Stretchable physical sensors that can detect and quantify human physiological signals such as temperature, are essential to the realization of healthcare devices for biomedical monitoring and human-machine interfaces. Despite recent achievements in stretchable electronic sensors using various conductive materials and structures, the design of stretchable sensors in optics remains a considerable challenge. Here, an optical strategy for the design of stretchable temperature sensors, which can maintain stable performance even under a strain deformation up to 80%, is reported. The optical temperature sensor is fabricated by the incorporation of thermal-sensitive upconversion nanoparticles (UCNPs) in stretchable polymer-based optical fibers (SPOFs). The SPOFs are made from stretchable elastomers and constructed in a step-index core/cladding structure for effective light confinements. The UCNPs, incorporated in the SPOFs, provide thermal-sensitive upconversion emissions at dual wavelengths for ratiometric temperature sensing by near-infrared excitation, while the SPOFs endow the sensor with skin-like mechanical compliance and excellent light-guiding characteristics for laser delivery and emission collection. The broad applications of the proposed sensor in real-time monitoring of the temperature and thermal activities of the human body, providing optical alternatives for wearable health monitoring, are demonstrated.

has been effectively utilized to generate considerable power, attracting the increasing attention because of the ubiquitous water molecules migration behavior in nature. [11][12][13][14][15] In this regard, we and others have designed and constructed various moisture-triggered electric generators to convert the chemical potential energy of moisture diffusion into useful electric energy. [14][15][16] The electricity generation process on these newly developed hygroelectric generator (HEG) devices is efficient and clean without much heat loss, mechanical movement, or byproduced pollutant. [10,16] However, the monotonous structure and poor mechanical properties of these devices have extremely restricted their portable applications in complex and mutable conditions. Meanwhile, the systematical integration of well-arranged generator units on a large scale is severely difficult and waiting for proper processing strategies. Graphene oxide (GO) possesses abundant oxygencontaining groups (e.g., COOH) and high specific surface area, allowing the excellent water molecules absorption between quasi-2D planar structures and generating substantial ionized protons under the hydration effect. [16][17][18][19][20][21] Gradient oxygen-containing groups can be constructed in GO materials by an electric polarization method developed in our previous studies, [16][17][18][19] which will induce inner ion concentration gradient and accordingly produce electricity under humidity variation. Moreover, the high mechanical tolerance and the ease of manufacturing of GO film could provide an ideal platform for construction of electricity generation device with special configuration. [15][16][17][18] Herein, we develop a series of rollable, stretchable, and even 3D space-deformable graphene-based HEG (GHEG) devices (Figure 1a) by laser processing strategy. Serial generator units have been directly embedded in the flexible GO film and exhibit excellent electricity generation ability without any significant performance loss despite being bent arbitrarily (Figure 1a,b). Strikingly, the serpentine or fractal bridge-island-structured GHEGs can power a light-emitting diode (LED) bulb in atmosphere under 100-2000% strain change (Figure 1c). Furthermore, 3D space-deformable architectures of GHEGs (Figure 1d) can be automatically assembled in the shapes of cubic boxes, pyramids, football, and even complex origami structures (Figure 1d,e). These deformable GHEGs will be promising for applications in many complicated conditions. Moisture-triggered electricity generation has attracted much attention because of the effective utilization of the water-molecule diffusion process widely existing in atmosphere. However, the monotonous and rigid structures of previously developed generators have heavily restricted their applications in complex and highly deformable working conditions. Herein, by a rational configuration design with a versatile laser processing strategy, graphenebased hygroelectric generators (GHEGs) of sophisticated architectures with diversified...

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Flexible and stretchable strain sensors are essential to developing smart wearable devices for monitoring human activities. Such sensors have been extensively exploited with various conductive materials and structures, which, however, are normally in need of complex manufacturing processes and confronted with the challenge to achieve both large stretchability and high sensitivity. Here, we report a simple and low-cost optical strategy for the design of stretchable strain sensors which are capable of measuring large strains of 100% with a low detection limit (±0.09%), a fast responsivity (<12 ms), and high reproducibility (over 6000 cycles). The optical strain sensor (OS2) is fabricated by assembling plasmonic gold nanoparticles (GNPs) in stretchable elastomer-based optical fibers, where a core/cladding structure with step-index configuration is adopted for light confinement. The stretchable, GNP-incorporated optical fiber shows strong localized surface plasmon resonance effects that enable sensitive and reversible detection of strain deformations with high linearity and negligible hysteresis. The unique mechanical and sensing properties of the OS2 enable its assembling into clothing or mounting on skin surfaces for monitoring various human activities from physiological signals as subtle as wrist pulses to large motions of joint bending and hand gestures. We further apply the OS2 for quantitative analysis of motor disorders such as Parkinson’s disease and demonstrate its compatibility in strong electromagnetic interference environments during functional magnetic resonance imaging, showing great promises for diagnostics and assessments of motor neuron diseases in clinics.

We report a new kind of polarization splitter based on dual-core photonic crystal fibers. The polarization splitter has a symmetric directional coupler configuration. Each core exhibits high birefringence, which gives rise to an adequate difference in the coupling lengths for the two orthogonal polarizations. A 1.7-mm-long splitter is obtained with the splitting ratio better than -11 dB and a bandwidth of 40 nm. The relationship between the length of the polarization splitter and the diameter of the air hole in the middle of the two cores is discussed.