JPS61243946A - Optical head - Google Patents

Abstract

PURPOSE:To execute focusing by moving a convex lens which is provided between a collimating means and a condensing means, and changing a diverging or converging state of a luminous flux which is made incident on the condensing means. CONSTITUTION:A luminous flux L from a laser light source 21 is collimated by a collimating means 23, and the collimated luminous flux L is condensed by a condensing means (objective lens) 25 and irradiated to an information storage medium 22. The luminous flux which is emitted from this storage medium 22 is made incident on photodetector through a half mirror prism 24, and the emitted luminous flux is detected. Between the means 23, 25 of this optical head, a luminous flux state variable means 61 having a convex lens 60 is placed. The convex lens 60 of this means 61 is moved in the direction of its optical axis by focusing driving circuit 33 for inputting a signal of a focus shift from a detector 28. In such a way, focusing is executed by changing a diverging or converging state of the luminous flux L which is made incident on the means 25.

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 collimated by 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 supplied to the tracking drive circuit 10 via the signal processing circuit 9, and the tracking drive circuit 10 responds to the tracking drive device 11 in accordance with the signal. 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. The objective lens 4 is moved in the direction of its optical axis by driving the optical drive device 14.

However, by moving the objective lens 4 in its optical axis direction, force tracking 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.

[Purpose of the invention]

The present invention has been made based on the above circumstances, and its object is to perform tracking by a condensing means and to perform force focusing by a convex lens provided between the collimating means and the condensing means. This eliminates the need for a drive device for movement in two directions, which not only simplifies the structure and adjustment, but also eliminates the need to move the focusing means in the direction of its optical axis, reducing focus deviation. An object of the present invention is to provide an optical head in which there is no possibility that a light condensing means will collide with an information storage medium even if the collision occurs.

[Summary of the invention]

In order to achieve the above object, the present invention changes the state of divergence or convergence of the light beam incident on the condensing means by moving a convex lens provided between the collimating means and the condensing means. This feature is characterized in that it performs shinging.

[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 divergent nature of the divergent laser beam generated from the laser beam is slightly weakened by the collimating lens (collimating means) 23. The diverging laser beam that has passed through the collimator lens 23 is guided to the half prism 24 via the convex lens 60. After passing through the half prism 24, the laser beam guided to the half prism 24 is incident on an objective lens (focusing means) 25, and is focused by the objective lens 25 toward the information storage medium 22. Here, the convex lens 60 is supported so as to be movable in the direction of its optical axis, and the objective lens 25 is supported so as to be movable in the direction (radial direction) perpendicular to the optical axis. When the convex lens 60 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 convex lens 60 is kept in a focused state, and the objective lens 25 is kept in a focused track state, making it possible to write and read information. When writing information, bits are formed on the tracking guide on the information storage medium 22 by a laser beam whose intensity is modulated, and when reading information,
A laser beam having a constant light intensity is modulated in light intensity and reflected by a bit formed on the tracking guide.

The diverging laser beam reflected from the information storage medium 22 is returned to the half prism 24 again. The laser beam reflected by the half prism 24 passes through a condensing lens 26 and a cylindrical lens 27 sequentially and is irradiated onto a photodetector 28 equipped with four divided cells 28a to 28d as shown in FIG. . 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-twisting driving circuit 33 drives the force-twisting driving device 34 according to the signal,
The convex lens 60 is moved in the direction of its optical axis. The forcing driving device 34 and the convex lens 60 constitute a beam state changing means 61 that changes the divergence or convergence state of the laser beam incident on the objective lens 25.

Next, a description will be given of the tracking drive means 31 that moves 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, which 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. And coil 40.4
The objective lens 25 can be moved by a predetermined amount in the radial direction by applying a current corresponding to the track deviation to zero.

Next, the force-twisting drive device 3 moves the convex lens 60 in its optical axis direction, that is, in the force-twisting direction.
4 will be explained.

As shown in FIGS. 5 and 6, the convex lens 60 is held by a holding frame 41, which is supported by a pair of support rods 42.
．． It is attached to one end of 42. Also, this support rod 4
The other end of 2.42 is fixed to the middle frame 43. The inner frame 43 is supported by the outer frame 45 via a pair of spiral springs 44, 44, so that the convex lens 60 can be freely displaced in the direction of its optical axis, as shown by the arrow. moreover,
A coil 47 is attached to the inner frame 43 via a ring 46, while a permanent magnet 48' and yokes 49, 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 convex lens 60 can be moved by a predetermined amount in the direction of its optical axis.

Next, the force thudding operation will be explained.

When the convex lens 60 is moved away from the collimating lens 23 as shown in FIG. 7(b) from the state shown in FIG. 7(a), the light enters the objective lens 25.

The laser beam becomes strongly convergent, and the objective lens 2
The laser beam that has passed through the lens 5 is condensed at a position close to the objective lens 25. Moreover, as shown in FIG. 7(C),
When the convex lens 60 is brought close to the collimating lens 23,
The laser beam incident on the objective lens 25 is in a weak convergence state, and the laser beam that has passed through the objective lens 25 is focused at a position away from the objective lens 25. That is,
By moving the convex lens 60 in the direction of its optical axis,
The divergence or convergence state of the laser beam incident on the objective lens 25 is changed, and as a result, 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 convex lens 60 is moved away from the collimating lens 23, and when the information storage medium 22 moves away from the objective lens 25, the convex lens 60 is moved closer to the collimating lens 23, thereby achieving a focused state. can be retained.

According to the above configuration, the convex lens 60 is provided between the collimating lens 23 and the objective lens 25, and the convex lens 60
By moving the lens in the direction of its optical axis to change the divergence or convergence state of the laser beam incident on the objective lens 25, the force tsusing is performed. 60 respectively. therefore,
Since each drive device 31, 34 only needs to move in one direction, its structure and adjustment are simplified. Furthermore, since there is no need to move the objective lens 25 in the direction of its optical axis, there is no risk that the objective lens 25 will collide with the information storage medium 22 even if a focus shift occurs.

〔Effect of the invention〕

As explained above, according to the present invention, an optical head capable of reading at least information from an information storage medium using focused light includes a light source, a collimating means for collimating the light beam emitted from the light source, A condensing means for condensing the luminous flux collimated by the collimating means onto the information storage medium, a photodetector for detecting the luminous flux emitted from the information storage medium, and a divergence of the luminous flux incident on the condensing means. or a luminous flux state variable means for changing a convergence state, and the luminous flux state varying means has a convex lens disposed on an optical path between the collimating means and the condensing means, and is configured to move this convex lens. , tracking can be performed by the condensing means, and force focusing can be performed by a convex lens provided between the collimating means and the condensing means, thereby eliminating the need for a drive device for movement in two directions. This not only simplifies the structure and adjustment, but also eliminates the need to move the light condensing means in the direction of its optical axis, and eliminates the risk of the light condensing means colliding with the information storage medium even if a focus shift occurs. It has excellent effects.

[Brief explanation of drawings]

Figures 1 to 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 ...Force force shinging drive device, 60
. . . Convex lens, 61 . . . Luminous flux state variable means. Applicant's Representative Patent Attorney Takehiko Suzue Figure 1 JU Figure 2 25C750 Figure 3 Figure 4 [lEs Genus Figure 6 Figure 7

Claims (3)

[Claims] (1) A device capable of reading at least information from an information storage medium using focused light, including a light source, collimating means for collimating the light beam emitted from the light source, and collimating the light beam collimated by the collimating means. A light condensing means for condensing light onto the information storage medium, a photodetector for detecting the light flux emitted from the information storage medium, and a light flux state variable means for changing the divergence or convergence state of the light flux incident on the light condensing means. An optical head comprising: a convex lens disposed on an optical path between the collimating means and the condensing means, and the light flux state variable means moving the convex lens. (2) The optical head according to claim 1, wherein the light flux state changing means is configured to move a convex lens in the direction of its optical axis. (3) The optical head according to claim 1, wherein the collimating means is arranged so that the light beam passing through the collimating means becomes diverging light.