JPS6089844A - Optical disc - Google Patents

Abstract

PURPOSE:To ensure the focus locking operation in a disc player or the like by coating a reflection preventing film decreasing the reflectance of light beam at the outer surface on the outer surface of an optical beam incident side of an optical disc. CONSTITUTION:The difference between the reflectance at a signal recording face 1b' and the reflectance at the outer surface 1e' of the light beam incident side is increased by a reflection preventing film 1d. Thus, when an optical disc 1' is loaded on an optical disc player and reproduced, a level V1 of a signal SSE when the incident light beam is converged to the signal recording face 1b' and a level V2 of the signal SSE when the light beam of the base 1a' is converged to the outer surface 1e' of the incident side is increased. Thus, a reference voltage level VR fed to a reference input terminal of a level comparator circuit 15 is set easily and surely between both the levels and the proper focus locking operation starting the focus servo control operation is attained surely.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical disk having a signal recording surface between a pair of outer surfaces that has a relatively low reflectivity for a signal reading light beam.

Background technology and its problems Optical discs, on which information signals recorded on a signal recording surface by an optical disc player are optically reproduced, are conventionally formed on a transparent substrate la, as shown by / in FIG. For example, a recording track consisting of an array of pits on which an information signal such as a television signal is recorded is coated with aluminum or the like to form a light reflecting layer. C, and is mounted on a disc player and rotated at, for example, a constant angular velocity.

The reproduction of such an optical disc/ is, for example, shown in FIG. 1! This is accomplished by a disc player having a focus control mechanism with a focus pull-in circuit, designated by the reference numerals below, and this disc player is configured as shown below to read the recording signal of the recording track of the optical disc. It looks like this.

In the figure, λ is a laser light source, for example, a semiconductor laser is used, and a laser light beam from this laser light source enters a polarizing beam splitter j via a diffraction grating plate 3 and a collimator lens≠.

The laser beam that has passed through the polarizing beam splitter j is
Objective lens 7 that constitutes an optical head via a 7-wavelength plate B
The light is then focused by the objective lens 7 and incident on the signal recording surface /b of the optical disc / via the transparent substrate /a or the transparent protective layer /C. The objective lens 7 is
In order to perform focus servo control, the focus control driving means g can control the position in a direction toward or away from the signal recording surface /b of the optical disc /. The incident laser beam that enters the signal recording surface /b of the optical disk / is modulated by the recording track and is reflected at the signal recording surface /b, enters the objective lens 7 again, and passes through the L wavelength plate B. and returns to enter the polarizing beam splitter j. This returned laser beam is then refracted to the right in the figure by a polarizing beam splitter j, and reaches the light receiving section 10 via a lens system. Then, a return laser light beam modulated by the optical disc/reading light beam from the objective lens 7 forming the optical head is detected by the photodetector forming the light receiving section 10, and the change is detected as an electrical signal. is extracted as.

Each part from the laser light source λ to the light receiving section 10 constitutes an optical pickup l/, and the entire optical pickup l/ can be moved integrally.

The electrical signal from the light receiving unit IO is supplied to the signal forming circuit/2, and from the signal forming circuit/2, an output signal Ss, which is an information signal component recorded on the optical disc l, and an incident laser light beam on the optical disc l are supplied. A focus error voltage SF is obtained according to the focus state of . This focus error voltage 5ptj: For example, the focus error voltage 5ptj becomes zero in a state where the focal position of the incident laser beam is placed on the signal recording surface /b which is the reflective surface of the optical disk l, that is, in a so-called just focus state. In the so-called overfocus state, where the focusing position of the incident laser beam is closer to the signal recording surface /b when viewed from the incident side, the focusing position of the incident laser beam takes a negative value corresponding to the degree of overfocus. In a state in which the position is farther than the signal recording surface /b when viewed from the incident side, that is, in a so-called under-focus state, the level changes in the shape of a figure-eight curve, taking a positive value corresponding to the extent. Further, the output signal Ss takes a relatively low level in an over-focus state or an under-focus state, and takes a high level in a just-focus state and a state close to the just-focus state. The signal is supplied to a reproduced signal processing circuit system including a demodulation circuit (not shown), and is also supplied to an envelope detection circuit/≠. A signal 88B having a level corresponding to the envelope level of the output signal Ss is obtained from the envelope detection circuit /ll-, and is supplied to the comparison input terminal of the level comparison circuit /j. The reference input terminal of the level comparison circuit /j is supplied with a predetermined level V It from the voltage source /2 that is exceeded only by the level of the signal 888 in the just focus state and a state relatively close to the just focus state.
A reference voltage is supplied to the output terminal of the level comparator circuit /j, which takes a constant high level when the level of the signal SSL' is equal to or higher than the level VB, and takes a constant low level at other times. Output C is obtained.

