JPS62200542A - Optical head - Google Patents

Abstract

PURPOSE:To miniaturize and lighten a device by using an optical parts arranged on an optical path from a light source to an information recording medium, also as the optical parts arranged on the optical path from the information recording medium to a photo detecting apparatus. CONSTITUTION:The titled device is equipped with a light source 42 for a semiconductor laser, an objective lens 48 which condenses light from the light source 42 on a photomagnetic disk 49, a half mirror 45 which separates the light returned through the disk 49 from the light advancing from the light source 42 to the disk 49, and a polarizing splitter 52 which reflects a part of the light separated with the half mirror 45, and transmits the other part. And also, it is equipped with a light reflecting member 54 which reflects the light transmitted through the splitter 52, and introduces it to the splitter 52, and a photo detecting apparatus 43 which detects the light reflected at the reflecting member 54, and the light reflected at the splitter 52. Furthermore, the light source 42 and the photo detecting apparatus 43 are arranged at positions approaching with each other.

Description

Detailed Description of the Invention [Objective of the Invention 1 [Field of Industrial Application] The present invention relates to an optical system used in an information recording/reproducing device that records, reproduces, or erases information on an information storage medium using focused light. Regarding the head.

[Conventional technology]

2. Description of the Related Art Conventionally, devices have been known that optically record and reproduce information from an information storage medium using a magneto-optical effect such as the Kerr effect or the Faraday effect. Such an apparatus employs an optical head having an optical system as shown in FIG. 3 or 4, for example.

That is, in the optical system shown in FIG. 3, a laser beam emitted from a semiconductor laser 1 is guided to an objective lens 6 via a collimating lens 2, a prism 3, a beam splitter 4, and a mirror 5 in this order. It is focused onto the information storage medium 7 by the objective lens 6.

The laser beam reflected by the information storage medium 7 is transmitted through the objective lens 6 and then reflected by the mirror 5 and the beam splitter 4 in sequence. This reflected laser light is separated into two systems by a beam splitter 8, and one of the laser lights is separated by a long plate 9 and a convex lens 10.
The light is then separated into a p component and an s component by a polarizing beam splitter 11 and irradiated onto first and second photodetectors 12 and 13, respectively. Then, the information on the information storage medium 7 is read using the difference between the output signals of the first and second photodetectors 12.13, and the output of the first or second photodetector 12.13 is Track deviation detection is performed using the signal. The other laser beam separated by the beam splitter 8 sequentially passes through a convex lens 14 and a cylindrical lens 15 and is irradiated onto a third photodetector 16. Then, focal defocus detection is performed using the astigmatism method.

In the optical system shown in FIG. 4, the laser light emitted from the semiconductor laser 21 passes through the collimating lens 22 and the beam splitter 23 in order and is guided to the objective lens 24, which allows the information storage medium to be 25.

The laser beam reflected by the information storage medium 25 passes through the objective lens 24 and then is reflected by the beam splitter 23.
The light is guided to a polarizing beam splitter 29 via a 1/2 wavelength plate 26, a convex lens 27, and a concave lens 28 in this order. This laser light is separated into a p component and an S component by a polarizing beam splitter 29, and the p component laser light is irradiated onto a photodetector 31 via a cylindrical lens 30, which allows defocus detection using the astigmatism method. It will be done. Further, the separated S component laser beam is irradiated onto a photodetector 32, and tracking detection is performed by this device. Furthermore, information on the information storage medium 25 is read based on the difference in output signals of the photodetectors 31 and 32.

Note that 17.33 in Figures 3 and 4 is a magnet frenzy.

[Problem that the invention seeks to solve]

As is clear from the figures, the optical system shown in FIGS. 3 and 4 has a large number of optical parts, is large, and has a heavy mff1, so it is not suitable for high-speed access.
There was a problem with high costs.

The present invention has been made based on the above-mentioned circumstances, and its purpose is to reduce the number of optical components and achieve a reduction in size and weight, thereby not only enabling high-speed access but also reducing cost. An object of the present invention is to provide an optical head that can be used in a variety of ways.

