Optical information recording medium and information recording and reproducing method thereof

Claims

What is claimed is:

1. An optical information recording medium comprising a substrate and a recording layer formed thereon;

said substrate comprising a guide groove with a concave portion, and a convex portion;

a width of the groove being made smaller than a spot diameter of a light beam focused on the recording layer;

the recording layer undergoing optically detectable changes by an application of the light beam which is modulated according to an information signal;

the optically detectable changes of the recording layer caused by the light beam being a state change of the layer from a first state into a second state before an application of the light beam of a first intensity;

and changed into the first state from the second state before the application of the light beam of a second intensity which is lower than the first intensity;

the first state and the second state having different complex refractive indices;

an optical phase of a reflected light beam from the recording layer being different between a region of the first state and a region of the second state;

a change of the optical phase from the first state to the second state reducing an optical phase difference between the concave portion and the convex portion of the guide groove.

2. The optical information recording medium as defined in claim 1, wherein the width of the groove W is in relationship to:

0.13<W.times.NA/.lambda.<0.51

where a wave length of the light beam is .lambda., and a numerical aperture of a lens for focusing the light beam into the recording layer is NA.

3. The optical information recording medium as defined in claim 1, wherein an amount of the optical phase change of the recording film layer is equal to the optical phase difference between the concave portion and the convex portion of the guide groove, and a direction of the optical phase change of the recording layer is opposite in relation to a direction of the optical phase difference.

4. The optical information recording medium as defined in claim 3, where a depth of the guide groove is equal to or smaller than .lambda./4n, where a wavelength of the light beam is .lambda., a refractive index of the substrate is n, and a numerical aperture of the lens for focusing the light beam onto the recording layer is NA.

5. The optical information recording medium as defined in claim 3, wherein a recording mark from the second state composed of a pattern identifiable from the data signal is provided on the recording layer.

6. The optical information recording medium as defined in claim 1, wherein the recording medium further comprises:

a first transparent layer formed between the substrate and the recording layer, the first transparent layer having a different refractive index from that of the substrate;

a second transparent layer formed on an opposite side of the recording layer from the first transparent layer; and

a reflection layer formed on said second transparent layer, a film thickness of the first transparent layer, the second transparent layer, the recording layer, and the reflection layer being selected to have the change of the optical phase in response to the change into the second state from the first state of the recording layer.

7. The optical information recording medium as defined in claim 6, wherein the recording layer is composed of a state change medium having reversible changes between an amorphous state and a crystalline state corresponding to the first intensity or the second intensity of the application of the light beam.

8. An optical information recording medium comprising a substrate and a recording layer formed thereon;

said substrate comprising a guide groove with a concave portion and a convex portion;

and at least two sample pits shifted on both sides from a central line of the guide groove on a region where the guide groove is interrupted;

said recording layer undergoing optically detectable changes by an application of a light beam;

the optically detectable changes of the layer being caused by a change in an optical phase of a reflection light or a transmission light from the recording layer;

the change in the optical phase is in a direction of reducing an optical phase difference between the concave portion and the convex portion of the guide groove.

9. The optical information recording medium as defined in claim 8, wherein the groove width W of the concave and convex guide grooves is in the relationship of

0.13<W.times.NA/.lambda.<0.51

where a wavelength of the light beam is .lambda., and a numerical aperture of a lens for focusing the light beam into the recording layer is NA.

10. The optical information recording medium as defined in claim 8, wherein an amount of the optical phase change of the recording layer is equal to the optical phase difference between the concave portion and the convex portion of the guide groove.

11. The optical information recording medium as defined in claim 8, wherein a depth of the guide groove is equal to or smaller than .lambda./4n where a wavelength of the light beam is .lambda. a refractive index of the substrate is n, and a numerical aperture of a lens for focusing the light beam into the recording layer is NA.

12. An optical information recording medium comprising a substrate and a recording layer formed thereon;

said substrate comprising a pit capsule string composed of a circular concave portion or a convex portion provided at a constant interval on a track;

and at least two sample pits provided in a position shifted from a central line of the pit capsule string where the pit capsule string is interrupted;

said recording layer undergoing optically detectable changes by an application of a light beam;

the optically detectable changes of the layer being caused by a change in the optical phase of a reflection light or a transmission light from the recording layer;

and the change in the optical phase is in a direction of reducing an optical phase difference between the concave portion and the convex portion of the pit capsule string.

13. The optical information recording medium as defined in claim 12, wherein an amount of the optical phase change of the recording layer is equal to the optical phase difference to the concave portion or the convex portion of the pit capsule string.

14. The optical information recording medium as defined in claim 13, wherein a depth of the pit capsule is equal to or smaller than .lambda./4n, where a wavelength of the light beam is .lambda. a refractive index of the substrate is n, and a numerical aperture of a lens for focusing the light beam onto the recording layer is NA.

