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To elastically design a dual-concentric-core photonic crystal fiber (DCC-PCF) for dispersion compensation, we use double layers of cladding holes as an outer ring core (ORC), instead of single layer ORC, of the DCC-PCF. For a DCC-PCF with single ORC structure, the design process of maximum dispersion coefficient becomes entangled with that of the compensated wavelength. By using double ORC, the optimum value of chromatic dispersion can be kept when the compensated wavelength is adjusted. The numeric results indicate that the negative chromatic dispersion coefficient for the proposed DCC-PCF is approximately 15 % larger than that of the previous DCC-PCF at around the wavelength of $$1.55\,\upmu \hbox {m}$$ .

A novel optofluidically tunable Thulium-doped fiber laser (TDFL) based on a multimode interference (MMI) fiber filter is experimentally demonstrated with a wide tuning range from 1813.52 to 1858.70 nm. The wavelength tuning of the TDFL is achieved by employing an MMI fiber filter which is formed by splicing a segment of a special no-core fiber that is an all silica fiber without fiber core to single mode fibers. The no-core fiber with a large diameter of 200 μm is gradually vertically covered by refractive index matching liquid, which leads to a wavelength tuning of the transmission peak of the MMI fiber filter. The relationship between the refractive index of the refractive index matching liquid and the peak wavelength shift of the MMI fiber filter is also discussed. Using the MMI fiber filter, a Thulium-doped fiber laser with a tuning range of 45.18 nm, a side-mode suppression ratio better than 40 dB, and a 3 dB bandwidth less than 0.16 nm is demonstrated.

A broad Stark splitting of Yb 3+ -doped fluorophosphate (FP) core glass and phosphate cladding glass with outstanding thermal and mechanical performance were prepared in this work. Yb 3+ -doped FP core and phosphate cladding heterogeneous fiber with hexagonal-shape inner cladding was fabricated by the stack-and-draw method. A maximum output power of 2 W was obtained with slope efficiency of 25.6% from a 35 cm fiber. The laser spectrum had a full width at half maximum (FWHM) of 1.5 nm with the central wavelength at 1013 nm. Therefore, FP glass fiber might be a good alternative for gain medium in short-linear-cavity single-frequency fiber laser.

A method based on the uptapering of photonic crystal fiber for low-loss coupling between photonic crystal fibers and single-mode fibers is presented. The impacts of uptapering ratio on coupling loss are investigated by beam propagation method. The results show that this method can greatly reduce the coupling loss between the two types of fiber. Besides, this method is available for the coupling between a variety of photonic crystal fibers and single mode fibers, especially for those with large difference between mode field diameters.

A method of obtaining optical fiber with a refractive-reflective cladding formed in the process of extrusion from a single-spinneret vessel as a result of the interaction between the spinneret material and the glass melt of the light-guiding fiber core. Using glass with highly volatile components for the light-guiding core in order to best match the compositions of the initial glass and the light-guiding core the method affords the creation of a polycrystalline or glassy layer with the same composition along the surface during the extrusion process.

Yb3+/Al3+ co-doped silica glass with the composition of 0.1Yb2O3-1Al2O3-98.9SiO2 was prepared by sol–gel method combined with high-temperature sintering. Using this glass as active core, a photonic crystal fiber (PCF) with 105- $\mu \text{m}$ core was fabricated by the stack-capillary-draw technology. The refractive index fluctuation of this core rod is as low as $2 \times 10^{\mathrm {\mathbf {-4}}}$ , implying that highly homogenous silica preform can be realized in this method. Furthermore, this PCF achieved a maximum amplified power of 255 W, with a slope efficiency of 65.7%. It indicates that Yb3+-doped silica preform prepared by the sol–gel method can be employed in the field of high-power laser.

For the first time, to the best of our knowledge, we report on the realization of a laser from a Yb-doped phosphate core/silicate cladding double-clad hybrid fiber. 5 W output power was extracted with 14.6% slope efficiency and a laser spectrum of a 1027 nm central wavelength from a 20 cm long single-mode fiber with a ∼10 μm core diameter in a 20%–4% laser cavity. The laser efficiency can be significantly enhanced by correspondingly adjusting and optimizing the laser oscillator.

The diameter of long-period fiber gratings (LPFGs) fabricated in optical fibers with a low cutoff wavelength was be reduced by hydrofluoric acid etching, enhancing the sensitivity to refractive index by more than a factor of 3, to 2611 nm/refractive index unit in the range from 1.333 to 1.4278. The grating period selected for the LPFGs allowed access to the dispersion turning point at wavelengths close to the visible range of the optical spectrum, where optical equipment is less expensive. As an example of an application, a pH sensor based on the deposition of a polymeric coating was analyzed in two situations: with an LPFG without diameter reduction and with an LPFG with diameter reduction. Again, a sensitivity increase of a factor of near 3 was obtained, demonstrating the ability of this method to enhance the sensitivity of thin-film-coated LPFG chemical sensors. This work was supported by the Spanish Agencia Estatal de Investigación (AEI) and Fondo Europeo de Desarrollo Regional (FEDER) (TEC2016-79367-C2-2-R, TEC2016-78047-R), by the Government of Navarre through the project with reference 2017/PI044 and with funding from the Engineering and Physical Sciences Research Council (EPSRC) UK, EP/L010437/1.

