JPH097213A - Optical information recording and reproducing device - Google Patents

Abstract

PURPOSE: To provide an optical information recording/reproducing device hardly causing the generation of an automatic tracking offset, the lowering of intensity of a reproducing signal and the decrease of SN ratio by setting the effective diameter of optical parts composing a detecting optical system larger than the coverage range of a light beam from a light spot on a recording medium. CONSTITUTION: An optical head, movable to an optical system fixed part including an irradiating optical system and a detecting optical system, converges a light beam from the irradiating optical system, irradiates an optical card 1 with the beam as a light spot and introduces a reflected light beam from the light spot on the optical card 1 to the detecting optical system. By setting the effective diameter of optical parts composing the detecting optical system larger than the coverage range of the returned light beam from the light spot on the optical card 1, the vignetting of a light beam traveling to the detecting optical system in the optical system fixed part is avoided. Consequently, an optical information recording/reproducing device hardly causing the disadvantage of deterioration such as the generation of an automatic tracking offset, the lowering of intensity of a reproducing signal and the decrease of SN ratio, etc., is obtained.

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 apparatus for recording information on an optical information recording medium and reproducing the information recorded on the recording medium. The present invention particularly relates to an optical information recording / reproducing apparatus in which an optical head optical system is divided into a fixed portion and a movable portion.

[0002]

2. Description of the Related Art Various types of information recording media for recording and reproducing information using light, such as a disk, a card, and a tape, have been known. 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.

Here, the optical information recording / reproducing method will be described with reference to FIG.
The optical head optical system shown in FIG.

In FIG. 14, reference numeral 21 denotes a semiconductor laser which is a light source, and in this example, emits light having a wavelength of 830 nm which is polarized in the direction perpendicular to the track. Further, 22 is a collimator lens, 23 is a beam shaping prism, 11 is a diffraction grating for splitting a light beam, and 25 is a polarization beam splitter. Further, 36 is a quarter wavelength plate, 33a is a mirror,
37 is an objective lens, 40 is a convex spherical lens, 41 is a convex cylindrical lens, and 42 is a photodetector. Photodetector 4
2 is composed of two light receiving elements 42a and 42c and a light receiving element 42b divided into four.

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. After that, the light enters the diffraction grating 11 and is split into three effective light beams (0th-order diffracted light and ± 1st-order diffracted light) by the diffraction grating 11. These three light beams are polarized beam splitter 2
5 as a P-polarized light beam. Nearly 100% of the P-polarized light that has entered the polarization beam splitter 25 is transmitted.

Next, the three light beams are converted into a quarter wave plate 3
When it passes through 6, it is converted into circularly polarized light, reflected by the mirror 33a, and focused on the optical card 1 by the objective lens 37. As shown in FIG. 14, the focused light has three minute beam spots S ₁ (+ _{1st order} diffracted light) and S ₂ (0
Second-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. The spot position on the optical card 1 is
The light beam spots S ₁ and S ₃ are located on the adjacent tracking tracks 4, and the light beam spot S ₂ is located on the information track 2 between the tracking tracks.
Thus, the reflected light from the light beam spot formed on the optical card 1 again passes through the objective lens 37 to become a parallel light flux, is reflected by the mirror 33a, and is transmitted through the quarter-wave plate 36, thereby being incident. And are converted into a light beam whose polarization direction is rotated by 90 °. Then, it enters the polarization beam splitter 25 as an S-polarized beam, is reflected by nearly 100%, and is guided to a detection optical system.

In the detection optical system, the spherical lens 40 and the cylindrical lens 41 are combined, and the AF control by the astigmatism method is performed by this combination. The three light fluxes reflected from the optical card 1 are collected by the detection optical system, enter the photodetector 42, and
Form three light spots. Light receiving elements 42a, 42c
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, the four-divided light receiving element 42b is used for the light spot S ₂
The reflected light is received, the AF control is performed using the output, and the recorded information is reproduced.

By the way, the optical head optical system as described above is
As shown in FIG. 14, by dividing the fixed portion 20 and the movable portion 30 and moving only the movable portion as shown by the arrow, the information track can be scanned with the light beam spot S _2. it can. In such a separation type optical head, the amount of movement of the movable portion needs to be about the length of the optical card 1 in the vertical direction, and is usually about 100 mm.

