JP2664451B2 - Optical recording method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording method for reading recorded information using a laser beam, such as a video disk, a compact disk, and the like. In which information is recorded on a recording master using the modulated light.

[Conventional technology]

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

First, a photoresist is applied on a glass plate as a substrate to form a recording master, and by controlling on / off of irradiation of laser light according to a recording signal, the photoresist at a desired position on the recording master is exposed to light and a signal is generated. Record. Next, the photoresist is removed in the current process to form a desired concavo-convex pattern. Next, the formed concavo-convex pattern is transferred to a metal master by electroforming to produce a stamper. Finally, the produced stamper is duplicated, and a reflection film and a recording film are formed on the signal surface to manufacture an optical disk.

In the above-described manufacturing process, on / off control of laser light irradiation in a process of exposing a photoresist, that is, a laser cutting process, is performed by an optical modulator. As such an optical modulator, an electro-optic optical modulator (EO modulator) utilizing a change in the refractive index of a crystal when a voltage is applied, and an acousto-optic utilizing an interaction between light and ultrasonic waves. An optical modulator (AO modulator) is known.

FIG. 4 is a schematic view for explaining the principle of the electro-optic light modulator. The electro-optic light modulator usually includes KDP (crystal: KH ₂ PO ₄ ) and ADP (crystal: NH ₂ H ₂ PO ₄ ) Pockels cell etc.
41 are used. When a voltage is applied to such a Pockels cell 41, an anisotropy occurs in the refractive index of the crystal, and a phase difference occurs between the polarization component of light passing through the Pockels cell 41. And this phase difference is related to the magnitude of the applied voltage. Is incident linearly polarized wave L ₁ to the Pockels cell 41, is converted from a signal source 42 to the elliptically polarized light waves L ₂ corresponding to the voltage applied to the Pockels cell 41. The elliptically polarized light L ₂ is passed through the polarizer 43 to form an elliptical component (linearly polarized light L ₁
By extracting only the polarized light component in the direction perpendicular to the polarized light direction, light having an intensity corresponding to the applied voltage can be obtained. In the electro-optic light modulator, on / off of light irradiation on the glass substrate coated with the photoresist is controlled by setting an applied voltage of the signal source 42 based on a desired recording signal.

By the way, the crystal azimuth of the Pockels cell 41 and the polarizer 43
Is 45 °, the relationship between the amount of transmitted light I from the polarizer 43 and the applied voltage V is as shown in the following equation (1) (see FIG. 5).

I = I ₀ sin ² (α · V) (1) I ₀ : Incident light amount α: Constant Here, assuming that the applied voltage at which I = max (I ₀ ) is V _m ,
The above equation (1) becomes the following equation (2).

I = I ₀ sin ² (V / V _m ) (2) Therefore, by changing the applied voltage V in the range of 0 to V _m , the range of ₀ to I ₀ is obtained according to the characteristic of the square of sin. Can be obtained.

Then, in the electro-optic light modulator, an information signal such as video or audio is formed into an on / off signal of 1 or 0 by a predetermined method, and is changed to 1 → V _m , 0 → 0 to effectively use the laser light. In consideration of the above, laser cutting is performed by setting ON and OFF between I ₀ and I ₀ so that the extinction ratio (the ratio between the maximum transmitted light amount and the minimum transmitted light amount) can be maximized.

However, in an actual electro-optic light modulator, as shown in FIG. 6, the minimum value of the light output is not 0 but I _min , and the extinction ratio in this case is I ₀ / I _min .

When the applied voltage is 0, the light output does not become the minimum value (I _min ) due to the birefringence inherent in the crystal of the Pockels cell 41. Therefore, the light output is minimized (I _min )
Requires a constant bias voltage V _B ,
To obtain an extinction ratio I ₀ / I _min is necessary to vary the applied voltage within a range of V _B ~V _mo (see Figure 6). In other words, the V _B is applied as a bias voltage, as an operating reference point of this voltage, by applying a voltage in the range of _{V I (= V mo -V B} ) from 0, the modulated light I _min ~I ₀ Obtainable.

Furthermore, the phase of a polarization component of an element (Pockels cell) used in an electro-optic light modulator also changes with temperature. Accordingly, the operation reference point may fluctuate due to a change in the ambient temperature or a change in the temperature of the element due to a change in the intensity of the laser beam to be modulated, and a sufficient extinction ratio may not be obtained. Therefore always sufficient so the extinction ratio can be taken, it is necessary to change the bias voltage V _B according to this variation.

FIG. 7 is a schematic diagram showing the principle of a conventional method for controlling the bias voltage V _B. The reflected light and transmitted light of the polarizer 43 are received by the respective light receiving elements 46 and 47 via the half mirrors 44 and 45 having low reflectance, respectively, and the output after photoelectric conversion from each of the light receiving elements 46 and 47 is obtained. as will become constant, to control the bias voltage V _B. In the cutting process using laser light, I ₀ (1)
And since cutting at two values of I _min (0) it is common to be performed, the control of the bias voltage V _B at the control method as described above, the average value of the output of the light receiving elements 46 and 47 respectively It is performed based on. The words More specifically, by comparing the average value of the output from the light receiving element 46 and 47 respectively, always maintaining the best extinction ratio by changing the value of the bias voltage V _B as the difference therebetween is zero while, is performed light modulation by applying a modulation voltage of 0 to V _I.

