JPH11110791A - Reproduction pickup device for optical information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reproduction pickup device, with which short pit signals can be simultaneously read from a lot of tracks. SOLUTION: This device is composed of an optical radiation system having an objective lens with the prescribed number of apertures for forming an irradiated area narrowed to an almost diffraction limit in the extending direction of tracks by irradiating a plurality of adjacent tracks on a recording plane with the light beam of a prescribed wavelength, optical image formation system for forming a real image at a recording section due to the reflected light of the light beam with a prescribed lateral magnification, and photodetecting means having a plurality of photodetectors arranged almost vertically to the tracks of the real image at the recording section. In this case, concerning photodetectors 38a-38c, width (d) of each real image in the extending direction of the track has a length within the range shown by d<=1.2×α×λ/NA (α expresses a prescribed lateral magnification of the optical image formation system, NA expresses a prescribed number of apertures on the objective lens and λ expresses a prescribed wavelength of the light beam) and the photodetectors 38a-38c exist at the positions corresponding to a pitch (q) of tracks for the real image shown by q=p×α (p) expresses a prescribed track pitch of the optical information recording medium and αexpresses a prescribed lateral magnification of the optical image formation system} on the surface of the real image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reproduction pickup device for reproducing a signal recorded on an optical information recording medium such as an optical disk, and more particularly, to a multi-track recording system using very fine pits and marks arranged on tracks of a recording medium. The present invention relates to a reproduction pickup device for reproducing a signal at the same time.

[0002]

2. Description of the Related Art FIG. 1 shows a configuration example of an optical system of a conventional pickup device. In FIG. 1, 11 is a laser as a light source, 12 is a half mirror, 13 is a collimator lens,
14 is an objective lens, 16 is an optical disk, and 17 is a photodetector. In FIG. 1, a light beam emitted from a laser is converted into a substantially parallel light by a collimator lens 13 via a half mirror 12 and is incident on an objective lens 14. The objective lens is a diffraction-limited spot on an optical disc 16 (the diameter of this spot is Wavelength λ of light beam and numerical aperture NA of objective lens
Is called the minimum diameter specified in).

[0003] The reflected light of the optical disk is again transmitted to the objective lens 1.
Photodetector 1 collected at 4 and positioned out of focus
7, the entire amount of reflected light is detected. here,
A tracking error signal for tracing a predetermined track can be obtained from the difference in the amount of reflected light based on the deviation of the light intensity distribution on the light receiving element of the light detector in the vertical direction of the track, or the spread of the reflected light on the light receiving element. A focus error signal for controlling the focus position can be obtained from the area.

The pit period that can be read by this light spot must be larger than this spot diameter.
Further, in a short pit period close to the spot diameter, the signal modulation is greatly reduced, so that only a longer pit can be actually used. Therefore, in order to record a large amount of information, for example, digital data for high-definition television for two hours on an optical disk having a diameter of 12 cm, measures such as using a short-wavelength light source or using an objective lens having a larger numerical aperture are used. is necessary. Therefore, in order to satisfy these requirements, there has been a problem that the configuration of the pickup device becomes complicated or lacks stability.

That is, in the above-described non-confocal pickup optical system, even in the band within the cutoff frequency, the signal modulation degree becomes small in a fine pit structure close to the cutoff frequency, and the noise component contained in the signal is reduced. There was a problem that a good signal could not be read out of the way. As one of measures for solving such a problem, a confocal optical system is known. This is the Japanese Journal of Applied Physics, Vol. 28 (19
39) This is an optical system having a pinhole just before a light receiving element that receives reflected light as shown in Supplement 28-3, pp103108. FIG. 2 shows a configuration example of such an optical system.

In FIG. 2, reference numeral 21 denotes a laser serving as a light source; 22, a half mirror; 23, a collimator lens;
4 is an objective lens, 26 is an optical disk, 27 is a photodetector,
Reference numeral 28 denotes a pinhole placed on the image plane. In FIG. 2, a light beam emitted from a laser is a half mirror 22.
Through the collimator lens 23 to become substantially parallel light,
The light enters the objective lens 24 and forms a diffraction-limited spot on the optical disk 26. The image of the recording surface of the optical disk at this time is formed on a plane where the pinhole 28 exists, and only the central portion of the image passes through the pinhole and enters the photodetector 27. According to this method, the influence of the side lobe generated on the point image (diffraction limited spot) on the optical disk can be reduced, so that the signal modulation degree near the cutoff frequency can be increased, and high density recording has been achieved. The medium can be read.

