Abstract:
The purpose of the present invention is to minimize increase in the number of types of medium control information, and increase in time required for OPC, in association with a greater number of recording layers in a multilayer optical information recording medium. Provided is a multilayer optical information recording medium having two or more recording layers, the multilayer optical information recording medium characterized in that the recording layers are classified into layer groups that are fewer in number than the number of recording layers, each of the layer groups so classified being assigned medium control information that is shared within the layer group, and the medium control information assigned to each layer group being pre-registered in an administrative domain.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an optical information recording medium and an information recording and playback method. In particular, the present invention relates to media control information written on a multilayer optical information recording medium and a recording and playback control technique using the media control information. 
       BACKGROUND ART 
       [0002]    Optical information recording media represented by optical discs such as a DVD (Digital Versatile Disc) and a BD (Blu-ray Disc) have a recording layer for recording information in the medium, and information recording is conducted by irradiating the top of the recording layer with light and changing the reflectance of light. Furthermore, playback of recorded information is conducted by irradiating the top of the recording layer with light and detecting a change of reflectance caused by information recording. 
         [0003]    In optical discs, the so-called multilayer technique which increases the information recording capacity by providing a plurality of recording layers in one medium is developed. For example, in BD-RE and BD-R standards, a medium having one recording layer and a medium having two recording layers are stipulated. Furthermore, recently, standards of optical discs having three or four recording layers based on the BD format have also been made. In this way, attempts to increase the number of recording layers are now continued at the present time as well. Furthermore, a technique of a multilayer optical disc medium including a plurality of recording layers having a groove-less structure that doesn&#39;t have a guide groove for tracking servo and a guide layer exclusively for tracking independent of the recording layers is also proposed. 
         [0004]    In general, media control information for conducting information recording and playback on a medium is written in advance in an optical disc medium. As such information, there is, for example, physical format information (PFI) in DVD-RAMs, DVD-RWs, DVD+RWs, DVD-Rs and DVD+Rs. Furthermore, in the case of an optical disc described in Patent Literature 1, disc information (DI) is equivalent to the media control information. 
         [0005]    Media control information in conventional optical discs will now be described by taking the DI in Patent Literature 1 as an example.  FIG. 1  is a diagram illustrating a data structure of a conventional optical disc medium schematically. A lead-in area  101 , a data area  102 , and a lead-out area  103  are disposed in the optical disc medium in order from an inner circumference. Media control information  104  is written in the lead-in area  101 . Media control information units 0, 1, 2, . . . , N−1 classified into N kinds in accordance with combinations of a recording layer, a recording speed, and a recording pulse kind are written in the media control information  104  in order. In the present specification, one set of media control information given by classifying according to conditions in this way is referred to as media control information unit. By the way, in the case of a two-layer disc having two recording layers, media control information having the same contents and corresponding to two layers is written in each of the recording layers and media control information corresponding to two layers can be acquired from either of the recording layers. 
         [0006]    A structure of the media control information unit in the conventional optical disc will now be described.  FIG. 2  is a diagram illustrating a structure of the media control information unit in an optical disc described in Patent Literature 1. One media control information unit is formed of data of 112 bytes in total including header information  201 , recording and playback control information  202 , and footer information  203 . The header information  201  includes the number of media control information units, a recording pulse classification used at the time of recording, or information of a recording layer to which the media control information unit is applied, and the like. Contents of the recording and playback control information  202  are divided into media information  204 , playback power setting information  205 , recording power setting information  206 , and recording pulse setting information  207 , and parameters concerning the respective items are written in them. For example, as a parameter concerning the playback power setting information  205 , there is maximum playback power information which specifies an upper limit value of power with which the medium is irradiated when playing back information. As parameters concerning the recording power setting information  206 , there are parameters for executing OPC (Optimum Power Control) which will be described later. Furthermore, as parameters concerning the recording pulse setting information  207 , there are parameters that specify timing of respective pulses included in recording pulses. 
         [0007]    The OPC in the optical disc will now be described. The OPC means a series of procedures for finding optimum recording power according to differences in conditions such as a recording medium, a recording layer, a recording and playback device, and an ambient temperature. Specifically, trial writing is conducted in a predetermined area on a medium while changing recording power step by step, and optimum recording power is derived on the basis of a relation between the recording power and an evaluated value obtained from a played back signal. 
         [0008]    As an adjustment method of the recording power using trial writing, OPC in a κ system using a relation between the recording power and modulation is recommended in, for example, BD-RE and BD-R standards. In this method, calculation of an optimum recording power P WO  is conducted by using a relation between recording power P W  and a modulation m, and specified recording power P IND , a coefficient target value κ, a coefficient ρ and the like which are predetermined parameters. These parameters are recorded in advance on the medium as the recording power setting information in the media control information described above. First, a predetermined signal is recorded in a predetermined area of an optical disc by using recording power P W  of a plurality of kinds in the vicinity of the specified recording power P IND , and the recorded signal is played back. As a result, the modulation m which is a value obtained by dividing an amplitude of a played back signal by an upper envelope level is acquired in association with the recording power P W . Subsequently, linear approximation is conducted on a relation between an evaluated value m*P W  and the recording power P W  in a predetermined power range around P IND . A value of the recording power P W  in a case where the evaluated value m*P W  becomes zero is calculated as recording power threshold P thr . In a relation between a target recording power P target =κ*P thr  obtained by multiplying the calculated P thr  by the coefficient target value κ and the recording power P W , recording power P W  satisfying P target =P W  is determined as optimum target recording power P targeto . A value obtained by multiplying the optimum target recording power P targeto  by the coefficient ρ is determined as optimum recording power P WO . 
         [0009]    Furthermore, as another form of OPC recommended in the standards of BD-R, there is a β system. In this method, supposing that an upper envelope level of an AC-coupled played back signal is A1 and a lower envelope level thereof is A2, recording power that causes asymmetry β represented by β=(A1+A2)/(A1−A2) to coincide with a predetermined value is determined as optimum recording power. 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         Patent Literature 1: JP-A-2006-313621 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0011]    In the conventional multilayer optical information recording medium, there are following problems caused as the number of recording layers increases. 
         [0012]    A first problem is increase of the total data amount of the media control information caused by increase of kinds of the media control information units. In the conventional optical disc described in Patent Literature 1, a media control information unit is given for every combination of the recording layer, recording speed, and recording pulse classification. If the number of recording layers increases, therefore, the number of kinds of media control information units increases in proportion to the number of recording layers and the total data amount of media control information increases. In the optical disc described in Patent Literature 1, the same media control information unit is written in a predetermined area on the medium a plurality of times repetitively as described above. This is considered to be conducted in order to improve tolerance to degradation causes, such as scratches and fingerprints, of the optical disc. If the kinds of the media control information units increase, however, the number of times of repetition decreases, resulting in lowered reliability of media control information data. In addition, if kinds of media control information units increases, the number of parameters increases correspondingly, and consequently burden for determining those values increases in the medium manufacturer. 
         [0013]    A second problem is the increase of time required for OPC. In general, the parameters for executing OPC are different every recording layer. In the conventional optical disc described, for example, in Patent Literature 1, therefore, a media control information unit is given for every recording layer. As a result, the parameter for executing the OPC is also given every recording layer. And for determining recording power for some recording layer, it is necessary to execute the OPC in the recording layer. For determining recording power for all recording layers, therefore, it is necessary to execute the OPC as many times as the number of recording layers. If the number of recording layers increases, therefore, the time required for the OPC increases and time required for setup processing of the recording and playback device increases. In other words, time required from a medium is inserted into the recording and playback device until the medium becomes usable, or time required from a recording command is given to the recording and playback device until recording is actually started increases and convenience in use by a user is hampered. 
         [0014]    A first object of the present invention is to provide means for suppressing the increase of the number of kinds of media control information units caused by the increase of the number of recording layers in order to solve the first problem. 
         [0015]    Furthermore, a second object of the present invention is to provide means for suppressing the increase of OPC required time caused by the increase of the number of recording layers in order to solve the second problem. 
       Solution to Problem 
       [0016]    In the present invention, the following means are used to achieve the objects. 
         [0017]    (1) In a multilayer optical information recording medium including at least three recording layers, the recording layers are classified into layer groups that are fewer in number than the recording layers, media control information common in a layer group is provided for every layer group generated by the classification, and the media control information provided every layer group is recorded in advance in a predetermined area on the multilayer optical information recording medium. 
         [0018]    In the present configuration, a plurality of recording layers included in a multilayer optical information recording medium are classified into several groups (hereafter referred to as layer groups), and a media control information unit given for every recording layer in the conventional optical disc is given for every layer group. Since the number of layer groups is set to be less than the number of recording layers, the kinds of media control information units can be decreased as compared with the conventional optical disc. The media control information unit is given at least for every layer group. However, it is also possible to add conditions such as, for example, recording speed and recording pulse classification as shown in  FIG. 9  and give a media control information unit every combination of them. By the way, it is necessary to determine a way of classification into layer groups (such as the number of layer groups and assignment of recording layers to each layer group) to be able to suitably conduct recording and playback on respective recording layers even if common media control information is used for every same layer group. Owing to the present configuration, it is possible to suppress increase of the data quantity of the media control information caused by increase of the number of recording layers. As a result, the first object in the present invention is achieved. 
