just to modify the output beam properties without affecting the modes. They can also be integrated monolithically with lasers through waveguides, or work in an external cavity configuration. These integrated devices provide novel optical functions, such as direct orbital angular momentum (OAM) mode generation, wavelength tuning and holographic pattern generation. We hope this Review will help extend the use of metasurface-integrated semiconductor lasers to scientific and industrial systems that employ lasers.

The remarkable advances in nanofabrication that have occurred over the last decade present opportunities for the realization of new types of holograms. In this work, for the first time to the best of our knowledge, a method for phase multicolor holograms based on nanohole arrays is described. The nanoholes are in an aluminum film that is interposed between the glass substrate and a silicon dioxide layer. The nanoholes serve as color filters for blue, green, and red wavelengths and provide the necessary phase distribution via the detour phase method. Our nanohole arrays are optimized to maximize the transmission efficiency of the red, green, and blue channels and to minimize the cross-talk between them. We design two multicolor holograms based on these filters and simulate their performance. The results show good fidelity to the desired holographic images. The proposed structure has the advantages of being very compact, of requiring only a simple fabrication method with one lithography step, and of employing materials (aluminum and silicon dioxide) that are compatible with standard CMOS technology.

Smartphones are a potentially powerful platform for scientific instruments. Here, we demonstrate speckle spectroscopy with smartphone-level hardware. This technique promises greater performance thresholds than traditional diffraction gratings. Light is injected into an optical fiber and the emergent speckle patterns are imaged by a reversed-lens smartphone camera. The smartphone then uses an algorithm, running on a mobile computing app, to determine, in less than one second, the (hitherto unknown) input spectrum. We reconstruct a variety of visible-wavelength (470-670 nm) single and multi-peaked spectra using a tunable source. The latter also include a metameric pair, i.e., two spectra that are different, yet represent colors that are indistinguishable to the human eye.

2D materials, with distinct characteristics compared to their conventional bulk counterparts, have been a popular topic in various optoelectronic research fields. Herein, indium selenide (InSe), a monochalcogenide van der Waals layered semiconductor, which has been studied due to its thickness dependent optical characteristics is explored. For InSe to be used as a versatile light source, enhancing the emission of InSe is required. Here, enhanced photoluminescence (PL) from multi‐layer InSe is demonstrated using a gap plasmon induced between Ag nanocube dimer and an Au substrate. Such plasmonic structures support multiple resonances, one of those overlapping with InSe's band edge PL emission. The calculated Purcell factor shows a 200‐fold increase on the short edge of nanocube dimers. Experimentally, PL enhancement of 6‐fold is demonstrated at room temperature. In addition, a method for determining the thickness of 2D materials via dark‐field spectroscopy using white light illumination is shown. This study paves the way for the incorporation of 2D InSe into nanophotonic structures.

Gallium nitride (GaN) technology has matured and commercialised for optoelectronic devices in the ultraviolet (UV) spectrum over the last few decades. Simultaneously, atomically thin materials with unique features have emerged as contenders for device miniaturization. However, the lack of successful techniques to produce ultra‐thin GaN prevents access to these new predicted properties. Here, this important gap is addressed by printing millimeter‐large ultra‐thin GaN nanosheets (NS) (≈1.4 nm) using a simple two‐step process that simultaneously introduces nitrogen point defects. This extends the photoelectrical spectral response from UV (280 nm) to near infrared (NIR) (1080 nm). The GaN‐based photodetectors display excellent figures of merit, having a responsivity (2.72 × 104 A W−1) up to four orders of magnitude higher than the commercial photodetectors at room temperature, despite being 102–103 times thinner. The photodetectors exhibit fast switching, with rise and decay time in the range of microseconds. The state‐of‐the‐art device performance originates from the ultra‐thin nature of GaN NS coupled with nitrogen point vacancies in the synthesis process. This work presents the opportunity to significantly expand the reach of GaN semiconductor technology and may lead to applications in high‐performance miniaturized imaging systems, spectroscopy, communication, and integrated optoelectronic circuits.

