JPS61165828A - Optical head - Google Patents

Abstract

PURPOSE:To attain at least the out-of-focus detection and the track shift detection by dividing the light radiated from an information recording medium into two systems by means of a projection means containing a plane part and a curved surface part on the same surface. CONSTITUTION:The laser light L having the dispersing properties which is reflected from a light reflecting layer 3 of an optical disk 2 is converted into parallel luminous fluxes by an objective lens 7 at a focused time point. These beams are sent back to a polarized beam splitter 5 through a 1/4 wavelength plate 6 and reflected by this splitter 5. The light L reflected by the splitter 5 is led to a projection lens 9 containing a curved surface part 13 and a plane part 14. The lens 9 divides the light L into the 1st laser light component L1 for the out-of-focus detection system and the 2nd laser light component L2 for the track shift detection system. Thus the out-of-focus detection, the detection for read signal and the track shift detection can be performed just with a single photodetector 140 from the mechanical viewpoint.

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 Problems Therewith) In the above type of optical head, the objective lens must be moved to control the focal point so that it is located on the light reflecting layer of the information storage medium.

Therefore, in the past, as a defocus detection method to detect the positional shift between the light condensing point and the light reflection layer, a part of the light reflected from the light reflection layer was asymmetrically extracted using a light shielding material such as knife etching. There is a so-called knife etch method that detects this.

However, when the knife etching method is used as the defocus detection method, the optical path of the light reflected by the light reflection layer is divided using a half prism, etc., and the defocus detection system, track deviation detection, and read signal detection system are divided. It is necessary to divide it into For this reason, not only a half prism is required;
Two photodetectors are also required, resulting in a problem that the optical system becomes larger and more complex.

[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 provides an optical head capable of reading at least information from an information storage medium using focused light, in which light emitted from a light source is focused onto the information storage medium by an objective lens. The light emitted from the information storage medium is divided into two systems by a light projecting means having a flat part and a curved part on the same surface, and at least one of defocus detection, track deviation detection, and signal reading is detected. This is characterized in that light is projected onto a photodetector that performs detection and track deviation detection.

[Embodiments of the invention]

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

1 in FIG. 1 is a semiconductor laser (light source), and this semiconductor laser 1 generates diverging laser light. In this case, when writing information to the light reflective layer (recording! l) 3 of the optical disc (information storage medium) 2, laser light whose light intensity is modulated according to the information to be written is generated, and the information is transferred to the optical disc 2. When reading from the light reflecting layer 3, laser light having a constant light intensity is generated. The diverging laser beam generated by the semiconductor laser 1 is converted into a parallel beam by the collimator lens 4 and guided to the deflection beam splitter 5. After passing through this polarizing beam splitter 5, the laser beam guided to this polarizing beam splitter 5 is 1/4
The light passes through the wavelength plate 6 and enters the objective lens 7, and is focused by the objective lens 7 toward the light reflection layer 3 of the optical disc 2. Here, the objective lens 7 is supported movably in the direction of its optical axis by a voice coil 8, and when the objective lens 7 is positioned at a predetermined position, the objective lens 7
The beam waist of the focused laser light emitted from the laser beam is projected onto the surface of the light reflective layer 3, and a minimum beam spot is formed on the surface of the light reflective layer 3. In this state, the objective lens 7 is maintained in a focused state and a focused track state, as will be described later, and information can be written and read. When writing information, bits are formed on the tracking guide on the light reflective layer 3 by a laser beam whose light intensity is modulated, and when reading information, a laser beam having a constant light intensity is used to form bits. , the light intensity is modulated and reflected by the bits formed on the tracking guide.

Divergent and diffuse laser light reflected from the light reflection layer 3 of the optical disk 2 is converted into a parallel beam by the objective lens 7 when it is focused, passes through the quarter-wave plate 6 again, and is returned to the polarizing beam splitter 5. It will be done.

As the laser beam goes back and forth through the quarter-wave plate 6, the plane of polarization of this laser beam is rotated by 90 degrees compared to when it passes through the polarization beam splitter 5, and the plane of polarization is rotated by this 90 degree. The laser beam is reflected by the polarizing beam splitter 5 without passing through the polarizing beam splitter 5. The laser beam reflected by the deflection beam splitter 5 is guided to the projection lens 9.

As shown in FIG. 2, this projection lens 9 includes a prism 11 having a trapezoidal cross section on a part of the light exit surface side of a convex lens 1o having convex curved surfaces on both sides, and a prism 11 having a trapezoidal cross section on the upper base side of the convex lens 1o. In other words, one surface of the prism 11 is processed into a concave curved surface corresponding to the convex curved surface of the convex lens 10 and is bonded.
exists, and a curved surface portion 13 and a flat portion 14 exist on the light exit surface.