In this paper, we propose the design of fiber optic refractive index sensor based on a thin core fiber, sandwiched between an input and output single mode fibers. This structure is characterized by a refractive index sensitivity about 187.98 nm/RIU (refractive index unit). In order to enhance the sensitivity, we designed a tapered single mode-thin core-single mode fiber structure where the sensitivity with different waist-diameters (90, 60 and 30 μm) is investigated. As a result, we obtained an ultra-high sensitivity of the tapered sensor about 783.19 nm/RIU in the refractive index range of 1.3346-1.3899, using sucrose and water mixture solution, achieved for a waist diameter equal to 30 μm and a taper length of 675μm.The designed structure presents the merits of high sensitivity which is 4 times higher than that of the thin core fiber modal interferometer which makes it an excellent candidate for biochemical sensing applications.

A new type of polymer and silica connection is proposed. A tapered SMF-28 silica optical fiber tip is fabricated using a CO2 laser by focusing and stretching the fiber. The tapered silica tip is inserted in one of the holes of a microstructured polymer optical fiber using a 3D alignment system. Using a supercontinuum source, the spectrum is observed after one and after two connections. The polymer fiber is characterized in curvature while using the previous connection.

We investigate the influence of air holes on phase sensitivity in microstructured optical fibers to longitudinal strain. According to the numerical simulations performed, large air holes in close proximity to a fiber core introduce significant compression stress to the core, which results in an increase in the effective refractive index sensitivity to longitudinal strain. The theoretical investigation is verified by an experiment performed on four fibers drawn from the same preform and differentiated by air hole diameter. We show that introducing properly designed air holes can lead to a considerable increase in normalized effective refractive index sensitivity to axial strain from −0.21 e−1 (for traditional single mode fiber) to −0.14 e−1.

We demonstrate an active random fiber laser by directly pumping a 100 m erbium-doped fiber at 980 nm wavelength, with a fiber loop mirror forming a half-open cavity. Random lasing with competing spectral modes in the range from 1535 nm to 1560 nm is achieved, with the maximum lasing slope efficiency around 10%. We also study the effect of combining a dispersion compensated fiber with the erbium-doped fiber. The kilometers long dispersion compensated fiber reduces the random lasing threshold and increases the signal to noise ratio, while enhancing the tunability of the random laser’s spectrum range by the fiber loop mirror feedback.

We present an experimental study of the temperature sensitivity of three different step-index 1-mm PMMA fibers. Two of these fibers have a special jacket to sustain high temperatures: BH-4001 and LHXE-4001 and the other is a standard, GH-4001 fiber with a polyethylene jacket. We show that the fibers perform well within the manufacturer specified temperature operating ranges. Predictably, higher than specified temperatures can result in permanent damage and permanent performance degradation. This work expands our previous work on modelling POF on various fiber types and lengths, focusing on the short links found on airplanes.

We present the experimental demonstration of in-fiber acousto-optic coupling in a polyimide-coated optical fiber. Although the presence of the polyimide coating increases is significantly the attenuation of the acoustic wave, we show that acousto-optic interaction can still be produced with reasonable efficiency. The effect of the polyimide coating on the acousto-optic interaction process is analyzed in detailed. Theoretical and experimental results are in good agreement. To our knowledge, this is the first experimental demonstration of acousto-optic coupling in optical fibers with robust protective coating.

This goal of our research was to show that E-glass fiber bundles used for reinforcing composites can be enabled to transmit light in a common resin without any special preparation (without removing the sizing). The power of the transmitted light was measured and the attenuation coefficient, which characterizes the fiber bundle, was determined. Although the attenuation coefficient depends on temperature and the wavelength of the light, it is independent of the power of incident light, the quality of coupling, and the length of the specimen. The refractive index of commercially available transparent resins was measured and it was proved that a resin with a refractive index lower than that of the fiber can be used to make a composite whose fibers are capable of transmitting light. The effects of temperature, compression of the fibers, and the shape of fiber ends on the power of transmitted light were examined. The measurement of emitted light can provide information about the health of the fibers. This can be the basis of a simple health monitoring system in the case of general-purpose composite structures.

