This application claims priority to Taiwan Patent Application No. 101131505 filed on Aug. 30, 2012, which is hereby incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention provides a lighting device, and more particularly, a laser lighting device.
2. Descriptions of the Related Art
Due to the advancement of science and technology, projectors which once had a bulky volume, a heavy weight and poor portability can now be made to be pocketsize, lightweight and portable. This kind of portable projector is also known as “miniaturized projectors”.
Unlike conventional projectors that utilize non-solid-state light sources such as high pressure mercury lamps, a miniaturized projector typically projects an image by using light rays emitted by a solid-state light source (i.e., a laser diode or a light emitting diode (LED)). Furthermore, miniaturized projectors require a specific collimation degree and symmetry of the light rays of the solid-state light source; however, the collimation degree and symmetry of light rays emitted by the solid-state light source are inadequate for this, so a collimator and a beam shaper must be used to improve the collimation degree and symmetry of the light rays.
However, both the collimator and beam shaper are designed to be aspheric, which is difficult to manufacture, and adds to the overall cost of the miniaturized projector. Additionally, during the assembly process, the solid-state light source and the collimator must be aligned accurately for the light rays of the solid-state light source to be collimated effectively; and if any alignment error exists, the collimation of the light rays will be greatly affected.
In view of the aforesaid shortcomings of the collimator and the beam shaper, other devices capable of collimating or symmetrizing light rays have been proposed to replace the collimator and the beam shaper in the projector. For example, the lighting structure disclosed in Taiwan Patent Publication No. 1282480 (also published as U.S. patent Publication No. U.S. Pat. No. 7,354,178) employs a material layer with a multi-step reflecting surface to collimate light rays emitted by an LED.
However, this lighting structure is unable to make the light rays symmetric. Moreover, this lighting structure requires the LED to be located only in the material layer but not outside the material layer; otherwise, it would be impossible for light rays with a large diffusion angles that are emitted by the LED to be effectively collimated.
Accordingly, a need is existed in the art to provide a lighting device which can improve at least one of the aforesaid shortcomings
An objective of the present invention is to provide a laser lighting device which can effectively collimate laser rays.
Another objective of the present invention is to provide another laser lighting device which can effectively make the laser rays symmetrical.
A further objective of the present invention is to provide a further laser lighting device in which a laser light source can be flexibly arranged.
To achieve at least one of the aforesaid objectives, a laser lighting device disclosed in the present invention comprises the following: a laser light source, for producing a laser beam with a diffusion angle not larger than 30 degrees; and a light pipe, disposed in an optical path of the laser beam to collimate the laser beam, wherein the light pipe has a light incident surface, a light exiting surface and a plurality of first cut planes. The light incident surface faces the laser light source, while the first cut planes are located between the light incident surface and the light exiting surface. Each of the first cut planes is normal to a longitudinal direction of the light pipe, and each of the first cut planes has an area smaller than an area of the light exiting surface and larger than an area of the light incident surface; wherein the areas of the first cut planes increase sequentially along the longitudinal direction of the light pipe.
The detailed technology and preferred embodiments implemented for the subject invention are described in the following paragraphs accompanying the appended drawings for people skilled in this field to well appreciate the features of the claimed invention.
Referring to
The laser light source 10 may be a laser diode and is adapted to produce a laser beam 11. The laser beam 11 has an initial diffusion angle θ not larger than 30 degrees. In other words, the diffusion angle θ can have a maximum value of 30 degrees. In this embodiment, the laser beam 11 has a diffusion angle θ of about 18 degrees. The laser beam 11 further has an optical path 12 along which the laser beam 11 travels. The optical path 12 is normal to the light exiting surface of the laser light source 10.
The light pipe 20 is disposed in the optical path 12 of the laser beam 11 to allow the laser beam 11 to propagate into the light pipe 20; in other words, the light pipe 20 and the laser light source 10 are optically coupled to each other. Furthermore, in this embodiment, the light pipe 20 may be disposed apart in front of the laser light source 10; in other words, the laser light source 10 does not come into contact with the light pipe 20 but maintains a spacing S therefrom (as shown in
The light pipe 20 may be a solid structure having a refractive index of no less than 1.4 to facilitate the laser beam 11 traveling in the light pipe 20 through total internal reflection. To have a refractive index of no less than 1.4, the light pipe 20 may be made of polymethylmethacrylate (PMMA), polycarbonates (PC), highly refractive glass (BK7) or glass.
The light pipe 20 is further defined with a length L and a longitudinal direction D. The relationship between the length L and the longitudinal direction D is such that the two ends of the light pipe 20 define a distance therebetween in a specific direction. The specific direction is the longitudinal direction D, while the distance value is the length L. In this embodiment, the longitudinal direction D may be parallel to or overlap with the optical path 12.
The first cut planes 23 are located between the light incident surface 21 and the light exiting surface 22, with each of the first cut planes 23 being normal to the longitudinal direction D of the light pipe 20. It should be appreciated that because the first cut planes 23 as a whole can not be seen directly from the outside of the light pipe 20, only the side lines of the first cut planes 23 are illustrated in
Each of the first cut planes 23 has an area smaller than that of the light exiting surface 22 but larger than that of the light incident surface 21. Moreover, the areas of the first cut planes 23 increase sequentially along the longitudinal direction D of the light pipe 20 (i.e., along the optical path 12). Accordingly, the first cut planes 23 closer to the light incident surface 21 have a smaller area which is at least larger than the area of the light incident surface 21. The first cut planes 23 farther away from the light incident surface 21 have a larger area which is at least smaller than the area of the light exiting surface 22.
It can be known that the light pipe 20 is a frustum in view of the relationship between the areas of the light incident surface 21, the light exiting surface 22 and the first cut planes 23.