Vanadium oxides (VOx) are highly promising materials for heat retardant coatings, enabled by their insulator-to-metal phase transition (IMT). Currently, this IMT typically occurs at 68 °C, well above room temperature. Here, we develop a dopant-free approach to lower the IMT temperature to ∼40 °C enabling near-room temperature infrared modulation, by simple, solution phase synthesis. This is achieved by both controlling the stoichiometry of the metal oxide and by using a SiO2 shell around the VOx particles, with the difference in thermal expansion coefficient between SiO2 and VOx inducing sufficient strain in the VOx to dramatically lower the IMT temperature. This approach enables the production of a functional solution of suspended VOx nanoparticles with near-room temperature IMT. The combination of near-room temperature IMT and solution phase nanoparticles dramatically increases the ease, scalability, and efficacy of VOx application.

Black phosphorus has emerged as a unique optoelectronic material, exhibiting tunable and high device performance from mid-infrared to visible wavelengths. Understanding the photophysics of this system is of interest to further advance device technologies based on it. Here we report the thickness dependence of the photoluminescence quantum yield at room temperature in black phosphorus while measuring the various radiative and non-radiative recombination rates. As the thickness decreases from bulk to ~4 nm, a drop in the photoluminescence quantum yield is initially observed due to enhanced surface carrier recombination, followed by an unexpectedly sharp increase in photoluminescence quantum yield with further thickness scaling, with an average value of ~30% for monolayers. This trend arises from the free-carrier to excitonic transition in black phosphorus thin films, and differs from the behaviour of conventional semiconductors, where photoluminescence quantum yield monotonically deteriorates with decreasing thickness. Furthermore, we find that the surface carrier recombination velocity of black phosphorus is two orders of magnitude lower than the lowest value reported in the literature for any semiconductor with or without passivation; this is due to the presence of self-terminated surface bonds in black phosphorus.

Miniaturized mid-infrared spectrometers present opportunities for applications that range from health monitoring to agriculture. One approach combines arrays of spectral filters with infrared photodetectors, called filter-array detector-array (FADA) microspectrometers. A paper recently reported a FADA microspectrometer in tandem with machine learning for chemical identification. In that work, a FADA microspectrometer with 20 filters was assembled and tested. The filters were band-pass, or band-stop designs that evenly spanned the microspectrometer's operating wavelength range. However, given that a machine learning classifier can be trained on an arbitrary filter basis, it is not apparent that evenly spaced filters are optimal. Here, through simulations with noise, we use a genetic algorithm to optimize six bandpass filters to best identify liquid and gaseous chemicals. We report that the classifiers trained with the optimized filter sets outperform those trained with evenly spaced filter sets and those handpicked to target the absorption bands of the chemicals investigated.

2D materials, such as graphene, transition metal dichalcogenides, black phosphorus, and tellurium, have been demonstrated to be promising building blocks for the fabrication of next‐generation high‐performance infrared (IR) photodetectors with diverse device architectures and impressive device performance. Integrating IR photodetectors with nanophotonic structures, such as surface plasmon structures, optical waveguides, and optical cavities, has proven to be a promising strategy to maximize the light absorption of 2D absorbers, thus enhancing the detector performance. In this review, the state‐of‐the‐art progress of IR photodetectors is comprehensively summarized based on 2D materials and nanophotonic structures. First, the advantages of using 2D materials for IR photodetectors are discussed. Following that, 2D material‐based IR detectors are classified based on their composition, and their detection mechanisms, key figures‐of‐merit, and the principle of absorption enhancement are discussed using nanophotonic approaches. Then, recent advances in 2D material‐based IR photodetectors are reviewed, categorized by device architecture, i.e., photoconductors, van der Waals heterojunctions, and hybrid systems consisting of 2D materials and nanophotonic structures. The review is concluded by providing perspectives on the challenges and future directions of this field.

