Abstract:
A device for checking the recording state of a magneto-optical recording disk includes a detector for detecting a s-polarized light component and a p-polarized light component from a reflected light reflected from the portion of the magneto-optical recording disk. One of the s-polarized and p-polarized light components is subtracted from the other to produce a difference signal and the s-polarized and p-polarized light components are added to produce an addition signal. The difference signal is divided by the addition signal to produce a normalized detection signal. The recording state is determined based on a level change of the normalized detection signal while data is being recorded onto the magneto-optical recording disk.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to an optical disk recording apparatus, and in particular to method and device for checking or verifying the recording state of data. 
     2. Description of the Related Art 
     As a type of information recording technology, magneto-optical recording has been widely used to store a large amount of data onto a magneto-optical disk in which a laser beam is used to heat a small portion of the disk. The heating causes a weak magnetic field to change the orientation of the portion, thus recording onto the disk. The recorded data onto the disk is reproduced by using the magneto-optical Kerr effect which occurs when plane polarized light is reflected from the surface of the disk with slight elliptical polarization depending on the polarity of the reflecting portion on the disk. The magneto-optical Kerr effect is also used to check or verify the recording state of data. 
     There has been proposed a check method which can check the recording state while data is being recorded on the magnetic-optic disk in Japanese Patent Unexamined Publication No. 8-221911. According to this conventional method, when a recording beam produces a spot on the disk, s-polarized and p-polarized light components are detected from the reflected light at the spot and then a difference signal is produced by subtracting the one light component from the other. The amplitude of the different signal is initially increased and then decreased when the heating by the recording beam causes a decrease in the Kerr rotation angle. Since such an amplitude change of the difference signal ideally reflects the Kerr rotation angle, it can be used to check the recording state of data on the disk while data is being recorded. 
     SUMMARY OF THE INVENTION 
     However, the inventor found that actually an amplitude change of the difference signal (ΔV AMP ) is proportional to the product of intensity of recording laser beam (Pw), reflectance of the disk (R), and a change of the Kerr rotation angle (θk1-θk2), where θk1 is a Kerr rotation angle at the initial time when the amplitude of the difference signal reaches the maximum and θk2 is a Kerr rotation angle when the recording laser beam has heated the spot of the disk, that is, ΔV AMP  ∝ Pw×R×(θk1-θk2). In other words, the amplitude change of the difference signal reflects not only the change of the Kerr rotation angle (θk1-θk2) but also the laser beam power (Pw) and the disk reflectance (R) which are noise components, resulting in the reduced accuracy of verify operation. 
     An object of the present invention is to provide method and device which can check the recording state of data on a magneto-optic disk with sufficiently high accuracy. 
     According to an aspect of the present invention, a device for checking a recording state of a magneto-optical recording medium is comprised of a recording head for emitting a recording laser beam onto a portion of the magneto-optical recording medium. Further, the device includes a first detector for detecting a change of Kerr rotation angle from a reflected light reflected from the portion of the magneto-optical recording medium to produce a change detection signal, a second detector for detecting an intensity of the reflected light to produce an intensity detection signal, and a compensator for compensating the change detection signal using the intensity detection signal to produce a normalized detection signal. The recording state of data is determined based on a level change of the normalized detection signal. 
     According to another aspect of the present invention, a device includes a detector for detecting a first and second polarized light components from a reflected light reflected from the portion of the magneto-optical recording medium, wherein the first and second polarized light components are orthogonal to each other. The device further includes a subtracter, an adder, and a division calculator. The subtracter subtracts one of the first and second polarized light components from the other to produce a difference signal. The adder adds the first and second polarized light components to produce an addition signal. And the division calculator divides the difference signal by the addition signal to produce a normalized detection signal. The recording state is determined based on a level change of the normalizing detection signal. 
     As described before, an amplitude change (ΔV AMP ) of the difference signal reflects not only a change of the Kerr rotation angle (θk1-θk 2 ) but also the laser beam power (Pw) and the disk reflectance (R), that is, ΔV AMP  ∝ Pw×R×(θk1-θk2). According to the present invention, the adder produces the addition signal which is proportional to the product of the laser beam power (Pw) and the disk reflectance (R). Therefore, by dividing the difference signal by the addition signal to produce the normalized detection signal, the difference signal is compensated for noise components of the laser beam power (Pw) and the disk reflectance (R). Therefore, an amplitude change of the normalized detection signal reflects only the Kerr rotation angle (θk1-θk2), resulting in accurate verify operation of the magneto-optical recording medium 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing a magneto-optical disk recording apparatus employing a recording state check device according to an embodiment of the present invention; and 
     FIGS. 2A-2E are waveform diagrams for explanation of a verify operation of the embodiment as shown in FIG. 1. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, a magnetic-optical disk recording apparatus is provided with a disk rotating mechanism and an information read/write system. A magneto-optical disk 101 is detachably fixed to a turntable 102 which can be rotated by a driving motor 103. Information reading and writing are performed by an optical head which is provided on the recording side of the magneto-optical disk 101. 
     The optical head includes a recording head 104, an s-polarized light detector 105 and a p-polarized light detector 106. Further, the optical head is equipped with an auto-focusing and auto-tracking mechanism, a seek mechanism, and a magnetic field generator which are not shown in this figure for simplicity. The magnetic field generator such as an electromagnet is used to apply a magnetic field to a small portion which is heated by a recording laser beam so as to record data onto the magneto-optical disk 101. 
