Method of and device for writing and reading optical data by using phase transition optical medium

Abstract: The writing and reading of optical data is made using an optical data writing medium (5) and a single light spot, and the verification is made simultaneously with the writing of data. A phase transition optical disk is used as the optical data writing medium. The verification is made by checking magnitude of I w × (P r /P W ) and that of I r , wherein I w is a return light dose from the optical data writing medium during writing, I r is a return light dose from the optical data writing medium in a crystal state of the writing film, P w is laser power during writing, and P r is laser power during reading. The device for writing and reading optical data includes a divider (7) for dividing a return light dose I w from the optical data writing medium during writing by P w ,/P r , and a comparator (8) for judging magnitude of I w × (P r /P w ) and that of a return light dose from the optical data writing medium. The verification by a single beam spot while data is being written enables the reduction of writing time.

Description: BACKGROUND OF THE INVENTION (1) Field of the Invention The present invention relates to a method of and a device for writing and reading optical data on an optical data writing medium (hereinafter referred to as optical disk), and more particularly to a method of and a device for writing and reading data by using a phase transition medium. (2) Description of the Related Art In an optical disk device, data is written on an optical disk by irradiating the disk with a laser beam. The irradiation of the optical disk with the laser beam results in a local temperature rise in a writing film of the optical disk due to light absorption. The local temperature rise causes changes in the state of the writing film, thus enabling the writing. In the optical disk device, it is necessary, during the signal writing, to verify whether the writing data has been correctly written on the optical disk. In a prior art optical disk device, which is commercially available at present, the verification of writing data is made by reading the written area after the writing. In other prior art examples, a plurality of light sources are used, or a plurality of beam spots formed by diffraction grating are used, as disclosed in Japanese Patent Application Kokai Publication No. Hei 2-9024 or Japanese Patent Application Kokai Publication No. Hei 3-41632, whereby one or more beam spots are used for the verification. With respect to a magneto-optical disk, there is a proposal as disclosed in Japanese Patent Application Kokai Publication No. Hei 5-144112 in which a single beam verification using a single beam spot, is realized by utilizing characters unique or inherent to an opto-magnet. In the prior art verification methods applied to the optical disk devices described above, there have been problems that, in the case where the verification is made after the writing operation, the time required for the writing is extended. In the case where a plurality of beam spots are used, there have been problems that the cost is high and the adjustment of optical system is difficult. With the phase transition type optical disks in which the writing and reading principles are different from those in the magneto-optical disk, a method for realizing a single beam verification using a single beam spot verification has not heretofore been known. EP 276 808 which is used for the two-part form delimitation, describes the verification of writing data, using the reflected intensity during the beginning of the writing as a reference level. US 4,727,531 discloses an optical data recording system which has real time error checking by sensing the level of reflected radiation from the high energy level pulse used to form a spot on a disc, and then comparing the sensed level with a reference signal to thus sense a recording failure or defect in the disc. SUMMARY OF THE INVENTION An object of at least the preferred embodiments of the invention, therefore, is to overcome the problems existing in the prior art, and to provide a method of and device for writing and reading optical data, which can verify the data written on a phase transition optical disk with a single light beam spot simultaneously with a writing operation. In one aspect the invention provides a method of writing and reading optical data using an optical data writing medium (5) having a writing film in which at least one of reflectivity and optical phase is variable depending on light irradiation, the method comprising verifying, simultaneously with the writing of the data, whether said data has been correctly written on said optical data writing medium (5), said method being characterized by comprising: writing and reading data with a single light spot generated by a laser (1); wherein the verification of writing the data is performed by comparing the magnitude of I w x (P r /P w ) with that of I r , wherein I w is a return light intensity from said optical data writing medium (5) during writing, I r is a return light intensity from said optical data writing medium (5) in a crystal state of the writing film during reading, P w is the laser power during writing, and P r is the laser power during reading. In another aspect