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This letter presents the design, fabrication, and testing of a diaphragm-based, all-silica fiber tip pressure sensor. A piece of 1.2- $\mu \text{m}$ -thick silica diaphragm was thermally bonded to the end face of an etched fiber with an outer diameter (OD) of 125 $\mu \text{m}$ to form a Fabry–Perot (FP) interferometer. The diameter of the etched FP cavity is $105~\mu \text{m}$ , enabling the sensing area to be large, and thus, a static pressure sensitivity of 12.4 nm/kPa (85.3 nm/psi) is accomplished without the need for any post polishing or etching. The sensor also shows a low-temperature cross sensitivity during tests, owing to its all-silica structure. It is suitable for extensive production, and it has a great potential to work in applications, where miniature size and high sensitivity are essential such as medical applications.

We report a 40 μm core-diameter single-mode multitrench fiber (MTF) based on Nd-doped silicate glass. Both the delocalization effect and leaky nature were considered in the design of the MTF. The silicate MTF was designed and fabricated using the rod-in-tube method. A maximum laser output power of ∼8.4 W with a slope efficiency of 54% was obtained from a 10-cm-long single-mode MTF.

The structure and interfacial shear strength (IFSS) of polypropylene-glass fiber/carbon fiber hybrid composites fabricated by a new method called direct fiber feeding injection molding (DFFIM) process were investigated based on the skin-core-skin structure and modified Kelly-Tyson equation, respectively. The fiber dispersion state was evaluated qualitatively by scanning electron microscopy (SEM) and quantitatively by the fiber distribution index (FDI). Carbon fiber agglomeration is more likely to occur in hybrid composites and was present in the core layer of DFFIM composites in this study. However, glass fiber has shown relatively uniform dispersion in hybrid composites with a greater tendency to be distributed in the skin layers. This is attributed to the difference in feeding method, where glass fibers were fed through the hopper while carbon fibers were inserted from the vent hole. The IFSS between fibers and polypropylene of different composites in different layers is discussed by considering fiber length and orientation distributions in the core and skin layers, respectively.

This paper focuses on the energetic evaluation of the single fiber pull-out test (SFPT) using regenerated cellulose fibers (RCF) in a PP matrix with a varying MAPP content. Glass fibers were used for reference purposes. By means of the SFPT the interfacial shear strength (IFFS), the critical fiber length (lc), the consumed energy of a fiber pull-out and the consumed energy of a fiber rupture were determined. Results were related to the fiber length distribution in injection molded specimens. It was shown that theoretically more fiber ruptures appear in composites with RCF than with GF. But RCF composites offer a larger number of long fibers, slightly underneath the critical fiber length, consuming a high amount of energy by being pulled out at a composite failure. The consumed energy of a fiber pull-out per length was increased by using MAPP but simultaneously the critical fiber length was significantly reduced.

A multicore fiber design with more than 10 coupled cores is investigated numerically and experimentally. It is revealed that a randomly coupled 12-core structure with a square lattice core arrangement can be realized within a 125 μm cladding by employing fiber twisting of more than a few π rad/m. A 125 μm-clad twisting-rate-controlled 12-core fiber is then fabricated and a relative core density of 12 compared with conventional single-mode fiber is achieved while maintaining a low spatial mode dispersion characteristic of 8.4 ps/√km at 1550 nm. Finally, we experimentally evaluated the performance of 12 spatial channels by conducting a 24 × 24 MIMO transmission experiment.

We investigate the hydrostatic pressure dependence of the Bragg wavelength of a fiber Bragg grating (FBG) inscribed in a perfluorinated graded-index (PFGI-) polymer optical fiber (POF) at 1550 nm. At 0.5 MPa, the Bragg wavelength increased with time and became almost constant ~150 min later. Such a long time constant probably originates from the unique structure of the PFGI-POF, which has a thick overcladding around its core and cladding. The pressure-dependence coefficient without considering the time constant was estimated to be 1.3 nm/MPa; this is over five times the values of other types of POF-FBGs. This indicates that by removing the overcladding of the PFGI-POF, fast-response high-sensitivity pressure sensing will be feasible. Once the Bragg wavelength became constant at 0.5 MPa, the pressure-dependence coefficient of the Bragg wavelength was measured to be −0.13 nm/MPa, the absolute value of which was comparable with those of other POF-FBGs, but with an opposite sign.

