JPS63856B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical recording and reproducing device that optically records and reproduces information, and is capable of detecting a good tracking error signal without sacrificing light gathering ability or optical transmission efficiency. The purpose of the present invention is to provide an optical recording/reproducing device that is capable of

FIG. 1 shows a conventional device of this type. In FIG. 1, 1 is a semiconductor laser, 2 is a collimator lens, 3 is a half prism, 4 is an objective lens, 5 is a disk, 6 is a convex lens, 7 is a photodetector, and 8 is a diffraction grating. Light from the semiconductor laser 1 is converted into parallel light by a collimator lens 2, and separated by a diffraction grating 8 into a main beam of 0th-order diffracted light and a sub-beam of 1st-order diffracted light.
Each beam is incident on a disk 5 by an objective lens 4. FIG. 5 shows the state of incidence on this disk, where 10 is a light spot by the main beam, 11 is a light spot by the sub beam, and 13 is an information pit. The diffraction grating 8 is adjusted in FIG. 1 so that the respective relationships are as shown in FIG. 2. The reflected light from the disk 5 follows the opposite optical path, is reflected by the half prism 3, and is reflected by the convex lens 6.
The light then enters the photodetector 7. FIG. 3 shows the shape of the photodetector 7 and the incident state of the light spot. The photodetector 7 is divided into three parts as shown in the figure, and a tracking error signal can be detected by taking the difference between the electrical signals generated by the optical spot 11 caused by the sub beam. The light spot 10 produced by the main beam contains information about the pit 13 as shown in FIG. 2, and if this is detected as shown in FIG. 3, an information signal can be obtained.

The above-mentioned device is generally called a three-beam system, and has been put into practical use because it can detect tracking error signals with high accuracy. However, as shown in FIG.
However, due to the poor transmittance of the diffraction grating itself, it is difficult to increase the light intensity of both the main beam and the sub beam. Although it is a part of the light, by dividing this luminous flux into three parts, the light intensity of the main beam itself is further reduced. These problems are not so much of a problem in the case of optical systems for reproduction only, since a large optical output is not required, but in the case of optical systems for recording and reproduction, a large optical output is required during recording. The device shown in FIG. 1 had the drawback of large loss of light.

The present invention eliminates the above-mentioned drawbacks of the conventional art, and one embodiment of the present invention will be described below with reference to FIGS. 4 to 6. In Figure 4, 1,
3, 4, 5, 6, and 7 are the same as in FIG. Fourth
In the figure, 12 is a collimator lens like 2, but the aperture and numerical aperture of 12 are larger than those of 2. 9 is a prism with a trapezoidal side shape;
Its shape is shown in FIG. FIGS. 6a and 6b show the state of deflection of the light beam by the prism 9, where a is a plan view and the diagonal lines indicate the state of the incident light beam. As shown in the figure, the peripheral portion of the incident light beam is deflected by the refraction action of the prism and becomes two sub-light beams 11', while the central portion passes through as is and becomes the main light beam 10'. Unlike the case where a diffraction grating is used, the sub beams 11' are each deflected inwardly, so they are not cut off by the edges of the optical element. In addition, since the prism has good transmittance, the main luminous flux is 10' and the secondary luminous flux is 1.
1', sufficient light intensity can be obtained.

Collimator lenses 2, 12 and objective lens 4
Let f ₁ , f ₁ ′, and f ₂ be the focal lengths of , respectively. In the case of the device shown in Figure 1, the geometrical optical magnification of the condensing system is
It is expressed as f ₂ /f ₁ . Here, if f ₁ ′=f ₁ ,
The magnification of the condensing system of the present invention is f ₂ / f ₁ , which is the first
It is possible to image a minute light spot on the disk similar to the case shown in the figure. At this time,
If the condensing angle θ' of the collimator lens 12 is made larger than the condensing angle θ of the collimator lens 2, that is, the numerical aperture of the collimator lens 12 is made larger than that of the collimator lens 2, as shown in FIG. The device of the present invention can condense the diverging light of the semiconductor laser 1 with higher efficiency than the conventional example shown in FIG. Here, if the length d of the portion through which the principal beam 10' passes, as shown in FIG. Since the light does not pass through materials with poor optical efficiency, it enters the objective lens 4 without causing a decrease in light intensity, and a light spot with high light intensity is formed on the disk 5. As mentioned above, the recording/reproducing optical system requires a large optical power during recording, so the present invention, which has little loss, is very advantageous.

By appropriately rotating the prism 9 about the optical axis of the lens, the prism 9 can be rotated on the disk 5 and on the photodetector 7 in the same way as when the diffraction grating 8 is used in the conventional example.
As shown in FIGS. 2 and 3 above, it is possible to make a main beam and a sub-luminous beam incident.

The device of the present invention has the above-mentioned configuration, has excellent optical transmission efficiency, is capable of forming a minute image of a high-intensity light spot on a disk, and is also capable of detecting a tracking error signal with high precision. It has the advantage of being able to

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the optical system of a conventional optical recording/reproducing device, Fig. 2 is a diagram showing the state of incidence of light onto the disk of the same device, and Fig. 3 is a diagram showing the state of incidence of light onto the photodetector of the same device. A diagram showing the incident state, FIG. 4 is a schematic diagram of the optical system of an optical recording and reproducing apparatus in an embodiment of the present invention,
Figure 5 is a perspective view of the prism of the device, Figure 6a,
b is a plan view and a side view respectively showing the deflection state of a light beam by a prism of the same device. 1... Semiconductor laser, 3... Half prism, 4
...Objective lens, 5...Disc, 6...Convex lens, 7
...3-split photodetector, 9...prism, 12...collimator lens.

Claims (1)

[Claims] 1. A laser light source, a collimator lens that converts the diverging light from the laser light source into parallel light, an objective lens that has an aperture smaller than the aperture of the collimator lens and focuses the parallel light onto a disk, and the collimator lens and the objective lens, the prism has a trapezoidal side surface and separates the parallel light from the collimator lens into a main beam and two sub beams, and the disc is disposed between the objective lens and the prism. A half mirror that separates the reflected light from the half mirror, and a three-split photodetector that receives the reflected light from the half mirror,
An optical recording/reproducing device characterized in that each divided portion of the three-split photodetector independently receives the main beam and two sub-beams of reflected light from the disk.