JPS61267939A - Optical head - Google Patents

Abstract

PURPOSE:To make the titled head small in size remarkably by constituting the head for irradiating focusing light to an information storage medium and reading the information by using a generated reflected light, of a projecting means on which an out-of-focus detecting reflecting surface and a track shift detecting reflecting surface is provided, and a photodetector for detecting these reflected lights. CONSTITUTION:A divergent laser beam originating from a semiconductor laser 21 is changed to a parallel luminous flux by a collimating lens 23, and irradiated and recorded to an information storage medium 22 through a polarized beam splitter 24, a 1/4 wavelength plate 25 and an objective lens 26. Subsequently, read-out reflected light from the medium 22 is returned to the splitter 24, and this reflected light is detected by a photodetector 29 through a projecting means 27 and a condenser lens 28, but in the projecting means 27 of the optical head consisting of them, one fan-type out-of-focus detecting light reflecting surface 27a and two track shift detecting light reflecting surfaces 27b, 27c of a fan type in the same way are provided, and also in the photodetector 29, as well, out-of-focus detecting cells 29a, 29b and track shift photodetecting cells 29c, 29d corresponding to them are provided, and the focal displacement is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an optical head used for reading at least information from an information storage medium by, for example, irradiating the same with focused light.

[Technical background of the invention and its problems]

Some of the above types of optical heads use a push-pull method to detect track deviation and a knife-edge method to detect defocus.

That is, as shown in FIG. 4, a diverging laser beam L generated by a semiconductor laser 1 is converted into a parallel beam by a collimator lens 2, and is directed toward a polarizing beam splitter 3. The parallel laser beam L that has passed through the polarizing beam splitter 3 passes through a quarter-wave plate 4 and is incident on an objective lens 5, and is focused by this objective lens 5 toward an information storage medium 6. The diverging laser beam L reflected from the information storage medium 6 is converted into a parallel beam by the objective lens 5 at the time of focusing, and is again 1
The light passes through the /4 wavelength plate 4 and is returned to the polarizing beam splitter 3. This returned laser beam L is reflected by a polarizing beam splitter 3 and divided into two systems by a half mirror 7, and one of the laser beam components L1 is sent to a first photodetector 9 by a first condensing lens 8. is irradiated.

Here, track deviation detection is performed by the push-pull method, and information detection is also performed. In addition, the other laser beam component L2 divided by the half mirror 7
is extracted asymmetrically with respect to the optical axis by a light shielding plate (light extracting member) 10, passes through a projection lens 11, and enters the photodetector 12 of the rear tube 2. Here, defocus detection is performed using a knife etching method.

However, in the above optical head, the laser beam L
The half prism 7 converts the first and second laser beam components L1. L2, the first laser beam component L
Since track deviation detection and information detection are performed by the laser beam component L2, and defocus detection is performed by the second laser beam component L2, there is a problem that the number of optical parts increases and the optical system becomes complicated and large.

[Purpose of the invention]

The present invention has been made based on the above circumstances, and its object is to provide an optical head that has a relatively simple structure and is extremely compact.

[Summary of the invention]

In order to achieve the above object, the present invention directs a light beam emitted from an information storage medium to at least three or more light beams by means of a light projecting means constituted by at least three light reflecting surfaces adjacent to each other with a predetermined inclination. The present invention is characterized in that the light beam is divided into light beams and projected onto a photodetector that detects at least defocus and track deviation.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 1 to 3.

The first factor 21 is a semiconductor laser (light source), and this semiconductor laser 21 generates a diverging laser beam L. In this case, when writing information to the information storage medium 22, a laser beam L whose light intensity is modulated according to the information to be written is generated, and when reading information from the information storage medium 22, a constant light intensity is generated. A laser beam L is generated having . Then, the diverging laser beam L generated by the semiconductor laser 21 is converted into a parallel light beam by the collimating lens 23 and enters the polarizing beam splitter 24 . After passing through the polarizing beam splitter 24, the laser beam L incident on the polarizing beam splitter 24 passes through the 1/4 wavelength plate 2.
5 and enters the objective lens 26, and is focused by the objective lens 26 toward the information storage medium 22.

Here, the objective lens 26 is supported so as to be movable in its front axis direction and radial direction, and when the objective lens 26 is positioned at a predetermined position, a focused laser beam L emitted from the objective lens 26 is generated. beam waist is projected onto a track (not shown) of the information storage medium 22 to form a minimum beam spot.

In this state, the objective lens 26 is kept in focus and on track, allowing information to be written and read. When writing information, a laser beam L modulated in light intensity is used to write information onto the information storage medium 22.
Bits are formed in the upper track, and when reading information, a laser beam L having a constant light intensity is modulated and reflected by the pits formed in the track.

The diverging laser beam L reflected from the information storage medium 22 is converted into a parallel beam by the objective lens 26 when focused, passes through the quarter-wave plate 25 again, and is returned to the polarizing beam splitter 24.

As the laser beam L travels back and forth through the quarter-wave plate 25, the plane of polarization of the laser beam L is rotated by 90 degrees compared to when it passes through the polarizing beam splitter 24, and the plane of polarization is rotated by this 90 degrees. The laser beam L thus generated is reflected by the polarizing beam splitter 24 without passing through the polarizing beam splitter 24. The laser beam L reflected by the polarizing beam splitter 24 is guided to the light projecting means 27.

