Bloch surface waves on a fiber tip

Monitoring the geometry of an moving element is a crucial task for example in robotics. The robots equipped with fiber bend sensor integrated in their arms can be a promising solution for medicine, physiotherapy and also for application in computer games. We report an all-fiber intensity bend sensor, which is based on microstructured multicore optical fiber. It allows to perform a measurement of the bending radius as well as the bending orientation. The reported solution has a special airhole structure which makes the sensor only bend-sensitive. Our solution is an intensity based sensor, which measures power transmitted along the fiber, influenced by bend. The sensor is based on a multicore fiber with the special air-hole structure that allows detection of bending orientation in range of 360°. Each core in the multicore fiber is sensitive to bend in specified direction. The principle behind sensor operation is to differentiate the confinement loss of fundamental mode propagating in each core. Thanks to received power differences one can distinguish not only bend direction but also its amplitude. Multicore fiber is designed to utilize most common light sources that operate at 1.55 μm thus ensuring high stability of operation. The sensitivity of the proposed solution is equal 29,4 dB/cm and the accuracy of bend direction for the fiber end point is up to 5 degrees for 15 cm fiber length. Such sensitivity allows to perform end point detection with millimeter precision.

This paper describes ultra-high capacity long haul optical transmission technologies based on multicore fibers (MCFs) with space-division multiplexing. First, we discuss the factors limiting the total capacity and the attainable distance of MCF, and show that the transmission distances are severely limited by crosstalk (XT) between adjacent cores. Next, we discuss a propagation-direction interleaving (PDI) technique to suppress XT. In PDI, adjacent cores have different propagation directions, and thus, bidirectional transmission is realized by a single MCF. We discuss spectral efficiency and attainable distance of several MCFs and show that three-fold reach extension is possible by using PDI in 12-core fiber with dual-ring structure. We also describe a long haul transmission experiment on a 12-core DRS fiber with PDI.

Multimode and multicore optical fibers are pivotal for spatial division multiplexing, a key technology for future high-capacity optical communication systems. A critical transmission characteristic of these fibers is modal dispersion, which is made random by unpredictable perturbations and manufacturing imperfections. While the statistical properties of modal dispersion are well-explored, the underlying local phenomenon of mode coupling—its primary cause—has received comparatively less attention. Accurate modeling of mode coupling is essential for a deeper understanding of both the linear and nonlinear propagation dynamics in these fibers and for advancing their practical implementation. This paper provides a comprehensive review of mode coupling in multimode and multicore fibers, highlighting aspects of general validity and conducting an in-depth analysis of bending and twisting—the two most common perturbations affecting deployed fibers. The results reveal significant similarities between the mode coupling behaviors of multimode and multicore fibers, along with some remarkable differences.

The selection of an appropriate pump concept has a major impact on amplifier cost and power consumption. The energy efficiency of different pump concepts is compared for multi core and multi mode active fibers. In preamplifier stages, pump power density requirements derived from full C-band low noise WDM operation result in superior energy efficiency of direct pumping of individual cores in a multi core fiber with single mode pump lasers compared to cladding pumping with uncooled multi mode lasers. Even better energy efficiency is achieved by direct pumping of the core in multi mode active fibers. Complexity of pump signal combiners for direct pumping of multi core fibers can be reduced by deploying integrated components.

In this letter, we report on coupling optics for connecting single-core single-mode fibers with multicore single-mode fibers. After a brief discussion of the options for such coupling systems, we describe our approach of using bulk optics to fabricate low-loss and low-crosstalk devices for both 7- and 19-core multicore fibers with the free-space design approach. This enables the use of the same coupling device with a variety of multicore fibers whose structural parameters differ from one sample to another. We present the results of experimental evaluations of these devices, discuss various causes of insertion loss, and analyze the coupling loss in detail.

