A quantum dots optical fiber (QDOF) sensor is proposed for temperature sensing in this paper. The sensor is fabricated by the drop-on-demand inkjet printing technology. By controlling the diameter of droplet, the spacing between droplets and the number of printed layers, the QDOF is printed on the polymer substrate. The loss of QDOF is less than 0.35dB· $\text{mm}^{-1}$ at the fluorescence wavelength. The experimental results show that the temperature sensitivity of sensor is 109pm/°C. As far as we know, this is the first time that a QDOF sensor is manufactured by the inkjet printing technology to realize the temperature measurement.

Lead pollution, especially in water, threatens human health. Therefore, it is crucial to quickly and accurately determine the content of lead ions (Pb2+) in drinking water. In this paper, a highly sensitive Pb2+ optical fiber sensor based on a hydrogel-coated Mach-Zehnder interferometer (MZI) is presented. The hydrogel, crosslinked by hydroxyethyl methacrylate (HEMA), acrylic acid, and acrylamide, exhibits excellent specificity, and its porous structure enhances adsorption, ensuring high detection sensitivity and accuracy. Additionally, the MZI with a refractive index sensitivity of -11235.4 nm/RIU is fabricated by fusing three sections of NCF with a lateral offset structure. Then, the hydrogel is coated onto the misalignment area to complete the sensor. The chemical reaction between HEMA and Pb2+ alters the refractive index of the hydrogel, allowing the MZI to detect Pb2+. The sensor has a compact structure with a sensing length of only 0.6 mm. Experimental results show that the proposed Pb2+ sensor has a high detection sensitivity of 4.933×107 nm/(mol/L) and a limit of detection (LOD) of 2.007×10-9 mol/L (0.4199 ppb). Through comparison, the response of Pb2+ is 3.3 times higher than that of other heavy metal ions, indicating that the sensor has good selectivity. In addition, the sensor has excellent repeatability and can be used as a disposable detection product, ensuring the accuracy of the detection results. The sensor demonstrates significant potential applications for Pb2+ detection.

Recently appeared OAM-based interferometers have high requirements on the quality of vortex beam and system calibration, otherwise, the rotational symmetry interferogram will be destroyed. A novel OAM-based optical fiber interferometer with Moiré techniques for temperature sensing is proposed. A visualized Moiré probe technique is employed to realize the temperature change indication by rotation calculation. The Moiré probe achieves immunity to vortex wavefront aberrations and precise calibration exemption. The validation experiments were presented with a comparison to existing OAM-based OFIs. The sensing system with a linear temperature measurement sensitivity of about 29 rad/°C with only 0.5 cm PDMS as the sensing part. The temperature measurement resolution is discussed in theory and experiment. The resolution is 7.05*10⁻⁵ °C in theory and 0.003 °C in experiments.

Owing to their applications in high-temperature superconductivity and aerospace fields, sensors capable of high-sensitivity detection at cryogenic temperatures have gained significant importance. This study proposes a high-sensitivity, wide-range optical fiber sensor designed for cryogenic temperature detection. The sensor consists of an optical fiber Sagnac interferometer (SI), multiple matched optical fiber reflective Lyot interferometers (RLIs), and an optical switch. The sensor achieves high sensitivity in cryogenic environments by leveraging the Vernier effect. To extend the measurement range, an optical switch is utilized to dynamically adjust the sensor's structural parameters in response to varying temperatures. To the best of our knowledge, this study represents the first reported application of the Vernier effect for cryogenic temperature detection. The optical sensor maintains a high sensitivity of over 37 nm/K across the temperature range of 80 K to 100 K. Compared to a single SI, the sensitivity is enhanced by a factor of 43, significantly exceeding that of previously reported optical fiber cryogenic temperature sensors. The measurement range can be further extended by incorporating switches with additional channels.

Overcoming the impact of pH on the performance of random lasers (RLs) has emerged as a significant challenge in its application for biomedical therapy. To tackle this issue, this paper proposes a pH-insensitive hydrogel fiber RLs. The RLs consists of Rhodamine B dye-doped p(acrylamide-co-acrylic acid, AM-co-AA) hydrogel as the fiber core and calcium alginate (Ca-alginate) hydrogel as the cladding, termed as p(AM-co-AA)/Ca-alginate hydrogel fiber RLs. The prepared RLs not only operate reliably at different pH levels but also allow for tuning of its emission wavelength by adjusting the temperature, ensuring the reliability and safety of photothermal therapy. Experimental results demonstrate that the threshold of p(AM-co-AA)/Ca-alginate hydrogel fiber RLs is only 0.23 mJ/cm². Moreover, within the range of 20∼80 °C, the random laser emission wavelength can be tuned by controlling the temperature, with a maximum tunable range of 5.6 nm and good reversibility. Most importantly, the random laser intensity and wavelength of the p(AM-co-AA)/Ca-alginate hydrogel fiber RLs exhibit excellent stability when the pH value changes within the range of 3.5 to 9.5, indicating its exceptional ability to resist pH interference. We believe that the hydrogel fiber RLs proposed in this paper, leveraging the porous structure of hydrogel to reduce the laser threshold and employing the “core-cladding” structure to enhance stability, holds broad potential applications in the biomedical field.