JPH0927135A - Optical information recording/reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive optical information recording/reproducing device improving recording density and hardly causing out-of-AT without using a special optical element. SOLUTION: A light beam outgoing from a semiconductor laser 21 becomes parallel light ray beams by a collimate lens 22 to be shaped to the beam with a prescribed intensity distribution by a beam shaping prism 23. Then, the beam is divided to three luminous flux by a diffraction grating 26, and further, the luminous flux S polarized by a polarizing beam splitter 27 are totally reflected to be converged on an optical card 1 by an objective lens 301 through a mirror 28. Three light beam spots converged on the optical card 1 are used for recording, reproducing, AF control and AT control respectively. The reflected light from light beam spots formed on the optical card 1 become the parallel luminous flux through the objective lens 301 again, and are reflected by the mirror 28, and are P polarized by the polarizing beam splitter 27, and further, are reflected by a reflection mirror 31 to be led to a photodetector 34.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording / reproducing technique, and more particularly to recording information on an optical information recording medium and reproducing the information recorded on the recording medium. The present invention relates to an optical information recording / reproducing device that erases information recorded on the recording medium.

[0002]

2. Description of the Related Art Conventionally, various types of information recording media such as discs, cards, tapes, etc. are known for recording and reproducing information by using light.
These optical information recording media include those capable of recording and reproduction and those capable of reproduction only. Recording of information on a recordable medium is performed by scanning an information track with a light beam that is modulated according to the recording information and narrowed down into a minute spot, and the information is recorded as an optically detectable information bit sequence. .

In reproducing information from a recording medium, an information bit sequence of an information track is scanned with a light beam spot having a constant power such that recording is not performed on the medium, and reflected light or transmitted light from the medium is read. This is performed by detecting

[0004] The optical head used for recording and reproducing information on and from the recording medium described above is relatively movable with respect to the recording medium in the information track direction and in the direction crossing the direction. Information track scanning of the beam spot is performed. As a lens for narrowing a light beam spot in the optical head, for example, an objective lens is used. The main body of the optical head is such that the objective lens can be independently moved in its optical axis direction (focusing direction) and in a direction (tracking direction) orthogonal to both the optical axis direction and the information track direction of the recording medium. Is held in. Such an objective lens is generally held via an elastic member, and the movement of the objective lens in the above two directions is generally driven by an actuator utilizing magnetic interaction.

[0005] Among the above-mentioned optical information recording media, a card-shaped optical information recording medium (hereinafter referred to as an optical card) will be a large and small-sized information recording medium that is convenient to carry in the future. Demand is expected.

FIG. 7 is a schematic plan view of a write-once optical card, and FIG. 8 is a partially enlarged view thereof.

In FIG. 7, a large number of information tracks 2 are arranged on the information recording surface of the optical card 1 in parallel with the LF direction. On the information recording surface of the optical card 1, a home position 3 serving as a reference position for accessing the information track 2 is provided. The information track 2 is 2-1 to 2-2, 2-3,.
As shown in FIG. 8, the tracking track 4 is adjacent to each of these information tracks, and
.., Are provided sequentially. These tracking tracks 4 are used as guides for auto tracking (hereinafter, referred to as AT) for controlling the beam spot so as not to deviate from a predetermined information track when scanning a light beam spot during information recording and reproduction. .

The AT servo detects a deviation (AT error) of the light beam spot from the information track in the optical head, gives a negative feedback to the detection signal to the tracking actuator, and connects the objective lens to the optical head body. This is performed by moving the light beam spot in a tracking direction (D direction) to follow a desired information track.

In information recording and reproduction, when an information track is scanned with a light beam spot, the light beam is formed into an appropriately sized spot on the optical card surface (focusing). Focusing (hereinafter, referred to as AF) servo is performed. The AF servo detects a deviation (AF error) of the light beam spot from the in-focus state in the optical head, feeds back the detection signal to the focusing actuator, and moves the objective lens to the optical head body in the focusing direction. To focus the light beam spot on the optical card surface.