[0012]

In the case of the above-mentioned separation type optical head, the optical path length, especially the diffraction grating 1 depends on the position of the movable portion.
The optical path length from 1 to the movable portion, the optical card 1 and the movable portion again to the photodetector 42 changes. This change in the optical path length is approximately twice the amount of movement of the movable portion, and therefore, the deviation of the light beam from the predetermined position with respect to the optical system (hereinafter, simply “light beam deviation”).
It is easy to occur. That is, when the angle error of the arrangement of the optical card (recording medium) 1 with respect to the optical system is large, or when the precision error of the mechanical parts and the optical parts and the assembly error thereof are large, the reflected light flux from the optical card 1 is optical. It tilts or shifts in parallel from the reference position for the system. When the deviation of the light flux becomes large, vignetting occurs due to the effective diameter of the optical component in only one of the two AT (auto tracking) control light fluxes, which causes disadvantages such as AT offset and reproduction signal deterioration. There was a point. Further, since the optical path length changes according to the position of the movable part, the amount of light beam vignetting also changes, and there is also a problem that the signal strength and the magnitude of the AT offset change depending on the position of the movable part.

In order to avoid the disadvantages such as AT offset generation and reproduction signal strength reduction, it is conceivable to make the precision of each component and the assembling precision of these components severe. In that case, it is necessary to process and assemble the components. It takes a lot of time and labor and it becomes difficult to reduce the cost.

Therefore, an object of the present invention is to prevent the light beam traveling to the detection optical system from being vignetted at the optical system fixing portion. And, the present invention is thus made
It is an object of the present invention to provide an optical information recording / reproducing apparatus that is less likely to suffer from disadvantages such as offset generation, reproduction signal strength reduction and deterioration such as S / N ratio reduction.

[0015]

According to the present invention, in order to achieve the above-mentioned object, a light beam from an irradiation optical system is focused to irradiate an optical information recording medium as a light spot and the light on the recording medium is irradiated. An optical head for guiding the light beam from the spot to the detection optical system is provided, and the optical head is movable with respect to the fixed portion including the irradiation optical system and the detection optical system and the fixed portion, and includes the objective lens. And a detection optical system in an optical information recording / reproducing apparatus for recording information on the recording medium and / or reproducing recorded information by irradiation of a light beam from the irradiation optical system. There is provided an optical information recording / reproducing apparatus, characterized in that the effective diameter of the optical component is larger than the reachable range of the light beam from the light spot on the recording medium.

In one aspect of the present invention, the optical head includes a diffraction grating that divides a light beam into a plurality of light beams, and a plurality of light beams are formed on the recording medium by the plurality of light beams divided by the diffraction grating. It

In one aspect of the present invention, the diffraction grating is arranged in the movable portion.

In one aspect of the present invention, the diffraction grating has a plurality of diffraction regions having different grating pitches.

In one aspect of the present invention, the diffraction grating has a plurality of diffraction regions having different grating pitches and different grating pitch directions.

In one aspect of the present invention, the irradiation optical system and the detection optical system share a polarization beam splitter, and a light beam traveling from the irradiation optical system to the movable portion and the detection from the movable portion. The light beam traveling toward the optical system passes through a common optical path from the polarization beam splitter to the movable portion.

In one aspect of the present invention, the irradiation optical system and the detection optical system share a beam splitter, and a light beam traveling from the irradiation optical system to the movable portion and the detection optical system from the movable portion. A light beam traveling toward the system passes through a common optical path from the beam splitter to the movable portion.

In one aspect of the present invention, the reachable range of the light beam from the light spot on the recording medium is determined by the angular error of the arrangement of the recording medium, the accuracy error of the mechanical parts and optical parts of the optical head, and these errors. Is determined based on the assembling error and the moving range of the movable part.

In one aspect of the present invention, the reachable range of the light beam from the light spot on the recording medium is the angular error of the arrangement of the recording medium, the accuracy error of the mechanical parts and optical parts of the optical head, and these errors. This is a range that the luminous flux can reach when the movable part moves within the entire movement range when the assembly error of (1) occurs to the maximum extent that is usually considered.

In one aspect of the present invention, the detection optical system includes an optical component having a light converging function.

In one aspect of the present invention, the optical component having the light converging function is a convex lens.

In one aspect of the present invention, the optical component having the light converging function is a cylindrical lens.

In one aspect of the present invention, the optical component having the light converging function is a toric lens.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described below with reference to the drawings.

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

In FIG. 1, reference numeral 1 is an optical card. The irradiation optical system includes a semiconductor laser, a collimator lens, and a beam shaping prism as described with reference to FIG. 14, and a beam-shaped parallel light flux is emitted from this. Further, the detection optical system includes a spherical lens, a cylindrical lens and a photodetector as described with reference to FIG.

