Patent Publication Number: US-2007121438-A1

Title: Method of testing an optical information medium and optical information medium testing apparatus

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a method of testing an optical information medium and an optical information medium testing apparatus that test whether a fault is present on an optical information medium.  
      2. Description of the Related Art  
      One example of a method of testing an optical information medium is disclosed by Japanese Laid-Open Patent Publication No. H09-138979. In this method of testing an optical information medium, when carrying out an optical process (such as initialization) on the optical information medium, faults on the optical information medium are also detected using the light emitted in such optical process. In more detail, faults are detected using a focus error signal generated by calculations carried out on signals outputted from a light detector that has received the light. Accordingly, by using this method of testing an optical information medium, it is possible to detect localized faults such as localized deformation of the substrate of the optical information medium or streak-like faults in the hard coat layer reliably, accurately, and at effectively the same time as an optical process such as initialization. Also, since faults can be detected at the same time as the optical process, it is possible to simplify the apparatus and procedure.  
     SUMMARY OF THE INVENTION  
      However, by investigating the method of testing the optical information medium described above, the present inventors found the following problem. That is, in the method of testing an optical information medium described above, although there is a large change in the voltage of the focus error signal when the irradiation position of laser light outputted from an optical pickup passes directly above a fault such as a bubble or foreign matter on the optical information medium, thereby making it possible to detect such faults on the optical information medium, when the irradiation position of laser light passes close to but not directly above a fault, the change in the voltage of the focus error signal is extremely small. Accordingly, with this method of testing an optical information medium, there is the problem that it may not be possible to detect faults on an optical information medium where faults are not positioned at the centers of the tracks, for example.  
      The present invention was conceived in view of the problem described above and it is a principal object of the present invention to provide a method of testing an optical information medium and an optical information medium testing apparatus that can detect a fault on an optical information medium with higher reliability.  
      To achieve the stated object, a method of testing an optical information medium according to the present invention comprises comparing a voltage of a tracking error signal generated based on return light from the optical information medium received by an optical pickup and a reference voltage set in advance and judging that a fault is present on the optical information medium when the voltage of the tracking error signal is equal to or greater than the reference voltage.  
      According to this method of testing an optical information medium and an optical information medium testing apparatus described below, by judging that a fault such as a bubble or foreign matter is present on the optical information medium when the voltage of the tracking error signal generated based on return light from the optical information medium received by an optical pickup is equal to or greater than the reference voltage, it will be possible to reliably detect a fault such as a bubble or foreign matter in a light transmitting layer (formed by spin coating, for example) of the optical information medium even when the laser light passes over a deformed part in the periphery of the bubble or foreign matter without the laser light passing directly over or in close proximity to the bubble or foreign matter itself, thereby greatly improving the testing precision for the optical information medium.  
      Testing for the fault using the tracking error signal may be carried out at intervals of a predetermined number of tracks.  
      According to this method of testing an optical information medium and an optical information medium testing apparatus described below, since a deformed part present in a wide range in the periphery of a bubble or foreign matter in the light transmitting layer can be precisely detected on an optical information medium where such deformed part is present, it is possible to reliably detect a fault by testing only two tracks located at predetermined intervals that are sampled cut of a plurality of tracks present within a range of the size of the deformed part. Therefore, according to the method of testing an optical information medium and the optical information medium testing apparatus, since it is possible to test for a fault across the entire optical information medium by merely judging whether a fault is present at predetermined tracks set at intervals within the range of the size of the deformed part, the testing efficiency can be greatly improved.  
      Testing for the fault using the tracking error signal may be carried out on the optical information medium that has already been tested using an optical fault testing apparatus.  
      According to this method of testing an optical information medium, by testing for the fault using the tracking error signal on the optical information medium that has already been tested using an optical fault testing apparatus, testing using the tracking error signal will be carried out only on the optical information medium for which such testing is necessary, which makes it possible to significantly improve the efficiency of fault testing.  
      An optical information medium testing apparatus according to the present invention includes: an optical pickup that receives return light from an optical information medium and generates a tracking error signal; and a calculation control unit that compares a voltage of the tracking error signal and a reference voltage set in advance and judges that a fault is present on the optical information medium when the voltage of the tracking error signal is equal to or greater than the reference voltage.  
      The optical information medium testing apparatus may further include a feed mechanism that moves the optical pickup in a radial direction of the optical information medium, and may be constructed so that the calculation control unit controls the feed mechanism to move the optical pickup in the radial direction while judging whether the fault is present at intervals of a predetermined number of tracks.  
