JPS6093645A - Optical head - Google Patents

Abstract

PURPOSE:To obtain an optical head sufficiently stable to the shift of a movable part of a condenser lens in an unpreferable direction by detecting the positional shift of the 1st condenser lens from the housing of the optical head within a plane parallel to a recording medium by a two-divided optical sensor. CONSTITUTION:Incident light and reflected light separated from the incident light are made incident on a half mirror 11 and divided into two parts. One divided light is made incident to a two-divided optical sensor 14 through a convex lens 12 and a knife edge 13 to detect a focus error. The detected focus error signal is fed back to a focus controlling actuator 15 through a focus control circuit. The movable part 16 is connected to one end of an arm 20 through a pair of supporting springs 19 so as to be moved in a direction almost vertical to a recording medium 9. The other reflected light divided by the half mirror 11 is made incident on a two-divided optical sensor 24 to detect the tracking position error of an optical spot 10 from a tracking guide groove.

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 read information that has already been recorded.

In an optical head that uses a laser beam as a light source and modulates this laser beam with a pulsed signal from an external information source to record binary information on the surface of a recording medium or to read information that has already been recorded, In order to accurately record or reproduce information, focus control controls the position of the condenser lens in the optical axis direction so that the focal point of the condenser lens is always on the surface of the recording medium. A guide formed in advance so that the optical spot of the emitted laser beam on the surface of the recording medium has an optimal width for the optical spot and an optimal depth for the wavelength of the laser beam used on the medium. Tracking position control is performed by driving the condenser lens in a direction perpendicular to the guide groove so that it is accurately positioned with respect to the groove. Furthermore, when accessing the optical spot within a narrow range, a tracking actuator inside the optical head moves a movable part including a condensing lens in a direction perpendicular to the guide groove (tracking driving direction). Access over a wide range is achieved by moving the entire optical head together with the focusing lens using an external actuator. In this access method, the optical head is moved so that the condenser lens is located at the center of the movable range by the tracking actuator in order to suppress the deviation of the optical axis of the optical system when the light spot is following the information track. It is desirable to control the position of
By suppressing the vibration of the condensing lens near the stop position,
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→no-vo method, it is necessary to accurately detect the position of the condenser lens with respect to the optical head. In the conventional servo method, it is impossible to accurately detect the position of the condenser lens relative to the optical head, so a position sensor dedicated to the external actuator is usually used to detect the position of the condensing lens relative to the optical head. The position of the condenser lens is controlled based on the position signal output from the position sensor, while the position of the condenser lens is controlled based on the position signal of the light spot relative to the guide groove ζ. is being carried out. As described above, since the positions of the condenser lens and the optical head are controlled independently, the operation of the internal actuator is not reflected in the operation of the external actuator, making it impossible to track a wide range. When the optical head is moved toward the target track at high speed during track access, vibration of the condensing lens occurs near the stop position, and track following cannot be performed until the vibration stops to the right. The downside was that it only cost you extra time and track access time.

In recent years, in order to eliminate these drawbacks, a beam splitter has been installed that splits a part of the incident light from the semiconductor laser, and one of the lights split by the beam splitter is sent through a condensing lens to a microscopic beam on the surface of the recording medium. While the light is focused on a spot, the other light split by the beam splitter is received by the two-split optical sensor, and the condensing lens and the beam splitter are made to perform the same operation in the tracking driving direction 1, etc., and the two-split optical sensor An optical head has been proposed that can detect a positional shift of a condensing lens with respect to an optical head in the tracking drive direction. For example, the patent application 1987-
18025057-180251.57-187704
and 57-187705 correspond to this.

Although these optical heads can certainly detect positional deviations in the tracking and driving directions of the condensing lens relative to the optics and throat, the beam solutor is located on the movable part, and undesirable vibrations of the movable part may occur. Even a slight angular deviation in direction resulted in a large deviation on the two-split sensor, and the detection characteristics were worse.

The object of the present invention is to eliminate this drawback by fixing the beam splitter on the optical head housing, and preventing the positional deviation of the condensing lens from the optical head housing against undesirable deviation of the movable part. The object of the present invention is to provide an optical head that can perform detection with sufficient stability.

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

FIG. 1 (,) (bl is the optical system according to the present invention) FIG. 1 is a plan view and a front view of a block diagram showing an embodiment of the present invention.

The same laser light emitted from the semiconductor laser 2 passes through a collimating lens 3, enters a beam stabilizer 4, and is split into two. One of the split laser beams is sent to a polarizing beam splitter 5. Mirror 6. 174 wave plate 7. The light is focused into a minute light spot 10 on the recording medium 9 through the first condensing lens 8, and is used for recording or reading information. The reflected light from the recording medium 9 is reflected by a first condenser lens 8.1/4 wavelength plate 7. The light passes through the mirror 6 and enters the polarizing beam splitter 51, where it is separated from the incident optical path. The reflected light thus separated from the incident light enters the half mirror 11, where it is further divided into two. One of the divided lights passes through a convex lens 12. The light passes through the knife lens 13 and enters the two-split optical sensor 14, where a focus error is detected. This focus error detection method is a conventionally well-known technique called the knife method, and the detected focus error signal is fed back to the focus control actuator 15 via a focus control circuit (not shown). is,
1 so that the surface of the recording medium 9 is always at the focal point of the first condensing lens 8, and a movable part 1 including the first condensing lens 8.
6 is driven in the direction indicated by arrow 17. Here, the movable part 16
is connected to one end of an arm 20 via a set of support springs 19 so as to be movable in a direction substantially perpendicular to the recording medium 9, and the arm 20 is further movable in a rotational direction in a plane parallel to the recording medium 9. The other end is connected to the head housing l as shown in FIG.

The other reflected light split by the half mirror 11 is incident on the two-split optical sensor 24, and the light spot 10 is directed to a tracking guide groove provided on the surface of the recording medium 9 (not shown). A tracking position error signal is generated.

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 fed back to the tracking actuator 18 via a tracking control circuit (not shown). Move the movable part 16 so that the light spot 10 is located at the center of the tracking guide groove. Support spring 1
9. The arm 20 is driven in a tracking drive direction perpendicular to the plane of the paper (FIG. 1(b)) with the connection point 21 between the arm 20 and the head housing 1 as the center of rotation.

On the other hand, the other laser beam, which is the incident light from the semiconductor laser 2 and is split by the beam splitter 4, is condensed into a minute spot 25 via the second condensing lens 22, and is focused on the second laser beam installed on the arm 20. In this way, as will be explained in detail after C, the tracking drive direction of the first condensing lens 8 perpendicular to the plane of the paper is
Due to a small change in position, the position of the two-split optical sensor 23 also changes in the same direction, and the amount of light incident on the two optical sensors of the two-split optical sensor 23 changes greatly, and the difference between the two optical sensors is calculated. Thus, the displacement of the first condensing lens 8 in this direction can be obtained. The beam brick 4 is fixed to the head housing 1, and the two-split optical sensor 23 is fixed to the arm 20, so that the positional deviation of the first condensing 1/lens 8 in the tracking direction with respect to the head housing l is prevented. This means that it can be detected. As a result, as described above, when the light spot 10 is following the guide groove, the first condenser lens 8 is always located near the preferable center position of the head housing l so as to suppress the deviation of the optical axis of the optical system. The position of the head housing 1 can be controlled so that it does not shift from the position of the head housing 1, and the position of the first condensing lens 8 can be controlled to prevent it from shifting from the head housing 1.
It is possible to suppress vibration of the first condensing lens 8 at the end of track access.

FIGS. 2(a) and 2(b) are diagrams explaining in detail the function of the two-split optical sensor 23, in which the first condenser lens 8, the two-split optical sensor 23. Connection point 21 between arm 20 and head housing l. It shows the positional relationship of the minute spot 25 of the laser beam.
It is a view seen from a position corresponding to Senryo-zu in the figure.

