JPH05298705A - Optical recorder/reproducer - Google Patents

Abstract

PURPOSE:To provide an optical recorder/reproducer in which a high signal/noise ratio can be obtained by effectively reducing groove noise caused by fluctuation of the wall face profile of a guide groove. CONSTITUTION:The optical recorder/reproducer records/reproduces information by projecting a light beam 18 through an objective lens 19 onto an optical recording medium 10 which records the information by forming a record mark in a guide groove 17. In such optical recorder/reproducer, the guide groove 17 is formed such that the ratio of average width of the guide groove 17 to a value (lambda/NA), obtained by dividing the wavelength lambda of the light beam 18 by the numerical aperture(NA) of the objective lens 19, will come within a range of 0.25-0.4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording / reproducing apparatus for recording / reproducing information by irradiating a light beam.

[0002]

2. Description of the Related Art An optical disk device is a typical optical recording / reproducing device for recording / reproducing information by irradiating a light beam. In an optical disc device, recording and / or reproducing are performed by irradiating a light beam such as a laser beam along a spiral or concentric circular track on a disc-shaped optical recording medium called an optical disc.
As an optical disk device that allows users to record information on an optical disk, a document file system etc. was initially commercialized, and a product for use as a peripheral storage device of a computer that requires higher reliability was also put to practical use. Has been done. Further, a device that can erase recorded information and rewrite the information has also been put into practical use. Further, development of an optical card memory device, an optical tape memory, and the like, in which the same technique as that of the optical disc is applied to a card-shaped or tape-shaped recording medium, is being advanced.

In an optical recording medium used in such an optical recording / reproducing apparatus, for example, a recording mark having a size of about 1 μm has a track pitch of about 1.6 μm by a laser beam whose spot diameter is narrowed to about 1.2 μm. Formed on the track. The recording mark is formed by causing local destruction or deformation in the recording layer, pits or bubbles due to deformation, or change in optical properties due to phase change.

As a technique for so-called tracking in which a recording mark train, that is, a track is followed by a laser beam at the time of reproduction, a guide groove for tracking is previously formed on an optical disk, and a tracking error signal is obtained from diffracted light by this groove. A method of generating and tracking, a method of sampling signals obtained from marks such as wobbled pits formed by slightly shifting to the left and right of the track, comparing both sample values, and generating a tracking error signal to perform tracking Are known.

The optical recording / reproducing apparatus as described above is required to have a large capacity and a small size as the application or the application field is expanded, like the other storage apparatuses. Therefore, the recording density is being improved. .. Further, various recording materials and film structures of media have been developed in order to realize rewriting and overwriting of information.

FIG. 4 is a diagram showing a typical structure of a conventional optical recording medium such as an optical disk, together with a part of a recording / reproducing optical system. In FIG. 4, the optical recording medium 100 is a substrate 1.
01, an inner protective layer 102, a recording layer 103, an outer protective layer 104, a reflective layer 105 made of a metal film, and a disc protective layer 106 are sequentially laminated.
It is set to about m to several hundred nm. Light beam 108
Is emitted from the substrate 101 side through the objective lens 109.

A guide groove 107 for tracking is formed continuously along the track direction or continuously except a part of the area. The guide groove 107 is set so as to sufficiently secure the signal levels of the track cross signal and the push-pull signal generated during reproduction, and not to lower the level of the information signal too much. In designing the guide groove 107, conventionally, the shape parameters of the groove have been determined by theoretical calculation of a diffracted light by a computer, measurement experiments of various signal levels, and the like.

However, even if a recording medium having a structure in which the shape of the guide groove is determined in this manner is manufactured, the expected reproduction signal quality cannot always be obtained. One of the biggest causes is noise caused by minute fluctuations in the wall shape of the guide groove due to roughness of the medium surface, non-uniformity generated in processes such as exposure and development during the substrate manufacturing process, and so-called This is because groove noise mixes in the reproduced signal. For this reason, a desired signal-to-noise ratio cannot be obtained for the reproduced signal, which is an obstacle to improvement of recording density and reliability.

