Optical information reading and reproducing apparatus using pseudo DC-free codes

An optical information recording and reproducing apparatus includes a random information generating section for generating predetermined random information. A recording information generating section generates recording information on the basis of non-DC-free information and the predetermined random information. A synchronization sensing section senses a synchronization information. A recording section records the recording information in the recording area of a recording medium, on the basis of the synchronization information. A reproducing section reproduces the recording information recorded by the recording section.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an optical information reading and reproducing 
apparatus which records and reproduces onto and from an optical 
information recording medium pseudo DC free codes generated on the basis 
of non-DC-free code information. 
2. Description of the Related Art 
Various methods of recording information onto an optical information 
recording medium such as an optical disk have been proposed. 
For example, the existing optical information recording and reproducing 
apparatuses using 130-mm or 90-mm ISO standardized optical disks have been 
using a method of recording information onto an optical information 
recording medium by assigning information to the distance between pits by 
pit-position recording techniques. To double the memory capacity of the 
130-mm ISO standardized optical disk, a second-generation optical 
information recording and reproducing apparatus has been proposed which 
employs the MCAV system that records information at almost equal recording 
density from the innermost to the outermost circumference. Even the 
second-generation optical information recording and reproducing apparatus 
uses a method of recording information onto an optical information 
recording medium by assigning information to the distance between pits by 
pit-position recording techniques. 
In contrast, to triple the memory capacity of optical disks, mark-edge 
recording techniques have been proposed which assign information to the 
length of the pit, since it is difficult to increase the recording density 
by pit-position recording techniques. 
With pit-position techniques, information exists between peak points of the 
reproduced signal from the recording medium. Thus, by obtaining the 
first-order 10 differential of the reproduced signal and then slicing its 
zero-crossing point, the information can be reproduced. Specifically, even 
when the recording information is modulated in 2-7 modulation codes, not 
DC-free codes, as shown in FIG. 11A, the resulting pit-position recording 
signal is a signal corresponding to "0" and "1" in the 2-7 modulation code 
system, as shown in FIG. 11B. Thus, the pit-position recording pits are 
formed as shown in FIG. 11C, which therefore introduces no problem to the 
reproduction of information at all. 
In the case of mark-edge recording techniques proposed to increase the 
recording density, however, the resulting mark-edge recording signal is a 
signal corresponding to the change from "0" to "1" in the 2-7 modulation 
code system, so that the mark-edge recording pits are as shown in FIG. 
11E. Specifically, because information is assigned to the distance between 
edges of the reproduced signal from the recording medium, accurate 
reproduction of information from the reproduced signal from the recording 
medium can be achieved by obtaining the second-order differential of the 
reproduced signal and then slicing its zero-crossing point. The 
second-order differential technique wherein the reproduced signal is 
passed through a differentiator twice has an S/N disadvantage in that it 
amplifies noises in high-frequency bands. 
A level-slicing method as disclosed in Jpn. Pat. Appln. KOKAI Publication 
No. 61-45470 can be considered to be another method of reproducing the 
information recorded by mark-edge recording techniques. In this case, when 
recording information is modulated in 2-7 or 1-7 modulation codes, not 
DC-free codes, the level-slicing method cannot accurately sense the edges 
of the reproduced signal from the recording medium, since the slicing 
level varies with the pattern of the reproduced signal due to AC coupling 
in the reproduction system. 
To overcome this drawback, there has been proposed a method which, in the 
case of optical disks complying with a proposal for 130-mm ECMA 
standardization (ECMA/TC31/92/36) using a method of recording by assigning 
information to the length of the pit by mark-edge recording techniques, 
obtains the DSV (digital sum value) of 1s and 0s of the recording pits in 
the data portion before and after the resink pattern of the data area on 
the optical disk (i.e., obtaining the sum of 1s and that of 0s), and 
selecting and recording two types of resink patterns, depending on whether 
the number of 1s is larger than that of 0s. Then, the polarity of the 
recording pattern in the following data section is reversed to form a 
pseudo DC-free code, which is then recorded. In a reproducing operation, 
the two types of resink patterns are sensed and it is judged whether the 
following data is reversed or not. Then, the signal is further processed 
to reproduce the data. 
