JPH06274895A - Recording medium and device for optical information - Google Patents

Abstract

PURPOSE:To provide an optical information recording medium capable of further making the pitch of a guide groove smaller and recording information with high density by specifying the effective range of depths of the guide groove and a pit formed on a recording surface. CONSTITUTION:Assuming that the wavelength of a laser beam transmitted from a semiconductor laser 20 is lambda, the effective depth of a guide groove 2 formed on the recording surface 4 of an optical information recording medium 100 is made to be >=lambda/8 and <=lambda/4. The effective depths of plural pits recorded on the guide groove 2 or between the guide grooves 2 are made to be >=lambda/4. Consequently, even when the pitch of the guide groove 2 is made smaller than the spot size of a light beam, sufficient information signal and tracking error signal are obtained. Consequently, an optical information recording medium capable of recording information with high density is obtained by further making the pitch of the guide groove smaller.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium having a guide groove for detecting a tracking error signal and a pit recorded on or between the guide grooves and an information recording / reproducing operation using the same. The present invention relates to an optical information reproducing device for performing.

[0002]

2. Description of the Related Art Conventionally, as an optical information recording medium (hereinafter also referred to as an optical disc), the one disclosed in JP-A-60-50733 is known. This is a guide groove formed in parallel, concentric circles, or a spiral shape on the surface of a transparent substrate, and a plurality of pits having different lengths are previously formed in a land portion between the guide grooves in accordance with recorded information. . Then, a light reflecting film is formed on such a transparent substrate to form a recording surface. When the wavelength of the light beam for reading is λ, the effective depth of the guide groove is λ / 8 to λ / 4 so that the reading of the tracking error signal and the information signal of the light beam can be performed reliably and stably. , The effective depth of the pit is λ / 4. This is because the change in the light amount depending on the presence or absence of the pit is maximum when the pit depth is λ / 4, and the tracking error signal is maximum when the guide groove depth is λ / 8 when the push-pull method is used. Is. However, this optimum value does not take into consideration the polarization of the light beam incident on the optical disc.

In such an optical information reproducing apparatus, the light source wavelength of the light beam spot is 780 nm or 830 nm, and the pitch of the guide groove of the optical information recording medium is 1.6 μm.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical information recording medium and an optical information reproducing device, which are capable of recording information at a high density by further reducing the pitch of the guide grooves. .

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to have a guide groove for tracking and a recording surface having a plurality of pits recorded on or between the guide grooves, and to collect light in a spot shape. An optical system for irradiating the recorded surface with the formed light beam, detecting the change in the intensity of the diffracted light from the guide groove, and controlling the position of the light beam at the center of the pit to read the recorded information. In the information recording medium, when the wavelength of the light beam is λ, the effective depth of the guide groove is λ / 8 or more and λ / 4 or less, and the effective depth of the pit is λ / 4 or more. The pitch of the guide groove is smaller than the spot size of the light beam, which is achieved by an optical information recording medium.

Further, an object of the present invention is to provide a guide groove having a depth of λ / 8 or more and λ / 4 or less for tracking, and a plurality of depths λ / 4 or more recorded on or between the guide grooves. An optical information recording medium having a pit recording surface is irradiated with a light beam having a wavelength λ condensed in a spot shape, and a change in the intensity of diffracted light from the guide groove is detected to detect the light beam at the center of the pit. In the optical information reproducing device, which controls the position of to read the recorded information,
The polarization state of the light beam irradiating the recording surface is circularly polarized light or at least a linearly polarized light component parallel to the guide groove is 50
It is achieved by an optical information reproducing device characterized by being at least%.

[0007]

According to the present invention, the effective depth of the guide groove of the optical information recording medium is λ / 8 or more and λ / 4 or less, and the effective depth of the pit is λ / 4 or more. Even when the pitch of the guide groove is smaller than that of the conventional optical information recording medium, it is possible to obtain a sufficient information signal and tracking error signal. Further, as an optical information reproducing apparatus for reproducing information from such an optical information recording medium, the polarization state of the light spot is circularly polarized or at least linearly polarized light component parallel to the guide groove is 50% or more. It is possible to improve the stability of the information signal and improve the reproduction of the information signal.

