JPH07210874A - Optical recording medium and its reproducing device - Google Patents

Abstract

PURPOSE:To widen latitude as a reproducing system of an optical recording medium at the time of recording information at a high density on this recording medium. CONSTITUTION:High light transmittance parts 11 which have high light transmittance and are approximately transparent to light are continuously formed in a track direction on pits P formed on the surface of the optical recording medium. The parts between the adjacent tracks are low light transmittance parts 12 which are low in light transmittance and absorb light. The light is absorbed in the low light transmittance parts 12 even if the surface of such optical recording medium 1 is irradiated with a reading out laser beam R of a spot diameter equal to about twice the track pitch TP and, therefore, there is no reflected light of these parts or the reflected light is extremely small and the light intensity distribution of the light cast onto the pits P is a light intensity distribution 15. The deterioration in the signals by the crosstalks of the adjacent tracks is lessened and stable reproduced signals are obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium capable of reproducing information by using light, such as a disc, tape, card, etc., and more particularly to storing information at high density in the optical recording medium. .

[0002]

2. Description of the Related Art In recent years, there have been optical recording media such as discs, tapes, and cards that reproduce information by using light. In these optical recording media, increasing the storage capacity has been studied and various optical recording media have been studied. Proposals have been made. Since this optical recording medium can form a recording mark smaller than the light spot diameter by controlling the laser light intensity at the time of recording, there is no limit in principle to the density improvement at the time of recording. However, the diameter of the light spot when the laser light is focused by a lens is
Since there is a limit value that cannot be narrowed down to a certain value or less, how to increase the density of the optical recording medium depends on how to reduce the reproduction laser spot. Since the spot diameter of the laser beam when condensed by the lens is proportional to λ / NA (λ is the wavelength of the light, NA is the numerical aperture of the lens), it is possible to identify and reproduce a recording mark with a shorter recording wavelength. Can be reproduced by using light having a short wavelength λ or using a lens having a large numerical aperture NA. Here, for example, the current CD, which is widely known as a disc-shaped optical recording medium (hereinafter, simply referred to as an optical disc), has a track pitch of 1.6 μm and has a recording capacity of about 12 cm for an audio disc (one side). 780 MB, about 7 digital audio signals
It can record for 4 minutes.

In recent years, in order to increase the recording density of such an optical recording medium, the wavelength of the laser beam used for reproduction is shortened and a high NA lens is used to substantially reduce the spot light diameter of the reproducing apparatus. There is a lot of research done. For example,
In the technology of shortening the laser light wavelength, the second harmonic generation element (SHG) is used to change the laser light wavelength used for reproducing the current CD or video disk from about 800 nm to 400 nm.
Research is being carried out. If the wavelength of the laser beam is halved in this way, the recording density can be increased by about 4 times. In terms of stability, performance, price, etc., this SHG is not at the stage of being put into practical use at present, but if it is put into practical use in the future,
It is possible to record information at a higher density than the current optical recording medium system. The wavelength that can be practically used at present as a single wavelength laser is 680 nm to 670 nm. Further, the spot diameter of the laser beam can be reduced by using a high NA lens, but the use of a high NA lens results in a shallow depth of focus, which requires precision in the distance between the lens and the optical recording medium, and optical recording The manufacturing precision of the medium becomes strict. For this reason, the NA of the lens cannot be increased so much at present, and the lens NA that can be put to practical use is about 0.6 at the most. From the above, for example, the currently practical wavelength 6
If a high-density optical recording medium system is constructed using a 70 nm semiconductor laser as a light source and a lens with an aperture of 0.6 as an objective lens, the track pitch and the pit-to-pit spacing can be shortened, so that it is now widely used. It is theoretically possible to improve the recording density up to about 4 to 6 times that of the existing CD system (wavelength 780 nm, NA = 0.45).

[0004]

By the way, as described above, the wavelength of the read laser beam is shortened and the NA of the condenser lens is increased.
Although it is theoretically possible to reproduce high-density information due to the increase in the number of optical discs, there is a problem in that an optical recording medium with such high-density recording becomes an unstable system with a small margin. .

