JPH0531219B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an optical information storage system that modulates a light beam such as a laser beam according to information, and irradiates a rotating recording medium with the modulated light beam to record information on the rotating recording medium. Regarding recording devices, in particular, information is recorded so that a recording track in the form of an array of pits or bumps is formed on a rotating recording medium, either directly or after a predetermined process, using a light beam modulated according to the information. This invention relates to improvements to optical information recording devices.

Video discs and digital audio
A disk is an information recording disk that has a surface on which information is recorded with a spiral recording track formed by an arrangement of a large number of pits, and is rotated for information reproduction. One method of recording information in the process of creating such video discs and digital audio discs is to irradiate an unrecorded rotating recording medium with a light beam such as a laser beam modulated according to the information. Then, recording is performed using an optical information recording device that directly forms a large number of pits in an array on the rotating recording medium, or changes it through subsequent processing so that a large number of pits or bumps are formed in an array. .

Such a conventional optical information recording device is constructed as shown in FIG. In Figure 1, 1
is a laser light source, such as an argon laser or a helium laser.
This laser light source 1 consists of a neon laser, etc.
A parallel laser light beam 2 from is guided to an optical modulator 4 via a mirror 3. The optical modulator 4 is composed of an electro-optic modulator that uses an electro-optic effect or an acousto-optic modulator that uses an acousto-optic effect, and the signal source 5
The information signal S to be recorded is supplied from. The optical modulator 4 then intensity-modulates the laser beam 2 according to the information signal S to obtain a modulated optical beam 2'. This modulated light beam 2' is guided to an objective lens 8 via mirrors 6 and 7, focused by the objective lens 8, and made incident on a rotating recording medium 9. The rotary recording medium 9 is, for example, a disc-shaped base with a photoresist layer provided thereon, and a turntable 11 rotated by a motor 10.
and rotated at a predetermined rotational speed. Then, the photoresist layer of the rotating recording medium 9 is exposed by the modulated light beam 2' focused by the objective lens 8, and an exposure pattern is formed so that a large number of pits or bumps are later formed in an array. Recording of the information signal S with respect to 9 is performed. In this case, the incident position of the modulated light beam 2' on the rotating recording medium 9 is gradually moved in the radial direction of the rotating recording medium 9, and as a result, the exposure pattern formed on the photoresist layer has a spiral shape. Become something. Furthermore, the spot formed by the modulated light beam 2' on the photoresist layer is circular, and its dimensions are
For example, the diameter (D) is the wavelength (λ) of the modulated optical beam 2'.
and the numerical aperture (NA) of the objective lens, D=
k·λ/NA (k is a constant).

The exposure pattern thus formed on the photoresist layer of the rotating recording medium 9 is an intermittent exposure trajectory having a width corresponding to the diameter of the spot P of the modulated light beam 2', as shown in FIG. Q is arranged. Here, the rotating recording medium 9 is being rotated in the direction of arrow X. Then, development processing and other processing are performed on the photoresist layer on which such an exposure pattern is formed, and pits or bumps corresponding to the exposure locus Q are formed. A recording track is provided with an array of pits or bumps corresponding to the information signal S from the recording medium.

Based on the rotating recording medium 9 on which the information signal S has been recorded as described above, an information recording disk having a pit arrangement similar to that of the pits or bumps formed in the photoresist layer is reproduced. , video disks and digital audio disks. In evaluating the case of reproducing an information signal from an information recording disk on which a recording track is formed by such an arrangement of pits, the degree of modulation of the reproduced information signal, that is, the reproduction obtained in the portion of the disk where pits are not formed, is evaluated. Two light receivers installed in parallel receive the read light beam from the disk, which is used to control the ratio of the playback output level obtained at the pit to the output level, and to control the tracking of the read light beam that scans the recording track during playback. The level of the push-pull signal received by the element and obtained by calculating the difference between the outputs of both light-receiving elements is mainly determined by the direction of the rotation tangential direction of the rotating disk of the pit (in the direction corresponding to the arrow T in Fig. 2). , hereinafter referred to as the tangential direction) (corresponding to the arrow R in Fig. 2, hereinafter referred to as the radial direction), and the frequency characteristics of the reproduced information signal, the degree of DC component content, etc. , mainly depends on the shape of the tangential end of the pit. Regarding the above-mentioned modulation degree and level of the push-pull signal, it is desirable that the radial dimension of the pit is large, while on the other hand, regarding the frequency characteristics of the reproduced information signal, the degree of DC component content, etc. It is desirable that the shape of the end portion of the holder is such that the protruding portion thereof is small.

