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Energy harvesting and energy transmission are the key technologies for self-powered systems; thus, the combination of these two is urgently needed. An innovative electric field resonance (EFR)-based wireless triboelectric nanogenerator (TENG) is proposed herein. By integrating the TENG with a capacitive coupler, the output of the TENG can be transmitted wirelessly from the transmitter to the receiver in the form of an oscillating signal with an energy-transfer efficiency of 67.8% for a 5 cm distance. Theoretical models of the EFR-TENG system are established, showing excellent agreement with the experimental results. It is demonstrated that the flexible EFR-TENG worn on the wrist can drive a digital watch wirelessly or light up at least 40 light-emitting diodes in series. The EFR-TENG is further utilized for spontaneous wireless sensing with a transmission distance up to 2.3 m with high system tolerance, showing the great potential of this novel strategy for energy harvesting and real-time wireless sensing applications.

Generation of electricity from flowing salt water is extremely attractive as the resources are abundant and green. We propose a generator to harvest DC electricity from flowing ionic solution. The device consists of a substrate with fixed surface charges, a top electrode and a bottom electrode separated with a distance. The electrostatic field originated from the surface charges separates charges of opposite polarities in the solution, while the flow directs the charges to different electrodes in a closed circuit. By utilizing ultrahigh charge density of ferroelectric substrate and ionic solution, the device produces pulsed DC output for droplets and constant current for continuous flow. The output could be greatly enhanced by using substrates with high surface charge densities and high ion concentration solutions. It could also be scaled up by connecting the devices in series or parallel. This work provides a new strategy to harvest low hydrodynamic energy from sea.

Laser based on single plasmonic nanoparticle can provide optical frequency radiation far beyond the diffraction limit and is one of the ultimate goals of nanolasers, yet it remains a challenge to be realized because of the inherently high Ohmic loss. Here, we report the direct observation of lasing in microfiber-coupled single plasmonic nanoparticles enabled by strong mode coupling. We show that, by strongly coupling a gold nanorod (GNR) with the whispering gallery cavity of a dye-doped polymer microfiber (with diameter down to 2.0 μm), the substantially enhanced optical coherence of the hybrid photon-plasmon mode and effective gain accumulated from the active microfiber cavity enable single-mode laser emission from the GNR at room temperature with a threshold as low as 2.71 MW/cm 2 and a linewidth narrower than 2 nm.

Chemically synthesized metal nanowires are promising building blocks for next-generation photonic integrated circuits, but technological implementation in monolithic integration will be severely hampered by the lack of controllable and precise manipulation approaches, due to the strong adhesion of nanowires to substrates in non-liquid environments. Here, we demonstrate this obstacle can be removed by our proposed earthworm-like peristaltic crawling motion mechanism, based on the synergistic expansion, friction, and contraction in plasmon-driven metal nanowires in non-liquid environments. The evanescently excited surface plasmon greatly enhances the heating effect in metal nanowires, thereby generating surface acoustic waves to drive the nanowires crawling along silica microfibres. Advantages include sub-nanometer positioning accuracy, low actuation power, and self-parallel parking. We further demonstrate on-chip manipulations including transporting, positioning, orientation, and sorting, with on-situ operation, high selectivity, and great versatility. Our work paves the way to realize full co-integration of various functionalized photonic components on single chips., Implementing metal nanowires in photonic circuits is challenging due to lack of suitable manipulation techniques. Here, the authors present an earthworm-like peristaltic crawling motion mechanism, based on surface plasmons and surface acoustic waves, and show on-chip manipulations of single nanowires.

Flexographic printing is promising for large-area electronics due to high print-speed and roll-to-roll capability. There have been recent attempts in using graphene as an active pigment in inks, most notably for slower techniques such as inkjet and screen printing. However, formulation of graphene-enhanced inks for high-speed printing and its effect on key metrics have never been investigated. Herein, graphene nanoplatelets (GPs) are incorporated to a conductive flexographic ink without compromising the rheological properties. An industrial scale at 100 m min−1 is printed on paper and polyethylene terephthalate (PET) substrates using a commercial flexographic press, and statistical performance variations are investigated across entire print runs. It is shown that GP-incorporation improves sheet-resistance (Rs) and uniformity, with up to 54% improvement in average Rs and 45% improvement in the standard-deviation on PET. The adhesion on both the substrates improves with GP-incorporation, as verified by tape/crosshatch tests. The durability of GP-enhanced samples is probed with a 1000 cyclic bend-test, with 0.31% average variation in resistance in the flat state on PET between the first and last 100 bends, exhibiting a robust print. The statistically scalable results show that GP-incorporation offers a cost-performance advantage for flexographic printing of large-area conductive patterns without modifications to traditional high-speed graphics printing presses. Published version We acknowledge funding from the Engineering and Physical Sciences Research Council (EP/L016087/1) and Alphasense Limited in United Kingdom.