         [0019]    (2) In addition, for every layer group, parameters for specifying maximum playback power with respect to each of the recording layers belonging to the layer group are included in the media control information. 
         [0020]    The present configuration further concretizes contents of the media control information in the configuration of (1). The maximum playback power means an upper limit of the power of light with which the medium is irradiated at the time of information playback. The maximum playback power is specified mainly by a manufacturer of the medium in order to prevent a recorded track from being degraded by light irradiation. The maximum playback power is determined, for example, to cause playback signal qualities such as amplitude, jitter, and errors to satisfy criteria after a predetermined number of times of playback. In the present configuration, every layer group, parameters for specifying maximum playback power with respect to each of recording layers belonging to the layer group are given and written in media control information. Even if the data quantity in the media control information is reduced, therefore, it becomes possible to play back information with suitable playback power in the recording and playback device. A more desirable configuration is obtained in achieving the first object in the present invention. 
         [0021]    (3) In addition, the recording layers are respectively provided with consecutive integer layer numbers in order from back when viewed from a light incidence plane of the multilayer optical information recording medium or in order from front. The maximum playback power for each of the recording layers is given by a polynomial function of the layer number. Parameters for specifying maximum playback power for each of the recording layers are parameters indicating respective coefficients of the polynomial function of the layer number. And the parameters are set every layer group. 
         [0022]    The present configuration further concretizes the parameters for specifying the maximum playback power in the configuration of (2). In the present configuration, the recording layers are provided with consecutive integer layer numbers such as, for example, 0, 1, 2, . . . in order from a back recording layer when viewed from a light incidence plane or in order from a front recording layer. The maximum playback power for each of the recording layers is given by a polynomial function (mth order function; where m is an integer of at least 0) of the layer number. In other words, when the layer number is n, maximum playback power Pr max (n) for the nth recording layer is given by the following MATH. 1. 
         [0000]      [MATH. 1] 
         [0000]        Pr   max ( n )= c   0   +c   1   n+c   2   n   2   +Λ+c   m-1   n   m-1   +c   m   n   m   MATH. 1
 
         [0023]    Here, c x  is a coefficient of an xth order term of n. In other words, the present configuration approximates a relation between the layer number and actual maximum playback power by using a polynomial function, and states parameters indicating c 0 , c 1 , c 2 , . . . , C m-1 , C m  for specifying the polynomial function, in the media control information. For example, in a case where a second order function is used as the polynomial function, parameters indicating c 0 , c 1  and c 2  are written in the media control information. The set of coefficients c 0 , c 1 , c 2 , . . . , c m-1 , c m  is written at least for every media control information unit classified according to the layer group. If the layer group differs, therefore, values of the respective coefficients differ. In the present configuration, a polynomial function is used. Even if the relation between the layer number and the maximum playback power is complicated, therefore, the error between the value of the polynomial function and the actual value of the maximum playback power can be made small if a polynomial function that is high in degree is used. In a case where the medium having the present configuration is used, a maximum playback power for a recording layer (playback object layer) to be played back can be calculated by referring to a media control information unit corresponding to a layer group to which the playback object layer belongs, specifying a polynomial function by using respective coefficients written in the media control information unit, and substituting a layer number of the playback object layer into the specified polynomial function. In other words, maximum playback power for each of the recording layers can be found from the media control information given for every layer group. Even if the data quantity in the media control information is reduced, therefore, it becomes possible to play back the information with respect to each of the recording layers with suitable playback power. In achieving the first object in the present invention, therefore, a more desirable configuration is obtained. 
         [0024]    (4) In the multilayer optical information recording medium of (3), the polynomial function of the layer number is a first order function of the layer number. 
         [0025]    The present embodiment further concretizes the polynomial function of the layer number giving maximum playback power in the configuration of (3). In the present configuration, maximum playback power for each of the recording layers is given by a first order function of the layer number. In other words, when the layer number is n, maximum playback power Pr max (n) for the nth recording layer is given by the following MATH. 2. 
         [0000]      [MATH. 2] 
         [0000]        Pr   max ( n )= c   0   +c   1   n   MATH. 2
 
         [0026]    Here, c 0  and c 1  are coefficients of zero-th and first order terms of n. In other words, the present configuration approximates the relation between the layer number and the actual maximum playback power by using a first order function, and states parameters indicating the coefficients c 0  and c 1  for specifying the first order function, in the media control information. The set of coefficients c 0  and c 1  is written at least for every media control information unit classified according to the layer group. If the layer group differs, therefore, values of the respective coefficients differ. In the present configuration, parameters for specifying the coefficients c 0  and c 1  of the first order function are written on the medium as a part of the media control information. Since the polynomial function is restricted to the first order function, information for specifying the first order function is only the coefficients c 0  and c 1 , and is kept to a minimum required. The data quantity in the media control information can be reduced. Owing to the present configuration, a more desirable configuration is obtained in achieving the first object in the present invention. 
         [0027]    The case where the relation is represented by a first order function has been described above. In a case where maximum playback power for all recording layers belonging to the same layer group is made the same, only a parameter indicating c 0  is written. In this case, it is possible to obtain an effect that the data quantity can be further reduced. 
         [0028]    (5) In addition, parameters for executing OPC on each of the recording layers are included in the media control information. 
         [0029]    The present configuration further concretizes contents of the media control information in the configurations of (1) to (4). In the present configuration, parameters for executing OPC on the recording layers are written in the media control information. Since parameters for executing OPC are given for every layer group, OPC is executed on recording layers belonging to the same layer group by using the same parameters. Furthermore, in the present configuration, the parameters for executing OPC are written in media control information. Owing to the present configuration, it becomes possible to record information on respective recording layers with optimum recording power, even if the data quantity of the media control information is reduced. In achieving the first object in the present invention, therefore, a more desirable configuration is obtained. 
         [0030]    (6) In the multilayer optical information recording medium of (5), at least specified recording power for executing OPC of a κ system is included in the parameters for executing OPC, the recording layers are respectively provided with consecutive integer layer numbers in order from back when viewed from a light incidence plane of the multilayer optical information recording medium or in order from front, the specified recording power for each of the recording layers is given by a polynomial function of the layer number, and parameters for specifying specified recording power for each of the recording layers are parameters indicating respective coefficients of the polynomial function of the layer number and are set every layer group. 
         [0031]    The present configuration further concretizes the parameters for executing OPC in the configuration of (5). Here, the specified recording power is a supposed value of optimum target recording power in the OPC of the above-described κ system, and is in a proportional relation to the supposed optimum recording power. In the present configuration, at least specified recording power is used as the parameters for executing OPC of the κ system in the configuration of (5), and specified recording power for each of the recording layers is given by a polynomial function (mth order function; where m is an integer of at least 0). In other words, when the layer number is n, specified recording power for an nth recording layer P IND (n) is given by the following MATH. 3. 
         [0000]      [MATH. 3] 
         [0000]        P   IND ( n )= c   0   +c   1   n+c   2   n   2   +Λ+c   m-1   n   m-1   +c   m   n   m   MATH. 3
 
         [0032]    Here, c x  is a coefficient of an xth order term of n. In other words, the present configuration approximates a relation between the layer number and actual specified recording power by using a polynomial function, and writes parameters indicating c 0 , c 1 , c 2 , . . . , c m-1 , C m  for specifying the polynomial function, in the media control information. The set of coefficients c 0 , c 1 , c 2 , . . . , c m-1 , c m  is written at least for every media control information unit classified according to the layer group. If the layer group differs, therefore, values of the respective coefficients differ. In the present configuration, a polynomial function is used. Even if the relation between the layer number and the specified recording power is complicated, therefore, the error between the value of the polynomial function and the actual value of the specified recording power can be made small if a polynomial function that has high in degree is used. In a case where the medium having the present configuration is used, a specified recording power for a recording layer (recording object layer) to be recorded can be calculated by referring to a media control information unit corresponding to a layer group to which the recording object layer belongs, specifying a polynomial function by using respective coefficients written in the media control information unit, and substituting a layer number of the recording object layer into the specified polynomial function. In other words, specified recording power for each of the recording layers can be found from the media control information given for every layer group. Even if the data quantity in the media control information is reduced, therefore, it becomes possible to execute OPC of the κ system with respect to each of the recording layers with suitable specified recording power. In achieving the first object in the present invention, therefore, a more desirable configuration is obtained. 
         [0033]    (7) In the multilayer optical information recording medium of (6), the polynomial function of the layer number is a first order function of the layer number. 
         [0034]    The present embodiment further concretizes the polynomial function of the layer number giving specified recording power in the configuration of (6). In the present configuration, specified recording power for each of the recording layers is given by a first order function of the layer number. In other words, when the layer number is n, specified recording power P IND (n) for the nth recording layer is given by the following MATH. 4. 