15. The optical information recording medium as defined in claim 13, wherein the recording medium further comprises:

a first transparent layer formed between the substrate and the recording layer, the first transparent layer having a different refractive index from that of the substrate;

a second transparent layer formed on an opposite side of the recording layer from the first transparent layer; and

a reflection layer formed on said second transparent layer, a film thickness of the fist transparent layer, the second transparent layer, the recording layer, and the reflection layer being selected to have the change of the optical phase in response to the changed into the second state from the first state of the recording layer.

16. An information recording and/or reproducing method using an optical information recording medium comprising a substrate and a recording layer formed thereon,

said substrate comprising a guide groove with a concave portion and a convex portion;

and at least two sample pits shifted on both sides from a central line of the guide groove on a region where the guide groove is interrupted;

said recording layer undergoing optically detectable changes by an application of a light beam;

the optically detectable changes of the layer being caused by a change in an optical phase of a reflection light or a transmission light from the recording layer;

the change in the optical phase is in a direction of reducing an optical phase different between the concave portion and the convex portion of the guide groove

irradiating a light beam onto a guide groove formed on a recording medium or onto a pair of sample pits provided in a region where capsule pits are interupted;

detecting reflected light or transmitted light from the recording medium; and

effecting a tracking control by reducing a difference in an amount of light between the reflected light and the transmitted light between a pair of the sample pits.

17. An apparatus for recording and/or reproducing information on and/or from a recording medium, said recording medium comprising:

a recording layer disposed on a substrate, said layer undergoing optically detectable changes by an application of a light beam;

said substrate being provided with a guide groove having concave and convex portions;

a width of said grove being smaller than a spot diameter of the light beam focused on the recording layer;

said recording layer undergoing a change of optically detectable states by application of the light beam modulated in accordance with an information signal;

the change of the optically detectable states of the recording layer with absorption of the light beam being from a first state into a second state upon receipt of the application of the light beams at a first intensity of the light while the optically detectable states of the recording layer being changed into the first state from the second state upon receipt of the application of the light beam at a second intensity lower than the first intensity;

the regions of the first and second states of the recording layer having complex refractive indexes which are different from each other, the difference of the complex refractive indexes causing a change in an optical phase of light reflected from the recording layer having the light beam applied thereto;

the change of the optical phase from the first state to the second state being in a direction towards reducing an optical phase difference between the concave portion and the convex portion of said guide groove;

said light beam being composed of at least three spot strings;

a line passing through the centers of the spots of the three light strings being oblique with respect to the guide groove on the recording layer;

the information signal of said recording layer being reproduced by detecting the reflected light or transmitted light from a first spot positioned at the center of a first spot string;

the first spot being tracked on the guide groove to effect a tracking control by detecting the transmitted light or reflection light from the second and third spots positioned before and after the first spot.

18. The apparatus as defined in claim 17, wherein a focus control of the optical information recording medium is effected with reception of the transmitted light or reflected light from the second and third spots by a photodetector divided into at least two parts.

BACKGROUND OF THE INVENTION

The present invention generally relates to an optical information recording medium, and a recording and reproducing method for recording and reproducing information with high speed and high density.

When a laser beam is focused by a lens system, the diameter of optical spots can be made smaller, on the order of the wavelength of the light. Therefore, light spots having a high energy density per unit area can be made even from a low level light source. Minute regions of a material can be changed by such light spots, and the changes in the minute regions can be read out. An optical information recording medium uses such changes in recording and reproducing operations. The optical information recording medium is hereinafter referred to as "an optical recording medium" or simply "a medium".

A recording film layer is provided, in the basic construction of the optical recording medium, on the substrate whose surfaces are flat. The recording film layer changes in some condition by the application of laser light spots. The signal recording and reproducing operations on the medium are effected by the method described hereinafter. The recording medium is moved by a rotating means and a translating means such as a motor so as to apply focused laser beams onto the recording film face of the medium. The recording film absorbs the laser beams so as to raise its temperature. When the output of the laser beams is at least a threshold value, the condition of the recording film is varied so as to record the information. The threshold value is a quantity depending upon the thermal characteristics of the substrate, in addition to the characteristics of the recording film itself, and the relative speed of the medium with respect to the optical spots. Laser beam spots of an output sufficiently lower than the threshold value are applied to the recording portion of the medium and the differences of some optical characteristics in one of the transmission light intensity, the reflection light intensity, the polarization directions or the like between the recording portion and the non-recording portion are detected for reproducing the recorded information.

A metallic film with Bi or Te as principal components, or a compound film including Te are known recording films. They are shape change types of recording mediums using the steps of melting or evaporating the films with a laser beam, and forming small holes. The signal reproduction from the recorded portion is effected by the detection of the difference between the amount of light reflected or the amount of light transmitted between a small hole portion and the peripheral portion thereof.