On the other hand, the focus error voltage SF from the signal forming circuit /2 is supplied to the zero cross detection circuit /7, and a high level generated corresponding to the zero cross point of the focus error voltage Sp is outputted to its output terminal. A pulse PO is obtained. This pulse Po and the comparison output C from the level comparison circuit /j
is supplied to the and gate/g, and the and gate/g
From then on, the pulse P is generated while the comparison output C takes a high level.
A pulse P8 is obtained which occurs only when O is obtained, and S
-R is supplied to the set terminal S of the flip-flop. S-R flip-flop/recent terminal RK
is a falling pulse generated in response to the fall of the comparison output C from a high level to a low level, which is obtained at the output terminal of the comparison output C from the level comparison circuit/event and is supplied to the fall detection circuit 20. 1] 1L is supplied. Then, from the output terminal Q of the S-R flip-flop, for example, an output Sw is obtained which is at a certain high level during the period from set to reset and at a constant low level during the other periods. is supplied to the control end of /.

switch,! The pair of switching contacts 2/A and 2/B of
- is supplied to the fixed contact 2/c, and a focus pull-in voltage VFO or a focus error voltage SF is selectively obtained at the fixed contact 2/c, and this is supplied to the drive control circuit 23. The drive control circuit 23 is a focus pull-in voltage V
A drive signal corresponding to FO or focus error voltage SF is supplied to focus control drive means g to operate focus control drive means ♂. In this case, the position of the objective lens 7 of the optical pickup/l is controlled, and the focus state of the incident laser beam is adjusted. Here, the portions indicated by reference numerals 1-2 in FIG. 1 constitute a focus pull-in circuit.

When focus servo control is performed under such a configuration, first, the switch 2/ is brought into a state where its switching contact 2/A is connected to the fixed contact 2/, and the focus is pulled in. A focus pull-in voltage VFO from the voltage generator 22 is supplied to the drive control circuit 23.

As a result, the focus control driving means g is operated in response to the focus pull-in voltage VFO, and the objective lens 7 is moved in the direction of its optical axis, so that the focusing position of the laser beam incident on the optical disk is adjusted to For example, the position may be changed from a position farther away from the signal recording surface /b of the optical disc / to approaching the signal recording surface /b. That is, the object moves from an over-focus state or an under-focus state to a just-focus state. When the state is relatively close to the just focus state, the level of the signal Ss + U from the envelope detection circuit /1 becomes higher than the level VR of the reference voltage from the voltage source /B, and the level comparison circuit / The comparison output C takes a high level. Thereafter, when the just focus state is reached, the level of the focus error signal becomes zero, and a pulse Po is obtained from the zero cross detection circuit/7. At this time, a pulse ps is obtained from the AND gate 1-/8', the S-R flip-flop/2 is set, and the output Sw from its output terminal Q becomes high level. When the output Sw of the S-R Freelough Flora 7'/9 becomes a high level, the switch No/ is switched and its switching contact 2/ is connected to the fixed contact 210, and the focus pull-in voltage is The focus error IE pressure Sl- is supplied to the drive control circuit 23 instead of the VFO.

As a result, the focus control driving means r
A focus servo control is performed in which the laser beam is operated based on the error voltage sy and controlled so that the incident laser beam maintains a just-focused state. Then, when the focal position of the incident laser beam moves out of the range where focus servo control can be performed, the comparison output C from the level comparison circuit lj falls from the high level to the low level, and in response to this fall, the comparison output C falls from the high level to the low level. A falling pulse Pa is obtained from the falling detection circuit 20, and the S-R flip-flop/Takari is reset.
The output Sw will be at a low level. For this reason,
Switch 2/ is again the focus pull-in voltage VFO
is supplied to the drive control circuit 23.

In this way, the focus pull-in circuit allows the focusing position of the laser beam incident on the optical disc to be in a just-focus state or a position relatively close to that L, that is, the signal recording surface of the optical disc. Focus servo control is performed on the ridges placed within a certain retraction range centered on lb. In such a case, the laser light beam incident on the optical disc / will be reflected on the outer surface of the optical disc / on the incident side, but as in the above example, if the optical disc /b is made of aluminum or the like, If the reflectance of the incident laser beam at the signal recording surface /1 is significantly higher than the reflectance of the outer surface of the optical disc, the optical disc Reflections on the outer surface of / can be ignored.