However, since the spot diameter due to the reflected light on the photodetector passing through the pinhole does not change depending on the focal position, a tracking and focusing error detecting mechanism cannot be incorporated in the light receiving element side, and these position signals are obtained. It is necessary to use another means such as using another optical path system. In addition, the number of pit tracks that can be read at a time to irradiate a diffraction limited spot on the optical disk is limited to one track.

Further, as a method for solving such a problem, there is a technique called “semi-confocal pickup” described in “Optics”, Vol. 12, No. 7, page 442.
In this semi-confocal pickup method, a diffraction-limited spot is also formed on the optical disk, and the pinhole 2 shown in FIG.
An elongated slit is used in place of 8. The effect of confocal detection is provided in the vertical direction of the extending slit, and detection similar to the method shown in FIG. 1 is performed in the slit extending direction, and focus detection is also performed in the slit extending direction, so that a line requiring high resolution is required. The detection resolution can be increased in the speed direction, and focus detection can be performed simultaneously.

However, this method still has a problem that signals can be detected only from one track at a time.

[0010]

SUMMARY OF THE INVENTION The present invention makes it possible to capture signals from many tracks at once,
A signal recorded by a short pit or mark or a signal of a track disposed in close proximity that could not be read well by such a conventional method can be read without shortening the wavelength or increasing the numerical aperture. The purpose is to make it possible.

[0011]

According to the present invention, there is provided a reproduction pickup apparatus having a recording surface in which recording portions having different optical compositions or structures as signals are arranged in a line and formed as tracks, and the tracks have a predetermined track pitch. What is claimed is: 1. A reproduction pickup device for reading a recorded signal from an optical information recording medium formed, comprising: an objective lens having a predetermined numerical aperture; An irradiation optical system for irradiating a track to form one irradiation area narrowed to a diffraction limit in a direction in which the track of the recording medium extends, and reflected light from an irradiated portion of the light beam on the recording medium An imaging optical system for forming a real image of the recording portion on the image plane at a predetermined lateral magnification by an optical system, and a direction substantially perpendicular to a track of the real image of the recording portion on the image surface. And a plurality of consists of a light detection means having a light receiving element, each of the width d satisfies the following formula in the extension direction of the track of the real image of said light receiving element (1)

[0012]

D <= 1.2 × α × λ / NA (1) (In the equation (1), α is a predetermined lateral magnification of the imaging optical system and N
A indicates a predetermined numerical aperture of the objective lens, and λ indicates a predetermined wavelength of the light beam).
The light receiving element is provided by the following equation (2) on the real image plane.

[0013]

Q = p × α (2) (where p represents a predetermined track pitch of the optical information recording medium and α represents a predetermined lateral magnification of the imaging optical system) At a position corresponding to the pitch q of the track.

In the above-described reproducing pickup apparatus, the irradiation optical system has a cylindrical lens having a refracting power on a plane formed by an optical axis thereof and an extending direction of the track. In the reproduction pickup device,
The light receiving elements are arranged symmetrically with respect to the track direction of the real image.

In the above-mentioned reproducing pickup apparatus, one of the light receiving elements is divided symmetrically with respect to a track direction of the real image passing through the center. In the present invention, while irradiating a light beam as a linear spot extending in a direction perpendicular to the track on the optical disk, the size of each of the light receiving elements arranged at a position where a real image of the track and pit is formed is adjusted. By making the size of the linear spot unaffected by the side lobe and arranging the light receiving element at a position corresponding to the track pitch of the real image, it is possible to detect a semi-confocal signal while simultaneously taking in multiple tracks. According to the present invention,
The reproduction pickup device can be made compatible with optical disks having different track pitches.

[0016]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a reproduction pickup apparatus according to an embodiment of the present invention. FIG. 3 is a diagram showing the configuration of such an embodiment. In FIG. 3, reference numeral 31 denotes a semiconductor laser serving as a light source; 32, a half mirror;
Denotes a collimator lens, 34 denotes an objective lens, 36 denotes an optical disk, 38 denotes a photodetector, and 39 denotes a cylindrical lens.

