Phase change type optical recording apparatus and optical recording method using an overwrite system

Abstract

An optical recording apparatus that rewrites recorded information on a modified constant angular velocity type phase change optical disk by overwriting using at least a recording light beam, erasing light beam and off-pulse light beam irradiation. The apparatus comprises a semiconductor laser for irradiating the optical disk with the light beam and a control unit for controlling the intensities P1, P2 and P3, wherein P1>P2>P3, of the light beam with which the optical disk is irradiated and their irradiation periods .tau.1 and .tau.3 to obtain a relation of{(P2-P3).times..tau.3}/{(P1-P2).times..tau.1}=below 1.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a phase change type optical recording apparatus and optical recording method for recording information by creating crystal and amorphous states in a recording layer of an optical disk through the application of heat resulting from irradiation with a light beam.

2. Description of the Related Art

The so-called phase change type optical recording apparatuses have been researched and developed as one form of a rewritable optical recording apparatus, which record information through the utilization of a crystal/amorphous phase change of a recording material of which an optical recording medium is comprised. The phase change type optical recording apparatus and optical recording method using the so-called overwrite system record information by creating crystal/amorphous states in a recording layer of an optical disk through the application of heat resulting from irradiation with a light beam.

Stated in more detail, the phase change type optical recording apparatus controls the intensity of a light beam which is directed as a condensing beam onto an optical recording medium in accordance with the recording information and is basically of such a type so as to record the information on an optical recording medium at an amorphous area formation position with an irradiated light beam of a first intensity and at a crystal area formation position with an irradiated light beam of a second intensity lower than the first intensity which is used to record information at an amorphous area formation position on the optical recording medium.

In the phase change type optical recording apparatus of such a basic arrangement, a method has been proposed in U.S. Pat. No. 4,939,717 for obtaining a great reproduction signal by, during a given period following the completion of irradiation with a light beam of a first intensity, irradiating the medium with a light beam of a third intensity still lower than a second intensity, and allowing a melted area, which is formed with the irradiated light beam of the first intensity, to be rapidly cooled and, by doing so, enlarging the amorphous area.

In this known method, when the irradiation period of the light beam of the third intensity is too long, an area is created on the optical recording medium where it reaches no crystallization temperature. This makes the crystallization of an amorphous area of a previously recorded mark insufficient. That is, there occurs cases where new information is recorded on the medium at those recorded marks (amorphous areas) where they are not completely erased. This decreases recording reliability. Further, if the irradiation period of the light beam of the third intensity is too short, the recording mark becomes too large so that a reconstruction signal is lower in quality and no adequate recording reliability is obtained.

In the known method described above, only the irradiation period is specified for the light beam of the third period. Stated in more detail, according to U.S. Pat. No. 4,939,717, a relation 0<.tau.<.lambda./V is prescribed, where .tau. represents the irradiation period of the light beam of the third intensity, .lambda. the wavelength of the light beam, and V the relative speed between the light beam and the optical recording medium. From the research by the inventors, it has been found that, even if the irradiation period of the light beam of the third intensity is given as being equal, the excess or shortage of the irradiation period differs depending upon the intensity of the light beam of the third intensity. That is, irrespective of a recognition that the excess or shortage of the irradiation period of the light beam of the third intensity is determined by a relation between a temperature rise process ascribed to the light beam of the first intensity and its irradiation period and a temperature fall process ascribed to the light beam of the third intensity and its irradiation period, no suitable condition is considered, in the known patent above, about the relation. For this reason, it is impossible to obtain adequate recording reliability, because there arise incomplete erasure and a lowering in quality of a reproduction signal.

As set out, the known patent above simply specifies the irradiation period of the light beam of the third intensity and, because the irradiation period of the light beam of the third intensity becomes too long or too short, no adequate recording reliability is obtained by the known technique.

It is the object of the present invention to provide a phase change type optical recording apparatus and optical recording method which obtains adequate recording reliability by solving the incomplete erasure and lowering in quality of a reproduction signal problems resulting from the excess or shortage of an irradiation period of a light beam of a third intensity.

SUMMARY OF THE INVENTION

In one aspect of the present invention, there is provided an optical recording apparatus for recording information on a disk-like optical recording medium by irradiating the recording medium with a light beam of a first intensity P1 during an irradiation period .tau.l so as to form an amorphous state area at the recording medium and then with a light beam of a third intensity P3 during a period .tau.3 and irradiating the recording medium with a light beam of a second intensity P2 so as to form a crystal state area at the recording medium, comprising:

light beam irradiating means for irradiating the optical recording medium with the light beam; and control means for controlling the intensities P1, P2 and P3 (P1>P2>P3) and the irradiation periods .tau.1 and .tau.3 of the light beam to satisfy {(P2 -P3).times..tau.3}/{(P1-P2).times..tau.1}=below 1.

In another aspect of the present invention, there is provided an optical recording method for recording information on an optical recording medium by irradiating the recording medium with a light beam of a first intensity P1 during an irradiation period .tau.1 so as to form an amorphous state area at the recording medium and then with a light beam of a third intensity P3 during an irradiation period .tau.3 and irradiating the recording medium with a light beam of a second intensity P2 (P1>P2>P3) period .tau.2 so as to form a crystal state area at the recording medium, comprising the step of enabling a latter half of the amorphous state area which is formed with the irradiated light beam of the first intensity P1 and enlarged with irradiated light beam of the third intensity P3 to be crystallized with the irradiated light beam of the second intensity P2 so that the latter half of the amorphous state area is erased.

In another aspect of the present invention, there is provided a method for rewriting recorded information on a zone constant angular velocity type phase change optical disk of a plurality of zones by overwriting at least with a recording light beam, erasing light beam and off-pulse light beam, characterizing the step of varying at least an irradiation time of the recording light beam and irradiation time of the off-pulse light beam in accordance with a respective recording zone of the optical disk.

