JP2013168199A - Playback method and playback device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a playback method capable of reducing power consumption without deteriorating a playback signal characteristic when playing back an optical information recording medium having a high recording density, and a playback device.SOLUTION: Information recorded in an optical information recording medium 1 in which information is recorded by a recording mark shorter than an optical system resolution limit belonging to a playback device 100 is played back by using reproduction light generated by a DC current.

Description

  The present invention relates to a reproduction method and apparatus for reproducing information recorded on an optical information recording medium with low power consumption and high reliability.

  In recent years, in an optical information recording medium, it is required to increase an information recording capacity for processing a huge amount of information such as an image. As a solution, there is a method using a super-resolution technique, which is one of information processing improvement techniques during reproduction.

  The super-resolution technique is shorter than the optical system resolution limit (the limit determined by the laser wavelength (λ) and the numerical aperture (NA) of the optical system (λ / (4NA))) of the reproducing apparatus. This is a technique for reproducing a mark length signal. As a result, recording using a smaller mark length becomes possible, so that the substantial recording density increases. This is due to the fact that the reproducing technique is a problem when the density is increased, and not the recording technique.

  These techniques will be described first from the super-resolution technique.

  Conventionally, many optical information recording media (hereinafter referred to as super-resolution optical information recording media or super-resolution media) for reproducing signals having a mark length shorter than the optical system resolution limit of the reproducing apparatus have been proposed.

  As such a technique, a technique that can be applied to a read-only medium in which information that cannot be rewritten due to the unevenness of the substrate is recorded, a thin metal film or the like is formed on the substrate on which information is recorded by the concave and / or convex. There is a technique for providing a layer called a functional layer (see Patent Document 1).

  At present, most of the principle of the super-resolution medium relating to Patent Document 1 has not been elucidated, but a signal having a mark length shorter than the optical system resolution limit can be reproduced by the temperature change of the functional layer. Is.

  As another technique that can be applied to a read-only medium, a technique is also known in which a thermochromic dye layer whose optical characteristics (transmittance) change with temperature is used as a mask layer on the reproduction light incident surface of a reflective film. (See Patent Document 2).

  Note that the mask layer is a layer that causes a super-resolution phenomenon by artificially constricting a laser spot, which will be described later.

  In these optical information recording media, the laser spot generated by the reproducing laser irradiated on the reproducing surface has a light intensity distribution, and this makes use of the fact that a temperature distribution is generated.

  More specifically, a temperature or light intensity distribution is generated in the reproduction laser spot on the mask layer that is closer to the reproduction light incident surface than the reflection layer, thereby generating a distribution of optical characteristics in the laser spot.

  For example, when a material that increases the transmittance when the temperature is high is used for the mask layer, only the transmittance at the high temperature portion is increased, so that the laser spot generated on the reflective layer surface is reduced in a pseudo manner. . As a result, a signal having a mark length shorter than the optical system resolution limit can be reproduced.

  However, in the super-resolution medium described in Patent Document 1 or 2, the laser spot is artificially reduced by masking the laser light with a functional layer or a mask layer, so that the utilization efficiency of reproduction light is reduced ( Naturally, the light reflected by the reflective layer is reduced). For this reason, there is a limit to the reduction of the laser spot, and the improvement of the recording density is limited to about twice the linear density.

  Conventionally, a method for increasing the capacity of an optical information recording medium using the super-resolution technique as described above has been proposed.

  By the way, in general, a semiconductor laser is used as a light source of light irradiated on an optical information recording medium for reproducing and / or recording information.

  However, it has been known that when a semiconductor laser is used as a light source, noise is generated by the return light (reflected light) from the optical information recording medium, which adversely affects reproduction signal characteristics.

  Therefore, when reproducing an optical information recording medium such as a BD (Blu-ray disc: registered trademark), high-frequency superposition as described in Patent Document 3 has been used. In order to reproduce information recorded at a higher density, super-resolution optical information recording media such as Patent Documents 1 and 2 that are considered to be sensitive to noise use high-frequency superposition for reproduction. I came.

