KR100633476B1 - Optical recording medium - Google Patents

Abstract

An optical recording medium having a grooved recording layer is disclosed. The structure of the plurality of unrecorded tracks should allow the scanning device to derive the radial tracking error signal in accordance with the push-pull method. In addition, the structure of the plurality of recorded tracks should allow the scanning device to induce a radial tracking error signal in accordance with the high frequency phase detection method. To this end, the width and depth of the grooves range from 0.3 to 0.6 times the wavelength divided by the numerical aperture of the radiation beam used to scan the recording medium, and 1/24 to 1/1 of the wavelength divided by the refractive index. It has a range of 7 times. The phase difference between the radiation beam reflected from the area on the track between the plurality of recorded marks and the radiation beam reflected from the mark ranges from 0.4 to 2.0 radians.

Optical record carrier, tracking error, push pull method, phase detection method, scanning device, phase difference, recording layer

Description

Optical recording medium {OPTICAL RECORDING MEDIUM}             

The present invention records and reads information using a radiation beam having a predetermined wavelength and a predetermined numerical aperture, and includes a recording layer, wherein the recording layer is from a first state to a second state upon irradiation with a radiation beam. And the recorded information is indicated by a plurality of recorded marks having a second state in the region of the first state, the plurality of marks being disposed inside a plurality of tracks having guide grooves having a width and a depth. And a first optical phase difference exists upon reflection from an area on the track in the first state and an area on the track in the second state, the first optical phase difference being between the first and the plurality of tracks in the first state. An optical record carrier for increasing an optical phase difference between regions on a track in a state.

Information can be stored inside such a recording medium by a scanning device having an optical head. This head focuses the radiation beam on the information layer inside the recording medium and follows the unrecorded track using tracking information derived from the grooves inside the track. In the case where the recording medium has a disc shape, the groove has a circular or spiral shape, and the tracking information has the form of a radial tracking error signal. When a relatively high power radiation beam is modulated by a signal representing the information to be recorded, the information is recorded inside a track in the form of a plurality of optically readable marks. During the reading process, the radiation beam has a relatively low output, and when reflected from the information layer, the radiation beam is modulated by a plurality of marks. The above tracking information can be derived from the plurality of grooves or from the recorded information during the reading process.

Optical record carriers such as those described in the preamble are known from Japanese Patent Application JP-A 5174380. The recording medium has a laminate comprising a plurality of optical thin film layers into which a recording layer is inserted. The thickness of the transparent layer of the stack adjacent to the recording layer is the area on the track in the first state, similarly to the area between the plurality of tracks in which the first optical phase difference between the unrecorded area of the track and the recorded area is in the first state. Is adjusted to increase the second optical phase difference therebetween. This relationship between the optical phase differences increases the information signal derived from the plurality of scanned marks. A disadvantage of such a conventional recording medium is that the track device can be properly followed by a scanning device using a so-called push-pull method and a phase detection method to derive a tracking signal from a plurality of marks recorded inside the information layer. It can not be. Push-pull and phase detection methods for deriving tracking information are known in particular from US Pat. Nos. 4 057 833 and 4 785 441, respectively.

After all, it is an object of the present invention to provide an optical recording medium capable of deriving tracking information from a plurality of marks recorded by the push-pull method and from the recorded information.

The purpose of this is that the recording medium described in the preamble has a width in the range of 0.3 to 0.6 times the width of the guide groove divided by the numerical aperture, and the depth of the guide groove divided by the refractive index that the wavelength encounters the radiation beam. Is in the range of 1/24 to 1/7 times, and the first optical retardation is in the range of 0.4 to 2.0 radians. The combination of the width of the groove and the specific value of the phase difference provides both the high quality push-pull signal and the phase detection signal and the high quality information signal from the plurality of recorded marks. At this time, the phase difference increases both the information signal and the push-pull signal. The minimum groove depth allows the injection device to derive a high quality push-pull signal from the plurality of grooves. Grooves deeper than the maximum groove depth degrade the quality of the phase detection signal. Moreover, the phase detection signal from the deeper grooves is strongly dependent on the defocus of the radiation beam. The depth of the groove is then given as the mechanical depth. The refractive index encountered by the radiation beam corresponds to the refractive index of the material between the plurality of grooves. When the radiation beam is incident on the recording layer through the substrate or through the protective layer, this material corresponds to the material of the transparent substrate or the protective layer, respectively. The width of the groove is preferably larger than the width of the plurality of marks intended to be recorded in the recording layer.

The tracking signal formed by the phase detection method is generally affected by the axial position of the focal point of the radiation beam relative to the position of the recording layer. When the radiation beam is not focused on the recording layer, the amplitude of the tracking signal is significantly reduced and even the sign is changed. If the first retardation falls in the range of 0.4 to 2.0 radians, this effect is reduced. Further reduction of this effect is obtained when the width and depth of the guide groove satisfy the following equation:

8.33 NA D / n + 121 NA / λ-400 NA Φ / λ <W,

Where NA is the numerical aperture, λ is the wavelength with nanometer units, Φ is the first optical phase difference with units in radians, n is the refractive index, D is the depth with units of λ / n, and W is width with units of λ / NA.

It is preferable that said 1st optical phase difference has a range of 0.4-1.1 radians. The recording medium having a phase difference smaller than this value exhibits an asymmetric tracking signal when induced by the phase detection method. When the radiation beam is focused below and above the recording layer, asymmetry appears as different amplitudes of the tracking signal. Possible measurements of this asymmetry correspond to (xy) / (2z), where x is the maximum value of the phase detection tracking error signal when the radiation beam is focused at a 1 μm location on the information surface, and y is The maximum value of the phase detection tracking error signal when the radiation beam is focused at a position of 1 μm below the information plane, and z is the maximum value of the phase detection tracking error signal when the radiation beam is focused on the information plane. .

When the ratio of the reflection intensity of the area on the track in the second state to the area on the track in the first state is greater than 0.15, the phase detection tracking signal is further improved. Such a recording medium is called a dark-writing recording medium. In the so-called white-writing recording medium, it is preferable that the ratio of the reflection intensity between the area on the track in the first state and the area on the track in the second state is greater than 0.15. When induced by the phase detection method, the symmetry of the tracking signal is improved when the ratio falls in the range of 0.3 to 0.5 for both the dark recording medium and the back recording medium.

In order to be able to derive an excellent information signal from the radiation reflected from the information layer, it is preferable that the reflection intensity of the area on the track in the first state is larger than 0.15. For the back recording recording medium, it is preferable that the reflection intensity of the area on the track in the second state is larger than 0.15.

Homes within the information layer may be used to store information, such as the address used to access the information. Such information may be stored in the form of a wobble of the depth or location of the groove. Therefore, the depth of the groove preferably has a range of 1/12 to 1/7 times the value obtained by dividing the wavelength of the radiation beam by the refractive index.

The optical retardation of the recording medium can be implemented by inserting the recording layer into a stack composed of a plurality of optical thin film layers and adjusting the thicknesses of the plurality of layers. In the case where the material of the recording layer in the first state has an imaginary part with a refractive index larger than 3.4, the design of the laminate becomes easy.

It is preferable that the material of the recording layer is a phase change type. When a plurality of amorphous marks are recorded inside the crystalline layer, the recording speed can be relatively high. At this time, the first state is a crystal state and the second state is an amorphous state.

Considering the unpublished International Patent Application No. IB97 / 01470, the recording medium has a combination of groove depth, groove width and track period as follows: 40 nm, 500 nm, 900 nm and 55 nm, 400 nm, 900 nm and Disclosed is a recording medium having a refractive index of 1.58 and a design wavelength of 670 nm, all of which are 51 nm, 500 nm and 870 nm.

These and other inventions of the present invention will become more apparent from the examples described below.

In the drawings,             

1 is a cross-sectional view of a recording medium according to the present invention;

2 is a plan view of the recording layer of the recording medium;

3 shows an injection apparatus for scanning a recording medium according to the present invention,

4A shows a circuit diagram of an apparatus for forming a push-pull radial tracking error signal,

4B shows a circuit diagram of an apparatus for forming an error signal in the DTD radial direction.