With reference to both
Thus, the laser lighting device 1 of this embodiment can provide a more collimated laser beam 11, so the laser lighting device 1 can be advantageously used in devices such as miniaturized projectors.
With reference to
It is also worth noting that “the spacing S between the light pipe 20 and the laser light source 10” and “the length L of the light pipe 20” can be maintained as fixed values; and preferably, “the spacing S between the light pipe 20 and the laser light source 10” is smaller than “the length L of the light pipe 20”.
For example, when the sum of the spacing S and the length L is fixed to 4.5 millimeters, the combinations of the spacing S and the length L may be any of the following combinations: a spacing S of 0.5 millimeters and a length L of 4 millimeters; a spacing S of 0.3 millimeters and a length L of 4.2 millimeters; a spacing S of 0.1 millimeters and a length L of 4.4 millimeters. The laser beam 11 can be collimated effectively by the light pipe 20 no matter which of the combinations is adopted.
It is also worth noting that the light incident surface 21 of the light pipe 20 may be a flat surface instead of a curved surface. In this case, the alignment tolerance between the laser light source 10 and the light pipe 20 during the assembly process may be large, but the laser beam 11 produced by the laser light source 10 is still collimated by the light pipe 20. The light exiting surface 22 may be a flat surface or a curved surface; and when the light exiting surface 22 is a curved surface, the collimating capability of the light pipe 20 can be further improved.
In case of a flat surface, the light exiting surface 22 may further be a flat surface of an asymmetrical shape (e.g., a rectangular shape or an elliptic shape shown in
The first preferred embodiment of the present invention has been described above. Next, the laser lighting devices according to other preferred embodiments of the present invention will be described. For purpose of simplicity, similarities between the other preferred embodiments and the first preferred embodiment and between the other preferred embodiments will be omitted from description.
The curved side line 241 can be defined by an aspheric equation of
in which c is a conic constant and r is a radius from the optic axis.
It should be noted that the distribution graphs of the light intensity of
When the laser beam 11 propagates into the hollow light pipe 20 of the third preferred embodiment, portions of the laser beam 11 having large angles will impinge on the reflective layer 27 of the light pipe 20 and be reflected by the reflective layer 27; and the angle between the laser beam 11 and the optical path 12 will become smaller through the reflection, thus, achieving the purpose of collimation. It should be noted that the reflective layer 27 preferably has a reflectance of no less than 90%, so that only a small portion of the laser beam 11 impinging on the reflective layer 27 will be absorbed by the reflective layer 27 while the remaining portions are reflected by the reflective layer 27.
Here, it should be further noted that according to the Etendue theory, the product of the area of the light incident surface and the diffusion angle of the light source is equal to the product of the area of the light exiting surface and the diffusion angle of the exiting light, and the area is proportional to the radius if the light incident surface or the light exiting surface is circular. Therefore, if the output light rays are to be collimated (i.e., to make the diffusion angle of the exiting light close to zero), then the larger the divergence angle of the light source, the smaller the area of the light incident surface of the light pipe or the larger the area of the light exiting surface will need to be.
However, in consideration of the gap between the light source and the light pipe, too small of area of the light incident surface would lead to a decreased optical coupling efficiency of the incident light. Therefore, when the diffusion angle of the light source becomes larger, the area of the light exiting surface of the light pipe must be increased to make it possible for the light to be collimated.
The diffusion angle of the conventional light emitting diode (LED) is about 120 degrees which is significantly different from the diffusion angle of the laser light source (i.e., LD) of this application that is less than 30 degrees.
As can be known from the aforesaid Etendue theory, the area of the light exiting surface of the light pipe must be increased to obtain the same light collimating effect. Therefore, using the LED having a diffusion angle of 120 degrees shown herein as an example, the area of the light exiting surface of the light pipe used in conjunction with the LED should be quadruple that of the light pipe of the present invention, making it very bulky and uneconomical.
In the lighting structure disclosed in Taiwan Patent Publication No. 1282480 (also published as U.S. patent Publication No. U.S. Pat. No. 7,354,178), the LED thereof cannot be replaced directly with a laser diode in practice. The reason is that to collect all the light rays emitted by the LED in the conventional lighting structure, the volume of the light pipe is certainly made much greater than that of the present invention to ensure the optical characteristics of the LED. Consequently, even if the LED in the conventional structure is directly replaced with the laser diode, there is still no interaction between most of the multi-step reflecting surface of the material layer in the conventional lighting structure and the laser rays. In summary, the LED in the conventional lighting structure cannot be directly replaced with the laser diode, or those of ordinary skill in the art cannot use a common conventional LED directly in conjunction with the light pipe of the present invention to achieve the light collimating effect.
According to the above descriptions, the laser lighting device of the present invention can overcome the shortcomings of the prior art to provide a laser beam that has a relatively small diffusion angle or a laser beam that is relatively symmetrical. Moreover, the spacing between the laser light source and the light pipe of the laser lighting device can be adjusted, so the laser light source can be arranged flexibly. In addition, since the spacing between the laser light source and the light pipe can be determined by the diffusion angle and the area of the light incident surface, a desirable optical coupling efficiency can be obtained between the laser light source and the light pipe most portion of the light pipe is exposed to impinging of the laser rays to serve the function of collimating the light rays, thereby achieving the purpose of making full use of the light pipe.
The above disclosure is related to the detailed technical contents and inventive features thereof. People skilled in this field may proceed with a variety of modifications and replacements based on the disclosures and suggestions of the present invention as described without departing from the characteristics thereof. Nevertheless, although such modifications and replacements are not fully disclosed in the above descriptions, they have substantially been covered in the following claims as appended.
Number | Date | Country | Kind |
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101131505 | Aug 2012 | TW | national |