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.

Acousto-optic coupling in polyimide-coated single-mode optical fibers using flexural elastic waves is demonstrated. The effect of the polyimide coating on the acousto-optic interaction process is analyzed in detailed. Theoretical and experimental results are in good agreement. Although the elastic attenuation is significant, we show that acousto-optic coupling can be produced with a reasonably good efficiency. To our knowledge, it is the first experimental demonstration of acousto-optic coupling in optical fibers with robust protective coating.

In this work, we report on a twin-core fiber sensor system that provides improved spectral efficiency, allows for multiplexing and gives low level of crosstalk. Pieces of the referred strongly coupled multicore fiber are used as sensors in a laser cavity incorporating a pulsed semiconductor optical amplifier (SOA). Each sensor has its unique cavity length and can be addressed individually by electrically matching the periodic gating of the SOA to the sensor’s cavity roundtrip time. The interrogator acts as a laser and provides a narrow spectrum with high signal-to-noise ratio. Furthermore, it allows distinguishing the response of individual sensors even in the case of overlapping spectra. Potentially, the number of interrogated sensors can be increased significantly, which is an appealing feature for multipoint sensing. © 2022, The Author(s).

In this article, we report on a carbon-coated optical fiber that is suitable to be used simultaneously as a transmission medium and as a sensor. It consists of a standard single mode fiber (SMF) sleeved in two layers of coating, which provide protection and isolation from external elements. The inner layer is made of carbon, whereas the outer is made of polymer. When the fiber is subjected to mechanical stress, the electrical resistance of the carbon layer changes accordingly. The voltage variations caused by the former can be measured with high accuracy and without interfering with the light propagating through the SMF. In this work, the feasibility of this operating principle is demonstrated in a low coherence Michelson interferometer in which electrical and optical signals were measured simultaneously and compared to each other. Results indicate that electrical measurements are as precise as the optical ones and with linear behavior, reaching a sensitivity of 1.582 mV/με and able to detect vibrations down to 100 mHz. © 2024 The Authors

Optical properties of nanorods in the presence of external electric field when confined to a special optical fiber was investigated, showing an increase of the longitudinal absorption peak in the presence of the field.

We study the creation and erasure of the linear electrooptical effect in silicate fibers by optical poling. Carriers are released by exposure to green light and displaced with simultaneous application of an internal dc field. The second order nonlinear coefficient induced grows with poling bias. The field recorded (~108 V/m) is comparable to that obtained through classical thermal poling of fibers. In the regime studied here, the second-order nonlinearity induced (~0.06 pm/V) is limited by the field applied during poling (1.2 × 108 V/m). Optical erasure with high-power green light alone is very efficient. The dynamics of the writing and erasing process is discussed, and the two dimensional (2D) field distribution across the fiber is simulated.

In this work the inner surface of a microstructured optical fiber, where a Bragg grating was previously inscribed, has been functionalized using peptide nucleic acid probe targeting a DNA sequence of the cystic fibrosis disease. The solution of DNA molecules, matched with the PNA probes, has been infiltrated inside the fiber capillaries and hybridization has been realized according to the Watson - Crick Model. In order to achieve signal amplification, oligonucleotide-functionalized gold nanoparticles were then infiltrated and used to form a sandwich-like system. Experimental measurements show a clear wavelength shift of the reflected high order mode for a 100 nM DNA solution. Several experiments have been carried out on the same fiber using the identical concentration, showing the same modulation and proving a good reproducibility of the results, suggesting the possibility of the reuse of the sensor. Measurements have been also made using a 100 nM mis-matched DNA solution, containing a single nucleotide polymorphism, demonstrating the high selectivity of the sensor.

A shear sensor based on a ferrofluid infiltrated microstructured optical fiber Bragg grating is presented. Shear displacements between 250μm and 4.5mm are measured, corresponding to spectral changes in the reflected spectra greater than 5dB.

A novel DNA sensing platform based on a Peptide Nucleic Acid-functionalized Microstructured Optical Fibers gratings has been demonstrated. The inner surface of different MOFs has been functionalized using PNA probes, OligoNucleotides mimic that are well suited for specific DNA target sequences detection. The hybrid sensing systems were tested for optical DNA detection of targets of relevance in biomedical application, using the cystic fibrosis gene mutation, and food-analysis, using the genomic DNA from genetic modified organism soy flour. After the solutions of DNA molecules has been infiltrated inside the fibers capillaries and hybridization has occurred, oligonucleotidefunctionalized gold nanoparticles were infiltrated and used to form a sandwich-like system to achieve signal amplification. Spectral measurements of the reflected signal reveal a clear wavelength shift of the reflected modes when the infiltrated complementary DNA matches with the PNA probes placed on the inner fiber surface. Measurements have also been made using the mismatched DNA solution for the c, containing a single nucleotide polymorphism, showing no significant changes in the reflected spectrum. Several experiments have been carried out demonstrating the reproducibility of the results and the high selectivity of the sensors, showing the simplicity and the potential of this approach.

Silica fibers with internal electrodes biased with HV are poled when simultaneously excited by green light. The x(2) induced measured through the Pockels effect at 1.55 μm reaches ~0.11 pm/V. Poling and erasure are studied.

Potentially low-cost polarization controllers were studied with a current-driven internal electrode fibers. The return loss was determined for the device. An EDFA was used as light source, and five devices were constructed and tested. The polarization dependent loss (PDL) of the polarization controllers was measured between 1530 nm and 1570 nm using the Jones-matrix method. The response times for the controllers was found to be relatively slow. The rise time of the optical response was significantly improved by overshooting the current pulse.

In this work, we present a quantitative (statistical) 3D morphological characterization of optical fibers used in electric-field sensing. The characterization technique employs propagation-based x-ray phase-contrast microcomputed tomography (micro-CT). In particular, we investigate specialty optical fibers that contain microstructured holes that are electro-optically modified by thermal poling to induce second-order nonlinear effects (SONE). The efficiency of the SONE is reflected in the characterization parameter, Vπ, which is highly dependent on the dimensions of the fiber. The fiber microstructures must be uniform to support the fabrication of reproducible devices. The results obtained using the micro-CT technique show that uncertainty of ±1.7% arises in the determination of the expected value of the voltage that causes a change in the phase of the electromagnetic wave equal to π rad (Vπ ), demonstrating a great advantage, compared with other techniques e.g. SEM, which would need at least 1000 images of the cross-section of an optical fiber, taken at different points, making the process more expensive and time-consuming.

Gold nanoparticles have been used since antiquity for the production of red-colored glasses. More recently, it was determined that this color is caused by plasmon resonance, which additionally increases the material's nonlinear optical response, allowing for the improvement of numerous optical devices. Interest in silica fibers containing gold nanoparticles has increased recently, aiming at the integration of nonlinear devices with conventional optical fibers. However, fabrication is challenging due to the high temperatures required for silica processing and fibers with gold nanoparticles were solely demonstrated using sol-gel techniques. We show a new fabrication technique based on standard preform/fiber fabrication methods, where nanoparticles are nucleated by heat in a furnace or by laser exposure with unprecedented control over particle size, concentration, and distribution. Plasmon absorption peaks exceeding 800 dB m-1 at 514-536 nm wavelengths were observed, indicating higher achievable nanoparticle concentrations than previously reported. The measured resonant nonlinear refractive index, (6.75 ± 0.55) × 10-15 m2 W-1, represents an improvement of >50×.

Here, we present an overview of the ellipsometric characterization of hybrid thin films and metal nanoparticles by surface plasmon resonance (SPR) spectroscopy, together with the dynamic control of the optical properties of the latter for applications in optoelectronic devices. A description of traditional techniques used for the determination of the thickness and refractive index of organic thin films deposited over the SPR planar sensing platforms is presented, with a discussion of the most recent applications in the ellipsometric characterization of thin film of metal nanoparticles and graphene layers. We conclude by describing recent results developing a dynamically tunable plasmonic pixel, where the electric-field-controlled alignment of gold nanorods in a colloidal suspension can enable optical switching at frequencies greater than megahertz.

Using confocal luminescence microscopy and detailed evaluation of the luminescence spectra in terms of intensity, spectral position and width, we determined the erbium doping profiles and their inhomogeneities in high index profile singly mode fibers. 

We illuminate particles in a solution using fibers with cladding holes. Particles sufficiently near the fiber tip and with the correct optical signature are collected into the holes with good specificity, mimicking cell-collection for diagnostics.

Optofluidics is exploited in an all-fiber component to detect and identify through fluorescence particles flowing at high rate and inertially focused in a capillary. The system represents a first step towards an in-fiber flow cytometer.

We demonstrate the digital electric field induced switching of plasmonic nanorods between "1" and "0" orthogonal aligned states using an electro-optic fluid fiber component. We show by digitally switching the nanorods that thermal rotational diffusion of the nanorods can be circumvented, demonstrating an approach to achieve submicrosecond switching times. We also show, from an initial unaligned state, that the nanorods can be aligned into the applied electric field direction in 110 ns. The high-speed digital switching of plasmonic nanorods integrated into an all-fiber optical component may provide opportunities for remote sensing and signaling applications. © 2017 Author(s).

