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This letter reports a multiplexed optical oil level meter using a thin core fiber (TCF) cladding mode exciter. Weak cladding mode reflection (

In this paper, a new circular microstructured optical fiber (C-MOF) based upon photonic band gap (PBG) light guiding mechanism is proposed which can be used for dispersion compensation in optical transmission systems. The C-MOF core is made up of silica glass and the holes in the cladding network are filled with As 2 Se 3 chalcogenide glass. By selecting an appropriate geometrical parameters for the structure, the dispersion and confinement losses of the proposed C-MOF at 1.55 μm are respectively calculated to be −2450 ps/nm/km and 0.013 dB/m. Relative dispersion slope (RDS) of the C-MOF at 1.55 μm is about 0.00332 nm −1 . The proposed C-MOF is suitable for use in wavelength division multiplexing and dispersion compensating systems in optical fiber transmission networks.

We present a long-period fiber grating sensor composed of a tapered optical fiber embedded in a polymeric grating. The fabrication process is based on a mold-replica approach, thus yielding low-cost reproducible structures. We evaluate the sensitivity to temperature and refractive index changes showing that the proposed structures could render useful for developing sensors with biocompatible polymers.

We demonstrate a high refractive index (RI) liquid level sensor based on coreless multimode fiber (CMF) which is capable of measuring the liquid level and discriminating the high RI. The direct exposure of the CMF enables a strong interaction between the high-order modes guided in it and the surrounding medium through evanescent wave. Part of the energy leak out at the fiber/liquid interface when the RI of the liquid exceeds that of the CMF. The transmission of the single-mode fiber (SMF)-CMF-SMF structure is a function of both the liquid level and RI which experiences leakage loss with the increasing liquid level. Liquid level information can be determined by simply selecting a wavelength range with linear power variation. The proposed sensor with 4.1-cm CMF has approximately linear responses of −0.223, −0.253, −0.316, −0.392, and −0.461 dB/mm for glycerol solution concentrations of 98%, 96%, 92%, 88%, and 84% in a 2-nm wavelength range, respectively. Such a simple and low-cost sensor may be integrated as biochemical probes, indicating preferable sensing performance and practicability.

Nonlinear microstructured optical fibers (MOFs) offer better prospects in various interdisciplinary fields than conventional nonlinear fibers. High air filling fraction and small core are necessary to ensure high nonlinearity of MOFs. The air holes adjacent to the core can be elongated and tapered into the core in a controlled way during fiber drawing so that the solid core seems to be suspended in air with very thin silica struts connecting it to the matrix. This reduces the effective core area thereby increasing nonlinearity. In this study, the effect of core suspension on the nonlinearity and dispersion of MOFs are systematically investigated on the basis of a geometrical design parameter called suspension factor (SF). Detailed study reveals that MOF designs with enhanced nonlinearity can be obtained even with larger pitch and such MOF structures are easier to fabricate. Fiber drawing parameters which control the SF are precisely identified and optimized. Several fiber samples were drawn at different drawing conditions under constant monitoring and it was observed that high furnace temperature and high drawing speed are the two key parameters that ensure high SF. Further, the role of SF on nonlinear spectral broadening was experimentally investigated and it was found that MOF having high SF offers almost two octave-spanning supercontinuum.

We reported a gas pressure sensor based on CO 2 -laser-induced long-period fiber grating (LPFG) in an air-core photonic bandgap fiber (PBF). The LPFG was inscribed in an air-core PBF by the use of an improved CO 2 laser system with an ultraprecision 2-D scanning technique, which induced periodic collapses of air holes along the axis of the PBF. Such an LPFG could be used to develop a promising gas pressure sensor with a sensitivity of -137 pm/MPa. Moreover, a simplified fiber model with a relatively similar elastic response was developed to qualitatively study the gas pressure response of the LPFG inscribed in the air-core PBF. A simulated stress distribution along the LPFG revealed that the gas pressure leads to a stress concentration at the collapsed area of the air holes in the fiber cladding, which finally results in a resonant wavelength shift of the LPFG through an elastooptical effect.

