JPS60175223A - Optical information reader - Google Patents

Abstract

PURPOSE:To attain a focusing action with high accuracy and high sensitivity by setting a 4-split photodetector at the focal position of a convex lens and differentiating the output of the photodetector produced by the variation of the spot size on said photodetector. CONSTITUTION:A photodetector 8 is set at the focal position of a convex lens 7, and the photodetecting surface of the detector 8 contains four detectors 8c-8f. A detector 8a consisting of detectors 8e and 8f and a detector 8b consisting of detectors 8c and 8d are divided concentrically into two parts in the right and left sides respectively. Thus both detectors 8a and 8b work independently of each other. Therefore the incident light quantity of detectors 8c and 8d is smaller than that of detectors 8e and 8f at the focal position. This gives virtually no effect to the information signal 19 despite the disturbance of the focus signal. Furthermore an offset is reduced since the differential output is used as a focus error signal. At the same time, the focusing sensitivity is improved.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to optical disc players and the like.

The present invention relates to an optical information reading device that optically reads information from recording pits recorded on a disk-shaped recording medium (hereinafter referred to as a disk) and focuses reading light onto the recording pits on the disk.

In optical disc players, etc., an optical information reading device is used to read information signals from the recording pits recorded on the disc, and a focused spot for information reading is placed on the disc surface where the recording pits are located. and
In addition, it is necessary to track the recording pits so that the reading light always accurately hits the recording pits on the disk surface, and to receive the reflected light from the recording pits. [Prior art] Figure 1 shows a conventional method for reading this type of information. The device is shown. 1st
In the figure, (1) is a semiconductor laser, (2j is a collimator lens, (3) is a polarizing beam splitter, and (4) is ÷
A wavelength plate, (5) an objective lens, 16I a convex lens for a disk, and (8) a photodetector. Semiconductor laser (1)
The light is converted into parallel light by the collimator lens (2), passes through the polarizing beam splitter (T wavelength plate (4), enters the objective lens (5), and is directed onto the disk (61) by the objective lens (5). The light is focused on the disk (6
) The reflected light from the convex lens (7) follows the opposite optical path, bends the optical path by 90 degrees by the polarizing beam splitter, passes through the convex lens (7), and reaches the photodetector ( 8”.

Here, the operation of the wave plate (4) is well known.

FIG. 2 shows the shape of the photodetector (8) and the incident state of the spot. In FIG. 2, (9) is a differential amplifier. The light receiving surface of this photodetector (8) is concentrically divided into two parts as shown in Fig. 2, and the inner detector (8a) and outer detector (8b) are electrically insulated from each other. , which acts as an independent photodetector.

When light enters the light-receiving surface as shown by the diagonal lines in the same figure, signal outputs are generated in the inner and outer photodetectors depending on the amount of incident light, so the difference in the way the signals are output can be calculated using the above-mentioned differential amplifier. By doing so, it is possible to obtain a signal output corresponding to the spot diameter of the light incident on the light receiving surface of the photodetector, that is, a focus error signal aU.

As shown in FIG. 1, when the disk surface (61) is in focus, the position of the photodetector (8) is adjusted so that the differential output of the photodetector (8) becomes zero.

Next, in FIG. 1, the disk surface +61 is displaced in the direction away from the objective lens (5), and the disk surface (6a)
When the light beam reaches the position shown in FIG. 2, the spot diameter of the light incident on the photodetector (8) becomes larger than that in the focused case shown in FIG. Figure 3 (a) shows the spot on the photodetector (81) in this case, and on the photodetector (8), the amount of light hitting the outside increases more than the inside, and the difference output becomes negative.Also, as shown in Figure 1,
When the disk surface (6) is displaced in the direction approaching the objective lens (5) and reaches the position of the disk surface (6b), the spot diameter of the light incident on the photodetector (8) is shown in Figure 2. The diameter is smaller than when it is in focus. FIG. 3(b) shows the spot on the photodetector (8) in this case.

On the photodetector (8), the amount of light hitting the outer side is smaller than the inside, and the difference output between them is exactly /X. in this way.

Since the output of the differential amplifier (9) changes depending on the focus shift, if the objective lens (5) is moved in the axial direction according to the difference output, the readout light can always be focused on the disk surface (6). Can be light.

The above method of obtaining the focusing error signal is also called the areal density method, but if the method is used as it is, the drawback is that when the sensitivity to defocus is increased, the pull-in range becomes narrower, and conversely, when the pull-in range is widened, the sensitivity decreases. , and the light intensity distribution on the photodetector +81 is not uniform, the accuracy of the error signal deteriorates.

[Summary of the invention]

The present invention is intended to eliminate the drawbacks of the conventional optical information reading device, and one embodiment of the present invention will be described below with reference to the drawings.

[Embodiments of the invention]

FIG. 4 shows an embodiment of the present invention, and (8) is a photodetector having a light-receiving surface shaped as shown in FIG.

It is installed at the focal point of the convex lens (7). The circle is the 6th
FIG. 5 shows the shape of the photodetector (8), which is a signal processing circuit having the electrical connections shown in the figure.

The light receiving surface of this photodetector (8) consists of four detectors (8c) (8d) (8e) (8f) as shown in FIG. ) and detector (
Similar to the photodetector (8) shown in Fig. 3, the detector (8b) consisting of (8c) (8a) is concentrically divided into two halves, and is also divided into left and right halves, each of which is electrically connected to the other. The photodetectors (8a) and (8b) are insulated from each other and operate as independent photodetectors.The photodetectors (8a) and (8b) are divided into two parts. It is.

Figure 6 shows details of the signal processing circuit 0υ.
FIG. 3 is an electrical wiring diagram for obtaining a focus error signal, a tracking signal αη, and an information signal Q9.

a2 is an amplifier for obtaining the sum signal of the photodetectors (8C) and (8d), the other side is a differential circuit, (141 (lω is an amplifier, αe is a differential amplifier, and ul is an amplifier for obtaining an information signal. be.

Now, in FIG. 4, the light from the semiconductor V-za (1) passes through the collimator lens (2j) as shown in FIG.

The light passes through a polarizing beam splitter (3), a 4-wave plate (4) and an objective lens (5) and is focused onto a disk (6). Next, the reflected light from the disk (6) follows the opposite optical path, the optical path is bent by 90 degrees by a polarizing beam splitter, and passes through a convex lens (7) to a photodetector installed at the focal point of the convex lens (7). (Injects into Arata.

Figure 1 shows the change in the spot on the photodetector (8) when the disc (61) is displaced from the focal position. Figure 7 (a) shows the disc (6) moving from the objective lens (5) The figure shows the case where the light is displaced in the direction away from the disk and reaches the position of the disk surface (6a), and the light that enters the convex lens (7) is a convergent light, and after exiting the convex lens (7), the light enters the convex lens (7). ) and the photodetector (8) and enters the photodetector (8). Figure 1(b) shows the case where the disk (6) is at the focal position of the objective lens (5). As shown.

The light incident on the convex lens (7) is parallel light.

After exiting the convex lens (71f), it forms an image on the photodetector (8).The spot on the photodetector (8) at this time is the smallest.Next, the first Figure (C) shows the case where the disk +61 is displaced in the direction approaching the objective lens (5) and the disk surface comes to the position (6b) shown in Figure 4.At this point, the convex lens (force The incident light is diverging light, and after exiting the convex lens (7), it forms an image at a location farther than the installation position of the photodetector (8).Therefore, the spot diameter on the one-element detector (8) is larger than when the disk +61 is at the focal position of the objective lens (5).

Figure 8 shows the change in spot size on the photodetector when the disk (6) is displaced from the focal position of the objective lens (5).The spot size becomes minimum at the focal position and approaches Even if you move away from it, it will get bigger.

Figure 9 (a) shows the sum output of the photodetector (80 x 8 (L) when the disk (6) is deviated from the focal position.
). As shown in Figure 8g8, the spot size on the photodetector increases whether the disk +61 approaches or moves away from the focal position, but the power remains the same;
If only the power around the spot is extracted using a photodetector having the shape shown in the figure, the result will be as shown in FIG. 9(a). 9th
Figure (b) is the output obtained by differentiating the sum output of the photodetectors (8c) (8d) by the differentiating circuit q3, which changes as shown in Figure 1. That is, a focus error signal is obtained.

〔Effect of the invention〕

As shown in Fig. 9(a), the amount of light incident on the photodetector (8CX8(L)) at the focal position is
8f), and even if there is a disturbance in the focus signal, it will have almost no effect on the information signal a9, and since the differential output is used as the focus error signal, the offset will be small, and It has the advantage of increasing sensitivity.

Note that above 9 describes the case where a photodetector divided into four parts is used as the photodetector (8) to obtain a tracking signal, but if the purpose is to obtain a focus error signal, the light divided into two parts concentrically can be used. Needless to say, a detector may also be used. Also.

Although the case where information signals are read from recording bits recorded on a disk has been described above, the present invention may also be used in a recording apparatus that records pits on a disk. It goes without saying that a half prism or a half mirror may be used in place of the polarizing beam splitter and wave plate.

As described above, in the optical information reading device according to the present invention,
A photodetector divided into four parts is installed at the focal point of the convex lens,
Highly accurate and highly sensitive focusing is possible by differentiating the photodetector output due to changes in spot size on the detector. Further, by using the differential output, there is an advantage that the offset is small, the output is large and the sensitivity is high, and the pull-in range can be made symmetrical about the focal position. Furthermore, since the configuration of the photodetector is simple, the device can be made smaller.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the configuration of a conventional optical information reading device, Fig. 2 is a diagram showing the shape of a photodetector and a light spot, and Fig. 3 is a diagram showing a light spot on the photodetector when the focus is shifted. , FIG. 4 is a configuration diagram of an optical information reading device according to an embodiment of the present invention, and FIG. 5 is a diagram showing the shape of a photodetector according to the present invention.
FIG. 6 is a diagram showing the electrical connection of the signal processing circuit according to the present invention, FIG. 1 is a diagram showing the incident state on the photodetector according to the present invention, and FIG. 8 is a diagram showing the spot size on the photodetector. The diagram shown in FIG. 9 is a diagram showing the electrical output. In the figure, (1) is a semiconductor laser, (2) is a collimator lens, (3) is a polarizing beam splitter, and (4) is a τ wavelength plate. (5) is the objective lens, +61 is the disk, and (7) is the convex lens. +81 (8a) (ab) (sc) (sa) (se) (
8f) is a photodetector, (9) is a differential amplifier, 4 is a focus error signal, nu is a signal processing circuit, 111 (141Q)
! ja & is an amplifier, α rise is a differential circuit, txe is a differential amplifier, Qη is a tracking error signal, (19 is an information signal. In Figure 1, the same or equivalent parts are indicated with the same symbols. 〇No. 1 Sui Do a No. 2 No. 4 No. 6 ('0) <C) No. 8 No. 9 [α)

Claims (1)

[Claims] A light source, a collimator lens that converts the diverging light from the light source into a parallel light beam, an objective lens that focuses the parallel light beam onto an information recording medium, and an optical path from the collimator lens to the objective lens that includes the information recording medium. It has a polarizing beam splitter and a 4-wave plate for splitting a parallel light flux that is opposite to the parallel light flux produced when the light flux reflected by the object lens passes through the objective lens again, and the above-mentioned light beam separated by the polarization beam splitter is provided. In an optical information reading device equipped with a photodetector that receives reflected light, a convex lens is provided between the polarizing beam splitter and the photodetector, and a concentric circle is divided into two at the focal position of the convex lens; A photodetector is divided into two through the center, and a differentiation circuit is provided for differentiating the output from the outer detector of the concentric photodetector, and a focus error signal is obtained by the output of the differentiation circuit. Characteristic optical information reading device 0