JP2653105B2 - How to measure a wobbling truck - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a measuring method suitable for measuring a wobbling amount of a wobbling track preformatted on a recordable optical disc or the like.

[Summary of the Invention]

In the present invention, for example, a wobbling group is formed in order to measure wobbling of a wobbling track formed on an optical disc capable of writing information in response to light by an electrical detection method. A laser beam is applied to the optical disk, and the levels of a wobbling signal and a traverse signal (tracking error signal) output when the beam crosses a track are detected from the reflected light. And the above 2
Normalized ratio of two output levels Wobbling value (NWS)
The actual wobbling amount is obtained from this value.

[Conventional technology]

2. Description of the Related Art A recording type optical disc is known in which information is recorded by modulating a laser beam based on recording information and irradiating the laser beam to an optical disc whose reflectance or the like changes in response to light.

In such a recordable optical disk, a spiral group (groove) is preformatted in advance by embossing or the like in order to irradiate a laser beam onto a spiral track.

In addition, the spiral groove is subjected to wobbling, and the period of the wobbling is FM (frequency) modulated by data of an absolute time so that an absolute address on a disk can be detected. ing.

Wobbling of wobbling groove, for example, the track pitch are the ± 30 nm about the time of 1.6 [mu] m, wobbling period as the pickup does not respond directly, for example, a frequency-modulated wave of the spatial frequency 22.05KH _Z It is set to be.

In such a writable optical disk, if the wobbling amount of the track is appropriate, the dot information recorded in the track can be reproduced with high reliability, but if the wobbling amount is ± 10% or more of the track pitch. The fluctuation of the reproduction RF signal increases, and the recording / reproduction characteristics deteriorate depending on the optical disk device.

Therefore, in order to inspect whether or not the wobbling amount of the optical disc is set within a certain range, conventionally, a sample product of the optical disc was directly photographed by an electron microscope or the like, and the wobbling amount was measured. .

[Problems to be solved by the invention]

However, in order to take a group photo of the recording surface with an electron microscope, it is necessary to destroy the optical disk, take out a small piece of material, apply metal sputtering to this small piece of material, and make a material that can be inspected with a microscope. However, there has been a problem that the measuring operation becomes complicated.

Furthermore, the wobbling amount is 1.6μ track pitch.
Since the distance is set to about ± 30 nm with respect to m, it is extremely difficult to actually measure the wobbling amount, and there is a problem that it is not easy to evaluate the quality of the optical disk.

[Means for solving the problem]

SUMMARY OF THE INVENTION The present invention has been made in view of such a problem. When an optical disk under test is set in a player, an output level of a wobbling signal which can be obtained in a normal tracking state, and when the tracking off state is set. The normalized wobbling value (NWS) that can normalize the wobbling amount is detected by comparing the output level of the tracking error signal that is output to the microcomputer, and the actual wobbling amount is calculated from the NWS. It is made possible.

[Action]

It was confirmed by simulation that the normalized wobbling value (NWS) was almost proportional to the amount of wobbling without being affected by the groove shape of the groove or the reproducing optical system.

Therefore, this normalized wobbling value (hereinafter, NW
The wobbling amount can be evaluated based on the S value, and the actual wobbling amount can be measured from the NWS value.

〔Example〕

Figure 1 is shows a part of a wobbling track for explaining a method of measuring the wobbling tracks of the present invention, Waugh Brin group G _W that is pre-formatted on the recording surface of the optical disc D, for example, pitch
Q, its depth is d, and the amount of wobbling is W.

The wobbling amount W is, for example, frequency-modulated at a frequency of 22.05 KHz, and records the absolute time of a groove on a disk.

Wobbling groove G _W of such an optical disc
The laser spot P _S which is irradiated on the recording surface moves in the circumferential direction (arrow A) along the groove in a state where the tracking is turned on (the disc rotates), wobble signal I _W is, for example, It can be detected by a detector using the push-pull method.

However, the wobble signal I _W is and sensitivity of the reproducing optical system, the shape of the groove, for influenced by the reflectivity of the recording surface, it can not be said that shows the wobbling amount W of the groove.

Therefore, in the measuring method of the wobbling track of the present invention, at the same time to detect the wobble signal I _W described above, the tracking error signal when the reproducing optical system (optical head) is moved in the radial direction of the disk (arrow B) ( Traverse signal) | I _T |.
The ratio of I _W / | I _T | is defined as a normalized wobbling value (Normzlized Wobble Signal) NWS, and the wobbling amount W is calculated based on the normalized wobbling value.

That is, the traverse signal wobbling signal I _W
By dividing by | I _T |, the wobbling information which is free from the influence of the reproducing optical system and the influence of the groove shape, the reflectance, etc. and depends only on the wobbling amount is obtained.
This is a normalized wobbling value (NWS value).

The actual wobbling amount W is determined by setting the track pitch to Q,
If the traverse signal I _T to a sine wave may be calculated to △ A from the first view of signal waveforms. That is, By obtaining the NWS value (I _W / I _T ) from the detection signal of the reproduction optical system, △ A, that is, the wobbling amount W can be obtained by the Sin approximation.

FIG. 2 shows a reproduction optical system in which the wavelength λ = 780 nm, the NA of the objective lens is 0.5, the NA of the collimation lens is 0.3, the laser diffusion angle θ of the laser emission source is 27.0 ° in the circumferential direction and 18.3 ° in the radial direction. The NWS value of the sample disk (● □ ○) where the groove groove shape is type 1 to type 3
The values were obtained by simulation.

From this graph, it was confirmed that the optical disks having the same wobbling amount show the same NWS value in all the sample disks (● □ ○).

FIG. 3 is a block diagram showing one embodiment of the measuring method of the present invention.

The optical disk D to be measured is irradiated with a laser beam LB from the reproduction optical system 1.

The reproducing optical system 1 including the light emitting diode LD, the lenses L1 and L2, the deflecting beam splitter BS, and the push-pull detector PPD is in a state of moving (tracking off) in the radial direction of the optical disk.

The output of the push-pull detector PPD is input to the differential amplifier 10, to detect the tracking error signal component (I _T component) and wobble signal component (I _W component).

11, for example, indicates the bandpass filter 10～30KH _Z, detects the wobble signal I _{W (22.05KHz).}

Further, 12 denotes a low-pass filter cutoff frequency is a 5 KHz, and outputs only the traverse signal I _T which is output when the reproduction optical system 1 is moving.

Wobble signal I _W, and the traverse signal I _T is input to an effective value converter circuits 13 and 14, is supplied to a dividing circuit 15.

The NWS value is output from the division circuit 15, and the NWS value is input to the next arithmetic circuit 16 and converted into the wobbling amount W based on the above-mentioned equation (1).

Further, the NWS value can be observed by the monitor CRT17.

Note that a peak / peak value detection circuit can be used instead of the effective value conversion circuits 13 and 14.

The measurement method bandpass filter 11 of the above embodiment, wobble signal I _W by the low-pass filter _12, and is configured so as to detect a traverse signal I _T, the reproducing optical system, i.e., applying the tracking servo in the optical pickup by detecting only the wobble signal I _W, or may be detected traverse signal I _T by turning off the tracking servo of the same optical pickup.

Although the above embodiment has been described with respect to an optical disc in which a wobbling groove is formed for wobbling a track, the present invention is also applicable to an optical disc in which wobbling information is added to a track by wobbling pits. It goes without saying that a wobbling track measurement method can be used.

〔The invention's effect〕

As described above, the method of measuring a wobbling track according to the present invention detects a laser beam applied to an optical disc and detects a wobble signal and a traverse signal from the laser beam, thereby obtaining a normalized value of the wobble amount. Is detected, so that there is an effect that it is possible to omit a complicated operation such as destroying an optical disk to be measured and observing it with a microscope as in the related art.

In addition, a delicate wobble amount can be detected on the order of nm, and there is an advantage that quality control of a recordable optical disk can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining the measuring method of the present invention, FIG. 2 is a graph showing a simulation of measured data, and FIG. 3 is a block diagram showing an outline of the measuring method. In the figure, D is the measured optical disc, G _W is wobbling groove, I _W is wobble signal, I _T is the traverse signal, W is wobbling amount, 1 reproduction optical system, 10 is a differential amplifier, 11 a band A pass filter, 12 is a low-pass filter, 13 and 14 are effective value circuits, 15 is a division circuit, and 16 is an arithmetic circuit.

Claims (2)

(57) [Claims] A laser beam is applied to a recording surface of an optical disk to be measured, on which a wobbling track is formed, and an output signal of a detector for detecting the reflected light is supplied to a band-pass filter so that a wobbling signal is obtained. The output level (I _W ) is detected, and the output signal of the detector is supplied to a low-pass filter to detect a traverse signal. The output level of the wobbling signal (I _W ) and the output level of the traverse signal (I _T ) are detected. A wobbling track measuring method, wherein a wobbling amount of a track is calculated by using a ratio of output levels as a normalized wobbling value. 2. A laser beam applied to an optical disk to be measured on which a wobbling track is formed is detected as a wobbling signal (I _W ) by a reproduction optical system in a tracking-on state, and the reproduction optical system is used. By turning off the tracking of the system, the traverse signal (I _T ) is detected, and the wobbling signal (I _T ) is detected.
_W ) and the output level of the traverse signal (I _T ) are used as normalized wobbling values to detect the wobbling amount of the track.