Refractive index sensor based on a multi-notched plastic optical fiber

Novel Corrugated Long Period Grating Surface Balloon-Shaped Heterocore-Structured Plastic Optical Fibre Sensor for Microalgal Bioethanol Production

A novel long period grating (LPG) inscribed balloon-shaped heterocore-structured plastic optical fibre (POF) sensor is described and experimentally demonstrated for real-time measurement of the ultra-low concentrations of ethanol in microalgal bioethanol production applications. The heterocore structure is established by coupling a 250 μm core diameter POF between two 1000 μm diameter POFs, thus representing a large core-small core-large core configuration. Before coupling as a heterocore structure, the sensing region or small core fibre (SCF; i.e., 250 μm POF) is modified by polishing, LPG inscription, and macro bending into a balloon shape to enhance the sensitivity of the sensor. The sensor was characterized for ethanol-water solutions in the ethanol concentration ranges of 20 to 80 %v/v, 1 to 10 %v/v, 0.1 to 1 %v/v, and 0.00633 to 0.0633 %v/v demonstrating a maximum sensitivity of 3 × 10⁶ %/RIU, a resolution of 7.9 × 10^-6 RIU, and a limit of detection (LOD) of 9.7 × 10^-6 RIU. The experimental results are included for the intended application of bioethanol production using microalgae. The characterization was performed in the ultra-low-level ethanol concentration range, i.e., 0.00633 to 0.03165 %v/v, that is present in real culturing and production conditions, e.g., ethanol-producing blue-green microalgae mixtures. The sensor demonstrated a maximum sensitivity of 210,632.8 %T/%v/v (or 5 × 10⁶ %/RIU as referenced from the RI values of ethanol-water solutions), resolution of 2 × 10^-4%v/v (or 9.4 × 10^-6 RIU), and LOD of 4.9 × 10^-4%v/v (or 2.3 × 10^-5 RIU). Additionally, the response and recovery times of the sensor were investigated in the case of measurement in the air and the ethanol-microalgae mixtures. The experimentally verified, extremely high sensitivity and resolution and very low LOD corresponding to the initial rate of bioethanol production using microalgae of this sensor design, combined with ease of fabrication, low cost, and wide measurement range, makes it a promising candidate to be incorporated into the bioethanol production industry as a real-time sensing solution as well as in other ethanol sensing and/or RI sensing applications.

Intensity-Modulated Polymer Optical Fiber-Based Refractive Index Sensor: A Review

The simple and highly sensitive measurement of the refractive index (RI) of liquids is critical for designing the optical instruments and important in biochemical sensing applications. Intensity modulation-based polymer optical fiber (POF) RI sensors have a lot of advantages including low cost, easy fabrication and operation, good flexibility, and working in the visible wavelength. In this review, recent developments of the intensity modulation POF-based RI sensors are summarized. The materials of the POF and the working principle of intensity modulation are introduced briefly. Moreover, the RI sensing performance of POF sensors with different structures including tapered, bent, and side-polished structures, among others, are presented in detail. Finally, the sensing performance for different structures of POF-based RI sensors are compared and discussed.

Wearable Wrist Movement Monitoring Using Dual Surface-Treated Plastic Optical Fibers

Regarding high-sensitivity human wrist joint motion monitoring in exercise rehabilitation; we develop a pair of novel wearable and sensitivity-enhanced plastic optical fiber (POF) strain sensors consisting of an etched grating fiber and a side-polished fiber stitched into a polyamide wrist brace. The two flexible and surface-treated fibers are; respectively; featured with an etched periodic gratings with a pitch of 6 mm and a depth of 0.5 mm and a D-shaped side-polished zone of ~300 µm depth and ~30 mm length; which, correspondingly, show the sensitivities of around 0.0176/° and 0.0167/° in a normalized bending angle by far larger than a conventional commercial POF, because it achieves a more sensitive strain-induced evanescent field interaction with the side-machined fibers. Moreover, in terms of the sensor response to bending deformation in the range of -40°~+40°, the former exhibits a better sensitivity in lower angle change, while the latter is superior as the bending angle increases; thereby arranging the two modified POFs separately at the side and back of the human wrist, in order to decouple the wrist joint behaviors induced by typical flexion-extension or abduction-adduction movements. Then, the circular and pentagonal wrist motion trajectory patterns are investigated, to demonstrate the maximum average single-axis motion error of 2.94° via the transformation of spatial angle to plane coordinate for the fabricated couple of POF sensors, which is lower than a recognized standard of 5°, thus suggesting the great potential in wearable exercise rehabilitation of human joints in the field of medical treatment and healing.

Plastic optical fiber sensor for temperature-independent high-sensitivity detection of humidity

A simple U-shaped plastic optical fiber evanescent-wave sensor was fabricated for temperature-independent highly sensitive detection of humidity. The sensing region of the sensor was subjected to five cycles of heating-cooling to improve temperature independence. The effects of the polyimide (PI) coating thickness, number of graphene oxide (GO) coating layers, and alternate PI-GO coating sequence were investigated to optimize sensitivity. The fabricated sensor exhibited high-temperature independence and good sensitivity of 0.17×10^-2 (% relative humidity)^-1 in the temperature range of 10°C to 70°C.

Fabricating fiber probes for optical tweezers by an improved tube etching method

An improved tube etching method to fabricate high-quality fiber probes for optical tweezers by reserving a certain length of bare fiber to form a T-type composite structure was proposed and implemented. This method can overcome the impact of fiber types on the quality of probes in the conventional tube etching effectively. Based on the influence of gravity and diffusion on the motion of reactants, the analysis of formation mechanism was proposed for this method. This procedure retained the advantage of smooth surface in traditional tube etching but shortened the etching time. Our results also demonstrated that light transmittance of the probe fabricated by this method was improved by 6.8 times, resulting in a greater force in cells trapping. This work provided a way of designing and fabricating optical fiber tweezers with a high trapping efficiency.

Latest Achievements in Polymer Optical Fiber Gratings: Fabrication and Applications

Grating devices in polymer optical fibers (POFs) have attracted huge interest for many potential applications in recent years. This paper presents the state of the art regarding the fabrication of different types of POF gratings, such as uniform, phase-shifted, tilted, chirped, and long period gratings, and explores potential application scenarios, such as biosensing and optical communications.