JPH02165437A - Production of optical recording medium - Google Patents

Abstract

PURPOSE:To allow laser cutting while maintaining a good extinction ratio even when the duty of the signal for executing laser cutting changes by controlling a bias voltage in accordance with the crest value of a monitor which indicates modulating light. CONSTITUTION:The signal outputs having square waves from both photodetectors 1, 2 are respectively inputted to corresponding peak hold circuits 3, 4 by which the crest values of these square waves are maintained. The outputs thereof are then inputted to a comparison control circuit 5. The crest values of both the systems are compared in the circuit 5 and the differential signal thereof is inputted to a bias voltage control circuit 6 where the controlled variable of the bias voltage to be impressed to an optical modulator 7 is so determined as to decrease the difference in the crest values of the two systems to zero in accordance with the differential signal obtd. in such a manner. Since the bias voltage is controlled by the crest values of the outputs of the photodetectors 1, 2 in such a manner, the crest values do not change even if the duty of the signal to execute laser cutting is continuously changed. The laser cutting is executed while the extinction ratio is maintained in the optimum state in this way without deteriorating the same.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing an optical recording medium such as a video disc, a compact disc, etc., in which recorded information is read out using a laser beam. This relates to the process of recording information on a recording master using modulated light from an optical modulator.

[Conventional technology]

Optical recording media (hereinafter referred to as optical discs) such as video discs and compact discs are generally manufactured through a manufacturing process as shown in the block diagram of FIG.

First, a recording master is prepared by coating a photoresist on a glass plate as a substrate, and by controlling the on/off of laser light irradiation according to the recording signal, the photoresist at a desired position on the recording master is exposed to light and the signal is output. Then, the photoresist is removed by a development process to form a desired uneven pattern. Next, the formed uneven pattern is transferred to a metal master disk by electroforming to produce a stamper. The stamper manufactured in H1& is duplicated, a reflective film and a recording film are formed on the signal surface, and an optical disc is manufactured.

By the way, in the manufacturing process described above, the ON/OFF control of laser light irradiation in the process of exposing the photoresist, that is, the laser cutting process, is performed by an optical modulator. Such optical modulators include electro-optic modulators (EO modulators) that utilize the change in the refractive index of crystals when a voltage is applied, and acousto-optic modulators that utilize the interaction of light and ultrasound. An optical modulator (AO modulator) is known.

FIG. 4 is a schematic diagram for explaining the principle of an electro-optic light modulator, and this electro-optic light modulator usually has a KDP (
Crystal: KH2PO, ), ADP (Crystal: NH4H
A Pockels cell 41 such as 2PO4) is used.

When a voltage is applied to such a Pockels cell 41, anisotropy occurs in the refractive index of the crystal, and a phase difference occurs between the polarized light components of the light passing through the Pockels cell 41.

This phase difference is related to the magnitude of the applied voltage. When a linearly polarized light wave L1 is made incident on the Pockels cell 41, it is converted into an elliptically polarized light wave L2 according to the voltage applied to the Pockels cell 41 from the signal source 42. If this elliptically polarized light wave L2 is passed through the polarizer 43 and only the elliptical component (polarized component in the direction perpendicular to the polarization direction of the linearly polarized light wave) is extracted, light with an intensity corresponding to the applied voltage can be obtained. can get.

In the electro-optic light modulator, the applied voltage of the signal source 42 is set based on a desired recording signal to control on/off of light irradiation to the glass substrate coated with photoresist.

By the way, the crystal orientation angle of the Pockels cell 41 and the polarizer 4
When the angle with the polarization plane of 3 is 45 degrees, the relationship between the transmitted light 11 from the polarizer 43 and the applied voltage V is as shown in equation 11 below (see FIG. 5).

I = I, sin” (α・V) ・(1) ■
. Amount of light emitted from two people α: constant Here, if the applied voltage that gives I-max (I o) is V, the above equation (1) becomes the following equation (2).

I = r, sin”(V/V.) ・(2
) Therefore, by changing the applied voltage (2) in the range of 0 to (1), the voltage ranges from 0 to (1) depending on the characteristic of sin squared. It is possible to obtain transmitted light 331 in the range of .

