JPH05258380A - Optical head - Google Patents

Abstract

PURPOSE:To realize a high C/N ratio and to display stable performance in a short time by holding a convex lens and a detection element at a prescribed distance and moving them in the direction of the optical axis of an incident luminous flux. CONSTITUTION:An optical head is provided with a supporting member 25 and the convex lens 6 is held at a prescribed distance from the detection element 21 and by moving them in the direction of the optical axis W1, an astigmatism amount for a focus error signal generated by the convex lens 6 and a nearly cylindrical surface 21b consisting of a quadratics of the detection element 21 is held constantly always and adjusted. That is, by such a constitution, the component is reduced and the cost of the head is reduced and further, time detection of an information signal and an error signal are performed independently and the high C/N ratio is realized and on the other hand, the stable performance is displayed in a short time by holding the fluctuation of the error signal constantly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head of an optical disk memory which is an apparatus for optically recording and reproducing information.

[0002]

2. Description of the Related Art It is said that the present age is the information age, and the technological development of high-density and large-capacity memory, which is the core of it, is being actively conducted. In addition to the above-mentioned high density and large capacity, the capabilities required for memory include high reliability, high-speed access, rewriting function, and so on. However, the present invention relates to an optical head in the magneto-optical disk memory.

Conventionally, many reports have been made on the technology relating to the optical head for the magneto-optical disk. Less than,
A conventional optical head for a magneto-optical disk will be described with reference to the drawings.

FIG. 5 is a schematic configuration diagram of a conventional optical head and a diagram for explaining the operation principle thereof. As shown in FIG. 5, the conventional optical head includes a semiconductor laser 1, a collimator lens 2, a beam splitter 3, and an objective lens 4.
, A half-wave plate 5, a convex lens 6, a polarization beam splitter 7, a two-division photodetector 8, a convex cylindrical lens 9, and a four-division photodetector 10.
Incidentally, 11 is a disk, and 12 and 13 are focal points of the light spot.

The operation of the conventional example configured as described above will be described below. Light emitted from the semiconductor laser 1 is converted into parallel light by a collimator lens 2, passes through a beam splitter 3, and an objective lens 4 incorporated in an objective lens driving device (not shown) causes a diameter of 1 on the disc 11. It is condensed as a light spot of about micron. The reflected light from the disk 11 follows the reverse path, is reflected and separated by the beam splitter 3, and
It is incident on the two-wave plate 5. The semiconductor laser 1 is installed so that the polarization direction is parallel to the paper surface, and the half-wave plate 5
Is set so that the polarization direction of the reflected light is rotated by about 45 degrees. The reflected light transmitted through the half-wave plate 5 becomes convergent light by the convex lens 6 and is separated into two polarization components orthogonal to each other by the polarization beam splitter 7, one of which is transmitted and is incident on the two-split photodetector 8. The other is reflected and enters the four-division photodetector 10 through the convex cylindrical lens 9. The tracking error signal is detected by the so-called push method by subtracting the electric signal generated by the two-division photodetector 8.

The light reflected by the polarization beam splitter 7 causes astigmatism by a convex cylindrical lens 9 which is a focus error signal detecting means. In the paper,
The optical path becomes a solid line and converges at the focal point 12. In the plane perpendicular to the paper surface, the optical path becomes a broken line and converges at the focal point 13.

The four-division photodetector 10 has a light-receiving surface located approximately in the middle of the focal points 12 and 13, and sums the diagonals of the electric signals generated in the four light-receiving areas and subtracts them. Thus, the focus error signal is detected by the so-called astigmatism method.

Further, the total amount of light received by the four-division photodetector 10 is calculated, the total amount of light reception by the two-division photodetector 8 is calculated, and the difference between them is calculated to obtain magneto-optical disk information by the differential detection method. The signal can be detected. Further, by taking the sum of them, it is possible to detect the amplitude modulation disc information signal and the prepit signal.

[0009]

However, the above-mentioned conventional configuration realizes the detection of the magneto-optical disk information signal by the so-called differential detection method using the polarization beam splitter 7, and is sufficient in function. However, because of the large number of components, there is a problem that it is difficult to achieve downsizing and cost reduction of the optical system.

