OPTICAL CAVITY FOR GAS SENSOR AND GAS SENSOR HAVING OPTICAL CAVITY

Abstract

Provided are an optical cavity 100 for a gas sensor which has a space therein and a gas sensor using the optical cavity, in which in the space of the optical cavity 100, an elliptical reflective surface 133, which constitutes a part of an ellipse (133, 133a) and reflects the light emitted from a position of one focal point F.sub.1 of the ellipse to concentrate the light on the other focal point F.sub.2 of the ellipse, is formed, a hyperbolic reflective surface, which constitutes a part of a hyperbola (135a, 135b) having one focal point that coincides with the other focal point of the ellipse, and reflects the light, which is reflected by the elliptical reflective surface and concentrated on the other focal point of the ellipse, to concentrate the light on the other focal point f.sub.2 of the hyperbola, is formed, and a hyperbola centerline B-B, which connects one focal point of the hyperbola and the other focal point of the hyperbola, is inclined toward a side opposite to the elliptical reflective surface by a predetermined angle with respect to an ellipse centerline A-A which connects one focal point of the ellipse and the other focal point of the ellipse.

Claims

1. An optical cavity for a gas sensor which has a space therein, wherein, in the space of the optical cavity, an elliptical reflective surface, which constitutes a part of an ellipse and reflects the light emitted from one focal point position of the ellipse to concentrate the light on the other focal point of the ellipse, is formed, a hyperbolic reflective surface, which constitutes a part of a hyperbola having one focal point that coincides with the other focal point of the ellipse, and reflects the light, which is reflected by the elliptical reflective surface and concentrated on the other focal point of the ellipse, to concentrate the light on the other focal point of the hyperbola, is formed, and a hyperbola centerline, which connects one focal point of the hyperbola and the other focal point of the hyperbola, is inclined toward a side opposite to the elliptical reflective surface by a predetermined angle with respect to an ellipse centerline which connects one focal point of the ellipse and the other focal point of the ellipse.

2. The optical cavity of claim 1, wherein: a partition wall is further formed between the one focal point of the ellipse and the other focal point of the hyperbola.

3. The optical cavity of claim 1, wherein: a light source for the gas sensor is disposed at the one focal point of the ellipse, and a photodetector, which receives light emitted from the light source and converts the received light into an electrical signal, is disposed at the other focal point of the hyperbola.

4. A gas sensor for measuring gas concentration, comprising: the optical cavity for the gas sensor according to claim 1; a light source which is disposed at one focal point of the ellipse; and a photodetector which is disposed at the other focal point of the hyperbola, receives the light emitted from the light source, and converts the received light into an electrical signal.

5. A gas sensor for measuring gas concentration, comprising: the optical cavity for the gas sensor according to claim 2; a light source which is disposed at one focal point of the ellipse; and a photodetector which is disposed at the other focal point of the hyperbola, receives the light emitted from the light source, and converts the received light into an electrical signal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 is an exploded perspective view of an optical cavity according to an exemplary embodiment of the present invention.

[0018] FIG. 2 is a top plan view of the optical cavity according to the exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] Hereinafter, an optical cavity and a gas sensor using the optical cavity according to an exemplary embodiment of the present invention will be described in detail with respect to the accompanying drawings.

[0020] FIG. 1 is an exploded perspective view of an optical cavity according to an exemplary embodiment of the present invention, and FIG. 2 is a top plan view of the optical cavity according to the exemplary embodiment of the present invention.

[0021] First, an optical cavity for a gas sensor according to the present invention uses natural aspects of an ellipse and a hyperbola. A focal point of at least one ellipse and a focal point of at least one hyperbola are geometrically coincident with each other based on the nature in which light, which travels toward any one focal point of the two focal points of the ellipse or hyperbola, is reflected by the ellipse or hyperbola and then travels toward the other focal point and the nature in which on an elliptical mirror surface, light, which exits any one focal point of the two focal points of the ellipse, is reflected by an elliptical surface and then reaches the other focal point, and then the light, which exits the one focal point of the ellipse, is reflected by a reflective surface and then concentrated on the other focal point of the ellipse, that is, the light, which is concentrated on any one focal point of the two focal points of the hyperbola which are geometrically coincident with the other focal point of the ellipse, is reflected by a hyperbolic surface and then concentrated on the other focal point of the hyperbola, and as a result, the light, which initially exits the one focal point of the ellipse, is concentrated by changing a traveling direction of the light.

[0022] Further, the optical path may be further expanded continuously by allowing one focal point of a new hyperbola to coincide with the other focal point of the hyperbola on which the light, which exits the one focal point of the ellipse, is concentrated by changing the traveling direction, and by changing an angle of the new hyperbola to change the traveling direction of the light again.

