Optical information recording and reproducing apparatus

1. Field of the Invention

The present invention relates to an optical information recording and reproducing apparatus which is capable of recording information data on an optical recording medium and reproducing it therefrom.

2. Description of the Related Art

In order to read recorded information with high accuracy from an optical recording medium in which the information is recorded in a high-density state, it is necessary to exclude the influence of crosstalk exerted from tracks contiguous to both sides of a target track to be read.

To remove such crosstalk, in a pickup optical system, a laser beam is divided into three by means of, for example, a grating element so as to generate three laser beams, then irradiating the beams onto the target track and the contiguous tracks, whereby, the recorded information is read from three tracks simultaneously. Thereafter, a crosstalk component that has been superimposed in a readout signal that has been read from the target track is calculated, based on a readout signal that has been read from each of the contiguous tracks. The crosstalk component is then subtracted from the readout signal that has been read from the target track so as to remove the crosstalk.

When, however, the aforementioned optical system is also used to record information data on a target track, such a problem occurs that the laser beam is irradiated onto not only the target track but also contiguous tracks thereto and therefore the already recorded data on the contiguous tracks will be deleted because of the irradiation of the recording spot onto those contiguous tracks.

The present invention has been conceived to solve such a problem as mentioned above, and it aims to provide an optical information recording and reproducing apparatus which is capable of preventing recorded data from being unwontedly deleted within a recording operation mode and is capable of reading information with high accuracy as a result of the removal of crosstalk in the reproduction operation mode.

An optical information recording and reproducing apparatus according to the present invention is an optical information recording and reproducing apparatus for recording information on a recording medium and reproducing the information therefrom by irradiating a beam of light onto the recording medium. The apparatus has a laser generating element that generates a single laser beam and a laser beam irradiating means for, within a reproduction operation mode, dividing the laser beam into a plurality of divided laser beams and irradiating the laser beams individually toward a target track of the recording medium and, within a recording operation mode, reducing the quantity or amount of light of all but one beam of the laser beams in comparison with that one beam and irradiating them all onto the recording medium.

FIG. 1 shows a construction of an optical information recording and reproducing apparatus according to the present invention.

FIG. 2 shows a structure of a liquid crystal panel 102 .

FIG. 3 shows a reproduction start control flow in the optical information recording and reproducing apparatus according to the present invention.

FIG. 4 shows a record start control flow in the optical information recording and reproducing apparatus according to the present invention.

FIG. 5 shows operation timing at the start of recordal.

FIG. 6 shows a construction of the optical information recording and reproducing apparatus of another embodiment of the present invention.

Embodiments of the present invention will be described hereinafter.

FIG. 1 shows a construction of the optical information recording and reproducing apparatus of the present invention.

In FIG. 1, a record modulation circuit 1 applies an appropriate modulation processing to information data D supplied from a control circuit 20 which will be described later, and supplies a recording signal carrying thereon the modulated information data to a laser driver 2 . The laser driver 2 generates a laser driving signal that has a signal level corresponding to the recording signal and supplies the laser driving signal to a laser generating element 101 mounted in a recording and reproducing head 10 . The maximum value of the laser driving signal is adjusted in accordance with an optical power error value supplied from a subtracter 3 which will be described later.

The laser generating element 101 generates a laser beam that has an optical power corresponding to the laser driving signal supplied from the laser driver 2 and irradiates the laser beam to a liquid crystal panel 102 . An optical power detector 103 detects the optical power of the laser beam and supplies an optical power value LP, which indicates the level of the detected optical power, to a subtracter 3 . The subtracter 3 supplies a differential value between a target optical power value LP P supplied from a selector 4 and the optical power value LP to the laser driver 2 , the differential value being an optical power error value. The selector 4 selects either a read-optical power value LP R or a record-optical power value LP W in accordance with an optical power selection signal P SEL supplied from a control circuit 20 , and supplies the selected value to the subtracter 3 as a target optical power value LP P . The read-optical power value LP R is an optimum optical power of a laser beam that should be irradiated onto a recording disk in an information reading operation mode, and the record-optical power value LP W is the optical power of a laser beam needed in an information recording operation mode or an information deleting operation mode.

Therefore, according to the thus formed construction, the laser generating element 101 generates a laser beam that has an optical power indicated by the reading optical power value LPR in the information reading operation mode and irradiates this laser beam to the liquid crystal panel 102 . On the other hand, in the information recording operation mode or information deleting operation mode, the laser generating element 101 generates a laser beam that has an optical power indicated by the recordal optical power value LP W and irradiates this laser beam to the liquid crystal panel 102 .