[0009]

As described above, in the conventional optical recording / reproducing apparatus, since the groove noise caused by the fluctuation of the wall shape of the guide groove is mixed in the reproduced signal, the desired signal-to-noise ratio at the time of reproducing is desired. However, there is a problem in that it is an obstacle to improvement of recording density and reliability.

The present invention has been made in order to solve such a problem, and optical recording / reproducing in which a large signal-to-noise ratio can be obtained by effectively reducing the groove noise caused by the variation of the wall shape of the guide groove. The purpose is to provide a device.

[0011]

In order to solve the above-mentioned problems, the present invention provides an optical recording medium for recording information by forming a recording mark in a guide groove by irradiating a light beam through an objective lens. In an optical recording / reproducing apparatus of the in-groove recording system for recording / reproducing information, the wavelength (λ) of the light beam is divided by the numerical aperture (NA) of the objective lens (λ
/ NA), the guide groove is formed so that the ratio of the average width from the top to the bottom of the guide groove falls within the range of 0.25 to 0.4.

Further, the present invention is directed to a case where the guide grooves are
That is, in the optical recording / reproducing apparatus of the inter-groove recording system for recording / reproducing information by irradiating the optical beam on the optical recording medium for recording information by forming recording marks on the land through the objective lens, The ratio of the value obtained by dividing the average width from the top to the bottom of the guide groove from the track pitch to the value (λ / NA) obtained by dividing the wavelength (λ) by the numerical aperture (NA) of the objective lens is 0.25 to 0.4. It is characterized in that the guide groove is formed so as to fall within the range.

[0013]

In this way, in the groove recording method, λ
The ratio of the average width from the top of the guide groove to the bottom of the guide groove is set in the range of 0.25 to 0.4. In the inter-groove recording method, the average width from the top to the bottom of the guide groove is set to λ / NA. By setting the ratio of the value subtracted from the track pitch in the range of 0.25 to 0.4, noise caused by the fluctuation of the reflected light caused by the fluctuation of the wall shape of the guide groove during reproduction, so-called groove noise, interferes. Greatly suppressed by the effect.

The spot of the light beam applied to the optical recording medium during reproduction is composed of a central portion (main lobe) which is not diffracted and a peripheral portion (side lobe) which is generated by diffraction in the optical system. Since the reflected light from the medium surface due to the light beam spot is detected and the reproduction is performed, the fluctuation of the wall shape of the guide groove, which causes the groove noise, affects the reproduced signal through both lobes. However, conventionally, the size of the light beam spot is made relatively small with respect to the width of the region where the recording mark is formed (the guide groove in the case of recording in the groove, and the land in the case of recording between the grooves). The influence on the reproduced signal due to the change in shape is dominated by the side lobe, which is the peripheral portion of the light beam spot.

Here, according to the present invention, the ratio of the average width from the top to the bottom of the guide groove or the value obtained by subtracting the average width from the track pitch and λ / NA representing the spot size of the main lobe of the light beam is calculated. If the setting is made smaller as in the invention, the degree to which the main lobe touches the wall surface of the guide groove becomes large. As a result, the influence of the fluctuation of the wall shape of the guide groove on the reproduced signal through the main lobe is moderately large, so that the influence of the fluctuation of the wall shape of the guide groove on the reproduced signal through the side lobe is reduced, and the groove noise is reduced. Is reduced.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a view showing the arrangement of an optical recording / reproducing apparatus according to an embodiment of the present invention, and particularly shows a sectional structure of an optical recording medium and a part of a recording / reproducing optical system.