In electro-optic light modulators, information signals such as video or audio are shaped into on/off signals of 1 or 0 using a predetermined method, resulting in 1-V, O-0, and effective use of laser light. In order to maximize the extinction ratio (the ratio between the maximum amount of transmitted light and the minimum transmitted sight) in consideration of the above, laser cutting is performed with the on and off settings between Io and 0.

However, in an actual electro-optic optical modulator, the minimum value of the optical output is not 0 but 1.0 as shown in FIG. in, and the extinction ratio in this case is r o/I ff1in.

In addition, due to the inherent birefringence of the crystal of the Pockels cell 41, when the applied voltage is 0, the optical output is the minimum value (
1, i, , ). Therefore, the light output is set to the minimum value (1
,i,), a constant bias voltage V, is required and the extinction ratio I,/I,i.

To obtain , the applied voltage is V, ~V,. It is necessary to change it within the range of (see Figure 6). In other words, the bias voltage is V! By applying a voltage in the range of 0 to V+ (=V, -Va) with this voltage as the operating reference point, I+ain~■. modulated light can be obtained.

Furthermore, in the element (Pockels cell) used in the electro-optic light modulator, the phase of the polarized light component changes due to temperature changes.

Therefore, as the temperature of the element changes due to a change in ambient temperature or a change in the intensity of the laser beam that is modulated, the operating reference point may change and a sufficient extinction ratio may not be obtained. Therefore, it is necessary to change the bias voltage vl in accordance with this variation so that a sufficient extinction ratio can always be obtained.

FIG. 7 is a schematic diagram showing the principle of a conventional method for controlling the bias voltage V. The reflected light and transmitted light from the polarizer 43 are received by each light receiving element 46, 47 via low reflectance half mirrors 44, 45, respectively.
The bias voltage vIl is controlled so that the output after photoelectric conversion from 47 is constant. In the cutting process using laser light, ■. (1) and 1+++tn (0), so the bias voltages V and l in the control method described above are
The control is performed based on the average value of the outputs of the respective light receiving elements 46 and 47. In other words, more specifically, the average value of the output from each of the light receiving elements 46 and 47 is compared, and the value of the bias voltage V is changed so that the difference between the two becomes 0, thereby always maintaining the best extinction ratio. At the same time, a modulation voltage of O-V is applied to perform optical modulation.

Conventionally, by using an electro-optic ordinary light modulator that has such a control function, it is possible to maintain the best extinction ratio without being affected by ambient temperature changes or temperature changes when changing the incident intensity. Laser cutting was possible in this state.

[Problem to be solved by the invention]

However, in the method described above in which the bias voltage is controlled based on the average value of the outputs of both light receiving elements, −CAV(c
continuous angular velocity
y) To maximize the extinction ratio of the optical modulator when the duty of the signal waveform used for laser cutting is changed continuously, as in the case of a disk, or when the duty of the signal waveform is shifted from 1=1. If the frequency of the canting signal input to the optical modulator that has been adjusted changes significantly, the average value of the output of both photodetectors will differ, causing the optical modulator's operating reference point to fluctuate. There was a problem that the best extinction ratio could not be maintained.

The present invention has been made in view of the above circumstances, and by controlling the bias voltage based on the peak value of a monitor indicating modulated light, even when the duty of the signal for laser cutting changes. , laser cutting can be performed while maintaining the best extinction ratio,
It is an object of the present invention to provide an optical recording medium manufacturing method that can produce a good optical recording medium as a result.

[Means to solve the problem]

An optical recording medium manufacturing method according to the present invention includes a step of recording information on a recording master using modulated light from a light modulator equipped with an electro-optic modulation element. The device is characterized in that it has a monitor that shows the modulated light, and maintains the extinction ratio of the modulated light from the optical modulator in the best state based on the signal peak value of the monitor.

[Effect]

In the optical recording medium manufacturing method of the present invention, a part of the modulated light from the optical modulator is displayed on a monitor, and the extinction ratio of the modulated light is maintained in the best state according to the peak value displayed on the monitor. do. In this way, even if the duty of the signal waveform to be recorded changes, the extinction ratio is always maintained at its best, and laser cutting is performed under optimal recording conditions.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on drawings showing embodiments thereof. Of all the steps in the method for manufacturing an optical recording medium, only the bias voltage control in the laser cutting step, which is the gist of the present invention, will be explained here, and the other steps are the same as the conventional method, so they will not be explained here. The explanation will be omitted.