A hollow-core single-ring photonic crystal fiber (SR-PCF) consists of a ring of capillaries arranged around a central hollow core. Spinning the preform during drawing introduces a continuous helical twist, offering a novel means of controlling the modal properties of hollow-core SR-PCF. For example, twisting geometrically increases the effective axial propagation constant of the LP01-like modes of the capillaries, providing a means of optimizing the suppression of HOMs, which occurs when the LP11-like core mode phase-matches to the LP01-like modes of the surrounding capillaries. (In a straight fiber, optimum suppression occurs for a capillary-to-core diameter ratio d/D=0.682.) Twisting also introduces circular birefringence (to be studied in a future Letter) and has a remarkable effect on the transverse intensity profiles of the higher-order core modes, forcing the two-lobed LP11-like mode in the untwisted fiber to become three-fold symmetric in the twisted case. These phenomena are explored by means of extensive numerical modeling, an analytical model, and a series of experiments. Prism-assisted side-coupling is used to measure the losses, refractive indices, and near-field patterns of individual fiber modes in both the straight and twisted cases.

Made available in DSpace on 2018-11-26T17:28:20Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-04-01. Added 1 bitstream(s) on 2019-10-09T18:26:39Z : No. of bitstreams: 1 S2175-91462017000200231.pdf: 643499 bytes, checksum: aa178039bf1fb7a726c5bdf3c8cb85c0 (MD5) Multifunctional composites combine structural and other physicochemical properties, with major applications in aeronautical, space, telecommunication, automotive, and medical areas. This research evaluates electromagnetic properties of multifunctional composites based on glass fiber woven fabric pre-impregnated with epoxy resin laminated together carbon fiber non-woven veil metalized with Ni. In this way, searching for possible application as radar absorbing structures or electromagnetic interference shielding structures. The scattering parameters, in the frequency range of 8.2 to 12.4 GHz, show that the epoxy resin/glass fiber prepreg allows the transmission of the electromagnetic waves through its microstructure, independently of the glass fiber reinforcement orientation (98% transmission, S-24 = -0.09 dB). However, the carbon fiber/Ni veil shows highly reflector behavior (91% reflection, S-22 = -0.43 dB). Energy dispersive spectroscopy of the veil, before and after nitric acid attacks, confirmed the Ni coating removal from the carbon fiber surface. Still, the scattering parameters show reflector behavior (77% reflection, S-22 = -1.13 dB), attributed to the electrical conductivity of carbon fibers. Multifunctional composites based on glass fiber/epoxy/carbon fiber/Ni veil laminates were processed by hot compression molding. The scattering parameters show that the laminates do not behave as good radar absorbing structures. Nevertheless, the laminates present promising results for application as light weight and low thickness structural composites with electromagnetic interference shielding effectiveness (91.4% reflection for 0.36 mm thickness and 100% for similar to 1.1 mm) for buildings, aircraft, and space components. Univ Estadual Paulista, Fac Engn Guaratingueta, Dept Mat & Tecnol, Ave Dr Ariberto Pereira Cunha,333 Portal das Coli, BR-12516410 Guaratingueta, SP, Brazil Inst Technol Aeronaut, Dept Ciencia & Tecnol Aeroespacial, Lab Guerra Elect, Sao Jose Dos Campos, SP, Brazil Univ Fed Sao Paulo, Inst Ciencia & Tecnol Curso Engn Mat, Sao Jose Dos Campos, SP, Brazil Univ Estadual Paulista, Fac Engn Guaratingueta, Dept Mat & Tecnol, Ave Dr Ariberto Pereira Cunha,333 Portal das Coli, BR-12516410 Guaratingueta, SP, Brazil

When a photosensitive (PS) fiber is exposed to UV-irradiation, a permanent refractive index change is induced in the core. As a result, according to Kramers-Kronig relations, the absorption coefficient (α) is also increased. This increment of the absorption can lead to a significant heating of the fiber when it is illuminated by a moderate optical power. Thermal effects may produce spectral changes in some fiber devices, as for example Long Period Gratings (LPGs) or Fiber Bragg Gratings (FBGs) [1].

An acoustic/elastic wave propagating along an optical fiber has the capability to produce coupling between optical fiber modes. A variety of all-fiber, dynamic, and reconfigurable components has been demonstrated over the last decades using either flexural· longitudinal· or torsional elastic modes [1· 2]. From the practical point of view, the main limitation of such devices arises from the huge elastic attenuation in fibers with protective polymer coating. Consequently, the polymer jacket of the fiber section along which the acousto-optic interaction takes place must be removed. The bare fiber section compromises the long-term reliability of the component. Recently, acousto-optic coupling using torsional wave was demonstrated in thin metal-coated optical fibers [3]. The metal coating provides low attenuation of the elastic wave and surface protection of the fiber, but still fiber handling is compromised. In this paper, we present the first experimental demonstration of in-fiber acousto-optic coupling in polyimide-coated optical fibers.

