JPH01211330A - Optical head - Google Patents

Abstract

PURPOSE:To eliminate the need for a shaping prism and to constitute the optical head of a thin optical element so as to make the optical head thin in thickness, small in size, and light in weight by using a reflecting mirror with a cylindrical surface instead of a 45 deg.-plane reflecting mirror which changes the optical axis of parallel rays of light in an orthogonal direction. CONSTITUTION:A reflecting mirror 14 having a cylindrical surface is used instead of a 45 deg.-plane reflecting mirror. When elliptical parallel rays of light are projected on the reflecting mirror 14, the optical axis of the rays of light is changed in the orthogonal direction and the rays of light are projected toward an information recording medium and, at the same time, since the reflecting surface is formed to a cylindrical surface, the rays of light are expanded in the minor-axis direction and the light quantity distribution of the light converged by an objective lens 7 can be made almost uniform between the radial direction and peripheral direction. Therefore, the beam converged by the lens 7 can become a uniform circular beam with a small diameter. Therefore, the reflecting mirror can be used as a shaping prism and 45 deg.-plane reflecting mirror without spoiling the characteristic of the beam. Accordingly, no shaping prism is required and this optical head can be made thinner in thickness, smaller in size, and lighter in weight.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is used for image files, document files, external memory devices for computers, etc., and records and reproduces information using a light beam of a semiconductor laser. This invention relates to an optical head for an optical recording and reproducing device.

2. Description of the Related Art In recent years, high-density, large-capacity optical memory devices have been expected to be developed as external memory devices for computers. Information is recorded by condensing light onto an information recording medium, creating recesses in the information recording film, etc., and extracting information signals by taking advantage of the change in light intensity between the flat and recessed areas of the information recording surface during playback. It is something.

A conventional optical recording/reproducing device will be explained using FIG. 2. 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. Since this parallel beam is an elliptical beam, it is modified into a circular beam by a shaping prism 3, and then transmitted through a polarizing beam splitter 4 and a quarter-wave plate 6, and then passed through a 46° flat reflecting mirror 6. It is bent at right angles towards the information recording medium. The light beam bent at right angles enters the objective lens 7 and is focused onto the information recording medium. At this time, if the light beam incident on the objective lens 7 is made larger than the effective diameter of the objective lens γ, the beam focused by the objective lens 7 exhibits a shearly disk distribution due to the single diffraction effect, and the beam The diameter is narrowed down. If we try to make the still narrowed beam a uniform beam diameter in the radial direction and one circumference direction, the diameter of the parallel beam incident on the objective lens 7 will be a circular beam, and the intensity distribution will be made uniform in the radial direction and the circumferential direction. It is necessary. If the beam diameter becomes a circular beam on the information recording medium and can be converged to a small size, the energy of the laser beam will be focused and a recessed portion can be provided in the recording film. Further, the light beam irradiated onto the information recording medium is reflected and enters the objective lens 7 again to become a parallel beam. This parallel beam is again incident on the quarter-wave plate 5, the plane of polarization is rotated by 90 degrees, and the total amount of reflected light is reflected by the polarizing beam splitter 4, and is incident on the polarizing beam splitter 8. A polarizing beam splitter 8 separates the light beam into P-polarized light and S-polarized light beam, and the reflected S-polarized light beam is focused by a convex lens 9.
An image is formed on the two-split phototicketor 10, and a tracking error signal is detected. On the other hand, the transmitted P-polarized beam is focused by the convex lens 11, astigmatism is generated by the cylindrical lens 12, and imaged by the 4-split photodetector 13, where a focus error signal is detected. Ru. Due to these focus error signals and tracking error signals, even if the information recording medium has surface runout or eccentricity to some extent, the focal beam angle is within ±1 μm in the focus direction and ±0.1 μm in the tracking direction. This positioning control is achieved by driving the objective lens 7 with a lens drive coil.

Problems to be Solved by the Invention The trend in the development of optical recording and reproducing devices and erasable optical recording devices is toward smaller size and larger capacity, with the aim of replacing external memory devices for computers.

High-speed access is being considered. Even when it comes to miniaturization and thinning, optical recording heads are much larger and thicker than magnetic recording heads. Also, for high-speed access,
Some parts are almost slower than fixed magnetic disk devices. The reason for this is that the optical head shown in Figure 2 is nearly an order of magnitude heavier than the magnetic head.

