WO1999049302A1

WO1999049302A1 - Optical sensor

Info

Publication number: WO1999049302A1
Application number: PCT/EP1999/001616
Authority: WO
Inventors: Akihiro Tagaya; Hironobu Yamamoto; James Stamatoff
Original assignee: Aventis Research & Technologies Gmbh & Co. Kg
Priority date: 1998-03-20
Filing date: 1999-03-12
Publication date: 1999-09-30
Also published as: JPH11271217A

Abstract

An optical sensor capable of preventing noise causing materials from being produced in or introducing into a light path is provided. The optical sensor is composed of a sensor chip (2) having a polymer thin film (2B) which exhibits a change in a physical or chemical property due to an interaction with a chemical material, a light source (1) for emitting light for irradiating the sensor chip (2) therewith, a light receiving element (3) for receiving light emitted from the light source (1) and reflected off the sensor chip (2), and a housing (6) for integrally holding the sensor chip (2), the light source (1) and the light receiving element (3). The housing (6) has a portion (8) which includes a light path, along which light from the light source (1) is reflected off the sensor chip (2) and reaches the light receiving element (3), and is formed of a light transmitting resin having a large refractive index compared with the refractive index of air.

Description

1

Description

Optical Sensor

1. Field of the Invention

This invention relates generally to a sensor for optically detecting a physical and/or chemical change which occurs in a sensor chip, and more particularly to a simple and inexpensive optical sensor which is capable of detecting such a change with lower noise even under a dusty environment and under an environment which may cause a temperature change in the sensor.

2. Description of the Related Art

Optical sensors for detecting the existence and/or the concentration of an organic material dissolved in water or an organic material existing in atmosphere are known. For example, such a sensor is described in Laid-open Japanese Patent Application No. 9-329553. Fig. 1A illustrates the basic configuration of the optical sensor described in this patent document. Referring specifically to Fig. 1A, a light source (for example, a laser diode) 1 , a sensor chip 2, a light receiving element (for example, a photodiode) 3, a prism 4, and an optical system 5 including a collimating lens, all of which constitute the optical sensor, are integrally held in an upper portion of a housing 6, made of aluminum, having a cavity formed therein. The sensor chip 2 disposed below the prism 4 in the housing 6 is composed of a glass substrate 2A and a polymer thin film 2B formed on the bottom surface of the glass substrate 2A.

The polymer thin film 2B is positioned to be in contact with water or air which passes through a passage 7. As illustrated in Fig. 1 B, the polymer thin film 2B reflects light from the light source 1 off the top and bottom surfaces, so that reflected light rays are incident on the light receiving element 3 while interfering with each other. The prism 4 desirably has a refractive index in a range of 1.2 to 2.5. For example, for light at wavelength of 670 nm, a BK7 glass prism has a refractive index of 1.51 ; an SF11 glass substrate has a refractive index of 1.77; and a poly methyl methacrylate 2 prism has a refractive index of 1.49.

Since the polymer thin film 2B physically or chemically interacts with a particular kind of chemical material, the existence of such a chemical material around the housing 6 causes a change in a characteristic of the polymer thin film 2B formed on the glass substrate 2A such as refractive index, thickness, light absorbance or the like, resulting in a change in the intensity of light reflected by the polymer thin film 2B, i.e., the intensity of light detected by the light receiving element 3. Such an optical detecting method is called an "interference enhanced reflection method" (IER method). It is therefore possible to know the existence and/or the concentration of a particular chemical material from a change in the intensity of light detected by the light receiving element 3.

Light emitted from the light source 1 is refracted on the top surface of the glass substrate 2A, and is incident on the polymer thin film 2B at an angle θ. In this event, an optimal incident angle θ exists for the optical sensor to provide the highest sensitivity depending on the refractive indexes and the thicknesses of the glass substrate 2A and the polymer thin film 2B. A variety of methods such as a waveguide mode method (WG method), a surface plasma resonance method (SPR method), and so on have been known as detecting methods which utilize an optimal incident angle from a certain medium to another medium, similar to the foregoing example.

Such optical sensors, however, are used for purposes of monitoring a leaked chemical material or the like in a storage area, manufacturing facilities, and so on in which the chemical material to be detected is handled. Therefore, the sensors are often installed outdoors, more specifically, in places where the sensors are exposed to wind, rain, dust and/or moisture or where the sensors experience a large temperature change. For this reason, when materials which may cause scattering, reflection, refraction, interference of light introduce into a light path within an optical sensor, or are produced within the optical sensor, this can result in degraded performances such as increased noise in sensor output, a lower resolution of the 3 sensor, a lower detectable lower limit, and so on. In the worst cases, the optical sensor may falls into an inoperative condition under an environment which is largely affected by the existence of such materials that cause noise as mentioned. Particularly, the inability of detecting a leak and erroneous detection in a site involving a large amount of chemical materials would lead to serious damages such as environmental destruction, shut-down of large scaled facilities, or the like.