Moreover, since the differential detection method, which also serves to detect the information signal and the error signal, is used, it is not suitable for the optical disk memory of the type requiring a high CN ratio, and the electrical signal is detected from the photodetector. To the amplifier that covers both the servo band and the information band from DC (0Hz) to several tens of MHz
It has a drawback that frequency characteristics up to are required.

Further, by the signal of the four-division photodetector 10,
The focus error signal is detected by the astigmatism method,
Since the convex lens 6 and the convex cylindrical lens 9 that determine the amount of astigmatism are independent of each other, it is not possible to keep the fluctuation of the signal constant.

Further, since the two-division photodetector 8 and the four-division photodetector 10 are independent of each other, it is difficult to make adjustments with high mass productivity. The present invention solves the above-mentioned conventional problems, and from the aspect of construction, it is possible to reduce the number of constituent parts and realize a low price, and to realize a high CN ratio by independently detecting an information signal and an error signal. It is an object of the present invention to provide an optical head that can be adjusted, and that can be adjusted for exhibiting stable performance in a short time, thereby improving mass productivity.

[0013]

In order to solve the above problems, an optical head according to the present invention comprises a semiconductor laser, a condensing means for condensing light from the semiconductor laser onto an information recording medium, and the information. A light beam separating means for separating reflected light from the recording medium, and a focus error signal on the information recording medium,
An optical head comprising a detection means for detecting a tracking error signal and an information signal, wherein the detection means is placed in the light beam separated by the light beam separation means and rotates a polarization plane by 45 degrees. A wave plate, a convex lens for converging the light beam transmitted through the half-wave plate, and a converging light beam by the convex lens are arranged to separate incident light into two light beams of transmitted light and reflected light, and the transmitted light. Is transmitted through a substantially cylindrical surface formed by a quadric surface, and reflected light from the beam splitter is incident, and the incident light is separated by a polarizing film into two light beams, transmitted light and reflected light, and transmitted by the beam splitter. A detection element composed of a polarization beam splitter that emits light in the same direction, a multi-segment photo detector that receives the light flux from the detection element, and an electrical signal generated by the multi-segment photo detector That it is composed of an arithmetic circuit, wherein the detection element and the lens has a configuration which is movable in the optical axis direction of the incident light beam is maintained at a predetermined constant distance.

Further, instead of using the half-wave plate, the detection element and the multi-divided photodetector are installed by rotating by 45 degrees with respect to the polarization plane of the light flux about the optical axis of the light flux incident on the detection element. You may.

Further, the convex lens and the detection element may be an integrated optical element. Further, the emitted light, which is separated by the beam splitter constituting the detection element and transmitted through the substantially cylindrical surface formed by the quadric surface, is perpendicular to the emitted light at a position where the emitted light is incident on a predetermined position of the light receiving region in the multi-divided photodetector. The configuration is such that an adjusting means for adjusting the position of the multi-divided photodetector in the plane is provided.

[0016]

With the above structure, the number of constituent parts is reduced to realize a low price, and the light quantities received in the plurality of light receiving regions of the photodetector are converted into electric signals, and the plurality of electric signals are calculated. Thus, it is possible to detect the magneto-optical disk information signal, the pre-pit signal, the focus error signal, and the tracking error signal. Moreover, since the information signal and the error signal are detected independently, an optical head suitable for an optical disk memory that requires a high CN ratio can be realized. In addition, the convex lens and the detection element are held at a certain fixed distance and can move in the optical axis direction of the incident light flux, so that the fluctuation of the error signal can be kept constant and stable performance can be achieved in a short time. It is possible to make adjustments and improve mass productivity.

Further, the position of the multi-split photodetector is adjusted so that the outgoing light, which is the transmitted light of the beam splitter constituting the detection element and transmitted through the substantially cylindrical surface formed by the quadric surface, enters the predetermined position of the light receiving region. By providing the adjusting means, it is possible to achieve stable performance in a short time with respect to the adjustment of the multi-segment photodetector, and it is possible to further improve mass productivity.

[0018]

【Example】

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings. The same functions as those of the conventional one are designated by the same reference numerals.

As shown in FIG. 1, the optical head includes a semiconductor laser 1, a collimator lens 2, a beam splitter 3 as a light beam separating means, an objective lens 4, a half-wave plate 5, and a convex lens 6. , A detection element 21 including a beam splitter 20A and a polarization beam splitter 20B, a photodetector 22, an adder 23, and three subtractors 24A, 2
4B and 24C, and a holding member 25 that keeps the convex lens 6 and the detection element 21 at a predetermined constant distance L and is movable in the optical axis direction W1.

