JPS61246936A - Optical head - Google Patents

Abstract

PURPOSE:To dispense with a driving device for shifting in two directions and to simplify the structure and adjustment by providing a luminous flux changing device that changes the state of divergence and convergence of luminous flux that passed a collimating device shifting a light source. CONSTITUTION:In focused state, if the state of flux L of laser light that passed a collimating lens 23 is set to parallel luminous flux, flux L of laser light that passed the collimating lens 23 becomes the state of convergence when a semiconductor laser 21 is put away from the collimating lens 23, and flux L of laser light that passed an objective 25 is converged at a position near the objective 25. When the semiconductor laser 21 is brought near the collimating lens 23 becomes the state of divergence, and flux L of laser light that passed the objective 25 is converged at a position off from the objective 25. That is, by making tracking with a converging device and making focusing with the light source, a driving device for shifting in two directions becomes unnecessary, and the structure and adjustment become simple.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an optical head used in, for example, an optical disk device.

[Technical background of the invention and its problems]

Conventionally, the optical heads of the above type are shown in FIGS. 8 and 9.
There is one configured as shown in the figure. In other words, 1 in the figure
is a semiconductor laser (light source), and the laser beam emitted from this semiconductor laser 1 is passed through a collimating lens 2.
and the objective lens 4 after passing through the half prism 3 in sequence.
is focused onto the information storage medium 5 by. Further, the laser beam reflected from the information storage medium 5 passes through the objective lens 4 again and is returned to the half prism 3.

The laser beam reflected by the half prism 3 passes through a condenser lens 6 and a cylindrical lens 7 in order and is irradiated onto a photodetector 8 having four divided cells 8a to 8b. As a result, information signal detection, track deviation detection, and defocus detection are performed.

Further, the track deviation detection signal detected by the photodetector 8 is sent to the tracking drive circuit 1 via the signal processing circuit 9.
According to the signal, the tracking drive circuit 10 drives the tracking drive device 11 to move the objective lens 4 in its radial direction. Further, the focus shift detection signal detected by the photodetector 8 is supplied to the force-twisting drive circuit 13 via the signal processing circuit 12, and the force-twisting drive circuit 13 performs the force-twisting according to the signal. A driving device 14 is driven to move the objective lens 4 in the direction of its forward axis.

However, by moving the objective lens 4 in its forward axial direction, force focusing is performed, and by moving it in its radial direction, tracking is performed.

Therefore, the objective lens 4 can be
A driving device is required to move the device in each direction independently, and its structure and adjustment are difficult.

Also, when force tucking is performed using objective lens 4,
Due to dust, scratches, external vibrations, etc. on the information storage medium 5, the force pushing operation cannot be performed, and there is a risk that the objective lens 4 will move instantaneously and collide with the information storage medium 5.

[Object of the Invention] The present invention has been made based on the above-mentioned circumstances, and its purpose is to enable tracking to be performed by a light condensing means and to perform force focusing by a light source, thereby achieving two This eliminates the need for a driving device to move the light in this direction, which simplifies its structure and adjustment. It also eliminates the need to move the light focusing means in the direction of its tip axis, and the light focusing means can be moved even if the focus shifts. An object of the present invention is to provide an optical head that is free from the possibility of colliding with an information storage medium.

[Summary of the invention]

In order to achieve the above object, the present invention is characterized in that the light source is moved to change the state of divergence or convergence of the light beam that has passed through the collimating means, thereby performing force tucking.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 1 to 7.

Reference numeral 21 in FIG. 1 is a semiconductor laser (light source), and this semiconductor laser 21 generates a divergent laser beam beam. In this case, when writing information to the information storage medium 22, a beam of laser light whose light intensity is modulated according to the information to be written is generated, and when reading information from the information storage medium 22, a beam of light with a constant light intensity is generated. A laser beam is generated having a . And the semiconductor laser 21
The diverging laser beam generated by the laser beam is converted into a parallel beam by a collimating lens (collimating means) 23 and guided to a half prism 24 .