[Construction of the Invention] [Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention records information on light emitted from a light source using an objective lens. ! The light is focused on the medium and the light returned from the information storage medium is used as a half mirror.
separates the light from the light source toward the information storage medium, a polarizing beam splitter reflects part of the separated light and transmits the other part, and the light that has passed through the polarizing beam splitter is reflected by a light reflecting member, The light is transmitted through the polarizing beam splitter again, and the light reflected by the light reflecting member and the light reflected by the polarizing beam splitter are detected by a photodetector, and the light source and the photodetector are arranged close to each other. It is characterized by this.

[Effect]

An optical component placed on the optical path from the light source to the information storage medium is also used as an optical component placed on the optical path from the information storage medium to the photodetector.

(Example) An example of the present invention will be described below with reference to FIGS. 1 and 2.

In the figure, reference numeral 41 denotes a mount, and this mount 4 includes a semiconductor laser 42 that emits laser light, cells 43a and 43b for detecting defocus, cells 43G and 43dJ5 for detecting track deviation, and a cell 43e for reading information. A photodetector 43 is mounted.

A diverging laser beam emitted from a semiconductor laser (light source) 42 is converted into substantially parallel light by passing through a collimator lens 44 which also serves as a 19-light lens, and then guided to a half mirror 45. This half mirror 45 has prisms 46 and 47 bonded together, and a half mirror surface 4 on the bonded surface.
5a, and an ellipse correction refractive surface 45b is formed on one surface of one prism 46. The guided laser beam is then incident from the ellipse correction refraction surface 45b. This ellipse correction refractive surface 45t) is tilted with respect to the optical axis, so refraction occurs when the laser beam is incident, and the spot size of the laser beam is changed in the refracted direction, thereby correcting the ellipse of the laser beam. will be held.

The laser light incident on the prism 46 passes through the half mirror 45a, and is then guided to the objective lens 48.
The light is focused on 49.

This magneto-optical disk 49 is, for example, an amorphous...
The recording layer has a recording layer made of a magnetic alloy, and tracking guides are formed concentrically or spirally on its surface in a concave or convex shape. Roughly speaking, preliminary information such as a track address and a sector address, that is, a bluff T-mat signal, is formed in advance on the tracking guide as concave or convex pre-pits. In the recording layer of this magneto-optical disk, when no information is recorded, the directions of all magnetic domains are aligned in a certain direction.
During recording, when a magnetic field is applied and the area is rapidly heated, the magnetization direction of the magnetic domain in that area is reversed.

The semiconductor laser 42 is driven by a drive circuit (not shown). During reproduction, the semiconductor laser 42 generates laser light with a constant light intensity, and during recording, the semiconductor laser 42 generates laser light whose light intensity is modulated according to the information to be recorded. Light is generated, and during erasing, laser light having a constant light intensity greater than during reproduction is generated.

During recording, a static magnetic field generated from the magnet device 50 is applied to the magneto-optical disk 49, and when the tracking guide of the magneto-optical disk 49 is traced with recording laser light, a specific vAil is rapidly heated and the magnetization direction is reversed. The information will be distributed. Furthermore, during reproduction, when the tracking guide is traced with a reproduction laser beam and the laser beam is focused on a magnetized region that has been reversely magnetized, the positive side of the laser beam is slightly rotated. During erasing, a static magnetic field generated by the magnet device 50 is applied to the magneto-optical disk 49, and when laser light for erasing is irradiated to a specific region where the tn direction has been reversed, this region is gently heated and magnetized. The direction is reversed again so that it is the same as the other regions.

The laser light emitted from four magneto-optical disks is
After passing through the objective lens 48, it is returned to the half mirror 45. The laser beam reflected by this half mirror 45 is transmitted through a 1772 wavelength plate 51 (the solar surface is rotated approximately 45 degrees) in order to increase the ratio of S wave components. The laser light L+, tfQ including the L + and S-wave components is incident on the optical beam splitter 52. This polarized beam subric 52 has a polarized beam split surface 52a, 1 (!! The incident laser beam is guided to the polarized beam splitting surface 52a, the S-wave component is reflected by the polarized beam splitting surface 52a, and the p-wave component is reflected by the polarized beam splitting surface 52a. It passes through the surface 52a.

