JPS62284221A - Measuring method for beam spot diameter of optical head for optical disk - Google Patents

Abstract

PURPOSE:To easily and accurately take a measurement by detecting time intervals of time when a measurement edge provided to a rotary substrate passes through a beam spot and measuring the diameter of the beam spot from the time intervals and the moving speed of the measurement edge. CONSTITUTION:The rotary substrate 1 is irradiated with the light beam so that the beam spot is formed on the plate surface of the rotary substrate 1. Then when the rotary substrate 1 is rotated at a constant speed, intervals of time when the measurement edge 4a passes through the beam spot are detected optically and the beam spot diameter is found from the time intervals and the moving speed of the measurement edge. Thus, the beam spot diameter of the optical head for the optical disk is easily and accurately measured with good reproducibility.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a method for measuring the beam spot diameter of an optical head in an optical disc device capable of recording and reproducing information at high density. It is something.

[Technical background of the invention and its problems] An optical disc device capable of recording and reproducing information at high density has a photoconductor 7f for storage on a transparent disc base.
An optical disc is configured by providing a J layer.

On the other hand, the optical head is equipped with a light source such as a laser diode and an optical system including an objective lens, and the beam spot of the light beam focused by the objective lens is irradiated onto the photoreceptor thin layer to record information. Alternatively, information that has already been recorded is read out.

At this time, the efficiency during recording and the resolution during reproduction are controlled by the beam spot diameter, and these performances improve as the beam spot diameter becomes smaller.

Therefore, in quality inspection of optical heads for optical discs, one of the extremely important inspection items is how well the optical head can focus light down to a minute beam spot diameter.

Examples of methods for measuring the beam spot diameter of conventional optical heads for optical discs that have been used for such inspections include the following.

This traditional measurement method uses a knife
The beam spot of the focused light beam is determined by cutting the beam waist of the focused light beam perpendicularly to the traveling direction of the light beam with a knife moving at a constant speed and measuring the profile of changes in the amount of light passing through the knife. This is to find the diameter.

In order to accurately measure the beam spot diameter using this method, it is necessary to find the profile when the knife crosses the center of the beam waist perpendicularly to the traveling direction of the light beam.

As a means of this, in this conventional measurement method, the scanning position of the knife is translated in parallel with an accuracy of 0.1 μm by fine adjustment, and the profiles of changes in light amount obtained each time are compared to indicate the steepest light change. The beam spot diameter was determined from the profile.

However, in the above method for measuring the beam spot diameter of an optical head for an optical disk, the scanning position of the knife is moved with an accuracy of about 0.1 μm by fine adjustment, and each time the knife is moved perpendicular to the traveling direction of the light beam. Since it is necessary to scan in the same direction, there are problems in that measurement is troublesome and time-consuming, and measurement accuracy is low and reproducibility is poor. Furthermore, there was also the problem that the measurement accuracy was affected by the measurement environment, and the measurement accuracy deteriorated if there was filming.

[Object of the Invention] The present invention was made based on the above circumstances, and an object of the present invention is to provide a method for measuring the beam spot diameter of an optical head for an optical disk, which can easily and accurately measure the beam spot diameter with good reproducibility. shall be.

[Summary of the Invention] In order to achieve the above object, the present invention provides a rotating substrate with a measurement edge for optically detecting a beam spot of a light beam emitted from an optical head to be measured by rotation of the rotating substrate. By detecting the time interval at which the measuring edge passes through the beam spot, and measuring the beam spot diameter from this time interval and the moving speed of the measuring edge, the beam spot diameter can be easily, accurately, and reproducibly measured from an optical head for an optical disk. The beam spot diameter of the irradiated light beam can be measured.

[Embodiments of the Invention] Examples of the present invention will be described below with reference to FIGS. 1 to 3.

FIG. 1 is a plan view of the rotating board, FIG. 2 is a configuration diagram of the measuring device, and FIG. 3 is a waveform diagram showing an example of a measurement waveform displayed on an oscilloscope in the measuring device.

First, the configuration of a measuring device including a rotating substrate used in this example will be explained.

In FIG. 1, reference numeral 1 denotes a rotating substrate (probe substrate), and the substrate body 2 is a transparent plate material made of a glass plate with a thickness of about 1.2 mm, and a metal reflective film 3 is formed on the entire surface of the substrate body 2. is coated.

A first translucent slit 4 with a width of about 5 μm, which is sufficiently wider than the expected beam spot diameter, is formed in the metal and reflective film 3 at 1 aM! iQ is eclipsed, and its sides constitute a measurement edge 4a.

In addition, a second slit with a width of 1 μm, which is approximately the same width as the expected beam spot diameter, is placed adjacent to the first translucent slit 4.
Translucent slits 5 are arranged in an array of 10al.

The circumferential arrangement pitch of the second translucent slits 5 at the radial position where the beam spot is irradiated is as follows:
For example, it is correctly defined as 2 μm. As mentioned above, the moving speed (linear speed) of the measuring edge 4a is measured by the slit row of the second translucent slits 5.

In the example of FIG. 1, two sets of the first translucent slit 4 and the plurality of second translucent slits 5 are formed at the same radial position with the same size and shape.

6 is a mounting hole for the rotation stage.

FIG. 2 shows the overall configuration of the measuring device including the above-mentioned rotating board 1, where 7 is a rotating stage for rotating the mounted rotating board 1 at a constant speed, 8 is a photodetector, and 9 is an oscilloscope. , 11 is an optical head for an optical disk to be measured.

The optical head 11 is positioned at a predetermined radial position of the rotating substrate 1 so that the light beam is perpendicular to the surface of the rotating substrate 1 and is correctly irradiated to the formation positions of the first and second translucent slits 4.5. It is placed in a position opposite to. Further, the photodetector 8 is
It is placed on the opposite side of the optical head 110 with the rotating substrate 1 in between.

Next, the measurement method will be explained.

First, the rotating substrate 1 is mounted on the rotating stage 7, and the optical head 11 is placed directly below the rotating substrate 1 at a predetermined radius position.

and a focusing system 11 including an objective lens within the optical head 11;
The 1 m structure is operated so that a beam spot of the light beam irradiated from the optical head 11 is formed on a 1 m 3 film surface of the metal reflection on the rotating substrate 1.

When the rotating stage 7 side is operated and the rotating substrate 1 is rotated at a constant speed, transmission occurs when the light beam crosses the slit rows of the first transparent slit 4 and the second transparent slit 5. Changes in the amount of light are detected by a photodetector 8 and displayed on an oscilloscope 9.

FIG. 3 shows measurement waveforms displayed on the oscilloscope 9. In FIG. This is a waveform of a change in light amount due to the optical slit 4.

Next, while observing the waveform displayed on the oscilloscope 9, the focus control mechanism of the optical head 11 is finely adjusted so that the waveform amplitude 12 of the waveform A is maximized.

When the waveform amplitude 12 of the waveform A is adjusted to be maximum, the reading resolution by the slit row of the second translucent slit 5 is maximum, and this state is at the center of the beam waist of the light beam. This means that the portion correctly matches the forming surface of the translucent slit 4.5.

Therefore, a translucent slit 4 is placed at the center of the beam waist.
．． 5 can be easily and accurately positioned.

After adjusting in this way, measure edge 4 from waveforms A and B.
The moving speed of a and the beam spot diameter are measured.

First, the moving speed (linear speed) of the measurement edge 4a is measured from the waveform.

In the slit row, ten second translucent slits 5 are arranged at a pitch of 2 μm, so that the entire length of the 1-slit row is 20 μm. Therefore, if the time required for the beam spot to pass through this 20 μm slit array is read from the waveform A, the moving speed of the measurement edge 4a can be determined from the distance and the distance (15).

Next, the beam spot diameter of the light beam is measured from waveform B.

In waveform B, 13 indicates the blocking level when the beam spot is completely blocked by the parts of the substrate body 2 other than the first translucent slit 4, and 14 indicates the level at which the beam spot is inside the first translucent slit 4. The light amount change curve 15 between the two levels 13 and 14 is the change curve of the transmitted light a when the measuring edge 4a crosses the beam spot.

Since the time required for the light intensity change between the cutoff level 13 and the transmitted light intensity level 14 described above corresponds to the time for the measurement edge 4a to pass through the beam spot, the moving speed V of the measurement edge 4a obtained previously and this The beam spot diameter can be determined from the required time for passage.

By the way, in the light amount change curve 15 in FIG. 3, the center position in the vertical direction corresponds to the center position of the beam spot, and this is the maximum light intensity point. Then, assuming that the light intensity distribution in the radial direction of the beam spot from this maximum light intensity point is a Gaussian distribution, the beam spot diameter is
The beam spot diameter at a light intensity point of 1/e or the beam spot diameter at a light intensity point of 1/e2 (0,135) when normalized by the maximum light intensity is the 1 e beam spot diameter or 1 e beam spot diameter, respectively. /e2 beam spot diameter, and the beam spot diameter is expressed by the diameter of these Gaussian beams.

Note that 1/e2 beam spot diameter is usually used as the beam spot diameter.

In waveform B in FIG. 3, 17 is a level difference of 84% of the maximum previous level difference 16 between the cutoff level 13 and the transmitted light amount level 14, and the value obtained from this 84% level difference is 1/ This is the e-beam spot diameter.

To obtain the 1/e beam spot diameter, the time t required for the measurement edge 4a to pass through the 84% level difference 17 is read using the oscilloscope 9.

At this time t, the previously determined moving speed of the measurement edge 4a ■
It is obtained from the value v-t multiplied by .

The commonly used 1/e2 beam spot diameter can be obtained by further multiplying the 1/e vinyl spot diameter obtained as described above by root 2.

To give a specific example of the measured values, the 1/e2 beam spot diameter of the optical head using an objective lens with NA (numerical aperture) of 0.5 was 1.5 μm.

In this way, the method for measuring the beam spot diameter according to this embodiment calculates the beam spot diameter from the measurement waveform of the light m change surface 115 etc. displayed on the oscilloscope 9 by rotating the measurement edge 4a. Even if there is some imaging, the measurement accuracy is hardly affected.

In the measuring device shown in FIG. 2, the photodetector 8 is connected to the rotating substrate 1.
The beam spot diameter was measured from the change in the amount of light transmitted through the transparent slit 4.5, with the metal reflective film 3 on the surface of the rotating substrate 1. Since it is coated, the beam spot diameter can be similarly measured by placing the photodetector 8 on the same side as the optical head 11 and detecting changes in the amount of reflected light.

[Effects of the Invention] As explained above, according to the configuration of the present invention, the rotating substrate is irradiated with a light beam so that a beam spot is formed on the plate surface of the rotating substrate, and then the rotating substrate is rotated at a constant speed. Then, the time interval during which the measurement edge passes through the beam spot is optically detected, and the beam spot diameter is determined from this time interval and the moving speed of the measurement edge. Therefore, it is possible to measure the beam spot diameter of an optical head for an optical disk easily, accurately, and with good reproducibility, and even in a somewhat vibrating environment, high measurement accuracy can be obtained. This method has the advantage of being able to perform quality inspections, etc. accurately in a short period of time, and providing an extremely practical method for measuring beam spot diameter.

Further, according to an embodiment, a plurality of translucent slits are arranged at a predetermined pitch on a rotating substrate, and the moving speed of the measurement edge is measured from the time it takes for the beam spot to pass through the plurality of translucent slits. In addition to the above-mentioned common effects, there is an additional advantage that the moving speed of the measurement edge for determining the beam spot diameter can be easily and accurately determined.

[Brief explanation of drawings]

FIG. 1 is a plan view showing an example of a rotating substrate used in an embodiment of the method for measuring the beam spot diameter of an optical head for an optical disk according to the present invention, and FIG. 2 is a plan view showing an example of a measuring device used in the same embodiment. The configuration diagram and FIG. 3 are waveform diagrams showing an example of measurement waveforms by the same device.・1: Rotating substrate, 3: Metal reflective film, 4: First
4a: measurement edge; second light-transmitting slit constituting the 5-ni slit row; 7: rotation stage; 8: photodetector; 9: oscilloscope; 11: optical head as the object to be measured. Agent Patent Attorney Yasuo Miyoshi Figure 1 Figure 2

Claims (3)

[Claims] (1) A measurement edge is provided on the rotating substrate to optically detect the beam spot of the light beam irradiated from the optical head to be measured by rotation of the rotating substrate, and the time interval during which the measurement edge passes the beam spot is determined. 1. A method for measuring a beam spot diameter of an optical head for an optical disc, the method comprising detecting the time interval and measuring the beam spot diameter from the moving speed of the measurement edge. (2) A reflective film is formed on the surface of the rotating substrate, a translucent slit is provided in the reflective film, and the measurement edge is formed by a side of the translucent slit. A method for measuring a beam spot diameter of an optical head for an optical disk according to claim 1. (3) A plurality of other translucent slits are arranged at a predetermined pitch on the rotating substrate, and the moving speed of the measurement edge is measured from the time it takes for the beam spot to pass through the plurality of translucent slits. A method for measuring a beam spot diameter of an optical head for an optical disk according to claim 2, characterized in that: