The present invention relates to a recording (including erasing) and reproducing method in information recording apparatuses such as an optical disk system wherein information is recorded by projecting an energy beam. More particularly, it relates to a method of recording and reproducing information which employs a recording film, e.g., a magneto optic recording film, or a reversible phase transition type capable of high-speed phase transition and which is capable of the so-called "overwrite" wherein new information is recorded while existing information is being erased.
There have been known various systems which perform recording on the basis of the projection of an energy beam such as a light beam or an electron beam. Among them, a method wherein a laser beam, for example, is projected on a reversible phase transition type optical recording medium to rewrite recording includes (1) a method disclosed in Japanese Patent Application Laid-open No. 71140/1984. In this method, an elliptical light spot longer in the direction of a track (guide groove) and a circular light spot are employed. The track in which information is to be written is first crystallized by the continuous light projection of the elliptical light spot. Subsequently, the power of the circular light spot passing on the track is raised in the shape of pulses in accordance with information signals, whereby the information is recorded by amorphization, namely, the turning of the crystal into an amorphous state, attendant upon melting and quenching. In addition,
(2) Japanese Patent Application Laid-open No. 28530/1980 discloses a method wherein the power of a single light beam is changed between a noncrystallization power level and a crystallization power level, thereby to record or erase information. Further, as another example employing a single light beam, (3) Japanese Patent Application Laid-open No. 145530/1981 discloses a method wherein, in writing or rewriting information into a recording film crystallized up to perfect saturation, a light beam is projected which is intensity-modulated according to information signals between a amorphization power level and a crystallization power level.
Meanwhile, in case of recording information on or erasing recorded information from an optical disk, it is necessary to verify if the information to be recorded or erased is actually recorded or erased. In a prior-art method which employs an optical head having a single laser beam, the verification is done in such a way that one revolution of the disk is awaited after the recording or erasure, whereupon the power of the laser beam is lowered to a read power level. Besides, as regards a pitting write-once type optical disk, a method wherein, if recording is properly performed is verified by detecting the reflected light of recording light during a recording operation, is disclosed in (4) Japanese Patent No. 1264450. However, as regards a write-once or rewritable type optical disk utilizing the change of an atomic arrangement such as the phase transition, the reflected light waveform of recording light differs from that of the pitting type, and hence, there has not been an example wherein the propriety of recording or erasure is verified by detecting the reflected light of the recording light or erasing light.
Among the prior-art techniques mentioned above, the method which employs the two beams of a light beam for forming the elliptical light spot and a light beam for forming the circular light spot is further classified into two. One of them is a method wherein, in order to project the two beams on an identical track, the relative positions between the beams are fixed so that when one beam is positioned on the track, the other beam may be projected on the same track. With this method, however, a positional error is prone to develop due to, e.g., the deviation of an optical system ascribable to a temperature change or vibrations. With the other method which uses both the beams for tracking, the above problem is solved. Since, however, the elliptical light spot affords a low resolution, it is difficult to read a concavity or convexity or the like on the disk expressive of a track address, and it cannot be verified that the two beams fall on an identical track.
Among the aforementioned prior-art techniques, each method employing the single light beam is free from such problems. However, the certainty of rewriting might degrade, and recording information at high reliability is not easy.
Besides, in the prior-art technique concerning the optical disk which utilizes the atomic arrangement change such as phase transition, a period of time corresponding to one revolution of the disk (for example, 33 ms. for 1800 r.p.m.) is expended in surplus for verifying the recording or erasure. This leads to the problem of a long access time.
USPTO Backgrounds
USPTO Backgrounds