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

Optical Sensor for Real-Time Detection of Trichlorofluoromethane

Trichlorofluoromethane was once a promising and versatile applicable chlorofluorocarbon. Unaware of its ozone-depleting character, for a long time it was globally applied as propellant and refrigerant and thus led to significant thinning of the ozone layer and contributed to the formation of the so-called ozone hole. Although production and application of this substance were gradually reduced at an early stage, we still face the consequences of its former careless use. Today, trichlorofluoromethane is released during recycling processes of waste cooling devices, traded on the black market, and according to recent findings still illegally manufactured. Here, we present an optical sensor device for real-time in-situ detection and measurement of this environmentally harmful chlorofluorocarbon. The described sensor is based on a planar Bragg grating that is functionalized with cyclodextrin derivatives and operates on the principle of a chemical sensor. In our study, the sensor is sensitized using per-methyl-, per-ethyl-, and per-allyl-substituted α -, β -, and γ -cyclodextrins as affinity materials for airborne trichlorofluoromethane. These functional coatings have been proven to be highly efficient, as an up to 400-times stronger signal deflection could be achieved compared to an identical but uncoated sensor. The presented sensor device shows instantaneous response to trichlorofluoromethane exposure, and features a limit-of-detection of less than 25 ppm, depending on the applied affinity material

Waveguide Bragg gratings in Ormocer hybrid polymers

We report on the fabrication of Bragg gratings within rib-type waveguides of previously UV-cured inorganic-organic Ormocer hybrid polymers by applying the interferometric phase mask technique in conjunction with deep-UV laser radiation. The fabrication process as well as the influence of the applied laser fluence and the length of the Bragg grating on the characteristics of the Bragg gratings transmission and reflection spectra are discussed and compared to numerical simulations and calculations. Depending on the applied laser fluence and the chosen grating length, waveguide Bragg gratings with strong reflectivities of up to 98% and narrow bandwidths of down to 120 pm have been achieved

Methyl-substituted α-cyclodextrin as affinity material for storage, separation, and detection of trichlorofluoromethane

The severely ozone-depleting trichlorofluoromethane is still appearing in several recycling processes or industrial applications. A simple and selective supramolecular complex formation of per-methylated α-cyclodextrin (1) with the highly volatile trichlorofluoromethane (2) is reported. This interaction moreover leads to thermally stable crystals. Per-methylated α-cyclodextrin is successfully exploited as a reversible and selective adsorption material for liquid and airborne trichlorofluoromethane as well as an affinity material for the chemical sensing and detection of this particular volatile organic component

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/%

One-step nanoimprinted Bragg grating sensor based on hybrid polymers

Bragg grating sensors are used for real-time analysis of gases or liquids. Complex processing methods are typically required for the sensor fabrication. A reduction of process steps and costs during their fabrication is essential in order to broaden the field of application. Within this work, we demonstrate an innovative process for a one-step fabrication of integrated Bragg grating sensors and their successful application for temperature and refractive index sensing. UV-enhanced substrate conformal imprint lithography (UV-SCIL) is used to replicate surface relief Bragg grating (SBG) sensors on a full wafer scale. Multiple chips of a planar waveguide system including couplers and junctions were etched into a silicon wafer. Nanostructured SBGs were locally added on the waveguides by focused ion beam processing. The sensor structures were replicated by UV-SCIL into a commercially available hybrid polymer (OrmoComp®). Reflection measurements with different Bragg gratings were performed and compared to simulations. The results reveal narrow-band Bragg reflections, coinciding with the simulations. Further, the temperature dependence of the SBGs was investigated. The imprinted grating structures featured a very high temperature sensitivity of −202 pm/°C. The sensor response to a varying refractive index of the surrounding medium was determined for index matching liquids and aqueous solutions

TiO2 surface functionalization of COC based planar waveguide Bragg gratings for refractive index sensing

We demonstrate the applicability of a planar waveguide Bragg grating in cyclo-olefin copolymer (COC) for refractive index sensing. The polymer planar waveguide Bragg grating fabricated using a single writing step technique is coated with a high-index layer of titanium dioxide (TiO2) leading to a distinct birefringence. This in turn results in the splitting of the Bragg reflection into two distinct Bragg wavelengths, which strongly differ regarding their refractive index sensitivities. Where one wavelength is only slightly affected by the ambient refractive index, the second Bragg peak shows a strong sensitivity. Furthermore, we investigate the temperature behaviour of the functionalized sensor and discuss it with respect to applications in refractive index sensing