Reference numeral 11 is a disk which is an information recording medium, 21a is a joint surface of the beam splitter 20A which constitutes the detecting element 21, and 21b is a substantially cylindrical surface which is a quadric surface of the beam splitter 20A which constitutes the detecting element 21. Two
1c is a polarization beam splitter 2 which constitutes the detection element 21.
0B polarizing film surface, 26 to 29 are first to fourth focal points, 30
To 32 are first to third light spots formed on the photodetector 22, and 33a to 33d, 34 and 35 are light receiving regions of the photodetector 22.

The operation of the optical head having the above structure will be described below. Light emitted from the semiconductor laser 1 is converted into parallel light by a collimator lens 2, passes through a beam splitter 3, and an objective lens 4 incorporated in an objective lens driving device (not shown) causes a diameter of 1 on the disc 11. It is condensed as a light spot of about micron. The reflected light from the disk 11 follows the reverse path, is reflected and separated by the beam splitter 3 which is a light beam separating means, and enters the ½ wavelength plate 5. The semiconductor laser 1 is installed so that the polarization direction is parallel to the paper surface, and the half-wave plate 5 sets the polarization direction of the reflected light to approximately 4
It is set to rotate 5 degrees.

The reflected light that has passed through the half-wave plate 5 is converged by the convex lens 6 and enters the detection element 21.
The detection element 21 separates the incident light into two light fluxes of transmitted light and reflected light at the joint surface 21a of the beam splitter 20A constituting the detection element 21, and the transmitted light of the first surface 21a is a quadric surface. It is configured to pass through the substantially cylindrical surface 21b, and also has the function of the conventional cylindrical lens shown in the conventional example. In this embodiment, it is provided so as to have a lens effect in the direction of about 45 degrees with respect to the image of the recording track of the disk 11 existing in the direction W4 in the plane parallel to the paper surface.

Of the light beams incident on the joint surface 21a of the beam splitter 20A constituting the detection element 21, the transmitted light flux on the joint surface is a substantially cylindrical surface 21b which is a quadric surface.
However, the substantially cylindrical surface 21b is approximately 4 times larger than the image of the recording track of the disk 11 existing in the W4 direction.
Since it is provided so as to have a lens effect in the direction of 5 degrees, the in-plane light flux having a lens effect is substantially cylindrical surface 21.
The degree of convergence is strengthened by the lens effect of b, and the lens converges at the first focus 26. Further, with respect to the light flux in the plane orthogonal to the surface having the lens effect, since the substantially cylindrical surface 21b is a flat surface, the light flux after passing through the optical path shown by the broken line is converged on the second focal point 27. To do. That is, the detection element 2
The transmitted light of the beam splitter 20A that has passed through the joint surface 21a of the beam splitter 20A and the substantially cylindrical surface 21b that is a quadric surface produces astigmatism.

On the other hand, of the luminous fluxes incident on the joint surface 21a of the beam splitter 20A constituting the detecting element 21, the reflected luminous flux of the joint surface 21a is incident on the polarizing film surface 21c of the polarizing beam splitter 20B constituting the detecting element 21. To do.
Of the light flux incident on the polarization film surface 21c of the polarization beam splitter 20B, S-polarized light (polarization component perpendicular to the paper surface) is reflected by the polarization film surface 21c and emitted in the same direction as the transmitted light of the bonding surface 21a of the beam splitter 20A. And then the third focus 28
Converge in. P-polarized light (polarized light component parallel to the paper surface)
After passing through the polarizing film surface 21c, is emitted in the same direction as the transmitted light of the joint surface 21a of the beam splitter 20A, and is focused on the fourth focal point 29. That is, all three emitted light beams from the detection element 21 are emitted in the same direction.

The photodetector 22 has a light receiving surface located approximately in the middle between the first focus 26 and the second focus 27, and on the light receiving surface, first to third light spots 30, 31, which are substantially circular, are formed. 32 is formed. On the light receiving surface of the photodetector 22, a light receiving area 33
a formed of a, 33b, 33c, 33d and having a substantially cruciform dividing line for receiving the first light spot 30 4
Two light receiving regions 3 that receive the divided light receiving region 33 and the second light spot 31 and the third light spot 32 independently of each other.
There are 4,35.

Of the four-divided light receiving regions 33 of the photodetector 22 on which the first light spot 30 is incident, the signals electrically connected to the light receiving regions 33a and 33b, and the light receiving regions 33c and 33d. The tracking error signal is detected by the so-called push-pull method by subtracting the signal electrically connected to the signal and the signal by the subtractor 24B.

Further, in the four-divided light receiving area 33, a signal obtained by electrically connecting the light receiving areas 33a and 33d and a signal obtained by electrically connecting the light receiving areas 33b and 33c are subtracted. The focus error signal is detected by the so-called astigmatism method by subtracting by 24A, that is, by connecting the diagonals of the four light-receiving areas and taking the sum, and taking the difference between them by the subtractor 24A.

Further, the second light spot 31 of S-polarized light is used.
Subtracts the difference between the electric signal generated in the light receiving area 34 of the photodetector 22 and the electric signal generated in the light receiving area 35 of the photodetector 22 into which the P-polarized third light spot 32 enters. By using 24C, the information signal of the disk 11 can be detected.

Further, the electric signal generated in the light receiving area 34 and the electric signal generated in the light receiving area 35 are added to each other by the adder 23.
It is possible to detect the information signal and the prepit signal of the amplitude modulation disk by taking the sum of the above.

That is, the focus and tracking error signals can be detected by the electric signal from the light receiving area 33 of the photodetector 22, and the light receiving areas 34 and 35 of the photodetector 22 can be operated independently of this error signal. With the electric signal of 1, the detection of information signals and prepit signals of the magneto-optical disc and the amplitude modulation disc can be realized.

Here, the holding member 25 keeps the convex lens 6 and the detection element 21 at a predetermined constant distance L, and holds them in the optical axis direction W1.
The convex lens 6 and the detection element 21
It is possible to adjust the astigmatism amount for the focus error signal generated by the second surface 21b having the substantially quadric surface and having a substantially cylindrical shape, which is always kept constant.

2 (a), 2 (b) and 2 (c) are enlarged views of the essential parts for explaining the operation of the focus error signal detection in this embodiment. 2A shows the case where the disk 11 is at the focal position of the objective lens 4 in FIG. At this time, the first light spot 30 on the photodetector 22 becomes substantially circular and the focus error signal obtained as the output of the subtractor 24A becomes zero. Further, in this way, when the objective lens 4 is in the in-focus position with respect to the disc 11, a signal electrically connected to the light receiving area 33a and the light receiving area 33b, and the light receiving area 33c and the light receiving area 33.
The tracking error signal can be detected by the so-called push-pull method by subtracting the signal electrically connected to d from the subtractor 24B.

FIG. 2B shows the disk 11 in FIG.
Is when the object lens 4 approaches the objective lens 4. In this case, since the light flux incident on the convex lens 6 becomes divergent light, the first to fourth
The focal points 26 to 29 of are displaced in the direction away from the detection element 21. Therefore, the first light spot 30 on the photodetector 22 has an elliptical shape as shown in FIG. 2B, in which case a positive focus error signal is obtained. 2C shows the case where the disk 11 in FIG. 1 is displaced in the direction away from the objective lens 4, contrary to FIG. 2B. In this case, contrary to the case of FIG. 2B, a negative focus error signal can be obtained.