However, if the optical disk / is such that the reflectance of the incident laser beam on its signal recording surface /b is relatively low, the reflectance of the incident laser beam on the signal recording surface /b There is a small difference between the reflectance at the outer surface of the optical disc/, and the focusing position of the laser beam 30 incident on the optical disc/ is as shown by the solid line in FIG. When the just-focus state is on the signal recording surface lb of the optical disk, and the focusing position of the incident laser beam 30 as shown by the broken line in FIG. , the difference in the output signal S8 obtained from the signal forming circuit /2 and the difference in the focus error voltage SF on the surface opposite to the signal recording surface /b of the transparent substrate /a, respectively. become smaller. Therefore, in the focus pull-in circuit as described above, the voltage source /B is set so that the pulse P8 is obtained from the AND gate /g in the just focus state, and the S-R flip-flop /g is set. Once the level of the reference voltage from the answer gate/g is selected, a pulse ps can be obtained from the answer gate/g even when the focus position of the incident laser beam 30 is on the outer surface of the incident side of the optical disc/. This pulse Ps sets the S-R flip-flop, and switches the switch 2/ to supply the focus error voltage to the drive control circuit 3 instead of the focus pull-in voltage VPO. As a result, a proper focus pull-in operation may not be performed, and as a result, there is a risk that correct focus servo control may not be performed.

Purpose of the Invention In view of the above, the present invention aims to improve the reflectance of a light beam incident on an optical disk on a signal recording surface and the reflectance of the outer surface of the base or transparent protective layer of the optical disk on the light beam incident side. By reducing the reflectance on the outer surface on the light beam incident side, when the difference in The purpose of the present invention is to provide an optical disc that can perform focus servo control.

Summary of the Invention An optical disc according to the present invention includes a base body provided with a signal recording surface that reflects a light beam between a pair of opposing outer surfaces, and a transparent protective layer formed to cover the signal recording surface. It is characterized in that the outer surface on the light beam incident side is coated with an antireflection film that reduces the reflectance of the light beam on the outer surface.

By doing this, even if the reflectance on the signal recording surface of the optical disk is relatively low, there is a large difference between that reflectance and the reflectance on the outer surface of the substrate, etc. When this optical disc is played back, when the focus control means of the optical disc player is operated depending on the focus pull-in voltage, the focus position of the light beam incident on the disc is adjusted. However, there is a clear distinction between the state at or near the outer surface of the disk and the state at or near the signal recording surface, and the focusing position of the incident light beam on the disk is set at or near the signal recording surface. Thereafter, an appropriate focus pull-in operation is reliably performed by supplying the focus error voltage instead of the focus pull-in voltage to the focus control means.

Example Embodiments of the present invention will be described with reference to the drawings.

FIG. 3 is a cross-sectional view schematically showing an embodiment of the optical disc according to the present invention. In the figure, /' indicates the entire optical disc, and /a' indicates a transparent disc made of acrylic or the like. One of the planar surfaces is a signal recording surface /b', and a transparent protective layer /C' is formed to cover this signal recording surface /b'. The incident light beam is
Signal recording surface /b via a' or transparent protective layer /C'
' is irradiated from one direction, but the reflectance of the incident light beam at the signal recording surface/b' is relatively low. rate and signal recording surface/b' of substrate/a' or transparent protective layer/C'
The difference in reflectance from the outer surface, which is the opposite surface, is considered to be small.

Then, a transparent anti-reflection film /d is coated over almost the entire outer surface of the light beam incident side, in this embodiment, the outer surface of the substrate /a' on the side opposite to the signal recording surface /b'. Ru.

In general, anti-reflection coatings are used to reduce reflection loss on the surface of transparent materials such as glass and to increase transmittance.
A thin film applied to the surface of glass, etc., if its optical thickness is an odd multiple of 7 wavelengths of incident light or a value close to it,
The reflected light from the front and back surfaces has a phase difference that is opposite to each other or close to it, and the reflectance on the surface of the glass, etc. can be reduced. Furthermore, if the refractive index of the film is chosen to be the square root of the refractive index of the glass, etc. The reflectance on the surface of glass or the like can be O. And, such anti-reflection coating is
A visible single-layer film is formed by coating the surface of glass, etc. with MgF2, etc. using means such as vacuum evaporation, but a single-layer film can only reduce the reflectance for specific wavelengths. Therefore, in practice, the wavelength range in which the reflectance can be reduced is expanded by applying a multilayer coating such as a two-layer film or a three-layer film.

From the above point, the thickness of the epi-reflection prevention film /d is set to d/, and the wavelength of the reading light beam, for example, a laser beam, is λ/.
If the refractive index is 1]/, then the film thickness d/ and the refractive index n
The film thickness d/ of the anti-reflective film /d is set so that the product of /, that is, the film thickness above the anti-reflective film λ/
is determined. Note that since the laser beam has a single wavelength, a single layer of antireflection film can sufficiently reduce the reflectance on the outer surface of the substrate/a'. At this time, the base/
The phase change etc. of the anti-reflection film/d are determined so that the refractive index nλ of the acrylic or the like forming a' is different from the refractive index n7 of the anti-reflection film/d.