K 2 In Figure (a), the first condensing lens 8 is attached to the head housing 1.
It shows the case where it is located at the preferred center position of
FIG. 6B shows a case where there is a slight deviation in the tracking direction. Further, the head housing 1 of the first condensing lens 8
The center line corresponding to the preferred center position 1 above is the center line 2
6. If the first condensing lens 8 is located at a preferable center position, a minute spot 25 as shown in FIG.
As soon as the two-split optical sensor 23 is placed on the optical sensor dividing line, the difference between the two optical sensor outputs becomes zero.

As shown in FIG. 2(b)J, if the first condenser lens 8 shifts slightly in the tracking direction, the first condenser lens 8
A two-part sensor 2 mounted on an arm 20 connected to
3 will also move accordingly. Laser light minute spot 25
Since the optical system is fixed to the head housing 1, the positional relationship fixed to the head housing 1 is maintained.
center, occurring on l1126. As a result, the laser beam is 2
Since most of the light is incident on one sensor of the split light sensor 23,
The difference between the outputs of the two photosensors is not zero, but within a certain range, it shows a value that is approximately proportional to the amount of deviation of the first condensing lens 8 from the preferred center position. Conversely, although not shown in the figure, a case in which the first condenser lens 8 is shifted in the opposite direction to that shown in FIG. 2(b) shows a value with a polarity opposite to that described above.

Moreover, since the beam splitter 4 is fixed on the optical head housing 1 and the minute spot 25 also maintains a fixed positional relationship on the optical head housing l, the movable parts are slightly moved in an unfavorable direction as in the conventional example. Optical sensor 23 with split into two
It does not have the disadvantage of causing a large deviation on the two-split sensor 23 due to the deviation of the entire optical path leading to the . In addition, since the laser light incident on the two-split optical sensor 23 is narrowed down to a minute spot by the second condensing lens 22, even if the first condensing lens 8 is slightly shifted, the two-split sensor The amount of light incident on each of the 23 optical sensors changes greatly, and a large conversion gain can be obtained.

As explained above, by using the configuration of the present invention, the positional deviation of the first condensing lens 8 with respect to the head housing 1 can be stably obtained with a high conversion gain, and as described above, the optical spot lo is guided to the guide groove. It can greatly improve tracking characteristics and track access performance.

[Brief explanation of drawings]

FIGS. 1(d) and (b) are block diagrams showing one embodiment of the optical head according to the present invention, and FIGS. 2(,) and (b) show details of the function of the two-split optical sensor 23 of FIG. 1. It is a diagram. In the figure, 1... Head housing, 2... Semiconductor laser, 3... Collimating lens, 4... Beam splitter, 5... Polarizing beam splitter, 6... Mirror, 7... 1 /4 wavelength plate, 8...first condenser lens 9
. . . Recording medium, 10 . . . Light spot, 11 .
... Focus control actuator, 16... Movable part, 1
8... Tracking actuator, 19... Support spring, 20... Arm, 21... Connection point, 22...
- Second condensing lens, 25... Each shows a minute spot. Figure 1

Claims (1)

[Claims] An optical head that records or reads information by condensing laser light emitted from a semiconductor laser onto the surface of a recording medium through a first condenser lens ζ, the first condenser lens and the semiconductor laser an optical head housing that splits a portion of the light incident on the first condenser lens; a beam splitter fixed to the optical head housing; and a second condenser lens that condenses the light split by the beam splitter. a lens movable section including the first condensing lens; a set of lens support springs; and a lens movable section configured to move the lens movable section in a direction substantially perpendicular to the recording medium. an arm that is connected at one end to the lens movable section through the lens movable section and connected to the optical head housing at the other end so as to be movable in a rotational direction in a plane parallel to the recording medium; a two-split optical sensor that receives the laser beam focused by the second condensing lens, and the two-split optical sensor allows the recording of the first condensing lens to the optical head housing. An optical head characterized by detecting positional deviation in a plane parallel to a medium.