As information technologies move from electron- to photon-based systems, the need to rapidly modulate light is of paramount importance. Here, we study the evolution of the electric-field-induced alignment of gold nanorods suspended in organic solvents. The experiments were performed using an all-fiber optofluidic device, which enables convenient interaction of light, electric fields, and the nanorod suspension. We demonstrate microsecond nanorod switching times, three orders of magnitude faster than a traditional Freederickcz-based liquid crystal alignment mechanism. We find that the dynamics of the alignment agrees well with the Einstein–Smoluchowski relationship, allowing for the determination of the rotational diffusion coefficient and polarizability anisotropy of the nanorods as well as the effective length of the ligands capping the nanorods. The ability to dynamically control the optical properties of these plasmonic suspensions coupled with the point-to-point delivery of light from the fiber component, as demonstrated in this work, may enable novel ultrafast optical switches, filters, displays, and spatial light modulators.

A fiber probe traps single micrometer-particles by fluid suction into a hollow microstructure and enables optical identification by the fluorescence light collected in a fiber core. The probe finds applications in life-science and environmental monitoring.

A micro-structured fiber-based system for identification and collection of fluorescent particles is demonstrated. An optical fiber probe with longitudinal holes in the cladding is used to retrieve fluorescent particles by exerting microfluidics forces. Laser induced fluorescent (LIF) is carried out by the fiber probe and an optical setup. When a particle with a previously chosen fluorescence wavelength is identified, a vacuum pump is activated collecting the particle into a hole. Green and red fluorescent polystyrene particles were detected and selectively retrieved.

Liquid crystal based devices can arbitrarily control the amplitude, phase and polarization of light, enabling disruptive technologies such as flat screen televisions and smart phones. Yet, the Achilles heel of these devices are their slow, millisecond switching speeds, constraining potential applications. Here we develop the concept of a dynamic plasmonic pixel as a novel paradigm for liquid crystal devices using the electric field controlled alignment of gold nanorods. Experiments were performed using an electro-optic fluid fiber device, which enabled convenient interaction of light, electric fields and the nanorod suspension. We studied the evolution of the electric-field induced alignment of gold nanorods and demonstrate microsecond switching times, 3 orders of magnitude faster than a traditional Freederickcz-based liquid crystal alignment mechanism. We find that the dynamics of the alignment agrees well with the Einstein-Smoluchowski relationship. Furthermore, by digitally switching the nanorods between orthogonally aligned states, we show switching frequencies greater than MHz can be achieved. The development of these dynamically tunable plasmonic pixels may lead to ultrafast optical switches, filters, displays and spatial light modulators.

Towards a portable point of care flow cytometry platform, we present here an integrated all optical fiber-based optofluidic system capable of counting and discriminating fluorescent particles and cells. The robust and compact device incorporates optical fibers and circular capillaries to build an all-fiber optofluidic device to enable counting particles based on their fluorescent and back-scatter light emission. Here, we combine this with inertial- and elasto-inertial microfluidics for sheathless particle and cell focusing for integrated detection with scattering and fluorescence detections - all necessary components of standard cytometers. We validated the system for cell counting based on scattering and fluorescence.

We report in an original nonlinear optofluidic fiber arrangement the observation of an octave-spanning Raman cascade that subsequently broadens towards supercontinuum generation due to the stimulated Raman-Kerr scattering. © 2014 Optical Society of America.

Integrated liquid-core optical fibers (LCOF) have recently emerged as new photonic platforms for their wide range of potential applications in nonlinear photonics [1,2]. Their advantages over solid-core glass fibers include broad transparency from the UV to the mid-IR and enhanced nonlinear optical effects. For instance, enhanced stimulated Raman scattering (SRS) has recently been demonstrated using carbon disulfide, Toluene or ethanol nonlinear liquids in integrated all-fiber systems compatible with standard single-mode fibers (SMFs) [1,2].

Distributed sensors based on phase-optical time-domain reflectometry (phase-OTDR) are suitable for aircraft health monitoring due to electromagnetic interference immunity, small dimensions, low weight and flexibility. These features allow the fiber embedment into aircraft structures in a nearly non-intrusive way to measure vibrations along its length. The capability of measuring vibrations on avionics structures is of interest for what concerns the study of material fatigue or the occurrence of undesirable phenomena like flutter. In this work, we employed the phase-OTDR technique to measure vibrations ranging from some dozens of Hz to kHz in two layers of composite material board with embedded polyimide coating 0.24 numerical aperture single-mode optical fiber. © 2017 SPIE.