[0008]

1 is a partial structural view showing an embodiment of an optical pickup of an apparatus of the present invention, and FIG. 2 is an enlarged sectional view showing an optical information recording medium of the present invention. In the figure, 100 is an optical disc which is an optical information recording medium of the present invention, 1 is a transparent substrate of an optical disc 100 made of a transparent synthetic resin such as glass or polycarbonate and having a refractive index n, and 2 is fixed on the transparent substrate 1. The guide grooves 3 formed with a pitch, 3 are pits formed in the land portion between the guide grooves 2 on the transparent substrate 1,
Reference numeral 4 is a recording surface on which the guide groove 2 and pits 3 of the transparent substrate 1 are formed, 5 is a reflective film made of light-reflective aluminum or the like provided on the recording surface 4, 6 is a protective layer made of synthetic resin or the like,
Reference numeral 20 is a semiconductor laser which is a linearly polarized light source, 21 is a collimator lens, 22 is a semi-transparent prism which is a cube formed by adhering a semi-transparent film to one of the two right-angled prisms and bonding it, and 23 is an objective lens. Reference numeral 24 is a two-divided light receiving element that outputs a tracking error signal, 25 is a differential amplifier, and the light receiving element for reading out the focus error signal and recorded information, the actuator and the driving circuit for focusing tracking the objective lens are omitted. There is.

It should be noted that d2 is the actual depth (height) of the guide groove 2, d3 is the actual depth (height) of the pit 3, p is the pitch of the guide groove 2, and the pit 3 and the guide groove 2 are shown. The effective optical depths (heights) of these are n × d2 and n × d3, respectively.

The laser light emitted from the semiconductor laser 20 is collimated by the collimator lens 21 and then reflected by the semitransparent prism 22 and passes through the objective lens 23 to the recording surface 4 of the optical disc 100 from the transparent substrate 1 side. It is focused and irradiated in a spot shape. The semiconductor laser 20 and the semitransparent prism 22 are installed so that the polarization direction of the condensed light beam is parallel to the longitudinal direction of the guide groove 2 of the recording surface 4 formed on the transparent substrate 1 in the optical disc 100. Since the direction is set, the polarization direction of most of the condensed light beam is parallel to the direction of the guide groove 2. The reflected light from the recording surface 4 passes through the objective lens 23 again, the semitransparent prism 22 and is received by the two-divided light receiving element 24. The light amount distribution on the light receiving surface of the two-divided light receiving element 24 becomes asymmetrical when the light beam applied to the recording surface 4 is diffracted by the guide groove 2 and there is a shift between the light beam and the track. Therefore, each of the light receiving elements 24a, 24a of the two-divided light receiving element 24
By inputting the detection outputs A and B of b to the operational amplifier 25, the tracking error signal TE = AB can be obtained. Such a tracking error signal detection method is generally called a push-pull method. The tracking error signal TE by the push-pull method represents the direction and degree of track deviation of the light spot by its sign and size. Based on the tracking error signal TE, the irradiation position of the light beam is centered on the track. The objective lens 23 is moved by, for example, an actuator (not shown) so as to return to tracking.

The magnitude of the tracking error signal TE changes depending on the presence or absence of pits on the track, and the return control amount for correcting the track deviation changes (gain variation). In order to prevent this gain variation, instead of TE = AB as the tracking error signal TE,
In some cases, it is preferable to use TE = (A−B) / (A + B) because the tracking stability is improved.

In such an optical information reproducing apparatus,
It is desired that the tracking control is performed so that the light beam is always focused and irradiated on a desired information track, and the recorded information from the recording surface 4 is sufficiently detected. Conventionally, based on the scalar diffraction integral, the effective depth of the guide groove 2 with respect to the wavelength λ of the light beam from the semiconductor laser 20 is set so that the tracking error signal TE can be sufficiently obtained by the optical pickup shown in FIG. The height (height) is about λ / 8,
On the other hand, the effective depth (height) of the pit 3 was set to about λ / 4. However, as a result of calculation by vector diffraction integration, it was found that it was slightly different.

FIG. 3 is a cross-sectional view showing a case where the recording surface 4 of the optical disc 100 is irradiated with a light beam in a focused manner. In the figure, w is the spot size of the light beam, and m is the guide groove 2 or the pit 3.
The width of a groove (hereinafter referred to as the groove 9) corresponding to the above, d is the actual depth of the groove 9, and the spot size w of the light beam is assumed to have a Gaussian intensity distribution in the cross-sectional diameter direction of the light beam. The diameter represents the strength of 1 / e ² of the central strength.

FIGS. 4, 5 and 6 show the relative value of the reflected light amount (vertical axis) when the recording surface 4 of the optical disc 100 is focused and irradiated with a light beam, and the effective depth of the groove 9 (horizontal axis). It is a figure which shows the relationship of). In both figures, the spot size of the light beam is
1.4 μm, the solid line shows the calculation result when the polarization direction of the linearly polarized light is parallel to the longitudinal direction of the groove 9, and the broken line shows the calculation result when the polarization direction is perpendicular to the direction of the groove 9. When the light beam is circularly polarized, it is located between the solid line and the broken line. 4, 5 and 6 show the cases where the widths m of the grooves 9 are 0.8 μm, 0.7 μm and 0.5 μm, respectively. Here, when the width m is 0.8 μm, there is not much difference from the case of the scalar diffraction integration, but as the width m becomes smaller,
Especially when the polarization direction is parallel to the direction of the groove 9, the minimum point of the reflected light amount moves toward a deeper direction. As a result, the contrast of the information signal of the pit 3 (difference in the amount of light depending on the presence or absence of the pit 3) is maximum when the polarization direction is perpendicular to the groove 9 and the effective depth λ / 4 regardless of the width. However, when the polarization direction is parallel to the groove 9, it moves toward the effective depth λ / 2 as the width m becomes smaller.

FIG. 7 shows that the width m of the groove 9 is almost equal to the pitch p of the groove 9.
Tracking error signal TE = (A-
B) / (A + B) signal relative values. FIG. 7A shows a case where the width of the groove 9 is 0.8 μm, and FIG. 7B shows a case where the width m of the groove 9 is about 0.
The case of 5 μm is shown. As a result, when the polarization direction is perpendicular to the groove 9, it becomes maximum at the depth λ / 8 regardless of the width m as in the conventional case, but when the polarization direction is parallel to the guide groove 2, the maximum point is the depth λ / 8. It can be seen that the maximum point is closer to the depth λ / 4 as the width m becomes smaller.

Further, the minimum value is at the depth λ / 4 regardless of the pitch p when the polarization direction is perpendicular to the guide groove, but becomes minimum at a depth deeper than λ / 4 when the polarization direction is parallel to the guide groove, which is It becomes remarkable as the pitch p becomes smaller.

As a result, if the polarization direction is perpendicular to the guide groove and the pit depth is λ / 4, even if the spot causes a track shift with respect to the pit row, a push-pull signal (tracking error signal) is generated depending on the pit row. do not do.

However, when the polarization direction is parallel to the guide groove and the pit depth is λ / 4, as can be seen from FIG. 7A, a push-pull signal component is also generated due to the pit row, which becomes remarkable as the pitch p becomes smaller. . When the polarization direction is parallel to the guide groove, the push-pull signal (tracking error signal) is generated from the guide groove, and in order to reduce the push-pull signal component generation from the pit row, the guide groove depth should be deeper than λ / 8. , The pit depth is deeper than λ / 4, preferably 5 /
It is better to set it to 16λ or more.

In this way, the polarization direction is parallel to the guide groove,
The optimum depth of the guide groove and the pit depends on the vertical direction, but as a medium, it can track well for any polarization state and can reproduce information. Is preferred. As conditions for such guide grooves and pits, it is only necessary to select an optimum value between the case where the polarization directions are parallel and the case where they are vertical, as shown in FIGS. The guide groove is deeper than λ / 8 and λ / 4 or less, and the pit is deeper than λ / 4, preferably λ / 2 or less. As a result, a sufficient tracking error and information signal can be obtained regardless of the polarization state of the information reproducing apparatus, and the pitch p of the guide groove 2 is 1.
It can be made smaller than about 3 μm and the light spot size of 830 nm wavelength around 1.4 μm.

FIG. 8 is a plan view showing a part of the optical disc 100, and FIGS. 9 and 10 are diagrams for explaining the signal waveforms obtained when the spot of the light beam moves along the line AA 'in FIG. is there.

The pitch of the guide groove of the disk is smaller than the spot size, the spot size is 1.4 μm and the pitch is 1.0 μm as in the example of FIG. 6, the guide groove depth is about λ / 8, and the pit depth λ.
/ 4.

FIG. 9 shows the case where the polarization direction of the light beam is parallel to the guide groove 2, and FIG. 10 shows the case where the polarization direction is perpendicular to the guide groove 2. In the figure, 12 is an area only having the guide groove 2 and no pit 3, 13
Indicates the area where the pit 3 is located, the alternate long and short dash line indicates the center position of the pit 3, (a) is the cross section of the recording surface 4, (b) is the output signal A of the two-divided light receiving element 23a, and (c) is the two. Light receiving element 23
b is the output signal B, (d) is the tracking error signal A
-B, (e) shows the A + B signal. Here, FIGS. 9 and 10 show the case where the disk is rotating, and in the pitted area 13, the outputs A and B are modulated at high speed by a plurality of pits, which are shown by hatching. or,
The envelope of the modulated signal is shown by the broken line. The change in the amount of light generated by the guide groove 2 is shown by a solid line.

In the area 13 having the pits 3 in FIG. 9, the push-pull signal component (tracking error signal) generated by the pits 3 is mixed into A-B as noise, which is shown in FIGS. 5, 6 and 7. As can be seen, the effective depth n × d3 of the pit 3 can be reduced by making it larger than λ / 4, and the degree of modulation by the pit can also be increased.

FIG. 10 shows the case in which the polarization direction is perpendicular to the guide groove, and as can be seen from FIGS. 4 and 7, the push-pull signal component is not generated by the pit 3 and the tracking error signal AB depends on the pit. No noise is mixed. However, the level of the AB signal itself becomes smaller than that when the polarization direction is parallel to the guide groove.

As described above, particularly when the guide groove pitch is smaller than the spot size and the polarization direction is perpendicular to the guide groove, the tracking error signal becomes small and the tracking stability deteriorates. Therefore, when the tracking error signal level from the guide groove can be made large and the guide groove pitch is made small in order to increase the density and the reading spot size is reproduced at the conventional size, the guide groove should be λ / 8 or more λ / 4 or less, the pit depth is λ / 4 or more, preferably 5 / 16λ or more, and the polarization state of the light beam is circularly polarized or at least 50% or more of linearly polarized components parallel to the guide groove, preferably parallel linear It may be polarized.

In FIG. 11, the guide groove pitch is made smaller than that of FIG. 9, the guide groove depth is optimally set to λ / 8 or more and λ / 4 or less, and the pit depth is optimally set to λ / 4 or more and λ / 2 or less. It is a value. Noise due to pits does not occur in the tracking error signals A-B, and a large amplitude can be obtained.

Although the example in which the pit 3 is provided in the land portion between the guide grooves 2 has been described above, the same effect can be obtained when the pit 3 is provided on the guide groove 2.

The information surface may be a magneto-optical film or a phase change film instead of a simple reflection film.

[0029]

As described above, in the present invention, a light beam containing 50% or more of a linearly polarized light component parallel to the recording surface is irradiated, and the effective depth of the guide groove of the optical information recording medium is adjusted. Since λ / 8 or more and λ / 4 or less and the effective depth of the pits is λ / 4 or more, the pitch of the guide grooves is smaller than the pitch of the conventional optical information recording medium, that is, the pitch of the guide grooves is An optical information recording medium and an optical information reproducing apparatus capable of obtaining a sufficient information signal and a tracking error signal by making them smaller than the spot size of a light beam and capable of recording and reproducing information at a higher density than ever before. Can be provided.

[Brief description of drawings]

FIG. 1 is a main part configuration diagram showing an embodiment of an optical pickup of an apparatus of the present invention.

FIG. 2 is an enlarged sectional view showing an optical information recording medium of the present invention.

FIG. 3 is a cross-sectional view showing a case where a recording surface of an optical disc is focused and irradiated with a light beam.

FIG. 4 is a diagram showing the relationship between the relative value of the reflected light amount (vertical axis) and the effective depth of the guide groove or pit (horizontal axis) when a light beam is focused and irradiated onto the recording surface of the optical disc. .

FIG. 5 is a diagram showing the relationship between the relative value of the reflected light amount (vertical axis) and the effective depth of the guide groove or pit (horizontal axis) when the recording surface of the optical disc is focused and irradiated with a light beam. .

FIG. 6 is a diagram showing the relationship between the relative value of the reflected light amount (vertical axis) and the effective depth of the guide groove or pit (horizontal axis) when a light beam is focused and irradiated onto the recording surface of the optical disc. .

FIG. 7 is a diagram showing a relationship between an (AB) / (A + B) signal and an effective depth of a guide groove.

FIG. 8 is a plan view showing a part of an optical disc.

FIG. 9 is a diagram illustrating a signal waveform obtained when a light beam traverses a recording surface of an optical disc when the polarization direction of the light beam is parallel to a guide groove.

FIG. 10 is a diagram illustrating a signal waveform obtained when a light beam traverses the recording surface of an optical disc when the polarization direction of the light beam is perpendicular to the guide groove.

FIG. 11 is a diagram illustrating a signal waveform when the polarization direction of the light beam is parallel to the guide groove, the pitch of the guide groove is smaller than the spot size, and the guide groove and the pit depth are optimized.

[Explanation of symbols]

 1 Transparent substrate 2 Guide groove 3 Pit 4 Recording surface 5 Reflective film 6 Protective layer 9 Groove (groove corresponding to guide groove or pit) 20 Semiconductor laser 22 Semi-transparent prism 23 Objective lens 24 Two-division light receiving element 25 Differential amplifier 100 Optical disk (Optical information recording medium)

Claims (3)

[Claims] 1. A guide groove for tracking, and a recording surface having a plurality of pits recorded on or between the guide grooves, and a light beam focused in a spot shape is applied to the recording surface. In the optical information recording medium, which detects the change in the intensity of the diffracted light from the guide groove and controls the positioning of the light beam at the center of the pit to read the recorded information, When λ, the effective depth of the guide groove is λ / 8 or more and λ / 4 or less, and the effective depth of the pit is λ / 4 or more. Medium. 2. The optical information recording medium according to claim 1, wherein a pitch of the guide groove is smaller than a spot size of the light beam. 3. Depth λ / 8 or more λ for tracking
A wavelength λ condensed in a spot shape on an information recording medium having a recording surface having a guide groove of / 4 or less and a plurality of pits recorded on or between the guide grooves and having a depth of λ / 4 or more.
In the optical information reproducing device, which irradiates the light beam of, detects the diffracted light intensity change from the guide groove, controls the position of the light beam at the center of the pit, and reads the recorded information, The optical information reproduction is characterized in that the spot size of the light beam is larger than the pitch of the guide groove, and the polarization state of the light beam is circular polarization or at least 50% or more of linearly polarized light component parallel to the guide groove. apparatus.