JP2946998B2 - Optical head device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device used for an optical recording / reproducing apparatus for reproducing information on a recording medium or recording / reproducing or recording / reproducing / erasing information on a recording medium. Things.

[0002]

2. Description of the Related Art In optical recording, devices such as optical disks for optically reproducing information on concentric or spiral tracks formed on a disk have already been put to practical use.

A conventional optical head device used in this optical disk device will be described with reference to the drawings.

FIG. 5 is a structural view of an optical system of a conventional optical head device, FIG. 6 is a sectional view of an intensity distribution of a beam focused on a recording medium in the optical system of FIG. 5, and FIG. 7 is an optical system of FIG. It is a block diagram of the light receiving part of the photodetector of a system.

In FIG. 5, this optical head device comprises a laser light source 1, a diffraction grating 2b, a beam splitter 3,
The recording medium 6 includes a collimating lens 4, an objective lens 5, a cylindrical lens 7, and a photodetector 8.
To form a minute spot and reflect the light.

The laser light emitted from the laser light source 1 is
The beam is split into three beams by the diffraction grating 2b, passes through the beam splitter 3, is collimated by the collimator lens 4, and is condensed by the objective lens 5 to form a minute spot on the recording medium 6. The information signal light reflected from the recording medium 6 passes through the objective lens 5 and is condensed by the collimator lens 4.
The cylindrical lens 7 reflected by the beam splitter 3
Generates astigmatism, and the light is received by the photodetector 8.

The diffraction grating 2b is a linear grating as shown by a diffraction grating shape 21, and the beam shape focused on the recording medium 6 by the diffraction grating 2b is different from the main beam 22 shown in FIG. Beams 23 and 24 are divided into three beams, and in a direction perpendicular to the three beams, an intensity distribution 25 is obtained as shown in section C in the direction perpendicular to the three beams. Become. The three divided beams are applied to the track 10 on the recording medium 6 while being rotated by a small angle.

Further, the beam reflected from the recording medium 6 is applied to a light receiving section 27 of the photodetector 8 shown in FIG. Received in the state, side beam 2
3 and 24 are received by the light receiving sections 29 and 30 for detecting the tracking error signal in the states of 23 'and 24', respectively.

Next, the operation of the conventional optical head device will be described.

In this optical head device, as a method of focusing the beam focused on the recording medium 6 by the objective lens 5 of FIG. 5, a beam reflected from the recording medium 6 is reflected by the beam splitter 3, and a cylindrical lens is used. By detecting the astigmatism generated at 7 by the photodetector 8,
The focus error signal is detected by a known astigmatism method.

As a method for causing the beam focused on the recording medium 6 to follow a predetermined track, the diffraction grating 2b
The beam splitter 3 reflects the reflected light of the side beams 23 and 24 reflected by the recording medium 6 by the beam splitter 3, and detects a tracking error signal from the difference in the amount of light received by the light receiving units 29 and 30 of the photodetector 8. The three-beam method is used.

The detection of the information signal is obtained by the sum of all the light amounts applied to the photodetector 8.

When assembling the optical head device, the recording medium 6
It is necessary to adjust the rotation of the diffraction grating 2b with respect to the optical axis so that the side beams 23 and 24 split by the diffraction grating 2b with respect to the track 10 are focused on both sides of the same track. Therefore, it is necessary to adjust the rotation of the diffraction grating 2b and the position of the photodetector 8 as adjustment points of the optical head.

[0014]

In the structure of the above-described conventional optical head device, the diffraction grating is illuminated so that the side beam split by the diffraction grating with respect to the track of the recording medium is focused on both sides of the same track. Since it is necessary to adjust the rotation with respect to the axis, there is a disadvantage that it is difficult to improve the assemblability of the optical head device.

[0015]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical head device capable of reducing the number of adjustment points of the optical head device, improving the assemblability, and achieving high productivity and low cost. is there.