The identification of chemicals from their mid‐infrared spectra has applications that include industrial production of chemicals, food production, pharmaceutical manufacturing, and environmental monitoring. This is generally done using laboratory benchtop tools, such as the Fourier transform infrared spectrometer. Although such systems offer high performance, alternative platforms offering reduced size, weight, and cost can enable a host of new applications, e.g. in consumer personal electronics. Here a compact microspectrometer platform for chemical identification, comprising a mid‐infrared metasurface integrated with a lightweight (≈1 g) and very small (≈1 cm3) microbolometer‐based thermal camera is experimentally demonstrated. A machine learning algorithm is trained to analyze the microspectrometer output and classify chemicals based on their mid‐infrared fingerprints. High accuracy identification of four liquid chemicals, concentration quantification of ethyl lactate in cyclohexane down to subpercentage levels, and the classification of food and drug samples is demonstrated.

Beams with spatially‐varying polarization states have been the topic of much interest recently due to the unusual ways in which they can interact with matter. Cylindrical vector beams (CVBs) represent the most commonly used type and feature cylindrically‐symmetric polarization distributions. The optical systems employed thus far for their generation have usually only been able to produce a single CVB. To generate and observe multiple CVBs, bulky optical systems with stringent alignment tolerances have been needed. Here, a method to generate an array of CVBs using a single optical element, namely a transmission‐mode dielectric metasurface, is demonstrated. The incident light is split into an array of left and right‐handed circularly polarized vortex beams that superpose with a controllable phase difference. An array of CVBs with 12 channels over a broad wavelength range is experimentally demonstrated. This study's method produces a significant increase in the number of polarization channels compared to previous reports and solves the long‐standing challenge of unequal intensity distributions. It furthermore improves the flexibility of the vector field control by not only generating CVBs of different orders but also controlling their polarization rotation. This method may pave the way for applications in optical communications, laser machining, and optical trapping.

The mid-wave infrared (MWIR) wavelength range plays a central role in a variety of applications, including optical gas sensing, industrial process control, spectroscopy, and infrared (IR) countermeasures. Among the MWIR light sources, light-emitting diodes (LEDs) have the advantages of simple design, room-temperature operation, and low cost. Owing to the low Auger recombination at high carrier densities and direct bandgap of black phosphorus (bP), it can serve as a high quantum efficiency emitting layer in LEDs. In this work, we demonstrate bP-LEDs exhibiting high external quantum efficiencies and wall-plug efficiencies of up to 4.43 and 1.78%, respectively. This is achieved by integrating the device with an Al2O3/Au optical cavity, which enhances the emission efficiency, and a thin transparent conducing oxide [indium tin oxide (ITO)] layer, which reduces the parasitic resistance, both resulting in order of magnitude improvements to performance.

Mid-infrared (MIR) spectroscopy has numerous industrial applications and is usually performed with Fourier-transform infrared (FTIR) spectrometers. While these work well for many purposes, there is currently much interest in alternative approaches that are smaller and lighter, i.e., MIR microspectrometers. Here we investigate all-dielectric metasurfaces as spectral filters for MIR microspectrometers. Two metasurface types are studied. For the first, we design, fabricate, and test a metasurface with a narrow and angularly tunable transmission stop band. We use it to reconstruct the transmission spectra of various materials. The second metasurface, investigated theoretically, possesses narrow passband features via symmetry-protected bound states in the continuum.