The laser light flux that has traveled along the incident optical path substantially parallel to the surface of the optical card 1 is divided into three light fluxes by the diffraction grating 11 and is incident on the polarization beam splitter 12 as S-polarized light and reflected. After that, the polarization direction is rotated by 90 degrees by passing through the quarter-wave plate 15, the objective lens 16, the optical card 1, the objective lens 16 and the quarter-wave plate 15, and is again incident on the polarization beam splitter 12 as P-polarized light. Then, the light is transmitted, is incident on the total reflection surface of the total reflection prism 13 as P-polarized light, is reflected, and travels straight along the reflected optical path to reach the detection optical system. The reflected light path is substantially parallel to the surface of the optical card 1, and the incident light path and the reflected light path are located on opposite sides with respect to the movable part and are parallel to each other. Then, the light flux that has traveled along the reflected optical path is detected by the detection optical system.

In this case, the light beam from the irradiation optical system is focused by the objective lens 16 and irradiated onto the optical card 1 as a light spot, and the light beam from the light spot on the optical card 1 is projected onto the detection optical system. There is. The optical system of the optical head is composed of a fixed part including an irradiation optical system and a detection optical system, and a movable part movable in the arrow direction with respect to the fixed part.

FIG. 2 is a schematic configuration diagram of the detection optical system in this embodiment. In FIG. 2, 40 is a convex spherical lens, 41 is a cylindrical lens, and 42 is a photodetector. The outer diameter (effective diameter) D of the spherical lens 40 is larger than the light flux outermost diameter (outer diameter including a plurality of light fluxes) d when there is no light flux deviation, and the size thereof is the angle at which the optical card 1 is arranged. Assuming that the error, the accuracy error of the mechanical parts and the optical parts of the optical head, and the assembly error thereof occur to the maximum extent that is usually considered, it is (Dd) Is supposed to be large. That is, the outer diameter D is larger than the light beam reachable range when the maximum light beam shift is taken into consideration.

For example, if the light beam is inclined by 1 ° from the predetermined angle with respect to the optical system, the difference between the distance between the movable portion and the convex spherical lens 40 of the detection optical system is 10 mm and 100 mm is (100- 10) tan 1 ° = 1.5
It becomes 7 mm, and in an optical head in which the diameter of the light flux used is about 5 mmφ, there is a considerable variation in the amount of light. In the present embodiment, the effective diameter is set so that the light flux heading for the convex spherical lens 40 also moves within the effective diameter of the convex spherical lens 40 due to such movement of the movable portion.

In FIG. 2, A shows an angular error in the arrangement of the optical card 1, precision errors of mechanical parts and optical parts, and a certain luminous flux when there is no assembly error of these, and B shows the optical card 1.
The following shows the corresponding luminous flux when the angular error of the arrangement, the accuracy error of the mechanical parts and the optical parts, and the assembly error thereof are large. The light flux A is not vignetted even if the outer diameter of the convex spherical lens 40 is d, but the light flux B is vignetted at the shaded portion when the outer diameter of the convex spherical lens 40 is d. On the other hand, in the present embodiment, since the outer diameter of the convex spherical lens 40 is D, the light beams A and B are not vignetted.

The convex spherical lens 4 of the detection optical system is used here.
However, the same can be said for the outer diameter (effective diameter) of the cylindrical lens 41.

Further, in this embodiment, the luminous flux is a convex spherical lens 4
It has reached the cylindrical lens 41 through 0,
It may be arranged so as to reach the convex spherical lens through the cylindrical lens.

FIG. 3 is a schematic block diagram of an embodiment of an optical head of an optical information recording / reproducing apparatus according to the present invention. In this figure, members having the same functions as those in FIGS. 1 and 2 are designated by the same reference numerals. This embodiment is shown in FIG.
2 is different from that shown in FIG. 2 only in the arrangement state of the total reflection prism 13 and the arrangement of the detection optical system. Also in this embodiment, the same effect as that of the embodiment of FIGS. 1 and 2 can be obtained.

FIG. 4 is a schematic block diagram of an embodiment of the optical head of the optical information recording / reproducing apparatus according to the present invention. In this figure, members having the same functions as those in FIGS. 1 to 3 are designated by the same reference numerals. This embodiment is shown in FIG.
~ The structure of the diffraction grating and the structure of the photodetector are different from those of FIG.

