JPS606017B2 - optical recording and reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for optically recording, reproducing, and only reproducing information, and particularly to a polarizing beam splitter and an arrangement in an input/quarter plate used therein.

A device that optically performs recording/reproduction or only reproduction uses an optical system to focus a light beam from a light source into a finely focused light beam, irradiates it onto an information recording medium, and modulates the intensity of the light beam with a recording signal to determine the optical properties of the recording medium. changes and records information.

In addition, a light beam whose intensity is weaker than that during recording is narrowed down to a fine 4.0 mm in the same way as during recording, and is irradiated onto the medium, optical changes in the medium are detected, and information is reproduced. This optical recording and reproducing device has many features such as being able to increase the density of information, but when recording and reproducing information, it is necessary to always focus and irradiate the information recording medium with a very small light beam. , focus control to keep the distance between the information recording medium and the optical system constant, and tracking control to follow the locus of recorded information are required.
Generally, in an optical recording and reproducing device, in order to obtain an information signal when reproducing information using a reflective disk, and to obtain a control signal when performing the focus control and tracking control described above, "information It is necessary to extract the reflected light from the recording medium.A beam splitter is generally used to extract the reflected light from the information recording medium, and this beam splitter is inserted into the optical path from the light source to the recording medium. It is required to efficiently transmit the light to the recording medium, and to efficiently separate the light reflected by the recording medium from the optical path to detect the information signal and the control signal.

The beam splitter can be constructed by inserting an ordinary glass plate into the optical path of the optical system of the apparatus. However, it is difficult to satisfy the above requirements with a simple glass plate. On the other hand, a polarizing beam splitter and a ^/4 plate can satisfy the above requirements. A polarizing beam splitter has the property that it reflects very little of the polarized light component (P component) parallel to the light incident plane, and highly reflects the polarized light component (S component) perpendicular to the light incident plane. The light source used in an optical recording/reproducing device is generally a laser, and its polarization state is linearly polarized light. Therefore, if a polarizing beam splitter is placed in the optical path of the device optical system so that the polarization plane of the light source is the P component,
Since there is almost no reflection, the transmission efficiency of light from the light source to the recording medium is not reduced. On the other hand, if an input/4 plate corresponding to the wavelength of the light source is placed after the polarizing beam splitter, the light from the light source will pass through the ^/4 plate and change from linearly polarized light to circularly polarized light, and the light reflected from the information recording medium will be further polarized. It passes through the 4th plate again and changes from circularly polarized light to linearly polarized light.
At this time, the plane of polarization is rotated by 90 degrees with respect to that of the light source, and it reflects well because it becomes an S component to the polarizing beam splitter. In this way, a beam splitter consisting of a polarizing beam splitter and a 4-plate is extremely useful for efficiently extracting reflected light from an information recording medium in an optical recording/reproducing device. The polarizing beam splitter and the input/fourth plate are placed in the optical path of the device optical system, but if there are other optical system components installed on the recording medium side in the optical path after the input/fourth plate, The reflected light is also emphasized and extracted as floating light, which adversely affects focus control and tracking control.Next, the adverse effects of the conventional example will be described.

FIG. 1 shows an example of an optical system of an optical recording/reproducing apparatus using a semiconductor laser as a light source. Semiconductor lasers have characteristics such as being able to be directly modulated without using an optical modulator and being extremely 4-inch in size compared to gas lasers, making them suitable as light sources for optical recording and reproducing devices. In Figure 1, a shows a side view of a conventional optical system, and b shows a plan view. is required.

Therefore, the shape of the light emitting surface of a semiconductor laser tortoise is generally flat, with a size of 1 to 2 mm in the direction perpendicular to the semiconductor bonding surface and 7 to 15 mm in the direction parallel to the bonding surface. 3 is a condensing lens composed of, for example, an objective lens,
The light beam of the semiconductor laser (light beam perpendicular to the bonding surface) and the light beam 12 parallel to the bonding surface are parallel beams with a rectangular cross section.

A concave cylindrical lens 4 is arranged to have a curvature relative to the light beam 12, and expands the beam diameter of the light beam i2 as shown in the figure.

5 is a polarizing beam splitter, and 6 is an input/quarter plate through which the light beams 1 and 12 of the semiconductor laser 1 pass.

A convex cylindrical lens 7 has a curvature with respect to the light beam 12 like the concave cylindrical lens 4, and is arranged so that its focal plane almost coincides with the focal plane of the concave cylindrical lens 4. Let be parallel light whose diameter is expanded again.

In this way, the output light of the convex cylindrical lens 7 is converted into substantially circular (or substantially square) parallel light. A mirror 8 changes the optical paths of the light beams 1 and 12 and causes them to enter an aperture lens 9 comprising, for example, an objective lens.

The light beams 1 and 12 are finely focused by an aperture lens 9 and irradiated onto the information recording medium 2. Here, if the focal length of each lens is f for the condenser lens 3, f for the diaphragm lens system 9, f3 for the concave cylindrical lens 4, and & for the convex cylindrical lens 7, then from a geometric optics point of view, the semiconductor laser The size of the light emitting surface of is 1 in the direction perpendicular to the bonding surface.
~2 meters When the distance is 7 to 154 m in the direction parallel to the joint surface, (1 to 2) x (ra/stop,
) Buddha m, in the direction parallel to the joint surface (7 to 15) × {(f2
×f3)ノ(f,×)mm, and by appropriately selecting the focal length of each lens, it is possible to narrow down the spot to a circular minute spot with a diameter of about 1 to 2mm. Although not shown, the information recording medium 2 is mounted on a rotating body driven by a motor or the like and rotated, and the semiconductor laser 1 is irradiated with a light beam modulated by a recording signal.

On the other hand, when reproducing information, the optical power of the semiconductor laser 1 is made smaller than that at the time of breaking information recording, and the reflected light from the information recording medium 2 is transmitted to the polarizing beam splitter 5 and the inlet 4 as described above.
The light beams L' and 12' are taken out by the plate 6, and further narrowed down to a certain size by an intermediate lens. The reflected light from the information recording medium 2 is extracted between the concave cylindrical lens 4 and the convex cylindrical lens 7 by a polarizing beam splitter 5 and an input plate 6. , T is the part where the light beam is not parallel light.
Extracting the reflected light from here is advantageous in that the optical path length of the optical system can be made the shortest, and in order to obtain a control signal for focus control using an astigmatism method, which will be described later. This is light beam 12
This is because the reflected light is imaged by the convex cylindrical lens 7, so that astigmatism-based focus control becomes possible with 101 intermediate lenses. Focus control necessary for recording and reproducing information is performed by dividing the photodetector 11 into four parts and using an astigmatism method.

That is, the reflected lights 1,' and 1 from the information recording medium 2
2' (reflected lights corresponding to the light beams 1 and 12 in Fig. 1) are imaged from the convex cylindrical lens 7 and the intermediate lens 1, but as shown in Fig. 2, the image formation positions are different. come. Therefore, the cross-sectional shapes of the light beam at points A to C in FIG. 2 have different shapes as shown in the figure. In FIG. 2, the same parts as in FIG. 1 are given the same numbers. Here, if the photodetector 11 is divided into four parts as shown in FIG. 3 and placed at point B in FIG. The distance between them changes as shown by A to C in FIG. 3 as the distance between them changes due to surface runout of the information recording medium 2 and the like. Here, when each element of the four divisions of the photodetector 11 is designated as D to G as shown in FIG. )−(F+
G) may be controlled to be zero. When actually performing focus control, the aperture lens 9 is held by a holder having a structure such as a known voice coil (not shown), and the distance between the information recording medium 2 and the aperture lens 9 is made variable by an electric signal. , by driving the voice coil using the control signal. On the other hand, the tracking information required when reproducing information is
The information appears as an optical change in the information track on the aforementioned four-divided photodetector 11, as shown in FIGS. 4a and 4b'.

FIG. 4a shows a case where the light beam is correctly irradiating the information track, and FIG. 4b shows a case where the light beam is irradiating the information track with a deviation. Here, the output (D-E) of the photodetector 11 becomes a control signal for tracking control, and it is sufficient to perform control so that (D-E) becomes zero. When tracking control is actually performed, the mirror 8 is configured as a galvanometer mirror (not shown) that can be rotated by a known electric signal, and the mirror 8 is rotated by the control signal. Focus control in an optical recording/reproducing device using a semiconductor laser as a light source as described above,
Tracking control and information signal detection are performed by extracting reflected light from the information recording medium 2 by a beam splitter consisting of a polarizing beam splitter and an input quarter plate, and detecting it by a photodetector 11. It is desirable that the light detected by this photodetector 11 be only the reflected light from the information recording medium 2, but in reality there is reflected light (floating light) from each element of the optical system, and this light is the focal point. This will adversely affect control and tracking control. That is, the control signals for focus control and tracking control divide the photodetector 11 into four,
Like the above-mentioned (D+E)1 (F+G) and D-E),
Since the sum and difference of the outputs of the respective photodetection parts are calculated, if floating light is incident on the photodetector 11 in a biased manner, the control signal will include an error, which is not desirable. In the conventional optical system shown in Fig. 1,
An input/fourth plate 6 is placed after the polarizing beam splitter 5,
Furthermore, a convex cylindrical lens 7 is arranged. In this case, there is reflected light from the convex cylindrical lens 7, this reflected light passes through the input plate 6, becomes an S component, is efficiently reflected by the polarizing beam splitter 5, and is irradiated onto the photodetector 11. The floating light is transmitted to the photodetector 11.
This will result in an error in the light amount balance at the top, and a difference signal will be generated. The present invention provides an optical device that eliminates the optically generated error factors and enables high-density focus control and tracking control.