In FIG. 8, S₁ , S_Two , S_Three Is
Indicates a light beam spot, S₁ And S _Three Light spot
AT_Two AF using light spot
And creation of information bits during recording,
Perform reading. In each information track, 6-
1, 6-2 and 7-1, 7-2 are preformatted respectively
The left address part and the right address part are shown.
By reading the address part, the information track can be identified.
Be done. 5 (corresponding to 5-1 and 5-2 in the figure)
Data section, in which predetermined information is recorded.

Here, the optical information recording method will be described with reference to the schematic view of the optical head optical system shown in FIG. 9 as the background art of the present invention.

In FIG. 9, reference numeral 21 denotes a semiconductor laser which is a light source, and in this example, it is polarized in the direction of the plane of the paper 83.
It emits light with a wavelength of 0 nm. Further, 22 is a collimator lens, 23 is a beam shaping prism, 24 is an aperture,
Reference numeral 25 is a half-wave plate, 26 is a diffraction grating for splitting a light beam, and 27 is a polarization beam splitter. Further, 28 is a surface reflection mirror, 29 is a quarter wavelength plate, 30 is an objective lens, 31 is a surface reflection mirror, 32 is a spherical lens, 33 is a cylindrical lens, and 34 is a photodetector. The photodetector 34, as shown in FIG.
a, 34c and a four-divided light receiving element 34b.

The light beam emitted from the semiconductor laser 21 enters the collimator lens 22 as a divergent light beam. Then, the light is converted into a parallel light beam by the lens, and further shaped by the beam shaping prism 23 into a beam having a predetermined light intensity distribution, that is, a circular intensity distribution. Then, the light flux passes through the aperture 24 to have a desired light flux diameter, and reaches the half-wave plate 25. By passing through the half-wave plate 25, the polarization direction of the light flux becomes a direction perpendicular to the paper surface. After that, the light beam enters the diffraction grating 26, and is split into three effective light beams (0th-order diffracted light and ± 1st-order diffracted light) by the diffraction grating 26. These three light beams enter the polarization beam splitter 27 as S-polarized light beams.
The polarization beam splitter 27 has a spectral characteristic as shown in FIG. 10, and the incident S-polarized light is reflected by nearly 100%.

Next, the three light beams pass through the quarter-wave plate 29 through the mirror 28, are converted into circularly polarized light at this time, and are focused on the optical card 1 by the objective lens 30. As shown in FIG. 8, the focused lights are three minute beam spots S ₁ (+ _{1st order} diffracted light), S ₂ (0th order diffracted light), and S ₃ (−1st order diffracted light). S ₂ is recording, reproducing, used in AF control, S ₁ and S ₃ are used for AT control. As shown in FIG. 8, the spot positions on the optical card 1 are such that the light beam spots S ₁ and S ₃ are located on adjacent tracking tracks 4 and the light beam spot S ₂ is an information track 2 between the tracking tracks. Located on top. Thus, the reflected light from the light beam spot formed on the optical card 1 passes through the objective lens 30 again to be a parallel light beam, and passes through the quarter-wave plate 29 to have a polarization direction of 90 degrees from that at the time of incidence. ° Converted to a rotated light beam. Then, it enters the polarization beam splitter 27 as a P-polarized beam, is transmitted by nearly 100% according to the spectral characteristics shown in FIG. 10, is reflected by the mirror 31, and is guided to the detection optical system.

In the detection optical system, the spherical lens 32 and the cylindrical lens 33 are combined, and the AF control by the astigmatism method is performed by this combination. The three light beams reflected from the optical card 1 are respectively collected by the detection optical system and enter the photodetector 34,
Form three light spots. Light receiving elements 34a, 34c
Receives the reflected light of the light spots S ₁ and S ₃ , and performs AT control using the difference between the outputs of these two light receiving elements. Further, fourth light receiving 34b of split light spot S ₂
The reflected light is received, the AF control is performed using the output, and the recorded information is reproduced. As shown in FIG.
In the light receiving elements 34a, 34b, 34c, the respective light spots S _a , S _b , S _c are the light receiving elements 34a, 34b, 34.
It is completely contained in c.

As shown in FIG. 9, the optical head optical system as described above is divided into a fixed portion and a movable portion, and only the movable portion is moved as shown by an arrow to obtain a light beam spot. The information track can be scanned in S ₂ . In such a separation type optical head, the moving amount of the movable portion needs to be about the length of the optical card 1 in the vertical direction, and is usually 100 m.
m.

Reference numeral 35 is an outer wall of the optical head fixing portion.

[0018]

In the optical head as described above, all the three light beams pass through the effective diameter of the objective lens, and recording, reproduction and AF control on the optical card 1 are performed. Since the size of the 0th-order diffracted light spot and the ± 1st-order diffracted light spot for AT control are the same, the diameter of the 0th-order diffracted light spot is increased in order to improve the recording density of an optical information recording medium such as an optical card. If it is attempted to reduce, the diameter of the ± 1st-order diffracted light spot also becomes smaller. By the way, for AT control, the diameter of the ± 1st-order diffracted light spot for AT control is the cross-track direction (tracking direction).
It is desirable to have a large Therefore, it is contradictory that the occurrence of the AT deviation is unlikely to occur and that the recording density is improved.

In Japanese Patent Laid-Open No. 63-25843, a special optical element in which a diffraction grating portion is formed only in the center of a transparent member such as glass is used to form a light spot on an optical card by a 0th-order diffracted light beam. Is smaller than the light spot of the ± 1st-order diffracted light flux, thereby improving the recording density and
It has been proposed to make the detachment less likely to occur.

Therefore, the present invention is based on the above-mentioned JP-A-63-25.
It is an object of the present invention to improve recording density and prevent AT deviation from occurring without using a special optical element as described in Japanese Patent Publication No. 843, and thus at low cost.

[0021]

According to the present invention, in order to achieve the above object, a light beam from an irradiation optical system including a light beam splitting member for splitting a light beam from a light source into three light beams is narrowed to be optically. One of three light beams from the irradiation optical system, which has an optical head for irradiating the optical information recording medium as three light spots and projecting the light beams from the light spots on the recording medium onto a detection optical system. In the optical information recording / reproducing apparatus for recording and / or reproducing information on the recording medium by using the other two, and performing auto-tracking control using the other two. At least one of the optical elements arranged in the optical path between them has an effective diameter set so as to block an outer part of each of the two outer parts of the three light beams. Emotion Recording and reproducing apparatus, is provided.

In one aspect of the present invention, an objective lens is arranged in the optical path between the light beam splitting member and the recording medium, and the effective diameter of the objective lens is outside the three light beams. It is set to block a part of the outside of each of the two.

In one aspect of the present invention, a reflection mirror is arranged in the optical path between the light beam splitting member and the recording medium, and the effective diameter of the reflection mirror is outside the three light beams. It is set to block a part of the outside of each of the two.

In one aspect of the present invention, a 1/4 wavelength plate is arranged in the optical path between the light beam splitting member and the recording medium, and the effective diameter of the 1/4 wavelength plate is the above-mentioned three. It is set so as to block a portion of each of the two outer sides of the light flux.

In one aspect of the present invention, at least a part of a light beam from a light spot on the recording medium is separated from the irradiation optical system in the optical path between the light beam dividing member and the recording medium. A light beam separating means for directing the light to the detection optical system is provided.

In one aspect of the present invention, the light beam splitting means is a polarization beam splitter.

In one aspect of the present invention, the effective diameter of the light beam separating means is set so as to block a part of each of the outer two of the three light beams.

In one aspect of the present invention, an aperture is arranged in the optical path between the light beam splitting member and the recording medium, and the two outer sides of the three light beams are respectively provided by the aperture. It is set so that a part of is blocked.

In one aspect of the present invention, a polarization beam splitter, a reflection mirror, and a quarter mirror are provided in the optical path between the light beam splitting member and the recording medium in order from the light beam splitting member side.
A wave plate and an objective lens are arranged, and at least one of these optical elements is set so that its effective diameter blocks a portion of each of the two outer sides of the three light beams.

In one aspect of the present invention, between the polarization beam splitter and the reflection mirror, between the reflection mirror and the quarter wavelength plate, and between the quarter wavelength plate and the objective lens. An aperture is arranged in at least one of the two, and the aperture is set so as to block a part of each of the two outer sides of the three light beams.

In one aspect of the present invention, the light beam splitting member is a diffraction grating, and one of the three light beams is used.
One is a 0th-order diffracted light flux, and the other two outside the above are ± first-order diffracted light fluxes.

[0032]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing an example of an optical head of an optical information recording / reproducing apparatus according to the present invention. In this figure, the same members as those in FIG. 9 are designated by the same reference numerals.

In FIG. 1, reference numeral 21 denotes a semiconductor laser which is a light source, and in this example, it is polarized in the direction of the plane of the paper 83.
It emits light with a wavelength of 0 nm. Further, 22 is a collimator lens, 23 is a beam shaping prism, 24 is an aperture,
Reference numeral 25 is a half-wave plate, 26 is a diffraction grating for splitting a light beam, and 27 is a polarization beam splitter. Further, 28 is a surface reflection mirror, 29 is a quarter wavelength plate, 301 is an objective lens, 31 is a surface reflection mirror, 32 is a spherical lens, 33
Is a cylindrical lens, and 34 is a photodetector. The photodetector 34, as shown in FIG.
a, 34c and a four-divided light receiving element 34b.

The light beam emitted from the semiconductor laser 21 enters the collimator lens 22 as a divergent light beam. Then, the light is converted into a parallel light beam by the lens, and further shaped by the beam shaping prism 23 into a beam having a predetermined light intensity distribution, that is, a circular intensity distribution. Then, the light flux passes through the aperture 24 to have a desired light flux diameter, and reaches the half-wave plate 25. By passing through the half-wave plate 25, the polarization direction of the light flux becomes a direction perpendicular to the paper surface. After that, the light beam enters the diffraction grating 26, and is split into three effective light beams (0th-order diffracted light and ± 1st-order diffracted light) by the diffraction grating 26. These three light beams enter the polarization beam splitter 27 as S-polarized light beams.
The polarization beam splitter 27 has a spectral characteristic as shown in FIG. 10, and the incident S-polarized light is reflected by nearly 100%.

Next, the three light beams pass through the mirror 28 and the quarter wavelength plate 29, are converted into circularly polarized light at this time, and are converged on the optical card 1 by the objective lens 301. As shown in FIG. 8, the focused lights are three minute beam spots S ₁ (+ _{1st order} diffracted light), S ₂ (0th order diffracted light), and S ₃ (−1st order diffracted light). S ₂ is recording, reproducing, used in AF control, S ₁ and S ₃ are used for AT control. As shown in FIG. 8, the spot positions on the optical card 1 are such that the light beam spots S ₁ and S ₃ are located on adjacent tracking tracks 4 and the light beam spot S ₂ is an information track 2 between the tracking tracks. Located on top. Thus, the reflected light from the light beam spot formed on the optical card 1 is again reflected by the objective lens 301.
Is converted into a parallel light beam through the ¼ wavelength plate 29 and is converted into a light beam whose polarization direction is rotated by 90 ° from that at the time of incidence. Then, it enters the polarization beam splitter 27 as a P-polarized beam, is transmitted by nearly 100% according to the spectral characteristics shown in FIG. 10, is reflected by the mirror 31, and is guided to the detection optical system.

The detection optical system including the mirror 31, the spherical lens 32 and the cylindrical lens 33 is used to perform the AF control by the astigmatism method by the combination of the spherical lens 32 and the cylindrical lens 33. The three light fluxes reflected from the optical card 1 are respectively collected by the detection optical system and enter the photodetector 34 to form three light spots. The light receiving element 34a, 34c will receive the reflected light of the foregoing light spot S _1, S _3, AT control is performed using the difference between the outputs of the two light receiving elements. The light receiving element 34b of the 4 division receives the reflected light of the light spot S _2, and recorded information is carried out AF control using the output is reproduced.

The optical head optical system as described above is divided into a fixed portion and a movable portion as shown in FIG. 1, and only the movable portion is moved as shown by an arrow to obtain a light beam spot. The information track can be scanned in S ₂ .
Reference numeral 35 is an outer wall of the optical head fixing portion.

In the above embodiment, the objective lens 30
The effective diameter of 1 is set so as to block two parts on the both sides of the three light beams (0th-order diffracted light and ± 1st-order diffracted light), that is, a part of the outside of each ± 1st-order diffracted light. FIG.
It is a schematic diagram showing a state of shading by such an objective lens.

In FIG. 2, the 0th-order diffracted light beam is not limited by the effective diameter of the objective lens 301 and the ± 1st-order diffracted light beams are limited in the cross-track direction (a part of the outer side is vignetted to cause a vignetting part). 0 on optical card 1
It is possible to make the ± first-order diffracted light spots S ₁ and S ₃ elongated in the track crossing direction while keeping the diameter of the _second-order diffracted light spot S ₂ small, thus improving the recording density and making it difficult for AT deviation. be able to. Hereinafter, the reason will be described.

FIG. 3 is a diagram showing the relationship between the cross-sectional shape and size of the effective incident laser beam on the objective lens and the shape and size of the light spot on the optical card when the laser light is focused. As shown in FIG. 3 (a), if the diameter of the light beam entering the effective diameter of the objective lens is large, the diameter of the light spot becomes small, and as shown in FIG. The smaller the diameter of the incident light beam, the larger the diameter of the light spot. Therefore, as shown in FIG. 3C, when the light beam entering the effective diameter of the objective lens is elongated in the first direction, the light spot moves in the second direction orthogonal to the first direction. It has an elongated shape.

The above embodiment is as shown in FIG. 3A for the 0th-order diffracted light beam and is shown in FIG.
This corresponds to the one shown in (c).

FIGS. 4 and 5 show the AT using the three-beam method.
Light spot S formed on the optical card for control
₁ is a diagram showing relationship between the (a) and AT error signal (b) and S _2, S ₃ and the track 4. FIG. 4 shows the background art shown in FIG. 9 (that is, when the 0th-order diffracted light and the ± 1st-order diffracted light incident on the effective diameter of the objective lens have the same diameter), and FIG. 5 shows the embodiment of the present invention. is there. In the case of the embodiment of the present invention, since the ± first-order diffracted light spots S ₁ and S ₃ are formed elongated in the track crossing direction, the AT pull-in range becomes larger than that in the background art, thus causing AT deviation. It becomes difficult, and highly reliable AT control can be performed.

FIG. 6 is a schematic view showing a modification of the state of light shielding by the objective lens in the optical head of the modified embodiment of the optical information recording / reproducing apparatus according to the present invention as described above.

In this modification, the direction of division into three light beams (0th-order diffracted light and ± 1st-order diffracted light) by the diffraction grating 26 is different from that shown in FIG. In this case, the ± first-order diffracted light spots S ₁ and S ₃ are formed elongated in a direction slightly inclined with respect to the track crossing direction, but the AT pull-in range becomes larger than that in the background art, thus causing AT deviation. It becomes difficult, and highly reliable AT control can be performed.

In the above embodiments, the optical head optical system is shown as a separate type, but the present invention is also applicable to an optical information recording / reproducing apparatus having an optical head optical system that is not a separate type. Can be applied.

Next, another modification of the present invention will be described.

The effective diameter of the reflection mirror 28 arranged in the optical path between the diffraction grating 26 which is the light beam splitting member and the optical card 1 which is the recording medium is the outer side of the three light beams divided by the diffraction grating 26. The example is set so as to block a part of the outside of the ± 1st-order diffracted light of. Also in this case, FIG. 2 and FIG.
In the reflection mirror 28, the vignetting of the ± first-order diffracted light as described with respect to the objective lens 301 is generated.

The effective diameter of the quarter-wave plate 29 arranged in the optical path between the diffraction grating 26, which is the light beam splitting member, and the optical card 1, which is the recording medium, has the effective diameter of the three light beams divided by the diffraction grating 26. An example in which it is set so as to block a part of the outer ± first-order diffracted light on the outer side. Also in this case, the vignetting of the ± first-order diffracted light as described with respect to the objective lens 301 in FIGS. 2 and 6 occurs in the quarter-wave plate 29.

The effective diameter of the polarization beam splitter 27, which is the light beam splitting means, disposed in the optical path between the diffraction grating 26, which is the light beam splitting member, and the optical card 1, which is the recording medium, is the three light beams split by the diffraction grating 26. ± of the outside of the beam
An example set so as to block a part of the outer side of the first-order diffracted light. Also in this case, the objective lens 30 shown in FIGS.
Vignetting of the ± first-order diffracted light as described with reference to No. 1 occurs in the polarization beam splitter 27.

An aperture (not shown) arranged in the optical path between the diffraction grating 26, which is a light beam splitting member, and the optical card 1, which is a recording medium, blocks two outer parts of the two outer lights of the three light beams. An example that is set to be able to. Also in this case, the objective lens 30 shown in FIGS.
Vignetting of the ± first-order diffracted light as described with respect to 1 occurs at the aperture. The apertures are between the polarization beam splitter 27 and the reflection mirror 28 (on the fixed portion side or the movable portion side), between the reflection mirror 28 and the quarter wavelength plate 29, and between the quarter wavelength plate 29 and the objective lens 301. Can be located in at least one of the spaces.

Although the effective diameter of the optical element is circular in the above description, the effective diameter of the optical element may be rectangular or other shapes in the present invention.

[0053]

As described above, according to the present invention, the recording density is improved and AT deviation is less likely to occur, and the reliability of recording and reproduction is improved without using a special optical element and at a low cost. Can be increased.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an optical head of an optical information recording / reproducing apparatus according to the present invention.

FIG. 2 is a schematic diagram showing how light is shielded by an objective lens in the optical head of the optical information recording / reproducing apparatus according to the present invention.

FIG. 3 is a diagram showing a relationship between a cross-sectional shape and size of a laser beam incident on an objective lens and a shape and size of a light spot on an optical card.

FIG. 4 is a diagram showing a relationship between a light spot and a track formed on an optical card and an AT error signal.

FIG. 5 is a diagram showing a relationship between a light spot and a track formed on an optical card and an AT error signal.

FIG. 6 is a schematic diagram showing how light is shielded by an objective lens in the optical head of the optical information recording / reproducing apparatus according to the present invention.

FIG. 7 is a schematic plan view of the optical card.

FIG. 8 is a partially enlarged view of the optical card.

FIG. 9 is a diagram of a separated optical head optical system.

FIG. 10 is a spectral characteristic diagram of a polarizing beam splitter.

FIG. 11 is a diagram showing a relationship between the shape and arrangement of a photodetector and a light spot in an optical information recording / reproducing apparatus.

