JPS6331858B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for optically detecting a position, and particularly to a tracking error in which a light spot is deviated from a part having a diffraction effect on a target object having a part that diffracts light. An object of the present invention is to provide an optical position detection device capable of easily detecting a focus error in which a light spot focused on a target object deviates from an accurate focus position and without loss of light amount.

In general, the portion having the above-mentioned diffraction effect is provided in a band shape, or can be considered to be substantially formed in a band shape with the low frequency to be controlled, so the light spot is controlled so that it lies on this band shape. This will be referred to as tracking control, and the control so that the light spot will be accurately focused on the object surface will be referred to as focus control.

Conventionally, the Foucault method and the four-field method have been used as means for detecting focus errors and tracking errors.

However, these methods have drawbacks such as requiring two or more optical detectors and causing a large amount of light loss. Since a semiconductor laser is often used as a light source, the loss of light quantity must be small from the viewpoint of the cost and life of the semiconductor laser.

FIG. 1 shows a schematic diagram of the main parts of a conventional example. In the figure, 1 is a semiconductor laser, 2 is a collimating lens, 3 is a beam splitter, 4 is an objective lens,
Reference numeral 5 denotes a groove (concave or convex portion) formed as recorded information on a target object such as a record disc, and is a belt-shaped track as shown in the figure. 6 is a cylindrical lens whose half (the shaded part) is opaque, and 7 is a 4-split light detector.

The light emitted from the semiconductor laser 1 is turned into parallel lines by the collimating lens 2, and then transmitted through the beam splitter 3.
The objective lens 4 focuses the light onto the target object plane. The light reflected from the target object is separated from the incident light by the beam splitter 3 and taken out, and enters the cylindrical lens 6.
The light is focused onto a light detector 7. Here, since half of the cylindrical lens 6 is opaque, when the focus shifts, the center of the focused light on the detector moves in a direction perpendicular to the edge 14 of the opaque portion.

Detectors 8 and 9, 10 and 11 in the four-split optical detector 7 are arranged in a direction parallel to the edge 14 as shown, and detectors 8 and 10, 9 and 11 are arranged in a direction perpendicular to the edge 14. ing.

Therefore, by taking the difference between the sum of 8 and 9 and the sum of 10 and 11 in the four-division optical detector 7, the focus error can be detected. This method of obtaining a focus error signal by focusing only half of the focused light onto an optical detector is called the Foucault method.

It is also assumed that the light spot deviates from the track 5 in a direction perpendicular to the groove (in the direction of arrow 15 shown).
That is, the tracking control detects the deviation of the light spot in the direction perpendicular to the track, and performs control so that the deviation becomes zero. When the light spot deviates from the track, the front field pattern of the reflected light becomes unbalanced due to diffraction effects. Generally, in order to detect a tracking error of a light spot, it is sufficient to pay attention to the imbalance in the amount of light that occurs on the front field pattern of reflected light in the direction of the shift to be detected. In the case of FIG. 1, a plane including the track and perpendicular to the target object plane is used as the dividing plane, and attention is paid to the light quantity imbalance that occurs in the direction perpendicular to the dividing plane. In Figure 1, rays 12 and 13
It is easy to understand if you consider that an imbalance in the amount of light occurs between the two.

The reflected lights 12 and 13 enter the cylindrical lens 6 after passing through the beam splitter 3. Since this cylindrical lens 6 has no focusing effect on the unbalanced light beams 12 and 13 divided into two, this unbalance remains on the four-split optical detector 7 as a light quantity unbalance in the direction parallel to the edge 14. That is, by taking the difference between the sum of 8 and 10 and the sum of 9 and 11 in the four-division detector 7, the tracking error signal can be detected. A method that focuses on the far-field light intensity imbalance of the diffracted and reflected light that occurs in the direction in which tracking control is to be performed and extracts it as an error signal is called the far-field method.

The device shown in FIG. 1 has only one optical detector and is easy to adjust, but because half of the cylindrical lens 6 is transparent, there is a loss of 50% in the amount of light. The output of the semiconductor laser used in Figure 1 is 4
mW, the output can be reduced to 2 mW if there is no light loss. This value is extremely large in terms of the cost and lifespan of the semiconductor laser.

The present invention provides an optical position detection device that includes one photodetector and has no loss of light amount.
Hereinafter, the present invention will be explained based on illustrated embodiments.

FIG. 2 is a schematic configuration diagram of main parts showing an embodiment of the present invention, and parts having the same functions as those of the conventional example shown in FIG.

In FIG. 2, when a tracking error occurs in the direction of the arrow 15, an imbalance in the amount of reflected light beams 12 and 13 occurs as explained in FIG. 1. The reflected light is divided into two regions by a plane that includes a band-shaped track on the target object and a light spot perpendicular to the target object surface, and the light from these two regions is sent to the beam splitter 3.
After passing through the beam splitter 3, the direction of the plane may change after passing through the beam splitter 3, and the two-split plane after passing through the beam splitter 3 is called the conversion two-split plane. to be deflected in different directions.
Prisms 21, 22 are provided for this purpose.

The prism 22 in FIG. 2 uses the surface of the beam splitter itself. It is sufficient if the above conditions are met in a different aspect from the prism 21.

The light exiting the prisms 21 and 22 is focused onto a light detector 24 by a light detector focusing lens 23.

Each detector 2 in the 4-split optical detector 24
5 and 26, 27 and 28 are arranged in a direction perpendicular to the conversion plane, and 25 and 27, 26 and 28 are arranged in a parallel direction.

The light that has passed through the prism 21 appears on the detector as 2
At 7, the light passing through the prism 22 is focused on the detector 29.

Since the light from the prism 21, that is, half of the focused light does not contribute to the focusing spot 30, when a focus error occurs, the focusing spot 30
In the figure, it moves up and down on the detector 24. That is,
A focus error signal is obtained by taking the difference between the output signals of the detectors 27 and 28. The same applies to the focusing spot 29. However, for the same focus error, focusing spot 29 moves in the opposite direction to focusing spot 30. Therefore, the focus error signal can be obtained by subtracting the sums of the diagonal outputs of the four-split optical detector, or by calculating (25+28)-(26+27).

When a tracking error occurs, as can be seen from what has been explained with reference to FIG. 1, a difference occurs in the amount of light in the two divided regions. That is, the amount of light passing through the prisms 21 and 22 changes. Therefore, there is a difference in the amount of light between the focusing spots 29 and 30.

In this way, the sum of detectors 25 and 26 and 2
By taking the difference between the sums of 7 and 28, a tracking error signal can be obtained. That is, the tracking error signal is obtained by subtracting the outputs of the optical detectors separated by a plane parallel to the conversion plane, (25+27)-(26
+28).

The optimum position of the optical detector 24 is adjusted by performing focus adjustment in a direction perpendicular to the conversion plane and tracking adjustment in a parallel direction, as shown in FIG.

In this manner, in the present invention, the focus adjustment and tracking adjustment directions are perpendicular to each other, so adjustment is extremely easy.

Conventionally, it has been said that in order to obtain a tracking error signal using the far-field method, the spot must not be focused on the detector, but according to the present invention, this is not the case as is clear from the above description. Of course, it is not necessary to focus. FIG. 3 shows another embodiment of the present invention. In FIG. 3, parts having the same functions as those explained in FIG. 2 are designated by the same reference numerals, and redundant explanation will be omitted.

In FIG. 3, a cylindrical lens 33 is used instead of the lens 23. The cylindrical lens 33 is arranged so as not to have a focusing effect in a direction parallel to the conversion plane. As a result, on the optical detector 24, the light is focused into a light band shape as shown at 31 and 32.
It is clear that in this case as well, focus and tracking error signals can be obtained in the same manner as in FIG.

A lens intermediate between lens 23 and lens 33 may be used. These are determined by considering the size of the photodetector, the adjustment method, etc.

FIG. 4 shows an embodiment in which the direction of the track 5 in FIG. 2 is changed to a perpendicular direction.
Similar to FIG. 2, the reflected light is considered to be divided by a two-part plane that includes a band-shaped track on the target object and is perpendicular to the target object surface. Conversion after passing through the beam splitter on the two-split plane It is obvious that the prisms 21' and 22' can be used to polarize the light after passing through the beam splitter 3 in mutually different directions parallel to the two-split plane. It is. This light is transmitted to the optical detector 4 by the lens 23'.
It is focused on 1. The light that has passed through the prism 21' is focused on a spot 47, and the light that has passed through the prism 22' is focused on a spot 47. It is clear that focus errors and tracking errors can be detected using exactly the same concept as in FIG.

In the present invention, the lenses 23 and 23' which are the optical detector focusing means shown in FIG. 2 (FIG. 4) can be used in common with the lens 2. FIG. 5 shows such an embodiment, and parts having the same functions as those in FIG. 2 are given the same reference numerals. That is, a beam splitter 3 and a prism serving as a deflecting means are placed between the semiconductor laser 1 and the collimating lens 2. Since the light reflected from the object is focused after passing through the collimating lens 2, there is no need to focus the light after passing through the beam splitter as shown in FIG.

In the embodiments shown in FIGS. 2 to 4, the lenses 23, 23', and 33 are preferably integrated into the beam splitter 3. It would be better to integrate the objective lens 4 and the collimating lens 2, but this is not always a good idea due to various other problems.

FIG. 5 shows an example of a beam splitter that is effective for use in the present invention, in which prisms 21, 22 and a lens 33 are integrated. This is made by any suitable means known in the art, such as molding.

As described above, the optical position detection device of the present invention has no loss of light quantity, is simple with only one optical detector, and in the adjustment of the optical detector, the focus adjustment and tracking adjustment directions are orthogonal and independent. It has many excellent features such as easy adjustment.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the main part of the conventional example, FIGS. 2, 3, 4, and 5 are schematic diagrams of the main part of the embodiment of the present invention, and FIG. 6 is used in the present invention. FIG. 2 is a perspective view showing an example of the configuration of a possible beam splitter. 1... Semiconductor laser, 2... Collimating lens, 3, 61... Beam splitter, 4... Objective lens, 5... Groove (track), 21, 21', 2
2, 22'...prism, 23, 23', 33...
Optical detector converging lens, 24...four-division optical detector.

Claims (1)

[Claims] 1. A light source, a light focusing means for focusing the light emitted from the light source onto the surface of the target object, a light separating means for separating the reflected light from the target object from the incident light, and an optical If the light diffracted and reflected from the uneven and band-like track is divided into two regions that include the band-like track on the target object and are perpendicular to the surface of the target object, the light of the two regions can be separated by the light separating means. a deflection means that deflects the light in different directions parallel to the conversion bisecting plane after passing through the light separating means; and an optical detector focusing having a focusing action at least in a direction perpendicular to the bisecting plane after passing through the light separating means. a four-split optical detector disposed near a convergence position of the light focused by the optical detector focusing means, and a focus error signal calculation means for subtracting the sum of diagonal outputs of the four-split optical detector. and tracking error signal calculation means for subtracting the outputs of the optical detectors separated by a plane parallel to the two-part conversion plane.