A graded-index fiber with yttrium aluminosilicate (YAS) glass core was fabricated by a “Melt-in-Tube” method. The refractive index and stress profiles of the fibers exhibit a highly symmetrical gradient tendency along the radial axis which is in accordance with the results of element migration. Based on the formation mechanism of YAS glass core, the relationships between the refractive index/stress profile and the spontaneous migration are discussed. A linear all-fiber laser based on the obtained fiber shows a laser output threshold of 11.48 mW and slope efficiency of 8.3%. The near-field beam intensity distribution of fiber laser with spectrum FWHM of 0.24nm indicates the good laser beam quality. The facile “Melt-in-tube” method was proved to be reliable in designing graded-index fiber through the dissolution and diffusion process, which is more advanced than commonly used “Rod-in-tube” method. This article is protected by copyright. All rights reserved.

The focus of this work is to extend optical frequency domain reflectometry sensing to sapphire optical fiber, by creating a cladding in the fiber. A cladding was created by irradiating a sapphire optical fiber, which was surrounded by an annulus of Li-6 enriched lithium carbonate (Li2CO3) powder, in The Ohio State University Research Reactor. The 6Li(n, $\alpha)^{3}\text{H}$ reaction created high energy alpha particles and tritons that irradiated the fiber simultaneously to a depth of 24 microns along the entire periphery of the sapphire fiber, thereby slightly reducing the index of refraction in the fiber’s periphery and creating a cladding within the fiber. Transmitted light intensity profiles show that the ion implanted cladding made the fiber’s intensity profile nearly single mode. The cladding survived to the highest temperature that was tested (1500 °C). The cladding made the fiber sufficiently single mode that the cladded sapphire fiber, when read out with an optical backscatter reflectometer, produced distributed temperature measurements along the entire length of the fiber.

Detailed investigation is made of the thermoluminescence (TL) response of various sizes of optical fiber, fibers being developed with either a fixed core-to-cladding ratio or various core-to-cladding ratios. Two Ge-doped optical fiber preforms have been used to reconfirm the experimental findings. For further clarification, a pure silica rod has also been used to fabricate different diameter rods. Experimental investigations show the main TL signal to be generated from the fiber core within which the Ge is doped, the fiber cladding producing insignificant TL signal. Prior to normalization, the results show that in doubling the fiber diameter the TL signal quadruples. Conversely, subsequent to normalizing the different sizes of optical fiber to their mass or fiber cross sectional area, the smaller diameter fibers show slightly greater sensitivity compared to the larger diameter fibers. Relating to the fiber drawing-down process, this is due primarily to the greater shearing effect that the smaller fibers experience compared to the larger fibers within the fiber preform neck-down region.

Photostable and flexible materials transparent at the wide spectral range are necessary for the development of optical fiber units. Solid solutions of silver and monadic thallium halides are the most suitable crystal media for this purpose. The goal of our research was the search of optimum structure for the fibers with a single mode operation and a rather large core diameter. We modelled fiber structures (solid-core, hollow-core, active-core PCF) with various ratio of inserts diameters and increments between the inserts, basing on two crystal systems: AgCl-AgBr and AgBr-TlI. Then we chose the single mode fiber structure and manufactured it by means of extrusion.

The series of SiO2-Bi2O3-PbO-ZnO-BaO and SiO2-TiO2-Bi2O3-PbO-Na2O glasses were synthetized to obtain non-crystallizing materials, dedicated to fabrication of photonic crystal fibers. During composition development, the thermal properties were investigated according to the change of chemical composition. The glasses contain high concentrations of heavy metal oxides for high refractive index, large nonlinear refractive index and spectrally broad transmission window from 0.5 to 4.5 μm. Their thermal properties are optimized to enable drawing of all-solid glass photonic crystal fibers in tandem with previously designed highly nonlinear glass PBG81 based on SiO2-Ga2O3-Bi2O3-PbO-CdO system. This creates novel dual glass combinations for PCF fibers. We have also investigated influence of melting conditions on the final thermal and optical properties, including absorption from water contamination at around 2.8 μm.

We investigate the evolution of optical transmission through a double cladding fiber-optic structure during etching. The structure is formed by a section of SM630 fiber with inner depressed cladding between standard SMF-28 fibers. Its transmission spectrum exhibits two resonance dips at wavelengths where two cladding modes have almost equal propagation constants. We measure transmission spectra with decreasing thickness of the cladding and show that the resonance dips shift to shorter wavelengths, while new dips of lower order modes appear from long wavelength side. We calculate propagation constants of cladding modes and resonance wavelengths, which we compare with the experiment.

