CHIP LEVEL WAVEGUIDE SENSOR

Abstract: Waveguide sensors are formed on a chip package which contains at least one source and at least one detector. Simple waveguide elements are mounted on the chip. Waveguide defining elements can also be formed integrally with the chip package so that simple waveguide bodies can be inserted or removed. Various geometries of source, reference detector, and sensing detector can be produced. A liquid waveguide sensor is formed by filling a waveguide channel with a liquid reagent.

Description: CHIP LEVEL WAVEGUIDE SENSOR BACKGROUND OF THE INVENTION The invention relates generally to optical chemical sensors, and more particularly to optical waveguide chemical sensors. A variety of optical chemical sensors based on optical fibers and other waveguides have been developed. U.S. Patent 5,165,005 to Klainer et al, shows a planar waveguide structure with a thin film metal coating. An external source and detector are optically coupled to the waveguide. A problem with the prior art is that the entire sensor is not integrated, i.e., external source and detector and the entire waveguide must be replaced for a different sensing chemistry. Accordingly, it would be desirable to provide a waveguide chemical sensor with integrated structure and in which the sensing chemistry can be easily changed. SUMMARY OF THE INVENTION Accordingly, it is an aspect of the invention to provide a waveguide chemical sensor with an integrated structure. It is also an aspect of the invention to provide a waveguide chemical sensor with interchangeable sensing chemistries. The invention is a waveguide chemical sensor having at least one waveguide arm mounted on a substrate or chip having at least one source and at least one detector formed integrally therein. The waveguide arms can be fixedly mounted on the substrate (e.g., by gluing) or removably attached (e.g., by mechanical clips) . The waveguide arms, or parts thereof, can also be formed (e.g., molded) as part of the substrate or chip itself. A reference channel can be included. Different sensing arms can be coated with or formed of different sensing chemistries. Reflective end faces of the waveguide arms direct light transmitted therethrough to a detector in the substrate. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1A,B are side and perspective views of a waveguide sensor having a reference arm and sensing arm. Fig. 1C is a perspective view of the waveguide sensor of Figs. 1A,B wherein the sensing arm waveguide is formed of the sensing chemistry. Figs. 2A,B are side and perspective views of an alternate embodiment of a waveguide sensor having a reference arm and sensing arm. Fig. 2C is a perspective view of the waveguide sensor of Figs. 2A,B wherein the sensing arm waveguide is formed of the sensing chemistry. Figs. 3A-C show a multiple arm waveguide sensor. Fig. 3D shows an alternate embodiment of the waveguide sensor of Figs. 3A-C wherein the sensing arms are formed of sensing chemistries. Fig. 3E is a top view of the waveguide sensor of Figs. 3A-C showing the assembly of the waveguide arms. Fig. 3F shows a multiple arm waveguide sensor with multiple sources. Figs. 3G,H show an alternate embodiment of a multiple arm waveguide sensor with multiple sources. Figs. 4A-D show of a molded chip package with integral waveguide forming elements. Figs. 4E-H show an alternate embodiment of a molded chip package with integral waveguide forming elements. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in Figs. 1A,B, a waveguide sensor 10 is formed on a substrate of chip 12 which contains a light source 14 and a pair of detectors 16,18 integrally formed therein. The source 14 and detectors 16,18 are linearly aligned, with source 14 at one end; however, different geometries can also be used. A waveguide 20 formed of a reference arm 22 and sensing arm 24 is mounted on substrate 12 in alignment with source 14 and detectors 16,18. Arms 22,24 are separated by beam splitter 26. Beam splitter 26 is formed by abutting the sloped ends of reference arm 22 and sensing arm 24, and applying suitable optical coatings to produce desired reflection and transmission. Light from source 14 under sloped reflective end face 28 is incident thereon and reflects to send a light beam down waveguide 20. Beam splitter 26 reflects a portion of the light down to the underlying reference detector 16 and transmits the remainder of the light through sensing arm 24 which has a sensing chemistry 30 coated on a portion thereof. The light beam passing through sensing arm 24 is affected by sensing chemistry 30 as it interacts with a sample. Various types of sensing chemistries can be used, including absorption, fluorescence and refractive index. The resulting light is incident on sloped reflective end face 32 which reflects the light downward onto detector 18. Reference arm 22 is covered by coating 23. As shown in Fig 1A, the substrate 12 is preferably a molded semiconductor chip package. Source 14 is typically an LED or laser diode. Detectors 16,18 are typically photodiodes (e.g., silicon photodiodes) . The source 14 and detectors 16,18 are integrally formed in the chip package but are not on the surface thereof. The chip package is made of optically