Polarization plays a critical role in optical systems that range from optical communications to imaging, lithography, metrology, and data storage. Thus, in systems that need to generate a certain polarization state, a light source (e.g., laser) is combined with polarization control elements such as polarizers, polarizing beam splitters, and waveplates. Similarly, in systems requiring polarization state detection, such elements are combined with photodetectors. There is currently a trend toward miniaturized optical systems. This motivates the question of how to achieve what may be argued as an ultimate level of miniaturization: a single chip that can both generate light with a prescribed polarization state and detect the polarization state of light impinging upon it. This paper demonstrates this via vertical cavity surface emitting lasers (VCSELs) with on‐facet metasurfaces. Two classes of devices are demonstrated. The first class uses high‐index dielectric metasurfaces (amorphous silicon nanofins), whereas the second class uses plasmonic metasurfaces (aluminum bilayer gratings). Each can operate as a laser (to generate) and as a photodetector (to detect) circularly or linearly polarized light.

Multicolor holograms have numerous applications, including in art, data storage, security, and advanced displays. In recent years, there has been much interest concerning multicolor holograms based on metasurfaces [1]. Wen et al [2] demonstrated multicolor holograms using dielectric nanoparticles, with the nanoparticle size defining its resonant wavelength and its position defining its phase via the detour phase concept [3]. While this approach worked, it required good control over nanoparticle size and shape, achieved using inductively coupled reactive ion etching (ICP-RIE). This motivates the development of multicolor metasurface holograms that are also based on detour phase, but using other nanostructure types. Here we show that arrays of nanoholes in aluminum films enable the realization of multicolor holograms. We design nanohole arrays that serve as color (i.e. red/green/blue) filters with high transmission and low cross-talk. We then design two multicolor holograms based on these filters and simulate their performance, demonstrating that they show good fidelity to the desired holographic images. Our device is based on aluminum and silicon dioxide, giving it the advantage of CMOS compatibility.

We experimentally demonstrate a nanostructured silicon microspectrometer chip that consists of 144 pixels, each comprising an array of vertical waveguides of subwavelength period. We show that both broad- and narrow-band visible spectra can be reconstructed.

The past decade has witnessed the rapid development of metasurfaces. In this paper, we outline our thinking on what we regard as two important trends in metasurface research, namely, the continual improvement in the light field modulation capacity of metasurfaces and the integration of metasurfaces with other devices to achieve fully contained optical systems. We first describe one of the fastest growing branches of the former, which is known as metasurface-based vectorial holography. This aims to control the wavefront and the polarization state of a light beam simultaneously. In comparison with single function devices, i.e., those that modulate the wavefront or polarization but not both, metasurface vectorial holography represents a significant improvement in our ability to modulate light fields. We then discuss the integration of metasurfaces with lasers for the goal of direct modulation of the polarization of the output beam or for the generation of beams with tailored orbital angular momenta. Two methods for doing so are discussed, namely, on-facet integration and in-cavity integration. We hope this Perspective will provide readers with new insights and thus help extend applications of metasurface-based optical devices.

Metasurface-based holography presents opportunities for applications that include optical displays, data storage, and optical encryption. Holograms that control polarization are sometimes referred to as vectorial holograms. Most studies on this topic have concerned devices that display different images when illuminated with different polarization states. Fewer studies have demonstrated holographic images whose polarization varies spatially, i.e., as a function of the position within the image. Here, we experimentally demonstrate a vectorial hologram that produces an image with a spatially continuous distribution of polarization states, for the first time to our knowledge. An unlimited number of polarization states can be achieved within the image. Furthermore, the holographic image and its polarization map (polarization vs position in image) are independent. The same image can be thus encoded with different polarization maps. As far as we know, our approach is conceptually new. We anticipate that it could broaden the application scope of metasurface holography.