1 shows an information recording medium 1 according to the invention designed to record and read information using a focused radiation beam having a specific design wavelength and numerical aperture. The recording medium 1 comprises a transparent substrate 2 and a recording layer 3. The recording layer can be scanned by a radiation beam incident on the recording layer through the substrate 2. The recording layer 3 is inserted into the stack 4 composed of a plurality of optical thin film layers disposed on the substrate 2. This laminate includes a transparent interference layer 5, a recording layer 3, another interference layer 6, and a reflection layer 7 when viewed from the substrate side. The laminate 4 is isolated from environmental influences by the protective layer 8.

The substrate 2 has a groove pattern on a surface on which the laminate 4 is disposed. For a disc shaped record carrier, the groove pattern has a plurality of circular or helical grooves. When viewed from the side of the laminate, the portion of the groove pattern shown in the figure for forming a depression inside the substrate is called a groove 9. From the same point of view, the part of the pattern shown in the figure forming the raised portion is called the land 10. At this time, the width of the groove is determined at the upper end of the groove, that is, at the land height. The thickness of the layer inside the laminate 4 is so small that the pattern on the substrate 2 is also present inside the recording layer 3. The following embodiment is designed to record in the groove 9 of the recording medium. In contrast, if the recording medium is designed to record in part 10, the optimum parameter values for the depth and width of the grooves according to the invention apply likewise, but part 9 of the pattern shown in the figure should be called as land, and part You should call 10 home.

Example I

The substrate of the recording medium is made of polycarbonate (PC) having a refractive index of 1.58 at a design wavelength of 670 nm and a numerical aperture of 0.60. The interference layer 5 is a 90 nm thick layer consisting of 80% ZnS and 20% SiO ₂ with a refractive index of 2.13. The recording layer 3 is a 30 nm thick layer of GeSb ₂ Te ₄ having a refractive index of 4.1-i 2.1 when in an amorphous state and a refractive index of 3.6-i 4.2 when in a crystalline state. The interference layer 6 is a 30 nm thick layer of the same material as the interference layer 5. The reflective layer 7 is a 100 nm thick layer of aluminum alloy with a refractive index of 1.98-7.81. The mechanical thickness d of the grooves 9 is 55 nm, the width w of the grooves is 450 nm, and the pitch of the grooves which is the track pitch is 740 nm. The thickness D of the groove without dimension is equal to dn / λ, where n is the refractive index of the substrate and the width W of the groove without dimension is w NA / λ = 0.403.

2 shows a part of the recording layer 3 having grooves 9 and lands 10. At this time, the information is recorded in the home. Initially, the recording layer 3 is in a crystalline state. During the recording process, an amorphous region 11 called a mark is formed inside the recording layer. The length and position of the mark indicates the information recorded on the recording medium. In the amorphous state, the reflection intensity of the laminate 4 in the region of the recording layer is 0.07. The reflection intensity of the laminate 4 in the region in the crystalline state is 0.18. Therefore, the ratio of amorphous reflectivity to crystal reflectivity is 0.39. At this time, these two reflection intensities were measured using a radiation beam focused on the grooveless area.

The radiation reflected from the region in the crystalline state on the track, denoted 'a' in FIG. 2, is between the tracks and is similarly ahead of phase by 1.64 compared to the radiation reflected from the region 'b' in the crystalline state. The radiation reflected from the region in the amorphous state on the track, denoted by 'c' in FIG. 2, is out of phase with the radiation reflected from the region reflected in the region in the crystalline state on the track by 0.6 radians. Thus, the phase difference between the land and the groove is increased by the phase difference between the area between the mark and the plurality of marks. In other words, the effective depth of the groove is increased at the position of the mark.

The push-pull tracking error signal has a measured maximum value greater than 95% of the value obtained for a record carrier having a groove depth optimized for the maximum push-pull signal. The so-called DTD-2 type phase detection tracking error signal has a maximum value of 0.69 clock periods at a radial tracking deviation of 0.1 mu m of the focal spot when measured by a scanning device described later. The value of the tracking error signal corresponds to a time difference normalized to the channel clock period used to record the information on the recording medium. When the focus spot is out of focus by one depth of focus, the tracking error signal changes less than 10%.