That is, in this embodiment, it is shown in FIG.
A plurality of diffraction regions 11 having different grating pitch directions from each other.
A composite diffraction grating 11 'having a, 11b and 11c is used.
Have been. By using the composite diffraction grating 11 ',
The 0th and
It produces three diffracted lights of the ± 1st order, thus shown in FIG.
As shown, the 0th-order diffracted light spot S on the optical card_AF, First
+ 1st order diffracted light spot S diffracted in the direction of 1_DV1 , First
-1st-order diffracted light spot S diffracted in the direction of 1 _DV2 , First
+ 1st order diffracted light spot S diffracted in the direction of 2_AT1 , First
-1st-order diffracted light spot S diffracted in the direction 2_AT2 , First
+ 1st-order diffracted light spot S diffracted in the direction of 3_RF1 as well as
-1st-order diffracted light spot S diffracted in the third direction_RF2 To
Form and light spot S_AFRecording and AF control using
Light spot S_DV1 , S_DV2 Confirmation immediately after recording using
Playback (direct verification) is performed and the optical spot S
_AT1, S_AT2 AT control is performed using_RF1
 And light spot S_RF2 And light spot S_DV1 , S_DV2 , S
_AFPlayback of 3 tracks simultaneously with one of
In addition, the recording / playback described above is performed in either L or F direction.
Can also be done (ie round trip). In addition, in FIG.
4 is a tracking track and 2 is an information track.
It is.

FIG. 7 is used in this embodiment.
The figure which shows arrangement | positioning of the light receiving element of the photodetector 42 'of a detection optical system.
It is. Light spot S on the optical card_AF, S_DV1 , S
_DV2 , S _AT1 , S_AT2 , S_RF1 , S_RF2 Corresponding to
Pot S '_AF , S '_DV1, S '_DV2, S '_AT1, S '_AT2, S '
_RF1, S '_RF2Are the light receiving elements D_AF, D_DV1 , D_DV2
 , D_AT1 , D_AT2 , D_RF1 , D_RF2 Formed on.

FIG. 8 is a schematic diagram of the detection optical system in this embodiment. In FIG. 8, 40 is a convex spherical lens, 41 is a convex cylindrical lens, and 42 'is a photodetector. The outer diameter (effective diameter) D of the spherical lens 40 is
It is larger than the outermost diameter of the light flux (outer diameter containing a plurality of light fluxes) d when there is no light flux deviation, and the size thereof depends on the angle error of the arrangement of the optical card 1 and the accuracy error of the mechanical and optical parts of the optical head. Further, assuming that these assembling errors occur to the maximum extent that is usually considered, (D-d) is set to be larger than the above-described light beam deviation that occurs in the entire moving range of the movable portion. That is, the outer diameter D is larger than the light beam reachable range when the maximum light beam shift is taken into consideration.

For example, if the light beam is inclined by 1 ° from a predetermined angle with respect to the optical system, the difference between the distance between the movable portion and the convex spherical lens 40 of the detection optical system is 10 mm and the distance is 100 mm is (100- 10) tan 1 ° = 1.5
It becomes 7 mm, and in an optical head in which the diameter of the light flux used is about 5 mmφ, there is a considerable variation in the amount of light. In the present embodiment, the effective diameter is set so that the light flux heading for the convex spherical lens 40 also moves within the effective diameter of the convex spherical lens 40 due to such movement of the movable portion.

[0044] In FIG. 8, X is 0 'indicates (light flux forming the _AF, Y, Z are each diffraction angle maximum ± 1-order diffracted light (spot S-order diffracted light spot S)' _RF1, to form the S _'RF2 Luminous flux). In this figure, each light beam is represented by the optical card 1.
This is a case where the angle error of the arrangement of the components, the precision error of the mechanical components and the optical components, and their assembly error are large. If the outer diameter of the convex spherical lens 40 is d, the shaded portions of the light fluxes Y and Z will be vignetted even if the light flux X is not vignetted. On the other hand, in the present embodiment, since the outer diameter of the convex spherical lens 40 is D, the light beams A and B are not vignetted.

The convex spherical lens 4 of the detection optical system is used here.
However, the same can be said for the outer diameter (effective diameter) of the cylindrical lens 41.

Further, in this embodiment, the luminous flux is a convex spherical lens 4
It has reached the cylindrical lens 41 through 0,
It may be arranged so as to reach the convex spherical lens through the cylindrical lens.

