Ultrafast Laser 3D Nanolithography of Fiber-Integrated Silica Microdevices.

Fiber-integrated micro/nanostructures play a crucial role in modern industry, mainly owing to their compact size, high sensitivity, and resistance to electromagnetic interference. However, the three-dimensional manufacturing of fiber-tip functional structures beyond organic polymers remains challenging. It is essential to construct fiber-integrated inorganic silica with designed functional nanostructures for microsystem applications. Here, we develop a strategy for the 3D nanolithography of fiber-integrated silica from hybrid organic-inorganic materials by ultrafast laser-induced multiphoton absorption. Without silica nanoparticles and polymer additives, the acrylate-functionalized precursors can be locally cross-linked through a nonlinear effect. Followed by annealing at low temperature, the as-printed micro/nanostructures are transformed to high-quality silica with sub-100 nm resolution. Silica microcantilever probes and microtoroid resonators are directly integrated onto the optical fiber, showing strong thermal stability and quality factors. This work provides a promising strategy for fabricating desired fiber-tip silica micro/nanostructures, which is helpful for the development of integrated functional device applications.

Femtosecond Laser Inscribed Excessively Tilted Fiber Grating for Humidity Sensing.

We propose a humidity sensor using an excessively tilted fiber grating (Ex-TFG) coated with agarose fabricated using femtosecond laser processing. The processed grating showcases remarkable differentiation between TE and TM modes, achieving an exceptionally narrow bandwidth of approximately 1.5 nm and an impressive modulation depth of up to 15 dB for both modes. We exposed the agarose-coated TFG sensor to various relative humidity levels and monitored the resonance wavelength to test its humidity sensing capability. Our findings demonstrated that the sensor exhibited a rapid response time (2-4 s) and showed a high response sensitivity (18.5 pm/%RH) between the humidity changes and the resonant wavelength shifts. The high sensitivity, linearity, repeatability, low hysteresis, and excellent long-term stability of the TFG humidity sensor, as demonstrated in our experimental results, make it an attractive option for environmental monitoring or biomedical diagnosis.

High-sensitivity methane sensor composed of photonic quasi-crystal fiber based on surface plasmon resonance.

A photonic quasi-crystal fiber (PQF) methane sensor based on surface plasmon resonance (SPR) is designed and described. The double-side polished six-fold photonic quasi-crystal fiber coated with a silver film produces enhanced SPR effects and sensitivity. A nanostructured thin film with cryptophane-E-doped polysiloxane is deposited on silver as the methane-sensitive surface layer and to mitigate oxidation of silver. The sensor is analyzed and optimized numerically by the full-vector finite element method. For methane concentrations in the range of 0% to 3.5%, the maximum sensitivity of the sensor is 8 nm/%, and the average sensitivity is 6.643 nm/%. Compared to traditional gas sensors, this sensor provides accurate sensing of methane besides offering advantages such as the low cost, miniaturized size, online monitoring, and immunity to electromagnetic field interference.

Optical Anapole Modes in Gallium Phosphide Nanodisk with Forked Slits for Electric Field Enhancement.

High refractive index dielectric nanostructures represent a new frontier in nanophotonics, and the unique semiconductor characteristics of dielectric systems make it possible to enhance electric fields by exploiting this fundamental physical phenomenon. In this work, the scattered radiation spectral features and field-enhanced interactions of gallium phosphide disks with forked slits at anapole modes are investigated systematically by numerical and multipole decomposition analyses. Additional enhancement of the electric field is achieved by opening the forked slits to create high-intensity hot spots inside the disk, and nearby molecules can access these hot spots directly. The results reveal a novel approach for near-field engineering such as electric field localization, nonlinear optics, and optical detection.

High-sensitivity SPR sensor based on the eightfold eccentric core PQF with locally coated indium tin oxide.

A highly sensitive surface plasmon resonance (SPR) sensor comprising an eccentric core photonic quasi-crystal fiber (PQF) coated with indium tin oxide is designed and numerically analyzed. The novel, to the best of our knowledge, structure with an eccentric core layout and local coating not only strengthens coupling between the core mode and surface plasmon polariton mode but also provides higher refractive index sensitivity in the near-infrared region. Analysis based on the finite element method to assess the performance of the sensor and optimize the structural parameters reveals that the maximum wavelength sensitivity and resolution are 96667 nm/RIU and 1.034×10-6RIU in the sensing range between 1.380 and 1.413, respectively. Meanwhile, the average sensitivity is enhanced to 25458 nm/RIU. The sensor is expected to have broad applications in environmental monitoring, biochemical sensing, food safety testing, and related applications due to the ultrahigh sensitivity and resolution.

Fano resonances in symmetric plasmonic split-ring/ring dimer nanostructures.

The optical properties of symmetric split-ring/ring dimer (SRRD) nanostructures composed of a small nanoring surrounded by an Ag splitting nanoring with a larger diameter are calculated theoretically. The apparent asymmetric Fano line shape in the spectra is related to fast switching of the bonding modes between the split-ring plasmon and ring dipole. The influence of the dimensions of the SRRD nanostructures on the spectral positions and intensity of Fano resonance is studied, and the asymmetric Fano line shape can be flexibly adjusted by varying the geometric parameters. In addition, relatively simple SRRD nanostructures have the same overall sensing figures of merit as conventional nanoparticles, thus rendering them suitable for high-performance optical sensors.

Surface plasmon resonance sensor based on eccentric core photonic quasi-crystal fiber with indium tin oxide.

