Search Results (24)

This paper presents the results of a detailed theoretical study of the bending properties of all-glass leakage channel microstructured optical fibers (LC MOFs) with a polymer coating over a bending radius range from 4.8 cm to 10 cm. The dependencies of the effective refractive indices of the LC MOF modes on the bending radius have a number of crossings and anticrossings for different mode pairs. A detailed analysis showed that eight modes for each polarization have to be considered to correctly calculate the bending losses. These modes can be classified into relatively strong modes (three for each polarization) and relatively weak modes. The three strong modes have the most direct effect on the loss calculation. However, the relatively weaker modes also play a role through their coupling with the stronger modes, resulting in the appearance of local loss maxima in the loss dependencies for the strong modes. At a bending radius of 10 cm, the final leakage loss of the LC MOFs with a polymer coating is approximately four times lower than that of the LC MOFs without a coating. The significant reduction in losses paves the way for further optimization of the LC MOF geometric structure, leading to a reduction in the allowable bending radius. Full article

This paper presents the results of a detailed theoretical study of the bending properties of original all-glass leakage channel microstructured optical fibers (LC MOFs) over a bending radius range from 3 cm to 11 cm. These LC MOFs contain two layers of fluorine-doped silica glass elements with reduced refractive index, different diameters, and different distances between them. We determined the spatial distributions of the electric field components of different modes in addition to the usual parameters such as effective refractive indices, bending losses, and spatial intensity distributions. A detailed analysis showed that three modes for each polarization have to be considered to correctly calculate the bending losses. Two pairs of these three modes couple in two distinct bending radius ranges, specifically near 3.68 cm and near 5.95 cm, and the mode coupling in these pairs is resonant. The resulting bending losses of the LC MOF for two polarizations are very close to each other and have two maxima at bending radii of 3.68 cm and 5.95 cm. However, the nature of these maxima is not resonant; they are caused by the combined influence of all three modes, each of which has specific dependencies of losses and other parameters on the bending radius that exhibit quasi-resonant behavior near the corresponding bending radii. Full article

With the development of laser technology, microstructured optical fibers (MOFs) have become an important part of ultrafast optics, providing excellent platforms for ultrafast laser pulse generation, amplification, and compression, promoting the development of fiber laser systems to generate high power, high pulse energy, and few-cycle duration pulses. MOFs extend the ultrafast laser spectrum to the vacuum ultraviolet (VUV) and even extreme ultraviolet (EUV) regions based on dispersive wave emission and high harmonic generation, as well as to the mid-infrared region based on soliton self-frequency shift (SSFS), contributing compact and low-cost light sources for precision microscopy and spectroscopy. In this paper, first several common types of MOFs are introduced, then the various applications of MOFs in ultrafast optics are discussed, mainly focusing on the aspects of ultrafast laser pulse scaling in pulse energy and spectral bandwidth, and finally the possible prospects of MOFs are given. Full article

With an increase in the volume of information exchange and perception, the demands for intelligent, miniaturized, and integrated optical devices for information acquisition are also increasing. As the core component of optical networks for transmitting information, further optimization of their structural characteristics to generate richer optical characteristics and apply them to information exchange and optical field control has become a key research hotspot. The introduction of chiral twist characteristics has led to new phenomena and applications in optical field transmission and the transformation of traditional optical fibers or microstructured optical fibers (MOF). Therefore, this review mainly begins with the principle of chiral optical fibers, introduces their preparation and latest application scenarios, and finally discusses their potential future development prospects. Full article

This work presents the first instance of a silica few-mode microstructured optical fiber (MOF) being successfully fabricated with a hollow GeO₂-doped ring core and by strongly inducing twisting up to 790 revolutions per meter. Some technological issues that occurred during the manufacturing of the GeO₂-doped supporting elements for the large hollow cores are also described, which complicated the spinning of the MOFs discussed above. We also provide the results of the tests performed for the pilot samples—designed and manufactured using the untwisted and twisted MOFs described above—which were characterized by an outer diameter of 65 µm, a hollow ring core with an inner diameter of 30.5 µm, under a wall thickness of 1.7 µm, and a refractive index difference of Δn = 0.030. Moreover, their geometrical parameters, basic transmission characteristics, and the measurements of the far-field laser beam profile patterns are also provided. Full article

The paper presents the results of theoretical and experimental studies of all-glass leakage channel microstructured optical fibers (MOFs) with a large mode area and low bending losses. These MOFs contain two layers of fluorine-doped silica glass elements with a reduced refractive index, different diameters, and different distances between them. A numerical analysis of the properties of these MOFs was performed using the finite element method. The leakage losses for the fundamental and higher-order modes were calculated in the spectral range from 0.65 μm to 1.65 μm. Simulation results show that the proposed MOF design allows for single-mode guidance in the spectral range from 0.92 μm to 1.21 μm with a bending radius of down to 0.08 m. The measured losses of the fabricated MOF with a core diameter of 22.5 μm and a bending radius of 0.1 m were less than 0.1 dB/m in the spectral range from 0.9 μm to 1.5 μm. It is demonstrated that the segments of this MOF longer than 5 m are single-mode. Full article