We propose and experimentally demonstrate a spatially tunable phase-OTDR based distributed microphone for listening to the sound of multiple machines. The distributed acoustic sensing capability, allied with the real-time spatial tuning, enables listening to a drill and to a cooling water system pump placed in two different sections along a single optical fiber, one at a time. The recorded acoustic waveform profile of both machines agreed with their operating cycles. Moreover, the sounds generated by both engines are successfully distinguished with the proposed method even when both machines are operating simultaneously..

This work presents an on-field validation of an in-house built real-Time phase-OTDR for monitoring the status of roller bearings. The acoustic sensor prototype was designed and assembled at RISE and evaluated on a 1 m diameter bearing at SKF AB facilities in Göteborg, Sweden. A 0.24 numerical aperture single-mode optical fiber was installed in the bearing lubrication groove, which is 50 mm large and 5 mm deep. Tests were performed to verify the response of the phaseOTDR to acoustic emissions in the bearing such as hammer hits and running the rollers at different loads. The fiber optic sensor results agree with the measurements performed by a standard industrial high sensitivity electronic accelerometer used for comparison. Moreover, as opposed to the reference electronic sensor, the phase-OTDR proved to be insensitive to electrical disturbances present on the environment.

Certain applications of fiber sensors (e.g. avionics, oil industry) imply extreme operating conditions spurring the development of hermetic all-fiber devices. We present a hermetic all-fiber phase modulator based on Joule heating in a carbon-coated fiber. 

Joule effect and thermal response of several carbon coated fibers are modelled and analysed. An electro thermally driven all-fiber phase modulator based on these principles is proposed and a proof of concept of it is characterized. This kind of fibers could be the basis for developing all fiber components aimed to operate in environments where the strength increase and impermeability to hydrogen diffusion guaranteed by the carbon coating is crucial.

An all-fiber dye laser is demonstrated. The dye solution is kept under flow, allowing for high repetition rate pumping. Threshold average pump power of 2.15 mW and conversion slope efficiency of ~8.5% are achieved.

Optofluidic dye lasers may play a significant role in future laser applications in numerous areas, combining wavelength flexibility with integration and ease of operation. Nevertheless, no all-fiber integrated dye lasers have been demonstrated so far. In this paper, we report on a series of optofluidic all-fiber Rhodamine optical sources operating at a repetition rate as high as 1 kHz. Dye bleaching is avoided by circulating the Rhodamine dye during optical excitation. The laser radiation is extracted via conventional fibers that are spliced to the dye-filled capillary active medium. A tuneable amplified spontaneous emission source, a multimode laser, and a few transverse-mode laser are demonstrated by adjusting the setup. Threshold pump energies as low as similar to 1 mu J and slope efficiencies of up to mu 9% were obtained, indicating the potential for realworld applications in areas such as spectroscopy and biomedicine.

Recent progress in thermal poling of silica fibers is reviewed. It is demonstrated that state-of-the-art poled fibers can be used in a number of practical applications. Challenges for further development of poled fiber devices are discussed and possible solutions proposed.

An optical fiber component and setup were developed to insert and remove gases from hollow-core optical fibers, allowing gas/light mixing over the length of the fiber for gas sensing applications. Transmitted signals acquired at the output of the fiber contain information regarding absorption occurring inside the fiber, providing a spectroscopic signature of the gas or gases in the fiber. Spectra for 1 atm of acetylene (C2H2) around 1525 nm and 1 atm of carbon dioxide (CO2) around 1432 nm were obtained and compared to HITRAN data, showing good agreement. The setup can also be used to prepare gas cells.

E-field sensing with a thermally poled fiber in a Sagnac interferometer is presented. Contactless detection is achieved for fields > 0:23MV=m at 50Hz and higher sensitivity is obtained at higher frequencies.

A salinity sensor based on a Two-Core optical fiber is demonstrated. The sensor response and sensitivity can be easily adjusted by simply controlling an etching process to expose the off-axis core. The proposed RI sensor exhibits a sensitivity exceeding 1,400 nm/RIU for salinity concentrations below 1 M.

A Refractive Index sensor based on a Two-Core optical fiber is demonstrated. The sensor response and sensitivity can be easily adjusted by simply controlling an etching process to expose the off-axis core. The proposed RI sensor exhibits a sensitivity exceeding 2,100 nm/RIU.

