JPH02110839A - Optical pickup - Google Patents

Abstract

PURPOSE:To obtain a signal with less crosstalk and high resolution by passing a luminous flux from a light source through an optical system having a square aperture and making incident the resulting flux into a convergence lens so as to converge the light onto a disk as nearly a square spot. CONSTITUTION:A laser beam is a linearly polarized light vibrating in the horizontal direction, passes through a beam splitter 3 as it is and is made incident in a collimater lens 4 with a holder having a square aperture. The laser beam passing through the collimater lens 4 with the holder becomes a square collimated beam and is made incident in a 1/4 wavelength plate 5, in which the linearly polarized light is converted into a circularly polarized light, made incident in a focus lens 6 and the laser beam is converged onto a signal pit on the disk by the focus lens 6. Thus, a signal with less crosstalk and high resolution is obtained.

Description

[Detailed description of the invention] Industrial applications The present invention is applicable to, for example, a compact disc player.

The present invention relates to an optical pickup that optically reads signals from a rotating information recording disk such as a video disk player, and particularly to the configuration of its optical system.

2. Description of the Related Art In recent years, there have been remarkable improvements in reproduction technology for information recording disks (hereinafter referred to as disks). In particular, optical pickups are being improved day by day, and higher performance devices are being sought out.

An example of the conventional optical pickup mentioned above will be described below with reference to the drawings.

FIG. 5 shows the configuration of an optical system of a conventional optical pickup. In FIG. 6, numeral 1 is a semiconductor laser, which serves as a light source for an optical pickup.

2 is a diffraction grating, which serves to slightly separate the passing beam into three beams, one of which is used to reproduce the information signal and two of which are used for tracking. Reference numeral 3 denotes a polarizing beam splitter, which has the property of allowing linearly polarized laser beams vibrating in one direction, for example, in the horizontal direction, to pass through as is, but reflecting linearly polarized laser beams vibrating in the vertical direction. 4 is a collimator lens which functions to make the laser beam a parallel beam. 5 is a wavelength plate which has the function of converting linearly polarized light into circularly polarized light and circularly polarized light into linearly polarized light.

6 is a focus lens that focuses the laser beam onto a spot of about 1 μm. 7 is a cylindrical lens that gives astigmatism to the parallel beam passing through it.

A photodiode 8 is capable of detecting a signal by inputting a laser beam containing an information signal thereto.

Regarding the optical pickup configured as above,
The operation will be explained below.

First, as shown in FIG.
The beam is separated into three beams by the beam splitter 3 shown in FIG.

The laser beam in this case is linearly polarized light that vibrates in the left-right direction, passes through the polarizing beam splitter as it is, and enters the collimator lens 4. By passing through the collimator lens 4, this laser beam becomes a parallel beam and enters the blue wavelength plate 6.

The linearly polarized light is converted into circularly polarized light by the wavelength plate 6, and then enters the focus lens 6, which focuses the laser beam onto a signal bit on the disk. The laser beam reflected from the disk 15, which contains an information signal, is again focused by the focus lens 6, reverses its optical path, and enters the Z wavelength plate 6. The laser beam that has passed through this Z wave plate 6 is converted from circularly polarized light into linearly polarized light that vibrates in the vertical direction, and after passing through the collimator lens 4, it enters the polarizing beam splitter 3, but most of it is reflected right sideways and passes through the cylindrical lens. 7.

The laser beam imparted with astigmatism by this cylindrical lens 7 is incident on a photodiode 8 and detected as a signal. The astigmatism in this case is necessary for the photodiode 8 to perform the convergence state of the focus lens together with the detection of the information signal.

However, in the above configuration, although the laser beam emitted from the semiconductor laser has an elliptical shape, the collimator lens 4 inserted into the lens holder 9 shown in FIG. 6 generally has a circular aperture with a half width or less. The laser beam that has passed through the laser beam has a substantially circular shape, and the spot shape on the disk converged by the focus lens 6 also has a substantially circular shape as shown in FIG. 7 and 11.

Furthermore, it is ideal that the spot on the disk be sufficiently small relative to the size of the bit or the pitch between pits. Specifically, if the spot spreads in the direction of the track, so-called crosstalk, which involves detecting pits on adjacent tracks, becomes a problem, and if the spot spreads in the direction of travel, parts of the front and rear pits are simultaneously detected, resulting in poor resolution. This has become a problem, and attempts have been made to make the spot smaller by increasing the numerical aperture of the focus lens and making the wavelength of the laser beam as short as possible.

Problems to be Solved by the Invention However, there is a limit to the wavelength of the focus lens aperture 1&A laser beam. There is no state.

In view of the above problems, the present invention provides an optical pickup having an optical system that converges an ideal spot that can minimize crosstalk and improve separation performance.