To avoid such catastrophe, the optical sensor is required to have a highly air-tight structure so as to prevent dust, water droplets and so on from introducing into a light path. However, a highly air-tight structure, if employed, would involve complicated manufacturing steps and maintenance works, possibly resulting in an increase in manufacturing cost, in addition, when the optical sensor is built in an air-tight structure, the inside of the optical sensor must be maintained in a sufficiently low humidity state to prevent even a temperature change from causing any water droplet to attach in a light path, thereby possibly requiring further complicated manufacturing steps.

Moreover, when spaces between a variety of optics such as a light source, a light receiving element, a sensor chip, a lens, a prism, a mirror and so on disposed in an optical sensor are not filled with a transparent resin, the spaces between the optics are generally filled with a gas such as air, inert gas or the like. It is therefore necessary to design an optical system within the optical sensor on the assumption that light passing through such a filling gas is incident on the sensor chip and the other optics, thus implying a problem that the freedom of design is limited.

Object and Summary of the Invention

This invention has been made in view of the problems inherent to the conventional optical sensor, and its object is to proved an optical sensor which is simple in structure and inexpensive, easy to manufacture, highly free in designing, and capable of preventing a noise causing material from introducing into a light path or from being produced in the light path. 4

To achieve the above object, this invention provides an optical sensor comprising:

a sensor chip having a polymer thin film which exhibits a change in a physical or chemical property due to an interaction with a chemical material;

a light source for emitting light for irradiating the sensor chip therewith;

a light receiving element positioned to receive light emitted from the light source and reflected off the sensor chip; and

a housing for holding the sensor chip, the light source and the light receiving element at predetermined positions, wherein the housing has a portion including a light path through which light from the light source is reflected off the sensor chip and reaches the light receiving element, and the portion is formed of a light transmitting resin having a large refractive index compared with the refractive index of air.

Preferably, the housing includes:

a holding portion for integrally holding the light source, the sensor chip and the light receiving element; and

a light transmitting portion formed of the light transmitting resin in contact with an inner surface of the holding portion so as to include the light path.

In one embodiment of this invention, the holding portion is opaque, and the light transmitting portion is formed of a light transmitting resin.

In another embodiment of this invention, the light transmitting portion comprises a light guide path having a predetermined thickness and extending along the light path.

A difference in refractive index between the light transmitting resin and the sensor chip is desirably 0.01 or less preferably 0,001 or less. 5

The light transmitting portion may be formed of a combination of a plurality of transparent resins having different refractive indexes.

The optical sensor according to this invention is operated in accordance with any of an interference enhanced reflection method, a surface plasma resonance method and a waveguide mode method.

Light emitted from the light source passes the light transmitting portion made of a light transmitting resin, impinges on the sensor chip, and is reflected off the sensor chip to reach the light receiving element. In this event, the portion including the light path, along which the light from the light source is reflected off the sensor chip and reaches the light receiving element, is filled with a light transmitting resin having a large refractive index compared with the refractive index of air, including interstices between optics, so that the light will not be interfered by noise causing materials.

Brief Description of the Drawings

Fig. 1 A illustrates the basic structure of a conventional optical sensor;

Fig. 1B is an enlarged view of a main portion of the structure illustrated in Fig. 1A;

Fig. 2 is a schematic diagram illustrating a first embodiment of an optical sensor according to this invention;

Fig. 3 is a schematic diagram illustrating an exemplary modification to the first embodiment illustrated in Fig. 2;

Figs. 4A and 4B are schematic diagrams each illustrating a second embodiment of the optical sensor according to this invention;

Fig. 5 is a schematic diagram illustrating a third embodiment of an optical sensor according to this invention; and 6

Fig. 6 is a schematic diagram illustrating a fourth embodiment of an optical sensor according to this invention;

Description of the Preferred Embodiments

Several embodiments of an optical sensor according to this invention will hereinafter be described with reference to Figs. 2 to 6. In Figs. 1 - 6, identical or similar components are designated the same reference numerals.

Fig. 2 schematically illustrates the configuration of a first embodiment of an optical sensor according to this invention. Similar to the optical sensor illustrated in Fig. 1 , a light source 1 , an optical system 5 including a collimating lens, a sensor chip 2 and a light receiving element 3 are integrally held in a housing 6. The housing 6 is made of an opaque material, for example, aluminum, and is formed with a cavity therein such that light emitted from the light source 1 is reflected off the sensor chip 2 and received by the light receiving element 3. The sensor chip 2 fixed on the bottom surface of the housing 6 is composed of a glass substrate 2A, and a polymer thin film 2B formed on the bottom surface of the glass substrate 2A to allow for contact with water, air or the like.

The internal cavity of the housing 6 is filled with a transparent resin 8 to constitute a light transmitting portion for ensuring a light path along which light emitted from the light source 1 is reflected off the sensor chip 2 and reaches the light receiving element 3. In this way, the light source 1 , the optical system 5 including a collimating lens, the sensor chip 2 and the light receiving element 3 are embedded in the transparent resin 8 without any interstices therebetween. Alternatively, the prism 4 may be disposed on the sensor chip 2, as illustrated in Fig. 1 , and the internal cavity of the housing 6 may be filled with the transparent resin 8 in that state, if necessary. For example, an optically transparent adhesive, a sealing agent (silicon resin) or the like may be used to fill the cavity.

An important aspect involved in impinging light from the light source 1 to the sensor chip 2 and receiving the reflected light to extract it to the outside is how refractive 7 indexes are set for the glass substrate 2A of the sensor chip 2 and a medium surrounding the sensor chip 2. When the glass substrate 2A forming part of the sensor chip 2 has a refractive index larger than the surrounding medium, light reflected off the surface of the glass substrate 2A on the same side as the polymer thin film 2B to exit the cavity may be totally reflected depending on an incident angle, so that it cannot be extracted to the outside. As the difference in refractive index between the glass substrate 2A and the medium filling the cavity is larger, the condition for extracting the reflected light to the outside is more limited. Conversely, the difference in refractive index between the two is smaller, the condition for extracting the reflected light to the outside becomes looser, and accordingly the freedom in designing the optical sensor is also increased. The optical sensor of Fig. 1 requires the prism 4 in order to eliminate an inconvenience of directing light from the light source 1 onto the sensor chip 2 after passing through a medium having a low refractive index such as air, inert gas or the like to reduce the difference in refractive index between the medium and the glass substrate 2A.

In the first embodiment of this invention, in turn, the cavity of the housing 6 is filled with a transparent resin 8 having a large refractive index similar to the prism 4 used in the optical sensor illustrated in Fig. 1. Desirably, the transparent resin 8 has a refractive index substantially equal to that of the glass substrate 2A, and the difference between the two materials is approximately 0.01 or less. Similarly, the refractive index of the transparent resin 8 is desirably substantially equal to the refractive indexes of optics constituting the optical system of the optical sensor, and the difference between the two parts is approximately 0.01 or less.

The transparent resin 8 for use in the optical sensor of this invention may be selected as appropriate from a variety of hardenable resins such as thermosetting resins, ultraviolet hardenable resins, thermoplastic resins and so on that have an appropriate refractive index. In addition, the transparent resin 8 is not necessarily made of a single material, but may be made of a combination of two or more kinds of transparent resins to create a resin having a desired refractive index, such that a variety of actions such as reflection, refraction, interference, scattering or the like 8 may be exerted on light emitted from the light source 1. Further, additives may be added to the material of the transparent resin 8 to modify its properties such as the strength, stability, workability or the like. Furthermore, a highly refractive transparent resin is used for a portion along a light path from the light source 1 to the light receiving element 3 through the sensor chip 2, while a less refractive transparent resin is used for portions progressively away from the light path to provide the transparent resin 8 with appropriately distributed refractive indexes, in which case light from the light source 1 can be guided to a desired direction without using optics such as a collimating lens or the like, resulting in an increased freedom of designing the optical sensor with respect to the geometrical positioning of optics and a reduction in size and weight of the optical sensor.

It should be noted that the transparent resin 8 need not be highly transparent, but may have such a transparency that allows the light receiving element 3 to detect light from the light source 1 even if the light reflected off the sensor chip 2 is attenuated by the transparent resin 8 along the light path to the light receiving element 3.

As described above, since the optical sensor illustrated in Fig. 2 can eliminate a prism, which has been required on the conventional sensor chip, to omit a delicate step of highly accurately positioning a prism at an appropriate location in the cavity of the housing 6, and is merely required to fill the cavity with a transparent resin, the optical sensor of this invention can be readily manufactured at a lower cost and still reliably prevent noise causing materials from introducing into the light path and from being produced in the light path.

