JPH06202058A - Light quantity controller - Google Patents

Abstract

(57) [Summary] [Purpose] Linear light quantity control characteristics (output light quantity vs. command value) despite using a modulator with nonlinear light quantity characteristics.
A light amount control device capable of forming a uniform exposure groove on the entire surface during CAV exposure. A modulator for modulating coherent light and outputting the modulated light, a unit for spectrally converting the output modulated light for photoelectric conversion, and a unit for controlling the output modulated light amount by the photoelectrically converted signal and a command value. In a light quantity control device equipped with
The circuit configuration is such that the difference signal e ₁ between the photoelectrically converted signal and the command value approaches a predetermined value. That is, the difference signal e ₂ is generated again by a differential circuit that compares the difference signal e ₁ with a predetermined DC voltage value, and the light amount is controlled by e ₂ .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light quantity control of an optical disk master exposure apparatus and the like, and more particularly to a light quantity control apparatus capable of obtaining a light quantity control characteristic having good linearity.

[0002]

2. Description of the Related Art FIG. 6 shows a block diagram of a light quantity control device according to the prior art. In FIG. 6, the modulated coherent light L ₂ emitted from the acousto-optic modulator 4 is split by the half mirror 6, detected by the optical sensor 7, and photoelectrically converted by the photodetector circuit 5 together with the output thereof. The dynamic circuit 1 compares the command value with the command value, and the difference signal is output from the differential circuit. The difference signal is amplified by the phase compensation & gain circuit 2 and output as a feedback signal, the output of which is amplified by the acousto-optic modulation element drive circuit 3, and the acousto-optic modulation element 4 is output by the output signal.
Are driven, the coherent light L ₁ is modulated, and the light amount is controlled.

Here, the acousto-optic modulator driving circuit 3 is used.
The acousto-optic modulator 4 constitutes a modulator. Also,
Laser light is generally used as the coherent light.
The light passing through the half mirror 6 passes through an objective lens (not shown) to expose the exposure surface of the optical disc master.

[0004]

In the light quantity control method according to the above-mentioned prior art, since the light quantity characteristic of the acousto-optic modulator 4 of the modulator is an S-shaped non-linear characteristic as shown in FIG. When the closed loop feedback is performed on the value, the difference signal becomes large, and stable light amount control cannot be performed. Further, as shown in FIG.
No linearity can be obtained. The linearity of the light quantity characteristic (output modulated light quantity vs. drive voltage) cannot be obtained because K ₁ , K ₂ , K in FIG.
_As shown in FIG. ₃ , since the slope of the light amount characteristic differs depending on the operating point, when the servo circuit is configured by regarding the slope as K ₂ , the gain is increased or decreased in the part where the slope is different (K in the example above).
_This is because the gain decreases at ₁ and K ₃ ) and the servo deviation remains.

When the above-described light amount control device according to the prior art is used in a master exposure device for a CAV exposure type (constant angular velocity) optical disc, for example, as shown in FIG. 8, the exposure light amount corresponds to the disc radius at the normal exposure position. However, if the light amount characteristic with respect to the command value is S-shaped as shown in FIG. 7, the command value is changed with a constant change amount. When the exposure is performed by the CAV exposure method, a uniform exposure groove cannot be obtained on the entire surface. In order to solve the problem, a method of changing the command value in consideration of a non-linear light amount characteristic has been conventionally proposed, but the calculation of the command value becomes complicated and time-consuming, and the error becomes large. was there.

[0006]

It is an object of the present invention to solve the above-mentioned problems of the prior art and to obtain a linear light quantity control characteristic (output light quantity vs. command value) despite using a modulator having a non-linear light quantity characteristic. Another object of the present invention is to provide a light quantity control device capable of forming an exposure groove that is uniform over the entire surface during CAV exposure.

[0007]

In order to achieve the above object, the present invention provides a modulator that modulates coherent light and outputs the modulated light, and a means that splits the output modulated light and photoelectrically converts it. A light quantity control device having means for controlling an output modulated light quantity by the photoelectrically converted signal and a command value, comprising circuit means for making the difference signal e ₁ between the photoelectrically converted signal and the command value approach a predetermined value. It is characterized by having done. Further, the circuit means is configured to generate the difference signal e ₂ again by a differential circuit which compares the difference signal e ₁ with a predetermined DC voltage value, and controls the light amount by the difference signal e ₂ .