the invention provides a device for writing and reading optical data using an optical data writing medium (5) having a writing film in which at least one of reflectivity and optical phase is variable depending on light irradiation, the device having means (7, 8, 9) for verifying, simultaneously with the writing of the data, whether said data has been correctly written on said optical data writing medium (5), the device being characterized by means (1, 2, 3, 4, 6, 10) for writing and reading data with a single light spot; wherein said verifying means (7, 8, 9) is arranged to compare the magnitude of I w x (P r /P w ) with that of I r , wherein I w is a return light intensity from said optical data writing medium (5) during writing, I r is a return light intensity from said optical data writing medium (5) in a crystal state of the writing film during reading, P w is the laser power during writing, and P r is the laser power during reading. The method of and device for writing and reading optical data may use a phase transition optical disk. In a further aspect the present invention provides a device for writing and reading optical data using an optical data writing medium (5) having a writing film in which one of reflectivity and optical phase is variable depending on light irradiation, the device having means (7, 8, 9) for verifying, simultaneously with the writing of the data, whether said data has been correctly written on said optical data writing medium (5), said device being characterized by: means (1, 2, 3, 4, 6, 10) for writing and reading data with a single light spot; wherein said verifying means comprises a divider (7) for dividing a return light intensity I w from said optical data writing medium (5) during writing by P w /P r , wherein P w is the laser power during writing and P r is the laser power during reading; and a comparator (8) for comparing the magnitude of I w x (P r /P w ) with that of a return light intensity from said optical data writing medium (5) in a crystal state of the writing film during reading. In a preferred embodiment with the phase transition optical disk, data is written and read by utilizing the reversible phase transition of the disk between the crystal state and the amorphous state. For writing, the writing film melts due to irradiation with the writing power P w and then cooled down quickly to make it amorphous. The optical constants of the writing film in the melted state are different from those in the crystal state or the amorphous state. Thus, it is possible to verify whether the writing film has melted, that is, whether the proper writing has been made, by monitoring the return light intensity I w during the writing from the optical disk and comparing the return lightintensity I w with a reference value. Assuming that the reflectivities of the optical disk when the writing film is in the crystal state, melted state and amorphous state are respectively R c , R m and R a , a relation, R m <R c , is satisfied in the case where a medium structure is R c >R a , and a relation, R m >R c , is satisfied in the case where a medium structure is R c <R a . In either case, verification as to whether the writing film has melted, that is, whether the proper writing has been obtained, can be obtained from the check of the magnitude relation between R m and R c . The return light intensity I w from the writing disk during the writing is I w = P w × R m where P w is the laser power during the writing. On the other hand, the return light intensity I r from the optical disk during the reading in the crystal state of the writing film is I r = P r × R c wherein P r is the laser power during the reading. A check as to whether the writing film has melted so as to satisfy a relation, for example, R m <R c , thus may be made by checking whether a relation, I w /P w <I r /P r , has been satisfied. From the result of this check, verification as to whether the proper writing has been made can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and advantages of the present invention will be apparent from the following description of preferred embodiments of the invention explained with reference to the accompanying drawings, in which: Fig. 1 is a schematic representation of an optical system for describing an embodiment of the invention applied to the method of and device for writing and reading optical data; Fig. 2 is a waveform chart illustrating the verifying operation in the method of and device for writing and reading optical data shown in Fig. 1; Fig. 3 is a partial sectional view showing an example of the composition of the phase transition optical disk used for the method of and device for writing and reading optical data shown in Fig. 1; Fig. 4 is a graph showing an example of the relation between the number of write error generation times and the writing power in the method of and device for writing and reading optical data shown in Fig. 1; Fig. 5 is a graph showing a different example of the relation between the number of write error generation times and the writing power in the method of and device for writing and reading optical data shown in Fig. 1; and Fig. 6 is a partial sectional view showing a different example of the composition of phase transition optical disk used for the method of and device for writing and