Conventionally, by using an electro-optic light modulator having such a control function, the best extinction ratio is maintained without being affected by changes in the ambient temperature or changes in the incident intensity. In this state, laser cutting was possible.

[Problems to be solved by the invention]

However, in the method of controlling the bias voltage based on the average value of the outputs of both light receiving elements as described above, CAV (con
The extinction ratio of the optical modulator is maximized when the duty of the signal waveform for laser cutting is continuously changed like a disc or when the duty of the signal waveform is shifted from 1: 1. If the frequency of the cutting signal input to the optical modulator, which has been adjusted to make a significant change, greatly changes, the average value of the outputs of both light receiving elements will differ, and the operating reference point of the optical modulator will fluctuate. Therefore, there is a problem that the best extinction ratio cannot be maintained.

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

[Means for solving the problem]

The optical recording method according to the present invention is an optical recording method including a step of recording information on a recording master using modulated light from an optical modulator including an electro-optical modulator, wherein the optical modulator converts the modulated light to Characterized in that the extinction ratio of the modulated light from the optical modulator is maintained in the best condition based on the signal peak value of the monitor.

[Action]

According to the optical recording 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 an optimum state according to the peak value of the monitor display. Then, even when the duty of the signal waveform to be recorded changes, the extinction ratio is always maintained in the best state, and laser cutting is performed optimally under recording conditions.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings showing the embodiments. Here, of all the steps in the optical recording method, only the bias voltage control in the laser cutting step, which is the gist of the present invention, will be described, and the other steps are the same as the conventional method, and the description thereof will be omitted. .

FIG. 1 is a block diagram for explaining the concept of the optical recording method according to the present invention. In FIG. Peak hold circuits 3 and 4 that hold the peak values of the light receiving elements 1 and 2 are connected to the light receiving elements 1 and 2, respectively. The two peak hold circuits 3 and 4 are connected to a comparison control circuit 5 that compares the DC outputs from the two peak hold circuits 3 and 4 and outputs a difference signal to the bias voltage control circuit 6. And 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 zero.

 Next, the operation will be described.

In the configuration as shown in FIG. 7, the light reflected by the half mirror 44 of the light reflected by the polarizer 43 is transmitted to the light receiving element 46 (1).
The light receiving element 47 (2) receives and photoelectrically converts the light transmitted through the polarizer 43 and reflects the light reflected by the half mirror 45. The rectangular wave signal output from the light receiving elements 1 and 2 is input to the corresponding peak hold circuits 3 and 4, respectively. The peak values of these rectangular waves are held in both peak hold circuits 3 and 4, and the peak values are input to the comparison control circuit 5. The comparison control circuit 5 compares the peak values of both systems,
The difference signal is input to the bias voltage control circuit 6. Based on the difference signal, the bias voltage control circuit 6 determines the control amount of the bias voltage applied to the optical modulator 7 so that the difference between the peak values of the two systems becomes 0, and according to the control amount. The bias voltage is controlled.

In the present invention, the bias voltage is controlled by the peak values of the outputs of the light receiving elements 1 and 2, and the peak value does not change even if the duty of the signal for performing the laser cutting is continuously changed. When the control of the bias voltage to be applied is accurately performed, the extinction ratio of the modulated light is always maintained in the best state.

FIG. 2 shows a waveform of the modulated light according to the present invention monitored by an optical sensor. FIG. 2 (a) is a waveform diagram showing a case where the duty is fixed to 1: 1, and FIG. 2 (b). FIG. 7 is a waveform diagram showing a case where the duty is changed. Even when the duty is changed, the extinction ratio of the waveform does not change at all compared to the case where the duty is fixed.

〔The invention's effect〕

As described in detail above, in the optical recording 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 from the optical modulator is in the best state. Even when the duty changes, the laser cutting can be performed while maintaining the extinction ratio in the best state without deterioration.

As a result, the present invention has excellent effects, such as high-quality optical recording media can be manufactured.

[Brief description of the drawings]

FIG. 1 is a block diagram for explaining the concept of an optical recording method according to the present invention, FIG. 2 is a waveform diagram in which modulated light is monitored by an optical sensor, and FIG. 3 shows a manufacturing process of an optical recording medium. FIG. 4 is a block diagram, FIG. 4 is a schematic diagram for explaining the operation 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. FIG. 4 is a schematic diagram for explaining a control principle of a bias voltage of the optical modulator. 1,2 ... 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

Claims (1)

(57) [Claims] 1. A laser beam is modulated by an electro-optic modulation element based on recording information, and only a specific polarization component of the modulation beam is irradiated onto a recording master to optically record the laser beam. An optical recording method for monitoring the light amounts of the polarized light components, wherein a bias voltage applied to the electro-optical modulation element is controlled so that the peak values of the monitored light amounts become equal. .