Maria Konstantaki

Optical fiber long-period grating humidity sensor with poly(ethylene oxide)/cobalt chloride coating

A long-period fiber grating (LPFG) humidity sensor is reported utilizing poly(ethylene oxide)/cobalt chloride (PEO/CoCl2) as a hybrid hygrosensitive cladding coating. A thin overlay of the material is deposited on the LPFG and with exposure to different ambient humidity levels, its spectral properties are modified. The material parameters associated with the sensing mechanism may include those of refractive index, absorption, and morphological alterations of the overlaid material. Relative humidity variations in the range from 50% to 95% have been detected with a resolution better than 0.2%. The response time constant of the fiber sensor is of the order of a few hundred milliseconds.

Onion-like carbon and diamond nanoparticles for optical limiting

The present study reports on the experimental investigation of the nonlinear optical response of polydispersed and ultradispersed diamond powders and onion-like carbon structures in water suspension. It has been found that the onion-like carbon structures exhibit much stronger optical limiting action compared with the diamond powder suspensions. It is also shown that under our experimental conditions the nonlinear refraction of the onion-like structures was negligible.

A spectrally tunable microstructured optical fibre Bragg grating utilizing an infiltrated ferrofluid

The spectral response of a Bragg grating reflector inscribed in a microstructured optical fibre is tuned by employing an infiltrated ferrofluid, while modifying the overlap of the ferrofluidic medium with the grating length. Significant spectral changes in terms of Bragg grating wavelength shift and extinction ratio were obtained under static magnetic field actuation. Spectral measurements revealed non-bidirectional propagation effects dependent upon the relative position between the ferrofluid and the grating. The actuation speed of the device was measured to be of the order of few seconds.

An ethanol vapor detection probe based on a ZnO nanorod coated optical fiber long period grating

A new ethanol vapor detection probe based on an optical fiber long period grating overlaid with a zinc oxide (ZnO) nanorods layer is presented. The ZnO nanorod layer was developed onto the cladding of the fiber using aqueous chemical growth, seeded by a thin layer of metallic Zn. The growth of the ZnO nanorods overlayer onto the long period grating cladding is monitored in real time for investigating its effect on the spectral properties of the device and its subsequent role in the sensing mechanism. Results are presented, on the correlation between the growth time of the ZnO layer and the ethanol vapor detection performance. Reversible spectral changes of the notch extinction ratio of more than 4 dB were recorded for ~50 Torr of ethanol vapor concentration. In addition, photoluminescence emission studies of the ZnO overlayer performed simultaneously with the optical fiber spectral measurements, revealed significant ethanol induced changes in the intensity of the bandgap peak.

Detection of unamplified genomic DNA by a PNA-based microstructured optical fiber (MOF) Bragg-grating optofluidic system.

Microstructured optical fibers containing microchannels and Bragg grating inscribed were internally functionalized with a peptide nucleic acid (PNA) probe specific for a gene tract of the genetically modified Roundup Ready soy. These fibers were used as an optofluidic device for the detection of DNA by measuring the shift in the wavelength of the reflected IR light. Enhancement of optical read-out was obtained using streptavidin coated gold-nanoparticles interacting with the genomic DNA captured in the fiber channels (0%, 0.1%, 1% and 10% RR-Soy), enabling to achieve statistically significant, label-free, and amplification-free detection of target DNA in low concentrations, low percentages, and very low sample volumes. Computer simulations of the fiber optics based on the finite element method (FEM) were consistent with the formation of a layer of organic material with an average thickness of 39 nm for the highest percentage (10% RR soy) analysed.

Label-free DNA biosensor based on a peptide nucleic acid-functionalized microstructured optical fiber-Bragg grating

Abstract. We describe a novel sensing approach based on a functionalized microstructured optical fiber-Bragg grating for specific DNA target sequences detection. The inner surface of a microstructured fiber, where a Bragg grating was previously inscribed, has been functionalized by covalent linking of a peptide nucleic acid probe targeting a DNA sequence bearing a single point mutation implicated in cystic fibrosis (CF) disease. A solution of an oligonucleotide (ON) corresponding to a tract of the CF gene containing the mutated DNA has been infiltrated inside the fiber capillaries and allowed to hybridize to the fiber surface according to the Watson-Crick pairing. In order to achieve signal amplification, ON-functionalized gold nanoparticles were then infiltrated and used in a sandwich-like assay. Experimental measurements show a clear shift of the reflected high order mode of a Bragg grating for a 100 nM DNA solution, and fluorescence measurements have confirmed the successful hybridization. Several experiments have been carried out on the same fiber using the identical concentration, showing the same modulation trend, suggesting the possibility of the reuse of the sensor. Measurements have also been made using a 100 nM mismatched DNA solution, containing a single nucleotide mutation and corresponding to the wild-type gene, and the results demonstrate the high selectivity of the sensor.

Phase-shifted Bragg microstructured optical fiber gratings utilizing infiltrated ferrofluids

Results are presented on the efficient spectral manipulation of uniform and chirped Bragg reflectors inscribed in microstructured optical fibers utilizing short lengths of ferrofluids infiltrated in their capillaries. The infiltrated ferrofluidic defects can generate either parasitic reflection notch features in uniform Bragg reflectors of up to 80% visibility and ~0.1 nm spectral shift or tunability of the bandwidth and strength reflection up to 100% when introduced into chirped gratings. Spectra are presented for different spatial positions and optical characteristics of the ferrofluidic section.

Optofluidic magnetometer developed in a microstructured optical fiber

A directional, in-fiber optofluidic magnetometer based on a microstructured optical fiber (MOF) Bragg-grating infiltrated with a ferrofluidic defect is presented. Upon application of a magnetic field, the ferrofluidic defect moves along the length of the MOF Bragg grating, modifying its reflection spectrum. The magnetometer is capable of measuring magnetic fields from 317 to 2500 G. The operational principle of such in-fiber magnetic field probe allows the elaboration of directional measurements of the magnetic field flux.

Transient and instantaneous third-order nonlinear optical response of C60 and the higher fullerenes C70, C76 and C84

We report results on the transient and the instantaneous nonlinear optical (NLO) response of C60 and the higher fullerenes C70, C76, C84 dissolved in toluene using, respectively, the z-scan technique and energy-dependent transmission measurements with 532 nm, 10 ns laser pulses, and the optical Kerr effect with 800 nm, 100 fs laser pulses. The NLO measurements on C76 are the first reported for this fullerene. The second hyperpolarizability γ of the fullerenes has a negative sign in both nanosecond and femtosecond pulse regimes. The transient response value of γ(C70) and the instantaneous response of γ(C76) were much larger than expected from the theoretically predicted smooth dependence of γ on fullerene size. The degree of validity is discussed for factors such as molecular symmetry, molecular volume, aromaticity and other molecular properties previously considered as determining fullerene-size dependence of γ. The observed trends and anomalies are explained, for the transient response, in terms of electronic-state population-dependent photophysical properties and, for the instantaneous response, by inclusion of photon resonance effects.

Ultrafast nonlinear optical response of C60–polystyrene star polymers

Abstract The ultrafast nonlinear optical response of C 60 –polystyrene n -arm ( n =3,6) star polymers in toluene solution is studied using the optical Kerr effect technique under excitation with 800 nm, 100 fs laser pulses. Their response is found to depend on the number and the molecular weight of the arms and to be much larger than that of pure C 60 . Finally, the second hyperpolarizability of the C 60 –polystyrene n -arm star polymers is determined.