It is known that an acoustic/elastic wave propagating along an optical fiber has the capability to produce coupling between optical fiber modes. A variety of all-fiber, dynamic, and reconfigurable components based on this effect has been demonstrated over the last decades [1]. In the last years, acousto-optic (AO) interaction has been proved to be a powerful and highly sensitive method for the characterization of optical fibers [2, 3]. The key of the technique relies on the large sensitivity of the AO phase-matching condition with the structural and material properties of the fiber, being able the detection of sub-nanometer fiber radius variations, or core refractive index variations in the order of 10−8 in single-mode fibers. In this paper, we present our preliminary results on the use of in-fiber AO interaction for the measurement of the nonlinear refractive index in single-mode optical fibers.

Hollow-core anti-resonant (HC-AR) fibers with a “negative-curvature” of the core-cladding boundary have been extensively studied over the past few years owing to their low loss and wide transmission bandwidths. The key unique feature of the HC-AR fiber is that the coupling between the core and cladding modes can be made anti-resonant (strongly inhibited) by suitably arranging the anti-resonant tubes in the cladding, which results in low loss and broad spectral bandwidths. HC-AR fibers have been fabricated aimed at visible, near-or mid-IR transmission [1-4]. Here we fabricate and characterize a silica HC-AR fiber having a single ring of 7 non-touching capillaries, designed to have effectively single-mode operation and low loss from UV to near-IR.

Applications of high power lasers and amplifiers have been increasing because of its superior properties such as high wall-plug efficiency, excellent beam quality, and reliability [1]. Despite advances in high power fiber components, there is still component reliability based challenges on extraction process of unwanted cladding light [2]. There are several techniques to extract the cladding light from the fiber laser system such as high index polymer coating that of working principle is violating the total internal reflection [2], roughened cladding surface which uses the scattering to eliminate the cladding light [3], soft metal coating to absorb the cladding light [4] and CO2 laser processing of cladding to disturb the light path with the structural manipulations and strip the unwanted light from these structures. There are some limitations for each case. The high index polymer CLS are limited by the thermal degradation of recoated polymer [4]. For the roughened or etching CLS, even though very high attenuations levels were achieved, the roughing or etching process decrease the fiber strength. This could create undesired problems such as heat localization and microcrack formation on cladding wall. Here, we present novel method for practical, robust, compact, and all glass cladding light stripper fabrication on Ytterbium (Yb) doped octagonally shaped double clad fiber (DCF).

Gradient index (GRIN) fibers have recently been identified as the potential next generation components for today's classic fiber optic applications, ranging from telecommunications to laser technologies [1]. In particular the nonlinear beam self-cleanup leading in multimode (MM) GRIN fibers to spatial organization into a fundamental mode on a weak background of higher order modes, is hoped to disrupt telecommunications due to its potential to harness the MM and its promise of superb information density [2]. For lasers, this approach means a new quality of high power delivery with bending loss or speckle formation strongly mitigated against existing solutions. Yet, arbitrary transverse profiles of refractive index in GRIN fibers would even add to these advantages e.g. the possibility of transmitting nonstandard states of polarization or beam shaping without the need for bulk optics. Current CVD technologies however limit freedom of development of GRIN fibers. Only radially symmetric or, to some extent, elliptical refractive index distributions in are feasible. Recently we have presented a new approach to fibers with arbitrary GRIN profiles [3]. A continuous refractive index profile at the fiber cross-section is obtained by varying distribution of two types of subwavelength rods (Fig.1a). Since every single rod in the final nanostructured core fiber is sub-wavelength, the propagating light beam experiences a certain effective refractive index described with the Maxwell-Garnett effective medium model. This method allow to obtain arbitrary gradient distribution in the core. Here we report for the first time the development of fiber with effective parabolic GRIN profile in the core based on fused silica (FS) glass. The core is composed of 2107 rods of 200 nm diameters, made of two types of glass: low refractive index FS (nD= 1.4588) and high index Ge doped FS (nD= 1.4637). with 3.18% mol concertation (Fig.1b). The fiber core has an effective parabolic refractive index distribution with gradient g=0.077 m−1. The proposed fiber has a flat anomalous dispersion with ZDW varying between 1.26 μm and 1.37 μm for the fibers with different core diameters between 8 and 11 μm (Fig. 1d). The measured dispersion characteristics perfectly match simulation results obtained with continuous parabolic profiles. Such profile is used in our discussion to compare properties of the developed fiber with standard GRIN fibers, although arbitrary index profiles are possible using the same technological platform. Our results also prove, that the Ge dopant distribution is well controlled during fiber fabrication, as the effective refractive index profile of the nanostructured core perfectly matches the design specification.

The generation and amplification at wavelengths longer than 1100 nm is not straightforward when using Yb-doped optical fibers, since light emission of ytterbium occurs preferentially in the region of 1020 nm - 1100 nm with a maximum at 1030 nm. One well known approach is to heat the Yb-doped fiber up to temperatures above 100 °C. This increases the re-absorption in the lower emission band and also enhances at the same time the emission at longer wavelengths. Consequently, heating allows to extend the spectral gain-region of Yb-doped fibers by at least 60 nm up to 1160 nm. However, the drawback of this method is that it results in a shorter durability of the fiber, since heating damages the polymer-coating. Moreover, such a laser has a reduced overall efficiency, due to heating, isolation and heat removal issues. It has been reported, that at the presence of an aluminosilca host (silica doped with Al) efficient laser activity at around 1150 nm can be achieved by heating the Yb-doped fiber to only 60 °C. In this work we investigate the spectroscopy of a heated Yb-doped fiber with a high aluminum concentration. The fiber is drawn in our in-house fiber drawing tower. The preforms are produced by the sol-gel-based granulated silica method which allows us to vary the aluminum as well as the ytterbium concentrations within a large range. The fiber is investigated with respect to their spectroscopic data as well as their lasing performance.

We report unique thermo-optical characteristics of DNA-Cetyl tri-methyl ammonium (DNA-CTMA) thin solid film with a large negative thermo-optical coefficient of -3.4×10-4/°C in the temperature range from 20°C to 70°C without any observable thermal hysteresis. By combining this thermo-optic DNA film and fiber optic multimode interference (MMI) device, we experimentally demonstrated a highly sensitive compact temperature sensor with a large spectral shift of 0.15 nm/°C. The fiber optic MMI device was a concatenated structure with single-mode fiber (SMF)-coreless silica fiber (CSF)-single mode fiber (SMF) and the DNA-CTMA film was deposited on the CSF. The spectral shifts of the device in experiments were compared with the beam propagation method, which showed a good agreement.

In this paper, we present a study aimed at characterizing the optimal fiber optic components for Brillouin sensing in multimode fibers. For this purpose the use of single-mode and multimode circulators as well as couplers typically used in the Brillouin measurement setups was investigated. On the one hand the undesired coupling losses between conventional fiber optic measurement system components and a multimode sensor fiber can be overcome by replacing the single-mode components with their own multimode equivalents. On the other hand the use of multimode fiber optic circulators and multimode couplers affects the mode distribution of laser light which can impair the measurement signal backscattered in the multimode sensor fibers. In view of an increasing interest in high strain measurements using polymer optical fibers (POFs) as Brillouin-distributed sensors the investigation on Brillouin scattering effects in multimode fibers (MMFs) was performed on a low-loss perfluorinated graded-index polymer optical fiber (PFGI-POF). The obtained results were compared with those of a standard graded-index multimode (GI-MMF) silica glass optical fiber (GOF). This study confirms the relevance of the adaptation of the measurement system components to the use of the multimode sensor fibers. In addition, due to mode coupling effects occurring in the tested POF itself, the results show differences in the yield of the components adaptation in the sensory implementation of the two kinds of the tested optical fibers.

Silica optical fibers doped with rare-earth elements are key components of high-power fiber lasers operating in near-infrared region up to 2.1 μm. In this contribution we deal with preparation and optical characterization of silica-based optical preforms and fibers doped with thulium for fiber lasers operating around 2 μm. A set of fibers with thulium concentration ranges 1000-5000 ppm was prepared by the MCVD solution doping method and characterized. A decrease of fluorescence lifetime of thulium from 487 μs to 378 μs was observed with increasing rare-earth concentration in fiber core. This phenomenon can be explained by energy transfer between ions and ion clustering. Fabricated fibers were suitable for use in fiber lasers.

We demonstrate a novel type of tapered large mode area polarization-maintaining fiber. These birefringent fibers have an elliptical inner cladding and a core diameter that increases adiabatically from 8 μm to 70 μm. The polarization maintaining ability of the fiber samples was investigated by measuring the spatial distribution of polarization beat length by using optical frequency-domain reflectometry. The measurements show a clear correlation between the birefringence and the fiber core size, resulting in a modest 10-15% variation in polarization beat length along the fiber. There is no significant coupling of polarization modes or transverse modes in the tested fibers and, therefore, the linear polarization state of propagating light is preserved. publishedVersion

International audience; Hybrid optical fibers consisting of glass clad and semiconductor core materials are extensively investigated dueto their interesting properties that make them attractive for several technological applications. Here, we reporton a new approach for the fabrication of such multi-material optical fiber preform using the sol–gel technique. Itconsists in mechanically drilling a central hole in a silica xerogel rod, then in filling this hole with a centimeterlengthsilicon rod, and finally in densifying the silica glass jacket around the silicon core. By drawing thispreform, a homogenous hybrid rod-type fiber was obtained. The composition and the structural properties of thepristine silicon rod, of the hybrid preform and of the drawn fiber have been investigated using electron probemicroanalysis, Raman spectroscopy and transmission electron microscopy. We have shown that the silicon corematerial preserves its composition and polycrystalline structure all along the fabrication process.

