JPS6257135A - Pickup device in optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To prevent the generation of a crosstalk caused by an influence of an adjacent track, by providing a light absorbing film on one refracting surface of an objective lens, and forming this light absorbing film so that its thickness becomes thinner in the center part containing an optical axis. CONSTITUTION:A light absorbing film 23 is provided on one refracting surface of an objective lens 21 for focusing an irradiating light emitted from a light emitting element 1, to a recording surface of a disk 13. Thickness of this film 23 is thin in the center part containing an optical axis. By providing such a film 23, a light quantity distribution of a spot light focused to the recording surface of the disk 13 goes to a Gaussian distribution. Accordingly, this light quantity distribution has no side lobe, and when reading an information signal by making this spot light follow up and information recording track, a crosstalk by an influence of an adjacent track is scarcely generated.

Description

DETAILED DESCRIPTION OF THE INVENTION [11L] The present invention relates to a pickup device in an optical information recording/reproducing device.

Information recording media such as video discs and digital audio discs record information signals by forming minute bits (indentations) on their surfaces in the form of spiral tracks. It is. Conventionally, when reading information signals recorded in this way, what do you do? A pickup device whose main part is shown in FIG. 9 is used.

? As shown in FIG. 1, a light emitting element 1, a collimator lens 2, a beam splitter 3, and an objective lens 4 are coaxially arranged in parallel. The objective lens 4 is made up of a combination of three lenses 6, 7 and 8, and is held by a cylindrical holder 9. A convex lens 10 is disposed on the side of the beam splitter 3 in a direction perpendicular to the direction in which the optical elements are arranged side by side.
, a cylindrical lens 11 and a light receiving element 12 are arranged in parallel.

In such a pickup device, irradiation light emitted from a light emitting element 1 sequentially passes through a collimator lens 2 and a beam splitter 3, and is directed to a disk 1 by an objective lens 4.
The light beam is focused on the recording surface No. 3 as a minute spot light. Note that the collimator lens 2 is a lens for converting the irradiation light emitted from the light emitting element 1 into parallel light. The reflected light from the recording surface of the disk 13 travels backward through the objective lens 4, enters the beam splitter 3, is guided by the beam splitter to the convex lens 10, passes through the convex lens and the cylindrical lens 11, and reaches the light receiving element 12. As mentioned above, minute bits (indentations) corresponding to information signals are formed as spiral tracks on the recording surface of the disk 13, and the spot light is irradiated onto the tracks to detect the presence or absence of the bits. It converts changes in reflected light into electrical signals and reproduces them as original information signals. Although it will not be described in detail since it is well known, when reflected light given convergence by the convex lens 10 passes through the cylindrical lens 11, the light receiving surface of the light receiving element 12 forms two focal lines perpendicular to each other. Utilizing the upward focusing property, so-called focus servo and tracking servo are performed in which the objective lens 4 is servo-driven in the direction of the optical axis of the objective lens and in a direction perpendicular thereto. .

The light intensity distribution of the spot light is determined by the light emission pattern of the light emitting element 1, the numerical aperture of the collimator lens 2, the aperture of the objective lens 4, etc. In the conventional pickup device, this light intensity distribution is As shown in Figure 0, it is close to an Airy pattern and has many side lobes.As a result, when the spotlight is made to follow the track and the information signal is read, crosstalk from adjacent tracks occurs. The problem has arisen that it is easy to accept.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an object thereof is to provide a pickup device in which crosstalk is less likely to occur.

In the pickup device according to the present invention, a light absorption film is provided on at least one refractive surface of an objective lens that focuses the irradiation light emitted from the light emitting element onto the recording surface of the recording medium as a spot light, and the light intensity distribution of the spot light is The light absorbing film is characterized in that the thickness of the light absorbing film is thinner in the central portion including the optical axis so as to have a Gaussian distribution centered on the optical axis.

Friend 11 Hereinafter, a pickup device as an embodiment of the present invention will be described with reference to the accompanying drawings.

The pickup device of this example is shown below. The parts other than those to be explained are constructed similarly to the pick-up device shown in FIG. 9, and the same reference numerals are used for the same or corresponding parts as the pick-up device shown in FIG. 9.

