Arrangement for analysis of substances at the surface of an opti

Details Arrangement for analysis of substances at the surface of an opti Arrangement for analysis of substances at the surface of an opti

1995-07-07

1998-01-27

Font, Frank G.

Optics: measuring and testing

By dispersed light spectroscopy

Utilizing a spectrometer

356359, G01B 902

Patent

active

057127050

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

a) Field of the Invention
The invention is directed to an arrangement for analysis of substances at or near the surface of an optical sensor with at least one wave-guiding film and at least one multidiffraction grating coupler for in-coupling and out-coupling of light beams.
b) Description of the Related Art
Arrangements of this type are used, according to the prior art, for analyzing substances near the sensor surface. They are used in multiple applications for determining physical or chemical measured quantities interaction of guided light waves with the medium at and near the sensor surface. On this basis, such sensors can be used in combination with an arrangement for operation as universal spectrometers, since the index of refraction and the absorption of the medium in the vicinity of the sensor reference 5! are also known. In this case, the molecules to be determined bond selectively at the sensor surface and are determined through their interaction with the guided wave.
The use of one or more grating couplers for in-coupling and/or out-coupling 8!. The guided waves occurring when resonance is achieved are determined by detecting the light exiting laterally from the waveguide. This method imposes strict requirements on the planarity of the waveguide and on the accuracy of angular adjustment, which represents a drawback for economical application. determination of the autocollimation angle also requires a very precise mechanical angular adjustment.
Angular adjustment may be dispensed with if a grating is used for out-coupling and the exiting radiation is guided to one or two method requires that the guided waves be coupled in via the end face of the waveguide. This is disadvantageous due to the required preparation of the end faces and accuracy of positioning of the sensor when coupling in. 14! requires that two light sources be coupled in from different directions. This further increases the cost of the end face coupling. Moreover, the effect of temperature changes on the detection of measurement values is disadvantageous if the guided waves pass through the sensor in different directions.
A spectrometer based on optical waveguides with grating couplers is absorption characteristics at the waveguide surface are determined for different wavelengths.
A known advantageous construction of a grating coupler is the background with a method of this kind. bringing the probe containing the substance to be determined into contact with the wave-guiding film of an optical film waveguide, to couple coherent light into the wave-guiding film and guide it therein as a light wave and to couple the light out of the latter again, wherein a diffraction grating is provided in the plane of the wave-guiding film for in and out coupling of light. Two coherent (e.g., orthogonally polarized) light beams can be coupled into the film waveguide simultaneously and, by interference of two out-coupled partial beams produced by the two (e.g., orthogonally polarized) light waves which are guided conjointly in the waveguide, the relative phase position can be measured in the form of a phase difference of the two in-coupled light fields or the relative 11!.
A coherent light field can be coupled into and out of a waveguide in a simple manner by grating couplers without relying on a focussing optical system. The light field is coupled in when it strikes the region of the waveguide provided with the grating coupler at a determined angle of incidence which depends on the grating period and the effective mode refractive index. When a so-called multidiffraction grating structure is used for in-coupling and out-coupling, the diffraction angle and the intensities of the individual orders of diffraction can be varied independently from one another. The out-coupled partial beam guided in the waveguide can be separated from reflected, transmitted or directly diffracted partial beams, although the regions on the wave-guiding film in which the light fields are coupled in and coupled out partially overlap. 16!. Two light

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