The processes of surface plasmon resonance excitation in a bent single-mode optical fiber with a metallized cladding have been studied experimentally. It is shown that, for a certain combination of the bending radius of an optical fiber and the thickness of a metal film, a strong coupling between the fundamental and plasmon–polariton mode is achieved through a whispering gallery mode supported by the fiber cladding, which leads to the formation of a resonance dip with a depth of ~30 dB or more in the transmission spectrum of an optical fiber loop. The position of the dip depends strongly on the ambient refractive index, which provides the possibility of refractometric measurements with a spectral sensitivity of ~5 μm/RIU and a resolution of ~4 × 10–6. Limits of measurement of the refractive index are determined by the operating spectral range and the bending radius of the optical fiber and are 1.42–1.44 for the setup used.

Elemental bismuth (Bi) exhibits a high magnetoresistance as a typical example of semimetal, which has significant application in information technologies. Silicate glass-clad Bi core fibers were fabricated by a molten core method and maintained core diameter of 100–150 µm and overall diameter of 300–450 µm. X-ray diffraction (XRD) and micro-Raman spectra showed the core to be highly crystalline with no observed secondary phases. Electro-probe micro-analyzer (EPMA) measurements confirmed a very well-defined core-clad interface. Demonstration of fibers with high magnetoresistance core materials and the potential integration with current state of the art technologies represents the first step in providing the building blocks for all-fiber sensors.

We proposed an efficient and universal sensitivity amplification method for most kinds of sensors based on fiber in-line two-beam Fabry–Perot interferometers (FPIs) by using the femtosecond laser exposure. As an example of two beam FPI, a liquid-pressure sensor based on a micro-bubble at the end of the single mode fiber (SMF) was fabricated. To improve the sensitivity, a third refection mirror in SMF near the bubble at a certain distance was fabricated by using femtosecond laser exposure. As a result, the Vernier effect is generated, which improves the pressure sensitivity from −0.414 nm/MPa to −3.973 nm/MPa. Besides, the synchronous measurement of liquid-pressure and temperature can be achieved by monitoring the interference peak and the Vernier envelope at the same time.

We demonstrate a low noise, GHz sweeping bandwidth all silica fiber single-frequency distributed Bragg reflection laser and a 160W power fiber amplifier at 1992.6 nm for next-generation gravitational wave detection.

International audience; In this paper, we demonstrate a single-polarization feature out of passive very-large-mode-area fully aperiodic large-pitch fibers. It has been previously shown theoretically that one of the two polarizations of the fundamental mode is selectively coupled to a cladding mode. This coupling does not require fiber bending, which permits us to avoid any decrease in mode effective area. The coupling is achieved owing to boron-doped silica inclusions implemented into the microstructured cladding and acting as stress-applying parts. This mechanism has been assessed experimentally in this work using fibers of two different core diameters: 60 μm and 140 μm, providing mode field areas of 3637 μm2 and 14,590 μm2, respectively, at 1942 nm. The tested fibers have a length of 45 cm and an outer diameter exceeding 1 mm, yielding rod-type fibers. Each sample has been characterized using an unpolarized laser source emitting at 1942 nm. This laser, based on a thulium-doped large-mode-area step-index fiber, has a spectral bandwidth of about 0.5 nm. After passing through a piece of the passive fiber, a polarization extinction ratio higher than 16 dB has been achieved.

With a view towards the application in space-borne optical instruments, we first performed a world-wide market survey of infrared fibers designed for the wavelength range of 1.5 μm to 18 μm. Fiber samples purchased and tested comprise fluoride fibers, chalcogenide fibers, a germanate fiber and a silver-halide fiber, as well as hollow fibers. While the majority of infrared fibers offered are of the multi-mode type, three of the fluoride fibers are single-mode. We report on the polarization degrading effect of a single-mode fiber and present a possible solution to achieve polarization maintainance by twisting the fiber. Secondly we report on measurements of numerical aperture, output beam profile, and attenuation of a hollow fiber. The measurements were performed at the wavelengths of λ= 3.39 μm and λ= 10.6 μm.

We report a new efficient light guidance along a liquid core using an open V-groove. Guiding properties were analyzed using finite element method in terms of the single mode guidance condition, and the corresponding modal birefringence. We experimentally demonstrated a silica V-groove fiber with an opening angle of 40°, which was spliced to single mode fibers at both ends. A liquid with the refractive index of 1.455 was filled to serve as a core along a maximum length of 47cm. We confirmed the single mode guidance and birefringence consistent to theory, which will enable polarimetric liquid sensing.

We report on the fabrication and characterization of 19-cell hypocycloid-shape Kagome fibers with core size larger than 100 μm. These inhibited coupling fibers present low propagation loss (100 dB/km) over broad transmission range with low chromatic dispersion combined with ultra-low power overlap with silica surround, making them an efficient solution for ultra-high power laser handling, ultra-fast laser delivery, and plasma photonics applications.

Analysis of the experimental data on microscopic, absorptive, fluorescent, and Raman-scattering properties of Bismuth (Bi)-doped yttria-alumino-silicate glass (Y-Al-SiO 2 :Bi)-based nanoengineered optical fibers, exhibiting broadband near-infrared fluorescence, is presented. Among the other well-established characteristics, inherent to Bi-doped silica fibers codoped with Aluminum (Al), a trend of spatial distributions of Bi atoms and Bi-related fluorescence-active centers is determined, being their concentrating in ring-like areas around the core's center, at approximately a half-distance to core/cladding interface. At the same time, the formation in this region of nanosized Bi clusters, supposedly weakly or nonfluorescing, is revealed for the fibers. These phenomena are argued to underlie worsening of the pump-to-signal overlap factor, which deteriorates efficiency of lasers and amplifiers based on such or similar Bi-doped alumino-silicate fibers.

The paper demonstrates a standardized process of vapor phase doping to fabricate large core Yb–doped preforms with longer useful length in reproducible manner. The optimization of the process led to successful achievement of Yb-doped core thickness of 4.5 mm (in 14.8 mm of preform diameter) by depositing up to 30 number of core layers with controlled amount of generated precursor vapors. The influence of the process parameters was studied rigorously to enhance the useful preform length up to 380 mm. A combination of Yb and Al in different proportions was doped into the core with uniform dopant concentration along the length by adjusting few process parameters efficiently. The Al2O3 concentration up to the level of 17.8 mol% has been achieved successfully which resulted in NA of 0.31. This is the highest ever doping of Al in passive fibers by any modified chemical vapor deposition process. The Yb2O3 content in the active fibers is as high as 0.47 mol%.

The effect of the cross-sectional structure of metal-filled side-hole fiber on the birefringence and thermooptic properties was investigated by the fiber-optic Sagnac loop interferometry. The optical fibers having different cross-sectional structures filled with indium metal were fabricated by drawing a fiber preform with two side holes at different temperatures followed by metal infiltration. The original circular core and two identical holes in the fiber preform were deformed into the fiber core with various core ellipticities and different hole diameters after the drawing. It was found that the fiber birefringence ( ${\boldsymbol B}$ ) and the temperature dependence were strongly influenced by the deformation of the fiber cross section, the birefringence increased from $5.68 \,{\times}\, 10 ^{-5}$ to $1.16 \,{\times}\, 10^{-4}$ with the increase of the core ellipticity from $0.273$ to $0.412$ . Additional birefringence was found to be induced after the infiltration of indium into holes due to the large thermal expansion mismatch between indium and silica glass of the fiber. The temperature sensitivities of the unfilled side-hole fibers ( d( δλ $_{n}$ )/dT ) were almost the same and found to be constant of ∼− $0.60$ nm/K regardless of the fiber cross sections. On the other hand, the sensitivities of the indium-filled side-hole fibers ( d( δλ $_{m}$ )/dT ) were enhanced 10–15 times larger than those of the unfilled side-hole fibers, increased from − $5.98$ to − $11.03$ nm/K with the increase of the filler indium diameter from ∼ $18.5$ to $24.1$ μm, respectively.

We report a highly sensitive refractive index (RI) sensor in the aqueous solution, which is based on an 81°-tilted fiber grating structure inscribed into a thin cladding fiber with 40 μm cladding radius. The numerical analysis has indicated that the RI sensitivity of cladding resonance mode of the grating can be significantly enhanced with reducing cladding size. This has been proved by the experimental results as the RI sensitivities of TM and TE resonance peaks in the index region of 1.345 have been increased to 1180 nm/RIU and 1150 nm/RIU, respectively, from only 200 and 170 nm/RIU for the same grating structure inscribed in standard telecom fiber with 62.5-μm cladding radius. Although the temperature sensitivity has also increased, the change in temperature sensitivity is still insignificant in comparison with RI sensitivity enhancement.

