JP2671437B2 - Measuring method of track pitch unevenness - Google Patents

Description

The present invention relates to a track pitch unevenness measuring method suitable for measuring pitch unevenness of tracks pre-formatted on a recordable optical disk or the like. .

[Summary of the Invention]

The present invention measures the pitch unevenness of tracks pre-formatted on an optical disc capable of writing information in response to light by an electrical detection method. Therefore, two lasers separated by a track pitch are used. An optical system capable of irradiating a beam on the optical disc to be measured and detecting the reflected light by the two photodetectors is provided. When the optical system is in the tracking state, a wobble signal (ΔW ₁ , Δ
W ₂₎ and detects a traverse signal optical system is output when the tracking OFF state (I _T), The pitch unevenness of the track can be evaluated by calculating

[Conventional technology]

2. Description of the Related Art There is known a recordable optical disc in which information can be recorded by modulating a laser beam on the basis of recording information and irradiating the optical disc on which the reflectance or the like changes in response to light.

In such a recording type optical disc, the spiral groove is pre-formatted by embossing or the like in order to irradiate the spiral track with the laser beam.

It is also known that the spiral groove is subjected to wobbling and the wobbling frequency is FM-modulated by the absolute time data so that the absolute address on the disk can be detected.

The wobbling amount of the wobbling groove is, for example, about ± 30 nm when the track pitch is 1.6 μm, and the wobbling period is such that the tracking tracking servo of the pickup does not directly respond, for example, the spatial frequency is 22.05 KH _Z. It is set to be a frequency modulated wave.

With such a writable optical disc, if the wobbling amount is appropriate, the dot information recorded in the track can be reproduced with high reliability, but if the wobbling amount is ± 10% of the track pitch, it will be reproduced. The fluctuation of the RF signal increases, and the recording / reproducing 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. .

However, in order to take a picture of the groove on the recording surface with an electron microscope, it is necessary to destroy the optical disk, take out a small sample, and subject the small sample to metal sputtering to create a material that can be inspected by a microscope. However, there is a problem that the measurement work 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.

Therefore, in order to solve the above-mentioned problems, the present applicant sets the optical disc under test in the player and sets the output level of the wobbling signal obtained in the normal tracking state and the tracking off state. We proposed a method for detecting the normalized wobbling value (NWS) that can normalize the wobbling amount by comparing the output levels of the tracking error signals output to the above (Japanese Patent Application No. 63-147952).

FIG. 4 shows a part of a wobbling track for providing such a wobbling track measuring method. The wobbling group G _W preformatted on the recording surface of the optical disc D is, 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 KH _Z , and is used to record the absolute time of the groove on the disk.

Such optical disc wobbling groove G
_{When the} laser spot P _S irradiated on the recording surface moves in the circumferential direction (arrow A) along the groove with the tracking turned on (the disc rotates), a wobbling signal with a sinusoidal waveform is generated. I _W can be detected, for example, by a director using the push-pull method.

However, since the level of the wobbling signal I _W depends on the sensitivity of the reproducing optical system, the shape of the groove, the reflectance of the recording surface, etc., it cannot be said that the wobbling amount W of the groove is shown as it is.

Therefore, in the method of measuring the wobbling track proposed by the applicant, the tracking when the reproducing optical system (optical head) moves in the radial direction (arrow B) of the disk at the same time as detecting the wobbling signal I _W described above. The error signal (traverse signal) | I _T | is detected and the ratio of I _W / | I _T | is normalized by the normalized wobble sign.
al) NWS, which is the standard for wobble calculation based on this normalized wobbling value. Then, when the wobble amount ΔA is small, from the waveform diagram of FIG. And can be obtained by the Sin approximation.

[Problems to be solved by the invention]

By the way, the wobble amount in each track of the optical disk is measured by such a method, and even if the range of the wobble amount is equal to or less than the reference value in each track, there is a large unevenness in the pitch interval of the spiral cracks. When an optical disc is played back, the signals recorded on the adjacent tracks are output as crosstalk, and the S /
There is a problem of degrading N.

