JPS62276502A - Fresnel lens - Google Patents

Abstract

PURPOSE:To obtain a Fresnel lens having a good light condensing efficiency, by providing refracting bodies which refract rays of light reflected by a surface of total refraction in the direction of focal point at the high refractive index areas around the central part of the Fresnel lens. CONSTITUTION:Small lens bodies 2 of an ordinary Fresnel lens are continuously provided at the central part of this lens which is low in refractive index and refracting bodies 3 are continuously provided at the peripheral area of the central part which is high in refractive index. When rays of light are vertically made incident on the face (a) of the refracting body 3, all of the incident rays of light are reflected by the face (c) of the body 3 and the emitted rays of light are condensed to the focal point of the small lens bodies 2. Therefore, all of the incident rays of light are condensed to the focal point and the light condensing efficiency of this Fresnel lens 1 is improved.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Technical Field] The present invention relates to a Fresnel lens used for condensing light.

[Background Art 1] Conventionally, as this type of Fresnel lens, there has been a flat type Fresnel lens 1° as shown in No. 101J. In this 7-lens lens 7:1゜, the small lens element 2゜ in the center increases in height toward the ends. In other words, the angle of the ridges of the Fuyuyama-type lenslet 2' is determined by linear approximation to that of a normal convex plane lens. This Fresnel lens 1' uses the entire lens surface as a part necessary for condensing light. In other words, as shown in Fig. 12, all the light incident from the front is incident on the lens surface, and t
As shown in the pJio diagram, the light is focused on one point. However, when this planar Fresnel lens 1'' is used in a curved manner, there is a problem that the τ point shifts every 2 degrees for each small lens element (as shown in Figure 11), which tends to occur in the Fresnel lens. If lens 1 is used with a curve, f513
As shown in the figure, the problem is that light is incident on parts that cannot be used as lenses, resulting in a large amount of loss and poor light collection efficiency. Further, the Fresnel lens 1 used as a flat type also had the following problem. This Fresnel lens 1
°, the peak of the lenslet 2゛ in the central part is low, and the edge ff
l! Ill gets higher as you go to the side. and,
m 14 Hit 1 (a), (bN: Show-P,): '+
! : , 'a F, 3111 Since the small lens element 2° greatly deflects the light, the loss of incident light is smaller than that of the small lens element 2° with a low peak as shown in Figure 14 (a). growing. In addition, as shown in FIG. 15, in the conventional Fresnel lens 1, the focal length is
If the distance from the center of ゛ is r, then r/ rh' 0,
The area up to about G becomes a lens surface that is useful for condensing light, and the part where the distance from the center of the 7 Renel Lens

[Object of the Invention] The present invention has been made in view of the above-mentioned points, and its object is to provide a Fresnel lens with good light collection efficiency.

[Disclosure of the Invention 1 (Example 1) Figs. A small lens body 2 of a normal Fresnel lens is arranged in a row in a part with a small refractive index, and a refractive body 3 is arranged in a row in a part with a large refractive index at the periphery of the central part. The refractor 3 of this embodiment has a right triangular cross section as shown in FIG. 2. Assume that light is perpendicularly incident on a plane (A) forming a right angle to the refracting body 3 as shown in FIG. At this time, the surface (c) is formed as a total reflection surface that reflects all of this incident light. In other words, if the refractive index of the refracting body 3 is 1.5, the incident angle a of the light on the surface (C) necessary for total reflection of this light on the surface (C) is 41. 8° or more is required. Therefore, this surface (c) is formed at an angle greater than this angle of incidence. (l) When this totally reflected light passes through the surface (b), it is refracted downward and exits. In other words, the plane (
The angle at which the emitted light converges on the focal point of the small lens body 2, with (a) facing the front direction where the light enters, and (b) facing the center where the total reflected light comes out. Form the surface (c) so that the angle of incidence is greater than or equal to the above angle of incidence, and
are set up in succession. As a result, all of this incident light is focused at one focal point, and the light focusing efficiency of the Fresnel lens 1 is improved.

Note that using the Fresnel lens 1 of this embodiment, tj%
When condensing light three-dimensionally as shown in Figure 3, the fourth
As shown in the figure, the 7-Resnel lens x1 of this embodiment condenses the light in the evening direction in FIG. 3, and the conventional Fresnel lens 1'' is used to condense the light in the φ direction in FIG. By using these in combination, three-dimensional light can be focused.

