Patent Publication Number: US-2010118687-A1

Title: Optical information recording apparatus, optical information recording method, optical information reproducing apparatus, optical information reproducing method, and optical information recording medium

Description:
TECHNICAL FIELD 
     The present invention relates to an optical information recording apparatus, an optical information recording method, an optical information reproducing apparatus, an optical information reproducing method, and an optical information recording medium. The present invention is preferably applied to an optical information recording/reproducing apparatus that records information in an optical recording medium using, for example, a light beam, and reproduces the information from the optical information recording medium using the light beam. 
     BACKGROUND ART 
     In the past, optical disk drives that employ a disk-like optical disk as an optical information recording medium have widely prevailed as optical information recording/reproducing apparatuses. As the optical disk, a compact disc (CD), a digital versatile disc (DVD), a Blu-ray disk (registered trademark, BD), or the like is generally adopted. 
     In general, in the conventional optical disks, main data is recorded as information in the form of a record mark in a signal recording surface, which reflects a light beam, by forming irregularities or varying a reflectance. Among the optical disk drives, an optical disk drive that records sub-data by forming a code mark, which has a different reflectance, on a recording track on which a record mark is formed, so that the code mark will be superposed on the record mark has been proposed (refer to, for example, patent document 1). 
     In the optical disk drive, various contents including a musical content and a video content or various pieces of information including various kinds of data items for computers are recorded in an optical disk. In recent years, an amount of information has increased along with a trend toward high-definition video or high-quality music. In addition, the number of contents to be recorded in one optical disk is requested to be increased. Accordingly, the optical disk is requested to have a larger capacity. 
     As one of techniques for increasing the capacity of an optical disk, an optical disk drive that forms multiple record marks in the thickness direction of a homogeneous recording layer, and thus records information in multiple mark layers has been proposed (refer to, for example, patent document 2). 
     Patent document 1 refers to Patent No. 354410, and patent document 2 refers to JP-A-2008-71433. 
     As for the optical disk drive described in the patent document 2, the method of recording or reproducing main data is proposed. However, a method of recording or reproducing sub-data in the same manner as the conventional optical disk drive does has not been proposed. 
     DISCLOSURE OF THE INVENTION 
     The present invention is made in consideration of the foregoing point, and intended to propose an optical information recording apparatus and an optical information recording method capable of recording sub-data, an optical information reproducing apparatus and an optical information reproducing method capable of reproducing the sub-data, and an optical information recording medium from which the sub-data can be reproduced. 
     In order to accomplish the above object, an optical information recording apparatus in accordance with the present invention includes: an objective lens that concentrates information light and irradiates it to an optical information recording medium in which information is recorded in the form of a record mark by irradiating the information light, which is emitted from a light source and has an intensity equal to or larger than a predetermined intensity, to the optical information recording medium; a focus shift unit that shifts the focus of the information light to a target depth, to which the information light should be irradiated, by shifting the focus of the information light in a focusing direction in which the objective lens recedes from or approaches to the optical information recording medium; a main data recording unit that forms the record marks along a virtual irradiation line in the optical information recording medium by controlling the light source according to information based on the main data; and a sub-data recording unit that shifts the target depth in the focusing direction according to information based on the sub-data, and thus forms the record mark with the center of the record mark deviated from the irradiation line in the focusing direction. 
     Accordingly, in the optical information recording apparatus, the sub-data can be embedded in the record mark in the form of which the main data is recorded. 
     An optical information recording method in accordance with the present invention includes a record mark forming step of, when a record mark is formed along a virtual irradiation line in an optical information recording medium by irradiating information light, which is emitted from a light source, to the optical information recording medium in which information is recorded in the form of a record mark by irradiating information light, which is emitted from the light source and has an intensity equal to or larger than a predetermined intensity, to the optical information recording medium, shifting the focus of the information light in a focusing direction according to information based on sub-data, and thus forming the record mark by deviating the record mark from the irradiation line in the focusing direction. 
     Accordingly, the optical information recording method can embed sub-data in a record mark in the form of which main data is recorded. 
     Further, an optical information reproducing apparatus in accordance with the present invention includes: a light source that emits information light; an object lens that concentrates the information light and irradiates it to an optical information recording medium; a record mark detection unit that detects the presence or absence of a record mark, which is formed along a virtual irradiation line in the optical information recording medium, on the basis of a reflected light beam which is the information light reflected from the optical information recording medium: and a deviation detection unit that detects the presence or absence of a deviation of the center of the record mark from the irradiation line in a focusing direction, in which the objective lens recedes from or approaches to the optical information recording medium, on the basis of the reflected light beam. 
     Accordingly, the optical information reproducing apparatus can reproduce main data according to the presence or absence of a record mark, and reproduce sub-data according to the presence or absence of a deviation of the center of the record mark from the irradiation line. 
     An optical information reproducing method in accordance with the present invention includes: a light receiving step of receiving a reflected light beam that is light emitted from a light source and reflected from an optical information recording medium; and a detection step of detecting the presence or absence of a record mark on the basis of the reflected light beam, and detecting the presence or absence of a deviation of the center of the record mark from an irradiation line in a focusing direction, in which an objective lens recedes from or approaches to the optical information recording medium, on the basis of the reflected light beam. 
     Accordingly, the optical information reproducing method can reproduce main data according to the presence or absence of a record mark to be detected with modulated information light, and reproduce sub-data according to the presence or absence of a deviation of the center of the record mark from the irradiation line. 
     Further, an optical information recording medium in accordance with the present invention includes a recording layer in which: main data is recorded according to the presence or absence of a record mark to be formed with irradiation of information light; sub-data is recorded by forming the record mark with the center of the record mark deviated in a focusing direction parallel to the light axis of the information light; and the irradiated information light is modulated by the record mark. 
     Accordingly, the optical information recording medium makes it possible to reproduce main data according to the presence or absence of a record mark, and to reproduce sub-data according to the presence or absence of a deviation of the center of the record mark from an irradiation line. 
     An optical information recording apparatus in accordance with the present invention includes: an objective lens that concentrates information light and servo light for servo control and irradiates them to an optical information recording medium in which information is recorded in the form of a record mark by irradiating the information light, which is emitted from a light source and has an intensity equal to or larger than a predetermined intensity, to the optical information recording medium; an objective lens drive unit that drives the objective lens so that the servo light will be focused on a reflecting layer which is formed in the optical information recording medium and reflects at least part of the servo light; a focus shift unit that separates the focus of the information light from the focus of the servo light by an arbitrary distance in a focusing direction in which the object lens recedes from or approaches to the optical information recording medium, and squares the focus of the information light with a target depth to which the information light should be irradiated; a main data recording unit that forms a record mark along a virtual irradiation line in the optical information recording medium by controlling the light source according to information based on main data; and a sub-data recording unit that deviates the center of the record mark from the irradiation line by shifting the target depth in the focusing direction according to information based on sub-data. 
     Accordingly, the optical information recording apparatus can form a record mark along an appropriate irradiation line while implementing high-definition focusing control with a reflecting layer as a reference, and can appropriately deviate the record mark from the irradiation line. 
     Further, an optical information reproducing apparatus in accordance with the present invention includes: an objective lens that concentrates and irradiates information light for information reproduction and servo light for servo control; an objective lens drive unit that drives the objective lens so that the servo light will be focused on a reflecting layer which is formed in an optical information recording medium and reflects at least part of the servo light; a focus shift unit that separates the focus of the information light from the focus of the servo light by an arbitrary distance in a focusing direction in which the objective lens approaches to or recedes from the optical information recording medium, and squares the focus of the information light with a target depth to which the information light should be irradiated; a record mark detection unit that detects the presence or absence of a record mark, which is formed along a virtual irradiation line in the optical information recording medium, on the basis of a reflected light beam that is the information light reflected from the optical information recording medium; and a deviation detection unit that detects the presence or absence of a deviation of the center of the record mark from the irradiation line in the focusing direction, in which the objective lens recedes from or approaches to the optical information recording medium, on the basis of the reflected light beam. 
     Accordingly, the optical information reproducing apparatus can implement focusing control using servo light that is unsusceptible to a deviation of the center of a record mark from an irradiation line, and can therefore reliably detect the presence or absence of the deviation representing sub-data by reliably irradiating information light to the irradiation line. 
     An optical information recording medium in accordance with the present invention includes: a recording layer in which main data is recorded according to the presence or absence of a record mark formed along a virtual irradiation line, sub-data is recorded by forming the record mark with the center of the record mark deviated from the irradiation line, and irradiated information light is modulated by the record mark; and a reflecting layer that reflects at least part of servo light irradiated in order to square the position of the information light in the recording layer with an arbitrary position. 
     Accordingly, in the optical information recording medium, focusing control that employs servo light unsusceptible to a deviation of the center of a record mark from an irradiation line can be implemented. Therefore, the information light can be reliably irradiated to the irradiation line, and the presence or absence of the deviation representing sub-data can be reliably detected from the modulated information light. 
     According to the present invention, there are provided an optical information recording apparatus and an optical information recording method capable of embedding sub-data in a record mark in the form of which main data is recorded, and thus recording the sub-data. 
     According to the present invention, there are provided an optical information reproducing apparatus and an optical information reproducing method capable of reproducing main data according to the presence or absence of a record mark, reproducing sub-data according to the presence or absence of a deviation of the center of the record mark from an irradiation line, and thus reproducing the sub-data. 
     According to the present invention, there is provided an optical information recording medium from which main data can be reproduced according to the presence or absence of a record mark detected with demodulated information light, sub-data can be reproduced according to the presence or absence of a deviation of the center of the record mark from an irradiation line, and the sub-data can be reproduced. 
     Further, according to the present invention, there is provided an optical information recording apparatus capable of forming a record mark along an appropriate irradiation line while implementing high-definition focusing control with a reflecting layer as a reference, appropriately deviating a record mark from the irradiation line, and thus recording sub-data. 
     Further, according to the present invention, there is provided an optical information reproducing apparatus capable of implementing focusing control using servo light unsusceptible to a deviation of the center of a record mark from an irradiation line, reliably detecting the presence or absence of the deviation, which represents sub-data, by reliably irradiating information light to an irradiation line, and thus reproducing the sub-data. 
     Further, according to the present invention, there is provided an optical information recording medium in which since focusing control employing servo light unsusceptible to a deviation of the center of a record mark from an irradiation line can be implemented, information light can be reliably irradiated to an irradiation line, the presence or absence of the deviation which represents sub-data can be reliably detected from the modulated information light, and the sub-data can be reproduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram showing the appearance of an optical disk; 
         FIG. 2  is a schematic diagram showing the internal construction of the optical disk; 
         FIG. 3  includes schematic diagrams for use in explaining the formation (1) of a record mark; 
         FIG. 4  is a schematic diagram for use in explaining the formation (2) of a record mark; 
         FIG. 5  includes schematic diagrams for use in explaining embedment of sub-data and various kinds of signals; 
         FIG. 6  is a schematic diagram showing the configuration of an optical disk drive; 
         FIG. 7  is a schematic diagram showing the construction of an optical pickup; 
         FIG. 8  is a schematic diagram for use in explaining the light path of a red light beam; 
         FIG. 9  is a schematic diagram showing the construction (1) of a detection field in a photodetector; 
         FIG. 10  is a schematic diagram for use in explaining the light path of a blue light beam; 
         FIG. 11  is a schematic diagram for use in explaining selection of a light beam by a pinhole plate; 
         FIG. 12  is a schematic diagram showing the construction (2) of the detection field in the photodetector; 
         FIG. 13  is a schematic diagram showing the configuration of a recording control unit; 
         FIG. 14  is a schematic diagram for use in explaining information recording processing performed in a first embodiment; 
         FIG. 15  is a schematic diagram showing the configuration of a reproduction control unit employed in the first embodiment; 
         FIG. 16  is a schematic diagram for use in explaining information reproducing processing performed in the first embodiment; 
         FIG. 17  includes schematic diagrams showing the construction of an optical pickup employed in an optical information recording apparatus; 
         FIG. 18  is a schematic diagram for use in explaining information recording processing performed in a second embodiment; 
         FIG. 19  is a schematic diagram showing the construction of an optical pickup included in an optical information reproducing apparatus; 
         FIG. 20  is a schematic diagram showing the configuration of a reproduction control unit employed in the second embodiment; 
         FIG. 21  is a schematic diagram for use in explaining information reproducing processing performed in the second embodiment; and 
         FIG. 22  includes schematic diagrams showing the configuration of a copy prevention system. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Referring to the drawings, an embodiment of the present invention will be described below. 