Means for Solving the Problems In order to solve the above problems, the optical pickup of the present invention conventionally used a collimator lens with a circular aperture, but the collimator lens was configured to have a square aperture. It is something.

According to the present invention, an elliptical laser beam emitted from a semiconductor laser passes through a collimator lens having a rectangular aperture to form an approximately four-square parallel beam using the above-described configuration, and is converted into an approximately square-shaped spot by a focus lens. Converged onto disk. Therefore, by aligning the sides of the rectangle in the disk running direction and the track direction, the spot can be made smaller in both directions compared to a circular spot, and a signal with less crosstalk and high resolution can be obtained.

EXAMPLE Hereinafter, an optical pickup according to an example of the present invention will be described with reference to the drawings.

FIG. 1 shows the configuration of a collimator lens of an optical pickup in a first embodiment of the present invention.

In FIG. 1, 4 is the same collimator lens as the conventional one, but the collimator lens holder 12 has a configuration in which a substantially rectangular portion through which the bundle passes is left but light from the peripheral portion is blocked. This collimator lens with lens holder is provided in the portion shown in FIG. 2.

The operation of the optical pickup configured as described above will be explained using FIG. 2. First, semiconductor laser 1
The emitted linearly polarized elliptical laser beam vibrating in the left-right direction is separated into three laser beams by a diffraction grating 2, and the laser beams are incident on a beam tin liter 3. In this case, the laser beam is linearly polarized light that vibrates in the left-right direction, passes through the beam splitter 3 as it is, and enters the collimator lens 4 with a holder having a rectangular aperture in this embodiment.

By passing through the collimator lens 4 with this holder, the laser beam becomes a rectangular parallel beam and enters the wavelength plate 5. The linearly polarized light is converted into circularly polarized light by the wavelength plate 6, and then enters the focus lens 6, which focuses the laser beam onto a signal focus on the disk.

The shape of the spot converged on the disk is approximately rectangular as shown in FIG. 3, and the sides of the rectangle align with the disk running direction and the track direction, so there is little crosstalk and high resolution. The laser beam is reflected as a laser beam containing an information signal, is again focused by the focus lens 6, and returns to the optical path in the opposite direction to enter the leakage wave plate 6. The laser beam that has passed through the leakage wave plate 6 is converted from circularly polarized light into linearly polarized light that vibrates in the vertical direction. After passing through the collimator lens 4, it enters the beam splitter 3, but most of it is reflected right sideways to the cylindrical lens 7. The laser beam is incident on the photodiode 8 and is given astigmatism by the cylindrical lens 7, and is detected as a signal.

As described above, according to this embodiment, the light beam from the light source passes through an optical system with a square aperture, enters the focusing lens, and is converged as a substantially square spot on the disk, thereby reducing crosstalk and improving resolution. You can get a high signal.

A second embodiment of the present invention will be described below with reference to the drawings. FIG. 4 is a perspective view of a collimator lens having a square aperture of an optical pickup showing a second embodiment of the present invention. In the figure, reference numeral 14 is the same collimator lens as used conventionally, but a substantially rectangular portion is left on one end surface of the collimator lens to allow light to pass through, and 14 is designed to block light at the periphery.
As shown in 6, a light flux blocking material is attached. Similar effects can be obtained by using this special collimator lens as in the first embodiment.

Effects of the Invention As described above, the present invention allows the light beam from the light source to pass through an optical system having a square aperture and then enter the converging lens, and converge on the disk as a substantially square spot.
It is possible to obtain signals with low crosstalk and high resolution.

[Brief explanation of drawings]

FIG. 1 is a perspective view of optical system components used in the first embodiment of the present invention, FIG. 2 is a configuration diagram of the first embodiment of the present invention,
FIG. 3 is a schematic diagram showing spots and signal bits on a disk realized in an embodiment of the present invention, FIG. 4 is a perspective view of optical system components used in another embodiment of the present invention, and FIG. A configuration diagram of a conventional optical pickup, Fig. 6 is a perspective view of optical system components used in a conventional optical pickup, and Fig. 7 shows a spot on a disk and a signal bit realized by a conventional optical pickup. FIG. 4... Collimator lens, 9... Collimator lens holder, 11... Spot focused on the disk, 12... Collimator lens holder with square opening, 14...Light flux blocking material. Figure Figure Figure! 5 Figure Figure Figure Procedure Amendment Form) ■Indication of the Case 1982 Patent Application Attachment No. 291054 2 Name of the Invention Person who makes optical pickup amendment Relationship with the case Patent Application
Address: 1006 Kadoma, Kadoma City, Osaka Prefecture
(582) Akio Tanii, Representative of Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] (1) In an optical pickup that optically reads information recorded on a disk, a beam from a light source passes through an aperture with a rectangular opening and then enters a focus lens. An optical pickup characterized by being focused as a spot. (2) The optical pickup according to claim 1, wherein the aperture having a rectangular opening is configured as a collimator lens.