Standard Silica Optical Fiber Research Articles

Realization of optical fiber regenerated gratings by rapid cooling and split annealing.

Rapid cooling,or quenching,during regeneration of seed gratings in standard single-mode silica optical fiber is explored. It is shown that regeneration can be broken up into stages in time. The novel, to the best of our knowledge, method of "split annealing" offers a unique tool for optimizing regeneration and studying fundamental glass science within a one-dimensional bi-material system. We demonstrate regeneration at temperatures as high as T = 1200°C for the first time as well as opening up an approach suited to batch processing of regenerated gratings.

Rainbow Archimedean spiral emission from optical fibres

We demonstrate a new practical approach for generating multicolour spiral-shaped beams. It makes use of a standard silica optical fibre, combined with a tilted input laser beam. The resulting breaking of the fibre axial symmetry leads to the propagation of a helical beam. The associated output far-field has a spiral shape, independently of the input laser power value. Whereas, with a high-power near-infrared femtosecond laser, a visible supercontinuum spiral emission is generated. With appropriate control of the input laser coupling conditions, the colours of the spiral spatially self-organize in a rainbow distribution. Our method is independent of the laser source wavelength and polarization. Therefore, standard optical fibres may be used for generating spiral beams in many applications, ranging from communications to optical tweezers and quantum optics.

Raman scattering and self-steepening in nonlinear plasmonic waveguide pulse equation

In this paper, we use Maxwell equations and the first order perturbation theory to obtain pulse propagation equation in a plasmonic waveguide made of nonlinear dielectric material. In this study, the effects of nonlinear self-steepening and Raman scattering are considered. Nonlinear coefficients of phase modulation, Raman and self-steepening are calculated numerically in terms of frequency and compared with a standard silica fiber. Obtained values of the nonlinear coefficients are about up to 300 times larger than that of standard silica optical fibers. So they can be used as part of all optical integrated circuit such as continuum generation, optical switching and frequency conversion.

2-μm Brillouin laser based on infrared nonlinear glass fibers.

Infrared fiber materials such as chalcogenide, tellurite, and heavily germanium-doped silica glasses are attractive materials for many applications based on nonlinear optical effects such as Kerr, Raman, and Brillouin processes. Here, we experimentally demonstrate a close-to-single-frequency Brillouin fiber laser in the 2-μm wavelength region either based on tellurite (TeO2) glass or on heavily germanium-doped silica glass. Our results reveal a strong enhancement of the Brillouin gain efficiency at 2 μm of more than 50 times that of standard silica optical fibers. A lasing threshold and narrow linewidth of 98 mW and 48 kHz, respectively, have been demonstrated in the tellurite fiber-based laser. This simple Brillouin laser source configuration confirms the potential applications of such fibers for the development of nonlinear photonic devices in the important 2-μm spectral range.

Miniature optical fiber sensors using surface enhanced Raman spectroscopy (SERS) for remote biochemical sensing

In this study, we present facile fabrication of a miniaturized remote sensing SERS platform using highly tunable Nano-Sphere Lithography (NSL) technique. Using 200 μm diameter optical fibers with high numerical aperture (0.5NA), the SERS enhancement of remote sensing was found to be 98% of direct sensing configuration. Standard silica optical fibers were used for remote sensing using SERS without additional need of optical filtering to mitigate fluorescence and Raman background of these fibers which allows fabrication of miniaturized remote sensing platforms that can be used for remote biochemical sensing.

Birefringent π-Phase-Shifted Fiber Bragg Gratings for Sensing at 1000 °C Fabricated Using an Infrared Femtosecond Laser and a Phase Mask

Birefringent π-phase-shifted Bragg gratings for multi-parameter sensing at temperatures ∼1000 °C are written inside a standard single mode silica optical fiber (SMF-28) with infrared femtosecond pulses and a special phase mask one half of which is shifted with respect to the other by 5/4 of the mask period. The birefringence is caused by the presence of light-induced sub-wavelength periodic planar nanostructures in the fiber core, whose orientation is controlled by the laser polarization, and is maximized when the laser pulse polarization is aligned perpendicular to the fiber core. The birefringence can reach ∼4.2 × 10−4 at room temperature at the 1.5 × 10−4 level after 100 h annealing at 1000 °C. Erasure and rewriting of the planar nanostructures inside fiber Bragg gratings by changing the laser pulse polarization is demonstrated.

High-temperature stable π-phase-shifted fiber Bragg gratings inscribed using infrared femtosecond pulses and a phase mask.

