Technology
Introduction
The basic principle of the OWLS method is that linearly polarized light (He-Ne laser)
is coupled by a diffraction grating into the waveguide layer, provided that the
incoupling condition is fulfilled.
The incoupling is a resonance phenomenon, that occurs at a precise angle of incidence
which depends on the refractive index of the medium covering the surface of the
waveguide. In the waveguide layer the light is guided by total internal reflection
to the ends where it is detected by photodiodes. By varying the angle of incidence
of the light the mode spectrum can be obtained from which the effective refractive
indices are calculated for both the electric and magnetic modes. OWLS is a label
free technology for investigating adsorption, binding and adhesion processes.
Schematic drawing of the system
OWLS System product page
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Measured spectra
The graph shows a typical light mode spectra of an OW 2400
sensor. The light intensity is measured with the photo detectors as the angle of
incidence of the laser light is varied from -6o to +6o. From
the measured mode spectra, the BioSense application calculates the waveguide layer's
or the covering medium's physical parameters (thickness, optical refractive index,
density etc.)
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Theory and Models
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Ray-optic representation of a coupled and guided wave
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Electromagnetic field distribution for a zeroth mode
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See the demonstration video on how the laser light is incoupled into the planar waveguide when the optical grating is illuminated at a certain, resonance angle of incident.
Calculation: |
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The incoupling angles a(TE), a(TM) for electric and magnetic modes are evaluated
from the measured spectra
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The effective refractive indices N(TE), N(TM) of the waveguide structure are calculated
on the basis of incoupling condition.
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Supposing that N(TE), N(TM) has been calculated and the optical parameters of the
waveguide layer (nF,dF), of the substrate
(nS), of the covering medium (nC) are
known, the refractive index (nA) and the thickness (dA)
of the added layer can be calculated.
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Using the model that the refractive index in the adsorbed layer linearly depends
on the concentration of the adsorbed material, the mass per area of the adsorbed
material can be calculated.
Detailed theoretical background of planar waveguides as chemical and biochemical
sensors by Erzsebet Hild
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Sensor chips
The optical waveguide sensor chips made of
SOL-GEL technology are produced by MicroVacuum.
Technical specification of the OW sensor chips
Sensing principles
Immunosensor
Monomolecular chemoresponsive coating, which consists of immobilized antibody (Ab)
molecules, that bind the corresponding antigen (Ag) molecules.
Chemosensor
With a typically 0,1-1 mm thick chemoresponsive layer whose refractive index is
changed by binding the analyte molecules.
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