(Example 2) Fig. S5 and Fig. V6 are diagrams showing other embodiments of the present invention, and this embodiment effectively condenses light even in a part far from the center of the Fresnel lens 6. Regarding the planar Fresnel lens 6 that can be
As shown in the figure, one with a square cross-section is used. Note that the refractive body 3 described in the above embodiment may be used. This refracting body 7 has a surface (C) formed in the same manner as the above-mentioned refracting body 3 so that the light incident from the surface (A) is totally reflected at the surface (C). In other words, (c) is formed on the total reflection surface. In this refractive body 7, this totally reflected light exits from the surface (b) and is condensed onto the focal point, α, of the small lens body 2. The refractive body 7 of this embodiment is arranged so that the surface (A) is aligned with the bottom surface of the small lens body 2, that is, the ≠ surface of the Fresnel lens 6 as a convex plane lens. That is, the light incident from the surface (A) is incident on the surface (C) at an angle of 41.8 degrees or more, and therefore the incident light is totally reflected on this surface (C). and,
By forming the surface (b) so that the emitted light is in the focus and v directions of the small lens element 2, a planar Fresnel lens that condenses light to one point can be obtained. In this example,
Even when used as a Fresnel lens with a large diameter, the exit angle of the refractor 7 can be arbitrarily set, and the distance between the focal point 1 of the Fresnel lens 6 can be shortened. In other words, by using this Fresnel lens 6, the space of the optical system can be reduced. Moreover, the Fresnel lens light can be effectively focused on the focal point of the Fresnel lens 6 due to the 1° to 1± deviation of the conventional Fresnel lens.

FIG. 7 shows an example in which this embodiment is applied to a wide type Fresnel lens 4. Refractor 5 similar to the refractor 7 above
Like the small lens body 2 of the Fresnel lens 4, it is formed to protrude upward, with the surface (A) facing outward. The flat Fresnel lens 4 can be made into a wide type by turning the upper surface (A) outward and condensing the light incident from the side to the focal point of the lens. By forming the refracting body 5 in this way, it is possible to condense light in a wide range with a flat type, and since it is a flat type, 7Renelllen';r
An optical system using :4 can be made thin.

The tjIJS diagram and FIG. 9 show the case where the above-mentioned 7 Renel Len:XG is used in the optical system of a hot wire type detector A for vehicle theft prevention. As shown in FIG.
As shown in FIG. 8(a), the sensor is attached to the sensor to detect the diagonally upward direction. As described above, by using the Fresnel lens 6 of this embodiment, wide-angle detection is possible.The output to this hot wire type detector is connected to the security bell 10, and the door key (2 Switches sw2 and sw3, which close when the engine is turned on, and switch SW, which closes when the engine key is removed, are connected in parallel, and these switch circuits are connected in series with the on/off switch SWl of the hot wire detector A. The hot wire detector 48 is connected to the batch 17B via the hot wire detector 48.In other words, while the hot wire detector A is on, the security bell 10 is not activated unless the door is opened using the keys 8 and 8. It's starting to ring.

[Effect of the Invention 1] As described above, the present invention has a small lens body having a chevron-shaped cross section in the center of a lens having a small refractive index. ! ：The above-mentioned refractive body is equipped with a total reflection surface that internally totally reflects the incident light incident from the moe direction, and refracts the light reflected by this total reflection surface toward the focal point of the small lens element. Since it is connected to the area with a high refractive index at the periphery of the center, it is possible to condense incident light in areas far from the center of the lens, which conventionally had poor light collection efficiency, to the focal point of the small lens element. Therefore, the light collection efficiency of the Fresnel lens is improved, and the light collection position can be shortened with a refractor regardless of whether it is a flat or curved type, which has the effect of making the equipment using this Fresnel lens smaller or thinner. play.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a block diagram of the same refracting body as above, Figs. 3 and 4 are explanatory diagrams when performing three-dimensional detection using the same as above, and Fig. 5 is a block diagram of an embodiment of the present invention. 6 is a configuration diagram showing another embodiment of the present invention, FIG. 6 is a configuration diagram of the same refracting body, FIG. 7 is a configuration diagram showing an application example of the same, and FIGS. 8 and 9 are diagrams using the same. An explanatory diagram of a heat ray detector, FIG. 10 is a configuration diagram showing a conventional example, and FIGS. 11 to 15 are explanatory diagrams of the same operation. 1.6 is a Fresnel lens, 2 is a small lens body, 3°7 is a refractive body, and (c) is a total reflection surface. Agent Patent Attorney Ishi 1) Ai Figure 7 Figure 2 Figure 6 (b) Figure 9 Figure 1 o Figure 11 Figure 12 Figure 13 Figure 14

Claims (1)

[Claims] (1) A small lens body with a chevron-shaped cross section is arranged in a row at the center of a lens with a small refractive index, and is equipped with a total reflection surface that completely internally reflects incident light incident from the front, and this total reflection surface A Fresnel lens characterized in that a refractive body that refracts reflected light toward the focal point of the small lens body is connected to a portion having a large refractive index at the periphery of the center portion.