According to the present invention, the irradiation interval .tau.3 of the light beam of the intensity P3 is optimized by the total light amount ratio

{(P2-P3).times..tau.3}/{(P1-P2).times..tau.1}=below 1 where (P2-P3)'.tau.3: a total light amount by which a light amount reaching the medium with the irradiated light beam of the intensity P3 is lower than with the irradiated light beam of the intensity P2, and (P1-P2).times..tau.1: a total light amount by which a light amount reaching the medium with the irradiated light beam of the intensity P1 is higher than with the irradiated light beam of the intensity P2.

By doing so, it is possible to prevent incomplete erasure of the recorded mark when .tau.3 is too long and a lowering in quality of a reproduction signal when .tau.3 is too short, and hence, to enhance the recording reliability. This effect is more prominent the higher the relative speed of the light beam and optical recording medium and the smaller the interval of the recorded marks.

Further, according to the present invention, through the optimization of the irradiation period .tau.3 of the light beam of the third intensity P3, the amorphous area formed with the irradiated light beam of the first intensity P1 and enlarged with the irradiated light beam of the third intensity P3 has its latter half erased by being crystallized with the irradiated light beam of the second intensity P2. As a result, even if the interval of the recorded mark is made short so as to enhance the recording density of the information, there is less chance of producing incomplete erasure so that it is possible to improve the quality of a reproduction signal and hence to obtain high recording reliability.

Another object of the present invention is achieved by the following recording apparatus. That is, the apparatus for recording information on an optical recording medium by irradiating the recording medium with a light beam of a first intensity P1 during an irradiation period .tau.1 so as to form an amorphous state area at the recording medium and then with a light beam of a third light intensity P3 during an irradiation period .tau.3 and irradiating the recording medium with a light beam of a second intensity P2 so as to form a crystal state area at the recording medium, wherein an information recording area for recording the recording information and a recording condition recording area are formed on the optical recording medium and the recording condition recording area is formed on at least one of an outer circumference side and inner circumference side of the information recording area and stores, therein, recording condition data representing the intensities P1, P2 and P3 (P1>P2>P3) and irradiation period .tau.1 and .tau.3 of the light beam satisfying a condition

{(P2-P3).times..tau.3}/{P1-P2).times..tau.1)}=below 1.

Another object of the present invention is achieved by the following optical recording method. That is, an optical recording method for recording information on an optical recording medium by irradiating the recording medium with a light beam of a first intensity P1 during an irradiation period .tau.1 so as to form an amorphous state area at the recording medium and then with a light beam of a third intensity P3 during an irradiation period .tau.3 and with a light beam of a second intensity P2 so as to form a crystal state area at the recording medium, the method comprising the steps of:

detecting recording condition data from a recording condition recording area prior to recording the recording information on the recording medium, the recording condition recording area being formed on at least one of an outer circumference side and inner circumference side of the information recording area on the optical recording medium and storing, therein, recording condition data representing the intensities P1, P2 and P3 (P1>P2>P3) irradiation period .tau.1 and .tau.3 of the light beam satisfying a condition

{(P2-P3).times..tau.3}/{P1-P2).times..tau.1=below 1; and

recording the information on the recording medium on the basis of the recording condition data detected by the detecting step.

Another object of the present invention is achieved by the following recording medium. That is, the medium comprising; an information recording area and a recording condition recording area are formed on the optical recording medium and the recording condition recording area is formed on at least one of an outer circumference side and inner circumference side of the information recording area and stores, therein, recording condition data representing the intensities P1, P2 and P3 (P1>P2>P3) and irradiation period .tau.1 and .tau.3 of the light beam satisfying a condition

{(P2-P3).times..tau.3}/{P1-P2).times..tau.1)}=below 1.

Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention and, together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention.

FIG. 1 is a schematic view showing an optical recording apparatus according to an embodiment of the present invention;

FIG. 2 shows a relation between recording information and the intensity of a light beam in the present embodiment;

FIG. 3 is a schematic view showing one practical form of a controller in the present embodiment;

FIG. 4A to 4D are signal wavelength diagram for explaining an operation of the controller in FIG. 3;

FIGS. 5A and 5B illustrate the relation between an irradiation interval of a light beam of a third intensity and a recording mark configuration in the present embodiment;

FIGS. 6A to 6D are views showing a relation of an irradiation period of a light beam of a third intensity and a medium temperature;

FIG. 7 is a graph showing a dependence of a total light amount ratio upon a CNR and erase ratio in the present embodiment;

FIGS. 8A to 8D show a relation between respective light beam irradiation conditions and a proper .tau.3;

FIG. 9 is a plan view schematically showing a disk-like optical recording medium of the present invention;

FIGS. 10A and 10B are characteristic graphs showing a relation between the radius r of the disk-like optical recording medium and the irradiation period .tau.3 of a light beam of an intensity P3;

FIG. 11 is a schematic diagram of an optical recording apparatus according to another embodiment of the present invention; and

FIG. 12 is a flow chart showing the operation of the optical recording apparatus in FIG. 11.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be explained below with reference to the accompanying drawings.

FIG. 1 shows an arrangement of an optical recording apparatus according to one embodiment of the present invention. In FIG. 1, a light source 101 is comprised of, for example, a semiconductor laser. A light beam emitted from a light source 101, after being transformed into a parallel beam by a collimator lens 102, is guided past a beam splitter 103 to an object lens 104 and, by the object lens 104, it is focused as a very small spot on a disk-like optical recording medium 105. The optical recording medium 105 is rotated at a predetermined speed by a motor 106. The light source 101 is adapted to have its beam illumination and intensity controlled by a signal supplied from a controller 107. In the case where information recorded on the optical recording medium 105 is to be reproduced, a reflected beam from the optical recording medium 105 is passed through the object lens 104 on a backward path indistinct from a path of an incident beam, separated by the beam splitter 103 from the incident beam and conducted to a detecting system, such as a light detector, where a reproduction information signal is picked up.

