JPH04111239A - Optical pickup - Google Patents

Abstract

PURPOSE:To inexpensively comprise an optical recording and reproducing device by performing the detection and reproduction of a signal with only one optical pickup by providing a filter capable of emitting selectively light on one side out of the light of fundamental wave component and the one converted to a second higher harmonic out of the light from a light source. CONSTITUTION:The fundamental wave component and the second higher harmonic component of a laser beam are emitted by making the light 4 incident on an SHG element 12 via a convergence lens L, and generating the fundamental wave component and the second higher harmonic component of the laser beam by the SHG element 12. Also, the filter 11 is inserted between a collimator lens L and a beam splitter 15 to make a fundamental wave and the second higher harmonic incident on an optical disk D separately. In such a case, the fundamental wave and the second higher harmonic can be used simultaneously by moving the filter 11 on an optical system. Also, it is possible to use only the fundamental wave component or the second higher harmonic. In such a way, the reproduction of a laser disk or CD and that of the optical disk with high density of around four times can be performed only by switching the position of the filter 11.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical pickup, and in particular, is used in an apparatus for optically recording and/or reproducing information, and is used to record and/or reproduce information optically.
The present invention relates to an optical pickup configured to utilize both harmonic light.

[Prior art]

There are three types of optical discs (hereinafter also simply referred to as "optical discs") currently used in the industry:

■Playback-only type ■Additional recording type ■Rewritable type Playback-only disks include laser discs and CDs (
Compact Disc (registered trademark), both of which are already widely used. For playing laser discs and CDs,
A semiconductor laser with a wavelength of 780n11 or 830r+n is used. Additionally, additional recordable discs have recently begun to be used for document files and the like. Semiconductor lasers with a wavelength of 780 nm or 830 nm are also used for recording and reproducing on additional recordable disks. Furthermore, among rewritable disks, magneto-optical disks have recently been rapidly gaining popularity as computer memory. For recording and reproduction of this magneto-optical disk, the wavelength is 780 nm or 830 nm.
Semiconductor lasers are used for recording and reproduction.

When recording or reproducing information optically, 9t,
The density of information that can be reproduced is inversely proportional to the square of the diameter of the light spot focused on the recording medium.

The light spot (size) is proportional to the wavelength of the light used. Therefore, in order to increase the recording density, it is necessary to shorten the wavelength of the laser used for recording and reproduction.

FIG. 2 is a block diagram of an optical disc playback device. The optical disc D is placed on a turntable (not shown),
It is rotated by a motor M attached to this turntable. The motor M is controlled to a predetermined rotation speed by a rotation control section 3. The optical pickup 1 faces the back surface of the optical disc D and is sent in the radial direction of the optical disc D by a coarse movement motor 5. The rotation of the coarse motor 5 is controlled by a coarse motor control section 6, and is rotated at a predetermined rotational speed or a speed depending on the purpose. The laser beam 4 from the optical pickup 1 is
The pickup control section 7 includes a focus control section for always focusing the optical disc D in the best condition and a tracking control section for always correctly irradiating the laser beam 4 onto the track. The information detected from the optical disc D is processed by the signal processing unit 8, becomes desired data, and is sent to the drive via the drive controller 9.
Output from the interface.

FIG. 3 is a typical example of a conventional optical pickup used in such an optical disc reproducing apparatus.

As shown in this figure, the laser diode (laser light source)
The light (laser beam) 4 emitted from the laser beam 14 is made parallel by a collimator lens Ll, passes through a beam splitter 15 and a one-wavelength plate 16, and is focused onto an optical disc D by an objective lens L2. The light reflected from the optical disk D returns through the objective lens L2 and the one-wavelength plate 16, and then passes through the beam splitter 1.
5, passes through a detection optical system 17, and enters a photodetector 18 composed of a photodiode or the like, where a data signal and an error signal (a focus error signal and a tracking error signal) are detected.

Note that 13 is a laser power source.

[Invention or problem to be solved]

In recent years, the analogy is the IEEJ electromagnetic field theory study group material EHT-
89-104r 5) Optical wave characteristics of IG device using MaO solid solution LiNbO3 waveguide”, the laser wavelength can be halved using a SHG device (second harmonic generation device). As technology advances, it has become possible to use it for optical recording and playback.