Therefore, an optical head device according to the present invention comprises a beam splitter for separating outgoing light from a laser light source and an information signal light reflected from an information surface of a recording medium, a collimating lens for making outgoing light into parallel light, An objective lens for condensing light on the information surface of the recording medium to form a minute spot;
A concentric diffraction grating disposed between the laser light source and the objective lens for diffracting the light emitted from the laser light source, and the same grating on the information surface of the recording medium by the diffraction grating and the objective lens .
The main beam formed on the rack and the ring-shaped side
Of the main beam of the reflected light from each of the
The focus error signal is detected from the reflected light and the
A photodetector for detecting a tracking error signal from reflected light of the side beam .

[0017]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the optical system of the optical head device according to the first invention, and FIG. 2 is a sectional view of the intensity distribution of a beam focused on a recording medium in the optical system of FIG. FIG. 3 is a configuration diagram of a light receiving section of the photodetector of the optical system of FIG.

In FIG. 1, this optical head device comprises a laser light source 1, a diffraction grating 2a, a beam splitter 3,
The recording medium 6 includes a collimating lens 4, an objective lens 5, a cylindrical lens 7, and a photodetector 8.
To form a minute spot and reflect the light. The laser light emitted from the laser light source 1 generates diffracted light at the diffraction grating 2a, passes through the beam splitter 3, is collimated by the collimator lens 4, and is condensed by the objective lens 5 to form a minute spot on the recording medium 6. Form on top. The information signal light reflected from the recording medium 6 passes through the objective lens 5, is collected by the collimator lens 4, is reflected by the beam splitter 3, generates astigmatism by the cylindrical lens 7, and is received by the photodetector 8.

The diffraction grating 2a is a concentric grating shown in a diffraction grating shape 9, and the beam shape focused on the recording medium 6 by this diffraction grating 2a is the same as the main beam 11 shown in FIG. The intensity distribution of the beam split and condensed into the side beam 12 becomes an intensity distribution 15 as shown in a cross section A, and an intensity distribution 16 substantially the same as the intensity distribution 15 in a cross section B perpendicular to the cross section A.

Further, the beam reflected from the recording medium 6 is applied to the light receiving section 17 of the photodetector 8 shown in FIG. 3, and the main beam 11 is located at the center of the light receiving section 18 for detecting the focus error signal. In this state, the annular side beam 12 is received at the position 12 ', and is received on the light receiving units 19 and 20 for detecting a tracking error signal.

Next, the operation of the optical head device of this embodiment will be described.

In this optical head device, as a method of focusing the beam focused on the recording medium 6 by the objective lens 5 of FIG. 1, a beam reflected from the recording medium 6 is reflected by the beam splitter 3, and a cylindrical lens is used. By detecting the astigmatism generated at 7 by the photodetector 8,
The focus error signal is detected by a known astigmatism method.

The method of causing the beam focused on the recording medium 6 to follow a predetermined track is performed as follows. The annular side beam 12 diffracted by the diffraction grating 2a
Generate portions (diffraction portions) 13, 14 diffracted by the track 10. The light reflected by the recording medium 6 is reflected by the beam splitter 3 and received by the light receiving unit 17 of the photodetector 8. At this time, the diffracting portions 13 and 14 receive the diffracted light at the positions 13 'and 14' on the light receiving portions 19 and 20, and determine the difference between the light receiving amount of the light receiving portion 19 and the light receiving amount of the light receiving portion 20 as a tracking error signal. And the tracking is performed so that the tracking error signal becomes zero.

The detection of the information signal is obtained by the sum of all the light amounts applied to the photodetector 8.

In the above embodiment, the rotation adjustment of the diffraction grating 2a with respect to the track 10 of the recording medium 6 can be reduced when assembling the optical head device. Only adjustment is required.

Next, the case of a finite optical system that does not use a collimator lens will be briefly described with reference to the drawings.

FIG. 4 is a block diagram showing one embodiment of the optical system of the optical head device according to the second invention.