As an ideal miniaturized light source, wavelength-tunable nanolasers capable of emitting a wide spectrum stimulate intense interests for on-chip optoelectronics, optical communications, and spectroscopy. However, realization of such devices remains a major challenge because of extreme difficulties in achieving continuously reversibly tunable gain media and high quality (Q)-factor resonators on the nanoscale simultaneously. Here, exploiting single bandgap-graded CdSSe NWs and a Fabry-Pérot/whispering gallery mode (FP/WGM) coupling cavity, a free-standing fiber-integrated reversibly wavelength-tunable nanolaser covering a 42 nm wide spectrum at room temperature with high stability and reproducibility is demonstrated. In addition, a 1.13 nm tuning spectral resolution is realized. The substrate-free device design enables integration in optical fiber communications and information. With reversible and wide, continuous tunability of emission color and precise control per step, our work demonstrates a general approach to nanocavity coupling affording high Q-factors, enabling an ideal miniaturized module for a broad range of applications in optics and optoelectronics, with optical fiber integration.

Interactive displays have been intensively used in consumer electronics, e.g., smartphones, for providing highly efficient human-machine interactions, assisting users to process a vast amount of data. However, current mainstream interactive displays only support 2-dimensional detection, strongly limiting user experience. In this paper, we present a piezoelectric and capacitive based technique for obtaining 4-dimensional detection, including (x-y axis) location, force, and hovers sensing in interactive displays. Here, electrodes are located on and underneath the piezoelectric layer, constructing a sandwich structured device. A self-capacitance-based technique is employed for location and hover sensing. Force-induced charges are collected and interpreted as force amplitude. As capacitive and piezoelectric sensing techniques occupy different frequency bands, these two signals can be smoothly separated, and 4-dimensional touch sensing is achieved concurrently, with the recognition of static force and hovers touch events.

Miniaturizing spectrometers Optical spectroscopy is a widely used characterization tool in industrial and research laboratory settings for chemical fingerprinting and analysis. High-end spectrometers are typically benchtop based with bulky optical components, moving parts, and long path lengths, and they can deliver a wealth of information with ultrahigh precision and bandwidth. There is, however, a drive toward miniaturization of spectrometers, in which concepts in nanophotonics are used to control light on much smaller scales. Yang et al. reviewed recent developments in spectrometry systems, including various fabrication approaches of nanophotonics systems and the software that computationally determines the spectra, that strive to shrink their footprint and open up applications in portable spectroscopy. Science , this issue p. eabe0722

We demonstrate micro/nanofiber temperature sensors based on micro/nano particles fluorescence lifetime. Dependence of the fluorescence intensity, branching ratio and lifetime on temperature are investigated from 30°to 210°. Compared with the intensity-based micro sensors, the lifetime-based micro sensors perform better in terms of accuracy, stability, and response speed. Precision of the proposed temperature sensor is obtained as high as 2°in the temperature range of 30°to 210°. This lifetime-based sensing technology won‘t be affected by external deformation of the sensors, proving it is a temperature selective sensor enabling eliminating interference of surrounding environment and background noise. Experiments and simulations show that response time of the micro sensor can be 50–100 times faster than that of conventional sensors.

Photoactivating oxygen dangling bonds on tapered micro/nanofibers enhances monolayer photoluminescence quantum yields., Although monolayer transition metal dichalcogenides (TMDs) have direct bandgaps, the low room-temperature photoluminescence quantum yields (QYs), especially under high pump intensity, limit their practical applications. Here, we use a simple photoactivation method to enhance the room-temperature QYs of monolayer MoS2 grown on to silica micro/nanofibers by more than two orders of magnitude in a wide pump dynamic range. The high-density oxygen dangling bonds released from the tapered micro/nanofiber surface are the key to this strong enhancement of QYs. As the pump intensity increases from 10−1 to 104 W cm−2, our photoactivated monolayer MoS2 exhibits QYs from ~30 to 1% while maintaining high environmental stability, allowing direct lasing with greatly reduced thresholds down to 5 W cm−2. Our strategy can be extended to other TMDs and offers a solution to the most challenging problem toward the realization of efficient and stable light emitters at room temperature based on these atomically thin materials.