In the case where information is to be recorded on the optical recording medium, the intensity (light intensity) of the light beam is controlled by the controller 107 to a first intensity P1, a second intensity P2 and a third intensity P3 in accordance with recording information, as shown in FIG. 2. The first intensity P1 is used to form an amorphous state and the second intensity P2 to a crystal state and the third intensity P3 is lower in level than the second intensity P2. As will be seen from FIG. 2, in the case of the recording information being binary data .left brkt-top.0.right brkt-bot. and .left brkt-top.1.right brkt-bot., a light beam of the intensity P1 is directed only during a period .tau.1 to a position corresponding to .left brkt-top.1.right brkt-bot. and, after a light beam of the intensity P3 is directed only during a period .tau.3, a light beam of the intensity P2 is kept directed till an interval corresponding to the next .left brkt-top.1.right brkt-bot. position.

FIG. 3 is a practical circuit arrangement of the controller 107. FIG. 4 shows signal waveforms of respective parts of the circuit arrangement in FIG. 3. In FIG. 3, recording information 201 shows binary data entered in a reference clock cycle and is input to a clock input terminal CK of a first flip-flop 202 comprised of a D type flip-flop (DFF). An input terminal D of the flip-flop 202 is fixed to a "H" level. An inverting output of the flip-flop 202 is input to a clear terminal CLR of the flip-flop 202 via a delay line 203 with a delay amount .tau.1. In this way, a .tau.1-wide pulse is output from the flip-flop 202 in synchronization with a rise of data pulse of the recording information 201 as shown in FIG. 4A.

The output of the first flip-flop 202 is input to a clock input terminal CK of a second flip-flop 204 comprised of a D-FF. An input terminal D of the flip-flop 204 is fixed to a "H" level. An inverting output of the flip-flop 204 is input to a clear terminal CLR via a delay line 205 with a delay amount .tau.3. Thus a .tau.3-wide pulse is output from the flip-flop 204 in synchronization with a fall of the output pulse of the flip-flop 202 as shown in FIG. 4B.

Level setting values VP1, VP2 and VP3 are input to the controller 107 to set the light beam to the intensities P1, P2 and P3. The level setting values VP1, VP2 and VP3 are applied respectively through buffers 207, 208 and 209 to one-end of switches 210, 211 and 212. The other-end of switches 210, 211 and 212 are commonly connected to an input terminal of a drive amplifier 213. These switches are each comprised of a MOS transistor. A non-inverting output of the flip-flop 202 is connected to a control terminal of the switch 210, a NOR gate 206 is connected at its inputs to flip-flops 202 and 204 and at its output to a control terminal of the switch 211, and a non-inverting output of the flip-flop 204 is connected to a control terminal of the switch 212. FIG. 4C shows an output waveform of the NOR gate 206.

The drive amplifier 213 delivers a light source drive signal 214 for driving the light source 101 in FIG. 1. The light source drive signal 214 is modulated to the level setting values VP1, VP2 and VP3, as shown in FIG. 4D, by ON/OFF controlling the control terminals of the switches 210, 211 and 212 by those signals of FIGS. 4A, 4C and 4B.

The delay amounts .tau.1 and .tau.3 of the delay lines 203 and 205, that is, the irradiation periods of the light beams of the first and third intensities P1 and P3, are switched respectively by a .tau.1 switching signal 215 and .tau.3 switching signal 216 so as to set a proper condition on the recording medium 105 at respective recording radius positions (in radial positions of an information recording track). In a ZCAV (zone constant angular velocity) system, the surface of the optical recording medium 105 is divided in a radial direction into a plurality of zones and recording/reproduction is performed by varying a reference clock cycle at each zone, that is, a recording frequency at each zone. In this case, the setting conditions can readily be obtained by putting at least one of .tau.1, .tau.3 in proportion to the reference clock cycle at each recording radial position. The simplest method is by having the .tau.1 and .tau.3 coincide with the reference clock cycle. It is to be noted that the ZCAV is also called an MCAV (modified constant angular velocity).

Further, instead of varying only one of the .tau.1 and .tau.3 in proportion to such a reference clock cycle it is possible to put at least one of (P2-P3).times..tau.3 and (P1-P2).times..tau.1 in proportion to the reference clock cycle where

(P2-P3).times..tau.3: a total light amount by which a light amount reaching the medium with the irradiated light beam of the intensity P3 is lower than with the irradiated light beam of the intensity P2, and (P1-P2).times..tau.1: a total light amount by which a light amount reaching the medium with the irradiated light beam of the intensity P1 is higher than with the irradiated light beam of the intensity P2.

The circuit arrangement as shown in FIG. 3 can be changed in various practical forms and, for example, a monostable multivibrator may be used in place of the D type flip-flop (D-FF).

Now the information recording process of the present embodiment will be explained below with reference to FIGS. 5A and 5B.

FIGS. 5A and 5B each show a relation of the intensities of the light beam and their irradiation times to recorded marks on the recording medium 105. When the light beam of the first intensity P1 is directed on the optical recording medium in a way to correspond to the recording information .left brkt-top.1.right brkt-bot., a corresponding irradiated area is heated above a melting point and melted so that, after the completion of irradiation, the area becomes an amorphous state. By doing so, a recorded mark is formed at an amorphous area. When, on the other hand, the light beam of the second intensity P2 is directed on the optical recording medium 1 in a way to correspond to the recording information .left brkt-top.0.right brkt-bot., a corresponding irradiated area is heated to a level less than a melting point but more than a crystal temperature so that it becomes crystalline.

When the light beam of the third intensity P3 is directed on the optical recording medium over a period .tau.3 subsequent to directing the light beam of the first intensity P1, the melted area formed with the irradiated light beam of the intensity P1 is rapidly cooled and, after the directing of the light beam of the intensity P3, the light beam of the second intensity P2 is directed on the recording medium over an interval corresponding to the recording information.