Graphene photodetectors operating in the mid‐wave infrared (MWIR) face challenges that include the optical absorption of monolayer graphene being intrinsically low and the carrier lifetime in graphene being very short. Previous reports of graphene photoconductors in the MWIR have sought to overcome these challenges using approaches that include the integration of plasmonic nanoantennas and/or engineered electrodes. However, this has led to the photoresponse of these detectors being strongly polarization dependent. Here, a graphene photoconductor is reported that achieves polarization‐independent and fast response simultaneously via the integration of plasmonic nanoantennas that are termed Jerusalem‐cross antennas (JC‐antennas). Compared to previous works, the JC‐antennas concentrate the incident light onto graphene more efficiently with enhanced polarization‐independent optical absorption. MWIR detection is demonstrated at both room temperature and cryogenic temperatures, with measured responsivity of 14.5 V W−1 (room temperature) and 4400 V W−1 (78 K). Due to the carrier collection by the JC‐antennas and gapless band structure of graphene, the detector also shows significant and broadband photoresponse that extends to visible and near‐infrared wavelengths. The detector shows fast temporal response with a measured rise time of 3 ns, which would be more than sufficient for many practical applications (e.g., imaging).

Plasmonic apertures permit optical fields to be concentrated into sub‐wavelength regions. This enhances the optical gradient force, enabling the precise trapping of nanomaterials such as quantum dots, proteins, and DNA molecules at modest laser powers. Double nanoholes, coaxial apertures, bowtie apertures, and other structures have been studied as plasmonic nanotweezers, with the design process generally comprising intuition followed by electromagnetic simulations with parameter sweeps. Here, instead, a computational algorithm is used to design plasmonic apertures for nanoparticle trapping. The resultant apertures have highly irregular shapes that, in combination with ring couplers also optimized by algorithm, are predicted to generate trapping forces more than an order of magnitude greater than those from the double nanohole design used as the optimization starting point. The designs are realized by fabricating precision apertures with a helium/neon ion microscope and are studied them by cathodoluminescence and optical trapping. It is shown that, at every laser intensity, the algorithm‐designed apertures can trap particles more tightly than the double nanohole.

Graphene, a semi-metal with a gapless band structure, has been used in mid-infrared (MIR) photodetectors (PDs) for some time. However, these detectors often suffer from low responsivity due to the intrinsically low absorption and ultra-short carrier lifetime in graphene, large dark current, and low detectivity due to the semi-metallic nature of graphene. Over the past decade, much effort has been devoted to addressing these issues. A variety of metamaterials and related concepts has been employed to improve the detector responsivity by enhancing the graphene absorption and/or the carrier collection efficiency. Here, we provide an overview of the graphene MIR PDs with and without the use of approaches for responsivity enhancement. We focus our attention on the state-of-the-art graphene MIR PDs whose performance is improved by employing metamaterials and related concepts, including band structure engineering, the photogating effect, integration with plasmonic nanostructures and waveguides, the use of asymmetric plasmons, coupled plasmon–phonon polaritons, and small-twist-angle bilayer graphene. We conclude by providing possible directions for further performance improvement of graphene MIR PDs and a discussion on future applications of these detectors.

Optical anisotropy and thinness of 2D black phosphorous (bP) lead to weak light absorption, which limits the performance of bP-based photodetectors. We demonstrate that T-shaped nanoantennas can be integrated with bP to overcome this issue.

Plasmonic apertures for optical nanotweezers are designed by an algorithm and fabricated with a helium ion microscope. Optical trapping experiments are performed. At every laser intensity, an algorithm-designed structure can outperform a conventional plasmonic aperture.

We present a silicon-based Pancharatnam-Berry (PB) phase metasurface hologram that produces a triple-helix solenoid tractor beam from a Gaussian input beam. Our metasurface has a >90% diffraction efficiency and >75% transmission.