Type II π-phase-shifted Bragg gratings stable up to ~1000°C are written inside a standard single mode silica optical fiber (SMF-28) with infrared femtosecond pulses and a special phase mask. Inscription through the protective polyimide fiber coating is also demonstrated. The birefringence of the Bragg gratings and, as a result, the polarization dependence of their spectra are strongly affected by the femtosecond laser polarization. Using optimized writing conditions, the full width at half maximum of the π-phase-shifted passband feature can be ~30 pm in transmission, while the polarization-dependent shift of its central wavelength can be less than 8 pm, for a 7 mm long grating structure. This makes such gratings a unique tool for high-resolution measurements of temperature, load and vibration in extreme temperature environments.

Through-the-coating femtosecond laser inscription of very short fiber Bragg gratings for acoustic and high temperature sensing applications

Very short Type I and Type II Bragg gratings, on the order of 100 µm in length, are written through the protective polyimide coating of high NA and standard single mode silica optical fibers with infrared femtosecond pulses and a phase mask. By exploiting the transverse walk-off of apertured diffracted beams produced by the phase mask and a slit placed proximate the mask, complex grating structures are fabricated and characterized. These gratings are suitable for structural health monitoring based on acoustic measurements or localized high-temperature measurements.

Experimental stress–strain analysis of tapered silica optical fibers with nanofiber waist

We experimentally determine tensile force–elongation diagrams of tapered optical fibers with a nanofiber waist. The tapered optical fibers are produced from standard silica optical fibers using a heat and pull process. Both, the force–elongation data and scanning electron microscope images of the rupture points indicate a brittle material. Despite the small waist radii of only a few hundred nanometers, our experimental data can be fully explained by a nonlinear stress–strain model that relies on material properties of macroscopic silica optical fibers. This is an important asset when it comes to designing miniaturized optical elements as one can rely on the well-founded material characteristics of standard optical fibers. Based on this understanding, we demonstrate a simple and non-destructive technique that allows us to determine the waist radius of the tapered optical fiber. We find excellent agreement with independent scanning electron microscope measurements of the waist radius.

Development of a Fabrication Process for the Manufacturing of a Microspherical Probe for Coordinate Measuring Machine Applications

In recent years, downscaled coordinate measuring machines (CMMs) are in demand and bring challenges to the development of micro/nanoscale probes for a variety of microscale structure measurement applications. A working prototype apparatus is developed in which a microspherical optical fiber probe tip is created from a strand of standard single mode silica optical fiber using an electric discharge technique. The Taguchi method has been used to investigate the general effects of probe fabrication conditions that result in controllable fabrication of a quality probe tip. With proper control of the process parameters, spherical optical fiber probe tips with the desired diameters in the range of 133–360 μm with a diameter variance within 3% and minimum spherical tip center offset of about 2.2 μm have been achieved. An economical and flexible technique for the fabrication of a quality microspherical probe for micro/nano-CMM application is developed in this work.

Optical fiber sensor based on oblique angle deposition

The technique of oblique angle deposition has been extended to the fabrication of nanostructured metal coatings on the tips of standard silica optical fibers by thermal evaporation. The coatings are initiated as metal island films, which grow into extended rodlike structures as the deposition continues. The nanorod coatings demonstrate excellent surface-enhanced Raman scattering performance with variability of less than 10% as shown by direct measurements off the fiber tip with thiophenol as a test analyte. However, in the remote sensing configuration, the nanorod structures perform no better than thin metal island films. This appears to be mainly due to reduced transmission when nanorod lengths exceed ~100 nm. Moreover, the variability of remote measurements is increased to 18%. This is believed to be due to variations in coupling efficiency.

Fiber Optic Chemical Nanosensors Based on Engineered Single‐Walled Carbon Nanotubes: A Review

In this contribution, a review of the development of high‐performance optochemical nanosensors based on the integration of carbon nanotubes with the optical fiber technology is presented. The paper first provide an overview of the amazing features of carbon nanotubes and their exploitation as highly adsorbent nanoscale materials for gas sensing applications. Successively, the attention is focused on the operating principle, fabrication, and characterization of fiber optic chemosensors in the Fabry‐Perot type reflectometric configuration, realized by means of the deposition of a thin layer of single‐walled carbon nanotubes (SWCNTs) upon the distal end of standard silica optical fibers. This is followed by an extensive review of the excellent sensing capabilities of the realized SWCNTs‐based chemical nanosensors against volatile organic compounds and other pollutants in different environments (air and water) and operating conditions (room temperature and cryogenic temperatures). The experimental results reported here reveal that ppm and sub‐ppm chemical detection limits, low response times, as well as fast and complete recovery of the sensor responses have been obtained in most of the investigated cases. This evidences the great potentialities of the proposed photonic nanosensors based on SWCNTs to be successfully employed for practical environmental monitoring applications both in liquid and vapor phase as well as for space. Furthermore, the use of novel SWCNTs‐based composites as sensitive fiber coatings is proposed to enhance the sensing performance and to improve the adhesion of carbon nanotubes to the fiber surface. Finally, new advanced sensing configurations based on the use of hollow‐core optical fibers coated and partially filled by carbon nanotubes are also presented.

