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Experimental Validation of the Sensitivity of Waveguide Grating Based Refractometric (Bio)sensors.

Gartmann TE, Kehl F - Biosensors (Basel) (2015)

Bottom Line: Despite the fact that the theoretical foundations of the sensitivity of waveguide grating based (bio)sensors are well-known, understood and their implications anticipated by the scientific community since several decades, to our knowledge, no prior publication has experimentally confirmed waveguide sensitivity for multiple film thicknesses, wavelengths and polarization of the propagating light.The effective refractive indices and the corresponding sensitivity were determined via the sensors' coupling angles at different cover refractive indices for transverse electric as well as transverse magnetic polarized illumination at various wavelengths in the visible and near-infrared.The theoretical sensitivity was calculated by solving the mode equation for a three layer waveguide.

View Article: PubMed Central - PubMed

Affiliation: CSEM Centre Suisse d'Electronique et de Microtechnique SA, Bahnhofstrasse 1, Landquart CH-7302, Switzerland. thomas.gartmann@csem.ch.

ABSTRACT
Despite the fact that the theoretical foundations of the sensitivity of waveguide grating based (bio)sensors are well-known, understood and their implications anticipated by the scientific community since several decades, to our knowledge, no prior publication has experimentally confirmed waveguide sensitivity for multiple film thicknesses, wavelengths and polarization of the propagating light. In this paper, the bulk refractive index sensitivity versus waveguide thickness of said refractometric sensors is experimentally determined and compared with predictions based on established theory. The effective refractive indices and the corresponding sensitivity were determined via the sensors' coupling angles at different cover refractive indices for transverse electric as well as transverse magnetic polarized illumination at various wavelengths in the visible and near-infrared. The theoretical sensitivity was calculated by solving the mode equation for a three layer waveguide.

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Related in: MedlinePlus

Typical measurement of the transmitted light intensity at the coupling angle: (a) CCD camera image with the four measurement regions. (b) Measured intensity and inverted Gaussian fit for one region to determine the coupling angle. The intensity oscillations are caused by Fresnel reflections at cover and substrate. Configuration: λ = 532.3 ± 0.2 nm, hf = 122.8 ± 0.8 nm, nc = 1.5247.
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biosensors-05-00187-f006: Typical measurement of the transmitted light intensity at the coupling angle: (a) CCD camera image with the four measurement regions. (b) Measured intensity and inverted Gaussian fit for one region to determine the coupling angle. The intensity oscillations are caused by Fresnel reflections at cover and substrate. Configuration: λ = 532.3 ± 0.2 nm, hf = 122.8 ± 0.8 nm, nc = 1.5247.

Mentions: The experimental setup, similar to the one featured in [21] to study final grating length effects, is sketched in Figure 5. The sensor chips were mounted in a transparent PMMA sample holder and different cover media were applied to the corrugated Ta2O5 surface. The investigated media included air, purified water (Milli-QTM, EMD Millipore, Billerica, MA, USA) and index matching liquid (Series A, n = 1.52, Cargille Laboratories, Cedar Grove, NJ, USA). The mounted samples were placed on a motorized rotary stage with encoder (CR1/M-Z7, Thorlabs, Newton, NJ, USA) with an angular repeatability of less than 0.017 degree and an angular resolution of 6·10−4 degree. Afterwards, the samples were illuminated through the substrate with linearly polarized light at wavelengths of 532.3 ± 0.2 nm (CW532, Roithner LaserTechnik, Vienna, Austria), 632.8 ± 0.2 nm (1103P, Uniphase, Mateca, CA, USA), 779.7 ± 0.2 nm (LDM780/3LJ, Roithner LaserTechnik, Vienna, Austria) and 845.1 ± 0.2 nm (LDM850/3LJ, Roithner LaserTechnik, Vienna, Austria), according to the available laser sources within the investigated wavelength range. The emission spectra of the laser sources were previously measured with an optical spectrum analyzer (AQ6373, Yokogawa, Musashino, Japan). To determine the in-coupling angle, the angle dependent light transmission through the grating region was measured with a CCD camera combined with a telecentric lens (Guppy F-033B by Allied Vision Technologies, Stadtroda, Germany and 0.5× TML 63074 by Edmund Optics, Barrington, NJ, USA). For every combination of waveguide thickness, cover refractive index as well as polarization and wavelength of the incident light, 4 out of 24 individual grating regions per chip (Figure 2b and Figure 6a) were measured in parallel to allow for an accuracy estimate of the determined coupling angles. The angle of incidence was swept by turning the mounted sample on the rotary stage, which was controlled via a MATLAB [22] script from an external computer. At the in-coupling angle, the intensity of the transmitted light was decreased as a part of the incident light was coupled into the waveguide, resulting in a dip in the measured transmitted light intensity versus angle.


