JP2812764B2 - Optical head for optical disk device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head used in a writable optical disk device capable of recording and reproducing information.

[Conventional technology]

In a writable optical disk optical head, writing and reading of data are performed by the same mechanism by changing only the laser power.

FIG. 3 shows a basic configuration of a conventional optical head. In FIG. 3, 301 is an optical disk, 303 is an objective lens, and 305 is 1/4.
A wave plate, 307 is a polarizing beam splitter, 309 is a laser diode, 311 is a cylindrical lens, and 313 is a photodetector. The laser light 315 emitted from the laser diode 309 is applied to the optical disk 30 by the objective lens 303.
Squeezed on one side. At the time of data reading, data within the range of this spot is read, and the reflected light returns to the photo detector 313 to convey information.

In an optical disk device, it is essential to configure a focus and tracking servo system, and these servo information signals are also reflected by the photodetector 313 by reflected light.
The reflected light is required not only at the time of reading but also at the time of writing.

In the conventional optical head, since the reflected light returns through exactly the same path as the irradiation light, a mechanism for separating the reflected light is required.

For this mechanism, half mirrors and holograms are often used in the read-only type from the viewpoint of cost, but in the writable type in which the output power from the objective lens is important, the light use efficiency is reduced by these methods. Because of its lowness, a combination of a polarizing beam splitter 307 and a quarter-wave plate 305 is used.

[Problems to be solved by the invention]

In a writable optical disk device, the higher the power of the laser beam at the time of writing, the better from the viewpoint that the access time can be shortened by increasing the number of rotations of the disk and that the range of selection of the recording medium can be widened. However, there is a limit to the power of the laser diode, and therefore, the utilization efficiency of irradiation light becomes important.

As described in the previous section, the conventional optical head requires a mechanism for separating the reciprocating optical path, but the loss of light here deteriorates the utilization efficiency of irradiation light. Even when a polarizing beam splitter and a quarter-wave plate are used in combination, the utilization efficiency of irradiation light cannot be said to be high due to reflection on the element surface, loss due to polarization axis shift, and the like.

[Means for solving the problem]

In order to solve the above problems, the optical head of the present invention includes a means for irradiating a laser beam to a central portion of an objective lens in an oblique direction, and an optical path of irradiation light among reflected light of laser light from an optical disk surface. Means for separating and detecting reflected light passing through different optical paths.

〔Example〕

 FIG. 1 shows the configuration of an optical head according to the present invention.

In FIG. 1, 101 is an optical disk, 103 is an objective lens,
105 is a laser diode, 107 is a light separating optical member,
109 indicates a photodetector.

Irradiation light that is incident on the surface of the optical disk 101 at a slight angle from perpendicular is reflected with the irradiation light centering on the normal to the optical disk surface, so that part of the reflected light is within the optical path range of the irradiation light.
Laser diode 10 passing through the optical path range 121 which deviates from 120
Return to 5. The reflected light is separated by placing an optical member 107 such as a mirror or a prism in the optical path range 121 at the position of this shift, and a photodetector 109 for detection is placed at the focal point of the separated reflected light to provide a data signal and a lens position control servo. Detect signal. In this optical system, it is possible to detect signals without interrupting the irradiation light at all,
The transmission efficiency of irradiation light is improved, and the output power of the objective lens is increased.

As the objective lens 103, an aspheric lens whose astigmatism and field curvature are corrected is used.

FIG. 2 shows a configuration for detecting servo and data information from the separated reflected light. In FIG.
201 is reflected light, 203 and 205 are focus servo signals (FSS)
A photodetector for detection, 207 and 209 are photodetectors for tracking servo signal (TSS) detection, 211 is a photodetector substrate, 213 is an amplifier for FSS operation, 215 is an amplifier for TSS operation, and 217 is an amplifier for data signal operation.

Here, the photodetector substrate 211 is installed as follows. That is, in FIG. 1, when the surface of the optical disk 101 fluctuates in the direction of 110 or 111, the focal point of the reflected light passing through the optical path 121 fluctuates along the circular arc 112. Is set in the direction along the tangent 113 of the arc 112.

In this configuration, the difference between the left and right focus servo detectors (203, 205) is obtained by the FSS calculation amplifier 213, whereby the focus servo control signal 218 can be obtained.

Detection of the tracking servo control signal 219 is performed by the conventional push-pull method by the TSS calculation amplifier 215 using the inner two-part photodetectors (207 and 209).

Here, since the servo signal used in the optical system of the present invention is only one side of the totally reflected light, an offset occurs in the tracking servo signal in an on-track state, and thus the offset is electrically corrected.

The data signal 220 is the inner two-part photodetector (20
7, 209) by the data signal operation amplifier 217.

〔The invention's effect〕

According to the present invention, the use efficiency of light in the optical head for an optical disk is increased, and higher output power can be obtained.

Further, since only one optical element such as a mirror is used as an element for separating reflected light, it is useful for reducing the number of parts.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical head of the present invention, FIG. 2 is a configuration diagram of a photodetector used in the present embodiment, and FIG. 3 is a configuration diagram of a conventional optical head. 101 optical disc, 103 objective lens, 105 laser diode, 107 light beam separating optical member, 109 photodetector, 201 reflected light, 203 FSS detection photodetector left, 205 FSS Photodetector right for detection, 207… Photodetector left for TSS detection, 209… Photodetector right for TSS detection, 211 …… Photodetector board, 213… Amplifier for FSS calculation, 215… Amplifier for TSS calculation, 217 …… Data signal Operational amplifier, 301 optical disc, 303 objective lens, 305 quarter-wave plate, 307 polarization beam splitter, 309 laser diode, 311 cylindrical lens, 313 photo detector.

Claims (1)

(57) [Claims] An optical head for an optical disk apparatus for recording and reproducing information by irradiating a laser light from a laser light source to an optical disk surface, comprising an objective lens between the optical disk surface and the laser light source in parallel with the optical disk surface. The irradiation light from the laser light source enters the central portion of the objective lens in an oblique direction with respect to the objective lens, is reflected from the optical disk surface, and has a light separating means in a light path of reflected light passing through a light path different from the irradiation light. An optical head for an optical disk device, wherein the separated reflected light is detected by a light detecting means.