Abstract:
A device for reading from or writing to optical recording media having an optical assembly and a laser diode coupled thereto is described. The laser diode is a twin laser diode which is coupled to the optical assembly by means of a translationally displaceable rotary joint.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a device for reading from or writing to optical recording media having an optical assembly and a laser diode coupled thereto. 
   BACKGROUND OF THE INVENTION 
   It is a current desire in industry to further develop devices of such type. 
   SUMMARY OF THE INVENTION 
   It is provided according to the invention that the laser diode is a twin laser diode which is coupled to the optical assembly by means of a translationally displaceable rotary joint. This has the advantage that it is possible for the twin laser diode to be adjusted easily relative to the ideal beam path of the optical assembly, since both translation and rotation are possible. These are the two essential degrees of freedom in terms of which a twin laser diode is to be adjusted. Depending on the nature and requirement of the optical assembly, the adjustment is performed in a fashion optimized for one of the two beams of the twin laser diode. A compromise solution virtually adapted to both beams is also advantageously possible here. A twin laser diode is regarded as a laser diode or a general light source which is capable of emitting light of different wavelengths, each wavelength respectively being assigned different emission points spaced apart from one another. Twin laser diodes generate two wavelengths, but a larger number of different wavelengths is also within the scope of the invention. The known optical recording media of CD, DVD, or else other optical recording media, come into consideration as optical recording media. The optical assembly has the purpose of optical scanning of the optical recording medium, and detecting the information obtained from the optical recording medium. The laser diode serves for generating a light beam for scanning the optical recording medium by means of the optical assembly. It is coupled to the latter in order to feed a light beam generated by it into the optical assembly with the correctly adjusted orientation. 
   It is provided according to the invention that the translationally displaceable rotary element is a slide which is prestressed by a spring and can be displaced counter to the prestressing by means of a setting element, and is connected in rotary fashion to a holder for the laser diode. This has the advantage that only the slide need be displaced, and not the holder for the laser diode, while only a rotary setting is to be undertaken with the holder. Separate setting of these functions simplifies the setting and reduces possible erroneous settings. It is possible to dispense with special setting apparatuses, and this is particularly advantageous whenever only a small installation space is available which impedes the action of an external setting apparatus or renders it impossible. The holder for the laser diodes has generally relatively large dimensions, in order to offer a secure support for the laser diode and to dissipate corresponding waste heat effectively. The spring is advantageously a pressure spring which acts on one end of the slide, while the setting element is a pressure element which acts on the opposite end of the slide. However, it is also advantageously possible to have a single-ended arrangement of spring and setting element. In this case, tension spring and pressure element, or pressure spring and action element are combined. 
   The setting element is advantageously an eccentric. This has the advantage that it is possible thereby with particular ease to undertake translational settings. The eccentric is advantageously arranged at the opposite end of a pressure spring. 
   It is provided according to the invention that the mutually adjusted elements of laser diode, rotary joint and optical assembly are bonded together. This is a particularly simple and reliable measure for fixing the relative position of these elements after successful adjustment, and for preventing any displacements of the elements relative to one another that are possible owing to ageing or temperature. 
   Advantageous refinements of the invention are likewise to be gathered from the following description of an exemplary embodiment. It is self-evident that the invention is not limited to the combinations specified. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a device according to the invention in a schematic illustration, 
       FIG. 2  shows a rotary joint of a device according to the invention, 
       FIG. 3  shows a part of a device according to the invention, and 
       FIG. 4  shows a part of a device according to the invention with a laser diode. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1  shows a schematic illustration of the beam path in a device according to the invention. A laser diode, here a twin laser diode  1 , generates a linearly polarized scanning beam  2  which passes a beam splitter  3 , is deflected by a mirror  4 , passes a collimator  5  and a λ/4 plate  8 , and is focused by an objective lens  6  onto an optical recording medium (not illustrated here). From there, the scanning beam  2  is reflected and cast onto a detector element  7  by the polarizing beam splitter  3 . The twin laser diode  1  is capable of outputting scanning beams of different wavelength which are suitable for scanning different optical recording media such as CD and DVD. In this case, the emission points of the two scanning beams are displaced slightly from one another. The displacement is in this case of the order of magnitude of 100 μm, the figure being 110 μm in the exemplary embodiment. Provided for the purpose of adjusting the laser diode  1  with reference to the beam path of the optical assembly  9  consisting of the elements  3  to  8  is a displaceable rotary joint  10 . This is illustrated diagrammatically here, arrows indicate the translational and rotary mobility. 
     FIG. 2  shows details of the rotary joint  10  of a device according to the invention. A slide  11  is visible which is translationally displaceable in the direction of the double arrow  12 . At the right-hand end in the figure, the slide  11  is prestressed to the left by means of a pressure spring  13 . At the right-hand end in the figure, the slide  11  is supported by means of an eccentric  14 . Rotating the eccentric  14  causes the slide  11  to be displaced, in cooperation with the pressure spring  13 , to the left and right, respectively, in the direction of the arrow  12 . The eccentric  14  serves in this case as setting element. The slide  11  is provided on its top side with a pin  15  which is arranged in a cutout  16  of a holder  17 . The holder  17  and slide  11  are therefore connected to one another such that they can rotate about the axis of the pin  15 . The holder  17  is connected to a stop element  18 , advantageously being designed in one piece therewith, which stop element has a curved surface  19  whose cylinder axis coincides approximately with that of the pin  15 . The holder  17  is provided with stop surfaces  20 ,  20 ′ on which the laser diode  1  (that is not illustrated here) comes to bear and is thus aligned. 
     FIG. 3  shows a part of a device according to the invention in which the rotary joint  10  is arranged. The holder  17 , the slide  11  projecting below it, the eccentric  14  and the pressure spring  13  are to be seen. Also to be seen is that the holder  17  bears against a front stop  21  along which the translational movement caused by the eccentric  14  and pressure spring  13  takes place in the direction of the arrow  12 . During the rotary movement about the axis of the pin  15 , the curved surface  19  of the stop element  18  slides along an oppositely curved surface  22  of the optical assembly  9 . After both the translational and the rotary adjustment have been undertaken in an adjusting operation, the respective elements are connected to one another by means of an adhesive. This is performed, for example, by inserting the adhesive between the surfaces  19  and  22  as well as on the eccentric  14 , slide  11 , stop  21 , holder  17  and spring  13 . 
     FIG. 4  shows the same part of a device according to the invention as  FIG. 3 , but here with a laser diode  1 . Indicated diagrammatically here are the different emission points  23 ,  23 ′ for the different laser beams generated by the twin laser diode  1 . All other elements correspond to those described in relation to  FIG. 3 . 
   In the case of twin laser diodes  1 , the emission point of the diode for CD beam or DVD beam, which do not lie at one point, must be adjusted rotationally and also translationally in accordance with the optical design (CD or DVD priority). In order to avoid the need for the complete holder  17  of the laser diode  1  to be adjusted both rotationally and translationally, only the point of rotation of the laser holder is designed to be translationally displaceable. The rotary joint, for example fixed pin  15  and bore, of the laser holder is mounted on a slide  11 . This avoids the need for the complete holder  17  of the laser  1  to be displaced in the restricted installation space of the optical scanning unit (pick-up). If the slide  11  is pressed by means of a force, for example by a spring, against a stop which can be set, for example eccentric disc, it is possible to dispense with a special setting apparatus for the translational movement. Application is expedient whenever an adjustment with the aid of a translationally displaceable rotary joint is required in a small installation space and it is impossible to use setting apparatuses because of the need for space.