This article discusses recent advances in biocompatible and biodegradable polymer optical fiber (POF) for medical applications. First, the POF material and its optical properties are summarized. Then, several common optical fiber fabrication methods are thoroughly discussed. Following that, clinical applications of biocompatible and biodegradable POFs are discussed, including optogenetics, biosensing, drug delivery, and neural recording. Following that, biomedical applications expanded the specific functionalization of the material or fiber design. Different research or clinical applications necessitate the use of different equipment to achieve the desired results. Finally, the difficulty of implanting flexible fiber varies with its flexibility. We present our article in a clear and logical manner that will be useful to researchers seeking a broad perspective on the proposed topic. Overall, the content provides a comprehensive overview of biocompatible and biodegradable POFs, including previous breakthroughs, as well as recent advancements. Biodegradable optical fibers have numerous applications, opening up new avenues in biomedicine.

This paper proposes a real-time multi-class disturbance detection algorithm based on YOLO for distributed fiber vibration sensing. The algorithm achieves real-time detection of event location and classification on external intrusions sensed by distributed optical fiber sensing system (DOFS) based on phase-sensitive optical time-domain reflectometry (Φ-OTDR). We conducted data collection under perimeter security scenarios and acquired five types of events with a total of 5787 samples. The data is used as a spatial–temporal sensing image in the training of our proposed YOLO-based model (You Only Look Once-based method). Our scheme uses the Darknet53 network to simplify the traditional two-step object detection into a one-step process, using one network structure for both event localization and classification, thus improving the detection speed to achieve real-time operation. Compared with the traditional Fast-RCNN (Fast Region-CNN) and Faster-RCNN (Faster Region-CNN) algorithms, our scheme can achieve 22.83 frames per second (FPS) while maintaining high accuracy (96.14%), which is 44.90 times faster than Fast-RCNN and 3.79 times faster than Faster-RCNN. It achieves real-time operation for locating and classifying intrusion events with continuously recorded sensing data. Experimental results have demonstrated that this scheme provides a solution to real-time, multi-class external intrusion events detection and classification for the Φ-OTDR-based DOFS in practical applications.

A fiber-optic Mach Zehnder interferometer (MZI) refractive index (RI) sensor based on a double peanut-shaped structure in Er-doped fiber with a section of tapered fiber was fabricated using fusion splicer and experimentally demonstrated. The double peanut-shaped structures placed at both ends of the sensor function as beam splitting/combining. Besides, the tapered region works as the sensing area. With RI changes, the optical path difference between the core mode and the cladding modes will change correspondingly, resulting in interference spectrum shifting. By monitoring the shift, the measured RI can be obtained. The experimental results show that the RI sensitivity was significantly improved compared with other types of peanut-shaped fiber sensors. By comparing different taper diameters, it is found that the finer the tapered fiber, the higher the sensitivity of measuring RI.High RI sensitivity of 441.56 nm/RIU is obtained in the experiments. Compared with the similar-structure sensor consisted of single-mode fiber (SMF), the sensitivity of the proposed sensor based on Er-doped fiber is 115.22 nm/RIU higher than that of the former. The proposed sensor has the characteristics of a compact structure. In addition, it has potential in environmental, medical, and aerospace monitoring applications.

Electrical current monitoring plays an important role in power transmission system, electric instruments, etc. The stability of the monitoring system is highly demanded. In this paper, a new interrogation scheme for a fiber Bragg grating (FBG) current sensor based on a dual-loop optoelectronic oscillator (OEO) with high stability, high precision and simple structure is proposed and experimentally demonstrated. The wavelength shift of the FBG, which is bonded on a magnetostrictive alloy-strip, is converted into the frequency shift of the microwave signal through the OEO system utilizing the wavelength to frequency mapping mechanism. Different from previous single-loop OEO schemes, a length of ∼1 km single mode fiber is used to form the second loop in the OEO-cavity, which can enhance the mode-selection ability and reduce the total gain requirement of the system. In addition, a fiber-ring-laser (FRL) cavity is adopted by integrating the sensing FBG-head as the wavelength-selective component to improve the quality of the optical carrier signal. The measured side-mode suppression ratio (SMSR) is up to 62.59 dB and the free spectral range (FSR) is five times larger than the single-loop structure, resulting in highly-enhanced stability and so the precision. Most importantly, the frequency fluctuation is as low as 0.277 ppm, which is the minimum to the best of our knowledge. Compensating methods for the influence of the temperature and the hysteresis are also discussed. The proposed scheme provides a feasible solution to promoting the development of OEO-based interrogation technology and its commercial applications.

The performance of free-space optical data transmission is severely deteriorated by the fluctuation of optical signal intensity, which is resulted from the bias drift of electro-optical modulation devices. In order to improve the performance of free-space optical communication systems, a bias-drift avoiding, beam steered free-space optical wireless communication system is presented based on polarization modulation for the first time to the best of our knowledge. An in-fiber diffraction device based on a 45 tilted fiber grating (TFG) serves simultaneously as an in-fiber polarizer, free-space light emitter, and beam steerer in the proposed communication system, which endows the proposed system with the merits of highly efficient, compact, stable and bias-drift free. The usage of 45 TFG has three benefits: 1), it realizes polarization modulation preventing bias-drift due to its polarization sensitive feature; 2), it enables stable and highly efficient in-fiber compact free-space light emitter; and 3) it accomplishes free-space beam steering due to its wavelength-depending diffraction characteristic. A 2.1 m free-space optical wireless data transmission has been demonstrated with a data rate of 4.8 Gbps per beam using 1.2 GHz bandwidth OFDM signals. This proposal prevents the bias drift issue and maintains high stability. Hence, it can be applied in some harsh situations and confidential data transmission fields.