The fabrication and characterization of a tellurite based high numerical aperture magneto-optical glass fiber are presented. Different glass groups were investigated in terms of their structural, thermal, mechanical, optical and magnetic performance as a core/cladding pair and their refractive index contributions to the numerical aperture. A well matched core/cladding pair was selected: 75%TeO 2 –20%ZnO–5%Na 2 O (mol.%) for core glass, 42%TeO 2 –18%ZnO–15%K 2 O–20%Ge 2 O–5SiO 2 (mol.%) for cladding glass. The fibers have a good cross section and a numerical aperture as high as 0.9. The Verdet constant of this high numerical aperture fiber was close to that of bulk glass.

An optical fiber inclinometer applying modal interference based on an abrupt tapering cascading a peanut-shape configuration is proposed. The abrupt taper splits part of the core mode into cladding modes and the interference occurs when the peanut-shape recombines the cladding modes and core mode together. Four inclinometers with different lengths have been fabricated and characterized, and the high sensitivities of -1.76 and -4.49 nm/° are obtained in the angle range of 0°-3° and 3°-6.66°, respectively.

A highly sensitive temperature sensor based on an all-fiber Mach-Zehnder interferometer using a selectively polymer-filled two-core photonic crystal fiber is experimentally demonstrated. The sensor fiber was made by the manual gluing and subsequent infiltration of polymer; the cladding air holes surrounding one core were selectively filled with a polymer material with a high thermo-optic (TO) coefficient while leaving those of the other core unfilled, and this led to the large TO mismatch between two cores. It was found from measurements that a very high temperature sensitivity of 1.595 nm/°C could be achieved, which was more than two orders of magnitude higher than that of the sensor fiber before the selective filling process.

Glass-ceramic fibers containing Cr3+-doped ZnAl2O4 nanocrystals were fabricated by the melt-in-tube method and successive heat treatment. The obtained fibers were characterized by electro-probe micro-analyzer, X-ray diffraction, Raman spectrum and high-resolution transmission electron microscopy. In our process, fibers were precursor at the drawing temperature where the fiber core glass was melted while the clad was softened. No obvious element interdiffusion between the core and the clad section or crystallization was observed in precursor fiber. After heat treatment, ZnAl2O4 nanocrystals with diameters ranging from 1.0 to 6.3 nm were precipitated in the fiber core. In comparison to precursor fiber, the glass-ceramic fiber exhibits broadband emission from Cr3+ when excited at 532 nm, making Cr3+-doped glass-ceramic fiber a promising material for broadband tunable fiber laser. Furthermore, the melt-in-tube method demonstrated here may open a new gate toward the fabrication of novel glass-ceramic fibers.

A miniaturized fiber tip Fabry–Perot interferometer (FPI) with Pt/WO3 coating was demonstrated as a hydrogen sensor. The air-cavity of FPI was formed by inserting a single mode fiber into a partially polymer-filled glass capillary, which was highly sensitive to temperature. A layer of Pt/WO3 was coated on the glass capillary of the FPI serving as a reaction heater upon hydrogen exposure. The heat locally raised the FPI temperature, which led to the wavelength shift of interference spectrum. The average wavelength shift of sensor's two interference dips was –20.3 nm upon exposure to ∼20000-ppm hydrogen concentration. The hydrogen sensitivity of the sensor was estimated to be better than 1 pm/ppm.

A compact fiber Mach–Zehnder interferometer based on tapered hollow optical fiber (THOF) has been demonstrated. The THOF is sandwiched between two single mode fibers (SMFs), forming a SMF-THOF-SMF (STS) structure. The discharging during the splicing and tapering processes induces the collapsed regions in the hollow fiber, which form the modal coupling/re-coupling areas of the interferometer. The THOF has a length of about 2 mm and the taper waist diameter is about 66.5 $\mu \text{m}$ . The refractive index (RI), stress, and temperature response properties of the STS interferometer have been investigated, which show a high RI sensitivity and low temperature cross-sensitivity. The STS interferometer holds the merits of compact structure, low cost and easy fabrication, making it a suitable candidate in the biochemical and physical sensing fields.