As shown in FIG. 3, the light emitted from the semiconductor laser 31 is given a predetermined astigmatism by a cylindrical lens 39, and then converted into substantially parallel light by a collimator lens 33, and is incident on an objective lens 34. I do.
Since the cylindrical lens 39 has refracting power, that is, power, in only one direction, the light beam that has passed through the collimator lens 33 becomes a convergent light in one direction and a parallel light in a light beam perpendicular to one direction. , Objective lens 34
Incident on.

The converging light portion is focused on the information recording surface of the optical disk 36 by the objective lens 34. Further, the parallel light beam portion spreads without being focused on the information recording surface of the optical disk 36. Therefore, the light irradiated on the information recording surface becomes an elliptical or linear spot on the information recording surface, and one of the spots is narrowed to a diffraction limit in the direction in which the track of the recording medium extends. The cylindrical lens has a refractive power such that the longitudinal direction of the linear segment spot at the time of focusing substantially perpendicularly intersects with the extending direction of each information recording track of the optical disc 36, for example, the optical axis of the irradiation optical system and the track. Are arranged so as to generate astigmatism in a plane direction formed by the extension direction of the astigmatism. FIG. 4 shows an example of the spot shape at the time of focusing applied to the recording surface of the optical disc.

In the plan view of the recording surface in FIG. 4, reference numeral 40 denotes pits, 41, 42, and 43 denote center lines of information tracks formed of pit trains separated by a pitch p, 44 denotes a side lobe vertex position of a linear spot, Numeral 45 indicates the position of the end of the main lobe of the linear spot. Irradiation intensity distribution I (x ') with respect to position x' from the center of the linear spot on track 42
Is a width of a plane including the aperture radius, that is, the radius of curvature of the cylindrical lens 39, λ is the wavelength of the laser beam, f is the focal length of the objective lens 34, and e ′ is the aperture illuminance per unit angle.

[0020]

(Equation 5)

## EQU2 ## Where H1 is the primary Struve
They are called functions. NA = a / f
Then, this light intensity distribution I with respect to the position (Position) in units of λ / NA is shown in FIG. That is,

[0022]

At the position 2π × x ′ × λ / NA = 3.8 x ′ = 0.6λ / NA, it can be seen that the intensity of this linear spot has the first minimum from its center. This minimum value is the position 4 at the end of the main lobe of the linear spot in FIG.
It becomes 5.

In the present invention, the pit real image of the optical disk irradiated with the linear light spot is converted into an objective lens 34.
And the collimator lens 33 forms an image at a lateral magnification α on the light receiving element of the photodetector 38 arranged on the image plane.
That is, the numerical aperture NAc of the collimator lens 33 is set to the numerical aperture NAo of the objective lens 34.

[0024]

[Mathematical formula-see original document] By selecting so that NAo / NAc = α, the lateral magnification α of the imaging optical system can be obtained.
Set. When detecting reflected light with this imaging optical system,
As shown in FIG. 6, the light receiving elements 38a, 38b, 3 of the photodetector
On 8c, a linear spot, that is, a real image area 44a is formed by reflected light from the recording surface illuminated by the linear spot. Among them, the width d in the direction in which the formed pit image 40a moves is

[0025]

In the area where d <= 1.2 × α × λ / NA (1), the influence of the side lobe of the linear spot on the optical disk is reduced. Accordingly, each of the light receiving elements 38a, 38b, 38c has a size within the length range satisfying the above-described formula (1) at the center lines 41a to 43a (also referred to as track images) of the tracks of the pit row images on the image plane. Is set.

Further, at this time, the pitch q of the track image of the pit row on the image plane is represented by p, where p is the track pitch on the optical disk.

[0027]

## EQU9 ## Since q = p × α, each of the light receiving elements 38a, 38b, and 38c is provided in the direction perpendicular to the track image extending direction on the image plane.
It is formed at a pitch of q. The width of each light receiving element is within a range where adjacent light receiving elements do not overlap.

As described above, according to the present invention, by arranging a plurality of light receiving elements of a photodetector at positions corresponding to the pitch of a track image of a real image due to reflected light from a plurality of pit rows irradiated by linear light spots. Enables simultaneous playback of multiple tracks. Although the cylindrical lens 39 is used as the astigmatism generating means in FIG. 3, a hologram lens may be used.

Another embodiment according to the present invention, DVD and C
FIG. 7 shows a photodetector of a reproduction pickup device capable of performing dual-purpose reproduction with D. FIG. 7 shows another optical pickup device according to the present invention. The pickup device includes a semiconductor laser 31 as a light source, a cylindrical lens 39, a collimator lens 33, and an objective lens 34.
6, an irradiation optical system for forming a linear light spot by irradiating a light beam, an objective lens 34, a collimator lens 33,
An imaging optical system that includes a light beam splitter 32 and forms an actual image on the recording surface of the optical disk on the image surface at a predetermined lateral magnification; and a plurality of optical systems arranged on the image surface in a direction substantially perpendicular to the track direction of the real image of the recording portion. And a focusing servo circuit 113 and an actuator 51 for driving the objective lens in the optical axis direction of the irradiation light beam according to a focus error signal from the photodetector. And a tracking control drive mechanism including an actuator 52 and a tracking servo circuit 114 for driving the objective lens in the radial direction of the optical disk in accordance with a tracking error signal from the photodetector. Photodetector 62 for reading recorded information signal
Are arranged at an imaging position IP conjugate to the pits on the optical disk 36 in the imaging optical system.

FIG. 8 is a plan view of the photodetector 62. As shown in the figure, the light receiving element 62 has a track image formed at a pitch enlarged by the lateral magnification of the track pitch of the track image of the optical disk. Array along the direction perpendicular to the
A plurality (five in FIG. 8) of light receiving elements 621, 622, 623, 626, 627 for reproducing recorded information are provided. Therefore, when proper tracking control is performed, these light receiving elements 621, 622, 623, 626, and 627 can simultaneously receive reflected light modulated by pits corresponding to a plurality of tracks.

The light detector 62 includes light receiving elements 621, 622,
It has two pairs of inner and outer light receiving elements 90a and 90b sandwiching 623, 626, 627 and formed along the direction perpendicular to the track image extension direction for forming an image on the light receiving element. The pair of inner light receiving elements 90a are symmetric with respect to the center light receiving element 621, and are disposed on both outer sides adjacent to the light receiving elements 626 and 627 at both ends. The outer light receiving elements 90b are similarly arranged symmetrically on both outer sides of the pair of inner light receiving elements 90a.

The light detector 62 includes light receiving elements 621, 622,
A light receiving element located at the center along the direction substantially perpendicular to the arrangement direction of 623, 626, 627, that is, in the track image extension direction
It has a pair of track direction light receiving elements 100 formed symmetrically with respect to 621. The photodetector 62 receives the reflected light by the light receiving element pair groups 90a and 90b and the arrangement 100, and generates a light receiving output. Based on this, a focus error and tracking error signal and a read signal are generated.

FIGS. 9 and 10 show DVD and CD, respectively.
5 shows an image plane where a light receiving element is located at the time of reproduction. 9 and 10, reference numeral 61 denotes a center line of a central track image to be detected for DVD and CD. In FIG. 9, 62, 6
Reference numerals 3, 64, and 65 denote center lines of adjacent track images on the DVD optical disk, and reference numerals 611, 612, 613, 614, and 615 denote DVD pit images corresponding to the respective tracks. As an example, when the lateral magnification α of the optical system is α = 100, the adjacent track images 61 and 6
The track pitch q of the intervals on the image plane between 2, 62 and 64 is 74 μm since p = 0.74 μm for DVD. On the other hand, in FIG. 10, 66 and 67 are the center lines of the adjacent track images of the CD, and 610, 616 and 617 are also the CDs.
It is a pit image of. Similarly, since the track pitch of the CD is p = 1.6 μm, the track image pitch q is 160
μm.

The center line of the track image at the predetermined center is controlled to be aligned with the center of the light receiving element 621 by using the tracking control means to shift the objective lens in the radial direction of the optical disk. Such a pit image forms a real image area 68 on the image plane including side lobes by reflected light from the recording surface illuminated by the linear spot.
Each light-receiving element is formed within a smaller range 69, that is, the length in the track image extension direction is within the range of d in the above-described formula (1). Few.

As is clear from FIGS. 9 and 10, the light receiving elements 621, 622, 623, 626, and 627 are light receiving elements having a length in the track direction within the length range 69. CD track position 61
The pit images 610 to 617 are formed at positions and sizes that cover the pit images 610 to 617. Thereby, at the time of reproducing the DVD, the light receiving elements 621, 622, 623, 626, 62 as shown in FIG.
Pit images 611 to 511 of five tracks 61 to 65 adjacent to 7
615 functions as a photodetector that simultaneously detects the signal,
At the time of CD reproduction, as shown in FIG.
627 functions as a photodetector for simultaneously detecting signals of pit images 610, 616, 617 of three adjacent tracks 61, 66, 67. That is, on the image plane of the DVD in FIG. 9, the light receiving elements 621, 622, and 62 are used to detect the pit image at the track image pitch q where the pit images 611 to 615 exist.
3,626,627 are present and on the image plane of the CD in FIG.
The light receiving elements 621, 626, 62 detect the pit image at the position of the track image pitch q 'where the pit images 616, 610, 617 exist.
The light receiving elements 621, 622, 623, 626, 627 are arranged so that 7 exists.

In this embodiment, the light receiving element 621 is equally divided into two along the track image moving direction in order to perform tracking control. The light receiving element 621 is
It is set as follows. For example, in a DVD recording medium, a track or a pit has a track width or a pit width.
s (vertical direction of the track), the track width or pit width of the track images 61 to 65 on the light receiving element, which is the image plane, is given by the product of the lateral magnification α and the pit width s. Therefore, the width L of the light receiving surface of the two-divided light receiving element 621 in the direction perpendicular to the track image direction is set to a value smaller than twice the track pitch of the track image minus the width of the track image. That is, the two-divided light receiving element 62
When the track width or pit width on the optical disk is expressed as s, the sum L of the widths including the one divided gap is L <2 × α ×
p−α × s is set. With this setting, the two-part light receiving surface can have a width that can capture only the central track 61 and the surrounding image without being affected by the pit image of the adjacent track. The tracking error signal can be generated by detecting the difference between.

However, even if the central light receiving element is not divided into two, for example, tracking control is performed using another detector, tracking servo is possible. Regarding the focus position control in this embodiment, focus servo can be performed using the method described below. Light incident on the photodetector 62 is given astigmatism by the cylindrical lens 39, and forms a light spot on the light receiving element of the photodetector 62. Focus servo is performed by the change in the area of the light spot on the light receiving element at this time.

FIG. 11 shows that when the distance between the objective lens 34 and the information recording surface of the optical disk 36 changes due to the vertical movement of the objective lens, the light receiving surface of the light receiving element 62 is irradiated with the reflected light from the optical disk 36. It is the top view which showed the state (a)-(d) of the light spot near focusing. FIG.
(A) of FIG. 7 shows the case where the objective lens 34 is arranged at a focus position at a predetermined distance from the information recording surface of the optical disk 36 by focus control, that is, the information recording surface of the optical disk 36 and the light receiving element of the photodetector 62 This shows a case where the surfaces are in an imaging relationship. (B) shows a case where the objective lens 34 is located farther from the optical disc 36 than in the case (a). (C) shows the case where the objective lens 34 is closer to the optical disc 36 than in the case of (a), and (d) shows that the objective lens 34 is closer to the optical disc 36 than in the case of (c). It shows the case in which it is in the position.

When the objective lens 34 is located at a position corresponding to FIG. 11C, the light spot becomes substantially circular on the light receiving element of the photodetector 62, and before and after that, the arrangement direction of the light receiving elements 621, 622, 623, 626, 627 or An elliptical shape, that is, a linear spot having a major axis or a minor axis in a direction substantially perpendicular to the arrangement direction. In the present invention, one linear spot is used as the focus position.

In this case, the focus error signal is obtained by the output difference between the sum of the light receiving outputs of the pair of light receiving elements 90a and the pair of light receiving elements 100 and the sum of the light receiving outputs of the pair of light receiving elements 90b. In addition, each of the above light receiving elements,
In FIG. 11A, the focus error signal is almost zero.
The position and area of the light receiving element are set so as to have the following values.

Therefore, the focus error signal becomes 0 when the objective lens 34 is at the position shown in FIG. 11A, and becomes larger as the distance from or near the optical disk from the position of FIG. 11A. Set to have. Then, while the optical disk is rotating, the position of the objective lens 34 is moved in the optical axis direction so that the focus error signal becomes 0, so that the objective lens 34 is moved.
Can be performed so as to follow the in-focus position.

In this embodiment, the case of reproducing a DVD and a CD has been described, but the type of the optical disk is not limited to these. As described above, according to the present invention, the optical disk is irradiated with the linear spot, and the length of each light receiving element of the photodetector arranged on the imaging surface for detecting the linear spot in the track image extending direction is set to the above ( Since it is set within the range of d in the expression 1) and a plurality of light receiving elements are arranged in a direction perpendicular to the track image in accordance with the track pitch of the medium, it is hardly affected by intersymbol interference. Further, it is possible to provide a pickup capable of simultaneously reproducing multiple tracks even with media having different track pitches.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a conventional optical pickup device.

FIG. 2 is a diagram showing a schematic configuration of a conventional optical pickup device.

FIG. 3 is a diagram showing a schematic configuration of an optical pickup device according to an embodiment of the present invention.

FIG. 4 is a partially enlarged plan view of an optical disc showing a spot shape at the time of focusing applied to a recording surface in an embodiment of the present invention.

FIG. 5 is a graph showing a light intensity distribution from the center of a linear spot in a track direction of a disk.

FIG. 6 is a plan view of a linear spot and a pit image formed by reflected light on a light receiving element of a photodetector.

FIG. 7 is a diagram showing a schematic configuration of an optical pickup device according to another embodiment of the present invention.

FIG. 8 is a plan view of the photodetector of the embodiment.

FIG. 9 is a plan view of a linear spot and a pit image formed by reflected light on a light receiving element of the photodetector of the example.

FIG. 10 is a plan view of a linear spot and a pit image formed by reflected light on a light receiving element of the photodetector of the example.

FIG. 11 is a plan view of a photodetector of an example.

[Explanation of symbols]

Reference Signs List 31 semiconductor laser 32 half mirror, light beam splitter 33 collimator lens 34 objective lens 36 optical disk 37 photodetector 38a, 38b, 38c light receiving element of photodetector 39 cylindrical lens 40 pit 40a pit image 41, 42a, 43 center of information track Line 41a, 42a, 43a Track center of pit row image 44 Side lobe vertex position of linear spot 44a Real image range 45 End position of main lobe of linear spot 51,52 Actuator 62 Photodetector 621,622,623,626,627 Light receiving element 68 Real image range 69 Length range of light receiving element 62,63,64,65 Center line of adjacent track image of DVD optical disk 611,612,613,614,615 Pit image of DVD 610,616,617 Pit image of CD 90a Inner light receiving element 90b Outer light receiving element 100 Light receiving element in track direction 113 Focusing Robot circuit 114 Tracking servo circuit

Claims (2)

[Claims] 1. An optical information recording medium having a recording surface formed as a track by arranging recording portions having different optical compositions or structures as signals in a line and having the track formed at a predetermined track pitch. A reproduction pickup device for reading signals recorded on the recording medium, comprising: an objective lens having a predetermined numerical aperture; and irradiating a plurality of adjacent tracks on a recording surface of the recording medium with a light beam having a predetermined wavelength. An irradiation optical system that forms one irradiation area substantially narrowed to a diffraction limit in the extension direction of the recording medium; and an image of a real part of the recording part due to light reflected from the irradiation part of the light beam on the recording medium at a predetermined lateral magnification. An image forming optical system for forming an image on a surface, and a light detecting unit having a plurality of light receiving elements arranged in a direction substantially perpendicular to a track of a real image of the recording portion on the image surface. The width d of each of the light-receiving elements in the track extension direction of the real image is expressed by the following equation (1): d <= 1.2 × α × λ / NA (1) (in the equation (1), α is a predetermined lateral magnification of the imaging optical system, N
A indicates a predetermined numerical aperture of the objective lens, and λ indicates a predetermined wavelength of the light beam.) The light receiving element has the following formula (2) on the real image plane. Q = p × α (2) (where p represents a predetermined track pitch of the optical information recording medium and α represents a predetermined lateral magnification of the imaging optical system) A reproduction pickup device located at a position corresponding to a track pitch q. 2. The reproducing pickup apparatus according to claim 1, wherein said irradiation optical system has an optical element for generating astigmatism in a plane direction defined by an optical axis thereof and an extending direction of said track.