In this paper, a hexagonal structure of ethanol filled solid core photonic crystal fiber having dispersion shifted properties is presented. The guiding properties, like effective mode area and dispersion, of the ethanol filled photonic crystal fiber are studied by using the full vectorial finite element method. The numerical simulation results show that the selectively filling of the ethanol in the cladding holes of photonic crystal fiber shifts the zero dispersion wavelength from near infrared region (0.98 μm) to mid infrared region (1.55 μm). This kind of photonic crystal fiber structure is very useful for dispersion compensating tool, sensing applications, fiber laser devices and non-linear applications like supercontinuum generation.

A novel photonic crystal fiber design is presented. The design provides broadband high and uniform birefringence, large negative dispersion and low confinement loss. The fiber is based on double-hole assisted core in the conventional square lattice cladding. For the proposed PCF, high and uniform birefringence of 7.5 × 10 −3 , the negative dispersion of −150 ps/(nm km) and an extremely low confinement loss can be obtained over E+ S + C + L + U (1380 ∼ 1780 nm) wavelength bands.

Using fusion splicing and hydroxide catalysis bonding (HCB) technology, an all-silica inline fiber-optic sensor with high-pressure survivability, high-resolution salinity measurement capability, and corrosion resistance for deep sea explorations is proposed and experimentally demonstrated. Two extrinsic Fabry-Perot interferometers (EFPIs) and a fiber Bragg grating (FBG) are cascaded in one single-mode fiber (SMF), enabling structural integration of single lead-in fiber and versatility of the sensing probe for temperature, depth, and salinity monitoring. The HCB technology offers a polymer adhesive-free assembly of one open-cavity EFPI for refractive index (RI) (salinity) sensing under normal pressure and temperature (NPT) conditions, showing obvious advantages of strong bonding strength, reliable effectiveness, and no corrosive chemicals requirements. The other EFPI formed by a fused structure is designed for pressure (depth) measurement. The cascading of EFPIs, especially the open-cavity EFPI immersed in water, will result in large light transmission loss and bring challenges to signal interrogation. Graded-index fiber (GIF) micro-collimators and reflective films are added to prevent dramatic degradations of signal intensity and fringe visibility underwater. Thereby, a Fabry-Perot (FP) cavity of several hundreds of microns in length and an open cavity of a thousand microns can be cascaded for underwater applications, effectively enhancing sensitivities and underwater signal readout simultaneously. Results show that the proposed sensor can well operate in the deep-sea pressure range of 0∼2039.43 mH2O, RI range of 1.33239∼1.36885 RIU, and temperature range of 23∼80 °C, with resolutions of 0.033 MPa, 4.16×10−7 RIU, and 0.54 °C, respectively. With the multi-parameter measurement capability, all-silica construction, and inline compact structure, the proposed sensor could be a potential candidate for deep sea exploration.

We propose a high-linearity refractive index (RI) sensor based on an analyte-filled defect hollow core Bragg fiber (DHCBF) for large dynamic ranges. A resonant wavelength induced by the transverse coupling between core modes and defect modes is used as the characteristic wavelength for realizing a high-linearity RI sensor. The numerical results show that the linear correlation between characteristic wavelength and analyte RI can be significantly improved by optimizing structural parameters of a defect layer, which would be beneficial to the enlargement of dynamic measurement range. Furthermore, we numerically demonstrated an RI sensor with the sensitivity of 2062 nm/RIU and the adjusted R-Square value of 0.99967 in the measurement range of 1.324-1.432, by using an analyte-filled DHCBF with a low RI-contrast cladding. Compared with that based on a standard HCBF, our proposed high-linearity RI sensor can achieve high sensitivity in a larger dynamic range.

In this paper, a sensitive-enhanced single-mode fiber—tapered hollow core fiber—single-mode fiber Mach–Zehnder interferometer is demonstrated for refractive index sensing. The sensitivity was improved by forming an up-taper at the two splicing joints and concave cone in hollow core fiber. The up-tapered regions served as a more effective mode splitter/combiner, and the tapered hollow core fiber was used to generate a stronger evanescent field to enhance the interaction of light with the analyte. According to the principles of interference between the cladding and fundamental modes, we performed refractive index measurements. The experiments indicated that the proposed sensor has a high refractive index sensitivity of 214.97 nm/RIU in the refractive index range of 1.333–1.379, with a minimum refractive index measurement resolution of 9.3 × 10−5. In addition, the sensor had a low temperature response of 2.96 pm/°C in the range from 50 to 85°C and a low cross sensitivity of 1.377 × 10−5 RIU/°C. The p...