Here, in the case where irradiation period .tau.3 of the light beam of the intensity P3 is proper, an amorphous area formed with the irradiated light beam of the intensity P1 and rapidly cooled with the irradiated light beam of the intensity P3 has its latter half lost due to its crystallization starting on a part of the way through the irradiation of the light beam of the intensity P2 so that a length of a recorded mark is shortened in a relative direction of movement between the optical recording medium and the light beam. By doing so, even if an information recording density is enhanced by shortening an interval between those recorded marks formed as amorphous areas, it is possible to detect the recorded marks (amorphous areas) and non-recorded marks (crystallized areas) in a clearly distinguished way and hence to obtain a reproduction signal in excellent quality.

In a phase change type optical recording apparatus, areas that are broader than recording mark formation areas are melted on a recording medium upon recording of information and then cooled into an amorphous phase to form recorded marks. At that time, the outer edge of the melted area is crystallized upon cooling and, due to this effect, there hardly retains any previous history, that is, a trace (an irregularity among marks resulting from a difference in absorptivity between the amorphous area and the crystal area) of the recorded mark (amorphous area) so that better erasure can be obtained. That is a feature inherent in the phase change type optical recording apparatus.

As a result of strenuous investigations by the inventors, however, it has been found that when the relative speed of movement between the optical recording medium and the light beam upon information recording satisfies certain criteria, such as when the relative speed of movement between the medium surface and the light beam spot exceeds about 5 m/s, the above-mentioned effects are lessened because cooling takes place repeatedly at the outer edge of the melted area. As a result, there is more chance that the trace of the recorded mark will be left as an irregular mark and hence there will be poor erasure. In the case where recording/reproduction is performed on, for example, a 90 mm-diameter optical disk driven at 3,600 rpm, a relative speed of the light beam reaches as high as 15 m/s at an outermost circumference of the optical disk. Therefore, adequate consideration should be given to a possible poor erasure effect.

In a normal CAV system where the rotations speed of the optical disk is constant and a reference clock cycle is constant irrespective of a recording radial position, the greater the relative movement speed between the optical recording medium and the light beam, the greater the interval between those recorded marks. Therefore, even if there are some irregular marks resulting from poor erasure, any recorded mark can be detected in a way readily separable from an adjacent mark. For this reason, recorded information can be correctly reproduced, thus relatively readily securing the reliability of recorded information.

If, in order to increase a recording density, a ZCAV system by which the interval between recorded marks is made substantially equal at the inner and outer circumferences of a recording medium and made smaller than the spot size of a light beam (that is, the diameter of an area where the intensity of the light beam becomes more than the e.sup.-2 times its center intensity) is used, an adverse influence becomes prominent due to poor erasure, in particular, at an outer circumference side where the relative movement speed between the optical recording medium and the light beam is great. That is, in those recorded marks of a smaller interval, the reliability of recording information becomes extremely poor due to irregularity among marks.

In the case where the relative movement speed of the light beam is over 5 m/s and the interval between the recorded marks is decreased below the spot size of the light beam, if the irradiation period .tau. of the light beam of the intensity P3 is provided, then it becomes particularly effective to enhance the erasability. By doing so, it is possible to adequately enhance the reliability of recorded information even in the ZCAV system for instance.

If .tau.3 becomes too long, as shown in FIG. 5B, then a space is created between a melted area irradiated with the light beam of the period P1 and the leading edge portion of a crystal area irradiated with the light beam of the intensity P2 so that the space area is not adequately crystallized. That is, even if part of the recorded mark is present in that space area, it cannot be erased by being fully crystallized and it is left there as a non-erased area, as shown in FIG. 5B, thus adversely affecting the reliability of the recording information. According to the present invention, this problem can be solved by properly setting the irradiation period .tau.3, without being too short or too long, and setting the respective intensities P1, P2 and P3 to proper levels. Now, a relation of an excess or shortage of .tau.3 to the medium temperature will be explained with the use of FIGS. 6A to 6D.

FIG. 6A shows the shift of a medium temperature when .tau.3 is short. In this case, cooling is slow from a heating temperature (melting temperature) T1 resulting from the irradiation of the medium with the light beam of the intensity P1 to a crystallizing temperature T2 resulting from the irradiation of the medium with the light beam of the intensity P2 so that a recorded mark forming an amorphous area becomes longer than necessary and it becomes difficult to distinguish a recorded mark and a non-recorded mark upon reproduction. This produces a lowering in quality of a reproduction signal, that is, in reliability of recording information.

FIG. 6B shows a shift of the medium temperature when .tau.3 is a proper level. In this case, a shift of the medium from T1 to T2 is rapidly effected and it is possible to obtain a reproduction signal in excellent quality without the recorded mark being too long.

FIG. 6C shows a shift of the medium temperature when .tau.3 is too great. In this case, the medium temperature reaches a crystallization-short temperature T3 once on its way from T1 to T2. If, therefore, a recorded mark is formed on an area where the crystallization-short temperature T3 is reached, it cannot be erased by being crystallized. This lowers a reliability of the recording information.