In the proposal for 130 mm ECMA standardization, recording patterns are 
converted into pseudo DC-free codes on the basis of two types of sink 
patterns. However, it is virtually difficult to convert the recording data 
pattern into DC free codes on the basis of only two types of sink 
patterns. As a result, there is no guarantee that the DSV of 1s will be 
equal to the DSV of 0s. Therefore, it is impossible to basically overcome 
the problem encountered when a method of modulating recording information 
is not based on DC-free codes. 
SUMMARY OF THE INVENTION 
Accordingly, the object of the present invention is to provide an optical 
information recording and reproducing apparatus and an optical information 
reproducing apparatus which enable the high-density recording and 
reproducing of information by creating recording information on the basis 
of non-DC free information and random information. 
The foregoing object is accomplished by providing an optical information 
recording and reproducing apparatus which, on the basis of non-DC-free 
information, records information on a recording medium, the recording 
medium having a synchronization area in which synchronization information 
is recorded and a recording area for recording information, comprising: 
random information generating means for generating predetermined random 
information; recording information generating means for generating 
recording information on the basis of the non-DC-free information and the 
predetermined random information from the random information generating 
means; synchronization sensing means for sensing the synchronization 
information recorded in the synchronization area; recording means for 
recording the recording information from the recording information 
generating means in the recording area on the basis of the synchronization 
information sensed by the synchronization sensing means; and reproducing 
means for reproducing the recording information recorded by the recording 
means. 
The foregoing object is also accomplished by providing an optical 
information reproducing apparatus which reproduces information from a 
recording medium having a synchronization area in which synchronization 
information is recorded and a recording area in which recording 
information generated on the basis of non-DC-free information and 
predetermined random information is recorded, comprising: reproducing 
means for reproducing the recording information recorded in the recording 
area; and reproduction information generating means for generating 
reproduction information on the basis of the recording information 
reproduced by the reproducing means and the predetermined random 
information.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1 through 10 are related to a first embodiment of the present 
invention. Specifically, FIG. 1 is a block diagram of an optical-disk 
recording and reproducing apparatus; FIGS. 2A and 2B are circuit diagrams 
of the pit-position/mark-edge converting circuit and the 
mark-edge/pit-position converting circuit of FIG. 1, respectively; FIGS. 
3A through 3E are timing charts for explaining the operation of the 
mark-edge/pit-position converting circuit of FIG. 2; FIG. 4 is a 
conceptual diagram of the scramble circuit and the descramble circuit of 
FIG. 1; FIG. 5 is a block diagram of the scramble circuit and the 
descramble circuit of FIG. 1; FIG. 6 is a circuit diagram of the scramble 
circuit and the descramble circuit of FIG. 1; FIG. 7 is a circuit diagram 
of the sink/resink sensing circuit of FIG. 1; FIGS. 8A and 8B are timing 
charts for explaining the operation of the scramble/descramble control 
circuit of FIG. 1; FIG. 9 is a circuit diagram of the automatic optimum 
level slicing circuit of FIG. 1; and FIG. 10 is a circuit diagram of a 
modification of the automatic optimum level slicing circuit of FIG. 1. 
As shown in FIG. 1, the optical-disk recording and reproducing apparatus 1 
according to the first embodiment of the present invention records and 
reproduces information on and from an optical disk 6 conforming to, for 
example, 130-mm ECMA standardization. The apparatus 1 comprises: an 
optical head 8 which records and reproduces information by projecting 
laser light onto the optical disk 6 rotated by a spindle motor 4 actuated 
by a motor driving circuit 2; a head driving control section 10 which 
actuates the optical head 8, and a system control section 12 which 
transfers modulated data to be recorded to the head driving control 
section 10 and demodulates the data from the reproduced signal from the 
head driving control section 10. 
The optical head 8 gathers the laser light from a laser diode 14 onto the 
recording surface of the optical disk 6 through an object lens 16 via a 
beam splitter 15. The laser diode 14 is designed to project recording 
laser light in a recording operation and reproducing laser light in a 
reproducing operation. The reflected light of the reproducing laser light 
from the optical disk 6 passes through the object lens 16 and the beam 
splitter 15 and is sensed by a detector 17. The sensed light is amplified 
by a head amplifier 18 to form a reproduction signal. The object lens 16 
is designed to be driven by an actuator 20 for a known tracking and focus 
servo operation. 