The radial dimension and tangential edge shape of the pits formed on such information recording disks are determined by the pits or bumps formed on the photoresist layer of the rotating recording medium during the information recording process, and hence the tangential end shape of the pits. , as shown by Q in FIG. 2, is determined depending on the radial dimension of the exposure locus and the shape of the tangential end. In the above-mentioned conventional recording apparatus, the spot formed by the modulated light beam forming the exposure trajectory is circular as shown by P in FIG. The dimensions and the shape of the tangential end respectively depend on the diameter of this spot. For example, if the diameter of the spot created by the modulated light beam is increased to increase the radial dimension, the tangential direction The shape of the end portion of the protrusion becomes large. Therefore, the radial dimension and tangential end shape of the pits or bumps formed on the rotating recording medium, which are the sources of the pits formed on the information recording disk, can be obtained under optimal conditions. I had the inconvenience of not being able to do that.

Note that when recording information, a rotating recording medium provided with a thin metal layer or the like instead of a photoresist layer is used, and an array of pits is formed directly on the thin metal layer by the modulated light beam. Even when the Tozuki information recording disk is duplicated, the radial dimension and tangential end shape of the pit are as follows:
respectively, depending on the diameter of the circular spot created by the modulated light beam, resulting in the same problems as described above.

In view of these points, the present invention provides a modulated signal whose intensity is modulated according to an information signal and whose cross section in a plane perpendicular to the optical axis is elliptical using an acousto-optic effect. A light beam is obtained, and the modulated light beam causes a rotating recording medium to be
so that the radial dimension and tangential end shape of the pits or bumps that are arrayed directly or after a predetermined treatment are obtained under optimal conditions; An optical information recording device capable of recording information is provided. Examples of the present invention will be described below.

FIG. 3 shows an example of an optical information recording device according to the present invention. This example includes a laser light source 1, mirrors 3, 6 and 7, a signal source 5 and an objective lens 8 similar to those in the conventional recording apparatus shown in FIG. Furthermore, a turntable 11 rotated by a motor 10 similar to that shown in FIG. 1 is provided, and a rotating recording medium 9 is mounted on the turntable 11. As described above, this rotary recording medium 9 is, for example, a disc-shaped substrate with a photoresist layer provided thereon.

The parallel laser beam 2 from the laser light source 1 is
After passing through the mirror 3, the beam is made into a focused beam by the lens 12 and is made incident on the optical modulator 13. and,
The optical modulator 13 performs intensity modulation on the focused laser beam 2 according to the information signal S from the signal source 5, and a modulated optical beam 2'' is obtained from the optical modulator 13 as a diverging beam. , which is made into a parallel beam by the lens 14 and then passes through the aperture 15.The optical modulator 13 is composed of an acousto-optic modulator, and as shown in FIG. an ultrasonic generator 16 that generates ultrasonic waves under the control of the
It has As shown in FIG. 4, the lens 12 focuses the collimated laser beam 2 onto the medium 1.
The light is focused into the medium 17 so that it forms a single beam. At this time, the incident laser beam 2a is transmitted through the medium 17 in which the ultrasonic wave propagates, which is controlled by the control signal S'.
Diffraction occurs due to the acousto-optic effect, and the first-order diffracted light 2b exits the medium 17 as a diverging beam at a predetermined diffraction angle with respect to the non-diffracted zero-order light 2c. This first-order diffracted light 2b is made into a parallel beam by a lens 14, and then passes through an opening 15 through which only this first-order diffracted light 2b passes, and heads toward the mirror 6. Here, the first-order diffracted light 2b is the incident laser beam 2a.
It is obtained by diffraction generated in response to the control signal S' of becomes the modulated light beam 2''.In this case, the medium 17
Since the incident laser light beam 2a is a focused beam, a part of the part in the diffraction direction away from the optical axis does not satisfy the Bragg condition for diffraction, and no diffraction occurs. 0th order light 2
It exits the medium 17 as c. Therefore, the first-order diffracted light 2b has a short axis a in the direction of diffraction and a cross section in the plane perpendicular to the optical axis, as shown in FIG. It becomes an elliptical shape having a major axis b. Therefore, the lens 12, the light modulator 13, the lens 14 and the aperture 15
is the parallel laser light beam 2 from the laser light source 1
is modulated according to the information signal S to generate a modulated light beam 2'', and the cross section of the modulated light beam 2'' in a plane orthogonal to the optical axis thereof is made into an elliptical shape. It makes up the division. Then, the minor axis a of the elliptical cross section of the modulated light beam 2''
The ratio of the major axis b to the major axis b can be changed by changing the diameter of the focal point of the incident laser beam 2a in the medium 17 by the lens 12.

