JPWO2012025973A1 - Data recording method and optical disc apparatus for multilayer optical disc - Google Patents

Abstract

The present invention is a data recording method for recording data on a multilayer optical disc having a plurality of information recording layers having N layers (N is an integer of 2 or more). The kth information recording layer is the kth information recording layer (k is an integer satisfying 1 ≦ k ≦ N) from the innermost side of the multilayer optical disc. In this method, step A (disc discriminating) for obtaining the number of information recording layers included in the optical disc loaded in the optical disc apparatus, and when the number of layers is X (X is an integer of 2 or more), the m-th information recording is performed. Step B (OPC execution) in which test recording of data is performed in a test recording area in a layer (m is an integer satisfying 1 ≦ m ≦ X−1) and provisional initial recording optical power is determined, and data is recorded Step C for selecting a correction coefficient according to which information recording layer is the information recording layer and correcting the temporary initial recording light power based on the selected correction coefficient to determine the initial recording light power; And D for starting to record data on the target information recording layer with the initial recording light power.

Description

  The present invention relates to a data recording method performed on a multilayer optical disc having a plurality of information recording layers. The present invention also relates to an optical disc apparatus that executes this data recording method.

  Data recorded on the optical disk is reproduced by irradiating a rotating optical disk with a relatively weak light beam having a constant intensity and detecting reflected light modulated by the optical disk. In a reproduction-only optical disc, information by pits is previously recorded in a spiral shape at the manufacturing stage of the optical disc. On the other hand, in a rewritable optical disk, a recording material film capable of optically recording / reproducing data is deposited on the surface of a substrate on which a track having spiral lands or grooves is formed by a method such as vapor deposition. Has been. When data is recorded on a rewritable optical disc, the optical disc is irradiated with a light beam whose light intensity is modulated in accordance with the data to be recorded, thereby changing the characteristics of the recording material film locally to write the data. Do.

  The pit depth, track depth, and recording material film thickness are smaller than the thickness of the optical disk substrate. For this reason, the portion of the optical disc where data is recorded constitutes a two-dimensional surface and may be referred to as a “recording surface” or an “information surface”. In this specification, in consideration of the fact that such a surface has a physical size also in the depth direction, instead of using the phrase “recording surface (information surface)”, “information recording layer” We will use the phrase. The optical disc has at least one such information recording layer. One information recording layer may actually include a plurality of layers such as a phase change material layer and a reflective layer.

  In a recordable optical disc or a rewritable optical disc, when data is recorded on the information recording layer, the information recording layer is irradiated with the light beam whose light intensity is modulated as described above, so that the crystalline phase change material layer is irradiated. An amorphous recording mark is formed. This amorphous recording mark is formed by rapidly cooling after a part of the information recording layer irradiated with the recording light beam rises to a temperature higher than the melting point. If the light intensity at the time of irradiating the recording beam with the light beam is set low, the temperature of the recording mark irradiated with the light beam does not exceed the melting point and returns to crystalline after rapid cooling (erasing of the recording mark). In this way, the recording mark can be rewritten many times. If the intensity of the light beam (recording light power) when recording data is inappropriate, the shape of the recording mark may be distorted, making it difficult to reproduce the data.

  Since the reflectance of the amorphous recording mark is different from the reflectance of the surrounding crystalline part, the intensity of the reflected light during reproduction varies depending on the presence or absence of the recording mark. In the area where data is recorded (recorded area), there are rows of recording marks and spaces having different lengths depending on the contents of the data to be recorded. For this reason, the optical characteristics (light reflectance and transmittance) of the recorded area are different from the optical characteristics of the area where data is not recorded (unrecorded area).

  When reproducing data recorded on an optical disc or recording data on a recordable optical disc, the light beam must always be in a predetermined focused state on a target track in the information recording layer. For this purpose, “focus control” and “tracking control” are required. In “focus control”, the position of the objective lens is referred to as the normal direction of the information surface (hereinafter referred to as “the depth direction of the substrate”) so that the position of the focal point (focusing point) of the light beam is always on the information recording layer. There is a case.) On the other hand, the tracking control is to control the position of the objective lens in the radial direction of the optical disc (hereinafter referred to as “disc radial direction”) so that the spot of the light beam is located on a predetermined track.

  In order to perform the above-described focus control and tracking control, it is necessary to detect a focus shift or a track shift based on the light reflected from the optical disc and adjust the position of the light beam spot so as to reduce the shift. It is. The magnitudes of the focus shift and the track shift are indicated by a “focus error (FE) signal” and a “tracking error (TE) signal” generated based on the reflected light from the optical disc, respectively.

  In recent years, optical discs in which two information recording layers are laminated are put on the market, and multilayer optical discs in which three or more information recording layers are laminated are being developed. In this specification, an optical disc on which N layers (N is an integer of 2 or more) is referred to as a “multilayer optical disc”.

  When reproducing data from the target information recording layer of the multilayer optical disk or writing data to the target information recording layer, the optical disk apparatus aligns the focus position of the light beam on the target information recording layer, It is necessary to form a small light spot on the information recording layer. Since one multilayer optical disc has a plurality of information recording layers, when the focus position of the light beam is adjusted to the information recording layer located at the innermost position, for example, the light beam passes through the information recording layer located at the front side. It will be.

  Unless the light beam intensity (recording light power) at the time of writing data is optimized, the shape of the recording mark becomes inappropriate as described above, and the reproduction error rate increases. In order to optimize the recording light power, a plurality of data is recorded with different recording light powers in the test recording area of the information recording layer provided in the optical disc, and these data are reproduced. In this way, an index such as a reproduction error is measured in the test recording area, and the recording light power at which the index shows the most preferable value is determined. Strictly speaking, such optimization of recording light power is optimization of “initial recording light power”. After the data recording in the user area is started with the initial recording light power determined by the above method, the recording light power is changed from the initial recording light power to a more appropriate level at any time based on, for example, a β value described later. Can be corrected. In the present specification, the processing performed by the optical disc apparatus to determine the initial recording optical power in the test recording area is referred to as “Optimum Power Control (OPC)”.

  FIG. 1A is a diagram showing a multilayer optical disc 10, and FIG. 1B is a schematic sectional view thereof. A multilayer optical disc 10 shown in FIG. 1 includes a first information recording layer L0 located farthest from the disc surface 10a on which the light beam is incident, and a second information recording layer L1 closest to the disc surface 10a. ing. The multilayer optical disc 10 is provided with a user data area in which user data is recorded, and a test recording area (PCA: Power Calibration Area) located on the inner periphery side of the disc with respect to the user area. The multi-layer optical disc 10 is provided with a management area other than PCA, but for simplicity, it is not shown in FIG.

  FIG. 2 is a diagram showing a part of the cross section of the multilayer optical disc 10 shown in FIG. 1B in more detail. In FIG. 2, a light beam focused on three different areas a, b, and c in the information recording layer L0 is schematically shown. The area a is an area (unrecorded area) in which no data is recorded in any of the information recording layers L0 and L1 in the PCA. Similarly, the area b is an area (unrecorded area) in which no data is recorded in any of the information recording layers L0 and L1 in the user data area. On the other hand, the area c is an area (recorded area) in which data is recorded in the information recording layer L1 in the user data area.

  In the information recording layer L1, the light transmittance of an area where data is recorded is different from the light transmittance of an area where data is not recorded. In many optical discs, the light transmittance in an area where data is recorded is lower than the light transmittance in an area where data is not recorded. For this reason, the light beam focused on the information recording layer L0 in the region c is transmitted through the portion where the light transmittance is relatively low in the information recording layer L1. As a result, the intensity of the light beam on the information recording layer L0 is lower in the region c than in the region b.

  As described above, the amount of light that can be given to the information recording layer L0 by the light beam focused on the information recording layer L0 is applied to the information recording layer L1 located in front of the information recording layer L0 (side closer to the disk surface). It will change depending on whether data is recorded.

  FIG. 3 is a graph showing the relationship between the error rate and the recording light power when the data recorded in the information recording layer L0 is reproduced. The horizontal axis of the graph is the recording light power (power), and the vertical axis is the error rate during reproduction (L0 error rate). FIG. 3 shows a curve indicating the result in the areas a and b which are the unrecorded areas shown in FIG. 2 and a curve indicating the result in the area c which is the recorded area shown in FIG.

  As can be seen from FIG. 3, in areas a and b, the error rate is minimized when the recording light power is PWb. That is, it is understood that it is preferable to set the recording light power to PWb in the unrecorded areas (areas a and b). On the other hand, in the area c, the error rate is minimized when the recording light power is PWc. That is, it can be seen that in the recorded area (area c), it is preferable to set the recording light power to PWc larger than PWb. Thus, in the area c, which is a recorded area, it is preferable to write data with a recording light power higher than the recording light power for the areas a, b which are unrecorded areas.

  Conventionally, when data is recorded at a specific address position in a user data area of an optical disc, it is unknown whether the position is in a recorded area or an unrecorded area. For this reason, the initial recording light power at the start of data recording is set to an optimum value in the unrecorded area (PWb in the example of FIG. 3). In this case, after starting data recording in the user data area, the recording light power is corrected based on the index indicating the waveform of the reproduction signal while reproducing the data at short time intervals.

  FIG. 4A is a diagram showing a cross section of the multilayer optical disc 10 and corresponds to FIG. FIG. 4B is a diagram showing a temporal transition by correction of the recording light power when data is started to be recorded in the area b which is an unrecorded area with the initial recording light power PWb. On the other hand, FIG. 4C is a diagram showing a temporal transition due to correction of the recording light power when data is started to be recorded in the area c which is a recorded area with the initial recording light power PWb.

  In the example of FIG. 4B, the recording light power is held at PWb which is the optimum value in the region b. On the other hand, in the example of FIG. 4C, the recording light power is corrected so as to increase toward the optimum value PWc in the region c.

  As the number of information recording layers included in the multilayer optical disk increases, for example, when the information recording layer L0 located on the farthest side is in focus, the number of information recording layers positioned in front of the information recording layer L0 increases to 2 or more. . For this reason, in the recorded area in which data is recorded in a plurality of information recording layers positioned in front of them, the light transmittance is significantly reduced.

  FIG. 5A is a schematic cross-sectional view of a multilayer optical disc having three information recording layers L0, L1, and L2. FIG. 5B is a diagram showing a temporal transition by correction of the recording light power when data is started to be recorded in the area b which is an unrecorded area with the initial recording light power PWb. On the other hand, FIG. 5C is a diagram showing a temporal transition due to correction of the recording light power when data is started to be recorded in the area e which is a recorded area with the initial recording light power PWb.

  In the example of FIG. 5C, the recording light power is corrected so as to increase toward the optimum value PWe in the region e, but it takes a longer time to reach the optimum value PWe. It is thought that there is. The reason is that, in the area e, data is recorded in both of the two information recording layers L1 and L2, so that the degree of decrease in light transmittance due to them is large, and the optimum value PWe of the recording light power in the area e is This is because there is a possibility that the optimum value PWb of the recording light power in the areas a and b is greatly different.

  In the future, it is expected that the number of information recording layers included in the multilayer optical disc will increase further, for example, to become four or more. Even in such a multi-layer optical disc, when data recording is started with the recording light power PWb optimized in the area a which is an unrecorded area, there is a problem that the recording light power cannot be corrected to a more preferable magnitude in a short time. is there. Therefore, Patent Document 1 discloses a technique for performing OPC with PCA for each possible combination of a recorded area and an unrecorded area.

  In Patent Document 2, in addition to the disclosed contents of Patent Document 1, by managing the addresses of recorded areas and unrecorded areas, it is determined whether they are recorded areas or unrecorded areas, and initial recording is performed according to the determination result. A technique for changing optical power is disclosed.