The fabrication and characterization of an optical fiber refractometer based on lossy mode resonances (LMR) is presented. TiO2/poly (sodium 4-styrenesulfonate) (PSS) coatings deposited on side-polished D-shaped optical fibers are used as LMR supporting coatings. LMRs are sensitive to the external medium refractive index, and D-shaped optical fibers enable the observation of TE and TM LMR polarizations. These refractometers based on TE and TM LMR showed an average sensitivity of 2737 nm/RIU and 2893 nm/RIU, respectively, for a surrounding medium refractive index range from 1.35 to 1.41. This study also explores the utilization of previously described refractometers in the context of two common industrial applications, such as the determination of the sugar content or °Brix in beverages and the salt concentration in sea water.

We report the fabrication of a fiberized micrometer-size ridge waveguide using a sheet-stacking method. The fabrication conditions for maintaining the ridge geometry with micrometer dimensions were investigated and discussed. A loss of 3.9 dB/m was measured at 1.55 µm in the fiber ridge waveguide, showing no extra loss above the bulk loss of the glass. A high birefringence of 9.5 x 10-3 was measured in the waveguide at 1.55 µm which is close to the reported highest birefringence (1.1 x 10-2) in optical fibers. Fusion splicing was successfully employed to splice the fabricated waveguide to a conventional silica fiber with reasonable loss.

In this paper, a novel refractive index sensor based on liquid infiltrated dual-core photonic crystal fibers (PCFs) is proposed. The two fiber cores, separated by an air hole inside the cross-section of the designed PCFs, are filled with analyte liquids which form two independent waveguides. A novel and simple refractive index sensing system is proposed using mode coupling theory and its sensing performances have been studied numerically. The results show that the refractive index sensor with 1 cm length PCF has a large sensing range and high sensitivity of −65,166.10 nm/RIU at wavelength 1.25 μm.

The interaction between longitudinal acoustic waves and fiber Bragg gratings in suspended-core optical fibers is numerically investigated. The fiber core size and the air hole size are varied, and the mechanical and grating properties are simulated by means of the finite element method and the transfer matrix method, respectively. Changes of the effective index, confinement factor, silica area, strain and wavelength shift induced by the acoustic wave are evaluated, and the resultant side lobe reflectivity is estimated. A side lobe reflectivity increase of 66% compared to standard fibers is estimated, which allows reducing the modulation index or the grating length in as much as 75%. Besides, the larger reduction of the required acoustic power for achieving the acousto-optic modulation points out to more efficient modulator devices in suspended-core fibers.

A simple and compact optical fiber relative humidity (RH) sensor based on SiO2 nanoparticles has been proposed and experimentally demonstrated in this paper. S-taper fiber is fabricated as the sensitive element using simple fusion spicing and the S-tapered region is coated with a layer of hydrophilic material by direct immersion into the SiO2 nanoparticle solution. The resonance wavelength as well as peak transmission are both sensitive to environmental humidity due to the change of effective cladding refractive index caused by the strong surface absorption of the porous SiO2 nanoparticle coating with hydrate activity. Experimental results show that this humidity sensor has a good reversibility from 26.5%RH to 95.2%RH and a good linearity from 83.8%RH to 95.2%RH. The maximum sensitivities of 1.1718 nm/%RH and 0.441 dB/%RH have been achieved for a high humidity range of 83.8%RH to 95.2%RH. The proposed humidity sensor has such distinguished features as compact size, low cost, and ease of fabrication, and it has potential applications for high humidity environments.

In this letter, we reported long period fiber gratings (LPFGs) fabricated by femtosecond laser pulses direct writing in grapefruit microstructured fiber. The mode field distribution and dispersion property of this fiber was analyzed by finite-element method. Two LPFGs were fabricated with different periods of 230 and $250~\mu \text{m}$ , the resonant dips appeared at the wavelengths of 1325.8 and 1449.4 nm, respectively. In addition, sensing characteristics of the LPFG with the period of $250~\mu \text{m}$ were investigated in theory and experiment. The experimental results show that the strain and temperature sensitivities are 1.88 pm/ $\mu \varepsilon $ and 0.267 pm/°C, respectively. It indicates that the temperature cross sensitivity is as low as $0.142~\mu \varepsilon $ /°C.

Bandwidth and steady-state loss of multimode glass W-type optical fibers (doubly clad fibers with three functional layers) are evaluated for the varied fiber design and launch beam parameters. These transmission characteristics are determined from the solution of the time-dependent power flow equation by the explicit finite difference method. Results are presented in a graph form as functions either of the fiber length or loss for the varied thickness and depth of the fiber׳s intermediate layer (inner cladding), fiber׳s coupling strength, and input beam (mean angle and width). The trade-off relation between the bandwidth and steady-state loss for designing multimode glass W-type optical fibers is shown in graphs and highlighted the text. We found that bandwidth improves with thinner and shallower intermediate layers, narrower and more central launch-beam, and stronger mode coupling.

A novel Michelson interferometer based on a bi-taper is achieved. Such a device is fabricated by splicing a section of thin core fiber (TCF) at one end of single-mode fiber (SMF). Due to the fiber bi-taper at the splicing point of SMF and TCF, the light is coupled into the fiber core and cladding from lead in fiber core. The light will be reflected at the end of the fiber and then will be recoupled back into the lead out fiber core by the fiber bi-taper. While the light returns back to the lead out fiber, the intermodal interference will occur for the optical path difference between core mode and cladding mode. A high temperature sensitivity of 0.140 nm/°C is achieved from 30 to 800 °C, and the linearity is 99.9%. The configuration features the advantages of easy fabrication, a compact size, high sensitivity, wide sensing range and high mechanical strength, making it a good candidate for distant temperature sensing and oil prospecting.

Femtosecond laser exposure is used to fabricate a fiber Bragg grating (FBG) over a fiber core cladding on a short section of photon-sensitive thin-core fiber (TCF) using a side-illumination technique. The cladding modes are excited in the fusion region due to the core mismatch between the leading-in single-mode fiber and the TCF, and one resonant cladding mode and core mode are then transmitted downstream as separate wavelengths by the FBG. Furthermore, the transmission intensities for the two resonant dips could be controlled by changing the focal-line position of laser beam. Because the cladding modes have unique field shapes, they react to perturbations both inside and outside the fiber, which makes them good candidates for measuring fiber bending and ambient refractive index variation.

In this study, a model was set up for simulating the effects of varying fiber cross-sectional shapes on ultraviolet protection of fibers. The fiber diameter and fiber type were also involved in the model setting. Experiments of diffuse reflectance spectra measurement on natural (wool, cotton, silk), regenerated (bamboo viscose) and synthetic (polyester, nylon) fibers were conducted to verify the model predicted results. When a more complex shape was assumed as the fiber cross-section for model calculation, the predicted results have a better agreement with the actual results. The effects on ultraviolet absorption from fibers with different cross-sectional shapes were investigated at a single fiber, fiber bundle and yarn levels. With the same material, when the fiber cross-sectional area and the areal coverage of a single fiber were constant, the triangular shape had the lowest ultraviolet transmittance and the highest ultraviolet reflectance for a single fiber and also for a fiber bundle. The difference of fiber cross-sectional shapes was also significant in the ultraviolet protection of a single yarn.

A directional bend sensor based on selectively infiltrated photonic crystal fiber is demonstrated. The device is fabricated by use of femtosecond laser micromachining technique and fusion splicing of photonic crystal fiber with single-mode fiber. By infiltrating refractive index liquid into one of the air holes of the photonic crystal fiber, the core mode can be coupled into the higher order liquid rod mode, thus producing a resonant dip in the transmission spectrum of the device. Such a dip wavelength is sensitive to both the bending curvature and the direction, and has a linear response to curvature within a large range from 0 to 10.7 m $^{-1}$ .

We proposed and demonstrated a novel scheme for simultaneous measurement of temperature and refractive index (RI) by cascading a liquid-filled photonics crystal fiber (PCF) to a long period fiber grating (LPFG) written in a single-mode fiber. The liquid-filled PCF showed a high-temperature sensitivity of 1.695 nm/°C, which is two orders of magnitude higher than that of the LPFG (0.0642 nm/°C). The LPFG exhibited a blue shift with the increased RI. In contrast, liquid-filled PCF showed a total immunity to the surrounding RI. So, the temperature was solely measured by the liquid-filled PCF, and the RI information was extracted from the total response of the LPFG with the temperature effect having been compensated by the liquid-filled PCF.