      It should be noted that the disclosure of the present invention relates to the content of Japanese Patent Application 2005-341968 that was filed on 28 Nov. 2005, the entire content of which is herein incorporated by reference. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      These and other objects and features of the present invention will be explained in more detail below with reference to the attached drawings, wherein:  
       FIG. 1  is a block diagram of an optical information medium testing apparatus;  
       FIG. 2  is a block diagram of a signal generating unit;  
       FIG. 3  is a graph where the voltage of a tracking error signal when laser light is incident on deformed parts of an optical information medium on an inner periphery side and an outer periphery side of a fault such as a bubble is expressed as a proportion of a peak value of the voltage that appears in the tracking error signal during a track jump;  
       FIG. 4  is a flowchart showing a testing process carried out by the optical information medium testing apparatus; and  
       FIG. 5  is a flowchart showing the fault testing process in  FIG. 4 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Preferred embodiments of a method of testing an optical information medium and an optical information medium testing apparatus will now be described with reference to the attached drawings.  
      First, the construction of an optical information medium testing apparatus  1  will be described with reference to the drawings. Note that as one example, the following describes an optical information medium testing apparatus  1  that tests for faults such as bubbles and foreign matter present in a light-transmitting layer of an optical information medium whose light-transmitting layer has been formed by spin coating.  
      The optical information medium testing apparatus  1  shown in  FIG. 1  includes an optical pickup  2 , a servo control unit  3 , an A/D converting unit  4 , a feed mechanism  5 , a spindle motor  6 , a calculation control unit  7 , a storage unit  8 , and an output unit  9 .  
      As shown in  FIG. 1 , the optical pickup  2  includes a laser diode  21 , a diffraction grating  22 , a beam splitter  23 , an objective lens  24 , a two-axis actuator  25 , a converging lens  26 , and a signal generating unit  27 , and is constructed to irradiate an optical information medium  10  with laser light, to receive return light from the optical information medium  10 , and to generate, based on the return light, an information signal S 3  for reproducing information recorded on the optical information medium  10  and also a focus error signal S 1  and a tracking error signal S 2  (see  FIG. 2 ). When doing so, the diffraction grating  22  divides the laser light emitted from the laser diode  21  into three beams (a main beam and two sub-beams) that are outputted to the beam splitter  23 . The main beam and the two sub-beams outputted from the beam splitter  23  are irradiated onto the optical information medium  10  via the objective lens  24 . The incident positions of one sub-beam, the main beam, and the other sub-beam are set so as to be arranged in the mentioned order in a direction substantially perpendicular to the track direction of the optical information medium  10 , that is, the beams are arranged in the radial direction of the optical information medium  10 . The two-axis actuator  25  is constructed of a well-known mechanism (such as an shaft sliding and rotating type actuator or a hinged actuator) and is equipped with a function for moving the objective lens  24  in the optical axis of the objective lens  24  based on an inputted focus control signal S 4  and a function for moving the objective lens  24  in a direction that is substantially perpendicular to the track direction of the optical information medium  10  based on an inputted tracking control signal S 5 .  
      As shown in  FIG. 2 , the signal generating unit  27  includes an optical detector  27   a  and a signal processing circuit  27   b . More specifically, as one example, the optical detector  27   a  includes four light-receiving elements (in the present embodiment, photodiodes, for example) Pa, Pb, Pc, and Pd. As shown in  FIG. 2 , the four photodiodes Pa, Pb, Pc, and Pd are disposed in the four corners of a virtual square. One side of the virtual square where the two photodiodes Pa and Pb are disposed is parallel to the direction that is substantially perpendicular to the track direction of the optical information medium  10  and another side of the virtual square where the two photodiodes Pa and Pd are disposed is substantially parallel to the track direction of the optical information medium  10 . The four photodiodes Pa, Pb, Pc, and Pd arranged in this way are constructed so as to receive return light for the main beam. Out of these photodiodes, the two photodiodes Pa and Pd are respectively capable of receiving return light for one out of the two sub-beams. The other two photodiodes Pb and Pc are respectively capable of receiving return light for the other of the two sub-beams. The photodiodes Pa, Pb, Pc, and Pd respectively Output currents Ia, Ib, Ic, and Id corresponding to the intensity of the received light. The signal processing circuit  27   b  receives an input of the currents Ia to Id outputted from the photodiodes Pa to Pd and generates the focus error signal S 1 , the tracking error signal S 2 , and the information signal S 3  based on the currents Ia to Id. More specifically, if the values of the currents Ia, Ib, Ic, and Id are expressed as “A”, “B”, “C”, and “D”, as one example, the signal processing circuit  27   b  generates the focus error signal S 1  by calculating (A+C)−(B+D), generates the tracking error signal S 2  by calculating (A+D)−(B+C), and generates the information signal S 3  by calculating (A+B+C+D).  
      The servo control unit  3  receives an input of the focus error signal S 1  and the tracking error signal S 2 , generates the focus control signal S 4  based on the focus error signal S 1 , and generates the tracking control signal S 5  based on the tracking error signal S 2 . The A/D converting unit  4  receives an input of the tracking error signal S 2  and converts the tracking error signal S 2  to error data D 1  showing the voltage of the signal S 2 . Under the control of the calculation control unit  7 , the feed mechanism  5  moves the optical pickup  2  in the radial direction of the optical information medium  10 . Under the control of the calculation control unit  7 , the spindle motor  6  rotates the optical information medium  10 .  
      The calculation control unit  7  includes a CPU, carries out a fault testing process for the optical information medium  10  based on the error data D 1  inputted from the A/D converting unit  4 , and also carries out control over the optical pickup  2 , the feed mechanism  5 , and the spindle motor  6 . In the fault testing process, the calculation control unit  7  tests for the presence of faults on the optical information medium  10  at predetermined intervals (for example, 500 μm) in the radial direction. During such testing, when the voltage V 1  of the tracking error signal S 2  shown by the error data D 1  is equal to or greater than a reference voltage Vr stored in the storage unit  8 , the calculation control unit  7  judges that a fault such as a bubble or foreign matter is present in the light transmitting layer of the optical information medium  10 . This is based on the following data produced by extensive research by the present inventors.  
      According to research carried out by the inventors, when a bubble or foreign matter is present in the light transmitting layer of the optical information medium  10  being tested by the optical information medium testing apparatus  1  (in particular, an optical information medium  10  where the light transmitting layer has been formed by spin coating), in the periphery of the bubble or foreign matter, there will definitely be a part where the light transmitting layer is deformed (hereinafter such parts are referred to as “deformed parts”). It is thought that when a bubble or foreign matter included in the resin used to form the light transmitting layer flows together with the resin during spin coating, the flow of the resin in the periphery of the bubble or foreign matter will be disturbed and the resin whose flow has been disturbed will become deformed, thereby forming a deformed part. This deformed part will have a size that is around ten to twenty times larger than the size of the bubble or foreign matter, and the thickness of the resin in the deformed part will become gradually thicker toward the bubble or foreign matter. Also, although the tracking error signal S 2  has a voltage waveform that is substantially flat in a normal state (i.e., in a state where the tracking error signal S 2  is generated based on return light from a light transmitting layer with no bubble or foreign matter), when the tracking error signal S 2  is generated based on return light from a deformed part, the voltage will greatly fluctuate in the same way as when the signal is generated based on return light from above the bubble or foreign matter itself. When the tracking error signal S 2  is fluctuating, the voltage V 1  thereof will increase as the size (for example, the diameter) of the bubble or foreign matter increases. When the voltage V 1  of the tracking error signal S 2  that is fluctuating due to a fault reaches a voltage peak value Vp that appears in the tracking error signal S 2  during a track jump (that is, when the voltage V 1  of the tracking error signal S 2  reaches 100% of the peak value Vp), tracking servo control by a normal recording/reproducing apparatus is disabled, which can hinder recording or reproducing operations. According to the inventors&#39; research, when the size (for example, the diameter) of the bubble or foreign matter is 40 μm or below, the tracking error signal will remain in a range where tracking servo control is not disabled (i.e., V 1 &lt;Vp). When the size of the bubble or foreign matter is such that the length in the radial direction of the optical information medium  10  is 40 μm, the deformed part will normally be around 500 μm long in the same direction.  
