JPH11259895A - Optical head for multilayer recording - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To enable multiplex recording using a Bessel beam. SOLUTION: When a laser beam from a laser diode 1 is converted into a parallel light by a collimator lens 3 and converted into an annular light beam via a liquid crystal shutter panel 10, each annular portion of the liquid crystal shutter panel 10 is selectively used. By changing the diameter of the annular light beam by turning on and off the recording medium 7, multiplex recording can be performed in the depth direction of the recording medium 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head used for an optical disk device and the like, and more particularly to an optical head capable of writing and reading in a depth direction of a recording medium.

[0002]

2. Description of the Related Art Conventionally, an optical pickup device which has been put to practical use mainly on an optical disk technology such as an optical recording CD includes:
Depending on the method of recording and reproducing information on an optical disk, a system such as a phase change type or a magneto-optical type which can be written and erased many times, a CD-R and a DV which can be written only once
Systems such as DR, CDs for playback only, CD-RO
There are systems such as M, DVD, and DVD-ROM. Here, an optical pickup for a CD as a conventional representative technique will be described with reference to FIG.

That is, a laser beam 2 emitted from a semiconductor laser diode 1 is split by a diffraction grating 3A into three beams of a zero-order diffracted beam for detecting an optical signal and a diffracted beam for detecting a tracking error. The illustration of the diffracted light is omitted in the figure. The split laser light passes through the beam splitter 4 and is focused by the objective lens 5A to a beam having a depth of focus of about 1 μm and a beam diameter of about 1 μm. Focused on top.

Since the optical disk 7 has eccentricity and warpage,
In order to maintain the focal point of the laser beam 2 on the land or groove on which the recording pit is written, the objective lens 5A is movable in two directions, a radial direction and a plate thickness direction of the optical disk. This is done with a set of driving electromagnetic coils. The laser light reflected from the disk surface is
The light is reflected by the beam splitter 4 and received by the light receiving diode 9 and is converted into an electric signal. For the purpose of reducing the thickness of the optical pickup and the like, the semiconductor laser diode 1, the diffraction grating 3A, the beam splitter 4, and the lens are integrated, or a component having a configuration substantially equivalent to these components is integrated. A method of controlling the integrated components, that is, the entire module with a drive coil, has also been put to practical use.

A Bessel beam having a zero-order Bessel function-type intensity distribution and a deep depth of focus by an axicon prism or an equivalent hologram has attracted attention. Regarding the Bessel beam, reference is made to Durin et al. (J. Durin and JJ Micheli, J
r. “Diffraction-Free Beam
s. Phys. Rev. Lett. 58 (1987) 1
499; Durin “Exact Solution”
ns for Diffraction-FreeBe
ams I: the Scalar theory "
J. Opt. Soc. Am. A4 (1987) 651
Etc.) are described in detail.

Therefore, the applicant has proposed an optical head as shown in FIG. 5 (Japanese Patent Application No. 9-141831: also referred to as a proposed device). This uses an axicon prism. The light from the laser diode 1 is collimated by a collimator lens 3 and then bent by 90 degrees by a beam splitter 4 to enter an axicon prism 5. A bessel beam 6 is generated from the axicon prism 5, reflected by the disk, and passed through the axicon prism 5, the beam splitter 4 and the lens 8, and a signal detection PD 9.
Incident on. Here, since the Bessel beam has a long focal depth, a focus servo mechanism is not required.

[0007] Recently, with the increase of image data and the like, a higher density of the recording medium is required. One of the ways to increase the recording density of an optical disk system is to increase the pit density. This includes reducing the laser spot size by shortening the laser wavelength and increasing the numerical aperture (NA), and reducing the land size. A group recording method is being studied. The second method is a method of increasing the number of recording layers (three-dimensionalization). Already D
In VD, a two-layer system is being studied, and a method of moving the objective lens to change the focal position is being studied. In order to solve the problem of crosstalk associated with the multilayer structure, a wavelength multiplexing method for changing the readout wavelength of each phase has been studied.
According to this method, multiple reading and writing in the depth direction are possible.

[0008]

However, in the method using an ordinary objective lens, a mechanical focusing mechanism is required because the depth of focus is shallower than the unevenness of the disk.
In addition, there is a problem that multi-value recording of the wavelength multiplex system cannot be supported. Accordingly, an object of the present invention is to provide an aberration-free and mechanical focusing mechanism when recording, reproducing, and erasing multiplexed information in the depth direction of optical recording media having different thicknesses of substrates such as optical disks. It is an object of the present invention to provide an optical pickup capable of recording, reproducing, and erasing information on an optical disc and capable of coping with multi-value recording.

