JPH0312827A - Optical information reader - Google Patents

Abstract

PURPOSE:To reduce the influence of the surface inclination of a recording surface to be given on an information recording medium by respectively providing photodetectors different in focus position for reflected light from the recording surfaces, which are divided into more than three luminous fluxes and setting the total sum of signals which are obtained by applying current-voltage conversion to the output currents of respective photodetectors to be reproduction signals. CONSTITUTION:The photodetectors 9-11 different in the focus positions are respectively provided for reflected light from the recording surface, which are divided into >= three light fluxes. The total sum of the signals which are obtained by applying I/V-conversion 12 to the output currents from respective photodetectors 9-11 is set to be the reproduction signal. Thus, a focus depth at the time of detecting the reproduction signal is improved, and the influence of the information recording medium 5 owing to the surface inclination of the recording surface can be reduced, whereby an error rate at the time of reproduction owing to the influence of the surface inclination can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical information reading device for optical discs and the like.

[Conventional technology]

In recent years, optical information reading devices such as CDs, CD-ROMs, and optical video discs have been put into practical use.

FIG. 4(a) shows an example of the configuration of a conventional optical information reading device. In this optical information reading device, a light beam supplied from a light source 1 consisting of a semiconductor laser or the like is converted into a polarized beam. The light is focused on the recording surface of an information recording medium 5 such as an optical disk through an optical system consisting of a printer (PBS) 2, a λ/4 plate 3, and an objective lens 4, and the reflected light from the information recording medium 5 is reflected by the optical system and the objective lens 4. The light is received by a photodetector 20 via a cylindrical lens 6,
The output current from the photodetector 20, which changes according to the information signal recorded on the information recording medium 5, is converted into a voltage signal by a current-voltage converter (I/V converter) 21, and then converted into a voltage signal by an amplifier 22. It is configured to obtain a reproduced signal by amplifying the signal to a predetermined level.

Here, a feature of the conventional optical information reading device shown in FIG. 4(a) is that a focus error signal and the above-mentioned reproduction signal are simultaneously detected by one photodetector 20. That is, the photodetector 20 of the optical information reading device shown in FIG. 4(a) uses, for example, a 4-part light-receiving element having a light-receiving surface divided into four parts as shown in FIG. 4(b). In order to obtain a focus error signal F using the photodetector 20 consisting of the four-split light receiving element, the output from each split light-receiving surface of the photodetector 20 is divided into A and B as shown in FIG. 4(b).
,C.

As D, F = (A + C) - (B + D) It is determined by detecting the

Further, the reproduction signal W of the recorded information is determined by W=(A+B+C+D) and by detecting the sum of the outputs from all the divided light receiving surfaces.

[Problems to be Solved by the Invention] By the way, in order to obtain a focus error signal and a reproduction signal using one photodetector 20 as described above, the method shown in FIG.
As shown in I), press the information recording medium 5 or 3. Therefore, as shown in FIG. 6, the reproduced signal is
It decreases from o to vl.

In this way, in the optical information reading device having the configuration shown in Fig. 4, it takes time and effort to align the optical axis and adjust the position of the photodetector, and the focus error signal is offset due to the influence of the surface inclination of the information recording medium. There were problems such as voltage being generated and causing playback abnormalities.

The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to provide an optical information reading device that can reduce the influence of the surface inclination of the recording surface of an information recording medium and obtain a stable reproduction signal. purpose.

[Means to solve the problem]

In order to achieve the above object, the present invention focuses a light flux supplied from a light source onto an information recording medium via an optical system, and transmits reflected light from the recording surface of the information recording medium to a photodetector via the optical system. In an optical information reading device that obtains a reproduced signal by receiving light from the photodetector and converting the output current from the photodetector into a current-to-voltage, the photodetector 20 receives the reflected light by reducing the reflected light from the information recording medium. It is necessary to accurately focus the light on the center of the photodetector 20, and it is also necessary to align the position of the photodetector 20 on the optical axis with the focus position of the recording surface of the information recording medium 5. There is a problem that adjustment takes time and effort.