JP 2008-108388 A JP 2008-192258 A

  According to the technique of Patent Document 1, many portions are consumed for test recording by PCA, and the time required for test recording increases. These have the problem of increasing geometrically as the number of optical disc layers increases.

  According to the technique of Patent Document 2, since recorded areas / unrecorded areas in each information recording layer are managed on the basis of addresses, a positional deviation (bonding error) occurs between the upper and lower information recording layers to be stacked. The positions of the recorded area and the unrecorded area cannot be accurately determined based on the address. For example, when data is recorded at a specified address position of the information recording layer L0, an area before the address position is determined based on the address in the information recording layer L1, and whether or not data is recorded in the area. However, if there is a physical shift between the information recording layer L0 and the information recording layer L1, the correspondence based on the address may be incorrect.

  As described above, both Patent Documents 1 and 2 have problems and are not practical. Therefore, the present inventor did not obtain the best recording characteristics as a concept that is not disclosed in any of Patent Documents 1 and 2, and thought that the recording characteristics should be guaranteed within an allowable range. That is, the first initial optimum recording light power for recording data in a situation where data is not written in all other information recording layers in the multilayer optical disc, and data is written in all other information recording layers in the multilayer optical disc. The initial recording light power is determined so as to be positioned between the second initial optimum recording light power for recording data under the present circumstances, and after the initial recording using the initial recording light power, the reproduction characteristics are improved. The concept of dynamically changing the recording light power is adopted accordingly. With this concept, the PCA is not increased according to the number of layers of the optical disc, and the recording characteristics can be guaranteed within an allowable range regardless of whether the other layer is a recorded area or an unrecorded area.

  The present invention has been made to solve the above-mentioned problems, and its main purpose is to correspond to the position and thickness direction in which the data is recorded when the data is recorded in the user data area, and the data Provided is a data recording method that can be promptly corrected to the optimum size regardless of whether the position in the other information recording layer located before the information recording layer on which is recorded is in the recorded area or the unrecorded area There is. Another object of the present invention is to provide an optical disc apparatus for executing the data recording method.

  The data recording method of the present invention is a data recording method for recording data on a multilayer optical disc having a plurality of information recording layers having N layers (N is an integer of 2 or more), and is the innermost side of the multilayer optical disc. Step A for determining the number of information recording layers included in the optical disc loaded in the optical disc apparatus, where k is the kth information recording layer (k is an integer satisfying 1 ≦ k ≦ N) When the number of layers is X (X is an integer of 2 or more), data is stored in the test recording area in the m-th information recording layer (m is an integer satisfying 1 ≦ m ≦ X−1) for performing test recording. Step B for determining a temporary initial recording light power and selecting a correction coefficient in accordance with the number of the information recording layer as the target information recording layer for recording data, and selecting the selected correction Said provisional initial based on the coefficient Comprising a step C of determining the initial recording beam power to correct the Rokuko power, and a step D to start recording data on the target information recording layer in the initial recording light power.

  In one embodiment, in the step B, when the number of layers is X (X is an integer of 2 or more), the m-th information recording layer (m satisfies 1 ≦ m ≦ X−1) for performing test recording. A test recording of data in unrecorded areas in which no data is written in all the information recording layers from the (m + 1) th information recording layer to the Xth information recording layer, A temporary initial recording light power is determined.

  In one embodiment, the step C selects the correction coefficient depending on the type of the optical disk loaded in addition to the information recording layer of the target information recording layer.

  In one embodiment, for each information recording layer included in each multilayer optical disc supported by the optical disc apparatus, correction coefficient information in which the correction coefficient value is given for each type of the multilayer optical disc is recorded in a memory of the optical disc apparatus. Including the steps of:

  In one embodiment, the initial recording light power determined in the step C is larger than the temporary initial recording light power in the case of a light transmittance reduction type multilayer optical disc.

  In one embodiment, the method further includes a step of changing the recording light power from the initial recording light power as needed based on a signal waveform obtained from the optical disk after starting to record data in the step D.

  In one embodiment, after recording data in the step D, the recording light power is adjusted so that the β value indicating the symmetry of the signal amplitude with respect to the average value of the reproduction signal obtained from the optical disc approaches the target β value. The method further includes a step of correcting.

  In some embodiments, m = 1.

  The optical disk apparatus of the present invention is an optical disk apparatus for recording data on a multilayer optical disk having a plurality of information recording layers having N layers (N is an integer of 2 or more), and optically accesses the multilayer optical disk. For each of the information recording layers included in each multilayer optical disk supported by the optical pickup device, an optical pickup, a memory for storing correction coefficient information in which a correction coefficient value is given for each type of the multilayer optical disk, and a loaded multilayer After performing a test recording of data in a test recording area in an information recording layer included in an optical disc and determining a provisional initial recording light power, what number information recording layer is the target information recording layer for recording data The correction coefficient is selected from the memory according to the correction, and the temporary initial recording light power is corrected based on the selected correction coefficient. And a recording processing unit for determining a recording light power.

  According to the present invention, when data is recorded in the user data area, the other information recording layer corresponding to the position where the data is recorded and the thickness direction, and positioned before the information recording layer where the data is recorded It is possible to provide a data recording method that can be promptly corrected to an optimum size regardless of whether the position in the recorded area or unrecorded area.

(A) is a figure which shows the multilayer optical disk 10, (b) is the cross-sectional schematic diagram. It is a figure which shows a part of cross section of the multilayer optical disk 10 shown in FIG.1 (b) in detail. It is a graph which shows the relationship between the error rate when reproducing | regenerating the data recorded on the information recording layer L0, and recording optical power. The horizontal axis of the graph represents the recording light power (power), and the vertical axis represents the error rate during reproduction (error rate of the information recording layer L0). (A) is a schematic cross-sectional view of a multilayer optical disc including two information recording layers L0 and L1, and (b) is an information recording layer L0 in an area b where the information recording layer L1 is an unrecorded area with the initial recording light power PWb. FIG. 8C is a diagram showing a temporal transition due to correction of the recording light power when data is started to be recorded, FIG. 10C is an information recording layer L0 in the area c where the information recording layer L1 is a recorded area with the initial recording light power PWb. It is a figure which shows the time transition by correction | amendment of recording optical power when data is started to be recorded. (A) is a schematic cross-sectional view of a multilayer optical disc including three information recording layers L0, L1, and L2. (B) is an unrecorded area of the information recording layer L1 and the information recording layer L2 with the initial recording light power PWb. The figure which shows the time transition by correction | amendment of recording light power when data is started to be recorded on the information recording layer L0 of the area | region b, (c) is information recording layer L1 and information recording layer L2 with initial recording light power PWb. The figure which shows the time transition by correction | amendment of recording light power at the time of beginning to record data on the information recording layer L0 of the area | region e which is a recorded area | region, (d) is information recording layer L1 with initial recording light power PWmid. The figure which shows the time transition by correction | amendment of recording optical power when the information recording layer L2 starts recording data on the information recording layer L0 of the area | region b which is an unrecorded area, (e) is initial recording optical power PWmid. Information recording layer L1 and It is a timing chart showing a sequence by the correction of the recording light power when the broadcast recording layer L2 begins to record data on the information recording layer L0 of the region e is recorded area. (A) is a schematic cross-sectional view of a multilayer optical disc having three information recording layers L0, L1, and L2. (B) is an error when reproducing data recorded on the information recording layer L0 in the case of a three-layer optical disc. It is a graph which shows the relationship between a rate and recording optical power. (A) is a schematic cross-sectional view of a multilayer optical disc including three information recording layers L0, L1, and L2 in which the light transmittance of the recorded region is higher than the light transmittance of the unrecorded region, and (b) is the three layers. 4 is a graph showing a relationship between an error rate and recording light power when data recorded in an unrecorded recording layer L0 is reproduced on an optical disc. (A) is a schematic cross-sectional view of a multilayer optical disc including four information recording layers L0, L1, L2, and L3, and (b) is a case where data recorded on the information recording layer L0 is reproduced in the case of a four-layer optical disc. 5 is a graph showing the relationship between the error rate and the recording light power. It is a table which shows an example of a correction coefficient. It is a graph which shows typically the waveform of the reproduction signal (RF signal) obtained from the area where data was recorded. 5 is a graph showing a relationship between an error rate and recording light power when data recorded on an information recording layer L0 is reproduced in the case of a three-layer optical disc. It is a graph which shows typically the relation between beta value and recording light power. It is a block diagram which shows the structural example of embodiment of the optical disk apparatus by this invention. It is a flowchart which shows an example of the power setting method in this embodiment. It is a flowchart which shows the prior art example of a power setting method. It is a flowchart which shows an example of the data recording method in this embodiment. It is a figure which shows typically the cross section of the optical disk from which a sensitivity falls toward the outer peripheral side from a disc inner peripheral side. It is a graph which shows the relationship between the error rate and recording optical power in area | region a, b, b ', e, e'. It is a graph which shows the relationship between (beta) value and recording light power in area | region a, b, b ', e, e'. FIG. 6 is a diagram illustrating an example of changes in β value, recording light power, and error rate when data is recorded in areas e, b, c, d, e, and b in the embodiment of the present invention. In the embodiment of the present invention, the β value, the recording light power, and the error rate when data is recorded in the areas e ′, b ′, c ′, d ′, e ′, b ′ that are relatively less sensitive than PCA. It is a figure which shows an example of a change of.

  The data recording method of the present invention is a method of recording data on a multilayer optical disc having a plurality of information recording layers having N layers (N is an integer of 2 or more). Here, the k-th information recording layer (k is an integer satisfying 1 ≦ k ≦ N) from the information recording layer on the innermost side (position far from the light incident surface) of the multilayer optical disc is defined as the k-th information recording layer. . For example, in the case of the three-layer optical disc shown in FIG. 5A, the information recording layer L0 is a “first information recording layer”, and the information recording layer L1 is a “second information recording layer”. When the total number of layers of the multilayer optical disc is X (X is an integer of 2 or more), the test recording area in the m-th information recording layer (m is an integer satisfying 1 ≦ m ≦ X−1) for performing test recording Of these, an area in which no data is written in all the information recording layers from the (m + 1) th information recording layer to the Xth information recording layer is referred to as an “unrecorded area”. In the following description, the information recording layer for performing test recording for OPC is the “first information recording layer” located on the farthest side, but the present invention is not limited to this example. For example, test recording for OPC may be performed on the second information recording layer, or test recording for OPC may be performed on each information recording layer.

  First, the basic operation principle of the present invention will be described with reference to FIGS. 5 (d) and 5 (e). In the present invention, as shown in FIGS. 5D and 5E, an intermediate value (PWmid) of the recording light power in the region b and the region e is used as the initial recording light power. For this reason, in either the region b or the region e, it is necessary to correct the optimum power based on, for example, the β value after starting data recording. However, the time required to complete such correction can be shortened. The correction based on the β value is sometimes referred to as “running optimal power control (ROPC)” in order to distinguish it from OPC performed in PCA.

  The initial recording light power when starting the above data recording is obtained by multiplying the “temporary initial recording light power” by a correction coefficient described later. This “temporary initial recording light power” is the optimum value (PWa = PWb) of the recording light power obtained by performing the OPC in the unrecorded area in the test recording area.

  In the current optical disc technology, while one recording mark is formed by irradiation with a light beam, the light intensity of the light beam is not constant but changes in a pulse shape. The pulse waveform used to form the recording mark is determined by the write strategy. The “recording light power” in this specification means the peak value of each pulse constituting the recording light beam. The peak value of each pulse is common in one recording mark.

  Next, the relationship between the initial recording light power and the temporary initial recording light power (PWa = PWb) will be described with reference to FIGS. 6 (a) and 6 (b). FIG. 6 relates to a light transmittance decreasing type optical disc in which the light transmittance in the recorded area is lower than the light transmittance in the unrecorded area. FIG. 6A is a diagram corresponding to FIG. 5A, and FIG. 6B shows an error rate when data recorded in the unrecorded recording layer L0 is reproduced in the case of a three-layer optical disc. It is a graph which shows the relationship with recording optical power. FIG. 6B shows a curve indicating the result in the areas a and b which are unrecorded areas and a curve indicating the result in the area e which is the recorded area. A similar curve can be obtained by changing the vertical axis from error rate to jitter.

