Patent Application
20140362427
1. Field of the Invention
The invention relates to a fiber outcoupling with small fiber distances, therefore a new concept that improves the optical properties of the projection head in a scanning laser projection. For this purpose, a fiber outcoupling is presented which affords advantages over previous solutions with a fiber duo. It represents a possibility of being able to set the position of the intersection point between the light beams. Thus, it is possible to place the intersection point on the polygon facets. As a result, there are lower losses of light and edge discolorations during projection are reduced. The distance between the fibers is small (about 25-125 μm). As a result, it now becomes possible to incorporate more than two fibers, so that a plurality of lines can be scanned simultaneously. This enables a higher image resolution than can be realized hitherto with a fiber duo.
2. Description of the Background Art
In a laser projection the light is transported from a laser source to a projection channel via an optical fiber. The image quality is determined in this case decisively by the optics design in the area between the ends of the fiber duo and a two-axis scanner. The divergent light beams emerging from both light fibers are collimated by a collimating lens. Because of the distance of the fiber duo, different points of impact on the polygon result simultaneously. This beam displacement leads to a degradation of the image quality. In particular, the inhomogeneity of the brightness distribution in the image intensifies. In addition, edge discolorations can occur. The diaphragm eliminates a major part of the scattered light.
Such a known arrangement of the implementation of the fiber outcoupling for a fiber duo according to the state of the art is shown in
DE 10 2004 001 389 A1 discloses an arrangement and a device for minimizing edge discolorations in video projectors. In this regard, an image made up of pixels is projected onto a projection surface. The arrangement comprises at least one light beam-emitting, variable-intensity light source and an adjustment device, downstream of a fiber and containing an optical delay for symmetrizing the light beam, and a subsequent deflection unit.
The method and device for projecting an image onto a projection surface from DE 10 2008 063 222 A1 are based on a fiber from DE 10 2004 001 389 A1 and propose constructing the deflection device with a scanner unit and suitable deflection mirrors. Further, the deflection unit comprises fixedly or movably arranged dichroic mirrors, etc., and optionally a diaphragm system.
DE 10 2007 019 017 A1, which corresponds to US 20100188644, discloses a further method and a further device for projecting an image, made up of pixels, onto a projection surface with at least one light beam-emitting, variable-intensity light source and an outcoupling unit downstream of the fiber and a subsequent deflection unit, which directs the light beam onto the projection surface.
DE 41 40 786 A1, which corresponds to U.S. Pat. No. 5,136,675, concerns a projection system in which narrow fiber bundles are used for the optical connection between the light source and projector. The light beams emitted from the individual fibers are imaged via an optic on the projection screen. Different image contents can be blended by an optical element for beam coalescence. The structure of the optics is not explained in greater detail.
DE 601 24 565 T2, which corresponds to U.S. Pat. No. 7,102,700, presents a raster laser projection system, in which closely adjacent fiber optic bundles are used, to be able to scan a plurality of lines simultaneously on the projection screen. The fiber ends are imaged by an optic onto the projection screen. The different primary color components (red, green, blue) are carried by different optical fibers. So that all color hues can be produced, the colored light spots (red, green, blue) must be superimposed on the projection surface. Three or more optical fibers are used for this purpose. One or more points on the projection surface must be irradiated one after the other or simultaneously by different scans within an image, so that a superposition of the light spots, which emerge from the different optical fibers of the fiber bundle, occurs on the projection surface. The possible structure of the optic downstream of the fiber is not described in greater detail.
It is therefore an object of the invention to improve the properties of a projection head with a simple structure, so that the image quality is improved.
The problem of image improvement can be overcome in a first idea by enlargement of the polygon facet. The enlargement, however, would result in much higher costs and possibly limit the realizability of the polygon facets with sufficient quality.
The invention is therefore based on the idea of crossing collimated beams at the polygon facet mirror (intersection point), whereby the diaphragm is brought into a better position, without the functionality being negatively affected in any way. To this end, the known collimating lens is replaced by a new outcoupling system or outcoupling unit.