A low cost and simple to realize optical temperature sensor is proposed. The sensor is fabricated on the fiber end by removing, near the fiber tip, the cladding of a multimode plastic optical fiber (POF) with a polishing process, to deposit, by dip coating, a silicone layer around the fiber tip. We have experimentally tested the sensor by measuring, at different wavelengths, the temperature of a water bath. The best sensor's performances were obtained at a wavelength of 625 nm. The novel polymer optical fiber sensor exhibits a good linear response in the temperature range from 24°C to 46°C. This temperature range is interesting for hyperthermia in cancer treatment.

A fiber surface Bragg grating waveguide (BGW) fabricated in the surface of single-mode fiber by direct femtosecond laser inscription is demonstrated and successfully applied for refractive index (RI) measurements. Prior to laser inscription of the fiber surface BGW, an X-coupler is first inscribed across the fiber core to couple light from the core to the fiber surface. The light transmitted in the fiber surface BGW efficiently interacts with the surrounding medium due to a strong evanescent field, and obtains an acceptable RI sensitivity approaching ∼16 nm/RIU. The novel design efficiently couples the light guided in the core with the surrounding medium using a non-destructive, single-step micromachining process, and is expected to have potential applications in fiber biochemical sensing.

The operation speed of high-performance computers has increased dramatically over the last decades. For sustaining their growth, multimode fiber (MMF) links have been gradually deployed, and on-board interconnection is the next step. Polymer optical waveguides (POWs) have been expected as one of the key components for on-board interconnects: they are expected to connect the light source/ photo detector on-board and an MMF off-board. As a unique fabrication method for POWs, we developed the Mosquito method to obtain graded index (GI) circular core polymer waveguides and confirmed their low propagation loss compared to conventional step-index (SI) core waveguides. However, the connection loss of the light source to waveguide, and the waveguide to an MMF is a concern: insertion of the polymer waveguide between the light source and MMF would increase the optical loss. So, in this paper, a tapered GI core polymer waveguide is proposed for reducing the connection loss between the laser sources and fibers/waveguides by inserting it between the source and MMF. In the Mosquito method, a liquid core monomer is dispensed from a thin needle attached to a syringe into a cladding monomer, using a microdispenser. Hence, the core diameter is axially varied by changing the needle-scan velocity. First, the optimum refractive index profiles in the tapered core are theoretically predicted using the BPM method. Next, the refractive index profile formed in the core during the Mosquito method is also estimated by solving the Fick’s diffusion equation. Finally, we successfully fabricate a GI tapered core polymer waveguide as designed.

An improvement in light confinement in sapphire fiber is obtained by employing nanoporous alumina as a cladding. The fabrication strategy entails freeze-coating metal Al on sapphire fiber and its subsequent anodization to form alumina cladding with highly organized nanopore channels vertically aligned to the fiber axis with dimensions of ~20 nm. We investigated the confinement dependence on the porosity of the cladding, showing an improvement in comparison to unclad sapphire fibers. The versatility of anodized alumina cladding with tunable structural and optical characteristics has the potential to enable a new class of specialty sapphire optical fibers by engineering the light propagation for new sensor development.

A highly sensitive gas refractometer based on inverse mode-coupling is proposed and experimentally demonstrated. The sensor has a sandwiched configuration that a tapered four-core fiber is spliced between two standard single mode fibers. In the tapered four-core fiber, inverse mode-coupling from cladding modes to core modes leads to enhanced cladding modes and evanescent fields. The unique waveguide structure (multiple cores arranged close to the fiber cladding) of the four-core fiber enables multiple core modes to sense refractive index change after tapering. The abrupt taper also acts as a bridge between surround refractive index and interference modes (including both cladding and core modes). For the carbon dioxide refractive index (close to 1.0) measurement, the sensor presents a high sensitivity of 922.32 dB/refractive index unit without cross-sensitivity of temperature.

A novel orthogonal grating has been proposed and demonstrated. The grating is inscribed over inner cladding of a multi-cladding fiber containing two orthogonally cascaded "cladding" fiber Bragg gratings. Femtosecond laser side-illumination technique is utilized to ensure the two grating inscriptions are precisely positioned and compact in size. With such configuration, two pairs of well-defined cladding resonances have been achieved in reflection, which are originated from the internal cladding (two weakened resonances at shorter wavelength side) and from the fiber core (two stronger resonances at longer wavelength side), respectively. Most importantly, the "cladding" resonances are strongly directional sensitive to the small-vibration.

We review the unique properties of a so-called optical fiber fuse phenomenon in plastic optical fibers (POFs), including its slow propagation velocity (1–2 orders of magnitude slower than that in silica fibers) and threshold power density (1/180 of the value for silica fibers). We also show that an oscillatory continuous curve instead of periodic voids is formed after the passage of the fuse, and that the bright spot is not a plasma but an optical discharge, the temperature of which is ∼3600 K. We then discuss its impact on distributed Brillouin sensing based on POFs.