For example, as shown in FIG. 8, in the existing CD system, the pits P are formed so that the track pitch TP is about 1.6 μm and the pit width PW is about 0.5 μm. The above CD system (wavelength 780nm, NA =
The spot diameter of the read laser beam R irradiated from 0.45) is as shown in the figure on the pit P. Considering the influence of crosstalk with adjacent tracks, the spot diameter of the read laser light is 3.2.
It can be seen that the value should be less than μm, but in the current CD system, the spot diameter of the read laser beam is set to be almost the same as the track pitch TP in consideration of variations in the track pitch TP. Gives a margin in. Therefore, as can be seen from FIG. 7, even in the case of the current CD system (wavelength 780 nm, NA = 0.45), if the track pitch TP is reduced, it is possible to record information at a higher density than the current CD system. However, the allowable range of the thickness unevenness, surface wobbling, tilt angle, eccentricity, etc. of the medium becomes extremely small, and the margin of the system becomes small accordingly. this is,
This is also the case when the optical wavelength of the read laser light is shortened or when the high-density recorded optical recording medium is reproduced by using a high NA lens, and a stable reproduction signal is obtained only by reducing the spot diameter of the read laser light. Is difficult to obtain. Further, if the allowable range of the thickness unevenness, surface wobbling, tilt angle, etc. of the medium becomes extremely small, it will be very difficult to control it during manufacturing, and the system will have a problem in terms of cost.

Therefore, the present invention has been made by paying attention to the above points, and an object thereof is to increase the margin as a reproducing system when recording information on an optical recording medium with high density. To do.

[0007]

According to the present invention, as means for achieving the above-mentioned object, minute reproducible identification marks which are optically reproducible according to information are recorded as a plurality of identification mark rows on a light transmissive substrate. In the optical recording medium, a high light transmittance portion formed on the identification mark row, having a substantially identification mark width and having a high light transmittance continuously in the identification mark row direction, and a high light transmittance portion adjacent to the high light transmittance portion. An optical recording medium is provided, which has a window layer having a low light transmittance portion having a low light transmittance between the light transmitting portion and the index portion on the light transmitting substrate. Further, in the optical recording medium, the window layer has a low light transmittance in a state where it is not irradiated with light, and the light transmittance becomes irreversibly high by absorbing light of a specific wavelength or heat of light. It is an object of the present invention to provide an optical recording medium comprising a variable substance, wherein the high light transmittance portion is formed before reproducing the information.

As a means for achieving the above-mentioned object, the present invention provides a specific wavelength on a light-transmissive substrate on which minute identification marks that can be optically reproduced according to information are recorded as a plurality of identification mark rows. It has a window layer made of a light transmittance variable substance whose light transmittance becomes irreversibly increased by absorbing light or heat of light, and before reproducing the information, on the identification mark row of the window layer. A reproducing apparatus of an optical recording medium, wherein a high light transmittance portion having a substantially high light transmittance is continuously formed in a corresponding mark portion in an identification mark width direction in a corresponding portion, and the light transmittance of the window layer is Detecting means for detecting, and a light irradiating means for irradiating the spot light of the specific wavelength having a diameter substantially equal to the identification mark width on the window layer, the plurality of identification mark rows using the detecting means. In the cross direction The light transmittance of the wind layer is detected, and the spot where the high light transmittance is not detected at the interval of the identification mark row is irradiated with the spot light by using the light irradiating means to increase the high light transmittance. It is intended to provide a reproducing apparatus for an optical recording medium, which is characterized by forming a part.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings. First, the basic principle of the optical recording medium of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a sectional view of an optical recording medium according to an embodiment of the present invention. FIG. 2 is a partially enlarged view of the optical recording medium of one embodiment of the present invention. In the optical recording medium 1 shown in the figure, a window layer 3 whose light transmittance is irreversibly changed by irradiation of light is formed on a light-transmissive substrate 2 on which minute pits P corresponding to information are formed. A metal reflective layer 4 and a protective film 5 are further formed on the window layer 3. The optical recording medium 1 has the pits P as shown in FIG. That is, wind layer 3
On the pit row, the light transmittance is continuously high in the track direction, and the high light transmittance portion 11 is substantially transparent to light, particularly the read laser light R. The width W of the high light transmittance portion 11 is substantially the same as the width PW of the pit P, and the effective spot diameter of the read laser light R to be irradiated is reduced in the pit width PW direction. Although the width W of the high light transmittance portion 11 shown in the figure is described as being slightly narrower than the pit width PW, the window layer 3 determines the effective spot diameter of the read laser light R in the pit width PW direction. Since it is provided so as to be small, the signal reproduction is not affected even if it is formed wider than the pit width PW. Further, a low light transmittance portion 12 having a low light transmittance and absorbing light is provided between the adjacent tracks.

On such an optical recording medium 1, a read laser beam R having a spot diameter approximately equal to twice the track pitch TP is formed.
If the light intensity distribution of the laser light R is 16 shown in the same figure, the low light transmittance portion 12 of the window layer 3 is irradiated.
Since the light is absorbed, there is no reflected light at that portion, or the reflected light becomes very small. Further, since the high light transmittance portion 11 transmits light, the light intensity distribution of the reflected light is the light intensity distribution 15 shown in FIG. Will be detected. By the window layer 3 in which the high light transmittance portion 11 and the low light transmittance portion 12 are formed in this manner, even if the size of the spot of the read laser light is smaller than the conventional size and high density is recorded. Since the reflected light detected on the device side has the light intensity distribution 15, the deterioration of the signal due to the crosstalk can be reduced and the system margin can be improved.

For example, regarding the tracking offset, in the state where the window layer 3 is not provided, the occurrence of a slight offset causes the deterioration of the signal due to so-called crosstalk, which is influenced by the signals of the adjacent tracks. However, even if an offset occurs due to the provision of the window layer 3, a portion having a low light transmittance with an adjacent track absorbs light, so that the track can be reproduced without being affected by crosstalk. In addition, since light is absorbed between the adjacent rack and the rack, there is also an effect of suppressing a decrease in system margin due to variations in the track pitch TP. Further, as for the offset in the focus direction due to the surface wobbling of the optical recording medium 1, a slight offset occurs in the state without the window layer 3, and the change in the spot size also affects the adjacent track information. However, if the window layer 3 as described above is provided, the margin is large. The same applies to the tilt related to the tilt of the optical recording medium 1, and the problem that the diameter of the light spot irradiated on the optical disk becomes large due to the tilt of the disk is also solved.
By providing, the margin is increased.

Next, the window layer 3 will be described with reference to FIGS. 3 and 4. The window layer 3 contains a substance whose transmittance changes with irradiation light intensity as shown in FIG.
When the light intensity of the irradiating light becomes larger than I ₀ , the light transmittance thereof rapidly increases without changing the shape due to decomposition, sublimation or optical alteration, and the light or the heat of the light is not absorbed. As the substance used for the window layer 3, a substance having a high light transmittance that is kept for a predetermined period even after the light irradiation is stopped is selected and used. That is, the light transmittance variable substance used for the window layer 3 is only required to maintain an irreversible state with respect to the reproduction time level of the optical recording medium 1, and is longer than the reproduction time of the optical recording medium 1 (for example, reproduction). If the time is from several seconds to several minutes, it is from several tens of minutes to several hours, and from tens of minutes to several hours, it is several days.

Considering the above, suitable materials for the window layer 3 are phase change materials, nonlinear optical materials, supersaturated absorptive materials, optical bistable materials, photochromic materials, thermochromic materials, electrochromic materials, etc. As a result of the experiment, it was found that various materials are suitable, but the chromic material is suitable as a material whose transmittance changes irreversibly without changing the shape. Here, in general, a chromic substance is one that reversibly changes its color tone by light, heat or electrolysis (for example, a substance that causes reversible change by heat is called a thermochromic substance, and in the case of light, a photochromic substance That). However, especially in the case of thermochromic substances,
Rapid heating and quenching by laser light used in optical recording media often result in so-called irreversible changes that do not effectively exhibit their reversibility. It can be said that the thermochromic substance having such a property is suitable as the window layer 3 because it retains the irreversible state for a predetermined period. In addition to thermochromic substances, even photochromic compounds and electrochromic compounds,
It can be used when the reversibility cannot be sufficiently exhibited. However, in the case of electrochromic compounds,
Since it is necessary to apply a voltage or the like, the structure of the optical recording medium 1 becomes complicated.

Further, as the window layer 3 used in the optical recording medium 1, a part of the window layer 3 is continuously changed to transparent by reproducing with a light intensity higher than the reproducing light intensity, and the window layer 3 is formed on the pit P row. It is preferable to use a substance capable of providing a difference in reflectance between the pit rows in the track direction. For example, when a phase change material is used as the window layer 3, it can be used as the window layer 3 when it changes irreversibly. However, since the phase change substance is generally an inorganic substance, especially a metal compound in many cases, and it has a good thermal conductivity, it is difficult to change the light transmittance clearly with a small pit width size, and it is used as a material of the window layer 3. Is not suitable. From the above, as the substance suitable for the wind layer 3, a substance which is a chromic substance composed of an organic dye and which does not effectively exhibit reversibility is suitable.

