JPH0454295B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical recording/reproducing device that can be used in a system having equipment for optically recording or reproducing information. For example, it can be used in external memory for computers, audio recording/playback systems, video recording/playback systems, etc.

Configuration of a conventional example and its problems A conventional device of this kind will be explained using FIGS. 1 and 2.

In FIG. 1a, light from a light source 1 is converted into parallel light, reflected by a half mirror 2, and incident on a recording medium 4 by an objective lens 3, forming a minute light spot. The light reflected by the recording medium 4 passes through the objective lens 3 and the half mirror 2 and enters the convex lens 5. Half of the transmitted light is blocked by the light shielding plate 6, and the remaining light is focused near the central portion of the two-split photodetector 7. The output obtained by calculating the difference between the signals from the two-split photodetector 7 by the differential amplifier 8 becomes a focus error signal. FIG. 1a shows a case where the objective lens 3 is focused on the recording medium 4, and the same amount of light is incident on the left and right photodetectors 7,
The output of differential amplifier 8 is zero.

FIG. 1b shows a case where the recording medium 4 is displaced in a direction approaching the objective lens 3. Note that the light source 1 is omitted in this figure. In this case, the light incident on the convex lens 5 becomes diverging light, the light enters the two-split photodetector 7 on the left side, and the output of the differential amplifier 8 becomes negative. In Figure 1c, the recording medium 4 is the objective lens 3.
This is a case of displacement in the direction away from. In this case, the light incident on the convex lens 5 becomes convergent light,
Light enters the right side of the two-split photodetector 7, and at this time the output of the differential amplifier 8 becomes positive. In this way, the device shown in FIG. 1 can detect focus errors with a simple configuration. Also, it has the advantage of high detection sensitivity and wide detection range, but on the other hand, it blocks half of the reflected light from the recording medium 4, which is quite significant when considering information detection of the recording medium 4 and tracking error detection. It is inefficient.

FIG. 2 shows a conventional example that eliminates the above-mentioned drawbacks. A reflector 9 is used instead of the light-shielding plate 6, the reflected light is received by a photodetector 10, and an information signal and a tracking error signal are received by an amplifier 11. It is designed to be detected. The principle of this device is the same as the one in Figure 1, and it is excellent in that it uses light effectively, but on the other hand, the optical system is spread out spatially, making it difficult to miniaturize. have a problem

OBJECTS OF THE INVENTION The present invention solves the above-mentioned conventional drawbacks and provides a compact and efficient optical recording/reproducing device.

Structure of the Invention The present invention relates to a device that includes optical components such as a light source and an objective lens, and records a signal on a recording medium or reproduces a signal on the recording medium. It is characterized by comprising an optical element consisting of a pair of convex lenses that receives light and makes the light receiving area enter one or more multi-divided photodetectors. The optical element has a shape in which an arbitrary portion not including the optical axis is cut on a plane parallel to the optical axis of the convex lens, and the cut surfaces are glued or fixed to each other so that the optical axes of the convex lenses are parallel to each other. The optical axis of the reflected light from the recording medium is substantially parallel to the optical axis of the convex lens, and the optical axis is arranged so that the amount of light divided by the optical element is substantially the same. Note that the optical element may be configured by integrally molding the shape described above.

DESCRIPTION OF THE EMBODIMENTS An embodiment of the present invention is shown in FIG. In FIG. 3, light from a light source 1 is converted into parallel light and then enters a recording medium 4 through a half mirror 2 and an objective lens 3. The reflected light enters the optical element 12 via the objective lens 3 and the half mirror 2. Optical element 12
has the shape of two convex lenses, and 2
It has the optical axis of a book. Therefore, the optical element 12
The transmitted light converges into two light spots, one of which enters the two-split photodetector 7 and receives a focus error signal from the differential amplifier 8, and the other enters the photodetector 10 and receives an information signal from the amplifier 11. and tracking error signal. Note that what is shown in this drawing is just an example, and the information signal may be obtained by calculating the sum of the two-split photodetector 7, or a two-split photodetector may be used as the photodetector 10. , the two-split detector 7 and the photodetector 10 may be integrated to form a single photodetector with a multi-divided light receiving area.

Next, the shape of the optical element 12 and detection of the focus error signal will be explained using FIGS. 4 to 6. FIG. 4 shows the optical element 12 and the path of light. The optical element 12 has a shape similar to that of a convex lens that is partially cut and glued together. This outer shape may be processed into a shape that is easy to use. This optical element 12
Since it has two optical axes, the incident light flux shown by diagonal lines is divided into two and converged on the two-split photodetector 7 and the photodetector 10 placed at the focal position of the convex lens. In FIG. 4, the beam is in focus, a light spot is formed on the two-split photodetector 7 at the center of the dividing line, and the output of the differential amplifier 8, that is, the focus error signal, is zero.

FIG. 5 is a diagram when a focus shift occurs. First, FIG. 5a shows a case where the recording medium 4 in FIG. 3 is displaced in a direction approaching the objective lens 3. In FIG. At this time, since diverging light enters the optical element 12, a light spot is formed on the left side of the two-split photodetector 7, and a negative focus error signal is obtained from the output of the differential amplifier 8. On the other hand, FIG. 5b shows a case where the recording medium 4 in FIG. A light spot is formed on the right side of the split photodetector 7, and a positive focus error signal can be obtained from the output of the differential amplifier 8. The shape of the detector light-receiving area and the amplifier specifications can be determined so that information signals and tracking error signals can be obtained from the photodetector 10 and the amplifier 11.As mentioned above, the two-split photodetector 7 and the photodetector The detector 10 may be integrated into a single photodetector with a multi-divided light receiving area.

Effects of the Invention As described above, the present invention provides an optical system that can effectively utilize reflected light from a recording medium without wasting it, and that can perform highly sensitive focus error detection, information detection, and tracking error detection. It is possible to have a compact configuration. Moreover, the present invention can simplify the shape of the optical system and downsize it compared to conventional ones.

[Brief explanation of drawings]

1 and 2 are principle block diagrams showing a conventional example, and FIGS. 3, 4, and 5 are principle block diagrams showing an embodiment of the present invention. 1... Light source, 2... Half mirror, 3... Objective lens, 4... Recording medium, 5... Convex lens, 6...
... Light shielding plate, 7 ... Two-split photodetector, 8 ... Differential amplifier, 9 ... Reflector, 10 ... Photodetector, 11 ...
...Amplifier, 12...Optical element.

Claims (1)

[Claims] 1 Signal detecting means of a device for recording or reproducing signals on a recording medium, which consists of two convex lenses that split the reflected light from the recording medium and converge each, and whose optical axes are substantially parallel and are integrated. a two-split photodetector located near the focal point of one of the converged beams and having a dividing line substantially parallel to the cutting planes of the two convex lenses; and a light beam that receives the other of the converged beams. An optical recording/reproducing device characterized by comprising a detector.