We report a directional-coupler-based refractive index sensor and its cost-effective fabrication method using hydrofluoric acid droplet wet-etching and surface-tension-driven liquid flows. The proposed fiber sensor consists of a pair of twisted tapered optical fibers with low excess losses. The fiber cores in the etched microfiber region are exposed to the surrounding medium for efficient interaction with the guided light. We observe that the etching-based low-loss fiber-optic sensors can measure the water droplet volume by detecting the refractive index changes of the surrounding medium around the etched fiber core region.

In this paper a fiber optic metallic embedding technique is presented based on laser Brazing manufacturing process. The embedding strategy to follow by the laser Brazing, which consists in three steps, minimizes the thermal stress of the embedded fiber, relaxes microbending strains and reduces damage on the fiber. The minimum embedded fiber optic Ni coating total diameter is 237μm for a successful process with negligible optical loss on the fiber. Fiber Bragg Gratings were successfully embedded in metallic specimens and their strain response was in accordance with their specifications.

Kerr-lens self-channelling of femtosecond laser light offers a novel high-aspect geometry for laser processing inside transparent materials. In glass materials, the laser filaments enable white-light continuum generation, scribing, nanochannel formation, and refractive index modification. In the present work, refractive index matching oils were applied around optical fiber to eliminate astigmatic aberration and thereby form highly symmetric and uniform filaments selectively in the cladding or core waveguide of standard single-mode optical fibre (SMF-28). Under tight focusing, long filaments exceeding 20 um length were formed with single pulses to sub-micron diameter. Arrays of 0.5 um spaced filaments are verified by formation of strong fiber Bragg gratings (FBGs). Flexible positioning of the filament arrays within the fiber core offers wide scope for coupling to cladding and radiation modes and creating new types of in-fibre optical devices.

Semiconductor core fibers have numerous potential applications in optoelectronics and photonics, and the key to realizing these opportunities is controlled processing of the material. We present results on laser treatments for manipulating the core structure as well as the glass cladding. More specifically, using quasi-CW 10.6 µm radiation, the clad glass can be softened and the core can be controllably melted. This is shown to permit tapering, localized formation of optical resonators, and stress modification of the as-drawn fiber and structures within it. Shown for the first time to the authors' knowledge are Bragg gratings written by modification of the silicon/glass interface using fs laser illumination at 517 nm. The cores of these fibers show stress alterations, with indications of quasi-periodic stress relief in the glass. © 2017 Optical Society of America

Accurate control of both the doping distribution inside the fiber core and the low refractive index contrast between the fiber core and cladding materials is essential for the development of high-power fiber lasers based on the use of single-mode large-mode-area (LMA) optical fibers. Herein, sol-gel monolithic F/Yb3+-codoped silica glasses were prepared from porous large silica xerogels doped with ytterbium salt solution, which had been subjected to fluorination with hexafluoroethane gas, before subsequent sintering. The fluorine content inside the doped glass has been varied by adjusting the fluorination duration. The space homogeneity of fluorine and ytterbium concentrations in the cylindrical preforms has been checked by chemical analysis and Raman spectroscopy. Moreover, the glass with the lowest fluorine content has been successfully integrated as a core material in a microstructured optical fiber made using the stack-and-draw method. This fiber was tested in an all-fiber cavity laser architecture to evaluate potential lasing performances of the F/Yb3+-codoped silica glass. It presents a maximum efficiency of 70.4%, achieved at 1031 nm from a 1.16 m length fiber. These results confirm the potentialities of the obtained F/Yb3+-codoped glasses for the fabrication of LMA optical fiber lasers.

Bundled glass tubular fibers were fabricated by glass drawing technique for endoscopic infrared-thermal imaging. The bundle fibers were made of borosilicate glass and have a structure like a photonic crystal fiber having multiple hollow cores. Fabricated fibers have a length of 90 cm and each pixel sizes are less than 80 μm. By setting the thickness of glass wall to a quarter-wavelength optical thickness, light is confined in the air core as a leaky mode with a low loss owing to the interference effect of the thin glass wall and this type of hollow-core fibers is known as tube leaky fibers. The transmission losses of bundled fibers were firstly measured and it was found that bundled tube-leaky fibers have reasonably low transmission losses in spite of the small pixel size. Then thermal images were delivered by the bundled fibers combining with an InSb infrared camera. Considering applications with rigid endoscopes, an imaging system composed of a 30-cm long fiber bundle and a half-ball lens with a diameter of 2 mm was fabricated. By using this imaging system, a metal wire with a thickness of 200 μm was successfully observed and another test showed that the minimum detected temperature was 32.0 °C and the temperature resolution of the system was around 0.7 °C.

A novel fiber Bragg grating(FBG) with three reflection wavelengths is proposed and demonstrated experimentally by simply phase-mask-based grating inscription over the splice interface between a thin-core fiber (TCF) and a standard single-mode fiber (SMF). The key to the success of this device lies in the refractive index differences between SMF, TCF and splice interface, and the precisely localized grating inscription over the three regions. The reflection wavelengths present different sensitivities to temperature and strain, making it as a good candidate for the measurements of two parameters simultaneously.

