JP2603664B2 - Master exposure position adjustment method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a master exposure position adjusting method.

(Prior Art) When writing information on a master disc of an optical disc memory by exposure, it is necessary to converge an exposure beam correctly on the recording surface of the master disc. Since the exposure laser is turned on and off according to information to be written, it is difficult to perform accurate focus control using the exposure laser. Therefore, in addition to the exposure laser, a focus control laser is used to perform focus control using the focus control laser.

In this case, it is difficult to match the focal point of the exposure laser with the focal point of the focus control laser. Normally, a correction voltage corresponding to the shift of the focal point position is generated, and the focus voltage is adjusted by this correction voltage. The focus control of the exposure laser is performed by correcting the control signal. However, in this conventional focus control method, the correction voltage for correcting the focus control signal is set to be constant, and external fluctuation factors such as a change in the reflectance of the master glass and a change in the intensity of the focus control laser are considered. However, when the external fluctuation occurs, it is necessary to set the correction voltage again.

(Purpose) The present invention has been made in view of the above-mentioned circumstances, and has been made in consideration of the above-described circumstances. It is an object of the present invention to provide a novel master exposure position adjusting method capable of controlling the focus of a laser.

(Configuration) Hereinafter, the present invention will be described.

The master exposure position adjusting method of the present invention includes the steps of: generating a correction voltage corresponding to a shift between the converging positions of the exposure laser and the focus control laser during the master disk exposure of the optical disc memory; This is a method in which a signal is corrected with the correction voltage and the exposure laser is focused on the master recording surface, and has the following features.

That is, from the four-division light receiving element that receives the reflected light of the focus control laser from the master and generates a focus error signal,
A light amount signal corresponding to the total amount of received light is generated, and a correction voltage proportional to the light amount signal is generated using the light amount signal.

(Example) Hereinafter, a description will be given of a specific example with reference to the drawings.

FIG. 1 is a schematic illustration of only an essential part of an example of a master exposure apparatus to which the present invention is applied. Reference numeral 10 denotes a master.
The master 10 is formed by applying a photosensitive agent to a glass plate, and the photosensitive agent-coated surface is a recording surface.

Reference numeral 12 denotes a light source device for exposure. The exposure light source device 12 emits an exposure laser. This exposure laser is reflected by the mirror 16, passes through the dichroic mirror 18, the quarter-wave plate 21, and enters the objective lens 22,
The lens 22 irradiates the master disk 10 as a focused light beam.

Reference numeral 14 denotes a light source device for focus control. The light source device 14 emits a focus control laser. The focus control laser passes through the beam splitter 20 and is reflected by the dichroic mirror 18, and passes through the quarter-wave plate 21 through the objective lens 2.
The light is then incident on the master 2 and irradiates the master 10 as a focused light beam.

When the focus control laser is reflected by the recording surface of the master 10, the objective lens 22, the dichroic mirror 18, the quarter-wave plate 21, the beam splitter 20, and an astigmatism generating optical system (not shown) (for example, a cylinder lens) Via 4
The light enters the divided light receiving element 26.

From the four-division light receiving element 26, a signal corresponding to the focus error is generated. This signal is input to the focus error signal generation circuit 30,
The circuit 30 generates a focus error signal F corresponding to the signal. This focus error signal is applied to the voice coil 24 via a control circuit 32 that servo-controls the voice coil 24 that shifts the objective lens 22 in the optical axis direction. As a result, the objective lens 22 is displaced in the optical axis direction, and focus control is performed. This focus control is a method already well known as an astigmatism method.

If the exposure laser and the focus control laser are focused at the same position, the focus control method described above is sufficient. However, in general, the focus positions of the two lasers do not coincide with each other and are slightly shifted from each other. There are various possible causes of this shift. For example, chromatic aberration due to a difference in wavelength between an exposure laser (usually an Ar laser or a He-Cd laser is used) and a focus control laser (usually a He-Ne laser is used), A deviation from the parallel light beam due to both laser collimation errors can be mentioned. For this reason, the focal point of the exposure laser and the focal point of the focus control laser are shifted from each other in the optical axis direction of the objective lens 22.