[0008]

The difference signal e _{2 is} again detected by the differential circuit which compares the difference signal e ₁ between the photoelectrically converted signal and the command value with a predetermined DC voltage value.
Is generated and the light amount is controlled by the difference signal e ₂ , the gain of the servo system can be secured even in the non-linear region of the modulator, even though the modulator having the non-linear light amount characteristic is used. A linear light quantity control characteristic (output light quantity vs. command value) is obtained.

[0009]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a light quantity control device according to the present invention. In FIG. 1, this light quantity control device is mainly composed of a differential circuit 1 of the conventional light quantity control device shown in FIG.
In place of the first and second differential circuits 8 and 9, and other configurations, that is, the phase compensation & gain circuit 2, the acousto-optic modulator driving circuit 3, the acousto-optic modulator 4, The photodetector circuit 5 and the like are configured similarly to the conventional technique.

As shown in FIG. 1, a command value given from the outside is input to one input terminal of the first differential circuit 8 and photoelectrically converted by the photodetector circuit 5 to the other input terminal. The output signal is input and the difference signal e ₁ is generated. The light quantity characteristic of the acousto-optic modulator 4 is non-linear as shown in FIG. 2, and the output characteristic of the photodetector circuit 5 is linear as shown in FIG. The signal e ₁ generated by the first differential circuit 8 is input to one input terminal of the second differential circuit 9 and a predetermined DC voltage is applied to the other input terminal of the second differential circuit 9. (For example, OV), the second differential circuit 9 generates the difference signal e ₂ . The difference signal e ₁ is, for example, a signal that fluctuates at a level slightly lower than the predetermined DC voltage, and at that time, e ₂ is a minute positive (+) signal that fluctuates at a level close to OV. The difference signal e ₂ is input to the phase & gain circuit 2 and output as an amplified feedback signal, and further the acousto-optical modulator driving circuit 3
And is output as a positive drive voltage (in the case of the above example) of sufficient power to drive the acousto-optic modulator 4. The operating point in FIG. 2 showing the light quantity characteristic of the acousto-optic modulator 4 is determined by the command value. That is, the drive voltage in FIG. 2 is a positive value that fluctuates around v ₀ corresponding to the command value (in the case of the above example).

The acousto-optic modulator 4 is supplied with the drive voltage as described above, and modulates the light quantity of the laser beam L ₁ according to the drive voltage. The modulated laser light L ₂ is split by the half mirror 6, the split laser light is incident on the optical sensor 7, photoelectrically converted by the photodetector circuit 5, and the light amount control of the closed loop is performed. In the above light amount control device, e ₂ must always be positive in order to always change the drive voltage input to the acousto-optic modulator 4 in the positive region. For that purpose, e ₁ must always be lower than a predetermined DC voltage value. For example, if the predetermined DC voltage value is OV
If (grounded), then e ₁ will always be negative. Therefore, in this example, the signal input from the photodetector circuit 5 to the first differential circuit 8 is always smaller than the command value.

Here, if the output of the acousto-optic modulator 4 increases due to some factor, and the signal input from the photodetector circuit 5 to the first differential circuit 8 becomes large (more than the command value). Is smaller), the level of e ₁ is higher (less than OV), and thus the level of e ₂ is lower (however, a positive value). Therefore, the input voltage of the acousto-optic modulator 4 drops, and the output of the acousto-optic modulator 4 is pulled back. At this time, the operating point of the acousto-optic modulator 4 is shown in FIG.
A v ₀ shown in, even the gain of the system because of the non-linear region is smaller than the linear region (region of gain K _2), by the addition of the second differential circuit 9, the gain of the system Since it is sufficient, the servo deviation does not remain unlike the conventional case. That is, as shown in FIG. 3, when the amount of light incident on the photodetector circuit 5 changes, the output of the photodetector circuit 5 changes linearly, and following the change, the operating point of the acousto-optic modulator 4 is immediately changed. Since the output light quantity of the acoustic modulator is changed to a value that linearly corresponds to the command value, it is possible to obtain a linear light quantity characteristic as shown in FIG.

