High-temperature stable and sterilizable waveguide Bragg grating in planar cyclo-olefin copolymer.

In this Letter, we demonstrate a high-temperature stable polymer planar waveguide Bragg grating based on cyclo-olefin copolymers. The high glass transition temperature of the polymer material amounting to 178°C, in conjunction with a high-temperature stable UV-curable adhesive used to connect the polymer sensor to a standard single-mode fiber, enables temperature readings of up to 160°C while exhibiting a temperature sensitivity of -7.3 pm/°C. The reflected power of the Bragg wavelength remains constant up to a temperature of 130°C before declining at higher temperatures with an overall reduction of 2.5 dB at 160°C. However, decreasing temperature results in a complete recovery of the peak power, facilitating steam pressure sterilization (129°C, 0.17 MPa) of the polymer planar waveguide Bragg grating.

UV-Writing of a Superstructure Waveguide Bragg Grating in a Planar Polymer Substrate.

We report on the fabrication of a superstructure Bragg grating in a planar polymer substrate. Based on a twofold illumination process an integrated waveguide and a superstructure Bragg grating are subsequently written into bulk polymethylmethacrylate by UV-induced refractive index modification. The measured reflected spectrum of the superstructure Bragg grating exhibits multiple reflection peaks and is in good agreement with performed standard simulations based on the beam propagation method and coupled mode theory algorithms. By applying a varying tensile load we determine the strain sensitivity to be about 1.10 pm/µÎµ and demonstrate the applicability of the superstructure Bragg grating for strain measurements with redundant sensing signals.

Waveguide Bragg Gratings in Ormocer®s for Temperature Sensing.

Embedded channel waveguide Bragg gratings are fabricated in the Ormocer® hybrid polymers OrmoComp®, OrmoCore, and OrmoClad by employing a single writing step technique based on phase mask technology and KrF excimer laser irradiation. All waveguide Bragg gratings exhibit well-defined reflection peaks within the telecom wavelengths range with peak heights of up to 35 dB and -3 dB-bandwidths of down to 95 pm. Furthermore, the dependency of the fabricated embedded channel waveguide Bragg gratings on changes of the temperature and relative humidity are investigated. Here, we found that the Bragg grating in OrmoComp® is significantly influenced by humidity variations, while the Bragg gratings in OrmoCore and OrmoClad exhibit linear and considerably high temperature sensitivities of up to -250 pm/ ∘ C and a linear dependency on the relative humidity in the range of -9 pm/%.

Simultaneous 2D strain sensing using polymer planar Bragg gratings.

We demonstrate the application of polymer planar Bragg gratings for multi-axial strain sensing and particularly highlight simultaneous 2D strain measurement. A polymer planar Bragg grating (PPBG) fabricated with a single writing step in bulk polymethylmethacrylate is used for measuring both tensile and compressive strain at various angles. It is shown that the sensitivity of the PPBG strongly depends on the angle between the optical waveguide into which the grating is inscribed and the direction along which the mechanical load is applied. Additionally, a 2D PPBG fabricated by writing two Bragg gratings angularly displaced from each other into a single polymer platelet is bonded to a stainless steel plate. The two reflected wavelengths exhibit different sensitivities while tested toward tensile and compressive strain. These characteristics make 2D PPBG suitable for measuring multi-axial tensile and compressive strain.

Highly sensitive detection of naphthalene in solvent vapor using a functionalized PBG refractive index sensor.

We report an optical refractive index sensor system based on a planar Bragg grating which is functionalized by substituted γ-cyclodextrin to determine low concentrations of naphthalene in solvent vapor. The sensor system exhibits a quasi-instantaneous shift of the Bragg wavelength and is therefore capable for online detection. The overall shift of the Bragg wavelength reveals a linear relationship to the analyte concentration with a gradient of 12.5 ± 1.5 pm/ppm. Due to the spectral resolution and repeatability of the interrogation system, this corresponds to acquisition steps of 80 ppb. Taking into account the experimentally detected signal noise a minimum detection limit of 0.48 ± 0.05 ppm is deduced.

Surface functionalization allowing repetitive use of optical sensors for real-time detection of antibody-bacteria interaction.

In this study, sensor surface functionalization allowing the repetitive use of a sensing device was evaluated for antibody-based detection of living bacteria using an optical planar Bragg grating sensor. To achieve regenerable immobilization of bacteria specific antibodies, the heterobifunctional cross-linker N-succinimidyl 3-(2-pyridyldithio) propionate (SPDP) was linked to an aminosilanized sensor surface and subsequently reduced to expose sulfhydryl groups enabling the covalent conjugation of SPDP-activated antibodies via disulfide bonds. The immobilization of a capture antibody specific for Staphylococcus aureus on the sensor surface as well as specific binding of S. aureus could be monitored, highlighting the applicability of optical sensors for the specific detection of large biological structures. Reusability of bacteria saturated sensors was successfully demonstrated by cleaving the antibody along with bound bacteria through reduction of disulfide bonds and subsequent re-functionalization with activated antibody, resulting in comparable sensitivity towards S. aureus.