  As can be seen from FIG. 6B, in the areas a and b, the error rate becomes the minimum value when the recording light power is PWb. On the other hand, in the area e, the error rate becomes the minimum value when the recording light power is PWe. In the example of FIG. 6B, the minimum value of the error rate is level R1. When data is recorded in the area e with the recording light power set to PWb, the error rate during reproduction reaches level R2. Similarly, when data is recorded in the area b with the recording light power set to PWe, the error rate during reproduction reaches the level R2. If the level R2 exceeds the reproduction limit, when data recording is started, the data is recorded in a state where it cannot be normally reproduced.

  In the graph of FIG. 6B, for the sake of simplicity, the curve showing the results in the regions a and b and the curve showing the results in the region e have the same shape, but the actual curves are different. Also good. In that case, the minimum value of the curve indicating the result in the regions a and b is not equal to the minimum value of the curve indicating the result in the region e.

  In the embodiment of the present invention, the recording optical power at the start of data recording is set to PWmid (= PWb × correction coefficient) instead of PWb. In the example of FIG. 6B, the correction coefficient is a numerical value larger than 1. As can be seen from FIG. 6B, when data is recorded in the area b with the recording light power set to PWmid, the error rate during reproduction becomes level R3. Similarly, even if data is recorded in the area e with the recording light power set to PWmid, the error rate during reproduction can be suppressed to level R3. This prevents data from being recorded in a bad state so as to exceed the reproduction limit when data is recorded in either of the areas b and e.

  Furthermore, according to the present embodiment, when data recording is started, the difference between the initial value and the optimum value of the recording light power, that is, the value of “PWe-PWmid” or “PWmid-PWb” is “PWe-PWb”. Than enough. For this reason, it becomes possible to shorten the time required for the subsequent correction based on the β value. This is clear when FIG. 5C is compared with FIGS. 5D and 5E. In the examples of FIGS. 5D and 5E, the correction based on the β value is necessary when data is recorded in either of the areas b and e. The time required for the correction is shown in FIG. It won't be too long like in the example.

  Next, refer to FIGS. 7A and 7B. FIG. 7 relates to an optical transmittance increasing type optical disc in which the light transmittance in the recorded area is higher than the light transmittance in the unrecorded area. In such an optical disc, it is possible to form a recording mark having a preferable shape with a recording light power lower than that in the areas a and b which are unrecorded areas in the area e which is a recorded area. In this case, the optimum value PWe in the recorded area is smaller than the optimum value PWb in the unrecorded area. Also in the example as shown in FIG. 7, in this embodiment, the recording light power is set to PWmid (= PWb × correction coefficient). The correction coefficient at this time is smaller than 1.

  Next, refer to FIGS. 8A and 8B. FIG. 8A schematically shows a cross section of a four-layer disc, which relates to an optical disc with reduced light transmittance. In the area f which is a recorded area, data is recorded in the three information recording layers L1, L2, and L3. FIG. 8B is a graph showing the relationship between the error rate and the recording light power when the data recorded in the information recording layer L0 is reproduced in the case of a four-layer optical disc, and the area a, which is an unrecorded area, A curve indicating the result in b and a curve indicating the result in the area f which is the recorded area are described.

  In the example shown in FIG. 8B, the difference between the optimum recording light power values PWf and PWb is large. For this reason, the correction coefficient by which PWb is multiplied in order to obtain the intermediate value PWmid is also relatively large.

  FIG. 9 is a table showing an example of the correction coefficient. In the example shown in FIG. 9, since there are differences in the structure and material of the optical disk depending on the disk manufacturer, the correction coefficient is set to a different value. Further, the value of the correction coefficient changes depending on how many information recording layers exist before the information recording layer for recording data. For example, in the case of a BD-R three-layer disc manufactured by Company A, when data is recorded on the information recording layer L0, the correction coefficient is 1.30, but data is recorded on the information recording layer L1 of the same optical disc. The correction factor is 1.15. The reason is as follows.

  When data is recorded on the information recording layer L0, two information recording layers L1 and L2 exist before the information recording layer L0. For this reason, the light beam focused on the information recording layer L0 is transmitted through the two information recording layers L1 and L2. On the other hand, when data is recorded on the information recording layer L1, there is only one information recording layer L2 before the information recording layer L1. For this reason, the light beam focused on the information recording layer L0 transmits only one information recording layer L2. The smaller the information recording layer that is transmitted, the smaller the absolute value of the difference between the optimum value PWe in the recorded area and the optimum value PWb in the recorded area. As a result, the value of PWmid, which is an intermediate value, can be set to a value close to PWb, and the correction coefficient also approaches 1. When the total number of layers of the multilayer optical disc apparatus is X (X is an integer of 2 or more), the correction coefficient when data is recorded on the Xth information recording layer may be 1.

  As described above, since the correction coefficient depends on the type of the multilayer optical disk including the above-described disk type, it is necessary to determine the correction coefficient for each different type of optical disk in advance. For this purpose, test recording is performed on a plurality of different types of optical discs, and the relationship between the reproduction signal index (for example, error rate or jitter) and the recording optical power is measured for each information recording layer of the optical disc. It is necessary to determine PWb. Further, a correction coefficient (PWmid / PWb) is calculated by determining PWmid for each information recording layer of the optical disc. In this way, for example, correction coefficient data shown in FIG. 9 can be acquired. The magnitude of PWmid may be obtained, for example, by obtaining two curves as shown in FIG. 6B by test recording and calculating the intermediate values of the minimum values PWb and PWe of these curves. However, PWmid is not necessarily equal to (PWb + PWe) / 2, and may be between the minimum values PWb and PWe.

  The correction coefficient data is preferably stored in a memory provided in the optical disc apparatus. The correction coefficient stored in the memory of the optical disk device can be updated through, for example, communication / broadcasting for an optical disk that is newly manufactured after the optical disk device is purchased by the user. Further, the correction coefficient related to each optical disk may be recorded on the optical disk itself. In that case, the optical disk apparatus may read correction coefficient data from the loaded optical disk and calculate the initial recording light power using the correction coefficient.

  The optical disc apparatus according to a preferred embodiment of the present invention discriminates the type of the optical disc loaded in the optical disc apparatus in order to appropriately select the “correction coefficient” used when calculating PWmid from PWb. Then, the correction coefficient most suitable for the optical disc is read from a memory in which data as shown in FIG. 9 is recorded, for example. If there is no corresponding disk in the memory, update at that time or use a correction coefficient of a disk with the same number of recording layers. The type of the optical disc may be determined by any known method, but the type of the optical disc may be determined by reading the disc information from the management area of the reference layer (for example, the information recording layer L0).

  Next, the β value will be described with reference to FIG. FIG. 10 is a graph schematically showing a waveform of a reproduction signal (RF signal) obtained from an area where data is recorded. When the average value A of the RF signal is used as a reference and the upper and lower amplitudes are P and B, the β value is represented by (P−B) / (P + B). The higher the vertical symmetry with respect to the average value A, the closer the β value approaches zero. In the example shown in FIG. 10, since P> B, the β value is positive. If P <B, the β value is negative.

  In this specification, the β value obtained when the shape or size of the recording mark is optimum is described as “β_best”. In a preferred embodiment of the present invention, the recording light power is corrected from the initial setting value (PWmid) to another value using the β value as an index. In this correction, when the β value is larger than β_best, the recording light power is changed so as to decrease the β value. When the β value is smaller than β_best, the recording light power is changed so as to increase the β value. In this way, the recording light power is corrected so that the β value becomes substantially equal to β_best. Such correction of the recording light power is executed in the process of recording the user data in the user data area.

  Next, the relationship between the β value and the recording light power will be described with reference to FIGS. 11 and 12. FIG. 11 is a graph corresponding to FIG. FIG. 11 shows a lower limit value PWlow and an upper limit value PWhigh that define a recording light power range in which the error rate is below the reproduction limit. The error rates b_PWb and e_PWb at the optimum value PWb of the recording light power in the unrecorded area, the error rates e_PWe and b_PWe at the optimum value PWe of the recording light power in the recorded area, and the error rate e_PWmid at the intermediate value PWmid of the both recording light powers. , B_PWmid are also shown.

  PWmid may be set equal to the average value of the recording light powers PWlow and PWhigh which is the reproduction limit. When the shape of the curve shown in FIG. 11 is extremely asymmetric, it is preferable to employ an average value of the recording light powers PWlow and PWhigh that is the reproduction limit as PWmid. The intermediate value does not need to be an average value in a strict sense, and is preferably a value that is as far as possible from both the upper limit value and the lower limit value of the recording light power that becomes the reproduction limit. For example, when the left part of the curve in FIG. 11 is steep and the right part has a gentle shape, if data is recorded in the area e with the recording light power of the average value of PWb and PWe, the reproduction limit may be exceeded. Becomes higher. However, if the average value of PWlow and PWhigh is set to Pmid and data is recorded with the recording light power of that magnitude, it is easy to realize recording that can be reproduced in both the area b and the area e.

  The setting of PWmid is performed in advance for each optical disc. That is, for various optical disks, it is necessary to obtain the relationship between the recording light power and the error rate by actual measurement in both the unrecorded area and the recorded area. It is calculated how many times the minimum value PWb (= PWa) obtained in the unrecorded area is to be the PWmid set by the above method, and a correction coefficient (PWmid / PWb) is obtained. On the other hand, in OPC performed when an optical disk is loaded in the optical disk apparatus, test recording may be performed only in an unrecorded area in the PCA of the optical disk. That is, in OPC, PWmid can be obtained by multiplying PWb obtained in an unrecorded area by a correction coefficient.

  The method for obtaining PWmid is not limited to the case of multiplying PWb by a correction coefficient. The PWe may be obtained from the recorded area of the PCA, and the PWmid may be calculated from the PWe. In that case, the value of PWmid / PWe is obtained in advance as a correction coefficient and stored in the memory.

  FIG. 12 is a graph schematically showing the relationship between the β value and the recording light power. A straight line indicating the relationship in the regions a and b and a straight line indicating the relationship in the region e are described. In the areas a and b, the β value becomes equal to β_best when the recording light power is PWb, whereas in the area e, the β value becomes equal to β_best when the recording light power is PWe. In any region, the β value increases as the recording light power increases. This is because B in FIG. 10 tends to decrease as the recording light power increases. FIG. 12 also shows β_b_PWlow and β_e_PWhigh which are β values when the reproduction limit is reached.

  Next, a configuration example in the embodiment of the optical disc apparatus according to the present invention will be described with reference to FIG.

  The optical disk apparatus of this embodiment includes an optical head 11 that optically accesses the optical disk 10, a front end processor (FEP) 20 and a laser drive circuit 30 connected to the optical head.

  The optical disc 10 is a recordable optical disc. Examples of such optical disks include BE-R and BD-RE. When the optical disc 10 is inserted into the optical disc apparatus, the optical disc 10 is rotated by a motor (not shown), and then the optical head 11 irradiates the optical disc 10 with a light beam.

  The optical head 11 includes a laser light source (not shown) that emits a light beam and a photodetector (not shown) that receives reflected light from the optical disk 10.

  The FEP 20 receives a signal output from the optical head 11 and performs amplification and waveform equalization on this signal. The FEP 20 outputs the processed analog signal to the reproduction processing unit 21. The reproduction processing unit 21 converts the analog signal received from the FEP 20 into a digital signal. The decoder 22 demodulates the digital signal received from the reproduction processing unit 21 to reproduce and output user data (for example, video data) recorded on the optical disc 10.