This work presents a fabricated silica few-mode microstructured optical fiber (MOF) with a special six GeO₂-doped core geometry, an outer diameter of 125 µm (that corresponds to conventional commercially available telecommunication optical fibers), and improved induced twisting up to 500 revolutions per 1 m (under a rotation speed of 1000 revolutions per meter with a drawing speed of ~2 m per minute). The article discusses some technological aspects and issues of manufacturing the above-described twisted MOFs with complicated structures and geometry as GeO₂-doped silica supporting elements for them. We present results of some measurements performed for fabricated samples of chiral silica six-GeO₂-doped-core few-mode MOFs with various orders of twisting and both step and graded refractive indexes of “cores”. These tests contain research on MOF geometrical parameters, attenuation, and measurements of the far-field laser beam profile. Full article

The optical properties of solid-core micro-structured optical fibers (SC MOFs) have been studied for a long time. The process of the energy outflow of the core modes has always been associated with the process of constructive interference of the core modes fields under reflection from the photonic crystal cladding. In this paper, we want to offer a new look at the light localization in the core of SC MOFs related to the behavior of spin and orbital parts of the Poynting vector of these core modes and singularities arising in it. Such an approach can help in forming a better understanding of the process of the core modes energy leakage and also in the creation of SC MOFs with a simplified design and low losses. Full article

In this work a plasmonic sensor with a D-Shaped microstructured optical fiber $\left(\mathrm{MOF}\right)$ is proposed to detect a wide range of analyte refractive index $\left(\mathrm{RI} ;{\mathrm{n}}_{\mathrm{a}}\right)$ by doping the pure silica $\left({\mathrm{SiO}}_2\right)$ core with distinct concentrations of Germanium Dioxide $\left({\mathrm{GeO}}_2\right)$, causing the presentation of high spectral sensitivity. In this case, the fiber is shaped by polishing a coating of ${\mathrm{SiO}}_2$, on the region that will be doped with ${\mathrm{GeO}}_2$, in the polished area, a thin gold $\left(\mathrm{Au}\right)$ layer, which constitutes the plasmonic material, is introduced, followed by the analyte, in a way which the gold layer is deposited between the ${\mathrm{SiO}}_2$. and the analyte. The numerical results obtained in the study shows that the sensor can determine efficiently a range of 0.13 refractive index units $\left(\mathrm{RIU}\right)$, with a limit operation where ${\mathrm{n}}_{\mathrm{a}}$ varies from 1.32 to 1.45. Within this application, the sensor has reached an average wavelength sensitivity $\left(\mathrm{WS}\right)$ of up to $11,650.63 \mathrm{nm}/\mathrm{RIU}$. With this level of sensitivity, the D-Shaped format and wide range of ${\mathrm{n}}_{\mathrm{a}}$ detection, the proposed fiber has great potential for sensing applications in several areas. Full article

Surface-enhanced Raman spectroscopy (SERS) is a powerful technique for biosensing. However, SERS analysis has several concerns: the signal is limited by a number of molecules and the area of the plasmonic substrate in the laser hotspot, and quantitative analysis in a low-volume droplet is confusing due to the change of concentration during quick drying. The usage of hollow-core microstructured optical fibers (HC-MOFs) is thought to be an effective way to improve SERS sensitivity and limit of detection through the effective irradiation of a small sample volume filling the fiber capillaries. In this paper, we used layer-by-layer assembly as a simple method for the functionalization of fiber capillaries by gold nanoparticles (seeds) with a mean diameter of 8 nm followed by UV-induced chloroauric acid reduction. We also demonstrated a simple and quick technique used for the analysis of the SERS platform formation at every stage through the detection of spectral shifts in the optical transmission of HC-MOFs. The enhancement of the Raman signal of a model analyte Rhodamine 6G was obtained using such type of SERS platform. Thus, a combination of nanostructured gold coating as a SERS-active surface and a hollow-core fiber as a microfluidic channel and a waveguide is perspective for point-of-care medical diagnosis based on liquid biopsy and exhaled air analysis. Full article

