JPH11144284A - Optical pickup - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further simplify the arrangement of components, to further reduce the number of components and to reduce a projected area in an optical pickup for reproducing an optical recording medium by properly using a first laser and a second laser whose wavelengths are different with each other. SOLUTION: A laser beam source LD2 emitting a second laser L2 is arranged in the vicinity of the laser beam source LD1 of the unit 1 integrated with a laser beam source LD1 emitting a first laser L1 and a photodetecting means on which its return light is made incident and the laser L1 emitted from the unit 1 is reflected with a beam splitter 2 and its return light is reflected with the beam splitter 2 to be returned to the unit 1 and, on the other hand, the laser L2 emitted from the laser beam source LD2 is reflected with the beam splitter 2 and its return light is made transmit the beam splitter 2 and the light is made incident on a photodetecting means 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup for reproducing an optical recording medium by selectively using two kinds of lasers having different wavelengths, and more particularly to an optical pickup for reducing the number of parts and the projection area. .

[0002]

2. Description of the Related Art For example, in a DVD (Digital Video Disc) player, a short wavelength laser for a DVD (having a wavelength of about 650 nm) is used as an optical pickup mounted to enable reproduction of both a DVD and a CD (Compact Disc). ) And a CD laser (wavelength about 78)
(Hereinafter referred to as "two-wavelength compatible optical pickup").

In such a two-wavelength compatible optical pickup, all components are used as components for reproducing DVDs and CDs (laser diodes, optical systems such as objective lenses and beam splitters, and photodetectors). There is also a method of installing (discrete) as individual components without integrating them. However, as can be easily imagined, the two-wavelength compatible optical pickup constructed in this manner has a very complicated arrangement of components and a large number of components, so that the manufacturing process becomes complicated, large, and high. There are inconveniences such as an increase in cost and an inconvenience that the optical path of the laser from emission from the laser diode to incidence on the photodetector becomes long (projection area increases).

Therefore, a two-wavelength compatible optical pickup integrates a laser diode that emits one of the two types of lasers, a photodetector that receives the return light, and a photodetector (including a necessary optical system). There is also a laser diode that emits the other one of the lasers and a photodetector that makes the return light incident thereon employs a discrete system.

FIG. 2 shows an example of a conventional configuration of a two-wavelength compatible optical pickup employing such a method. The integrated unit 11 includes a laser diode LD (not shown) for emitting a laser L1 having a wavelength of about 650 nm for DVD reproduction, and a photodetector PD for receiving the return light thereof.
(Not shown) and a microprism (not shown) are integrated. The laser L1 emitted from the laser diode LD in the unit 11 (the optical axis of this laser is shown as L1 for convenience in the drawing. The same applies to the return light and the laser L2 described later) enter the beam splitter 12. The light is reflected by the reflecting surface, is made parallel by the collimator lens 13, is reflected by the mirror 14 at a 45-degree angle, is directed to the recording surface of the DVD (not shown) to be reproduced, and is converged by the objective lens 15. The recording surface is irradiated.

The return light from the recording surface of the DVD is reflected by the beam splitter 12 again through the objective lens 15, the 45-degree mirror 14, and the collimator lens 13, and returns to the unit 11, where the photo detector PD in the unit 11 is provided.
Is incident on. In a signal processing system (not shown) of the DVD player, detection of a tracking error signal and a focus error signal during reproduction of a DVD and detection of a reproduction signal are performed based on the light incident on the photodetector PD.

On the other hand, the laser diode 16 emits a laser L2 having a wavelength of about 780 nm for reproducing a CD. This laser L2 is provided by the beam splitters 17, 1
2 are transmitted through a collimator lens 13, a 45-degree mirror 14, and an objective lens 15, and are irradiated onto a recording surface of a CD (not shown) to be reproduced.

The return light from the recording surface of the CD passes through the objective lens 15, the 45-degree mirror 14, and the collimator lens 13 again, passes through the beam splitter 12, is reflected by the beam splitter 17, and detects a focus error signal. After the beam diameter is enlarged by a concave cylindrical lens 18 to improve the accuracy, the photodetector 19
Is incident on. In the signal processing system described above, detection of a tracking error signal and a focus error signal during reproduction of a CD and detection of a reproduction signal are performed based on the light incident on the photodetector 19. In the figure, 1/4 is used for convenience.
The illustration of the wave plate is omitted.

[0009]

However, in the configuration as shown in FIG. 2, since the arrangement of each component is still complicated and the number of components is large, the manufacturing process can be simplified, downsized, and reduced in cost. There was a limit.

The laser L2 for reproducing a CD must pass through two beam splitters 12 and 17, and its return light is also transmitted through these beam splitters 12 and 17.
Further, since all the light must pass through the cylindrical lens 18, the disadvantage that the optical path becomes longer (the projection area becomes larger) cannot be avoided.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an object of the present invention is to provide a two-wavelength compatible optical pickup in which the arrangement of parts is further simplified, the number of parts is further reduced, and the projection area is reduced. It is assumed that.

[0012]

SUMMARY OF THE INVENTION An optical pickup according to the present invention reproduces an optical recording medium by selectively using a first laser and a second laser having different wavelengths from each other (ie, an optical pickup supporting two wavelengths). 3), a second laser emitting a second laser is provided in the vicinity of the first laser light source of a unit in which a first laser light source for emitting a first laser and light detection means for receiving the return light thereof are integrated. 2 laser light sources are arranged, the first laser emitted from this unit is reflected by the beam splitter, and its return light is reflected by this beam splitter and returned to this unit, while the second laser light source is Is reflected by the beam splitter, and the return light is transmitted through the beam splitter, It is characterized in that so as to be incident on the light detecting means disposed on the optical axis of the transmitted light.

The light is emitted from a unit (corresponding to the unit 11 for emitting the laser L1 in FIG. 2) in which the first laser light source for emitting the first laser and the light detecting means for receiving the return light are integrated. Laser
As in the case of the laser L1 in FIG. 2, the light is reflected by the beam splitter to irradiate the optical recording medium, and the return light is reflected by the beam splitter and returns to the unit.

On the other hand, near the first laser light source,
A second laser light source for emitting the second laser (the laser diode 16 for emitting the laser L2 in FIG. 2)
The laser emitted from the second laser light source is reflected by the same beam splitter to irradiate the optical recording medium, and the return light is transmitted through the beam splitter. Then, the light enters the light detecting means arranged on the optical axis of the transmitted light.

As described above, according to this optical pickup, the second laser emitted from the second laser light source disposed near the first laser light source is reflected by the first laser to form an optical recording medium. The reflected beam is reflected by the same beam splitter as the beam splitter to be irradiated onto the optical recording medium, and the returned light is transmitted through the same beam splitter and incident on the light detecting means on the optical axis of the transmitted light. ing.

Accordingly, since the second laser light source is arranged near the first laser light source, as shown in FIG. 2, a conventional two-wavelength optical pickup in which these laser light sources are arranged at completely different positions from each other. In comparison, the arrangement of these laser light sources is simplified. Further, since only one beam splitter is required to guide the return light of the first laser and the return light of the second laser in different directions, a conventional device provided with a plurality of beam splitters as illustrated in FIG. Compared to the two-wavelength compatible optical pickup,
The number of parts is reduced. This realizes further simplification of the manufacturing process of the two-wavelength compatible optical pickup and further downsizing and cost reduction.

The laser emitted from the second laser light source is directly incident on the beam splitter, and the return light is directly incident on the light detecting means from the beam splitter. The optical path of the second laser is shorter than that of the two-wavelength compatible optical pickup (the projection area is reduced).

The first laser emitted from the first laser light source and reflected by the beam splitter, and the second laser emitted from a second laser light source disposed near the first laser light source and reflected by the beam splitter. The direction of the optical axis of the second laser is shifted according to the distance between the first laser light source and the second laser light source.
If this shift becomes large, even if one laser is irradiated perpendicularly to the recording surface of the optical recording medium, the other laser will not be irradiated perpendicularly to the recording surface of the optical recording medium.

Therefore, as an example, if the distance between the first laser light source and the second laser light source is increased to a certain degree or more, the first and second laser light sources reflected by the beam splitter are required.
It is preferable to provide a hologram element for matching the directions of the optical axes of the second laser with each other. By doing so, even when this distance is longer than a certain degree, both the first and second lasers can be irradiated perpendicularly to the recording surface of the optical recording medium.

[0020]

FIG. 1 shows an example of the configuration of an optical pickup for two wavelengths according to the present invention.
The same parts as those described above are denoted by the same reference numerals, and redundant description will be omitted.

The integrated unit 1 is composed of the unit 11 shown in FIG.
As in the above, a laser L with a wavelength of about 650 nm for DVD playback
The laser diode LD1 for emitting light 1 (the position of the light emitting point is shown as LD1 for convenience), a photodetector PD (not shown) for receiving its return light, and a microprism (not shown) are integrated. Along with
A laser diode LD2 that emits a laser L2 having a wavelength of about 780 nm for CD reproduction (the position of the light-emitting point is shown as LD2 for convenience in the drawing) and is integrated so as to be arranged near the laser diode LD1. It is.

Laser diode LD in unit 1
Lasers L1 and L2 emitted from LD1 and LD2 are both incident on beam splitter 2 and are all reflected on the reflection surface thereof.

Laser diode LD in unit 1
1 and the laser diode LD2, the angle of incidence of the laser L1 on the reflection surface of the beam splitter 2 is 45 degrees, while the angle of incidence of the laser L2 on this reflection surface is between 45 degrees and 60 degrees. Is determined to be a constant angle α. Therefore, the directions of the optical axes of the lasers L1 and L2 reflected by the beam splitter 2 are shifted by (α-45) degrees.

When this deviation is larger than a certain degree (that is, the laser diode LD1 and the laser diode LD2).
When the difference between the angle α and the 45 ° is larger than a certain degree due to the distance of the laser L1 having passed through the collimator lens 13, the 45 ° mirror 14 and the objective lens 15 being reproduced as it is, While the recording surface of the target DVD (not shown) is irradiated perpendicularly to the recording surface, the laser L2 passing through the recording surface of the target DVD (not shown) is separated from the perpendicular at an angle that is not negligible in terms of reproduction accuracy. ) Is irradiated on the recording surface.

Therefore, between the collimator lens 13 and the 45-degree mirror 14, the vertically incident laser L1 is transmitted as it is, while the + and −1 order light of the obliquely incident laser L2 is transmitted. Most (for example, 10, 80, and 90% of 0-order light, + order light, and -1 order light, respectively)
A hologram element 3 having a function of tilting the optical axis so that the direction of the optical axis coincides with the laser L1 is provided. Thereby, the laser L2 is also irradiated perpendicularly to the recording surface of the CD to be reproduced.

The return light of the laser L1 from the recording surface of the DVD passes through the objective lens 15, the 45-degree mirror 14, the hologram element 3, and the collimator lens 13 and is reflected by the beam splitter 2 to return to the unit 1. Is incident on the photodetector PD inside. In a signal processing system (not shown) of the DVD player, detection of a tracking error signal and a focus error signal during reproduction of a DVD and detection of a reproduction signal are performed based on the light incident on the photodetector PD.

On the other hand, the return light of the laser L2 from the recording surface of the CD again passes through the objective lens 15, the 45-degree mirror 14 and then perpendicularly enters the hologram element 3, so that it passes through the hologram element 3 as it is, and Meter lens 1
After passing through the beam splitter 2 through 3, the transmitted light is incident on a photodetector 4 arranged on the optical axis. The signal processing system detects a tracking error signal and a focus error signal and a reproduction signal during reproduction of a CD based on the light incident on the photodetector 4.

Note that no cylindrical lens for expanding the beam diameter of the transmitted light is provided between the beam splitter 2 and the photodetector 4 in order to improve the detection accuracy of a focus error signal during CD reproduction. Instead, the unit 1 is operated by an actuator (not shown).
It is slidable in the optical axis direction (Z direction in the figure) of the emitted laser L1. By sliding the unit 1 in this direction, it is possible to improve the detection accuracy of the focus error signal at the time of reproducing the CD through a small change in the incident angle α of the laser L2 on the reflection surface of the beam splitter 2. .

The photodetector 4 can be slid on a plane perpendicular to the optical axis of the light transmitted from the beam splitter 2 by an actuator (not shown). Thereby, the position of the photodetector 4 is adjusted so that the return light of the laser L2 is incident on the center of the photodetector 4.

As described above, according to the two-wavelength compatible optical pickup, since the laser diode LD2 is arranged near the laser diode LD1, the arrangement of these laser diodes is smaller than that of the conventional two-wavelength compatible optical pickup. Be simple. In addition, only one beam splitter 2 is required to guide the return light of the laser L1 and the return light of the laser L2 in different directions, and between the beam splitter 2 and the photodetector 4 for the laser L2. By not providing a cylindrical lens, the number of parts can be reduced as compared with a conventional two-wavelength compatible optical pickup provided with a plurality of beam splitters and a cylindrical lens as illustrated in FIG. This further simplifies the manufacturing process of the two-wavelength compatible optical pickup and further reduces its size.
Cost reduction can be realized.

The laser L2 emitted from the laser diode LD2 is directly incident on the beam splitter 2, and the return light is directly incident on the photodetector 4 from the beam splitter 2, so that the laser L2 can be compared with a conventional two-wavelength compatible optical pickup. As a result, the optical path of the laser L2 can be shortened (projected area can be reduced).

In the above example, the hologram element 3 is provided to make the optical axes of the lasers L1 and L2 coincide, but the deviation of the optical axes of the lasers L1 and L2 is small enough to be ignored (ie, In a case where the distance between the laser diode LD1 and the laser diode LD2 is sufficiently short), such a hologram element may be omitted.

In the above example, the laser diode L
D1 and the laser diode LD2 are integrated into the same unit 1 as a single unit.
A laser diode LD2 separate from the unit in which D1 and the photodetector PD are integrated may be arranged near the laser diode LD1.

In the above example, the components for reproducing the DVD are integrated and the components for reproducing the CD are discrete. On the contrary, the components for reproducing the CD are integrated and the DVD is integrated.
The components for reproduction may be discrete.

In the above example, the present invention is applied to a two-wavelength compatible optical pickup which uses a short-wavelength laser for DVD reproduction and a laser for CD reproduction properly. The present invention may be applied to a two-wavelength compatible optical pickup in which a laser is used properly. In addition, the present invention is not limited to the above-described embodiments, and may take various other configurations without departing from the gist of the present invention.

[0036]

As described above, according to the optical pickup for two wavelengths according to the present invention, the second laser light source is switched to the first laser light source.
, The arrangement of these laser light sources is simplified as compared with the conventional two-wavelength compatible optical pickup. Also, since only one beam splitter is required to guide the return light of the first laser and the return light of the second laser in different directions, the number of parts is smaller than that of a conventional two-wavelength compatible optical pickup. Be reduced. As a result, it is possible to further simplify the manufacturing process of the two-wavelength compatible optical pickup and to further reduce its size and cost.

The second laser is directly incident on the beam splitter, and the return light is directly incident on the light detecting means from the beam splitter. Therefore, the second laser is compared with the conventional two-wavelength compatible optical pickup. Can be shortened (projected area can be reduced).

The first and second beams reflected by the beam splitter
By providing a hologram element for matching the directions of the optical axes of the second laser with each other, even when the distance between the first laser light source and the second laser light source is larger than a certain degree, Both the first and second lasers can be irradiated perpendicularly to the recording surface of the optical recording medium.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of the configuration of an optical pickup according to the present invention.

FIG. 2 is a diagram illustrating an example of a configuration of a conventional optical pickup.

[Explanation of symbols]

1,11 integrated unit, 2,12,17 beam splitter, 3 hologram element, 4,19 photodetector, 13 collimator lens, 144
5 degree mirror, 15 objective lens, 16, LD1, L
D2 laser diode, 18 cylindrical lens

Claims (2)

[Claims] 1. An optical pickup for reproducing an optical recording medium by selectively using a first laser and a second laser having different wavelengths from each other, wherein: a first laser light source for emitting the first laser and a return light therefrom. A second laser light source that emits the second laser is disposed in the vicinity of the first laser light source of a unit that integrates a light detection unit that causes light to enter the first laser light source; The laser is reflected by the beam splitter, the return light is reflected by the beam splitter and returned to the unit, and the second laser emitted from the second laser light source is reflected by the beam splitter and the return light Is transmitted through the beam splitter and is incident on light detection means arranged on the optical axis of the transmitted light. Optical pickup. 2. The optical pickup according to claim 1, wherein said first laser beam emitted from said first laser light source and reflected by said beam splitter and said beam emitted from said second laser light source are reflected by said beam splitter. An optical pickup, further comprising a hologram element for matching the direction of the optical axis with the second laser reflected by the splitter.