The modulated light beam 2'' from the aperture 15 is guided to the objective lens 8 via the mirror 6, the lens 18 and the mirror 7, and is focused by the objective lens 8.
The light is made incident on the rotating recording medium 9. in this case,
The modulated light beam 2'' is made incident on the rotating recording medium 9 so that the major axis direction of the elliptical cross-section coincides with the radial direction on the rotating recording medium 9, and the modulated light beam 2'' is made to be incident on the rotating recording medium 9. Therefore, the mirror 6, the lens 18, the mirror 7, and the objective lens 8 direct the modulated light beam 2'' to the rotating recording medium with the major axis of the elliptical cross section thereof. A light beam guide section is configured to make the light beam incident on the rotating recording medium 9 in a direction perpendicular to the tangential direction of the light beam 9 . Here, in order to make the modulated light beam 2'' enter the rotating recording medium 9 while maintaining its elliptical cross section, the objective lens 8 is made to have a finite magnification and a large numerical aperture (NA), and the lens 18 is made to have a finite magnification and a large numerical aperture (NA). It is arranged to play the role of limiting the effective numerical aperture of the objective lens 8.

The photoresist layer of the rotating recording medium 9 is exposed by the modulated light beam 2'' made incident on the rotating recording medium 9, and a spiral exposure pattern is formed in the same manner as in the case of the recording apparatus shown in FIG. Then, the information signal S is recorded on the rotating recording medium 9. In this case as well, the exposure pattern formed on the photoresist layer of the rotating recording medium 9 is formed after a large number of pits as shown in FIG. Or an intermittent exposure trajectory where bumps are to be formed.
Q′ will be arrayed. In FIG. 6, arrow X indicates the direction of rotation of the rotating recording medium 9. However, at this time, the spot P' of the modulated light beam forming the exposure locus Q' becomes an ellipse similar to that shown in FIG. direction (direction of arrow R in Figure 6), and the minor axis
The direction of a' is the tangential direction (sixth direction) on the rotating recording medium 9.
(direction of arrow T in the figure), so the exposure trajectory
The radial dimension of Q' is determined by the long axis b' of spot P', and the shape of the end of the exposure trajectory Q' is determined by the spot P'.
It depends on the minor axis a′ of P′. The photoresist layer on which such an exposure pattern is formed is then subjected to development processing and other processing to form pits or bumps corresponding to the exposure locus Q'. A recording track is provided by an arrangement of pits or bumps corresponding to the information signal S from 5.