Long-range surface plasmon resonance (LRSPR), generated from a coupled plasmon polariton in a thin metal slab sandwiched by two dielectrics, has attracted more and more attention due to its merits, such as longer propagation and deeper penetration than conventional single-interface surface plasmon resonance. Many useful applications related to light–medium interaction have been demonstrated based on the LRSPR effect, especially in the sensing area. Here, we propose and demonstrate an LRSPR-based refractive index sensor by using a SiO${}_2$-Au-TiO${}_2$ heterostructure, in which a D-shaped honeycomb-microstructure optical fiber (MOF) is designed as the silica substrate and then deposited with a gold film and thin-layer titanium dioxide (TiO${}_2$). By using the full-vector finite-element method (FEM), this heterostructure is numerically investigated and demonstrated to excite LRSPR without a buffer layer, which is usually necessary in previous LRSPR devices. Through comprehensive discussion about the influence of structural parameters on the resonant wavelength, the excitation of the LRSPR in the proposed heterostructure is revealed to be highly related to the effective refractive index of MOF’s fundamental core mode, which is mainly determined by the MOF’s pitch, the thicknesses of the silica web and the planar-layer silica. Moreover, the thin-layer TiO${}_2$ plays an important role in significantly enhancing the resonance and the sensitivity to analyte’s refractive index as well, when it is coated on the top of the Au film rather than between the metal and waveguide. Finally, the proposed LRSPR sensor based on SiO${}_2$-Au-TiO${}_2$ heterostructure shows an ultra-high wavelength sensitivity of 20,100 nm/RIU and the corresponding minimum resolution is as low as $4.98\times {10}^{-7}$ RIU. Thus, the proposed LRSPR device offers considerable potential for sensing applications in biomedical and biochemical areas. Full article

A surface plasmon resonance (SPR) sensor based on a dual-side polished microstructured optical fiber (MOF) with a dual core is proposed for a large analyte refractive index (RI; n_a) detection range. Gold is used as a plasmonic material coated on the polished surface, and analytes can be directly contacted with the gold film. The special structure not only facilitates the fabrication of the sensor, but also can work in the n_a range of 1.42–1.46 when the background material RI is 1.45, which is beyond the reach of other traditional MOF-SPR sensors. The sensing performance of the sensor was investigated by the wavelength and amplitude interrogation methods. The detailed numerical results showed that the proposed sensor can work effectively in the n_a range of 1.35–1.47 and exhibits higher sensitivity in the n_a range of 1.42–1.43. Full article

Since the first publications related to microstructured optical fibers (MOFs), the development of optical fiber sensors (OFS) based on them has attracted the interest of many research groups because of the market niches that can take advantage of their specific features. Due to their unique structure based on a certain distribution of air holes, MOFs are especially useful for sensing applications: on one hand, the increased coupling of guided modes into the cladding or the holes enhances significantly the interaction with sensing films deposited there; on the other hand, MOF air holes enhance the direct interaction between the light and the analytes that get into in these cavities. Consequently, the sensitivity when detecting liquids, gasses or volatile organic compounds (VOCs) is significantly improved. This paper is focused on the reported sensors that have been developed with MOFs which are applied to detection of gases and VOCs, highlighting the advantages that this type of fiber offers. Full article

Microstructured optical fiber-based sensors (MOF) have been widely developed finding numerous applications in various fields of photonics, biotechnology, and medicine. High sensitivity to the refractive index variation, arising from the strong interaction between a guided mode and an analyte in the test, makes MOF-based sensors ideal candidates for chemical and biochemical analysis of solutions with small volume and low concentration. Here, we review the modern techniques used for the modification of the fiber’s structure, which leads to an enhanced detection sensitivity, as well as the surface functionalization processes used for selective adsorption of target molecules. Novel functionalized MOF-based devices possessing these unique properties, emphasize the potential applications for fiber optics in the field of modern biophotonics, such as remote sensing, thermography, refractometric measurements of biological liquids, detection of cancer proteins, and concentration analysis. In this work, we discuss the approaches used for the functionalization of MOFs, with a focus on potential applications of the produced structures. Full article

We demonstrate a three-port, light guiding and routing T-shaped configuration based on the combination of whispering gallery modes (WGMs) and micro-structured optical fibers (MOFs). This system includes a single mode optical fiber taper (SOFT), a slightly tapered MOF and a BaTiO₃ microsphere for efficient light coupling and routing between these two optical fibers. The BaTiO₃ glass microsphere is semi-immersed into one of the hollow capillaries of the MOF taper, while the single mode optical fiber taper is placed perpendicularly to the latter and in contact with the equatorial region of the microsphere. Experimental results are presented for different excitation and reading conditions through the WGM microspherical resonator, namely, through single mode optical fiber taper or the MOF. The experimental results indicate that light coupling between the MOF and the single mode optical fiber taper is facilitated at specific wavelengths, supported by the light localization characteristics of the BaTiO₃ glass microsphere, with spectral Q-factors varying between 4.5 × 10³ and 6.1 × 10³, depending on the port and parity excitation. Full article