We propose and study the characteristics of a novel gas-clad surface plasmon resonance (SPR)-based fiber optic sensor. The proposed fiber optic probe not only senses change in the refractive index of the environment surrounding the outer layer of the probe but also shows the potential of detecting different gases in cladding holes. We have carried out the study of sensing probe of gas-clad fiber with nitrogen gas filled in air holes of the primary cladding. Silica is used as a second cladding of the gas-clad fiber with ITO film over this secondary cladding as a plasmonic metal layer. To optimize the probe design, figure of merit (FOM) and detection accuracy (DA) are calculated for varying thicknesses of different layers.

Fibers exhibiting flattened and decreasing dispersion are important in nonlinear applications. Such fibers are difficult to design, particularly in soft glass. In this work, we develop a preliminary design of a highly nonlinear tapered hybrid microstructured optical fiber (TH-MOF) with chalcogenide glass core and tellurite glass microstructure cladding. We then numerically studied its dispersion, loss, and nonlinearity-related optical properties under fundamental mode systematically using the infinitesimal method. The designed TH-MOF exhibits low chromatic dispersion that is similar to a convex function with two zero-dispersion wavelengths and decreases with fiber length from 2 to 5 μm band. The potential use of the TH-MOF in nonlinear applications is demonstrated numerically by a supercontinuum spectrum of 20 dB bandwidth covering 1.96–4.76 μm generated in 2-cm-long TH-MOF using near 3.25-μm fs-laser pump.

The realization of an all-solid photonic bandgap optical fiber (PBGF) based on silicate glasses in spectral wave- length band ∼920 nm is achieved. The structure parameters and bandgap of the fiber are both demonstrated theoretically by plane-wave expansion method calculations and experimentally by near-field measurements. The all-solid silicate glass PBGF has one bandgap and has a core transmission band of 853-980 nm, which is important for laser generation at ∼920 nm in Nd-doped silicate glass fiber.

A novel long period fiber grating (LPFG) is inscribed in few mode fibers by CO2-laser-irradiation method. The experiment results and theoretical calculation demonstrate that the LPFGs are originated from the strong coupling between the fundamental core mode LP01 and the high-order core mode LP11. The resonant wavelength is found to shift toward the lower wavelength with temperature or force increasing, which is quite different from LPFGs fabricated in common single mode fibers. The gratings are quite sensitive to strain and slightly insensitive to temperature. Such structures are easy to be fabricate and can be promising candidates as strain sensors.

Preparation and characterization of a liquid level sensor based on macro-bending coupling of fibers are demonstrated in this Letter. The sensitive component can be obtained through a twisting and twining structure of transparent cladding plastic fibers. The difference in light power originating from the surrounding media in the fibers is tested. The light power loss for different tested media and the fiber bending magnitude are investigated. The sensing measurements show that the coupling light power in the passive fiber decreases in accordance with increasing liquid level, whereas it exhibits a steady tendency in the case of the active fiber.

Mirrorless graded-index polymer optical fibers doped with the organic dye rhodamine 6G result in very compact broadband fiber lasers in the visible region when pumped from the side. The emission spectrum, threshold, and efficiency obtained on both fiber ends depend on the lengths of the directly illuminated region and of the non-excited ones. The paper analyzes such parameters both experimentally and theoretically for the first time.

A novel reflective refractometer based on a fiber Bragg grating (FBG) inscribed in a thin-core-fiber (TCF) stub was demonstrated. The cladding modes are excited by the core diameter mismatch between the single-mode-fiber (SMF) and TCF. The core mode and specific cladding modes in the TCF are reflected by the FBG and partly recoupled into the back-propagating core mode in the SMF. Experimental results demonstrate that the power of the cladding mode reflection changes with the surrounding refractive index (SRI). The temperature-immune SRI measurement with linear sensitivity of 54.55 dB per refractive index unit has been achieved by the cost-effective power detection within the refractive index range from 1.33 to 1.42. To eliminate the measurement deviation caused by the fluctuation of light source, the simple self-referencing detecting has been carried out by measuring the ratio of the cladding mode reflection and the core mode reflection.

Based on pullout test, shear test, tensile test strip, studied the influence of three fibers and glass fibers of different lengths on mechanical properties of synchronization plus fiber stone layer. Test results show that, glass fiber and polyacrylonitrile fiber has little effect on the interfacial bonding performance difference compared with no fiber, polyester fiber has greater impact on the interfacial bonding performance; Adding fiber, crack resistance significantly enhanced, including glass fiber and polyacrylonitrile fiber are most obvious, considering, determined glass fiber as the best choice , 60mm as the optimum length.

