JPH0227534A - optical head device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field] This invention records information on an information recording medium.

The present invention relates to an optical head device for reproducing and erasing.

[Prior Art] Nos. 6 to 1080 show optical head devices previously filed by the present applicant. In the figure, l is a semiconductor laser as a light source. Reference numeral 2 denotes a condensing lens as a condensing means, which forms a condensing light beam 3 emitted from the light source 1 into a condensing spot 6 that irradiates an information track 5 on an optical disk as an information recording medium 4. Reference numeral 7 denotes a holographic element, which has a function of separating the reflected light beam 8 from the information recording medium 4 from the output light beam 3 and imparting astigmatism to the reflected light beam 8, and a function of generating three beams to obtain tracking. have. Specifically, as shown in FIG. 7, the tenographic element 7 is made by depositing SiOx, TiO, etc. on a glass substrate, or by depositing SiOx, TiO, etc. on a glass substrate.
Alternatively, it is configured as a phase type diffraction grating with a relief integrally molded on a plastic substrate, and has three grating regions A, B+, and Bt with the same grating thickness d and the same refractive index n.

These three grating regions A, B+, and By have the same zero-order diffraction efficiency. io is a photodetector that receives the reflected light beam 8, and is configured to have a six-divided detection area 10a=1Of.

To explain the operation of this, out of the light beam 3 emitted from the light source 1, the light beam 3 transmitted through the grating area A of the holographic element 7 is separated into three light beams including the 0th order diffracted light, and passes through the condenser 2. and focus the light spot 6 on the information track 5.
A, 6b, and 6c are irradiated. These focused spots 6a,
Since the information is read out using the focused spot 6λ of the focused spots 6b and 6c, the focused spot 6a must be correctly irradiated onto the information track 5 as shown in FIG. For this reason, the line connecting the focused spots 6a to 6c is arranged so as to be slightly inclined to the information track 5.

Then, the reflected light beam 8 from the information recording medium 4 at the focused spots 6a to 6c enters the holographic element 7, and three areas A of the holographic element 7 are formed.

The first-order diffracted light of the reflected light beam 8 that has entered areas B+ and Bt of B l and B t is received by the photodetector 10 .

Reflected light flux 8 from the condensing spot 6a out of the reflected light flux 8
is the spot ll in the central four-divided detection area 10a = 10d.
The light is received as a. This four-division detection area 10a=IO
The output of d is calculated by the calculation unit 12 as shown in FIG.
)) is applied to a focusing actuator (not shown) to drive the focusing means 2 in the optical axis direction to correct the focal shift. In addition, the reflected light flux 8 from the condensing spots 6b and 6c
is the detection area 10e of the photodetector IO.

The light is received at 10f. The outputs of the detection areas 10e and 10f are calculated by the computing unit 14, and the differential output is applied to a tracking actuator (not shown) to drive the light focusing means 2 in the X direction perpendicular to the information track 5 to correct the track deviation. Correct. Information recording medium 4 with focused spots 6a to 6c
The reflected light beam 8 is incident on the holographic element 7,
Three areas of the holographic element 7 A, B1. Bt
Of these, the reflected light beam 8 that has entered area A is not received by the photodetector 10 and remains as a spot 15. ~15. imaged as.

[Problems to be Solved by the Invention] This conventional optical head device has the following two problems.

■When the condensing means 2 is moved in the X direction according to the differential output (tracking error signal) of the arithmetic unit 14, the photodetector lO
The spot lla irradiated onto the four divided detection areas 10a to 10d is displaced in the X direction.

Then, as shown in FIG. 10(a), the spot 11λ becomes 4
Detection area lOa or 1 in the X direction in the divided detection area
Most of the irradiation occurs at 0c. As a result, the focus error signal, which is the calculation output of the calculation unit 12, does not become zero even if the focused spot 6a is focused, but is offset, and the information recording medium 4
As a result, the performance of the reproduced signal, which is the differential output of the computing units I and 4, deteriorates.

■The diffraction angle θ of the holographic element 7 is in the grating area B,
When the average grating period of B is P and the wavelength of the light source l is λ, sin θ=λ/P. However, the wavelength λ of the semiconductor laser as the light source 1 has temperature dependence. Therefore, assuming that the wavelength λ increases slightly, the diffraction angle θ also increases, causing the problem that the spot 11a# (displaces in the X direction and gives an offset to the focus error signal) in the same manner as in the case (2) above.

[Means for solving the problem] A light source 1 and a condensing spot 6 (6a to 6c) that irradiates an emitted light beam 3 onto an information track 5 on an information recording medium 4.
), a holographic element 7A that separates the reflected light beam 8 from the information recording medium 4 from the output light beam 3 and gives astigmatism to the reflected light beam 8, and a photodetector that receives the reflected light beam 8. In an optical head device equipped with a device 10A, a holographic element 7A prevents interference between a light beam of an achromatic light source corresponding to the light source 1 and a light beam of an astigmatic light source corresponding to the center position of the photodetector IO. This structure has a grating pattern corresponding to interference fringes that depict a circle of least confusion with focal lines at approximately +45 degrees and approximately 145 degrees with respect to the traveling direction of the information track 5 of the focused spot 6.