FIG. 1 is a block diagram for explaining the concept of the optical recording medium manufacturing method according to the present invention, and reference numeral 1.2 in the figure indicates the light receiving elements 46 and 47 in FIG. 7 described above. Peak hold circuits 3 and 4 are connected to each of the light receiving elements 1 and 2, respectively, for holding the peak value of each of the light receiving elements 1.2. A comparison control circuit 5 is connected to both peak hold circuits 3.4 for comparing the DC outputs from both peak hold circuits 3.4 and outputting the difference signal to a bias voltage control circuit 6. The bias voltage control circuit 6 controls the bias voltage applied to the optical modulator 7 (Pockels cell 41) so that the difference signal from the comparison control circuit 5 becomes O.

Next, the operation will be explained.

In the configuration shown in FIG.
L) receives light and performs photoelectric conversion, and the light receiving element 47 (2) receives light reflected by the half mirror 45 of the light transmitted through the polarizer 43 and performs photoelectric conversion. The signal output in the form of a rectangular wave from both light receiving elements 1.2 is transmitted to the corresponding peak hold circuits 3 and 4.
are input respectively.

Both peak hold circuits 3 and 4 hold the peak values of these rectangular waves, and the peak values are input to a comparison control circuit 5. The comparison control circuit 5 compares the peak values of both systems, and the difference signal is input to the bias voltage control circuit 6. Based on this difference signal, the bias voltage control circuit 6 determines the control amount of the bias voltage to be applied to the optical modulator 7 so that the difference between the peak values of both systems becomes 0, and the control amount is determined according to this control amount. Bias voltage is controlled.

In the present invention, the bias voltage is controlled by the peak value of the output of the light receiving element 1.2, and the peak value does not change even if the duty of the signal for laser cutting is changed continuously. If the bias voltage applied to the device 7 is accurately controlled, the extinction ratio of the modulated light is always maintained at its best.

Figure 2 shows the waveform of modulated light in the present invention monitored by an optical sensor, Figure 2 (a) is a waveform diagram showing the case where the duty is fixed at 1 = 1, Figure 2 (b) is a waveform diagram showing a case where the duty is changed. Even when the duty is changed, the extinction ratio of the waveform remains unchanged compared to when the duty is fixed.

〔Effect of the invention〕

As detailed above, in the optical recording medium manufacturing method of the present invention, the bias voltage is controlled based on the peak value of the monitor so that the extinction ratio of the output light of the optical modulator is in the best state. Even if the duty of the signal for performing the laser cutting changes, laser cutting can be performed while maintaining the extinction ratio in the best condition without deterioration.

As a result, the present invention exhibits excellent effects such as being able to manufacture a high quality optical recording medium.

[Brief explanation of the drawing]

Fig. 1 is a block diagram for explaining the concept of the optical recording medium manufacturing method according to the present invention, Fig. 2 is a waveform diagram of modulated light monitored by an optical sensor, and Fig. 3 is a manufacturing method of the optical recording medium. FIG. 4 is a block diagram showing the process, FIG. 4 is a schematic diagram for explaining the operating principle of the optical modulator, FIGS. 5 and 6 are graphs showing the relationship between the applied voltage of the optical modulator and the modulated light output, and FIG. Figure 7 is a schematic diagram for explaining the principle of controlling the bias voltage of an optical modulator. 2... Light receiving element 3, 4... Peak hold circuit 5... Comparison control circuit 6... Bias voltage control circuit 7... Optical modulator 41... Pockels cell
43...Polarizer patent, granted Applicant: Sanyo Electric Co., Ltd. Agent Patent attorney: Noboru Kono

Claims (1)

[Claims] 1. In an optical recording medium manufacturing method comprising a step of recording information on a recording master using modulated light from an optical modulator equipped with an electro-optic modulator, the optical modulator has a monitor that shows the modulated light. Then, based on the signal peak value of the monitor,
A method for manufacturing an optical recording medium, characterized in that the extinction ratio of modulated light from the optical modulator is maintained in the best state.