         [0000]      [MATH. 4] 
         [0000]        P   IND ( n )= c   0   +c   1   n   MATH. 4
 
         [0035]    Here, c 0  and c 1  are coefficients of zero-th and first order terms of n. In other words, the present configuration approximates the relation between the layer number and the actual specified recording power by using a first order function, and states parameters indicating the coefficients c 0  and c 1  for specifying the first order function, in the media control information. The set of coefficients c 0  and c 1  is written at least every media control information unit classified according to the layer group. If the layer group differs, therefore, values of the respective coefficients differ. In the present configuration, parameters for specifying the coefficients c 0  and c 1  of the first order function are written on the medium as a part of the media control information. Since the polynomial function is restricted to the first order function, information for specifying the first order function is only the coefficients c 0  and c 1 , and is kept to a minimum required. The data quantity in the media control information can be reduced. Owing to the present configuration, a more desirable configuration is obtained in achieving the first object in the present invention. 
         [0036]    (8) In addition, parameters indicating timing of recording pulses are included in the media control information. 
         [0037]    The present configuration further concretizes the configurations of (1) to (7). In the present configuration, parameters indicating timing of recording pulses are written in the media control information. Here, parameters indicating timing of recording pulses are parameters relating to timing of light emission of light with which the medium is irradiated when recording information. Specifically, the parameters are start time, end time or a time width of each of pulses included in a recording pulse train. In the present configuration, common recording pulse conditions are used for all recording layers belonging to the same layer group. Therefore, it is desirable to design recording characteristics of respective recording layers and a way of classifying the recording layers into layer groups in order to make it possible to record information in respective recording layers suitably in that case as well. Owing to the present configuration, it becomes possible to record information by using suitable recording pulses for respective recording layers, even if the data quantity of the media control information is reduced. In achieving the first object in the present invention, therefore, a more desirable configuration is obtained. 
         [0038]    (9) In addition, parameters for specifying a layer group to which each of the recording layers belongs are included in the media control information. 
         [0039]    The present configuration further concretizes the configurations of (1) to (8). For effectively utilizing the multilayer optical information recording medium according to the present invention in a recording and playback device, information as to which media control information unit should be applied to each of the recording layers becomes necessary. It is information for specifying a layer group to which each of the recording layers belongs. Relations between recording layers and layer groups may be determined in advance, for example, by standards of the medium or the like, or determined every medium by a supplier of the media. Supposing especially the case where the relations are determined arbitrarily by the media supplier, in the present configuration, parameters for specifying a layer group to which each of the recording layers belongs are recorded in advance on the medium as a part of media control information. Specifically, every media control information unit, parameters indicating a layer group and recording layers to which the media control information unit is applied are written. Owing to the present configuration, it becomes possible to apply suitable media control information to each of the recording layers in the recording and playback device, even if the data quantity of the media control information is reduced. In achieving the first object in the present invention, therefore, a more desirable configuration is obtained. 
         [0040]    (10) In addition, all recording layers belonging to the same layer group are formed of the same film configuration. 
         [0041]    The present configuration further concretizes the configurations of (4), (7) and (8). And the present configuration is one of means for implementing these configurations easily. 
         [0042]    For implementing a state in which common recording pulse conditions are given for every layer group as in the multilayer optical information recording medium of (8), i.e., information can be recorded by using the same recording pulse conditions for all recording layers belonging to the same layer group, it is necessary to cause recording characteristics of those recording layers to become equivalent. In the present configuration, therefore, all recording layers belonging to the same layer group are made to have the same film configuration. Here, the film configuration means composition and thickness conditions of recording films and other films (guard films and reflection films) that form recording layers. Furthermore, the same film configuration means making the composition and film thickness nearly the same by making the film forming conditions same. The same film configuration does not mean that the composition and film thickness of completed films are completely the same. As a result, recording characteristics of all recording layers in a layer group become nearly equivalent. Accordingly, it becomes possible to record information suitably by using the same recording pulse conditions. 
         [0043]    For implementing a state in which each of the maximum playback power and specified recording power is given by a first order function as in the multilayer optical information recording media of (4) and (7), it is necessary to make tolerance to playback light and sensitivity to recording light of those recording layers equivalent and make a power of light arriving at respective recording layers equivalent when the power of light incident on the medium is given according to a first order function of a layer number. This can also be implemented by providing all recording layers belonging to the same layer group with the same film configuration. This is because transmittance of each of recording layer having the same film configuration are equal as simple substance, and consequently under a condition that the transmittance is sufficiently large, medium incident light power that makes the power of light arriving at respective recording layers equivalent is approximately given by a first order function of a layer number. 
         [0044]      FIG. 3  is a graph showing a relation between a layer number in a layer group having eight recording layers and a power of light to be incident on the layer group in order to cause the power of light arriving at a recording layer having the layer number to become 1 mW. Here, the recording layers are provided with layer numbers 0, 1, . . . , 7 in order beginning with a recording layer farthest from the light incidence plane. Furthermore, it is supposed that the recording layers have equal transmittance of 95% and intermediate layers (transparent layers between recording layers) cause no light loss. A solid line on the graph indicates a regression first order function (regression straight line) obtained from data points. According to this graph, an error between power given by the first order function and truly required power is 1.1% at most and very small. It is appreciated that incident light power can be approximated well by the first order function of the layer number in the present configuration. 
         [0045]    By the way, in the medium of the present configuration, required power increases as the layer number becomes smaller, i.e., the recording layer is located nearer to the back when viewed from the light incident plane. When determining a way of classifying recording layers into layer groups, therefore, it is desirable to cause required power for every recording layer to be contained in a possible output range of a laser light source, for example, by making an optical absorption coefficient larger as the layer group is located nearer to the back. 
         [0046]    Owing to the present configuration, it becomes possible to conduct recording and playback with suitable power for each of the recording layers even if the data quantity of the media control information is reduced, as described heretofore. In achieving the first object in the present invention, therefore, a more favorable configuration is obtained. 
         [0047]    (11) An information playback method includes a process for reading out media control information corresponding to a layer group to which a playback object layer belongs, from a multilayer optical information recording medium including at least three recording layers, the recording layers being classified into layer groups that are fewer in number than the recording layers, media control information common in a layer group being given for every layer group generated by the classification, the media control information being recorded in advance in a predetermined area, parameters for specifying maximum playback power for each of the recording layers being included in the media control information; a process for extracting parameters for specifying maximum playback power for the playback object layer from the media control information read out; a process for specifying maximum playback power for the playback object layer by using the extracted parameters; and a process for playing back information of the playback object layer with playback power that does not exceed the specified maximum playback power. 
         [0048]    The present configuration is an information playback method supposing use of the multilayer optical information recording medium of (2). Media control information is classified by layer group and recorded on the medium of (2). Parameters for specifying maximum playback power for each of the recording layers are included in contents of the media control information. In order to execute playback control on a playback object layer, media control information corresponding to a layer group to which the recording layer belongs is read out in the present configuration. Parameters for specifying maximum playback power are extracted from the media control information read out. Maximum playback power is calculated from the extracted parameters. Information in the playback object layer is played back with playback power having magnitude that does not exceed the maximum playback power. Owing to the present configuration, it becomes possible to play back information without degrading recorded tracks with respect to each of the recording layers even if the data quantity of the media control information is reduced. In achieving the first object in the present invention, a desirable configuration is obtained. 
         [0049]    (12) In the information playback method of (11), the recording layers are respectively provided with consecutive integer layer numbers in order from back when viewed from a light incidence plane of the multilayer optical information recording medium or in order from front, the maximum playback power for each of the recording layers is given by a polynomial function of the layer number, and parameters for specifying maximum playback power for each of the recording layers are parameters indicating respective coefficients of the polynomial function of the layer number given for every layer group, the process for extracting parameters is a process for extracting parameters indicating respective coefficients of the polynomial function of the layer number for the playback object layer from the media control information read out, and the process for specifying maximum playback power is a process for specifying a polynomial function of the layer number by using the extracted parameters and calculating maximum playback power for the playback object layer by substituting the layer number of the playback object layer into the polynomial function of the layer number. 
         [0050]    The present configuration further concretizes the information recording and playback method of (11). The present configuration is an information playback method supposing use of the multilayer optical information recording medium of (3). In the medium of (3), the recording layers are respectively provided with consecutive integer layer numbers, such as, for example, 0, 1, 2, . . . in order from a back recording layer when viewed from a light incidence plane or in order from a front recording layer. The maximum playback power for each of the recording layers is given by a polynomial function of the layer number. And parameters indicating respective coefficients of the polynomial function are written as a part of media control information. In order to execute playback control on a playback object layer, media control information corresponding to a layer group to which the recording layer belongs is read out, in the present configuration. Parameters given for every layer group to indicate respective coefficients of the polynomial function giving maximum playback power for each of the recording layers are extracted from the media control information read out. The polynomial function is specified from the extracted parameters. Maximum playback power is calculated by substituting the layer number of the playback object layer into the specified polynomial function. Information in the playback object layer is played back with playback power having magnitude that does not exceed the calculated maximum playback power. Owing to the present configuration, it becomes possible to play back information without degrading recorded tracks for each of the recording layers even if the data quantity of the media control information is reduced. In achieving the first object in the present invention, therefore, a more desirable configuration is obtained. 