The head driving control section 10 comprises: a laser power controller 22 
which controls the laser power of the laser diode 14; a reproduction 
signal correction circuit 26 which takes in the reproduction signal from 
the head amplifier 18 via an AC coupling 24 and makes corrections 
including waveform shaping; an automatic optimum level slicing circuit 28 
which optimizes the slice level according to the output of the 
reproduction signal correction circuit 26 and converts the input into a 
logic level signal; and a data separator 30 which extracts the reproduced 
data synchronized with a specific reproducing clock from the logic level 
signal from the automatic optimum level slicing circuit 28. 
The system control section 12 is provided with a control MCU (multi-control 
unit) 32, which communicates with an external host computer (not shown) 
via an SCSI controller 34 with a buffer memory 35 capable of temporarily 
storing the recorded or reproduced data. The control MCU 32, which is 
started on the basis of a control program stored in a program ROM 36a of a 
main memory section 36, creates recording data in the data RAM 36b of the 
main recording section 36 according to the control program, and stores the 
reproduced data from the optical disk in the data RAM 36b. 
In a recording operation, the recording data created by the control MCU 32 
is modulated by a modulation and demodulation circuit 38 into non-DC-free 
codes, for example, a 2-7 modulation pit-position recording signal. This 
pit-position recording signal is converted into a mark-edge recording 
signal by a pit-position/mark-edge converting circuit 40. The mark-edge 
recording signal is scrambled at a scramble circuit 42 acting as random 
information generating means and converted into recording data of pseudo 
DC-free codes, which are then transferred to the laser power controller 22 
of the head driving control section 10. 
In a reproducing operation, the synchronized reproduction data from the 
data separator 30 is descrambled at a descramble circuit 44 to produce a 
mark-edge reproduction signal. This mark-edge reproduction signal is 
converted into a pit-position reproduction signal by a 
mark-edge/pit-position converting circuit 46. The pit-position 
reproduction signal is demodulated by the modulation and demodulation 
circuit 38. The demodulated signal undergoes error correction at an error 
correction LSI 48. The control MCU 32 stores this corrected signal as the 
reproduced data in the data RAM 36b. 
The scramble circuit 42 and the descramble circuit 44 are required to 
operate with the data area from which the VFO section, the sink section 
and the resink section on the optical disk 6 are excluded. In the present 
embodiment, to control the timing, the system control section 12 is 
provided with a switch 50 which selects the pit-position recording signal 
from the modulation and demodulation circuit 38 in a write operation and 
the synchronized reproduction data from the data separator 30 in a read 
operation under the control of the control MCU 32, and a sink/resink 
sensing circuit 52 which senses a sink byte or a resink byte from the 
pit-position data or the synchronized reproduction data. The 
scramble/descramble control circuit 54 generates a timing signal from the 
sink byte or the resink byte sensed at the sink/resink sensing circuit 52, 
the timing signal causing the scramble circuit 42 to operate in a write 
operation and the descramble circuit 44 to operate in a read operation for 
a certain period of time in order to scramble or descramble the data area 
from which the VFO section, the sink section, and the resink section are 
excluded. 
The pit-position/mark-edge converting circuit 40 can be composed of a 
flip-flop 40a as shown in FIG. 2A. After the flip-flop 40a has been reset 
by a reset signal (RESET) from the control MCU 32, the pit-position 
recording signal is supplied to a clock terminal (CK) and the inverted 
output is supplied to an input terminal (D). This causes the output of an 
output terminal (Q) to be inverted each time the pit-position recording 
signal is supplied, thereby producing a mark-edge recording signal. 
As shown in FIG. 2B, the mark-edge/pit-position converting circuit 46 can 
be made up of two flip-flops 46a and 46b and an exclusive OR gate 46c. As 
shown in FIGS. 2B and 3, the clock terminals (CKs) of the two flip-flops 
46a and 46b are supplied with a 2f clock acting as a synchronizing clock 
(f is a data transfer clock). In the flip-flop 46a, the mark-edge 
reproduction signal (FIG. 3A) is latched with a 2f clock (FIG. 3B) (output 
a: FIG. 3C). In the flip-flop 46 in a subsequent stage, the mark-edge 
reproduction signal is latched with a delay of a period of 2f clock 
(output b: FIG. 3D). By XORing output a and output b with the exclusive-OR 
gate 46c, a pit-position reproduction signal (FIG. 3E) can be obtained. 
The scramble circuit 42 and the descramble circuit 44 are each basically 
composed of an n-stage shift register with feedback from the mth stage. 
The scrambled data sequence is expressed by the equation: 
EQU Am=(Bm@Am-j@Am-n) 
where @ indicates addition in mode 2 (modulo 2). The descrambled data 
sequence is expressed by the equation: 
##EQU1## 
Thus, the output of the descrambling operation is equal to the original 
sequence. 
As shown in a block diagram of the scramble circuit 42 and the descramble 
circuit 44 in FIG. 5, each of them is composed of ten shift registers 55a 
through 55j, two adders 56a and 56b, and a switch 57. They produce a 
scramble signal meeting the following polynomial from the clock: 
EQU f(X)=X.sup.10 +X.sup.5 +1 
Then, they scramble the input signal using this scramble signal and 
produces a 10th-degree M-system PN signal. Here, the adders 56a and 56b 
add two inputs in mode 2 (modulo 2), giving the results shown in the table 
below: 
______________________________________ 
Input Output 
______________________________________ 
A B C 
0 0 0 
0 1 1 
1 0 1 
1 1 0 
______________________________________ 
As shown in a circuit diagram of the scramble circuit 42 and the descramble 
circuit 44 in FIG. 6, each of them is made up of a random data generator 
60 composed of 10 shift registers, each consisting of a flip-flop 68n and 
an OR circuit 70n (n=a to j), an exclusive OR gate 62, and a data selector 
64. Here, the clock frequency is the same as that of the medium VFO 
section, that is, 2f/6 for 2-7 modulation and 2f/4 for 1-7 modulation (f 
is a data transfer clock). A SET signal goes high (Hi) immediately before 
the transfer of the data following the sink or the resink, to reset the 
outputs Qs of all flop-flops 68n (n=a to j). 
The random data generator 60 may be composed of a memory circuit such as a 
ROM that has stored specified random data previously. It may read the 
random data in a scrambling or a descrambling operation, and then scramble 
or descramble the input data using the random data. 
with the circuit configuration as shown in FIG. 7, when, for example, the 
sink pattern (or the resink pattern) is "0001001101011110", the 
sink/resink sensing circuit 52, acting as synchronizing sensing means, can 
sense the sink pattern (or the resink pattern). On the basis of this sink 
sense signal, the scramble/descramble control circuit 54 generates a 
scramble control signal (or a descramble control signal) shown in FIG. 8B 
for the data area according to the data format of the optical disk 6 shown 
in FIG. 8A, and then controls the operation of the scramble circuit 42 (or 
the descramble circuit 44). 
A circuit diagram of the automatic optimum level slicing circuit 28 is 
shown in FIG. 9, and another circuit diagram of the slicing circuit is 
shown in FIG. 10. Since in the embodiment where pseudo DC-free codes and 
information mark-edge recorded are reproduced with the automatic optimum 
level slicing circuit 28, the average distance between 0 outputs and that 
between 1 outputs of a comparator that compares with a specified slice 
level are equal, the specified slice level can always be controlled, 
thereby making it possible to shape the waveform of a logic level signal 
with the optimum slice level. 
The optical disk 6 consists of such a disk as a postscript-type optical 
disk, a phase-change-type optical disk, or a magneto-optical disk. 
As described above, with the optical-disk recording and reproducing 
apparatus according to the first embodiment of the present invention, 
pseudo DC-free codes can be produced in a modulation method using 
non-DC-free codes such as those in 2-7 or 1-7 modulation, thereby 
recording information on an optical disk using a mark-edge recording 
method suitable for high recording density. In addition, a level slice 
method that does not amplify high-frequency components unlike a 
second-order differential method, can be used as a reproduction method. 
Consequently, it is possible to record and reproduce information 
accurately. 
Since in automatic optimum level slicing in the embodiment that realizes 
the above level slicing method, the specified slice level is always 
controlled, it is possible to correct the deviation of conditions in 
recording (in optical modulation recording, the deviation of the recording 
domain due to a change in the optimum light power and in the medium 
sensitivity, and in magnetic field modulation, the deviation of the 
recording domain due to a change in the recording magnetic field intensity 
and the medium sensitivity). 
Further, with the optical-disk recording and reproducing apparatus of this 
embodiment, 2-7 or 1-7 modulation data is scrambled or descrambled for 
mark-edge recording, thereby enabling the effective use of a circuit used 
in a conventional optical-disk recording and reproducing apparatus which 
provides pit-position recording by 2-7 or 1-7 modulation. This makes the 
apparatus of the embodiment compatible with conventional apparatuses, 
thereby lowering manufacturing costs. 