Miniaturizing spectrometers Spectroscopy is a ubiquitous characterization tool spanning most scientific and many industrial disciplines. Most handheld spectrometers are based on tabletop optical components, which limits the scale to which these spectrometers can be shrunk. To address the desire for miniaturized spectrometers with a micrometer-scale (and smaller) footprint, Yang et al. developed such a microspectrometer based on single, compositionally engineered nanowire. This result is a practical step forward for the use of other light-sensitive nanomaterials for such ultra-miniaturized spectroscopy platforms. Science , this issue p. 1017

We use liquid phase exfoliation to produce dispersions of molybdenum disulfide (MoS2) nanoflakes in aqueous surfactant solutions. The chemical structures of the bile salt surfactants play a crucial role in the exfoliation and stabilization of MoS2. The resultant MoS2 dispersions are heavily enriched in single and few (6) layer flakes with large edge to surface area ratio. We use the dispersions to fabricate free-standing polymer composite wide-band saturable absorbers to develop mode-locked and Q-switched fiber lasers, tunable from 1535 to 1565 and 1030 to 1070 nm, respectively. We attribute this sub-bandgap optical absorption and its nonlinear saturation behavior to edge-mediated states introduced within the material band-gap of the exfoliated MoS2 nanoflakes.

The primary goal of this book is to comprehensively review 2D materials that have gained research interest and present the use of printing as a low-cost, high-throughput method of exploiting 2D materials in mass produced devices and components. This chapter covers the existing demonstrations of printed 2D materials in a wide variety of devices and summarises their current status. In addition, this chapter also discusses the state-of-the-art literature on the trends and development stages, future technology directions and their likely convergence for next generation of applications, devices and systems.

The widespread use of printing of 2D materials in their relevant applications is highly dependent on the cost and scalability of their methods of production. This chapter serves as an introduction to the key methods for 2D material production and characterisation. Methods such as chemical vapour deposition, plasma cracking of hydrocarbons, intercalation, chemical exfoliation and liquid phase exfoliation are described and their relative merits are discussed. Particular emphasis is given to the 2D materials relevant to ink production. The latter half of the chapter discusses commonly used processing steps and characterisation methods for the 2D materials and their respective roles in qualifying and quantifying the material produced.

Early scientific investigations into graphene date back to the 1950s. The interest in graphene intensified when Konstantin Novosolev and Andre Geim were awarded the Nobel prize in physics for ‘groundbreaking experiments regarding the two-dimensional material graphene’. Since then, other two-dimensional (2D) materials have (re)gained increasing research interest. The most studied 2D materials to date include transition metal dichalcogenides (TMDs), black phosphorus (BP), hexagonal boron nitride (h-BN) and transition metal carbides and/or carbonitrides (MXenes). This chapter introduces these key material groups, and provides a review of the current understanding of their structures and properties. In particular, this chapter will focus on the (opto)electronic properties of the individual 2D materials and their potential applications.

The use of two-dimensional (2D) materials in low-cost, high-throughput printing as a scalable production method relies heavily on its successful incorporation into printable ink systems. However, industrial scale production of 2D material printing inks has proven to be a significant challenge. This chapter begins with a brief history of inks and progresses to the basic ink formulations and the techniques used in traditional printing technologies. This chapter also discusses ink properties, processing techniques and optimisation of formulation parameters using methods such as Design of Experiments (DOE), and useful characterisation techniques when formulating 2D material inks. Finally, the chapter covers ink–substrate interaction and optimisation strategies for ink formulation.

This paper reports a dramatic reduction in plasmon resonance line width of a single Au nanorod by coupling it to a whispering gallery cavity of a silica microfiber. With fiber diameter below 6 μm, strong coupling between the nanorod and the cavity occurs, leading to evident mode splitting and spectral narrowing. Using a 1.46-μm-diameter microfiber, we obtained single-band 2-nm-line-width plasmon resonance in an Au nanorod around a 655-nm-wavelength, with a quality factor up to 330 and extinction ratio of 30 dB. Compared to an uncoupled Au nanorod, the strongly coupled nanorod offers a 30-fold enhancement in the peak intensity of plasmonic resonant scattering.

Semiconductor nanowire (SNW) lasers have great potential applications in high density data storage, single molecule detection, direct RNA and DNA sequencing and integrated optoelectronic circuits etc. While for their practical applications, control and optimization of the parameters are of great significance and have been attracting growing interests in the past years. Here we present a review of the key parameters control and optimization about SNW lasers. After introducing the background of NW lasers in the first two chapters, wavelength control, mode optimization, threshold reduction and polarization measurement and modulation will be demonstrated in the following text successively. Finally, we will give a perspective on SNW lasers research to address important future directions and challenges for further enrichment of this emerging area.

Active modulation of light with large optical bandwidths (∼100 nm [1]) is required in photonic devices, such as modulators for fiber communications [1] and saturable absorbers for ultrafast pulse generation [2,3]. Present modulators use expensive materials, (e.g. LiNbO 3 [4], III-V semiconductors [5], and Ge on silicon-on-insulator (SOI) [6]), and are limited by narrowband operation (∼20 nm for quantum-confined Stark effect devices [7], or 3 N 4 ) while offering a full-band operation [10]. In all-fiber platforms, including ultrafast lasers [2,3], high coupling losses (∼60% from fiber to SOI waveguide [6]) are driving development of fiber-based modulators. Ref. 3 reported an electrically controllable all-fiber optical modulator with a SLG transistor on a side-polished fiber. However, its gating speed was limited to∼300 Hz [11] due to the low mobility of the ionic liquid used for gating. Here, we report a graphene-microfiber modulator by integrating a microfiber onto a graphene (SLG plated) capacitor (GC). By varying the microfiber size and length we control the light interaction with the biased SLG plates. This can be used for active control of ultrafast laser working in continuous wave, Q-switching and mode-locking operations.

We report a hybrid graphene-microfiber odulator with low insertion loss ~0.4dB, and active, ~6.7%, control of absorption. This can be used for active control of ultrafast laser working in continuous wave, Q-switching and mode-locking operations.

CdSxSe1–x nanowires with a graded bandgap along the length direction were utilized for field-effect transistors and Schottky junction solar cells. This novel type of nanowires suggests promising electronic and optoelectronic applications in the future.

On the basis of the transverse second harmonic generation (TSHG) in a highly nonlinear subwavelength-diameter CdTe nanowire, we demonstrate a single-nanowire optical correlator for femto-second pulse measurement with pulse energy down to femtojoule (fJ) level. Pulses to be measured were equally split and coupled into two ends of a suspending nanowire via tapered optical fibers. The couterpropagating pulses meet each other around the central area of the nanowire, and emit TSHG signal perpendicular to the axis of the nanowire. By transferring the spatial intensity profile of the transverse second harmonic (TSH) image into the time-domain temporal profile of the input pulses, we operate the nanowire as a miniaturized optical correlator. Benefitted from the high nonlinearity and the very small effective mode area of the waveguiding CdTe nanowire, the input energy of the single-nanowire correlator can go down to fJ-level (e.g., 2 fJ/pulse for 1064 nm 200 fs pulses). The miniature fJ-pulse correlator may find applications from low power on-chip optical communication, biophotonics to ultracompact laser spectroscopy.

Superiorly high photoconductivity is desirable in optoelectronic materials and devices for information transmission and processing. Achieving high photoconductivity via bandgap engineering in a bandgap-graded semiconductor nanowire has been proposed as a potential strategy. In this work, we report the ultrahigh photoconductivity of bandgap-graded CdSxSe1−x nanowires and its detailed analysis by means of ultrafast optical-pump terahertz-probe (OPTP) spectroscopy. The recombination rates and carrier mobility are quantitatively obtained via investigation of the transient carrier dynamics in the nanowires. By analysis of the terahertz (THz) spectra, we obtain an insight into the bandgap gradient and band alignment to carrier transport along the nanowires. The demonstration of the ultrahigh photoconductivity makes bandgap-graded CdSxSe1−x nanowires a promising candidate as building blocks for nanoscale electronic and photonic devices.

An integrated system consisting of a carbon fiber-ZnO hybrid nanowire (NW) multicolor photodetector is driven by a microbial fuel cell (see picture; PMMA = poly(methyl methacrylate), E = electrode). The self-powered photodetector can detect at light levels of as little as nW cm(-2) intensity with a responsivity of more than 300 A W(-1).

We discuss the emerging role of solution processing and functional ink formulation in the fabrication of devices based on two dimensional (2d) materials. By drawing on examples from our research, we show that these inks allow 2d materials to be exploited in a wide variety of applications, including in photonics and (opto)electronics.

Bandgap engineering of semiconductor nanowires is important in designing nanoscale multifunctional optoelectronic devices. Here, we report a facile thermal evaporation method, and realize the spatial bandgap engineering in single CdS(1-x)Se(x) alloy nanowires. Along the length of these achieved nanowires, the composition can be continuously tuned from x = 0 (CdS) at one end to x = 1 (CdSe) at the other end, resulting in the corresponding bandgap (light emission wavelength) being modulated gradually from 2.44 eV (507 nm, green light) to 1.74 eV (710 nm, red light). In spite of the existing composition (crystal lattice) transition along the length, these multicolor nanowires still possess high-quality crystallization. These bandgap engineered nanowires will have promising applications in such as multicolor display and lighting, high-efficiency solar cells, ultrabroadly spectral detectors, and biotechnology.

Designing lasing wavelengths and modes is essential to the practical applications of nanowire (NW) lasers. Here, according to the localized photoluminescence spectra, we first demonstrate the ability to define lasing wavelengths over a wide range (up to 119 nm) based on an individual bandgap-graded CdSSe NW by forward cutting the NW from CdSe to CdS end. Furthermore, free spectral range (FSR) and modes of the obtained lasers could be controlled by backward cutting the NW from CdS to CdSe end step-by-step. Interestingly, single-mode NW laser with predefined lasing wavelength is realized in short NWs because of the strong mode competition and increase in FSR. Finally, the gain properties of the bandgap-graded NWs are investigated. The combination of wavelength and mode selectivity in NW lasers may provide a new platform for the next generation of integrated optoelectronic devices.

A 1 Gbps 105.4 GHz wireless link is demonstrated by directly modulating a photonic integrated dual-laser source. A 50 m link is predicted to be able to achieve error free operation using FEC following optimisation.

Based on low-loss fusion splicing of microfibers using a CO_2 laser, we demonstrate free-standing microfiber closed-loop resonators. Loaded Q-factors of 110 500 with a finesse of 15.3 are obtained around 1.5- wavelength in a 2.4-mm-diameter closed-loop resonator suspended in air. The possibility of tuning resonant responses by changing the coupling efficiency is also demonstrated.

Multicolor lasing and dynamic color-tuning in a wide spectrum range are challenging to realize but critically important in many areas of technology and daily life, such as general lighting, display, multicolor detection, and multiband communication. By exploring nanoscale growth and manipulation, we have demonstrated the first active dynamical color control of multicolor lasing, continuously tunable between red and green colors separated by 107 nm in wavelength. This is achieved in a purposely engineered single CdSSe alloy nanowire with composition varied along the wire axis. By looping the wide-gap end of the alloy nanowire through nanoscale manipulation, two largely independent (only weakly coupled) laser cavities are formed respectively for the green and red color modes. Our approach simultaneously overcomes the two fundamental challenges for multicolor lasing in material growth and cavity design. Such multicolor lasing and continuous color tuning in a wide spectral range represents a new paradigm shift and would eventually enable color-by-design and white-color lasers for lighting, illumination, and many other applications.

We report a simultaneous two-color lasing with wavelength separation of 107 nm in a single CdSSe alloy nanowire. The output color can be tuned continuously from green to red by controlling two pump beams.

Asymmetric light propagation is crucial to the development of optical-based functional components in nanophotonics. Diverse configurations and structures have been proposed to allow asymmetrical propagation of photonic signal, but on-chip integration is difficult to achieve due to their complex structure and/or relatively large footprint. Here we report the first design and realization of asymmetric light propagation in single semiconductor nanowires with a composition gradient along the length. We show the asymmetric nanowire waveguides can be synthesized using a simple thermal evaporation and vapor transport approach without involving complicated and costly fabrication processes. Our studies demonstrate the asymmetric nanowire waveguides offer some significant advantages over previous designs, including ultra-low operation power, tunable working wavelength and nanoscale footprint, making them attractive building blocks for integrated photonic circuits.

Compact wavelength-sensitive optical components are desirable for optical information processing and communication in photonic integrated system. In this work, optical waveguiding along single composition-graded CdS(x)Se(1-x) nanowires were systematically investigated. Under a focused laser excitation, the excited light can be guided passively along the bandgap-increased direction of the nanowire, keeping the photonic energy of the guided light almost unchanged during the whole propagation. In comparison, the excited light is guided actively through incessantly repeated band-to-band reabsorption and re-emitting processes along the bandgap-decreased direction, resulting in a gradual wavelength conversion during propagation. On the basis of this wavelength-converted waveguiding, a concept of nanoscale wavelength splitter is demonstrated by assembling a graded nanowire with several composition-uniform nanowires into branched nanowire structure. Our study indicates that composition-graded semiconductor nanowires would open new exciting opportunities in developing new wavelength-sensitive optical components for integrated nanophotonic devices.