JPH10241179A - Hologram laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hologram laser by which the size of an optical pickup device can be reduced and, further, the reliability of the device can be improved. SOLUTION: Diffraction lattices 3 and 4 are formed on the emission side of a hologram glass 32 which has a hologram device 7 for beam deflection on its incident side. The central part diffraction grating 3 has rectangular grooves and the circumferential part diffraction grating 4 has blade-shaped asymmetrical grooves. As a laser beam emitted from one of semiconductor lasers transmits the diffraction gratings 3 and 4, its beam diameter is large. As a laser beam emitted from the other semiconductor laser transmits the diffraction grating 3 only, its beam diameter is small.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light source for reading a signal from an optical disk and a light receiving element for reading a signal housed in a single package, and a hologram element having a hologram pattern for beam deflection is adjusted to the package.
For more information on fixed hologram lasers, see CD
An optical pickup device capable of accurately recording and reproducing information signals on two types of optical disks having different standards, that is, different thicknesses (or refractive indexes) of the disks, such as a (compact disk) and a DVD (digital video disk). It relates to the hologram laser used.

[0002]

2. Description of the Related Art When two types of optical discs having different thickness standards, such as a CD and a DVD, are read with the same optical pickup device, an information signal is read as shown in FIG.
As shown in (1), in an optical system designed for a DVD having a thickness of 0.6 mm, a laser beam 102a can be focused on a pit of a DVD disk 101 by an objective lens 102.

However, a CD having a thickness of 1.2 mm
As shown in FIG. 2B, laser light 102a cannot be condensed on the pits of the disk 101 'because the same objective lens 102 causes aberration.

In order to solve this problem, in the conventional example shown in FIG. 5, two types of objective lenses 111 and 112 having different lens numerical apertures (hereinafter referred to as NA) are provided in an optical pickup device 110, and the type of disc is set. Thus, the objective lenses 111 and 112 are moved by the magnetic coil 113 to perform exchange. That is, the objective lens corresponding to each disk is selected, and this system is called a twin lens system.

FIG. 6 shows another conventional example. In this conventional example, a hologram pattern 121 is formed on an objective lens 120, and an NA depending on the type of disc
The method of changing is adopted. That is, DVD disk 1
In the case of No. 23, as shown in FIG.
The light 122 passing through the outer periphery of the optical disk 20 is condensed on a disk 123, and in the case of a CD disk 123 ', the light 122' passing through the hologram pattern 121 on the objective lens 120 as shown in FIG. Is focused on the disk 123 '.

FIG. 7 shows another conventional example. In this conventional example, the light beam 131 incident on the objective lens 130 is restricted by a liquid crystal shutter 132, the beam luminous flux diameter is changed depending on the type of the discs 133 and 133 ', and light is condensed on the discs 133 and 133'. I have. That is, as shown in FIGS. 7A and 7B, by turning on and off the liquid crystal shutter 132, the beam luminous flux diameter is changed according to the type of disk.

[0007]

By the way, in the twin lens system, the objective lenses 111 and 112 are mechanically provided.
In order to take the configuration of exchanging the lenses, mechanical accuracy of lens attachment is required, and a lens moving mechanism is required. For this reason, the reliability of the optical pickup device is impaired, and there is a limit in reducing the size and weight of the optical pickup device.

The method of forming the hologram pattern 121 on the objective lens 120 is based on the hologram pattern 1
Because precision processing technology is required to form 21 parts,
There is a problem that it is difficult to manufacture a lens, which causes a decrease in yield and an increase in cost.

Further, in the method using the liquid crystal shutter 132, the mounting accuracy of the liquid crystal is required and the liquid crystal shutter 132 is a separate part from the objective lens 130. Errors tend to occur, which has been a problem in improving the reliability of the optical pickup device.

[0010] The present invention has been made in view of such a situation, and an object of the present invention is to provide a hologram laser capable of reducing the size of an optical pickup device and improving reliability.

It is another object of the present invention to provide a hologram laser which can be easily manufactured by using existing manufacturing techniques, and as a result, the cost of the optical pickup device can be greatly reduced.

