JPS6310491B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical head that uses optical means to record information on a recording medium or to read information that has already been recorded.

A laser beam is used as a light source, and this laser beam is modulated with a pulsed signal from an external information source to record binary information on a recording medium on a disk surface, or
In an optical head that reads information that has already been recorded, in order to accurately record or reproduce information, focus control is used to condense light so that the surface of the recording medium is always at the focal point of the condenser lens. The position of the lens in the optical axis direction is controlled, and the tracking position control for the information track of the optical spot is usually performed by setting the optimal width for the optical spot on the recording medium and the optimal depth for the wavelength of the laser beam used. This is accomplished by providing a guide groove and driving the condenser lens in the radial direction of the disk so that the light spot follows the guide groove. Furthermore, in the track access of the optical spot, normally, within a narrow range, only the condensing lens is moved in the disk radial direction by a tracking actuator inside the optical head; This is accomplished by moving the entire optical head by means of an external actuator. In such a two-stage servo system, when the optical spot is following the information track, the condensing lens is placed at the center of the optical head, in order to suppress the adverse effects such as tracking offset signals caused by optical axis deviation. In other words, it is desirable to control the position of the optical head so that the optical axis always coincides with the center axis of the condenser lens.Furthermore, when accessing a wide range of tracks, it is desirable to control the vibration of the condenser lens near the stop position. In order to suppress the damage, it is desirable to move the optical head with the condenser lens fixed at a fixed position within the optical head. However, in order to achieve such a two-stage servo system, it is necessary to accurately detect the position of the condensing lens relative to the optical head. Since it is impossible to accurately detect the position of Position control is performed, and the position of the condenser lens is controlled based on the position signal of the light spot relative to the guide groove. In this way, the condenser lens and optical head are
Because each position is controlled independently, the movement of the internal actuator is not reflected in the movement of the external actuator, and when only the condensing lens is moved, tracking position errors and focus errors due to deviation of the reflected optical axis can be detected. If the optical head is moved toward the target track at high speed during track access, the condensing lens will vibrate near the stop position, and the condensing lens will vibrate until the vibration subsides. This method has the drawback that track following operation cannot be performed, and the track access time is increased by the waiting time. As explained above, it has been impossible to improve the performance of optical information recording and reproducing devices using conventional optical heads.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a new optical head capable of generating accurate position signals of the condenser lens relative to the optical head, in order to eliminate the above-mentioned drawbacks.

Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a block diagram showing one embodiment of an optical head according to the present invention. The laser beam emitted from the semiconductor laser 2 passes through a collimating lens 3, a polarizing beam splitter 5, a quarter-wave plate 6, and a condensing lens 7, and is focused on a light spot 16 on the recording medium surface of a disk 17. The information is recorded or read out. On the other hand, the reflected light from the recording medium passes through the condensing lens 7 and the 1/4 wavelength plate 6,
The light is separated from the incident light at the reflecting surface 8 of the polarizing beam splitter 5 and enters the half mirror 9 . The half mirror 9 divides the incident light into two parts, one of which passes through a convex lens 10 and a knife edge 11 and enters a two-split optical sensor 19, where a focus error is detected. This focus error detection method is a well-known technique known as the knife edge method, and the detected focus error signal is fed back to the focus control actuator 13 via a focus control circuit (not shown). The condenser lens 7 in the tracking movable part 4 is moved so that the recording medium surface of the disk 17 is always the focal point of the condenser lens 7.
drive in the direction shown by arrow 15.

The other reflected light split by the half mirror 9 is incident on a two-split optical sensor 20, and the tracking position of the light spot 16 is determined with respect to a tracking guide groove provided on the surface of the disk 17 (not shown). Error detection is performed. This tracking position error detection method is a conventionally well-known method as a push-pull method, and the detected tracking position error signal is sent to the tracking actuator 12 via a tracking control circuit (not shown). The tracking movable part 4 is driven in the direction shown by the arrow 14 so that the light spot 16 is returned to the center of the tracking guide groove. Since the polarizing beam splitter 5, the quarter-wave plate 6, and the condenser lens 7 are fixed on the tracking movable part in the direction shown by the arrow 14, when the tracking movable part 4 is moved in the direction shown by the arrow 14, The polarizing beam splitter 5, the quarter-wave plate 6 and the condenser lens 7 also move in the same direction so that the light spot 16 can be moved in the direction indicated by the arrow 14. At this time, the light from the semiconductor laser 2 that is incident on the polarization beam splitter 5 is not completely linearly polarized;
Since the degree of separation of the polarizing beam splitter 5 is not ideal, the reflected light 8 is slightly reflected in the direction shown by the arrow 21. This reflected light is incident on the two-split optical sensor 18, and by calculating the difference between the outputs of the two optical sensors, the tracking movable part, that is, the arrow of the condensing lens 7, relative to the optical head 1 is calculated, as will be explained in detail later. The position in the direction indicated by 14 can be detected. By detecting the position of the condensing lens 7 with respect to the optical head 1 in this way, the central axis of the condensing lens 7 and the incident optical axis can always be aligned, as described above, and the track access At times, the condenser lens 7 can be fixed at a fixed position within the optical head 1, and vibration of the condenser lens 7 at the end of track access can be suppressed.

