Patent Application: US-48137695-A

Abstract:
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 , in which at least two light beams enclosing an angle α relative to one another are coupled in and by which at least two light beams enclosing an angle φ relative to one another are coupled out , and with a detection system for detecting the out - coupled light beams , wherein in - coupling and out - coupling are effected on one and the same side of the sensor and the in - couple beams and out - couple beams lie in different quadrants of the plane of incident light , and the angle α between the in - couple beams is greater than the angle φ between the out - couple beams . the arrangement has multiple uses for determining physical or chemical measured quantities based on the interaction of the guided light waves with the medium at or near the sensor surface .

Description:
fig1 is a schematic view of a film waveguide 1 on a substrate 1a which supports a bidiffraction grating arrangement 2 in a known manner . two coherent , orthogonally polarized beam bundles t e , t m are coupled into the film waveguide 1 , these beam bundles t e , t m enclosing an angle α and lying in a first quadrant q 1 of the plane determined on the substrate side by incident and emergent beams . the beams t ea , t ma which are coupled out via the grating arrangement lie in quadrant q 2 and enclose an angle φ which is appreciably less than angle α . the out - coupled beams t ea , t ma advantageously lie within an angular region formed by the reflected beam components t mr , t er so that the reflected radiation components are separated from the out - coupled radiation components . with interference analysis , angle φ is less than 6 degrees , preferably approximately 0 . 2 - 3 degrees , and angle α is greater than 6 degrees and is preferably in the range of 26 degrees plus / minus 20 degrees , more preferably 16 plus / minus 10 degrees . at an angle α greater than 3 degrees , preferably 23 plus / minus 20 degrees or 13 plus / minus 10 degrees , φ is less than 3 degrees , preferably 0 . 2 - 3 degrees or 0 . 2 - 2 degrees . when measuring by means of a position - sensitive detection system , α is greater than 2 degrees , preferably 22 plus / minus 20 degrees or 12 plus / minus 10 degrees , and φ is less than 20 degrees , preferably 0 - 12 degrees or 0 - 8 degrees . fig2 is an overall view of the arrangement according to the invention . the light from a laser light source 3 is coupled into a lightguide 4 via an in - coupling element 5 and strikes a first mirror 7 via an out - coupling and beam - shaping element 6 and then , proceeding from this first mirror 7 , arrives at a polarizing beam splitter 8 which splits the light into two partial beam paths t e and t m which are coupled into the film waveguide via mirrors 9 , 10 , beam offsetting units 11 , 12 and imaging systems 13 , 14 . an optical window 33 is provided between the sensor plane 1 and the rest of the arrangement to protect against external influences . the sequence of focussing means 13 , 14 and beam offsetting units 11 , 12 is permutable . the lengths of the in - coupling paths for the two beam paths should be identical as far as possible , depending on the coherence length of the light source . maximum differences of the optical paths for the two in - couple beam paths must be less than the coherence length of the light source in order to ensure the interference capability of the out - coupled modes . the out - coupled beam modes t ea and t ma are imaged on a position - resolving receiver 18 , e . g ., a ccd array or diode array , via an imaging unit 15 which is shown in dashed lines and , as will be explained more fully with reference to fig7 is formed , e . g ., from a plurality of imaging mirrors , a polarizer 16 and an interference filter 17 . the in - couple beam path is shown in an enlarged view in fig3 . the laser beam of the light source 3 is focussed by the out - coupling element 6 in such a way that the beam neck at points p 1 , p 2 substantially corresponds to focal length f of the imaging lenses 13 , 14 . the beam offsetting units 11 , 12 are preferably swivelable plane - parallel glass parallelepipeds or plates and , depending on their rotational angle β , produce a beam offset v which causes a change in direction of the beam after passing through lenses 13 , 14 , wherein the in - coupling point in the sensor plane remains substantially stable . in order to prevent disturbing reflections , it is advisable to incline the rotational axes slightly relative to the plane of incidence . in so doing , the in - coupled beam bundles have a slight convergence . lenses 13 , 14 are likewise arranged approximately at a distance f from the film waveguide . the beam splitter 8 is preferably constructed as a semitransparent mirror . however , beam splitting can also be effected via a beam splitter cube with a semitransparent coating , a holographic element or a glass - fiber branching element . integration ( not shown ) of beam deflecting 7 and beam splitting 8 in a polygon prism with reflecting surfaces , where appropriate , or in an integrated optical element is particularly advantageous . fig4 shows an embodiment form as an alternative to fig3 in which the two beam components t e , t m are coupled in and changed