An embodiment of the present invention will be described below based on the drawings.

In FIG. 5, the same parts as in FIG. 1 are given the same numbers and symbols corresponding to those in FIG. In FIG. 5, an inlet plate 6 is placed between the aperture lens 95 and the information recording medium 2 within the focal plane of the aperture lens 9. Generally, the focal plane of this aperture lens 9 is located on or near the information recording medium 2. In this configuration, the reflected light 13' from the convex cylindrical lens 7 is not affected by the ^/4 plate unlike the case shown in FIG. The light enters as polarized light, and therefore is transmitted in the direction of the concave cylindrical lens 4 without being reflected in the direction of the photodetector 11 on the polarization plane x. Therefore, the optical image (third image) of the reflected light 12' from the information recording medium 2 on the photodetector 11
A', B', C' shown in the figure are not disturbed by the reflected light 13' of the convex cylindrical lens 7. Similarly, it is not affected by light reflected by the aperture lens 9 (which is actually composed of a combination of a plurality of lenses). On the other hand, the light reflected by the upper surface of the 4/4 plate 6, which is placed closer to the focal plane of the diaphragm lens 9, does not give floating light to the photodetector 11 for the same reason as described above. On the other hand, the light reflected from the lower surface 1 of the ^/4 plate passes through the incident/4 plate 6 twice through the incident path and the reflection path, so the polarization plane is 90
It rotates and enters the convex cylindrical lens 7 and is reflected by the polarizing beam splitter 15 toward the photodetector 11.However, the surface 1 of this ^/4 plate 6 is placed inside the focal plane of the aperture lens 9. Then, the light reflected by the surface 1 becomes light that diverges significantly after passing through the aperture lens 9. Therefore, the light included in a very small part of the solid angle of this reflected light enters the polarizing beam splitter 5 and becomes light. The light will be incident on the detector 11. Therefore, the entire area of the photodetector 11 shown in FIG. 3 will be irradiated with weak light with a uniform distribution. The optical images A', B', C
Do not disturb the difference in r. This is because due to the divergence effect, 4
This is because approximately the same amount of floating light is supplied to each of the divided photodetecting elements D, E, F, and G. As described above, according to the present invention, it is possible to eliminate the influence of reflected floating light from an optical element placed behind the polarizing beam splitter (on the side closer to the information recording medium in the optical path), perform accurate focus control and tracking control, and perform information It is now possible to record and play back optimally and stably. Furthermore, since the input/quarter plate can be installed at the exit of the diaphragm lens, the optical system can be made more compact than the configuration shown in FIG. Note that the present invention is the first
Although the explanation has been made using the optical system shown in the figure, it can also be applied to other optical systems.

[Brief explanation of drawings]

FIGS. 1a and 1b are a side view and a plan view showing an optical system of an optical recording/reproducing device using a conventional semiconductor laser as a light source,
Fig. 2 is an explanatory diagram showing the imaging position of the reflected light from the information recording medium and the cross-sectional shape of the light beam, Fig. 3 is an explanatory diagram showing the change in the shape of the light beam on the photodetector, and Fig. 4 a , D are explanatory diagrams showing the positions of information tracks on a photodetector, and FIG. 5 is a plan view of essential parts showing an embodiment of the present invention. 1...Semiconductor laser, 2...Information recording medium, 4...-Concave cylindrical lens, 5...
...Polarizing beam splitter, 6...in/4 plates, 7...
...Convex cylindrical lens "Possible 0...Intermediate lens, 1
1...Photodetector. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. In a device that uses a semiconductor laser, etc. as a light source and uses an aperture lens system to narrow the output light to a microscopic diameter and irradiates it onto an information recording medium to record or reproduce information, the optical path from the light source to the information recording medium is A polarizing beam splitter for separating reflected light from the information recording medium from the optical path is provided, and a λ/4 plate is installed in the focal plane of the aperture lens on the information recording medium side. Optical recording and reproducing device.