The medium temperature T1 after the irradiation period .tau.1 of the light beam of the intensity P1 corresponds to a level to which a normal temperature T2 rises while reflecting an intensity increase (P1-P2) of the light beam due to the irradiation of the medium with the light beam of the intensity P2. With t representing the time constant of the temperature variation of the medium, this relation can be given by

T1=T2+T2.times.(P1-P2)/P2.times.{1-exp (-.tau.1/t)} (1)

On the other hand, the medium temperature T3 after the irradiation period .tau.3 of the light beam of the intensity P3 corresponds to a level to which, relative to a crystallization temperature (normal temperature) T2 resulting from the irradiation of the medium with the light beam of the intensity P2, a temperature falls from T1 while reflecting both an initial temperature difference (T1-T2) of the medium and a decrease amount (P2-P3) of light beam intensity. This relation can be given by

T3=T1-{(T1-T2)+T2(P2-P3)/P2}.times.{1-exp (-.tau.3/t)} (2)

Assuming that, for example, .tau.1 and .tau.3 are adequately shorter than the time constant t, Equations (1) and (2) above can be simplified to

T1=T2+T2.times.(P1-P2)/P2.times..tau.1/t) (3) T3=T1-{(T1-T2)+T2.times.(P2-P3)/P2}.times..tau.3/t (4)

Finding a condition T3=T2 from Equations (3) and (4),

(P2-P3).times..tau.3=(1-.tau.3/t).times.(P1-P2).times..tau.1(5) Here, since .tau.3 is assumed to be adequately smaller than t and the right-hand first side of Equation (5) is nearly equal to unity, the following equation is obtained. (P2-P3).times..tau.3=(P1-P2).times..tau.1 (6) Equation (6) above can be understood in the following way.

FIG. 6D shows a relation among the light beam intensities P1, P2 and P3 at .tau.3=a proper value and the light beam irradiation periods .tau.1 and .tau.3. As seen from FIG. 6D, (P2-P3).times..tau.3 on the left-hand side of Equation (6) shows a total light amount by which a light amount reaching the medium upon irradiation with the light beam of the intensity P3 is lower than upon irradiation with the light beam of the intensity P2. (P1-P2).times..tau.1 on the right-hand side of Equation (6) above shows a total light amount by which a light amount reaching the medium upon irradiation with the light beam of the intensity P1 is higher than upon irradiation with the light beam of the intensity P2. In the case where the irradiation times .tau.1 and .tau.3 are adequately shorter than the time constant t of the temperature variation, the cancellation of an influence resulting from the irradiation of the medium with the light beam of the intensity P1 and that resulting from the irradiation of the medium with the light beam of the intensity P3, setting these total light amounts equal to each other, that is, a total light amount ratio {(P2-P3).times..tau.3}/{(P1-P2).times..tau.1} to be unity, shows a condition under which the medium temperature immediately converges toward the crystallization temperature T2 after the irradiation of the medium with the light beam of the intensity P1 as shown in FIG. 6B.

In actual practice, the temperature change of the medium takes an exponential function as shown in FIGS. 6A, 6B and 6C and .tau.1 or .tau.3 is not always adequately shorter than t. Thus, the total light amount ratio in a proper recording state of FIG. 6B somewhat varies from unity but, normally, it is lower than unity as seen from Equation (5) where the right-hand first term is smaller than unity. That is to say, the proper recording condition is such that the total light amount ratio {(P2-P3).times..tau.3}/{(P1)-(P2).times..tau.1} is set below unity. In a "mark position recording", in particular, where .tau.1 or .tau.3 is usually both short and nearly equal, a relation of Equation (5) is maintained. From the experiments by the inventors it may be safely concluded that the proper recording condition is in a total light amount ratio range of nearly 1/3 to 1.

FIG. 7 shows, as actually measured examples, a dependency of a CNR (carrier noise ratio) and erase ratio (dB) upon the total light amount ratio {(P2-P3).times..tau.3}/{(P1-P2).times..tau.1} when the irradiation time .tau.3 of the light beam of the intensity P3, as well as the intensity P2, varies. As an optical recording medium use is made of a phase change type disk having a structure with a protective layer, recording material layer, protective layer and reflective layer stacked on a resin substrate. The wavelength of the light source for recording/reproduction is 690 nm; the linear speed (relative movement speed between the optical recording medium and the light beam), 9 m/s; the light beam intensity P1, 12 mW and P3, 1 mW; and the irradiation time .tau.1 of the light beam of the strength P1, 39 ns.

The CNR and erase ratio on the ordinate in the graph of FIG. 7, respectively, represent a signal recording performance and erase performance, the total light amount ratio {(P2-P3).times..tau.3}/{(P1-P2).times..tau.1} both desirable from practical viewpoint being in a range of below 1 (100%). That is, for the total light exceeding unity, CNR is better but the erase ratio largely falls. For the total light amount ratio being below 1, more preperably 1/3 to 2/3, the CNR and erase ratio both reveal practically satisfiable values. Further, according to the present invention, the total light amount ratio, being about 1/2 (50%), manifests a best performance both in the CNR and in the erase ratio.

In the present embodiment the total light amount ratio, being in a range of 1/3 to 2/3 in particular, is desirable, noting that this range varies depending upon the relative movement speed of the light beam and optical recording medium, the mark interval, the medium structure, etc. Various experiments have been conducted by the inventors, taking the above into condition. From this it has been found that the total light amount ratio, being in the range of nearly 1/3 to 1, reveals a suitable recording condition.

The dependence of a proper .tau.3 on P1 to P3 and .tau.1 will be explained below with reference to FIGS. 8A and 8D.

FIGS. 8A to 8D are views showing a transfer of an optical recording medium temperature as in FIG. 6. FIG. 8A represents P1, P2, P3, .tau.1 and .tau.3 as a reference. The recording medium is irradiated with a light beam of an intensity P1 during an irradiation period .tau.1 and, after the end of the irradiation above, with a light beam of an intensity P3. The temperature of the medium irradiated with the light beam of the intensity P3 falls from a peak level T1 down toward a target level T3. At this time, an interval to which the medium temperature reaches an erase level T2 becomes a proper r value. This aspect corresponds to FIG. 6B.

FIG. 8B shows a variation of the proper .tau. value in the case where the intensity P1 of the light beam varies from a reference level. The peak level T1 when the intensity P1 of the light beam becomes too large becomes higher than the peak level T1 at a reference time. The peak level T" when the intensity P1 becomes too small becomes lower than T1. Thus, when, at the irradiation of the medium with the light beam of the intensity P3, the medium temperature falls toward the target level T3, a time reaching the level T2 differs between when the intensity P1 of the light beam becomes too large and when it becomes too small. That is, the proper .tau.3' becomes longer when P1 becomes too large and shorter when P1 becomes too small.