In FIG. 1, a recording medium 10 is formed, for example, in the shape of a disc as a whole, and an inner protective layer 12, a recording layer 13, an outer protective layer 14, a reflective layer 15 made of a metal film, and a disc protective layer 16 are provided on a substrate 11. The layers 12 to 15 are set to have a thickness of several tens to several hundreds of nm, and the disk protective layer 16 has a thickness of several tens to several hundreds of μm. At the time of recording / reproducing, a light beam 18 emitted from a light source (not shown) and guided through a known optical system is narrowed down by an objective lens 19 and irradiated from the substrate 11 side.

Further, a guide groove 17 for tracking, that is, for causing a light beam to follow a track, is formed continuously on the substrate 11 along the track direction or continuously except a part of the area. In this embodiment, a so-called in-groove recording method is used in which recording marks such as pits and changes in optical properties due to phase changes are formed in the guide grooves 17. Next, the cross-sectional shape of the guide groove 17 will be described in detail.

FIG. 2 shows the result of calculating the groove noise in the reproduced signal from the optical recording / reproducing apparatus of FIG. 1 by the diffracted light analysis method proposed by the present inventor. The diffracted light analysis method used here is the magazine “Optics” Vol. 20, No. 4, No. 314-
Page 215 “Analysis of Diffracted Light on Optical Disk” Edited by Japan Optical Society, April 1991. In FIG. 2, the vertical axis represents the groove noise included in the reproduced signal, that is, the noise power due to the variation in the wall shape of the guide groove 17, and the horizontal axis represents the guide groove 17 which is the area where the light beam is irradiated and tracked. The average width W _AVE , that is, the average value of the width from the top to the bottom of the groove.

As shown in FIG. 1, the guide groove 17 is usually formed so that the bottom portion is narrower than the top portion.
Then, the width W1 at the top and the width W2 at the bottom of the guide groove 17
Difference ΔW (= W1-W2) as a parameter, the average width W of the guide groove 17 for each value of ΔW
The change in noise power against _AVE is plotted. The wavelength λ of the light beam 18 was 690 nm, and the numerical aperture NA of the objective lens 19 was 0.55.

Further, according to the well-known conclusion that can be derived from the formula of the diffracted light analysis, the wavelength λ is set to the objective lens numerical aperture N.
The width W1 at the top of the guide groove 17, the width W2 at the bottom, and the average width W measured in units of the value λ / NA divided by A
If the values of _AVE , track pitch, and light beam spot size on the medium are the same, the distribution of diffracted light will be the same even if the actual physical dimensions are different. Therefore, in FIG. 2, λ / N
Shown together W ratio of _{AVE W AVE / (λ / NA} ) for A in the horizontal axis, further the ratio ΔW / (λ / NA) of the [Delta] W for in correspondence with each value lambda / NA of [Delta] W in Fig. 4 Shows. In this example, λ / NA = 690 nm / 0.55 =
It is 1.255 μm.

Looking at the calculation result of FIG. 2, it is characteristic that the noise power becomes minimum when the average width W _AVE of the guide groove 17 has a certain value regardless of the value of ΔW. It is the first time the present inventor has found that the noise power when W _AVE is plotted on the horizontal axis is the smallest, and in the example of FIG. 2, it is the optimum point where the noise power is the smallest. W _AVE is approximately 0.4 μm. W
_AVE = 0.4 μm is 0.3 for W _AVE / (λ / NA)
Equivalent to eighteen.

However, it is not necessary to strictly set W _AVE / (λ / NA) to 0.318, and practically 0.25 to 0.
A range of 4 is sufficient. Conventionally, the case of inter-groove recording, which will be described later, will be described. However, W _AVE / (λ
The value of / NA) is about 0.75. Compared to this,
It can be seen that when W _AVE / (λ / NA) is selected in the range of 0.25 to 0.4, the noise power is reduced by 10 dB or more. In particular, W _AVE / (λ / NA) is 0.29 to 0.
If it is selected within the range of 35, the noise power becomes smaller and the effect becomes more remarkable.

