JPH04143931A - Exposing device for optical disk master disk - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical disk master exposure apparatus, and particularly to an improvement in its focus error detection method.

[Prior Art] Generally, an optical disk master exposure device has one focus error detection optical system, and its wavelength (for example, 633 nm)
is the wavelength λ of the exposure laser beam. (for example, 458 nm). In addition, the focal position of the objective lens differs depending on the wavelength5, and as shown in Fig.
Even if the focus error signal characteristic (S
curve characteristics), the focal position (exposure point) of the exposure laser beam is, for example, S or t.

[Problems to be Solved by the Invention] However, the detection method of the focus error detection optical system of the conventional optical disk master exposure device described above is generally an astigmatism method, but its S-curve characteristic does not necessarily have linearity before and after focusing. not symmetric, therefore S and t
(See FIG. 3), the sensitivity differs and the focus servo gain changes. Furthermore, when changing the exposure groove shape, the focus servo gain is not constant even when adjusting the offset of the focus servo circuit to change the exposure point, resulting in inconsistent focus servo control accuracy and unstable exposure quality. There was a point.

Therefore, the present invention solves the above-mentioned conventional problems and provides an optical disc master exposure system that allows easy adjustment with a constant focus servo gain when adjusting the offset of the focus servo circuit to change the exposure point. The challenge is to provide equipment.

[Means for Solving the Problems] The gist of the present invention is to use a semiconductor laser as a light source, have a predetermined relationship between the displacement of an objective lens and a focus error voltage, and reduce the focus error of a laser beam for exposure. In an optical disk master exposure apparatus equipped with a focus error detection optical system for detecting, the semiconductor laser has a different wavelength from that of the focus error detection optical system, and another focus error detection optical system has different predetermined characteristics; a switching means for selecting the focus error detection optical system having the predetermined characteristic such that the focus servo gain is constant when performing exposure by shifting the exposure point near the focus position of the exposure laser beam; The reason is that it is equipped with the following.

[Function] Therefore, when changing the exposure point near the focal point of the exposure laser light source, the switching means is operated to select the focus error detection optical system having the optimal predetermined characteristics that keep the focus servo gain constant. Therefore, adjustment of the exposure point becomes easy and accurate.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a focus detection optical system of an optical disk master exposure device, and in the same figure, la.

1b are light sources with wavelengths λ1. λ2 semiconductor laser (LD), 2a and 2b are semiconductor lasers la.

A collimator lens that converts the diverging light from 1b into a parallel beam,
3a and 3b are wavelengths λ4. Polarizing beam splitter (P, B, S) at λ2, 4a, 4. b is a quarter wavelength plate,
5a and 5b, dichroic mirror 6 is an objective lens, 7
is the actuator of the objective lens 6, 8 is the disk master,
9a, 9b are mirrors 10a, 10b are condensing lenses, ll
a, llb are cylindrical lenses, 12a', 12b
is a 4-split Pin photodiode which is a light receiving element, 13
a.

Reference numeral 13b represents a focus error voltage detection circuit, and reference numeral 14 represents a changeover switch which is a switching means for selecting either of the two focus error detection optical systems.

In this way, separate focus error detection optical systems using astigmatism methods having different wavelengths are formed for the subscript a system and the subscript s system.

In the above configuration, for example, in the focus error detection optical system of the subscript a system (wavelength λ□), the diverging light from the semiconductor laser 1a is made into a parallel light beam by the collimator lens 2a, and is incident on the polarizing beam splitter 3a with a wavelength of 1/4 Board 4
a, is deflected and reflected at right angles by the dichroic ink mirror 58, and enters the objective lens 6. The light beam incident on the objective lens 6 is focused on the disk master 8 . Further, the exposure laser beam enters from the arrow 15, passes through the dichroic mirror 58, and is focused by the objective lens 6 onto the disk original fI18. The objective lens 6 is moved minutely by an actuator to adjust its focus.

On the other hand, the light beam that has hit the disk master 8 and is reflected is polarized and reflected at right angles by the dichroic mirror 58 and then passes through the quarter wavelength plate 4a to the polarizing beam splitter 3a and the mirror 9a.
are deflected and reflected at right angles by the condenser lens 10a.
, the light is focused on the photodiode 12a via the cylindrical lens lla. The disc master 8 is exposed in the optimum condition (the exposure point is on the disc master 8)
In this case, the photodiode 12a is also in focus and adjusted so that the smallest light spot hits it, so if the exposure point on the disk master 8 is even slightly shifted, the photodiode 12a will also be out of focus. As a result, the light spot becomes an ellipse, the difference signal of the 4-split bin photodiode increases or changes, and the amount of received light becomes greater than when in focus (focus error), which is detected by the focus error voltage detection circuit 13a. and outputs a focus error signal to a predetermined circuit (not shown).

By the way, the respective S-curve characteristics of the focus error detection optical system for wavelengths λ and λ2 are as shown in Fig. 2 (the direction of displacement is the direction approaching the objective lens), and the focused point in the exposure laser beam at the 0 point. (= point S in Figure 3) and are located approximately equidistant from each other, and v and u are λ0. This is the focal point at each wavelength of λ2. Further, t and s are the exposure points of the conventional focus error detection optical system of one wavelength λ shown in FIG. Now, if the detection optical system for the wavelength λ2 is appropriately selected by the changeover switch 14, a constant focus servo gain of, for example, -P (V) can be obtained.

Therefore, on the side where the displacement of the objective lens 6 is farther than V, the detection optical system with wavelength λ is used, and on the side where the displacement of objective lens 6 is closer than ■, the detection optical system with wavelength λ2 is used.
It is sufficient to select the detection optical system.

[Effects of the Invention] As explained above, according to the present invention, two focus error detection optical systems with different wavelengths are provided, and the optimum detection optical system is used by switching as necessary. When adjusting the offset of the focus servo circuit to change the exposure point near the focal point of the exposure laser beam, the focus servo gain remains constant without fluctuation, and the exposure quality is stabilized. Furthermore, compared to the conventional case of a single focus error detection optical system, there is an effect that the detection range of the focus error detection optical system is widened.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an optical disk master exposure apparatus of the present invention, FIG. 2 is a characteristic line diagram of focus error voltage of two focus error detection optical systems of different wavelengths, and FIG.
The figure is a characteristic diagram of focus servo gain of a conventional single focus error detection optical system. la, lb... semiconductor laser, 6... objective lens,
14...Switching means, 15...Laser beam for exposure. (1 other person)

Claims (1)

[Claims] An optical disc master using a semiconductor laser as a light source, which has a predetermined characteristic in the relationship between the displacement of an objective lens and a focus error voltage, and is equipped with a focus error detection optical system that detects a focus error of an exposure laser beam. In the exposure apparatus, the semiconductor laser having a different wavelength from the focus error detection optical system and another focus error detection optical system having the different predetermined characteristics, and the exposure apparatus include the semiconductor laser having a different wavelength from the focus error detection optical system, and another focus error detection optical system having different predetermined characteristics; An optical disk master exposure apparatus characterized by comprising: switching means for selecting the focus error detection optical system having the predetermined characteristics such that the focus servo gain is constant when performing exposure with shifted points. .