[0023] Therefore, it is possible to continuously increase the length of the optical path by adding a new hyperbola having a focal point coincident with the other focal point of the hyperbola on which the light, which initially exits the one focal point of the ellipse, is concentrated. In addition, the light, which is reflected by the hyperbolic surface, is concentrated on the other focal point of the corresponding hyperbola without being dispersed in other directions, and as a result, it is possible to minimize a loss of light caused by light dispersion even without using a separate light concentration means such as a Fresnel lens.

[0024] To this end, as illustrated in FIGS. 1 and 2, an optical cavity 100 according to the exemplary embodiment of the present invention is formed by coupling an upper casing 110 and a lower casing 130 each having a predetermined space therein. The space in the optical cavity 100 is formed by a ceiling surface (not illustrated) which is an inner surface of the upper casing 110, a bottom surface (not illustrated) which is an inner surface of the lower casing 130, and a wall surface which extends along an edge of the bottom surface toward an edge of the ceiling surface by a predetermined height. A part of the wall surface is an elliptical reflective surface 133, as illustrated in FIGS. 1 and 2.

[0025] Here, the terms ceiling surface and bottom surface are made for convenience of description. For example, the inner surface of the lower casing 130 is the bottom surface in a case in which the inner surface of the upper casing 110 is the ceiling surface, and vice versa.

[0026] In addition, as illustrated in FIG. 2, an ellipse (133, 133a) is formed by merging the elliptical reflective surface 133, which constitutes a part of the wall surface in the optical cavity 100, with a portion which extends along a shape of the elliptical reflective surface 133 and is indicated by a dotted line 133a in FIG. 2. The elliptical reflective surface 133 extends from a rear side of one focal point F.sub.1 of the two focal points F.sub.1 and F.sub.2 of the ellipse (133, 133a) to the vicinity of the other focal point F.sub.2. The elliptical reflective surface 133 surrounds the one focal point F.sub.1 at the side of the one focal point F.sub.1.

[0027] In addition, a light source 131 is disposed at the one focal point F.sub.1 of the ellipse (133, 133a), and a light source, which emits incandescent light or infrared light, may be used as the light source 131.

[0028] FIG. 2 illustrates the elliptical reflective surface 133 in the form of an ellipse, but actually, as illustrated in FIG. 1, the elliptical reflective surface 133 has a shape made by cutting a part of the ellipse in a major axis direction (in a direction parallel to a central axis A-A of the ellipse (133, 133a) in FIG. 2). Therefore, the elliptical reflective surface 133 has a predetermined width.

[0029] At a side of the other focal point F.sub.2 of the ellipse (133, 133a), one focal point f.sub.1 of the two focal points f.sub.1 and f.sub.2 coincides with the other focal point F.sub.2 of the ellipse (133, 133a) (f.sub.1=F.sub.2), and a central axis B-B, which connects the two focal points f.sub.1 and f.sub.2, is connected to a hyperbolic reflective surface 135 which is a part of a hyperbola (135a, 135b) disposed to be inclined by a predetermined angle with respect to a central axis A-A of the ellipse 133a.

[0030] Here, the hyperbolic reflective surface 135 is formed such that the other focal point F.sub.2 of the two focal points F.sub.1 and F.sub.2 of the ellipse (133, 133a) coincides with the one focal point f.sub.1 of the two focal points f.sub.1 and f.sub.2 of the hyperbola (135a, 135b) (f.sub.1=F.sub.2), and as a result, as illustrated in FIG. 2, the hyperbolic reflective surface 135 is of course positioned at a front side of the other focal point F.sub.2 of the ellipse (133, 133a) on the central axis A-A which is an axis connecting the two focal points F.sub.1 and F.sub.2 of the ellipse (133, 133a) (at a front side of the one focal point f.sub.1 of the hyperbola (135a, 135b) on the central axis B-B which is an axis connecting the two focal points f.sub.1 and f.sub.2 of the hyperbola (135a, 135b)).

[0031] In addition, the hyperbolic reflective surface 135 is a part of the portion 135b of the hyperbola (135a, 135b), 135a indicates an imaginary line, and no surface such as the hyperbolic reflective surface 135 is formed at a side of 135a.

[0032] Similar to the elliptical reflective surface 133, the hyperbolic reflective surface 135 is indicated by a line in FIG. 2. However, as illustrated in FIG. 1, the hyperbolic reflective surface 135 is also actually a surface having a predetermined width.

[0033] The terms ellipse and hyperbola are used for convenience of description in the present specification, but actually, the ellipse and the hyperbola are not lines but surfaces each having a predetermined width.

[0034] In addition, both of the elliptical reflective surface 133 and the hyperbolic reflective surface 135 are processed as mirror surfaces so as to reflect, at a predetermined angle, the light being incident on the corresponding surface.

[0035] In addition, the centerline B-B, which is a line segment connecting the two focal points f.sub.1 and f.sub.2 of the hyperbola (135a, 135b), is inclined, at a predetermined angle toward the wall surface opposite to the wall surface at the side of the elliptical reflective surface 133 in the optical cavity 100, with respect to the centerline A-A which is a line segment connecting the two focal points F.sub.1 and F.sub.2 of the ellipse (133, 133a).

[0036] Therefore, the other focal point f.sub.2 of the hyperbola (135a, 135b) is positioned in the optical cavity 100, at the same side as the one focal point F.sub.1 of the ellipse (133, 133a), so as to be spaced apart from the centerline A-A of the ellipse (133, 133a) by a distance corresponding to the angle formed between the centerline A-A of the ellipse (133, 133a) and the centerline B-B of the hyperbola (135a, 135b). A photodetector 137, which receives light (optical signal) emitted from the light source 131 and converts the received optical signal into an electrical signal, is disposed at the other focal point f.sub.2 of the hyperbola (135a, 135b).

[0037] A partition wall 111, which prevents interference between the light emitted from the light source 131 and the light received by the photodetector 137, is formed between the light source 131 disposed at the one focal point F.sub.1 of the ellipse (133, 133a) and the photodetector 137 disposed at the other focal point f.sub.2 of the hyperbola (135a, 135b).

[0038] In addition, although not illustrated in FIGS. 1 and 2, the optical cavity 100 according to the present exemplary embodiment has a gas inlet and a gas outlet which are passageways through which gas, of which the concentration is to be measured, enters and exits the interior of the optical cavity 100.

[0039] In addition, the gas sensor according to the exemplary embodiment of the present invention includes an amplifier which amplifies electrical signals from the photodetector 137, and a gas concentration calculation means which calculates gas concentration based on the electrical signal amplified by the amplifier. Because these configurations as well as the light source are made by using publicly known technologies, detailed descriptions thereof will be omitted.

[0040] As described above, in the optical cavity 100 according to the present exemplary embodiment, the light source 131 for emitting light and the photodetector 137 for receiving the light emitted from the light source 131 are disposed at an interval at one side in the optical cavity 100, and the light, which is emitted from the light source 131 and then reflected by the elliptical reflective surface 133, is reflected by the hyperbolic reflective surface 135 disposed opposite to the light source 131 and then received by the photodetector 137 disposed opposite to the hyperbolic reflective surface 135, as described below. As a result, the length of the optical path, which is a length until the light emitted from the light source 131 is concentrated on the photodetector 137, is about two times the length in the optical cavity 100. Therefore, it is possible to ensure the optical path having an appropriate length required to measure gas concentration.

[0041] In addition, since the light emitted from the light source 131 is reflected by the elliptical reflective surface 133 and the hyperbolic reflective surface 135 and then received by the photodetector 137, the light reflected by the elliptical reflective surface 133 and the light reflected by the hyperbolic reflective surface 135 are concentrated on one point and received by the photodetector 137 without being dispersed in other directions. Therefore, it is possible to minimize a loss of light caused by light dispersion occurring when the light is reflected by the reflective surfaces.

[0042] Next, the optical path, which is a path along which the light travels in the optical cavity 100 according to the present exemplary embodiment, will be described with reference to FIG. 2.

[0043] The light, which is emitted from the light source 131 disposed at the one focal point F.sub.1 of the two focal points F.sub.1 and F.sub.2 of the ellipse (133, 133a), is reflected by the elliptical reflective surface 133 which is processed as a mirror surface, and then the light travels toward the other focal point F.sub.2. The light is reflected by the hyperbolic reflective surface 135 positioned at the front side of the other focal point F.sub.2 (the one focal point F.sub.1 of the hyperbola (135a, 135b)) while the light travels, and then travels toward the other focal point f.sub.2 of the hyperbola (135a, 135b), such that the light is concentrated on the photodetector 137 positioned at the other focal point f.sub.2 of the hyperbola (135a, 135b).

[0044] While the exemplary embodiment of the present invention has been described above, the present invention is not limited to the exemplary embodiment, and various modifications or alterations may be implemented without departing from the scope of the present invention.

[0045] In the exemplary embodiment, the optical path is configured by the single ellipse and the single hyperbola, but the present invention is not limited thereto, and as described above, the length of the optical path may be further expanded by adding a new hyperbola while allowing one focal point of the new hyperbola to coincide with the other focal point f.sub.2 of the hyperbola (135a, 135b) on which the light, which exits the one focal point F.sub.1 of the ellipse (133, 133a), is concentrated by changing the traveling direction of the light, and simultaneously by changing the traveling direction of the light again by changing an angle of the new hyperbola.

[0046] In addition, in the exemplary embodiment, the optical cavity 100 is configured by the two members, the upper casing 110 and the lower casing 130, but the present invention is not limited thereto, and the optical cavity 100 may be configured integrally.

[0047] While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

DESCRIPTION OF REFERENCE NUMERALS OF DRAWINGS

[0048] 100 Optical cavity, 111 Partition wall, 131 Light source, 133 Elliptical reflective surface, 135 Hyperbolic reflective surface, 137 Photodetector