transparent material and also protects the source and detectors from the environment. Fig 1C shows a waveguide sensor 11 which is similar to sensor 10 of Figs 1A,B except that sensing arm 24 is replaced with sensing arm 25 which is formed of the sensing chemistry, i.e., sensing chemistry is not just coated on arm 24 of Fig 1A but the entire arm 25 is made of sensing chemistry. This is particularly advantageous in an absorption type or fluorescence type sensor, since the light will pass through considerably more sensing chemistry than if a surface coating is used. In the case of absorption, the effective path length is increased, and in the case of fluorescence more of the fluorescing wavelength is trapped in the waveguide, thereby giving greater change in the signal. The sloped reflective end face 32 of Fig 1A is replaced by reflective element 33 (e.g. a prism) to reflect light passing through arm 25 into detector 18. Figs 2A,B show a waveguide sensor 15 which is a variation of the sensor 10 of Figs 1A,B. In sensor 15, the position of the light source 14 and reference detector 16 are reversed, i.e., the arrangement is still linear but the source 14 is in the center instead of at the end. Reference arm 22 has a sloped reflective end face 29 positioned over source 14 for inputting a portion of the light into arm 22. The light passes along arm 22 to sloped reflective end face 28 which reflects the light down to reference detector 16. Sensing arm 24 of Figs 1A,B is replaced by sensing arm 27 which has sensing chemistry 30 coated on a portion thereof. Sensing arm 27 has a sloped reflective end face 31 over source 14 which inputs a portion of the light from source 14 into sensing arm 27. After the light interacts with sensing chemistry 30, it is reflected by sloped reflective end face 32 down into detector 18. Fig 2C shows a waveguide sensor 17 which is similar to sensor 15 of Figs 2A,B except that sensing arm 27 is replaced with a sensing arm 34 which is formed of the sensing chemistry. The sloped reflective end faces 31,32 of Figs 2A,B are replaced by reflective elements 35,36 (e.g., prisms) that reflect light into and out of arm 34. Figs 3A-C show a sensor 58 with multiple waveguides on a chip 56. In the arrangement shown, three different waveguides (sensing arms) 60,62,64 are used. This permits three different chemistries 30a,b,c to be used at once and also provides for a reference channel 66. The system uses a single light source 68 and multiple detectors 70,72,74. A fourth detector 76 can be used to look at the reference channel 66. Light from source 68 in chip 56 is incident on sloped reflective end face 61 of waveguide 59 which reflects the light down the waveguide 59 to beam splitter 71. Beam splitter 71 reflects a portion of the light to reference detector 76. Beam splitters 73,75 divide the transmitted light into the three waveguides 60,62,64 which are coated with a sensing chemistry 30a,b,c, respectively. The light passing through waveguides 60,62,64, which is affected by chemistries 30a,b,c, then is reflected by sloped reflective end faces 63, 65, 67 into detectors 70,72,74, respectively. This arrangement can be used in two approaches: (1) Three different analytes can be analyzed simultaneously or (2) If there is a question of specificity, then coincident or redundant analyses can be accomplished using two or more sensing chemistries which respond to the target analyte. The number of waveguides that can be used is only restricted by source strength and geometric considerations. Fig 3D shows a multiple waveguide sensor 77 which is similar to sensor 58 of Figs 3A-C except that sensing arms 60,62,64 are replaced by sensing arms 78,79,80 which are formed of the sensing chemistry and sloped reflective end faces 63,65,67 are replaced by reflective elements 81,82,83 (e.g., prisms). Fig 3E illustrates the construction of the multi-arm waveguide sensor 58 of Figs 3A-C. Waveguide 59 with reference channel 66 has a flat end face 84 distal from sloped end 61. Waveguide 60 is placed at right angles to waveguide 59 abutting end face 84. The end of waveguide 60 distal from sloped end 63 is sloped to form beam splitter 73. A matching prism 85 is placed against the sloped end of waveguide 60 (beam splitter 73) to form a flat face against which waveguide 64 is placed as right angles. The end of waveguide 64 distal from sloped end 67 is sloped to form beam splitter 75. Waveguide 62 has a sloped end face, at the end distal from sloped end 65, which matches the sloped end (beam splitter 75) of waveguide 64, so that waveguide 62 is aligned with waveguide 59. Beam splitters 73,75 are formed by applying suitable optical coatings to the ends of waveguides 60,62,64 to produce the desired reflection and transmission characteristics. Fig 3F illustrates a waveguide sensor 86 formed on a substrate or chip 56 which is similar to sensor 58 of Figs. 3A-C but which has multiple sources and a single detector. Detectors 70,72,74 of sensor 58 are replaced by three sources 90,92,94, typically at three different wavelengths, and source 68 is replaced by a detector 88 which is sufficiently broadband to detect light from all three sources 90, 92, 94. Beam splitter 73 is highly reflective to the