      As one example, when return light from a bubble with a diameter of around 43 μm and deformed parts of the optical information medium  10  on both the inner periphery and the outer periphery sides of the bubble is received by the optical pickup  2 , the fluctuation in the voltage V 1  of the tracking error signal S 2  when expressed as a proportion of the peak value Vp of the voltage of the tracking error signal S 2  during a track jump is shown in  FIG. 3 . Note that the horizontal axis in  FIG. 3  shows the displacement (distance) from the center of the bubble. As shown in  FIG. 3 , the voltage V 1  of the tracking error signal S 2  is around 20% or more of the peak value Vp across a wide range of around 600 μm to 650 μm that includes the bubble. The voltage of the tracking error signal S 2  reaches a maximum near the center of the bubble and has a maximum value that slightly exceeds the peak value Vp (the proportion described above is around 105%). Also, although not shown in the drawings, for a bubble whose diameter is around 40 μm, it was confirmed that the proportion described above of the voltage V 1  of the tracking error signal S 2  to the peak value Vp of the voltage V 1  is around 100% when return light is received by the optical pickup  2  from above the bubble and that the proportion is around 20% or more across a range of around 510 μm to 550 μm that includes the bubble. Accordingly, when testing for faults on the optical information medium  10 , by setting a voltage that is 20% of the peak value Vp of the voltage fluctuation that appears in the tracking error signal S 2  during a track jump as a reference voltage Vr and judging whether the voltage V 1  of the tracking error signal S 2  shown by the error data D 1  is equal to or greater than the reference voltage Vr, it is possible to reliably test whether a bubble or foreign matter with a size of 40 μm or larger, which is to be treated as a fault, is present by testing at predetermined intervals (500 μm) in the radial direction of the optical information medium  10 . In other words, faults can be found by “sampling” in the radial direction.  
      Note that although not shown in  FIG. 3 , when the return light from a bubble or the like is received by the optical pickup  2 , the voltage of the focus error signal S 1  also fluctuates. However, the voltage of the focus error signal S 1  greatly fluctuates only over the bubble itself and the periphery of the bubble, and such fluctuation suddenly decreases as the irradiation position of the laser light moves from the bubble or the like toward the inner periphery or the outer periphery of the optical information medium  10 . The reason why the tracking error signal S 2  greatly fluctuates over a wider range than the focus error signal S 1  is described below. The focus error signal S 1  shows the difference between the total of the currents A and C of the two photodiodes Pa, Pc disposed in opposite corners in the virtual square and the total of the currents B and D of the other two photodiodes Pb, Pd disposed in other opposite corners in the virtual square, and therefore is generated by calculation in a direction that cancels out any difference in the amount of light in the direction substantially perpendicular to the track direction of the optical information medium  10  (i.e., in the radial direction of the optical information medium  10 ). This means that when the irradiation position passes over a deformed part in the periphery of a bubble or foreign matter, even if the currents A, D of the photodiodes Pa, Pd positioned on the same side (the outer periphery side or the inner periphery side) of a track out of the photodiodes Pa, Pb, Pc, and Pd become larger or smaller relative to the currents B, C of the other photodiodes Pb, Pc due to changes in thickness of the light transmitting layer at the deformed part (i.e., due to the deformed part being slanted), the focus error signal S 1  generated by calculating (A+C)−(B+D) will not greatly fluctuate. On the other hand, since the tracking error signal S 2  shows the difference between the total of the currents A and D of the two photodiodes Pa, Pd positioned on the same side (the inner periphery side or the outer periphery side) of a track on the optical information medium  10  and the total of the currents B and C of the other two photodiodes Pb, Pc, the tracking error signal S 2  is generated by calculation in a direction that amplifies any difference in the amount of light in the direction substantially perpendicular to the track direction of the optical information medium  10 . This means that when the irradiation position passes over a deformed part in the periphery of a bubble or foreign matter, when the currents A to D of the photodiodes Pa to Pd have changed as described above due to the changes in thickness of the light transmitting layer at the deformed part (i.e., cue to the deformed part being slanted), the tracking error signal S 2  generated by calculating (A+D)−(B+C) will greatly fluctuate. Since the fluctuations in the tracking error signal S 2  when the irradiation position of the laser light passes the periphery of a fault such as a bubble are due to changes in the thickness of the light transmitting layer at the deformed part located in the periphery of the bubble or the foreign matter as described above (i.e., due to the deformed part being slanted), the fluctuations will resemble fluctuations that appear when the optical information medium  10  itself is tilted. Fluctuations in the tracking error signal S 2  due to tilting of the optical information medium  10  are normally corrected automatically when the optical information medium  10  is set in the optical information medium testing apparatus  1 . However, correction of tilting of the optical information medium  10  is carried out for the entire optical information medium  10  and is not a process carried out to correct localized faults such as bubbles. This means that even when tilting of the optical information medium  10  has been corrected, when the irradiation position of the laser light passes over a deformed part, a fluctuation of a level that can be used to detect the deformed part is produced in the tracking error signal S 2 .  
