JP2002342967A - Optical head device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such a problem that an aberration is generated in a diffracted optical beam when as diffraction grating is arranged on the diffusion optical path of a laser beam. SOLUTION: The diffraction grating 2 is arranged on the diffusion optical path of laser beams, among optical paths for guiding laser beams emitted from a semiconductor laser 1 to an objective lens 6, and an effective diffraction pattern 15 is formed only on the center part of the diffraction grating 2 which has a diameter smaller than the effective beam diameter of a laser beam. Thus, the degree of diffusion of a laser beam made incident on the effective diffraction pattern 15 of the diffraction grating 2 is narrowed, and aberration generated in a diffracted optical beam is suppressed.

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 for forming a diffracted light beam by diffracting a laser beam emitted from a semiconductor laser by a diffraction grating.
The present invention relates to an optical head device in which the diffraction grating is disposed on a diffusion optical path of a laser beam.

[0002]

2. Description of the Related Art An optical head device for optically reading or writing a signal on or from a signal recording medium such as a disk, diffracts a laser beam emitted from a semiconductor laser by a diffraction grating and converts the diffracted light beam. Forming, using ± 1st-order diffracted light beam in addition to 0th-order light beam,
What corresponds to the tracking control by the three-beam method or the differential push-pull method has become mainstream.

In an optical head device provided with such a diffraction grating, in order to reduce the size or to approach a semiconductor laser, the diffraction grating causes a laser beam emitted from the semiconductor laser to enter an objective optical path incident on an objective lens. In many cases, the laser beam is arranged on a diffusion optical path in which a laser beam is diffused.

[0004]

By the way, when the diffraction grating is arranged on the diffusion optical path of the laser beam, the angle of incidence of the laser beam on the diffraction grating is deviated from the vertical as the outer circumference is reached, and the collimator provided in the optical head device is provided. The diffused light is incident on a power lens such as a lens or an objective lens, and as a result, aberration occurs in the diffracted light beam.

[0005] Therefore, the light spot shape of the diffracted light beam converged on the disk is distorted, which adversely affects the light receiving output obtained from the sub-light receiving area for receiving the reflected light of the diffracted light beam in the photodetector.

That is, when the differential push-pull method is used for the tracking control, the sub-light receiving area of the photodetector is divided into two parts, and the distribution of light received in each of the two divided areas is important. However, if the shape of the light spot received by the sub light receiving area is irregular, the light receiving distribution in each of the two divided areas becomes unbalanced, and the calculation result of the tracking error signal used for tracking control becomes incorrect. .

[0007]

According to the present invention, a diffraction grating is arranged on a diffusion optical path of a laser beam among optical paths for guiding a laser beam emitted from a semiconductor laser to an objective lens. The effective diffraction pattern is formed limited to the central portion having a smaller diameter than the effective beam diameter. This narrows the diffusivity of the laser beam incident on the effective diffraction pattern of the diffraction grating,
Aberrations generated in the diffracted light beam are suppressed.

[0008]

FIG. 1 is an arrangement diagram showing an optical arrangement of an optical head device according to the present invention. FIG. 1 shows an example of an optical head device used in a disk recording / reproducing apparatus of a magneto-optical recording system.

Reference numeral 1 denotes a semiconductor laser that emits a laser beam, 2 denotes a diffraction grating that diffracts the laser beam emitted from the semiconductor laser 1 to form ± first-order diffracted light beams used for tracking control, and 3 denotes a parallel laser beam. A collimator lens 4 for turning light into light, a beam shaping prism 4 for shaping a parallel light laser beam obtained through the collimator lens 3, and a standing beam 5 for bending the optical axis direction of the laser beam obtained through the beam shaping prism 4. Raising mirrors 6 are objective lenses that receive the laser beam raised by the raising mirror 5 and converge the laser beam irradiating the disk 7.

The objective lens 6 is supported by an objective lens driving mechanism (not shown) so as to be drivable in a focus direction orthogonal to a signal surface of the disk 7 and a tracking direction orthogonal to a signal track of the disk 7.

The optical path from the semiconductor laser 1 to the objective lens 6 forms an incident optical path for guiding the laser beam to the disk 7.

In FIG. 1, in order to clearly show the objective lens 6 on the same drawing, the objective lens 6 is shown from a direction different from that of other optical parts. It is shown separately.