As described above, according to this embodiment, the half-wave plate 5 for rotating the polarization plane of the reflected light from the disk 11 by 45 degrees and the convex lens for converging the light flux transmitted through the half-wave plate 5 are used. 6 and the converging light flux formed by the convex lens 6, splitting the incident light into two light fluxes of the transmitted light and the reflected light at the joint surface 21a, and the transmitted light is transmitted through the substantially cylindrical surface 21b formed of the quadric surface. A beam splitter 20A and a polarized beam which is reflected by the beam splitter 20A and is split into two beams, a transmitted beam and a reflected beam, by the polarizing film surface 21c and emitted in the same direction as the transmitted beam of the beam splitter 20A. By using the detection element 21 composed of the splitter 20B and the multi-divided photodetector 22 that receives the light flux from the detection element 21, the focusing error signal and the tracking error can be obtained with a very simple structure. Ring detection error signal can be realized, this error signal can be realized to detect the independent magneto-optical disc and the information signal and the prepit signal of the amplitude modulation disk. Moreover, since the information signal and the error signal are detected independently, a high CN ratio can be realized, and the error signal subtractor 24A,
The frequency characteristic of 24B is only required for the so-called servo band from DC to several tens of kHz, and the adder 23 for information signal,
The frequency characteristic of the subtractor 24C is from several 100 kHz to several MH.
Only the so-called information band of z is required. Further, the holding member 25
Is provided to keep the convex lens 6 and the detection element 21 at a predetermined constant distance L and to be movable in the optical axis direction W1, thereby forming a substantially cylindrical surface 21b composed of a quadric surface of the convex lens 6 and the detection element 21. The amount of astigmatism for the focus error signal generated in 1 can always be kept constant and adjusted.

In other words, with these configurations, the number of components is reduced to realize a low price, and the information signal and the error signal are detected independently, so that a high CN ratio can be realized and the servo band and the information can be obtained. The optical head can be composed of an amplifier having a frequency characteristic independent of the band. In addition, it is possible to maintain the variation of the error signal constant and perform stable performance in a short time, thereby improving mass productivity.

In this embodiment, the substantially cylindrical surface 21b of the beam splitter constituting the detection element is an optically convex cylindrical transmitting surface, but this is also the case with a concave cylindrical transmitting surface. The effect can be obtained.

Further, as in the present embodiment, it is general that the half-wave plate 5 is used to rotate the plane of polarization incident on the detection element 21, but this is not always necessary, and in that case. If the whole of the detection element 21 and the photodetector 22 is installed by rotating the optical axis about the optical axis by 45 degrees in the direction W3, the same effect can be obtained with a smaller number of parts.

FIG. 3 is a diagram showing a combined detection element. In FIG. 3, reference numeral 41 is a detection element, 41d is a convex lens surface, and all other reference numerals are the same as the constituent elements in FIG. Since the detection element 41 is a detection element in which the convex lens 6 and the detection element 21 in FIG. 1 are integrated, the same effect can be obtained with a smaller number of parts as compared with FIG.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to the drawings. FIG. 4 is a view showing the adjustment process of the photodetector according to the second embodiment of the present invention, and the other structure is basically the same as that of FIG.

In FIG. 4, reference numeral 22 denotes a photodetector, and 30 to 3
Reference numeral 2 denotes first to third light spots formed on the photodetector 22, and a light receiving area 33 is provided on the light receiving surface of the photodetector 22.
a formed of a, 33b, 33c, 33d and having a substantially cruciform dividing line for receiving the first light spot 30 4
Two light receiving regions 3 that receive the divided light receiving region 33 and the second light spot 31 and the third light spot 32 independently of each other.
There are 4,35.

The operation of the optical head configured as described above will be described below. The reflected light from the disk 11 in FIG. 1 becomes convergent light by the convex lens 6,
It enters the detection element 21. The operation of the light beam incident on the detection element 21 is exactly the same as that in FIG. 1, and the description thereof is omitted here.

Here, FIG. 4 shows W2 of the photodetector 22 of FIG.
FIG. 6 is a view from the direction of the arrow, showing the adjustment process of the photodetector 22. That is, FIG. 4A is a diagram showing a state before adjusting the photodetector 22, that is, the first to third light spots 30 to 32 and the four-division light reception on the light receiving surface of the photodetector 22. The positional relationship between the region 33 and the light receiving regions 34 and 35 is shown. In this state, a stable focus error signal by the astigmatism method using the first light spot 30 and a stable tracking error signal by the push-pull method cannot be obtained.

FIG. 4B is a diagram showing a state when the photodetector 22 is adjusted. Of the three emitted lights from the detection element 21, the first light spot 30 by the emitted light that has passed through the substantially cylindrical surface 21b formed by the quadric surface is incident on a predetermined position of the four-division light receiving area 33 in the photodetector 22. To the position
The position of the photodetector 22 is adjusted in a plane perpendicular to the emitted light. Here, as shown in the figure, the predetermined position of the four-division light receiving region 33 is a position where the intersection of two dividing lines of the four-division light receiving region 33 coincides with the center of the first light spot 30. The adjustment of the photodetector 22 according to the second embodiment of the present invention is completed in this state. That is, in this state, a stable focus error signal by the astigmatism method using the first light spot 30 and a stable tracking error signal by the push-pull method can be obtained.

However, in this state, the positional relationship between the first light spot 30 and the remaining second and third light spots 31 and 32 may not be in the designed positional relationship due to element accuracy, mounting accuracy, and the like. is there. However, the second and third
Since the two light receiving regions 34 and 35 which independently receive the light spots 31 and 32 of No. 1 are independent light receiving regions, respectively, a predetermined electric signal is obtained as long as the light spots exist in the corresponding light receiving regions. Can, first light spot 3
It is possible to realize stable detection of the information signal and the prepit signal of the magneto-optical disk and the amplitude modulation disk independently of the error signal due to 0.

As described above, according to the present embodiment, as described with reference to FIGS. 1 and 2, the cost is reduced by reducing the number of components, and the information signal and the error signal are detected independently. Therefore, a high CN ratio can be realized, and the optical head can be configured by an amplifier having independent frequency characteristics of the servo band and the information band. In addition to the effect that the fluctuation of the error signal can be kept constant, adjustment that can exhibit stable performance in a short time can be performed, and mass productivity can be improved.
With respect to the adjustment of the photodetector 22, it is possible to perform stable performance in a short time, and further mass productivity can be improved.

In this embodiment, the adjusting means of the photodetector 22 is not mentioned, but the adjusting means is not particularly limited as long as it is an adjustment which goes through the steps of FIGS. 4 (a) and 4 (b). ..

[0047]

As described above, according to the present invention, the semiconductor laser, the condensing means for condensing the light from the semiconductor laser on the information recording medium, and the light beam separation for separating the reflected light from the information recording medium. An optical head comprising means and a detection means for detecting a focus error signal, a tracking error signal and an information signal on the information recording medium, wherein the detection means is provided in the light beam separated by the light beam separation means. The half-wave plate that is placed and rotates the plane of polarization by 45 degrees;
A convex lens that converges the light flux that has passed through the half-wave plate,
A beam splitter disposed in a convergent light flux formed by the convex lens to separate incident light into two light fluxes of transmitted light and reflected light, and the transmitted light is transmitted through a substantially cylindrical surface formed by a quadric surface, and the beam splitter. And a detection element including a polarization beam splitter that separates the incident light into two light beams of transmitted light and reflected light by a polarizing film and emits the light in the same direction as the transmitted light of the beam splitter; A multi-segment photodetector that receives a light beam from an element and an arithmetic circuit that computes an electric signal generated by the multi-segment photodetector, and the convex lens and the detection element are held at a predetermined constant distance. The configuration is such that it can move in the optical axis direction of the incident light beam.

Further, instead of using the half-wave plate, the detection element and the multi-divided photodetector are installed by rotating by 45 degrees with respect to the polarization plane of the light flux about the optical axis of the light flux incident on the detection element. You may.

Further, the convex lens and the detection element may be an integrated optical element. Further, the emitted light, which is separated by the beam splitter constituting the detection element and transmitted through the substantially cylindrical surface formed by the quadric surface, is perpendicular to the emitted light at a position where the emitted light is incident on a predetermined position of the light receiving region in the multi-divided photodetector. This is a configuration in which an adjusting means for adjusting the position of the multi-divided photodetector in the plane is provided.

With these configurations, the cost is reduced by reducing the number of constituent parts, the light quantities received by the plurality of light receiving regions of the photodetector are converted into electric signals, and the plurality of electric signals are calculated. By this, the magneto-optical disk information signal,
Pre-pit signal, focus error signal, tracking error signal can be detected, and a high CN ratio can be realized because the information signal and the error signal are detected independently, and the servo band and the information band have independent frequency characteristics. An optical head can be configured with an amplifier having.

Further, since the convex lens and the detecting element are held at a predetermined constant distance and are movable in the optical axis direction of the incident light flux, the fluctuation of the error signal is kept constant and stable performance is exhibited in a short time. It is possible to make adjustments and improve mass productivity. Further, the emitted light, which is separated by the beam splitter constituting the detection element and transmitted through the substantially cylindrical surface formed by the quadric surface, is perpendicular to the emitted light at a position where the emitted light is incident on a predetermined position of the light receiving region in the multi-divided photodetector. By providing adjustment means for adjusting the position of the multi-segment photo detector in the plane, it is possible to achieve stable performance in a short time even for the adjustment of the multi-segment photo detector, further improving mass productivity. it can.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an optical head in a first embodiment of the present invention.