[Means for solving the problem]

The present invention has been made in view of the above problems, and utilizes the method of measuring the wobble amount described above for the difference in the wobble amount of the tracks detected by the two laser beams that are substantially separated by the track pitch interval. It is intended to detect and measure the track pitch unevenness.

[Operation] Since the optical disk to be measured is simultaneously irradiated with two beams separated by a track pitch, the laser beams reflected from the optical disk to be measured are respectively detected by two photodetectors. The wobble amount can be detected simultaneously from the adjacent tracks, and the ratio of the wobble amount difference signal and the traverse signal at the time of tracking off is taken to determine the disc reflectivity and the groove shape. It is possible to obtain a measured value that can evaluate track pitch unevenness regardless of the above.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of a method for measuring track pitch unevenness according to the present invention.
Is symmetric with the pre-formatted wobbling groove.

In FIG. 1, an optical disc to be measured (hereinafter, simply referred to as a disc) D which is rotated by a spindle motor (not shown) is irradiated with two laser beams from the optical system 1.

The optical system 1 includes a light emitting diode LD and this light emitting diode.
A diffraction grating G (grating) that divides the laser light emitted from the LD into three spots is provided.
+ _1st- order light and −third-order light (which suppresses 0th-order light) generated by the lens L ₁ , the deflection beam splitter BS, and the objective lens L ₂
The two laser beams are separated from each other by a track pitch and are irradiated onto the disk D. Further, the two light beams P ₁ and P ₂ reflected from the disk D are split light reception of two push-pull detectors PPD ₁ and PPD ₂ (hereinafter referred to as directors PD ₁ and PD ₂ ) as shown in the figure. It is configured to be located at the center of the parts A, A'and B, B '.

Then, the first detector PD ₁ and the second detector P
The outputs of the light receiving portions A, B and A ', B'of D ₂ are input to the differential amplifiers 10A, 10B, respectively, and the deviation of the laser beam from the track center is detected. 11A and 11B are bandpass filters having the wobbling frequency of the track as the center frequency, and the bandpass filters 11A and 11B may be omitted for a disk where the measurement track is not wobbled.

12A and 12B are effective value output circuits, and 13A and 13B are division circuits.

The output of the other differential amplifier 10B is fed back via the servo circuit 20 and the switch S for tracking the optical system 1, and at the same time, via the low pass filter 14, the optical system 1 is in the tracking-off state. The output traverse signal I _T is detected and supplied to the effective value output circuit 15.

Reference numeral 16 is a memory circuit capable of storing the output value of the RMS value output circuit, which stores the peak-peak value or the RMS value of the error signal when the optical system 1 is not tracking, and stores the stored signal. The value can be output at the time of measurement. Reference numeral 17 is a differential amplifier, 18 is a signal monitoring circuit, and 19 is a display section.

Reference numeral 20 denotes a servo circuit for the optical system 1, and this servo circuit is formed so as not to respond to the wobbling frequency.

In the track pitch unevenness measuring method of the present invention, when the reflected light of the laser beam output without tracking the optical system ₁ is received by the detector PD ₁ in the circuit configuration as described above, the above-mentioned first method is used. Four
As shown in the figure, the traverse signal I _T output by the eccentricity of the disk D is input from the differential amplifier 10B to the low pass filter 14 and supplied to the effective value output circuit 15. The output signal I _T during the traverse is held in the memory circuit 16.

Next, when the switch S is turned on, the optical system 1 is brought into a tracking state by the tracking error signal output from the differential amplifier 10B, and the traverse signal is not output. Then, in this state, the tracking error signal of the detector PD ₁ detecting the laser beam reflected from the disk D causes the laser beam LB ₁ to rotate on one track T ₁ as shown in FIG. Tracking is done as if it were on center C ₁ .

In this tracking state, the two laser beams LB ₁ and LB ₂ are generated by the wobbling formed on the track.
The wobbling signals I _W1 and I _{W2 for} are extracted by the band-pass filters 11A and 11B, and the effective value output circuits 12A and 1
Supplied to 2B.

Then, the signal ( _IT ) of the memory circuit 16 in which the value obtained by detecting the traverse signal by the division circuits 13A and 13B is held.
When divided by, the normalized wobble amount is detected from each of the division circuits 13A and 13B as described with reference to FIG. That is, the laser beam LB ₁
There wobble amount [Delta] W ₂ of the track T ₂ adjacent to the wobble amount [Delta] W ₁ and track T ₁ of the track T ₁ being irradiated is detected.

By the way, the wobble amounts ΔW ₁ and ΔW ₂ are equal to ΔW when the laser beams LB ₁ and LB ₂ which are separated by a track pitch Q as shown in FIG. ₁ ≈ ΔW ₂ , and the output of the operational amplifier 17 which calculates the difference output becomes almost 0.

However, due to track pitch unevenness, the track pitch Q between adjacent tracks T _{1 and} T ₂ is
When Q'is larger, the untracked laser beam LB ₂ deviates from the center C ₂ of the track T ₂ , so the director PD ₂ detecting the reflected light of this laser beam LB ₂ The output wobble amount ΔW ₂ is larger than the wobble amount ΔW ₁ detected by the track T ₁ , and the output of the differential amplifier 17 is increased.

Similarly, even at a point where the track pitch Q is shorter than the reference value due to track pitch unevenness, ΔW ₂ > ΔW ₁ is also detected.
The output of 17 becomes large.

Therefore, by measuring the output of the differential amplifier 17 by the display unit 19 or the signal monitoring circuit 18, it becomes possible to measure the position where the pitch unevenness occurs on the disk.

In the above embodiments, the case where the pregroove of the disc D is wobbled has been described.
It is needless to say that even if the wobbling is not formed in the pregroup of the tracks, the track pitch unevenness can be detected by this method.

However, in this case, the bandpass filters 11A and 11B are omitted, and the track pitch unevenness is detected as the wobble amount of the reduced frequency.

When a track is pre-formatted with sample pits, a circuit for sampling the sample pits can be provided to detect pitch unevenness between tracks as in the pre-group.

FIG. 3 shows a second embodiment of the present invention.
The same reference numerals as those in the figure indicate the same blocks.

In the second embodiment, since the difference between the wobbling signals I _W1 and I _W2 is directly detected by the operational amplifier 20 in order to detect the unevenness of the track pitch, one operational circuit 21
There is an advantage that can be done in.

〔The invention's effect〕

As described above, the measurement method of the track pitch unevenness of the present invention, a traverse signal I _T which is output when swinging the optical system, the reflected light of the two laser beams spaced apart by approximately the track pitch Is detected by a push-pull director or the like to detect the wobble amount, and the track pitch unevenness is detected by calculating these signal amounts. Therefore, all track pitch unevenness is evaluated by electronic circuit means. The inspection work becomes extremely easy.

In addition, since the wobble amount of the track is normalized by dividing it by the traverse signal, it is possible to accurately evaluate the track pitch unevenness without being affected by the variations in the depth and shape of the track groove and the reflectance of the disk. There is an effect that can be.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a method for measuring track pitch unevenness of the present invention, FIG. 2 is an explanatory view showing the relationship between a track groove and two laser beams, and FIG. 3 is a block showing another embodiment of the present invention. FIG. 4 and FIG. 4 are explanatory views showing the principle of measuring the wobble amount. In the figure, 1 is an optical system, 10A and 10B are differential amplifiers, 11A and 11B are bandpass filters, 12A and 12B are effective value output circuits, and 13A and 13B.
Indicates a division circuit.

Claims (1)

(57) [Claims] 1. An optical system having two optical detectors for irradiating an optical disc to be measured with two optical beam spots which are separated from each other by a track pitch and detecting reflected light thereof, and the two optical beams. A means for achieving tracking of the optical head by a tracking error signal of either one of the beam spots is provided, and when the optical system is tracked, the wobble amount of tracks (ΔW ₁ , ΔW) obtained from the two photodetectors. and a difference signal of _2), wherein the ratio of the level of the optical system tracking traverse signal obtained when you turn off the (I _T), the measuring method of the track pitch unevenness and detecting a track pitch unevenness.