JPH0386936A - Optical head structure - Google Patents

Abstract

PURPOSE:To improve detection sensitivity and to improve the non-linearity of a detection property by composing a first photodetection part of a band- shaped area including the axial center of an optical axis in detection light and gradually increasing the width of the band-shaped area from the end part to a central position corresponding to the axial center. CONSTITUTION:A photodiode element (a) as the first photodetection part is composed of the band-shaped area extended to right and left and diamond- shaped, for which both end parts in a length-wise direction are cut, so that the width can be gradually increased from the right and left end parts to the central part corresponding to the axial core of the optical axis in detection light 2. Accordingly, the photodiode element (a) is formed so that the change rate of a focusing error, namely, the increasing / decreasing rate of a photodetection area to photodetect the central part of a spot in the detection light 2 can be widely changed. Thus, only by making suitable the shape of the first photodetection part arranged on the optical axis of the detection light 2, the detection sensitivity is improved and the non-linearity of the detection property can be improved.

Description

Detailed Description of the Invention [Objective of the Invention] <Industrial Application Field> The present invention relates to an optical system having a focusing error detection means for detecting an error state in the focusing direction of an optical system using convergent detection light. Regarding head structure.

<Prior Art> Conventionally, there is a high-density recording and reproducing apparatus that performs recording and reproducing by irradiating a recording surface of an optical disk as an optical head recording medium with convergent light and detecting the reflected light. Optical discs for which this device is used generally have some warpage or distortion, as well as eccentricity due to errors in mounting the optical disc to the rotating shaft. In order to make the optical head follow the fine recording tracks of the optical disk without being influenced by these, the position of the optical head is controlled by detecting focusing and tracking errors of the optical head.

For example, as shown in FIG. 10, emitted light 22 emitted from a semiconductor laser 21 as a light source is irradiated toward the recording surface of an optical disk 23 located at the upper part of the figure.
In the optical path of this emitted light 22, a collimator lens 24,
A polarizing beam splitter 25 and two λ/4 plates are arranged on six axes of metal plates. Furthermore, an objective lens 27 is disposed coaxially in the optical path of the emitted light 22 to condense the emitted light 22 onto the recording surface of the optical disk 23 .

The emitted light 22 passes through the λ/4 plate 2 and the metal plate 6, and then enters the optical disc 2.
3 and becomes the reflected light 28, which passes through the λ/4 plate 2 sheet metal 6 again and enters the polarizing beam splitter 25. The polarization planes of the reflected light 28 differ by 90 degrees. This reflected light 28 is deflected toward the right in the figure by a polarizing film 29 provided diagonally within the polarizing beam splitter 25, and is emitted as detection light 30 from the right side of the polarizing beam splitter 25. do. In the optical path of the detection light 30, there is a photometric sensor 3 for detecting focusing errors.
1 and a condensing lens 32 for converging the detection light 30 toward the photometric sensor 31 are coaxially arranged.

In order to detect focusing errors using the spot size method, the detection light 30 is focused in front of the photometric sensor 31 as shown in FIG. 10 in a normal state where no focusing errors occur. 11th
The photometric sensor 31 is irradiated in a spot shape as shown by the imaginary line in the figure. As shown in FIG. 11, the photometric sensor 31 is composed of a known three-part photodiode divided into strip-shaped regions by mutually parallel dividing lines extending in the left-right direction of the figure. Then, the sum of the detection signal R of the intermediate light receiving section d and the detection signals E and F of the side light receiving sections e and f provided adjacently so as to sandwich the intermediate light receiving section d is the amplifier 3.
3 is entered.

The amplifier 33 subtracts the detection signal RI from the sum of the detection signals E and F, and outputs the calculation result to a control circuit (not shown). During focusing, which is the normal state described above, the output of the amplifier 33 is 0. It is designed to be. Furthermore, if the optical disk 23 is too close to the objective lens 27, the detection light 30 will be focused on the photometric sensor 31 in a small amount, for example, as shown by the broken line in FIG. As shown by the dot-dashed line, the light is greatly condensed.

Therefore, the output of the amplifier 33 changes as shown in FIG.

According to the spot size method described above, the number of parts of the optical element can be reduced because the cylindrical lens in the astigmatism method and the knife means in the knife method are not required.

However, there have been problems in that the detection sensitivity near the focal point of the detection light is relatively low and the detection characteristics are relatively highly nonlinear.

<Problems to be Solved by the Invention> In view of the problems of the prior art, the main purpose of the present invention is to improve detection sensitivity and improve detection characteristics when detecting focusing errors using the spot size method. An object of the present invention is to provide an optical head structure that can improve the nonlinearity of the optical head.

