JPH02308431A - Pickup device for multi-layer optical disk - Google Patents

Abstract

PURPOSE:To execute read and write to different layers of a multi-layer optical disk by a variation of wavelength of a light source by using an optical system having a longitudinal chromatic aberration. CONSTITUTION:A laser light from a laser diode 1 is made parallel by a collimator 2 and deformed to a circle by a shaping prism 3, passes through a polarization beam splitter 4, a separating/synthesizing prism 5, a 1/4 wavelength plate 6 and an objective lens 7, and reads information on a layer 14 of an optical disk 8. By the polarization beam splitter 4 and the 1/4 wavelength plate, an optical isolator is formed. A reflected light of the layer 14 is emitted to a photodiode 9. Subsequently, a laser light from a laser diode 10 is made incident on the objective lens 7 through the same optical system. The lens 7 has an aberration of DELTAf in the case of a laser light of different wavelength, and DELTAf is equal to an interval (t) between the layer 14 and 15 of a multi-layer optical disk. Accordingly, the laser light of the laser diode 10 is converged onto the layer 15. By a condensing lens 11 and a parallel plate 12, the focusing control of a second laser light is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pickup device, and particularly to a pickup device for a multilayer optical disk used for a multilayer optical disk.

[Conventional technology]

Conventionally, such a pickup device includes a pickup device 100 as shown in FIG. 4, and such a pickup device 100 is used for two wavelengths. This pickup device 100 has a first laser diode 101.
Collimator lens 102 converts diverging light from 1 into parallel light
The light passes through a shaping prism 103 and enters a polarizing beam splitter 104. The light emitted from the polarizing beam splitter 104 is split into a separating/combining prism 105 and 1/4
The optical disc 1 passes through the wavelength plate 106 and is exposed to the objective lens 107.
It is converged on 08. The laser beam reflected from the optical disk 108 reaches the photodiode 111 via the polarizing beam splitter 104, a focus error detection optical device consisting of a condensing lens 109, and a parallel plate 110 arranged obliquely to the optical axis. .

On the other hand, a second laser diode 112 is arranged, and a second laser diode 112 is arranged.
The light emitted from the laser diode 112 is incident on the polarizing beam splitter 104 via the collimator lens 102 and the shaping prism 103. The light emitted from the polarizing beam splitter 104 is sent to the separating and combining prisms 105 and 174.
The optical disc 1 passes through the wavelength plate 106 and is exposed to the objective lens 107.
It is converged on 08. The light reflected from the optical disk 108 passes from the polarizing beam splitter 104 to the condensing lens 109.
The light reaches a four-split photodiode 113 via a focus error detection optical device consisting of a parallel plate 110 and a parallel plate 110.

After reading the information recorded on the first layer of the two-layer optical disc, when reading the information recorded on the second layer, the objective lens 107 of the optical system is moved by the optical system drive device, It is designed to read information.

In addition, on the contrary, when reading the information recorded in the first layer after reading the information recorded in the second layer, the objective lens 107 of the optical system is moved and read. (See Figures 5 and 6).

[Problems to be Solved by the Invention] However, according to such a conventional multilayer optical disk pickup device 100, an optical path for detecting a focus error passing through the condenser lens 109 and the parallel plate 110 is required for each wavelength, and the mechanism is complicated. There is a problem in that it becomes complicated and costs increase.

In addition, when only one objective lens 107 is used,
There is a problem in that it is difficult to read and write at each wavelength simultaneously, and reading and writing takes time.

The present invention has been devised in view of the above, and its purpose is to eliminate the need to provide a focus error signal detection device in each optical path when reading with multiple wavelengths, and to read and write simultaneously with multiple wavelengths. It is an object of the present invention to provide a pickup device for a multilayer optical disc that can be used.

[Means to solve the problem]

Therefore, the present invention provides a pickup for multilayer optical disks that includes a light source that generates light, an optical system that focuses and irradiates the wave light emitted from the light source onto the multilayer optical disk, and a photodetector that detects the light from the light source. In the apparatus, the optical system is configured to have longitudinal chromatic aberration to read and write different layers of the multilayer optical disk by changing the wavelength of the light source.