The optical disk /' whose outer surface is coated with the anti-reflection film /d thus formed is such that the reading laser beam incident on the signal recording surface /b' is focused on the signal recording surface /a'. Even if it is reflected on the outer surface opposite to surface /b', its reflectance is significantly reduced by the anti-reflection film /d, and the reflectance on signal recording surface /b' and the light beam incident on substrate /a' are significantly reduced. The difference in reflectance from the outer surface /e' of the side becomes large. Therefore, the optical disc/
When ' is installed in the optical disc player shown in FIG. The level of the signal SSI is / and the signal Ss+ when focused on the outer surface /e' of the light beam incident side of the substrate /a'.
The difference between the level V and the level V, 2 becomes so large that it is difficult to easily and reliably set the level VR of the reference voltage supplied to the reference input terminal of the level comparator circuit/j between the two levels. This makes it possible to reliably perform an appropriate focus pull-in operation that starts the focus servo control operation.

On the other hand, in the conventional optical disc shown in FIGS. 1 and 2, where the reflectance on the signal recording surface /b is relatively low, the reflectance on the signal recording surface /b Since the difference between the reflectance at the outer surface of the disk and
As shown in Figure B, the level V/ of the signal ssg when the incident light beam is focused on the signal recording surface /b and
The signal SSI when the light beam is focused on the outer surface of the incident side of
The difference between the levels V and 2 becomes smaller, and the reflectance on the signal recording surface /b and outer surface of the disc changes due to variations in the output of the laser light source, deterioration of the disc due to aging, etc. Due to this, regardless of fluctuations in the level of the signal 5SiN, the level of the reference voltage VIt supplied to the reference input terminal of the level comparison circuit/event is difficult to set reliably between the two levels. - It is not possible to reliably perform a proper focus pull-in operation to start the servo control operation.

Effects of the Invention As is clear from the above explanation, according to the optical disc according to the present invention, even if the reflectance of the light beam on the signal recording surface is relatively low, the reflection of the light beam on the signal recording surface is low. Even if the difference between the reflectance on the outer surface of the light beam incident side, which is the surface opposite to the signal recording surface of the transparent substrate or transparent protective layer, is small, the reflection on the outer surface of the light beam incident side is small. Since the disc is coated with a protective film, it is possible to reduce the reflectance on the outer surface on the side where the light beam enters, thus ensuring proper focus pull-in operation when it is installed in an optical disc player and played back. As a result, proper focus servo control can be performed.

1. Since the anti-reflection film can be made extremely thin, it has almost no effect on the external shape of the optical disc, and does not cause any inconvenience when it is mounted on a disc player or the like.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram used to explain when an optical disc is used for reproduction, Fig. 2 is a diagram used to explain the focusing state of a light beam on the optical disc, and Fig. 3 is an optical disc of the present invention. FIG. 1 is a schematic cross-sectional view showing an example of the present invention, and FIG. In the figure, 7' is an optical disk, /a' is a substrate, /b' is a signal recording surface, /C' is a transparent protective layer, and /d is an antireflection film. Agent: Patent attorney Sadaaki Kambara, ,l"'5.',:,1..
"+": i',, J. （、・、（＋：□ 、□ June 231, 1982) 1"1 Mr. Kazuo Wakasugi, Director General of the License Office (Mr. 4 Chief Examiner of the License Office) 1o Indication of the case Showa Sg Year Patent Application No. 1 Wag 90g 2. Name of the invention Optical Disc 3. Relationship with the case of the person making the amendment Patent applicant address 7-33 Otsu-chome, Kitashinyo-ku, Tokyo Parts Name
(21) The number of inventions will increase due to Sony Corporation representative Norio Oga 6, hli Masaru [None Kanji]
+7GO-F39844C7')+1.1 The claims are amended as shown in the attached document. 12C'2 Claims A base body having a signal recording surface that reflects a light beam between a pair of opposing outer surfaces, and a transparent protective layer formed to cover the signal recording surface. - An optical disc characterized in that the outer surface on the incident side of the light distribution beam is coated with an anti-fouling film that reduces the reflectance of the light beam on the outer surface.

Claims (1)

[Claims] a base body provided with a signal recording surface that reflects a light beam between a pair of opposing outer surfaces, and a transparent protective layer formed to cover the signal recording surface on the outer surface on the light beam incident side; An optical disc characterized in that it is coated with an antireflection film that reduces the reflectance of a light beam on the outer surface.