[0012]

According to the hologram laser of the present invention, the focal point of the objective lens is changed depending on the type of the disk.
A one-beam hologram laser used in an optical pickup device requiring a focus, in which a signal reading light source for a disc and a light receiving element are housed in one package, and a beam deflecting means is provided on an upper surface of the package, The beam deflecting means is a hologram glass in which a hologram pattern for beam deflection is formed on an incident side, and a diffraction grating for limiting a numerical aperture of a laser beam is formed on an emission side of the hologram glass. Objective is achieved.

Preferably, the diffraction grating has a configuration in which a central groove shape is a rectangular shape and a peripheral groove shape is a blazed shape.

Preferably, the light source for reading signals from the disk is a semiconductor laser chip, two of the semiconductor laser chips are housed in the same package, and the rectangular diffraction grating portion and the blazed shape are provided. The two semiconductor laser chips are arranged on each first-order diffraction angle of the diffraction grating portion.

The operation of the present invention will be described below.

As described above, the emission surface of the hologram glass on which the hologram element (hologram pattern) is formed,
That is, a rectangular diffraction grating (diffraction grating portion) is provided at the center of the upper surface.
And a blazed diffraction grating (diffraction grating portion) is formed around the diffraction grating, and a laser beam is emitted from a semiconductor laser chip disposed at the first diffraction angle of each diffraction grating. Is emitted, the laser light emitted from one of the semiconductor laser chips passes through the blazed diffraction grating and the rectangular diffraction grating, so that the light beam diameter is large.

On the other hand, the laser light emitted from the other semiconductor laser chip passes only through the rectangular diffraction grating at the center, because the blazed diffraction grating is asymmetrical. For this reason, the light beam diameter of the laser light emitted from the other semiconductor laser chip becomes smaller than the light beam diameter of the laser light emitted from the one semiconductor laser chip.

Here, in the optical pickup device, a collimator lens and an objective lens are disposed above the hologram laser, and the condensed beam condensed by the objective lens is divided into two types such as a DVD disk and a CD disk having different disk thicknesses. Is focused on the optical disk.

Therefore, according to the present invention, it is possible to focus a laser beam having a large light beam diameter on a DVD disk and a laser beam having a small light beam diameter on a CD disk. The recording and reproduction of the information signal can be performed accurately.

In addition, according to the present invention, it is only necessary to form a diffraction grating having a simple shape for limiting the beam luminous flux diameter on the hologram element of the hologram laser. A laser can be made. As a result, the cost of the optical pickup device on which the hologram laser is mounted can be reduced.

According to the present invention, a semiconductor laser chip as a light source, a hologram element for beam deflection, a light receiving element for signal reading, and a diffraction grating can be housed in the same package. As a result, the size of the optical pickup device can be reduced.

Further, since these elements are fixedly arranged in the same package, the reliability of the hologram laser and, consequently, the optical pickup device can be improved.

Further, since the number of parts can be reduced, the size and weight of the hologram laser and, consequently, the optical pickup device can be reduced.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the drawings. 1 and 2 show a schematic configuration of an optical pickup device provided with the hologram laser of the present invention. FIG. 3 shows details of a diffraction grating formed on the upper surface of the hologram glass. However, FIG. 1 shows a case in which information signals are recorded / reproduced on / from a DVD disk 22, and FIG. 2 shows a case where information signals are recorded / reproduced on / from a CD disk 22 '. The configuration and operation will be described below.

The hologram laser unit A includes a transparent substrate 30 and a cap 31 for packaging the transparent substrate 30.
And a hologram glass adjusted and fixed by a UV curable resin on the surface of the cap 31.

The right and left ends of the transparent substrate 30 in the drawing, that is, 18
At the 0 ° target position, semiconductor lasers 1 and 11 serving as light sources are disposed with their emission surfaces obliquely upward. A light receiving element 1 for signal reading is provided at the center of the surface of the transparent substrate 30.
0 is provided. The semiconductor lasers 1 and 11 and the light receiving element 10 are packaged together with the transparent substrate 30 by the cap 31.