     The recording head 104 has a laser source which emits a recording laser beam LB W  to the magneto-optical disk 101 depending on data received from a data processor 107. As described before, when the small portion on the magneto-optical disk 101 is radiated with the recording laser beam LB W , the portion is heated to change in magnetic orientation depending on the applied magnetic field. At the same time, the recording laser beam LB W  is reflected from the portion on the magneto-optical disk 101 and the reflected light is detected by the s-polarized light detector 105 and the p-polarized light detector 106. Since the reflected light changes in Kerr rotation angle depending on a change of the orientation caused by the heating and the applied magnetic field, the Kerr rotation angle can be detected based on the s-polarized and p-polarized components of the reflected light which are detected by the s-polarized light detector 105 and the p-polarized light detector 106, respectively. 
     The s-polarized component signal S s  detected by the s-polarized light detector 105 is output to a subtracter 108 and an adder 109. The p-polarized component S p  detected by the p-polarized light detector 106 is also output to subtracter 108 and the adder 109. The subtracter 108 subtracts the one from the other to produce a difference signal S SUB . The adder 109 adds them to produce an addition signal S ADD . An operational circuit 109 divides the difference signal S SUB  by the addition signal S ADD  to produce a normalized detection signal S DET  which is output to a recording state determination section. 
     Further, the recording state determination section receives a timing signal from the data processor 107 through a delay section 111. More specifically, the data processor 107 outputs a timing signal T WR  to the delay section 111 when the data to be written is output to the recording head 104. The delay section 111 delays the data timing signal T WR  by a predetermined delay time DL to produce a sampling duration signal T D  which is output to the recording state determination section. 
     The recording state determination section is implemented with a sampler 110, a level change detector 112, a comparator 113 and other necessary memories (not shown). The sampler 110 samples detection data from the normalized detection signal S DET  for a time period determined by the sampling duration signal T D . The level change detector 112 detects a level change ΔV from the normalized detection signal S DET  for the sampling duration. The comparator 113 compares the level change ΔV to a predetermined threshold ΔV TH  to produce a verify result depending on whether the level change ΔV is greater than the predetermined threshold ΔV TH . 
     The recording state determination section may be implemented with a single-chip microcomputer including a memory storing a verify operation program and the other circuit blocks 107-109 may be implemented with dedicated hardware circuits. The circuit blocks 107-113 may be also implemented with a program-controlled processor running the verify operation program. Alternatively, all the circuit blocks 107-113 may be also implemented with dedicated hardware circuits. Further, the verify operation program may be stored onto a storage such as a floppy disk or CD-ROM and if may be installed onto the microcomputer. 
     The details of the verify operation will be described hereafter referring to FIGS. 2A-2E. 
     Referring to FIG. 2A, it is assumed that the recording data is output to the recording head 104 which emits the recording laser beam LB W  to the magneto-optical disk 101 depending on the recording data. The recording laser beam LB W  is reflected from the portion on the magneto-optical disk 101 and the reflected light is detected by the s-polarized light detector 105 and the p-polarized light detector 106. As described before, when the small portion on the magneto-optical disk 101 is radiated with the recording laser beam LB W , the portion is not heated initially, resulting in no change in the Kerr rotation angle. Therefore, the amplitude of the difference signal S SUB  obtained by the subtracter 108 is initially increased and then decreased when the heating by the recording laser beam LB W  causes a change in the Kerr rotation angle as shown in FIG. 2B. 
     Referring to FIG. 2B, after a lapse of the delayed time DL, the amplitude of the difference signal S SUB  is increased to the peak value and is then decreased to a stable value when the heating by the recording laser beam LB W  causes a change in the Kerr rotation angle. As described before, the difference ΔV AMP  reflects not only a change of the Kerr rotation angle (θk1-θk2) but also the laser beam power (Pw) and the disk reflectance (R), that is, ΔV AMP  ∝ Pw×R×(θk1-θk2), when θk1 is a Kerr rotation angle at the initial time when the amplitude of the difference signal reaches the peak value and θk2 is a Kerr rotation angle at the time when the amplitude of the difference signal reaches the stable value. 
     As shown in FIG. 2C, on the other hand, the addition signal S ADD  obtained by the adder 109 is proportional to the product of the laser beam power (Pw) and the disk reflection (R), that is, S ADD  ∝ Pw×R. 
     As shown in FIG. 2D, the normalized detection signal S DET  is obtained by dividing the difference signal S SUB  by the addition signal S ADD , that is, S DET  =S SUB  /S ADD . Therefore, an amplitude change ΔV of the normalized detection signal S DET  is proportional to only a change of the Kerr rotation angle, that is, ΔV ∝ (θk1-θk2). In other words, by detecting the amplitude change ΔV of the normalized detection signal S DET , the recording state can be verified with accuracy. 
     Referring to FIG. 2E, the sampler 110 samples detection data from the normalized detection signal S DET  for a time period determined by the sampling duration signal T D  which is delayed by the delay section 111 by the delay time DL. The level change detector 112 sequentially receives the detection data from the sampler 110 and compares the current sampled data to the previous sampled data to detect a level change ΔV between them. 
     The comparator 113 compares the level change ΔV to the predetermined threshold ΔV TH  to produce a verify result. More specifically, when the level change ΔV is greater than the predetermined threshold ΔV TH , the recording state is determined to be good or acceptable and otherwise no good or unacceptable.