         [0051]    (13) An information recording method includes: a process for reading out media control information corresponding to a layer group to which a recording object layer belongs, from a multilayer optical information recording medium including at least three recording layers, the recording layers being classified into layer groups that are fewer in number than the recording layers, media control information common in a layer group being given for every layer group generated by the classification, the media control information given for every layer group being written in advance in a predetermined area on the multilayer optical information recording medium, and parameters for executing OPC on each of the recording layers being included in the media control information; a process for extracting parameters for executing OPC on the recording object layer from the media control information read out; a process for conducting the OPC in the recording object layer by using the extracted parameters and determining recording power for the recording object layer; and a process for recording information in the recording object layer by using the determined recording power. 
         [0052]    The present configuration is an information recording method supposing use of the multilayer optical information recording medium of (5). Media control information is classified by the layer group and recorded on the medium of (5). Parameters for executing OPC on each of the recording layers are included in contents of the media control information. In order to execute recording control on a recording object layer, media control information corresponding to a layer group to which the recording layer belongs, is read out in the present configuration. Parameters for executing OPC are extracted from the media control information read out. The OPC is executed in the recording object layer by using the extracted parameters, and recording power for the recording object layer is determined. Information is recorded in the recording object with the determined recording power. Owing to the present configuration, it becomes possible to record information in each of the recording layers with suitable recording power even if the data quantity of the media control information is reduced. In achieving the first object in the present invention, therefore, a desirable configuration is obtained. 
         [0053]    (14) In the information recording method of (13), at least specified recording power for executing OPC of a κ system is included in the parameters for executing OPC, the recording layers are respectively provided with consecutive integer layer numbers in order from back when viewed from a light incidence plane of the multilayer optical information recording medium or in order from front, the specified recording power for each of the recording layers is given by a polynomial function of the layer number, and parameters for specifying specified recording power for each of the recording layers are parameters indicating respective coefficients of the polynomial function of the layer number, the process for extracting parameters is a process for extracting parameters given for every layer group to indicate respective coefficients of the polynomial function, and the process for determining a recording power is a process for specifying the polynomial function from the extracted parameters, calculating a specified recording power for the recording object layer by substituting the layer number of the recording object layer into the specified polynomial function, executing OPC of the κ system in the recording object layer by using the calculated specified recording power, and determining a recording power for the recording object layer. 
         [0054]    The present configuration further concretizes the information recording and playback method of (13). The present configuration is an information playback method supposing use of the multilayer optical information recording medium of (6). In the medium of (6), the recording layers are respectively provided with consecutive integer layer numbers, such as, for example, 0, 1, 2, . . . in order from a back recording layer when viewed from a light incidence plane or in order from a front recording layer. The specified recording power for each of the recording layers is given by a polynomial function of the layer number. And parameters indicating respective coefficients of the polynomial function are written as a part of media control information. In order to execute recording control on a recording object layer, media control information corresponding to a layer group to which the recording layer belongs is read out, in the present configuration. Parameters given for every layer group to indicate respective coefficients of the polynomial function giving a specified recording power for each of the recording layers are extracted from the media control information read out. The polynomial function is specified from the extracted parameters. A specified recording power is calculated by substituting the layer number of the recording object layer into the specified polynomial function. OPC of the κ system is executed in the recording object layer by using the calculated specified recording power and the extracted κ value and ρ value. A recording power for the recording object layer is determined. Information is recorded with the determined recording power. Owing to the present configuration, it becomes possible to record information with a suitable recording power for each of the recording layers, even if the data quantity of the media control information is reduced. In achieving the first object in the present invention, therefore, a more desirable configuration is obtained. 
         [0055]    (15) In the information recording method of (14), the function of the layer number is a first order function of the layer number, and the information recording method includes a process for executing OPC in each of at least two recording layers among recording layers belonging to same layer group, and determining recording power for each of the recording layers, a process for calculating a regression first order function corresponding to relations between the layer number of the recording layer for which the OPC is executed and determined recording power, and a process for determining recording power for a different recording layer belonging to same layer group as the recording layer for which the OPC was executed, by substituting a layer number of the different recording layer into the calculated regression first order function. 
         [0056]    The present configuration further concretizes the configuration of (14). The present configuration is an information recording method supposing use of the multilayer optical information recording medium of (7). In the medium of (7), design is conducted to give specified recording power for each of the recording layers by a first order function of the layer number. Here, optimum recording power for each of the recording layers also follows the first order function of the layer number. In the present configuration, therefore, OPC is executed on a plurality of recording layers belonging to the same layer group. A regression first order function (regression straight line) corresponding to a relation between the layer number and determined recording power is found. Recording power for each of remaining recording layers belonging to the same layer group is determined by substituting the layer number of the recording layer into the regression first order function. Here, effects of the present configuration are obtained on condition that the actual specified recording power can be approximated well by a first order function of the layer number. Therefore, it is desirable to determine the number of layer groups and recording layers belonging to each layer group to cause an error between actual specified recording power and power given by the first order function of the layer number to be contained in a predetermined range based on a requested power precision. As a result, recording power for every recording layer can be determined without executing OPC on every recording layer in the layer group. As compared with the conventional optical disc, therefore, required time for OPC can be shortened and the first and second objects in the present invention are achieved. 
         [0057]    Furthermore, in the present configuration, recording power for every layer in a layer group can be determined if OPC is executed in one of recording layers in the layer group. Therefore, an effect equivalent to an increase of the size of the OPC area on the medium is obtained. This brings about an especially great advantage in media of incremental recording type in which overwriting of recording information cannot be conducted. 
         [0058]    The information recording method of (13) to (15) includes a process for extracting parameters for specifying the specified recording power, a process for calculating specified recording power for each of the recording layers by using parameters for the recording layers, a process for executing OPC on one of the recording layers and determining recording power for the recording layer, a process for determining recording power for remaining recording layers in a layer group to which the recording layer belongs, on the basis of the determined recording power and the parameters, and a process for recording information with the determined recording power for each of the recording layers. 
         [0059]    The present configuration further concretizes the configuration of (13). A ratio of a recording power determined by conducting OPC on one recording layer in a layer group to a recording power calculated by substituting the layer number into a polynomial function specified by parameters written in media control information is calculated. Recording power for each of remaining layers in the layer group is calculated by multiplying recording power for each of the recording layers calculated from the polynomial function by the ratio, Here, effects of the present configuration are obtained on condition that the actual specified recording power can be approximated well by a polynomial function of the layer number. Therefore, it is desirable to determine the number of layer groups and recording layers belonging to each layer group to cause an error between actual specified recording power and power given by the polynomial function of the layer number to be contained in a predetermined range based on a requested power precision. As a result, recording power for every recording layer can be determined without executing OPC on every recording layer in the layer group. As compared with the conventional optical disc, therefore, required time for OPC can be shortened and the first and second objects in the present invention are achieved. 
       Advantageous Effects of Invention 
       [0060]    According to the present invention, the increase of data amount of the media control information and increase of the OPC required time caused by the increase of the number of recording layers can be suppressed. As a result, it becomes possible to provide a large capacity, highly reliable multilayer optical information recording medium and an information recording and playback device using such a medium at low cost. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0061]      FIG. 1  is a diagram showing a data area in a conventional disc medium; 
           [0062]      FIG. 2  is a diagram showing a configuration of a media control information unit in the conventional disc medium; 
           [0063]      FIG. 3  is a graph showing a relation between a layer number and medium incident light power; 
           [0064]      FIG. 4  is a diagram schematically showing a cross-sectional structure of a multilayer optical disc medium in an embodiment of the present invention; 
           [0065]      FIG. 5  is a diagram showing a data structure of a multilayer optical disc medium in an embodiment of the present invention; 
           [0066]      FIG. 6  is a diagram showing a configuration of a media control information unit in an embodiment of the present invention; 
           [0067]      FIG. 7  is a diagram showing a configuration of an optical disc device in an embodiment of the present invention; 
           [0068]      FIG. 8  is a diagram showing recording pulse waveforms of an N−1 write strategy in an embodiment of the present invention; 
           [0069]      FIG. 9  is a diagram showing corresponding relations between media control information unit numbers and conditions under which the media control information unit numbers are applied, in an embodiment of the present invention; 
           [0070]      FIG. 10  is a flow chart showing one form of an information playback procedure in an embodiment of the present invention; 
           [0071]      FIG. 11  is a flow chart showing one form of an information recording procedure in an embodiment of the present invention; 
           [0072]      FIG. 12  is a flow chart showing one form of an information recording procedure in an embodiment of the present invention; 
           [0073]      FIG. 13  is a flow chart showing one form of an information recording procedure in an embodiment of the present invention; and 
           [0074]      FIG. 14  is a diagram showing a method for calculating an optimum recording power in an embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0075]    Hereafter, embodiments of the present invention will be described with reference to the drawings. 