Experimental Validation of the Sensitivity of Waveguide Grating Based Refractometric (Bio)sensors.

Gartmann TE, Kehl F - Biosensors (Basel) (2015)

Typical measurement of the transmitted light intensity at the coupling angle: (a) CCD camera image with the four measurement regions. (b) Measured intensity and inverted Gaussian fit for one region to determine the coupling angle. The intensity oscillations are caused by Fresnel reflections at cover and substrate. Configuration: λ = 532.3 ± 0.2 nm, hf = 122.8 ± 0.8 nm, nc = 1.5247.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4493545&req=5

biosensors-05-00187-f006: Typical measurement of the transmitted light intensity at the coupling angle: (a) CCD camera image with the four measurement regions. (b) Measured intensity and inverted Gaussian fit for one region to determine the coupling angle. The intensity oscillations are caused by Fresnel reflections at cover and substrate. Configuration: λ = 532.3 ± 0.2 nm, hf = 122.8 ± 0.8 nm, nc = 1.5247.
Mentions: The experimental setup, similar to the one featured in [21] to study final grating length effects, is sketched in Figure 5. The sensor chips were mounted in a transparent PMMA sample holder and different cover media were applied to the corrugated Ta2O5 surface. The investigated media included air, purified water (Milli-QTM, EMD Millipore, Billerica, MA, USA) and index matching liquid (Series A, n = 1.52, Cargille Laboratories, Cedar Grove, NJ, USA). The mounted samples were placed on a motorized rotary stage with encoder (CR1/M-Z7, Thorlabs, Newton, NJ, USA) with an angular repeatability of less than 0.017 degree and an angular resolution of 6·10−4 degree. Afterwards, the samples were illuminated through the substrate with linearly polarized light at wavelengths of 532.3 ± 0.2 nm (CW532, Roithner LaserTechnik, Vienna, Austria), 632.8 ± 0.2 nm (1103P, Uniphase, Mateca, CA, USA), 779.7 ± 0.2 nm (LDM780/3LJ, Roithner LaserTechnik, Vienna, Austria) and 845.1 ± 0.2 nm (LDM850/3LJ, Roithner LaserTechnik, Vienna, Austria), according to the available laser sources within the investigated wavelength range. The emission spectra of the laser sources were previously measured with an optical spectrum analyzer (AQ6373, Yokogawa, Musashino, Japan). To determine the in-coupling angle, the angle dependent light transmission through the grating region was measured with a CCD camera combined with a telecentric lens (Guppy F-033B by Allied Vision Technologies, Stadtroda, Germany and 0.5× TML 63074 by Edmund Optics, Barrington, NJ, USA). For every combination of waveguide thickness, cover refractive index as well as polarization and wavelength of the incident light, 4 out of 24 individual grating regions per chip (Figure 2b and Figure 6a) were measured in parallel to allow for an accuracy estimate of the determined coupling angles. The angle of incidence was swept by turning the mounted sample on the rotary stage, which was controlled via a MATLAB [22] script from an external computer. At the in-coupling angle, the intensity of the transmitted light was decreased as a part of the incident light was coupled into the waveguide, resulting in a dip in the measured transmitted light intensity versus angle.

Bottom Line: Despite the fact that the theoretical foundations of the sensitivity of waveguide grating based (bio)sensors are well-known, understood and their implications anticipated by the scientific community since several decades, to our knowledge, no prior publication has experimentally confirmed waveguide sensitivity for multiple film thicknesses, wavelengths and polarization of the propagating light.The effective refractive indices and the corresponding sensitivity were determined via the sensors' coupling angles at different cover refractive indices for transverse electric as well as transverse magnetic polarized illumination at various wavelengths in the visible and near-infrared.The theoretical sensitivity was calculated by solving the mode equation for a three layer waveguide.

View Article: PubMed Central - PubMed

Affiliation: CSEM Centre Suisse d'Electronique et de Microtechnique SA, Bahnhofstrasse 1, Landquart CH-7302, Switzerland. thomas.gartmann@csem.ch.

ABSTRACT
Despite the fact that the theoretical foundations of the sensitivity of waveguide grating based (bio)sensors are well-known, understood and their implications anticipated by the scientific community since several decades, to our knowledge, no prior publication has experimentally confirmed waveguide sensitivity for multiple film thicknesses, wavelengths and polarization of the propagating light. In this paper, the bulk refractive index sensitivity versus waveguide thickness of said refractometric sensors is experimentally determined and compared with predictions based on established theory. The effective refractive indices and the corresponding sensitivity were determined via the sensors' coupling angles at different cover refractive indices for transverse electric as well as transverse magnetic polarized illumination at various wavelengths in the visible and near-infrared. The theoretical sensitivity was calculated by solving the mode equation for a three layer waveguide.

Show MeSH
Related in: MedlinePlus