[Effect co-tracking: The direction of displacement of the spot in the four-divided detection area of the photodetector due to wavelength fluctuation is made to match the direction of the four-divided line.

Examples] Embodiments of the present invention will be described below based on the drawings.

As shown in FIG. 1, the optical head device of this embodiment includes a light source 1 and a condenser 6 (6a to 6c) that irradiates an emitted light beam 3 onto an information track 5 on an information recording medium 4.
a holographic element 7A that separates the reflected light beam 8 from the information recording medium 4 from the output light beam 3 and imparts astigmatism to the reflected light beam 8; and a photodetector that receives the reflected light beam 8. 10A.

Here, the four-divided detection areas 10a to IOd of the photodetector 10A
The center is located at a distance d from the light source l in the X direction, and the quarter dividing line is located in the X direction and in the Y direction perpendicular thereto. Moreover, the holographic element 7A is the above-mentioned light source! An aberration-free light source IA is placed at a position corresponding to the central position of the photodetector 10A, and an astigmatism light source 10B is placed at a position corresponding to the center position of the photodetector 10A. Focusing spot 6 by interference
Almost +4 for the information track 5 travel direction (Y direction)
The structure has a grating pattern corresponding to interference fringes that depict a circle of least confusion with focal lines at 5 degrees and approximately 145 degrees. Specifically, when the information recording medium 4 is out of focus, the spot Ila transmitted through the holographic element 7A having the above-mentioned lattice pattern is detected as shown in FIG. (a), (b) (
c). In other words, the direction of the ellipse (direction of the focal line) is approximately +4 with respect to the traveling direction (Y direction) of the information track 5.
It will be 5 degrees.

In the optical head device having such a structure, first, when the focusing means 2 is displaced in the X direction according to the tracking error signal, the four-divided detection area 10a- of the photodetector 10A is
Spot lla is displaced in the Y direction on 10d. As a result, areas 10c and 1 in the four divided detection areas 10a-10d
A large amount of light is received at 0d, but the detection areas 10c and 10
Since the light receiving increments of d are approximately equal, the calculation output of the calculation unit 13 does not change, so that no offset occurs in the focus error signal. The same applies even if the spot lla is displaced in the -Y direction.

Next, when the spot lla is displaced in the X direction due to the wavelength fluctuation of the light source 1, the four-divided detection area 10a of the photodetector 10A at this time~! Although a large amount of light is received in the detection area 10a and IOd in Od, the calculation output of the calculation unit 12 does not change, and no offset occurs in the focus error signal. Note that the reproduction signal and the tracking error signal are obtained from the arithmetic units 12 and 14 in the same manner as in the prior art described above.

Note that the present invention is not limited to the above-mentioned embodiment, and as shown in FIG. The lattice areas BI and Bt of the holographic element 7A correspond to interference fringes that draw a circle of least confusion with a focal line at approximately 45 degrees in the XY force direction. By using a lattice pattern, the same effects as in the previous embodiment can be obtained.

Further, as shown in FIGS. 5(a) to 5(d), the lattice pattern of the holographic element 7A may be configured.

[Effect of the invention] As described above, according to this invention, tracking is possible.

Since the displacement direction of the spot in the four-division detection area of the photodetector due to wavelength fluctuation can be made to match the direction of the four-division line, stable focus control can be performed without causing an offset in the focus error signal. .

[Brief explanation of the drawing]

6 is a schematic diagram showing different examples of grating patterns of the holographic element of the present invention, FIG. 6 is a configuration diagram showing a conventional optical head device, and FIG. 7 is an explanatory diagram of the diffraction grating of the holographic element of the conventional example. , FIG. 8 is a configuration diagram of the conventional photodetector, and FIG. 9 is an explanatory diagram of the conventional twin spot method.
FIG. 3 is an explanatory diagram of an astigmatic light beam of the first conventional example.

Claims (1)

[Claims] a light source; a condensing means for forming a future emitted light beam into a condensing spot that irradiates an information track on an information recording medium;
In an optical head device comprising a holographic element that separates a reflected light beam from an output light beam from an information recording medium and imparts astigmatism to the reflected light beam, and a photodetector that receives the reflected light beam, the holographic element comprises: Due to the interference between the light beam of the non-aberration light source corresponding to the light source and the light beam of the astigmatic light source corresponding to the center position of the photodetector, the focused spot is approximately +45 degrees and approximately -
An optical head device characterized by having a grating pattern corresponding to interference fringes that depict a circle of least confusion having a focal line at 45 degrees.