JP2000057591A - Information recording/reproducing device and its stray beam component correction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate an effect of a stray beam by dividing outputs of an operation means calculating electric outputs of plural photoelectric conversion means with a total output of plural photoelectric conversion means, and normalizing the result and adding a fixed correction value to the result. SOLUTION: An automatic gain control means divides the outputs of the operation means calculating the electric outputs of plural photoelectric conversion means with the total output of plural photoelectric conversion means to normalize the result. The output of an AGC: 29 being a normalized tracking error signal is inputted to an adder 34 together with an offset amount equivalent to that of the stray generated by an offset correction circuit so as to be canceled. Even though optical offset correction by a reflection means isn't performed, and even when a reflection beam amount and an emission beam quantity of a semiconductor laser are changed, since the offset by the stray beams 19, 20 is also normalized, and the adder 34 is operated while always placing the operation center of the tracking signal of the output of the adder 34 on electric ground, the effect of the stray beams is eliminated practically.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording / reproducing apparatus for recording / reproducing an information signal by irradiating a recording medium with a radiation light source, and more particularly to an information recording / reproducing apparatus for improving the stability of a servo signal and its stray light. It relates to a component correction method.

[0002]

2. Description of the Related Art When radiated light is used for recording and reproduction, stray light generated by scattering, refraction, reflection and the like of the radiated light inevitably accompanies. For example, in an optical disk, an optical element such as a beam splitter is used as a light splitting unit, and stray light is generated due to reflection on an end surface of the beam splitter. When this stray light is incident on the photoelectric conversion means for detecting radiation, a bias is generated in the electric output, which causes deterioration of signal characteristics. For this reason, conventionally, a method of correcting the bias output by the light by adjusting a photoelectric conversion element or the like to maintain the signal quality has been adopted. Hereinafter, a method generally used conventionally will be described with reference to the drawings.

FIG. 8 schematically shows a method for correcting bias light such as stray light which has been conventionally used. Here, an example of an optical disk device will be described for easy understanding. A light beam emitted from a radiation light source 41 such as a semiconductor laser passes through a beam splitter 42, is focused on an optical disk 40 by an objective lens 43, and is modulated and reflected by an information signal. The signal light beam 46 reflected by the optical disk 40 is reflected by the beam splitter 42 and enters a plurality of photoelectric conversion units 44 and 45. There are many known methods of using a plurality of photoelectric conversion elements to obtain a servo operation and a servo error signal for use in correcting off-track due to defocus or eccentricity due to surface deflection of an optical disk, and a description thereof will be omitted here. The plurality of photoelectric conversion units are basically two photoelectric conversion elements I44 and II45.
Since the operation is the same even if the number increases, the case of two photoelectric conversion elements 44 and 45 will be described below. End surface I47, end surface II4 of beam splitter 42
8, stray light I49 and stray light II50 reflected from each of
Is generally incident on one of the two photoelectric conversion elements in a biased manner due to insufficient accuracy of the reflection end face or insufficient optical axis adjustment accuracy. In extreme cases, for example, a large amount of light enters the photoelectric conversion element I44 and a small amount of light enters the photoelectric conversion element II45 Incident. At this time, the photoelectric conversion element I44
Even if the signal light beams 46 incident on the photoelectric conversion element II 45 are equal, the photocurrents flowing out of the photoelectric conversion element I 44 and the photoelectric conversion element II 45 are at different levels. In the servo of the optical disk, the servo operation is performed so as to make the difference 51 of the photocurrents equal, so that an offset occurs in the servo operation and causes a malfunction. Therefore, conventionally, in order to correct such a malfunction, the output of the photoelectric conversion element I44 and the output of the photoelectric conversion element II45 are adjusted so as to be equal to each other to compensate for the occurrence of the offset due to the stray light. Thus, when the reflectance of the information carrier is constant, a difference in photocurrent can be corrected and a normal servo operation can be performed. When the radiation light output is changed for recording and reproduction, in order to keep the loop gain of the servo loop constant, an AGC (AUTO GAIN) in which the photocurrent difference 51 is kept constant by the total amount of light incident on the photoelectric conversion element. CONTOROL
E) and normal servo operation can be performed. These servo technologies are almost established and will not be described in detail.

FIG. 9 specifically shows a state of a light beam on the photoelectric conversion elements I and II in FIG. In order to adjust the differential output of the photoelectric conversion element I44 and the photoelectric conversion element II45 to zero, the signal beam 46 is offset in the reverse direction of the photoelectric conversion element where stray light enters. Therefore, for example, the level of the tracking error signal obtained from the differential output of FIG. 9 decreases. The signal light beam 46 intensity and stray light I49, stray light II
If the rate of change of the 50 intensity is different, the servo error increases. This principle is the same in the case of a focusing servo for correcting a focus error. However, since the principle is the same, a detailed description of the focusing servo will be omitted.

[0005]

In the conventional method, when the reflectance of the information carrier or the transmittance of the light beam path changes, only the intensity of the signal light beam 46 on the photoelectric conversion element changes, and the stray light I49, Since the level of the stray light II50 does not change, the correction by the adjustment of the photoelectric conversion element is overcorrected or undercorrected, and as a result, a malfunction occurs in the servo operation.

In view of the above problems, the present invention does not correct the offset due to the stray light as in the prior art by adjusting the photoelectric conversion element, but instead adjusts the electrical offset by setting the output of the photoelectric conversion element to a constant level. It is an object of the present invention to provide an information recording / reproducing apparatus capable of performing a stable servo operation without malfunction by performing the correction of the above, and a method of correcting the stray light component thereof.

[0007]

In order to solve this problem, the present invention comprises a plurality of photoelectric conversion means for receiving a signal light beam reflected on an information carrier and branched by a light beam branching means, and a plurality of photoelectric conversion means. Calculating means for calculating the electrical output of the means, automatic gain adjusting means for dividing the output of the arithmetic means by the total output of the plurality of photoelectric conversion means for normalization, and adding a fixed correction value to the output of the automatic gain adjusting means And an offset correcting means.

Accordingly, stray light generated due to insufficient processing accuracy of the end face of the beam splitter or insufficient optical axis accuracy is determined by the optical system. Therefore, even if the reflectance of the information carrier changes or the transmittance of the light beam path changes, the stray light on the photoelectric conversion element changes. Even if the intensity of the signal light beam changes, the stray light does not change, and even if the amount of reflected light or the amount of emitted laser light changes, the output of the automatic gain adjustment means does not change in amplitude. Does not change, and since the offset corresponding to the stray light is corrected by adding a fixed correction value, it is not necessary to substantially consider the influence of the stray light.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is directed to a radiation light source, a light beam branching means for transmitting or reflecting a light beam emitted from the radiation light source, and a first light beam passing through the light beam branching means. Light beam condensing means for receiving the light beam on the information carrier, a plurality of photoelectric conversion means for receiving the signal light beam reflected on the information carrier and branched by the light beam branching means, and a plurality of photoelectric conversion means Calculating means for calculating the electric output of the automatic gain adjusting means, dividing the output of the calculating means by the total output of the plurality of photoelectric conversion means for normalization, and an offset for adding a fixed correction value to the output of the automatic gain adjusting means. In particular, the offset correction means sets a constant offset correction value in the initial adjustment, and holds and outputs the offset correction circuit;
An adder for adding the output of the offset correction circuit and the output of the automatic gain adjustment means is provided.

According to a third aspect of the present invention, there is provided a radiation light source, a light beam branching means for transmitting or reflecting a light beam emitted from the radiation light source, and a first light beam passing through the light beam branching means. A light beam focusing means for focusing on the information carrier, a plurality of photoelectric conversion means for receiving the signal light beam reflected on the information carrier and branched by the light beam branching means, and calculating an electric output of the plurality of photoelectric conversion means An information recording apparatus comprising: an arithmetic unit for performing an operation; an automatic gain adjusting unit for normalizing the output of the arithmetic unit by dividing the output of the arithmetic unit by a total output; and an offset correcting unit for applying an offset correction to the output of the automatic gain adjusting unit. A method of correcting a stray light component of a reproducing apparatus, wherein in an initial adjustment, first, a position of a photoelectric conversion unit is adjusted so that a center of a plurality of photoelectric conversion units is irradiated with a center of a signal light beam. The offset value of the output of the adjusting means is obtained, a correction value having the same polarity as that of the offset value and having the same amount is set and held by the offset correcting means, and thereafter, the correction value is output to the output of the automatic gain adjusting means by the offset correcting means. Is constantly added to the information recording / reproducing apparatus.

According to the above configuration and method, stray light generated due to insufficient processing accuracy of the end surface of the beam splitter or optical axis accuracy is determined by the optical system. Therefore, even if the reflectance of the information carrier changes or the transmittance of the light beam path changes, the photoelectric conversion may occur. Even if the intensity of the signal light beam on the conversion element changes, the stray light does not change,
In addition, since the amplitude of the output of the automatic gain adjustment means does not change even if the amount of reflected light or the amount of emitted laser light changes, the offset amount due to stray light does not change. Since the correction is performed by the initial adjustment, it is not necessary to substantially consider the influence of stray light.

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings.

(Description of Reference Example) FIG. 1 shows a reference example of the present invention. The light beam emitted from the semiconductor laser 11 passes through the beam splitter 12 and enters the objective lens 13. The light beam emitted from the objective lens is condensed on the optical disk 10 and reflected. The signal light beam 16 reflected by the optical disk is reflected by the beam splitter 12, and is split into two photoelectric conversion elements I14 and photoelectric conversion elements.
Each of them is incident on II15. An automatic gain adjustment (AGC) for taking the differential output of the output of the photoelectric conversion element I14 and the photoelectric conversion element II15 by the differential circuit 27 and normalizing the change in the amount of reflected light.
By driving the objective lens 13 with a signal that has passed through the Automatic Gain Control (29), it is possible to perform tracking servo for following the information track of the optical disc. The above-mentioned AGC can be realized by performing an operation such as division by an addition circuit 28 which takes the sum of the reflected light amounts.

The stray light I19 and the stray light II20 reflected from the end face I17 and the end face II18 of the beam splitter 12, respectively.
Is incident on one of the two photoelectric conversion elements in an extreme case due to insufficient processing accuracy of the reflecting end face and insufficient optical axis adjustment accuracy.
For example, many incident on the photoelectric conversion element I14 and the photoelectric conversion element II
15 slightly. On the other hand, the light beam 23 first reflected by the beam splitter 12 is adjusted so that it is reflected by the reflecting means 24 which is movable at least one-dimensionally, passes through the beam splitter 12, and is largely irradiated on the photoelectric conversion element II15 side. The photoelectric conversion element I14 and the photoelectric conversion element II
The differential output to the output 15 is zero in the absence of the information carrier. By correcting stray light with light in this manner, the offset level of the differential output of the photoelectric conversion element does not change even when the light amount changes during recording and reproduction.

Next, a second embodiment of the present invention will be described with reference to FIG. Since the light beam 23 first reflected by the beam splitter 12 has a light output proportional to the light beam emitted from the front end face of the semiconductor laser 11, the output of the second photoelectric conversion element 25 is fed back to the semiconductor laser to produce a semiconductor light. This can be used for controlling the laser output light to be constant. The reflectance of the second photoelectric conversion element 25 and the reflectance of the resin surface 26 for protecting the photoelectric conversion element and the reflectance of the second photoelectric conversion element 25 are equal to or greater than the reflectance of the end face of the prism. Conventionally, since it becomes a major factor, conventionally, a fixed angle is fixed to the optical axis so that the reflected light does not enter the photoelectric conversion element for signal detection so that the reflected light does not enter the photoelectric conversion elements I and II. Has been installed. In the present embodiment, stray light is corrected by making the angle variable and adjusting the angle. 1 and 2 show only the center of the light beam.
Actually, the signal light, the stray light, and the light beam have a spread, and the center of the light beam is incident on one of the photoelectric conversion elements, and is partially incident on the other photoelectric conversion element. When the center position is changed, the offset of the differential output of both photoelectric elements can change continuously. Therefore, the second photoelectric conversion element 25 is configured to be rotatable so that the light beam 23 can move in a direction perpendicular to the dividing line of the photoelectric conversion elements I14 and II15, so that the photoelectric conversion element I14 and the photoelectric conversion element II1 can be rotated.
The offset output due to the influence of stray light can be removed from the differential output of No. 5 and servo malfunction can be prevented.

FIG. 3 is a diagram showing a case where the method for removing the effect of stray light according to the present embodiment is applied to detection of a tracking error signal. Compared with FIG. 9 which is a conventional method, the influence of the stray light I19 and the stray light II20 is canceled by the light beam 23, so that the signal light beam 16 can be accurately positioned at the center of both photoelectric conversion elements. That is, the servo error does not increase due to the change of the signal light beam 16.

FIG. 4 shows how a tracking error signal is detected according to this reference example. Electrical ground 3
When the servo operation is performed on the tracking error signal 31 adjusted so that the plus and minus levels are symmetrical with respect to 0, the servo is drawn into the track center 32.
When the reflectivity of the optical disk or the like changes and the light amount of the signal light beam 16 decreases, the tracking error signal 33 decreases. However, since the position of the track center 32 does not change, no servo error occurs.

In the reference example of the present invention, the output of the second photoelectric conversion element 25 is given an appropriate gain and added or subtracted from the output of the photoelectric conversion element II instead of making the signal light beam 23 incident on the photoelectric conversion element II. There is a way to make it happen. As an actual configuration, a configuration in which resistance is added with an appropriate gain to a terminal to which the output of the photoelectric conversion element II of the differential circuit 27 of FIG. There is a method of separately providing a circuit for addition at the subsequent stage of the dynamic circuit. In this case, the second photoelectric conversion element 25 and its resin surface 26
The angle of reflection is set so that the reflected beam does not enter the photoelectric conversion element I14 and the photoelectric conversion element II15 unlike the first embodiment. Also in the case of this embodiment, since the influence of stray light can be removed in advance, the tracking error signal 33 becomes smaller when the reflectivity of the optical disk or the like changes and the amount of the signal light beam 16 decreases, but the position of the track center 32 changes. Therefore, no servo error occurs.

(Explanation of Embodiment) As an embodiment of the present invention,
A method of electrically correcting without using the above-described reflecting means 24 or the like will be described.

FIG. 5 shows a block diagram of an embodiment of the present invention. In this figure, the components from the semiconductor laser 11 to the AGC 29 are the same as those shown in FIG. 1, wherein 35 is an adder and 36 is an offset correction circuit. The offset correction circuit generates an amount of offset corresponding to stray light in the output of the AGC 29, which is the normalized tracking error signal, and cancels the offset by the adder 34.
Even if the reflected light amount or the emitted light amount of the semiconductor laser is changed without performing the optical offset correction by the reflection means 24, the offset due to the stray light I and II is also normalized. Since the operation center of the tracking error signal can always be operated at the electric ground 30, there is substantially no need to consider the influence of stray light.

The state of the above-mentioned signals will be described with reference to FIGS. FIG. 6 is a diagram when applied to detection of a tracking error signal as in FIG. FIG. 9 showing a conventional method
In comparison with the above, the effects of the stray light I19 and the stray light II20 are the same, but the center of the signal beam 16 can be accurately positioned at the center of both photoelectric conversion elements in the direction of arrow AA by using the following method. It has been adjusted to be able to. In FIG. 7, the outputs of the photoelectric conversion elements I and II are shown at 16e and 15e.
When the Lissajous waveforms of the AC components 16e and 15e are drawn using an oscilloscope or the like, the result is as shown in FIG.
Here, by moving the photoelectric conversion element in the direction of arrow AA in FIG. 6 and adjusting the AC components so that the AC components have the same amplitude and opposite polarities, the waveform of Re becomes substantially linear in the direction of -45 degrees. At this time, as shown in FIG. 6, the center position of the signal beam 16 is accurately located at the center of both photoelectric conversion elements.
The output of the AGC at this time is shown by Te in FIG. Here, since the tracking output 37 is normalized, the amplitude does not change even when the amount of reflected light or the amount of emission of the semiconductor laser changes, and the offset due to stray light does not change as indicated by 36. Therefore, if an offset correction of a fixed amount is initially performed electrically, the operation center of the tracking error signal output from the adder 34 can always be operated at the electric ground 30. The effect of can be neglected.

Although the above embodiment has been described using an optical disk device, application to a recording / reproducing device such as an optical card or an optical tape which is likely to be affected by stray light is within the scope of the present invention.

In the above embodiment, the tracking servo system has been described. However, the principle is the same in the case of the focusing servo system operation, and the method of the present invention can be applied.

[0024]

As described above, according to the present invention, the offset amount due to stray light caused by insufficient end face processing accuracy and optical axis accuracy of the beam splitter does not change, and the offset corresponding to the stray light is corrected by the initial adjustment. Therefore, there is an excellent effect that it is not necessary to substantially consider the influence of stray light.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a configuration of a reference example of the present invention.

FIG. 2 is a configuration diagram showing a second reference example of the present invention.

FIG. 3 is a layout diagram of a light beam on a photoelectric conversion element.

FIG. 4 is a diagram showing an example of a tracking error signal in the embodiment.

FIG. 5 is a configuration diagram of an embodiment of the present invention.

FIG. 6 is a layout view of a light beam on a photoelectric conversion element according to the present invention.

FIG. 7 is a diagram showing an example of a tracking error signal according to the present invention.

FIG. 8 is a diagram for explaining a servo signal detection method according to a conventional method.

FIG. 9 is an arrangement diagram of a light beam on a photoelectric conversion element according to a conventional method.

[Explanation of symbols]

 Reference Signs List 11 semiconductor laser 12 beam splitter 14, 15 photoelectric conversion element 16 signal light beam 19, 20 stray light 23 light beam 25 second photoelectric conversion element 26 resin surface of second photoelectric conversion element 27 differential circuit 28 addition circuit 29 AGC 34 Adder 35 Offset correction circuit 42 Beam splitter 47, 48 Beam splitter end face 51 Photocurrent

Claims (3)

[Claims] 1. A radiation light source, a light beam branching means for transmitting or reflecting a light beam emitted from the radiation light source, and a first light beam passing through the light beam branching means being focused on an information carrier. Light beam focusing means, a plurality of photoelectric conversion means for receiving a signal light beam reflected on the information carrier and branched by the light beam branching means, and an arithmetic means for calculating an electrical output of the plurality of photoelectric conversion means; Automatic gain adjustment means for dividing the output of the arithmetic means by the total output of the plurality of photoelectric conversion means for normalization, and offset correction means for adding a fixed correction value to the output of the automatic gain adjustment means. An information recording / reproducing apparatus characterized by the above-mentioned. 2. An offset correction means for setting a constant offset correction value in an initial adjustment, holding and outputting the offset correction value, and adding an output of the offset correction circuit and an output of the automatic gain adjustment means. 2. The information recording / reproducing apparatus according to claim 1, further comprising an adder. 3. A radiation light source, a light beam branching means for transmitting or reflecting a light beam emitted from the radiation light source, and a first light beam passing through the light beam branching means being focused on an information carrier. Light beam focusing means, a plurality of photoelectric conversion means for receiving a signal light beam reflected on the information carrier and branched by the light beam branching means, and an arithmetic means for calculating an electrical output of the plurality of photoelectric conversion means; An information recording / reproducing apparatus comprising: an automatic gain adjusting means for dividing an output of the arithmetic means by a total output of the plurality of photoelectric conversion means for normalization; and an offset correcting means for applying an offset correction to an output of the automatic gain adjusting means. A stray light component correction method for a device,
In the initial adjustment, first, the position of the photoelectric conversion unit is adjusted so that the center of the signal light beam irradiates the center of the plurality of photoelectric conversion units, and then the offset value of the output of the automatic gain adjustment unit is obtained. The offset correction means sets a correction value having the same polarity as the value and the same amount and holds the correction value, and thereafter, the offset correction means always adds the correction value to the output of the automatic gain adjustment means. A method for correcting a stray light component of a recording / reproducing apparatus.