FIG. 2 is an enlarged view of a main part for explaining an operation of detecting a focus error signal in the same optical head. (A) shows a disc at a focal position of an objective lens, (b) shows that the disc approaches the objective lens. In this case, (c) shows the case where the disc is displaced in the direction away from the objective lens.

FIG. 3 is a diagram showing a configuration of a detection element combined in the optical head of the first embodiment.

4A and 4B are views showing the adjustment process of the photodetector in the second embodiment of the present invention, FIG. 4A showing a state before adjusting the photodetector, and FIG. 4B showing the photodetector. It is a figure which shows the state at the time of adjusting.

FIG. 5 is a diagram showing a schematic configuration of a conventional optical head.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Collimator lens 3 Beam splitter 4 Objective lens 5 1/2 wavelength plate 6 Convex lens 11 Disk 20A Beam splitter 20B Polarization beam splitter 21,41 Detection element 21a Bonding surface 21b Substantially cylindrical surface 21c Polarization film surface 22 Photodetector 23 Adder 24A-24C Subtractor 25 Holding member 26-29 Focus 30-32 Light spot 33-35, 33a-33d Light receiving area

Claims (4)

[Claims] 1. A semiconductor laser, a condensing means for condensing light from the semiconductor laser on an information recording medium, a light beam separating means for separating reflected light from the information recording medium, and on the information recording medium. Of the focus error signal, the tracking error signal, and the information signal, and the detecting means is placed in the light beam separated by the light beam separating means and has a polarization plane of 45 degrees. It is arranged in a half-wave plate for rotation, a convex lens for converging the light flux transmitted through the half-wave plate, and a converging light flux by the convex lens for separating incident light into two light fluxes of transmitted light and reflected light. A beam splitter in which the transmitted light passes through a substantially cylindrical surface formed by a quadric surface, and reflected light from the beam splitter are incident, and the incident light is separated into two light fluxes of transmitted light and reflected light by a polarizing film. Then, a detection element composed of a polarization beam splitter that emits light in the same direction as the transmitted light of the beam splitter, a multi-split photodetector that receives the light flux from the detection element, and a multi-split photodetector An optical head comprising a calculation circuit for calculating an electric signal, wherein the convex lens and the detection element are held at a predetermined constant distance and movable in the optical axis direction of the incident light beam. 2. A semiconductor laser, a condensing means for condensing light from the semiconductor laser onto an information recording medium, a light beam separating means for separating reflected light from the information recording medium, and on the information recording medium. An optical head having a focus error signal, a tracking error signal, and a detection unit for detecting an information signal, wherein the detection unit is a convex lens for converging the light beam separated by the light beam separation unit, and a convergence by the convex lens. A beam splitter disposed in the light flux to separate the incident light into two light fluxes of transmitted light and reflected light, and the transmitted light is transmitted through a substantially cylindrical surface formed of a quadric surface, and reflected light of the beam splitter is It is composed of a polarization beam splitter that splits the incident light into two light beams of transmitted light and reflected light by a polarizing film and emits the light in the same direction as the transmitted light of the beam splitter. A detection element, a multi-segment photodetector that receives a light beam from the detection element, and an arithmetic circuit that computes an electrical signal generated by the multi-segment photodetector,
The detection element is provided together with the multi-segment photodetector by being rotated about the optical axis of the light beam incident on the detection element by 45 degrees with respect to the polarization plane of the light beam, and the convex lens and the detection element are provided in a predetermined manner. An optical head that is held at a fixed distance and is movable in the optical axis direction of the incident light beam. 3. The optical head according to claim 1, wherein the convex lens and the detection element are integrated optical elements. 4. An output light, which is separated by a beam splitter constituting a detection element and transmitted through a substantially cylindrical surface composed of a quadric surface, is incident on a predetermined position of a light receiving region in a multi-split photodetector, 4. The optical head according to claim 1, wherein the adjusting means is provided for adjusting the position of the multi-divided photodetector in a plane perpendicular to the emitted light.