A phase change type optical recording apparatus and optical recording method using an overwrite system

Abstract: An optical recording apparatus rewrites recorded information on a modified constant angular velocity type phase change optical disk (105) by overwriting with at least recording light beam, erasing light beam and off-pulse light beam irradiation. The apparatus comprises a semiconductor laser (101) for irradiating the optical disk (105) with the light beam and a control unit (107, 109) for controlling the intensities P1, P2 and P3 (P1 > P2 > P3) light beam with which the optical disk (105) is irradiated and their irradiation periods τ1 and τ3 to obtain a relation of {(P2-P3) × τ3}/{(P1-P2) × τ1} = below 1.

Description: 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. 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 has the function of allowing the intensity of a light beam which is directed as a condensing beam onto an optical recording medium to be controlled in accordance with the recording information and is basically of such a type 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, that is, to record the 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. Patent 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 leads to a decrease in recording reliability. Further, even 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 above, only irradiation period is specified for the light beam of the third period. Stated in more detail, according to U.S. Patent No. 4,939,717, a relation 0 < τ < λ/V is prescribed where τ represents the irradiation period of the light beam of the third intensity, λ the wavelength of the light beam, and V the relative speed between the light beam and the optical recording medium. In EP-A-0,265,971 reflecting the preamble of claim 1 it is suggested to use a beam of a first intensity of 6m W for 0.5µs for writing, a second intensity of 3mW for 0.4µs for erasing and a third intensity of 1m W for 0.1µs after the writing period for rapid cooling. 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 found impossible to obtain adequate recording reliability, because there arise incomplete erasure and a lowering in quality of a reproduction signal. As set out above, the known patent above simply specifies the irradiation period of the light beam of the third intensity and, since 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 above. It is the object of the present invention to provide a phase change type optical recording apparatus and optical recording method which can obtain adequate recording reliability by solving the incomplete erasure and lowering in quality of a reproduction signal resulting from the excess or shortage of an irradiation period of a light beam of a third intensity. 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 a first irradiation period τ1 so as to form an amorphous state area on the recording medium, irradiating the recording medium with a light beam of a third intensity P3 during a third irradiation period τ3, and irradiating the recording medium with a light beam of a second intensity P2 so as to form a crystal state area on 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, characterised in that the control means also controls the irradiation periods τ1 and τ3 of the light beam to satisfy the following relation: {(P2-P3) X τ3}/{(P1-P2)Xτ1} being in a range of 1/3 to bellow 1, and data indicative of the intensities P1, P2, and P3, and the irradiation periods τ1 and τ3 are stored in at least one of an outer circumference portion and an inner circumference portion of the optical recording medium. In another aspect of the present invention, there is provided an optical recording method for recording information on a disk-like optical recording medium comprising the steps of: irradiating the recording medium with a light beam of a first intensity P1 during a first irradiation period τ1 so as to form an amorphous state area on the recording medium, irradiating the recording medium with a light beam of a third intensity P3 during a third irradiation period τ3, 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 on the recording medium and characterised by controlling the irradiation periods τ1 and τ3 of the light beam to satisfy the following relation: {(P2-P3) X τ3}/{(P1-P2)Xτ1} being in a range of 1/3 to below 1, wherein data indicative of the first intensity P1, the second intensity P2, the third intensity P3, and the irradiation periods τ1 and τ3 are stored in at least one of an outer circumference portion and an inner circumference portion of the optical recording medium. According to the present invention, the irradiation interval τ3 of the light beam of the intensity P3 is optimized by the total light amount ratio {(P2-P3) × τ3}/{(P1-P2) × τ1} being in a range of 1/3 to claim 1 where (P2-P3) × τ3: 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) × τ1: 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 solve incomplete erasure of the recorded mark when τ3 is too long and a lowering in quality of a reproduction signal when τ3 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 τ3 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. The present invention further provides a system comprising a disk-like optical recording medium and an optical recording apparatus for recording information on the optical recording medium, comprising: a light beam generating unit; and a control circuit that causes the light beam to irradiate the recording medium of a first intensity P1 during a first irradiation period τ1 so as to form an amorphous state area on the recording medium, to irradiate the recording medium with a light beam of a third intensity P3 during a third irradiation period