JPH03147535A - Optical head - Google Patents

Abstract

PURPOSE:To obtain the optical head having high signal characteristics by subjecting the point where irregular reflection arises to a remedy to prevent suspended light. CONSTITUTION:The point of a beam splitter, on the reflected light side, where the irregular reflection arises, is subjected to the remedy to prevent the suspended light with substantially no change in the constitution of the optical head; for example, a suspended light preventive plate 19 is disposed or the end face of a lens barrel holding an objective lens 7 is blackened or the suspended light preventive plate 19 is stuck thereto or the end face is made into a sloped structure. Thus, the quantity of light exclusive of information signals, i.e. the suspended light, is decreased and the high CN optical head having the high signal characteristics is obtd. Further, the optical type driving device of a larger capacity and lower cost is obtd.

Description

[Detailed description of the invention] Industrial applications The present invention is a compact disc and a laser disc.

The present invention relates to an optical head used in an optical recording and reproducing device which is used in an image document file device, an external storage device for a computer, etc., and which reproduces, stores and reproduces information using a light beam of a semiconductor laser.

Conventional technology In recent years, optical storage devices with high density, large capacity, and non-contact features have been attracting attention as external storage devices for computers, but the development of magneto-optical recording is the most promising because it is rewritable. has been done. The optical head used in this magneto-optical disk device is required to have high precision and high performance, and increasing the CN is a major issue in order to increase the capacity.

The structure of a conventional optical head for a magneto-optical disk will be explained with reference to FIGS. 4 and 6.

In FIG. 4, 1 is a semiconductor laser, and the light beam emitted from this semiconductor laser 1 is a diverging and elliptical beam. Therefore, this diverging beam is converted into a parallel beam by the collimating lens 2. Furthermore, since this parallel beam is an elliptical beam, in order to convert it into a circular beam, the collimated emitted light is reflected by a reflecting mirror 3 at a constant angle of incidence with respect to the shaping prism 4. After being converted into a circular beam by the shaping prism 4, a part of the light is reflected by the non-polarizing beam sinter 6, but most of the light is transmitted and the optical axis is set at right angles by the right-angle reflecting mirror 6. Can be bent.

The light beam bent at right angles enters the objective lens 7 and is focused on the information recording medium 8 . In order to reduce the narrowed beam spot shape at this time, the 1/e2 diameter of the incident light is made larger than the effective diameter of the objective lens 7, thereby obtaining an Airy-Daimaku spot. Further, the light beam irradiated onto the information recording medium 8 is reflected and enters the objective lens 7 again to become a parallel beam. This parallel beam is again incident on the non-polarizing beam splitter 6, and the amount of light is reflected according to the reflectance Rp=Rs of P-polarized light and S-polarized light, and the half-wave plate 9
is transmitted and incident on the polarizing beam splitter 10, and P
The beam is separated into polarized light and S-polarized light. Of the separated light beams, the transmitted P-polarized beam is imaged by a tracking detection lens 11 on a two-split photodetecting element 12,
A tracking error signal is being detected. In addition, the beam of S (I light) reflected by the polarizing beam splitter 10 is focused by a focus detection lens 13, and
The beam is separated into two beams by a splitting mirror 14, and an image is formed on a four-split photodetecting element 16 provided at the midpoint between the focal lengths of the two beams, thereby detecting a focus error signal. These focus error signals and tracking error signals control the positioning of the information recording medium 8 by approximately ±1 μm in the focusing direction and ±0.1 μm in the racking direction even if the information recording medium 8 has some degree of surface runout or eccentricity. This is achieved by driving the objective lens 7 with 18 bobbins held in 17 lens barrels as shown in FIG. Further, the information signal obtained by the information recording medium 8 is polarized in four directions by the half wavelength plate 9.
As the light is tilted by 6 degrees, the phase is shifted by 180 degrees, and the light is separated into P-polarized light and S-polarized light by the polarizing beam splitter 1o, and as described above, the light is received by the 2-split photodetector element 12 and the 4-split photodetector element 16, and the difference is taken. In particular, many information signals are extracted.

Problems to be Solved by the Invention The playback principle of a rewritable magneto-optical disk is a compact disk. Rather than extracting changes in the light intensity of the recording pits of a write-once optical disk, when linearly polarized light is incident on the information recording medium, the Kerr effect causes clockwise and counterclockwise rotations due to the upward magnetic field or downward magnetic field of the overlapping magnetization film. The deflection direction is rotated, and the Kerr rotation angle is converted into a change in light amount to extract a reproduced signal.

In general, the Kerr rotation angle is as small as O, S ~ 0.5°, which is 1/100 of that of a light intensity change company compact disc and 1/30 of that of a write-once optical disc, so the CNR that can be used is If you want to achieve this, it is essential to suppress the noise to the same extent. Also, the fourth
In the configuration shown in the figure, the light beam reflected by the information recording medium 8 has an information signal, and it is desirable that only this light beam is received by the two-split photodetector element 12 and the four-split photodetector element 15. However, in reality, the light emitted from the semiconductor laser 1 is diffusely reflected at a certain point, and the light does not go to the information recording medium 8, but directly passes through the two-split photodetector element 1.
The light is received by a 2- or 4-split photodetector element 16. The light becomes noise and deteriorates the CN ratio.

