JPH0215435A - Optical pickup - Google Patents

Abstract

PURPOSE:To simplify the driving circuit system and optical system of a device by making the longitudinal direction of a pickup correspond to the track orthogonal direction of an optical disk, and preventing the output light of a laser diode from changing according to a track position. CONSTITUTION:A fixed optical device 13A provided at a pickup device converts the output light of a laser diode 5 having an oval generating pattern into diverged beams to be diverged from the external peripheral part to the internal peripheral part of an optical disk 7. A movable optical device 14 can be moved in the direction of the diverged beams, accesses the track of a disk 1,and condenses the converged beams on the recording surface of the disk 1. When the aperture diameter of an objective lens 12 of the device 14 is set at D1, and the beam diameter of the cross section shape longitudinal direction of the diverged geams to be made incident on the lens 12 is set at D2, the device makes the longitudinal direction correspond to the track orthogonal direction of the disk 1, and the output light of the diode 5 is prevented from changing according to the track position.

Description

[Detailed description of the invention] [Industrial application fields] The present invention relates to an optical pickup.

[Prior Art] An optical pickup is known as a device for writing optical information on and/or reproducing information from an optical disc.

FIG. 3 schematically shows an example of a conventionally known optical disc system.

An optical disc system is broadly divided into an optical disc, a rotating means for the optical disc, and an optical pickup.

In this example, the optical disc 1 is composed of a transparent substrate 2 and a recording film 3 formed on one side thereof, and is rotated at a constant rotation speed by a spindle motor 4 as a rotating means.

The optical pickup is composed of a fixed optical means 13, a movable optical means 14, and a moving mechanism (not shown) that displaces the movable optical means 14 in the direction of arrow 15.

Fixed optical means 13 are fixed with respect to the system and include a laser diode 5, a collimating lens 6, a deflection prism 7, a 114-wave plate 8 and a light receiver 9.

The movable optical means 14 has a mirror 11 and an objective lens 12 .

The laser beam emitted from the laser diode 5 is converted into a parallel beam 10 by a collimating lens 6, transmitted through a deflection prism 7 and a 174-wavelength plate 8, and then reflected by a mirror 11 fixed to a movable optical means 14. The light enters the objective lens 12 and is focused on the recording film 3 of the optical disc 1 by the action of the objective lens 12. Access to a desired track on the optical disc 1 is performed by displacing the movable optical means 14 in the direction of the arrow 15 by a northing mechanism (not shown). In the case of writing optical information, after the above access, the optical disc 1 is moved by the spindle motor 4. While rotating the laser diode, the output light of the laser diode is modulated in accordance with the recorded information to form information pits in the recording film 3 in accordance with the recorded information.

Further, when reproducing information, the reflected light from the optical disc 1 is photoelectrically converted by the light receiver 9 via the deflection prism 7 to obtain a reproduction signal 16. The objective lens 12 is provided with a focus actuator or a tracking actuator to perform focus and tracking servo control.

[Problems to be Solved by the Invention] The optical pickup described above has the following problems. That is, since the optical disk 1 rotates at a constant rotational speed, the linear velocity of the optical disk 1 with respect to the light beam irradiated onto the optical disk 1 gradually increases from the inner circumference side to the outer circumference side of the optical disk 1. Therefore, in order to make the irradiation energy of the light beam on the optical disc 1 uniform regardless of whether it is on the inner or outer circumference, it is necessary to make the light beam irradiation relatively weak on the inner circumference side and strong on the outer circumference side.

On the other hand, since the light beam incident on the movable optical means 14 is a parallel beam 10, the spot diameter and optical power of the beam focused on the recording film 3 do not change depending on the track position on the optical disc 1. Therefore, in order to irradiate light weakly on the inner circumferential side of the optical disk 1 and strongly on the outer circumferential side as described above, it is necessary to change the oscillation output of the laser diode 5 according to the track position on the optical disk l. For this reason, a high output laser diode is required, which increases the cost of the laser diode, and high output operation shortens the life of the laser diode, reducing the reliability of the optical pickup.

The present invention has been made in view of the above-mentioned circumstances, and its purpose is to make the irradiation characteristics of a light beam on an optical disk uniform without changing the oscillation output of a laser diode depending on the position on the optical disk. Our goal is to provide a new optical pickup.

[Means to solve the problem] The present invention will be explained below.