Thus, the average width W of the guide groove 17 is
_The noise power becomes minimum when _AVE and W _AVE / (λ / NA) have certain values. Under these conditions, the fluctuation of the wall shape of the guide groove 17 affects the reproduction signal through the main lobe of the light beam spot. It is considered that the influence and the influence exerted on the reproduction signal by the side lobe (particularly, the first side lobe) caused by the diffraction of the optical system are canceled out. Further, the reason why the noise power increases when W _AVE and W _AVE / (λ / NA) are made larger than the optimum point is that the latter effect is relatively large and the direction of the conventional technology is increased. It is considered that the noise is increased when the value is made smaller because the influence of the former is relatively increased.

As shown in FIG. 2, the noise power itself increases as the difference ΔW between the widths of the upper portion and the lower portion of the guide groove 17 increases. Therefore, it is desirable that the wall surface of the guide groove 17 stands up at a steep angle, and ideally ΔW = 0, but it is difficult to set it to 0 in reality in manufacturing. Therefore, in the present embodiment, Δ is taken into consideration in consideration of the degree of deterioration of the guide groove 17 and the noise allowable range of the system.
The guide groove 17 is formed while suppressing the value of W to about 0.2 μm.

Next, an embodiment in which the present invention is applied to the inter-groove recording system will be described with reference to FIG. 3, parts having the same functions as those in FIG. 1 are designated by the same reference numerals. The difference between this embodiment and the embodiment of FIG. 1 is that the recording marks are formed between the guide grooves 17 at the time of recording, that is, on the lands 20, so the method of setting the average width of the guide grooves 17 is different. is there.

The calculation result of the noise power by the diffracted light analysis method in this embodiment is equivalent to the result obtained by replacing the horizontal axis in FIG. That is, in FIG. 2, the horizontal axis is the guide groove 1.
The average width W _{AVE of} 7 and the ratio W _AVE / (λ / NA) of the average width to λ / NA are used. In this embodiment, the value Tp−W _AVE obtained by subtracting W _AVE from the track pitch Tp, and Ratio of value to λ / NA (Tp-W _AVE ) / (λ
/ NA). Since Tp- _WAVE corresponds to the average width of the land 20 which is the region where the light beam 18 is irradiated and tracked in this embodiment, such a replacement can be said to be appropriate.

Since the horizontal axis of FIG. 2 can be read in this way, the same tendency as in the previous embodiment can be concluded. That is, Tp-W _{AVE is} approximately 0.4 μm, and (Tp-W _AVE ) / (λ / NA) is 0 regardless of the value of the difference ΔW between the upper width W1 and the bottom width W2 of the guide groove 17. .318, the noise power becomes minimum. In this example, the track pitch Tp is 1.1 μm, and the average width W _AVE of the guide groove 17 is 0.7 μm. Also in this embodiment, it is not necessary to strictly set (W _AVE -Tp) / (λ / NA) to 0.318, and practically 0.25 to 0.
It is sufficient if it is within the range of 4, especially 0.29 to 0.3
If you select within the range of 5, the noise power will be further reduced,
The effect becomes more remarkable.

The conditions set in this embodiment will be compared with the conventional optical disk. Numerical examples conforming to the standard specifications of the 130 mm optical disk according to ISO, for example, the wavelength of the light beam is 830 nm, and the value of λ / NA is 1.59 μ.
m. The track pitch is 1.6 μm, and the inter-groove recording is performed as in the present embodiment. The shape of the guide groove is not specified as shape parameters such as width and depth. Instead, the push-pull signal obtained during reproduction is 0.4 to 0.65 of the baseline reflectance.
Double track crossing signal is 0.3 ~
It is specified as a reproduction signal characteristic such as 0.6 times. According to the diffracted light analysis and actual measurement, the average width of the guide groove satisfying this characteristic is slightly less than 0.4 μm, and the difference from the track pitch is 1.2 μm. When expressed as a ratio to λ / NA, it is 0.75 as described above.