Example II

The substrate of the record carrier is likewise made of polycarbonate (PC) having a refractive index of 1.58 at a design wavelength of 670 nm. The laminate has layers in the same order as shown in FIG. 1. The interference layer 5 is a 95 nm thick layer of 80% ZnS and 20% SiO ₂ with a refractive index of 2.13. The recording layer 3 is a 25 nm thick layer of a GeSb ₂ Te ₄ phase change material having a refractive index of 4.1-i 2.1 when in an amorphous state and a refractive index of 3.6-i 4.2 when in a crystalline state. The interference layer 6 is a 35 nm thick layer of the same material as the interference layer 5. The reflective layer 7 is also a 100 nm thick layer made of an aluminum alloy with a refractive index of 1.98-7.81. The depth of the grooves 9 is 35 nm, the width of the grooves is 550 nm and the pitch of the grooves is 740 nm.

The information is recorded inside the grooves in the form of amorphous marks inside the crystalline environment. The reflection intensity of the laminate 4 in the region of the recording layer in the amorphous state is 0.05. The reflection intensity of the laminate 4 in the region in the crystalline state is 0.16, therefore, the ratio of amorphous reflectivity to crystal reflectivity is 0.31, in which there are no grooves in the two regions.

The radiation reflected from the region 'a' in the amorphous state on the track shown in FIG. 2 is in phase by 1.04 radians between the tracks and likewise reflected from the region in the crystalline state. The radiation reflected from the region 'c' in the amorphous state on the track in FIG. 2 is out of phase by 0.7 radians compared to the radiation reflected from the region 'a' in the crystalline state on the track in FIG. 2.

The push-pull tracking error signal has a measured maximum value greater than 85% of the value obtained for a recording medium having a groove depth optimized for the maximum push-pull signal. The phase detection tracking error signal has a 0.72 clock period value at a radial tracking deviation of 0.1 mu m. When the focus spot is out of focus by one depth of focus, the tracking error signal changes less than 25%.

Although the above-described embodiment of the recording medium according to the present invention relates to a recording medium in which an amorphous mark is recorded in a crystalline environment, the present invention is equally well applied to a recording medium in which a crystalline mark is recorded in an amorphous environment. Can be. The present invention is not limited to a recording medium in which information is recorded in a groove, but can also be applied to a recording medium in which information is recorded in a land between a plurality of grooves. The laminate 4 may have various forms. Another reflective layer can be disposed between the substrate 2 and the interference layer 5 of the stack 4 as shown in FIG. 1. Alternatively, another interference layer and a reflective layer can be inserted between the stack and the substrate. The laminate may comprise only layers 3, 4 and 5, which laminate is very suitable for recording media for write once. The material of the recording layer may be a phase change material, a dye, or any other material suitable for optically recording information therein.

Injection device

3 shows an optical scanning device suitable for recording and reading information on a recording medium according to the present invention. In the figure, a part of the record carrier 1 is shown which contains embossed information in the form of a plurality of pits and a plurality of bumps. The information layer is scanned through the substrate 2. At this time, the recording medium may include more than one information layer disposed on each other.

The apparatus comprises a radiation source 12 of a semiconductor laser, for example for emitting a radiation beam 13. For the sake of simplicity, the radiation beam is focused on the information layer 3 by the objective lens 14 represented by one lens in the figure. The radiation reflected by the information layer is directed to the detection system 15 via the beam splitter. This beam splitter may be a translucent plate, a diffraction grating, and may have polarization dependence. The detection system converts the incident radiation into one or more electronic signals, which are supplied to the electronic circuit 16 to induce an information signal _Si and a control signal representing information read from the recording medium. . One of the control signals is a radial tracking error signal S _r representing the distance between the center of the spot formed on the information plane by the radiation beam and the center line of the track being scanned. Another control signal is a focus error signal S _f which represents the distance between the focus of the radiation beam and the information plane. These two error signals are input to the servo circuit 17, which controls the position of the focal point of the radiation beam. In the figure, focus control is realized by moving the objective lens 14 in the direction of its optical axis in response to the focus error signal, while radial tracking is the direction across the track in response to the radial tracking error. This is realized by moving the objective lens. During the recording process, the intensity of the radiation source is modulated by the information to be recorded.