FIG. 2 shows a structure of the liquid crystal panel 102 viewed from the optical axial direction of the laser beam.

As shown in FIG. 2, the liquid crystal panel 102 includes stripe-shaped transparent electrodes A and a liquid crystal layer C filled with liquid crystal molecules that have double refraction characteristics.

A liquid crystal driver 5 applies a predetermined liquid crystal driving potential to the transparent electrodes A of the liquid crystal panel 102 when a three-beam generation demand signal is supplied from the control circuit 20 , so that it results in changes of the twist angle of liquid crystal molecules that exist in a region covered with the transparent electrodes A among the liquid crystal molecules filled in the liquid crystal layer C. In this instance, the transparent electrodes A of the liquid crystal panel 102 as shown in FIG. 2 become a diffraction grating, and the liquid crystal panel 102 functions as a so-called grating element. Therefore, as shown in FIG. 2, when a beam spot SP formed by a laser beam is irradiated onto the liquid crystal panel 102 , first-order diffracted light in addition to zero-order diffracted light is generated by the diffraction grating. At this moment, the zero-order diffracted light and the first-order diffracted light are guided to a half mirror 104 as a main beam and as two side beams, respectively.

The liquid crystal driver 5 applies, for example, 0 volts to the transparent electrodes A when it receives a one-beam generation demand signal is supplied from the control circuit 20 , so that the liquid crystal panel 102 becomes a mere glass plate. Accordingly, the laser beam from the laser generating element 101 passes through the liquid crystal panel 102 without any division and is guided to the half mirror 104 as the main beam.

When, namely, a predetermined liquid crystal driving potential is applied to the transparent electrodes A, the liquid crystal panel 102 , serving as a grating element, divides a laser beam from the laser generating element 101 into a main beam and side beams and supplies the divided beams to the half mirror 104 , respectively. On the other hand, when a potential, such as 0 volts, lower than the predetermined liquid crystal driving potential is applied to the transparent electrodes A, the liquid crystal panel 102 supplies a laser beam supplied from the laser generating element 101 without any division to the half mirror 104 in the form of a main beam.

The half mirror 104 guides the main beam and the side beams that have been generated by the liquid crystal panel 102 to an objective lens 105 . The objective lens 105 converges the beams and irradiates them onto the recording surface of a recording disk 6 , such as a DVD (Digital Versatile Disc)-R, DVD-RW, DVD+RW, or DVD-RAM, that is a recordable optical recording medium. In more detail, the main beam is irradiated to a recording track at the center of three recording tracks that are contiguous to each other on the recording surface of the recording disk 6 , and the side beams are irradiated to the remaining recording tracks, respectively, that are contiguous to the center track. Thereafter, three reflected beams of light reflected from the three recording tracks are guided to optical detection surfaces of photodetectors 107 a - 107 c , respectively, through the objective lens 105 , the half mirror 104 , and a condensing lens 106 . The photodetectors 107 a - 107 c convert the three reflected beams condensed by the condensing lens 106 into readout signals a-c, respectively, each of which has a level corresponding to the quantity of light of each of the three reflected beams, and then output the signals a-c. In the output signals a-c, the readout signal b is what has been read from the center track of the three recording tracks, and the readout signals a and c are what have been read from the tracks contiguous to the center track.

A slider mechanism 7 transfers the recording and reproducing head 10 , on which the laser generating element 101 , the liquid crystal panel 102 , the optical power detector 103 , the half mirror 104 , the objective lens 105 , the condensing lens 106 , and the photodetector 107 are mounted, in a disk radial direction of the recording disk 6 .

Based on the readout signals a and c, a crosstalk removing circuit 8 calculates a crosstalk component superimposed on the readout signal b that has been read from the center recording track and subtract the crosstalk component from the component from the readout signal b so as to obtain a readout signal R which is free from the crosstalk.

Based on the signal level of the readout signal a or readout signal c, a side beam power judging circuit 9 judges whether the optical power of the side beam generated by the liquid crystal panel 102 has become lower than a predetermined value. If the circuit 9 judges that the optical power of the side beam has decreased to the predetermined value, it causes a side beam power judgment signal Sc to take the logical level “1”, and, if the circuit 9 judges that the optical power of the side beam is higher than the predetermined value, it causes the side beam power judgment signal Sc to take the logical level “0”. Thereafter, the circuit 9 supplies the judgment signal Sc to the control circuit 20 . If preferred, the side beam power judging circuit 9 may make the aforementioned judgment based on the signal level of the readout signal b of the main beam.

