JPH01211331A - Optical head - Google Patents

Abstract

PURPOSE:To eliminate the need for a shaping prism so as to reduce the weight and cost of an optical head by using such a collimate lens that the minor axis of the elliptically diverged beam radiated from a semiconductor lens can become longer than the effective diameter of the collimate lens and the rays of light in the minor-axis direction can become parallel rays of light. CONSTITUTION:When the effective diameter 2a of collimate lens 2 is made shorter than the minor axis of the elliptically diverged rays of light from a semiconductor laser 1, the rays of light become parallel rays of light with a circular cross section. The parallel rays of light transmits through the 1/4-wave plate 5 of a polarization beam splitter and are allowed to form a beam spot on an information recording surface 7 by means of an object lens 6. Therefore, when the specifications and position of the collimate lens 2 are set so that the elliptically diverged rays of light can become parallel beams having a circular cross section, the necessity of an expensive shaping prism which shapes an elliptical beam to a circular beam can be eliminated and, as a result, an optical head which is small in size, light in weight, and low in cost can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is an optical system that 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. The present invention relates to an optical head as a type recording and reproducing device.

Background of the Invention In recent years, high-density, large-capacity optical memory devices are expected to be developed as external memory devices for computers.In principle, a light beam emitted from a semiconductor laser is passed through an objective lens to record information. Information is recorded by condensing light onto the medium and creating recesses in the information recording film, and during reproduction, the information signal is extracted by taking advantage of the fact that the amount of light changes between the flat and recessed parts of the information recording surface. There is.

A conventional optical recording/reproducing device will be explained using FIG. 3. 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. Also, 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 transmitted through an objective lens 6 and a circular beam. The light is focused on the information recording surface T. At this time, if the light beam incident on the objective lens 6 is made larger than the effective diameter of the objective lens 6, the beam focused by the objective lens 6 exhibits an Airy disk distribution due to the diffraction effect, and the beam diameter is narrowed down. In addition, if the narrowed beam is to have a uniform beam diameter in the radial direction and one circumferential direction, the parallel beam diameter incident on the objective lens 6 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 narrowed by the objective lens 6 can be narrowed down to a small size, the energy of the laser beam can be focused, and a recess can be formed in the recording film. Further, the light beam irradiated onto the information recording surface 7 is reflected and enters the objective lens 6 again to become a parallel beam. This parallel beam is again incident on the quarter-wave plate 6, the polarization plane is rotated by 90 degrees, the total amount of 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 light beam is separated into light beams and reflected, and the reflected S-polarized light beam is focused by a convex lens 9 and imaged on a two-split photodetector 1o to detect a tracking error signal. On the other hand, the transmitted P-polarized beam is transmitted through the convex lens 11.
The light is focused by the cylindrical lens 12 to generate astigmatism, and an image is formed on a four-segment photodetector 13 to detect a focus error signal. With these focus error signals and tracking error signals,
Even if the information recording medium has some degree of surface wobbling or eccentricity, the objective lens 7 can be controlled within a focal depth of approximately ±1 μm in the focusing direction and within ±0.1 μm in the tracking direction using the lens drive coil. This is achieved by driving the

Problems to be Solved by the Invention The development trend of optical recording and reproducing devices and erasable optical recording and reproducing devices is aimed at the replacement market for external memory devices for computers, and smaller size, larger capacity, and faster access are being considered. . In terms of miniaturization and thinning, the optical head for optical recording shown in FIG. 3 is much larger than the magnetic head for magnetic recording.

Also, when it comes to high-speed access, it is nearly an order of magnitude slower than fixed magnetic disk drives. The reason for this is that the optical head is about two orders of magnitude heavier than the magnetic head. Therefore, in order for an optical recording/reproducing device to become a substitute for an external memory device for a computer, the biggest challenge is to make the optical head smaller, thinner, lighter, and more expensive.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention changes the effective diameter of the collimating lens so that the elliptical beam emitted from the semiconductor laser becomes a parallel circular beam. The length of the diverging beam in the minor axis direction or less.

Function As described above, by setting the collimating lens so that the short rectangular direction of the elliptically diverging beam emitted from the semiconductor laser is equal to or larger than the effective diameter of the collimating lens, and making the beam parallel, the output of the collimating lens can be improved. The emitted light becomes a circular beam of parallel light. Therefore, the conventional shaping prism can be removed and its decomposition can be achieved.

Cost reduction can be achieved.

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 reproduction is exactly the same as in the conventional example, and some of the component parts, namely the shaping prism 3 that converts the elliptical beam into a circular beam located behind the collimating lens 2 in the conventional example shown in FIG. 3, can be deleted. . In FIG. 1, the elliptically diverging light emitted from the semiconductor laser 1 becomes a circular beam when the effective diameter 21L of the collimating lens 2 is set to be equal to or less than the short axis length of the elliptical beam of the semiconductor laser 1 as shown in FIG. 2a. It becomes parallel light, passes through the quarter-wave plate 5 of the polarizing beam splitter 4, and passes through the objective lens 6.
As a result, a beam spot is focused on the information recording surface 7.

(Figure 2 shows a conventional example.) The irradiated light beam is reflected again by the information recording surface 7 and transmitted through the quarter-wave plate 6, and the total amount of reflected light is reflected by the polarizing beam splitter 4. The 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 and imaged on a two-split photodetector 10 to detect a tracking error signal. be done. On the other hand, the transmitted P-polarized light beam is condensed 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.

As described above, the present invention makes it possible to convert an elliptical diverging beam emitted from a semiconductor laser into an elliptical beam by simply arranging the collimating lens so that the 9 positions of the collimating lens become parallel beams without changing the configuration. An expensive shaping prism for shaping a circular beam can be omitted, and a small, lightweight, and low-cost optical head can be provided.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an optical head for an optical recording/reproducing apparatus according to an embodiment of the present invention, and FIGS. 2a and 2b are diagrams showing the shape of a beam incident on a collimating lens. FIG. 3 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, 6 ... Objective lens, End ... Information recording surface, 8 ... Polarizing beam splitter -19 ...・Convex lens, 10...
...2-split photodetector, 11...
Convex lens, 12... Cylindrical lens, 1
3...4-division photodetector. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Fig.2

Claims (1)

[Claims] An optical head that uses a semiconductor laser as a light source and makes the effective diameter of a collimating lens through which an elliptical beam from the semiconductor laser passes equal to or less than the short-axis length of the elliptical diverging beam emitted from the semiconductor laser.