  The laser driving circuit 30 drives the laser light source in the optical head 11 according to the recording waveform received from the recording processing unit 31, and emits a light beam from the optical head 11. The recording processing unit 31 receives a recording signal from the encoder 32 and sets a recording waveform. When recording user data on the optical disc 10, the encoder 32 receives data to be recorded (for example, video data), modulates it, generates an encoded recording signal, and inputs it to the recording processing unit 31. To do.

  The target β value storage memory 23 receives and holds the target β value obtained by the test recording after OPC from the reproduction processing unit 21. The target β value is used for laser power correction during the recording operation.

  The optical disk apparatus of this embodiment includes a target β value storage memory 23 and a correction coefficient storage memory 33. The target β value storage memory 23 receives and holds the target β value obtained by the test recording after OPC from the reproduction processing unit 21. As described above, this target β value is used for correcting the recording light power during recording of user data. On the other hand, the correction coefficient storage memory 33 stores a correction coefficient for the initial recording light power. The correction coefficient can be stored in the correction coefficient storage memory 33 as data shown in the table of FIG. When setting the recording waveform, the recording processing unit 31 receives the correction coefficient of the initial recording light power from the correction coefficient storage memory 33 and sets the initial recording light power.

  The FEP 20 has means for detecting an average value A and amplitudes B and P necessary for β value calculation shown in FIG.

  The reproduction processing unit 21 calculates the β value as described above using the average value A and the amplitudes B and P detected by the FEP 20. The recording processing unit 31 corrects the recording waveform based on the β value when recording user data (ROPC).

  The optical disc apparatus of the present embodiment is different in configuration from the conventional optical disc apparatus in that a correction coefficient necessary for determining the initial recording light power is stored in the memory, but other components are as follows: It may be the same as a component of a conventional optical disc.

  Next, an example of the power setting method in the present embodiment will be described with reference to FIG. 14A.

  First, in step ST1, when an optical disc is loaded in the optical disc apparatus, disc discrimination is executed. Here, it is assumed that an optical disc having three information recording layers as shown in FIG. 6 is loaded. In this case, the disc information is read from the management area of the information recording layer L0 in a state where the information recording layer L0 is focused, and the type of the loaded optical disc is thereby grasped. Specifically, for example, the total number of manufacturers and information recording layers is obtained based on the information read from the management area.

  Next, in step ST2, OPC is executed by the PCA of the information recording layer L0. At this time, test recording is executed in an area where no data is recorded in all the information recording layers existing before the information recording layer L0 (unrecorded area). In OPC, test recording of data is performed while changing the recording light power in multiple stages. As a result, the recording light power PWb having the lowest error rate is obtained. After the test recording, in step ST3, the target β value (β_best) is obtained by reproducing the data recorded using the recording light power PWb. In addition, the relationship between the β value and the recording light power using the beta value obtained by reproducing the data recorded using the recording light power other than the recording light power PWb and the target β value (for example, FIG. 12 is also obtained.

  Next, in step ST4, the correction coefficient is read out from the correction coefficient storage memory 33 in FIG. 13 according to the type of the disk obtained by disc discrimination and the information recording layer to be recorded. In step ST5, a value (correction power) obtained by multiplying the optimum value PWb of the recording light power in the areas a and b by the correction coefficient is calculated. In step ST6, this correction power is set as the initial recording light power.

  FIG. 14B is a flowchart illustrating an example of a conventional power setting method for reference. In the example of FIG. 14B, Steps ST20 to ST22 are the same as Steps ST1 to ST3. When power setting is performed in Step ST23 after obtaining the target β value, the optimum recording light power in the region a obtained by test recording is obtained. The value PWb is set as the initial recording light power.

  Next, a data recording method in the present embodiment will be described with reference to FIG.

  First, it is assumed that the setting of the initial recording light power is completed by the method described with reference to FIG. 14A. In this embodiment, in step ST10, user data recording is started with a recording light power of PWmid (= PWb × correction coefficient). When the recording end position has not been reached, the β value of the immediately preceding recording location is measured (step ST11, step ST12).

  In step ST13, the measured β value is compared with the target β value. Then, when the measured β value is larger than the target β value, the recording light power is decreased. Conversely, when the measured β value is smaller than the target β value, the recording light power is increased. At this time, if the difference Δβ between the measured β value and the target β value is found from the slope of the straight line shown in FIG. 12, the change amount ΔPW of the recording light power is calculated from the slope of the straight line shown in FIG. be able to. In other words, if the slope of the straight line in FIG. 12 is h, the relationship ΔPW × h = Δβ is established. Therefore, if Δβ is found by measurement, the recording light power may be increased or decreased by Δβ / h. However, in this embodiment, instead of changing the recording light power by Δβ / h at a time, data is recorded with the recording light power changed by 0.8 × Δβ / h (steps ST14 and ST15). Then, when reproducing the data recorded in that state, the β value is measured, and the recording light power is changed again by 0.8 × Δβ / h. In this way, by adjusting the recording light power so that the measured β value approaches the target β value stepwise, the recording light power can be reliably optimized within a range not exceeding the reproduction limit.

  After recording data in this manner, the recording position is confirmed. If the recording end position is reached in step ST11, the data recording is ended. If the recording end position has not been reached, the above operation is repeated.

  In an actual optical disc, the sensitivity to the recording light power of the information recording layer may differ depending on the location. The example shown in FIG. 16 schematically shows a cross section of an optical disc in which sensitivity decreases from the inner circumference side of the disc toward the outer circumference side of the optical disc with reduced light transmittance. The regions b ′, c ′, d ′, and e ′ correspond to the regions b, c, d, and e, but the sensitivity is relatively lowered. This will be further described with reference to FIGS. FIG. 17 is a graph showing the relationship between the error rate and the recording light power in the areas a, b, b ′, e, and e ′. Similarly, FIG. 18 is a graph showing the relationship between the β value and the recording light power in the areas a, b, b ′, e, and e ′.

  In the areas b ′ and e ′, the recording light power for achieving the same error rate or β value is relatively large compared to the areas b and e. This is because the sensitivity of the regions b 'and e' is relatively low, so that a larger recording light power is required to realize the same state.

  In the embodiment of the present invention, the initial recording light power is determined by test recording in the region a having the same sensitivity as the region b. In order to set the initial recording light power to PWmid (= PWb × correction coefficient), when data recording is started in the area e ′, the error rate in the area e ′ becomes e′_PWmid as can be seen from FIG. Become. If the initial recording light power is set to PWb and data recording is started in the area e ′ as in the prior art, in the example of FIG. 17, the error rate in the area e ′ exceeds the reproduction limit e ′. _PWb is reached. As described above, according to this embodiment, even when data recording is started in a region where the sensitivity is relatively low, the possibility that the error rate exceeds the reproduction limit can be reduced.

  Next, an example of changes in β value, recording light power, and error rate during data recording will be described with reference to FIG.

  In the example shown in FIG. 19, the area in which data is recorded changes in the order of areas e, b, c, d, e, and b on the light transmittance decreasing type optical disc. In the example of the figure, the area where data recording is started is the area e, and the initial recording light power is PWmid. When the recording light power is PWmid, the β value in the region e is smaller than β_best, for example, as shown in FIG. The β value is measured at the timing shown at the bottom of FIG. 19, and the recording light power correction (β correction) is executed based on the difference between the measured β value and the target β value. Due to the first β correction, the recording light power rises from PWmid to a level close to PWe. As a result, the error rate decreases and the β value can approach β_best. As a result of such β correction, the recording light power in the region e approaches the optimum value PWe in the region e. When the data recording area transitions from the area e to the area b, the recording light power approaching the optimum value PWe in the area e has a value far from the optimum value PWb in the area b. For this reason, in the region b, the β value of the data recorded with the recording light power of PWe rises to β_b_PWe which is larger than the target β value β_best. At this time, in the example of FIG. 19, the error rate approaches the reproduction limit. However, since the β correction is performed promptly, the recording light power can eventually approach PWb, which is the optimum value in the region b.

  As a result of performing β correction on the recording light power in this way, even when the data recording region changes from region b → region c → region d → region e → region b, the recording light power can be optimized. Performed quickly.

  Next, an example of changes in β value, recording light power, and error rate when data is recorded in a low sensitivity area will be described with reference to FIG. FIG. 20 is a diagram corresponding to FIG. 19, but is different in that data recording areas are changed in the order of areas e ′, b ′, c ′, d ′, e ′, and b ′. . FIG. 20 shows not only optimum recording light power values PWb ′ and PWe ′ in regions b ′ and e ′ but also optimum recording light power values PWb and PWe in regions b and e for comparison. .

  In this embodiment, since the initial recording light power is set to PWmid (= PWb × correction coefficient), the error rate does not exceed the reproduction limit even when data recording is first started in the low sensitivity area e ′. It is possible to quickly approach the optimum value by β correction. The operation after the area e is basically the same as described with reference to FIG. 19, but the recording light power determined by the β correction is adjusted to a level higher than the level shown in FIG. This is to compensate for low sensitivity with stronger recording light power.

  As in the prior art, when data is started to be recorded in a recorded area with low sensitivity while the initial optical disk device is set to PWb, the error rate may exceed the reproduction limit. According to this, the possibility can be made sufficiently small.

  In the above embodiment, data is recorded on the information recording layer L0. However, when data is recorded on the information recording layer L1, a correction coefficient suitable for the information recording layer is read from the memory, and a temporary initial recording light is recorded. By multiplying the power, the initial recording light power can be calculated. It should be noted that the correction coefficient may be set to 1 when data is recorded on the information recording layer L2 in the information recording layer located on the foremost side and the three-layer optical disc.

  In the above embodiment, when recording on, for example, the information recording layer L0 of a multilayer optical disc of the light transmittance decreasing type or the light transmittance increasing type in which the number of layers is N (N is an integer of 2 or more), information is recorded in the PCA. Test recording of data was performed in an unrecorded area where data was not written in all information recording layers from the recording layer L1 to the information recording layer L (N-1), and a temporary initial recording light power (PWb) was determined. However, the PCA performs test recording of data in the recording areas where data is written in all the information recording layers from the information recording layer L1 to the information recording layer L (N-1), and provisional initial recording light power (PWe) Then, the initial recording light power (PWmid) can be calculated by multiplying the provisional initial recording light power (PWe) by the correction coefficient (PWmid / PWe). Further, as a correction coefficient, a value between PWlow and PWhigh may be employed instead of an intermediate value between PWb and PWe.

  The present invention can be widely applied to an optical disc apparatus that records computer data and / or video / audio data on a multilayer optical disc such as a BD-R or a BD-RE.

10 Optical disk 11 Optical head (optical pickup)
20 Front End Processor (FEP)
21 Reproduction Processing Unit 22 Decoder 30 Laser Drive Circuit 31 Recording Processing Unit 32 Encoder

  The present invention relates to a data recording method performed on a multilayer optical disc having a plurality of information recording layers. The present invention also relates to an optical disc apparatus that executes this data recording method.

  Data recorded on the optical disk is reproduced by irradiating a rotating optical disk with a relatively weak light beam having a constant intensity and detecting reflected light modulated by the optical disk. In a reproduction-only optical disc, information by pits is previously recorded in a spiral shape at the manufacturing stage of the optical disc. On the other hand, in a rewritable optical disk, a recording material film capable of optically recording / reproducing data is deposited on the surface of a substrate on which a track having spiral lands or grooves is formed by a method such as vapor deposition. Has been. When data is recorded on a rewritable optical disc, the optical disc is irradiated with a light beam whose light intensity is modulated in accordance with the data to be recorded, thereby changing the characteristics of the recording material film locally to write the data. Do.