International audience; We report results on the processing and characterization of different glass preforms and single core fibers within the SiO2-Na2O-B2O3-Er2O3-P2O5-Al2O3 system. Micro-Raman spectroscopy was used to identify post-draw structural modification. The differences in the micro-Raman spectra recorded on the preform and on the fiber glass were attributed to a change in the structure induced by the drawing process. Changes in the silicate network organization and small scale molecular orientation within the glass matrix are suspected to occur during the fiber drawing process. We found that the extent in the changes between the preform and fiber properties depend on the glass composition. The glass network of the Al-containing fiber is expected to be less sensitive to the drawing process than that of the fiber matrix as the network of this Al-containing fiber is formed by a larger number of Si-BO units in the network and neutral three-coordinated boron compared to the network of the fiber matrix. From the micro-Raman spectra, formation of small crystals is suspected to occur in the P-containing glasses during the fiber drawing process. The resulting fibers were found to have propagation losses at 1330 nm and Er3+ absorption between (7 ± 1) and (25 ± 1) dB/m and (36 ± 1) and (47 ± 1) dB/m, respectively, depending on the glass composition.

We report on a low-loss fusion splice between a hollow-core photonic bandgap fiber (NKT's HC-1550-02) and a conventional single mode fiber (Corning's SMF28) using a high V-number intermediate fiber. Compared to the commonly used fiber postprocessing techniques, the intermediate fiber method offers a new adjusting degree of freedom of V-numbers, enabling the reduction of coupling loss to 0.35 dB. Experimentally, a low fusion splice loss of 0.63 dB has been achieved between Nufern's SM1950 (V =2.836) and HC-1550-02 fiber, resulting in an overall insertion loss of 0.73 dB from SMF28 to HC-1550-02 fiber. We believe this is the lowest splice loss value reported for HC-1550-02 fiber using an arc splicer, on the aspect of both using a step-index solid-core fiber (0.63 dB) and a SMF28 fiber (0.73 dB).

An OmniGuide fiber consisting of superconductor–dielectric cladding periodic multilayers is investigated. The theoretical results of the OmniGuide fiber are presented and compared with that of multicore photonic crystal fiber and step-index fiber. The large mode area and low loss with small bending radius are observed by the OmniGuide fiber.

A novel high birefringent polymer terahertz (THz) fiber with a suspended elliptical core is proposed in this paper. The introduction of an elliptical core can enhance asymmetry to realize high mode birefringence, and a large porous outer cladding effectively isolates the core-guided mode from interacting with the surrounding environment. A full-vector finite element method(FEM) is used to analyze the characteristics of the THz fiber. Simulation results show that the suspended elliptical fiber exhibits high mode birefringence on a level of $10^{-2}$ over a wide frequency range, and an extremely large mode birefringence( ${\approx}0.06226$ ) is obtained when ellipticity is 0.2. Moreover, a suspended hollow elliptical core fiber is also discussed for the purpose of lower loss, however high mode birefringence and low relative absorption loss can not coexist in such a kind of fiber.

A residual dispersion compensating photonic crystal fiber (PCF) is proposed having elliptical-shaped core and octagonal structure with isosceles triangular-latticed cladding. The finite element method with circular perfectly matched layer is used to investigate the guiding properties. It is demonstrated that it is possible to obtain average dispersion of -544.7 ps/(nm.km) in a wavelength range of 1.46-1.70 μm with ultrahigh birefringence of 2.2 × 10 -2 and nonlinear coefficient of 52.7 W -1 km -1 at a 1.55-μm wavelength. Besides, the proposed PCF shows confinement losses

A doubly clad optical fiber with an inner cladding made of negative refractive index material was proposed and the modes distribution, dispersion and time delay were investigated by fully vectorial numerical method. The results indicate that HE12 mode can be operated as a single mode, the cut-off frequency of modes shifts to low normalized frequency with increasing thickness of inner cladding made of negative index materials, large negative dispersion and time delay can be obtained and tailored by the inner cladding. These results provide theoretical basis for designing novel fibers or optical devices.