Furthermore, if a surface inclination or the like occurs on the recording surface of the information recording medium 5, the light condensing position on the light receiving surface of the photodetector 20 will shift from the center of the light receiving surface of the photodetector 20, and the offset voltage will increase. There is a problem that arises. That is, in the optical information reading device having the configuration shown in FIG. 4, even if the objective lens 4 is at the focused position, due to the influence of the surface inclination of the recording surface of the information recording medium 5, as shown in FIG. As shown in FIG. 2, the light condensing position on the light receiving surface of the photodetector 20 is shifted from the center, and an offset voltage is generated in the focus error signal. Therefore, in focus control, the objective lens 4 is moved so that the focus error signal F becomes 0, so the state of the light spot on the light receiving surface of the photodetector 20 is as shown in FIG.
The state II) changes to the state (m). That is, each beam is divided into three or more beams in a defocused state, a photodetector is provided for each divided beam, and the focus positions of the photodetectors with respect to the recording surface of the information recording medium are different from each other. They are arranged so as to form a point, and the output current from each photodetector is converted into a current to voltage, and the sum of the signals is used as a reproduction signal.

[For production]

In the optical information reading device according to the present invention, photodetectors with mutually different focus positions are provided for the reflected light from the recording surface that is divided into three or more beams, and the output current from each photodetector is converted into a current - By using the sum of the voltage-converted signals as the reproduced signal, the depth of focus when detecting the reproduced signal increases, and the influence of the surface inclination of the recording surface of the information recording medium can be reduced.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a general configuration diagram of an optical information reading device showing an embodiment of the present invention, in which reference numeral 1 is a light source made of a semiconductor laser or the like, reference numeral 2 is a polarizing beam splitter, and reference numeral 3 is a λ /4 plate, reference numeral 4 indicates an objective lens, reference numeral 5 indicates an information recording medium such as an optical disk, and reference numeral 6 indicates a cylindrical lens.Those with the same symbols as those shown in Fig. 4 are similar components. be.

Here, in the optical information reading device according to the present invention, the reflected light from the information recording medium 5 is divided into at least three beams using a half mirror 7.8, etc., and a photodetector 9 is used for each divided beam. .10.11 and each photodetector 9
．． 10.11 are arranged so that their focus positions with respect to the recording surface of the information recording medium 5 are different from each other, and the output current from each photodetector 9.10.11 is transferred to the I/V converter 12.
．． 13.14 is characterized in that the sum of the signals subjected to current-to-voltage conversion is amplified by an amplifier 15 to a signal of a predetermined level to produce a reproduced signal.

By the way, in the embodiment shown in FIG. 1, three photodetectors are used, and as described above, these three photodetectors 9, 10, and 11 are located close to each other on the recording surface of the information recording medium 5. The focus error signal is detected by a photodetector (n) 10 whose optical path length to the information recording medium is at an intermediate distance, and focus control is performed. There is. and,
With this photodetector (n) 10 as the center, a photodetector (■) 9 and a photodetector are placed on the side nearer and farther away from the focal position, that is, the side where the optical path length to the information recording medium is nearer and farther. (m)
11 are arranged. In this example,
The photodetector (■) 9 and the photodetector (m) 11 are arranged at the same distance from the photodetector (II) 10, as an example.

Now, in the optical information reading device having the configuration shown in FIG. The reflected light from the information recording medium 5 becomes focused light through the optical system and the cylindrical lens 6, and then is focused on the recording surface of the information recording medium 5 such as an optical disk. , 3 through 8
It is split into light beams and focused on each photodetector 9.10.11.

7 The output current from each photodetector 9.10.11 is converted into a voltage signal by the I/V converter 12.13.14 as described above. The reproduced signal is expressed as shown in FIG.

In addition, FIG. 2 shows the photodetector (1) 9 and the photodetector (n
) io and the reproduced signal values of the photodetector (m) 11 are plotted. Incidentally, as shown in FIG. 2, the reproduced signal from each photodetector reaches its maximum value when the focal position comes to the position of each photodetector.

Next, in FIG. 3, the sum of the signals from the three photodetectors 9, 10 and 11 is plotted as a reproduced signal in the same manner as in FIG. 2. In FIG. 3, the graph a represents the reproduced signal by the apparatus of the present invention shown in FIG. 1, and the graph b represents the reproduced signal by the conventional apparatus shown in FIG.

In Figure 3, the focus position is the focal position (''' in the figure).
At the 0''0'' position, the reproduced signal is a.

8-b both take the maximum value, but when an offset voltage occurs in the focus error signal due to the inclination of the recording surface of the information recording medium 5, the focus control position changes from the "O" position to "1" in the figure.
The reproduced signal in this state of IIIVI is v3 in the device of the present invention, and vl in the conventional device.Therefore, the device of the present invention reduces the amount of decrease in the reproduced signal than the conventional device. can be done, i.e.
This is equivalent to an apparent increase in the depth of focus.

As described above, in the optical information reading device according to the present invention, the photodetectors 9.10.1 have mutually different focus positions for the reflected light from the recording surface divided into three or more beams.
1, and the sum of the signals obtained by I/V conversion of the output current from each photodetector 9, 10, 11 is used as the reproduction signal, the depth of focus at the time of detection of the reproduction signal is increased, and the depth of focus of the information recording medium 5 is increased. The influence of the surface inclination of the recording surface can be reduced, and the error rate during reproduction due to the influence of the surface slope can be reduced.

In addition, the error rate with respect to the surface inclination is calculated using the device of the present invention (Fig. 1).
The results are shown in Table 1.
Shown below.

Table 1 In Table 1, each symbol of O2△ and × is ○...
- Error rate 10-6 or less Δ...Error rate 10-5 or less x...Error rate 10-4 or less.

Furthermore, in detecting the error rate, the objective lens 4 of the optical system used had a numerical aperture of NA=0.6. In addition, in the case of the device of the present invention shown in FIG. 1, focal positions of the photodetector (I), photodetectors (II) and (m) 1 - An example of the light-receiving surface of the photodetector used in the information reading device Figure 5 is an explanatory diagram of the light receiving state when using the photodetector with the light receiving surface shown in Figure 4 (b), Figure 6 is Sasa Figure 4 (b)
7 is a diagram showing the reproduced signal when using the photodetector with the light receiving surface shown in FIG. FIG.

1...Light source, 2...Polarizing beam splitter, 3
...λ/4 plate, 4...Objective lens, 5...
・Information recording medium, 6... Cylindrical lens, 7
, 8... Half mirror 19, 10, 11... Photodetector, 12.13° 14... Current-voltage converter, 1
5...Amplifier.

The amount of misalignment was 100 μm.

〔Effect of the invention〕

As described above based on the illustrated embodiments, according to the present invention, the influence of the surface inclination of the recording surface of the information recording medium can be reduced, so even when the surface slope occurs on the recording surface. The reproduced signal does not change significantly, a stable reproduced signal can be obtained, and the error rate can be reduced.

Therefore, by using the apparatus of the present invention, the specification value of the surface inclination of the information recording medium can be relaxed, and the yield of the information recording medium can be improved.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of an optical information reading device showing an embodiment of the present invention, FIG. 2 is a diagram showing reproduced signals from each photodetector of the device shown in FIG. 1, and FIG. A diagram when the sum of signals from each photodetector of the device shown in FIG. 1 is used as a reproduced signal, FIG. 4(a) is a schematic configuration diagram of an optical information reading device showing an example of the prior art, Figure 4(b) is Figure 4(a)
The optical system shown in Fig. 5 (I) ■ Fig.

Claims (1)

[Claims] A light flux supplied from a light source is focused on an information recording medium via an optical system, and reflected light from the recording surface of the information recording medium is received by a photodetector via the optical system, and output from the photodetector. In an optical information reading device that obtains a reproduced signal by converting current to voltage, the reflected light from the information recording medium is divided into at least three or more beams, and a photodetector is provided for each divided beam. In addition, the photodetectors are arranged so that their focus positions with respect to the recording surface of the information recording medium are different from each other, and the sum of signals obtained by current-voltage conversion of the output current from each photodetector is used as a reproduction signal. An optical information reading device characterized by: