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In recent decades, the Surface Plasmon Resonance (SPR) phenomenon has been utilized as an underlying technique in a broad range of application fields. Herein, a new measuring strategy which harnesses the SPR technique in a way that is different from the classical methodology was explored by taking advantage of the characteristics of multimode waveguides, such as plastic optical fibers (POFs) or hetero-core fibers. The sensor systems based on this innovative sensing approach were designed, fabricated, and investigated to assess their ability to measure various physical features, such as magnetic field, temperature, force, and volume, and to realize chemical sensors. In more detail, a sensitive patch of fiber was used in series with a multimodal waveguide where the SPR took place, to alter the mode profile of the light at the input of the waveguide itself. In fact, when the changes of the physical feature of interest acted on the sensitive patch, a variation of the incident angles of the light launched in the multimodal waveguide occurred, and, as a consequence, a shift in resonance wavelength took place. The proposed approach permitted the separation of the measurand interaction zone and the SPR zone. This meant that the SPR zone could be realized only with a buffer layer and a metallic film, thus optimizing the total thickness of the layers for the best sensitivity, regardless of the measurand type. The proposed review aims to summarize the capabilities of this innovative sensing approach to realize several types of sensors for different application fields, showing the high performances obtained by exploiting a simple production process and an easy experimental setup.

This study evaluates the efficacy of a single-mode, multimode, and single-mode (SMF-MMF-SMF) fiber configuration for low-dose optical radiation monitoring applications, such as UV detection and dosimetry. Particular attention is devoted to radiation-induced absorption (RIA) and radiation-induced refractive index change (RIRIC). Radiation exposure alters the refractive index of fiber materials, resulting in a shift in the peak wavelength. This study utilized a multimode fiber with a core diameter of 65 μm, and its sensing region was coated with anthracene solutions at varying concentrations of 1 wt%, 3 wt%, and 5 wt%. The experimental findings demonstrate that RIRIC and RIA depend on the energy of the applied radiation for all sensor configurations. A discernible shift in the peak wavelength was observed. When the impact of anthracene concentration on sensor efficiency was examined, the sensitivity of the 3 wt% solution was higher than that of the 1 wt% and 5 wt% solutions. This work contributed to the advancement of optical fiber sensor technology, specifically in the context of radiation detection. The results may encourage further exploration of hybrid fiber configurations and functional coatings, opening new avenues for the next-generation fiber optic dosimeters.

Optical fiber sensors have been studied, developed, and already used in the industry for more than 50 years due to their multiplexing capabilities, lightweight design, compact form factors, and electromagnetic field immunity. The scientific community continuously studies new materials, schemes, and architectures aiming to improve existing technologies. Navigating through diverse sensor technologies, including interferometry, intensity variation, nonlinear effects, and grating-based sensors, fiber specklegram sensors (FSSs) emerge as promising alternatives due to their simplicity and low cost. This review paper, emphasizing the potential of FSSs, contributes insights to the present state and future prospects for FSSs, providing a holistic view of advancements propelling FSSs to new frontiers of innovation. Subsequent sections explore recent research, technological trends, and emerging applications, contributing to a deeper understanding of the intricacies shaping the future of FFS sensor technologies.

Multimode optical fibers have been primarily (and almost solely) used as “light pipes” in short distance telecommunications and in remote and astronomical spectroscopy. The modal properties of the multimode waveguides are rarely exploited and mostly discussed in the context of guiding light. Until recently, most photonic applications in the applied sciences have arisen from developments in telecommunications. However, the photonic lantern is one of several devices that arose to solve problems in astrophotonics and space photonics. Interestingly, these devices are now being explored for use in telecommunications and are likely to find commercial use in the next few years, particularly in the development of compact spectrographs. Photonic lanterns allow for a low-loss transformation of a multimode waveguide into a discrete number of single-mode waveguides and vice versa, thus enabling the use of single-mode photonic technologies in multimode systems. In this review, we will discuss the theory and function of the photonic lantern, along with several different variants of the technology. We will also discuss some of its applications in more detail. Furthermore, we foreshadow future applications of this technology to the field of nanophotonics.

Propagation of light in multimode optical fibers usually gives a spatial and temporal randomization of the transmitted field similar to the propagation through scattering media. Randomization still applies when scattering or multimode propagation occurs in gain media. We demonstrate that appropriate structuration of the input beam wavefront can shape the light amplified by a rare-earth-doped multimode fiber. Profiling of the wavefront was achieved by a deformable mirror in combination with an iterative optimization process. We present experimental results and simulations showing the shaping of a single sharp spot at different places in the output cross-section of an ytterbium-doped fiber amplifier. Cleaning and narrowing of the amplifier far-field pattern was realized as well. Tailoring the wavefront to shape the amplified light can also serve to improve the effective gain. The shaping approach still works under gain saturation, showing the robustness of the method. Modeling and experiments attest that the shaping is effective even with a highly multimode fiber amplifier carrying up to 127 modes. Optical fibers: Getting amplified light into shape A technique that controls light propagation in rare earth-doped fiber optic cables makes it easier to peek inside disordered materials. Multimode optical fibers have large diametric cores that enable parallel transmission of multiple communication channels. Alain Barthélémy and colleagues at the Université de Limoges-Centre National de la Recherche Scientifique in France have used wave front shaping to turn multimode fibers into amplified imaging devices. Typically, random speckle patterns are seen when laser light scatters through large-core fiber optic cables. The French team used deformable mirrors and an iterative optimization process to modulate the phases of incoming light wave fronts so that the beam focused on a small, single spot. This approach eliminates the need for reference beams and preserves the amplification characteristics of doped fiber optic cables—a useful combination for imaging inside opaque, light-scattering substances.

