JPH03276427A - Optical head - Google Patents

Abstract

PURPOSE:To perform stable preheating with a simple constitution by using an objective lens to condense the preheating light as well as the write light. CONSTITUTION:A laser light source is used as the preheating light source, and the information write light is made incident on an objective lens 107 in the lens optical axis direction, and the preheating laser light is made obliquely incident on the lens 107, and a preheating light sport 105 preceding a recording spot 103 is formed in an information recording part and its diameter is kept constant. The diameter of a preheating light spot 203 is made larger than that of the recording light spot. The objective lens has the curvature of field, and the focal length of the light made incident obliquely to the optical axis is changed from that of the perpendicularly incident light. This characteristic is used for formation of the preheating light spot, and the classification of the lens and the angle of incidence are controlled to form a proper light spot.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical head that reads and writes information to and from an optical information recording medium such as an optical disk and an optical card.

[Traditional technique]

In an optical head for recording and reproducing optical information, the higher the power of the laser light during writing, the better in terms of increasing the seek speed to shorten the access time and expanding the range of recording media available.

However, the power of the laser diode that is the light source is limited, and increasing this power is not easy.

In order to compensate for the lack of laser power, it is a useful means to preheat the information recording section by placing a laser spot other than that for recording in advance of the recording spot during recording.

A conventional example of an optical head having a preheating light source is JP-A-1-211324.

The embodiment shown here is illustrated in FIG.

Laser light from a recording/reproducing laser light source 400 passes through an objective lens 405 and is focused onto a recording medium 407 .

On the other hand, the laser beam emitted from the preheating light source 401 is converged onto the recording medium 407 by a convex lens 403 separate from the objective lens 405 to create a preheating spot.

[Problem to be solved by the invention]

Generally, in optical recording, it is necessary to allow for considerable surface runout due to warping of the medium, surface irregularities, errors during chucking, etc. For example, for optical discs, the maximum
There is about 1 Lord's deviation in the face.

In the embodiment of FIG. 4, the convex lens 4 for the preheating spot
If 06 is used in a fixed manner, the size of the preheating spot on the recording medium will change significantly, making it impossible to perform a constant amount of preheating.

The above problem can be solved by providing the preheating spot lens with a focus servo mechanism, but if a dedicated photodetector or actuator is provided for this purpose, the number of parts will increase significantly.

For this reason, a method can be considered in which the preheating spot lens is linked with the objective lens, but this method has the problem that the tracking performance of the base servo deteriorates because the weight of the movable part of the servo system increases.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical head that solves the above problems and performs stable preheating with a simple configuration.

[Means for Solving the Problems] In order to achieve the above object, the optical head of the present invention has the following features.

That is, after preheating an information recording section on a recording medium by focusing preheating light from a preheating light source, writing light modulated according to the information is focused on the information recording section by an objective lens to write the information. In the optical head for recording, the objective lens is characterized in that it serves to collect both preheating light and writing light.

〔Example〕

The basic configuration of the present invention is shown in FIG.

In FIG. 1, 101 is a recording medium, 106 is a recording spot, 105 is a preheating spot, 107 is an objective lens, 109 is a photodetector, 111 is a beam splitter, 116 is a recording/reproducing laser light source, 1
Reference numeral 15 indicates a preheating light source. In this example, a laser light source was used as the preheating light source. The information writing light is incident on the objective lens 107 in the optical axis direction of the lens, and the preheating laser beam is made obliquely incident on the objective lens 107, thereby forming a recording spot 10 on the information recording section.
A preheating spot 105 is formed prior to step 3.

Generally, in an optical head for recording and reproducing optical information, a focus servo system is formed to control the distance between the medium and the objective lens to be constant.

Therefore, the preheating spot 105 in the present invention always maintains a substantially constant spot diameter.

FIG. 2 shows an enlarged view of a spot formed by the laser beam passing through the objective lens 205 on the recording medium. The preheating spot 203 is the recording spot 2 to avoid tracking problems and to prevent information from being written on its own.
The spot has a larger diameter than 01.

Generally, an objective lens has a curvature of field aberration, and the focal length of a ray of light incident obliquely to the optical axis changes with respect to a ray of light incident perpendicularly thereto. This characteristic of the objective lens is utilized to form a preheating spot, and a preheating spot of an appropriate size is created by adjusting the type of lens and the angle of incidence.

In the present invention, it is also possible to create a plurality of preheating spots as shown in FIG. 3, and even in that case, there is no increase in the number of parts other than the light source.

That is, preheating light sources 1.2 indicated by 601 and 606
are provided, and the respective laser beams are incident on the objective lens 107 at different incident angles to create preheating spots 1.2 shown at 605 and 307 on the recording medium 101. In FIG. 3, the same components as in FIG. 1 are given the same numbers.

〔Effect of the invention〕

According to the present invention, it is possible to perform a certain amount of preheating with a small number of parts, and it is possible to increase the writing speed and expand the selection range of recording media.

[Brief explanation of drawings]

Fig. 1 shows the basic configuration of an embodiment of the optical head according to the present invention, Fig. 2 shows an enlarged view of a spot on a recording medium, Fig. 3 shows the structure of another embodiment, and Fig. 4 shows a conventional optical head. Each of the basic configurations of the invention is shown. 103.201...Recording spot, 105.
203... Preheating spot, 5... Preheating spot 1. 7... Preheating spot 2. 3... Laser light source for recording and reproduction, 5.401.
... Light source for preheating, 1 ... Light source for preheating 1. 3... Light source for preheating 2゜Figure 1 2nd picture

Claims (1)

[Claims] After preheating an information recording section on the recording medium by focusing preheating light from a preheating light source, writing light modulated according to the information is focused onto the information recording section by an objective lens to record the information. An optical head characterized in that the objective lens also serves to condense the preheating light and the writing light.