Deutsche Thomson-brandt Gmbh

Thomson Multimedia S.a.

Akira Kawamura

Yoshiharu Chikazawa

Yasuaki Morimoto

Friedhelm Zucker

Christian Buchler

Nakao Akutsu

A multi beam track system and method is used for the retrieving of information stored in optical memories like optical disks. The information carrying beams reflected on the surface of such a optical disk results in spots on the surface of a detector array. Because these beams are very close to each other, the resulting spots tend to overlap so that cross talk conditions between neighboring channels occur. As result the S/N ratio becomes worse. According to the present invention a plurality of laser beams arranged in a row is used, where the laser beams are linear polarized and the polarization of neighboring beams differ by 90.o slashed., i.e. neighboring laser beams have perpendicular linear polarization. After reflection on the surface of the optical disk the row of reflected laser beams is separated into two rows by an separating means which is polarization dependent so that beams are separated in space according to the polarization. Such a separator can be a polarizing beamsplitter or a birefringent prism crystal. As a result two spacially separated rows of laser beams are achieved, which can be detected by two separate detectors. As result no overlap between neighboring spots occurs on the surface of the detectors, resulting in the elimination of crosstalk.

Multi beam track system and method for an optical memory

ROM-RAM Disk

In laser feedback systems of an optical memory the most suitable feedback gain value depends on the type of optical disks used. According to the invention a system and a method is provided which finds by way of an iteration a suitable maximum feedback gain value so that the feedback system does not oscillate. The method consists in starting with a low gain value for driving a laser diode, increasing the gain value by small amounts until an oscillation detecting unit detects that the laser feedback system is oscillating. Then the gain value is reset to the previous value or a little bit more. Then the laser feedback system is again in a non-oscillating area with a suitable maximum gain value. This iteration is performed by a system consisting mainly of a laser diode, a photodiode for detecting the reflected light, and an oscillation detecting unit which controls a gain controller. This gain controller sets the gain on a multiplier which drives the laser driver for the laser diode.

Laser intensity gain control for detecting oscillation in the feedback

A magneto optical disc system includes a disc having permanently recorded tracks overlain with magneto optical recording material. Data is recorded in the magneto optical material in tracks superimposed over the permanently recorded tracks, using the read-only data to define magneto optical tracks. The magneto optically recorded data is correlated with the prerecorded data for defining the location of data stored in the magneto-optic tracks.

Recording and reproduction of items of information using ROM-RAM storage

A system for reducing noise in a data recording/play-back device includes an optical system for scanning a recording medium and providing first and second polarization signals. The polarization signals are added to provide an added signal. The added signal is differentiated to provide a noise reduction signal. The polarization signals are substracted to provide a difference signal. The differentiated signal is substracted from the difference signal to provide a data signal having a substantially reduced noise level.

Growing community of inventors

Hachiouji, Japan

Akira Kawamura