Mechanical and chemical characteristics of hermetically coated silica optical fibre

The mechanical strength of carbon hermetically coated fibres, compared to standard single mode silica optical fibre, has been investigated through chemical exposure to fluorinated vapour reagents, known as the harshest reagents for silica. Two reagents were used: ammonium hydrogenofluoride and hydrofluoric acid. Dynamic fatigue tests for different stress rates were implemented using a two-point bending testing device in order to determine n-stress corrosion parameter from Weibull statistics. As-received and chemically etched fibres were compared. Hermetically coated fibres appeared extremely durable in harsh chemical conditions. No significant change in the Weibull distribution and the mean fibre strength was observed after 6 days of chemical exposure to hydrofluoric vapours. In the same conditions, the mechanical strength of the epoxy-acrylate polymer coated standard fibres has decreased to nearly 50% of the initial strength value. SEM observations revealed crystal deposition on the chemical exposed fibres. Chemical analysis provides partial information on the complex mechanisms of fibre corrosion.

A Novel Optochemical Sensor Based on $\hbox{SnO}_{2}$ Sensitive Thin Film for ppm Ammonia Detection in Liquid Environment

In this paper, a fiber optic sensing system, designed, and developed for the detection of ammonia in aqueous ambient at room temperature, is presented. The sensor is constituted by a standard silica optical fiber (SOF) coated by a tin dioxide sensitive layer. The SnO2 films have been transferred onto the distal end of the SOF by means of the simple and low-cost electrostatic-spray-pyrolysis deposition technique. The spectral characterization of the fabricated samples has been carried out in the wavelength range 400-1750 nm in order to estimate the thickness of the SnO2 fiber coatings. The morphology and the elemental composition of the deposited layers have also been investigated by means of scanning-electron-microscopy observation and energy-dispersive-spectrometer analysis, respectively. Single-wavelength reflectance measurements have been carried out to test the sensing performances of the realized sensors toward ammonia traces in water. A fiber-Bragg-grating temperature sensor has also been used for monitoring the temperature changes occurring inside the test ambient during the experimental measurements, in order to identify the effects of thermal drifts on the sensor response. The results here presented demonstrate that the developed refractometric chemical sensor is able to provide measurements of ammonia concentration in water and at room temperature with a high sensitivity, response times of few minutes, and a resolution as low as 2 ppm

Acoustic and Optical VOCs Sensors Incorporating Carbon Nanotubes

The authors investigate the sensing properties of single-walled carbon nanotubes (SWCNTs) films, which are used as nanostructured materials for chemical sensors onto three types of transducers using different principles of operation as surface acoustic waves (SAWs), quartz-crystal microbalance (QCM), and a standard silica optical fiber (SOF) for detection of volatile organic compounds at a room temperature. The sensing probes have been configured as 315- and 433-MHz SAW two-port resonator-based oscillator, 10-MHz QCM resonator, and SOF light-reflectometry-based system at a wavelength of 1310 nm. A nanocomposite film of SWCNTs embedded in a cadmium-arachidate matrix was deposited by Langmuir-Blodgett (LB) technique onto the SAW sensors. An LB multilayer of SWCNTs-onto-CdA buffer material was also deposited onto the QCM and SOF sensors. The experiments demonstrate that carbon-nanotubes acoustic and optical sensors are highly sensitive to a wide range of polar and nonpolar organic solvents up to a sub-ppm detection limit at a room temperature

Sensing properties of buffered and not buffered carbon nanotubes by fibre optic and acoustic sensors

Single-walled carbon nanotubes (SWCNTs) are advanced nanostructured materials with promising sensing properties in terms of sensitivity, low sub-ppm limit of detection, on-line and real-time vapour detection, at room temperature. This work is focused on the study of the sensitivity to aromatic volatile organic compounds (VOCs) of standard silica optical fibre (SOF) and quartz crystal microbalance (QCM) sensors incorporating Langmuir–Blodgett multilayers of SWCNTs. Multilayers of SWCNTs with different thicknesses and successfully transferred directly onto the sensors' surface were tested for the detection of toluene and xylene at room temperature and compared with the sensing performances of SWCNT multilayers buffered by a linker multilayer of cadmium arachidate. The optical and acoustic sensors' principle of operation relies respectively on the complex dielectric function and mass change induced by target analyte molecules adsorbed into the sensitive nanomaterials. A time division multiplexing approach for both optical and acoustic chemical sensors has been exploited in order to simultaneously test up to eight SOF and six QCM sensors. The results obtained demonstrate that the sensors based on SWCNTs provide high sensitivity, very low limits of VOC detection and fast response, at room temperature, with a clear dependence of the sensors' sensitivities on the nanomaterial thickness. Furthermore, higher sensitivity was observed in the case of optical fibre sensors exposed to xylene; in addition, behaviour with the opposite sign in the optical response occured between buffered and not buffered SWCNTs overlayers. Also, effects of humidity have been investigated in the case of optical fibre sensors demonstrating a linear dependence of the response at a constant temperature of 28 °C.