reading optical data shown in Fig. 1. PREFERRED EMBODIMENTS OF THE INVENTION Now, a preferred embodiment of the invention will be described with reference to the drawings. Fig. 1 schematically shows an optical system of an embodiment of the invention applied to the method of and device for writing and reading optical data according to the invention. The writing and reading device embodying the invention comprises a laser beam source 1, lenses 2 and 4, a beam splitter 3, a phase transition optical disk 5, a divider 7, and a comparator 8. The numeral 6 denotes a read signal, 9 denotes a verification signal, and 10 denotes a read data. The operation of the embodiment will now be described. A laser beam emitted from the laser beam source 1 and having a predetermined intensity, is converted by the lens 2 to a parallel beam, passes through the beam splitter 3 and the converging lens 4 and is focused on the phase transition optical disk 5. In writing, data is written with laser power P w . In reading, the written data is read with laser power P r , and passes through the lens 4 and beam splitter 3 to be detected as the read signal 6 to be outputted as the read data 10. In the writing operation, the read signal I w detected during the writing operation is divided by P w /P r (P w being the laser power during writing and P r being the laser power during the reading), and the quotient of the division is compared in the comparator 8 with the return light intensity I r from the phase transition optical disk 5 in the crystal state of the writing film during the reading. The result of the comparison is outputted as the verification signal 9. Fig. 2 is a waveform chart schematically illustrating the verifying operation during the writing and reading device shown in Fig. 1. Shown by 101 is a writing signal, 102 the return light intensity I w from the phase transition optical disk 5 shown in Fig. 1 during the writing, and by 103 the quotient I wn of division of I w by P w /P r . The levels of the return light intensity I r from the phase trans: tion optical disk 5 when the writing film is in the crystal state and I wn are compared. When I wn >I r , a writing error signal as shown by 104 is generated, which indicates that the proper writing has failed. Without detection of any writing error signal, it is verified that the proper writing has been obtained. Examples of application of this embodiment of the method of and device for writing and reading optical data according to the invention will now be described with reference to the drawings. Example 1 A phase transition optical disk having a structure as shown in Fig. 3 was used, which was obtained by depositing ZnS-SiO 2 to 150 nm, Ge 2 Sb 2 Te 5 to 20 nm, ZnS-SiO 2 to 20 nm and Al to 60 nm successively by spattering on a polycarbonate substrate. On the optical disk, (2-7) modulated random data was written by rotating the disk at a linear speed of 7.5 m/s and setting the writing pulse width to 50 ns. The writing power P w was set to 14 to 16 mW, the erasing power P e was set to 7 mW, and the reading power Pr was set to 1 mW. The reflectivities of the writing film were 25%, 10% and 8% when the film was in the crystal state, melted state and amorphous state, respectively. The return light intensity Ir from the optical disk in the crystal state of the writing film during the reading, was 1.5 V, and the writing error signal was generated while the light intensity level as a result of division of the light intensity I w of the optical disk during the writing by P w /P r was higher than 1.5 V. Fig. 4 shows the relation between the number of write error generation times and the writing power during the writing. Fig. 4 also shows, as a comparison, the result of checking of write errors by reading the written area after the writing as in the prior art. As is obvious from Fig. 4, the detected number of write error generation times in this example is in accord with that in the prior art example. Example 2 A phase transition optical disk having a structure as shown in Fig. 3 was used, which was obtained by laminating ZnS-SiO 2 to 100 nm, Ge 2 Sb 2 Te 5 to 25 nm, ZnS-SiO 2 to 20 nm and Al to 60 nm successively by sputtering on a polycarbonate substrate. On this optical disk, (2-7) modulated random data was written by rotating the disk at a linear speed of 7.5 m/s and setting the writing pulse width of 50 ns. The writing power P w was set to 16 to 18 mW, the erasing power P e was set to 8 mW, and the reading power P r was set to 1 mW. The reflectivities of the writing film were 20%, 8% and 6% when the film was in the crystal state, melted state and amorphous state, respectively. The return light intensity I r from the disk in the crystal state of the writing film during the reading was 1.2 V, and the writing error signal was generated while the intensity as a result of division of the return light amount I w from the optical disk during the writing by P w /P r was higher than 1.2 V. Fig. 5 shows the relation between the number of write error generation times during the writing and the writing power. Fig. 5 also shows, as a comparison, the result of checking write errors by reading the written area after writing as in the prior art. As is obvious from Fig. 5, the number of write error generation times detected in this example is in