Optimization, fabrication, and performance analysis of SMF-/MMF-based microfiber ball structure

Effective splicing technique of different cladding diameter-based optical fibers and performance evaluation

In this work, the fabrication and sensing performance of fusion structures based on single-mode fiber (SMF) and multimode fiber (MMF) with different cladding diameters are discussed, and the effects of different lengths of MMF and fiber etching on sensing performance are analyzed. First, the transmitted intensity measurement experiment is performed, and the results indicate that the performance of the SMF-MMF-SMF(SMS)-based structure is better for sensing purposes. In addition, the results demonstrate that the performance of etched fiber is better than that of non-etched fiber. The etched fiber structure with lower fiber diameters produces more evanescent waves and is better for sensing purposes. Therefore, the proposed structure has certain development potential as an application of future optical fiber sensors.

Refractive Index Fiber Laser Sensor by Using a Fiber Ball Lens Interferometer with Adjustable Free Spectral Range

In this work, a fiber laser refractometer based on a fiber ball lens (FBL) interferometer is proposed. The linear cavity erbium-doped fiber laser uses an FBL structure acting as a spectral filter and sensing element for determining the RI of a liquid medium surrounding the fiber. The optical interrogation of the sensor is the wavelength displacement of the generated laser line as a function of the RI variations. For the proposed FBL interferometric filter, the free spectral range of its wavelength-modulated reflection spectrum is adjusted to maximum in order to obtain RI measurements in a range of 1.3939 to 1.4237 RIU, from laser wavelength displacements in a range from 1532.72 to 1565.76 nm. The obtained results show that the wavelength of the generated laser line is a linear function of the RI variations on the medium surrounding the FBL with a sensitivity of 1130.28 nm/RIU. The reliability of the proposed fiber laser RI sensor is analytically and experimentally investigated.

Biofilm Detection by a Fiber-Tip Ball Resonator Optical Fiber Sensor

Bacterial biofilms are one of the most important challenges that modern medicine faces due to the difficulties of diagnosis, antibiotic resistance, and protective mechanisms against aggressive environments. For these reasons, methods that ensure the inexpensive and rapid or real-time detection of biofilm formation on medical devices are needed. This study examines the possibilities of using optical- and fiber-based biosensors to detect and analyze early bacterial biofilms. In this study, the biofilm-forming model organism Pseudomonas aeruginosa was inoculated on the surface of the optical sensor and allowed to attach for 2 h. The biosensors were made by a fiber-tip ball resonator, fabricated through a CO2 laser splicer on a single-mode fiber, forming a weak reflective spectrum. An optical backscatter reflectometer was used to measure the refractive index detected by the sensors during different growth periods. The early biofilm concentration was determined by crystal violet (CV) binding assay; however, such a concentration was lower than the detection limit of this assay. This work presents a new approach of biofilm sensing in the early attachment stage with a low limit of detection up to 10−4 RIU (refractive index units) or 35 ± 20 × 103 CFU/mL (colony formed units).

Simultaneous temperature and refractive index sensor based on an L-like Michelson interferometer

We experimentally demonstrate, to the best of our knowledge, temperature and refractive index (RI) sensing with a novel L-like Michelson interferometer (MI). Two MIs are designed based on single-mode fiber (SMF) and multimode fiber (MMF), respectively, fabricated via an oxyhydrogen flame and a rotatable platform. By comparative experiments on the size and bent degree of the sensor, the corresponding parameters of the sensor with excellent performance are determined for measurement experiments. The RI sensitivity of the SMF L-like MI reaches -131.0nm/RIU, and the highest temperature sensitivity is 94.17 pm/°C. The highest RI of the MMF L-like MI is 176.5 nm/RIU, and the temperature sensitivity is 104.2 pm/°C. The L-like MI has advantages of low cost and easy fabrication, and is a promising temperature and RI sensor in a wide range of measurements.