At the center of the lower surface of the hologram glass 32,
A hologram element 7 is formed. On the other hand, diffraction gratings 3 and 4 are formed on the upper surface of the hologram glass 32. The diffraction grating 3 is formed at the center of the upper surface of the hologram glass 32, and the diffraction grating 4 is formed around the diffraction grating.

Here, the diffraction grating 3 at the center is a simple rectangular diffraction grating as shown in an enlarged manner in FIG.
The diffraction grating 3 separates the diffracted light into 0 order light, ± 1 order light... ± 2 order light... ± n order light. On the other hand, the diffraction grating 4
As shown in FIG. 3, a diffraction grating having a sawtooth shape, that is, a blazed shape that is asymmetrical to the left and right (hereinafter, referred to as a blazed shape). Generally, the diffracted light by the diffraction grating 4 becomes + 1st-order light, + 2nd-order light,.
As compared with, the light is not diffracted in the −n order direction.

The above-described diffraction gratings 3 and 4 are manufactured in a groove etching step. That is, first, a rectangular or blazed pattern is formed in a photoetching step, and a pattern groove is formed in a dry etching step. Subsequently, a pattern not formed previously is formed again in the photoetching step, and a pattern groove is formed in the dry etching step.

At this time, in the second dry etching step, the pattern formed first is not etched because it is covered with the resist film applied at the time of photoetching. Therefore, according to the above-described process, two diffraction gratings 3 and 4 having different shapes can be continuously formed on the surface of the hologram glass 32. Note that the resist film is removed by O ₂ ashing after etching.

Next, numerical examples of the oscillation wavelengths of the semiconductor lasers 1 and 11 and specific groove shapes of the diffraction gratings 3 and 4 will be described.

Oscillation wavelength: 0.78 μm About diffraction grating 3 Groove pitch: about 1.5 μm Depth: 0.36 μm Groove shape: rectangular shape with 50% duty About diffraction grating 4 Groove pitch: about 1.5 μm Depth: 0 .36 μm Groove shape: sawtooth shape with a duty of 50% The diffraction angle of the diffracted light is a value determined by the groove pitch of the diffraction gratings 3 and 4, and in the present embodiment, the positions of the semiconductor lasers 1 and 11 are It is mounted on the third and fourth ± primary optical axes. That is, the semiconductor laser 1 on the left side of the drawing
Are arranged on the + 1st-order diffraction angle of the diffraction gratings 3 and 4, and the semiconductor laser 11 on the right side in the figure is arranged on the −1st-order diffraction angle of the diffraction gratings 3 and 4.

The hologram element 7 is also manufactured by etching.

Next, referring to FIG. 1, the operation of recording and reproducing information signals on the DVD disk 22 will be described together with the optical system of the optical pickup device.

The light (laser light) 2 emitted obliquely upward from the semiconductor laser 1 is divided into a diffraction grating 3 and a diffraction grating 4.
, And is diffracted here and enters the collimator lens 33. The incident light is converted into parallel light by the collimator lens 33, and is incident on an objective lens 34 disposed above the collimator lens. Then, the DVD disk 2 is
Light is collected at 2.

On the other hand, the return light 5 from the DVD disk 22
Passes through an objective lens 34 and a collimator lens 33,
Returning to the diffraction gratings 3 and 4 again, the 0th-order diffracted light 6 enters a hologram element (hologram pattern) 7 for beam deflection. Then, the incident light is separated into a focus error signal 8 and a tracking error signal 9, condensed on a light-receiving element 10 for signal reading, and converted into an electric signal.

Next, the operation for recording / reproducing information signals on / from the CD disk 22 'will be described with reference to FIG. The light 12 emitted from the semiconductor laser 11 is incident on the diffraction grating 3 and the diffraction grating 4 as described above.

Here, the diffraction grating 4 has a blazed shape and is symmetrical left and right as shown in FIG. For this reason, the light 12 emitted from the right semiconductor laser 11 is different from the light 2 emitted from the left semiconductor laser 1, and the light 12 incident on the region where the diffraction grating 4 is formed is not diffracted. Only the light 12 incident on the formation region of is diffracted to become a diffracted light 13. As a result, the luminous flux diameter of the light exiting the diffraction grating 3 and the diffraction grating 4 is limited (reduced) as compared with the case of FIG. 1 (see FIG. 3).