FIG. 8C shows a variation of the proper .tau.3 when .tau.1 alone varies from the reference level. As in the case where P1 varies, a peak level T1' at the time of .tau.1 becoming too large is higher than the peak T1 at the reference time and a peak level Ti" at the time of .tau.1 becoming too small is lower than T1. Even in this case, the proper .tau.3' is longer when .tau.1 becomes too large and the proper .tau.3" is shorter when .tau.1 becomes too small.

FIG. 8D shows a variation of the proper .tau.3 when P3 alone varies from the reference level. A target level T3 upon irradiation of the medium with the light beam of P3 varies depending upon the level of P3. A target temperature T3' when P3 becomes too large is higher than T3. Thus, when the temperature of the medium irradiated with the light beam of P3 falls from a peak level T1, the time to which the medium reaches the T2 level varies. The proper .tau.3' is longer when P3 becomes too large and shorter when P3 becomes too small.

As set out above, the proper .tau.3 varies depending upon P1, P2, P3 and .tau.1. In order to define the .tau.3 value, it is necessary to consider the above relation. Although, here, the variation of P2 is not set out, the proper .tau.3 value also varies since the variation of the medium temperature resulting from P1 and P3 is a phenomenon caused by (P1-P2) and (P2-P3).

One form of an optical recording medium of the present invention and another optical recording apparatus different from that in FIG. 1 will be explained below with reference to FIGS. 9 to 12.

As shown in FIG. 9, an information recording area 105A is formed on a disk-like optical recording medium 105. A first recording condition recording area 105B is formed on the outer circumference side of the information recording area 105A and a second recording condition recording area 105C on the inner circumference side of the information recording area 105A. All of P1 to P3 and .tau.1 to .tau.3 or at least .tau.3 is recorded on the first and second recording condition recording areas 105B and 105C. In this case, P1 to P3 and .tau.1 to .tau.3 are selected in accordance with a radius r.sub.n of the recording medium. A table below shows combinations of the number N of the radius r.sub.n and .tau.3n, by way of example, which are recorded in the first and second recording condition recording areas 105B and 105C.

______________________________________ recording condition______________________________________radius r.sub.n r.sub.1 r.sub.2 r.sub.3 . . . r.sub.Nproper .tau..sup.3 n .tau.3.sub.1 .tau.3.sub.2 .tau.3.sub.3 . . . .tau.3.sub.N______________________________________

It is to be noted that the recording condition, such as .tau.3, may be recorded on the first recording condition recording area 105B, on the second recording condition recording area 105C, or on both the first and the second recording condition recording area. Needless to say, the intensities P1, P2, P3 (P1>P2>P3) of the light beam and their irradiation periods .tau.1, .tau.2 and .tau.3 satisfy the following condition:

{(P2-P3).times..tau.3/{(P1-P2).times..tau.1}=below 1.

In the case where the optical recording medium is rotated at a given rate, the intensities P1, P2, P3 (P1>P2>P3) of the beam and their irradiation periods .tau.1 and .tau.3 satisfy the following condition. That is, in order to satisfy {(P2-P3).times..tau.3}/{(P1-P2).times..tau.1}=below unity, at least one of (P2-P3).times..tau.3 and (P1-P2).times..tau.1 is varied in accordance with the recording radius r.sub.n at which the disk-like optical recording medium 105 is irradiated with the light beam.

FIG. 11 is a block diagram showing an optical recording apparatus according to another embodiment of the present invention. The operation of this apparatus is performed in accordance with a flow chart as shown in FIG. 12. When the operation of the optical recording apparatus is started at step 301 in FIG. 12, the disk-like optical recording medium 105 is rotationally driven. A detection system 108 detects recording condition data, such as .tau.3, recorded on the first and second recording condition recording area of at least one of 105B and 105C of the disk-like optical recording medium 105. The recording condition data, such as .tau.3, thus detected is sent via controller 107 to a memory 109 where it is stored (steps. 301 and 302 in FIG. 12). A recording operation, if being done on a per-mark basis, is performed (step 303 in FIG. 12) in accordance with the recording condition data, such as .tau.3, stored in the memory 109. When the operation with the recording and determining the condition has been performed on all associated marks, the operation of the optical recording apparatus is completed (at step 304 in FIG. 12).

The optical recording apparatus of the present embodiment is defined as follows. That is, the optical recording apparatus records information on the recording medium by irradiating the recording medium with a light beam of a first intensity P1 during an irradiation period .tau.1 so as to form an amorphous state area at the recording medium and then with a third light beam of a third intensity P3 during an irradiation period .tau.3 and the recording medium with a second beam of a second intensity so as to form a crystal state area at the recording medium.

In this case, an information recording area for recording the information and a recording condition recording area are formed on the optical recording medium in which the recording condition recording area is formed on at least one of the outer circumference side and inner circumference side of the information recording area and stores, therein, the recording condition data representing the intensities P1, P2, P3 (P1>P2>P3) and their irradiation period .tau.1 and .tau.3 of the light beam satisfying {(P2-P3).times..tau.3}/{(P1-P2).times..tau.1}=below 1.

The recording condition recording area stores, therein, the recording condition data representing the intensities P1, P2 and P3, and at least .tau.3 of irradiation periods .tau.1 and .tau.3 of the light beam.

The optical recording apparatus of the present embodiment includes a recording condition data detecting means for detecting the recording condition data from the recording condition recording area prior to recording the information on the recording medium and a determining means for determining the intensities P1, P2, P3 at least .tau.3 of their irradiation periods .tau.1 and .tau.3 of the light beam in a plurality of radius positions on the information recording areas as used when the information is recorded on the recording medium on the basis of the recording condition data detected by the detecting means.