Therefore, in order for an optical recording/reproducing device to become a substitute product for external memory devices for computers, the biggest challenge is to make the optical head smaller, thinner, and lighter.

Means for Solving the Problems In order to solve the above problems, the present invention arranges a reflection mirror with a cylindrical surface on the edge of the 46° flat reflection mirror 6 that converts the optical axis of the conventional parallel light to the right angle direction. It is something.

Function As mentioned above, a reflecting mirror with a cylindrical surface is placed on the edge of the 46° flat reflecting mirror, so when elliptical parallel light is incident on this reflecting mirror, the optical axis is converted to the vertical direction. , is irradiated in the direction of the information recording medium, and 1
Since the reflecting surface is cylindrical, the light is expanded in the short axis direction, making the distribution of light incident on the objective lens almost uniform in both the radial and circumferential directions, and therefore narrowed down by the objective lens. The beam becomes a uniform circular beam and can be narrowed down to a small size. Therefore, it is possible to provide the function of both a shaping prism and a 46° flat reflection mirror without deteriorating the characteristics of the beam focused by the objective lens.

Embodiment An embodiment of the present invention will be described with reference to FIG. FIG. 1 shows a configuration diagram of an optical head for an optical recording/reproducing apparatus according to the present invention. The principle of recording and playback is exactly the same as the conventional example, and only some of the component parts are used.

That is, the conventional 46° flat reflecting mirror 6 is simply replaced with a reflecting mirror 14 having one surface having a cylindrical shape.

When the semiconductor laser 1 is arranged so that the long and short directions are in the horizontal direction, the elliptically diverging light emitted from the semiconductor laser 1 is converted into parallel light by the collimating lens 2, and then the polarizing beam splitter 4 and the quarter The light passes through the one-wavelength plate 6 and is incident on the cylindrical surface of the reflecting mirror 14 . Then, at this point, the optical axis becomes vertical, and at the same time the rectangular shape of the elliptical parallel beam changes to a diverging beam and becomes an almost circular beam. Since the objective lens 7 is placed here, a beam spot is focused on the information recording medium. The irradiated light beam is again reflected by the information recording medium, transmitted through the quarter-wave plate 5, the total amount of reflected light is reflected by the polarization beam splitter 4, and the polarization beam splitter 8 separates the P-polarized light and the S-polarized light. The S-polarized beam, which is separated into light beams and reflected, is focused by a convex lens 9.

An image is formed on the two-segment photodetector 10, and a tracking error signal is detected. On the other hand, the transmitted P-polarized light beam is focused by a convex lens 11, astigmatism is generated by a cylindrical lens 12, and an image is formed on a 4-split photodetector 13, where a focus error signal is detected. Ru.

As described above, the present invention not only makes it possible to reduce the number of conventional shaping prisms used to shape an elliptical beam into a circular beam, but also to reduce the need for a shaping prism for shaping a conventional elliptical beam into a circular beam without changing the configuration. It is possible to transmit parallel light through the optical element, so it can be constructed with a thin optical element.

It is possible to achieve a thin, compact, and lightweight optical head, and to provide an inexpensive, thin, and lightweight optical head.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an optical head according to an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional optical recording/reproducing optical head. 1... Semiconductor laser, 2... Collimating lens. 4...Polarizing beam splitter-16...
・Quarter wavelength plate, 7...Objective lens, 8・Mountain...Polarizing beam splitter-19・Mountain...Convex lens, 1
0...2-split photodetector, 11・Mountain・
・Convex lens, 12... Cylindrical lens,
13. River... 4-split photodetector, 14. River...
reflective mirror. Name of agent: Patent attorney Toshio Nakao and 1 other person

Claims (2)

[Claims] (1) A semiconductor laser that emits elliptically diverging light, a collimating lens that converts the diverging light into parallel light, a mirror that converts the optical axis of the parallel light to a right angle direction, and an objective lens that focuses the light beam on the recording medium. An optical head comprising: a reflecting mirror having a cylindrical surface as the mirror. (2) The optical head according to claim 1, wherein the elliptical parallel beam is made incident on a portion of the cylindrical reflecting mirror that converts the optical axis to a right angle.