In this paper, the stochastic 2-dimensional nonlinear Schrödinger equation with multiplicative Brownian motion is investigated. This equation deals with beam propagation in a Graded-Index multimode optical fiber with a parabolic index profile. The spectral, temporal, and spatial features of ultrashort light pulses can be controlled in novel ways by this kind of nonlinear multimode optical fiber, which is gaining popularity. The bifurcation analysis, chaotic and sensitivity behavior of the wave solutions are examined using the qualitative theory for planar dynamical systems. The generalized exponential rational functional method is used to get the exact optical soliton solutions under the effect of noise. This method provides us the rational, exponential, dark, bright, combined dark-bright, singular, and solitary waveform solutions. Moreover, we use the MATHEMATICA11.1 tools to plot the 3-dimensional, 2-dimensional, and their corresponding contour diagrams to show the effects of multiplicative time noise on the optical solitons for the GRIN multimode optical fiber. Finally, we will show the multiplicative Brownian motion stabilizes the solutions of 2D-nonlinear Schrödinger equation of Graded-Index multimode optical fiber a round zero.

We report on the properties of the Power over Fiber (PoF) transmission link using a High-Power Laser Source operating at 976 nm and using three types of optical fiber with a core diameter of 50 µm. Two step-index profile multimode optical fibers and one fiber with a gradient index were used for optical power transmission. Optical light was converted to electricity using commercially available Photovoltaic Power Convertors (PPCs) with a maximal optical input power of 1.5 W and experimental PPCs with a maximal optical input power of 4.0 W. We experimentally proved optical power transmission up to a distance of 300 m. In the case of the commercially available working PPC and using the gradient index fiber we achieved a result of 0.534 W of electrical power and using the experimental PPC we achieved 0.645 W. In the case of the step-index optical fiber, the result was 1.3 W.

Significance: Monitoring the movement and vital signs of patients in hospitals and other healthcare environments is a significant burden on healthcare staff. Early warning systems using smart bed sensors hold promise to relieve this burden and improve patient outcomes. We propose a scalable and cost-effective optical fiber sensor array that can be embedded into a mattress to detect movement, both sensitively and spatially. Aim: Proof-of-concept demonstration that a multimode optical fiber (MMF) specklegram sensor array can be used to detect and image movement on a bed. Approach: Seven MMFs are attached to the upper surface of a mattress such that they cross in a 3  ×  4 array. The specklegram output is monitored using a single laser and single camera and movement on the fibers is monitored by calculating a rolling zero-normalized cross-correlation. A 3  ×  4 image is formed by comparing the signal at each crossing point between two fibers. Results: The MMF sensor array can detect and image movement on a bed, including getting on and off the bed, rolling on the bed, and breathing. Conclusions: The sensor array shows a high sensitivity to movement, which can be used for monitoring physiological parameters and patient movement for potential applications in healthcare settings.

This work proposes a highly sensitive sandwich heterostructure multimode optical fiber microbend sensor for heart rate (HR), respiratory rate (RR), and ballistocardiography (BCG) monitoring, which is fabricated by combining a sandwich heterostructure multimode fiber Mach–Zehnder interferometer (SHMF-MZI) with a microbend deformer. The parameters of the SHMF-MZI sensor and the microbend deformer were analyzed and optimized in detail, and then the new encapsulated method of the wearable device was put forward. The proposed wearable sensor could greatly enhance the response to the HR signal. The performances for HR, RR, and BCG monitoring were as good as those of the medically approved commercial monitors. The sensor has the advantages of high sensitivity, easy fabrication, and good stability, providing the potential for application in the field of daily supervision and health monitoring.

Multimode fibers (MMF) are miniaturized, flexible, and high‐capacity information channels, promising to open up new applications in endoscopic imaging. However, precise light control through an MMF with continuous deformations is still a challenge. Here, a scalable calibration framework for a dynamically deformed MMF using deep learning is proposed. The proof‐of‐concept experiments demonstrate that the proposed continual generative adversarial model has the ability to characterize the MMF transmission states sequentially and detect the fiber deformation using proximal reflection in real‐time synchronously, allowing self‐adaptively cross‐state focusing through a semi‐flexible MMF without distal access after the scalable calibration. This framework is a continual learning scheme under extreme memory constraints where the model is able to synthesize training data and prevent forgetting the previously learned bending states. The proposed method paves the way for the experimental realization of scalable calibration of a dynamically deformed MMF. A scalable calibration framework is proposed for a dynamically deformed multimode fiber (MMF) using deep learning. The proof‐of‐concept experiments demonstrate that the proposed continual generative adversarial model enables characterizing the MMF transmission states sequentially, detecting the fiber deformation using proximal reflection in real‐time synchronously, and allowing self‐adaptively cross‐state focusing through a semi‐flexible MMF without distal access after the scalable calibration.