The determining means includes a means for setting a plurality of radius areas into which the information recording area is divided and a means for determining .tau.3 belonging to each radium area set by the setting means. For example, FIG. 10A shows the case where divided radius areas are provided for each data points of the recording condition data and the .tau.3 value on the data point in each area is set as an inherent .tau.3 to be constant in the area.

The determining means includes a means for setting a plurality of radius areas into which the information recording area is divided, a means for determining .tau.3 belonging to each radius area set by the setting means, and a means for calculating interporated .tau.3 obtained through the interpolation processing of the determined .tau.3 between the set radius areas. For example, FIG. 10B shows the case where divided radius areas are provided for each data points of the recording condition data and, with the .tau.3 value on the data points in each area set as an inherent .tau.value, .tau.3 in each radius position is determined through an interpolation of the value .tau.3 between the areas.

As shown in FIG. 10B, for example, upon interpolation with a straight line it follows that, from both data points r.sub.n, r.sub.n +1 and their value .tau.3n, .tau.3n+1, .tau.3 in r is found as ##EQU1##

To be specific, with r.sub.12 between data points r1, r2, ##EQU2##

Further, the optical recording method of the present embodiment can be defined as follows. That is, an optical recording method is provided for recording information on an optical recording medium by irradiating the recording medium with a light beam of a first intensity P1 during an irradiation period .tau.1 so as to form an amorphous state area at the recording medium and then with a light beam of a third intensity P3 during irradiation period .tau.3 and the recording medium with a light beam of a second intensity P2 so as to form a crystal state area at the recording medium, comprising the steps of:

detecting recording condition data from the recording condition data area prior to recording the information on the recording medium, the recording condition data being stored in a recording condition recording area formed on at least one of an outer circumference side and an inner circumference side of an information recording area of the recording medium and representing the intensities P1, P2, P3 (P1>P2>P3) and irradiation periods .tau.1 and .tau.3 of the light beam satisfying {(P2-P3).times..tau.3}/{(P1-P2).times..tau.1}=below 1; and recording the information on the recording medium on the basis of the recording condition data detected by the detecting step.

The information recording step comprises determining the intensities P1, P2, P3 and at least .tau.3 of the irradiation periods .tau.1 and .tau.3 of the light beam at a plurality of radius positions on the information recording area when the information is recorded on the recording medium on the basis of the recording condition data.

According to the present invention, as set out above, an amorphous area formation position on the optical recording medium is irradiated with the light beam of the first intensity P1 and then with the light beam of the third intensity P3 and a crystal formation area is irradiated with the light beam of the second intensity P2. When recording is made by doing so, the irradiation period .tau.3 of the light beam of the intensity P3 is made suitable. This solves poor erasure and a decline in quality of a reconstruction image and hence achieves improved recording.

Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative devices, and illustrated examples shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

Claims

1. An optical recording apparatus for recording information on a disk-like optical recording medium by irradiating the recording medium with a light beam of a first intensity P1 during a first irradiation period .tau.1 so as to form an amorphous state area at the recording medium and then irradiating the recording medium with a light beam of a third intensity P3 during a third irradiation period .tau.3 and irradiating the recording medium with a light beam of a second intensity P2 so as to form a crystal state area at the recording medium, comprising:

light beam irradiating means for irradiating the optical recording medium with the light beam; and

control means for controlling the intensities P1, P2 and P3 so that P1>P2>P3 and for controlling the irradiation periods .tau.1 and .tau.3 of the light beam to satisfy the following relation:

{(P2-P3).times..tau.3}/{(P1-P2).times..tau.1}=below 1, and

wherein the control means causes data indicative of the first intensity P1, the second intensity P2, the third intensity P3, and the irradiation periods .tau.1 and .tau.3 to be stored in at least one of an outer circumference portion and an inner circumference portion of the disk-like optical recording medium.

2. The optical recording apparatus according to claim 1, wherein the control means comprises means for setting a relative movement speed of the light beam and optical recording medium to be above 5 m/s and for setting a minimal interval between recorded marks formed at amorphous state areas irradiated with the light beam to be below a spot size where the intensity of the light beam becomes e.sup.-2 times its center intensity.

3. The optical recording apparatus according to claim 1, further comprising driving means for driving the optical recording medium at a given rate of rotation, and wherein the control means includes means for varying at least one of (P2-P3).times..tau.3 and (P1-P2).times..tau.1 in accordance with a recording radius zone on the optical recording medium irradiated with the light beam.

4. The optical recording apparatus according to claim 3, wherein the control means comprises means for setting a relative movement speed of the light beam and optical recording medium to be above 5 m/s and for setting a minimal interval between recorded marks formed at amorphous state areas irradiated with the light beam to be below a spot size where the intensity of the light beam becomes e.sup.-2 times its center intensity.

5. The optical recording apparatus according to claim 1, further comprising clock varying means for varying a reference clock cycle for modifying the recording information carried by the light beam in accordance with a recording radius zone on the optical recording medium driven at a given rate of rotation by the driving means, and wherein the control means includes means for varying at least one of the irradiation periods .tau.1 and .tau.3 of the light beam in proportion to the reference clock cycle to satisfy the relation

{(P2-P3).times..tau.3}/{(P1-P2).times..tau.1}=below 1.

6. The optical recording apparatus according to claim 5, wherein the control means comprises means for setting a relative movement speed of the light beam and optical recording medium to be above 5 m/s and for setting a minimal interval between recorded marks formed at amorphous state areas irradiated with the light beam to be below a spot size where the intensity of the light beam becomes e.sup.-2 times its center intensity.