τ3, and to irradiate the recording medium with a light beam of a second intensity P2 so as to form a crystal state area on 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, and the recording condition recording area is disposed on at least one of an outer circumference portion and an inner circumference portion of the optical recording medium and storing therein recording condition data representing the intensities P1, P2, and P3, wherein P1 > P2 > P3, and irradiation periods τ1 and τ3 of the light beam, wherein P1, P2, P3, τ1 and τ3 satisfy the following condition: {(P2-P3)Xτ3}/{(P1-P2)Xτ1} being in a range of 1/3 to below 1. The present invention further provides a phase change type optical recording medium comprising: an information recording area in which information is recorded by irradiating the recording medium with a light beam of a first intensity P1 during a first irradiation period τ1 so as to form an amorphous state area on the recording medium, irradiating the recording medium with a light beam of a third intensity P3 during a third irradiation period τ3, 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 on the recording medium, characterised in that: the intensities P1, P2 and P3 and irradiation periods τ1 and τ3 of the light beam satisfy a condition: {(P2-P3) X τ3}/{(p1-p2)Xτ1} being in a range of 1/3 to below 1; and a recording condition recording area is formed on the optical recording medium, and the recording condition recording area is formed on at least one of an outer circumference portion and an inner circumference portion of the information recording area and stores therein recording condition data representing the intensities P1, P2 and P3 and irradiation periods τ1 and τ3. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: 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 are a relation between an irradiation interval of a light beam of a third intensity and a recording mark configuration in the present embodiment; FIGS. 6A and 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 view 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 τ3; FIG. 9 is a plan view schematically showing a disk-like optical recording medium of the present invention; FIGS. 10A and 10B are a characteristic graph showing a relation between the radius r of the disk-like optical recording medium and the irradiation period τ3 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. 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 in distinct 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 being used to form an amorphous state and the second intensity P2 to a crystal state and the third intensity P3 being 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 ┌ 0 ┘ and ┌ 1 ┘, a light beam of the intensity P1 is directed only during a period τ1 to a position corresponding to ┌ 1 ┘ and, after a light beam of the intensity P3 is directed only during a period τ3, a light beam of the intensity P2 is kept directed till an interval corresponding to the next ┌1 ┘ 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 τ1. In this way, a τ1-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 τ3. Thus a τ3-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 sides of switches 210, 211 and 212. The other-end sides of the 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 τ1 and τ3 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 τ1 switching signal 215 and τ3 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 τ1, τ3 in proportion to the reference clock cycle at each recording radial position. The simplest method is by having the τ1 and τ3 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 τ1 and τ3 in proportion to such a reference clock cycle it may be possible to put at least one of (P2-P3) ×τ3 and (P1-P2) × τ1 in proportion to the reference clock cycle where (P2-P3) × τ3: 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) × τ1: 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 form 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 ┌ 1 ┘, 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 ┌ 0 ┘, 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 τ3 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. τ3 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, those areas broader than those 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 remains 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 strictly, the relative speed of movement between the medium surface and the light beam spot exceeds about 5 m/s, the above-mentioned effect acts to less extent because cooling is done, repedly, 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. Even if, therefore, 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, use is made of 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 -2 times its center intensity) 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 τ 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 τ3 becomes too long as shown in FIG. 5B, then a space is created between a melted area irradiated with the light beam of the intensity 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 τ3, 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 τ3 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 τ3 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 τ3 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 τ3 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 τ1 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 × (P1-P2)/P2 × {1-exp(-τ1/t)} On the other hand, the medium temperature T3 after the irradiation period τ3 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} × {1-exp(-τ3/t)} Assuming that, for example, τ1 and τ3 are adequately shorter than the time constant t, Equations (1) and (2) above