Optical Fiber Technology最新文献

The study demonstrates a new type of laser that generates wavelength-tunable h-shaped noise-like pulses (NLPs). We incorporated the nonlinear polarization rotation (NPR) mechanism into a figure-eight erbium-doped hybrid mode-locked fiber laser based on the nonlinear amplifier loop mirror (NALM). Under an intra-cavity net dispersion of −5.535 ps², the system produced NLPs with a maximum pulse duration of 24.54 ns, a maximum single energy of 19.96 nJ and a maximum output average power of 14.46 mW when the pump power was set to 543 mW. By adjusting the pump power and fine-tuning the polarization controller, the laser can output NLPs with tunable wavelengths ranging from 1560 to 1601 nm. The flexibility of wavelength-tunable techniques has potential applications in laser detection, high-energy physics experiments, and other fields, enriching the research framework of noise-like applications.

Variations in humidity can significantly disrupt the proper functioning of precision instruments and meters across various industrial, medical, and scientific applications, thereby necessitating real-time humidity monitoring. Here, a high sensitivity fiber-optic relative humidity (RH) sensor based on Mach-Zender interferometer (MZI) is proposed and demonstrated. The humidity sensor consists of single-mode fiber (SMF), peanut structure (PS), and multi-mode fiber (MMF). A multi-mode interference (MMI) enhanced fiber-optic MZI was constructed using a SMF-PS-SMF-MMF-SMF-PS-SMF cascade structure to detect small changes in the refractive index (RI) and expansion force of gelatin film caused by humidity variation. PS, as a beam splitter and combiner of MZI, provides the possibility for simple, economical, and efficient manufacturing of the fiber-based part of humidity sensors. The addition of MMF will excite higher-order core and cladding modes, laying the foundation for achieving high-sensitivity fiber-optic humidity sensors. The fiber-optic RH sensor prototype demonstrate a high sensitivity of about 0.633 nm/% RH in the RH range of 50 % RH to 80 % RH, and a low temperature cross-sensitivity of 0.165 % RH/°C. This sensor has the advantages of safe and easy manufacturing process, low manufacturing cost, and high sensitivity, providing continuous high accuracy humidity measurement results for humidity sensing in different fields.

Violet phosphorus (VP) is a new type of two-dimensional nanomaterial that has unique electronic and optoelectronic properties, and has gained wide attention in the fields of physics, chemistry, and materials science. However, only a few instances of the use of VP in fiber lasers have been demonstrated. For instance, VP films have been utilized as saturable absorbers in Q-switched ytterbium-doped fiber lasers (YDFL) and erbium-doped fiber lasers (EDFL), operating at central wavelengths of 1033 nm and 1560 nm, respectively. Herein, VP films are prepared using a liquid phase exfoliation method and introduced in the ring cavity of a YDFL. Increasing the pump power from 113 mW to 245 mW, and repetition rates from 32.33 kHz to 107.12 kHz, resulted in a stable sequence of Q-switched pulses. A pulse width of 2.9 µs is obtained at a pump power of 245 mW. At a pump power of 230 mW, the pulse energy is 31.02 nJ. In the case of EDFL, stable Q-switched pulses are obtained at a maximum pump power of 150 mW, with the repetition rate, pulse width and pulse energy being 63.51 kHz, 6.4 µs, and 102.19 nJ, respectively. These results indicate that VP may be a promising broadband SA suitable for fiber lasers with wavelengths of 1 µm and 1.5 µm.

Small-field radiotherapy is an emerging technique that offers the potential to reduce damage to normal tissue, yet accurately measuring the dose distribution of small radiation fields presents a significant challenge. This study aims to develop an optical fiber X-ray sensor array (OFXSA) with high spatial resolution for dosimetry in small fields, thereby enhancing the effectiveness and safety of small-field radiotherapy treatments. The OFXSA combines the precision of single-point dosimeters with the ability to detect dose distribution across a small area. Two generations of sensor arrays were designed: the first-generation OFXSA comprises 7 optical fibers arranged in a hexagonal configuration (10.8 × 9.84 mm²), and the second-generation OFXSA consists of 37 optical fibers in a four-layer hexagonal distribution. These arrays were used to measure small field sizes of 1 × 1 cm² and 0.8 × 0.8 cm². Results from the first-generation OFXSA indicate dose distribution attenuation from the center to the periphery, while the second-generation OFXSA, with higher spatial resolution, captures more detailed and irregular dose attenuation, as well as non-uniform distribution across the field. This study demonstrates the viability of OFXSA for precise measurements in radiotherapy, particularly within small field dimensions, and lays the groundwork for future advancements in improving spatial resolution of sensor applications in small fields through complex fiber optic configurations.

An all-fiber optic light intensity sensor employing a three-core fiber (TCF) taper integrated by magnetic fluids (MFs) is proposed and fabricated. The three-beam interference and evanescent field characteristic of the TCF taper are combined with the laser-generated photothermal effect of the MFs for the first time. The effect of irradiation laser intensity on the interference spectrum of the proposed sensor is investigated experimentally. According to the experimental results, the interferential transmission spectrum is susceptible to the irradiation laser intensity. Under 473 nm laser irradiation, the maximum laser intensity sensitivity reaches −1.64425 nm/(mW/mm²). Moreover, the modal coupling processes of the TCF before and after tapering are investigated experimentally and by simulation. The proposed sensor is attractive because of its sensitive light response, simple structure, easy fabrication, and compact size. This work gives a significant reference for the manufacture and application of optically controlled microfluidic devices integrated by MFs.

Tens of millions or billions of single tapered fibers are independent optical transmission elements of tapered optical fiber array (TOFA) for imaging. The optical transmission trajectories of these single tapered fibers, which directly affect imaging qualities of TOFA, are rarely analyzed. This paper provides a method to numerically simulate it for fibers located at different positions along the radial direction of TOFA. The tapered curves of TOFA were firstly simulated by Finite Element Analysis (FEA) software and experimentally verified by the same preparation parameters. It is shown that the slope of tapered curve increases with stretching length. Meanwhile, the taper angle gets greater, and the profile of tapered deformation zone expands outward, while the radius of straight zone remains stable. Based on these, the optical transmission trajectory of single tapered fibers located from center to edge in TOFA was simulated, and then further verified by a self-developed instrument. Both simulation and experiment illustrate that the relative transmittance of single tapered optical fiber is decreased along the radial direction within the same TOFA. In comparison with the transmittance of the central axial fiber, the simulated and experimental unevenness on relative transmittance of peripheral fibers is within 7.11% and 9.74%, respectively. With the relative transmittance at the central position of the optical fiber being identical, the difference of relative transmittance (ΔT) between the simulation and experiment is gradually increased from center to peripheral regions along the radial direction of TOFA, reaching the maximum ΔT of 4.23%. The simulated results are well in agreement with the experimental ones.

With the rapid development of fiber lasers, the invention of novel ultrafast modulators based on the new materials is critical for furthering basic research and practical applications of mode-locked fiber lasers. Ge₂Sb₂Te₅ is a kind of phase-change and thermoelectric material. The fields of optical fiber temperature sensors, optical switches, and phase-change memories have all made extensive use of Ge₂Sb₂Te₅. Nevertheless, the performance of Ge₂Sb₂Te₅ is currently unproven in nonlinear optics and ultrafast laser applications. In this study, Ge₂Sb₂Te₅-based saturable absorbers (SAs), were successfully prepared by depositing nanosheets on a tapered optical fiber. Conventional solitons, second-order harmonic mode-locked, and double-, triple-, quadruple-, and quintuple-pulse phenomena at different net dispersions are observed. A conventional soliton was obtained at 166 mW-987 mW with a pulse interval of 102 ns and a signal-to-noise ratio of 59 dB. At 440 mW of pump power, second-order harmonic mode-locked with a 3 dB bandwidth of 3.29 nm was obtained. The experimental results show that Ge₂Sb₂Te₅ has a broad research prospect in designing ultrafast photonic devices in the future by virtue of its low cost, narrow bandgap, high damage threshold and high stability.

We present a feature extraction method for a feedforward-type neural network (FNN) designed to realize a distributed acoustic sensing (DAS) technique that suits conventional optical fiber. This is, to the best of our knowledge, the first trial in which an FNN is used to interpret the field communication infrastructure type surrounding optical cables. Three classes are taken to represent the field environment: the cable tunnel (class 1), circular duct (class 2), and overhead area (class 3). We investigate and compare frequency- and time-domain feature extraction. We also show that the frequency-domain features yielded by spectral envelope shape (SES) processing have better performance than simple fast Fourier transform features. Two types of time-domain features are verified: one is the short-time maximum magnitude (STMM), which shows the largest value in the time frame, and the other is the short-time average magnitude (STAM), which indicates the average value in a time frame. Note that all features are optimized for multi-class classification. In this paper, we present the suitable number of both features and the number of training iterations. An accuracy rate of 79.0% is achieved using FNN analysis with the features studied here. Furthermore, by considering the similarity of neighboring classes, classes are refined into higher probability classes. As a result, accuracy is improved to 87.2%.

Electronic computers have evolved drastically over the past years with an ever-growing demand for improved performance. However, the transfer of information from memory and high energy consumption have emerged as issues that require solutions. Optical techniques are considered promising solutions to these problems with higher speed than their electronic counterparts and with reduced energy consumption. Here, we use the optical reservoir computing framework we have previously described (Scalable Optical Learning Operator or SOLO [1]) to program the spatial-spectral output of the light after nonlinear propagation in a multimode fiber. The novelty in the current paper is that the system is programmed through an output sampling scheme, similar to that used in hyperspectral imaging in astronomy. Linear and nonlinear computations are performed by light in the multimode fiber and the high dimensional spatial-spectral information at the fiber output is optically programmed before it reaches the camera. We then used a digital computer to classify the programmed output of the multi-mode fiber using a simple, single layer network. When combining front-end programming and the proposed spatial-spectral programming, we were able to achieve 89.9 % classification accuracy on the dataset consisting of chest X-ray images from COVID-19 patients. At the same time, we obtained a decrease of 99 % in the number of tunable parameters compared to an equivalently performing digital neural network. These results show that the performance of programmed SOLO is comparable with cutting-edge electronic computing platforms, albeit with a much-reduced number of electronic operations.