Subsequently, the diffracted light 13 enters the collimator lens 33, becomes parallel light, and is condensed on the CD disk 22 'by the objective lens 34. Here, the diffracted light 13
Since the light beam diameter is reduced as described above, even with the same objective lens 34 as described above, it is focused on the CD disk 22 'without aberration.

For this reason, according to the optical pickup device of this embodiment, the DVD disk 22 and the CD disk 22 ′
It is possible to accurately record and reproduce information signals on two types of optical disks having different disk thicknesses.

The return light 1 from the CD disk 22 '
Reference numeral 4 denotes an objective lens 34 and a collimator lens 33, and returns to the diffraction grating 3 again. The 0th-order diffracted light enters the hologram element 7 for beam deflection, is separated into a focus error signal 8 and a tracking error signal 9, and The light is condensed at 10 and converted into an electric signal.

In the above configuration, the semiconductor lasers 1, 11
Is switched by a disk detection signal from a disk type determination unit (not shown).

[0043]

According to the hologram laser of the present invention described above, two types of laser beams having different light beam diameters can be transmitted through the same objective lens to two types of optical disks having different disk thicknesses.
For example, since the light can be focused on a DVD disk and a CD disk, information signals can be recorded / reproduced accurately on two types of optical disks.

In addition, according to the present invention, it is only necessary to form a diffraction grating having a simple shape for limiting the beam diameter on the hologram element of the hologram laser. A laser can be made. As a result, the cost of the optical pickup device on which the hologram laser is mounted can be reduced.

According to the present invention, a semiconductor laser chip as a light source, a hologram element for beam deflection, a light receiving element for signal reading, and a diffraction grating can be housed in the same package. As a result, the size of the optical pickup device can be reduced.

Further, since these elements are fixedly arranged in the same package, the reliability of the hologram laser and, consequently, the optical pickup device can be improved.

Further, since the number of components can be reduced, the size and weight of the hologram laser and, consequently, the optical pickup device can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a case where an optical pickup device including a hologram laser according to the present invention records and reproduces information signals on a DVD disk.

FIG. 2 is a schematic diagram showing a case where information signals are recorded / reproduced on / from a CD disk by an optical pickup device provided with a hologram laser of the present invention.

FIG. 3 is an enlarged view showing a glass plate on which a diffraction grating is formed.

FIGS. 4A and 4B are diagrams for explaining a problem when an information signal is read from two types of optical disks having different thickness standards by the same optical pickup device.

FIG. 5 is a perspective view showing a conventional optical pickup device of a twin lens system.

FIGS. 6A and 6B are views showing a conventional optical pickup device adopting a method of changing the NA depending on the type of a disk.

FIGS. 7A and 7B are views showing a conventional optical pickup device using a liquid crystal shutter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 11 Semiconductor laser 3 Rectangular diffraction grating 4 Blazed diffraction grating 7 Hologram element 10 Light receiving element 22 DVD disk 22 'CD disk 30 Transparent substrate 31 Cap 32 Hologram glass

Claims (3)

[Claims] 1. A condensing point of an objective lens is used in an optical pickup device requiring two focal points according to a type of a disc, and a light source for reading a signal of a disc and a light receiving element are housed in one package. A one-beam hologram laser having a beam deflecting unit on an upper surface, wherein the beam deflecting unit is a hologram glass having a beam deflecting hologram pattern formed on an incident side, and a laser beam is emitted on an emission side of the hologram glass. A hologram laser having a diffraction grating for limiting the numerical aperture. 2. The hologram laser according to claim 1, wherein the diffraction grating has a rectangular groove at a central portion and a blazed groove at a peripheral portion. 3. A light source for reading signals from the disk is a semiconductor laser chip, two of the semiconductor laser chips are housed in the same package, and the rectangular diffraction grating portion and the blazed diffraction grating portion are provided. 3. The hologram laser according to claim 1, wherein the two semiconductor laser chips are disposed on each of the first-order diffraction angles.