In order to realize remote and on-site pH detection, we design a simple, economical and hand-held optical fiber pH sensor based on smartphone platforms. All components of the sensor are encapsulated in a 3-D printed shell, including a semiconductor laser for exciting fluorescence signal, a smartphone with a filter for collecting fluorescence signal, a fiber coupler for transmitting light and batteries for laser power supply. With the combination tapered fiber probe modified with CdSe/ZnS quantum dots, whose fluorescence signal can be captured by the smartphone camera and calculated by a self-developed Android application, the sensor has a minimum sensitivity of 0.5 pH unit and a wide detection range between pH 4 and 12. Moreover, the sensor shows good reusability and stability. Considering its low cost, miniaturization, portability and the capability for remote detection, real-time monitoring and on-site analysis, the proposed smartphone based optical fiber pH sensor has great application potential in environmental monitoring and biomedicine.

The transmissive optical fiber localized surface plasmon resonance (LSPR) sensor has become an effective tool in refractive index sensing because of its compact structure, high sensitivity and strong designability. However, its special structure with the sensing region in the middle of the optical fiber leads to the shortcomings of difficult preparation and poor reproducibility, which greatly restricts its application scopes. In order to solve such problem, we design gold nanoparticle (AuNP)-based fusion spliced transmissive optical fiber LSPR probes, which are fabricated via the fusion splicing between the surface modified combination tapered optical fiber and another multimode quartz optical fiber but are totally different from other fabrications of the reported transmissive optical fiber LSPR probes. The fiber probe fabrication is rather simple and cost-effective, only relying on the procedures of combination tapered optical fiber preparation, surface modification and probe fusion splicing, and except for the probe fusion splicing, the other procedures can be mass prepared thus maintaining high efficiency and good reproducibility in fiber probe fabrications. Moreover, according to the experimental verifications, the proposed fiber probes can reach rather high sensitivity in refractive index sensing with high accuracy and good stability in both static and dynamic detecting modes. Therefore, the AuNP-based fusion spliced transmissive optical fiber LSPR probe is a preferred solution for refractive index sensing and can be widely used in various applications.

A method to miniaturize the aperture of a dual-polarized Quadruple-Folded-Dipole (QFD) antenna by bending its arms downward or upward is proposed in this letter. Two practical prototypes called downward-bending-arm (DBA) antenna and upward-bending-arm (UBA) antenna are presented and elaborated. Both the DBA and UBA antennas have four pairs of arms bent downward or upward along the four edges of the planar QFDs, respectively, which enables the aperture of the DBA and UBA antennas to shrink to around 0.24λ ₀ ×0.24λ ₀ (λ ₀ is the free-space wavelength at 2 GHz). Both antennas can achieve relatively small apertures while ensuring good matching, isolation, and radiation performances within the band of interest. Especially, the DBA antenna has a lower profile than the UBA antenna while the UBA antenna outperforms the DBA antenna in realized gain by approximately 1 dB. Meanwhile, the UBA antenna has narrower half-power beam width (HPBW), which will be beneficial in compact Massive multiple-input multiple-output (M-MIMO) antenna arrays for improved radiation patterns.