accord with that in the prior art example. It will be seen that in this example it is possible to verify the contents of the writing data by using the writing laser beam while data is written. Example 3 A phase transition optical disk having a structure as shown in Fig. 6 was used, which was obtained by laminating Au to 10 nm, ZnS-SiO 2 to 150 nm, Ge2Sb2Te5 to 20 nm, ZnS-SiO 2 to 45 nm and Al to 100 nm successively by sputtering on a polycarbonate substrate. On this optical disk, (2-7) modulated random data was written by rotating the disk at a linear speed of 7.5 m/s and setting the writing pulse width to 50 ns. The writing power P w was set to 18 to 20 mW, the erasing power P e was set to 9 mW, and the reading power P r was set to 1 mW. The medium structure was such that the reflectivity was higher in the amorphous state. The reflectivities of the writing film were 10%, 25% and 30% when the film was in the crystal state, melted state and amorphous state, respectively. The return intensity I r from the optical disk in the crystal state of the writing film during the reading was 0.6 V, and the writing error signal was generated while the light dose as a result of division of the return light intensity I w from the optical disk during the writing by P w /P r was higher than 0.6 V. The relation between the number of write error generation times and the writing power was checked, and it was confirmed that the same results as in the prior art example could be obtained in the same way as in Examples 1 and 2. As shown, in this example verification can be obtained with a single beam spot of laser beam for writing while the writing is made. As has been described in the foregoing, with the method of and device for writing and reading optical data according to the invention, verification of the writing data can be obtained with a single beam spot while data is written. Thus, the time necessary for writing can be reduced. In addition, since it is not necessary to use a plurality of beams spots, complicated adjustment of optical system is unnecessary, so that it is possible to reduce cost. While the invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than limitation and that the invention is defined by the claims.

Claims: A method of writing and reading optical data using an optical data writing medium (5) having a writing film in which at least one of reflectivity and optical phase is variable depending on light irradiation, the method comprising verifying, simultaneously with the writing of the data, whether said data has been correctly written on said optical data writing medium (5), said method being characterized by comprising: writing and reading data with a single light spot generated by a laser (1); wherein the verification of writing the data is performed by comparing the magnitude of I w x (P r /P w ) with that of I r , wherein I w is a return light intensity from said optical data writing medium (5) during writing, I r is a return light intensity from said optical data writing medium (5) in a crystal state of the writing film during reading, P w is the laser power during writing, and P r is the laser power during reading. The method according to claim 1, in which a phase transition optical disk is used as said optical data writing medium. A device for writing and reading optical data using an optical data writing medium (5) having a writing film in which at least one of reflectivity and optical phase is variable depending on light irradiation, the device having means (7, 8, 9) for verifying, simultaneously with the writing of the data, whether said data has been correctly written on said optical data writing medium (5), the device being characterized by means (1, 2, 3, 4, 6, 10) for writing and reading data with a single light spot; wherein said verifying means (7, 8, 9) is arranged to compare the magnitude of I w x (P r /P w ) with that of I r , wherein I w is a return light intensity from said optical data writing medium (5) during writing, I r is a return light intensity from said optical data writing medium (5) in a crystal state of the writing film during reading, P w is the laser power during writing, and P r is the laser power during reading. A device for writing and reading optical data using an optical data writing medium (5) having a writing film in which one of reflectivity and optical phase is variable depending on light irradiation, the device having means (7, 8, 9) for verifying, simultaneously with the writing of the data, whether said data has been correctly written on said optical data writing medium (5), said device being characterized by : means (1, 2, 3, 4, 6, 10) for writing and reading data with a single light spot; wherein said verifying means comprises a divider (7) for dividing a return light intensity I w from said optical data writing medium (5) during writing by P w /P r , wherein P w is the laser power during writing and P r is the laser power during reading; and a comparator (8) for comparing the magnitude of I w x (P r /P w ) with that of a return light intensity from said optical data writing medium (5) in a crystal state of the writing film during reading.

Inventors: OHKUBO SHUICHI, OHKUBO, SHUICHI
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1996
Main classification: G11B7
IPC codes: G11B7, G11B20, G11B27