A state change type of recording film has optical changes without being accompanied by the shape changes. The state change type recording film changes its state condition by the application of a laser beam, and changes its complex refractive index during the time. Generally the refractive index n and the extinction coefficient k of the complex refractive index change in the same direction. Most materials considered as optical recording mediums increase the complex refractive index when the state condition changes to a crystalline state from an amorphous state. A weak light is applied to the signal pattern formed as the difference of the phase condition and the amount light transmitted or reflected from the medium is measured so as to effect the signal reproducing operation from the recording film.

Light is described by amplitude and optical phase. The information from the recording medium is effected by the detection of changes in the amount of light transmitted or reflected to a photodetector of the reproduction optical system. There is a case (amplitude change record) where a transmission beam amplitude or a reflection light amplitude in the minute region of the optical film itself changes, and a case (optical phase change record) where the phase of the transmitted light or the reflected light changes. Reproduction signals are obtained by the change in the complex refractive index by the state change being provided as the composition of the changes of both the amplitude change and the state change.

The phase change optical disk records signals by the formation of the difference (recording mark) of the local state condition on the recording film, by the application of a laser beam modulated in intensity on the rotating recording medium, and reproduces the signals with the detection, as a reflection difference, of the difference caused between the conditions. The size of the recording mark to be obtained becomes a size of the focusing optical spot, namely, on the order of a wavelength. Assume that a laser beam of approximately 780 nm in wavelength is focused using a lens system of approximately 0. 5 in N.A. (numerical aperture), and the full width half maximum in intensity is focused to spot of approximately 0.9 .mu.m. The intensity of the optical spot is generally of a Gausian distribution or a distribution of a shape which is closer to it. When a recording operation is effected using the optical spot, the state condition become a recording condition with the range of approximately 5 through 1 .mu.m being changed.

FIGS. 1(a)-1(c) show the relationship between the recording mark and the optical spot for obtaining the maximum signal change. In FIG. 1(a) the state change recording film is adapted to show the amplitude change record, and in FIG. 1(b) it is adapted to show the optical phase change record. In the construction showing the amplitude change records FIG. 1(a), the amplitude change recording mark 3 formed on the recording film 2 on the substrate 1 changes mainly in reflection index. In the scanning operation on the mark 3 by the optical spot 4 formed by a weak light beam I.sub.0 for reproduction, the amount of light change on the photodetector to be obtained by the reproduction optical system, that is, the conditions for making the signal amplitude maximum, namely, the conditions for making maximum the difference between the reflection light l.sub.2 of the recording mark portion and the reflection light l.sub.1 of the non-recording condition are to make the size of the recording mark 3 changed state condition is equal to or greater than the reproduction spot 4 size.

As in FIG. 1(b), even in the case of the optical phase change recording operation, the change of the recording film 2 itself is the same as the amplitude change, and the recording mark 6 is formed by the similar beam application. In the recording mark showing the ideal optical phase change record, the reflected light I.sub.4 of the same intensity as that of the reflected light I.sub.3 of the non-recording condition is reflected with respect to the incident light quantity I.sub.0 and changes by .phi. in the optical phase of the light. The recording condition by the optical phase change forms concave or convex pits 7 on a plane portion as shown in FIG. 1(c) with respect to the optical spot, and functions as when the optical phase has changed by the concave or convex stage difference. The conditions showing the maximum signal amplitude by the optical phase change records become conditions where the diffraction effect of the light by the optical phase difference by the optical phase change record is conditions where the diffraction effect of the light by the optical phase difference when the reproduction spot 4 has scanned the recording mark becomes maximum. When the optical intensity of the region incident to the recording mark 6 becomes equal to the amount of light incident on the peripheral portions of the optical spots 4, the effect of the interference becomes largest and the amount of light into the photodetector becomes minimum. The amount of reflected light becomes minimum under the cancelling conditions with interference between the reflected light I.sub.4 from the recording mark and the reflected light I.sub.3 from the non-recording portion, so that the maximum signal amplitude of the optical phase change record is obtained.

When the two recording modes are compared with the recording marks showing the maximum amplitude, it has been found that the recording and reproducing operation of high density in the optical phase change recording can be effected, because the optical phase change recording mark 6 can be recorded in a smaller shape than the amplitude change recording mark 3. It is possible to provide a recording medium which is interchangeable with an optical disk for reproduction only use where concave and convex pits like a compact disk or the like are used for recording information if the optical phase change recording can be realized.

As the state change medium showing the optical phase change recording is a recording method using a heat mode using the heat of the light, the application of the light to the recording film is accompanied by a thermal diffusion phenomenon. A portion which has absorbed the optical energies rises in temperature and also, at the same time, the generated heat is diffused to a portion where the peripheral temperature is lower. The recording mark formed in the application portion is distributed in the intensity of the light to be applied, with a problem in that the size thereof changes in accordance with the amount of energy (application power) to be made. In the case of the conventional reflected light change, the mark shape effects a maximum signal amplitude with the mark shape being equal to the spot diameter (a size which becomes 1/e.sup.2 in the intensity of light). A pitch of the mark to be reco