Room-temperature optoelectronic devices that operate at short-wavelength and mid-wavelength infrared ranges (one to eight micrometres) can be used for numerous applications1-5. To achieve the range of operating wavelengths needed for a given application, a combination of materials with different bandgaps (for example, superlattices or heterostructures)6,7 or variations in the composition of semiconductor alloys during growth8,9 are used. However, these materials are complex to fabricate, and the operating range is fixed after fabrication. Although wide-range, active and reversible tunability of the operating wavelengths in optoelectronic devices after fabrication is a highly desirable feature, no such platform has been yet developed. Here we demonstrate high-performance room-temperature infrared optoelectronics with actively variable spectra by presenting black phosphorus as an ideal candidate. Enabled by the highly strain-sensitive nature of its bandgap, which varies from 0.22 to 0.53 electronvolts, we show a continuous and reversible tuning of the operating wavelengths in light-emitting diodes and photodetectors composed of black phosphorus. Furthermore, we leverage this platform to demonstrate multiplexed nondispersive infrared gas sensing, whereby multiple gases (for example, carbon dioxide, methane and water vapour) are detected using a single light source. With its active spectral tunability while also retaining high performance, our work bridges a technological gap, presenting a potential way of meeting different requirements for emission and detection spectra in optoelectronic applications.

Black phosphorus (bP), a two-dimensional (2D) layered material, has shown great potential for infrared (IR) optoelectronics owing to the narrow and direct bandgap it exhibits when in multilayer form. However, its thinness and optical anisotropy lead to weak light absorption, which limits the performance of bP-based photodetectors. In this work, we explore plasmonic nanoantennas, optical cavities, and their hybrids that can be integrated with multilayer bP to enhance its light absorption. This is achieved by near-field light intensity enhancement and polarization conversion. In addition, we demonstrate that these nanostructures can boost the spontaneous emission from bP. Light absorption enhancements of up to 185 and 16 times are obtained for linearly polarized and unpolarized IR light, respectively, in comparison with a commonly used device architecture (bP on SiO2/Si). Moreover, IR light emission enhancements of up to 18 times are achieved. The optical nanostructures presented here can be exploited for enhancing the detectivity of photodetectors and electroluminescence efficiency of light-emitting diodes based on bP and other 2D materials.

Numerous applications exist for chemical detection, ranging from the industrial production of chemicals to pharmaceutical manufacturing, environmental monitoring, and hazardous risk control. For many applications, infrared absorption spectroscopy is the favored technique, due to attributes that include short response time, high specificity, minimal drift, in situ operation, negligible sample disruption, and reliability. The workhorse instrument for infrared absorption is the Fourier transform infrared (FTIR) spectrometer. While such systems are suitable for many purposes, new applications would be enabled by small, lightweight, low power and low cost infrared microspectrometers. Here we perform a detailed study on a microspectrometer chemical classifier comprising an array of plasmonic mid-infrared spectral filters used with a photodetector array, whose outputs are analyzed by a machine learning algorithm. We conduct simulations (including noise), demonstrating the identification of six gas-phase and six liquid-phase chemicals. We study the performance of our method at detecting the concentration of acetylene.

We demonstrate a microspectrometer comprising plasmonic filters integrated with an infrared camera. Blackbody light illuminates the material being studied, with transmitted light collected by the microspectrometer. The latter uses machine learning to identify the material.

We design a plasmonic filter array for a filter array-detector array microspectrometer. We perform numerical experiments, including noise, that predict that this configuration would enable the identification of various materials via their infrared fingerprints.

We present a geometric phase silicon metasurface hologram design intended to produce a non-diffracting solenoid beam. Such optical beams have been shown to exert long range retrograde (i.e. toward source) optical forces on light-scattering particles.

We demonstrate a spectrometer that uses a smaityhone to image the speckle pattern produced by a multimode optical fiber. A smarjihone-based algorithm uses the measured pattern and a calibration library to determine the input spectnrm.

Spectroscopy is a cornerstone in the field of optics. Conventional spectrometers generally require two elements. The first provides wavelength selectivity, for example, diffraction grating or Michelson interferometer. The second is a detector (or detector array). Many applications would benefit from very small and lightweight spectrometers. This motivates us to investigate what may be regarded as an ultimate level of miniaturization for a spectrometer, in which it consists solely of a detector array. We demonstrate a chip containing 24 pixels, each comprising a silicon nanowire (Si NW) array photodetector formed above a planar photodetector. The NWs are structurally colored, enabling us to engineer the responsivity spectra of all photodetectors in the chip. Each pixel thus combines wavelength selectivity and photodetection functions. We demonstrate the use of our chip to reconstruct the spectrum of an unknown light source impinging upon it. This is achieved by an algorithm that takes as its inputs the measured photocurrents from the pixels and a library of their responsivity spectra.