A novel coreless-D-shape-coreless (CDC) fiber structure for liquid-level sensing is proposed and experimentally investigated. The D-shape fiber with cladding partially etched is sensitive to the ambient refractive index change and the CDC structure transmission dip wavelength shifts related to the length of D-shape fiber immersed in the liquid, so liquid level is measured by monitoring the dip wavelength. The sensitivities for three different liquids with the RIs of 1.333, 1.355, and 1.377 are 191.89, 208.11, and 213.80 pm/mm, respectively. The temperature influence is also studied. The sensor exhibits a low-temperature cross-sensitivity of −0.128 mm/°C. The proposed modal interferometer based on the D-shape fiber with high sensitivity, low cost, and easy fabrication is suitable to liquid-level sensing applications.

results in visualization of fiber Bragg gratings of type II recorded in birefringent single-mode optical fibers with an elliptical stress cladding with a high concentration of germanium dioxide are shown. Periodic structures of the induced refractive index are inscribed by a single pulse of an excimer laser with a working- gas mixture of ArF using the phase mask. Fiber Bragg gratings into anisotropic optical fiber were investigated by optical and scanning-probe microscopes. It is shown that single-pulse recording by ArF excimer laser creates in the fiber, both inside and on the surface of the quartz cladding, periodic structures, the spatial period of which corresponds to the period of the phase mask, optimized for the +1/–1 diffraction order.

We have experimentally demonstrated the supercontinuum (SC) generation in the As2Se3–As 2S3 multimaterial chalcogenide glass fiber with ultrahigh-numerical aperture (NA∼1.4). The fiber preform was fabricated via a modified one-step coextrusion method before it was drawn into the small-core fiber. With a 10-μm diameter As2Se3 core and a 246-μm diameter As2S3 cladding, the fiber exhibited a zero-dispersion wavelength near 4.5 μm, and a minimum loss around 5.2 dB/m at 5.8 μm. The generated SC spanning from 1.4 to 8.8 μm was generated in a 20-cm-long fiber pumped by a 4.8 μm laser with a short-pulse width of ∼150 fs. The numerical modeling of midinfrared supercontinuum generation in a fiber with an exceptionally high NA at 3.5 and 4.8 μm was presented as well, which were in agreement with their respective experimental results.

A high-sensitive strain sensor based on the anti-resonant reflecting optical waveguide in a double-layered Fabry–Perot resonator is proposed and experimentally demonstrated. A section of the silica hollow core fiber with a small diameter was inserted into a polymethyl methacrylate hollow core fiber with a relative large diameter. A double-layered Fabry–Perot resonator can be formed between the silica cladding and polymethyl methacrylate cladding. Due to the photoelastic effect and thickness change of the cladding in the polymethyl methacrylate hollow core fiber, the resonant condition of the Fabry–Perot resonator is changed. The tensile strain is measured by interrogating the wavelength shift. The experimental results show that the resolution of the sensor can be achieved as 27.9 pm/ $\mu \varepsilon $ , and the temperature cross sensitivity is only 1.67 pm/°C. The proposed fiber sensor can be used for the accurate measurement of the strain.

For the first time, to the best of our knowledge, we demonstrate an all-fiber passively mode-locked thulium-doped fiber ring laser using evanescent field coupling in a tapered fiber with a single-layer graphene as a saturable absorber. The modulation depth limitation of a single-layer graphene is overcome by incorporating the graphene layer along the fiber longitudinal plane, effectively extending the interaction length between the single-layer graphene and the evanescent field. The fiber oscillator produces stable 0.98 ps soliton pulses with a pulse energy of 544 pJ, a 3 dB spectral bandwidth of 4.6 nm, and an RF signal-to-noise ratio of 70 dB.

The conventional optical fiber sensors based on hollow-core fiber (HCF) are suitable for high-temperature measurement. However, the limit effect of HCF’s air core on transmission light is weak and thus result in a large transmission loss. Therefore, this paper proposed and demonstrated a spectrum ameliorative optical fiber temperature sensor based on HCF and inner zinc oxide (ZnO) film. The HCF’s inwall is coated with a layer of thin ZnO film to enhance the limitation on the transmission light and improve the output spectrum. Experimental results show that the extinction ratio of transmission spectrum increase about 5 dB and the spectral pattern is more smooth and uniform. This method of coating film on the HCF’s inwall to improve output spectrum is effective. The proposed sensor can realize high temperature measurement up to 460 °C.