  The pit depth, track depth, and recording material film thickness are smaller than the thickness of the optical disk substrate. For this reason, the portion of the optical disc where data is recorded constitutes a two-dimensional surface and may be referred to as a “recording surface” or an “information surface”. In this specification, in consideration of the fact that such a surface has a physical size also in the depth direction, instead of using the phrase “recording surface (information surface)”, “information recording layer” We will use the phrase. The optical disc has at least one such information recording layer. One information recording layer may actually include a plurality of layers such as a phase change material layer and a reflective layer.

  In a recordable optical disc or a rewritable optical disc, when data is recorded on the information recording layer, the information recording layer is irradiated with the light beam whose light intensity is modulated as described above, so that the crystalline phase change material layer is irradiated. An amorphous recording mark is formed. This amorphous recording mark is formed by rapidly cooling after a part of the information recording layer irradiated with the recording light beam rises to a temperature higher than the melting point. If the light intensity at the time of irradiating the recording beam with the light beam is set low, the temperature of the recording mark irradiated with the light beam does not exceed the melting point and returns to crystalline after rapid cooling (erasing of the recording mark). In this way, the recording mark can be rewritten many times. If the intensity of the light beam (recording light power) when recording data is inappropriate, the shape of the recording mark may be distorted, making it difficult to reproduce the data.

  Since the reflectance of the amorphous recording mark is different from the reflectance of the surrounding crystalline part, the intensity of the reflected light during reproduction varies depending on the presence or absence of the recording mark. In the area where data is recorded (recorded area), there are rows of recording marks and spaces having different lengths depending on the contents of the data to be recorded. For this reason, the optical characteristics (light reflectance and transmittance) of the recorded area are different from the optical characteristics of the area where data is not recorded (unrecorded area).

  When reproducing data recorded on an optical disc or recording data on a recordable optical disc, the light beam must always be in a predetermined focused state on a target track in the information recording layer. For this purpose, “focus control” and “tracking control” are required. In “focus control”, the position of the objective lens is referred to as the normal direction of the information surface (hereinafter referred to as “the depth direction of the substrate”) so that the position of the focal point (focusing point) of the light beam is always on the information recording layer. There is a case.) On the other hand, the tracking control is to control the position of the objective lens in the radial direction of the optical disc (hereinafter referred to as “disc radial direction”) so that the spot of the light beam is located on a predetermined track.

  In order to perform the above-described focus control and tracking control, it is necessary to detect a focus shift or a track shift based on the light reflected from the optical disc and adjust the position of the light beam spot so as to reduce the shift. It is. The magnitudes of the focus shift and the track shift are indicated by a “focus error (FE) signal” and a “tracking error (TE) signal” generated based on the reflected light from the optical disc, respectively.

  In recent years, optical discs in which two information recording layers are laminated are put on the market, and multilayer optical discs in which three or more information recording layers are laminated are being developed. In this specification, an optical disc on which N layers (N is an integer of 2 or more) is referred to as a “multilayer optical disc”.

  When reproducing data from the target information recording layer of the multilayer optical disk or writing data to the target information recording layer, the optical disk apparatus aligns the focus position of the light beam on the target information recording layer, It is necessary to form a small light spot on the information recording layer. Since one multilayer optical disc has a plurality of information recording layers, when the focus position of the light beam is adjusted to the information recording layer located at the innermost position, for example, the light beam passes through the information recording layer located at the front side. It will be.

  Unless the light beam intensity (recording light power) at the time of writing data is optimized, the shape of the recording mark becomes inappropriate as described above, and the reproduction error rate increases. In order to optimize the recording light power, a plurality of data is recorded with different recording light powers in the test recording area of the information recording layer provided in the optical disc, and these data are reproduced. In this way, an index such as a reproduction error is measured in the test recording area, and the recording light power at which the index shows the most preferable value is determined. Strictly speaking, such optimization of recording light power is optimization of “initial recording light power”. After the data recording in the user area is started with the initial recording light power determined by the above method, the recording light power is changed from the initial recording light power to a more appropriate level at any time based on, for example, a β value described later. Can be corrected. In the present specification, the processing performed by the optical disc apparatus to determine the initial recording optical power in the test recording area is referred to as “Optimum Power Control (OPC)”.

  FIG. 1A is a diagram showing a multilayer optical disc 10, and FIG. 1B is a schematic sectional view thereof. A multilayer optical disc 10 shown in FIG. 1 includes a first information recording layer L0 located farthest from the disc surface 10a on which the light beam is incident, and a second information recording layer L1 closest to the disc surface 10a. ing. The multilayer optical disc 10 is provided with a user data area in which user data is recorded, and a test recording area (PCA: Power Calibration Area) located on the inner periphery side of the disc with respect to the user area. The multi-layer optical disc 10 is provided with a management area other than PCA, but for simplicity, it is not shown in FIG.

  FIG. 2 is a diagram showing a part of the cross section of the multilayer optical disc 10 shown in FIG. 1B in more detail. In FIG. 2, a light beam focused on three different areas a, b, and c in the information recording layer L0 is schematically shown. The area a is an area (unrecorded area) in which no data is recorded in any of the information recording layers L0 and L1 in the PCA. Similarly, the area b is an area (unrecorded area) in which no data is recorded in any of the information recording layers L0 and L1 in the user data area. On the other hand, the area c is an area (recorded area) in which data is recorded in the information recording layer L1 in the user data area.

  In the information recording layer L1, the light transmittance of an area where data is recorded is different from the light transmittance of an area where data is not recorded. In many optical discs, the light transmittance in an area where data is recorded is lower than the light transmittance in an area where data is not recorded. For this reason, the light beam focused on the information recording layer L0 in the region c is transmitted through the portion where the light transmittance is relatively low in the information recording layer L1. As a result, the intensity of the light beam on the information recording layer L0 is lower in the region c than in the region b.

  As described above, the amount of light that can be given to the information recording layer L0 by the light beam focused on the information recording layer L0 is applied to the information recording layer L1 located in front of the information recording layer L0 (side closer to the disk surface). It will change depending on whether data is recorded.

  FIG. 3 is a graph showing the relationship between the error rate and the recording light power when the data recorded in the information recording layer L0 is reproduced. The horizontal axis of the graph is the recording light power (power), and the vertical axis is the error rate during reproduction (L0 error rate). FIG. 3 shows a curve indicating the result in the areas a and b which are the unrecorded areas shown in FIG. 2 and a curve indicating the result in the area c which is the recorded area shown in FIG.

  As can be seen from FIG. 3, in areas a and b, the error rate is minimized when the recording light power is PWb. That is, it is understood that it is preferable to set the recording light power to PWb in the unrecorded areas (areas a and b). On the other hand, in the area c, the error rate is minimized when the recording light power is PWc. That is, it can be seen that in the recorded area (area c), it is preferable to set the recording light power to PWc larger than PWb. Thus, in the area c, which is a recorded area, it is preferable to write data with a recording light power higher than the recording light power for the areas a, b which are unrecorded areas.

  Conventionally, when data is recorded at a specific address position in a user data area of an optical disc, it is unknown whether the position is in a recorded area or an unrecorded area. For this reason, the initial recording light power at the start of data recording is set to an optimum value in the unrecorded area (PWb in the example of FIG. 3). In this case, after starting data recording in the user data area, the recording light power is corrected based on the index indicating the waveform of the reproduction signal while reproducing the data at short time intervals.

  FIG. 4A is a diagram showing a cross section of the multilayer optical disc 10 and corresponds to FIG. FIG. 4B is a diagram showing a temporal transition by correction of the recording light power when data is started to be recorded in the area b which is an unrecorded area with the initial recording light power PWb. On the other hand, FIG. 4C is a diagram showing a temporal transition due to correction of the recording light power when data is started to be recorded in the area c which is a recorded area with the initial recording light power PWb.

  In the example of FIG. 4B, the recording light power is held at PWb which is the optimum value in the region b. On the other hand, in the example of FIG. 4C, the recording light power is corrected so as to increase toward the optimum value PWc in the region c.

  As the number of information recording layers included in the multilayer optical disk increases, for example, when the information recording layer L0 located on the farthest side is in focus, the number of information recording layers positioned in front of the information recording layer L0 increases to 2 or more. . For this reason, in the recorded area in which data is recorded in a plurality of information recording layers positioned in front of them, the light transmittance is significantly reduced.

  FIG. 5A is a schematic cross-sectional view of a multilayer optical disc having three information recording layers L0, L1, and L2. FIG. 5B is a diagram showing a temporal transition by correction of the recording light power when data is started to be recorded in the area b which is an unrecorded area with the initial recording light power PWb. On the other hand, FIG. 5C is a diagram showing a temporal transition due to correction of the recording light power when data is started to be recorded in the area e which is a recorded area with the initial recording light power PWb.

  In the example of FIG. 5C, the recording light power is corrected so as to increase toward the optimum value PWe in the region e, but it takes a longer time to reach the optimum value PWe. It is thought that there is. The reason is that, in the area e, data is recorded in both of the two information recording layers L1 and L2, so that the degree of decrease in light transmittance due to them is large, and the optimum value PWe of the recording light power in the area e is This is because there is a possibility that the optimum value PWb of the recording light power in the areas a and b is greatly different.

  In the future, it is expected that the number of information recording layers included in the multilayer optical disc will increase further, for example, to become four or more. Even in such a multi-layer optical disc, when data recording is started with the recording light power PWb optimized in the area a which is an unrecorded area, there is a problem that the recording light power cannot be corrected to a more preferable magnitude in a short time. is there. Therefore, Patent Document 1 discloses a technique for performing OPC with PCA for each possible combination of a recorded area and an unrecorded area.

  In Patent Document 2, in addition to the disclosed contents of Patent Document 1, by managing the addresses of recorded areas and unrecorded areas, it is determined whether they are recorded areas or unrecorded areas, and initial recording is performed according to the determination result. A technique for changing optical power is disclosed.

JP 2008-108388 A JP 2008-192258 A

  According to the technique of Patent Document 1, many portions are consumed for test recording by PCA, and the time required for test recording increases. These have the problem of increasing geometrically as the number of optical disc layers increases.

  According to the technique of Patent Document 2, since recorded areas / unrecorded areas in each information recording layer are managed on the basis of addresses, a positional deviation (bonding error) occurs between the upper and lower information recording layers to be stacked. The positions of the recorded area and the unrecorded area cannot be accurately determined based on the address. For example, when data is recorded at a specified address position of the information recording layer L0, an area before the address position is determined based on the address in the information recording layer L1, and whether or not data is recorded in the area. However, if there is a physical shift between the information recording layer L0 and the information recording layer L1, the correspondence based on the address may be incorrect.

  As described above, both Patent Documents 1 and 2 have problems and are not practical. Therefore, the present inventor did not obtain the best recording characteristics as a concept that is not disclosed in any of Patent Documents 1 and 2, and thought that the recording characteristics should be guaranteed within an allowable range. That is, the first initial optimum recording light power for recording data in a situation where data is not written in all other information recording layers in the multilayer optical disc, and data is written in all other information recording layers in the multilayer optical disc. The initial recording light power is determined so as to be positioned between the second initial optimum recording light power for recording data under the present circumstances, and after the initial recording using the initial recording light power, the reproduction characteristics are improved. The concept of dynamically changing the recording light power is adopted accordingly. With this concept, the PCA is not increased according to the number of layers of the optical disc, and the recording characteristics can be guaranteed within an allowable range regardless of whether the other layer is a recorded area or an unrecorded area.

  The present invention has been made to solve the above-mentioned problems, and its main purpose is to correspond to the position and thickness direction in which the data is recorded when the data is recorded in the user data area, and the data Provided is a data recording method that can be promptly corrected to the optimum size regardless of whether the position in the other information recording layer located before the information recording layer on which is recorded is in the recorded area or the unrecorded area There is. Another object of the present invention is to provide an optical disc apparatus for executing the data recording method.

  The data recording method of the present invention is a data recording method for recording data on a multilayer optical disc having a plurality of information recording layers having N layers (N is an integer of 2 or more), and is the innermost side of the multilayer optical disc. Step A for determining the number of information recording layers included in the optical disc loaded in the optical disc apparatus, where k is the kth information recording layer (k is an integer satisfying 1 ≦ k ≦ N) When the number of layers is X (X is an integer of 2 or more), data is stored in the test recording area in the m-th information recording layer (m is an integer satisfying 1 ≦ m ≦ X−1) for performing test recording. Step B for determining a temporary initial recording light power and selecting a correction coefficient in accordance with the number of the information recording layer as the target information recording layer for recording data, and selecting the selected correction Said provisional initial based on the coefficient Comprising a step C of determining the initial recording beam power to correct the Rokuko power, and a step D to start recording data on the target information recording layer in the initial recording light power.

  In one embodiment, in the step B, when the number of layers is X (X is an integer of 2 or more), the m-th information recording layer (m satisfies 1 ≦ m ≦ X−1) for performing test recording. A test recording of data in unrecorded areas in which no data is written in all the information recording layers from the (m + 1) th information recording layer to the Xth information recording layer, A temporary initial recording light power is determined.

  In one embodiment, the step C selects the correction coefficient depending on the type of the optical disk loaded in addition to the information recording layer of the target information recording layer.

  In one embodiment, for each information recording layer included in each multilayer optical disc supported by the optical disc apparatus, correction coefficient information in which the correction coefficient value is given for each type of the multilayer optical disc is recorded in a memory of the optical disc apparatus. Including the steps of:

  In one embodiment, the initial recording light power determined in the step C is larger than the temporary initial recording light power in the case of a light transmittance reduction type multilayer optical disc.

  In one embodiment, the method further includes a step of changing the recording light power from the initial recording light power as needed based on a signal waveform obtained from the optical disk after starting to record data in the step D.

  In one embodiment, after recording data in the step D, the recording light power is adjusted so that the β value indicating the symmetry of the signal amplitude with respect to the average value of the reproduction signal obtained from the optical disc approaches the target β value. The method further includes a step of correcting.

  In some embodiments, m = 1.

  The optical disk apparatus of the present invention is an optical disk apparatus for recording data on a multilayer optical disk having a plurality of information recording layers having N layers (N is an integer of 2 or more), and optically accesses the multilayer optical disk. For each of the information recording layers included in each multilayer optical disk supported by the optical pickup device, an optical pickup, a memory for storing correction coefficient information in which a correction coefficient value is given for each type of the multilayer optical disk, and a loaded multilayer After performing a test recording of data in a test recording area in an information recording layer included in an optical disc and determining a provisional initial recording light power, what number information recording layer is the target information recording layer for recording data The correction coefficient is selected from the memory according to the correction, and the temporary initial recording light power is corrected based on the selected correction coefficient. And a recording processing unit for determining a recording light power.

  According to the present invention, when data is recorded in the user data area, the other information recording layer corresponding to the position where the data is recorded and the thickness direction, and positioned before the information recording layer where the data is recorded It is possible to provide a data recording method that can be promptly corrected to an optimum size regardless of whether the position in the recorded area or unrecorded area.

(A) is a figure which shows the multilayer optical disk 10, (b) is the cross-sectional schematic diagram. It is a figure which shows a part of cross section of the multilayer optical disk 10 shown in FIG.1 (b) in detail. It is a graph which shows the relationship between the error rate when reproducing | regenerating the data recorded on the information recording layer L0, and recording optical power. The horizontal axis of the graph represents the recording light power (power), and the vertical axis represents the error rate during reproduction (error rate of the information recording layer L0). (A) is a schematic cross-sectional view of a multilayer optical disc including two information recording layers L0 and L1, and (b) is an information recording layer L0 in an area b where the information recording layer L1 is an unrecorded area with the initial recording light power PWb. FIG. 8C is a diagram showing a temporal transition due to correction of the recording light power when data is started to be recorded, FIG. 10C is an information recording layer L0 in the area c where the information recording layer L1 is a recorded area with the initial recording light power PWb. It is a figure which shows the time transition by correction | amendment of recording optical power when data is started to be recorded. (A) is a schematic cross-sectional view of a multilayer optical disc including three information recording layers L0, L1, and L2. (B) is an unrecorded area of the information recording layer L1 and the information recording layer L2 with the initial recording light power PWb. The figure which shows the time transition by correction | amendment of recording light power when data is started to be recorded on the information recording layer L0 of the area | region b, (c) is information recording layer L1 and information recording layer L2 with initial recording light power PWb. The figure which shows the time transition by correction | amendment of recording light power at the time of beginning to record data on the information recording layer L0 of the area | region e which is a recorded area | region, (d) is information recording layer L1 with initial recording light power PWmid. The figure which shows the time transition by correction | amendment of recording optical power when the information recording layer L2 starts recording data on the information recording layer L0 of the area | region b which is an unrecorded area, (e) is initial recording optical power PWmid. Information recording layer L1 and It is a timing chart showing a sequence by the correction of the recording light power when the broadcast recording layer L2 begins to record data on the information recording layer L0 of the region e is recorded area. (A) is a schematic cross-sectional view of a multilayer optical disc having three information recording layers L0, L1, and L2. (B) is an error when reproducing data recorded on the information recording layer L0 in the case of a three-layer optical disc. It is a graph which shows the relationship between a rate and recording optical power. (A) is a schematic cross-sectional view of a multilayer optical disc including three information recording layers L0, L1, and L2 in which the light transmittance of the recorded region is higher than the light transmittance of the unrecorded region, and (b) is the three layers. 4 is a graph showing a relationship between an error rate and recording light power when data recorded in an unrecorded recording layer L0 is reproduced on an optical disc. (A) is a schematic cross-sectional view of a multilayer optical disc including four information recording layers L0, L1, L2, and L3, and (b) is a case where data recorded on the information recording layer L0 is reproduced in the case of a four-layer optical disc. 5 is a graph showing the relationship between the error rate and the recording light power. It is a table which shows an example of a correction coefficient. It is a graph which shows typically the waveform of the reproduction signal (RF signal) obtained from the area where data was recorded. 5 is a graph showing a relationship between an error rate and recording light power when data recorded on an information recording layer L0 is reproduced in the case of a three-layer optical disc. It is a graph which shows typically the relation between beta value and recording light power. It is a block diagram which shows the structural example of embodiment of the optical disk apparatus by this invention. It is a flowchart which shows an example of the power setting method in this embodiment. It is a flowchart which shows the prior art example of a power setting method. It is a flowchart which shows an example of the data recording method in this embodiment. It is a figure which shows typically the cross section of the optical disk from which a sensitivity falls toward the outer peripheral side from a disc inner peripheral side. It is a graph which shows the relationship between the error rate and recording optical power in area | region a, b, b ', e, e'. It is a graph which shows the relationship between (beta) value and recording light power in area | region a, b, b ', e, e'. FIG. 6 is a diagram illustrating an example of changes in β value, recording light power, and error rate when data is recorded in areas e, b, c, d, e, and b in the embodiment of the present invention. In the embodiment of the present invention, the β value, the recording light power, and the error rate when data is recorded in the areas e ′, b ′, c ′, d ′, e ′, b ′ that are relatively less sensitive than PCA. It is a figure which shows an example of a change of.

  The data recording method of the present invention is a method of recording data on a multilayer optical disc having a plurality of information recording layers having N layers (N is an integer of 2 or more). Here, the k-th information recording layer (k is an integer satisfying 1 ≦ k ≦ N) from the information recording layer on the innermost side (position far from the light incident surface) of the multilayer optical disc is defined as the k-th information recording layer. . For example, in the case of the three-layer optical disc shown in FIG. 5A, the information recording layer L0 is a “first information recording layer”, and the information recording layer L1 is a “second information recording layer”. When the total number of layers of the multilayer optical disc is X (X is an integer of 2 or more), the test recording area in the m-th information recording layer (m is an integer satisfying 1 ≦ m ≦ X−1) for performing test recording Of these, an area in which no data is written in all the information recording layers from the (m + 1) th information recording layer to the Xth information recording layer is referred to as an “unrecorded area”. In the following description, the information recording layer for performing test recording for OPC is the “first information recording layer” located on the farthest side, but the present invention is not limited to this example. For example, test recording for OPC may be performed on the second information recording layer, or test recording for OPC may be performed on each information recording layer.

  First, the basic operation principle of the present invention will be described with reference to FIGS. 5 (d) and 5 (e). In the present invention, as shown in FIGS. 5D and 5E, an intermediate value (PWmid) of the recording light power in the region b and the region e is used as the initial recording light power. For this reason, in either the region b or the region e, it is necessary to correct the optimum power based on, for example, the β value after starting data recording. However, the time required to complete such correction can be shortened. The correction based on the β value is sometimes referred to as “running optimal power control (ROPC)” in order to distinguish it from OPC performed in PCA.

  The initial recording light power when starting the above data recording is obtained by multiplying the “temporary initial recording light power” by a correction coefficient described later. This “temporary initial recording light power” is the optimum value (PWa = PWb) of the recording light power obtained by performing the OPC in the unrecorded area in the test recording area.

  In the current optical disc technology, while one recording mark is formed by irradiation with a light beam, the light intensity of the light beam is not constant but changes in a pulse shape. The pulse waveform used to form the recording mark is determined by the write strategy. The “recording light power” in this specification means the peak value of each pulse constituting the recording light beam. The peak value of each pulse is common in one recording mark.

  Next, the relationship between the initial recording light power and the temporary initial recording light power (PWa = PWb) will be described with reference to FIGS. 6 (a) and 6 (b). FIG. 6 relates to a light transmittance decreasing type optical disc in which the light transmittance in the recorded area is lower than the light transmittance in the unrecorded area. FIG. 6A is a diagram corresponding to FIG. 5A, and FIG. 6B shows an error rate when data recorded in the unrecorded recording layer L0 is reproduced in the case of a three-layer optical disc. It is a graph which shows the relationship with recording optical power. FIG. 6B shows a curve indicating the result in the areas a and b which are unrecorded areas and a curve indicating the result in the area e which is the recorded area. A similar curve can be obtained by changing the vertical axis from error rate to jitter.

  As can be seen from FIG. 6B, in the areas a and b, the error rate becomes the minimum value when the recording light power is PWb. On the other hand, in the area e, the error rate becomes the minimum value when the recording light power is PWe. In the example of FIG. 6B, the minimum value of the error rate is level R1. When data is recorded in the area e with the recording light power set to PWb, the error rate during reproduction reaches level R2. Similarly, when data is recorded in the area b with the recording light power set to PWe, the error rate during reproduction reaches the level R2. If the level R2 exceeds the reproduction limit, when data recording is started, the data is recorded in a state where it cannot be normally reproduced.

  In the graph of FIG. 6B, for the sake of simplicity, the curve showing the results in the regions a and b and the curve showing the results in the region e have the same shape, but the actual curves are different. Also good. In that case, the minimum value of the curve indicating the result in the regions a and b is not equal to the minimum value of the curve indicating the result in the region e.

  In the embodiment of the present invention, the recording optical power at the start of data recording is set to PWmid (= PWb × correction coefficient) instead of PWb. In the example of FIG. 6B, the correction coefficient is a numerical value larger than 1. As can be seen from FIG. 6B, when data is recorded in the area b with the recording light power set to PWmid, the error rate during reproduction becomes level R3. Similarly, even if data is recorded in the area e with the recording light power set to PWmid, the error rate during reproduction can be suppressed to level R3. This prevents data from being recorded in a bad state so as to exceed the reproduction limit when data is recorded in either of the areas b and e.