The S-wave component laser light reflected by the polarized beam split surface 52a passes through the light refraction surface 52b and the collimating lens 44 which also serves as a projection lens, and becomes the information reading laser beam 1a.
The light is guided onto the information reading cell 43e of the photodetector 43 as a signal. On the other hand, the laser light transmitted through the polarized beam splitter surface 52a is guided to a light splitting member 54 provided so as to overlap the polarized beam splitter 52a of the polarized beam splitter 52.

The light splitting member 54 has a light reflecting plane 54a and a cylindrical reflecting surface 54b slightly inclined with respect to the light reflecting plane 54a. Then, the laser beam of the p-wave component is directed to the reciprocal plane 54a and the cylindrical reflection surface 54.
b, a defocus detection laser beam L for detecting defocus of the objective lens 48 with respect to the magneto-optical disk 49;
b and a track deviation detection laser beam LC that detects the deviation of the laser beam focused on the four magneto-optical disks with respect to the tracking guide. The light is guided through the surface 52b and the collimator lens 44 which also serves as a projection lens to onto the defocus detection cells 43a and 43b and the track deviation detection cells 43c and 43d of the photodetector 43, respectively.

When the objective lens 48 is focused on the magneto-optical disk 49 (hereinafter, this state will be referred to as "in-focus"), the laser beam La reflected by the light reflecting plane 54a is at the boundary of the defocus detection cell. The light is focused on the cell 43 depending on the out-of-focus peak.
a, 43b, and thereby defocus detection is performed using the so-called knife etching method (see Japanese Patent Application Laid-Open No. 56-146546, pages 9 to 11). On the other hand, the laser beam LC reflected by the cylindrical reflection surface 54b is stretched in one direction by the action of the cylindrical reflection surface 54b, and the track deviation detection cells 43c and 43d are moved to the magneto-optical disk 49 when in focus in this stretched direction. Since a far field pattern is formed for the track deviation detection cell 43C143d, the track deviation is detected using the so-called bush-pull method, which detects the track deviation using the diffraction pattern of the reflected light from the tracking guide of the laser beam focused using the tracking deviation detection cell 43C143d. Detection takes place. Note that a composite signal of the output signals of the track deviation detection cells 43c and 43d and the output signals of the defocus detection cells 43a and 43b,
Information is read by a comparison signal with the output signal of the information reading cell 43e.

According to the above configuration, since the photodetector 43 is arranged near the semiconductor laser 42, the laser light emitted from the semiconductor laser 42 is collimated by the single projecting lens/collimating lens 44, and the photodetector A laser beam can be projected onto 43. That is, the collimating lens disposed on the optical path from the semiconductor laser 42 to the magneto-optical disk 49 can also be used as a projection lens disposed on the optical path from the magneto-optical disk 49 to the photodetector 43. Therefore, it is possible to reduce the number of optical parts and achieve a reduction in size and weight, which not only enables high-speed access but also to reduce costs.

[Effects of the Invention] As explained above, according to the present invention, optical components disposed on the optical path from the light source to the information storage medium can be used as information storage media! ! Since it can also be used as an optical component placed on the optical path from the medium to the photodetector, it is possible to reduce the number of optical components and achieve a reduction in size and weight, which not only enables high-speed access. This has excellent effects such as cost reduction.

[Brief explanation of drawings]

1 and 2 show an embodiment of the present invention,
Figure 1 is a block diagram schematically showing the entire structure, Figure 2 is a front view showing the photodetector and semiconductor laser, Figures 3 and 4.
The figures are configuration diagrams showing different conventional examples. 42... Light source (semiconductor laser), 43... Photodetector, 45... Half mirror 148... Objective lens,
49...Information! , 4a medium (magneto-optical disk), 5
2...Polarized light and -musplitter, 54...Light reflecting member. Applicant's agent Patent attorney Suzue Takehiko'AS 3 Figure

Claims (1)

[Claims] a light source, an objective lens that focuses light emitted from the light source onto an information storage medium, and a light that is focused by the objective lens and returned via the information storage medium from the light source toward the information storage medium. a polarizing beam splitter that reflects part of the light separated by the half mirror and transmits the other part; and a polarizing beam splitter that reflects the light that has passed through the polarizing beam splitter and guides it to the polarizing beam splitter. The light source includes a reflecting member and a photodetector for detecting the light reflected by the light reflecting member and the light reflected by the polarizing beam splitter, and the light source and the photodetector are arranged in close proximity. Features an optical head.