In FIG. 4, the optical head device comprises a laser light source 1, a diffraction grating 2a, a beam splitter 3,
It comprises an objective lens 5, a cylindrical lens 7, and a photodetector 8, and forms a minute spot on the recording medium 6 and reflects it. The laser light emitted from the laser light source 1 generates diffracted light at the diffraction grating 2a, passes through the beam splitter 3, and is condensed by the objective lens 5 to form a minute spot on the recording medium 6. The information signal light reflected from the recording medium 6 passes through the objective lens 5, is reflected by the beam splitter 3, generates astigmatism by the cylindrical lens 7, and is received by the photodetector 8.

The other points are the same as those described in the first embodiment of the present invention.

The concentric diffraction grating shown in this embodiment may be of any type, such as a light-shielding band or a phase grating.

Furthermore, the present apparatus is applicable to all optical head devices used for a read-only recording medium, a write-once recording medium, or a rewritable recording medium.

In this embodiment, one method of detecting a focus error on a recording medium has been described. However, any other known method can be applied.

[0034]

As described above, the optical head device of the present invention uses the concentric diffraction grating to condense the annular diffracted light on the recording medium. There is an effect that the rotation adjustment of the diffraction grating can be reduced, and the productivity can be improved and the cost can be reduced by improving the assemblability.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of an optical system of an optical head device according to the first invention.

FIG. 2 is a cross-sectional view of an intensity distribution of a beam focused on a recording medium in the optical system of FIG.

FIG. 3 is a configuration diagram of a light receiving section of the photodetector of the optical system of FIG. 1;

FIG. 4 is a configuration diagram showing an embodiment of an optical system of the optical head device according to the second invention.

FIG. 5 is a configuration diagram of an optical system of a conventional optical head device.

6 is a sectional view of an intensity distribution of a beam focused on a recording medium in the optical system of FIG.

7 is a configuration diagram of a light receiving unit of the photodetector of the optical system of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Laser light source 2a, 2b Diffraction grating 3 Beam splitter 4 Collimator lens 5 Objective lens 6 Recording medium 7 Cylindrical lens 8 Photodetector 9, 21 Diffraction grating shape 10 Track 11 Main beam 11 'Main beam receiving position 12 Ring side beam 12 'Ring zone side beam light receiving position 13 Diffraction part 13' Diffraction part light receiving position 14 Diffraction part 14 'Diffraction part light receiving position 15 Intensity distribution 16 Intensity distribution 17 Photodetector light receiving part 18 Light receiving part (for focus error signal detection) 19, 20 Light receiving section (for tracking error signal detection) 22 Main beam 22 'Main beam receiving position 23, 24 Side beam 23', 24 'Side beam receiving position 25, 26 Intensity distribution 27 Light receiving section 28 Light receiving section (for focus error signal detection) 29, 30 Light receiving unit (tracking For error signal detection)

Claims (2)

(57) [Claims] A beam splitter for separating light emitted from a laser light source from information signal light reflected from an information surface of a recording medium; a collimator lens for collimating the emitted light; An objective lens that condenses on a surface to form a minute spot; a concentric diffraction grating that is disposed between the laser light source and the objective lens and that diffracts light emitted from the laser light source; The same track on the information surface of the recording medium
The main beam and the annular side beams formed on click
Of the main beam out of the reflected light from each of
A focus error signal is detected from the light and the ring-shaped site is detected.
An optical detector for detecting a tracking error signal from reflected light of the de- beam. 2. A beam splitter for separating outgoing light of a laser light source from information signal light reflected from an information surface of a recording medium, and an object for condensing the outgoing light on the information surface of the recording medium to form a minute spot. A lens, a concentric diffraction grating disposed between the laser light source and the objective lens for diffracting light emitted from the laser light source, and the same on the recording medium information surface by the diffraction grating and the objective lens.
Main beam and annular side formed on the track
The main beam of reflected light from each of the beams
The focus error signal is detected from the reflected light of the
An optical detector for detecting a tracking error signal from reflected light of the side beam of the optical head.