[Effect]

In the case of two wavelengths, the divergent light from the first laser diode is
The light passes through a collimator lens, becomes parallel, passes through a shaping prism, and enters a polarizing beam splitter. The light emitted from the polarizing beam splitter is split into a splitting/combining prism and 1/4
The light passes through a wave plate and is focused onto an optical disk by an objective lens. Thereafter, the laser beam reflected from the optical disk reaches the photodiode from the polarizing beam splitter via a focus error detection optical device consisting of a condensing lens and a parallel plate.

Laser light emitted from another second laser diode also reaches the photodiode through almost the same optical path. In this case, an optical device for detecting a focus error consisting of a condensing lens and a parallel plate is not required in one optical path.

Therefore, when reading with a plurality of wavelengths, there is no need to provide a focus error signal detection device in each optical path, and reading and writing can be performed simultaneously with each wavelength.

〔Example〕

Embodiments of the present invention will be described below based on the drawings. Referring to FIG. 1, the pickup device has a first laser diode 1, and divergent light from the first laser diode 1 is incident on a collimator lens 2. The collimator lens 2 is a lens for converting the diverging light from the first laser diode 1 into parallel light. The light emitted from the lens 2 passes through a shaping prism 3 that corrects an ellipse into a circle and enters a polarizing beam splitter (PBS) 4, and the light emitted from there is sent to a wavelength-1 separation/synthesis prism 5. Next, the light emitted from the wavelength separation/synthesis prism 5 is passed through a 1/4 wavelength plate (QWP).
It is injected at 6. The 1/4 wavelength plate 6 forms an optical isolator together with the polarizing beam splitter 4 to separate and extract reflected light. Thereafter, the reflected light is focused onto the multilayer optical disc 8 by the objective lens 7. here,
Objective lens.

7 has longitudinal chromatic aberration. That is, the objective lens 7 as an optical system has a property that the position of its image changes depending on laser beams of different wavelengths. Reference numeral 9 denotes a first photodiode (PD) as a photodetector.

On the other hand, a second laser diode 10 that emits laser light having a different wavelength from that of the first laser diode 1 is arranged. The laser light emitted from the second laser diode 10 is incident on the collimator lens 2 in order to convert the diverging light from the second laser diode 10 into parallel light. The laser beam incident on the collimator lens 2 is incident on a shaping prism 3 that transforms an ellipse into a circle, and the laser beam exiting from the shaping prism 3 is sent to a wavelength separation/synthesis prism 5 via a polarizing beam splitter 4. , is sent to an objective lens 7 via a quarter-wave plate 6 which together with a polarizing beam splitter 4 forms an optical isolator. Thereafter, the laser beam that has passed through the objective lens 7 is focused onto the multilayer optical disk 8.

Further, reference numeral 1 is a condensing lens, which together with a parallel plate 12 arranged obliquely to the optical axis constitutes an optical device for detecting a focus error. Reference numeral 13 denotes a second quadrant photodiode (PD) as a photodetector.
It is.

Next, the operation of the multilayer optical disc pickup device of the present invention will be explained.

First, to explain with reference to FIG. 3, when a first laser beam is emitted from the first laser diode 1, the laser beam is made into parallel light by the collimator lens 2, and transformed from an ellipse to a circle by the shaping prism 3. After that, it is sent to a quarter-wave plate 6 via a polarizing beam splitter 4 and a layer-separating and combining prism 5. Next, the laser light emitted from the quarter wavelength plate 6 is
The first laser beam irradiated onto the optical disk 8 through the objective lens 7 reads information on the first layer 4 on the optical disk 8.

Incidentally, the polarizing beam splitter 4 forms an optical isolator together with the quarter-wave plate 6, irradiates the diverging light from the first laser diode 1 toward the first layer 14 of the optical disk 8, and directs the reflected light to the first layer 14 of the optical disk 8. The light is emitted to the photodiode 9 of No. 1. Next, when a second laser beam is emitted from the second laser diode 10, the laser beam is made parallel by the collimator lens 2, transformed from an ellipse to a circle by the shaping prism 3, and then passed through the polarizing beam splitter 4. The signal is sent to a quarter-wave plate 6 via a separation/synthesis prism 5 and a separation/combination prism 5. after that,
The laser light emitted from the quarter-wave plate 6 is incident on the objective lens 7.