  Furthermore, according to the present embodiment, when data recording is started, the difference between the initial value and the optimum value of the recording light power, that is, the value of “PWe-PWmid” or “PWmid-PWb” is “PWe-PWb”. Than enough. For this reason, it becomes possible to shorten the time required for the subsequent correction based on the β value. This is clear when FIG. 5C is compared with FIGS. 5D and 5E. In the examples of FIGS. 5D and 5E, the correction based on the β value is necessary when data is recorded in either of the areas b and e. The time required for the correction is shown in FIG. It won't be too long like in the example.

  Next, refer to FIGS. 7A and 7B. FIG. 7 relates to an optical transmittance increasing type optical disc in which the light transmittance in the recorded area is higher than the light transmittance in the unrecorded area. In such an optical disc, it is possible to form a recording mark having a preferable shape with a recording light power lower than that in the areas a and b which are unrecorded areas in the area e which is a recorded area. In this case, the optimum value PWe in the recorded area is smaller than the optimum value PWb in the unrecorded area. Also in the example as shown in FIG. 7, in this embodiment, the recording light power is set to PWmid (= PWb × correction coefficient). The correction coefficient at this time is smaller than 1.

  Next, refer to FIGS. 8A and 8B. FIG. 8A schematically shows a cross section of a four-layer disc, which relates to an optical disc with reduced light transmittance. In the area f which is a recorded area, data is recorded in the three information recording layers L1, L2, and L3. FIG. 8B is a graph showing the relationship between the error rate and the recording light power when the data recorded in the information recording layer L0 is reproduced in the case of a four-layer optical disc, and the area a, which is an unrecorded area, A curve indicating the result in b and a curve indicating the result in the area f which is the recorded area are described.

  In the example shown in FIG. 8B, the difference between the optimum recording light power values PWf and PWb is large. For this reason, the correction coefficient by which PWb is multiplied in order to obtain the intermediate value PWmid is also relatively large.

  FIG. 9 is a table showing an example of the correction coefficient. In the example shown in FIG. 9, since there are differences in the structure and material of the optical disk depending on the disk manufacturer, the correction coefficient is set to a different value. Further, the value of the correction coefficient changes depending on how many information recording layers exist before the information recording layer for recording data. For example, in the case of a BD-R three-layer disc manufactured by Company A, when data is recorded on the information recording layer L0, the correction coefficient is 1.30, but data is recorded on the information recording layer L1 of the same optical disc. The correction factor is 1.15. The reason is as follows.

  When data is recorded on the information recording layer L0, two information recording layers L1 and L2 exist before the information recording layer L0. For this reason, the light beam focused on the information recording layer L0 is transmitted through the two information recording layers L1 and L2. On the other hand, when data is recorded on the information recording layer L1, there is only one information recording layer L2 before the information recording layer L1. For this reason, the light beam focused on the information recording layer L0 transmits only one information recording layer L2. The smaller the information recording layer that is transmitted, the smaller the absolute value of the difference between the optimum value PWe in the recorded area and the optimum value PWb in the recorded area. As a result, the value of PWmid, which is an intermediate value, can be set to a value close to PWb, and the correction coefficient also approaches 1. When the total number of layers of the multilayer optical disc apparatus is X (X is an integer of 2 or more), the correction coefficient when data is recorded on the Xth information recording layer may be 1.

  As described above, since the correction coefficient depends on the type of the multilayer optical disk including the above-described disk type, it is necessary to determine the correction coefficient for each different type of optical disk in advance. For this purpose, test recording is performed on a plurality of different types of optical discs, and the relationship between the reproduction signal index (for example, error rate or jitter) and the recording optical power is measured for each information recording layer of the optical disc. It is necessary to determine PWb. Further, a correction coefficient (PWmid / PWb) is calculated by determining PWmid for each information recording layer of the optical disc. In this way, for example, correction coefficient data shown in FIG. 9 can be acquired. The magnitude of PWmid may be obtained, for example, by obtaining two curves as shown in FIG. 6B by test recording and calculating the intermediate values of the minimum values PWb and PWe of these curves. However, PWmid is not necessarily equal to (PWb + PWe) / 2, and may be between the minimum values PWb and PWe.

  The correction coefficient data is preferably stored in a memory provided in the optical disc apparatus. The correction coefficient stored in the memory of the optical disk device can be updated through, for example, communication / broadcasting for an optical disk that is newly manufactured after the optical disk device is purchased by the user. Further, the correction coefficient related to each optical disk may be recorded on the optical disk itself. In that case, the optical disk apparatus may read correction coefficient data from the loaded optical disk and calculate the initial recording light power using the correction coefficient.

  The optical disc apparatus according to a preferred embodiment of the present invention discriminates the type of the optical disc loaded in the optical disc apparatus in order to appropriately select the “correction coefficient” used when calculating PWmid from PWb. Then, the correction coefficient most suitable for the optical disc is read from a memory in which data as shown in FIG. 9 is recorded, for example. If there is no corresponding disk in the memory, update at that time or use a correction coefficient of a disk with the same number of recording layers. The type of the optical disc may be determined by any known method, but the type of the optical disc may be determined by reading the disc information from the management area of the reference layer (for example, the information recording layer L0).

  Next, the β value will be described with reference to FIG. FIG. 10 is a graph schematically showing a waveform of a reproduction signal (RF signal) obtained from an area where data is recorded. When the average value A of the RF signal is used as a reference and the upper and lower amplitudes are P and B, the β value is represented by (P−B) / (P + B). The higher the vertical symmetry with respect to the average value A, the closer the β value approaches zero. In the example shown in FIG. 10, since P> B, the β value is positive. If P <B, the β value is negative.

  In this specification, the β value obtained when the shape or size of the recording mark is optimum is described as “β_best”. In a preferred embodiment of the present invention, the recording light power is corrected from the initial setting value (PWmid) to another value using the β value as an index. In this correction, when the β value is larger than β_best, the recording light power is changed so as to decrease the β value. When the β value is smaller than β_best, the recording light power is changed so as to increase the β value. In this way, the recording light power is corrected so that the β value becomes substantially equal to β_best. Such correction of the recording light power is executed in the process of recording the user data in the user data area.

  Next, the relationship between the β value and the recording light power will be described with reference to FIGS. 11 and 12. FIG. 11 is a graph corresponding to FIG. FIG. 11 shows a lower limit value PWlow and an upper limit value PWhigh that define a recording light power range in which the error rate is below the reproduction limit. The error rates b_PWb and e_PWb at the optimum value PWb of the recording light power in the unrecorded area, the error rates e_PWe and b_PWe at the optimum value PWe of the recording light power in the recorded area, and the error rate e_PWmid at the intermediate value PWmid of the both recording light powers. , B_PWmid are also shown.

  PWmid may be set equal to the average value of the recording light powers PWlow and PWhigh which is the reproduction limit. When the shape of the curve shown in FIG. 11 is extremely asymmetric, it is preferable to employ an average value of the recording light powers PWlow and PWhigh that is the reproduction limit as PWmid. The intermediate value does not need to be an average value in a strict sense, and is preferably a value that is as far as possible from both the upper limit value and the lower limit value of the recording light power that becomes the reproduction limit. For example, when the left part of the curve in FIG. 11 is steep and the right part has a gentle shape, if data is recorded in the area e with the recording light power of the average value of PWb and PWe, the reproduction limit may be exceeded. Becomes higher. However, if the average value of PWlow and PWhigh is set to Pmid and data is recorded with the recording light power of that magnitude, it is easy to realize recording that can be reproduced in both the area b and the area e.

  The setting of PWmid is performed in advance for each optical disc. That is, for various optical disks, it is necessary to obtain the relationship between the recording light power and the error rate by actual measurement in both the unrecorded area and the recorded area. It is calculated how many times the minimum value PWb (= PWa) obtained in the unrecorded area is to be the PWmid set by the above method, and a correction coefficient (PWmid / PWb) is obtained. On the other hand, in OPC performed when an optical disk is loaded in the optical disk apparatus, test recording may be performed only in an unrecorded area in the PCA of the optical disk. That is, in OPC, PWmid can be obtained by multiplying PWb obtained in an unrecorded area by a correction coefficient.

  The method for obtaining PWmid is not limited to the case of multiplying PWb by a correction coefficient. The PWe may be obtained from the recorded area of the PCA, and the PWmid may be calculated from the PWe. In that case, the value of PWmid / PWe is obtained in advance as a correction coefficient and stored in the memory.

  FIG. 12 is a graph schematically showing the relationship between the β value and the recording light power. A straight line indicating the relationship in the regions a and b and a straight line indicating the relationship in the region e are described. In the areas a and b, the β value becomes equal to β_best when the recording light power is PWb, whereas in the area e, the β value becomes equal to β_best when the recording light power is PWe. In any region, the β value increases as the recording light power increases. This is because B in FIG. 10 tends to decrease as the recording light power increases. FIG. 12 also shows β_b_PWlow and β_e_PWhigh which are β values when the reproduction limit is reached.

  Next, a configuration example in the embodiment of the optical disc apparatus according to the present invention will be described with reference to FIG.

  The optical disk apparatus of this embodiment includes an optical head 11 that optically accesses the optical disk 10, a front end processor (FEP) 20 and a laser drive circuit 30 connected to the optical head.

  The optical disc 10 is a recordable optical disc. Examples of such optical disks include BE-R and BD-RE. When the optical disc 10 is inserted into the optical disc apparatus, the optical disc 10 is rotated by a motor (not shown), and then the optical head 11 irradiates the optical disc 10 with a light beam.

  The optical head 11 includes a laser light source (not shown) that emits a light beam and a photodetector (not shown) that receives reflected light from the optical disk 10.

  The FEP 20 receives a signal output from the optical head 11 and performs amplification and waveform equalization on this signal. The FEP 20 outputs the processed analog signal to the reproduction processing unit 21. The reproduction processing unit 21 converts the analog signal received from the FEP 20 into a digital signal. The decoder 22 demodulates the digital signal received from the reproduction processing unit 21 to reproduce and output user data (for example, video data) recorded on the optical disc 10.

  The laser driving circuit 30 drives the laser light source in the optical head 11 according to the recording waveform received from the recording processing unit 31, and emits a light beam from the optical head 11. The recording processing unit 31 receives a recording signal from the encoder 32 and sets a recording waveform. When recording user data on the optical disc 10, the encoder 32 receives data to be recorded (for example, video data), modulates it, generates an encoded recording signal, and inputs it to the recording processing unit 31. To do.

  The target β value storage memory 23 receives and holds the target β value obtained by the test recording after OPC from the reproduction processing unit 21. The target β value is used for laser power correction during the recording operation.

  The optical disk apparatus of this embodiment includes a target β value storage memory 23 and a correction coefficient storage memory 33. The target β value storage memory 23 receives and holds the target β value obtained by the test recording after OPC from the reproduction processing unit 21. As described above, this target β value is used for correcting the recording light power during recording of user data. On the other hand, the correction coefficient storage memory 33 stores a correction coefficient for the initial recording light power. The correction coefficient can be stored in the correction coefficient storage memory 33 as data shown in the table of FIG. When setting the recording waveform, the recording processing unit 31 receives the correction coefficient of the initial recording light power from the correction coefficient storage memory 33 and sets the initial recording light power.

  The FEP 20 has means for detecting an average value A and amplitudes B and P necessary for β value calculation shown in FIG.

  The reproduction processing unit 21 calculates the β value as described above using the average value A and the amplitudes B and P detected by the FEP 20. The recording processing unit 31 corrects the recording waveform based on the β value when recording user data (ROPC).

  The optical disc apparatus of the present embodiment is different in configuration from the conventional optical disc apparatus in that a correction coefficient necessary for determining the initial recording light power is stored in the memory, but other components are as follows: It may be the same as a component of a conventional optical disc.

  Next, an example of the power setting method in the present embodiment will be described with reference to FIG. 14A.

  First, in step ST1, when an optical disc is loaded in the optical disc apparatus, disc discrimination is executed. Here, it is assumed that an optical disc having three information recording layers as shown in FIG. 6 is loaded. In this case, the disc information is read from the management area of the information recording layer L0 in a state where the information recording layer L0 is focused, and the type of the loaded optical disc is thereby grasped. Specifically, for example, the total number of manufacturers and information recording layers is obtained based on the information read from the management area.

  Next, in step ST2, OPC is executed by the PCA of the information recording layer L0. At this time, test recording is executed in an area where no data is recorded in all the information recording layers existing before the information recording layer L0 (unrecorded area). In OPC, test recording of data is performed while changing the recording light power in multiple stages. As a result, the recording light power PWb having the lowest error rate is obtained. After the test recording, in step ST3, the target β value (β_best) is obtained by reproducing the data recorded using the recording light power PWb. In addition, the relationship between the β value and the recording light power using the beta value obtained by reproducing the data recorded using the recording light power other than the recording light power PWb and the target β value (for example, FIG. 12 is also obtained.

  Next, in step ST4, the correction coefficient is read out from the correction coefficient storage memory 33 in FIG. 13 according to the type of the disk obtained by disc discrimination and the information recording layer to be recorded. In step ST5, a value (correction power) obtained by multiplying the optimum value PWb of the recording light power in the areas a and b by the correction coefficient is calculated. In step ST6, this correction power is set as the initial recording light power.

  FIG. 14B is a flowchart illustrating an example of a conventional power setting method for reference. In the example of FIG. 14B, Steps ST20 to ST22 are the same as Steps ST1 to ST3. When power setting is performed in Step ST23 after obtaining the target β value, the optimum recording light power in the region a obtained by test recording is obtained. The value PWb is set as the initial recording light power.

  Next, a data recording method in the present embodiment will be described with reference to FIG.

  First, it is assumed that the setting of the initial recording light power is completed by the method described with reference to FIG. 14A. In this embodiment, in step ST10, user data recording is started with a recording light power of PWmid (= PWb × correction coefficient). When the recording end position has not been reached, the β value of the immediately preceding recording location is measured (step ST11, step ST12).

  In step ST13, the measured β value is compared with the target β value. Then, when the measured β value is larger than the target β value, the recording light power is decreased. Conversely, when the measured β value is smaller than the target β value, the recording light power is increased. At this time, if the difference Δβ between the measured β value and the target β value is found from the slope of the straight line shown in FIG. 12, the change amount ΔPW of the recording light power is calculated from the slope of the straight line shown in FIG. be able to. In other words, if the slope of the straight line in FIG. 12 is h, the relationship ΔPW × h = Δβ is established. Therefore, if Δβ is found by measurement, the recording light power may be increased or decreased by Δβ / h. However, in this embodiment, instead of changing the recording light power by Δβ / h at a time, data is recorded with the recording light power changed by 0.8 × Δβ / h (steps ST14 and ST15). Then, when reproducing the data recorded in that state, the β value is measured, and the recording light power is changed again by 0.8 × Δβ / h. In this way, by adjusting the recording light power so that the measured β value approaches the target β value stepwise, the recording light power can be reliably optimized within a range not exceeding the reproduction limit.

  After recording data in this manner, the recording position is confirmed. If the recording end position is reached in step ST11, the data recording is ended. If the recording end position has not been reached, the above operation is repeated.

  In an actual optical disc, the sensitivity to the recording light power of the information recording layer may differ depending on the location. The example shown in FIG. 16 schematically shows a cross section of an optical disc in which sensitivity decreases from the inner circumference side of the disc toward the outer circumference side of the optical disc with reduced light transmittance. The regions b ′, c ′, d ′, and e ′ correspond to the regions b, c, d, and e, but the sensitivity is relatively lowered. This will be further described with reference to FIGS. FIG. 17 is a graph showing the relationship between the error rate and the recording light power in the areas a, b, b ′, e, and e ′. Similarly, FIG. 18 is a graph showing the relationship between the β value and the recording light power in the areas a, b, b ′, e, and e ′.

  In the areas b ′ and e ′, the recording light power for achieving the same error rate or β value is relatively large compared to the areas b and e. This is because the sensitivity of the regions b 'and e' is relatively low, so that a larger recording light power is required to realize the same state.

  In the embodiment of the present invention, the initial recording light power is determined by test recording in the region a having the same sensitivity as the region b. In order to set the initial recording light power to PWmid (= PWb × correction coefficient), when data recording is started in the area e ′, the error rate in the area e ′ becomes e′_PWmid as can be seen from FIG. Become. If the initial recording light power is set to PWb and data recording is started in the area e ′ as in the prior art, in the example of FIG. 17, the error rate in the area e ′ exceeds the reproduction limit e ′. _PWb is reached. As described above, according to this embodiment, even when data recording is started in a region where the sensitivity is relatively low, the possibility that the error rate exceeds the reproduction limit can be reduced.

  Next, an example of changes in β value, recording light power, and error rate during data recording will be described with reference to FIG.

  In the example shown in FIG. 19, the area in which data is recorded changes in the order of areas e, b, c, d, e, and b on the light transmittance decreasing type optical disc. In the example of the figure, the area where data recording is started is the area e, and the initial recording light power is PWmid. When the recording light power is PWmid, the β value in the region e is smaller than β_best, for example, as shown in FIG. The β value is measured at the timing shown at the bottom of FIG. 19, and the recording light power correction (β correction) is executed based on the difference between the measured β value and the target β value. Due to the first β correction, the recording light power rises from PWmid to a level close to PWe. As a result, the error rate decreases and the β value can approach β_best. As a result of such β correction, the recording light power in the region e approaches the optimum value PWe in the region e. When the data recording area transitions from the area e to the area b, the recording light power approaching the optimum value PWe in the area e has a value far from the optimum value PWb in the area b. For this reason, in the region b, the β value of the data recorded with the recording light power of PWe rises to β_b_PWe which is larger than the target β value β_best. At this time, in the example of FIG. 19, the error rate approaches the reproduction limit. However, since the β correction is performed promptly, the recording light power can eventually approach PWb, which is the optimum value in the region b.

  As a result of performing β correction on the recording light power in this way, even when the data recording region changes from region b → region c → region d → region e → region b, the recording light power can be optimized. Performed quickly.

  Next, an example of changes in β value, recording light power, and error rate when data is recorded in a low sensitivity area will be described with reference to FIG. FIG. 20 is a diagram corresponding to FIG. 19, but is different in that data recording areas are changed in the order of areas e ′, b ′, c ′, d ′, e ′, and b ′. . FIG. 20 shows not only optimum recording light power values PWb ′ and PWe ′ in regions b ′ and e ′ but also optimum recording light power values PWb and PWe in regions b and e for comparison. .

  In this embodiment, since the initial recording light power is set to PWmid (= PWb × correction coefficient), the error rate does not exceed the reproduction limit even when data recording is first started in the low sensitivity area e ′. It is possible to quickly approach the optimum value by β correction. The operation after the area e is basically the same as described with reference to FIG. 19, but the recording light power determined by the β correction is adjusted to a level higher than the level shown in FIG. This is to compensate for low sensitivity with stronger recording light power.

  As in the prior art, when data is started to be recorded in a recorded area with low sensitivity while the initial optical disk device is set to PWb, the error rate may exceed the reproduction limit. According to this, the possibility can be made sufficiently small.

  In the above embodiment, data is recorded on the information recording layer L0. However, when data is recorded on the information recording layer L1, a correction coefficient suitable for the information recording layer is read from the memory, and a temporary initial recording light is recorded. By multiplying the power, the initial recording light power can be calculated. It should be noted that the correction coefficient may be set to 1 when data is recorded on the information recording layer L2 in the information recording layer located on the foremost side and the three-layer optical disc.

  In the above embodiment, when recording on, for example, the information recording layer L0 of a multilayer optical disc of the light transmittance decreasing type or the light transmittance increasing type in which the number of layers is N (N is an integer of 2 or more), information is recorded in the PCA. Test recording of data was performed in an unrecorded area where data was not written in all information recording layers from the recording layer L1 to the information recording layer L (N-1), and a temporary initial recording light power (PWb) was determined. However, the PCA performs test recording of data in the recording areas where data is written in all the information recording layers from the information recording layer L1 to the information recording layer L (N-1), and provisional initial recording light power (PWe) Then, the initial recording light power (PWmid) can be calculated by multiplying the provisional initial recording light power (PWe) by the correction coefficient (PWmid / PWe). Further, as a correction coefficient, a value between PWlow and PWhigh may be employed instead of an intermediate value between PWb and PWe.

  The present invention can be widely applied to an optical disc apparatus that records computer data and / or video / audio data on a multilayer optical disc such as a BD-R or a BD-RE.

10 Optical disk 11 Optical head (optical pickup)
20 Front End Processor (FEP)
21 Reproduction Processing Unit 22 Decoder 30 Laser Drive Circuit 31 Recording Processing Unit 32 Encoder

Claims (9)

A data recording method for recording data on a multilayer optical disc having a plurality of information recording layers with N layers (N is an integer equal to or greater than 2), wherein the data is k-th (k is 1) from the innermost side of the multilayer optical disc. ≦ k ≦ N, an information recording layer) is the kth information recording layer,
Step A for determining the number of information recording layers included in the optical disc loaded in the optical disc apparatus;
When the number of layers is X (X is an integer of 2 or more), data is tested in the test recording area in the m-th information recording layer (m is an integer satisfying 1 ≦ m ≦ X−1) for test recording. Step B for recording and determining a temporary initial recording light power;
A correction coefficient is selected according to which information recording layer is the target information recording layer for recording data, and the initial initial recording light power is corrected by correcting the temporary initial recording light power based on the selected correction coefficient. Step C for determining
A data recording method including a step D of starting recording data on the target information recording layer with the initial recording light power. Step B includes
When the number of layers is X (X is an integer of 2 or more), among the test recording areas in the m-th information recording layer (m is an integer satisfying 1 ≦ m ≦ X−1) in which test recording is performed, A test recording of data is performed in an unrecorded area in which no data is written in all the information recording layers from the (m + 1) th information recording layer to the Xth information recording layer, and a provisional initial recording light power is determined. Item 4. The data recording method according to Item 1.   2. The data recording according to claim 1, wherein the step C selects the correction coefficient depending on a type of the loaded optical disc in addition to an information recording layer of the target information recording layer. Method.   And recording the correction coefficient information to which the correction coefficient value is given for each type of the multilayer optical disk in the memory of the optical disk apparatus for each of the information recording layers included in each multilayer optical disk supported by the optical disk apparatus. Item 4. The data recording method according to Item 3.   2. The data recording method according to claim 1, wherein the initial recording light power determined in step C is larger than the temporary initial recording light power in the case of a light transmittance decreasing type multilayer optical disc.   2. The data recording method according to claim 1, further comprising a step of changing a recording light power from the initial recording light power as needed based on a signal waveform obtained from the optical disk after starting data recording in the step D. 3.   A step of correcting the recording light power so that the β value indicating the symmetry of the signal amplitude with respect to the average value of the reproduction signal obtained from the optical disc approaches the target β value after starting to record data in the step D; The data recording method according to claim 1.   The data recording method according to claim 1, wherein m = 1. An optical disc apparatus for recording data on a multilayer optical disc having a plurality of information recording layers with N layers (N is an integer of 2 or more),
An optical pickup for optically accessing the multilayer optical disc;
For each of the information recording layers provided in each multilayer optical disk supported by the optical disk device, a memory for storing correction coefficient information in which a correction coefficient value is given for each type of the multilayer optical disk;
After the test recording of data is performed in a test recording area in a certain information recording layer included in the loaded multi-layer optical disc and the provisional initial recording light power is determined, the target information recording layer for recording the data is in what number information recording A recording processing unit that selects the correction coefficient from the memory according to whether it is a layer, corrects the temporary initial recording light power based on the selected correction coefficient, and determines an initial recording light power;
An optical disc device comprising:

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