wavelength of source 90 and highly transmissive to the wavelengths from sources 92, 94. Beam splitter 75 is highly reflective to the wavelength of source 94 and highly transmissive to the wavelength of source 92. The beam splitter characteristics are obtained by suitable optical coatings. Sloped end faces 63,65,67 direct light from sources 90, 92, 94 down waveguides 60,62,64 and beam splitters 73, 75 direct the light beams into waveguide (sensing and reference arm) 59. Waveguide 59 includes beam splitter 91 which directs a portion of the light to reference detector 96. The rest of the light beam passes through waveguide 59 which is coated with (or contains) sensing chemistry 30. The modulated beam is then reflected by end face 61 down to detector 88. Thus, in this configuration, there is only one sensing chemistry but three different light sources. Waveguides 60,62,64 do not contain any sensing chemistry. Figs 3G,H show an alternate embodiment of sensor 86 of Fig 3F which has multiple sources and multiple sensing chemistries. Waveguide sensor 87 on chip 56 has three sources 90,92,94, typically at three wavelengths, and a detector 88. Sloped end faces 63,65,67 direct light from sources 90,92,94 into waveguides 60,62,64 where the light first encounters a beam splitter 93,95,97 which directs a portion of the light down to reference detectors 51,52,53. The remainder of the light passes down waveguides 60,62,64 which are coated with (or contain) sensing chemistry 30a,b,c. Beam splitters 73,75 pass or direct the modulated light beams from waveguides 60,62,64 to waveguide 59, where the light is reflected at end face 61 down to detector 88. Thus, in this configuration, there is a sensing chemistry on each arm with a source, but there is also a reference detector on each sensing arm. Although waveguide sensors can be formed as described above by mounting waveguide structures on a molded chip package which contains the source(s) and detector(s), it is also possible according to the invention to further integrate the waveguide structures into the molded chip package. The waveguide structures of Figs 1A-3H can be molded as part of the substrate or chip package 12 or 56. It is also possible to form parts of the waveguide structures, as illustrated in Figs 4A-H. In these embodiments, the elements defining the direction of light propagation are formed with the chip as part of the chip fabrication process. Only very simple elements need then be inserted to form a working sensor and these elements are easily interchanged to produce a wide variety of sensors. The design even provides for liquid waveguides, enabling the use of liquid sensing chemistries. As shown in Fig 4A, chip 12 with source 14 and detectors 16,18, is formed with waveguide defining elements 36,38,39 formed integrally thereon, i.e., when chip 12 is molded, elements 36,38,39 are formed as part of the molding process. Elements 38,39,36 are formed over source 14 and detectors 16,18, respectively. Source 14 is at one end of the linear arrangement. Elements 36,38 are corner reflectors and element 39 is a beam splitter. A waveguide body 41 can be easily inserted between elements 38,39 and a waveguide body 42, which is coated with sensing chemistry 30 (or alternatively is partly formed of the sensing chemistry) can be easily inserted between elements 39,36 to form a waveguide sensor 37. As shown in Fig 4B, the spaces between elements 36,38,39 can be enclosed by lateral walls 44, defining channels 45,46. Figs 4C,D are top and side sectional views. Inserts 41,42 of Fig 4A can be inserted in channels 45,46 or channels 45,46 can be filled with liquid reagents and then covered with a membrane 50, as shown in Fig 4D. Membrane 50 can be attached to side walls 44. Fig 4E shows an alternate embodiment of a chip 12 with integral waveguide defining elements 35,36,38,39. In this case, source 14 is in the center with detectors 16,18 at the ends. Again, elements 35,36,38,39, which are corner reflectors, are formed as part of the fabrication process of chip 12. A waveguide body 41 can be easily inserted between elements 38,39 and a waveguide body 43 which is coated with (or contains) a sensing chemistry 30, can be easily inserted between elements 35,36 to form a waveguide sensor 40. As shown in Fig 4F, the spaces between elements 35,36,38,39 can be enclosed by lateral walls 44, defining channels 47,48. Figs 4G-H are top and side sectional views. Inserts 41,43 of Fig 4E can be inserted in channels 47,48 or channels 47,48 can be filled with liquid reagents and then covered with a membrane 50, as shown in Fig 4H. Membrane 50 can be attached to side walls 44. The molded integrated chip package 12 which contains the source 14 and detectors 16,18 can also include other electronics, as shown in Figs 1A,2A. Associated with each detector 16,18 can be an amplifier 98 or other signal processing electronics. A feedback circuit 99 can also be included, connected between source 14 and reference detector 16 to maintain a constant source output. Changes and modifications in the specifically described embodiments can be carried out without departing from the scope of the invention which is intended to be limited only by the scope of the appended claims.