Further, if the window layer 3 absorbs the reproducing laser light too much, not only power is required for forming the high light transmittance portion 11, but also the reflectance becomes too low. , It becomes difficult to apply tracking and focus servo. However, on the contrary, if the absorption is too small, the difference in reflectance after forming the high light transmittance portion 11 becomes small, so that the margin of the system cannot be improved.
Therefore, the light absorption of the window layer 3 is such that the light transmittance of the low light transmittance portion 12 is 5% or more at the reproduction light wavelength used.
It is considered that it is preferably 0% or less. More preferably, it is not less than 15% and not more than 35%, and the servo is satisfactorily applied, and the reflectance difference can be made large. or,
The film thickness of the window layer 3 cannot be uniquely limited because it has a relationship with the absorption coefficient with respect to the light wavelength of the read laser light, but if it is too thick, tracking may be affected or the high light transmittance portion 11 may be formed. At this time, the thickness is preferably 500 nm or less from the viewpoint that it is difficult to form the transparent portion clearly. More preferably 20 nm to 300
nm.

The high light transmittance portion 11 is formed on the window layer 3 constructed as described above by using a laser beam having a predetermined intensity. The light intensity distribution of the laser light indicates a normal Gaussian distribution, the temperature distribution because even has a substantially similar distribution, the light intensity I ₀ or more as shown in FIG. 4 by controlling the irradiation light intensity of the laser beam to be irradiated A laser beam I having a diameter d ₀ of a portion having a light intensity (hatched portion in the figure) substantially equal to the width PW of the pit P is used. If the laser beam I is irradiated onto the pit row in the track direction, the window layer 3 maintains an irreversible state for a predetermined period as described above, so that the light transmittance should be continuously increased on the pit row. You can Since the window layer 3 made of the variable light transmittance material that retains the irreversible state for a predetermined period as described above has a low light transmittance in the absence of light irradiation, the high light transmittance portion 11 is formed. Should be performed before signal reproduction. Then, at the time of signal reproduction, the laser light R (see FIG. 4) having a light intensity lower than that of the laser light I used when forming the high light transmittance portion 11 is used.

Next, a method of making the above optical recording medium 1 will be described. First, a photoresist is applied on a polished glass master, and pits P are recorded by a recording laser. There is no particular limitation on the method of recording pits on the substrate 2. When the optical recording medium 1 is an optical disc, the pits P to be recorded at this time are formed with a smaller pit width and a narrower track pitch than in the current CD. Then, after development and formation of a conductive film, a stumper is prepared by plating, and the substrate 2 is prepared using this stumper. As a method for producing the substrate 2, any method such as a method of obtaining a substrate by injection molding, a method by etching, a so-called 2P method, an embossing method by an ultraviolet curable resin, or the like can be used. As well known, various materials can be used as the material of the substrate 2, and glass, epoxy resin, polycarbonate resin, polymethacrylate ester resin, amorphous polyolefin resin, etc. all have good transparency. If there is, it can be used.

The window layer 3 is formed on the substrate 2 having the pits P formed therein. Here, there is a spin coating method as a method for forming a thin film of an organic material which has been widely known from the past. However, this spin coating method is not excellent in film thickness controllability, and it becomes difficult to control the film thickness difference between the pit portion and the land portion. In particular, when the pits are formed with high density, it is very difficult to control the film thickness by the spin coat method. Therefore, the vacuum evaporation method is used for forming the window layer 3. This vacuum deposition method has excellent film thickness controllability,
A slightly different film thickness can be controlled according to the absorption coefficient of the light transmittance variable substance, and a thin film having a uniform film thickness can be formed with respect to minute irregularities on the substrate 2, so that the film thickness can be easily controlled.
The film thickness at the pits and lands can be formed almost evenly.

When the optical recording medium 1 is an optical disk, it is desirable to provide the reflection layer 4 on the window layer 3. This is because almost all of the currently popular optical disc systems are of the reflective type, which is advantageous in consideration of compatibility with these systems. The reflective layer 4 is not particularly limited as long as it is a thin film having high reflectance, and aluminum, gold, silver, copper, which is generally used as the reflective film 4,
It is possible to arbitrarily select a material having a high reflectance property, such as a metal or alloy such as nickel or a multilayer thin film of a dielectric. The method for forming the reflective layer 4 may be appropriately selected according to the material of the reflective layer 4 such as a vacuum vapor deposition method or a sputtering method. When the vacuum deposition method is used as the method for forming the reflective layer 4, the device used for forming the window layer 3 can be used, and there is an advantage in manufacturing cost. The optical recording medium 1 of the reflection type is not limited to the optical disc,
It is also possible to make a transmissive system without providing the reflective layer 4. A protective film 5 for protecting the reflective layer 4 is formed on the reflective layer 4. The protective film 5 is formed of a UV curable resin or the like by a conventional method such as a spin coating method.

Next, the reproducing apparatus for the optical recording medium 1 will be described. The optical recording medium 1 has various shapes such as a disk shape, a tape shape, and a card shape. Here, a reproducing apparatus for a disk-shaped optical recording medium, which is widely known as one of optical recording media, that is, an optical disk. 5 and 6
Will be explained. First, the structure of the reproducing apparatus will be described with reference to FIG. FIG. 5 is a schematic configuration diagram of a main part of an optical disc reproducing apparatus according to an embodiment of the present invention. In FIG. 1, the reproducing device 21 includes an optical head 23 that irradiates the optical disc 1 with laser light and outputs an output signal a corresponding to the light intensity of the reflected light that returns from the optical disc 1 with information. The output signal a from the optical head 23 is amplified by using the minute signal amplifier circuit 24, and the output signal b from the minute signal amplifier circuit 24 is waveform-equalized by the waveform equalizing / demodulating circuit 25 to demodulate information. Then, the reproduction signal c based on the information recorded on the optical disc 1 is output. The output signal a from the optical head 23 is
It is also input to a control circuit 26 that controls the system of the entire apparatus. In this control circuit 26, the output signal a is used for focus servo, tracking servo, and the like. The control circuit 26 outputs drive signals d, e, and f to the laser driver 27, the optical head drive circuit 28, and the motor driver 29, respectively, according to the output signal a and the output signal f output from the initialization determination circuit 31. Output.

The laser driver 27 is the optical head 23.
It controls the optical output of a laser diode (not shown) which is a light source of the laser beam provided therein, and causes the optical head 23 to output a laser beam of an optical output according to the drive signal d. Further, the optical head drive circuit 28 includes the optical head 23.
For moving the optical disc in the radial direction of the optical disc and for driving a condenser lens (not shown) for condensing the laser light output from the laser diode for focus control. That is, the drive signal f from the control circuit 26 is based on focus servo and tracking servo, or based on functional operations such as track jump and track search. As a feed mechanism for moving the optical head 23 in the radial direction of the optical disc 1, there are a conventionally known rack and pinion system, a swing arm system, a linear motor system, and the like, and these are appropriately selected and adopted. . The drive mechanism of the condenser lens is composed of an actuator composed of a magnet and a coil. Further, when the drive signal e is input, the motor driver 29 controls the rotation of the spindle motor 30 according to the drive signal e.

The output signal a is also input to the initialization determination circuit 31. The initialization determination circuit 31 detects whether the high light transmittance portion 11 is formed on the window layer 3 and outputs an output signal f corresponding to the result to the control circuit 26. Here, the optical disc 1 reproduces a signal after forming the high light transmittance portion 11 as described above. Therefore, the formation of the high light transmittance portion 11 is performed when the optical disc 1 is mounted on the reproducing device 21 or when a reproducing command is input to the control circuit 26, and an initialization operation (= initial setting) of optical disc reproduction is performed. Operation). The initialization determination circuit 31 determines whether or not the initialization operation has been performed on the optical disc 1 to be reproduced. Hereinafter, the determination operation by the initialization determination circuit 31 will be described together with the initialization operation of the reproducing device 21 with reference to the flowchart shown in FIG.

When the necessity of the initialization operation arises, the control circuit 26 outputs a drive signal f for moving the optical head 23 to the innermost peripheral position of the optical disc 1 to the optical head drive circuit 28, and at the same time, the spindle motor. A drive signal e for rotating 30 is output to the motor driver 29 (101). When the optical head 23 moves to the innermost position, the control circuit 26 irradiates the optical disc 1 with laser light to apply focus servo (102). Here, in order to apply the focus servo, it is necessary that the amount of light reflected from the optical disc 1 is equal to or larger than a predetermined amount of light. Optical disc 1
The upper window layer 3 usually has a low light transmittance and absorbs light or its heat to increase the light transmittance.
When the focus servo is applied, laser light having a light intensity that gives a reflected light amount equal to or larger than a predetermined light amount is emitted. But,
The window layer 3 maintains a high light transmittance for a predetermined period of time, so that when the focus servo is applied, the optical disk 1
It is performed in a region other than the signal recording region (including the lead-in signal recording region) above. That is, the innermost position moved in step 101 is further inside than the lead-in signal recording area. When the focus servo is applied in the lead-in signal recording area, an area for applying the focus servo is provided in the lead-in signal recording area.

Next, the control circuit 26 outputs an output signal d for setting the light intensity of the laser light output from the optical head 23.
Is output to the laser driver 27, and laser light corresponding to the light intensity is output from the optical head 23 (103). At this time, the laser light output from the optical head 23 is for detecting whether or not the high light transmittance portion 11 is formed in the window layer 3. Here, since the window layer 3 maintains an irreversible state for a predetermined period, a portion having a high light transmittance should not be formed in an unnecessary portion by the laser light irradiated for detecting the high light transmittance portion 11. . Therefore, the light intensity of the laser light for detecting the high light transmittance portion 11 is set to a light intensity smaller than the light intensity I0 shown in FIG.
The light output is set so as to have the light intensity distribution of the reproducing laser light R shown in FIG. When the light intensity of the laser light for detecting the high light transmittance portion 11 is set, the optical head 23 located at the innermost circumferential position of the optical disc 1 is subjected to tracking servo while irradiating the laser light according to the light intensity. An output signal f for moving the optical disc 1 largely in the radial direction without being applied is output to the optical head drive circuit 28 (104).

While the optical head 23 is moving in the radial direction of the optical disc 1, the control circuit 26 drives the initialization determination circuit 31 to determine whether the high light transmittance portion 11 is formed (105). ). The initialization determination circuit 31 outputs an output signal a corresponding to the state of the window layer 3 by moving the optical head 23 in the radial direction.
Will be input from the optical head 23. The initialization determination circuit 31 determines whether or not the initialization operation is performed by looking at the state of the output signal a. For example, as shown in FIG.
During the periods a1 and a3 which are moving in the portion where 1 is not formed, the output light a is very small because the reflected light from the optical disk 1 is very small or absent.
Is the same state as is not output. Thus, when the output signal a is not output, the initialization determination circuit 3
In No. 1, the high light transmittance portion 11 is not formed, that is,
Assuming that the initialization operation is not performed, a predetermined output signal g such as pulse repetition as shown in FIG.
Is output to the control circuit 26. Also, during the period of a2 during which the optical head 23 is moving in the portion where the high light transmittance portion 11 is formed, the reflected light from the optical disc 1 can be detected periodically, so the output signal a corresponding to this reflected light Is periodically input to the initialization determination circuit 31. The initialization determination circuit 31 stops the output of the output signal g while the output signal a is being input. The control circuit 26 compares the start time and end time of output of the output signal g and the position of the optical head 23, and compares the positions ((y1, Y1), (y2,
Y2)) is detected and the position information is stored in a RAM (not shown).

In step 105, when the high light transmittance portion 11 of the optical disk 1 is not formed at all, or when it is detected that only a part of the high light transmittance portion 11 is formed, the process proceeds to step 106, and the high light transmittance portion is formed. The forming operation 11 is performed. First, the control circuit 26 moves the optical head 23 to the first formation start position y1 of the high light transmittance portion 11, and the light intensity of the laser light output from the optical head 23 becomes the laser light I shown in FIG. Thus, the drive signal d is output to the laser driver 27 (106). When the laser light intensity is set, the optical head 23 outputs laser light according to the light intensity. Next, the control circuit 26 detects the output signal a from the optical head 23 and applies the tracking servo (107), while irradiating the laser beam until the optical head 23 reaches the formation end position Y1 and wind layer. The high light transmittance portion 11 is formed on the surface 3 (108). When the formation of one place is completed, the optical head 23 is moved to the next formation start position.
By moving to y2, the high light transmittance portion 11 is formed in the same manner. When the high light transmittance portion 11 is formed in all parts,
The control circuit 26 sets the light intensity of the laser light to the light intensity for reproduction, and ends the initialization operation. Here, the reproduction light intensity may be the same as that set in the above step 102, but is not particularly limited as long as the light intensity does not cause a change in the light transmittance of the window layer 3. If it is detected in step 105 that the optical disc 1 does not need to have the high light transmittance portion 11, the initialization operation is terminated without performing the formation operation of the high light transmittance portion 11.