FIG. 9 is a schematic configuration diagram of an embodiment of an optical head of an optical information recording / reproducing apparatus according to the present invention. In this figure, members having the same functions as those in FIGS. 4 to 8 are designated by the same reference numerals. In the present embodiment, FIG.
8 is different from that shown in FIG. 8 only in the arrangement state of the total reflection prism 13 and the arrangement of the detection optical system. Also in this embodiment, the same effect as that of the embodiment of FIGS. 4 to 8 can be obtained.

FIG. 10 is a schematic block diagram of an embodiment of the optical head of the optical information recording / reproducing apparatus according to the present invention. In this figure, members having the same functions as those in FIGS. 1 to 9 are designated by the same reference numerals.

In FIG. 10, 1 is an optical card as a recording medium, 20 is an optical system fixed part, and 30 is an optical system movable part.

The optical system fixing section 20 is constructed as follows. That is, 21 is a semiconductor laser which is a light source and emits linearly polarized light having a wavelength of 830 nm. 22
Is a collimator lens, 23 is a beam shaping prism, and 24
Is a 1/2 wavelength plate, 25 is a polarization beam splitter, 26 is a condenser lens, and 27 is a light quantity monitor. Further, 40 is a convex spherical lens, 41 is a convex cylindrical lens, and 42 is a photodetector. The photodetector 42 includes light receiving elements 42a, 42
b, 42c. The light receiving element 42b is a four-divided element. The semiconductor laser 21, collimator lens 22, beam shaping prism 23, half-wave plate 24, and beam splitter 25 form an irradiation optical system. The beam splitter 25, the condenser lens 26, and the light amount monitor 27 form a monitor optical system. The beam splitter 25, the spherical lens 40, the cylindrical lens 41, and the photodetector 4
2 constitutes a detection optical system.

The optical system movable section 30 is constructed as follows. That is, 31 is a polarization beam splitter, 32 is a quarter wavelength plate, 33 is a reflection mirror, 34 is a quarter wavelength plate, 35 is a reflection type diffraction grating, and 36 is a quarter wavelength plate. Has been done. 37 is an objective lens. The optical system movable unit 30 is capable of reciprocating in the direction indicated by the arrow with respect to the optical system fixing unit 20 and the optical card 1.

The light beam emitted from the semiconductor laser 21 enters the collimator lens 22 as a divergent light beam. Then, it is made into a parallel beam by the lens, and is further shaped by the beam shaping prism 23 into a beam having a circular cross section having a predetermined light intensity distribution. Then, the light passes through the half-wave plate 24 and enters the polarization beam splitter 25.
The above-mentioned half-wave plate 24 is rotatably supported around the optical axis.
It is possible to control the ratio of the amount of reflected light to the amount of transmitted light in the light reaching the beam splitter 25 from the / 2 wave plate 24.

The light transmitted through the beam splitter 25 passes through a condenser lens 26 and enters a light quantity monitor 27. The amount of light reflected by the beam splitter 25 is adjusted to a desired value by adjusting the rotation angle of the half-wave plate 24 or the applied voltage of the semiconductor laser 21 based on the received light amount monitor by the light amount monitor. Can be controlled.

On the other hand, the light reflected by the polarization beam splitter 25 enters the optical system movable section 30. The progress of this light will be described with reference to FIG. The light reflected by the polarization beam splitter 25 and incident on the optical system movable unit 30 first passes through the polarization beam splitter 31 and
It is reflected by the reflection mirror 33 via the four-wave plate 32. Since this reflected light passes through the quarter-wave plate 32 again, the polarization direction is 90 degrees from that when it is incident on the quarter-wave plate 32.
The light beam is converted into a rotated light beam and returned to the polarization beam splitter 31, and is reflected by the polarization beam splitter 31. The reflected beam is incident on the reflection type diffraction grating 35 via the quarter-wave plate 34 as in the case described above. The light reflected by the diffraction grating 35 is divided into three effective light beams (0th-order diffracted light and ± 1st-order diffracted light). Since these three light fluxes pass through the quarter-wave plate 34 again, they are converted into a light beam whose polarization direction is rotated by 90 ° as compared with the time of incidence on the quarter-wave plate 34, and then to the polarization beam splitter 31. Return, and therefore the polarization beam splitter 31
Pass through. Thus, the three light beams that have passed through the polarization beam splitter 31 are converted into circularly polarized light by passing through the quarter-wave plate 36, and are converged on the optical card 1 by the objective lens 37.