Reference numeral 8 denotes a beam splitter surface 9 for separating a reflected beam reflected by the disk 7 and passing through the objective lens 6 and the rising mirror 5 from an incident optical path, on a joint surface to be joined to the beam shaping prism 4. A reflecting prism 8 having a reflecting surface 8a that bends the optical axis of the reflected beam separated from the incident optical path by the beam splitter surface 9 by internal reflection, is joined to the exit surface of the reflecting prism 8, and reflects the reflected beam according to the polarization direction. It is a Wollaston prism that separates. The beam shaping prism 4, the reflecting prism 8, and the Wollaston prism 10 are joined and integrated.

Reference numeral 11 denotes a collimator lens for converting the reflected beam via the Wollaston prism 10 from parallel light to convergent light. Reference numeral 12 denotes a cylindrical lens function for generating astigmatism used for focus control, and a focal position of the reflected beam. An anamorphic lens 13 having both functions of a power lens to be adjusted, and a photodetector 13 having a light receiving element 14 for receiving a reflected beam through the anamorphic lens 12.

In the optical head device shown in FIG. 1, the diffraction grating 2 is arranged adjacent to the semiconductor laser 1, and is arranged on the diffusion optical path of the laser beam among the incident optical paths for guiding the laser beam to the objective lens 6. .

As shown in FIG. 2, the diffraction grating 2 has a circular effective diffraction pattern 15 which effectively acts to form a diffracted light beam at the center thereof. A dummy diffraction pattern 16 that is not effective for forming a light beam is formed.

The dummy diffraction pattern 16 is provided to eliminate a phase difference between the laser beam and the portion that has passed the effective diffraction pattern 15 so as to eliminate the phase difference. And a grating having an angle of 45 degrees, so that it is not effectively used to form a diffracted light beam.

The effective diffraction pattern 15 has a smaller diameter than the effective beam diameter of the laser beam. When the entire surface of the diffraction grating 2 is an effective diffraction pattern, the numerical aperture NA of the collimator lens 3 is equivalent to 0.2. The effective diffraction pattern 15 so that the laser beam whose light flux is restricted by the effective diffraction pattern 15 is equivalent to 0.1.
Is set.

Therefore, the effective diffraction pattern 1 of the diffraction grating 2
5, the degree of diffusion of the laser beam incident on the collimator lens 3 is reduced, and the angle of incidence of the laser beam at the outermost peripheral portion of the effective diffraction pattern 15 is deviated from vertical. , The collimator lens 3 can be used with a smaller NA.

Therefore, aberrations generated in the diffracted light beam diffracted by the effective diffraction pattern 15 of the diffraction grating 2 are suppressed.

On the other hand, with respect to the zero-order light beam that is passed through the diffraction grating 2 without being diffracted, the effective diffraction pattern 15
There is no laser beam phase difference between the portion that has passed through and the portion that has passed through the dummy diffraction pattern 16.

Therefore, the effect of the phase difference due to the formation of the effective diffraction pattern 15 only at the central portion of the diffraction grating 2 is prevented, and the quality of the zero-order light beam is prevented from deteriorating.

[0023]

As described above, according to the present invention, since the effective diffraction pattern of the diffraction grating is made smaller in diameter than the effective beam diameter of the laser beam, a diffraction light beam diffracted by the effective diffraction pattern is generated. Aberration can be suppressed.

Further, since the dummy diffraction pattern is formed around the effective diffraction pattern, the zero-order light beam that is passed without being diffracted by the diffraction grating is a portion that has passed through the effective diffraction pattern and the dummy diffraction pattern. Thus, a phase difference between the laser beams does not occur, and quality deterioration can be prevented.

[Brief description of the drawings]

FIG. 1 is an arrangement diagram showing an optical arrangement of an optical head device according to the present invention.

FIG. 2 is an explanatory diagram for explaining a diffraction grating 2 used in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Diffraction grating 3 Collimator lens 6 Objective lens 15 Effective diffraction pattern 16 Dummy diffraction pattern

Claims (2)

[Claims] 1. An optical head device comprising a diffraction grating for diffracting a laser beam emitted from a semiconductor laser, wherein the diffraction grating comprises a laser beam in an optical path for guiding the laser beam emitted from the semiconductor laser to an objective lens. An optical head device, wherein an effective diffraction pattern is formed on the diffused optical path, and has an effective diffraction pattern limited to a central portion having a smaller diameter than the effective beam diameter of the laser beam. 2. A dummy diffraction pattern, which is not effective for forming a diffracted light beam, is formed around the effective diffraction pattern of the diffraction grating, and a position of a laser beam between a portion passing through the effective diffraction pattern by the dummy diffraction pattern. 2. The optical head device according to claim 1, wherein the phase difference is eliminated.