[Explanation of symbols]

 1 Optical Card 21 Semiconductor Laser 22 Collimator Lens 23 Beam Shaping Prism 24 Aperture 25 1/2 Wavelength Plate 26 Diffraction Grating 27 Polarizing Beam Splitter 28 Mirror 29 1/4 Wavelength Plate 30,301 Objective Lens 31 Reflection Mirror 32 Spherical Lens 33 Cylindrical Lens 34 Photodetector 34a, 34b, 34c, 34d Light receiving element 35 Fixed part outer wall

Claims (11)

[Claims] 1. A light beam from an irradiation optical system including a light beam splitting member for splitting a light beam from a light source into three beams is focused and irradiated onto an optical information recording medium as three light spots, and on the recording medium. An optical head that projects a light beam from a light spot onto a detection optical system is used, and information is recorded on the recording medium and / or recording information is recorded using one of the three light beams from the irradiation optical system. In an optical information recording / reproducing apparatus for reproducing and performing auto-tracking control using the other two, at least one of optical elements arranged in an optical path between the light beam splitting member and the recording medium has an effective diameter. Is set so as to block a portion of each of the two outer sides of the three light fluxes, and an optical information recording / reproducing apparatus. 2. An objective lens is arranged in an optical path between the light beam splitting member and the recording medium, and an effective diameter of the objective lens is two outside of the three light beams. The optical information recording / reproducing apparatus according to claim 1, wherein the optical information recording / reproducing apparatus is set so as to block a part. 3. A reflection mirror is arranged in an optical path between the light beam splitting member and the recording medium, and an effective diameter of the reflection mirror is set to an outer side of each of two outer sides of the three light beams. The optical information recording / reproducing apparatus according to any one of claims 1 to 2, wherein the optical information recording / reproducing apparatus is set so as to block a part. 4. A quarter-wave plate is arranged in the optical path between the light beam splitting member and the recording medium, and the effective diameter of the quarter-wave plate is outside the three light beams. The optical information recording / reproducing apparatus according to any one of claims 1 to 3, wherein the optical information recording / reproducing apparatus is set so as to block a part of each of the two outer sides. 5. An optical path between the light beam splitting member and the recording medium, wherein at least a part of a light beam from a light spot on the recording medium is separated from the irradiation optical system and directed to the detection optical system. The optical information recording / reproducing apparatus according to any one of claims 1 to 4, further comprising: a light beam separating means for changing over. 6. The optical information recording / reproducing apparatus according to claim 5, wherein the light beam splitting means is a polarization beam splitter. 7. The effective diameter of the light beam splitting means is set so as to block a part of each of the two outer sides of the three light beams.
The optical information recording / reproducing device according to any one of the above. 8. An aperture is arranged in an optical path between the light beam splitting member and the recording medium, and the aperture blocks an outer part of each of the two outer lights of the three light beams. 8. The optical information recording / reproducing apparatus according to claim 1, wherein the optical information recording / reproducing apparatus is set. 9. A polarization beam splitter, a reflection mirror, a quarter-wave plate and an objective lens are arranged in this order from the light beam splitting member side in the optical path between the light beam splitting member and the recording medium. At least one of the optical elements
2. The optical information recording / reproducing apparatus according to claim 1, wherein the effective diameter is set so as to block an outer part of each of two outer parts of the three light fluxes. 10. At least one of a position between the polarization beam splitter and a reflection mirror, a position between the reflection mirror and the ¼ wavelength plate, and a position between the ¼ wavelength plate and the objective lens. 10. The optical system according to claim 9, wherein an aperture is arranged in the aperture, and the aperture is set so as to block an outer portion of each of the outer two of the three light beams. Information recording / reproducing apparatus. 11. The beam splitting member is a diffraction grating,
11. The optical information according to claim 1, wherein the one of the three light fluxes is a 0th-order diffracted light flux and the other two outside are ± 1st-order diffracted light fluxes. Recording / playback device.