      Position information for a plurality of target tracks for which the fault testing process is carried out and the reference voltage Vr used in the fault testing process are stored in advance in the storage unit  8 . In the present embodiment, to test for the presence of faults such as bubbles with a diameter of around 40 μm, the positions of the target tracks for which the fault testing process is carried out are set at predetermined intervals (500 μm) based on the research described above. Also, data D 2  showing the test results of the fault testing process is stored by the calculation control unit  7  in the storage unit  8 . The output unit  9  is constructed of a display apparatus, for example, and displays the results of the fault testing process based on the data D 2  inputted from the calculation control unit  7 .  
      Next, a testing operation for the optical information medium  10  carried cut by the optical information medium testing apparatus  1  will be described with reference to the drawings.  
      First, when testing the optical information medium  10 , as shown in  FIG. 1 , the optical information medium  10  is loaded into the optical information medium testing apparatus  1 . By doing so, it becomes possible to rotate the optical information medium  10  using the spindle motor  6 .  
      Next, in an operating state of the optical information medium testing apparatus  1 , the calculation control unit  7  operates the spindle motor  6  to start rotation of the optical information medium  10 . Next, the calculation control unit  7  controls the optical pickup  2  to operate the laser diode  21 . By doing so, the laser diode  21  starts emitting the laser light, and the emitted laser light is irradiated onto the optical information medium  10  via the diffraction grating  22 , the beam splitter  23 , and the objective lens  24 . Part of the laser light reflected by the optical information medium  10  passes through the objective lens  24 , the beam splitter  23 , and the converging lens  26  to become incident on the signal generating unit  27  as return light. In the signal generating unit  27 , the optical detector  27   a  receives the return light, starts to generate currents Ia to If and the signal processing circuit  27   b  starts to generate the focus error signal S 1 , the tracking error signal S 2 , and the information signal S 3  based on the currents Ia to If.  
      Next, the calculation control unit  7  carries out the testing process shown in  FIG. 4 . As shown in  FIG. 4 , in this process, the calculation control unit  7  reads position information of the first target track on which the fault testing process is to be carried out from the storage unit  8  (step  51 ). Next, by controlling the feed mechanism  5  based on the position information, the calculation control unit  7  moves has the optical pickup  2  to a position above the target track (step  52 ). When moving the optical pickup  2 , the calculation control unit  7  moves the optical pickup  2  to a position over the target track by counting a number of track jumps based on the error data D 1 . When the movement of the optical pickup  2  has been completed, the servo control unit  3  generates the focus control signal S 4  and the tracking control signal S 5  based on the focus error signal S 1  and the tracking error signal S 2  outputted from the optical pickup  2  and thereby starts controlling the two-axis actuator  25 . By doing so, the distance between the objective lens  24  and the optical information medium  10  and the position of the objective lens  24  in a direction perpendicular to the tracks are finely adjusted by the two-axis actuator  25 , thereby achieving proper focus and tracking servo control.  
      Next, when the laser light from the optical pickup  2  is incident on the target track, the calculation control unit  7  carries out a fault testing process (step  53 ). As shown in  FIG. 5 , in the fault testing process, the calculation control unit  7  first calculates the voltage V 1  of the tracking error signal S 2  based on the error data D 1  (step  61 ). Next, the calculation control unit  7  reads the reference voltage Vr from the storage unit  8  and judges whether the calculated voltage V 1  of the tracking error signal S 2  is equal to or greater than the reference voltage Vr (step  62 ). When the result of this judgment is that the voltage V 1  of the calculated tracking error signal S 2  is below the reference voltage Vr, the calculation control unit  7  judges that there is no fault such as a bubble in a range of 500 μm in the radial direction that includes the present target track (step  63 ) and stores the result together with the position information of the track in the storage unit  8  as the data D 2  showing the test results. On the other hand, when the result of the comparison is that the calculated voltage V 1  of the tracking error signal S 2  is equal to or greater than the reference voltage Vr, the calculation control unit  7  judges that a fault such as a bubble is present in a range of 500 μm in the radial direction that includes the present track (step  64 ), and stores the result together with the position information of the track in the storage unit  8  as the data D 2 . The calculation control unit  7  carries out the process in one of steps  63  and  64  and then completes the fault testing process.  