X in FIG. 3 indicates the amount of defocus of the focus control laser, that is, the defocus amount of the focus control laser, and F indicates the focus error signal generated from the focus error signal generation circuit 30.
A straight line 3-1 indicates a linear portion of the so-called S-shaped characteristic of the focus error signal F. The focus control laser can be focused on the recording surface by performing focus control so that F = 0 according to the straight line 3-1. However, as described above, the focus position of the exposure laser is Since the focal point of the laser for focus control is shifted in the optical axis direction, even if the laser for focus control is focused on the recording surface as described above, the focal point of the laser for exposure is shifted from the recording surface. Since the shift of the focal point is constant, the laser beam for exposure is focused on the recording surface by shifting the focal point of the focus control laser so as to offset the shift amount from the focal point of the focus control laser. good.

That is, as shown in FIG. 3, when the voice coil 24 is driven by superimposing the correction voltage Vref corresponding to the shift of the focal point on the focus error signal, the S-shaped characteristic is represented by a straight line 3-2 in FIG. Thus, the focal point of the focus control laser is shifted from the recording surface, but the exposure laser can correctly focus the laser on the recording surface. However, if the reflectivity of the glass of the master changes or the intensity of the focus control laser changes, the slope of the linear portion of the S-shaped characteristic of the focus error signal changes. For example, considering the case where the reflectance is lowered, as shown in FIG. 4, the slope of the straight line portion of the S-shaped characteristic is reduced from the correct straight line portion 3-1 to the straight line portion 4-1.
It becomes like.

In this case, even if the actual defocus amount is Xo, this is controlled as the defocus amount X ', so that proper focus control cannot be performed on the exposure laser. In order to properly deal with such a change in the external fluctuation factor, it is necessary to change the correction voltage for correcting the focus error signal in accordance with the change in the external fluctuation factor.

In the present invention, the following is performed in order to make the correction voltage follow the fluctuation of the external fluctuation factor. That is, as shown in FIG. 1, a four-divided light receiving element 26 generates a light quantity signal S1 corresponding to the total light reception quantity of this element 26, that is, the total light quantity of the focus control laser incident on the element 26, The correction voltage Vref1 proportional to the light amount signal is generated by the correction voltage generation circuit 34 using the signal S1.

Then, the focus error signal is corrected by the correction voltage Vref1.

 This correction is performed by the control circuit 32.

That is, in this embodiment, the control circuit 32 is an amplifying circuit as shown in FIG. 2, to which a focus error signal F and a correction voltage Vref1 are applied to superimpose the two, and an output signal thereof is used. The voice coil 24 is servo-controlled. Control circuit
The gain at 32 may be changed to various values while performing writing on the master, finding a gain that performs writing best, and fixing this as a set value.

(Operation and Effect) As described above, according to the present invention, a novel master disk exposure position adjusting method can be provided. In this method, as described above, the correction voltage for correcting the focus error signal in accordance with the positional shift between the focus point of the focus control laser and the focus point of the exposure laser is used to adjust the reflectance of the master glass and the focus control laser. Therefore, the in-focus state of the exposure laser can be always realized irrespective of the fluctuation of the external fluctuation factor.

[Brief description of the drawings]

FIG. 1 is a view showing one embodiment of the present invention, and FIGS.
The figure is a diagram for explaining the present invention. 10 master disk, 12 light source device for exposure, 14 light source device for focus control, 26 four-divided light receiving element, 32 control circuit

Claims (1)

(57) [Claims] In an exposure of a master of an optical disk memory,
A correction voltage corresponding to the shift of the focusing position between the exposure laser and the focus control laser is generated, and the focus error signal obtained by the focus control laser is corrected by the correction voltage so that the exposure laser is recorded on the master recording surface. A light amount signal corresponding to the total amount of light received is generated from a four-divided light receiving element that receives reflected light from the master disk of the focus control laser and generates a focus error signal. A master disc exposure position adjusting method, wherein a correction voltage proportional to a light quantity signal is generated using a signal.