The laser beam guided to this half prism 24 is
After passing through the half prism 24, the light enters an objective lens (condensing means) 25, and is focused by the objective lens 25 toward the information storage medium 22. Here, the semiconductor laser 21 is supported movably in the optical axis direction,
Further, the objective lens 25 is supported so as to be movable in a direction (radial direction) perpendicular to its optical axis. When the semiconductor laser 21 and the objective lens 25 are respectively positioned at predetermined positions, the beam waist of the focused laser beam emitted from the objective lens 25 is guided to a predetermined tracking guide (not shown) on the information storage medium 22. ) and a minimum beam spot is formed on the tracking guide. In this state, the semiconductor laser 21 is kept in a focused state, and the objective lens 25 is kept in a focused track state, so that writing and reading of information becomes possible.

When writing information, pits are formed on the tracking guide on the information storage medium 22 by a laser beam whose light intensity is modulated, and when reading information, a laser beam having a constant light intensity is used to form pits on the tracking guide on the information storage medium 22. The light intensity is modulated and reflected by pits formed in the tracking guide.

The diverging laser beam reflected from the information storage medium 22 passes through the objective lens 2 when the semiconductor laser 21 is in focus.
5, it is converted into a parallel beam by half prism 2.
Returned to 4. The laser beam reflected by the half prism 24 passes through a condensing lens 26 and a cylindrical lens 27 in order to form a four-part cell 28a as shown in FIG.
~28d onto a photodetector 28. As a result, information signal detection, track deviation detection, and defocus detection are performed.

Further, the track deviation detection signal detected by the photodetector 28 is supplied to the tracking drive circuit 30 via the signal processing circuit 29, and the tracking drive circuit 30 drives the tracking drive device 31 according to the signal. Then, the objective lens 25 is moved in its radial direction. Further, the focus shift detection signal detected by the photodetector 28 is sent to a force shifting drive circuit 33 via a signal processing circuit 32.
and the force shinging drive circuit 33 drives the force shinging drive device 34 according to the signal,
The semiconductor laser 21 is moved in the optical axis direction.

Next, a description will be given of the dragging drive means 31 for moving the objective lens 25 in its radial direction, that is, in the tracking direction.

As shown in FIGS. 3 and 4, the objective lens 25 is held by a holding frame 35, and this holding frame 35 is attached to the other ends of a pair of parallel plate springs 36, 36, one end of which is fixed. Therefore, the objective lens 25 is movable in its radial direction, that is, in the tracking direction, as shown by the arrow. Further, the holding frame 35 is provided with a movable magnetic body 37, and a pair of yokes 38, 38 and a pair of yokes 38 and 38 that surround the movable magnetic body 37 and cooperate with the movable magnetic body 37 are provided in the vicinity of the movable magnetic body 37. A permanent magnet 39° 39 is fixedly arranged. Further, a coil 40.40 is wound around the yoke 38.38.

The objective lens 25 can be moved by a predetermined amount in the radial direction by passing a current corresponding to the track deviation through the coils 40 and 40.

Next, the force-twisting drive device (luminous flux state converting means) 34 for moving the semiconductor laser 21 in the optical axis direction, that is, the force-twisting direction, will be explained.

As shown in FIGS. 5 and 6, the semiconductor laser 21
is held by a holding frame 41, which is attached to one end of a pair of support rods 42,42. Further, the other ends of the support rods 42, 42 are fixed to the middle frame 43. This middle frame 43 is supported by an outer frame 45 via a pair of spiral springs 44, 44, so that the semiconductor laser 21 can be freely displaced in the optical axis direction as shown by the arrow. Further, a coil 47 is attached to the inner frame 43 via a ring 46, while a permanent magnet 48 and a yoke 49.degree. 49, which cooperate with the coil 47, are attached to the outer frame 45. By passing a current corresponding to the focus shift through the coil 47, the semiconductor laser 21 can be moved by a predetermined amount in the optical axis direction.

Next, the force thudding operation will be explained.

For example, as shown in Figure 7 (a), if the state of the laser beam that has passed through the collimating lens 23 is set to be a parallel beam in the focused state, the semiconductor When the laser 21 is moved away from the collimating lens 22, the laser beam passing through the collimating lens 23 is converged, and the laser beam passing through the objective lens 25 is focused at a position close to the objective lens 25.

Further, as shown in FIG. 7(C), the semiconductor laser 21
When brought close to the collimating lens 23, the laser beam passing through the collimating lens 23 becomes divergent,
The laser beam passing through the objective lens 25 is focused at a position away from the objective lens 25. That is, by moving the semiconductor laser 21 in the optical axis direction, the position where the laser beam is focused by the objective lens 25 moves back and forth in the optical axis direction. Therefore, when the information storage medium 22 approaches the objective lens 25, the semiconductor laser 21 is moved away from the collimating lens 23, and when the information storage medium 22 moves away from the objective lens 25, the semiconductor laser 21 moves away from the collimator lens 23.
By bringing the lens close to the collimating lens 23, the focused state can be maintained.

According to the above configuration, the laser beam 21 is moved in the optical axis direction to change the state of divergence or convergence of the laser beam that has passed through the collimating lens 23, thereby performing force shifting. At 25, the force is applied to semiconductor laser 2.
1 can be performed respectively. Therefore, each drive device 31, 34 only needs to move in one direction, which simplifies its construction and adjustment.

Furthermore, since there is no need to move the objective lens 25 in the direction of its optical axis, even if a focus shift occurs, the objective lens 25
There is no risk of collision with the information storage medium 22. Note that there is a risk that the semiconductor laser 21 will collide with the collimating lens 23, but if a stopper is provided in front of the fixed collimating lens 23, this collision can be prevented.

[Effects of the Invention] As described above, according to the present invention, it is possible to read at least information from an information storage medium using focused light, and a light source and a collimating means for collimating the light beam emitted from the light source are provided. and an optical head comprising a condensing means for condensing the luminous flux collimated by the collimated means on the information storage medium, and a photodetector for detecting the luminous flux emitted from the information storage medium, Since the light flux state variable means is provided to change the divergence or convergence state of the light flux passing through the collimating means by moving the light source, tracking can be performed by the focusing means and force focusing can be performed by the light source, respectively. Therefore, 2
This eliminates the need for a driving device to move the light in the direction, which not only simplifies its structure and adjustment, but also eliminates the need to move the light focusing means in the direction of its optical axis, so even if a focus shift occurs, the light focusing means can be moved. This provides excellent effects such as no risk of collision with the information storage medium.

[Brief explanation of the drawing]

Section 1 to FIG. 7 show one embodiment of the present invention.
The figure is a schematic configuration diagram of the optical head, Figure 2 is a front view of the photodetector, Figure 3 is a plan view of the tracking drive, and Figure 4 is a sectional view of the tracking drive. , FIG. 5 is a partially sectional plan view of the drive device for force tweezing, FIG. 6 is a sectional view similarly showing the drive device for force tweezing, FIG. 7 is an explanatory diagram of the force tweezing operation, and FIG. 8 and 9 show a conventional example. FIG. 8 is a schematic configuration diagram of an optical head, and FIG. 9 is a front view of a photodetector. 21... Light source (semiconductor laser), 22... Information storage medium, 23... Collimating means (collimating lens), 25... Focusing means (objective lens), 28... Photodetector, 34 ... Luminous flux state variable means (driving device for force shifting). Applicant's agent Patent attorney Takehiko Suzue Figure 1 6c 28d Figure 3 Figure 4 Figure 5 Figure 6

Claims (2)

[Claims] (1) It is possible to read at least information from an information storage medium using focused light; a light source; a collimating means for collimating the light beam emitted from the light source; In a device comprising a light condensing means for condensing light onto a storage medium and a photodetector for detecting a light flux emitted from the information storage medium, the light flux passing through the collimating means is diverged by moving the light source. An optical head characterized in that it is provided with a beam state variable means for changing the convergence state. (2) The optical head according to claim 1, wherein the light flux state changing means is configured to move the light source in the optical axis direction.