with respect to their in - coupling angle in an analogous manner via a large lens 19 . in so doing , it is necessary to guide the partial beams t e , t m striking the elements 11 , 12 substantially parallel to one another by means of suitable optical deflection ( not shown ). fig5 shows another method of angular displacement of the in - coupled beams . the beam bundles t e , t m expanded by lenses 22 fully illuminate the cross section of the lenses 13 , 14 . controllable slit diaphragms 20 , 21 are arranged downstream of these lenses 13 , 14 and only allow a partial beam bundle to pass , which partial beam bundle has an in - coupling angle which is changeable depending on the diaphragm position . these controllable slit diaphragms can be constructed mechanically and as lcd units or as diaphragms which are mechanically adjustable linearly or as filters with position - variable transmission characteristics . the focussing value in the sensor plane is adjusted by changing the focal length of the lenses 13 , 14 and / or the slit width or via a variable optical system . the focussing shape is influenced by the dimensions and shape of the slit . to compensate for the different focussing value in directions oriented vertically to one another , corrective optics , e . g ., cylindrical optics , are included in the beam path upstream of the slit diaphragm or lenses 13 , 14 are constructed in an appropriate manner . a suitable beam shaping system for adapting the beam parameters which is formed of one or more imaging elements which can be constructed as reflective , refractive , holographic or fresnel lenses can also be arranged downstream of the light source 3 . in fig6 the lenses 13 , 14 according to fig5 are replaced by a common lens 19 , the diaphragms 20 , 21 being provided in a combined arrangement , although they may be controlled separately . as in fig4 substantially parallel partial beam bundles t e , t m are generated by suitable optical means and pass through lens 19 . fig7 shows an enlarged view of the out - coupled beam components t ea and t ma shown in fig2 imaged on a position - resolving receiver 18 . the change in the spatial interference pattern of t e and t m modes is recorded and evaluated as a measurement quantity in a known manner . the interference pattern of the out - coupled beam components occurring at the point of exit is projected on the line receiver via cylindrical mirrors 23 , 24 and spherical mirrors 25 , 26 as an imaging magnified in the drawing plane . the cylindrical mirrors simultaneously cause a reduction in the interference pattern vertically to the drawing plane and accordingly adapt to the detector geometry in an optimal manner . the optical imaging on the receiver array can also be realized by a lens system or by a combination of refractive imaging optics and reflective imaging optics . the refractive elements can be constructed as holographic elements or fresnel lenses which can have different imaging characteristics in different directions . the line geometry can be adapted to in this way . a polarizing filter 16 which causes the interference of the out - coupled modes required for the measuring process is to be arranged upstream of the detector 18 . further , a filter 17 with spectral selectivity can be arranged upstream of the detector for suppressing extraneous light . a window 33 , preferably a plate with anti - reflection coating on both sides , can be arranged between the sensor plane and all optical components in order to protect against environmental influences . the overall dimensions of the arrangement can be reduced and the receiver can be protected from unwanted influence of radiation by the folded beam paths within the imaging units . the distance between the interference lines is determined from the interference pattern on the array as a measurement of the differential angle between the out - coupled beam components t ea , t ma , which is influenced in turn by the analysis substance on the film waveguide 1 and by its refractive index . the overall dimensions of the arrangement can be reduced and the receiver can be protected from unwanted influence of radiation by the folded beam paths within the imaging unit . high thermal stability of magnification is achieved for the imaging part 15 by constructing the optical element of fused quartz in combination with a mechanical support formed of material with adapted expansion coefficients , e . g ., invar . the imaging optical elements are held in the support block 31 which has drilled channels 32 for the optical beam paths . in order to compensate for thermal influences of the receiver 18 and the interference structure imaged on the array , a bushing 34 formed of a material with appropriately selected expansion coefficients is arranged between the support block 31 and the receiver 18 . the expansion coefficient of the bushing 24 is determined from the difference in the expansion coefficients of the imaging elements and support block 31 and from the length ratio of the beam lengths extending in the support block 31 and in the bore holes . this is explained further with reference to fig7 a : two structural component parts 34 and 35 of different material which are connected with one another only at points 36 and 37 are otherwise movable relative to