[0009]

According to the first aspect of the present invention, there is provided a laser diode and a first optical element for condensing laser light from the laser diode on an optical recording medium. A second optical element for condensing an optical signal modulated by the optical recording medium and reflected from the optical recording medium surface onto a light receiving element, an optical head including the light receiving element, or a laser diode; A third optical element having a function of condensing a laser beam on an optical recording medium and condensing an optical signal modulated by the optical recording medium and reflected from the optical recording medium surface on a light receiving element; In a multi-layer recording optical head, a fourth optical element for converting light emitted from the laser diode into parallel light, and a fifth optical element for converting the parallel light into an annular light beam having a variable diameter. Establishment Thereby enabling focusing the light beam condensed on the optical recording medium at a desired position in the recording medium.

In the first aspect of the invention, the light beam may have a zero-order Bessel function type intensity distribution (the second aspect of the invention), or the annular light beam may be A predetermined annular area of the concentric liquid crystal shutter panel can be formed by opening and closing (an invention according to claim 3), or a plane wave is converted into ring-shaped divergent light to form the annular light beam. A first axicon prism and a second axicon prism for converting the ring-shaped divergent light into a ring-shaped collimated light are provided, and the relative distance between the first and second axicon prisms can be varied. By doing so, the diameter of the ring-shaped collimated light can be made variable (the invention of claim 4).

According to the fifth aspect of the present invention, the laser diode, the first optical element for condensing the laser light from the laser diode on the optical recording medium, and the laser light modulated by the optical recording medium and reflected from the optical recording medium surface. A second optical element for condensing an optical signal on a light receiving element, an optical head or a laser diode including the light receiving element, and a laser beam from the laser diode condensed on an optical recording medium; A third optical element having a function of condensing the optical signal reflected by the optical recording medium surface on the light receiving element onto the light receiving element, and a plurality of light beams having different wavelengths in the multilayer recording optical head including the light receiving element. After changing the beam into parallel light, the beam is incident on an axicon prism to form a plurality of zero-order Bessel beams corresponding to each wavelength, and data is written by the main lobe of the zero-order Bessel beam. And to perform the write.
In the invention according to claim 5, a plurality of optical signals having different wavelengths, which are modulated by the optical recording medium and reflected from the optical recording medium surface, are condensed on each light receiving element via a plurality of wavelength selecting means. (Invention of claim 6).

[0012]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention. That is, the laser light emitted from the laser diode 1 is converted into a plane wave by the collimator lens 3 and enters the liquid crystal shutter panel 10 as shown in FIG. This liquid crystal shutter panel 10
Are concentric transparent electrodes 10A-1A as shown in FIG.
0D, and can be opened and closed depending on whether or not a predetermined voltage is applied. Therefore, when the liquid crystal shutter is turned on by biasing one annular portion, for example, 10A, an annular light beam corresponding to the selected annular portion 10A is formed. After this light is turned back by the beam splitter 4, it is converted into a conical wavefront wave by an axicon 5, which is a kind of conical prism, to produce a Bessel beam 6 having a deep focal depth.

The reflected light from the recording surface 7 passes through the axicon 5 and is converted into an annular plane wave, passes through the beam splitter 4 and enters the light receiving PD 9. Here, the beam is also an annular beam, and the optical signal is converted into an electric signal by the concentric CCD, so that recording on the optical disk can be reproduced. The CCD and the liquid crystal shutter have the same number of divisions here, and the mutual positions are (c)
Correspond as shown in FIG. Therefore, for example, when the bias position of the liquid crystal shutter panel 10 is 10A (outside), the recording surface is 71, and the reproduction position is 9A. Here, if the light output of the laser diode 1 is modulated, it is possible to write, erase, and reproduce information on a phase change type or magneto-optical disk. Further, optical elements such as the collimator lens 3 and the axicon 5 can be replaced with a diffraction grating such as a hologram element or a binary hologram element having the same function.

FIG. 2 is a block diagram showing a second embodiment of the present invention. That is, by providing an axicon 51 for forming a ring-shaped divergent light and an axicon 52 for forming a ring-shaped collimated light and changing the distance between these two axicons, the diameter of the annular light beam to the axicon 5 can be made variable. In this embodiment, the use efficiency of the laser beam is improved as compared with the example of FIG.

