Yanina Shevchenko

Plasmon resonances in gold-coated tilted fiber Bragg gratings

The transmission spectrum of fiber Bragg gratings with gratings planes tilted at a small angle (2 degrees -10 degrees) relative to the fiber axis shows a large number of narrowband cladding mode resonances within a 100 nm wide spectrum. When a gold coating with a thickness between 10 and 30 nm is deposited on the fiber, the transmission spectrum shows anomalous features for values of the outside medium refractive index between 1.4211 and 1.4499. These features are shown to correspond to the excitation of surface plasmon resonances at the external surface of the gold film.

High resolution interrogation of tilted fiber grating SPR sensors from polarization properties measurement.

The generation of surface plasmon resonances (SPRs) in gold-coated weakly tilted fiber Bragg gratings (TFBGs) strongly depends on the state of polarization of the core guided light. Recently, it was demonstrated that rotating the linear state of polarization of the guided light by 90° with respect to the grating tilt allows to turn the SPR on and off. In this work, we measure the Jones matrix associated to the TFBG transmission properties in order to be able to analyze different polarization-related parameters (i.e. dependency on wavelength of polarization dependent loss and first Stokes parameter). As they contain the information about the SPR, they can be used as a robust and accurate demodulation technique for refractometry purposes. Unlike other methods reported so far, a tight control of the input state of polarization is not required. The maximum error on refractive index measurement has been determined to be ~1 10(-5) refractive index unit (RIU), 5 times better than intensity-based measurements on the same sensors.

Polarization-selective grating excitation of plasmons in cylindrical optical fibers

We show that the tilted-grating-assisted excitation of surface plasmon polaritons on gold coated single-mode optical fibers depends strongly on the state of polarization of the core-guided light, even in fibers with cylindrical symmetry. Rotating the linear polarization of the guided light by 90 degrees relative to the grating tilt plane is sufficient to turn the plasmon resonances on and off with more than 17 dB of extinction ratio. By monitoring the amplitude changes of selected individual cladding mode resonances we identify what we believe to be a new refractive index measurement method that is shown to be accurate to better than 5 x 10(-5).

In situ biosensing with a surface plasmon resonance fiber grating aptasensor.

Surface plasmon resonance (SPR) biosensors prepared using optical fibers can be used as a cost-effective and relatively simple-to-implement alternative to well established biosensor platforms for monitoring biomolecular interactions in situ or possibly in vivo. The fiber biosensor presented in this study utilizes an in-fiber tilted Bragg grating to excite the SPR on the surface of the sensor over a large range of external medium refractive indices, with minimal cross-sensitivity to temperature and without compromising the structural integrity of the fiber. The label-free biorecognition scheme used demonstrates that the sensor relies on the functionalization of the gold-coated fiber with aptamers, synthetic DNA sequences that bind with high specificity to a given target. In addition to monitoring the functionalization of the fiber by the aptamers in real-time, the results also show how the fiber biosensor can detect the presence of the aptamers target, in various concentrations of thrombin in buffer and serum solutions. The findings also show how the SPR biosensor can be used to evaluate the dissociation constant (K(d)), as the binding constant agrees with values already reported in the literature.

Intrinsic temperature sensitivity of tilted fiber Bragg grating based surface plasmon resonance sensors

A miniature surface plasmon resonance sensor is fabricated from a gold-coated standard optical fiber with an in-core tilted fiber Bragg grating fabricated by UV exposure. The sensor has a measured refractive index sensitivity of 571.5 nm/RIU (refractive index unit) at constant temperature. We show here that the intrinsic temperature sensitivity of this device is reduced to less than 6.3 pm/degrees C (between 23 degrees C and 59 degrees C) when measurements are referenced to a core mode reflection resonance of the grating. This residual sensitivity is essentially that of the 50 nm thick deposited gold layer but it is bigger by one order of magnitude than the expected value (0.51 pm/degrees C) for a gold-water interface.

In situ monitoring of the formation of nanoscale polyelectrolyte coatings on optical fibers using Surface Plasmon Resonances

Deposition of a conformal nanoscale polymer coating was characterized using a fiber SPR sensor. The sensor platform consisted of an unmodified gold-coated single mode fiber where SPR was excited through the coupling of the core mode into the cladding modes using a Tilted Fiber Bragg Grating. The results from this study show how the sensor can monitor in real time the formation of polyelectrolyte coatings during a process consisting of several stages of immersion. The experimental data was further calibrated by simulations and Atomic Force Microscope imaging allowing us to determine the thickness and refractive index of the adsorbed polyelectrolyte.

DNA target detection using gold-coated tilted fiber Bragg gratings in aqueous media

Plasmon resonances in the transmission spectrum of a tilted Bragg grating in gold coated fibers are used to detect the binding of thiolated single stranded DNA and the further binding of the complementary target DNA.

Surface Plasmon Resonance optical fiber biosensor for label-free characterization of biomolecular interactions

A fiber sensor was applied to monitor the interaction of biomolecules. Results indicate that the biosensor can be successfully applied for a wide range of biomolecular characterizations including identification of the biomolecules’ binding constants

Demodulation technique for plasmonic fiber grating sensors using orthogonally polarized light states

The generation of surface plasmon resonances (SPRs) in gold-coated weakly tilted fiber Bragg gratings (TFBGs) strongly depends on the state of polarization of the core guided-light. Recently, it was demonstrated that rotating the linear state of polarization of the guided light by 90° with respect to the grating planes allows to turn the SPR on and off. In this paper, we demonstrate that this strong polarization dependence can be advantageously used to demodulate the TFBG amplitude spectrum and retrieve the SPR shift induced by a change of the surrounding refractive index. The correlation between two amplitude spectra recorded with two particular orthogonally polarized light states yields a new refractive index measurement method accurate to ~2 10-5.

Surface plasmon resonance fiber sensor for in situ monitoring of the deposition of nm-scale polymer films

This paper presents a Surface Plasmon Resonance (SPR) fiber sensor capable of monitoring the deposition of thin nm-scale polymer films. The sensor was used for in situ monitoring of the adsorption of 30 mono-layers of oppositely charged polyelectrolytes with an overall thickness of each individual monolayer less than 0.55 nm. The in situ monitoring of the formation of multi-layer structures was implemented through the excitation of SPR on the surface of a gold-coated fiber with a Tilted Fiber Bragg Grating (TFBG) written in the core of the optical fiber.