By performing the initialization operation as described above, the high light transmittance portion 11 can be formed on the window layer 3. The output signal g output from the initialization determination circuit 31 may be output during the period when the output signal a is detected. Further, since the formation start position and the formation end position of the high light transmittance portion 11 detected by the control circuit 26 may deviate from the actual position, the high light transmittance portion formation is performed in consideration of this detection deviation. The irradiation start position of the application laser beam I may be started from the inner circumference of one track, and the irradiation end position may be set to the outer circumference of one track.

The window layer 3 of the optical recording medium 1 of the present invention is not a substance that maintains an irreversible state for a predetermined period as described above, but once the light transmittance becomes high, the state becomes almost permanent. It may be a substance to be retained. Examples of such substances include indolenine type polymethinecyanine, thiazole type polymethinecyanine, oxazole type polymethinecyanine, quinoline type polymethinecyanine, naphthoquinone type pigments, and squarylium, which are known as recording layer materials for write-once (WO: Write Once) type optical disks. There are dyes and azurenium dyes. Since these materials change the light transmittance by absorbing light or heat thereof, the high light transmittance portion is changed by using a laser beam having a light intensity such that the light transmittance changes like the above-described initialization operation. 11,
Alternatively, the low light transmittance portion 12 is formed. This high light transmittance part 1
1 or the low light transmittance portion 12 may be formed at the manufacturing stage of the optical recording medium 1. If the window layer 3 is made of such a substance, the reproducing device 21 does not need the circuit structure for the above initialization operation, and the circuit structure necessary for the high-density system is added to the conventional reproducing device or such a circuit is added. All you have to do is change the configuration. Further, since it is not necessary to perform the initialization operation one by one before reproducing the optical recording medium 1,
It also shortens the playback time.

Next, an optical disc 1 was produced based on the above-mentioned optical recording medium producing method, and a reproduction experiment for examining the effect of the window layer 3 was conducted. The pits P recorded on the substrate 2 have a track pitch narrower than that of the current CD, and the pit shape is further reduced to achieve 4 times higher density recording.
Further, as the window layer 3, various organic dye materials as shown in Table 1 below were used and formed by the forming method and film thickness shown in Table 1, respectively.

[0030]

[Table 1] Further, aluminum is vacuum-deposited with a thickness of 70 nm as a reflective layer 4 on each window layer 3 of the optical disk 1, and an ultraviolet curable resin layer (trade name SD-17: Dainippon Ink and Chemicals, Inc.) as a protective layer 5. About 5μ
The optical discs 1-1 to 1-4 were formed with a thickness of m. In addition, as a comparative example, the above-mentioned optical disks 1-1 to 1-4
An optical disk 1-5 having the same recording density as (4 times denser) and having no window layer 3 was prepared.

These optical discs 1-1 to 1-5 are mounted on the reproducing apparatus 21 whose optical system is designed with a reproducing light wavelength of 690 nm and an objective lens NA0.6, and after performing the initializing operation, a signal is outputted. Was reproduced, and the jitter of the reproduced output signal was measured. High light transmittance section 11
Was formed at a laser light intensity of 1.5 mW, and reproduction was similarly performed at 0.5 mW. Further, in order to evaluate the margin of the system, the optical disc 1 was forcibly tilted by 0.3 degree and the jitter amount was measured. The results of these measurements are shown in Table 2 below.

[0032]

[Table 2] As shown in Table 2, the optical discs 1-1 to 1-4 in which the high light transmittance portion 11 is formed can reduce the amount of jitter due to the crosstalk affected by the adjacent tracks, and can reduce the tilt. It can be seen that the system margin can be expanded. Further, in the optical disc 1-4 on which the window layer 3 is formed by the spin coating method, there is a difference in the film thickness on the pits and the film thickness on the land portion, and the optical discs 1-1 to 1- 1-on which the window layer 3 is formed by vapor deposition. It can be seen that the effect is slightly smaller than 3.