In this embodiment, the width of the guide groove 17 is set to be wider than the width based on the above-mentioned reproduction signal characteristic specification, and the width of the land 20 where the light beam spot is formed is narrowed. The guide groove 17 is provided more. As a result, the influence of the fluctuation of the wall shape of the guide groove 17 on the reproduction signal through the main lobe of the light beam spot becomes moderately larger than in the conventional case, and the noise power is reduced by the same principle as in the previous embodiment. You can In this embodiment, the push-pull signal and the track crossing signal may not satisfy the standard specifications, but it can be dealt with by adjusting the amplification factor of the servo system control circuit, etc. is there.

The present invention is not limited to the above embodiments, but can be implemented with various modifications. For example, the present invention can be applied even when the structure of the optical recording medium, the material of the substrate or each layer, and the like are different from those shown in the embodiments.
Further, the numerical values such as the wavelength of the light beam, the numerical aperture of the objective lens, and the track pitch given in the examples are merely examples, and may be variously changed, and accordingly, the average width of the guide groove may be changed.

Furthermore, although the embodiments are mainly directed to the write-once or rewritable optical recording medium, the present invention is also effective when a read-only optical recording medium such as a video disc is used. is there. In the case of a read-only type, generally, a medium is formed with pit rows corresponding to information almost periodically, and at the time of reproduction, a light beam tracks the pit row to perform reproduction. This is physically equivalent to scanning with a light beam on a guide groove formed discontinuously. Therefore, in this case, by considering the pit row as a guide groove and forming the average width of the pits under the same conditions as in the embodiment of FIG. 1, a noise reduction effect can be expected by the same principle.

[0033]

As described above, according to the present invention, it is possible to effectively reduce the groove noise caused by the fluctuation of the reflected light due to the fluctuation of the wall shape of the guide groove at the time of reproducing, and thereby the signal-to-noise of the reproduced signal. It is possible to increase the ratio. As a result, it is possible to improve the recording density and the recording reliability. Moreover, the present invention can be easily implemented only by setting the average width of the guide groove or the difference between the average width and the track pitch.

[Brief description of drawings]

FIG. 1 is a diagram showing a main part of an optical recording medium and a recording / reproducing system according to an embodiment of the present invention.

FIG. 2 is a diagram showing a calculation result of noise power by a diffracted light analysis method for the example.

FIG. 3 is a diagram showing a main part of an optical recording medium and a recording / reproducing system according to another embodiment of the present invention.

FIG. 4 is a diagram showing a part of a conventional optical disc and a recording / reproducing system.

[Explanation of symbols]

10 ... Optical recording medium 11 ... Substrate 12 ... Inner protective layer 13 ... Recording layer 14 ... Outer protective layer 15 ... Reflective layer 16 ... Disk protective layer 17 ... Guide groove 18 ... Light beam 19 ... Objective lens 20 ... Land

Claims (2)

[Claims] 1. A guide groove for tracking,
An optical recording medium for recording information by forming recording marks in the guide groove and a recording / reproducing means for recording / reproducing information by irradiating the optical recording medium with a light beam through an objective lens are provided. In the optical recording / reproducing apparatus provided with, the guide groove has a ratio of an average width from the top to the bottom of the groove to a value obtained by dividing the wavelength of the light beam by the numerical aperture of the objective lens is 0.25 to 0.4. An optical recording / reproducing apparatus characterized by being set so as to fall within the range. 2. A guide groove for tracking is provided,
An optical recording medium for recording information by forming recording marks between the guide grooves, and a recording / reproducing means for recording / reproducing information by irradiating the optical recording medium with a light beam through an objective lens. In the optical recording / reproducing apparatus provided with, the guide groove is a ratio of a value obtained by subtracting an average width from the groove top to the bottom to a value obtained by dividing a wavelength of the light beam by a numerical aperture of the objective lens from the track pitch. Is set to fall within the range of 0.25 to 0.4.