We experimentally investigate the cutoff wavelength shortening effect that occurs when the cladding diameter is reduced. The influence of coating thickness, and thus, cladding diameter, on the transmission loss is also discussed. We derive an empirical model of cutoff wavelength and transmission loss as a function of the cladding diameter and coating thickness. The empirical model reveals that a further reduction in the cladding diameter of step index type bending-loss insensitive fiber (BIF) is possible. The validity of the proposed BIF design is confirmed using a 70-μm cladding diameter BIF and jumper cords. This BIF enables us to construct optical fiber networks with higher reliability.

We have proposed and demonstrated a new refractive index (RI) modulation method based on crystallization in sapphire-derived fibers (SDFs), which are special fibers with a high concentration of alumina in the silica fiber core. Reheating and cooling an SDF with an arc discharge can generate mullite particles in the fiber core. Such crystallization can achieve a maximum RI modulation of ~0.015. Using the point-by-point arc discharge method, crystallization-based long-period gratings (LPGs) can be inscribed in the core of the SDF. Due to the highly modulated RI at the inscribed points, only three to four arc discharge points are required to achieve a strong resonant dip of up to 16 dB in the transmission spectrum of the SDF. The obtained results show that RI modulation by crystallization in SDFs has great potential for the fabrication of functional fiber components that can be applied in high-temperature and -pressure environments.

In this letter, we investigate the response of poly(methylmethacrylate) (PMMA) microstructured polymer optical fiber Bragg gratings (POFBGs) after immersion in methanol/water solutions at room temperature. As the glass transition temperature of solution-equilibrated PMMA differs from the one of solvent-free PMMA, different concentrations of methanol and water lead to various degrees of frozen-in stress relaxation in the fiber. After solvent evaporation, we observe a permanent blue-shift in the grating resonance wavelength. The main contribution in the resonance wavelength shift arises from a permanent change in the size of the fiber. The results are compared with conventional annealing. The proposed methodology is cost-effective as it does not require a climate chamber. Furthermore, it enables an easy-to-control tuning of the resonance wavelength of POFBGs.

A spiral shaped plastic optical fiber (POF) has been constructed and applied for sensing of the refractive index of a sucrose solution. The sensing mechanism is based on evanescent wave interaction between the light travelling within the fiber and the medium surrounding it. Difference in output voltage is observed as the concentration of sucrose solution is varied from 10% to 50%, demonstrating a uniform relation among them. By varying the pitch of the spiral shape and applying strain to the same, the sensitivity of the POF is refined. This spiral-shaped POF sensor is comparatively easy to fabricate, has low cost of operation, and provides real-time sensing-based data.

This work presents method for precision microstructure defects “tapers” and “up-tapers” forming in conventional silica telecommunication multimode optical fibers by commercially available field fusion splicer with modified software sets. We developed technique for micro-defect geometry parameters estimation via analysis of photo-image performed after defect writing and displayed on fusion splicer monitor. Some research results of defect geometry dependence on fusion current and fusion time values re-set in splicer program are represented that provided ability to choose their “the best” combination. Also we produced experimental statistical researches of “taper” and “up-taper” diameter stability as well as their insertion loss values during their writing under fixed corrected splicer program parameters which results are presented in this paper.

We report a fiber-optic sensor for pH measurement, which is a long-period fiber grating (LPFG) coated with smart hydrogel. When the pH of a solution that surrounds the hydrogel coating changes, the volume of the coating and hence its refractive index are changed, which results in a shift in the resonance wavelength of the LPFG. Our experimental sensor shows a sensitivity of ∼0.66 nm/pH over the pH range from 2 to 12 and a response time of less than 2 s. The effects of the refractive index of the surrounding solution and temperature variations on the sensor are also measured.

A capillary covered silica hollow core fiber (HCF) has been designed and tested for the measurement of displacement based on antiresonant reflecting optical waveguide. A section of the silica HCF was inserted into a silver coated capillary. A Fabry–Perot resonator can be formed in the silica cladding. The leaky mode of the guided light can be achieved at resonant wavelengths of the Fabry–Perot resonator, which results in lossy dips in the transmission spectrum. The transmission power of the dip is sensitive with the displacement of the capillary since the effective reflectivity of the Fabry–Perot resonator is affected by the location between the capillary and the silica HCF. The experimental results show that the sensitivity of up to 0.578 dB/μm is achieved, and the proposed sensor is insensitive with the temperature.