[Structure of the Invention] <Means for Solving the Problems> According to the present invention, it is an object of the present invention to create a state in which no focusing error occurs on the axis of detection light that is reflected and converged from an optical recording medium. a first light receiving section disposed at a certain distance from the focal point position, and a second light receiving section provided adjacent to the first light receiving section, and each of the two light receiving sections In the optical head structure in which the error is detected based on a difference in detected values, the first light receiving section is formed of a band-shaped area including the axis of the optical axis of the detection light, and the width of the band-shaped area is This is achieved by providing an optical head structure that is characterized in that it gradually increases from its end toward a central position corresponding to the axis.

In this way, the spot size of the detection light changes according to the change in focusing error, and the difference between the detection values of both light receiving parts changes according to the increase or decrease in the light receiving area of the first light receiving part. Since the change is large, detection sensitivity can be improved and the first
By optimizing the shape of the light-receiving section, the nonlinearity of the detection characteristics can be improved.

<Embodiments> Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a diagram showing a photometric sensor 1 based on the present invention applied to a known optical head structure similar to a conventional example. This photometric sensor 1 is divided into 3 parts in the vertical direction in the figure.
It is composed of a split photodiode and receives detection light 2 obtained by deflecting reflected light from an optical disk (not shown) using a polarizing beam splitter. The intermediate photodiode element a in the figure as the first light receiving section consists of a strip-shaped area that is long in the left-right direction of the figure, and its width extends from its left and right ends to the axis of the optical axis of the detection light 2. In other words, as clearly shown in the figure, it is formed into a diamond shape with both ends in the longitudinal direction cut off. Therefore, the photodiode element a is formed so that the rate of change in focusing error, that is, the rate of increase or decrease in the light receiving area that receives the center of the spot of the detection light 2 changes greatly.

Further, a second light receiving section is constituted by each photodiode element bSc provided vertically adjacent to the middle photodiode element a in the drawing.

The photometric sensor 1 is irradiated with the detection light 2 in the spot shape shown by the imaginary line in the figure when in focus without a focusing error, and in this state, the amount of light received by the intermediate photodiode element a and The difference between the amount of light received by the upper and lower photodiode elements b and C is O. If the optical disc is too close to an objective lens (not shown), the detection light 2 is irradiated as shown by the broken line in the figure, and if the optical disc is too far from the objective lens, it is irradiated as shown by the dashed line in the figure. is irradiated. Detection value A of the middle photodiode element a and detection values B and C of both photodiode elements b%C
is input to the amplifier 3, and the detected value (B
+C) and the detected value A is subtracted from the result (B+C-
A) is output from the amplifier 3 to a control circuit (not shown).

In FIG. 2, the horizontal axis represents the distance of the optical disc, and the vertical axis represents the output value of the amplifier 3, so that the detection characteristics are
Since the waveform is shown by the solid line in FIG. 2, the direction and magnitude of the focusing error can be detected based on its sign and magnitude. As mentioned above, since the photodiode element a is formed so that the rate of increase/decrease in the light-receiving area changes greatly with respect to the rate of change in focusing error, the imaginary line as shown in FIG. Compared to the detection characteristics of the conventional example shown by , the output value of the amplifier 3 as the detection characteristics of the present invention shown by the solid line changes much more when the focusing error near the in-focus point changes. . Therefore, the detection sensitivity of the amount of focusing error can be improved.

In addition, each photodiode element aSb of the photometric sensor 1,
The shape of the dividing line 12 that divides c is not limited to the straight line shown in the above embodiment. For example, as shown in FIG. 3, the photodiode element a may have a convex shape outward with respect to the center line in the longitudinal direction, or as shown in FIG. It can be formed into various shapes so as to be convex inwardly with respect to the center line. Therefore, by optimizing the shape of the photodiode element a, the nonlinearity of the detection characteristics can be further improved.

The above embodiment is explained based on the same optical head structure as the conventional example, and it is assumed that the focal position of the detection light 2 is on the front side of the photometric sensor 1 during focusing when no focusing error occurs. Although explained above, the relative positional relationship between the focal point position and the position of the photometric sensor 1 is not limited, and for example, the photometric sensor is set such that the focal position of the detection light 2 at the time of focusing is on the back side of the photometric sensor 1. 1 may be placed. In this case as well, when focusing without a focusing error, the light is irradiated onto the photometric sensor 1 as shown by the imaginary line in FIG. The photometric sensor 1 is arranged so that the difference between the amount of light received by both photodiode elements S and C is zero.

In FIG. 5, the detection light 2 is directed in two different directions using, for example, a half prism 4, and the back side of the focal point of the first direction detection light 5 that passes through the half prism 4 in a straight line, and the half A second embodiment is shown in which first and second photometric sensors 7.8 similar to those described above are disposed on the near side of the focal point of the second direction detection light 6 whose optical path is deflected by the prism 4, respectively. ing. Note that the double-sided optical sensors 7.8 only need to be arranged at symmetrical positions with respect to the focal point, and each detection light 5.6
The focal point position may be opposite to that described above.

In this second embodiment, as shown in FIG. A2 to C2 are input to a pair of amplifiers 9.10 provided in parallel with each other, each having a circuit configuration similar to that of the previous embodiment. Furthermore, the output values P1 and P2 of each amplifier 9.10 are input manually to the amplifier 11, and the output value PL (B1+C1-Al) is outputted by the amplifier 11.
The output value p2 (B2+C2-A2) is subtracted from.

Since the change in the spot size of the first direction detection light 5 with respect to the first photometric sensor 7 is the same as in the embodiment described above, the output value P1 of the amplifier 9 is shown by the broken line in FIG. The second photometric sensor 8 includes the first photometric sensor 7
Since the spot size of the second direction detection light 6 changes in the opposite direction, the output value P2 of the amplifier 10 becomes as shown by the imaginary line in FIG. Therefore, amplifier 11
The output value (Pi-P2) from the amplifier 1 is calculated from the output value P1 of the amplifier 9 shown by the broken line to the output value P1 of the amplifier 1 shown by the imaginary line.
Since the output value P2 of 0 is subtracted, it becomes as shown by the solid line in FIG. 7, and the detection sensitivity and nonlinearity can be further improved.

Furthermore, when one photometric sensor 1 is used, as shown in FIG. 2, there are zero cross points at points other than the in-focus point, but as shown in the second embodiment, a pair of photometric sensors 7.
8 in a mutually compensatory manner, it is possible to eliminate zero cross points other than the in-focus point, and the amount of focusing error can be detected over a wide range. Moreover, the mutual compensation type can also suppress changes in detection characteristics due to fluctuations in the light emission pattern of the semiconductor laser.

FIG. 8 shows an optical head structure in which the emitted light 22 in a conventional example is divided into an O-th order traveling light and a pair of 1st-order diffracted lights, and focusing errors and tracking errors are detected by a so-called three-beam method. It is shown. Furthermore, the second
As in the embodiment described above, the detection light 2 is deflected in two directions, and each error is detected by a mutual compensation type that combines both directions. Note that the same reference numerals are given to the same parts as those shown in FIGS. 10 and 5 described above, and detailed explanation thereof will be omitted.

In this third embodiment, the output light 22 is connected between a collimator lens 24 and a polarizing beam splitter 25 by a main beam 17 consisting of a 0th-order diffracted beam for detecting a focusing error and a pair of primary beams 17 consisting of a 1st-order diffracted beam for detecting a tracking error. A diffraction grating 13 is disposed as a means for generating sub-beams 17a and 17b.Similar to the known three-beam method, the main beam 17 is irradiated onto the pits of the optical disk, and a pair of sub-beams 17a and 17b are generated. is irradiated onto both side edges of the track. Therefore, the detection light 2 that is reflected from the optical disk 23, deflected by the polarizing beam splitter 25, and then converged is composed of the main beam 17 and the pair of sub beams 17a, 17.
Furthermore, as in the second embodiment, the main beam and a pair of sub beams are separated into two different directions by a half prism 4 for each combination of a main beam and a pair of sub beams. In the first direction traveling straight through the half prism 4, a first direction main detection light 5 consisting of the reflected light of the main beam 17 and a sub beam 17a,
The first direction sub-detection beams 5a and 5b consisting of the reflected light of the main beam 17b are deflected downward in the figure by the half prism 4. Second-direction sub-detection light 6a, 6b consisting of the two-direction main detection light 6 and the reflected lights of sub-beams 17a, 17b are taken out, respectively.

In this third embodiment, a photometric sensor 7 similar to that of the previous embodiment is arranged in front of the focal point of the first direction main detection light 5,
A pair of double-sided optical sensors 7a, 7b as a corresponding third light receiving section are also arranged on the near side of the focal point of the first direction sub-detection light 5a, 5b, and the second direction main detection light 6 is also disposed. A photometric sensor 8 similar to that of the embodiment described above is arranged on the back side of the focal point, and a pair of third light receiving sections corresponding to the second direction sub-detection lights 6a and 6b are also provided on the back side of the focal point. Sensors 8a and 8b are arranged. Other conditions are the same as those in the second embodiment, so their explanation will be omitted. Similarly, focusing errors are detected in the same manner as in the second embodiment using two photometric sensors 7.8 corresponding to each main detection light beam 5.6, so detailed explanation thereof will be omitted.

The tracking error is caused by each of the photometric sensors 7a.

7b and each of the photometric sensors 8a and 8b are combined and detected. As shown in FIG. 9, the detection values D1 and El of the one side optical sensors 7a and 7b are input to the amplifier 14, and the output value P3 (Di-El
) is output, the detection values D2 and E2 of the other double-sided optical sensors 8a and 8b are input to the amplifier 15, the output value P4 (D2-E2) is output from the amplifier 15, and the output value is further output from the amplifier 16. The detected tracking error value is calculated by adding the value P3 and the output value P4.

According to the third embodiment, the photometric sensor groups corresponding to the first and second directions are arranged symmetrically with respect to the focal point of the detection light 2. Therefore, in the circuit configuration described above, the tracking error is calculated from the output value of the amplifier (P3+P4
), and by performing both error detection in a mutually compensated manner, the error in the change in error value due to the tilt of the optical disc 23 is reduced, and the noise generated in the focusing error signal when crossing the track is reduced. be able to. In this way, the present invention can be easily applied to an optical head structure using the three-beam method.

In each of the embodiments described above, an optical head for an optical disk is shown, but the present invention is not limited to an optical head for an optical disk.
For example, the present invention can also be applied to an optical head structure for transmitting and receiving information to and from a known optical card having tracks as an information recording medium on the surface of the card. In this case,
The structure includes the two λ/4 plates and six metal plates provided in the embodiment described above.

[Effects of the Invention] As described above, according to the present invention, detection sensitivity can be improved and the nonlinear detection characteristics The effect is extremely large because the optical head can be made smaller and the focusing error detection characteristics can be improved with a simple structure.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the shape and detection procedure of a photometric sensor based on the present invention. FIG. 2 is a diagram showing detection characteristics. 3 and 4 are diagrams showing another example of the divided shape of the photometric sensor. FIG. 5 is a diagram showing a second embodiment using a photometric sensor based on the present invention. FIG. 6 is a diagram showing the detection procedure of the second embodiment. FIG. 7 is a diagram showing the detection characteristics of the second embodiment. FIG. 8 is a diagram showing a third embodiment using a photometric sensor based on the present invention. FIG. 9 is a diagram showing the detection procedure of the third embodiment. FIG. 10 is a schematic diagram of main parts showing the structure of a conventional optical head. FIG. 11 is a diagram showing the shape and detection procedure of a conventional photometric sensor. FIG. 12 is a diagram showing detection characteristics of a conventional photometric sensor. 1... Photometry sensor 2... Detection light 3... Amplifier 4... Half prism 5... First direction main detection light 5a, 5b... First direction sub detection light 6... Third Two-direction main detection light 6a, 6b...Second direction sub-detection light 7...First photometry sensor 7a, 7b...Photometry sensor 8...Second photometry sensor 8a, 8b...Photometry Sensor 9.10.11... Amplifier 12... Parting line 13... Diffraction grating 14-1
6... Amplifier 17... Main beam 17a, 17b.
...Sub-beam 21...Semiconductor laser 22...Emitted light 23...Optical disk 24...
... Collimator lens 25 ... Polarizing beam splitter

Claims (2)

[Claims] (1) a first light receiving section disposed at a certain distance from a focal position in a state where no focusing error occurs on the axis of the detection light reflected and converged from the optical recording medium; A second light receiving section provided adjacent to the first light receiving section.
In the optical head structure of the type having a light receiving section and detecting the error based on the difference between detection values of both the light receiving sections, the first light receiving section is located at the center of the optical axis of the detected light. What is claimed is: 1. An optical head structure comprising a band-shaped area including a band-shaped area, wherein the width of the band-shaped area gradually increases from an end thereof toward a center position corresponding to the axis. (2) means for generating a main beam for focusing error detection and a pair of sub-beams for tracking error detection toward an optical recording medium; a first light receiving section disposed at a certain distance from the focal position in a state where no focusing error occurs on the axis of the detection light;
a second light receiving section provided adjacent to the first light receiving section; and a pair of second light receiving sections for separately detecting each of the sub detection lights reflected from the optical recording medium of the pair of sub beams. 3, and detects the focusing error based on the difference between detection values of the first and second light receiving parts,
In the optical head structure in which the tracking error is detected based on the difference between detection values of the pair of third light receiving sections, the first light receiving section has a band-like shape including the axis of the optical axis of the detection light. What is claimed is: 1. An optical head structure characterized in that the width of the band-shaped area gradually increases from an end thereof toward a center position corresponding to the axis.