As shown in FIG. 5, in the present invention, the first-order diffracted light of the laser light L ₂ modulated by the acousto-optic modulator 4 is used. This is because the extinction ratio of the 1st-order diffracted light can be made larger than that of the 0th-order diffracted light. If the extinction ratio is small, even if the drive voltage is turned off, the light is not extinguished immediately. Therefore, when pulse modulation is performed (in the present invention, pulse modulation is performed), pulsed light cannot be obtained. Since the 0th-order diffracted light is not used in the optical system thereafter, it is necessary to shield it.

FIG. 5 shows an embodiment in which the light quantity control device according to the present invention is mounted on an optical disk master exposure device. In the figure, a portion surrounded by a dotted line is a light amount control device. Also, 11
Is a laser beam L ₁ to the acousto-optic modulator 4 in the light quantity control device.
Is an argon laser for giving a beam expander, 12 is a beam expander, 13 is a reflection mirror, 14 is an objective lens, 15 is an optical disk master, and 16 is a motor for rotating the optical disk master. It should be noted that although the acousto-optic modulator is used as the modulator in the above embodiment, an electro-optic modulator can also be used. It is also possible to use a general amplifier in place of the second differential circuit.

[0015]

As described above, according to the present invention,
Since a linear light quantity control characteristic (output light quantity vs. command value) can be obtained despite using a modulator having a non-linear light quantity characteristic, in a CAV exposure type optical disk master exposure apparatus or the like, a uniform exposure groove is formed over the entire surface of the disk. Can be formed. Moreover, since the first-order diffracted light of the acousto-optic modulator is used, the extinction ratio becomes large, and pulse modulation becomes possible.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a light amount control device according to the present invention.

FIG. 2 is a diagram showing a light amount characteristic of the acousto-optic modulator shown in FIG.

FIG. 3 is a diagram showing output characteristics of the photodetector circuit shown in FIG.

FIG. 4 is a diagram showing a light amount characteristic with respect to a command value of the light amount control device according to the present invention.

FIG. 5 is a schematic diagram showing a case where the light amount control device according to the present invention is applied to an optical disc master exposure device.

FIG. 6 is a block diagram showing an example of a light amount control device according to a conventional invention.

FIG. 7 is a diagram showing a light quantity characteristic with respect to a command value of a light quantity control device according to a conventional invention.

FIG. 8 is a diagram showing an exposure light amount corresponding to a disc radius of a CAV exposure type optical disc master exposure device to which the conventional invention and the present invention are applied.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Differential circuit, 2 ... Phase compensation & gain circuit, 3 ... Acousto-optic modulator drive circuit, 4 ... Acousto-optic modulator, 5 ... Photodetector circuit, 6 ... Half mirror, 7 ... Photosensor, 8 ... 1st Differential circuit, 9 ... second differential circuit, 11 ... argon laser,
12 ... Beam expander, 13 ... Reflecting mirror, 14 ... Objective lens, 15 ... Optical disc master, 16 ... Motor,

Claims (3)

[Claims] 1. A modulator that modulates coherent light and outputs the modulated light, a unit that disperses the outputted modulated light and photoelectrically converts it, and an output modulated light quantity is controlled by the photoelectrically converted signal and a command value. In the light amount control device including means for controlling the light amount, the light amount control device is provided with circuit means that works so that the difference signal e ₁ between the photoelectrically converted signal and the command value approaches a predetermined value. 2. The circuit means regenerates the difference signal e ₂ by a differential circuit that compares the difference signal e ₁ with a predetermined DC voltage value, and controls the light amount by the difference signal e _2. The light quantity control device according to claim 1, wherein 3. The light quantity according to claim 1, wherein the modulator is composed of an acousto-optic modulation element, and the first-order diffracted light of the acousto-optic modulation element is modulated to control the light quantity. Control device.