      After the fault testing process has been completed, as shown in  FIG. 4 , the calculation control unit  7  judges whether the fault testing has been completed across the entire optical information medium  10  based, for example, on whether any untested target tracks remain in the storage unit  8  (step  54 ), and when the testing has not been completed, position information of the next target track is read from the storage unit  8  (step  55 ), the processing returns to step  52  described above, and the fault testing process continues on the optical information medium  10 . By repeatedly carrying out the steps  52  to  55  described above, the calculation control unit  7  carries out fault testing on every target track stored in the storage unit  8 . Finally, on judging in step  54  that the fault testing has been completed on every target track, the calculation control unit  7  reads the data D 2  showing the test results from the storage unit  8  and outputs the results to the output unit  9 , for example (step  56 ). In this embodiment, since the output unit  9  is constructed of a display apparatus, the output unit  9  displays the test results for every track subjected to testing, based on the inputted data D 2 . By doing so, the fault testing is completed for the optical information medium  10 .  
      In this way, according to the optical information medium testing apparatus  1  and the method of testing an optical information medium, by having the calculation control unit  7  judge that a fault such as a bubble or foreign matter is present on the optical information medium  10  when the voltage of the tracking error signal S 2  generated based on return light from the optical information medium  10  received by the optical pickup  2  is equal to or greater than the reference voltage Vr set in advance, it will be possible to reliably detect a fault such as a bubble or foreign matter in the light transmitting layer (formed by spin coating) of the optical information medium  10  even when the laser light passes over a deformed part in the periphery of the bubble or foreign matter without the laser light passing directly over or in close proximity to the bubble or foreign matter itself, thereby greatly improving the testing precision for the optical information medium  10 .  
      For an optical information medium  10  where a deformed part is present in a wide range in the periphery of a bubble or foreign matter in the light transmitting layer, by using the optical information medium testing apparatus  1  and the method of testing an optical information medium that use the tracking error signal S 2  to precisely detect such deformed part, it is possible to reliably detect a fault by testing only two tracks located at predetermined intervals that are sampled out of a plurality of tracks present within a range of the size of the deformed part. This means that by using the optical information medium testing apparatus  1  and the method of testing an optical information medium, since it is possible to test for a fault across the entire optical information medium  10  by merely judging whether a fault is present at predetermined tracks set at intervals within the range of the size of the deformed part, the testing efficiency can be greatly improved.  
      Note that the present invention is not limited to the construction described above. For example, it is also possible to carry out fault testing for the optical information medium  10  by combining the fault testing of the optical information medium  10  that uses the optical information medium testing apparatus  1  described above (i.e., fault testing that uses the tracking error signal S 2 ) and optical testing that is normally carried out by a conventional optical fault testing apparatus (for example, testing that uses the optical fault testing apparatus disclosed in Japanese Laid-Open Patent Publication No. 2001-241931). With this construction, first after optical testing has been carried out by the optical fault testing apparatus, fault testing of the optical information medium  10  is carried out using the optical information medium testing apparatus  1 . By carrying out fault testing on the optical information medium  10  in the mentioned order, it is possible to discard in advance optical information media  10  with large faults found by the optical fault testing apparatus. Although fault testing using the tracking error signal S 2  normally requires more time than an optical fault testing apparatus because the fault testing is performed by carrying out focus servo or tracking servo control on the optical information medium  10 , it is possible to properly test for smaller faults. Accordingly, by carrying out testing using the optical information medium testing apparatus  1  only on optical information media  10  for which such testing is necessary, it is possible to significantly improve the efficiency of fault testing.  
      Also, as one example, although an example has been described where the predetermined intervals between tracks to be tested are set at 500 μm in order to test for a fault such as a bubble with an external diameter of 40 μm or larger, it should be obvious that it is possible to set the predetermined intervals between the tracks to be tested in accordance with the size of the bubble and the like treated as a fault, such as by extending the predetermined intervals between the tracks to be tested to 600 μm when testing for a fault such as a bubble with an external diameter of around 43 μm or larger as shown in  FIG. 3 .  
      Although an example has been described where the object being tested is the optical information medium  10  where the light transmitting layer is formed by spin coating, the optical information medium testing apparatus  1  and the method of testing an optical information medium according to the present invention can be applied to testing for a fault in the light transmitting layer of an optical information medium where the light transmitting layer is formed by a method aside from spin coating.