The experimental thulium fiber laser (TFL) is being explored as an alternative to the current clinical gold standard Holmium:YAG laser for lithotripsy. The near single-mode TFL beam allows coupling of higher power into smaller optical fibers than the multimode Holmium laser beam profile, without proximal fiber tip degradation. A smaller fiber is desirable because it provides more space in the ureteroscope working channel for increased saline irrigation rates and allows maximum ureteroscope deflection. However, distal fiber tip burnback increases as fiber diameter decreases. Previous studies utilizing hollow steel sheaths around recessed distal fiber tips reduced fiber burnback but increased stone retropulsion. A “fiber muzzle brake” was tested for reducing both fiber burnback and stone retropulsion by manipulating vapor bubble expansion. TFL lithotripsy studies were performed at 1908 nm, 35 mJ, 500 ?? ? s , and 300 Hz using a 100 - ? m -core fiber. The optimal stainless steel muzzle brake tip tested consisted of a 1-cm-long, 560 - ? m -outer-diameter, 360 - ? m -inner-diameter tube with a 275 - ? m -diameter through hole located 250 ?? ? m from the distal end. The fiber tip was recessed a distance of 500 ?? ? m . Stone phantom retropulsion, fiber tip burnback, and calcium oxalate stone ablation studies were performed ex vivo. Small stones with a mass of 40 ± 4 ?? mg and 4-mm-diameter were ablated over a 1.5-mm sieve in 25 ± 4 ?? s

Multicore fibers with linearly coupled cores are considered as a means of the coherent transport needed for high-capacity communication systems and high-power fiber lasers. The conditions of the existence and stability of coherent light propagation in multicore fibers with circularly arranged cores are derived. The multicore fiber is modeled by the linear discrete complex Ginzburg–Landau equation, while its eigenvalues are found analytically. The inverse eigenvalue problem proposing the commensurability of eigenvalues is solved to find the intercore coupling coefficients that support periodic revivals of the input state. Both planar modes and vortices are considered. Effects of the central core and material loss/gain on eigenvalue commensurability conditions and mode dynamics are studied in detail.

Space-division multiplexing (SDM) systems based on few-mode multi-core fibers (FM-MCFs) utilize both spatial channels (fiber cores) and modes (optical modes per core) to maximize transmission capacity. Unlike laboratory FM-MCFs or field-deployed single-mode multi-core fibers (SM-MCFs), SDM transmissions over field-deployed FM-MCFs in outdoor settings have not been reported. Therefore, concerns remain that environmental interference and cabling stress could worsen inter-core and intra-core modal crosstalk and impact the performance of SDM systems over FM-MCFs. In this paper, we demonstrate successful bidirectional SDM transmission over a 5-km, field-deployed seven ring-core fiber (7-RCF) with a cladding diameter of 178 μm. Our measurements show no significant differences in attenuation and mode coupling compared to pre-cabling conditions, confirming the fiber’s resilience to environmental disturbances and adaptability to cable deployment. Using the field-deployed 7-RCF, bi-directional SDM transmission is implemented, achieving spectral efficiency (SE) of 2×201.6 bit/(s Hz) which sets a new record in field-deployed fiber cables that is a tenfold increase over previous systems. Furthermore, these results were achieved using a small-scale 4×4 multiple-input multiple-output (MIMO) scheme with a time-domain equalization (TDE) tap number not exceeding 15. These results demonstrate the substantial potential of using SDM techniques to significantly enhance SE and expand capacity in practical fiber-optic transmission applications.

Development of a surface plasmon resonance sensor using an optical fiber prepared by electroless displacement gold plating and its application to immunoassay.

Micro-Lab on Tip: High-Performance Dual-Channel Surface Plasmon Resonance Sensor Integrated on Fiber-Optic End Facet

We propose an approach for highly-stable and low-phase-noise microwave signal generation based on an actively stabilized multi-loop optoelectronic oscillator (ASML-OEO) by leveraging the distinctive spatial multiplexing capability of multi-core fiber (MCF). In the proposed ASML-OEO, a MCF is employed to create spatially parallel optical delay paths within a single cladding. This enables a compact multi-loop OEO design with intrinsically high side-mode suppression ratio (SMSR). To enhance the long-term frequency stability, an active time-delay compensation scheme is introduced by leveraging the inherent chromatic dispersion effect of the MCF. By precisely tuning the optical carrier wavelength, the environmentally induced time delay variations in the MCF can be dynamically compensated, thereby actively stabilizing the OEO loop. Notably, the compact multi-loop OEO design enabled by the MCF offers superior frequency stability compared to conventional designs. This enhancement stems from the fact that all fiber cores in the MCF experience nearly identical environmental disturbances, enabling precise and simultaneous time-delay compensation. The proposed system is experimentally validated, generating a 10.1-GHz signal with an SMSR of 69.6 dB and a phase noise of -124.5 dBc/Hz@10 kHz. Furthermore, active stabilization yields a remarkable improvement in long-term frequency stability, reducing the hourly peak-to-peak frequency drift from 40.2 kHz to 0.44 kHz and lowering the Allan deviation from 5.6×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-11</sup>@1000s to 9.3×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-13</sup>@1000s. With its simultaneous achievement of high SMSR, low phase noise, and superior frequency stability, the proposed ASML-OEO architecture is uniquely suited for demanding applications including high-resolution radar imaging, modern broadband wireless communications and advanced electronic warfare systems.

