JPH06180855A - Device for evaluating optical head - Google Patents

Abstract

PURPOSE:To improve measuring precision by providing steps on a reference member and making the focus offset measurement of an optical head limitted to the movement in uniaxial direction. CONSTITUTION:The evaluation of an optical head recording, reproducing or erasing information is performed by measuring a defocus characteristic and converging a beam outgoing from a laser light source by an objective lens and irradiating a light spot on an optical information recording medium. Then, the constitution of the surface of a reference surface member 1 to be the target of the optical head is made so as to be provided with plural reference surfaces 3 having a periodical reference step shape consisting of the groove 2 of projecting and recessing tracks in an optical head evaluating device. Then, the steps 4 are provided between respective reference surfaces so as to make higher toward the right side in the figure. For instance, when one track width of the track groove 2 is defined nearly 1.6mum, and the height of the step 4 is defined 0.5mum, the same result as that in the conventional method where defocusing is performed at a 0.5mum step, is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head evaluation apparatus for recording, reproducing or erasing information on a recording medium such as an optical disk by optical means.

[0002]

2. Description of the Related Art A conventional example of an evaluation method of an optical head for recording, reproducing or erasing information on a recording medium such as an optical disk by optical means is as follows. That is, position adjustment of the light receiving element,
As a method of finally evaluating the static characteristics of the optical head, the defocus characteristics are generally measured. The difference between the in-focus point and the position where the focus signal is at the zero point is the focus offset, and when adjusting the light receiving element, the position of the light receiving element is adjusted so that the focus offset value becomes zero.

The measuring method of the above measuring apparatus will be described in more detail with reference to FIGS. 7 to 9. That is, conventionally, as shown in FIG. 7, a piezoelectric vibrator such as a piezo 102 vibrates the reference surface member 101 in the X-axis direction shown by the arrow, while the auto-micro 104 moves the Z-axis stage 103 in the arrow Z-axis direction.
For example, the analog signal from the optical head 100 is converted into a digital signal by the A / D converter 106 while stepwise feeding by 0.5 μm, and a Fo (focus) signal and a Tr signal are obtained.
The (track) signal is taken into the computer 105, and T
r- (track) signal PP (peak to peak)
The focus offset of ΔFo shown in the figure was obtained from the peak of k) and the zero-cross point of the Fo (focus) signal (see FIG. 8).

Therefore, in general, as described above, as a method of evaluating the focus offset of the optical head, the reference surface member 101 having the same step shape as that of the recording medium (optical disc or the like) is set in the tracking direction (radial direction of the optical disc).
A method of obtaining the difference between the defocus position where the maximum difference and the minimum difference of the track signal are maximum and the defocus position where the focus signal is 0 is performed by defocusing in the focus direction while slightly vibrating. . However, this method has a drawback that since the movement is biaxial, that is, the X axis and the Z axis, the probability of an error in the measured value is higher than that in the case of the uniaxial movement.

[0005]

The above-mentioned conventional evaluation device for focus offset of an optical head for recording, reproducing or erasing information on a recording medium by an optical means is X-type.
Since the movement is performed in two axes, that is, the Z-axis and the Z-axis, there is a problem that the probability that an error will appear in the measured value becomes high.

[0006]

SUMMARY OF THE INVENTION Therefore, the present invention is intended to solve such a problem. That is, the present invention provides an optical head evaluation apparatus in which the focus offset measurement of the optical head is performed in a movement in only one axis direction to further improve the measurement accuracy, simplify the measurement work, and further reduce the cost. It is intended.

[0007]

In order to achieve the above-mentioned object, the present invention collects light emitted from a laser light source by an objective lens and irradiates an optical spot on an optical information recording medium. In the optical head evaluation apparatus for recording, reproducing, or erasing, the reference surface member serving as the target of the light spot has a plurality of reference surfaces having a periodic reference step shape formed of uneven track grooves. An optical head evaluation device having a step between each reference plane, a configuration in which the reference plane member is a light transmissive reference plane member, and a light transmissive reference plane. It is characterized in that it has a microscope for observing the light spot irradiated on the member and that the reference surface of the reference surface member is a mirror surface.

[0008]

The optical head evaluation device configured as described above is
By providing the step on the reference surface member, the movement for moving in the Z-axis direction is unnecessary, and the accuracy of focus offset measurement is improved. The accuracy of defocus measurement is determined only by the processing accuracy of the step of the reference surface member, and the accuracy can be easily improved. Furthermore, since a single measurement can be completed by a minute (μm unit) measurement displacement, the measurement work can be speeded up and repeated measurement can be easily performed, so that the measurement accuracy can be improved. Furthermore, to provide a reference surface member that can be evaluated closer to the actual state by setting the material of the reference surface member to be equal to the transmittance of the actual light-transmitting medium (optical disk). You can

Furthermore, by using a light transmissive reference surface member having a step, not only a PD (photo detector) signal of an optical head on which a noise signal such as flare information may be placed, but also an actual reference surface Not only is it possible to observe the light spot to clarify the measurement target and improve the reliability of measurement, but also to provide a step on the reference surface member and move it in the Z-axis direction. By doing so, the accuracy of focus offset measurement can be improved. Further, the unevenness of the reference surface of the reference surface member can be measured by making it a mirror surface without a groove, so that the number of work steps at the time of creating the reference surface member can be reduced and the cost can be greatly reduced. Not only will this be possible, but further the measurement system will be simplified.

[0010]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a sectional view of a reference surface member of an optical head evaluation apparatus according to an embodiment of the present invention. In the present invention, the light emitted from a laser light source is measured by an objective lens by measuring the above defocus characteristics. Information is recorded by converging and irradiating an optical spot on the optical information recording medium.
In an optical head evaluation device for evaluating an optical head for reproducing or erasing, the structure of the surface of the reference surface member 1 which is the target of the light spot is characteristic. That is, the surface of the reference plane member 1 is provided with a plurality of reference planes 3 each having a periodical reference step shape composed of uneven track grooves 2, and a step (step wall surface) 4 is provided between the reference planes 3. It is higher as you go to the right of the drawing. In this embodiment, if the track width of the track groove 2 is set to about 1.6 μm and the height of the step 4 is set to 0.5 μm, defocusing is performed in 0.5 μm steps by the conventional measuring method. The same result is obtained.

FIG. 2 is a cross-sectional view of a reference surface member which is an essential part of an optical head evaluation apparatus according to another embodiment of the present invention. As the reference surface member 1, a semi-transmissive film is used as a reflective film. The light transmissive reference surface member 5 is used, and the incident light incident on the light transmissive reference surface member 5 in the direction of the arrow A is indicated by the arrow B.
The incident light is partially reflected, and a part of the incident light is transmitted in the arrow C direction. The light transmittance of the light-transmitting reference surface member 5 is preferably set to be equal to the transmittance of the actual medium (optical disk).

FIG. 3 is a structural explanatory view of a focus offset measuring apparatus of an optical head evaluating apparatus according to another embodiment of the present invention, in which the light radiated on the light-transmissive light-transmissive reference surface member 5 is described. It is an optical head evaluation device having a microscope 6 for observing spots. In this embodiment, the height of the step 4 of the light-transmissive light-transmitting reference surface member 5 is set to 0.5 μm. The microscope 6 is focused on the reference surface 3 of the light-transmissive reference surface member 5 having a specific light transmittance. The objective lens (not shown) of the optical head 0 so that the light spot from the optical head 0 is focused on the reference surface 3 of the light-transmissive reference surface member 5, and the reference of the light-transmissive light-transmissive reference surface member 5 described above. Adjust the distance from surface 3. From this state, the light-transmissive reference surface member 5 is attached to the arrow X shown by a piezoelectric vibrator such as a piezo 9.
By vibrating in the direction, it is possible to obtain the same light spot intensity change as when defocusing is performed in 0.5 μm steps. Light observed by the monitor camera 7 and the monitor display 8 via the microscope objective lens 12 that collects the transmitted light flux from the light spot in the microscope 6 and the illumination light source 13 that illuminates the visual field of the reference plane. The intensity of the spot changes. A symbol M is a dichroic mirror, and a part of the light is guided to the camera 7 side. This change in the intensity of the light spot is output to the computer 11 via the A / D converter 10 and is found to change as shown in FIG. 4 by the processing by the computer 11. At this time, in order to improve the measurement accuracy, it is necessary to perform the tracking operation on the reference surface 3 of each of the light transmissive reference surface members 5. Since the change in the light spot intensity during defocusing corresponds to the change in the difference between the maximum value and the minimum value of the track signal described above, the focus offset can be measured.

5 (a) and 5 (b) are cross-sectional views of a reference surface member of an optical head evaluation apparatus according to another embodiment of the present invention, and FIG. 5 (a) is an upper side of a step 4 on both sides. 5 shows a light-transmissive reference surface member 5a having a mirror surface 14 having no reference step shape on the reference surface 3 of the lower light-transmissive reference surface member 5, and FIG.
(B) is a mirror surface 1 having no reference step shape on the reference surface 3 of the light transmissive reference surface member 5 above or below the step 4 on one side.
Even if the reference surface 3 is the light-transmitting reference surface member 5b having the reference surface 3 and the reference surface 3 is the mirror surface 14 having no reference step shape, the same measurement result as described above can be obtained, and the focus offset can be evaluated.

FIG. 6 is an explanatory view of the structure of a focus offset measuring device of an optical head evaluating device according to another embodiment of the present invention, which is a reference step shape composed of concave and convex grooves, that is, the track groove 2 (the above-mentioned one track width). Is about 1.6 μm), in order to focus the microscope 6a on the mirror surface 14 of the reference surface 3 of the light transmitting reference surface member 5 (FIG. 5), the optical head The mirror surface 14 of the reference surface 3 of the light transmissive reference surface member 5 is irradiated with laser light from the side of the symmetric side of the microscope 6a, and the reflected light is used to reflect the mirror surface 1 of the reference surface 3.
Reference plane focus detection system 1 for performing focus detection of No. 4
This is possible by providing 5. That is, the microscope 6a
A laser beam is incident from the side, and a focus signal obtained by using the astigmatism method or the like from the reflected light is processed by the computer 11, and the position of the light transmissive reference surface member 5 or the objective lens 12 for the microscope is processed. The position can be adjusted and controlled to the in-focus point. In the figure, M is a dichroic mirror, PB
S indicates a deflecting beam splitter.

[0015]

Since the present invention is constructed as described above, by providing a step on the reference surface member,
Since the movement for moving in the Z-axis direction is unnecessary, the accuracy of focus offset measurement can be improved. Since the accuracy of defocus measurement is determined only by the processing accuracy of the step of the reference surface member, the accuracy can be easily improved. Further, since one measurement is completed by a minute (μm unit) measurement displacement, the measurement work can be speeded up and repeated measurement can be easily performed, so that the measurement accuracy can be improved. Furthermore, since the material of the reference surface member is set to be equal to the transmittance of the actual light-transmitting medium (optical disk), a reference surface member that can be evaluated more closely to the actual state is provided. Can be provided.

Further, by using a light transmissive reference surface member having a step, a PD (photo detect) of an optical head in which a noise signal such as flare information may be carried.
not only the signal but also the light spot on the actual reference surface can be observed, so not only was it possible to clarify the measurement target and improve the reliability of the measurement, Since there is no need to provide a step and move in the Z-axis direction, the accuracy of focus offset measurement can be improved. Furthermore, since the reference surface member can be measured by making the grooved surface of the reference surface uneven with a mirror surface without a groove, the number of work steps at the time of creating the reference surface member can be reduced, and a large cost reduction can be achieved. Not only was it possible, but it was also possible to simplify the measurement system.

[Brief description of drawings]

FIG. 1 is a sectional view of a reference surface member of a main part of an optical head evaluation apparatus showing an embodiment of the present invention.

FIG. 2 is a sectional view of a reference surface member of a main part of an optical head evaluation apparatus showing another embodiment of the present invention.

FIG. 3 is an explanatory diagram of focus offset measurement of an optical head evaluation apparatus showing another embodiment of the present invention.

FIG. 4 is a graph showing an example of results obtained by the measurement of FIG.

5A and 5B are cross-sectional views of a reference surface member of a main part of an optical head evaluation apparatus showing another embodiment of the present invention.

FIG. 6 is an explanatory diagram of focus offset measurement of an optical head evaluation apparatus showing another embodiment of the present invention.

FIG. 7 is an explanatory diagram of focus offset measurement.

8 is a graph showing an example of results obtained by the measurement of FIG.

FIG. 9 is a cross-sectional view of a conventional reference surface member.

[Explanation of symbols]

0 ... Optical head, 1 ... Reference surface member, 2 ... Track groove, 3 ... Reference surface, 4 ... Step, 5 ... Light transmissive reference surface member, 6 ... Microscope, 7 ... Monitor camera, 8 ... Monitor, 9 ... Piezo, 10 ... A
/ D converter, 11 ... Computer, 12 ... Microscope objective lens, 13 ... Illumination light source, 14 ... Mirror surface, 15 ... Reference plane focus detection system, 100 ...
Optical head, 101 ... Reference plane member, 102 ... Piezo, 103 ... Z-axis stage, 104 ... Auto micro, 105 ... Computer, 106 ... A /
D converter.

Claims (4)

[Claims] 1. An optical head evaluation apparatus for recording, reproducing or erasing information by condensing light emitted from a laser light source by an objective lens and irradiating a light spot on an optical information recording medium, The reference surface member that is the target of the light spot has a plurality of reference surfaces having a periodical reference step shape that is composed of uneven track grooves, and there is a step in the thickness direction between each of the plurality of reference surfaces. An optical head evaluation device characterized by. 2. The optical head evaluation device according to claim 1, wherein the reference surface member is a light transmissive reference surface member that is light transmissive. 3. The optical head evaluation apparatus according to claim 1, further comprising a microscope for observing a light spot applied to a light transmissive reference surface member which is light transmissive. 4. The optical head evaluation apparatus according to claim 1, wherein the reference surface of the reference surface member is a mirror surface.