We demonstrate a novel all-fiber-optic humidity sensor comprised of a WS₂ film overlay on a side polished fiber (SPF). This sensor can achieve optical power variation of up to 6 dB in a relative humidity (RH) range of 35%-85%. In particular, this novel humidity fiber sensor has a linear correlation coefficient of 99.39%, sensitivity of 0.1213 dB/%RH, and a humidity resolution of 0.475%RH. Furthermore, this sensor shows good repeatability and reversibility, and fast response to breath stimulus. This WS₂ based all-fiber optic humidity sensor is easy to fabricate, is compatible with pre-established fiber optic systems, and holds great potential in photonics applications such as in all-fiber optic humidity sensing networks.

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AbstractSecond harmonic generation (SHG) with a material of large transparency is an attractive way of generating coherent light sources at exotic wavelength range such as VUV, UV and visible light. It is of critical importance to improve nonlinear conversion efficiency in order to find practical applications in quantum light source and high resolution nonlinear microscopy, etc. Here an enhanced SHG with conversion efficiency up to 10−2% at SH wavelength of 282.7 nm under 11 GW/cm2 pump intensity via the excitation of anapole in lithium niobite (LiNbO3, or LN) nanodisk through the dominating d33 nonlinear coefficient is investigated. The anapole has advantages of strongly suppressing far-field scattering and well-confined internal field which helps to boost the nonlinear conversion. Anapoles in LN nanodisk is facilitated by high index contrast between LN and substrate with properties of near-zero-index via hyperbolic metamaterial structure design. By tailoring the multi-layers structure of hyperbolic metamaterials, the anapole excitation wavelength can be tuned at different wavelengths. It indicates that an enhanced SHG can be achieved at a wide range of pump light wavelengths via different design of the epsilon-near-zero (ENZ) hyperbolic metamaterials substrates. The proposed nanostructure in this work might hold significances for the enhanced light–matter interactions at the nanoscale such as integrated optics.

We report on an 800 nm center-wavelength metal/multilayer-dielectric grating (MMDG) with broadband, high diffraction efficiency. The trapezoidal grating ridge consists of an HfO2 layer sandwiched between two SiO2 films. Combining the advantages of SiO2 and HfO2, the grating ridge reduces the difficulties of grating ridge attainment. For such a configuration, high-performance MMDG can be successfully fabricated using the existing technology. Experimentally we demonstrated a 163 nm bandwidth MMDG with -1st-order diffraction efficiency greater than 90%. The fabricated MMDG achieved high performance as the design with large fabrication tolerances.

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Second harmonic generation (SHG) is an important nonlinear process which is critical for applications, such as optical integrated circuit, nonlinear microscopy, laser, etc. Many challenges remain in the improvement of nonlinear conversion efficiency, since the typical value is of only 10−5 in nanostructures. Here, we theoretically demonstrate a periodic structure consisting of a lithium niobate (LN) bar and an LN disk, on a nanoscale (~300 nm) thin-film platform, which is proposed for a highly efficient SHG. By breaking the structure symmetry, a Fano resonance with a high Q, up to 2350 and a strong optical field enhancement reaching forty-two folds is achieved, which yields a high conversion efficiency, up to 3.165 × 10−4. In addition to its strong second harmonic (SH) signal, we also demonstrate that by applying only 0.444 V on the planar electrode configurations of the nanostructured LN, the wavelength of SH can be tuned within a 1 nm range, while keeping its relatively high conversion efficiency. The proposed structure with the high nonlinear conversion efficiency can be potentially applied for a single-molecule fluorescence imaging, high-resolution nonlinear microscopy and active compact optical device.

A novel strategy to modify the plasmonic interface by spin-coating an overlayer of graphene oxide sheets (GOSs) on top of the surface plasmon resonance (SPR) sensor is proposed and demonstrated. Thanks to the excellent electrical conductivity, large surface area, and high-refractive index of the GOSs layer, the GOSs-modified SPR (GOSs-SPR) sensor achieves an improved sensitivity in the detection of bulky refractive index solutions and bovine serum albumin (BSA) solutions. The maximum sensitivity of 2715.1 nm/RIU achieved by three spin-coatings shows an enhancement of 20.2% than the case without the modification of the GOSs overlayer. Benefiting from the large surface area and abundant surface functional groups, the GOSs-SPR sensor has a greater sensitivity enhancement (up to 39.35%) in the detection of the BSA molecules. Most importantly, we have firstly experimentally demonstrated that the GOSs overlayer with thickness over hundreds nanometers can still lead to a great enhancement of sensitivity of SPR sensors. Additionally, the proposed modification method for the plasmonic interface is a simple and effective strategy to boost the sensitivity in a chemical-free and environment-friendly manner, without additional chemical or biological amplification steps. These unique features make the proposed GOSs-SPR biosensor a low-cost and biocompatible platform in the fields of biochemical sensing, drug screening, and environmental monitoring.