In this way, an information recording disk having a pit or bump arrangement similar to that formed in the photoresist layer is reproduced based on the rotating recording medium 9 on which the information signal S is recorded. However, the rotating recording medium 9
pits or bumps formed on the
The radial dimension of the pits or bumps formed on the duplicated information recording disk is determined depending on the long axis b' of the spot P' caused by the above-mentioned modulated light beam 2'', and the tangential direction thereof The shape of the end is also determined depending on the minor axis a' of the spot P'.Therefore, when reproducing information recording discs, the degree of modulation of the reproduced information signal, the level of the push-pull signal, etc. In order to obtain a large radial dimension of the pit or bump such that
b' is selected to a predetermined large value, and the protrusion of the tangential end of the pit or bump is such that the frequency characteristics and DC component content of the reproduced information signal are appropriate. In order to obtain a small shape, select the minor axis a' of the spot P' of the modulated light beam 2'' to a predetermined small value and form an exposure pattern on the photoresist layer of the rotating recording medium 9. Then, the short axis a' and long axis b' of the spot P' of the modulated light beam 2'' are changed by changing the short axis a and the long axis b of the elliptical cross section of the modulated light beam shown in FIG. The selection can be made by That is, by appropriately selecting the minor axis a and the major axis b of the elliptical cross section in the plane perpendicular to the optical axis of the modulated light beam, the information recording disk to be copied can be The radial dimension and the shape of the tangential end of the pit or bump formed can be obtained under optimal conditions.

The rotating recording medium 9 is assumed to have a thin metal layer, etc., instead of a photoresist layer, on a disk-shaped base, and an array of pits is directly formed on this thin metal layer by the modulated light beam 2''. Even when the information signal S is recorded, the radial dimension and tangential end shape of the pit formed in the thin metal layer are determined by the modulated light beam 2'' on the thin metal layer. Since it is determined depending on the major axis and minor axis of the elliptical spot, the same effect as described above can be obtained.

As explained above, the optical information recording device according to the present invention includes a light modulating means with a medium that produces an acousto-optic effect, and a state in which a light beam is directed to the light modulating means to form a focal point in the medium. a first lens means that causes the first-order diffracted light beam to enter the light modulating means, and a second lens means that causes diffraction due to an acousto-optic effect in the medium of the light modulating means and converts a first-order diffracted light beam emitted from the medium in a divergent state into a parallel beam; As a result, a modulated light beam whose intensity is modulated according to the information signal and whose cross section in a plane perpendicular to the optical axis is elliptical is obtained. By making the ellipse major axis direction perpendicular to the tangential direction of rotation of the rotating recording medium and making it incident on the rotating recording medium, the optical system of the entire apparatus can be simplified, and it is possible to It is possible to obtain a modulated light beam that is intensity-modulated and has an elliptical cross section in a plane perpendicular to the optical axis, and by using such a modulated light beam, Information is provided in such a way that the radial dimension and the shape of the end in the rotational tangential direction of the pits or bumps to be arrayed directly or after a predetermined process are obtained under optimal conditions. Records can be made.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing a conventional optical information recording device, FIG. 2 is a diagram used to explain the operation of the recording device shown in FIG. 1, and FIG. 3 is an optical information recording device according to the present invention. Schematic configuration diagram showing an example of a recording device, No. 4
5 and 6 are diagrams used to explain the operation of the example shown in FIG. 3. In the figure, 1 is a laser light source, 5 is a signal source, 8 is an objective lens, 9 is a rotating recording medium, 11 is a turntable, 12, 14 and 18 are lenses, and 13 is an optical modulator.

Claims (1)

[Scope of Claims] 1. A light beam generating means, an ultrasonic generating section that generates ultrasonic waves according to an information signal, and a medium that causes the ultrasonic waves generated by the ultrasonic generating section to propagate to produce an acousto-optic effect. a first lens means that focuses the light beam from the light beam generating means and causes it to enter the light modulation means in a state where a focal point is formed in the medium; Diffraction occurs in the medium of the modulation means due to the acousto-optic effect, and the intensity is modulated according to the information signal, and the cross section in the plane perpendicular to the optical axis is elliptical, and the signal is diverged from the medium. a second lens means for converting the emitted first-order diffracted light into a parallel beam and passing it as a modulated light beam; an optical information recording device comprising: a light beam guiding means for recording information on the rotating recording medium by making the light beam incident in a state perpendicular to a rotational tangent direction of the rotating recording medium.