Claims: CLAIMS 1. An optical waveguide chemical sensor comprising: a modular substrate having at least one light source and at least one light detector formed internally therein and covered by an optically transparent material; a waveguide structure mounted on said substrate and extending over said at least one source and at least one detector, said waveguide structure including direction turning means for guiding light from said at least one source into said waveguide structure and direction turning means for guiding light from said waveguide structure to said at least one detector; and a sensing chemistry formed on or in a portion of the waveguide structure. 2. The sensor of Claim 1 wherein the modular substrate has one source and first and second detectors in a linear arrangement with the source at one end, and the waveguide structure is formed of a first waveguide body which extends from said source to the first detector and a second waveguide body forming a junction with the first waveguide body and extending between the two detectors. 3. The sensor of Claim 2 wherein the means for guiding light from the source into the waveguide structure comprises a sloped reflective end face formed on the first waveguide body, and the means for guiding light from the waveguide structure to the two detectors comprises a beam splitter formed at the junction between the first and second waveguide bodies and a sloped reflective end face formed at the distal end of the second waveguide body. 4. The sensor of Claim 3 wherein the sensing chemistry is formed on or in the second waveguide body, and the first detector forms a reference detector. 5. The sensor of Claim 1 wherein the modular substrate has one source and two detectors in a linear arrangement with the source between the two detectors, and the waveguide structure is formed of a first waveguide body which extends from said source to one detector and an adjacent second waveguide body which extends from said source to the other detector. 6. The sensor of Claim 5 wherein the means for guiding light from the source into the waveguide structure comprises a sloped reflective end face formed on one end of each waveguide body and the means for guiding light from the waveguide structure to the detectors comprises a sloped reflective end face formed on the distal end of each waveguide body from said one end. 7. The sensor of Claim 6 wherein the sensing chemistry is formed on or in one waveguide body and the other waveguide body forms a reference arm. 8. The sensor of Claim 1 wherein the modular substrate has one source and a plurality of detectors in a geometric pattern, and the waveguide structure comprises a plurality of interconnected arms extending from the detectors to the source. 9. The sensor of Claim 8 wherein a sensing chemistry is formed on or in each arm which extends to a detector. 10. The sensor of Claim 9 wherein each arm which extends to a detector has a different sensing chemistry formed thereon or therein. 11. The sensor of Claim 8 wherein the modular substrate has one source and three detectors and the waveguide structure comprises a first waveguide arm extending from the source and three sensing arms extending from the first waveguide arm to a respective detector, one sensing arm being aligned with the first waveguide arm and two being orthogonal, and further comprising a pair of beam splitters formed in the sensing arms for splitting light from the source among the three sensing arms. 12. The sensor of Claim 11 further comprising a beam splitter in the first waveguide arm and a reference detector below the beam splitter. 13. The sensor of Claim 1 wherein the modular substrate has one detector and a plurality of sources in a geometric pattern, and the waveguide structure comprises a plurality of interconnected arms extending from the sources to the detector. 14. The sensor of Claim 13 wherein the sensing chemistry is formed on or in an arm of the waveguide structure near the detector, and further comprising a beam splitter between the waveguide arms from the sources and the sensing chemistry and a reference detector below the beam splitter. 15. The sensor of Claim 13 wherein a sensing chemistry is formed on or in each arm which extends to a source, and further comprising a beam splitter in each said arm between the source and sensing chemistry and a reference detector below each beam splitter. 16. The sensor of Claim 1 wherein the modular substrate is a semiconductor chip package. 17. The sensor of Claim 1 wherein the waveguide structure is molded as part of the modular substrate. 18. The sensor of Claim 1 wherein the means for guiding light from said at least one source and means for guiding light to said at least one detector are molded as part of the modular substrate. 19. The sensor of Claim 18 further comprising removable waveguide body inserts which fit between said guiding means. 20. The sensor of Claim 19 wherein the sensing chemistry is formed on or in a waveguide body insert. 21. The sensor of Claim 18 further comprising lateral walls defining open channels between said guiding means. 22. The sensor of Claim 21 further comprising a liquid reagent filling said open channels and a membrane covering said liquid reagent which forms the sensing chemistry filled channels.

Inventors: SAINI DEVINDER P, SAINI, DEVINDER, P.
Applicants: FIBERCHEM INC, FCI-FIBERCHEM, INC.
Application year: 1995
Main classification: G01N21
IPC codes: G01N21, G02B6