In the prior art, the light beam emitted from the semiconductor laser 1 is partially reflected by a non-polarized beam splitter 6, and then reflected by the side surface of a 16 optical base, and the light is converted into 6 non-polarized beams. The light passes through the splitter 6 and is separated by the polarizing beam splitter 10, and is received as floating light by a two-split photodetector element 12 and a four-split photodetector element 15, respectively. Further, a lens barrel 17 holding the objective lens 7
A portion of the light is reflected at the end face of the optical base 16, reflected by the reflecting mirror 6, and reflected by the non-polarizing beam splitter 6. In the same way as in the case of the floating light reflected by the side surface of the optical base 16, The light is received by the two-split photodetector and the four-split photodetector as floating light, which increases noise and causes signal deterioration.

The present invention eliminates the above-mentioned conventional drawbacks, and aims to provide an optical head with high signal characteristics.

Means for Solving the Problems In order to solve the above problems, the present invention includes installing a floating light prevention plate on the reflected light side of the beam splitter and blackening the end face of the lens barrel that holds the objective lens.

The structure employs measures to prevent floating light in areas where stray light can occur due to diffuse reflection, such as by attaching a stray light prevention plate or by making the end face of the lens barrel sloped.

Function: As mentioned above, by taking measures to prevent floating light in areas where it can become floating light due to diffuse reflection, the amount of so-called floating light that does not have an information signal and is received by the photodetector element is reduced. It is possible to reduce signal deterioration.

Example FIGS. 1 and 2 show an embodiment according to the present invention.

This will be explained using FIG. FIG. 1 is a configuration diagram of a magneto-optical optical head according to the present invention, FIG. 2 is an external view of a stray light prevention plate, and FIG. 3 is a configuration sectional view of a lens barrel portion that holds an objective lens. The configuration of the magneto-optical optical head is exactly the same as the conventional example, and the difference is that a stray light prevention plate has been installed on the reflected light side of the beam splitter, and the configuration of the objective lens barrel has been improved. . Therefore, a detailed explanation of the structure of the magneto-optical optical head will be omitted, and only the different points will be explained in the second section.
This will be explained using FIG. In FIG. 2, a black floating light prevention plate 19 is installed on the side surface of the optical base 716, and a sawtooth shape is formed on the front surface side, so that the semiconductor laser 1
The light beam emitted from the non-polarizing beam splitter 5
The light beam reflected by the floating light prevention plate 19 is absorbed or diffusely reflected by the floating light prevention plate 19, and the reflected light is further reflected and transmitted through the non-polarizing beam splitter 6 to the two-split light detection element 1.
This prevents light from being received by the 2 and 4-split photodetecting elements 16. Furthermore, in FIG. 3, the objective lens 7 is held by the lens barrel 17, but the end surface of the marking barrel 17 is blackened.
Alternatively, a black stray light prevention plate 22 may be pasted, or the end face of the lens barrel 20 may be configured as a slope, so that the light beam bent at right angles to the reflecting mirror 6 is reflected by the end face and returns to the reflecting mirror 6, resulting in a non-polarized beam. This prevents the light from being reflected by the ivy 6 and received by the two-split photodetector element 12 and the four-split photodetector element 16.

By the above method, it is possible to reduce the amount of floating light and provide an optical head with high signal characteristics.

Effects of the Invention As described above, according to the present invention, the configuration of the optical head is hardly changed, a stray light prevention plate is installed on the reflected light side of the beam splitter, and the end surface of the lens barrel that holds the objective lens is made black. By taking measures to prevent stray light at locations where diffuse reflection occurs, such as attaching a floating light prevention plate or creating a sloped structure, the amount of light other than information signals, that is, floating light, can be reduced, and the signal characteristics can be improved. A high ON optical head can be provided, and furthermore, a large capacity, low cost optical drive device can be provided.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of an optical head according to an embodiment of the present invention, Fig. 2 is an external view of a stray light prevention plate of the present invention, and Fig. 3 is a configuration cross-sectional view of a lens barrel section that holds an objective lens. , FIG. 4 is a configuration diagram of a conventional optical head, and FIG. 6 is a configuration sectional view of a conventional objective lens barrel section. 1...Semiconductor laser, 2...Collimating lens, 3...Reflecting mirror, 4...
Shaping prism, 5...Non-polarizing beam splitter, 6...Reflecting mirror 7...Objective lens, 21...Objective lens driving coil, 16.・
...Optical base stand, 19... Stray light prevention plate, 9... Half wavelength plate, 1o... Polarizing beam splitter -11... ...Tracking detection lens, 12...Two-split light detection element, 13.
...Focus detection lens, 14...2
Split mirror, 15... 4-split light detection element, 17
, 2Q... Lens barrel, 18... Bobbin.

Claims (6)

[Claims] (1) A radiation means for emitting a light beam, a reflecting mirror for changing the traveling direction of the light beam, a beam splitter for separating the light beam, and an objective lens for focusing the light beam on an information recording medium. , an optical base that holds at least the reflecting mirror and beam splitter, and a photodetecting element that receives the reflected light from the information recording medium and converts it into an electrical signal, and prevents stray light from occurring in areas where diffused reflection occurs. Optical head with countermeasures. (2) The optical head according to claim 1, further comprising a floating light prevention plate on the reflected light side of the beam splitter. (3) The optical head according to claim 2, wherein the light beam incident side of the floating light prevention plate has a sawtooth shape. (4) The optical head according to claim 1, wherein the end face of the lens barrel that holds the objective lens is blackened. (5) The optical head according to claim 1, further comprising a stray light prevention plate on an end face of the lens barrel that holds the objective lens. (6) The optical head according to claim 1, wherein the end surface of the lens barrel that holds the objective lens is sloped.