4A and 4B show an associated electronic circuit 16 for deriving a radial tracking error signal from the layout of the detection system 15 and the detection signal. 4A shows a circuit for deriving a radial tracking error signal in accordance with the push-pull method. The detector 15 is provided with a quadrant detector having detection elements A, B, C and D which are sensitive to four radiations. The detection signals generated from the detection elements A and B are added to the amplifier 18 and amplified. Similarly, the detection signals generated from the detection elements C and D are added and amplified by the amplifier 19. The outputs of the amplifiers 18 and 19 are connected to a differential amplifier 20 which forms the difference between the two input signals. The output signal of the differential amplifier 20 corresponds to the tracking error signal S _r (PP) in the push pull radial direction. Such an error signal is well suited for controlling a radial tracking servo in a portion of a recording medium having a track without a recorded mark.

Figure 4b shows a circuit for inducing a radial error signal in accordance with the high frequency phase detection method. Detector signals generated from elements A and C of the detection system 15 are added and amplified by the amplifier 21. The output of the amplifier 21 is given inside the slicer 22. The slicer digitizes the input signal by detecting the level crossing point of the input signal using the detection level. The detection signals of the elements B and D of the detection system 20 are added and amplified in the amplifier 23, and the output of this amplifier is connected to the input of the slicer 24. The output signals of amplifiers 21 and 23, before being given to slicers 22 and 24, respectively, can be shaped by an equalizer to compensate for the effect of the optical system of the scanning device on the detector signal. The digital output signals of slicers 22 and 24 are given to a phase comparator 25, which produces an output signal depending on the phase between the pulses at the two inputs of the comparator. The output signal of the comparator 25 is low pass filtered by the filter 26. The output signal S _r of filter 26 corresponds to a radial tracking error signal derived according to a diagonal time-difference (DTD) method corresponding to a particular embodiment of the phase detection method. This error signal is suitable for controlling the radial tracking servo in the portion of the recording medium comprising a plurality of recorded marks.

The plurality of recorded tracks on the record carrier according to the invention may be arranged at different high frequency frequencies, such as the analogue method of the method shown in FIG. 4b, or in particular the analogue or digital method of the phase detection method known from US Pat. No. 4,785,441. It may be followed using a radial tracking error signal derived according to the phase detection method.

Claims (10)

Record and read information using a radiation beam having a predetermined wavelength and a predetermined numerical aperture, and having a recording layer, the recording layer changing from a first state to a second state upon irradiation with a radiation beam, The recorded information is represented by a plurality of recorded marks having a second state in an area of the first state, the plurality of marks being disposed inside a plurality of tracks having guide grooves having a width and a depth, There is a first optical phase difference upon reflection from the area on the track in the state and the area on the track in the second state, the first optical phase difference being the area between the plurality of tracks in the first state and the track in the first state. In an optical recording medium for increasing the optical phase difference between the areas of the image, the width of the guide groove has a range of 0.3 to 0.6 times the wavelength divided by the numerical aperture, and the depth of the guide groove is such that the radiation beam encounters the wavelength. Has a range of 1/24 to 1/7 times the value divided by the refractive index, the first optical phase difference is in the range of 0.4 to 2.0 radians, and the recording layer contains a material whose imaginary part of the refractive index in the first state is larger than 3.4. An optical record carrier, characterized in that. The method of claim 1, An optical recording medium, characterized in that the width and depth of the guide groove satisfy the following equation: 8.33 NA D / n + 121 NA / λ-400 NA Φ / λ <W, Where NA is the numerical aperture, λ is the wavelength of the radiation beam with nanometers, Φ is the first optical retardation with radians, n is the refractive index, and D is the depth with units of λ / n. , W is a width with units of lambda / NA. The method of claim 1, And the ratio of the reflection intensity between the area on the track in the second state and the area on the track in the first state is greater than 0.15. The method of claim 1, And the ratio of the reflection intensity of the area on the track in the first state to the area on the track in the second state is greater than 0.15. The method of claim 4, wherein And the reflection intensity of the area on the track in the first state is greater than 0.15. The method of claim 5, And the reflection intensity of the area on the track in the second state is greater than 0.15. The method of claim 1, And the depth of the guide groove has a range of 1/12 to 1/7 times the wavelength divided by the refractive index. delete The method of claim 1, And the recording layer comprises a phase change material. The method of claim 9, And the second state is amorphous.

Images