As shown in FIG. 1, an objective lens 21 for focusing the irradiation light emitted from the light emitting element 1 on the recording surface of the disk 13 as a spot light is fitted into a cylindrical holder 22. Objective lens 21 consists of a single aspherical lens. As shown in FIG. 2, a light absorber 1123 is provided on one refractive surface of the objective lens 21. Third
The figure shows the change in the thickness t of this light absorption film 23 in the radial direction of the objective lens. As shown,
The thickness of the light absorption film 23 is thinner at the central portion including the optical axis. By providing such a light absorption film 23, the fourth
As shown in Figures (a) and (b), the disk 13
The light intensity distribution of the spot light focused on the recording surface is a Gaussian distribution.

Therefore, the light amount distribution has no side lobes, and crosstalk due to the influence of adjacent tracks is less likely to occur when the spot light is made to follow the information recording track and the information signal is read.

FIG. 5 shows a situation in which a light absorption layer 11123 is provided on the refractive surface of the objective lens 21 by vacuum evaporation. As shown in FIG. 5, an objective lens 21 is mounted at a predetermined position in a vacuum chamber 25, and an evaporation plate 27 holding a light absorbing substance 26 such as chromium or aluminum is placed below the objective lens. There is. Although not shown, a heat source such as an electron beam irradiation device is provided for evaporating the light absorbing material 26. Objective lens 21
A mesh-like mask 28 is provided between the evaporating plate 27 and the evaporating dish 27 for controlling the state of vapor deposition of the light-absorbing substance on the objective lens 21.
is provided movably in the optical axis direction of the objective lens 21. That is, by appropriately adjusting the distance between the mask 28 and the objective lens 21, the light absorption film 2
3 (shown in the second figure) is set. Moreover, in this way, the light absorption film 2 is placed on the refractive surface of the objective lens 21.
3, a single layer or multilayer coating (not shown) of a material different from the light absorbing material 26 is formed on the light absorbing material 26 to provide an antireflection effect.

In addition, in the pickup device described above, the objective lens 2
The thickness of the light absorption film 23 at the center of the refraction surface of No. 1: t is zero, but as shown in FIGS. 6 and 7, the thickness of the light absorption film 23 at the center of the refraction surface is Even if =to is set to some extent, an effect equal to or greater than the above can be obtained.

In addition, in the above pickup device, the light absorption film 23
is provided only on one side of the objective lens 21, but may be provided on both sides.

Effects of the Invention As detailed above, in the pickup device according to the present invention, a light absorption film is provided on at least one refractive surface of the objective lens that focuses the irradiation light emitted from the light emitting element onto the recording surface of the recording medium as a spot light. The thickness of the light absorption film is formed to be thin at the central portion including the optical axis so that the light intensity distribution of the spot light becomes a Gaussian distribution centered on the optical axis. Therefore, the light amount distribution does not have side lobes, and when the spot light is made to follow the information recording track and the information signal is read, there is no interference due to the influence of adjacent tracks.
This makes it difficult for stalk to occur. In addition, since the light absorption film is provided on the objective lens itself, the center of the spot light and the center of the light amount distribution are determined by the servo drive (
Even during tracking servo operation, they always match, ensuring a stable information reading state.

[Brief explanation of drawings]

Fig. 1 is a side view including a partial cross section of the pickup device according to the present invention, Fig. 2 is a side sectional view of the objective lens, and Fig. 3 is a diagram showing changes in the thickness of the light absorption film in the radial direction of the objective lens. , FIGS. 4(a) and 4(b) are diagrams showing the light intensity distribution of the spot light focused on the disk, FIG. 5 is a diagram showing the state of forming a light absorption film by the vacuum evaporation method, and FIG. 7 is a diagram showing a partially modified example of the pickup device, and FIG. 9 and the second diagram are diagrams for explaining the conventional pickup device. Explanation of symbols of main parts 21...Objective lens 23...Light absorption film

Claims (1)

[Claims] a light emitting element, a collimator lens that converts the irradiated light emitted from the light emitting element into parallel light, and an objective lens that focuses the parallel light on a recording surface of a recording medium as a spot light, and at least one refraction of the objective lens. A light-absorbing film is provided on the surface, and the thickness of the light-absorbing film is formed to be thin at a central portion including the optical axis so that the light intensity distribution of the spot light becomes a Gaussian distribution centered on the optical axis. A pickup device in an optical information recording/reproducing device characterized by: