JPS5860436A - Optical reproducing or recording and reproducing device - Google Patents

Abstract

PURPOSE:To increase the focus sensitivity of an optical system without increasing its scale, by focusing reflected light from a disk through a convex lens and also split it into two beams through a total reflection mirror, and then obtaining a tracking error signal from one beam while obtaining a focus error signal from the other beam through a concabe lens. CONSTITUTION:Light emitted from a light source 1 is focused on a disk 6 through a convergent lens 2 and a diaphragm lens 7. Its reflected light travels backward, and is stopped down by a convex lens 7 and then split into two beams through a total reflection mirror 11; one beam is made incident to two- split photodetectors 12a and 12b, and a tracking error signal is obtained from the difference between their outputs. The other beam is spread slightly by a concave lens 13 and guided to two-split photodetectors 14a and 14b to obtain a focus error signal from their output difference. Use of the concave lens 13 increases focus sensitivity without increasing the scale of the obtical system.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical reproducing device that optically reads information recorded on a disc, such as a video disc, or a device that optically records information on a disc and The present invention relates to an optical recording/reproducing apparatus, and in particular to an optical system for obtaining a servo signal and a reproduction signal for applying each 4m-IJ-bore using reflected light from a disk.

In general, in video discs and optical recording/reproducing devices, in order to record and reproduce information at high density, the tracks on the disc have a width of, for example, 0.6 μm and a pitch of 1.6 μm. Spiral J) Or has the shape of concentric circles. The disc is irradiated with a very small spot light of less than 1 gm, and the information on the disc is extracted from the reflected light.

In such a device, at least two servo techniques are required. One is due to the deterioration of the disk, and when the disk causes surface wobbling in a direction perpendicular to the rotation direction, a minute spot light focused to less than -lμl in Qtr is always focused on the disk. This servo is called a focus servo, which causes the optical system to follow the light so that it can irradiate light.

The other is a servo that causes an optical system to follow this when the trunk moves in the radial direction of the disk due to eccentricity or the like as the disk rotates, so that the minute spot light illuminates the track. , this servo is called a tracking servo.

The servo signal for performing the focus and tracking servo is obtained from the reflected light of the disk, and as a specific optical system, for example, the optical system shown in the first factor has been proposed.

In the optical system shown in Fig. 1, (1) is a light source made of, for example, a semiconductor laser, (2) is a condensing lens that collects the light emitted from the semiconductor laser, and (3) is a polarizing beam splitter that separates the light from the semiconductor laser (1). The emitted light is guided through a bent disk i as shown in FIG. (4) is an A/4 board, (5) is an aperture lens for narrowing down the light to a minute spot, and (6) is a disk.The minute spot light is irradiated onto the disk (6), and the signal is recorded or reproduced. The reflected light from the disk (6) passes through the V4 plate eight times, its polarization direction is changed, and it passes through the polarizing beam splitter (3). (7) is a convex lens, (Aug. A triangular prism called a wedge, ffdL wedge (
At step 8), the light is split into two and redirected to the photodetector (
9) (each guided by 10), said wedge (8
) is shown in FIG. The photodetector (9) is divided into two parts as shown in (9a) and (9b) when viewed from the direction of light incidence.
) (9b) A focus error signal for the focus servo is obtained from the difference in the outputs of (9b). In addition, the photodetector 01 is divided into two parts as shown in (10aXxob) when viewed from its light incident surface, and each photodetector (
The tracking -
A tracking error signal for servo is obtained, and a reproduction signal for reading information recorded on the disk is obtained from the sum of the outputs of the four photodetectors (9aX9b) (10a) (10b).

The optical system shown in FIG. 1 has the following drawbacks. That is, (1) the reflected light from the disk (6) is reflected from the wedge (8
), the beam width is wide when passing through the wedge (8)
Due to the aberration caused by this, the wavefront of the reflected light on each photodetector, especially the photodetector 01 which obtains the tracking error signal from the far-field image, is disturbed by one deviation from the focused position of the reflected light, resulting in a tracking error signal. It gives a bad impression.

(2) Photodetector for focus error signal detection (9)
is Δ! in the focus position adjustment direction (direction perpendicular to the direction of 2 divisions)! Assuming that the light condensing position on the disk (6) moves by ΔX in the optical axis direction when moving, the focus sensitivity m becomes m=Δt/ΔX (1) . The focus sensitivity m is determined by the focal length k of the aperture lens (5).
fs, and the focal length of the convex lens (7) is f7.m, then it is given by fs. If we try to increase the focus sensitivity m using equation (2), then the focal side of the convex lens (7) ′M1fy
However, if f1 is increased, Ff between the convex lens (7) and the photodetector (9) can be increased.
H R A F J'z <, the U-D in the optical system becomes large, and the position of the photodetector (9) σ) tends to move due to temperature changes, etc., and the incident light stably falls on the disk. It becomes difficult to focus.

The present invention was made mainly in view of the following points, and in the optical system shown in FIG.
The structure is such that a 1-racking error signal is obtained from one light that is divided into two, and the other light is slightly expanded and narrowed down by a four-lens lens, and a focus error signal is obtained from the light that has passed through the concave lens. By doing so, the reflected light from the disk for obtaining each control value J is not subjected to aberrations, therefore, there is no disturbance of the wavefront, and by inserting the concave lens, the optical system is not enlarged.

The present invention will be described in detail below with reference to the drawings, which aims to provide a novel optical system characterized by increasing the focus (m). This is a diagram showing an embodiment, and the same numbers are given to the components opposite to those in FIG. 1. In FIG.
6) The incident optical path until the light is irradiated is the same as that shown in FIG. The reflected light from the disk (6) is condensed by a convex lens (7), divided into two parts by a total reflection mirror (ii), and one of the lights is guided to a photodetector (b) as shown in the figure. When looking at the photodetector 0 years old from its light incident direction, (12a) (12
It is divided into two parts as shown in b).

The other of the two divided beams is slightly expanded and condensed by a concave lens, and guided to a photodetector 04 placed approximately at the convergence position of the light that has passed through the concave lens.

In this optical system, both curved servos are realized as follows. The disk (6) is rotated by a motor (g), and due to the rotation, the disk surface wobbles in the direction of arrow X.
The track on the disk moves in the direction of arrow Yh due to eccentricity. Therefore, a focus servo is applied to move the aperture lens (5) in the direction of the arrow A tracking servo is applied to move the aperture lens (5) in the direction of arrow Y by a tracking driver 11X11 device 0η so that the incident light focused on the disk surface follows the movement of the track. The tracking error signal for the tracking turbo is transmitted to the photodetector Q'
The focusing error signal for the focusing servo is obtained from the near field image on the photodetector α→.

@8 The principle of obtaining a focusing error signal with the configuration shown in FIG. 8 will be explained in detail. FIG. 4 is a simplified diagram of FIG. 8 in order to explain only the method of obtaining the focusing error signal, and the same reference numerals are given to the same components as the eighth factor.

In Figure 4, (a) indicates that the aperture lens (5) and the disk (6) are too close together than the desired distance, and (2) indicates that the incident light is focused at exactly the desired distance, that is, on the disk surface. In this case, (c) indicates a case where the distance is longer than the desired distance. First, as shown in the fourth factor (A), if the diaphragm lens (5) and the disk (6) are too close to each other than the desired distance, the condensing position Pi of the reflected light focused by the concave lens Q3 will be shifted to the photodetector α. ◆It becomes further away. Therefore, in this case, the amount of light received by the photodetector (1ab) is greater than the amount of light received by the photodetector (14a). Conversely, as shown in the fourth factor (c), when the aperture lens (5) and the disk (6) are separated from each other by more than the desired distance, the amount of light received by the photodetector (x4b) is lower than the amount of light received by the photodetector (x4b). ) will receive more light. In addition, when the incident light is focused on the disk (6) as shown in FIG. 4 (b), the focused light is irradiated onto the photodetector α
The amounts of light received by 14a and 14b are equal. Therefore, by taking the difference between the outputs of the two photodetectors (14a) and (14b), a focus error signal of 8 characters as shown in FIG. 6 is obtained, and using the focus error signal, the photodetector (14b) 1
Focus servo can be achieved by applying servo so that the amounts of light received in 4a and 14b are equal. Figure 5 shows the state of the focus error signal in the optical system f in Figure 8, where the vertical axis 1i1flVe is the focus error signal, and the horizontal axis ΔX
indicates the amount of focus deviation (hereinafter referred to as defocus amount) from the just focus position (FIG. 4(b)).

to On the other hand, the racking error signal is expressed by the light Δ It is obtained from the difference between the detectors (x2a) and (t2b).

The features of the optical system of the present invention shown in FIG. 8 will be described below.

(1) There is no disturbance in the wavefront of reflected light. Figure t13a (In the configuration of the optical system shown here, there is no optical component that causes aberrations such as the aforementioned wedge in the reflected optical path, so the reflected light wave ml is not disturbed. Therefore, the reflected light wave ml is not disturbed. In this method, which obtains the tracking error signal from the movement of one field elephant, the quality of the tracking error signal is
This is considerably better than the conventional configuration shown in the figure.