A hologram records the wavefront of light from an object, but it is usually not an image itself, and looks unintelligible under diffuse ambient light. Here a new paradigm to encode a color hologram onto a color printed image is experimentally demonstrated. The printed image can be directly viewed under white light illumination, while a low‐crosstalk color holographic image can be seen when the device is illuminated with red (R), green (G), and blue (B) laser beams. The device is a dielectric metasurface that consists of titanium dioxide (TiO2) cones on a glass substrate. The dimensions of the TiO2 cones are chosen to allow them to support visible‐wavelength resonances, thereby producing the desired reflection spectra and thus the color printed image. The detour phase method is furthermore used to encode the hologram into the metasurface. The approach is conceptually different from previously demonstrated color printed images or holograms and presents opportunities for optical document security and data storage applications.

In recent years there has been much interest concerning the development of modulators in the mid- to long-wave infrared, based on emerging materials such as graphene. These have been frequently pursued for optical communications, though also for other specialized applications such as infrared scene projectors. Here we investigate a new application for graphene modulators in the mid- to long-wave infrared. We demonstrate, for the first time, computational spectroscopy in the mid- to long-wave infrared using a graphene-based metasurface modulator. Furthermore, our metasurface device operates at low gate voltage. To demonstrate computational spectroscopy, we provide our algorithm with the measured reflection spectra of the modulator at different gate voltages. We also provide it with the measured reflected light power as a function of the gate voltage. The algorithm then estimates the input spectrum. We show that the reconstructed spectrum is in good agreement with that measured directly by a Fourier transform infrared spectrometer, with a normalized mean-absolute-error (NMAE) of 0.021.

Biomolecule sensing plays an important role in both fundamental biological studies and medical diagnostic applications. Infrared (IR) spectroscopy presents opportunities for sensing biomolecules as it allows their fingerprints to be determined by directly measuring their absorption spectra. However, the detection of biomolecules at low concentrations is difficult with conventional IR spectroscopy due to signal-to-noise considerations. This has led to recent interest on the use of nanostructured surfaces to boost the signals from biomolecules in a method termed surface enhanced infrared spectroscopy. So far, efforts have largely involved the use of metallic nanoantennas (which produce large field enhancement) or graphene nanostructures (which produce strong field confinement and provide electrical tunability). Here, we propose a nanostructured surface that combines the large field enhancement of metallic nanoantennas with the strong field confinement and electrical tunability of graphene plasmons. Our device consists of an array of plasmonic nanoantennas and graphene nanoslits on a resonant substrate. We perform systematic electromagnetic simulations to quantify the sensing performance of the proposed device and show that it outperforms designs in which only plasmons from metallic nanoantennas or plasmons from graphene are utilized. These investigations consider the model system of a representative protein-goat anti-mouse immunoglobulin G (IgG) - in monolayer or sub-monolayer form. Our findings provide guidance for future biosensors for the sensitive quantification and identification of biomolecules.

We experimentally demonstrate vertical-cavity surface-emitting lasers (VCSEL) with integrated plasmonic and dielectric metasurfaces. The metasurfaces shape the polarization of the laser emission from the VCSELs and also enable them to serve as polarization-dependent photodetectors.

Chip-scale microspectrometers, operational across the visible to long-wave infrared spectral region will enable many remote sensing spectroscopy applications in a variety of fields including consumer electronics, process control in manufacturing, as well as environmental and agricultural monitoring. The low weight and small device footprint of such spectrometers could allow for integration into handheld, unattended vehicles or wearable-electronics based systems. This review will focus on recent developments in nanophotonic microspectrometer designs, which fall into two design categories: (i) planar filter-arrays used in conjunction with visible or IR detector arrays and (ii) microspectrometers using filter-free detector designs with tailored responsivities, where spectral filtering and photocurrent generation occur within the same nanostructure.

Atomically thin materials face an ongoing challenge of scalability, hampering practical deployment despite their fascinating properties. Tin monosulfide (SnS), a low‐cost, naturally abundant layered material with a tunable bandgap, displays properties of superior carrier mobility and large absorption coefficient at atomic thicknesses, making it attractive for electronics and optoelectronics. However, the lack of successful synthesis techniques to prepare large‐area and stoichiometric atomically thin SnS layers (mainly due to the strong interlayer interactions) has prevented exploration of these properties for versatile applications. Here, SnS layers are printed with thicknesses varying from a single unit cell (0.8 nm) to multiple stacked unit cells (≈1.8 nm) synthesized from metallic liquid tin, with lateral dimensions on the millimeter scale. It is reveal that these large‐area SnS layers exhibit a broadband spectral response ranging from deep‐ultraviolet (UV) to near‐infrared (NIR) wavelengths (i.e., 280–850 nm) with fast photodetection capabilities. For single‐unit‐cell‐thick layered SnS, the photodetectors show upto three orders of magnitude higher responsivity (927 A W−1) than commercial photodetectors at a room‐temperature operating wavelength of 660 nm. This study opens a new pathway to synthesize reproduceable nanosheets of large lateral sizes for broadband, high‐performance photodetectors. It also provides important technological implications for scalable applications in integrated optoelectronic circuits, sensing, and biomedical imaging.

We demonstrate long wave infrared photodetectors based on the transition metal dichalcogenide platinum diselenide (PtSe2) in its bulk form for the first time to our knowledge. Fabricated devices show sub-millisecond response times.

We discovered an error in the video analysis code used to track the position of trapped nanoparticles. Here, we provide a corrected version of the affected figure (Figure 4) of the original paper, obtained using the corrected video analysis code. The corrected panels comprise the scatter plots of trapped particle location (Figure 4e) and position histograms (Figure 4f,g). The other panels of that figure (Figure 4a-d) are unchanged. We provide a corrected version of the Table of Contents and Abstract image, as this includes Figure 4e. In addition, we provide a corrected discussion of Figure 4f,g below. This discussion starts and ends with the sentences to be corrected and includes for convenience the intervening sentences in the original paragraph (for which no correction is needed). In Figure 4f,g, we plot the measured NP center positions (xc and yc) as histograms. The full-widths-at-half-maximum (fwhms) of fitted Gaussian distributions are 486 and 332 nm along the x- and y-directions when the illumination intensity is 6.6 mW/µm2 (see Supporting Information, Movie 2). When the illumination intensity is 22 mW/µm2, the fwhms are 38 and 76 nm along the x- and y-directions, respectively. It can be seen that there is suppression of Brownian motion at the higher laser intensity. At the higher intensity, DNH results in the NPs being confined in an elliptical region, where the position histogram is narrower along the x-direction than the y-direction. This anisotropy can be ascribed to the near field being more strongly confined along the x-direction than the y-direction (see Figure 1c). In addition, the trapped NP experiences the steric hindrance from DNH edge in x-direction rather than in y-direction. To obtain experimental trapping stiffness for a rough estimate, we determine the “ef fective” trapping stiffness (keff = kBT/var(x), var(x) is the position variance) for both illumination intensities (6.6 and 22 mW/µm2). This is extracted from the measured variance of positio

We demonstrate room-temperature photodetectors at wavelengths from visible (450 nm, 532 nm) to near- (850 nm), short-wave (1550 nm), mid-wave (4.5 \mu m) and long-wave (8.35 \mu m) infrared. These are based on drop-cast Cu TCNQ crystals.