JPS61123029A - Optical head - Google Patents

Abstract

PURPOSE:To simplify the constitution of a photodetector by providing a two- divided light detecting part with the first band-shaped mask and the second band-shaped mask which shield the light having the effective diameter of reflected light and using the difference between quantities of light made incident on both photoelectric conversion areas as a focus error. CONSTITUTION:When a light spot 102 is placed in the in-focus position, the light having an effective diameter 220 indicated by a broken line of reflected light 106b is shielded by the first band-shaped mask 223 and the second band- shaped mask 225. A two-divided light detecting part 221 is so arranged that a boundary 222 is placed near a center line 240 of the reflected light 106b, and the incident reflected light 106b is divided to two effective photoelectric conversion areas with equal areas of photoelectric conversion areas 280a and 280b, and a focus error signal 229 obtained from a difference operator 228 is zero. The focus error signal obtained by subtracting the value of an output signal 227 from the value of an output signal 226 is a positive value if the distance between a condenser lens 101 and a recording medium 103 is too short, and the focus error signal is a negative value if said distance is too long.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to an optical head, and particularly to an optical head that detects recorded information using a light spot.

[Prior art]

In this type of optical head, in order to correctly reproduce information, it is necessary to accurately irradiate a light spot made by converging laser light onto the recording medium. The relative position to the irradiation position must always be accurately detected. Conventionally, the focus detection means used is an astigmatic method that detects the reflected light from the recording medium using a combination of a cylindrical lens and a 4-split photodetector. An aberration method, a knife method using a combination of a knife and a two-split photodetector, etc. were adopted.

However, these methods use a cylindrical lens in addition to a split photodetector as a focusing means.

Alternatively, since it uses a knife etc., C2 includes several problems. First, the position adjustment during construction of the optical head is very complicated.

Second, the optical head becomes large.

Next, the astigmatism system shown in FIGS. 6 and 4 (-) will be cited as a typical example of the conventional method, and the principle, configuration, and above-mentioned problems will be described.

FIG. 3 shows the structure of the optical head. In this figure, a light spot 102 finely focused by a condenser lens 101 is reflected from a recording medium 103, passes through a polarizing beam splitter 104, and then enters a semi-transparent mirror 105. One side of the reflected light 106 split into two from the semi-transparent mirror 105 passes through a track detector 107 , and the other passes through a cylindrical lens 108 and is focused on a four-split photodetector 109 . Each output signal from the 4-split photodetector 109 is input to an adder/subtractor 114, and the sum value X of the A area 110 and B area 111 is obtained.

The difference value between the sum Y of the C area 112 and the D area 116 (
X-Y) is added to the adder/subtractor 11 as a focus error signal.
Output from 4. Note that the 4-split photodetector 109 is located at a position where the recording surface of the recording medium 106 matches the focal point of the optical spot 102, that is, the position of the circle of least confusion 115 formed by the nine cylindrical lenses 108 as shown in FIG. It is located in Therefore, when the recording surface of the recording medium 106 is at a position that matches the focal point of the optical spot 102, the circle of least confusion 115 occurs, so the difference value (x-y) between the added value X and the added value Y is zero. The adder/subtractor 114 outputs a zero signal. The recording medium 106 is the condensing lens 10
1, the imaging plane of the 2-reflected light 106 moves away, and the image on the 4-split photodetector 109 becomes an ellipse 116 long on the y-axis.
Therefore, the sign of the difference value (x-y) becomes positive. Conversely, as the distance increases, the imaging plane approaches, forming an ellipse 117 that is long along the y-axis, and the sign of the difference value (x-y) becomes negative. Therefore, the condensing lens 101 is servo-controlled so that these differential signals are constantly detected and the focal point position 9 is reached.

In such a configuration, the first problem is as follows.

When arranging the cylindrical lens 108 and the 4-split photodetector 109, a uniform reflection pattern from a reflective surface is set at a position called a pit on the recording medium 103 that does not receive diffraction from recorded information, that is, within the optical spot 102. Generally, alignment is performed.

In this case, the 9 reflection patterns are concentric (-spread and 9
It is also necessary to align the center line of the cylindrical lens 108 with the center of the reflection pattern, and also to align the center of the four-part detector 109 with the position of the circle of least confusion 115 of the cylindrical lens 108. What to do when making adjustments.

After positioning the cylindrical lens 108 accurately on the optical axis.

The output from each detection element of the 4-split photodetector 109 is made equal on the left, right, top and bottom in the split area.

X direction? /The center of one reflection pattern and the center of the 4-split photodetector 109 are made to coincide by performing force direction movement, X-axis rotation, and X-axis rotation. Furthermore, the 4-split photodetector 109 is moved in the Z direction, and the circle of least confusion 115 of the cylindrical lens 108 is aligned by 1 so that the output from each detection element is equalized. Because it is done with an accuracy of less than milliradians.

The adjustment operation becomes very complicated and requires a lot of effort and time, resulting in high costs.

The second problem is that the focal length of the two cylindrical lenses 108 is generally about 5M to 1 crn, and the thickness of the cylindrical lens 108 is also a problem. The distance must be at least 1 tM or more. This has the disadvantage that by inserting the two cylindrical lenses 108, the optical path length becomes longer and the structure becomes ('-dog-shaped).

The problems of the focus detection means using the conventional astigmatism method have been described above, but the knife method and the like have similar drawbacks. In any case, the conventional system has disadvantages such as complicated position adjustment, high cost, and large optical head.

[Purpose of the invention]

An object of the present invention is to provide a two-split light detection section of a focus detector with a first band-shaped mask and a second band-shaped mask that block the effective diameter of nine reflected lights, Both sides of the photodetector are illuminated, and the number of man-hours required for adjustment is reduced.

An object of the present invention is to provide an optical head that can be made smaller and more economical.

[Structure of the invention]

The present invention provides an optical to rad system that detects recorded information using a light spot that follows and irradiates a track on a recording medium, in which a focus detection means for detecting the formation position of the light spot moves from the recording medium at a focal point position of 9. The boundary of the two-split light detection section is placed near the center line of the unmodulated reflected light.

A first band-shaped mask that blocks light in the vicinity of the center line in a circular band shape, and a second band-shaped mask that blocks the reflected light in an arc shape on the surface of the two-split light detection section.

It is characterized in that the two effective photoelectric conversion regions of the reflected light at the focal point position are provided in mutually opposite regions so that they are equal.

EMBODIMENTS OF THE INVENTION Next, the present invention will be described in detail with reference to embodiments and drawings.

FIG. 1 is a perspective view showing the configuration of an embodiment according to the present invention, and FIG. 2 is a diagram illustrating the incident state of reflected light in the embodiment of FIG. 1. In FIG. 1, linearly polarized light 202 emitted from a laser light source 201 is transmitted through a collimating lens 203.
The light becomes parallel light 204. The parallel light 204 passes through a polarizing beam splinter 104 having a wavelength plate 206 at an output end face 2o5+:'/, and is converged by a condenser lens 101. The converged light spot 102 is reflected by the recorded information 210 on the track 209 of the rotating recording medium 106, and the two reflected beams 106 pass through the condenser lens 101 again and return to the polarizing beam splitter 104. The reflected light 106 is the A wavelength plate 206
By passing through the light again, it becomes linearly polarized light with a plane of polarization perpendicular to that at the time of incidence.

The pattern is projected onto a two-part track detector 107 to output a track error signal 211. The other divided reflected light 106b enters the focus detector 250,
An output signal (A) 226 and an output signal (B) 227 from the photoelectric conversion region 280 are obtained as outputs. After these outputs are input to a difference calculator 228, a focus error signal 229 is obtained from the output side.

The focus detector 250 detects the effective diameter 220 of the reflected light 106b when the light spot 102 is in the focused position (=the center line 240 of the same pattern as the parallel light 204) when the non-modulated area of the recording medium 103 is irradiated. The two-split light detection section 221 is arranged so that the vicinity of the two-split light detection section 221 coincides with the boundary 222 of the two-split light detection section 221.
On the surface of
A strip mask 223 is arranged. Furthermore, a second band-shaped mask 225 is provided on the other surface of the photoelectric conversion region 280 in the two-split light detection section 221 to shield the reflected light 106b in an arcuate shape. Namely.

The first strip-shaped mask 223 and the second strip-shaped mask 225 divide the light detection section 22 into two with the vicinity of the center line 240 as a boundary.
It is provided in the reciprocal area above 1. Further, when the light spot 102 is irradiated onto the recording medium 103 at a focal point position, one reflected light beam 106b is transmitted to two photoelectric conversion regions 280, each having an equal effective area, on the surface of the two-split photodetector 2210. It is divided into transformation areas. As described above, the focus detector 250 includes the two-split light detection section 221.

It is composed of a first band-shaped mask 223 and a second band-shaped mask 225.

FIG. 2 is a diagram for more specifically explaining the situation in which the reflected light 106b enters the focus detector 250. (A) in the diagram shows the case where the light spot 102 is at the focused position. The effective diameter 220 shown by the broken line of the reflected light 106b is between the first strip mask 223 and the second strip mask 2.
The light is blocked by 25. The two-split light detection unit 221 detects the boundary 2
22 is arranged so that it is located near the center line 240 of the reflected light 106b, and the incident reflected light 106b is divided into two effective photoelectric conversion regions each having an equal area of the photoelectric conversion regions 280a and 280b. .

Therefore, the focus error signal 229 obtained from the difference calculator 228 becomes zero. Also.

Part (B) of the figure shows a case where the distance between the condensing lens 101 and the recording medium 103 is too short. And it's getting bigger.

In this case, the amount of light entering the photoelectric conversion region 280a increases by the amount that the reflected light 106b spreads. On the other hand, the amount of light on the photoelectric conversion region 280b side is also higher than that at the focused point, but 1
Since the peripheral portion of the circle, that is, the arcuate portion, is shielded from light, the rate of increase in the amount of light is smaller than that on the photoelectric conversion region 280a side.

Therefore, from the value of the output signal (A) 226, the output signal (B
)227, the focus error signal obtained is a positive value. Furthermore, ←→ in FIG. 9 indicates a case where the distance between the condenser lens 101 and the recording medium 103 is too large, and the diameter of the reflected light 106b is smaller than the effective diameter 220.

Therefore, the value of the output signal (A) 226 is small, and the value of the output signal (Bl) 227 is not large. Parallel light 20 is sent to the split light detection section.
A first band-shaped mask 223 and a second band-shaped mask 22 that block the effective diameter 220 of reflected light having the same pattern as 4.
5, and the difference in the amount of light incident on both photoelectric conversion regions of the two-split light detection section 221 restricted by these masks is used as a focus error signal, thereby eliminating the use of a conventional cylindrical lens, and It has become possible to simplify the configuration of the photodetector. Also, during assembly and adjustment, unlike the astigmatism method, there is no need to adjust the photodetector in the Z direction, which saves labor and time and reduces costs. Since there is no limit to the distance between the two, the optical head can be made smaller, which has great effects.

Margin below

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the configuration of an embodiment according to the present invention, and FIG.
The figure is a diagram for explaining in more detail the situation in which reflected light is incident on the focus detector in the embodiment of Figure 1, and Figure 3 shows an example of the configuration of an optical head that applies the conventional astigmatism method. The perspective view shown in FIG. 4 is a diagram for explaining the astigmatism method in the conventional example of FIG. 3. In the figure, 101 is a condensing lens, 106 is a recording medium,
104 is a polarizing beam splitter, 105 is a semi-transparent mirror, 10
7 is a track detector, 201 is a Rade light source, 206 is a cotsmate lens, and 206 is a % wavelength plate. 209 is a track, 228 is a difference calculator, 221 is a two-split photodetector, 226 is a first strip mask, and 225 is a second
250 is a focus detector.

Claims (1)

[Claims] 1. In an optical head that detects recorded information by a light spot irradiated following a track on a recording medium, a focus detection means for detecting the formation position of the light spot detects non-modulated light from the recording medium at a focused position. The boundary of the two-split light detection section is placed near the center line of the reflected light, and the two
A first band-shaped mask that blocks light in the vicinity of the center line in a circular band shape and a second band-shaped mask that blocks the reflected light in an arc shape are arranged on the surface of the split light detection unit to detect the reflected light at the focused position. An optical head characterized in that both effective photoelectric conversion regions are provided in opposite regions so that both effective photoelectric conversion regions are equal.