FIG. 3 is a block diagram showing a third embodiment of the present invention, and shows an example in which multi-level recording is performed in the depth direction of a medium. That is, three laser diode chips 1A, 1B, 1
C are provided, and light of wavelengths λ1, λ2, λ3 is emitted from each of them, and is converted into a plane wave by the collimator lens 3. After this plane wave is turned back by the beam splitter 4, it is converted into a conical wave surface wave by the axicon 5, and a Bessel beam 6 having a deep focal depth is produced.

That is, three types of Bessel beams 6 are produced corresponding to the wavelengths λ1, λ2, λ3.
Therefore, in the recording medium 7, three types of recording layers 71, 72, 73 made of a material having sensitivity to the wavelengths λ1, λ2, λ3 are provided.
Is formed. Thereby, recording and reproduction can be performed with the main lobe of the Bessel beam of each wavelength, and there is no interference from other layers. PD for receiving light (91, 92, 9
3) is the same as that shown in FIG. 1 and FIG. 2, but as shown in FIG.
By splitting λ1, λ2, and λ3 using A and 11B, simultaneous reading in the depth direction of the medium can be performed.

[0017]

According to the present invention, there is obtained an advantage that an optical head for recording, reproducing, and erasing information in a depth direction of a recording medium with a relatively simple structure can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing a second embodiment of the present invention.

FIG. 3 is a configuration diagram showing a third embodiment of the present invention.

FIG. 4 is a configuration diagram showing a conventional example.

FIG. 5 is a configuration diagram showing a proposed device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 2 ... Laser light, 3 ... Collimator lens, 4 ... Beam splitter, 5A, 8 ... Lens, 5, 5
1, 52: axicon, 6: Bessel beam, 7: optical disk, 71, 72, 73: recording layer (recording pit),
9, 91, 92, 93 ... photodiode for light reception, 10
... liquid crystal shutter panel, 11A, 11B ... dichroic mirror.

Continuation of the front page (72) Inventor Yoichi Shindo 1-1-1, Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fuji Electric Co., Ltd.

Claims (6)

[Claims] 1. A laser diode, a first optical element for condensing laser light from the laser diode on an optical recording medium, and a light receiving element for receiving an optical signal modulated by the optical recording medium and reflected from the optical recording medium surface A second optical element for focusing light on the top,
An optical head or laser diode comprising the light receiving element, and a laser beam from the laser diode focused on an optical recording medium, and an optical signal modulated by the optical recording medium and reflected from the optical recording medium surface is reflected on the light receiving element. In a multi-layer recording optical head comprising a third optical element having a function of condensing light and a light receiving element thereof, a fourth optical element for converting light emitted from the laser diode to parallel light, A fifth optical element that converts the light beam into an annular light beam having a variable diameter, so that the light beam focused on the optical recording medium can be focused on a desired position in the recording medium. Optical head for multilayer recording. 2. The optical head according to claim 1, wherein the light beam has a zero-order Bessel function type intensity distribution. 3. The optical head according to claim 1, wherein the annular light beam is formed by opening and closing a predetermined annular area of a concentric liquid crystal shutter panel. 4. The method for forming the toroidal light beam,
A first axicon prism for converting a plane wave into a ring-shaped divergent light, and a second axicon prism for converting the ring-shaped divergent light into a ring-shaped collimated light;
2. The multi-layer recording light according to claim 1, wherein the relative distance between the first and second axicon prisms is variable, so that the diameter of the ring-shaped collimated light is variable. head. 5. A laser diode, a first optical element for condensing laser light from the laser diode on an optical recording medium, and a light receiving element for receiving an optical signal modulated by the optical recording medium and reflected from the optical recording medium surface. A second optical element for focusing light on the top,
An optical head or laser diode comprising the light receiving element, and a laser beam from the laser diode focused on an optical recording medium, and an optical signal modulated by the optical recording medium and reflected from the optical recording medium surface is reflected on the light receiving element. In a multi-layer recording optical head composed of a third optical element having a function of condensing light and a light receiving element, a plurality of light beams having different wavelengths are changed into parallel light, and then are incident on an axicon prism to be applied to each wavelength. An optical head for multilayer recording, wherein a plurality of corresponding zero-order Bessel beams are formed, and data is written using a main lobe of the zero-order Bessel beam. 6. A plurality of optical signals having different wavelengths, which are modulated by the optical recording medium and reflected from the surface of the optical recording medium, are condensed on each light receiving element via a plurality of wavelength selecting means. An optical head for multilayer recording according to claim 5.