[0033]

As described above, according to the optical recording medium of the present invention, high optical transmission formed on the identification mark row, having a substantially identification mark width, and having a high light transmittance continuously in the identification mark row direction. Since an index portion and a low light transmittance portion having a low light transmittance between the high light transmittance portion and an adjacent high light transmittance portion are formed on the light transmissive substrate, an identification mark is provided. Even if the identification marks are recorded at high density by narrowing the row spacing, etc., the low light transmittance is provided between the identification mark rows, so a stable reproduction signal is obtained without being affected by the adjacent identification mark rows. It will be possible to obtain. Further, in the above optical recording medium, the window layer has a low light transmittance in a state where it is not irradiated with light, and the light transmittance is irreversibly increased by absorbing light of a specific wavelength or heat of light. Since the high light transmittance portion is formed of a material before reproducing the information, a chromic material composed of an organic dye capable of clearly changing the light transmittance in minute units is used. Therefore, it is possible to form the high light transmittance portion at an accurate position with an accurate size.

Further, in the reproducing apparatus, the light transmittance of the window layer in the direction crossing the plurality of identification mark rows is detected by using the detection means, and the light transmittance is high at the intervals of the identification mark rows. Since the high light transmittance portion is formed by irradiating the spot light to the portion where the high light transmittance portion is not detected, the portion where the high light transmittance portion necessary for the reproducing device is not formed is formed. The structure of the detection means for detecting can be made simple.

[Brief description of drawings]

FIG. 1 is a sectional view of an optical recording medium according to an embodiment of the present invention.

FIG. 2 is a partially enlarged view of an optical recording medium according to an embodiment of the present invention.

FIG. 3 is a diagram showing light transmittance characteristics of the window layer in FIGS. 1 and 2.

FIG. 4 is a diagram for explaining a laser beam for forming a high light transmittance portion.

FIG. 5 is a schematic configuration diagram of a main part of an optical disk reproducing apparatus according to an embodiment of the present invention.

FIG. 6 is a flowchart showing an operation of the reproducing apparatus in FIG.

FIG. 7 is a diagram showing a part of the operation of the reproducing apparatus in FIG.

FIG. 8 is a diagram showing the sizes of pits and laser light spots of a conventional optical disc.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical recording medium (optical disk) 2 Substrate (light transmissive substrate) 3 Window layer 4 Reflective layer 5 Protective film 11 High light transmissivity part 12 Low light transmissivity part 21 Reproducing device 23 Optical head (light irradiation means) 26 Control circuit 27 Laser driver 28 Optical head drive circuit 29 Motor driver 31 Initialization determination circuit (detection means) d Spot diameter I Laser light for forming high light transmittance portion (light of specific wavelength) P pit (identification mark) PW pit width R Read laser light TP Track pitch

Claims (3)

[Claims] 1. An optical recording medium in which minute identification marks capable of being optically reproduced according to information are recorded as a plurality of identification mark rows on a light-transmissive substrate. A width, a high light transmittance portion having a high light transmittance continuously in the identification mark row direction, and a low light transmittance portion having a low light transmittance between the high light transmittance portion and the adjacent high light transmittance portion. An optical recording medium having the formed window layer on the light transmissive substrate. 2. The optical recording medium according to claim 1, wherein the window layer has a low light transmittance when not irradiated with light, and the light transmittance is irreversible by absorbing light of a specific wavelength or heat of light. An optical recording medium, which is made of a material having a variable light transmittance, which is increased in height, so that the high light transmittance portion is formed before reproducing the information. 3. A light transmittance is obtained by absorbing light of a specific wavelength or heat of light on a light-transmissive substrate on which minute identification marks that can be optically reproduced according to information are recorded as a plurality of identification mark rows. It has a window layer made of an irreversibly high light transmittance variable substance, and before reproducing the information, in a portion corresponding to the identification mark row of the window layer in the identification mark row direction with a substantially identification mark width. A reproducing device for an optical recording medium, which is configured to continuously form a high light transmittance portion having a high light transmittance, wherein a detecting means for detecting the light transmittance of the window layer, and a diameter substantially equal to the identification mark width. Light irradiation means for irradiating the spot light of the specific wavelength onto the wind layer, and using the detection means to detect the light transmittance of the wind layer in the direction crossing the plurality of identification mark rows. , The identification mark Reproduction of an optical recording medium, characterized in that the high light transmittance portion is formed by irradiating the spot light to the portion where high light transmittance is not detected at intervals by using the light irradiation means. apparatus.