A polarization-maintaining Yb-doped large mode area fiber with depressed-index inner cladding layer and confinement of rare-earth dopants has been drawn as a long tapered fiber. The larger end features a core/clad diameter of 56/400 μm and core NA ~ 0.07, thus leading to an effective mode area over 1000 μm2. The fiber was tested up to 100 W average power, with near diffraction-limited output as the beam quality M2 was measured < 1.2. As effective single-mode guidance is enforced in the first section due to enhanced bending loss, subsequent adiabatic transition of the mode field in the taper section preserves single-mode amplification towards the larger end of the fiber.

Transverse mode instability (TMI) has been recognized as a major limit to average power scaling of single-mode fiber laser besides the optical nonlinear effects. One key to mitigate TMI is to suppress the higher-order modes (HOMs) propagation in the optical fiber. By implementing additional cores in the optical fiber cladding, HOMs can be resonantly coupled from the main core to the surrounding cladding cores, leading to better HOMs suppression. Here, we demonstrate an Yb-doped multiple-cladding-resonant all-solid photonic bandgap fiber with a ~60μm diameter core for high power fiber lasers. The fiber has a multiple-cladding-resonant design in order to provide better HOMs suppression. Maximum laser power of 910w is achieved for a direct diode-pumped fiber laser without TMI with a 9m long fiber at 60cm coil diameter, breaking the TMI threshold of 800w that has been observed in large-mode-area PCFs with ~40μm core. This result is limited by fiber end burning due to the un-optimized thermal management. Later experiment demonstrates maximum laser power of 1050w with 90% lasing efficiency versus absorbed pump power in a 8m long fiber coiled at 80cm diameter, limited by the pump source. However, the fiber bending condition needs to be optimized in order to produce a better laser beam quality.

We experimentally demonstrate mid-infrared supercontinuum (SC) generation in chalcogenide multi-step index fibers (MSIF) pumped by a femtosecond laser. The fabricated chalcogenide MSIF is composed of a high refractive index core (C1) in the center, which is enclosed by a lower refractive index core layer (C2) and an outer cladding. This fiber structure is advantageous to tailor the chromatic dispersion with higher freedom and to keep the effective mode area small at long wavelengths. The high refractive index core, low refractive index core, and the outer cladding materials are As 2 Se 3 , AsSe 2 and As 2 S 5 , respectively. When the diameter of C1 and C2 are 7.8 and 30 μm, respectively, the zerodispersion wavelength (ZDW) of the fiber is 12.5 μm. The chromatic dispersion profile is near-zero and flattened within the range of ±20 ps/km/nm in the wavelength range from 4 to 17 μm and a broad normal dispersion region is obtained in the wavelength range shorter than the ZDW. In practice, a 2.8 cm long fiber is pumped at 10 μm by using a femtosecond laser whose pulse width is ~200 fs. The SC generation extending from 2 to 14 μm is obtained. Most of its spectrum is in the normal dispersion region of the fiber. These results are promising for the highly coherent mid-infrared SC generation.

We report here the design of a new chalcogenide hybrid microstructured optical fiber (HMOF) with a buffer layer around the core and its potential performance of tailoring chromatic dispersion and supercontinuum (SC) generation. The new chalcogenide HMOF has an AsSe 2 core. The refractive index difference Δn between the AsSe 2 core and cladding material is supposed to be 0.3. The fiber microstructure and the Δn between the core and buffer materials are designed in order to obtain broad anomalous dispersion regimes with near-zero and flattened chromatic dispersion profiles for broadband SC generation. Moreover, the suppression of chromatic dispersion fluctuation caused by fiber transverse geometry variation is investigated. By using the proposed chalcogenide buffer-embed HMOFs, the calculation shows that near-zero and flattened anomalous chromatic dispersion regimes from 4.5 μm can be obtained. When the variation of fiber structure occurs for ±1, ±5 and ±10 %, the chromatic dispersion fluctuation can be greatly suppressed. In addition, the calculation shows that a broad SC spectrum from 2.5 to more than 16.0 μm can be obtained when a 0.9-cmlong section of the new chalcogenide buffer-embed HMOF is pumped at 5.0 μm by a femtosecond laser with 1-kW peak power.

With all-normal-dispersion fibers, highly coherent supercontinuum (SC) can be obtained, which has several applications. Traditional air-hole photonic crystal fibers encountered some limitations for such light emission. In this study, all solid composite fibers with a silica glass cladding and a yttria-alumino-silicate glass core were fabricated, which were designed for flat coherent SCs. We achieved a flat normal dispersion in this composite fiber. Flat SCs were experimentally demonstrated with different pump conditions. The simulated SC spectra coincided well with the experimental results. It also indicated that a coherent SC with more than one octave can be obtained with higher input power.