We analyze the effect of launch beam distribution on space-division multiplexing (SDM) performance in multimode multicore silica optical fibers (MM MC SOF) with seven cores. The time-independent power flow equation (TI PFE) is used to explore the effect of the width of the distribution of the Gaussian launch beam on power flow in each of the seven cores. We show that the optical fiber length at which the equilibrium mode distribution (EMD) and steady-state distribution (SSD) are obtained is greatly influenced by the width of the Gaussian launch beam distribution. We further show that when the width of the Gaussian launch beam distribution widens, the optical fiber length at which angular division multiplexing (ADM) in each of the seven cores can be realized with minimal crosstalk between neighboring angular optical channels decreases. We demonstrate that, for increasing the capacity of an optical fiber transmission system, an SDM system with two- and three-channel ADM and multicore optical fiber multiplexing can be implemented with the proposed seven-core MM MC SOF at optical fiber lengths up to ≈1 km (2 ADM channels × 7 cores) and ≈200 m (3 ADM channels × 7 cores), respectively. Such characterization of MM MC SOFs under various launch conditions is important for building a multicore optical fiber SDM transmission system.

Multi-core fiber (MCF) has been one of the main innovations in fiber optics in the last decade. Reported work on MCF has been focused on increasing the transmission capacity of optical communication links by exploiting space-division multiplexing. Additionally, MCF presents a strong potential in optical beamforming networks. The use of MCF can increase the compactness of the broadband antenna array controller. This is of utmost importance in platforms where size and weight are critical parameters such as communications satellites and airplanes. Here, an optical beamforming architecture that exploits the space-division capacity of MCF to implement compact optical beamforming networks is proposed, being a new application field for MCF. The experimental demonstration of this system using a 4-core MCF that controls a four-element antenna array is reported. An analysis of the impact of MCF on the performance of antenna arrays is presented. The analysis indicates that the main limitation comes from the relatively high insertion loss in the MCF fan-in and fan-out devices, which leads to angle dependent losses which can be mitigated by using fixed optical attenuators or a photonic lantern to reduce MCF insertion loss. The crosstalk requirements are also experimentally evaluated for the proposed MCF-based architecture. The potential signal impairment in the beamforming network is analytically evaluated, being of special importance when MCF with a large number of cores is considered. Finally, the optimization of the proposed MCF-based beamforming network is addressed targeting the scalability to large arrays.

A compact all-fiber plasmonic Airy-like beam generator is demonstrated. A single slit and a 1D groove array were fabricated by focused ion beam milling on the gold deposited end facet of a single-mode optical fiber. The single slit excites the surface plasmonic polaritons (SPPs), which are decoupled into free space by the groove array. The phase of decoupling SPPs is adjusted by the grooves position. Experimental generation of the single Airy-like beam has good consistency with theoretical predictions. The transverse acceleration and nondiffraction properties are observed. The interference of double Airy-like beams in the free space is also analyzed. The presented plasmonic Airy-like beam generator is of importance to realize all-fiber optical trapping, beam shaping, and fiber integrated devices.

A novel refractive-index (RI) Michelson interferometer based on a waist-enlarged taper is achieved. Such a device is fabricated by splicing a section of multimode fiber (MMF) at one end of single-mode fiber (SMF). Due to the fiber bitaper at the coupling point of SMF and MMF, the light is coupled into the MMF from lead in fiber core, and the intermodal interference will occur for the optical path difference between core mode and cladding mode. Then, the light will be reflected at the end of the fiber and recoupled back into the lead out fiber core by the fiber bitaper. When the lights return back to the lead out fiber, the intermodal interference will occur for the optical path difference between core mode and high order mode. The sensor has a linear response to RI with a sensitivity of −178.424 dB/RIU in the range of 1.351–1.4027 RIU. The temperature cross sensitivity is also analyzed, and the influence can be eliminated by simultaneous measurement of RI and temperature through the matrix equation. The proposed sensor features the advantages of easy fabrication, low cost, high mechanical strength, which make it a good candidate for bio-chemical measurement.