7. An optical recording method for recording information on an optical recording medium comprising the steps of:

irradiating the recording medium with a light beam of a first intensity P1 during an irradiation period .tau.1 so as to form an amorphous state area on a recording area of the recording medium and then irradiating the recording medium with a light beam of a third intensity P3 during an irradiation period .tau.3 and irradiating the recording medium with a light beam of a second intensity P2, wherein P1>P2>P3, so as to form a crystal state area at the recording medium;

enabling a latter half of the amorphous state area which is formed by irradiation with the light beam of the first intensity P1 and enlarged by irradiation with the light beam of the third intensity P3 to be crystallized by irradiation with the light beam of the second intensity P2 so that the latter half of the amorphous state area is erased; and

storing data indicative of a first irradiation intensity P1, a second irradiation intensity P2, a third irradiation intensity P3, and irradiation periods .tau.1 and .tau.3 in at least one of an outer circumference portion and an inner circumference portion of the optical recording medium.

8. A method for recording and reproducing information on and from a zone constant angular velocity type phase change optical disk having a plurality of zones comprising the steps of:

recording and reproducing information using at least a recording light beam, erasing light beam and off-pulse light beam, by varying at least an irradiation time of the recording light beam and an irradiation time of the off-pulse light beam in accordance with a respective recording zone of the optical disk; and

recording and reproducing data indicative of irradiation intensities and irradiation periods of the recording light beam in at least one of an outer circumference portion and an inner circumference portion of the optical recording medium.

9. The method according to claim 8, wherein the irradiation time of the recording light beam and irradiation time of the off-pulse light beam are selectively varied in accordance with the respective recording zone of the optical disk.

10. The method according to claim 8, wherein the relative movement speed of the light beam and optical recording medium to be above 5 m/s and the irradiation time of the recording light beam and irradiation time of the off-pulse light beam are selectively varied in accordance with a position of the respective zones of the optical disk.

11. An optical recording apparatus for recording information on an optical recording medium comprising;

a light beam generating unit; and

a control circuit that causes the light beam to irradiate the recording medium at a first intensity P1 during an irradiation period .tau.1 so as to form an amorphous state area on the recording medium and then to irradiate the recording medium with the light beam at a third light intensity P3 during an irradiation period .tau.3 and to irradiate the recording medium with the light beam at a second intensity P2 so as to form a crystal state area at the recording medium, wherein an information recording area for recording the recording information and a recording condition recording area are disposed on the optical recording medium, the recording condition recording area being disposed on at least one of an outer circumference side and inner circumference side of the information recording area and storing therein recording condition data representing the intensities P1, P2 and P3, wherein P1>P2>P3, and irradiation periods .tau.1 and .tau.3 of the light beam, wherein P1, P2, P3, .tau.1 and .tau.3 satisfy the following condition: {(P2-P3).times..tau.3}/{P1-P2).times..tau.1)}=below 1.

12. The optical recording method according to claim 11, wherein the recording condition recording area stores therein recording condition data representing the intensities P1, P2, P3 and at least .tau.3 of the irradiation periods .tau.1 and .tau.3 of the light beam at a plurality of radius position in the information recording area.

13. The optical recording apparatus according to claim 11, further comprising recording condition data detecting means for detecting the recording condition data from the recording condition recording area prior to recording the information on the recording medium and determining means for determining the intensities P1, P2, P3 and at least .tau.3 of irradiation periods .tau.1 and .tau.3 of the light beams of a plurality of radius position on the information recording area as used when the information is recorded on the recording medium on the basis of the recording condition data detected by the detecting means.

14. The optical recording apparatus according to claim 13, wherein the determining means comprises means for setting a plurality of radius areas into which the information recording area is divided and means for determining .tau.3 belonging to each radius area set by the setting means.

15. The optical recording apparatus according to claim 13, wherein said determining means comprises means for setting a plurality of radius areas into which the information recording area is divided, means for determining .tau.3 belonging to each radius area set by the setting means and means for calculating interpolated .tau.3 obtained through the interpolation processing of the determined .tau.3 between the radius areas.

16. An optical recording method for recording information on an optical recording medium comprising the steps of:

detecting recording condition data from a recording condition recording area prior to recording information on the recording medium, the recording condition data being stored in a recording condition recording area disposed on at least one of an outer circumference side and an inner circumference side of an information recording area of the recording medium and representing intensities P1, P2, P3, wherein P1>P2>P3, and irradiation periods .tau.1 and .tau.3 of the light beam satisfying the following condition:

{(P2-P3).times..tau.3}/{(P1-P2).times..tau.1}=below 1; and

recording the information on the recording medium based on the recording condition data detected by the detecting step by performing the steps of:

irradiating the recording medium with a light beam of a first intensity P1 during an irradiation period .tau.1 so as to form an amorphous state area at the recording medium,

irradiating the recording medium with a light beam of a third intensity P3 during irradiation period .tau.3, and

irradiating the recording medium with a light beam of a second intensity P2 so as to form a crystal state area at the recording medium.

17. The optical recording method according to claim 16, wherein the information recording step comprises determining intensities P1, P2, P3 and at least .tau.3 of the irradiation periods .tau.1 and .tau.3 of the light beam at a plurality of radius positions on the information recording area as used when the information is recorded on the recording medium on the basis of the recording condition data.

18. An optical recording medium, comprising:

an information recording area; and

a recording condition recording area being formed on the optical recording medium, and the recording condition recording area being formed on at least one of an outer circumference side and an inner circumference side of the information recording area and stores therein recording condition data representing the intensities P1, P2 and P3, wherein P1>P2>P3 and irradiation period .tau.1 and .tau.3 of the light beam satisfying a condition

{(P2-P3).times..tau.3}/{P1-P2).times..tau.1)}=below 1.

19. The optical recording medium according to claim 18, wherein the recording condition recording area stores therein recording condition data representing the intensities P1, P2, P3 and at least .tau.3 of the irradiation periods .tau.1 and .tau.3 of the light beam at a plurality of radius position in the information recording area.