This work experimentally demonstrates the supercontinuum (SC) generation in a three-hole arsenic free Ge 20 Sb 15 Se 65 chalcogenide suspended-core fiber. Mechanical drilling was used to prepare the chalcogenide glass preform, which was drawn into suspended-core fibers. The zero-dispersion wavelength of the fiber is moved toward the shorter wavelength of about 3.2 μm through changing the fiber core diameter by controlling the pressure of inert gas during fiber drawing. When a 15 cm-long fiber with a core diameter of 6 μm is pumped using 150 fs pulses at 3.3 μm, SC spanning from ∼3 μm to ∼8 μm was generated.

A new type of thermally sensitive fibers with an antimony selenide (Sb 2 Se 3 ) core and phosphate glass cladding is demonstrated. The fibers were fabricated by a molten core method and maintained overall diameters ranging from 250 to 800 μm and core diameters of 35–200 μm. A 2.8 cm long Sb 2 Se 3 core fiber, electrically contacted to external circuitry through fiber end facets, exhibited a four orders of magnitude change in conductivity after the whole fiber was heated from 25 to 195 °C. In addition, the fiber exhibited enhanced photoconductivity under illumination. These results indicate that Sb 2 Se 3 core multimaterial fibers have promising applications in temperature sensing, optical switches and photodetectors.

This paper describes a dual-wavelength demonstration for a proposed ytterbium-doped fiber laser in the 1 μm region. A microfiber and a D-shaped fiber, functioning as a wavelength selective filter, is inserted into the laser ring cavity setup to ensure a stable dual wavelength operation. The dual-wavelength output from both the microfiber and the D-shaped fiber possess a wavelength spacing of 4.01 and 4.62 nm, respectively. Both the microfiber and D-shaped fiber use the ytterbium doped fiber as gain medium, and has a stable peak power and side-mode suppression ratio of more than 30 dB.

This paper presents a novel hydrostatic pressure sensor using high birefringence photonic crystal fibers (PCFs), featuring an enhanced sensitivity with wide range of detection along the length of fiber. The proposed PCFs exhibit higher order of birefringence as ~10−2, which is achieved by the introduction of two elliptical hollow channels stressed at major axis in the cladding region. The consequence of these two elliptical air holes is investigated to enhance the pressure sensitivity. This paper promises to yield very large pressure sensitivity of 87.5 pm/MPa through its transmission spectrum at a pitch constant of $1.5~ {{\mu }} \mathrm{m}$ with $0.468~{{\mu }} \mathrm{m}$ of minor axis of elliptical cladding in a fiber length of 1 cm.

We investigate a few-mode multicore fiber structure suitable for realizing a high spatial density while maintaining a feasible cladding diameter. First, we discuss the impact of cladding diameter on mechanical reliability, and set a target cladding diameter of less than 250 μm to maintain a comparable reliability to conventional fiber. We then optimize the 6-mode core profile to obtain a low differential mode delay (DMD) characteristic and reveal that a hexagonally arranged 19-core structure can realize more than 100 spatial channels with a cladding diameter of less than 250 μm. Finally, we fabricate 6-mode 19-core fiber with a 246 μm cladding diameter and realize a relative core multiplicity factor of more than 60 with a low loss and a DMD of less than 0.24 dB/km and 0.33 ns/km, respectively.

We demonstrated remarkably enhanced 2.7 μm emission in glass-ceramic (GC) fibers containing NaYF4:Er3+ nanocrystals with 980 nm excitation for the first time. The melt-in-tube technique is of scientific and technical significance for the fabrication of GC fibers in comparison to the conventional rod-in-tube technique. The obtained precursor fibers, in which the structure can be maintained well, exhibit no obvious element diffusion or crystallization during the fiber-drawing process. After a careful heat treatment, NaYF4 nanocrystals were controllably precipitated in the glass fiber core. Owing to the incorporation of Er3+ ions into the low phonon energy NaYF4 nanocrystals, enhanced 2.7 μm emission was achieved from the Er3+-doped GC fibers, which was almost undetectable in precursor fibers due to the high phonon energy of the borosilicate glass fiber matrix. Moreover, the 2.7 μm emission lifetime was obtained due to the excellent emission properties of Er3+ in the GC fibers. The transmission loss values of precursor fibers and GC fibers at 1310 nm were measured to be 7.44 dB m−1 and 11.81 dB m−1, respectively. In addition, a theoretical simulation based on the rate equations and propagation equations was performed to evaluate the possibility of 2.7 μm laser output. The excellent optical properties endow the GC fibers with potential applications for mid-infrared fiber lasers.