On the other hand, laser discs, which are read-only optical discs, and C
As is well known, the pit depth of D is set to be slightly shallower than the tenth dimension of the laser wavelength used. Focused spot (sp) and pit (p +.

The relationship with P2) is shown in FIG. 4. This is because the modulation degree of reproduction is large and the tracking signal also obtains a certain value. Therefore, laser discs and CDs have 780nl'I
The depth is 190 nm, which is 1/4 of the depth of the substrate, and the depth is approximately 110 nm, which is slightly shallower than the depth of 120 ni corrected for the refractive index of the substrate.

In addition, there are also read-only discs that use light with a second harmonic of 415ni, as described in Japanese Patent Application Laid-Open No. 2-12135 "Second Harmonic Generation Element" and the above-mentioned Institute of Electrical Engineers of Japan Electromagnetic Field Theory Study Group material. It is appropriate that the depth be approximately 60r+n, which is slightly shallower than 65nn, which is approximately half the depth of a laser disk or CD. This depth can be measured using a laser disc or CD.
If the depth is set to , the modulation depth etc. cannot be obtained sufficiently and good reproduction cannot be achieved. That is, it is difficult for an optical reproducing device using light with a short wavelength of 415 nn, for example, to reproduce laser discs and CDs, which are currently widely used. Therefore, a user who purchases a high-density disk reproducing device that uses short wavelengths has to purchase both the current laser disk and CD reproducing device, resulting in disadvantages such as a heavy economic burden.

[Means to solve the problem]

The optical pickup of the present invention includes an optical system that focuses and irradiates light from a light source onto a part of the recording surface of an information recording medium and emits reflected light or transmitted light from the information recording medium, and the above-mentioned reflected light or transmitted light. In an optical pickup that is installed in an optical device that has a detection section that detects a signal, and that plays the information recording medium by inputting and signal processing a signal from the detection section, the light source is at least a laser light source; A second harmonic generating element generates a second harmonic based on the light emitted from the laser light source and emits the second harmonic and the fundamental wave. The above problem was solved by configuring a filter that can selectively emit at least one of the fundamental wave component light and the light converted to the second harmonic.

〔Example〕

The device of the present invention solves the above-mentioned drawbacks and provides a recording/playback device or a playback device that can play back high-density disks using short wavelengths as well as laser disks and CDs, which are currently contradictory, with the same playback device. 6. The present invention In this embodiment, recording and reproduction of an optical disk will be explained, but the present invention is also effective not only for optical disks but also for optical tapes, optical cards, or other recording media. Furthermore, it is clear that the present invention can be applied not only to optical recording and reproduction but also to optical devices that use such two wavelengths. Hereinafter, specific embodiments of the device of the present invention will be described with reference to the drawings.

FIG. 1 shows a specific embodiment of an optical pickup 1 according to the present invention. In this figure, the same components as those in the conventional example shown in FIG. 3 are given the same numbers, and detailed explanation thereof will be omitted. In FIG. 1, 11 is a filter, 12 is an SH
It is a G element. The main differences between this optical pickup 1 and the conventional optical pickup 2 shown in the third figure are the following two points.

(1) In the optical pickup 2 of the conventional device, the light 4 emitted from the laser diode 14 is directly incident on the collimator lens L1, whereas in the pickup 1 used in the present invention, the light 4 emitted from the laser diode 14 is directly incident on the collimator lens L1. is made incident on the SHG element 12 via the condenser lens L3. The SHG element 12 generates a second harmonic component based on the fundamental wave component of the laser beam, and emits the fundamental wave component and the second harmonic component of the laser beam.

(2) The pickup 1 for the apparatus of the present invention is provided with a filter 11 in order to separate the fundamental wave and the second harmonic and make them incident on the optical disc D. As a result, it becomes necessary to change the one-wavelength plate 16 to, for example, a ten-wavelength plate depending on the light to be used, but since the folded wavelength plate is not necessarily required, the following description will be made assuming that it is not provided.

Further, in the configuration example shown in the first figure, the filter 11 is inserted between the collimator lens L1 and the beam splitter 15, but it does not necessarily need to be placed here, and for example, between the collimator lens L1 and the SHG element 12. But that's fine.

Furthermore, it is also possible to omit the condensing lens L3 and arrange the laser diode 14 and the SHG element 12 close to each other, or to configure them integrally.

FIG. 5 shows an example of the configuration of a filter used in the optical pickup 1 of the present invention, and FIGS. 5A and 5B are a side view and a plan view, respectively. In the figure, 21 is a substrate made of glass or the like, 22 and 23 are antireflection films, 24 is a first filter film, and 25 is a second filter film. That is, in this filter 11, the anti-reflection portion 11!23 passes both the fundamental wave and the second harmonic, and the portion of the first filter film 24 cuts the fundamental wave.

The second harmonic transmission portion, the second filter WA25, is the fundamental wave transmission and second harmonic cut portion.

By moving this filter 11 on the optical system in the direction of the arrow β, it is possible to use the fundamental wave and the second harmonic at the same time, and by moving the filter 11 in the direction of the arrow α, it is possible to use only the fundamental wave component or It is also possible to utilize only the second harmonic. Note that the detailed explanation of the mechanism for holding the filter 11 and the specific structure for moving (sliding) it will be omitted because it can be easily inferred.

By installing the filter 11 having such a configuration in the optical pickup 1 as shown in FIG. 1 and installing it in the optical disc playback device shown in FIG. Reproduction of an optical disk with four times higher density can be performed simply by changing the position of the filter 11. It is preferable to correct chromatic aberration so that optical components such as the objective lens L2 can be used for both the fundamental wave and the second harmonic.In order to set the second harmonic wavelength to 415 nn, the fundamental wave must be Is it necessary to set it to 830nn?
This is different from 780 nm, which is generally used for CDs, etc., but this level of difference does not cause any problems.

If 780n1m light is used as the fundamental wave, the second harmonic will be 39Onl'N, and the transmittance of polycarbonate, which is commonly used as an optical disk substrate, will deteriorate rapidly. It is better to use

In addition, in the above explanation, for convenience, only the case of reproduction was described, but the movement of the filter 11 (
It is obvious that this can be done with slides). Further, although only the second harmonic has been described, it is clear that the case of the third harmonic or higher harmonics can also be dealt with by increasing the number of filters 11. Furthermore, although the optical pickup of the present invention detects reflected light from an optical disc, it can also be configured to detect transmitted light from an optical disc by arranging a light receiving element on the back surface of the disc.

[Effects] As described above, according to the optical pickup of the present invention, it is possible to detect and reproduce signals of laser discs and CDs, which are widely contradictory, and optical discs with about four times the density of these discs, using only one optical pickup. Therefore, it has excellent features such as being able to construct an optical recording/reproducing device or an optical reproducing device at low cost.

[Brief explanation of drawings]

FIG. 1 is a schematic block diagram of an optical pickup according to the present invention, FIG. 2 is a block diagram of an optical disc playback device equipped with an optical pickup, FIG. 3 is a schematic block diagram of a conventional optical pickup, and FIG. FIG. 5(A) is a conceptual perspective view showing the relationship between the pits of a read-only optical disc and the playback light spot.
, (B) are a side view and a plan view, respectively, showing an example of the configuration of a filter used in the optical pickup of the present invention. 1... Optical pickup, 3... Rotation control section, 4...
- Laser light, 5... Coarse motor, 6... Coarse motor control section, 7... Pickup control section, 8... Signal processing section, 9... Drive controller, 11... Filter, 12... SHG element, 13... Laser power supply, 14... Laser diode, 15... Beam splitter, 17... Detection optical system, 18... Photodetector, 21... Substrate , 22.23...Antireflection film, 24...First filter film, 25...Second filter film, D...Optical disk, L]...Collimator lens, L2...Objective Lens, L3...Condensing lens, M...Motor. Patent applicant Takube Bogami, Representative of Victor Japan Co., Ltd.

Claims (1)

[Claims] Focusing light from a light source on a part of the recording surface of an information recording medium,
It has an optical system that emits reflected light or transmitted light from the information recording medium while irradiating the information recording medium, and a detection section that detects the reflected light or transmitted light, and inputs a signal from the detection section and processes the signal. An optical pickup installed in an optical device for reproducing the information recording medium, which comprises: the light source being at least a laser light source; and a second harmonic generated from the light emitted from the laser light source. It is composed of a second harmonic generating element that emits a second harmonic and a fundamental wave, and among the light from the light source, the light of the fundamental wave component and the second harmonic are
An optical pickup comprising a filter capable of selectively emitting at least one of the lights converted into harmonics.