The laser light guided to the projection lens 9 is refracted by the curved surface portion 12 on the light incident side when it is brought into focus, and becomes a convergent light. Furthermore, some of the lenser light is transmitted to the curved surface 1 on the light exit side.
3, the first laser beam component Lr (defocus detection system) has a strong focusing property, and the other laser beam passes through the flat part 14, resulting in the first laser beam component Lr. The first
Laser light component! The second laser beam component L2 (read signal detection and track deviation detection system) is focused at a farther distance. Then, these first laser beam components are divided into two laser beam components.

L2 is projected onto the same photodetector 140.

This photodetector 140 is equipped with photodetection cells 15a and 15b for defocus detection and photodetection cells 16a and 16b for read signal detection and track deviation detection, as shown in groups in FIG. , the first laser beam component of the defocus detection system that has passed through the curved surface portion 13 of the projection lens 9 when in focus is placed at the focal point 1. Therefore, the condensing point of the second laser beam component L2 of the read signal detection and track deviation detection system that has passed through the flat part 14 of the light projection lens 9 at the time of focus is the photodetection cell 16a at the time of focus.

It will be located at a position shifted to the rear of 16b.

The first laser beam component L1 of the defocus detection system is irradiated between the photodetection cells 15a and 15b when the focus is focused, and is irradiated to either of the photodetection cells 15a and 15b when the focus is out of focus. As a result, defocus detection is performed using the difference between the outputs of the photodetection cells 15a and 15b. Furthermore, since the focal point of the second laser beam component L2 of the read signal detection and track deviation detection system is shifted from the digit 1 of the photodetector 140, the photodetection cell 168
．． 16b, the spot size becomes larger, which creates a far field pattern (fa) for the optical disc 2.
r field pattern ) is obtained, and using this, that is, using the photodetection cells 16a and 16b, track deviation detection is performed by the OuSh-Dull method. Further, a read signal is obtained from the sum signal from the photodetection cells 16a, 16t).

According to the above configuration, the projection lens 9 having the curved surface part 13 and the flat part 14 is used to convert the laser light into the first laser light component L! of the defocus detection system! Since the second laser beam component of the read signal detection and track deviation detection system is divided into This can be done using the detector 140, and A
-7 prisms etc. are no longer needed. Therefore, the number of optical parts is reduced, the price is reduced, and the device is extremely compact.

As shown in FIG. 4, by tilting the light exit surface 5a of the deflection beam splitter 5 with respect to the optical axis, the laser beam is inscribed in the circular cross-sectional shape and the first laser beam of the defocus detection system. Since the cross-section has an elliptical shape with the short axis along the direction of movement of the light component, the sensitivity of defocus detection can be increased.

Further, the surface of the projection lens 9 without the prism 11 may be a concave curved surface or a flat surface, and the laser beam may be incident from the surface without the prism 11.

Furthermore, as shown in FIG. 5, the projection lens 9 includes a prism 16 having a triangular cross section on a part of the light exit surface side of a convex lens 15 having convex curved surfaces on both sides, with its base side facing the optical axis of the convex lens 15. The convex lens 15 may be embedded in the curved surface portion 17 of the convex lens 15 by polishing and flattening the portion 17- that protrudes from the flat surface portion 18 of the prism 16.

〔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 and light emitted from the light source onto the information storage medium. an objective lens for condensing light, a photodetector for detecting the light emitted from the information storage medium and performing at least defocus detection and track deviation detection among defocus detection, track deviation detection, and signal reading; a light projecting means disposed on an optical path between the information storage medium and the information storage medium and projecting light emitted from the information storage medium onto the photodetector, at least a part of the light projecting means; Since the flat part and the curved part are provided on the same surface, the structure is relatively simple and has excellent effects such as being extremely compact.

[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 lens, FIG. 3 is a front view showing a photodetector, and FIG. 4 is an optical head showing another embodiment of the present invention. Schematic configuration diagram,
FIG. 5 is a perspective view showing another embodiment of the projection lens. 1... Light source (semiconductor laser), 2... Information storage medium (optical disk), 7... Objective lens, 140...
Photodetector, 9... Light projecting lens, 13.17... Curved surface portion, 14.18... Plane portion.

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 light emitted from the light source onto the information storage medium, and the information storage medium. A photodetector that detects light emitted from a medium and performs at least defocus detection and track deviation detection out of defocus detection, track deviation detection, and signal reading, and a connection between the photodetector and the information storage medium. a light projecting means disposed on the optical path and projecting light emitted from the information storage medium onto the photodetector;
An optical head characterized in that at least a part of the light projecting means is constructed by providing a flat part and a curved part on the same surface. (2) At least a part of the light emitted from the information storage medium passes through the flat part of the light projecting means, and a part of the remaining light passes through the curved part of the light projecting means. An optical head according to claim 1.