Figures 2a and b show the tracking movable part 4 in Figure 1.
FIG. 2 is an enlarged view for explaining position detection of the condenser lens 7 in the tracking direction with respect to the optical head 1 in an easy-to-understand manner. FIG. 2a shows a case where the condenser lens 7 is aligned with the center of the optical head 1, that is, the central axis of the condenser lens 7 coincides with the incident optical axis 30, and FIG. 2b shows the tracking movable part. 4 is deviated from the optical head 1 in the direction shown by the arrow 31, that is, the central axis of the condenser lens 7 is deviated from the incident optical axis 30 in the direction shown by the arrow 31. .

In the figure a, incident light 30 passes through a polarizing beam splitter 5, a quarter-wave plate, and a condensing lens 7, and is condensed onto a spot 16 on the recording surface of the disk 17, and the reflected light there is condensed. Optical lens 7, 1/4
The light passes through the wavelength plate 6 and is reflected in the direction indicated by the arrow 32 at the reflective surface 8 of the polarizing beam splitter 5, and is subjected to focus error detection, tracking position error detection, and information signal detection. At this time, as described above, the incident light 30 is slightly reflected in the direction shown by the arrow 33 by the reflected light 8 of the polarizing beam splitter 5, and enters the two-split optical sensor 18. Since the incident optical axis and the central axis of the condensing lens coincide, the optical axis of the incident light to the two-split optical sensor 18 is located on the dividing line of the two-split optical sensor 18, so that the two optical sensors The amount of light received becomes equal, and the difference between the two optical sensors becomes zero. In other words, the position error signal indicates that there is no position error.

On the other hand, as shown in Figure b, when the incident optical axis 30 and the central axis of the condensing lens 7 are deviated in the direction shown by the arrow 31, the light reflected by the reflective surface 8 of the incident light 30 is 2 Since a large amount of light is incident on one of the optical sensors of the split optical sensor 18, the difference between the two optical sensors is not zero, but shows a value proportional to the amount of deviation of the condenser lens 7 from the optical axis 30. Conversely, although not shown in the figure, if the condenser lens 7 is shifted in the opposite direction to the direction indicated by the arrow 31, it will exhibit a value of polarity opposite to the polarity described above.

As explained above, by simultaneously moving the condensing lens 7 and the polarizing beam splitter 5 in the tracking direction and receiving the reflected light of the incident light from the polarizing beam splitter with the two-split optical sensor, the optical head of the condensing lens is The position in the tracking direction can be detected accurately.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the optical head according to the present invention, and FIGS. 2a and 2b are enlarged views of the tracking movable part in FIG. It is a diagram for easy-to-understand explanation. In the figure, 1... optical head, 2... semiconductor laser, 3... collimating lens, 4... tracking movable part, 5... polarizing beam splitter,
6...1/4 wavelength plate, 7...Condensing lens, 8...Reflecting surface, 9...Half mirror, 10...Convex lens,
DESCRIPTION OF SYMBOLS 11... Knife edge, 12... Tracking actuator, 13... Focus control actuator, 16... Light spot, 17... Disk, 1
8, 19, 20 . . . indicate two-split optical sensors, respectively.

Claims (1)

[Claims] 1. In an optical head that records or reads information by condensing light emitted from a semiconductor laser onto the recording medium surface using a condensing lens, the incident light from the semiconductor laser and the recording medium surface are combined. a polarizing beam splitter that separates the reflected light from the reflected light; a condensing lens that focuses the incident light from the semiconductor laser passing through the polarizing beam splitter onto a minute spot on the surface of the recording medium; The polarization angle of the incident light and the reflected light from the recording medium surface is rotated by 90 degrees, and a 1/4 wavelength plate located between the polarizing beam splitter and the condenser lens and the semiconductor laser and a two-split optical sensor that detects reflected light from the polarizing beam splitter of the incident light, and the polarizing beam splitter, the quarter-wave plate, and the condensing lens perform the same operation in the disk radial direction. An optical head characterized in that the position of the condenser lens in the disk radial direction with respect to the optical head is detected by the two-split optical sensor.