At present, prisms made of materials such as BK7 glass (borosilicate crown glass), synthetic fused quartz, acrylic resin, and so on are commercially available. Thus, an optical sensor constructed as illustrated in Fig. 1 using a commercially available prism (former) and an optical sensor constructed as illustrated in Fig. 2 by filling the cavity of the housing 6 with a transparent resin having the same refractive index as the prism were fabricated to compare their responses with each other. As a result, it was confirmed that the two optical sensors exhibited similar responses. Also, when 9 a temperature around the housing 6 was periodically changed in a range of 5° to 40°, the former optical sensor suffered from water droplets produced on an incident surface and an exit surface of the prism 4 and on a light receiving surface of the light receiving element 3, increased noise by 50 times or more as compared with the optical sensor without water droplets, resulting in the resolution and detection lower limit of the optical sensor degraded by 50 times or more. In the latter optical sensor, however, such increased noise was not observed, and the optical sensor did not experience degraded resolution or detection lower limit. Further, it is confirmed that the latter optical sensor can finely adjust the refractive index of the transparent resin 8 by adding an inert low molecular material such as, for example, benzyl butyl phthalate to the transparent resin 8.

As described above, the first embodiment illustrated in Fig. 2 has the internal cavity of the housing 6 filled with a transparent material to prevent noise causing materials from introducing into the light path or from being produced in the light path, such that any interstices existing in the light path from the light source 1 to the light receiving element 3 through the sensor chip 2, for example, an interstice between the light source 1 and the optical system 5, and interstices between optics constituting the optical system 5 are filled with the transparent resin.

Fig. 3 illustrates an exemplary modification to the configuration of the first embodiment illustrated in Fig. 2. In Fig. 3, a half mirror 9 is disposed in a midway of a light path from an optical system 5 to a sensor chip 2, such that light exiting the optical system 5 is split into two by the half mirror 9. Light reflected by the half mirror 9 is received by a light receiving element 3ι, while light passing through the half mirror 9 is reflected off the sensor chip 2 and received by another light receiving element 3₂.

Figs. 4A and 4B each illustrate the structure of a second embodiment according to this invention. In Fig. 4A, a prism 4 disposed on a sensor chip 2 as illustrated in Fig.

1 and a light source 1 or an optical system 5 are interconnected through an optical fiber 10, and a cavity inside a housing 6, an interstice between the light source 1 and 10 the optical fiber 10, and an interstice between the optical fiber 10 and the prism 4 are filled with a transparent resin 8. In Fig. 4B, a light source 1 and a prism 4 are interconnected through an optical fiber 10, the prism 4 and a light receiving element 3 are interconnected through another optical fiber 11 , while an interstice between the light source 1 and the optical fiber 10, an interstice between the optical fiber 10 and the prism 4, an interstice between the prism 4 and the optical fiber 11 , and an interstice between the optical fiber 11 and the light receiving element 3 are filled with a transparent material.

Alternatively, the optical system 5 may be interposed between the light source 1 and the optical fiber 10, in which case an interstice between the light source 1 and the optical system 5 and an interstice between the optical system 5 and the optical fiber 10 are also filled with the transparent resin 8.

While in the optical sensors illustrated in Figs. 2 to 4, the internal cavity of the housing 6 and interstices between the optics are filled with the transparent resin 8, an alternate embodiment excluding the housing 6 is also possible. Fig. 5 illustrates an example of such an optical sensor. For example, after a light source 1 , an optical system 5, a sensor chip 2 comprising a glass substrate 2A and a polymer thin film 2B formed on one surface of the glass substrate 2A, and a light receiving element 3 have been arranged in a mold made of Teflon in a predetermined positional relationship, a transparent resin is injected into the mold and cured by heating, irradiation of ultraviolet rays, or any other appropriate method. In this way, an optical sensor can be provided, as illustrated in Fig. 5, as having the light source 1 , the optical system 5, the sensor chip 2 and the light receiving element 3 held in a body

12 made of the transparent resin in the predetermined positional relationship.

The transparent resin body 12 may have an arbitrary shape. While Fig. 5 illustrates the body 12 in which the light source 1 , the optical system 5 and the light receiving element 3 are embedded, the body 12 may be formed in a prism shape such that the sensor chip 2 is adhered on the bottom surface of the body 12 with a transparent adhesive, the light source 1 and the optical system 5 are adhered on one of the 11 remaining two surfaces, and the light receiving element 3 is adhered on the other surface.

The optical sensor of Fig. 5 eliminates the need for fabricating the housing 6, so that it can be fabricated at a lower cost and is more suitable for mass production as compared with the first embodiment. It should be noted that since the description on the transparent resin 8 used in the first embodiment of this invention can be applied to the resin constituting the body 12, repetitive description on the resin for use in the body 12 is omitted here.

When the optical sensor constructed as illustrated in Fig. 5 and the optical sensor constructed as illustrated in Fig. 2 were actually fabricated to compare their performances, it was confirmed that there was no difference in performance between the two optical sensors.

Fig. 6 illustrates a fourth embodiment of the optical sensor according to this invention. Likewise, in Fig. 6, a light source 1 , a sensor chip 2 and a light receiving element 3 are held in a housing 6 made of a resin such that light emitted from the light source 1 and reflected off the sensor chip 2 reaches the light receiving element 3, as is the case of the foregoing first to third embodiments. In the fourth embodiment, the housing 6 contains a light guide path 13 having a predetermined thickness, which surrounds a line connecting the center of a light emitting surface of the light source 1 and the center of the sensor chip 2, and a line connecting the center of the sensor chip 2 and the center of the light receiving surface of the light receiving element 3. The light guide path 13 is formed of a resin having a refractive index higher than a resin surrounding this portion. Since the description on the transparent resin 8 used in the first embodiment of this invention can also be applied to the resin for use in the light guide path 13, repetitive description on the resin for use in the light guide path 13 is omitted here.

By thus constructing the optical sensor, the optical system 5 can be eliminated, thereby making it possible to fabricate the optical sensor at a lower cost. When the optical sensor constructed as illustrated in Fig. 6 and the optical sensor constructed 12 as illustrated in Fig. 2 were actually fabricated to compare their performances, it was confirmed that there was no difference in performance between the two optical sensors.

The optical sensor according to this invention so far described is operable in any of an interference enhanced reflection method, a surface plasma resonance method and a waveguide mode method, similarly to conventional optical sensors.

As will be apparent from the foregoing detailed description with reference to several embodiments, this invention produces particular effects as follows by virtue of a predetermined portion including the light path from the light source to the light receiving element through the sensor chip formed of a transparent material:

(1) since the transparent material is also filled in interstices in the predetermined portion including the light path from the light source to the light receiving element through the sensor chip, noise causing materials such as dust, water droplets, or the like are prevented from being produced in or introducing into the light path from the light source to the light receiving element through the sensor chip, so that the optical sensor is not interfered by the noise causing materials. In addition, since the optical sensor can be installed in any desired place, and a noise component is largely reduced in a signal output from the light receiving element to correspondingly improve the resolution of the sensor, the optical sensor can detect even the existence of a very small amount of chemical material;

(2) not only the freedom of designing the optical sensor is increased with respect to the geometric positioning of the light source and other optics, but also the optics can be mounted at predetermined positions in a high accuracy; and

(3) the optical sensor provides for a reduction in the number of parts, simplified manufacturing steps, labor-saving, and consequently a reduction in manufacturing cost.

Claims

13What is claimed is:

1. An optical sensor comprising: a sensor chip having a polymer thin film which exhibits a change in a physical or chemical property due to an interaction with a chemical material; a light source for emitting light for irradiating said sensor chip therewith; a light receiving element positioned to receive light emitted from said light source and reflected off said sensor chip; and a housing for holding said sensor chip, said light source and said light receiving element at predetermined positions, said housing having a portion including a light path through which light from said light source is reflected off said sensor chip and reaches said light receiving element, said portion being formed of a light transmitting resin having a refractive index difference between said resin and the substrate of the sensorchip being 0.01 or less.

2. An optical sensor according to claim 1 , further comprising optics disposed along the light path from said light source to said sensor chip, said optics including a lens, a mirror, a prism and so on.

3. An optical sensor according to claim 1 or 2, wherein said housing includes: a holding portion for integrally holding said light source, said sensor chip and said light receiving element; and a light transmitting portion formed of said light transmitting resin in contact with an inner surface of said holding portion so as to include said light path.

4. An optical sensor according to claim 2 or 3, wherein said holding portion is opaque, and said light transmitting portion is formed of a light transmitting resin.

5. An optical sensor according to any of claims 2 - 4, wherein said light transmitting portion comprises a light guide path having a predetermined thickness and extending along said light path. 14

6. An optical sensor according to any of claims 2 - 4, wherein said holding portion and said light transmitting portion are formed of the same light transmitting resin.

7. An optical sensor according to any of claims 1 - 6, wherein a difference in refractive index between said light transmitting resin and said sensor chip is 0.001 or less.

8. An optical sensor according to any of claims 1 - 6, wherein said light transmitting portion comprises a combination of a plurality of transparent resins having different refractive indexes.

9. An optical sensor according to any of claims 1 - 8, wherein said optical sensor is operated in accordance with any of an interference enhanced reflection method, a surface plasma resonance method and a waveguide mode method.