In a first variant, the system is formed by two converging lenses. The first converging lens produces a focal point of the two light beams in the vicinity of the focal plane of the second converging lens, which collimates them. The two light beams cross in the focal plane of the first converging lens. This intersection point is imaged by the second converging lens in the plane of the polygon facet, where then a second intersection point is located. The diaphragm is located at the first intersection point. In this regard, the system must be dimensioned so that an intersection point of the two light beams is located at the polygon facet mirror. The angle formed by the two light beams with one another and the beam diameter at the projection screen, in contrast, preferably remain unchanged. Because the system is not limited to a fiber duo, more than two fibers can also be used.
The advantage of this outcoupling unit is that the distance between the fibers can be selected as small (i.e., they lie closely adjacent to one another) (about 25-125 μm), so that now also more than two fibers can be incorporated, as a result of which a plurality of lines can be scanned simultaneously.
In a further variant, the system can be made up of converging and diverging lenses. Each fiber has a converging lens, which creates a virtual focal point in the focus of a diverging lens. The collimation is realized in the second step by the diverging lens. Upstream of the diverging lens, there is preferably a slight tilting of the beams emerging from the (two) fibers with respect to the optical axis.
A third variant results with the addition of a telescope. Even the overall length can be reduced as a result. As in the second variant, collimation occurs via the diverging lens, whereby the beam diameter is now smaller immediately thereafter and the tilt angle is greater. The telescope then broadens the beam and reduces the tilt angle to the required values. As a result, a plurality of optical fibers can be incorporated.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:
a-c show an illustration of different fiber arrangements;
Each lens 2, 3, 8, 9 is in practice representative of a lens group. As already shown in
A wide variety of different possible realizations of fiber group 10 is conceivable. Thus
As is generally known, the requirements for production tolerances are high. Fibers must be arranged very accurately with respect to position and angle (tolerable distance error of about 0.5-2 μm). Fiber arrays 21 can be realized with a high precision, e.g., silicon plates 22 (or glass) with parallel V-grooves 23, as
Outcoupling 1 is to be dimensioned so that there is an intersection point of the light beams at polygon facet mirror 7, whereby the beam diameter on projection screen 20 or on polygon facets 7 remains unchanged here in comparison with the prior art. In other words, the outcoupling during use of the same optical fibers on the projection screen and on the facets of the polygon mirror should have the same beam diameter as in the prior art. The distance of converging lenses 4, 6 itself can be determined with the aid of Newtonian imaging equations, etc.
The total length can be calculated according to the relationship
where:
a is the distance of the fiber end surfaces to converging lens 1,
b is the distance of converging lens 4 to focal point f2,
c is the distance of focal point f1 (diaphragm) to converging lens 2,
d is the distance of converging lens 6 to polygon facet mirror 7,
f is the focal length of the system to be replaced (
f1, f2 are the focal lengths of the two converging lenses 4, 6 in
s is the total length from the fiber end to the polygon.
The angle between the light beams on projection screen 20 is determined as
where “e” is the lateral distance between optical fibers 2, 3 (8, 9).
The other two variants are not discussed further, because it is assumed that a structure of this type is easily explained as such. Based on the basic functionality of converging lenses and a diverging lens, each fiber has a converging lens, which creates a virtual focal point in the focus of the subsequent diverging lens. The collimation is then realized in the second step by the diverging lens and this is projected onto the polygon facet mirror. The fibers are tilted to one another such that the beams emerging from the fibers are tilted slightly relative to the optical axis and cross at the virtual intersection point.
The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2012 202 636.3 | Feb 2012 | DE | national |
This nonprovisional application is a continuation of International Application No. PCT/EP2013/053241, which was filed on Feb. 19, 2013, and which claims priority to German Patent Application No. 10 2012 202 636.3, which was filed in Germany on Feb. 21, 2012, and which are both herein incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2013/053241 | Feb 2013 | US |
| Child | 14465672 | US |