one another . due to the thermal expansion of the structural component parts 34 and 35 in opposite directions , it is possible to adjust a certain &# 34 ; effective &# 34 ; thermal expansion coefficient for the holder in its entirety by selecting the individual lengths and individual expansion coefficients . in this way , it is possible to compensate practically entirely for thermal drift between optical components and the housing relative to the detector . if the change in the differential angle φ of the out - coupled beam modes is not determined via the interference pattern , a position - sensitive detector 27 is provided as in fig8 an image being formed on this position - sensitive detector 27 via a lens 28 and a mirror system 29 . the detector 27 is at a distance from the lens 28 corresponding to the focal length . the angular difference is determined on the basis of the difference in position of the points of impingement . the lens 28 can also be replaced by a plurality of lenses which can also be constructed as holographic elements or fresnel lenses . in an alternative arrangement of the out - couple beam path , a focus is produced in the detector plane for both out - coupled light fields . changes in the distance between the two foci are utilized for analysis . for this purpose , a position - sensitive detector 27 is provided in fig8 imaging being effected upon this detector 27 via a lens 28 and a mirror system 29 . the detector 27 is arranged at a distance from lens 28 corresponding to the focal length . in another possible out - couple beam path , the exiting light is focussed on a position - sensitive detector by a lens . in this embodiment form of the out - couple beam path of the te mode and tm mode , a focus is produced in the detector plane in each instance and the in - couple beam paths are alternately switched by suitable optical means , e . g ., shutters , in order to evaluate the distance between the two foci on the detector . further , the out - coupled light beams can be focussed on two position - sensitive detectors by a common lens or by two different lenses . a sufficient angular difference can be achieved in a simple manner when using a sensor with a bidiffraction grating coupler by selection of the grating constants . in this arrangement , the angles of the out - coupled te and tm fields can be detected in parallel so that there is no need to switch the in - couple beams as was necessary in the embodiment form described above . in fig9 the beam offsetting elements 11 , 12 are actuated in synchronous phase by means of a control unit 30 . images of the individual beam components appear on the receiver in temporal sequence at the times when the beam modes t e and t m are coupled . the signal difference on the psd is a measurement for the differential angle of the out - coupled beams . high thermal stability of magnification is achieved for the imaging part 15 by constructing the optical element of fused quartz in combination with a mechanical support formed of material with adapted expansion coefficients , e . g ., invar . alternative combinations of materials with adapted thermal expansion coefficients for optical elements / optical supports are , e . g ., zero - expansion glass ceramics ( zerodur , crown glass / gray cast iron , borosilicate glass ( bk7 , ubk7 ), crown glass / ceramics , crown glass / high - grade steel , crown glass / brass . fig1 shows the arrangement of the optical elements and beam paths in a common support block 31 , shown in section , which has drilled channels 32 for the optical beam paths . the optical elements according to fig2 are arranged , preferably cemented , externally at a common support block 31 . bore holes 32 are provided for the optical beam paths . an extremely stable arrangement , particularly with respect to occurring microphonics , is achieved by the defined relative position of the optical components . optimal thermal stability of the arrangement can be realized by the selection of materials for the optical elements ( e . g ., glass , fused quartz ) and for the support block ( e . g ., zerodur , invar and gray cast iron ) based on the thermal expansion coefficients . reference is made to the preceding statements pertaining to selection of materials . an arrangement with an in - coupled beam which is suitable for absorption measurement is shown in fig1 . while the foregoing description and drawings represent the preferred embodiments of the present invention , it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the true spirit and scope of the present invention . 1 ! k . tiefenthaler , w . lukosz , &# 34 ; integrated optical switches and gas sensors &# 34 ;, optics letters 10 , 137 ( 1984 ) 2 ! t . suhara , h . nishihara , ieee j . quantum electron . 22 845 ( 1986 ) 5 ! k . tiefenthaler , w . lukosz , &# 34 ; sensitivity of grating couplers as integrated - optical chemical sensors &# 34 ;, j . opt . soc . am . b6 , 209 ( 1989 ) 7 ! w . lukosz , ph . m . nellen , ch . stamm , p . weiss , &# 34 ; output grating couplers on planar waveguides as integrated optical chemical sensors &# 34 ;, sensors and actuators b1 , 585 ( 1990 ) 8 ! ph . m . nellen , w . lukosz , &# 34 ; integrated optical input grating couplers as chemo - 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