Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
2000-02-16
2002-04-02
Henry, Jon (Department: 2873)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S205100, C359S208100, C359S434000
Reexamination Certificate
active
06366383
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is directed to relay optics for a deflection system in which two scanning devices are provided, each of which changes the angle of a light bundle from a location predetermined separately for each scanning device in a predetermined deflection plane within a predetermined deflection area, and the relay optics have a first optical system which focuses a parallel light bundle proceeding from the predetermined location for the first scanning device onto a focal surface and a second optical system which parallelizes the light bundle coming from the focal surface and deflects it to the predetermined location of the second scanning device. Further, the invention is directed to a deflection system in which these types of relay systems can be used.
2. Description of the Related Art
Deflection systems of the type mentioned above are used in laser printing technology as well as in laser video technology. In both of these technologies, a matrix arrangement of picture points is illuminated in a raster by means of a laser light bundle or another intense parallel light bundle in order to present an image. For this purpose, the light bundle is scanned over a surface to be illuminated, for example, on a picture screen, over a plurality of lines in the horizontal direction or line direction, as it is called. Scanning is also effected in the direction perpendicular to the line direction, usually referred to as the vertical direction or image direction, although at reduced speed, so that a right-angled image area is formed by means of the light bundle in time average.
While illuminating different picture points on the surface as a result of: the raster scan, the light bundle is modulated at every moment with a different color and brightness depending on the information content desired for every illuminated picture point. In this way, with suitable modulation, a color image is formed on the surface as is known from conventional television technique which, of course, uses electron beams instead of laser bundles and which first makes the picture visible on a screen as light by means of phosphors.
A laser video system of this type is known, for example, from DE 43 24 849 C2. The deflection is carried out in the line direction by means of a polygon mirror; the vertical scan deflection is carried out by means of a swiveling mirror. However, for the purposes of the set of problems presently under consideration, the type of mirror used for deflection is entirely inconsequential. The exclusive concern of the invention is that a pure angular deflection is carried out in a predetermined plane and that the angle of the angular deflection is carried out during raster scanning with a virtually stationary vertex for the respective deflection angle.
In the case of the video projection described above, these planes for the angular deflection in the line direction and image direction are usually at right angles to one another. However, in the case of oblique projection proceeding from the corner of the image field, geometric distortions occur which can possibly be reduced in part in that an angle more favorable for compensation of distortions than 90° is selected between the plane for line deflection and the plane for image deflection; that is, an arrangement is provided which deviates from the example with planes at right angles. But the problem statement which will be made more explicit in the following applies for all angles of the deflection planes relative to one another and can be solved by the same principles as those in the conventional arrangement with planes extending at right angles to one another.
When the locations for line deflection and image deflection are distanced from one another, distortion occurs which becomes especially significant when the deflection device is followed by transformation optics for line deflection and image deflection for the purpose of altering and, especially, enlarging the raster-scanned image field. Such transformation optics are described, for example, in DE 43 24 849 C2.
With transformation optics of the kind mentioned above, it has turned out that in the case of planar screens these transformation optics can be suitably corrected for color aberrations and image distortions only on condition that the tangent of the exit angle and the tangent of the incidence angle for the illumination of every picture point are in a fixed ratio or relationship to one another. When the deflection locations for the two deflections are separated, however, the tangent relationship cannot be realized at all because one or the other location is dominant over the course of time; there is no a fixed location given as vertex for the deflection angle.
The above-mentioned tangent relationship relates only to planar picture screens. With spherical projections, for example, in the dome of a planetarium or a partial cylindrical surface such as in many flight simulators, correction is carried out to corresponding relationships of other functions.
The problem resulting from different deflection points is solved according to DE 43 24 849 C2 through compensation by means of complicated optics. These transformation optics could be expected to have a substantially simpler design while avoiding different deflection locations for the two deflections. It is particularly noteworthy in this regard that this problem becomes especially important when choosing to reduce, rather than enlarge, the image, for example when the projection surface is very far from the deflection device. While a reduction of the raster amplitudes could also be considered, the possible picture point number would be drastically reduced in this case because the picture point diameter is substantially determined by the diameter of the laser beam. This reduction in image resolution is not desirable, as a rule.
U.S. Pat. No. 4,297,723 suggests the apparent displacement of the deflection location of one deflection mirror to the other deflection mirror by means of relay optics, so that the angular deflection is then carried out from a point of the deflection location of the final deflection device in the light path.
Relay optics of the type mentioned above can be constructed, e.g., as an afocal lens system, that is, as a lens system comprising two optical systems in which a light bundle terminating at an angle in the focal point of the first system is focused on an intermediate image plane, proceeding from which a second optical system parallelizes the light coming from the intermediate image plane and deflects it into its exit-side focal point. The first scanning device and second scanning device are then arranged in such a way that their deflection locations lie in the object-side focal point of the first optical system and in the image-side focal point of the second optical system.
When the vertex for the deflection angles of one deflection direction in a system of the type mentioned above lies in the entrance-side focal point of the first optical system and the vertex of the deflection angle for the other deflection direction lies in the exit-side focal point of the second system, both angle deflections proceed from the same location, namely, from the exit-side focal point of the second optical system. Therefore, the problems which accordingly result from different deflection locations for the two deflection angles are overcome.
Nevertheless, this solution is poorly suited to practice. Especially in the case of light bundles having a broad wavelength spectrum, color correction with simultaneous correction of other optical aberrations of the first optical system and second optical system is extremely complicated. The complexity is comparable, for example, to that of a non-vignetting telecentric microscope objective of good imaging quality for the entire visible spectrum with object field diameters in the range of 4 to 5 mm and numeric apertures between 0.2 and 0.25. Further, with respect to raster scanning technique, a large distance between the objective and the scanning dev
Carl Zeiss Jena GmbH
Henry Jon
Reed Smith LLP
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