JPH01150805A - Measuring instrument for groove shape of optical disk substrate - Google Patents

Abstract

PURPOSE:To obtain a more accurate groove shape by allowing the title instrument to have a function for measuring a reflected light on an optical disk substrate and detecting a camber angle of the substrate therefrom, and also, correcting a pitch calculating expression by using a result of measurement of this camber angle. CONSTITUTION:When an optical disk substrate 1 has no curvature (or has a camber angle psi), a reflected light beam which has been reflected by the reverse side of the substrate 1 (or 1') is fetched by a beam splitter 4 as indicated with a reflected light path 7 (or 7'), and radiated to the center [or a part shifted from the center by a distance (l) being proportional to the camber angle psiof the substrate 1'] of a linear image sensor 6. Accordingly, the camber angle psican be derived in reverse from the distance (l). In such a way, when the substrate has a curvature, an incident laser light beam is made incident diagonally against the substrate by the camber angle psi. Accordingly, an accurate groove shape can be derived by using a prescribed calculating expression in case of the camber angle psi instead of a prescribed calculating expression in which a vertical incidence has been supposed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical disc substrate groove shape measuring device having spiral or concentric signal recording guide grooves.

[Conventional technology].

Next, a conventional optical disk substrate and groove shape measuring device will be explained.

FIGS. 2(a) and 2(b) are a schematic diagram and an enlarged view of part A showing a conventional example.

The optical disk substrate groove shape measuring device shown in FIG. 2(a) is as follows:
A parallel laser beam generated by a laser light source 2 is irradiated perpendicularly to the optical disk substrate 1, and after the laser beam passes through the optical disk substrate 1, the intensity and direction of each order of diffraction light are measured by detectors 3a to 3e.

Regarding the relationship between the intensity of the diffracted light and the shape of the diffraction grating (corresponding to the groove shape of the optical disc substrate), relational expressions have been derived for various shapes of the diffraction grating. The groove shape of the optical disk substrate can be determined from the measurement results. f),' For example, the measurement result of the diffraction light is the 0th order diffraction light intensity measurement.

1st diffraction 1st order light intensity L (I+=I++=■-+), diffraction 2
Order light intensity I2 (I2=I+2=l-2).

Assuming that the angle formed by the 0th-order diffracted light and the 1st-order light is θ, and the groove shape is a rectangular groove, the pitch (P), width (W), and depth (D) of the groove are determined by the following equation (1) ~ It is obtained as shown in equation (3).

λ P knee (1) sin θ (λ: laser light wavelength), n:
Substrate ffi refractive index where 5inCX= , The drawback was that it did not take into account the effects of substrate warpage.

The incident angle of the laser beam on the substrate is the warp angle φ with respect to the designed incident angle.
This correction is necessary because a deviation will occur.

In addition, warpage of optical disc substrates cannot be avoided in practice, and the amount of warpage in optical disc substrates made by injection molding varies greatly depending on the molding conditions.
It is important to consider warpage.

[Means for solving problems]

The optical disc substrate groove shape measuring device of the present invention includes: a laser light source that generates collimated laser light; a detector that measures the intensity and direction of diffracted light generated when the optical disc substrate is irradiated with laser light from the laser light source; The direction of the reflected light on the optical disk substrate is measured, and the warp angle φ of the optical disk substrate is determined from the direction of the measured reflected light. In addition, when calculating the groove shape, a correction formula is used in which the incident angle of the laser beam is changed by the warp angle φ. [Embodiments] Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention.

The optical disk substrate groove shape measuring device shown in FIG. 1 allows collimated laser light generated from a laser light source 2 to enter an optical disk substrate 1 perpendicularly.

At this time, the laser beam is transmitted to the beam splitter 4. Ten wavelength plate 5
and enters the optical disc substrate 1.

The diffracted light is detected by diffracted light detectors 3a to 3e. Further, the reflected light reflected from the back surface of the optical disk substrate 1 passes through the ten-wavelength plate 5 again, and is transmitted to the beam splitter 4.
The light is then taken out and irradiated onto the linear image sensor 6.

Therefore, it has the advantage that most of the light returning to the laser light source is cut off.

In the above configuration, when the optical disc substrate 1 is not warped, the center of the back sensor 6 of the optical disc substrate 1 is irradiated with light.

On the other hand, when the optical disk substrate has a warp angle φ, the reflected light reflected from the back surface of the optical disk substrate 1' is taken out by the beam splitter 4 along the reflected light path 7', and the linear image is The reflected light is irradiated onto the sensor 6, but the position where the reflected light is irradiated is the optical disc substrate 1.
' can be shifted from the center by a distance l proportional to the warp angle φ.

Further, when the optical disk substrate 1 has a warp in this way, the incident laser beam will be obliquely incident on the substrate by the warp angle φ.

Therefore, by using the pitch calculation formula (1) shown below instead of the pitch calculation formula (1) shown above which assumes normal incidence, it is possible to more accurately groove the groove. You can find the shape.

λ P= (1)'5in
(θ+φ) -5inφ [Effects of the Invention] The optical disk groove shape measuring device of the present invention has a function of measuring the reflected light of the optical disk substrate and detecting the warpage angle of the optical disk substrate from the reflected light, and furthermore, it has the function of measuring the reflected light of the optical disk substrate and detecting the warpage angle of the optical disk substrate from the reflected light. This has the effect of correcting the pitch calculation formula and determining the groove shape more accurately.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing an embodiment of the present invention, Fig. 2(a)
, (b) is a schematic diagram and an enlarged view of part A showing a conventional example. l, 1'... Optical disc substrate, 2...
Laser light source, 3a to 3e...diffraction light detector,
4... Beam splitter, 5... Wave plate, 6... Linear image sensor-17, 7
'...Reflected light path, φ... Warp angle, l
······distance. Agent Patent Attorney Oto Uchihara: Warp angle Figure 1

Claims (1)

[Claims] a laser light source that generates laser light with a small spread angle; a detector that measures the intensity and direction of diffracted light generated when the laser light source irradiates the optical disc substrate with the laser light; Measure the direction of the reflected light, determine the warp angle of the optical disk substrate from the measured direction of the reflected light, and calculate the groove shape.
An optical disk substrate groove shape measuring device comprising: a reflected light detector for measuring the groove shape using a correction formula in which the incident angle is changed by the warpage angle.