can be simplified to T1 = T2 + T2 × (P1-P2)/P2 × τ1/t) T3 = T1 - {(T1-T2) + T2 × (P2-P3)/P2} × τ3/t Finding a condition T3=T2 from Equations (3) and (4), (P2-P3) × τ3 = (1-τ3/t) × (P1-P2) × τ1 Here, since τ3 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) × τ3 ≒ (P1-P2) × τ1 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 τ3 = a proper value and the light beam irradiation periods τ1 and τ3. As seen from FIG. 6D, (P2-P3) ×τ3 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) × τ1 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 τ1 and τ3 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) ×τ3}/{(P1-2) × τ1} 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 τ1 or τ3 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) ×τ3}/{(P1)-(P2) ×τ1} is set below unity. In a "mark position recording", in particular, where τ1 or τ3 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) × τ3}/{(P1-P2) × τ1} when the irradiation time τ3 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 τ1 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) ×τ3}/{(P1-P2) xτ1} 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 τ3 on P1 to P3 and τ1 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, τ1 and τ3 as a reference. The recording medium is irradiated with a light beam of an intensity P1 during an irradiation period τ1 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 τ value. This aspect corresponds to FIG. 6B. FIG. 8B shows a variation of the proper τ 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 τ3' becomes longer when P1 becomes too large and shorter when P1 becomes too small. FIG. 8C shows a variation of the proper τ3 when τ1 alone varies from the reference level. As in the case where P1 varies, a peak level T1' at the time of τ1 becoming too large is higher than the peak T1 at the reference time and a peak level T1" at the time of τ1 becoming too small is lower than T1. Even in this case, the proper τ3' is longer when τ1 becomes too large and the proper τ3" is shorter when τ1 becomes too small. FIG. 8D shows a variation of the proper τ3 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 τ3' is longer when P3 becomes too large and shorter when P3 becomes too small. As set out above, the proper τ3 varies depending upon P1, P2, P3 and τ1. In order to define the τ3 value, it is necessary to consider the above relation. Although, here, the variation of P2 is not set out, the proper τ3 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 τ1 to τ3 or at least τ3 is recorded on the first and second recording condition recording areas 105B and 105C. In this case, P1 to P3 and τ1 to τ3 are selected in accordance with a radius r n of the recording medium. A table below shows combinations of the number N of the radius r n and τ3n, by way of example, which are recorded in the first and second recording condition recording areas 105B and 105C. recording condition radius r n r 1 r 2 r 3 ···r N proper τ 3 n τ3 1 τ3 2 τ3 3 ···τ3 N It is to be noted that the recording condition, such as τ3, 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 τ1, τ2 and τ3 satisfy the following condition: {(P2-P3) × τ3/{(P1-P2) × τ1} being in a range of 1/3 to 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 τ1 and τ3 satisfy the following condition. That is, in order to satisfy {(P2-P3) × τ3}/{(P1-P2) × τ1} = below unity, at least one of (P2-P3) × τ3 and (P1-P2) × τ1 is varied in accordance with the recording radius r 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 τ3, recorded on the first and second recording condition recording area at least one of 105B and 105C of the disk-like optical recording medium 105. The recording condition data, such as τ3, 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 τ3, 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 τ1 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 τ3 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 τ1 and τ3 of the light beam satisfying {(P2-P3) × τ3}/{(P1-P2) × τ1} being in a range of 1/3 to below 1. The recording condition recording area stores, therein, the recording condition data representing the intensities P1, P2 and P3, and at least τ3 of irradiation periods τ1 and τ3 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 τ3 of their irradiation periods τ1 and τ3 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 τ3 belonging to each radius 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 τ3 value on the data point in each area is set as an inherent τ3 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 τ3 belonging to each radius area set by the setting means, and a means for calculating interpolated τ3 obtained through the interpolation processing of the determined τ3 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 τ3 value on the data points in each area set as an inherent τ value, τ3 in each radius position is determined through an interpolation of the value τ3 between the areas. As shown in FIG. 10B, for example, upon interpolation with a straight line it follows that, from both data points r n , r n+1 and their value τ3n, τ3n+1, τ3 in r is found as τ3 = τ3 n + (r-r n ) τ3 n+1 - τ3 n r n+1 - r n . To be specific, with r 12 between data points τ1, r2, τ3 12 = τ3 1 + (r 12 -r 1 ) τ3 2 - τ3 1 r 2 - r 1 . 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 τ1 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 τ3 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 τ1 and τ3 of the light beam satisfying {(P2-P3) × τ3}/{(P1-P2) × τ1} being in a range of 1/3 to 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 τ3 of the irradiation periods τ1 and τ3 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 τ3 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.