An operating device 21 is operated by an operator to accept a reproduction mode start operation and a recording mode start operation, and generates a reproduction start instruction signal and a recording start instruction signal that correspond to the respective operations. The operating device 21 supplies the instruction signal to the control circuit 20 .

When the reproduction start instruction signal is supplied from the operating device 21 , the control circuit 20 causes a reproduction mode for reproducing recorded data from the recording disk 6 . On the other hand, when the recording start instruction signal is supplied from the operating device 21 , the control circuit 20 causes a recording mode for recording data on the recording disk 6 .

FIG. 3 shows the schematic flow of the reproduction-mode control executed by the control circuit 20 when the reproduction start instruction signal is supplied from the operating device 21 .

In FIG. 3, the control circuit 20 first supplies to the slider mechanism 7 a slider-transferring signal for transferring the recording/reproducing head 10 to a desired reproducing start position on the recording disk 6 (step S 1 ). Then, the control circuit 20 supplies to the selector 4 an optical power selection signal P SEL for selecting the read-optical power value LP R as the optical power of a laser beam to be irradiated onto the recording surface of the recording disk 6 (step S 2 ). By carrying out the step S 2 , the laser generating element 101 generates a laser beam that has an optical power indicated by the read-optical power value LP R optimal in reading information. The laser generating element 101 then irradiates this laser beam to the liquid crystal panel 102 . Thereafter, the control circuit 20 supplies a three-beam generation demand signal to the liquid crystal driver 5 (step S 3 ). By carrying out step S 3 , the liquid crystal driver 5 applies a predetermined liquid crystal driving potential to the transparent electrodes A of the liquid crystal panel 102 . As a result, the liquid crystal panel 102 generates three beams that are one main beam and two side beams. At this moment, the side beams are each required to have such a quantity of light so as to enable the crosstalk removing circuit 8 to perform the crosstalk elimination process. The three beams are irradiated to three recording tracks, respectively, which are contiguous to each other on the recording surface of the recording disk through the half mirror 104 and the objective lens 105 . Thus, readout signals a-c are obtained that correspond to three reflected beams, respectively, that have been reflected from the three recording tracks. A readout signal R from which the crosstalk has been removed by the crosstalk removing circuit 8 is output finally.

Highly accurate information reading in which the influence of the crosstalk from the neighboring tracks has been excluded is performed by simultaneously reading recorded information from the three recording tracks contiguous to each other on the recording surface of the recording disk 6 in the reproduction operation mode in this way.

On the other hand, FIG. 4 shows the schematic flow showing the recording mode control executed by the control circuit 20 when a recording start instruction signal is emitted from the operating device 21 .

In FIG. 4, the control circuit 20 first supplies to the slider mechanism 7 a slider transferring signal for transferring the recording and reproducing head 10 to a desired reproducing start position on the recording disk 6 (step S 11 ). Thereafter, the control circuit 20 supplies a one-beam generation demand signal to the liquid crystal driver 5 (step S 12 ). By carrying out step S 12 , the liquid crystal driver 5 applies a potential of 0 volts to the transparent electrodes A of the liquid crystal panel 102 . Thus, the liquid crystal panel 102 reduces the quantity of light of the side beams among the three beams in comparison with that of the main beam. In other words, by carrying out step S 12 , the liquid crystal panel 102 substantially extinguishes the side beams so as to shift to a one-beam generation state of only the main beam.

Then, the control circuit 20 continues to judge whether the side beam power judgment signal Sc supplied from the side beam power judging circuit 9 is logical level “1” or not until the judgment signal Sc is judged as logical level “1” (step S 13 ). In other words, it waits is until the optical power of the side beam decreases to a predetermined value after applying the potential of 0 volts to the transparent electrodes A of the liquid crystal panel 102 .

When the side beam power judgment signal Sc is judged to be the logical level “1” in step S 13 , the control circuit 20 controls the optical power selection of a laser beam to be irradiated onto the recording surface of the recording disk 6 . That is, the control circuit 20 supplies an optical power selection signal P SEL for selecting the recordal optical power value LP W to the selector 4 (step S 14 ). By carrying out step S 14 , the laser generating element 101 generates a laser beam that has an optical power indicated by the recordal optical power value LP W that is required when information data is recorded. This laser beam is then irradiated onto the liquid crystal panel 102 . Then, the control circuit 20 initiates to supply information data D, which corresponds to an inputted information signal, to the record modulation circuit 1 (step S 15 ). By carrying out steps S 14 and S 15 , only the laser beam that has the optical power indicated by the recordal optical power value LP W is irradiated onto one recording track of the recording disk 6 as a main beam, so that an information signal that corresponds to the information data D is recorded. Since, at this moment, the two side beams have been substantially extinguished by step S 12 , recorded data is prevented from being deleted even though the two side beams are irradiated onto the recording surface.