     (1) First Embodiment 
     (1-1) Construction of an Optical Disk 
     To begin with, an optical disk  100  employed as an optical information recording medium in the present invention will be described below. As seen from the appearance diagram shown in  FIG. 1 , the optical disk  100  is formed like a disk, which has a diameter of approximately 120 mm, as a whole similarly to the conventional CD, DVD, and BD, and has a bore  100 H in the center thereof. 
     The optical disk  100  includes, as seen from the sectional view shown in  FIG. 2 , a recording layer  101 , in which, information is recorded, in the center thereof, and has the surfaces of the recording layer  101  sandwiched between substrates  102  and  103 . 
     Incidentally, the thickness t 1  of the recording layer  101  is approximately 0.3 mm, and the thicknesses t 2  and t 3  of the substrates  102  and  103  are approximately 0.6 mm. 
     The substrates  102  and  103  are made of a material, for example, polycarbonate or glass, and each transmit light, which is routed through one surface thereof, to the opposite surface at a high transmittance. The substrates  102  and  103  have a certain degree of strength and fill the role of protecting the recording layer  101 . The surfaces of the substrates  102  and  103  may be finished by non-reflection coating in order to prevent unnecessary reflection. 
     The optical disk  100  includes a reflecting surface  104  on the interface between the recording layer  101  and substrate  103 . The reflecting layer  104  is made of a dielectric multilayer film or the like, and reflects both a blue light beam Lb 1  that is blue laser light having a wavelength of 405 nm, and a red light beam Lr 1  that is red laser light having a wavelength of 660 nm. 
     The reflecting layer  104  has guide grooves for tracking servo formed therein. More particularly, helical tracks are formed with lands and grooves similar to those in typical BD-R (recordable) disks. To the tracks, addresses that are serial numbers are assigned at intervals of a predetermined recording unit. A track in or from which information is recorded or reproduced can be identified with the address. 
     In the reflecting layer  104  (that is, the interface between the recording layer  101  and substrate  103 ), pits or the like may be formed in place of the guide grooves. Otherwise, the guide grooves and pits may be combined. 
     When the red light beam Lr 1  is irradiated from the side of the substrate  102 , the reflecting layer  104  reflects the red light beam to the side of the substrate  102 . Hereinafter, the reflected light beam shall be called a red light beam Lr 2 . 
     The red light beam Lr 2  is supposed to be employed in, for example, an optical disk drive in positional control for an objective lens OL (that is, focusing control and tracking control), which concentrates the red light beam Lr 1 , for the purpose of squaring the focus Fr of the red light beam Lr 1  with a target track (hereinafter called a desired servo track) in the reflecting layer  104 . 
     In reality, when information is recorded in the optical disk  100 , the red light beam Lr 1  is, as shown in  FIG. 2 , concentrated by the objective lens OL having been positionally controlled, and focused on a desired servo track in the reflecting layer  104 . 
     The blue light beam Lb 1  that shares a light axis Lx with the red light beam Lr 1  and is concentrated by the objective lens OL is transmitted by the substrate  102 , and focused on a position in the recording layer  101  equivalent to the desired servo track. At this time, with the objective lens OL as a reference, the focus Fb of the blue light beam Lb 1  is located nearer than the focus Fr on the common light axis Lx is, that is, on a closer side. 
     When information is recorded in the optical disk  100 , a record mark RM realized with, for example, a bubble is formed in a portion within the recording layer  101  in which a light intensity is equal to or larger than a predetermined intensity because of the concentration of the blue light beam Lb 1  for information recording having a relatively large light intensity (that is, in the vicinity of the focus Fb). For example, assuming that the wavelength λ, of the blue light beam Lb 1  is 405 nm, the numerical aperture NA of the objective lens OL is 0.5, and the refractive index n of the objective lens OL is 1.5, the record mark RM whose diameter RMr and height. RMh are on the order of 1 μm and 10 μm respectively is formed. 
     Further, the optical disk  100  is designed so that the thickness t 1  of the recording layer  101  (=0.3 mm) will be much larger than the height RMh of the record mark RM. Therefore, the optical disk  100  undergoes multilayer recording during which the record mark RM is recorded by varying a distance d within the recording layer  101  from the reflecting layer  104  (hereinafter called a depth), and multiple mark recording layers Y are thus, as shown in  FIGS. 3(A)  and (B), accumulated on one another in the thickness direction of the optical disk  100 . The mark recording layers Y refer to virtual layers, and the border between adjoining mark recording layers Y does not exist in reality. 
     In this case, when the depth d of the focus Fb of the blue light beam Lb within the recording layer  101  of the optical disk  100  is adjusted, the depth of the record mark RM is varied. For example, if the distance p 3  between mark recording layers Y (that is, the height of the mark recording layer Y) is set to approximately 15 μm in consideration of the mutual interference between record marks RM, approximately twenty mark recording layers Y can be formed within the recording layer  101 . As for the distance p 3 , aside from approximately 15 μm, any of other various values may be adopted in consideration of the mutual interference between record marks RM. 
     In the recording layer  101 , as shown in  FIG. 3(A) , record marks RM whose mark lengths range from 3T to 11T are formed. Main data representing main information is supposed to be recorded according to the length of the record mark RM and the length of a space in a tracking direction in which the record mark RM is not formed. 
     The recording layer  101  is, as shown in  FIG. 4 , supposed to have the blue light beam Lb 1  irradiated to any of helical irradiation lines in each of the mark recording layers Y therein. Therefore, when the record marks RM are formed along the irradiation lines TL in the recording layer  101 , helical tracks TR having the irradiation lines TL as centers thereof are formed. The tracks TR refer to virtual tracks, and the border between adjoining tracks TR does not actually exist. 
     When information is reproduced from the optical disk  100 , similarly to when information is recorded therein, the objective lens OL ( FIG. 2 ) is positionally controlled so that the red light beam Lr 1  concentrated by the objective lens OL will be focused on a desired servo track in the reflecting layer  104 . 
     Further, the optical disk  100  is designed so that the focus Fb of the blue light beam Lb 1  for information reading which is concentrated via the same objective lens OL and has a relatively small light intensity will be focused on a position in the recording layer  101  equivalent to both a position on a closer side of a desired servo track and a target depth (hereinafter called a target mark position). 
     At this time, the record mark RM recorded at the position of the focus Fb reflects the blue light beam Lb 1  due to a difference in a refractive index from the surroundings, and the blue light beam Lb 2  is generated from the record mark RM recorded at the target mark position. Specifically, the recording layer  101  modulates the blue light beam Lb 1  according to the presence or absence of the record mark RM, and produces the blue light beam Lb 2 . 
     As mentioned above, when information is recorded in the optical disk  100 , if the red light beam Lr 1  for positional control and the blue light beam Lb 1  for information recording are employed, the record mark RM is formed as information at a position in the recording layer  101  to which the focus Fb is irradiated, that is, a target mark position equivalent to both a position on the closer side of a desired servo track in the reflecting layer  104  and a position at a target depth. 
     When recorded information is reproduced from the optical disk  100 , if the red light beam Lr 1  for positional control and the blue light beam Lb 1  for information reading are employed, the blue light beam Lb 2  is generated from the record mark RM recorded at the position of the focus Fb, that is, at the target mark position. 
     In addition to the foregoing constitution, the optical disk  100  is designed so that when the record mark RM is formed while being deviated from the irradiation line TL in a focusing direction, not only main data representing main information is recorded but also sub-data representing subordinate information is embedded or recorded. 
     Specifically, in the recording layer  101  of the optical disk  100 , the record mark RM is formed along the irradiation line TL. However, the center line C FC  of the record mark RM in the focusing direction is slightly deviated from the irradiation line TL according to sub-data. 
     The out-of-focus quantity ΔMc of the center line C FC  from the irradiation line TL is set to, for example, about 1/50 of the thickness p 3  of the mark recording layer Y (that is, the height of the track TR) for fear it may adversely affect an amount of light of the blue light beam Lb 2 . 
     Therefore, as shown in  FIG. 5(B) , the optical disk  100  hardly affects a reproduction signal SRF to be produced based on the blue light beam Lb 2 . Therefore, the optical disk  100  permits, similarly to the conventional optical disk drives, reproduction of main data based on the reproduction signal SRF. 
     As mentioned above, during information reproducing processing, the objective lens OL is displaced so that the red light beam Lr 1  will be focused on the reflecting layer  104  of the optical disk  100 , and focusing control is implemented. As shown in  FIG. 5(C) , the optical disk  100  will not affect a red focusing error signal SFEr produced based on the red light beam Lr 2 . 
     In contrast, the signal level of a blue focusing error signal SFEb produced based on the blue light beam Lb 2  varies depending on the presence or absence of a deviation of the record mark RM. Therefore the optical disk  100  produces, as shown in  FIG. 5(D) , the blue focusing error signal SFEb, and thus permits detection of the presence or absence of the deviation of the record mark RM in the focusing direction (that is, an out-of-focus quantity ΔMc) and also permits reproduction of sub-data based on the presence or absence of the deviation. 
     As mentioned above, the record mark RM is formed while being deviated from the irradiation line TL in the focusing direction according to sub-data. Therefore, main data can be reproduced from the reproduction signal SRF as it conventionally is, but the reproduction signal SRF will not hardly affected. Further, sub-data can be reproduced from the optical disk  100  by detecting the out-of-focus quantity ΔMc on the basis of the blue focusing error signal SFEb. 
     (1-2) Configuration of an Optical Disk Drive 
     An optical disk drive  20  compatible with the foregoing optical disk  100  will be described below. The optical disk drive  20  has, as shown in  FIG. 6 , the whole thereof organized and controlled by a system controller  21 . 
     The system controller  21  is formed mainly with a central processing unit (CPU) that is not shown, reads various kinds of programs including a basic program and an information recording program from a read-only memory (ROM) that is not shown, develops the programs in a random access memory (RAM) that is not shown, and thus executes various kinds of pieces of processing including information recording processing and information reproducing processing. 
     For example, when the system controller  21  receives an information recording instruction, recording information, and recording address information from external equipment, which is not shown, with the optical disk  100  loaded, the system controller feeds a driving instruction and the recording address information to a driving control unit  22 , and also feeds the recording information to a signal processor  23 . Incidentally, the recording address information is information representing an address, at which the recording information should be recorded, among the addresses assigned to the recording layer  101  of the optical disk  100 . 
     In response to the driving instruction, the driving control unit  22  rotates the optical disk  100  at a predetermined rotating speed by controlling driving of a spindle motor  24 , controls driving of a sled motor  25 , and thus moves an optical pickup  26  to a position consistent with recording address information in a radial direction of the optical disk  100  (that is, in an internal-circumference direction or external-circumference direction) along moving shafts  25 A and  25 B. 
     The signal processor  23  produces a record signal by performing various kinds of pieces of signal processing including predetermined encoding processing and modulating processing (for example, eight-to-fourteen modulation (EFM) processing) on fed recording information, and feeds the record signal to the optical pickup  26 . 
     The optical pickup  26  performs focusing control and tracking control under the control of the driving control unit  22  so as to square the irradiated position of the blue light beam Lb 1  with a track (hereinafter called a target track) in the recording layer  101  of the optical disk  100  indicated with the recording address information, and thus records the record mark RM consistent with the record signal sent from the signal processor  23  (a full detail will be given later). 
     On receipt of an information reproduction instruction and reproducing address information indicating an address of recording information from, for example, external equipment (not shown), the system controller  21  feeds a driving instruction to the driving control unit  22 , and feeds a reproducing processing instruction to the signal processor  23 . 
     Similarly to a case where information is recorded, the driving control unit  22  rotates the optical disk  100  at a predetermined rotating speed by controlling driving of the spindle motor  24 , controls driving of the sled motor  25 , and thus moves the optical pickup  26  to a position consistent with the reproducing address information. 