Claims: An optical recording apparatus for recording information on a disk-like optical recording medium (105) by irradiating the recording medium (105) with a light beam of a first intensity P1 during a first irradiation period τ1 so as to form an amorphous state area on the recording medium (105), irradiating the recording medium (105) with a light beam of a third intensity P3 during a third irradiation period τ3, and irradiating the recording medium (105) with a light beam of a second intensity P2 so as to form a crystal state area on the recording medium (105), comprising: light beam irradiating means (101, 102, 103, 104, 108) for irradiating the optical recording medium (105) with the light beam; and control means (107, 109) for controlling the intensities P1, P2, and P3 so that P1 > P2 > P3, characterised in that the control means also controls the irradiation periods τ1 and τ3 of the light beam to satisfy the following relation: {(P2-P3) X τ3}/{(P1-P2)Xτ1} being in a range of 1/3 to below 1, and wherein data indicative of the intensities P1, P2, and P3, and the irradiation periods τ1 and τ3 are stored in at least one of an outer circumference portion and an inner circumference portion of the optical recording medium (105). The optical recording apparatus according to claim 1, further comprising driving means (106) for driving the optical recording medium (105) at a given rate of rotation, and characterised in that said control means (107, 109) includes means for varying at least one of (P2-P3) X τ3 and (P1-P2) X τ1 in accordance with a recording radius zone on the optical recording medium (105) irradiated with the light beam. The optical recording apparatus according to claim 1, further comprising clock varying means (107, 109) 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 (105) driven at a given rate of rotation by the driving means (106), and characterised in that said control means (107, 109) includes means for varying at least one of the irradiation periods τ1 and τ3 of the light beam in proportion to the reference clock cycle to satisfy the relation {(P2-P3) X τ3}/{(p1-p2)Xτ1} being in a range of 1/3 to below 1. The optical recording apparatus according to one of claims 1, 2, and 3, wherein said control means (107, 109) comprises means for setting a relative movement speed of the light beam and optical recording medium (105) 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 -2 times its center intensity. An optical recording method for recording information on a disk-like optical recording medium (105) comprising the steps of: irradiating the recording medium (105) with a light beam of a first intensity P1 during a first irradiation period τ1 so as to form an amorphous state area on the recording medium (105), irradiating the recording medium (105) with a light beam of a third intensity P3 during a third irradiation period τ3, and irradiating the recording medium (105) with a light beam of a second intensity P2, wherein P1 > P2 > P3, so as to form a crystal state area on the recording medium (105) and characterised by controlling the irradiation periods τ1 and τ3 of the light beam to satisfy the following relation: {(P2-P3) X τ3}/{(P1-P2)Xτ1} being in a range of 1/3 to below 1, wherein data indicative of the first intensity P1, the second intensity P2, the third intensity P3, and the irradiation periods τ1 and τ3 are stored in at least one of an outer circumference portion and an inner circumference portion of the optical recording medium (105). The optical recording method according to claim 5, wherein the information recording step comprises determining intensities P1, P2, P3 and at least τ3 of the irradiation periods τ1 and τ3 of the light beam at a plurality of radius positions on the information recording area (105A) as used when the information is recorded on the recording medium (105) on the basis of the recording condition data. A system comprising a disk-like optical recording medium (105) and an optical recording apparatus for recording information on the optical recording medium (105), comprising: a light beam generating unit (101); and a control circuit (107, 109) that causes the light beam to irradiate the recording medium (105) of a first intensity P1 during a first irradiation period τ1 so as to