The optical pickup of the present invention is an optical pickup used in a constant rotation speed type optical disk system, and has a fixed optical means and a movable optical means.

The fixed optical means is a means for converting the output light of a laser diode having an elliptical emission pattern into a diverging beam that diverges from the outer circumference toward the inner circumference of the optical disk.

The movable optical means is movable in the direction of the diverging beam, and is a means for accessing the tracks of the optical disc and focusing the divergent beam on the recording surface of the optical disc.

It goes without saying that it has a displacement mechanism for displacing the movable optical means.

When the aperture diameter of the objective lens provided in the movable optical means is D1, and the beam diameter in the longitudinal direction of the cross-sectional shape of the diverging beam incident on this objective lens is 02, D1≠D2 at the outermost circumference of the optical disc, and the above-mentioned The longitudinal direction corresponds to the direction perpendicular to the tracks of the optical disk, and the output light of the laser diode does not change depending on the track position.

[Function] As described above, in the present invention, the light beam emitted from the fixed optical means diverges from the outer circumferential side of the optical disc toward the inner circumferential side. Therefore, the beam diameter D2 in the longitudinal direction of the cross-sectional shape of the diverging beam gradually increases from the outer circumferential side to the inner circumferential side of the optical disc. On the other hand, the aperture diameter DI of the objective lens is constant, and the relationship between DI and 02 is D1≠D2 at the outermost periphery of the optical disc, so as you move toward the inner periphery of the optical disc, D2>DI becomes As it moves towards the inner circumference, the diverging beam becomes smaller due to the aperture diameter of the objective lens.
The vignetting, and the amount of vignetting, increases toward the inner circumference of the optical disc. Therefore, even if the oscillation output of the laser diode is kept constant, the power of the light condensed onto the optical disc becomes smaller inside the optical disc due to the vignetting of the diverging beam.

Therefore, the outer circumferential portion of the optical disk is irradiated with high optical power, and the inner circumferential portion of the optical disk is irradiated with relatively low optical power.

As a result, the non-uniformity of light irradiation due to the difference in linear velocity between the outer and inner peripheries can be automatically corrected without changing the oscillation output of the laser diode depending on the position on the optical disc.

Furthermore, since the longitudinal direction of the beam cross section of one diverging beam corresponds to the direction perpendicular to the track of the optical disk, the transversal direction corresponds to the track direction. If the diameter in the short direction is Do, then Do
<02, therefore, the DO gradually increases from the outer circumference to the inner circumference of the optical disc, but at the outermost circumference the DO increases from 01 to 02.
>Do, the size of DO increases toward the inner circumference of the optical disk and approaches the aperture diameter DI of the objective lens. Therefore, the diameter of the focused spot in the track direction by the objective lens is large at the outer periphery and becomes smaller as it approaches the inner periphery. Further, the diameter of the focused spot in the direction perpendicular to the track hardly changes depending on the track position.

[Example code] Hereinafter, description will be given based on specific examples.

FIG. 1 schematically depicts one embodiment of the invention.

In addition, in order to avoid complexity, the same reference numerals as in FIG. 3 are used for items that are considered to have no risk of confusion.

In FIG. 1, numerals 1, 2, 3.4 indicate an optical disk, a transparent substrate, a recording film, and a spindle motor, as in FIG. Also, as in Fig. 3, numeral 5 is a laser diode, numeral 7 is a deflection prism, and numeral 8 is a 1
74 wavelength plate, 9 is a light receiver, 11 is a mirror, 12 is an objective lens, and 14 is a movable optical means.

Reference numeral 13A is a fixed optical means, which is fixed to the system. This optical means 13A and the optical means 13 of FIG.
The difference is that in the optical means 13A, a lens 20 is arranged to convert the light from the laser diode 5 into a diverging beam 21.

The movable optical means 14 can be moved in the direction of the arrow 15, ie in the direction of the diverging beam 21, by means of a known suitable drive mechanism (not shown).

Referring to FIG. 2, in this FIG.
The dashed lines indicated by 2 and 33 schematically indicate the tracks of the optical disc 1. Track 31 indicates a track located at the inner circumference of the optical disc 1, track 33 indicates a track located at the outer circumference, and track 32 indicates a track located at an intermediate portion between the outer circumference and the inner circumference. Reference numeral DA indicates the aperture of the objective lens, and the diameter of this aperture DA is the aperture diameter D1 described above.