JP 2001-250274 A (published on September 14, 2001) JP 2001-035012 A (published on February 9, 2001) JP 2000-149302 A (released on May 30, 2000)

  However, since the super-resolution techniques such as Patent Documents 1 and 2 both use heat generated by irradiating reproduction light, compared to the case of reproducing a mark longer than the optical system resolution limit. In general, it is necessary to irradiate high intensity reproduction light, and there is a problem that power consumption increases.

  In addition, when high-frequency superposition is used during reproduction, high-power reproduction light is irradiated, which increases the burden on the laser body and various optical components, and shortens the life of the reproduction apparatus. .

  The present invention has been made in view of the above problems, and its purpose is to reproduce an optical information recording medium on which information is recorded with a recording mark shorter than the optical system resolution limit of the reproducing apparatus. An object of the present invention is to provide a reproducing method and a reproducing apparatus with low power consumption and high reliability.

  In order to solve the above problems, a reproducing method according to an aspect of the present invention is a reproducing method of an optical information recording medium in which information is recorded with a recording mark shorter than the optical system resolution limit of the reproducing apparatus. The information recorded on the optical information recording medium is reproduced by reproduction light generated by a direct current.

  In order to solve the above problems, a reproducing apparatus according to an aspect of the present invention is an optical information recording medium reproducing apparatus in which information is recorded with a recording mark shorter than an optical system resolution limit of the reproducing apparatus. And irradiating means for irradiating the information recorded on the optical information recording medium with reproduction light generated by direct current.

  According to the above configuration, the information recorded on the optical information recording medium on which information is recorded by the recording mark shorter than the optical system resolution limit of the reproducing apparatus is reproduced by the reproducing light generated by the direct current. .

  According to said structure, the information recorded on the optical information recording medium is reproduced | regenerated with the reproduction light produced | generated by direct current. Therefore, since it is not necessary to use a commonly used high frequency superposition, it is not necessary to drive an oscillator for high frequency superposition. Therefore, power consumption is reduced when reproducing an optical information recording medium with the same reproduction optical power. Can be reduced.

  In addition, since high frequency superposition is not required, there is no need to instantaneously generate a large output. Therefore, since the burden on the semiconductor laser and various optical components is reduced, the life of the optical components can be extended, and the reliability of the reproducing method and the reproducing apparatus can be improved.

  In order to solve the above problems, a reproducing method according to an aspect of the present invention provides an optical information recording medium on which information is recorded by a recording mark group in which an average length of a minimum mark length and a minimum space length is shorter than 119 nm. A reproduction method for reproducing using an optical system having an objective lens numerical aperture of 0.85 and a reproduction light wavelength of 405 nm, wherein information recorded on the optical information recording medium is reproduced by reproduction light generated by a direct current. It is characterized by playing.

  In order to solve the above problems, a reproducing apparatus according to an aspect of the present invention provides an optical information recording medium on which information is recorded by a recording mark group in which an average length of a minimum mark length and a minimum space length is shorter than 119 nm. A reproduction apparatus for reproducing using an optical system having an objective lens numerical aperture of 0.85 and a reproduction light wavelength of 405 nm, wherein information recorded on the optical information recording medium is reproduced with a reproduction light generated by a direct current. Irradiation means for irradiating is provided.

  According to said structure, the information recorded on the optical information recording medium is reproduced | regenerated with the reproduction light produced | generated by direct current. Therefore, since it is not necessary to use a commonly used high frequency superposition, it is not necessary to drive an oscillator for high frequency superposition. Therefore, power consumption is reduced when reproducing an optical information recording medium with the same reproduction optical power. Can be reduced.

  In addition, since high frequency superposition is not required, there is no need to instantaneously generate a large output. Therefore, since the burden on the semiconductor laser and various optical components is reduced, the life of the optical components can be extended, and the reliability of the reproducing method and the reproducing apparatus can be improved.

  In addition, according to the above configuration, in particular, there is an effect that it is possible to extend the life of the optical component for a wavelength of 405 nm, which generally has a shorter life than a normal optical component.

  As described above, the reproducing method and the reproducing apparatus according to the present invention are configured to reproduce information recorded on an optical information recording medium with reproducing light generated by a direct current.

  In addition, as described above, the reproducing method and the reproducing apparatus according to the present invention are configured to include irradiation means for irradiating the information recorded on the optical information recording medium with the reproducing light generated by the direct current.

  Therefore, the reproducing method and the reproducing apparatus according to the present invention reduce power consumption when reproducing an optical information recording medium on which information is recorded with a recording mark shorter than the optical system resolution limit of the reproducing apparatus. In addition, it is possible to provide a highly reliable reproducing method and apparatus.

It is a block diagram which shows the outline of the reproducing | regenerating apparatus which concerns on one Embodiment of this invention. It is a figure which shows the flow of the reproduction | regeneration processing in the reproducing | regenerating apparatus which concerns on one Embodiment of this invention. It is sectional drawing of the optical information recording medium used for the verification test. It is sectional drawing of another optical information recording medium used for the verification test. It is sectional drawing of another optical information recording medium used for the verification test. It is a perspective view which shows the prepit provided on the board | substrate of an optical information recording medium. It is a table | surface regarding the signal characteristic obtained by the verification test.

  A playback apparatus 100 according to an embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a block diagram showing an outline of the configuration of the playback apparatus 100.

  The playback device 100 is a device for playing back the optical information recording medium 1. In the optical information recording medium 1, a mark length shorter than the optical system resolution limit of the reproducing apparatus 100 is recorded. For example, the optical information recording medium 1 is provided with a disc information area having the same density and the same recording format as a normal BD-ROM only in a predetermined area on the inner circumference in order to provide compatibility, and the data area portion is converted to φ120 mm. Information is recorded at a density of 33.3 GB.

  As illustrated, the playback apparatus 100 includes a spindle 101, a pickup unit 102 (irradiation unit), and a control unit 108. The control unit 108 includes a pickup control unit 103, an output control unit 104, a reproduction control unit 105, a clock generation unit 106, and a data reproduction unit 107.

  The pickup unit 102 includes a laser diode (not shown), a laser driver, a condensing optical system including an objective lens, and a light receiving element. In the present embodiment, the numerical aperture of the objective lens is 0.85, and the wavelength of the laser light is 405 nm. Note that the pickup unit 102 may include a high-frequency superimposing circuit.

  The condensing optical system including the objective lens condenses the laser light emitted from the laser diode and irradiates the information recording layer of the optical information recording medium 1 with the light. The light receiving element detects the laser light reflected by the reflective layer of the optical information recording medium 1 and converts it into an electrical signal indicating the intensity of the reflected light. Then, the pickup unit 102 outputs the electrical signal to the data reproducing unit 107.

  The reproduction control unit 105 determines a reproduction position (track) on the optical information recording medium 1. The playback control unit 105 determines a playback speed (linear speed) based on information on which of the disc information area and the data area the track to be played back and the radius of the track to be played back. The playback control unit 105 transmits information indicating the determined playback speed to the spindle 101. The spindle 101 rotates the optical information recording medium 1 based on the information indicating the reproduction speed transmitted from the reproduction control unit 105. Further, the reproduction control unit 105 outputs information on the radius of the track reproduced from the optical information recording medium 1 to the pickup control unit 103.

  The pickup control unit 103 controls the position of the pickup unit 102 and moves the pickup unit 102 to a position corresponding to the track to be reproduced on the optical information recording medium 1.

  The output control unit 104 controls the laser driver of the pickup unit 102 so that the surface of the optical information recording medium 1 is irradiated with laser light having a desired intensity. The laser driver supplies a drive current to the laser diode in accordance with a control signal transmitted from the output control unit 104.