We report a new fiber optic sensor for temperature measurement at a temperature range of up to 900 °C with excellent stability and repeatability. The sensing head is comprised of a short hollow-core fiber segment spliced between two single-mode fibers using a commercial splicer. Optical power from the lead-in fiber is partly coupled to silica cladding of the hollow-core fiber with the remainder propagating in air core by short distance. The two beams are then re-coupled to the core of the lead-out fiber, owing to the offset splicing joint. Due to the effective index difference between the two beams, an interference pattern in the transmission spectrum is obtained. The distinct thermo-optic coefficients between silica and air result in a high-temperature sensitivity of 41 pm/ °C, and the enclosed structure ensures its immunity to the external refractive index.

All solid-state PbS quantum dot (QD)-doped glass fibers with tunable near-infrared (NIR) emission were successfully fabricated by using the “melt-in-tube” method for the first time. The precursor fibers were first prepared without any obvious element diffusion or crystallization by drawing the fiber preform at a heating temperature at which the fiber core was already melted while the fiber cladding was softened. Then the PbS QDs were precipitated evenly in the matrix of the glass fiber core after a careful heat treatment at low temperature. From the PbS QD-doped glass fibers, intense wavelength-tunable broad NIR emission bands were observed upon excitation with an 808 nm laser. The transmission loss of the fibers can be reduced by further matching the thermal expansion of the fiber core and cladding glass. Therefore, after further optimizing the composition and optical properties of the PbS QD-doped glass fiber, it is expected to be a potential gain medium for the development of wavelength-tunable lasers and broadband fiber amplifiers. More importantly, the melt-in-tube method exhibits a feature of completely controllable crystallization in the fiber formation process, which would open a new route for fabricating novel functional QD-doped glass fibers.

We propose a model and then demonstrate a technique that can be used to optimize pump absorption in active multimode fibers with different cladding geometries, by varying the angle of pump light excitation. The analysis of the contribution of different ray groups at different wavelengths enables the design optimization of active and passive fiber components in fiber lasers. Refereed/Peer-reviewed

This paper presents a study of propagation of radially and azimuthally polarized cylindrical vector modes in six-strut suspended core fibers based on finite element simulations. The study shows that large effective index differences in the order of $10^{-3}- 10^{-2}$ of these modes can be achieved in the suspended core fibers with core diameter of less than 2 μ m, material index 1.45 of silica to 2.0 of tellurite, and wavelength of 750 nm, allowing the stable propagation of the first higher order modes in doughnut shape within these fibers. The effective index difference and the field intensity of these cylindrical vector modes can be tuned by selecting appropriate fiber material and core size. The study shows that the suspended core fiber can be a competitive candidate for fiber-based high-resolution stimulated emission depletion nanoscopy application.

Photonic Crystal Fibers (PCFs) generate great interest in the field of optical fiber technology because of its ability to tailor different optical characteristics such as birefringence, dispersion, mode area, nonlinearity etc. High index non silica based glass fibers have high nonlinearity and low loss in mid-infrared wavelength transmission. Out of this, tellurite glass is a highly suitable fiber material for infrared nonlinear applications because of its high nonlinear coefficient compared to other non-silica glasses. Typically in Photonic Crystal Fibers, air holes are arranged in hexagonal or octagonal structure. In the present investigation, a circular lattice PCF is designed with tellurite core and various optical properties such as confinement loss, effective mode area, dispersion and nonlinear coefficient are analyzed using COMSOL MultiPhysics. The proposed fiber gives very high nonlinearity with a maximum of 12,100 W −1 km −1 at 0.45 μm, ultra high negative dispersion and very low confinement loss for a wide range of wavelengths. High nonlinearity is suitable for super continuum generation. This fiber can also be used as a dispersion compensation fiber.

We present composition development of borosilicate glasses for fabrication of high refractive index contrast, all-solid photonic crystal fibers. An oxide system composed of SiO 2 B 2 O 3 Al 2 O 3 Li 2 O Na 2 O K 2 O was adjusted to match thermal properties of selected highly nonlinear, lead bismuth gallium silicate glass. A high difference of refractive index of 0.376 is achieved at a wavelength of 1550 nm. We proved experimentally that the developed pair of glasses enables to draw optical fibers, and we propose a design of a photonic crystal fiber structure for broadband supercontinuum generation.