     The optical pickup  26  performs focusing control and tracking control under the control of the driving control unit  22  so as to square the irradiated position of the blue light beam Lb 1  with a track in the recording layer  101  of the optical disk  100  indicated with the reproducing address information (that is, a target track), and then irradiates a light beam of a predetermined amount of light. At this time, the optical pickup  26  detects the blue light beam Lb 2  generated from the record mark RM in the recording layer  101  of the optical disk  100 , and feeds a detection signal consistent with the amount of light to the signal processor  23  (a full detail will be given later). 
     The signal processor  23  produces reproductive information by performing various kinds of pieces of signal processing including predetermined demodulating processing and decoding processing on the fed detection signal, and feeds the reproductive information to the system controller  21 . The system controller  21  in turn sends the reproductive information to the external equipment (not shown). 
     As mentioned above, the optical disk drive  20  uses the system controller  21  to control the optical pickup  26 , and records information at a target mark position in the recording layer  101  of the optical disk  100 , or reproduces information from the target mark position. 
     (1-3) Construction of the Optical Pickup 
     Next, the construction of the optical pickup  26  will be described below. The optical pickup  26  includes, as shown in  FIG. 7 , a servo optical system  30  for servo control and an information optical system  50  for reproduction or recording of information. 
     The optical pickup  26  routes the red light beam Lr 1 , which serves as servo light and is emitted from a laser diode  31 , and the blue light beam Lb 1 , which serves as information light and is emitted from a laser diode  51 , to the same objective lens  40  via a servo optical system  30  or an information optical system  50  respectively, and thus irradiates the beams to the optical disk  100 . 
     (1-3-1) Light Path of the Red Light Beam 
     As shown in  FIG. 8 , in the servo optical system  30 , the red light beam Lr 1  is irradiated to the optical disk  100  via the objective lens  40 , and the red light beam Lr 2  reflected from the optical disk  100  is received by a photodetector  43 . 
     Specifically, the laser diode  31  emits rid laser light that is p-polarized light having a wavelength of approximately 660 nm. In reality, the laser diode  31  irradiates the red light beam Lr 1  of a predetermined amount of light, which includes diverging rays, under the control of the system controller  21  ( FIG. 6 ), and routes it to a collimator lens  33 . The collimator lens  33  converts the red light beam Lr 1  from the diverging rays to parallel rays, and routes it to a polarization beam splitter  34 . 
     The polarization beam splitter  34  uses a reflecting/transmitting surface  34 S thereof to reflect or transmit a light beam at a ratio that varies depending on the deflecting direction of the light beam. The reflecting/transmitting surface  34 S nearly totally transmits a light beam that is p-polarized light, and nearly totally reflects a light beam that is s-polarized light. 
     The polarization beam splitter  34  nearly totally transmits the red light beam Lr 1  that is p-polarized light, and routes it to a quarter-wave plate  36 . 
     The quarter-wave plate  36  converts the red light beam Lr 1  that is p-polarized light into, for example, left-handed circularly polarized light, and routes it to a dichroic prism  37 . The dichroic prism  37  uses a reflecting/transmitting surface  37 S thereof to reflect or transmit a light beam according to the wavelength of the light beam. Accordingly, the dichroic prism  37  reflects the red light beam Lr 1  and routes it to the objective lens  40 . 
     The objective lens  40  concentrates the red light beam Lr 1 , and irradiates it to the reflecting layer  104  of the optical disk  100 . At this time, the red light beam Lr 1  is, as shown in  FIG. 2 , transmitted by the substrate  102 , reflected by the reflecting layer  104 , and then oriented in a direction opposite to the red light beam Lr 1 . This results in the red light beam Lr 2  whose deflecting direction is reverse to that of the red light beam Lr 1 . 
     Thereafter, the red light beam Lr 2  is converted into parallel rays by the objective lens  40 , and routed to the dichroic prism  37 . The dichroic prism  37  reflects the red light beam Lr 2 , and routes it to the quarter-wave plate  36 . 
     The quarter-wave plate  36  converts the red light beam Lr 2 , which is right-handed circularly polarized light, into s-polarized light, and routes it to the polarization beam splitter  34 . The polarization beam splitter  34  reflects the red light beam Lr 2 , which is s-polarized light, according to the polarizing direction of the red light beam, and routes it to a multi-lens  41 . 
     The multi-lens  41  allows the red light beam Lr 2  to converge, and irradiates the red light beam Lr 2 , to which an astigmatism is applied by a cylindrical lens  42 , to the photodetector  43 . 
     In the optical disk drive  20 , there is a possibility that a surface shake or the like may occur in the rotating optical disk  100 . Therefore, there is a possibility that the position of a desired servo track relative to the objective lens  40  may vary. 
     Therefore, in order to cause the focus Fr ( FIG. 2 ) of the red light beam Lr 1  to follow a target track, the focus Fr has to be shifted in a focusing direction that is an approaching or receding direction with respect to the optical disk  100 , and a tracking direction that is an internal-circumference or external-circumference direction of the optical disk  100 . 
     The objective lens  40  can be driven in two axial directions, which are the focusing direction and tracking direction, by a biaxial actuator  40 A. 
     In the servo optical system  30  ( FIG. 8 ), the optical positions of various kinds of optical parts are adjusted so that an in-focus state attained when the red light beam Lr 1  is concentrated by the objective lens  40  and irradiated to the reflecting layer  104  of the optical disk  100  will be reflected on an in-focus state attained when the red light beam Lr 2  is concentrated by the multi-lens  41  and irradiated to the photodetector  43 . 
     The photodetector  43  has, as shown in  FIG. 9 , four detection fields  43 A,  43 B,  43 C, and  43 D segmented in the form of a lattice on a surface thereof to which the red light beam Lr 2  is irradiated. A direction indicated with an arrow a 1  (lengthwise direction in the drawing) corresponds to a track traveling direction in which the red light beam Lr 1  propagates when irradiated to the reflecting layer  104  ( FIG. 2 ). 
     The photodetector  43  uses the detection fields  43 A,  43 B,  43 C, and  43 D thereof to detect parts of the red light beam Lr 2 , produces detection signals SDAr, SDBr, SDCr, and SDDr according to detected amounts of light, and sends them to the signal processor  23  ( FIG. 6 ). 
     The signal processor  23  implements focusing control according to a so-called astigmatism method, calculates a red focusing error signal SFEr according to an equation (1) presented below, and feeds it to the driving control unit  22 . 
         SFEr =( SDAr+SDCr )−( SDBr+SDDr )  (1) 
     The red focusing error signal SFEr represents a magnitude of a deviation of the focus Fr of the red light beam Lr 1  from the reflecting layer  104  of the optical disk  100 . 
     The signal processor  23  implements tracking control according to a so-called push-pull method, calculates a tracking error signal STEr according to an equation (2) presented below, and feeds it to the driving control unit  22 . 
         STEr =( SDAr+SDDr )−( SDBr+SDCr )  (2) 
     The tracking error signal STEr represents a magnitude of a deviation of the focus Fr from a target track in the reflecting layer  104  of the optical disk  100 . 
     The driving control unit  22  produces a focusing driving signal SFDr on the basis of the red focusing error signal SFEr, feeds the focusing driving signal SFDr to the biaxial actuator  40 A, and thus implements feedback control (that is, focusing control) in the objective lens  40  so that the red light beam Lr 1  will be focused on the reflecting layer  104  of the optical disk  100 . 
     The driving control unit  22  produces a tracking driving signal on the basis of the tracking error signal STEr, feeds the tracking driving signal STDr to the biaxial actuator  40 A, and thus implements feedback control (that is, tracking control) in the objective lens  40  so that the red light beam Lr 1  will be focused on a desired servo track in the reflecting layer  104  of the optical disk  100 . 
     Incidentally, the biaxial actuator  40 A is formed with a so-called voice coil motor that is a combination of, for example, a magnet and a coil, and designed to displace the objective lens  40  to a position dependent on a driving current applied to the coil. 
     As mentioned above, the servo optical system  30  irradiates the red light beam Lr 1  to the reflecting layer  104  of the optical disk  100 , and feeds the result of reception of the red light beam Lr 2 , that is the reflected light of the red light beam Lr 1 , to the signal processor  23 . Accordingly, the driving control unit  22  implements focusing control and tracking control in the objective lens  40  so that the red light beam Lr 1  will be focused on a target track in the reflecting layer  104 . 
     (1-3-2) Light Path of the Blue Light Beam 
     In the information optical system  50 , as shown in  FIG. 10  similar to  FIG. 7 , the blue light beam Lb 1  emitted from the laser diode  51  via the objective lens  40  is irradiated to the optical disk  100 , and the blue light beam Lb 2  reflected from the optical disk  100  is received by a photodetector  63 . 
     Specifically, the laser diode  51  emits blue laser light having a wavelength of approximately 405 nm. In reality, the laser diode  51  emits the blue light beam Lb 1  of a predetermined amount of light, which includes diverging rays, under the control of the system controller  21  ( FIG. 4 ), and routes it to a collimator lens  52 . The collimator lens  52  converts the blue light beam Lb 1  from the diverging rays to parallel rays, and routes it to a polarization beam splitter  54 . 
     The polarization beam splitter  54  uses the reflecting/transmitting surface  54 S thereof to reflect or transmit a light beam according to the deflecting direction of the light beam. For example, the reflecting/transmitting surface  54 S nearly totally transmits a light beam that is p-polarized light and nearly totally reflects a light beam that is s-polarized beam. 
     The polarization beam splitter  54  transmits the blue light beam Lb 1  that is p-polarized light, and routes it to a quarter-wave plate  57  via a liquid crystal panel (LCP)  56  that corrects a spherical aberration or the like. 
     The quarter-wave plate  57  converts the blue light beam Lb 1  from p-polarized light to, for example, left-handed circularly polarized light, and routes it to a relay lens  58 . 
     The relay lens  58  uses a movable lens  58 A to convert the blue light beam Lb 1  from parallel rays to converging rays, uses a stationary lens  58 B to adjust the degree of convergence or divergence (hereinafter called a converging state) of the blue light beam Lb 1  that become diverging rays after converging, and then routes it to a mirror  59 . 
     The movable lens  58 A is moved in the light-axis direction of the blue light beam Lb 1  by an actuator  58 Aa. In reality, the relay lens  58  is designed so that the movable lens  58 A is moved by the actuator  58 Aa under the control of the driving control unit  22  ( FIG. 4 ) in order to change the converging state of the blue light beam Lb 1  emitted through the stationary lens  58 B. 
     The mirror  59  reflects the blue light beam Lb 1 , reverses the deflecting direction of the blue light beam Lb 1  that is circularly polarized light (for example, from left-handed circularly polarized light to right-handed circularly polarized light), deflects the advancing direction thereof, and routes it to the dichroic prism  37 . The dichroic prism  37  uses the reflecting/transmitting surface  37 S thereof to transmit the blue light beam Lb 1 , and routes it to the objective lens  40 . 
     The objective lens  40  concentrates the blue light beam Lb 1 , and irradiates it to the optical disk  100 . At this time, the blue light beam Lb 1  is, as shown in  FIG. 2 , transmitted by the substrate  102 , and focused on the inside of the reflecting layer  101 . 
     The position of the focus Fb of the blue light beam Lb 1  is determined with the converging state thereof attained when the blue light beam is emitted through the stationary lens  58 B of the relay lens  58 . Specifically, the focus Fb is shifted in the focusing direction within the recording layer  101  according to the position of the movable lens  58 A. 
     More particularly, the information optical system  50  is designed so that the moving distance of the movable lens  58 A and the shifting distance of the focus Fb of the blue light beam Lb 1  will have a nearly proportional relationship. For example, when the movable lens  58 A is moved 1 mm, the focus Fb of the blue light beam Lb 1  is shifted 30 μm. 
     Incidentally, the actuator  58 Aa is formed with a so-called voice coil motor that is a combination of, for example, a magnet and a coil, and displaces the movable lens  58 A to a position dependent on a relay driving current Uf applied to the coil. 
     In reality, in the information optical system  50 , when the position of the movable lens  58 A is controlled by the driving control unit  22  ( FIG. 4 ), the depth d of the focus Fb ( FIG. 2 ) of the blue light beam Lb 1  in the recording layer  101  of the optical disk  100  (that is, the distance from the reflecting layer  104 ) is adjusted in order to square the focus Fb with a target mark position. 
     As mentioned above, the information optical system  50  irradiates the blue light beam Lb 1  via the objective lens  40 , which is servo-controlled by the servo optical system  30 , in order to square the focus Fb in the tracking direction of the blue light beam Lb 1  with the target mark position. Further, the depth d of the focus Fb is adjusted according to the position of the movable lens  58 A included in the relay lens  58 , whereby the focus Fb in the focusing direction is squared with the target mark position. 
     During recording processing during which information is recorded in the optical disk  100 , the blue light beam Lb 1  is concentrated on the focus Fb by the objective lens  50  in order to form the record mark RM at the focus Fb. 
     In contrast, during reproducing processing during which information recorded in the optical disk  100  is read, if the record mark RM is recorded near the target mark position, the blue light beam Lb 1  concentrated on the focus Fb is reflected as the blue light beam Lb 2  from the record mark RM, and routed to the objective lens  40 . At this time, the deflecting direction of the blue light beam Lb 2  that is circularly polarized light is reversed (for example, from right-handed circularly polarized light to left-handed circularly polarized light) due to the reflection from the record mark RM. 
     When the record mark RM is not recorded at the focus Fb, the blue light beam Lb 1  diverges after converging on the focus Fb. The blue light beam Lb 1  is then reflected from the reflecting layer  104 , and routed as the blue light beam Lb 2  to the objective lens  40 . At this time, the rotating direction of the blue light beam Lb 2  that is circularly polarized light is reversed (for example, from right-handed polarized light to left-handed polarized light) due to the reflection from the reflecting layer  104 . 
     The objective lens  40  causes the blue light beam Lb 2  to converge to some extent, and routes it to the dichroic prism  37 . The dichroic prism  37  transmits the blue light beam Lb 2 , and routes it to the mirror  59 . 
     The mirror  59  reflects the blue light beam Lb 2  so as to reverse the polarizing direction of the blue light beam Lb 1  that is circularly polarized light (for example, from left-handed circularly polarized light to right-handed circularly polarized light), and routes it to the relay lens  58 . 
     The relay lens  58  converts the blue light beam Lb 2  into parallel rays, and routes it to the quarter-wave plate  57 . The quarter-wave plate  57  converts the blue light beam Lb 2  that is circularly polarized light into linearly polarized light (for example, from right-handed circularly polarized light to s-polarized light), and routes it to the polarization beam splitter  57  via the LCP  56 . 
     The polarization beam splitter  54  uses the reflecting/transmitting surface  54 S thereof to reflect the blue light beam Lb 2  that is s-polarized light, and routes it to a multi-lens  60 . The multi-lens  60  concentrates the blue light beam Lb 2  and routes it to a cylindrical lens  61 . The cylindrical lens  61  applies an astigmatism to the blue light beam Lb 2 , and irradiates it to the photodetector  63  via a (pinhole plate  62 . 
     As shown in  FIG. 11 , the pinhole plate  62  is disposed so that the focus of the blue light beam Lb 2  concentrated by the multi-lens  60  ( FIG. 9 ) will be located in a bore  62 H, and therefore transmits the blue light beam Lb 2  without any change. 
     As shown in  FIG. 12 , the pinhole plate  62  nearly intercepts light that has a different focus and is reflected from, for example, the surface of the substrate  102  included in the optical disk  100 , the record mark RM located at a position different from the target mark position, or the reflecting layer  104  (hereinafter called stray light (LN)). As a result, the photodetector  63  hardly detects an amount of light of the stray light LN. 
     As a result, the photodetector  63  is unsusceptible to the stray light LN, produces a detection signal SDb consistent with the amount of light of the blue light beam Lb 2 , and feeds it to the signal processor  23  ( FIG. 6 ). 
     The photodetector  63  includes, as shown in  FIG. 12 , four detection fields  63 A,  63 B,  63 C, and  63 D segmented in the form of a lattice on the surface thereof to which the red light beam Lr 2  is irradiated. A direction indicated with an arrow a 2  (a sideway direction in the drawing) corresponds to a track traveling direction in which the blue light beam Lb 1  propagates when irradiated to the recording layer  101 . 
     The photodetector  63  uses the detection fields  63 A,  63 B,  63 C, and  63 D thereof to detect parts of the blue light beam Lb 2 , produces detection signals SDb (SDAb, SDBb, SDCb, and SDDb) according to detected amounts of light, and sends them to the signal processor  23  ( FIG. 6 ). 
     The signal processor  23  uses a so-called astigmatism method to calculate a blue focusing error signal SFEb according to an equation (3) presented below. 
         SFEb =( SDAb+SDCb )−( SDBb+SDDb )  (3) 
     The signal processor  23  produces a reproduction signal SRF according to an equation (4) presented below, and feeds it to the signal processor  23 . 
         SRF=SDAb+SDBb+SDCb+SDDb   (4) 
     In this case, the reproduction signal SRF highly precisely represents information recorded as the record mark RM in the optical disk  100 . Therefore, the signal processor produces reproductive information by performing predetermined demodulating processing or decoding processing on the reproduction signal SRF, and feeds the reproductive information to the system controller  21 . 
     As mentioned above, the information optical system  50  receives the blue light beam Lb 2  routed from the optical disk  100  to the objective lens  38 , and feeds the result of reception to the signal processor  23 . 
     (1-4) Information Recording Processing 
     As described previously, during information recording processing, the optical disk drive  20  records main data, which represents main information, in the form of the record mark RM, displaces the record mark RM in the focusing direction so as to record sub-data representing subordinate information. 
     More particularly, the signal processor  23  ( FIG. 6 ) of the optical disk drive  20  separates recording main-data information Da represented by main data and recording sub-data information Db represented by sub-data from the recording information fed from the system controller  21 , and feeds them to a recording control unit  70 . 
     As shown in  FIG. 13 , a recording clock production block included in the recording control unit  70  produces a recording clock CLw serving as a reference, and feeds it to a main-data record signal production block  72  and an embedded signal production block  73 . At this time, the recording main-data information Da is fed to the main-data record signal production block  72 , while the recording sub-data information Db is fed to the embedded signal production block  73 . 
     The main-data record signal production block  72  performs, as shown in  FIGS. 14(A)  and (B), various kinds of pieces of signal processing including encoding processing and modulating processing on the recording main-data information Da, thus produces a main-data record signal Sw, which is a record signal, while squaring the rising and falling timings of the signal with those of the recording clock CLw, and feeds it to the embedded signal production block  73  and a laser control block  74 . 
     The embedded signal production block  73  ( FIG. 13 ) performs various kinds of pieces of signal processing including encoding processing and modulating processing on the recording sub-data information Db, produces a plus embedded signal Sm+ and a minus embedded signal Sm− while squaring the rising and falling timings of the signals with those of the main-data record signal Sw, and feeds them to the driving control unit  22 . 
     As shown in  FIG. 14(C) , the plus embedded signal Sm+ represents the timing of displacing the record mark RM in a plus direction, that is, toward the incident surface  100 A of the optical disk  100 , and has the signal level thereof set to High over a period equivalent to the record mark RM that should be displaced in the plus direction. 
     As shown in  FIG. 14(D) , the minus embedded signal Sm− represents the timing of displacing the record mark RM in a minus direction, that is, toward the back surface  100 B of the optical disk  100 , and has the signal level thereof set to High over a period equivalent to the record mark RM that should be displaced in the minus direction. 
     The driving control unit  22  produces a relay driving current Uf by shifting a current value, which is associated with the mark recording layer U in which a target track is located, by a predetermined shift current value Δ±m during a period during which each of the plus embedded signal Sm+ and minus embedded signal Sm− goes High, and feeds it to the actuator  58 Aa included in the relay lens  58 . 
     The driving control unit  22  designates as a target mark position (that is, a target depth) a position deviated in the focusing direction (that is, a plus direction or a minus direction) by a predetermined out-of-focus quantity ΔMc from the irradiation line TL in a target track, and irradiates the blue light beam Lb 1  to the target mark position. 
     As a result, the optical disk drive  20  can deviate the record mark RM in the focusing direction from the irradiation line TL, to which the blue light beam Lb 1  should originally be irradiated, according to the recording sub-data information Db, and can embed the recording sub-data information Db at a position in the focusing direction in the record mark RM representing the recording main-data information Da. 
     For example, at a time point t 0 , the main-data record signal production block  72  raises the signal level of the main-data record signal Sw from a Low level to a High level on the basis of the recording main-data information Da ( FIG. 14(B) ). At this time, the embedded signal production block  73  retains the signal levels of the plus embedded signal Sm+ and minus embedded signal m− at the Low level on the basis of the recording sub-data information Db ( FIGS. 14(C)  and (D)). 
     Accordingly, the driving control unit  22  retains the relay driving current Uf at a current value associated with the mark recording layer Y. The laser control block  74  produces a laser driving current according to the main-data record signal Sw, and feeds it to the laser diode  51 . As a result, the blue light beam Lb 1  emitted from the laser diode  51  is irradiated to the irradiation line TL, and the record mark RM is formed on the irradiation line TL ( FIG. 14(F) ). 
     At a time point t 1 , the main-data record signal production block  72  lowers the signal level of the main-data record signal Sw from the High level to the Low level on the basis of the recording main-data information Da ( FIG. 14(B) ). At this time, the laser control block  74  produces a laser driving current according to the main-data record signal Sw, and almost ceases emission of the blue light beam Lba from the laser diode  51 . 
     At a time point t 2 , the main-data record signal production block  72  raises the signal level of the main data record signal Sw from the Low level to the High level on the basis of the recording main-data information Da ( FIG. 14(B) ). At this time, the embedded signal production block  73  raises the signal level of the plus embedded signal Sm+ to the High level on the basis of the recording sub-data information Db (FIG.  14 (C)), while retains the minus embedded signal m− at the Low level ( FIG. 14(D) ). 
     Accordingly, the driving control unit  22  adds the predetermined shift current value Δ+m to the current value of the relay driving current Uf associated with the mark recording layer Y. The laser control block  74  produces a laser driving current according to the main-data record signal Sw, and feeds it to the laser diode  51 . As a result, the blue light beam Lb 1  emitted from the laser diode  51  is irradiated to a position deviated in a plus direction from the irradiation line TL by the out-of-focus quantity ΔMc, and the record mark RM is formed at the deviated position ( FIG. 14(F) ). 
     At a time point t 3 , the main-data record signal production block  72  lowers the signal level of the main-data record signal Sw from the High level to the Low level on the basis of the recording main-data information Da ( FIG. 14(B) ). At this time, the embedded signal production block  73  lowers the signal level of the plus embedded signal Sm+from the High level to the Low level. The laser control block  74  produces a laser driving current according to the main-data record signal Sw so as to almost cease emission of the blue light beam Lb 1  from the laser diode  51 . 
     At a succeeding time point t 4 , the main-data record signal production block  72  raises the signal level of the main-data record signal Sw from the Low level to the High level on the basis of the recording main-data information Da ( FIG. 14(B) ). At this time, the embedded signal production block  73  retains the signal level of the plus embedded signal Sm+ at the Low level on the basis of the recording sub-data information Db (FIG.  14 (C)), while raises the minus embedded signal m- to the High level ( FIG. 14(D) ). 
     Accordingly, the driving control unit  22  adds the predetermined shift current value Δ−m to the current value of the relay driving current Uf associated with the mark recording layer Y. The laser control block  74  produces a laser driving current according to the main-data record signal Sw, and feeds it to the laser diode  51 . As a result, the blue light beam Lb 1  emitted from the laser diode  51  is irradiated to a position deviated in a minus direction from the irradiation line TL by the out-of-focus quantity ΔMc, and the record mark RM is formed at the deviated position ( FIG. 14(F) ). 
     At a time point t 5 , the main-data record signal production block  72  lowers the signal level of the main-data record signal Sw from the High level to the Low level on the basis of the recording main-data information Da ( FIG. 14(B) ). At this time, the embedded signal production block  73  lowers the signal level of the plus embedded signal Sm− from the High level to the Low level. The laser control block  74  produces the laser driving current according to the main-data record signal Sw so as to almost cease emission of the blue light beam Lb 1  from the laser diode  51 . 
     As mentioned above, the optical disk drive  20  irradiates the blue light beam Lb 1  to a target track at the timing corresponding to the timing of the recording main-data information Da, and thus forms the record mark RM so as to record the recording main-data information Da in the recording layer  101 . The optical disk drive  20  deviates each record mark RM in the focusing direction according to the recording sub-data information Db, and thus records the recording sub-data information Da in the recording layer  101 . 
     While displacing the objective lens  40  on the basis of the red focusing error signal SFEr, the optical disk drive  20  controls the movable lens  58 A included in the relay lens  58  so that the blue light beam Lb 1  will be irradiated to a target mark position separated by a depth d with the reflecting layer  104  as a reference. At this time, the optical disk drive  20  designates as the target mark position a position deviated in the focusing direction from the irradiation line TL by the out-of-focus quantity ΔMc. 
     Accordingly, the optical disk drive  20  displaces the objective lens  40  so that the red light beam Lr 1  will be focused on the reflecting layer  104 . Thereafter, control should be implemented so that the focus Fb of the blue light beam Lb 1  will be located at a target depth corresponding to the target mark position with the red light beam reflecting layer  104  as a reference. Therefore, the optical disk drive  20  can embed sub-data according the position in the focusing direction of the record mark RM merely by implementing simple control so as to slightly displace the movable lens  58 A according to the recording sub-data information Db. 
     (1-5) Information Reproducing Processing 
     During information reproducing processing, the signal processor  23  included in the optical disk drive  20  produces reproductive main-data information Ra corresponding to the recording main-data information Da and reproductive sub-data information Rb corresponding to the recording sub-data information Db on the basis of the blue light beam Lb 1 , and feeds them as reproductive information to the system controller  21 . 
     More particularly, the signal processor  23  produces a reproduction signal SRF and a blue focusing error signal SFEb from a detection signal SDb, and feeds them to a reproduction control unit  80 . 
     As shown in  FIG. 15 , the reproduction control unit  80  feeds the reproduction signal SRF to a reproductive clock production block  81  and a main-data information reproduction block  82 , while feeds the blue focusing error signal SFEb to a sub-data information reproduction block  83 . 
     As shown in  FIGS. 16(B)  and (C), the reproductive clock production block  81  uses, for example, a phase-locked loop (PLL) circuit to extract a reproductive clock CLr from the reproduction signal SRF, and feeds it to the main-data information reproduction block  82 . 
     As shown in  FIG. 16(D) , the main-data information reproduction block  82  binary-codes the reproduction signal SRF with the reproductive clock CLr as a reference so as to produce a reproductive binary-coded signal SRO, and feeds it to the sub-data information reproduction block  83 . In addition, the main-data information reproduction block  82  performs various kinds of pieces of signal processing including demodulating processing and decoding processing on the reproductive binary-coded signal SRO so as to produce the reproductive main-data information Ra, and feeds it to the system controller  21 . 
     The sub-data information reproduction block  83  recognizes the presence or absence of the record mark RM according to the rising and falling timings of the reproductive binary-coded signal SRO (that is, the length of the record mark RM and the length of a space in which the record mark RM is not formed), detects the presence or absence of a deviation of the record mark RM in the focusing direction on the basis of the signal level of the blue focusing error signal SFEb obtained from the record mark RM, and produces a deviation detection signal (not shown). 
     The sub-data information reproduction block  83  performs various kinds of pieces of signal processing including demodulating processing and decoding processing on the deviation detection signal so as to produce the reproductive sub-data information Rb, and feeds it to the system controller  21 . 
     For example, at a time point t 10 , since the reproductive binary-coded signal SRO rises from the Low level to the High level, the sub-data information reproduction block  83  acknowledges that the blue light beam Lb 1  is irradiated to the record mark RM (that is, the record mark RM is detected). 
     At a time point t 11 , since the reproductive binary-coded signal SRO falls from the High level to the Low level, the main-data information reproduction block  82  acknowledges that irradiation of the blue light beam Lb 1  to the record mark RM has been completed, and recognizes the record mark RM as a 3T mark. At this time, the sub-data information reproduction block  83  calculates a mean value of signal levels of the blue focusing error signal SFEb obtained from the time point t 10  to the time point t 11  (hereinafter, called an SFE mark mean value). 
     Further, the sub-data information reproduction block  83  decides whichever of three levels the SFE mark mean value ranks. Specifically, the sub-data information reproduction block  83  decides whether the SFE mark mean value is equal to or larger than a first sub-information threshold, falls below the first information threshold and is equal to or larger than a second sub-information threshold, or falls below the second sub-information threshold. 
     More particularly, if the sub-data information reproduction block  83  decides at the time point t 11  that the SFE mark mean value falls below the first information threshold and is equal to or larger than the second sub-information threshold, the sub-data information reproduction block  83  acknowledges that the record mark RM is formed on the irradiation line TL, and sets the signal level of the deviation detection signal to 0. 
     If the reproductive binary-coded signal SRO rises from the Low level to the High level at a time point t 12 , and lowers to the Low level at a time point t 13 , the main-data information reproduction block  82  recognizes the space as a 3T space. At this time, the sub-data information reproduction block  83  decides, similarly to it does at the time point t 11 , whichever of three levels the SFE mark mean value ranks. 
     At the time point t 13 , the main-data information reproduction block  82  recognizes the record mark RM as a 7T mark. At this time, if the sub-data information reproduction block  83  decides that the SFE mark mean value is equal to or larger than the first threshold, the sub-data information reproduction block  83  acknowledges that the record mark RM is formed while being deviated in a plus direction, and sets the signal level of the deviation detection signal to +1. 
     If the reproductive binary-coded signal SRO rises from the Low level to the High level at a time point t 14 , and lowers to the Low level at a time point t 15 , the main-data information reproduction block  82  recognizes the space as a 4T space and recognizes the record mark RM as a 4T mark. 
     At this time, the sub-data information reproduction block  83  decides, similarly to it does at the time point t 11 , whichever of the three levels the SFE mark mean value ranks. 
     If the sub-data information reproduction block  83  decides that the SFE mark mean value falls below the second threshold, the sub-data information reproduction block  83  acknowledges that the record mark RM is formed while being deviated in a minus direction, and sets the signal level of the deviation detection signal to −1. 
     As mentioned above, the optical disk drive  20  produces the reproduction signal SRF on the basis of the blue light beam Lb 2  so as to reproduce the reproductive main-data information Ra corresponding to the recording main-data information Da. The optical disk drive  20  detects the presence or absence of a deviation of the record mark RM from the irradiation line TL on the basis of the blue focusing error signal SFEb, and thus reproduces the reproductive sub-data information Rb corresponding to the recording sub-data information Db. 
     The optical disk drive  20  detects the presence or absence of a deviation of the record mark RM on the basis of the blue focusing error signal SFEb while implementing focus control in the objective lens  40  on the basis of the red focusing error signal SFEr. 
     Specifically, the optical disk drive  20  does not implement control so that the blue light beam Lb 1  will be irradiated to the center of the record mark RM according to the blue focusing error signal SFEb. Therefore, the amplitude of the blue focusing error signal SFEb will depend on the out-of-focus quantity ΔMc by which the record mark RM is deviated from the irradiation line TL. 
     Accordingly, the optical disk drive  20  can irradiate the blue light beam Lb 1  nearly to the irradiation line TL all the time, and can therefore largely vary the blue focusing error signal SFEb according to the out-of-focus quantity ΔMc of the record mark RM from the irradiation line TL. As a result, the optical disk drive  20  can reliably detect a slight deviation of the record mark RM from the irradiation line TL, and can reproduce sub-data with high precision. 
     (1-6) Actions and Advantage 
     In the foregoing constitution, the optical disk drive  20  concentrates the blue light beam Lb 1  serving as information light, and irradiates it to the optical disk  100  serving as an optical information recording medium. At this time, the optical disk drive  20  shifts the focus Fb of the blue light beam Lb 1  in the focusing direction in which the objective lens  40  recedes from or approaches to the optical information recording medium, and thus shifts the focus Fb of the blue light beam Lb 1  to a target depth to which the blue light beam Lb 1  should be irradiated. 
     The optical disk drive  20  forms the record mark RM along the virtual irradiation line TL in the optical disk  100  by controlling the laser diode  51 , which is a light source, according to the recording main-data information Da based on main data. The optical disk drive  20  shifts a target depth in the focusing direction according to the recording sub-data information Db based on sub-data, and thus forms the record mark RM with the center of the record mark RM deviated from the irradiation line TL in the focusing direction. 
     In the recording layer  101  of the optical disk  100 , the three-dimensional record mark RM is supposed to be formed in the thick recording layer  101 , and a space in which the record mark RM is not formed exists in the focusing direction. 
     In the optical disk drive  20 , the space in the focusing direction is utilized so that the record mark RM can be formed while being deviated in the focusing direction. Thus, the storage capacity of the recording layer  101  for main data will not be varied but sub-data can be recorded. Namely, the optical disk drive  20  permits substantial improvement of the storage capacity of the optical disk  100 . 
     In the recording layer  101 , the height of the track TR is larger than the height RMh of the record mark RM, and the record marks RM are supposed to be equidistantly formed in the focusing direction. 
     The optical disk drive  20  records sub-data by slightly deviating the center line C FR  of the record mark RM from the irradiation line TL. Eventually, since the record mark RM is deviated from the irradiation line TL, the necessity of closely disposing the record marks RM is nearly obviated. The optical disk drive  20  can therefore suppress a so-called crosstalk that is interference of the record marks RM during information reproduction. 
     The optical disk drive  20  can form the record mark RM along the irradiation line TL, though the center line C FR  of the record mark RM deviates from the irradiation line TL. Therefore, during information reproducing processing, an amount of light of the blue light beam Lb 2  is hardly affected and the excellent reproduction signal SRF can be produced. 
     Further, the optical disk drive  20  uses the biaxial actuator  40 A serving as an objective lens drive unit to drive the objective lens  40 , and uses the objective lens  40  to concentrate the red light beam Lr 1  that is servo light for focus control. The optical disk drive  20  drives the objective lens  40  so that the red light beam Lr 1  will be focused on the reflecting layer  104  included in the optical disk  100 . 
     At this time, the optical disk drive  20  uses the movable lens  58 A serving as a focus shift unit to separate the focus Fb of the blue light beam Lb 1  from the focus Fr of the red light beam Lr 1  by an arbitrary distance, and thus squares the focus Fb of the blue light beam Lb 1  with a target depth to which the blue light beam Lb 1  should be irradiated. 
     Therefore, the optical disk drive  20  can square the focus Fb of the blue light beam Lb 1  with the irradiation line TL on the basis of the red light beam Lr 1 . Eventually, the focus Fb can be squared with a target mark position by implementing simple control to drive the movable lens  58 A according to the out-of-focus quantity ΔMc. 
     In short, the optical disk drive  20  merely shifts the position of the movable lens  58 A according to the mark recording layer Y in which the record mark RM should be formed, but does not normally displace the movable lens  58 A during a period during which the record mark RM is formed in the same mark recording layer Y. Therefore, the optical disk drive  20  should merely slightly displace the movable lens  58 A, which is hardly displaced, according to sub-data. A large load need not be imposed on the movable lens  58 A. 
     Now, for example, for displacing the center line C FC  of the record mark RM, the peak of the blue focusing error signal SFEb is detected as information during information reproducing processing. In this case, there is a possibility that a noise abruptly generated in the blue focusing error signal SFEb cannot be discriminated from information. 
     In contrast, the optical disk drive  20  forms each record mark RM with the center line C FC  of the record mark RM deviated from the irradiation line TL in the focusing direction. Therefore, the optical disk drive  20  can vary the signal level of the blue focusing error signal SFEb over a period corresponding to the record mark RM, and can therefore reliably reproduce information embedded in the record mark RM. 
     The optical disk drive  20  drives the movable lens  58 A disposed among diverging rays, and can thus freely shift the focus Fb in the focusing direction without any restriction imposed on the moving distance of the movable lens  58 A. 
     Further, the optical disk drive  20  produces the reproduction signal SRF on the basis of the blue light beam Lb 2  serving as a reflected light beam that is the blue light beam Lb 1  reflected from the optical disk  100 , and thus detects the presence or absence of the record mark RM formed along the virtual irradiation line TL in the optical disk  100 . Based on the presence or absence of the record mark RM, the optical disk drive  20  reproduces main data as the reproductive main-data information Ra. 
     Based on an amount of light of the blue light beam Lb 1 , the optical disk drive  20  produces the blue focusing error signal SFEb, which represents the out-of-focus quantity between the focus Fb of the blue light beam Lb 1  and the record mark RM in the focusing direction in which the objective lens  40  recedes from or approaches to the optical disk  10 . The optical disk drive  20  thus detects the out-of-focus quantity. The optical disk drive  20  reproduces sub-data, which is recorded by deviating the center line C FC  of the record mark RM from the irradiation line TL, as the reproductive sub-data information Rb on the basis of the blue focusing error signal SFEb. 
     Thus, the optical disk drive  20  can reproduce both main data and sub-data that are recorded as the record mark RM in the recording layer  101 . 
     Further, the optical disk drive  20  drives the objective lens  40  so that the red light beam Lr 1  will be focused on the reflecting layer  104  of the optical disk  100 , and squares the focus Fb of the blue light beam Lb 1  with a target depth, to which the blue light beam Lb 1  should be irradiated, by separating the focus Fb of the blue light beam Lb 1  from the focus Fr of the red light beam Lr 1  by an arbitrary distance. 
     Accordingly, the optical disk drive  20  can implement focusing control for the focus Fb using the red focusing error signal SFEr that is unsusceptible of deviation of the record mark RM from the irradiation line TL, and can therefore implement the focusing control highly precisely similarly to the conventional optical disk drive. 
     The optical disk drive  20  is an optical information recording/reproducing apparatus capable of recording or reproducing main data and sub-data in or from the recording layer  101 . Accordingly, the optical disk drive  20  separates recording information into main data and sub-data at a predetermined ratio, and records or reproduces the data items. Therefore, the recording capacity of the optical disk  100  can be increased. 
     The optical disk  100  includes the reflecting layer  104  that reflects at least part of the red light beam Lr 1  to be irradiated for positional control. Since the optical disk  100  allows the optical disk drive  20  to implement focusing control in the objective lens  40  using the red light beam Lr 1 , the blue focusing error signal SFEb whose signal level is varied by embedding sub-data need not be used for the focusing control. Therefore, the optical disk  100  makes it possible to reproduce main data and sub-data without affecting the focusing control to be implemented in the objective lens  40  during information reproducing processing. 
     Since positional information is recorded with a groove and a land, which are irregularities, in the optical disk  100 , the optical disk drive  20  can readily implement tracking control. 
     According to the foregoing constitution, the optical disk drive  20  can displace the record mark RM, which represents main data, toward a space in the focusing direction which is created inside the recording layer  101  which is thick and in which the three-dimensional record mark RM is formed. 
     Thus, the optical disk drive  20  can embed sub-data in the record mark with a displacement in the focusing direction. Accordingly, an optical information recording apparatus and an optical information recording method capable of recording sub-data, an optical information reproducing apparatus and an optical information reproducing method capable of reproducing the sub-data, and an optical information recording medium in which the sub-data is recorded can be realized. 
     (1-7) Other Embodiments 
     In the foregoing first embodiment, a description has been made of a case where the movable lens  58 A is adopted as a focus shift unit that shifts the focus Fb of the blue light beam Lb 1 . The present invention is not limited to this case. In short, a spherical aberration generation means that applies a spherical aberration to the blue light beam Lb 1  will do. For example, any of various optical elements including a diffractive element, a phase modulation element such as a liquid crystal element, and an expander which change the phase of the blue light beam Lb 1  will do. These optical elements may be made movable. 
     In the aforesaid first embodiment, a description has been made of a case where each record mark RM is formed with the center line C FC  of the record mark RM deviated in the focusing direction. The present invention is not limited to this case. For example, the record mark RM may be formed by gradually deviating the center line C FC  within the record mark RM, so that the record mark RM will be inclined in the focusing direction with respect to the irradiation line TL. Multiple out-of-focus quantities ΔMc may be designated in order to deviating the center line C FC  of the record mark RM in multiple stages in the same direction. 
     In the aforesaid first embodiment, a description has been made of a case where after the record mark RM is formed with the center line C FC  of the record mark RM deviated from the irradiation line TL, the next record mark RM is formed with the center line C FC  of the next record mark RM displaced with respect to the position of the deviated center line. The present invention is not limited to this case. For example, after the record mark RM is formed while being deviated in a plus direction, if the next record mark RM is formed while being aligned with the irradiation line TL, the same advantage as that of the aforesaid embodiment can be provided. Otherwise, the record mark RM and the next record mark RM may be successively formed while being deviated from each other in the same direction (plus or minus direction). 
     In the aforesaid first embodiment, the present invention is applied to the optical disk  100  in which the record mark RM is formed with a bubble in the recording layer  101  according to the blue light beam Lb 1  having a predetermined intensity or more. The present invention is not limited to the optical disk. The present invention may be applied to, for example, an optical disk in which a hologram is formed in advance all over the recording layer  101  whose refractive index varies with irradiation of light, and the record mark RM is formed by destroying the hologram through irradiation of the blue light beam Lb 1 , or an optical disk  100  in which the three-dimensional record mark RM having a three-dimensional shape is formed by changing a refractive index. 
     Further, the blue light beam Lb emitted from a light source may be separated into the blue light beams Lb 1  and Lb 2 , and irradiated to the same target mark position through both the surfaces of a voluminal medium  121   v  (not shown) in order to form the record mark RM with a hologram. The constitution of this type of optical disk drive is described in the aforesaid patent document 2. 
     Further, in the aforesaid first embodiment, a description has been made of a case where the red light beam Lr 1  whose wavelength is different from that of the blue light beam Lb 1  is adopted as servo light. The present invention is not limited to this case. For example, the blue light beam Lb 1  may be separated into portions, and one of the portions may be irradiated as a servo light beam to the reflecting layer. In this case, a film that reflects at least part or the whole of the blue light beam Lb 1  and red light beam Lr 1  is adopted as the reflecting layer. 
     Further, in the aforesaid first embodiment, a description has been made of a case where the reflecting layer  104  is interposed between the substrate  103  located on a side opposite to the object lens  40  and the recording layer  101 . The present invention is not limited to this case. In short, as an optical disk, a disk having at least the recording layer and reflecting layer will do. 
     For example, the reflecting layer may be interposed between the substrate  102  located on the side of the objective lens  40  and the recording layer  101 . In this case, the reflecting layer  104  is formed as a reflecting/transmitting layer that reflects 100% light (red laser light) whose wavelength is used for servo control of the objective lens  40  and transmits 100% light (blue laser light) whose wavelength is used for recording or reproduction. Thus, the red light beam Lr 1  is reflected in order to produce the red light beam Lr 2 , and the blue light beam Lb 1  is irradiated to a target mark position. 
     Further, in the aforesaid first embodiment, a description has been made of a case where the optical pickup  26  has the construction shown in  FIG. 7 . The present invention is not limited to this case. The arrangement of optical parts, the number thereof, and the types thereof can be varied. For example, a quarter-wave plate may be interposed between the dichroic prism  37  and objective lens  40  in place of the quarter-wave plates  36  and  57 . The positional relationship between the servo optical system  30  and information optical system  50  may be changed, and a dichroic prism that transmits the red light beam Lr 1  and reflects the blue light beam Lb 1  may be substituted for the optical dichroic prism  37 . 
     Further, in the aforesaid first embodiment, a description has been made of a case where the record mark RM is formed in the optical disk  100  shaped like a disk. The present invention is not limited to this case. For example, the record mark RM may be recorded in an optical information recording medium shaped like a cube (parallelepiped). 
     Further, in the aforesaid first embodiment, a description has been made of a case where: the blue light beam Lb 1  whose wavelength is 405 nm is adopted as information light; and the red light beam Lr 1  whose wavelength is 660 nm is adopted as servo light. The present invention is not limited to this case. There is no limitation in the wavelength of the information light or servo light. Appropriate wavelengths can be selected based on the properties of the optical disk  100  and optical disk drive  20 . 
     Further, in the aforesaid first embodiment, a description has been made of a case where the blue focusing error signal SFEb is produced based on the blue light beam Lb 2  according to an astigmatism method. The present invention is not limited to this case. The blue focusing error signal SFEb may be produced according to any of various methods including, for example, a knife edge method and an internal/external differential method. The same applies to the red focusing error signal SFEr. The red tracking error signal STEr can be produced according to any of various methods including a differential push-pull (DPP) method and a differential phase detection (DPD) method. 
     Further, in the aforesaid first embodiment, a description has been made of a case where recording information is modulated through EFM modulation, and main data is recorded with the record mark RM whose mark length ranges from 3T to 11T and a space. The present invention is not limited to this case. The recording information may be modulated according to any of other various modulation methods. Information may be recorded in such a manner that one record mark RM represents 1-bit information and the presence or absence of the record mark RM represents 1 or 0. 
     Further, in the aforesaid first embodiment, a description has been made of a case where the movable lens  58 A is moved to a position dependent on the relay driving current Uf. The present invention is not limited to this case. For example, the movable lens may be controlled so that it will be moved based on the driving current but will not be displaced until the driving current is fed next. 
     Further, in the aforesaid first embodiment, a description has been made of a case where the helical irradiation lines TL are imagined in the optical disk  100 . The present invention is not limited to this case. For example, the irradiation lines TL may be concentrically or linearly imagined. 
     Further, in the aforesaid first embodiment, a description has been made of a case where the center line C FC  of the record mark RM is deviated in the focusing direction from the irradiation line TL. The present invention is not limited to this case. The record mark RM may be formed with the center line C FC  thereof deviated in the tracking direction that is the radial direction of the optical disk  100 . 
     In this case, sub-data can be reproduced using the blue tracking error signal STEb, which is produced according to an equation (5) below, in the same manner as it is in the aforesaid embodiment. Even in this case, similarly to the aforesaid embodiment, the optical disk drive implements tracking control according to the tracking error signal STEr based on the red light beam Lr 2 . Therefore, the sub-data embedded in the record mark RM can be reproduced without any adverse effect imposed on the tracking control of the objective lens. 
         STEb =( SDAb+SDDb )−( SDBb+SDCb )  (5) 
     Further, in the aforesaid first embodiment, a description has been made of a case where the objective lens  40  serving as an objective lens, the movable lens  58 A serving as a focus shift unit, the main-data recording signal production block  72  and driving control unit  22  serving as a main-data recording unit, and the embedded signal production block  73  and driving control unit  22  serving as a sub-data recording unit are used to constitute the optical disk drive  20  serving as an optical information recording apparatus. The present invention is not limited to this case. Alternatively, the objective lens, focus shift unit, main-data recording unit, and sub-data recording unit that are realized with any other various components may be used to constitute the optical information recording apparatus in accordance with the present invention. 
     Further in the aforesaid first embodiment, a description has been described of a case where the laser diode  51  serving as a light source, the objective lens  40  serving as an objective lens, the photodetector  63  serving as a record mark detection unit, and the reproduction control unit  80  serving as a deviation detection unit are used to constitute the optical disk drive  20  serving as an optical information reproducing apparatus. The present invention is not limited to this case. Alternatively, the objective lens, focus shift unit, record mark detection unit, and deviation detection unit realized with any other various components may be used to constitute the optical information reproducing apparatus in accordance with the present invention. 
     Further, in the aforesaid first embodiment, a description has been made of a case where the recording layer  101  serving as a recording layer is used to form the optical disk  100  serving as an optical information recording medium. The present invention is not limited to this case. The optical recording medium in accordance with the present invention may be formed using the recording layer realized with any of other various components. 
     Further, in the aforesaid first embodiment, a description has been made of a case where the recording layer  101  serving as a recording layer and the reflecting layer  104  serving as a reflecting layer are used to form the optical disk  100  serving as an optical information recording medium. The present invention is not limited to this case. Alternatively, the recording layer and reflecting layer realized with other various components may be used to form the optical information recording medium in accordance with the present invention. 
     (2) Second Embodiment 
       FIG. 17  to  FIG. 21  show the second embodiment. The same reference numerals are assigned to components corresponding to those of the first embodiment shown in  FIG. 1  to  FIG. 16 . An iterative description will be omitted. The second embodiment is different from the first embodiment in a point that an optical disk  200  does not include the reflecting layer  104  and in a point that an optical information recording apparatus  120  dedicated to recording is used to record information and an optical information reproducing apparatus dedicated to reproduction is used to reproduce information. 
     (2-1) Construction of an Optical Disk 
     The optical disk  200  (not shown) has a three-layer structure having both the surfaces of the recording layer  101  sandwiched between the substrates  102  and  103  with the recording layer  101 , in which information is recorded, as a center. 
     Therefore, unlike the optical disk  100  employed in the first embodiment, the reflecting layer  104 , and the lands and grooves in the reflecting layer  104  are not formed. 
     The thicknesses t 1 , t 2 , and t 3  of the recording layer  101  and substrates  102  and  103  included in the optical disk  200  are identical to those in the optical disk  100 . An iterative description will be omitted. 
     (2-2) Configuration of an Optical Information Recording Apparatus 
     The optical information recording apparatus  120  (not shown) is nearly identical to the optical disk drive  20  ( FIG. 6 ) except a point that it does not include the reproduction control unit  80  and a point that an optical pickup  126  has a different construction. An iterative description will be omitted. 
     As shown in  FIG. 17 , the optical pickup  126  of the optical information recording apparatus  120  irradiates the blue light beam Lb 1  to the optical disk  200 . 
     More particularly, a laser diode  151  of the optical pickup  126  emits the blue light beam Lb 1  of 405 nm under the control of the driving control unit  22 , and routes it to a collimator lens  152 . 
     The collimator lens  152  converts the blue light beam Lb 1 , which includes diverging rays, into parallel rays, and routes it to an objective lens  140 . The objective lens  140  concentrates the blue light beam Lb 1 , and irradiates it to the optical disk  200 . 
     In the optical pickup  126 , the objective lens  140  includes a distance detector that detects a disk distance HA between the objective lens  140  and an incident surface  200 A of the optical disk  200 . 
     Assuming that HA denotes a focal length attained when the objective lens  140  concentrates the blue light beam Lb 1 , Hd denotes an incident surface depth that is a distance from the incident surface  200 A to a target mark position, and n denotes a refractive index of the optical disk  200  (substrate  102  and recording layer  101 ), the disk distance HA is expressed as follows: 
         HA=HX −( Hd×n )  (6) 
     In the optical information recording apparatus  120 , when the objective lens  140  is driven in the focusing direction in order to retain the disk distance HA at a designated disk distance HAs designated based on the incident surface depth Hd of the target mark position, the blue light beam Lb 1  can be irradiated to the target mark position. 
     More particularly, the distance detector produces a distance signal consistent with the disk distance HA, and feeds it to the signal processor  23 . As shown in  FIG. 18(E) , the signal processor  23  produces an incident surface displacement signal SCK, which represents a magnitude of a difference between the designated disk distance HAs and detected disk distance HA, on the basis of the distance signal, and feeds it to the driving control unit  22 . 
     When the plus embedded signal Sm+ and minus embedded signal Sm− which are produced by the embedded signal production block  73  of the recording control unit  70  are fed in the same manner as they are in the first embodiment ( FIG. 13 ), the driving control unit  22  superposes the incident surface displacement signal SCK, plus embedded signal Sm+, and minus embedded signal Sm− on one another so as to produce a focusing driving current SFD. 
     Specifically, the driving control unit  22  produces a product by multiplying the incident surface displacement signal SCK by a predetermined coefficient. According to a period during which the signal level of the plus embedded signal Sm+ and minus embedded signal Sm− is High, the predetermined shift current value Δm± is added to the product. 
     For example, at a time point t 31 , when the plus embedded signal Sm+ rises to be High, the shift current value Δ+m is added to the product in order to produce a focusing driving current SFD. At a time point  32 , when the plus embedded signal Sm+ falls to be Low, the driving control unit  22  ceases addition of the shift current value Δ+m, and the product is calculated as the focusing driving current SFD as it is. 
     At a time point t 33 , when the minus embedded signal Sm− rises to be High, the driving control unit  22  produces the focusing driving current SFD by adding the shift current value Δ−m to the product. At a time point t 34 , when the plus embedded signal Sm− falls to be Low, the driving control unit  22  ceases addition of the shift current value −m, and calculates the product as the focusing driving current SFD as it is. 
     The driving control unit  22  feeds the focusing driving current SFD to a biaxial actuator  140 A. The biaxial actuator  140 A drives the objective lens  140  to a position dependent on the focusing driving current SFD. 
     As a result, when both the plus embedded signal Sm+ and minus embedded signal Sm− take on the Low level, the optical information recording apparatus  120  can retain the disk distance HA at the designated disk distance HAs, and can square the focus Fb of the blue light beam Lb 1  with the irradiation line TL. 
     When either the plus embedded signal Sm+ or the minus embedded signal Sm−is High, the optical information recording apparatus  120  drives the objective lens  140  so that the disk distance HA will become different from the designated disk distance HAs by a distance dependent on the shift current value Δ±m (that is, an out-of-focus quantity ΔMc×a refractive index n). 
     Accordingly, the optical information recording apparatus  120  squares the focus Fb of the blue light beam Lb 1  with a target mark position deviated by the out-of-focus quantity ΔMc in the focusing direction (plus direction or minus direction) from the irradiation line TL. 
     As mentioned so far, the optical information recording apparatus  120  displaces the objective lens  140  with respect to the optical disk  200 , which does not include the reflecting layer  104  serving as a reference, so as to shift the focus Fb of the blue light beam Lb 1 , and controls the disk distance HA so as to square the focus Fb with a target mark position. 
     Accordingly, the optical information recording apparatus  120  does not, unlike the first embodiment, require the servo optical system  30 . Eventually, the construction of the optical pickup  126  is simplified. 
     (2-3) Configuration of the Optical Information Reproducing Apparatus 
     The optical information reproducing apparatus  130  (not shown) is nearly identical to the optical disk drive  20  ( FIG. 6 ) except a point that it does not include the recording control unit  70  and a point that the constructions of an optical pickup  160  and a reproduction control unit  180  are different. An iterative description will be omitted. 
     As shown in  FIG. 19 , the optical pickup  160  of the optical information reproducing apparatus  130  irradiates the blue light beam Lb 1  to the optical disk  200 , and receives the blue light beam Lb 2  that is the blue light beam Lb 1  reflected from the optical disk  200 . 
     More particularly, the laser diode  161  of the optical pickup  160  emits the blue light beam Lb 1  of 405 nm under the control of the driving control unit  22 , and routes it to a collimator lens  162 . 
     The collimator lens  162  converts the blue light beam Lb 1 , which includes diverging rays, into parallel rays, and routes it to a polarization beam splitter  163 . The polarization beam splitter  163  uses the reflecting/transmitting surface  163 S thereof to transmit or reflect the blue light beam Lb 1  according to the deflecting direction, transmits the blue light beam Lb 1  that is p-polarized light, and routes it to a quarter-wave plate  164 . 
     The quarter-wave plate  164  converts the blue light beam Lb 1 , which is linearly polarized light, into circularly polarized light, and routes it to an objective lens  165 . The objective lens  165  concentrates the blue light beam Lb 1 , and irradiates it to the optical disk  200 . 
     When the record mark RM is formed near a target mark position in the optical disk  200 , the blue light beam Lb 1  is reflected from the record mark RM, and routed as a blue light beam Lb 2 , of which rotating direction is reverse to that of the blue light beam Lb 1  and which advances in an opposite direction, to the objective lens  165 . Further, the blue light beam Lb 2  is converted into s-polarized light by the quarter-wave plate  164 , and then routed to the polarization beam splitter  163 . 
     The polarization beam splitter  163  reflects the blue light beam Lb 2 , which is s-polarized light, according to the deflecting direction thereof, and routes it to a condenser lens  166 . The condenser lens  166  concentrates the blue light beam Lb 2 . An astigmatism is applied to the blue light beam Lb 2  by a cylindrical lens  167 . The blue light beam Lb 2  is then irradiated to a photodetector  169  via a pinhole plate  168 . 
     The photodetector  169  has the same construction as the photodetector  63  ( FIG. 12 ) does, produces detection signals SDAb to SDBd in the same manner as the photodetector  63  does, and feeds them to the signal processor  23  ( FIG. 6 ). 
     The signal processor  23  produces the reproduction signal SRF and blue focusing error signal SFEb according to the equations (3) and (4). 
     Supposedly, information is already recorded in the optical disk  200 , and the record mark RM is formed therein. The optical information reproducing apparatus  160  uses the reflected light beam Lb 2 , which is the blue light beam Lb 1  reflected from the record mark RM, to implement focusing control in the objective lens  165 . 
     More particularly, the signal processor  23  of the optical information reproducing apparatus  130  feeds, as shown in  FIG. 20 , the reproduction signal SRF ( FIG. 21(B) ) to each of the reproductive clock production block  81  and main-data information reproduction block included in a reproduction control unit  180 , and feeds the blue focusing error signal SFEb to a band-pass filter block  183 . 
     The main-data information reproduction block  82  produces a reproductive binary-coded signal SRO ( FIG. 21(D) ) while squaring the timing of production with the timing of the reproductive clock CLr ( FIG. 21(C) ) fed from the reproductive clock production block  81  in the same manner as that included in the first embodiment. Further, the main-data information reproduction block  82  produces the reproductive main-data information Ra on the basis of the reproductive binary-coded signal, and feeds it to the system controller  21 . 
     When the blue focusing error signal SFEb ( FIG. 21(E) ) is fed to the band-pass filter block  183 , the band-pass filter block  183  performs filtering processing on the blue focusing error signal SFEb in a predetermined frequency band. As a result, the blue focusing error signal SFEb is, as shown in  FIGS. 21(F)  and (G), separated into a high-frequency band focusing signal SFEbH having a relatively high frequency and a low-frequency band focusing signal SFEbL having a relatively low frequency. 
     When the objective lens  165  is made stationary, the optical information reproducing apparatus  130  irradiates the focus Fb of the blue light beam Lb 1  to the same position all the time. The irradiated position gradually changes along the track TR according to the rotation of the optical disk  200 . 
     A deviation of the focus Fb from the record mark RM derived from a surface shake caused by a distortion of the optical disk  200  or a trouble occurring during mounting is often manifested as a low frequency at intervals of a cycle dependent on the rotation of the optical disk  200 . 
     As described previously, in the optical disk  200 , each record mark RM is formed while being deviated in the focusing direction from the irradiation line TL. Thus, sub-data is embedded. Therefore, the deviation of the focus Fb from the record mark RM derived from the sub-data is manifested as a high frequency in association with each record mark RM. 
     Therefore, the high-frequency band focusing signal SFEbH that is a high-frequency component of the blue focusing error signal SFEb represents sub-data. The low-frequency band focusing signal SFEbL that is a low-frequency component of the blue focusing error signal SFEb represents the out-of-focus quantity of the focus Fb from the irradiation line TL. 
     The band-pass filter block  183  ( FIG. 20 ) feeds the high-frequency focusing signal SFEbH to the sub-data information reproduction block  184 , and feeds the low-frequency band focusing signal SFEbL to the driving control unit  22 . 
     The sub-data information reproduction block  184  performs various kinds of pieces of signal processing on the high-frequency band focusing signal SFEbH in the same manner as that of the first embodiment does, thus produces the reproductive sub-data information Rb, and feeds it to the system controller  21 . 
     The driving control unit  22  produces a focusing driving current SFD on the basis of the low-frequency band focusing signal SFEbL, and feeds it to the biaxial actuator  165 A. Thus, the driving control unit  22  drives the objective lens  165  so that although the record mark RM is deviated from the irradiation line TL, the blue light beam Lb 1  can be irradiated to the irradiation line TL. 
     As mentioned above, the optical information reproducing apparatus  130  separates the blue focusing error signal SFEb into the high-frequency band focusing signal SFEbH that is a high-frequency component and the low-frequency band focusing signal SFEbL that is a low-frequency component. The optical information production apparatus  130  produces the reproductive sub-data information Rb on the basis of the high-frequency band focusing signal SFEbH, and implements focusing control in the objective lens  165  on the basis of the low-frequency band focusing signal SFEbL. 
     Accordingly, the optical information reproducing apparatus  130  can reproduce sub-data embedded in the record mark RM without inclusion of the servo optical system  30  and distance detector, and can thus have the configuration thereof simplified. 
     The optical information reproducing apparatus  130  drives the objective lens  165  on the basis of the low-frequency band focusing signal SFEbL produced by removing the high-frequency component based on sub-data from the blue focusing error signal SFEb, and can irradiate the blue light beam Lb 1  to the irradiation line TL. Eventually, the optical information reproducing apparatus  130  can vary the blue focusing error signal SFEb according to the sub-data. 
     (2-4) Actions and Advantage 
     According to the foregoing constitution, the optical information recording apparatus  120  detects the disk distance HA between the objective lens  140  and the incident surface  200 A of the optical disk  200  serving as an optical information recording medium, and thus detects the relative positional relationship between the objective lens  140  and optical disk  200 . The optical information recording apparatus  120  drives the objective lens  140  so as to control the disk distance HA, and thus shifts the focus Fb of the blue light beam Lb 1  to a target depth. 
     Accordingly, in the optical information recording apparatus  120 , a distance detector that detects the disk distance HA should merely be substituted for the servo optical system  30 , and numerous optical parts for use in servo control become unnecessary. The configuration of the optical information recording apparatus  120  can be simplified. 
     In the optical information recording apparatus  120 , the objective lens  140  is driven in the focusing direction in order to shift the focus Fb of the blue light beam Lb 1 . Thus, in the optical information recording apparatus  120 , unlike in the optical disk drive  20 , the movable lens  58 A need not be included. The configuration of the optical information recording apparatus  120  can be simplified. 
     Further, in the optical information reproducing apparatus  130 , the objective lens  165  is driven in the focusing direction in order to shift the focus Fb of the blue light beam Lb 1 , and the blue focusing error signal SFEb representing an out-of-focus quantity is separated into the high-frequency band focusing signal SFEbH, which is a high-frequency component, and the low-frequency band focusing signal SFEbL that is a low-frequency component. In the optical information reproducing apparatus  130 , sub-data is reproduced based on the high-frequency band focusing signal SFEbH, and the objective lens is driven based on the low-frequency band focusing signal SFEbL. 
     Accordingly, in the optical information reproducing apparatus  130 , main data and sub-data are reproduced from the record mark RM in which the sub-data is embedded. Based on the blue light beam Lb 2  reflected from the record mark RM, that is, using the record mark RM that has already been recorded, the objective lens  165  is subjected to focusing control so that the blue light beam Lb 1  will be irradiated to the irradiation line TL. 
     In the optical information recording apparatus  120 , during information recording processing, the record mark RM is formed with the center line C FC  thereof deviated in the focusing direction from the irradiation line TL. Thereafter, the next record mark RM is formed with the center line C FC  thereof displaced with respect to the position of the deviated center line. 
     Accordingly, in the optical information recording apparatus  120 , the record mark RM next to the record mark RM recorded while being deviated from the irradiation line TL can be recorded on the irradiation line TL or while being deviated in a reverse direction. The record mark RM recorded while being deviated from the irradiation line TL will not be continuously formed, but the record mark RM can be intermittently deviated from the irradiation line TL. 
     Accordingly, the optical information recording apparatus  120  can set a variation in a signal level, which is derived from sub-data represented by the blue focusing error signal SFEb produced during information reproducing processing performed in the optical information reproducing apparatus  130 , to a high frequency, and can separate the blue focusing error signal SFEbH into the high-frequency focusing signal SFEbH and low-frequency band focusing signal SFEbL using the band-pass filter block  183 . 
     According to the foregoing constitution, the optical information recording apparatus  120  drives the objective lens  140  on the basis of the relative positional relationship between the optical disk  200  and objective lens  140 , and thus irradiates the blue light beam Lb 1  to a target depth. Therefore, the optical information recording apparatus  120  does not require an optical part that receives light for servo control, and can have the configuration thereof simplified. 
     The optical information reproducing apparatus  130  drives the objective lens  165  on the basis of the blue light beam Lb 2 , and thus irradiates the blue light beam Lb 1  to a target depth. Therefore, compared with a case where light for servo control is used separately, the optical information reproducing apparatus  130  does not require optical parts that irradiate or receive the light for servo control, and can have the configuration thereof simplified. 
     (2-5) Other Embodiments 
     In the aforesaid second embodiment, a description has been made of a case where the objective lens  140  included in the optical information recording apparatus  120  is provided with a distance detector that measures the disk distance HA. The present invention is not limited to this case. For example, a sensor that measures the disk distance HA may be disposed in a stage on which the optical disk  200  is placed or in the spindle motor  24 . 
     A target mark position need not be determined based on the disk distance HA. For example, when a servo record mark for servo control is formed in advance in the optical disk  200 , the servo record mark may be used to implement focusing control. The focusing control may be implemented by irradiating a servo light beam for servo control to the already recorded record mark RM. 
     In the aforesaid second embodiment, a description has been made of a case where the optical information reproducing apparatus  130  implements focusing control in the objective lens  165  on the basis of the blue focusing error signal SFEb. The present invention is not limited to this case. For example, similarly to the optical information recording apparatus  120 , the disk distance HA measured by a distance detector may be used to implement the focusing control. 
     Further, in the aforesaid second embodiment, a description has been made of a case where the low-frequency band focusing signal SFEbL is used to implement focusing control in the objective lens  165 . The present invention is not limited to this case. For example, when the amplitude of a high-frequency component of the blue focusing error signal SFEb representing sub-data is relatively small, the blue focusing error signal SFEb may be used as it is. In this case, the high-frequency focusing signal SFEbH is fully amplified in order to reproduce the sub-data. 
     (3) Application of the Present Invention 
     Next, an applied example of the present invention will be described below by presenting a concrete example. For convenience&#39; sake, the reference numerals employed in the optical disk  100  and optical disk drive  20  in accordance with the first embodiment will be used to make a description. However, the second embodiment can also be applied. 
     (3-1) Copy Prevention System 
     As shown in  FIG. 22(A) , in a copy prevention system  210 , main data such as video data or music data is recorded in the optical disk  100  in the form of the record marl RM. In the copy prevention system  210 , a disk identification code ED signifying that the optical disk  100  is an authentic optical disk  100  is modulated according to a predetermined method, and recorded as sub-data in the form of a modulated identification code EDr. The modulated identification code EDr is recorded in, for example, a table-of-contents (EOC) field on an innermost circumference by deviating the record mark RM from the irradiation line TL in the focusing direction. 
     If the optical disk drive  20  that reproduces the optical disk  100  can reproduce the disk identification code ED from the modulated identification code EDr read from the optical disk  100 , the optical disk drive  20  decides that the optical disk has been legitimately fabricated, and reproduces main data recorded in the optical disk  100 . 
     In contrast, as shown in  FIG. 22(B) , if the modulated identification code EDr is not recorded in the optical disk and the disk identification code ED cannot be reproduced, the optical disk drive  20  decides that the optical disk is a fraudulent optical disk  100 X such as a so-called pirated disk, which is illegally duplicated, but is not an authentic optical disk, and does not reproduce main data from the fraudulent optical disk  100 X. 
     In the optical disk  100 , since the out-of-focus quantity ΔMc is set to a small value, the optical disk drive  20  that records the record mark RM is requested to implement precise focusing control, and can discourage a third party from fabricating the fraudulent optical disk  100 X. 
     In this case, in the optical disk  100 , preferably, the disk identification code ED is modulated according to the predetermined method and recorded as the modulated identification code EDr. Supposing that a third party tries to record the modulated identification code EDr in the fraudulent optical disk  100 X, it becomes necessary for the third party to modulate the disk identification code ED according to the same method as the method adopted by the optical disk  100 . As a result, the optical disk  100  further discourages the third party from recording the modulated identification code EDr. As for the modulating method, refer to the patent document 1 or the like. 
     Specifically, in the copy prevention system  210 , a process of fabricating the fraudulent optical disk  100 X that is reproducible can be made very hard to do, and sale of the fraudulent optical disk  100 X by a third party can be substantially prevented. 
     As another copy prevention system  211  (not shown), main data may be encrypted and recorded in the form of the record mark RM and space, and key information necessary to decrypt the main data may be recorded as sub-data. In this case, both the main data and sub-data are recorded all over the optical disk  100 . 
     Further, as sub-data, data necessary to select or decode key information may be recorded, or any of various data items necessary for decryption may be recorded. 
     (3-2) Other Applied Example 
     Further, the present invention may be applied to any system other than the copy prevention system. 
     For example, address information may be recorded as sub-data. In this case, main data is recorded in the form of the record mark RM in the leading part of a sector, and address information is embedded in the record mark RM by displacing the record mark RM in the leading part with respect to the irradiation line TL. This obviates the necessity of recording the address information as main data. Therefore, the recording capacity of the optical disk  100  can be improved. 
     Incidentally, subordinately generated information such as the reproductive frequency of data or the copying frequency may be recorded as sub-data. 
     INDUSTRIAL APPLICABILITY 
     The present invention can be applied to optical disk drives that record or reproduce a large amount of information, for example, a video content or an audio content, in or from a recording medium such as an optical disk. 
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
         
           
               20 : OPTICAL DISK DRIVE, 
               21 : SYSTEM CONTROLLER, 
               22 : DRIVING CONTROL UNIT, 
               26 ,  126 ,  160 : OPTICAL PICKUP, 
               30 : SERVO OPTICAL SYSTEM, 
               31 ,  51 ,  151 ,  161 : LASER DIODE, 
               34 ,  54 ,  163 : POLARIZATION BEAM SPLITTER, 
               37 : DICHROIC PRISM, 
               36 ,  57 : QUARTER-WAVE PLATE, 
               40 : OBJECTIVE LENS, 
               40 A: BIAXIAL ACTUATOR, 
               43 ,  63 : PHOTODETECTOR, 
               50 : INFORMATION OPTICAL SYSTEM, 
               62 : PINHOLE PLATE, 
               70 : RECORDING CONTROL UNIT, 
               71 : RECORDING CLOCK PRODUCTION BLOCK, 
               72 : MAIN-DATA RECORDING SIGNAL PRODUCTION BLOCK, 
               73 : EMBEDDED SIGNAL PRODUCTION BLOCK, 
               80 ,  180 : REPRODUCTION CONTROL UNIT, 
               81 : REPRODUCTIVE CLOCK PRODUCTION BLOCK, 
               82 : MAIN-DATA INFORMATION REPRODUCTION BLOCK, 
               83 ,  184 : SUB-DATA INFORMATION REPRODUCTION BLOCK, 
               183 : BAND-PASS FILTER BLOCK, 
             Lb 1 , Lb 2 : BLUE LIGHT BEAM, 
             Lr 1 , Lr 2 : RED LIGHT BEAM, 
               100 ,  200 : OPTICAL DISK, 
               100 X: FRAUDULENT OPTICAL DISK, 
               101 : RECORDING LAYER, 
               102 ,  103 : SUBSTRATE, 
               104 : REFLECTING LAYER, 
             SRF: REPRODUCTION SIGNAL, 
             SFEr: RED FOCUSING ERROR SIGNAL, 
             SFEb: BLUE FOCUSING ERROR SIGNAL, 
             SFEbH: HIGH-FREQUENCY BAND FOCUSING SIGNAL, 
             SFEbL: LOW-FREQUENCY BAND FOCUSING SIGNAL, 
             TL: IRRADIATION LINE, RM: RECORD MARK