  Here, when reproducing information (contents) recorded on a super-resolution medium, a semiconductor laser is oscillated only by a DC (direct current) current in a laser diode, and reproduction light (hereinafter referred to as DC reproduction light) is generated in an optical information recording medium. The information recorded on the optical information recording medium is reproduced.

  However, the reproduction light emitted from the laser diode is not limited to the reproduction light described above. If the pickup unit 102 includes high-frequency superimposing means, the laser driver may supply a drive current obtained by superimposing the DC current and the high-frequency current to the laser diode.

  The clock generation unit 106 generates a reproduction clock and outputs the reproduction clock to the data reproduction unit 7.

  The data reproduction unit 107 receives the reproduction clock from the clock generation unit 106 and receives an electrical signal indicating the intensity of the reflected light from the pickup unit 102. Then, the data reproducing unit 107 reproduces information read from the optical information recording medium 1 using an electric signal indicating the reproduction clock and the intensity of the reflected light.

(Reproduction processing flow)
The flow of reproduction processing in the reproduction apparatus 100 will be described with reference to FIG. FIG. 2 is a flowchart showing the flow of playback processing in the playback apparatus 100.

  When the optical information recording medium 1 is loaded into the reproducing apparatus 100, the reproducing apparatus 100 reproduces disc information provided on the inner periphery of the optical information recording medium 1. More specifically, the reproduction control unit 105 transmits information indicating the track to be reproduced to the pickup control unit 103 in order to reproduce a track in the disc information area. Further, the reproduction control unit 105 outputs information indicating that the track in the disc information area to be reproduced is a track formed in the non-super-resolution reproduction area to the output control unit 104 and the clock generation unit 106. Further, the playback control unit 105 determines the playback speed as a predetermined first playback speed (S1). In the present embodiment, the first reproduction speed is 4.92 m / s.

  The spindle 101 rotates the optical information recording medium 1 at a rotation speed corresponding to the first reproduction speed determined by the reproduction control unit 105.

  The pickup control unit 103 controls the position of the pickup unit 102 based on information indicating a track to be reproduced, which is input from the reproduction control unit 105. That is, the pickup control unit 103 moves the pickup unit 102 to the track position in the disc information area designated by the reproduction control unit 105 (S2).

  The clock generation unit 106 generates a first reproduction clock (single speed reproduction clock) for non-super-resolution reproduction (S3), and transmits it to the data reproduction unit 107.

  The output control unit 104 sets the output of the reproduction light as the first output for non-super-resolution reproduction, and superimposes it on the DC output output from the laser driver via the high frequency signal modulation means of the high frequency superimposing circuit (S4).

  The reproduction light is reflected by the reflection layer of the optical information recording medium 1 and becomes reflected light. The reflected light is detected by the light receiving element of the pickup unit 102 and converted into an electric signal indicating the intensity of the reflected light. The data reproduction unit 107 reproduces the disc information recorded in the disc information area using the electric signal and the first reproduction clock, and obtains reproduction speed information for reproducing the data area (S5).

  The data reproduction unit 107 outputs the reproduction speed information to the reproduction control unit 105. Here, the reproduction speed information is a second reproduction speed of 7.39 [m / s] (= 4.92 [m / s] /33.3 GB × 25 GB × 2), which is double the reproduction clock of 1 × speed. . Further, the data reproducing unit 107 acquires information on the reproduction light output recorded in the disc information area. The data reproduction unit 107 outputs information on the reproduction light to the output control unit 104. The reproduction light information indicates the reproduction light output recommended by the manufacturer of the optical information recording medium 1.

  The playback device 100 plays back information in the data area (super-resolution area) of the optical information recording medium 1 at the second playback speed indicated by the playback speed information.

  The reproduction control unit 105 instructs the pickup control unit 103 to reproduce the track in the data area. Further, the reproduction control unit 105 sends information indicating that the track to be reproduced is a super-resolution reproduction region to the output control unit 104 and the clock generation unit 106. Further, the reproduction control unit 105 determines the second reproduction speed (7.39 [m / s]) based on the reproduction speed information read from the optical information recording medium 1 (S6).

  The reproduction control unit 105 outputs information indicating the second reproduction speed to the spindle 101. The spindle 101 rotates the information recording medium 1 at a speed corresponding to the second reproduction speed. In addition, the reproduction control unit 105 outputs the determined second reproduction speed to the clock generation unit 106.

  The pickup control unit 103 outputs a control signal to the pickup unit 102, and moves the pickup unit 102 to the position of the track in the data area designated by the reproduction control unit 105 (S7). The clock generation unit 106 generates a second reproduction clock (double reproduction clock) for super-resolution reproduction according to the second reproduction speed (S8). The clock generation unit 106 outputs the generated double-speed reproduction clock to the data reproduction unit 107.

  The output control unit 104 sets the reproduction light output to the second output based on the reproduction light output information supplied from the data reproduction unit 107 (S9). The second output is an output of DC reproduction light for performing super-resolution reproduction. The output control unit 104 outputs the second output to the laser driver of the pickup unit 102. The laser driver drives the laser diode with a DC current corresponding to the second output. As a result, the laser diode oscillates the second output laser beam. The magnitude of the second output is larger than the magnitude of the first output.

  Then, the data reproduction unit 107 reproduces the content recorded in the data area using the electric signal indicating the intensity of the reflected light and the second reproduction clock (S10).

(Effects of the playback device 100)
In this way, the playback apparatus 100 can perform super-resolution playback of the data area with DC playback output. Therefore, the reproducing apparatus 100 can suppress power consumption at the time of super-resolution reproduction, and can suppress deterioration of the laser diode, the condensing optical system including the objective lens, and the light receiving element. 100 reliability can be improved.

  Note that the pickup unit 102 of the playback apparatus 100 may include high-frequency superimposing means. Since the pickup unit 102 includes high-frequency superimposing means, the reproducing apparatus 100 (i) improves compatibility between a super-resolution medium and a normal optical information recording medium (hereinafter also referred to as a normal medium) during reproduction. (Ii) It is possible to cope with the optical information recording 1 having a disc information area having the same density as that of a normal medium in a predetermined area on the inner periphery.

  On the other hand, the pickup unit 102 does not have to include high-frequency superimposing means unless considering good compatibility with a normal medium. If the pickup unit 102 does not include the high frequency superimposing means, the number of parts constituting the pickup unit 102 can be reduced, and the reliability of the reproducing apparatus 100 can be improved in that respect.

〔Verification test〕
A test was conducted to demonstrate the effect of high-frequency superposition on playback signal characteristics when playing back content recorded on super-resolution media and normal media. The test results will be described with reference to FIGS.

  FIG. 3 is a cross-sectional view illustrating a configuration of an optical information recording medium 10 that is an example of a super-resolution medium. FIG. 4 is a cross-sectional view illustrating a configuration of an optical information recording medium 20 that is an example of a super-resolution medium. FIG. 5 is a cross-sectional view illustrating a configuration of an optical information recording medium 30 that is an example of an optical information recording medium that is not a super-resolution medium.

(Optical information recording media 10 and 20)
The optical information recording media 10 and 20 used for the demonstration test will be described below. Since the optical information recording media 10 and 20 are super-resolution media, they are provided with a recording mark group including a recording mark or a space shorter than the resolution limit.

  As shown in FIG. 3, the optical information recording medium 10 includes a substrate 12, an information recording layer (functional film) 13, and a light transmitting layer 14. The information recording layer 13 and the light transmitting layer 14 are sequentially stacked on the surface of the substrate 12.

  The substrate 12 is made of polycarbonate. The information recording surface, which is the surface of the substrate 12 on which the information recording layer 13 is provided (the side irradiated with the reproduction light), has a shape (length in the scanning direction) corresponding to the information to be recorded. A pre-pit group is formed (see FIG. 6). Details of the pre-pit group will be described later.

  The information recording layer 13 is a thin film formed along the unevenness of the information recording surface of the substrate 12 and is a functional film that enables super-resolution reproduction. Specifically, the information recording layer 13 is a Ta thin film layer having a thickness of 5 nm.

  The translucent layer 14 is made of an ultraviolet curable resin having a thickness of 100 μm. The refractive index of this ultraviolet curable resin is 1.50 at a wavelength of 405 nm. The translucent layer 14 has an incident surface that is a surface on which the reproduction light is incident, and protects the information recording layer 13 and the information recording surface of the substrate 12.

  As shown in FIG. 4, the optical information recording medium 20 includes a substrate 22, an information recording layer 23, and a light transmitting layer 24. The information recording layer 23 includes a reproduction layer 23A and a reflection layer 23B. The information recording layer 23 and the light transmitting layer 24 are sequentially stacked on the surface of the substrate 22.

  The substrate 22 is made of polycarbonate. The information recording surface, which is the surface of the substrate 22 on which the information recording layer 23 is provided (the side irradiated with the reproduction light), has irregularities with a shape (length in the scanning direction) corresponding to the information to be recorded. A pre-pit group is formed.

  The information recording layer 23 is a thin film formed along the unevenness of the information recording surface of the substrate 22. The information recording layer 23 is a thin film layer having a configuration different from that of the information recording layer 13 and realizes super-resolution reproduction. Specifically, a reflective film 23B and a reproduction film 23A are formed on the information recording surface of the substrate 22 in that order. The reproducing film 23A is made of a 50 nm thick ZnO thin film, and the reflecting film 23B is made of a 6 nm thick Ta thin film.

  The light transmissive layer 24 is made of an ultraviolet curable resin having a thickness of 100 μm. The refractive index of this ultraviolet curable resin is 1.50 at 405 nm which is the wavelength of the reproduction light. The light transmissive layer 24 has an incident surface that is a surface on which reproduction light is incident, and protects the information recording layer 23 and the information recording surface of the substrate 22.

(Optical information recording medium 30)
As shown in FIG. 5, the optical information recording medium 30 is an optical information recording medium used as a comparative example of the optical information recording media 10 and 20 in the verification test. Specifically, it is a normal optical information recording medium that does not include a mark or space shorter than the resolution limit.

  The optical information recording medium 30 includes a substrate 32, an information recording layer (reflection film) 33, and a light transmitting layer 34. The information recording layer 33 and the light transmitting layer 34 are sequentially stacked on the surface of the substrate 32.

  The substrate 32 is made of polycarbonate. The information recording surface, which is the surface on which the information recording layer 33 of the substrate 32 is provided (the side irradiated with the reproduction light), has irregularities with a shape (length in the scanning direction) corresponding to the information to be recorded. A pre-pit group is formed.

  The information recording layer 33 is a thin film formed along the abrupt of the information recording surface of the substrate 32. The information recording layer 33 is made of an Au thin film having a thickness of 50 nm and functions as a normal reflecting film that does not realize super-resolution reproduction.

  The translucent layer 34 is made of an ultraviolet curable resin having a thickness of 100 μm. The refractive index of this ultraviolet curable resin is 1.50 at 405 nm which is the wavelength of the reproduction light. The translucent layer 34 has an incident surface that is a surface on which reproduction light is incident, and protects the information recording layer 33 and the information recording surface of the substrate 32.

(Prepit group and storage capacity)
FIG. 6 is a perspective view showing a pre-pit group formed on the information recording surfaces of the substrates 12, 22 and 32 of the optical information recording media 10, 20 and 30. FIG. Information to be recorded is recorded on each of the optical information recording media 10, 20 and 30 as marks and spaces having a plurality of lengths (D2T to D8T) according to the 1-7 RLL modulation method. In each of the optical information recording media 10, 20 and 30, the prepits formed on the respective optical information recording media represent marks, and the space between adjacent prepits in the direction along the track represents a space.

  Of the marks and spaces having a plurality of lengths, the average length of the minimum mark length (D2T) and the minimum space length is 112 nm for the substrate 12 and 83 nm for the substrate 22. That is, the average of the minimum mark length and the minimum space length on the substrates 12 and 22 is shorter than the resolution limit (119 nm) when the wavelength of the reproduction light is 405 nm and the numerical aperture of the objective lens is 0.85. Therefore, the optical information recording media 10 and 20 are super-resolution media.

  In the substrate 32, the average of D2T and the minimum space length is 149 nm, which is the same as Blu-ray disk (registered trademark). That is, the average of D2T and the minimum space length is longer than the resolution limit (119 nm). Here, both the minimum mark length and the minimum space length are the same D2T. On the other hand, the track pitch (TpD) of the pre-pit group is 0.32 μm in each of the optical information recording media 10, 20 and 30. This TpD is the same value as TpD in Blu-ray disk (registered trademark).

  The storage capacity of a Blu-ray disk (registered trademark) having a diameter of 120 mm is 25 GB. The optical information recording medium 30 has the same average length of D2T and minimum space length as the Blu-ray disk (registered trademark), and TpD. Therefore, the storage capacity of the optical information recording medium 30 having a diameter of 120 mm is 25 GB, which is the same as that of the Blu-ray disk (registered trademark).

  The optical information recording media 10 and 20 have the same TpD as the Blu-ray disk (registered trademark), but have an average length of D2T shorter than the Blu-ray disk (registered trademark) and the minimum space length. In other words, the optical information recording media 10 and 20 have a higher recording density than the Blu-ray disk (registered trademark). The storage capacities of the optical information recording media 10 and 20 having a diameter of 120 mm are 33.3 GB and 45 GB, respectively.

(Signal reproduction characteristics)
Using the optical information recording media 10, 20, and 30, the signal reproduction characteristics of each optical information recording medium were evaluated. When evaluating signal reproduction characteristics, (i) a drive current obtained by applying high-frequency superposition to a DC drive current, and (ii) a DC drive current are used as drive currents when oscillating a laser beam as reproduction light. Using.

  FIG. 7 is a table relating to the evaluation results of the signal reproduction characteristics in the optical information recording media 10, 20 and 30. “With high-frequency superposition” in FIG. 7 means a case where the laser diode is driven by a drive current in which high-frequency superposition is applied to a DC drive current. On the other hand, “no high frequency superposition” means that the laser diode is driven only by a DC drive current. That is, FIG. 7 shows a comparison result of signal characteristics between the optical information recording media 10, 20, and 30 when high frequency superimposition is applied with the optimum reproduction laser power and when reproduction is performed with DC reproduction light without applying high frequency superposition. Indicates. In this demonstration test, each setting parameter for high-frequency superposition was set to a value compliant with the Blu-ray disk (registered trademark) standard.

  The signal characteristics of the optical information recording media 10 and 20 are as follows: BD evaluator (DDU-1000 manufactured by Pulse Tech / Reproduction optical system: reproduction light wavelength (λ) 405 nm, numerical aperture (NA) 0.85) It measured using the signal detector 3 for BD evaluation.

  The signal characteristics of the optical information recording medium 30 were measured using a Pulse Tech BD evaluation machine (DDU-1000), a Pulse Tech BD evaluation signal detector, and a Pulse Tech time interval analyzer TA720. Note that the reproducing optical system described in the BD evaluation note has a reproducing light wavelength of 405 nm and a numerical aperture of 0.85.

  The i-MLSE (Maximum Likelihood Sequence Estimation) described in FIG. 7 is an evaluation index generally used when evaluating signal reproduction characteristics in an optical information recording medium recorded at a high recording density. The smaller the i-MLSE, the better the signal reproduction characteristics of the optical information recording medium. Jitter is an evaluation index generally used when evaluating signal reproduction characteristics in an optical information recording medium recorded at a recording density lower than i-MLSE. The smaller the Jitter, the better the signal reproduction characteristics of the optical information recording medium.

  As shown in FIG. 7, in the optical information recording media 10 and 20 which are super-resolution media, the same signal reproduction characteristics were obtained with or without applying high frequency superposition to the laser diode drive current. In other words, regardless of the structure of the information layer and the difference in recording density, when reproducing a super-resolution medium, reproduction is performed using DC reproduction output light without applying high-frequency superposition. It turned out to be enough.

  On the other hand, in the optical information recording medium 30 that is not a super-resolution medium, the jitter is reduced by applying high frequency superposition to the drive current of the laser diode. That is, the signal reproduction characteristic of the optical information recording medium 30 that is not a super-resolution medium is improved by using high-frequency superposition.

  As described above, signal reproduction characteristics are improved by using high-frequency superposition when reproducing a normal optical information recording medium. On the other hand, when reproducing the super-resolution medium, even if the DC reproduction output light is used without using the high frequency superimposition, the reproduction signal characteristics equivalent to those using the high frequency superimposition can be obtained.

  High-frequency superposition instantaneously generates a large laser beam output as a characteristic. That is, in high frequency superimposition, a current obtained by superimposing a high frequency current on a DC current is used as a laser diode drive current. Therefore, in the high frequency superposition, there is a moment when the laser diode is driven with a larger driving current than in the case where only the DC current is used as the driving current, and this increases the power consumption when reproducing the super-resolution medium. To do.

  In this demonstration test, when the super-resolution medium was reproduced using only the DC reproduction output light, the same signal reproduction characteristics as those obtained using high frequency superposition were obtained. Therefore, when reproducing the super-resolution medium, power consumption when reproducing the super-resolution medium can be suppressed by not using high-frequency superposition. In addition, since the output of the laser light that is the reproduction output light can be suppressed to a low level, deterioration due to heat generation in the laser diode, the condensing optical system, and the light receiving element can be suppressed. This means that the life of the laser diode, the condensing optical system, and the light receiving element is extended, and as a result, the reliability of the reproducing apparatus 100 is improved.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  The present invention relates to a reproduction method and a reproduction apparatus that reproduces information recorded on an optical information recording medium with low power consumption and high reliability, and in particular, is shorter than the optical system resolution limit of the reproduction apparatus. The present invention can be suitably applied to an optical information recording medium in which information is recorded by a recording mark.

1, 10, 20, 30 Optical information recording medium 12, 22, 32 Substrate 13, 23, 33 Information recording layer 14, 24, 34 Translucent layer 100 Playback device 101 Spindle 102 Pickup unit (irradiation means)
103 pickup control unit 104 output control unit 105 reproduction control unit 106 clock generation unit 107 data reproduction unit 108 control unit

Claims (4)

A method for reproducing an optical information recording medium in which information is recorded with a recording mark shorter than the optical system resolution limit of the reproducing apparatus,
A reproduction method for reproducing information recorded on the optical information recording medium by reproduction light generated by a direct current. An optical information recording medium on which information is recorded by a recording mark group in which the average length of the minimum mark length and the minimum space length is shorter than 119 nm is used with an optical system having an objective lens numerical aperture of 0.85 and a reproduction light wavelength of 405 nm. Playback method,
A reproduction method for reproducing information recorded on the optical information recording medium by reproduction light generated by a direct current. A reproduction apparatus for an optical information recording medium in which information is recorded with a recording mark shorter than the optical system resolution limit of the reproduction apparatus,
A reproducing apparatus comprising irradiation means for irradiating information recorded on the optical information recording medium with reproduction light generated by a direct current. An optical information recording medium on which information is recorded by a recording mark group in which the average length of the minimum mark length and the minimum space length is shorter than 119 nm is used with an optical system having an objective lens numerical aperture of 0.85 and a reproduction light wavelength of 405 nm. A playback device for playback,
A reproducing apparatus comprising irradiation means for irradiating information recorded on the optical information recording medium with reproduction light generated by a direct current.

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