JP2663466B2 - Optical disk inspection method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting an optical disk which is suitably applied to, for example, a modulation degree of a magneto-optical disk. [Summary of the Invention] The present invention irradiates an optical disc with light emitted from a light source,
In a method of inspecting an optical disk in which a return light from the optical disk is received by a detector and an output signal of the detector is observed by an oscilloscope, the light emitted from the light source is intermittently stopped for a predetermined time, and the oscilloscope outputs a zero light level. The RF lamp system can be easily configured with an AC-coupled amplifier, and pinholes can be easily identified by displaying. [Prior Art] Items of inspection of an optical disk include a modulation degree of an address or a group, a reflectance, a common mode rejection ratio (in the case of a magneto-optical disk), a level of a reflected light amount, a pinhole, a defect, and the like. Conventionally, these inspections are performed using an inspection device having the same configuration as that of the optical disk player. [Problems to be Solved by the Invention] In the inspection of the degree of modulation, the reflectance and the like, it is necessary to compare the absolute values from the zero light level, so that the RF amplifier system needs to be constituted by a DC-coupled amplifier. However, for example, in order to accurately observe the degree of groove modulation, the RF amplifier system must have a wide band.However, such a wide band type is easily configured by an AC couple, and a DC couple is difficult to configure. there were. An object of the present invention is to eliminate the above-mentioned inconvenience in consideration of such points. [Means for Solving the Problems] The present invention irradiates the optical disc (9) with light emitted from the light source (4), and returns the returned light from the optical disc (9) to the detectors (13A) (13B) (20). ), The output signals of the detectors (13A), (13B), and (20) are observed by an oscilloscope (18). By stopping, the reference level on the oscilloscope (18) is set. [Operation] As described above, by intermittently stopping the light emitted from the light source for a predetermined time, a zero light level is displayed on the oscilloscope (18). Therefore, even if the RF amplifier system is configured by an AC-coupled amplifier, a zero light level can be obtained. Further, it is easy to identify a pinhole whose reflected light level is substantially the same as the zero light level. Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an optical disk inspection apparatus used in this embodiment. In the figure, (1) is an oscillator, and a frequency signal of, for example, 80 MHz is generated from the oscillator (1). In this case, this frequency signal is intermittently turned off by a user operation. For example, 3 at 12.5 msec cycle
It is turned off for μsec. That is, the off period is set to such an extent that the servo system is not affected, and the on / off period is set to an order that can be reproduced with sufficient frequency characteristics. The frequency signal from the oscillator (1) is supplied to a pulse generator (2)
Is supplied to a laser diode (4) via a drive circuit (3), and the laser diode (4) is pulse-driven. In this case, when the frequency signal from the oscillator (1) is intermittently turned off, the laser light generated from the laser diode (4) is also intermittently turned off for a predetermined time. The laser light from this laser diode (4)
After being collimated by the collimator lens (5), the light is emitted to the recording surface (9a) of the magneto-optical disk (9) via the beam splitters (6) and (7) and the objective lens (8). The reflected light from the magneto-optical disk (9) is incident on a beam splitter (7) via an objective lens (8), and the laser beam whose optical axis direction has been changed by the beam splitter (7) is one beam. The polarization plane is rotated by 45 degrees by the half-wave plate (10), is incident on the polarization beam splitter (11), and is separated into polarization components having polarization planes orthogonal to each other. The polarization component having one polarization plane whose optical axis direction can be changed by the polarization beam splitter (11) is irradiated to a photodetector (13A) constituted by, for example, a PIN photodiode via a light receiving lens (12A). On the other hand, the polarization component having another polarization plane that has passed through the polarization beam splitter (11) without changing the optical axis direction passes through the light receiving lens (12B) after the optical axis direction is changed by the mirror (14). For example PIN
