Optical: systems and elements – Lens – Including a nonspherical surface
Patent
1990-11-19
1994-04-26
Sugarman, Scott J.
Optical: systems and elements
Lens
Including a nonspherical surface
359671, 359714, 359823, G02B 1318
Patent
active
053072081
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an optical system for imaging the light from light sources having varying angles of emission in different planes and/or the light of which appears to emanate from spaced dot light sources in different planes.
STATE OF THE ART
The light from a series of light sources, including laser diodes, which presently are increasingly gaining in importance, appears to emanate from "dot light sources" in different planes, the dot light sources being spaced in the direction of the optical axis. This space, which is referred to as the astigmatic difference of focus, amounts to several m in the case of laser diodes now commonly used. This astigmatic difference of focus leads to a collimation of the pencil of light, by way of illustration, of laser diodes using conventional collimators, to a "non-dotshaped" image, which is especially troublesome in the case of laser scanners or so-called "light pens". For this reason it is usually necessary to consider correcting the astigmatism.
Furthermore, the laser diodes frequently have different angles of emission in different planes. If one collimates this type of pencil of light with a conventional collimator, one gets a light pencil with a non-circular cross-section. In a number of applications, this deviation from the circular shape is, however, undesirable.
In addition, reference is made to the general survey "Specifying Laser Diode Optics" in Laser Focus/Electro-Optics, March 1984, p. 44 ff. Moreover, it is expressly pointed out that this article is to be referred to for the explanation of all terms that have not been made more apparent herein.
In order to correct astigmatism, it is known, by way of illustration from DE-PS 22 66 032 or from the aforementioned general survey, to place a cylindrical lens in the path of the beam, which at least decreases the "astigmatic aberration" for a specific astigmatic difference of focus.
Furthermore, U.S. Pat. No. 3 396 344 proposes placing two cylindrical lenses in the parallel path of the beam after the collimator.
This possible way of correcting astigmatism, however, has not found widespread use. Instead, it has been suggested to correct the astigmatism with laser diodes having two anamorphotic prisms and, if need be, an additional cylindrical lens. Here reference is made to the previously mentioned general article and to Fa. Melles Griot's laser head.
However, astigmatic difference of focus, by way of illustration of laser diodes varies not only from construction type to construction type, but also with a production series due to the production tolerances between different production batches. Moreover, the astigmatic difference of focus changes in the course of conventional period of use of a laser diode due to aging.
Therefore, it is desirable to be able to set the value of the astigmatic correction. This is not possible in the case the state of the art systems or only in such a manner that both emission directions are influenced when setting the astigmatism correction, so that the collimation has to be "readjusted".
From the previously mentioned general survey "Specifying Laser Diode Optics" in Laser Focus/Electro-Optics, March 1984, p. 44 ff., it is known to use two anamorphotic prisms to alter the cross-section of the pencil of light. Furthermore, U.S. Pat. No. 3 396 344, also already mentioned, proposes placing two cylindrical lenses in the parallel beam path after the collimator, one cylindrical lens having a short focal length and the other a long focal length. This possible mode of correcting the beam cross-section, however, has not gained wide acceptance.
Instead, in the practical realization thereof, it has been repeatedly attempted to correct the beam cross-section of laser diodes with two anamorphotic prisms. In this connection, reference is made to the laser head of the firm Melles Griot. Laser heads of this type have the drawback that they are comparatively large in construction and weigh a good deal due to the two anamorphotic prisms. Furthermore, it takes very elaborat
REFERENCES:
patent: 3051051 (1962-08-01), Jeffree
patent: 3871748 (1975-03-01), Day
patent: 4555164 (1985-11-01), Feinbloom
patent: 4826269 (1989-05-01), Streifer et al.
Bleicher Jakob
Hetz Siegfried
Hofbauer Engelbert
Matern Ulrich
Schehrer Ingrid
Optische Werke G. Rodenstock
Sugarman Scott J.
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