       Embodiment 1 
       [0076]    An example in which a multilayer optical information recording medium according to the present invention is applied to an optical disc will now be described. An optical disc medium in the present embodiment is based upon a physical format of incremental write type BD-R, and designed on the assumption that a light source having a wavelength of 405 nm and an objective lens having a numerical aperture of 0.85 are used. The disc has a diameter of 120 mm and a thickness of 1.2 mm. 
         [0077]      FIG. 4  is a diagram schematically showing a cross-sectional structure of a multilayer optical disc medium in the present embodiment. A multilayer optical disc medium  401  is formed by stacking a substrate  402 , a zero-th recording layer  403 , an intermediate layer  404 , a first recording layer  405 , an intermediate layer  406 , a second recording layer  407 , an intermediate layer  408 , a third recording layer  409 , an intermediate layer  410 , a fourth recording layer  411 , an intermediate layer  412 , a fifth recording layer  413 , an intermediate layer  414 , a sixth recording layer  415 , an intermediate layer  416 , a seventh recording layer  417 , and a cover layer  418  in order. The substrate  402  is a disc having a thickness of 1.05 mm, and polycarbonate resin is used as its material. On a surface of the substrate, a guide groove for causing an optical spot to track a determinate radial position is formed spirally with a pitch of 0.32 μm. Denoting a channel bit length by T, recording marks and recording mark spaces each 6 having a length in the range of 2T to 8T are formed along the guide groove. Here, the channel bit length is 74.5 nm, and the data capacity per recording layer becomes 25 GB under this condition. The zero-th recording layer  103  is formed next to the substrate  402 . A recording layer has a structure in which a recording film is interposed between guard films. As a material of the recording film, a Bi—Ge nitride alloy which is an inorganic material is used. Recording is conducted by assigning bi-valued data “0” and “1” to a high reflectance portion and a low reflectance portion, respectively. Data is played back by utilizing a reflectance difference between them and distinguishing the bi-valued data “0” and “1.” The intermediate layers are formed to separate recording layers from each other. The intermediate layers  404 ,  408 ,  412  and  416  have a thickness of approximately 12 μm. The intermediate layers  406 ,  410  and  414  have a thickness of approximately 16 μm. An ultraviolet curing resin is used as their material. Finally, the cover layer  418  made of an ultraviolet curing resin having a thickness of 54 μm is formed to guard the surface of the disc. 
         [0078]    The recording layers are classified into two layer groups. Three recording layers in the range of the zero-th recording layer to the second recording layer are classified into a zero-th layer group, and five recording layers in the range of the third recording layer to the seventh recording layer are classified into a first layer group. Recording layers belonging to the same layer group are formed of the same recording film and guard films. Tolerance to playback light, sensitivity to recording light, and optical characteristics such as transmittance, reflectance and absorbance are nearly equal in the layer group. Although the composition and film thickness of the recording films in all recording layers are the same, the guard films in the zero-th layer group are made to differ in thickness from the guard films in the first layer group, and the zero-th layer group differs from the first layer group in the above-described recording and playback characteristics and optical characteristics. 
         [0079]    With a standard recording speed being set equal to 4.92 m/s, recording films in respective recording layers are designed to cope with recording at one-time speed, double speed, and quadruple speed according to N−1 write strategy and recording at quadruple speed according to Castle write strategy. 
         [0080]    By the way, besides the items described above, the composition and film thickness of the recording film may be changed every layer group. 
         [0081]    Description concerning a way of classifying the recording layers into the layer groups will now be complemented. If characteristics of all recording layers are made the same (the number of layer groups is set equal to one), intensity of return light from each of the recording layers becomes small as the recording layer is located in a deeper position, and consequently a lower limit of a signal-to-noise ratio (SN ratio) requested by the recording and playback device is not satisfied and it becomes impossible to ensure reliability of the playback of information in a recording layer located in a deeper position in some cases. In that case, recording layers which are insufficient in SN ratio are classified into a different layer group and the recording layers belonging to the different layer group are made large in reflectance. In the present embodiment, the recording layers belonging to the zero-th group located in a deeper position are made larger in reflectance than the recording layers belonging to the first layer group. As a result, in both the zero-th recording layer which is the deepest layer in the zero-th layer group and the third recording layer which is the deepest layer in the first layer group, a predetermined return light intensity can be ensured. The method described heretofore is also the same in cases where the number of recording layers is not eight. In a case where the number of recording layers is further increased, the number of layer groups is increased as the occasion may demand. 
       Embodiment 2 
       [0082]    A configuration of the media control information in the present invention will now be described.  FIG. 5  is a diagram showing a data structure of a multilayer optical disc medium in the present invention. Data in each of the recording layers of the multilayer optical disc medium  501  is formed of a lead-in area  502 , a data area  503 , and a lead-out area  504  in order from the inner circumference side. The lead-in area  502  includes a media control information area  505  in which media control information is written, an OPC area  506  on which recording power learning is conducted, and other areas. 
         [0083]    Details of the media control information written in the media control information area  505  will now be described. The structure of the media control information is basically the same as that in the conventional optical disc shown in  FIG. 1 . The media control information  104  is written in the lead-in area  101 . The media control information  104  includes twelve media control information units respectively given according to combinations of the recording speed, the layer group, and the recording pulse classification.  FIG. 9  is a diagram showing corresponding relations between media control information unit numbers and conditions under which the media control information unit numbers are applied, in the present embodiment. Media control information units are first classified in an ascending order according to the recording speed, then classified in an ascending order according to the layer group, and finally classified according to the recording pulse classification. The recording speeds that the medium in the present embodiment copes with are of three kinds, i.e., one-time speed, double speed, and quadruple speed. The layer groups are of two kinds: the zero-th layer group and the first layer group. As for the recording pulse classification, there is one kind, i.e., the N−1 write strategy, in the case of the one-time speed and the double speed. In the case of the quadruple speed, there are two kinds, i.e., the N−1 write strategy and the Castle write strategy. As a result, media control information units of eight kinds in total are given. Such a set in the range of media control information unit 0 to media control information unit 7 is written repetitively in the media control information area  505 . 
         [0084]    A configuration of each media control information unit will now be described with reference to  FIG. 6 . Each media control information unit is formed of data of 112 bytes in total including header information  601 , recording and playback control information  602 , and footer information  603 . 
         [0085]    The header information  601  is formed of parameters described hereafter. Identification information  629  indicates that the data unit is media control information. Format information  630  indicates a classification of contents of the media control information unit. The number of units/applied layer group information  631  indicates the number of kinds of media control information units and a layer group to which the media control information units are applied. Applied recording layer information  632  indicates recording layers to which the media control information unit is applied. Here, a layer group to which each of the recording layers belongs can be identified on the basis of information of the number of units/applied layer group information  631  and the applied recording layer information  632 . Furthermore, the form of combination of the kind of the recording speed and the recording pulse classification shown in  FIG. 9  is determined in advance by standards of the medium. An identification number for specifying this form is written in the format information  630 . Therefore, it is made possible to know the number of layer groups as well by knowing the number of media control information units on the basis of information in the number of units/applied layer group information  631 . Unit number information  633  indicates a series number of the media control information unit in the media control information area. Continuation flag/the number of byte information  634  indicates whether there is description of media control information extending over the next media control information unit and the number of bytes assigned in the media control information unit to recording and playback control information. Reserve  635  is a reservation parameter for future expansion, and all zero data is written provisionally. 
         [0086]    Contents of the recording and playback control information  602  are divided into media information  604 , playback power information  605 , OPC information  606 , and recording pulse information  607 , and parameters relating to respective items are written. Information of the manufacturer of the medium and manufacture year and month of the medium is included in the footer information  603 . 
         [0087]    The media information  104  includes parameters described hereafter. Disc type information  608  indicates which of the rewritable type/incremental recording type is the classification of a recording layer to which the media control information is applied. Disc size/class/version information  609  indicates a diameter of the disc, a class of a disc format, and a version. Disc structure information  610  indicates the number of recording layers and a classification (rewritable type/incremental recording type/playback only type) of recording layers to which the media control information is applied. Hybrid disc/channel bit length information  611  indicates whether there is a CD-DVD layer and a channel bit length. Push-pull signal polarity information  612  indicates a polarity of a tracking error signal using a push-pull system. Recording mark polarity information  613  indicates which of “High-to-Low” (reflectance of a recording mark is less than that in unrecorded portions) and “Low-to-High” (reflectance of a recording mark is greater than that in unrecorded portions) represents characteristics of the recording mark. BCA information  614  indicates whether there is a BCA (Burst Cutting Area) code. Transfer speed information  615  indicates a maximum data transfer speed requested of an application. Reserve  616  is a reservation parameter similar to the reserve  635 . Data area disposition information  617  indicates an address range of the data area in the recording layer. Recording speed information  618  indicates a range of the recording speed to which the media control information is applied. 
         [0088]    The playback power information  605  is formed of parameters described hereafter. Maximum playback power (DC) information  619  indicates a maximum value of medium incident light power at the time when conducting playback using DC light at a recording speed to which the media control information unit is applied. This maximum playback power is determined to cause the quality of the played back signal to satisfy a predetermined reference value even after a recorded track is played back 10 6  times. Maximum playback power (HF) information  620  indicates a maximum value of medium incident light power at the time when conducting playback using high frequency superposed light. Reserve  621  is a reservation parameter similar to the reserves  635  and  616 . 
         [0089]    The OPC information  606  is formed of recording power setting information  622  which indicates conditions at the time when executing the OPC. The recording power setting information  622  is formed of a specified recording power for executing OPC of the κ system P IND , target modulation m IND , coefficient ρ, bias power to peak power ratio ε BW , cooling power to peak power ratio ε C , space power to peak power ratio ε S , coefficient target value κ, and asymmetry β for executing OPC of the β system. 
         [0090]    The recording pulse information  607  is formed of parameters that specify timing of recording pulses used at the time of recording. In the present embodiment, either “N−1 write strategy” or “Castle write strategy” can be used as the recording pulse classification. It is now assumed in the description that the “N−1 write strategy” shown in  FIG. 8  is used.  FIG. 8  shows recording pulse waveforms for forming 2T to 5T marks. Here, power level P W  is referred to as peak power, P BW  is referred to as bias power, P S  is referred to as space power, and P C  is referred to as cooling power. In the N−1 write strategy, there is one recording pulse having a peak power level in a case of a 2T mark. The number of recording pulses having a peak power level is two in a case of a 3T mark. Subsequently, the number of recording pulses having a peak power level increases by one each time 1T increases. 
         [0091]    A first pulse having a peak power level included in a recording pulse train is referred to as top pulse. A last pulse having a peak power level is referred to as final pulse. A plurality of pulses having a peak power level between the top pulse and the final pulse are referred to as intermediate pulses. A recording pulse waveform in the N−1 write strategy is specified by a time width of intermediate pulses T MP , start time of the top pulse dT top , time width of the top pulse T top , time width of the final pulse T LP , and end time of a cooling pulse dT S . The recording pulse information  607  includes T MP  setting information  623 , dT top  setting information  624 , T top  setting information  625 , T LP  setting information  626 , and dT S  setting information  627 . A parameter area corresponding to unused  628  is not used. Parameter values of three ways in total, i.e., in a case where the length of the recording marks is 2T, a case where the length of the recording marks is 3T, and a case where the length of the recording marks is at least 4T, are written. As for the dT top  setting information  624  and the T top  setting information  625 , the length of the recording marks is classified into cases of 2T, 3T and at least 4T, and in addition the length of a space preceding the recording marks is classified into four cases of 2T, 3T, 4T and at least 5T, and parameter values of 3*4=12 ways are written. As for the T LP  setting information  626  and the dT S  setting information  627 , parameter values of three ways in total, i.e., in a case where the length of the recording marks is 2T, a case where the length of the recording marks is 3T, and case where the length of the recording marks is at least 4T. 
         [0092]    As regards each of representative parameters, a concrete description method of its value will now be described. As for the number of units/applied layer group information  631 , the number of the media control information units is written in five high-order bits in 1 bite (8 bit) data assigned to this information, and a number of a layer group to which the media control information unit is applied is written in three low-order bits. For example, 000 is written if the layer group is the zero-th layer group, and 001 is written if the layer group is the first layer group. 
         [0093]    As for the applied recording layer information  632 , a range (a minimum value and a maximum value) of the layer number to which the media control information unit is applied is written in one byte assigned to this information. Specifically, for example, when the range of the layer number to which the media control information unit is applied is 3 to 7, a minimum value 0011 of the layer number is written in four high-order bits and a maximum value 0111 of the layer number is written in four low-order bits. As for the disc structure information  610 , the total number of recording layers is written in four high-order bits of 1 byte data assigned to this information. For example, 0001 is written in case of one layer, and 1000 is written in case of eight layers. Furthermore, a classification of the recording layer to which the media control information is applied is written in four low-order bits. In case of the rewritable type/incremental recording type/playback only type, 0100/0010/0001 is written, respectively. Since the medium in the present embodiment is the incremental recording type, 0010 is written here. 
         [0094]    The maximum playback power (DC) information  619  will now be described. It is now supposed that maximum playback power (unit is mW) generated by DC light irradiation of an nth recording layer is given by a first order function of the layer number n as represented by the following MATH. 5. 
         [0000]      [MATH. 5] 
         [0000]        Pr   max ( n )= c   0   +c   1   n   MATH. 5
 
         [0095]    At this time, an integer value i satisfying i=100*c 0  is written in first 1 byte in 2 byte data assigned to this information, in a sign-less 8 bit form. An integer value i satisfying i=1,000*c 1  is written in the next 1 byte in an 8 bit form of 2&#39;s complement representation. A concrete example will now be described. It is now supposed that the maximum playback power Pr max (n) is given by the following MATH. 6. 
         [0000]      [MATH. 6] 
         [0000]        Pr   max ( n )=1.42−0.062 n   MATH. 6
 
         [0096]    As for c 0 , 100*1.42=142, and consequently “10001110” which is a binary number representation of 142 is written in a byte representing c 0 . As for c 1 , 1,000*(−0.062)=(−62), and consequently “11000010” which is a binary number representation (2&#39;s complement) of (−62) is written in a byte representing c 1 . As for the maximum playback power (HF) information  620  as well, maximum playback power (unit is mW) generated by high frequency superposed light irradiation is written in a similar form. By the way, values of c 0  and c 1  are different every layer group. The above-described example is a concrete example in the case where the maximum playback power is given by a first order function of the layer number. In general, however, the same is also true of a case where the maximum playback power is given by an mth order function of the layer number n as represented by the following MATH. 11. 
         [0000]      [MATH. 11] 
         [0000]        Pr   max ( n )= c   0   +c   1   n+c   2   n   2   +Λ+c   m-1   n   m-1   +c   m   n   m   MATH. 11
 
         [0097]    In this case, the configuration of the media control information unit is changed to assign data of (m+1) bytes to each of the maximum playback power (DC) information  619  and the maximum playback power (HF) information  620 . And integer values indicating values of c 0 , c 1 , c 2 , . . . , C m-1 , c m  are written in respective bytes of (m+1) byte data. 
         [0098]    The recording power setting information  622  will now be described. A specified recording power (unit is mW) for the nth recording layer is written in first 2 bytes in 8 byte data assigned to this information. It is now supposed that the specified recording power is given by a first order function of the layer number n as represented by the following MATH. 7. 
         [0000]      [MATH. 7] 
         [0000]        P   IND ( n )= c   0   +c   1   n   MATH. 7
 
         [0099]    At this time, an integer value i satisfying i=100*c 0  is written in first 1 byte in 2 byte, in a sign-less 8 bit form. An integer value i satisfying i=1,000*c 1  is written in the next 1 byte in an 8 bit form of 2&#39;s complement representation. By the way, values of c 0  and c 1  are different every layer group. An integer value i satisfying i=200*m IND , an integer value i satisfying i=100*ρ, an integer value i satisfying i=200*ε BW , an integer value i satisfying i=200*ε C , an integer value i satisfying i=200*ε S , an integer value i satisfying i=20*κ, and an integer value i satisfying i=500*(β+0.2) are written respectively in remaining 7 bytes assigned to the recording power setting information  622 , at a rate of one byte per value. The above-described example is a concrete example in the case where the specified recording power is given by a first order function of the layer number. In general, however, the same is also true of a case where the specified recording power is given by an mth order function of the layer number n as represented by the following MATH. 12. 
         [0000]      [MATH. 12] 
         [0000]        Pr   IND ( n )= c   0   +c   1   n+c   2   n   2   +Λ+c   m-1   n   m-1   +c   m   n   m   MATH. 12
 
         [0100]    In this case, the configuration of the media control information unit is changed to assign data of (m+8) bytes to the recording power setting information  622 . And integer values indicating values of c 0 , c 1 , C 2 , . . . , C m-1 , c m  are written in first (m+1) bytes in the (m+8) bytes. 
         [0101]    As for parameters other than those mentioned above as well, parameter values are written by using a similar method, although contents and description forms of parameter values are respectively different. 
       Embodiment 3 
       [0102]    A configuration example of an optical disc device suitable for embodying the present invention will now be described with reference to  FIG. 7 . A multilayer optical disc medium  700  mounted on the device is rotated by a spindle motor  760 . At the time of playback, a laser power/pulse controller  720  controls a current so as to flow through a semiconductor laser  712  via a laser driver  716  in an optical head  710  to attain a light intensity ordered by a CPU  740 , and causes the semiconductor laser  712  to generate laser light  714 . The laser light  714  is focused by an objective lens  711  to form an optical spot  701  on some recording layer in the multilayer optical disc medium  700 . At this time, spherical aberration is corrected according to a thickness from a light incidence face of the multilayer optical disc medium  700  to a recording layer in which the optical spot  701  is formed, by a spherical aberration correction mechanism which is disposed between the semiconductor laser  712  and the objective lens  711  and which is not illustrated. Reflected light  715  from the optical spot  701  is detected by a photodetector  713  via the objective lens  711 . The photodetector includes a photodetector element divided into a plurality of portions. A readout signal pre-processor  730  reads out information recorded on the multilayer optical disc medium  700  by using a signal detected by the optical head  710 . The whole device including them is controlled by a system controller  750 . 
       Embodiment 4 
       [0103]    A concrete example of an information readout method using the multilayer optical disc medium according to the present invention will now be described.  FIG. 10  is a flow chart showing one form of an information playback procedure in the present embodiment. In the present embodiment, it is supposed to use a medium in which recording layers are classified into layer groups, media control information for each of the recording layers is given for every layer group, maximum playback power for each of the recording layers is given by a polynomial function, and parameters indicating respective coefficients of the polynomial function are written in the media control information, as in the multiplayer optical disc medium in the embodiment 2. In the ensuing description, it is supposed that the polynomial function that gives maximum playback power is a first order function as in the optical disc medium in the embodiment 2. 
         [0104]    First, at step S 1001 , a media control information unit corresponding to the combination of a layer group to which a recording layer (playback object layer) to be played back belongs and a playback speed is selected and read out from the media control information area  505  shown in  FIG. 5  in some recording layer in the multilayer optical disc medium, by referring to the correspondence relations shown in  FIG. 9 . Since media control information for all recording layers is written in all recording layers in the multilayer optical disc medium in the embodiment, necessary information can be read out from any recording layer. 
         [0105]    Subsequently at step S 1002 , parameters indicating coefficients c 0  and c 1  of the following MATH. 8 which is a first order function of a layer number that gives the maximum playback power are extracted from the media control information unit read out. 
         [0000]      [MATH. 8] 
         [0000]        Pr   max ( n )= c   0   +c   1   n   MATH. 8
 
         [0106]    These parameters are written in either the maximum playback power (DC) information  619  or the maximum playback power (HF) information  620  shown in  FIG. 6 . Selection as to which information is to be used is conducted according to the laser drive condition at the time of playback (either DC light or high frequency superposed light). 
         [0107]    Subsequently, at step S 1003 , the first order function of the layer number n is specified by using the extracted coefficients c 0  and c 1 . 
         [0108]    Subsequently, at step S 1004 , maximum playback power Pr max (n) for the playback object layer is calculated by substituting a layer number n of the playback object layer into the specified first order function of the layer number n. At this time, maximum playback power can also be calculated for remaining recording layers that belong to the same layer group as the playback object layer by using the same method. 
         [0109]    Finally, at step S 1005 , a control target value of playback power is set equal to a magnitude that does not exceed the calculated maximum playback power, and information in the playback object layer is played back. Here, it is also possible to take a control error of playback power in the recording and playback device into consideration and set the control target value to a value that is lower by that amount in order to prevent the maximum playback power from being exceeded during the playback. 
         [0110]    The present embodiment is a concrete example in the case where the maximum playback power is given by a first order function of the layer number. In the case of a polynomial function (mth order function) other than the first order function as well, however, the same procedure can be applied except that the number of coefficients written in the media control information becomes (m+1). Specifically, at the step S 1002 , coefficients c 0 , c 1 , . . . , C m-1 , c m  of the mth order function of the layer number giving the maximum playback power are extracted. At the step S 1003 , the mth order function of the layer number is specified by using the extracted coefficients. At the step S 1004 , maximum playback power Pr max (n) for the playback object layer is calculated by substituting a layer number n of the playback object layer into the specified mth order function of the layer number. The procedure other than this is the same. The precision of the maximum playback power calculated from the polynomial function can be improved by using the polynomial function which is greater in degree than the first order function in this way. For example, in a case where the relation between the layer number and the incident light power shown in  FIG. 3  is approximated by using a first order function as described above, a maximum error is 1.1%. On the other hand, the maximum error becomes 0.12% in a case where the relation is approximated by using a second order function. 
       Embodiment 5 
       [0111]    A concrete example of an information recording method using a multilayer optical disc medium according to the present invention will now be described.  FIG. 11  is a flow chart showing one form of an information recording procedure in the present embodiment. In the present embodiment, it is supposed to use a medium in which recording layers are classified into layer groups, media control information for each of the recording layers is given for every layer group, parameters for executing OPC on each of the recording layers are written, specified recording power included in the parameters is given by a polynomial function of the layer number, and parameters indicating respective coefficients of the polynomial function are written in the media control information, as in the multiplayer optical disc medium in the embodiment 2. In the ensuing description, it is supposed that the polynomial function that gives a specified recording power is a first order function as in the optical disc medium in the embodiment 2. In the case of a polynomial function other than the first order function as well, only the number of coefficients written in the media control information is different, and consequently the same procedure can be applied. 
         [0112]    First, at step S 1001 , a media control information unit corresponding to the combination of a layer group to which a recording layer (recording object layer) to be recorded belongs, a recording speed, and a recording pulse classification to be used is selected and read out from the media control information area  505  shown in  FIG. 5  in some recording layer in the multilayer optical disc medium, by referring to the corresponding relations shown in  FIG. 9 . Since media control information for all recording layers is written in all recording layers in the multilayer optical disc medium in the embodiment, necessary information can be read out from any recording layer. 
         [0113]    Subsequently at step S 1102 , parameters indicating coefficients c 0  and c 1  of the following MATH. 9 which is a first order function of a layer number that gives the specified recording power, 
         [0000]      [MATH. 9] 
         [0000]        Pr   IND ( n )= c   0   +c   1   n   MATH. 9
 
         [0000]    target modulation m IND , coefficient ρ, bias power to peak power ratio ε BW , cooling power to peak power ratio ε C , space power to peak power ratio ε S , and coefficient target value κ are respectively extracted from the media control information unit read out. 
         [0114]    Subsequently, at step S 1103 , the first order function of the layer number n is specified by using the extracted coefficients c 0  and c 1 . 
         [0115]    Subsequently, at step S 1104 , a specified recording power P IND (n) for the recording object layer is calculated by substituting a layer number n of the recording object layer into the specified first order function of the layer number n. At this time, a specified recording power can also be calculated for remaining recording layers that belong to the same layer group as the recording object layer does by using the same method. Furthermore, m IND , ρ, ratios ε BW , ε C , and ε S , and κ extracted at the step  1102  can be used in common with remaining recording layers that belong to the same layer group as the recording object layer. 
         [0116]    Subsequently, at step S 1105 , OPC of the κ system is executed in the OPC area  506  of the recording object layer on the basis of the extracted parameters, and a recording power is determined. Specifically, calculation of the optimum recording power P WO  is conducted by using the relation between the recording power P W  and the modulation m, and P IND , κ, and ρ. Here, target modulation m IND  is a reference value related to P IND  as a modulation m at the time when P W =P IND . The target modulation m IND  is not used in OPC in the present embodiment. A calculation method of the optimum recording power will now be described with reference to  FIG. 14 . First, a predetermined signal is recorded in the OPC area  506  shown in  FIG. 5  by using the recording power P W  of a plurality of kinds in the vicinity of the specified recording power P IND , and the recorded signal is played back. As a result, the modulation m which is a value obtained by dividing an amplitude of a played back signal by an upper envelope level is acquired in association with the recording power P W . Subsequently, linear approximation is conducted on a relation between an evaluated value m*P W  and the recording power P W  in a predetermined power range around P IND . A value of the recording power P W  in a case where the evaluated value m*P W  becomes zero is calculated as recording power threshold P thr . In a relation between a target recording power P target =Λ*P thr  obtained by multiplying the calculated P thr  by the coefficient target value κ and the recording power P W , recording power P W  satisfying P target =P W  is determined as optimum target recording power P tageto . A value obtained by multiplying the optimum target recording power P targeto  by the coefficient ρ is determined as an optimum recording power P WO . 
         [0117]    Finally, at step S 1106 , the determined recording power is set and information is recorded in the recording object layer. 
         [0118]    The present embodiment is a concrete example in the case where the specified recording power is given by a first order function of the layer number. In the case of a polynomial function (mth order function) other than the first order function as well, however, the same procedure can be applied except that the number of coefficients written in the media control information becomes (m+1). Specifically, at the step S 1102 , coefficients c 0 , c 1 , . . . , C m-1 , c m  of the mth order function of the layer number giving the specified recording power are extracted. At the step S 1103 , the mth order function of the layer number is specified by using the extracted coefficients. At the step S 1104 , a specified recording power Pr IND (n) for the recording object layer is calculated by substituting a layer number n of the playback object layer into the specified mth order function of the layer number n. The procedure other than this is the same. The precision of the specified recording power calculated from the polynomial function can be improved by using the polynomial function which is greater in degree than the first order function in this way. 