Since the objective lens 7 has longitudinal chromatic aberration as described above, it is configured to have an aberration of Δf when the second laser beam has a different wavelength from the first laser beam. Here Δf
is equal to the distance t between the first layer 14 and the second layer 15 of the multilayer optical disc 8.

Therefore, when the second laser beam enters the objective lens 7 and exits from the objective lens 7, it is focused onto the second layer 15 of the optical disk 8 due to the longitudinal chromatic aberration of the objective lens 7.

In this way, by using the laser beams having two wavelengths from the first laser diode 1 and the second laser diode 10 which generates laser beams having different wavelengths from the first laser diode 1, it is possible to simultaneously record images in the multilayer optical disk 8. Can be read from two layers.

Note that the focus error detector consisting of the condensing lens 11 and the parallel plate 12 is not required in the optical path of the first laser diode 1. This is because if the focus error of the laser beam of the second laser diode 10 is detected and focusing control is performed, the aberration caused by the first laser diode 1 is determined in advance. This is because the light is precisely focused on the layer ]-5 on the multilayer optical disc 8.

Next, FIG. 2 shows a second embodiment of the multilayer optical disk pickup device of the present invention.

In the second embodiment, three layers of information are formed on the optical disc 8. According to this embodiment, the first core laser diode and the second core laser diode emit laser beams with different wavelengths.
A laser diode 10 and a third laser diode 30 are provided, and the laser light emitted from each laser diode is transmitted through a collimator lens 2 and a polarizing beam splitter 4.
The light is incident on the wavelength separation/synthesis prism 5 via the wavelength separation/synthesis prism 5. Thereafter, the light is incident on the objective lens 7 via the 174-wavelength plate 6.

Since the objective lens 7 has longitudinal chromatic aberration, each of the three information layers in the optical disc 8 is irradiated with light. Then, the reflected light from each information layer is transmitted from the wavelength separation/synthesis prism 5 to the photodiodes 9 and 1 via the polarization beam splitter 4.
3.15.

Reference numerals 11 and 12 denote a condenser lens and a parallel plate, which constitute a focus error detection device.

In this example, an example was shown in which a three-layer optical disc is read using laser beams with three wavelengths, but if laser diodes with three or more wavelengths are provided, information on even more layers can be read. can.

Although the objective lens 7 has been mainly described as an optical convergence system, the collimator lens 2 may have longitudinal chromatic aberration.

〔Effect of the invention〕

As explained above, according to the present invention, the optical system has longitudinal chromatic aberration so that it reads and writes to different layers of a multilayer optical disk depending on the change in wavelength. The layers can also be automatically focused and can be read and written simultaneously.

Furthermore, since only one focus error detection device for obtaining a focus error signal needs to be provided, the configuration is simplified and costs are reduced.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a first embodiment of a pickup device for a multilayer optical disc of the present invention, FIG. 2 is a block diagram of a second embodiment of a pickup device for a multilayer optical disc of the present invention, and FIG. FIG. 4 is an explanatory diagram of the operation of the multilayer optical disk pickup device of the invention, FIG. 4 is a block diagram of the conventional pickup device, and FIGS. 5 and 6 are explanatory diagrams of the operation of the conventional multilayer optical pickup device. DESCRIPTION OF SYMBOLS 1... First laser diode, 2... Collimator lens, 3... Shaping prism, 4... Polarizing beam spur, 5... Wavelength separation/synthesis prism, 6... l/
4-wavelength plate, 7... objective lens, 8... multilayer optical disk, 9... first photodiode, -. Applicant's representative Yasushi Ishikawa Younger brother 1 Figure # Yoina 2nd 3rd Jin 4 Figure

Claims (1)

[Scope of Claims] A multilayer optical disc comprising a light source that generates light, an optical system that focuses and irradiates the light emitted from the light source onto a multilayer optical disc, and a photodetector that detects the light from the light source. A pickup device for a multilayer optical disc, characterized in that the optical system has longitudinal chromatic aberration so as to read and write to different layers of the multilayer optical disc according to changes in the wavelength of the light source.