A compact fiber capillary based microflow cytometer capable of detecting side-scattered-light is demonstrated by using a 450 angle-cleaved metal coated optical fiber tip.

We present an optical fiber-based selective cell picking module capable of picking up and transferring single cells or clusters. Our Lab-in-a-fiber (LIF) module detects labelled cancer cells (MCF-7) and picks them up for further analysis. 

Using various fiber capillaries with different diameters and multiple holes we develop an optofluidic component capable of separating micron-sized beads emulating cells and bacteria, exploiting particle focusing in a viscoelastic fluid and analyzed optically.  © 2020 The Author(s).

Applications of optical fibers in telecommunication and sensing are rapidly emerging where the fiber properties are related to the controlled addition of dopants such as germanium, phosphorous, fluorine and erbium. The modern ToF-SIMS instrument, with its high sensitivity and high lateral resolution, has shown to be an excellent tool to directly analyze cross-sections of as-manufactured fibers. The present work describes ToF-SIMS imaging of the dopant distribution in fluorine, germanium and rare-earth doped fibers where dopants are confined to a few μm in the core. The increased fluorine diffusion in the fluorine doped fibers due to chemical reactions with hydroxyl groups was examined. This process is utilized in the manufacture of thermally stable chemical composition fiber Bragg gratings. We were able to produce ToF-SIMS elemental images with a lateral resolution around 0.5μm showing the detailed distribution of the dopants.

The cement industry is facing pressure to find technological solutions in reducing greenhouse gas emissions owing to the large amount of process emissions originating from the calcination of limestone. In this communication, an all-fibre gas monitoring system based on anti-resonant hollow-core fibres is proposed. An on-field test was performed in the harsh environment of a cement factory and it demonstrated the feasibility of using this system for low-concentration carbon dioxide and carbon monoxide monitoring in exhaust fumes

The temperature characteristics of the birefringence of side-hole fibers filled with liquids or metal are investigated, aiming at providing a basis for on/off temperature sensing. Short pieces of fiber are filled and the change in birefringence is registered using measurements in reflective mode of the transmitted power through a linear polarizer at 1550 nm. The rapid change in the birefringence behavior of the fiber at the temperature of the phase transition of the filler substance is shown, and from the measurement data the phase transition temperatures can be determined as well as an estimation of the birefringence change with temperature. The experimental results are supported by numerical simulations.

A novel all-fiber spliced microcavity for chemical and biological optical studies is described. Its design allows coupling with low loss light from a fiber into a liquid or gas contained in a capillary or PCF. 

The integration of a microspherical whispering gallery mode (WGM) resonator inside a microstructured optical fiber taper is demonstrated. Preliminary WGM spectra of this in-fiber resonator in transmission mode are presented and discussed.

Herein, we demonstrated a T-shaped whispering gallery modes (WGMs) excitation system including a tapered single mode fiber (SMF), a tapered microstructured optical fiber (MOF) and a BaTiO3 microsphere for efficient light coupling and routing between the two fibers. The BaTiO3 microsphere is semi-immersed into the capillary of a tapered MOF, while the tapered SMF is placed perpendicularly to MOF in a contact with equatorial region of the microsphere. Based on that, three channels joined by the microsphere are formed, and excitation and measurement of WGMs is possible either using the SMF or the MOF taper. The measured WGMs spectra reveal light routing along Q-factors between 4500 and 6100, along with scattering signal with all three fiber ports and parities.

An all-fiber integrated device capable of separating and counting particles is presented. A sequence of silica fiber capillaries with various diameters and longitudinal cavities are used to fabricate the component for size-based elasto-inertial passive separation of particles followed by detection in an uninterrupted continuous flow. Experimentally, fluorescent particles of 1 μm and 10 μm sizes are mixed in a visco-elastic fluid and fed into the all-fiber separation component. The particles are sheathed by an elasticity enhancer (PEO - polyethylene oxide) to the side walls. Larger 10 μm particles migrate to the center of the silica capillary due to the combined inertial lift force and elastic force, while the smaller 1 μm particles are unaffected, and exit from a side capillary. A separation efficiency of 100% for the 10 μm and 97% for the 1 μm particles is achieved at a total flow rate of 50 μL min−1. To the best of our knowledge, this is the first time effective inertial-based separation has been demonstrated in circular cross-section microchannels. In the following step, the separated 10 μm particles are routed through another all-fiber component for counting and a counting throughput of ∼1400 particles per min is demonstrated. We anticipate the ability to combine high throughput separation and precise 3D control of particle position for ease of counting will aid in the development of advanced microflow cytometers capable of particle separation and quantification for various biomedical applications.