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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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Schematic representation of a waveguide grating coupler, consisting of a substrate S, waveguide film F with a layer thickness of hf and cover layer C with refractive indices ns, nf and nc, respectively. A corrugated grating with a depth of hg, period Λ and duty-cycle D acts as a coupling element for coherent light with wavelength λ, polarization ρ incident at an angle θc, thereby creating a guided mode with evanescent tails with penetration depths Δzc and Δzs.
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biosensors-05-00187-f001: Schematic representation of a waveguide grating coupler, consisting of a substrate S, waveguide film F with a layer thickness of hf and cover layer C with refractive indices ns, nf and nc, respectively. A corrugated grating with a depth of hg, period Λ and duty-cycle D acts as a coupling element for coherent light with wavelength λ, polarization ρ incident at an angle θc, thereby creating a guided mode with evanescent tails with penetration depths Δzc and Δzs.

Mentions: In its simplest configuration, a planar, step-index waveguide grating coupler exhibits a 3-layer structure consisting of the supporting substrate S, a high refractive index waveguide layer F and the investigated cover layer C (Figure 1) [2,15,16]. A corrugated grating region in the waveguide acts both as a light coupling element into the waveguide by means of diffraction as well as the sensitive element of the sensor. The sensing principle of a grating coupler can be illustrated by the resonance condition for light coupling into or out of the waveguide via the grating [1,17]:(1)nc/s* sin(θc)=neff−mgλΛwhere nc/s denotes the refractive index of the cover or the substrate, depending from which side the sample is illuminated, θc the coupling angle, mg the grating diffraction order, λ the vacuum wavelength of the incident light, Λ the grating period and(2)neff=f(nc, nf, ns,hf, hg, D, λ,ρ, m)the effective refractive index of the waveguide, which itself depends on the cover-, waveguide- and substrate refractive indices, the waveguide thickness hf, the depth hg and duty-cycle D of the corrugated grating, the wavelength λ and polarization ρ of the incident light, which can either be transverse electric (TE) or transverse magnetic (TM), as well as the mode number m of the propagating wave. Hereinafter, the influence of hg and D on neff are neglected as only shallow and therefore weak gratings with hg << λ and two conformally corrugated waveguide sides with D ≈ 0.5 are considered [13].


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

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

Schematic representation of a waveguide grating coupler, consisting of a substrate S, waveguide film F with a layer thickness of hf and cover layer C with refractive indices ns, nf and nc, respectively. A corrugated grating with a depth of hg, period Λ and duty-cycle D acts as a coupling element for coherent light with wavelength λ, polarization ρ incident at an angle θc, thereby creating a guided mode with evanescent tails with penetration depths Δzc and Δzs.
© Copyright Policy
Related In: Results  -  Collection

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

biosensors-05-00187-f001: Schematic representation of a waveguide grating coupler, consisting of a substrate S, waveguide film F with a layer thickness of hf and cover layer C with refractive indices ns, nf and nc, respectively. A corrugated grating with a depth of hg, period Λ and duty-cycle D acts as a coupling element for coherent light with wavelength λ, polarization ρ incident at an angle θc, thereby creating a guided mode with evanescent tails with penetration depths Δzc and Δzs.
Mentions: In its simplest configuration, a planar, step-index waveguide grating coupler exhibits a 3-layer structure consisting of the supporting substrate S, a high refractive index waveguide layer F and the investigated cover layer C (Figure 1) [2,15,16]. A corrugated grating region in the waveguide acts both as a light coupling element into the waveguide by means of diffraction as well as the sensitive element of the sensor. The sensing principle of a grating coupler can be illustrated by the resonance condition for light coupling into or out of the waveguide via the grating [1,17]:(1)nc/s* sin(θc)=neff−mgλΛwhere nc/s denotes the refractive index of the cover or the substrate, depending from which side the sample is illuminated, θc the coupling angle, mg the grating diffraction order, λ the vacuum wavelength of the incident light, Λ the grating period and(2)neff=f(nc, nf, ns,hf, hg, D, λ,ρ, m)the effective refractive index of the waveguide, which itself depends on the cover-, waveguide- and substrate refractive indices, the waveguide thickness hf, the depth hg and duty-cycle D of the corrugated grating, the wavelength λ and polarization ρ of the incident light, which can either be transverse electric (TE) or transverse magnetic (TM), as well as the mode number m of the propagating wave. Hereinafter, the influence of hg and D on neff are neglected as only shallow and therefore weak gratings with hg << λ and two conformally corrugated waveguide sides with D ≈ 0.5 are considered [13].

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