       Embodiment 6 
       [0119]    Another example of the information recording method using the multilayer optical disc medium according to the present invention will now be described.  FIG. 12  is a flow chart showing one form of an information recording procedure in the present embodiment. In the present embodiment, it is supposed to use a medium in which a specified recording power is given by a first order function of the layer number, and parameters indicating respective coefficients of the first order function are written in the media control information, as in the multiplayer optical disc medium in the embodiment 2. 
         [0120]    First, at step S 1201 , a media control information unit corresponding to the combination of a layer group to which a recording layer (recording object layer) to be recorded belongs, a recording speed, and a recording pulse classification to be used is selected and read out from the media control information area  505  shown in  FIG. 5  in some recording layer in the multilayer optical disc medium, by referring to the corresponding relations shown in  FIG. 9 . 
         [0121]    Subsequently at step S 1202 , parameters for executing OPC are extracted from the media control information unit read out. The parameters read out here are basically parameters for executing OPC of the κ system in the same way as the embodiment 5. Instead, however, a parameter indicating asymmetry β for executing OPC of the β system can also be extracted. In that case, OPC of the β system is executed in subsequent steps. 
         [0122]    Subsequently, at step S 1203 , OPC is executed in the OPC area  506  in the recording object layer by using the extracted parameters and recording power is determined. Here, the κ system may be used as the OPC in the same way as the embodiment 5, or instead the β system may be used. In that case, supposing that an upper envelope level of an AC-coupled played back signal is A1 and a lower envelope level thereof is A2, a recording power is determined to cause β represented by β=(A1+A2)/(A1−A2) to become equal to the extracted parameter value. 
         [0123]    Subsequently, at step S 1204 , it is determined whether to execute OPC in another recording layer that belongs to the same layer group as the recording layer subjected to OPC. In a case where OPC is to be executed in another recording layer (Yes), the processing returns to step S 1203 , OPC is executed in another recording layer, and a recording power for the recording layer is determined. In a case where no more OPC is executed in the determination at the step S 1204  (No), the processing proceeds to step S 1205 . However, OPC must be executed in at least two recording layers belonging to the same layer group. 
         [0124]    At step S 1205 , a regression first order function corresponding to relations between the layer number and determined recording power is found on the basis of a result of OPC executed in a plurality of recording layers. A recording power for a remaining recording layer that belongs to the same layer group as the recording layer subjected to OPC is calculated by substituting a layer number of the remaining recording layer into the found regression first order function. 
         [0125]    Finally, at step S 1206 , in each of the recording layers, a recording power determined for the recording layer is set and information is recorded. 
       Embodiment 7 
       [0126]    Another example of the information recording method using the multilayer optical disc medium according to the present invention will now be described.  FIG. 13  is a flow chart showing one form of an information recording procedure in the present embodiment. In the present embodiment, it is supposed to use a medium in which a parameter indicating a specified recording power is written in the media control information. In the ensuing description, it is supposed to use a medium in which a specified recording power is given by a first order function of the layer number, and parameters indicating respective coefficients of the first order function are written in the media control information, as in the multiplayer optical disc medium in the embodiment 2. 
         [0127]    First, at step S 1301 , a media control information unit corresponding to the combination of a layer group to which a recording layer (recording object layer) to be recorded belongs, a recording speed, and a recording pulse classification to be used is selected and read out from the media control information area  505  shown in  FIG. 5  in some recording layer in the multilayer optical disc medium, by referring to the corresponding relations shown in  FIG. 9 . 
         [0128]    Subsequently at step S 1302 , parameters indicating coefficients c 0  and c 1  of the following MATH. 10 which is a first order function of a layer number that gives the specified recording power, 
         [0000]      [MATH. 10] 
         [0000]        Pr   IND ( n )= c   0   +c   1   n   MATH. 10
 
         [0000]    target modulation m IND , coefficient ρ, bias power to peak power ratio ε BW , cooling power to peak power ratio ε C , space power to peak power ratio ε S , and coefficient target value κ are respectively extracted from the media control information unit read out. In a case where the β system is used when executing subsequent OPC, a parameter indicating asymmetry β is also extracted at this time. In that case as well, however, it is necessary to extract a parameter indicating the specified recording parameter P IND  at this time. 
         [0129]    Subsequently, at step S 1303 , the first order function of the layer number n is specified by using the extracted coefficients c 0  and c 1 . 
         [0130]    Subsequently, at step S 1304 , a specified recording power P IND (n1) for a first recording layer is calculated by substituting a layer number n1 of the first recording layer into the specified first order function of the layer number n. Furthermore, a specified recording power P IND (n2) for a second recording layer that belongs to the same layer group as the first recording layer does is calculated by substituting a layer number n2 of the second recording layer into the same first order function. In addition, a ratio of the specified recording power for the second recording layer to the recording power for the first recording layer α=Pn(n2)/P IND (n1) is calculated. 
         [0131]    Subsequently, at step S 1305 , OPC is executed in the OPC area  506  of the first recording layer by using the extracted parameters, and a recording power P WO1  for the first recording layer is determined. Here, the κ system may be used as the OPC in the same way as the embodiment 5, or instead the β system may be used. 
         [0132]    Subsequently, at step S 1306 , a recording power P WO2  for the second recording layer is calculated by multiplying the recording power P WO1  for the first recording layer determined at the step S 1305  by the ratio α. 
         [0133]    Finally, at step S 1307 , information is recorded by using the recording power P WO1  in the first recording layer and the recording power P WO2  in the second recording layer. 
         [0134]    The present embodiment is a concrete example in the case where the specified recording power is given by a first order function of the layer number. In the case of a polynomial function (mth order function) other than the first order function as well, however, the same procedure can be applied except that the number of coefficients written in the media control information becomes (m+1). Specifically, at the step S 1302 , coefficients c 0 , c 1 , . . . , c m-1 , C m  of the mth order function of the layer number giving the specified recording power are extracted. At the step S 1303 , the mth order function of the layer number is specified by using the extracted coefficients. At the step S 1304 , a specified recording power Pr IND (n1) for the first recording layer is calculated by substituting the layer number n1 of the first recording layer into the specified mth order function of the layer number n. A specified recording power Pr IND (n2) for the second recording layer is calculated by substituting the layer number n2 of the second recording layer into the same mth order function. The procedure other than this is the same. The precision of the specified recording power calculated from the polynomial function can be improved by using the polynomial function which is greater in degree than the first order function in this way. 
         [0135]    Embodiments of the present invention are not restricted to the above-described embodiments. In the above-described embodiments, a multilayer optical disc medium has been mentioned as an application example of the multilayer optical information recording medium according to the present invention. However, the application example of the multilayer optical information recording medium is not restricted to the multilayer optical disc medium. The multilayer optical information recording medium according to the present invention may be applied to other media as long as the medium has a plurality of stacked recording layers and recording and playback of information are conducted by light irradiation. For example, similar effects can be obtained by applying the present invention to a groove-less multilayer optical disc media including a plurality of recording layers that do not have a guide groove and a guide layer which is dedicated to tracking and which has a guide groove, non-rotating card media, tape-shaped media, or the like. In addition, as for the so-called volume recording medium having no recording layers in the medium and recording areas are formed in a plane form at various depths from the medium surface as well, it is a multilayer optical information recording medium in a broad sense if the plane-formed recording areas are regarded as recording layers. Therefore, the present invention can be applied to the so-called volume recording media in the same way. Furthermore, as for the way of assigning layer numbers to the recording layers, serial numbers extending over the whole medium are used in the above-described embodiments. However, the way of assigning layer numbers is not restricted to this. Even if serial numbers are used every layer group like a zero-th layer, a first layer, . . . in a zero-th layer group and a zero-th layer, a first layer, . . . in a first layer group, effects of the present invention can be obtained in the same way. Furthermore, as for the contents of the media control information and the parameter value description method as well, configurations other than those in the above-described embodiments may be used. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           201 : Header 
           202 : Main body 
           203 : Footer 
           401 : Multilayer optical disc medium 
           402 : Substrate 
           403 : zero-th recording layer 
           404 : Intermediate layer 
           405 : First recording layer 
           406 : Intermediate layer 
           407 : Second recording layer 
           408 : Intermediate layer 
           409 : Third recording layer 
           410 : Intermediate layer 
           411 : Fourth recording layer 
           412 : Intermediate layer 
           413 : Fifth recording layer 
           414 : Intermediate layer 
           415 : Sixth recording layer 
           416 : Intermediate layer 
           417 : Seventh recording layer 
           418 : Cover layer 
           501 : Multilayer optical disc medium 
           502 : Lead-in area 
           503 : Data area 
           504 : Lead-out area 
           700 : Multilayer optical disc medium 
           701 : Optical spot 
           710 : Optical head 
           711 : Objective lens 
           712 : Semiconductor laser 
           713 : Photodetector 
           714 : Laser light 
           715 : Reflected light 
           716 : Laser driver 
           720 : Laser power/pulse controller 
           730 : Readout signal pre-processor 
           740 : CPU 
           750 : System controller 
           760 : Spindle motor