As shown in detail in FIG. 2, the light projecting means 27 includes three light reflecting surfaces 27a adjacent to each other at a predetermined inclination, namely, one light reflecting surface 27a for detecting defocus and two light reflecting surfaces 27a for detecting track deviation. It is composed of light reflecting surfaces 27b and 27C. The light projecting means 27 includes three light reflecting surfaces 27.
The intersection of a, 27b, and 27C is the polarizing beam splitter 24
The information storage medium is aligned with the optical axis of the laser beam L from and within the beam spot on the boundary line (tangential line) of the light reflection surfaces 27b, 27G for track deviation detection and the light reflection surfaces 27a, 27b, 27c. The laser beam component 1-a for defocus detection is arranged such that the direction in which the extending direction of the tracks No. 22 is projected is substantially parallel to each other, and the incident laser beam L travels at a predetermined inclination to each other.
and track deviation detection laser beam components Lb, L
C, and the light is projected onto the same photodetector 29 through the same condensing lens 28.

The photodetectors 29 are arranged at the convergence points of the laser beam components La, Lb, and LC condensed by the condenser lens 28, and are adjacent to each other as shown in detail in the third factor. A pair of light detection cells 29a and 29b for detecting defocus are provided, and a pair of light detection cells 29c and 29d for detecting track deviation are provided spaced apart from each other.

When the laser beam component La reflected by the defocus detection light reflection surface 27a is focused, the light detection cell 29a,
The light is focused on the center of the photodetection cell 29b, and when the light does not match, the photodetection cell 29
It is designed to irradiate either a or 29b,
As a result, defocus detection is performed using the difference between the outputs of the photodetection cells 29a and 29b. That is, defocus detection is performed using a knife etching method. In addition, the light reflecting surface 27b for detecting track deviation
, 27c, the laser beam component 1-b reflected.

The LC is focused onto photodetection cells 29c and 29d, respectively. Here, the beam spot of the laser beam L that has been reflected and returned from the track of the information storage medium 22 has a far field pattern (fa) with respect to the information storage medium 22.
r field pattern),
Since a left-right asymmetrical intensity distribution occurs due to the track deviation state, by detecting a change in the light amount ratio between the laser light component Lb and the laser light component LC with the photodetection cell 29C229d, that is, by using the difference in the detection signal layer. Track deviation detection is performed. That is, track deviation detection is performed using a push-pull method. Note that the information read signal is transmitted to the photodetection cells 29a and 29.
It is obtained by the sum signal from b, 29c, and 29d.

According to the above configuration, there are three light reflecting surfaces adjacent to each other with a predetermined inclination, that is, one light reflecting surface 27a for detecting defocus and two light reflecting surfaces 27 for detecting track deviation.
Since the laser beam L is divided into a laser beam component 1a for defocus detection and a laser beam component Lb and LC for track deviation detection by the light projecting means 27 composed of parts b and 27c, defocus detection and track deviation detection can be performed mechanically. In terms of perspective, this can be done using a single photodetector 29, and a half prism or the like for dividing the laser beam L is not required. Moreover, the laser beam components La and Lb.

The LC can be focused by one focusing lens 28.

Therefore, the number of optical parts is reduced, the price is reduced, the size is very small, and assembly and adjustment can be easily performed.

〔Effect of the invention〕

As explained above, according to the present invention, an optical head capable of reading at least information from an information storage medium using focused light includes a light source, a light beam emitted from the light source, and a light beam emitted from the information storage medium. detecting the light beam emitted from the objective lens and the information storage medium;
a photodetector for detecting at least defocus and track deviation; and a photodetector disposed on an optical path between the photodetector and the information storage medium, the optical beam emitted from the information storage medium is transmitted to the photodetector. Since the light projecting means is composed of at least three light reflecting surfaces adjacent to each other at a predetermined inclination, the structure is relatively simple and very simple. It has excellent effects such as becoming smaller.

[Brief explanation of the drawing]

Figures 1 to 3 show one embodiment of the present invention.
2 is a perspective view showing a light projecting means, FIG. 3 is a front view showing a photodetector, and FIG. 4 is a schematic structure diagram showing a conventional example. 21... Light source (semiconductor laser), 22... Information storage medium, 26... Objective lens, 27... Light projection means,
27a, 27b, 27c... light-reflecting surfaces, 29...
Photodetector. Applicant's representative Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 3 Figure 4

Claims (2)

[Claims] (1) An optical head capable of reading at least information from an information storage medium using focused light, including a light source, an objective lens that focuses a light beam emitted from the light source onto the information storage medium, and the information storage medium. a photodetector that detects a light beam emitted from a storage medium and performs at least defocus detection and track deviation detection; and a light projection means for projecting the emitted light beam onto the photodetector, the light projection means being comprised of at least three light reflecting surfaces adjacent to each other with a predetermined inclination. optical head. (2) The boundary lines of two of the three light-reflecting surfaces of the light projecting means and the direction in which the extending direction of the track of the information storage medium is projected into the beam spot on the light-reflecting surface are mutually The optical head according to claim 1, characterized in that the optical head is configured to be substantially parallel.