form an amorphous state area on the recording medium, to irradiate the recording medium (105) with a light beam of a third intensity P3 during a third irradiation period τ3, and to irradiate the recording medium (105) with a light beam of a second intensity P2 so as to form a crystal state area on 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 (105), and the recording condition recording area is disposed on at least one of an outer circumference portion and an inner circumference portion of the optical recording medium (105) and storing therein recording condition data representing the intensities P1, P2, and P3, wherein P1 > P2 > P3, and irradiation periods τ1 and τ3 of the light beam, wherein P1, P2, P3, τ1 and τ3 satisfy the following condition: {(P2-P3) X τ3}/{(P1-P2)Xτ1} being in a range of 1/3 to below 1. The system according to claim 7, wherein the recording condition recording area stores (105B, 105C), therein, recording condition data representing the intensities P1, P2, P3 and at least τ3 of the irradiation periods τ1 and τ3 of the light beam at a plurality of radius positions on the information recording area (105A). The system according to claim 7, further comprising recording condition data detecting means (108) for detecting the recording condition data from the recording condition recording area (105B, 105C) prior to recording the information on the recording medium (105) and determining means for determining the intensities P1, P2, P3 and at least τ3 of irradiation periods τ1 and τ3 of the light beams of a plurality of radius position on the information recording area (105A) as used when the information is recorded on the recording medium (105) on the basis of the recording condition data detected by the detecting means (108). The system according to claim 9, wherein the determining means comprises means for setting a plurality of radius areas into which the information recording area (105A) is divided and means for determining τ3 belonging to each radius area set by the setting means. The system according to claim 9, wherein said determining means comprises means for setting a plurality of radius areas into which the information recording area (105A) is divided, means for determining τ3 belonging to each radius area set by the setting means and means for calculating interpolated τ3 obtained through the interpolation processing of the determined τ3 between the radius areas. A phase change type optical recording medium (105) comprising: an information recording area (105A) in which information is recorded by irradiating the recording medium (105) with a light beam of a first intensity P1 during a first irradiation period τ1 so as to form an amorphous state area on the recording medium (105), irradiating the recording medium (105) with a light beam of a third intensity P3 during a third irradiation period τ3, and irradiating the recording medium (105) with a light beam of a second intensity P2, wherein P1 > P2 > P3, so as to form a crystal state area on the recording medium (105), characterised in that : the intensities P1, P2 and P3 and irradiation periods τ1 and τ3 of the light beam satisfy a condition: {(P2-P3) X τ3}/{(p1-p2)Xτ1} being in a range of 1/3 to below 1; and a recording condition recording area (105B, 105C) is formed on the optical recording medium (105), and the recording condition recording area (105B, 105C) is formed on at least one of an outer circumference portion and an inner circumference portion of the information recording area (105A) and stores therein recording condition data representing the intensities P1, P2 and P3 and irradiation periods τ1 and τ3. The phase change type optical recording medium according to claim 12, wherein the recording condition recording area (105B, 105C) stores, therein, recording condition data representing the intensities P1, P2, P3 and at least τ3 of the irradiation periods τ1 and τ3 of the light beam at a plurality of radius positions on the information recording area (105A).

Inventors: HASEGAWA HIROSHI, KOBORI HIROMICHI, HASEGAWA, HIROSHI, KOBORI, HIROMICHI, Hasegawa, Hiroshi, c/o Intellectual Property Div., Kobori, Hiromichi, c/o Intellectual Property Div.
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1995
Main classification: G11B7
IPC codes: G11B7