(2) Focus sensitivity increases. In the conventional configuration, the focus sensitivity n] is given by 2m''2f5 as described above. Therefore, in order to increase the focus sensitivity m, it is necessary to increase the focal length 1 mfy of the convex lens (7), which has the disadvantage that the optical system becomes large. However, with the configuration of the present invention including the concave lens (c) in Figure 68, the equivalent focal length f can be obtained without enlarging the optical system.
Making 7 thicker has the same effect and can increase focus sensitivity. FIG. 6 shows a comparison of the reflected optical paths when there is no concave lens (A) and when there is a concave lens (0). In the case of the conventional configuration (a), the focus sensitivity 11]a is given by ma:ifs. - The focus sensitivity inb in the case (mouth) using the concave lens invented by Rikiki is given by mb-1□ f5. Therefore, according to the configuration of the present invention, the focus sensitivity can be adjusted to f without changing the size of the optical system at all. ;/f can be raised by 7 times. Concrete Ekof, ””80゜(fls-
7), the focus sensitivity can be increased by about 8 times f/f.

(3) Furthermore, since the focus error signal is obtained at the imaging position P2 of the reflected light, the influence of diffraction of the reflected light from the information (bits) recorded on the disk can be reduced. , so that a high-quality focus error signal can be obtained.

In addition, in the configuration shown in FIG. 3, the tracking error signal is obtained from the light reflected from the mirror 01), and the focus difference signal is obtained from the other light that is not reflected from the mirror 01, or the configuration is completely reversed. Effects similar to those described above can be obtained. However, the combination shown in Figure 8 is more stable. This is because the influence of optical axis fluctuations (movement of optical components) due to temperature changes and the like has a much more severe influence on the focus error signal than on the tracking error signal. Therefore, the structure shown in the eighth factor is used so that the focus error signal is not affected even if the total reflection mirror αη moves due to temperature changes.

Also, regarding the position of the total reflection mirror (II), as can be seen from Fig. 6 (b), it is placed at a position slightly shifted from the optical axis center More than half of the light enters the lenses (14a) and (14b).This is because the distance between the aperture lens (5) and the disc (6) is longer than the desired distance when the focus servo is pulled in. In the case (Fig. 4e)), the condensing position P3 (Fig. 4) of the reflected light is closer to the disk than the total reflection mirror (b), and all the reflected light is reflected from the total reflection mirror (14a). ) This is to prevent light from not entering the photodetector for detecting the focus error signal in (14b).

As explained above, according to the configuration of the present invention, the quality of the tracking error signal is particularly improved without using special optical components such as wedges that are expensive and disturb the wavefront of reflected light. Also, by inserting a new concave lens, it has great effects such as being able to adjust the focus sensitivity without increasing the size of the optical system.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an optical system of a conventional optical recording/reproducing device, FIG. 2 is a perspective view showing the wedge of FIG. 1, and FIG. 8 is a diagram showing an optical system of an optical recording/reproducing device of the present invention. The configuration diagram, Fig. 4 is an explanatory diagram showing the five states of reflected light when a focus shift occurs, and the sixth factor is a characteristic diagram showing the focus error signal obtained from the configuration of the present invention. FIG. 6 is a diagram for explaining the difference in focus brightness from a comparison of reflected light when the lens is not used and when it is used. (1)...Light source (half-body laser), (+i)...
・Aperture lens, (6)...disk, (7)...convex lens, OJ)...total reflection mirror, (12aX12b
)...2 minutes; q1] first photodetector, (g).
... Concave lens, (14a) (14b) ... Second photodetector agent divided into two Tamamoto-1) Hiro Figure 4 (112 ~ 1 h

Claims (1)

[Claims] 1. In an optical recording and reproducing device that focuses light emitted from a laser into a minute spot light using an aperture lens and irradiates it onto a disk to read or write information,
At least one or more convex lenses that converge the reflected light from the disk, and a total reflection mirror that divides the reflected light into two directions in the optical path of the reflected light to be converged, and a total reflection mirror that divides the reflected light into two directions. receive one of the reflected lights,
The first one detects the tracking servo signal from the difference between each output.
A photodetector that is divided into two parts, at least one concave lens that refocuses the other light that has been separated by two minutes, and a focus servo signal that receives the light that has passed through this concave lens and generates a focus servo signal from the difference in each output. 1. An optical reproducing or recording/reproducing apparatus, comprising a second divided photodetector for detection, and detecting a reproduction signal for reading information from the sum of respective outputs of the first and second photodetectors. 2. A patent claim characterized in that the first photodetector is placed at a position shifted from the position where the light reflected from the disk is focused, and the second photodetector is placed at the position where the light reflected from the disk is focused. The optical reproducing or recording/reproducing device according to scope 1. 8. The light reflected by the total reflection mirror is the first (7)
The optical detector according to claim 1 or 2, characterized in that the photodetector is guided so that the other reflected light that is not reflected by the total reflection mirror is guided to the second photodetector. Playback or recording/playback equipment. 4. Claim 1, 2, or 8, characterized in that a total reflection mirror is installed so as to guide at least half or more of the light reflected from the disk to the second photodetector. Optical playback or recording/playback device as described.