Photodetector composed of photodiodes (13
B) is irradiated. The output signal of the photodetector (13A) is supplied to an adder (16) and a subtractor (17) via an amplifier (15A), and the output signal of the photodetector (13B) is added via an amplifier (15B). Unit (16) and subtractor (17)
Supplied to And an adder (16) and a subtractor (17)
Are supplied to the input terminals of the oscilloscope (18). The laser light that has passed through the beam splitter (7) without changing the optical axis direction is incident on the beam splitter (6), and the laser light whose optical axis direction has been changed by the beam splitter (6) is condensed. The signal is supplied to a four-divided photodetector (20) for obtaining a servo signal via a lens (25) and a cylindrical lens (19). 4
A tracking error signal is formed by the push-pull method from an output signal of each of the divided detector units, and a focus error signal is formed by the astigmatism method. The first and second detection signals Sa and Sb for obtaining a tracking error signal by the push-pull method obtained from the photodetector (20) are added to an adder (22) via amplifiers (21a) and (21b), respectively. And a subtractor (23). The output signal of the adder (22) and the output signal of the subtractor (23) (tracking error signal by the push-pull method) are supplied to the input terminals of the oscilloscope (18), respectively. (24) indicates a spindle motor, and (30) indicates an optical pickup. In the example of FIG. 1, the magneto-optical disk (9) includes:
As shown in FIG. 2, a track T is formed in a spiral shape, and data is recorded along the track T. Each track T is divided into a plurality of sectors S, and data is recorded for each sector S. Here, as shown in FIG. 3, each track T has a groove-like groove (31).
And a land (32) between two grooves (31)
In each sector S, the first part of the land (32) includes a sector mark (33) and an address (3).
4) is formed in a pit shape. The portion without the groove (31) is called a mirror surface (35). In the above configuration, the focus, tracking, and slide servos are turned on and the still state (track T
A state in which a track jump is made for each lap to play.
The frequency signal from the oscillator (1) is intermittently turned off, and the laser light generated by the laser diode (4) is also intermittently turned off.
Observing the output signal of 6) with an oscilloscope (18),
The oscilloscope (18) displays a waveform as shown in FIG. FIG. 5 is a partially enlarged view. Although not described above, actually the fifth
As shown in the figure, a VFO signal indicating the shortest pit is recorded. A clock is formed by the VFO signal, and the address and data are reproduced by the clock. From this waveform, the total light amount _IO is obtained by measuring the light amount on the mirror surface (35). That is, the total light amount I _O is
It is obtained from the level difference between the zero light level and the mirror surface level. Further, the reflected light amount I _TOP corresponding to the land (32) is obtained from the level difference between the zero light amount level and the land level. When only the focus servo is turned on and the tracking servo is turned off and the output signal of the adder (16) is observed with an oscilloscope (18), the oscilloscope (18) has a waveform as shown in FIG. Is displayed. From this waveform, the amount of reflected light I _GR in the groove (31) can be obtained from the level difference between the zero light amount level and the groove level. Then, from the above I _O , I _TOP and I _GR , the degree of groove modulation (I _TOP −I _GR ) / I _O is obtained. Further, the amplitude I _SM corresponding to the sector mark (33) is obtained from the waveform of FIG. 5, and the sector mark modulation degree I _SM / I _O is obtained from I _SM and I _O. From the waveform of FIG. 5, the amplitude I corresponding to the VFO signal
_VFO is determined, from the I _VFO and I _O, the VFO signal modulation I _VFO
/ _IO is required. Further, the focus, tracking, and slide servos are turned on to set a still state, and the laser light generated by the laser diode (4) is set to be turned off intermittently. When observed in (18), a waveform as shown in FIG. 7 is displayed on the oscilloscope (18). In this case, unlike the example in FIG. 4, the level becomes small, so that the mirror surface level cannot be read. Therefore, the total light quantity I _O 'is obtained by _obtaining the reflected light quantity I _TOP ' corresponding to the land (32). In this case, the reflected light amount I _TOP 'corresponding to the land (32) is obtained from the level difference between the zero light amount level and the land level. Then, from I _TOP ′, I _TOP and I _O , I _O ′ = I _TOP ′ · I
_O / I _TOP is required. When the output signal of the subtracter (23), that is, the tracking error signal by the push-pull method is observed by the oscilloscope (18) in the same state, a waveform as shown in FIG. 8 is displayed on the oscilloscope (18). You. The push-pull amount _IPP is obtained from this waveform. And I _PP and
I _O 'than I _PP / I _O' is obtained. Also, the focus, tracking, and slide servos are turned on to set a still state, and the laser light generated by the laser diode (4) is set to be turned off intermittently. When observed in (18), a waveform as shown in FIG. 9 is displayed on the oscilloscope (18). From this waveform, the level difference ΔBF between the difference signal and the zero light level is obtained. Then, the common-mode rejection ratio CMRR is obtained as CMRR = −20 log | ΔBF / I _O |. In addition, by displaying the display as shown in FIG. 4 and observing a change in the amount of reflected light on the mirror surface in the same track, the reflectance unevenness and the like can be obtained. In this case, when the amount of reflected light fluctuates as shown in FIG. 10, when the maximum value is I _MAX and the minimum value is I _MIN , the reflectance unevenness ΔR is Is required. Further, the average value R of the reflected light amount is obtained as follows: = (I _MAX + I _MIN ) / 2 When the focus, tracking, and slide servos are turned on to set a still state, and the laser beam generated by the laser diode (4) is made continuous, the output signal of the adder (16) is observed with an oscilloscope (18). In (18), a waveform as shown in FIG. 11 is displayed. From this waveform, it is observed that defects such as scratches and dust are present on the surface of the substrate at points P and Q, and that a pinhole is present at point R. In this case, since the pinhole has a substantially zero light level, the laser light generated by the laser diode (4) is intermittently turned off and the zero light level is displayed as shown by the broken line in FIG. Can be confirmed. Although detailed description is omitted, an adder (1
6) Check for dropout from output signal, subtractor (1
Inspection of polarization defect can be performed from the output signal of 7). Thus, according to this example, the laser diode (4)
The intermittently turning off the laser light from the camera and displaying the zero light level on the oscilloscope (18) to inspect the magneto-optical disk. The RF amplifier system can be easily configured with an AC-coupled amplifier. Can be. In addition, since the light amount zero level is displayed on the oscilloscope (18) to inspect the magneto-optical disk (9), it is easy to identify the pinhole. In addition, an inspection such as a common-mode rejection ratio requiring a reference level can be accurately performed. In the above embodiment, the magneto-optical disk (9)
Although the inspection example described above is shown, inspection of other optical disks can be performed in the same manner. According to the above-described embodiment, the oscillator (1) outputs, for example, a signal in which a frequency signal of 80 MHz is intermittently turned off, but a DC signal, not a frequency signal, is intermittently turned off. May be output. [Effects of the Invention] According to the present invention described above, the light emitted from the light source is intermittently stopped for a predetermined time, and the oscilloscope is displayed with the zero light level for observation.
It has the advantage that it can be easily configured with a couple of amplifiers, and the pinhole can be easily identified. Further, an inspection requiring a reference level can be performed accurately.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an example of an inspection apparatus used in one embodiment, FIGS. 2 and 3 are diagrams for explaining a magneto-optical disk, and FIGS. FIG. 11 is a diagram showing a display waveform of the oscilloscope. (1) is an oscillator, (4) is a laser diode, (9)
Is a magneto-optical disk, (13A), (13B) and (20) are photodetectors, and (18) is an oscilloscope.

Claims (1)

(57) [Claims] In an optical disk inspection method, light emitted from a light source is irradiated onto an optical disk, return light from the optical disk is received by a detector, and an output signal of the detector is observed by an oscilloscope. A method for inspecting an optical disk, wherein a reference level on the oscilloscope is set by stopping the optical disk for a predetermined time.