As explained above, with the optical information recording and reproducing 
apparatus of the first embodiment, since non-DC-free code information is 
XORed with random information to produce recording information, and 
mark-edge recording the recording information in the recording area of an 
optical information recording medium on the basis of synchronizing 
information, this enables the recording information to be converted into 
pseudo DC-free codes, thereby making it possible to record and reproduce 
information at high density. 
Hereinafter, a second embodiment of the present invention will be 
described. In this embodiment, pseudo DC-free codes generated by the 
method of the first embodiment, or almost DC-free codes, are written onto 
a recording medium in a formatting operation or/and an erasing operation. 
FIGS. 12 through 15 are related to a second embodiment of the present 
invention. FIG. 12 is a schematic diagram of a magneto-optical disk 
apparatus of the second embodiment; FIG. 13 is a circuit diagram of the 
edge sensing circuit of FIG. 12; FIG. 14 shows the signal waveform of each 
portion in FIG. 13; and FIG. 15 is a flowchart for the operation of the 
second embodiment. 
As shown in FIG. 12, in a magneto-optical disk apparatus 101 of the second 
embodiment, a magneto-optical pickup (hereinafter, referred to as a 
pickup) 104 is positioned so as to face one surface of a magneto-optical 
disk 103 rotated by a spindle motor 102 at a specified rotational speed, 
and a bias magnetic field generating section 105 is located so as to face 
the other surface of the disk 103. The magneto-optical disk 103 is a 
recording medium allowing the rewriting of the recorded information. 
Information can be recorded on, reproduced from, and erased from the disk 
103 with the pickup 104. 
A laser diode (LD) 106 is housed in the pickup 104. The laser light 
generated by the laser diode 106 is gathered through a beam splitter, etc. 
(not shown) and through an object lens 107 and projected onto (the 
vertical magnetization film via the transparent substrate of) the 
magneto-optical disk 103 to form a very small light spot. 
The reflected light from the vertical magnetization film returns along an 
incident light path and directed by the beam splitter to the direction 
different from that of the incident light path. This light is then 
received by an optical sensor 108. This optical sensor is provided with a 
pair of photodiodes 108a and 108b (see FIG. 13) to sense the information 
signal recorded on the vertical magnetization film. The optical sensor 108 
also senses a control signal for focusing and tracking. The output signal 
from the optical sensor 108 is supplied to a reproduction signal 
processing section 109, which performs signal processes including 
binarization and modulation, and supplies the resulting signal via a CPU 
111 to an external controller 112 such as a personal computer. 
In a recording operation, the recording information sent from the external 
controller 112 is subjected to signal processing such as modulation at a 
recording (erasing) signal processing section 113. The processed signal is 
supplied to the laser diode 106, which then emits modulated light 
according to the recording information. At the same time, the bias 
magnetic field generating section 105 applies a recording magnetic field 
of a certain direction to the magneto-optical disk 103 to record 
information. 
The bias magnetic field generating section 105, which is made up of, for 
example, an electromagnet, generates a recording magnetic field of a 
certain direction, depending on the direction of the direct current 
supplied from the bias magnetic field control section 114 controlled by 
the CPU 111. 
An actuator section 115 and a coarse adjustment section 116 are provided as 
means for moving a light beam so that a position at which information is 
recorded or reproduced using a light beam can be changed, and for holding 
the beam in that place. The object lens 117 is moved a bit by the actuator 
section 115 across the tracks on the magneto-optical disk 103. The coarse 
adjustment section 116, which is composed of moving means such as a voice 
coil motor, can move the pickup 104 over the entire track area. 
The actuator section 115 and the coarse adjustment section 116 are 
controlled by the instruct signal from a beam position control section 
117. The beam position control section 117 is controlled by the CPU 111. 
In an erasing operation, the bias magnetic field control section 114 
supplies to the bias magnetic field generating section 105 a direct 
current whose direction is opposite to that of current used in generating 
a recording magnetic field, and applies to the magneto-optical disk 103 an 
erasing magnetic field whose direction is opposite to that of the 
recording magnetic field. Then, the laser diode 106 emits laser light 
whose level is almost the same as that in a recording operation. 
In the present invention, when an unformatted magneto-optical disk 103 is 
inserted in the magneto-optical disk apparatus 101, formatting is effected 
in an initialization process by recording a specific pattern in (all the 
sectors in) all the tracks in the data area of the user area. After normal 
formatting, a specific pattern may be written in all the sectors in all 
the tracks in the data area of the user area. 
To do this, the CPU 111 supplies a specific pattern signal to the recording 
(erasing) signal processing section 113. The specific pattern to be 
recorded is, for example, a periodic pattern of the order of several tens 
of KHz to several MHz. 
To minimize the generation of transitional response at a joint connecting 
user data patterns, the specific pattern is preferably a fully DC-free 
pattern. However, it is not necessarily a fully DC-free pattern. It is all 
right that it is an almost DC-free pattern. 
While in a conventional apparatus, a DC pattern was written in an erasing 
operation, the laser diode 106 is modulated using an almost DC-free 
specific pattern identical with that used in a format operation in the 
present embodiment. 
The almost DC-free specific pattern itself has only to be read from memory 
means such as a ROM (not shown) connected to the CPU 111. 
FIG. 13 shows the arrangement of the edge sensing circuit 121 based on a DC 
slicing method (of reading optically recorded information on the 
magneto-optical disk 103) of the reproduction signal processing section 
109. 
As shown in FIG. 14A, pits are formed in the direction of magnetization in 
a track. The photoelectric conversion signals from a pair of photodiodes 
108a and 108b shown in FIG. 13 are supplied to a differential amplifier 
122, which then produces a differential output. This output passes through 
a CR coupling circuit 123 for eliminating the influence of direct-current 
components due to double refraction and through a preamplifier 124, and is 
formed into a reproduced signal SO with a waveform corresponding to the 
pits as shown in FIG. 14B. The cut-off frequency of the low-frequency side 
of a filter consisting of capacitor C and resistor R of the CR coupling 
circuit 123 is set at approximately 1 KHz. 
The reproduced signal SO is supplied to a comparator 125, which compares it 
with slice level vs1 set by the division of resistors R1 and R2, and 
produces a binarized signal S1 shown in FIG. 14C. 
The binarized signal S1 supplied from the comparator 125 is supplied to a 
data input terminal of a flip-flop circuit 126. The signal S1 from the 
comparator 125 and the signal S2 of FIG. 14D from the flip-flop circuit 
126 are supplied to an exclusive OR circuit (hereinafter, referred to as 
an E-OR circuit) 127, which produces an output signal S3 of XOR shown in 
FIG. 14E. 
The output signal S3 of the E-OR circuit 127 is supplied to a one-shot 
multivibrator 128, which produces a short pulse at the rising edge of the 
output signal S3 from the E-OR circuit 127 and supplies the pulse to the 
clock input terminal of the flip-flop circuit 126, and which supplies this 
pulse as the output signal of the edge sensing circuit 121 (see FIG. 14F). 
Explained next will be the operation when a magneto-optical disk 103 is 
inserted in the magneto-optical disk apparatus of the second embodiment, 
referring to the flowchart of FIG. 15. 
When the power supply of the magneto-optical disk apparatus 101 is turned 
on, it is judged at step St1 whether or not a magneto-optical disk 103 has 
been inserted in the apparatus 101. Whether or not a magneto-optical disk 
103 has been inserted in the apparatus 101 is sensed by, for example, an 
optical sensor provided in the rear of a disk slot (not shown). On the 
basis of the sense output, the CPU 111 judges whether or not the disk has 
been inserted. 
If it is judged that the disk 103 has been inserted, the CPU 111 gives a 
motor driving circuit (not shown) an instruction to rotate the spindle 
motor 102 and causes the disk 103 to rotate at step St2. 
After that the disk 103 is being rotated at a constant rotational speed has 
been sensed by, for example, a rotation sensor (not shown), the CPU 111 
sends a control signal to the beam position control section 117, which 
then causes the coarse adjustment section 116, etc. to operate to make the 
pickup 104 access the control track in order to read the information from 
there, as shown in step St3. The information thus read is transferred to 
the CPU 111. 
At step St4, on the basis of the read-out information, the CPU 111 judges 
whether or not the disk 103 has been initialized. If it is judged that the 
disk 103 has not been initialized, at step St5, a specific pattern signal 
is sent to the recording (erasing) processing section 113, which performs 
initialization by recording a DC-free pattern in the entire sector area in 
the data area of the user area. 
