JPS61117740A - Optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To detect the track signal or information and thereby decrease the noise due to the dark current by receiving <=80% reflecting luminous flux from the recording medium by a photodetecting element as omitting both end-parts in the direction of track among the reflecting luminous flux from a recording medium. CONSTITUTION:The laser beam from a semiconductor laser 1 is made parallel by a coupling lens 2. The beam passes through a polarizing beam splitter 3 and a 1/4-wavelength plate 4, and further is made the specific spot by an objective lens 5, and focuses on the optical information recording medium 6. The reflected light from the recording medium 6 is changed of its plane of polarization by the wavelength plate 4, is separated from the incidence light by a prism 3, is focussed by a condenser lens 7, and is supplied to a photodetecting element 18 in place of the conventional photodetecting elements 8 and 9. This photodetecting element 18 for detecting the track signal or information signal is halved by the line parallel with the direction of track T. The <=80% of the reflected luminous flux 10 omitting the parts of both ends along the line parallel with the direction T, is received by photodetecting parts 18C and 18D. Accordingly, only the part of strong intensity of light is received to decrease the noise from the dark current.

Description

[Detailed Description of the Invention] (Technical Field) The present invention relates to an optical information recording and reproducing device,
In particular, it relates to the detection of track signals or information signals in optical pickup systems.

(Prior art) In the optical pickup optical system of an optical information recording/reproducing device,
In order to correctly detect the information signal recorded on the information signal recording medium, a track signal and a focus signal are detected to perform track servo and focus servo. As a method for detecting a track signal and a focus signal, a method called the Knifezi method as shown in FIG. 3 is known. In FIG. 3, the laser light emitted from the semiconductor laser 1 becomes parallel light at the coupling lens 2,
The light passes through a polarizing beam splitter 3 and further passes through a quarter-wave plate 4, and is converged onto an optical disk 6 by an objective lens 5 as a spot light with a diameter of about 1 μm. After passing through the objective lens 5, the reflected light from the optical disk 6 has its polarization plane changed by the quarter-wave plate 4, and is separated from the incident light by the polarization beam subrifter 3.
The light is converged by a condenser lens 7.

Approximately half of this convergent light enters the first light receiving element 8, and the remaining light flux enters the second light receiving element 9 placed at the convergence position of the light flux. As shown in FIG. 4, the first light-receiving element 8 is arranged so that the cross section of the light beam 10 cuts approximately in half at the edge thereof, and the first light-receiving element 8 is arranged along a line in the T direction, which is the track direction of the optical disc 6. It is divided into two light receiving sections C1D along the line. On the other hand, the second light receiving element 9 is divided into two light receiving parts A and B along a line parallel to the edge of the first light receiving element 8 which divides the luminous flux 10 into two.

Next, focus signal detection in the above conventional example will be explained. Figure 5 shows the principle of focus detection.
The light-receiving element 8 has a knife effect that blocks half of the reflected light from the recording medium, and when in focus, the image point P of the remaining half of the reflected light beam is focused on the second light-receiving element as shown in FIG. 5(a). 9
The outputs of the light receiving section A and the light receiving section B are adjusted to be equal. Now, assuming that the distance between the objective lens 5 and the recording medium 6 has become larger, as shown in FIG. 5(b)
As shown in FIG.
The light is incident unevenly on the light receiving part B of the light receiving element 9, and the output of the light receiving part B becomes larger than the output of the light receiving part A. On the other hand, if the distance between the objective lens 5 and the recording medium 6 is too close, the reflected light beam from the recording medium 6 will be reflected by the light receiving part of the second light receiving element 9, as shown in FIG. 5(C). The light is incident on the light receiving part A biasedly, and the output to the light receiving part becomes larger than the output of the light receiving part B. Therefore, by comparing the outputs of both light receiving sections A and H, it is possible to judge the in-focus state, and by controlling the position of the objective lens 5 so that the outputs of light receiving sections A and B are equal, it is possible to always obtain an appropriate state of focus. A focused state can be obtained.

Next, track signal detection will be explained. When the laser beam spot is on a predetermined track, the recording medium 6
The light flux 10 from Adjust to. Now, if the laser beam spot deviates from the predetermined track, as shown in Fig. 6(b), the output of one of the light receiving sections C and D will be larger than the output of the other due to the track deviation. Become. Therefore, if the objective lens 5 is controlled in the track direction so that the outputs of the light receiving portions CSD are equalized, it is possible to always maintain a proper track position. Note that the first light-receiving pointer 8 needs to be placed at a location other than the focal point. An information signal can be obtained by summing the output signals of both light receiving sections C and D of the first light receiving element 8.

By the way, the distribution of the intensity of light within the reflected light beam 10 is not uniform, and the peripheral portion of the cross section of the reflected light beam IO is weak.

Therefore, if the change in the track detection signal by the light receiving element 8 is observed while moving the light receiving element 8 in the direction T parallel to the track so as to cut the light beam 10 with its edge, the result will be as shown in FIG. In FIG. 2, "light receiving rate" refers to the proportion of the reflected light flux 10 that is received by the light receiving element 8. Light receiving rate 0% means that when the light flux 10 is not received at all by the light receiving element 8, the light receiving rate is 100%. means that all of the light beam 10 is received by the light receiving element 8. As is clear from FIG. 2, in the range of the light receiving rate from 0% to 20% and from 80% to 100%, the change in the track detection signal with respect to the change in the light receiving rate is small. This means that the light beams at both ends in the direction T parallel to the direction T have little influence on the track detection signal.

However, according to the conventional example, as is clear from FIG. 4, the light-receiving element 8 receives much of the end portion of the light beam 10 that has less influence on the track detection signal.
The light receiving state is inefficient.

On the other hand, as the light-receiving surface of a light-receiving element becomes larger, noise due to dark current increases in proportion to this, and responsiveness also decreases.

Therefore, it is desirable that the light-receiving surface of the light-receiving element be as small as possible. However, according to the above-mentioned conventional technology, the light-receiving surface of the light-receiving element 8 needs to be able to receive light up to the end of the reflected light beam 10, so the light-receiving surface becomes large. . Moreover, since the cross section of the reflected light beam 10 is circular, many surfaces of the light receiving element 8 are not irradiated with the reflected light beam lO. Therefore, there is a lot of noise due to the dark current of the light receiving element, and the response is not good.

(Objective) The object of the present invention is to make it possible to efficiently detect track signals or information signals, thereby making it possible to reduce the size of the light-receiving element that detects these signals.
Accordingly, it is an object of the present invention to provide an optical information recording/reproducing device which makes it possible to reduce noise due to dark current of a light receiving element and to improve responsiveness of the light receiving element.

(Structure) The optical information recording and reproducing apparatus of the present invention focuses a laser beam as a minute spot on an information signal recording medium using an objective lens, and collects a reflected light beam from the recording medium excluding both ends in the track direction. 80% or less of the light flux is received by a light receiving element to detect at least one of a track signal and an information signal.

FIG. 1 shows an embodiment of the present invention, and shows the relationship between a light receiving element for detecting a track signal or information signal and a reflected light beam. The detection light-receiving element 18 has light-receiving parts 18C and 180 divided into two by a line parallel to the track direction T, and the reflected light beam 1 is
0, except for both ends along a line parallel to the track direction T (80% or less of the reflected light flux is received).

The light receiving element 18 replaces the first light receiving element 8 of the conventional example, and the other configurations may be the same as those of the conventional example.

The remaining light beam 11 that is not received by the light receiving element 18 out of the reflected light beam 10 is received by the second light receiving element 9, as in the conventional example shown in FIG. 3, and thereby a focusing signal can be detected.

In this way, in the above-mentioned light-receiving element, the light flux at both ends of the track direction T out of the reflected light flux 1° is not received, and the light is focused on the part where the light is strong. Even if the light-receiving surface of the light-receiving element 18 is small, it is possible to efficiently receive light. Therefore, it is possible to reduce noise due to dark current, and it is also possible to improve responsiveness.

(Effects of the Invention) According to the present invention, a light receiving element receives 80% or less of the reflected light flux from the recording medium excluding both ends in the track direction to detect a track signal or an information signal. Therefore, the light-receiving element receives light mainly near the center of the reflected light flux, improving light-receiving efficiency, and making it possible to make the light-receiving element smaller by that amount.Therefore, there is less noise caused by light flowing in the dark. , it is possible to provide an optical FK information recording and reproducing device with good responsiveness.

[Brief explanation of drawings]

Figure 581 shows an embodiment of the present invention, and is a front view showing the relationship between the light receiving element and the reflected light flux, Figure 2 is a diagram showing the relationship between the light receiving rate of the light receiving element and the track detection signal, and Figure 3. is an optical layout diagram showing an example of a conventional optical information recording/reproducing device;
FIG. 4 is a front view showing the relationship between the light-receiving element and the reflected light flux in the conventional example, FIG. FIG. 3 is an explanatory diagram showing the principle of detecting a track signal. 5... Objective lens, 6... Information signal recording medium,
10... Reflected light flux, 18... Light receiving element. 2 mouths lost + (%)

Claims (1)

[Claims] The laser beam is focused as a minute spot on the information signal recording medium by an objective lens, and 80% of the reflected light flux from the recording medium excluding both ends in the track direction is
An optical information recording/reproducing apparatus characterized in that a light receiving element receives the following luminous flux to detect at least one of a track signal and an information signal.