Dynamic information storage or retrieval – Control of storage or retrieval operation by a control... – Mechanism control by the control signal
Patent
1986-03-12
1988-08-23
McElheny, Jr., Donald
Dynamic information storage or retrieval
Control of storage or retrieval operation by a control...
Mechanism control by the control signal
369112, 369118, 369122, G11B 7125
Patent
active
047665858
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an optical head tracking error detecting apparatus suitable for use with optical recording apparatus, reproducing apparatus and recording and reproducing apparatus.
BACKGROUND ART
A prior art optical head tracking error detecting apparatus will be described with reference to FIG. 3. Reference letter OH generally designates an optical head. Reference numeral 1 designates a semiconductor laser element (laser diode). A diverging laser beam L having a cross section of ellipse-shape and emitted from the side of a laser beam emission end face 1A of the semiconductor laser element is introduced into a collimator lens (not always necessary) 2 in which it is collimated as a parallel beam and then made incident on a diffraction grating (grating) 3. A 0-order beam L.sub.0 and .+-.1st-order beams L.sub.+1 and L.sub.-1 (beams of higher than +2nd-order and lower than -2nd-order will be neglected) are passed through a non-polarizing beam splitter 4 (half mirror) (if a polarizing beam splitter is used, a 1/4 wavelength plate is provided between the same and an objective lens 5) and then introduced into the objective lens 5 in which they are converged. The 0-order beam L.sub.0 and .+-.1st-order beams L.sub.+1 and L.sub. -1 converged are made incident on the recording surface of an optical recording medium (including a photo-magnetic recording medium) 6 with a predetermined spacing (e.g., 10 .mu.m).
The 0-order beam L.sub.0 and .+-.1st-order beams L.sub.+1 and L.sub.-1 reflected on the optical recording medium 6 are passed through the objective lens 5 and then made incident on the beam splitter 4. Parts of them are reflected on a reflection surface 4a of the beam splitter and introduced into a photodetector 7. This photodetector 7 is formed of three photodetecting sections into which the 0-order beam L.sub.0 and the .+-.1st-order beams L.sub.+1 and L.sub.-1 are introduced respectively. When a difference between the photodetection outputs from the pair of photodetecting sections on which the .+-.1st-order beams are respectively made incident is calculated, it is possible to obtain a tracking error signal corresponding to the tracking state of the 0-order beam L.sub.0 on the recording surface of the optical recording medium 6. Further, a reproduced signal, a focussing error signal and the like are obtained from the photodetecting section into which the 0-order beam is introduced.
Next, an example of the semiconductor laser element 1 will be described with reference to FIG. 4. This semiconductor laser element 1 is normally mounted on a heat sink 8 made of copper and the like which serves as one electrode. The structure of the semiconductor laser element 1 will be described in accordance with the sequential order from the upper layer to the lower layer in the drawing. Reference numeral 1a designates an electrode layer, 1b an n-GaAs layer (substrate layer), 1c an n-Ga.sub.1-y Al.sub.y As layer (cladding layer), 1d a Ga.sub.1-x Al.sub.x As layer (active layer), 1e a p-Ga.sub.1-y Al.sub.y As layer (cladding layer) and 1f a p-GaAs layer. The above mentioned laser beam L is emitted from the active layer 1d. If the laser beam emission end face (cleavage face) 1A of this semiconductor laser element 1 is taken as a front face, the semiconductor laser element 1 is selected such that its width is in a range from 100 to 300 .mu.m, the height (thickness) thereof is in a range from 80 to 100 .mu.m and the depth thereof is in a range from 200 to 300 .mu.m. The height of the active layer 1d from the upper surface of the heat sink 8 is several .mu.m.
By the way, if the tangential skew angle of the 0-order beam L.sub.0 relative to the recording surface of the optical recording medium 6 is changed, the tracking error signal is changed cyclically in response thereto so that the accurate tracking error can not be detected.
The present inventors have studied the cause thereof and found out the following fact. The 0-order beam L.sub.0 and the .+-.1st-order beams L.sub.+1 and L.sub.-1 reflected on
REFERENCES:
patent: 4160269 (1979-07-01), Kramer
patent: 4337535 (1982-06-01), Van Megan et al.
patent: 4349901 (1982-09-01), Howe
patent: 4460990 (1984-07-01), Opheij
patent: 4462095 (1984-07-01), Chen
patent: 4507772 (1985-03-01), Yamamoto
Fukumoto Atsushi
Ohsato Kiyoshi
Oka Michio
Eslinger Lewis H.
McElheny Jr. Donald
Sony Corporation
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