Further, the symbol DL indicates a beam cross section of the diverging beam 21.

Since the laser diode 5 has an elliptical light emitting pattern, the beam cross section DL is also elliptical, and its lengthwise diameter is D2 and its widthwise diameter is DO.

The beam cross section DL changes depending on the position of the diverging beam, but as shown in FIG. 2, it is ot402 at the trunk position at the outermost circumference of the optical disk, and its longitudinal direction corresponds to the direction perpendicular to the track, that is, the radial direction of the optical disk.

In FIG. 2, the symbol DS indicates a condensed light spot focused on the optical disk by the objective lens.

Looking at the diameter S2 of the focused spot DS in the direction perpendicular to the track, it hardly changes at the outer periphery, middle, and inner periphery of the optical disc. It is inversely proportional to the diameter, and as mentioned above, in the direction perpendicular to the track, D1#D at the outermost circumference of the optical disk.
2, and as you move toward the inner circumference of the optical disc, D
This is because I<02, and the spot diameter in the direction perpendicular to the track is ultimately determined by the aperture D1 of the objective lens 12. Therefore, the aperture diameter DI is set so that the diameter of the spot in the direction perpendicular to the tracks becomes an appropriate size according to the track spacing. Next, looking at the diameter SO of the spot DS in the track direction, this means that the diameter DO of the beam cross section OL in the track direction gradually increases from the outermost periphery to the inner periphery.
Since it approaches 1, it gradually becomes smaller from the outer circumference toward the inner circumference. Therefore, the diameter of the focused spot can be sufficiently narrowed down in the track direction at the innermost circumference. It is preferable that the diameter DO of the cross section of the light beam in the lateral direction is set to be ao=p1 at the innermost circumference of the optical disc, as shown in FIG.

In this way, the condensed spot diameter hardly changes in the direction perpendicular to the track, and becomes smaller toward the inner circumference in the track direction, so information pits can be recorded even at the innermost circumference of the optical disk, where the linear density of information is highest. Playback can be performed without any problems.

The optical power of the focused spot decreases toward the inner circumference of the optical disk due to vignetting caused by the aperture of the objective lens, and reaches its minimum at the innermost track, but since the rotational speed of the optical disk is constant, it decreases toward the inner circumference of the optical disk. Since the line speed is slow, information pits are recorded in just the right amount. Also,
For tracks on the outer circumference, the diameter of the focused spot becomes longer in the track direction, but the length of the information pit on the outer track also becomes longer (the length of the information pit on the outermost circumference is longer than that on the information pit on the innermost circumference). (approximately twice the length of There is no shortage of light energy even at the large outer periphery.

[Effects of the Invention] As described above, according to the present invention, a novel optical pickup can be provided.

Since this optical pickup has the above-described configuration, there is no need to change the oscillation output of the laser diode between the outer circumferential side and the inner circumferential side of the optical disk. Therefore, the drive circuit system of the optical pickup can be simplified. In addition, since the efficiency of light use at the outer periphery can be increased, it is now possible to record on low-sensitivity optical discs using low-output laser diodes.
It is economical and improves the reliability of the device. Furthermore, since there is no need to convert the light emission pattern of the laser diode into a circular one, the optical system is simplified. Note that the present invention can of course be applied to magneto-optical disk systems.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing only the essential parts of an embodiment of the present invention, FIG. 2 is a diagram for explaining the present invention based on the above embodiment, and FIG. 3 is a diagram showing the prior art and its related art. FIG. 3 is a diagram for explaining a problem. 181. Optical disc, 500. Laser diode, inner layer 41P1 external use side

Claims (1)

[Claims] An optical pickup used in a constant-rotation speed optical disc system, which directs output light from a laser diode having an elliptical light emission pattern from the outer periphery of the optical disc toward the inner periphery. fixed optical means for converting into a diverging beam that is diverging; and movable optical means movable in the direction of said diverging beam to access tracks of an optical disc and focusing said divergent beam onto a recording surface of the optical disc. If the aperture diameter of the objective lens provided in the movable optical means is D1, and the beam diameter in the longitudinal direction of the cross-sectional shape of the diverging beam incident on this objective lens is D2, then D1 at the outermost circumference of the optical disc. ≈D2, the longitudinal direction corresponds to a direction perpendicular to the track of the optical disk, and the output light of the laser diode does not change depending on the track position.