If it is judged that the disk 103 has been initialized, at step St6, 
control goes to Step St5 if the user has selected the choice of recording 
a DC-free pattern at step St6. If the user has not selected the choice of 
not recording a DC-free pattern, control proceeds to step 5 and the 
process is terminated without executing step St5. 
If the user has selected the choice of recording a DC-free pattern, a 
DC-free pattern may be recorded in all the sectors except for those in 
which information has already been recorded in the user area. 
In the second embodiment, as seen from the flowchart of FIG. 15, for an 
uninitialized magneto-optical disk 103, a DC-free pattern is written in 
all the sectors in the data area of the user area. After this, information 
is recorded. After information has been recorded, reproduction or erasure 
is effected. 
To record information, a bias magnetic field is applied to a sector in 
which the information is to be written, in the opposite direction to that 
in a recording operation, as with conventional apparatuses. Then, 
high-level light is projected onto the sector to erase the entire sector. 
After this, a recording bias magnetic field is applied and light is 
emitted in pulse form at a high level and a low level on the basis of the 
signal obtained by modulating the information to be recorded, thereby 
recording information. 
If the recording of information has finished in the middle of the sector, a 
code representing an end may be added (recorded) and a DC-free pattern be 
written in the portion after the end code to the end of the sector. 
To erase the recorded information, the contents of the flag indicating the 
presence and absence of the directory information as to whether the 
directory information to manage the recording position of the information 
is recorded in the sector, may be rewritten as absent (i.e., the 
information is not recorded in the sector), thereby equivalently erasing 
the sector in which the information is recorded. 
The information in the sector may be actually erased. In this case, like a 
case where it is judged that the disk 103 is uninitialized, a DC-free 
pattern is written in the entire sector. In accordance with this erasure, 
the directory information corresponding to the sector information is also 
modified. 
With the second embodiment, for an uninitialized magneto-optical disk 103, 
a DC-free pattern is written in all the sectors in the data area of the 
user area. Thus, when the information in a given sector is reproduced by a 
DC slicing method with AC coupling set at a relatively low cut-off 
frequency, the information can be reproduced accurately without causing a 
transitional response problem, because information is also recorded in the 
preceding sector (the information exists continuously). 
By recording or reproducing information using a magneto-optical disk 103 in 
which a DC-free pattern is written in all the sectors in the data area of 
the user area with the apparatus of the second embodiment 103, a 
transitional response problem can also be alleviated. 
While in the second embodiment, a magneto-optical disk 103 has been 
described, the present invention may be applied to an optical recording 
apparatus and an optical erasing apparatus which can erase and record 
information. Therefore, the invention can also be applied to a 
phase-change type optical recording apparatus and a phase-change optical 
erasing apparatus in which the reflectivity varies with the phase change. 
Similarly, a recording medium of the phase change type may be used. 
Although in the above embodiment, a DC-free pattern is written in all the 
sectors in the data area of the user area, a DC-free pattern or an almost 
DC-free pattern may be written at least at the end of each sector so that 
a transitional response problem can be practically or sufficiently 
alleviated between the end of the current sector and the beginning of the 
following sector. 
while in the above explanation, a specific pattern is read from memory 
means such as a ROM, the pattern signal from a pattern signal generator 
which is provided in the reproduction apparatus so as to produce a DC-free 
pattern signal may be used instead. 
For example, the pattern signal generator may supply a pattern signal to 
the comparator 125 until the time is reached when the beginning of the 
sector in which the information to be reproduced is recorded is read. 
Then, with the timing that the information on the beginning of a sector is 
read, the signal from the optical sensor 108 may be supplied to the 
comparator 125, thereby forming means free from a transitional response 
problem. 
As explained above, with the second embodiment, there is provided means for 
writing an almost DC-free pattern in all the sectors in the user area on 
an uninitialized optical information recording medium. Therefore, when the 
information in a given sector in the medium is reproduced, almost no 
effect of transitional response occurs because information has been 
already written in a portion immediately before the sector, thereby 
enabling reproduction with a DC slicing read circuit set at a relatively 
low cut-off frequency. 
Additional advantages and modifications will readily occur to those skilled 
in the art. Therefore, the invention in its broader aspects is not limited 
to the specific details, and representative devices, shown and described 
herein. Accordingly, various modifications may be made without departing 
from the spirit or scope of the general inventive concept as defined by 
the appended claims and their equivalents.