As mentioned above, in the optical information recording and reproducing apparatus shown in FIG. 1, the single laser beam generated by the laser generating element 101 is guided to the recording surface of the recording disk 6 through the liquid crystal panel 102 . The liquid crystal panel 102 divides the single laser beam generated by the laser generating element 101 into three laser beams that are one main beam and two side beams, and supplies them to the recording disk 6 , respectively.

In the reproduction operation mode of the optical information recording and reproducing apparatus, the crosstalk removal that uses readout signals simultaneously read from the three recording tracks contiguous to each other that are formed on the recording surface of the recording disk 6 is carried out by the three laser beams.

On the other hand, in shifting from the reproduction operation mode to the recording operation mode in the optical information recording and reproducing apparatus, the quantity of light of each of the two side beams is first reduced, and then the optical power of the laser beam is switched from the reading optical power value LP R to the recordal optical power value LP W so as to start recording on the recording disk 6 . This operation prevents data from being deleted even though the side beam are irradiated onto the recording track on which the data is recorded. Herein, the liquid crystal panel 102 consumes a time period T 1 shown in FIG. 5 from the emission of the one-beam generation demand signal to the substantial extinguishment of the side beam because the speed of response is slow. If, therefore, the switching operation of the optical power of the laser beam is waited until the side beam is extinguished, a too much time will be consumed until the start of the recording on the disk 6 .

Therefore, according to the present invention, the optical power of a laser beam to be generated by the laser generating element 101 is designed to be switched to a record-optical power value LP W when the optical power of a side beam becomes lower than an optical power value PP shown in FIG. 5 even if the side beam is not extinguished completely. Herein, the fact that the optical power of the side beam has become lower than the optical power value PP means that the generation efficiency of the side beam generated by the liquid crystal panel 102 has decreased to such an extent that recorded data cannot be deleted by the side beam even if the laser beam that has the record-optical power value LP W begins to be irradiated at this time. Therefore, according to this control, a shift from the reproduction operation mode to the recording operation mode can be carried out swiftly without waiting for extinction of the side beam.

Since the response time of the liquid crystal panel 102 is changed in dependence on the atmospheric temperature, the optical power of a laser beam to be generated by the laser generating element 101 may be switched after the expiration of the predicted response time that corresponds to the atmospheric temperature.

FIG. 6 shows a construction of the optical information recording and reproducing apparatus according to another embodiment of the present invention that has been made in view of the above.

The optical information recording and reproducing apparatus shown in FIG. 6 is different from that of FIG. 1 in that the side beam power judging circuit 9 is omitted and a temperature sensor 41 for measuring the atmospheric temperature and a liquid crystal response time memory 42 are provided. The predicted response time of a liquid crystal element is preserved corresponding to each temperature in the liquid crystal response time memory 42 . After step S 12 shown in FIG. 4 is carried out, the control circuit 20 reads the liquid crystal response time that corresponds to a temperature measured by the temperature sensor 41 from the liquid crystal response time memory 42 and the stage proceeds to the next step S 14 after the lapse of the read response time.

In this embodiment, in the recording operation mode, the side beam is substantially extinguished by applying a liquid crystal driving potential of 0 volts to the transparent electrodes A of the liquid crystal panel 102 . However, the side beam does not necessarily need to be extinguished. In fact, in the recording operation mode, the driving control liquid crystal panel 102 is merely required to be driven and controlled so as to reduce the quantity of light of the side beam to such an extent that recorded data cannot be deleted at least. In other words, the potential to be applied to the transparent electrodes A of the liquid crystal panel 102 may be other than that of 0 volts.

As described above in detail, according to the optical information recording and reproducing apparatus of the present invention, recorded data can be prevented from being deleted in the recording operation mode, and, in the reproduction operation mode, the data can be reproduced in a highly accurate state in which a crosstalk has been removed.

The present invention has been described above with reference to the preferred embodiments. Any person skilled in the art should understand that the present invention can be variously modified or varied without departing from the spirit of this disclosure and the scope of the appended claims. Such modifications or variants are all to be covered by the appended claims.