Carbon nanotube acoustic and optical sensors for volatile organic compounddetection

Carbon nanotube coated acoustic and optical sensors have been successfully studied forvolatile organic compound (VOC) sensing applications, at room temperature. Here,Langmuir–Blodgett (LB) films consisting of tangled bundles of single-walled carbonnanotubes (SWCNTs) have been transferred onto different transducing sensors by using alinker–buffer LB multilayered material of cadmium arachidate pre-deposited on thesensor surface to promote adhesion of SWCNTs. Two different kinds of sensorshave been designed, fabricated and utilized: quartz crystal microbalance 10 MHzAT-cut quartz resonators and standard silica optical fibre sensors based on lightreflectometry at a wavelength of 1310 nm. The proposed detection techniques are focusedon two key parameters in gas sensing applications: mass and refractive index,and their changes induced by gas molecule absorption. The results indicate highsensitivity, good repeatability and reversibility. Signals from each sensor type havebeen analysed and processed by using pattern recognition techniques such asprincipal component analysis and use of artificial neural networks. The recognitionof the hybrid system is successfully performed, improving the data fusion fromacoustic and optical sensors with SWCNT-functionalized sensors that are highlydiscriminating. To our knowledge, this is the first reported study of combined hybridintegration of acoustic sensors with optical fibre sensors using nanostructuredmaterials as single-walled carbon nanotubes for VOC detection, at room temperature.

Carbon nanotubes-coated multi-transducing sensors for VOCs detection

Langmuir–Blodgett (LB) films consisting of tangled bundles of single-walled carbon nanotubes (SWCNTs) have been used as sensing nanomaterials onto three different types of sensory systems using complementary transducing principles as surface acoustic waves (SAWs), quartz crystal microbalance (QCM) and standard silica optical fiber (SOF) for volatile organic compounds (VOCs) detection, at room temperature. The multi-transducing probes have been configured as 433 MHz SAW oscillator, 10 MHz QCM oscillator, and SOF reflectometry-based system at a wavelength of 1310 nm. A nanocomposite film of SWCNTs embedded in a cadmium arachidate (CdA) matrix was deposited by LB methodics onto SAW sensors. A LB multilayer of SWCNTs-onto-CdA buffer material was deposited onto QCM and SOF sensors. Highly sensitive, repeatable and reversible responses of the SWCNTs sensors indicate feasible VOCs detection in a wide mmHg vapor pressures range. The VOCs sensing performance of the SWCNTs-based multi-transducing sensors will be discussed.

Colloidal photonic crystal cladded optical fibers: Towards a new type of photonic band gap fiber

A facile approach of fabricating a new type of hollow photonic band gap fibers is proposed. Templates for generating such fibers are demonstrated by a complete and uniform coating of a standard silica optical fiber (125 mum diameter) with a three-dimensional colloidal photonic crystal through isothermal heating evaporation induced self-assembly. The photonic crystal cylindrical annulus is characterized by optical and scanning electron microscopy, and is found to yield a 1.4-mum stop band by optical reflection and transmission spectroscopy. The results also demonstrate a practical means of enveloping macro- or micro-curved surfaces with three-dimensional photonic crystals, a task that is geometrically challenging by other photonic crystal fabrication methods.

Novel Optoelectronic Sensing System for Thin Polymer Films Glass Transition Investigation

The glass transition zone of thin polystyrene films on silica substrates has been investigated by using a novel optoelectronic integrated sensor involving simultaneous refractive index and temperature measurements. The sensor design is based on the deposition of thin polymer film by chemical dipping on the distal end of a standard silica optical fiber. Direct reflectometric interrogation and fiber-Bragg grating sensor integration have been used to simultaneously retrieve information about the refractive index variation over the glass transition region revealed by a temperature ramping. Sensor modeling and sensitivity have been investigated. The glass transition has been identified by measuring the change of the thermooptic coefficient in cooling down experiments. The comparison between refractive index transition and standard calorimetric analysis has been carried out to test the optoelectronic integrated sensor reliability. The proposed sensing system has demonstrated that it is able to measure the glass transition temperature of thin polymer films; moreover, the system and procedure can be readily implemented to investigate the effect of polymeric sample finite size and specific energetic interactions on the glass transition zone.