In this article we compared two models of the highly birefringent photonic crystal fiber using a full vectorial finite element method with anisotropic perfectly matched boundary layers. High birefringence and low confinement loss are successfully achieved in both fibers. The zero dispersion wavelengths are achieved for both structures in the near infrared region. The simulation results revealed that it is possible to obtain the zero dispersion at the near infrared wavelength with low confinement loss and high birefringence by changing the structural parameters of the photonic crystal fiber. Such fibers are very useful for polarization maintaining devices, dispersion compensating devices, sensing applications and nonlinear application.

We propose a design for a hollow core photonic bandgap fiber (HC-PBF), with a quasi-elliptical core region stacked by modified periodic capillary tubes. This type of HC-PBF possesses birefringence > 4.6×10 -4 in the wavelength range of 1.46-1.59 μm, and a low confinement loss of

In this paper we present a large mode area photonic crystal fiber made of the heavy metal oxide glass CS-740, dedicated for a broadband light guidance in the visible, near- and mid-infrared regions of wavelengths from 0.4 to 4.7 μm. The fiber is effectively multi-mode in the considered wavelength range. It is composed of a ring of air-holes surrounding the core, with a high linear filling factor of 0.97. The fiber was made using a standard stack-and-draw technique. Each hole has a size of approx. 2.5 × 3.0 μm and diameter of core is 80 μm. Fiber attenuation is below 3 dB/m in the 0.9–1.7 μm wavelength range, while at 4.4 μm (mid-IR) it is approx. 5 dB/cm. Bending loss at the 1.55 μm wavelength is 0.45 dB per loop of 8 mm radius. Fiber numerical aperture is 0.53 at 1.55 μm. The effective mode area of the fundamental mode is approx. 2400 μm 2 in the wavelength range of 0.8–1.7 μm. We present a proof-of-concept demonstration that our large core photonic crystal fiber is able to efficiently collect light directly from a mid-IR quantum cascade laser without use of additional optics and can be used for pigtailing mid-IR sources and detectors.

Gain enhancement of single-mode Cr-doped crystalline core fiber (SMCDCCF) with longer fiber length fabricated by online laser-heated pedestal growth (LHPG) technique is demonstrated. In comparison with the SMCDCCF fabricated without online growth, the online technique enables real-time monitoring and controlling small molten zone in the LHPG to achieve longer length with better uniformity and smaller core diameter of the SMCDCCFs. The SMCDCCF exhibits a length of 10.6 cm, a core diameter of 25 mu m, and a V-value of 2.40, which confirms the LP01 single-mode operation by the far-field pattern measurement. A 3.9-dB gross gain and a 1.9-dB net gain of the SMCDCCF at the wavelength of 1400 nm were obtained. The gross and net gains are the highest yet reported of the SMCDCCFs. Further development on higher gain of the SMCDCCF may be functioned the SMCDCCF as a broadband fiber amplifier for use in the next-generation fiber transmission systems.

A plastic optical fiber (POF) probe with a macro-bending tapered structure was proposed and optimized for the refractive index (RI) sensing. The principle of operation is based on the macro-bending loss and evanescent wave, which are introduced by the macro-bending tapered structure on the fiber, and modulated by the environmental RI. A heating and drawing method and thermal setting process were used to fabricate a tapered POF and form a stable macro-bending structure for the probe. The probes with cladding and without cladding were fabricated. By changing the taper waist and curvature radius, the sensing performance of the probe was optimized. The highest sensitivity of the probe with cladding reached 937%/RIU in the RI range of 1.33–1.41. By removing the cladding, the RI sensing range was expanded to 1.33–1.45, and the sensitivity was about 800%/RIU, lower than the ones with cladding. In addition, the temperature dependence of the sensor was investigated. The POF probe is a low cost solution for RI sensing applications, which has the features of simple structure, compact, and intensity modulation at visible wavelength.

The paper presents a numerical analysis of influence of polymerization shrinkage on selected polymer and silica-based highly birefringent (HB) optical fibers embedded in a composite material. Since polymerization is a chemical process consisting in combining many molecules into a macromolecular compound, the direction of polymerization shrinkage depends on the number of constituent composite surfaces. A detailed analysis of the piezo-optic effects occurring in HB fibers before and after the lamination process is presented. An answer to the question to what extent we are able to properly diagnose a degree of degradation of the material is also provided.

Glass optical fibers are almost always made from silica; however, some other materials, such as fluorozirconate, fluoroaluminate, and chalcogenide glasses, are used for longer-wavelength infrared applications. Most glasses demonstrate a refractive index of about 1.5. Typically, the difference between core and cladding is less than 1 %.