A sensing device composed of an eccentric core photonic quasi-crystal fiber based on surface plasmon resonance is designed using indium tin oxide (ITO) as the sensitive materials. The ITO film is deposited on the outside surface of the fiber to excite plasmonic interactions and facilitate refractive index (RI) detection. This eccentric core structure makes the evanescent field coupled effectively with analyte to achieve higher sensitivity. The influence of RI and structural parameters of different analytes on sensor performance was calculated by the finite-element method. In the analyte RI range between 1.33 and 1.39, the wavelength sensitivity reaches 21,100 nm/RIU, and the average sensitivity of 8750 nm/RIU is achieved at a resolution of 4.739×10-6 RIU. The sensor has large potential in the detection of unknown RI analytes in the near-infrared region.

Tunable single-polarization bimetal-coated and liquid-filled photonic crystal fiber filter based on surface plasmon resonance.

A bimetal-coated single-polarization photonic crystal fiber (PCF) filter based on surface plasmon resonance (SPR) with a liquid-filled structure is designed and calculated by the finite element method (FEM). The filter has many excellent properties. The y-polarized and x-polarized modes can simultaneously filter at 1310 nm and 1560 nm with unwanted losses 544.3 dB/cm and 147.3 dB/cm, respectively, corresponding to polarized losses as low as 12.3 dB/cm and 24.0 dB/cm. The filtering range can be tuned by adjusting the diameter of the outer air holes (d1), the diameter of the inner air holes (d2), and liquid refractive index n. The filtering ranges of x-polarization and y-polarization are 1550-1990 nm and 1310-1830 nm, respectively. The crosstalk (CT) values are 462.0 dB and -107.1 dB and corresponding available bandwidths are 224 nm and 504 nm at 1310 nm and 1560 nm, respectively.

Dual-band directional scattering with all-dielectric trimer in the near-infrared region.

A silicon trimer is explored to tailor unidirectional forward scattering at multiple wavelengths in the near-infrared region with low loss using theoretical calculations and numerical simulations, which leads to the dramatic enhancement in unidirectional forward scattering and suppression of backward scattering. The higher moments in the trimer can be properly excited and balanced by breaking the symmetry of the trimer. The generalized Kerker conditions at two different wavelengths can be achieved in the trimer to further improve the scattering directivity. Our results provide insights into future development of all-dielectric low-loss nanoantennas in the near-infrared region.

Photonic spin Hall effect: a new window in D-shaped fiber by weak measurements.

The enhanced photonic spin Hall effect (SHE) based on the D-shaped fiber with Ag-Ni alloy/silicon layers is proposed and theoretically investigated under excitation of surface plasmon resonance (SPR). In order to achieve the maximum transverse spin-dependent displacements for practical photonic devices, parameters such as the thickness of the Ag-Ni alloy and silicon layers in the D-shaped fiber are optimized. Theoretical modeling and numerical simulation demonstrate that the multilayer structure can effectively enhance the photonic SHE. The maximum transverse shift of 420 µm obtained with optimized parameters is larger than those in the literature. In addition, a maximum angular sensitivity of 114.6°/RIU is achieved by the wavelength interrogation method. Our concept and theoretical assessment suggest a novel and effective means to enhance the photonic SHE, bring us one step closer to the possibility to characterize parameters of dielectric layers by weak measurements, and accelerate the development of optical fibers based on the photonic SHE.

Symmetrical dual D-shape photonic crystal fibers for surface plasmon resonance sensing.

Symmetrical dual D-shape photonic crystal fibers (PCFs) for surface plasmon resonance (SPR) sensing are designed and analyzed by the finite element method (FEM). The performance of the sensor is remarkably enhanced by the directional power coupling between the two fibers. We study the influence of the structural parameters on the performance of the sensor as well as the relationship between the resonance wavelengths and analyze refractive indexes between 1.36 and 1.41. An average spectral sensitivity of 14660 nm/RIU can be achieved in this sensing range and the corresponding refractive index resolution is 6.82 × 10-6 RIU. The characteristics of a single D-shape PCF-SPR sensor with the same structural parameters are compared with those of the dual PCFs sensor and the latter has distinct advantages concerning the spectral sensitivity, resolution, amplitude sensitivity, and figure of merits (FOM).

Nanoscale Mechanical Properties of Nanoindented Ni48.8Mn27.2Ga24 Ferromagnetic Shape Memory Thin Film.

The structure and nanoscale mechanical properties of Ni48.8Mn27.2Ga24 thin film fabricated by DC magnetron sputtering are investigated systematically. The thin film has the austenite state at room temperature with the L21 Hesuler structure. During nanoindentation, stress-induced martensitic transformation occurs on the nanoscale for the film annealed at 823 K for 1 hour and the shape recovery ratio is up to 85.3%. The associated mechanism is discussed.

Mid-infrared surface plasmon resonance sensor based on photonic crystal fibers.

A surface plasmon resonance (SPR) sensor with two open-ring channels based on a photonic crystal fiber (PCF) is described. The sensor is designed to detect low refractive indexes between 1.23 and 1.29 with the operation wavelength in mid-infrared region between 2550 nm and 2900 nm. The coupling characteristics and sensing properties are numerically analyzed by the finite element method. The average spectral sensitivity is 5500 nm/RIU and a maximum resolution of 7.69 × 10-6 RIU can be obtained. Our analysis shows that the PCF-SPR sensor is suitable for mid-infrared detection.