The light focused as described above is divided into three small beam spots S ₁ (+ _{1st order} diffracted light), S ₂ (0th order diffracted light), and S ₃ (−1st order diffracted light) shown in FIG. Is. The spots S ₁ and S ₃ are used for automatic tracking (hereinafter referred to as “AT”) control, and the spot S ₂ is used for recording, reproduction, and autofocus (hereinafter referred to as “AF”) control. On the optical card 1, as shown in FIG. 10, the light beam spots S ₁ and S ₃ are located on the adjacent tracking tracks 4, and the light beam spot S ₂ is located on the information track 2 between the tracking tracks. ing.

Reflected light from the light beam spot formed on the optical card 1 (AT signal light and reproduction / AF signal light)
Again passes through the objective lens 37 and becomes a parallel light beam.
As shown in FIG. 1, when the light beam is transmitted through the quarter-wave plate 36, it is converted into a light beam whose polarization direction is rotated by 90 ° from the time of incidence from the polarization beam splitter 31 and returns to the polarization beam splitter 31. Beam splitter 31
And is incident on the polarization beam splitter 25 of the optical system fixing section 20.

Thus, the AT incident on the optical system fixing portion 20
Since the polarization direction of the signal light and the reproduction / AF signal light is rotated by 270 ° with respect to the light incident on the polarization beam splitter 25 from the half-wave plate 24, the polarization beam splitter 25
Through the convex spherical lens 40 and the cylindrical lens 41, and is guided to the photodetector 42. Light receiving element 42a of the optical detector 42, 42b, the 42c, spots S ₁ on the optical card 1, respectively, S _2, signal light from the S ₃ is imaged as a spot Sa, Sb, Sc.

In the detection optical system, a combination of a convex spherical lens 40 and a convex cylindrical lens 41 is used, and the reproduction / AF signal light from the spot S ₂ on the optical card 1 is divided into four.
The divided light receiving element 42b receives light, AF control is performed by the astigmatism method, and recorded information is reproduced. Further, AT signal light from the spots S ₁ and S ₃ on the optical card 1 is received by the light receiving elements 42a and 42c, respectively, and AT control is performed.

FIG. 12 is an explanatory diagram of the diffraction grating. FIG.
In (a), a transmission type diffraction grating which is not used in this embodiment is shown, and (b) is a reflection type diffraction grating which is used in this embodiment. In these diffraction gratings, the width of the light transmitting portion and the width of the light shielding portion or the reflection portion are the same.

As shown in FIG. 12A, in the transmissive diffraction grating, the light shielding portion 5 having a predetermined width is formed on one surface of the transparent substrate 50.
2 are arranged at a pitch twice as large as the predetermined width, and the light transmitting portions 54 having the predetermined width are formed between the adjacent light shielding portions 52. The light is incident downward, the light incident on the light shielding portion 52 is reflected or absorbed and is lost, and only the light incident on the light transmitting portion 54 (50% of the incident light) is diffracted light such as 0th order and ± 1st order. It is divided into and transmitted.

As shown in FIG. 12B, in the reflection type diffraction grating 35, one surface of the transparent substrate 50 has a predetermined width of 99.
%, The reflective portions 53 having a high reflectance are arranged at a pitch twice the predetermined width, and the translucent portions 54 having the predetermined width are formed between the adjacent reflective portions 53. A reflective film 56 having a high reflectance of 99% or more is formed on the entire surface. The light is incident upward, and a part of the light incident on the reflector 53 is reflected to become the 0th-order diffracted light and ± 1 from the edge.
When the diffracted light of the second order or the like is generated, and the light that has entered the light transmitting portion 54 is reflected by the reflecting film 56 and exits through the light transmitting portion 54 again, part of the light passes through as it is to become the 0th order diffracted light and Diffracted light of ± 1st order or the like is generated from the edge of 53. Therefore, if the 0th-order light due to regular reflection is about twice as large as that in the case of FIG. And the reflected light from the reflective film 56 are temporally made incoherent and the two kinds of diffracted light are superposed without interference. Therefore, the light utilization efficiency of this reflection type diffraction grating is almost twice as high as that of the light transmission type diffraction grating of FIG.

The reflection type diffraction grating 3 in this embodiment is used.
A configuration in which the 5 and the reflection mirror 33 are interchanged may be adopted. Further, the polarization beam splitter 31 is replaced with the arrangement of the lower left and upper right portions in FIG. 11, and the arrangement of the upper left and lower right portions rotated by an angle of 90 degrees in FIG. 11 (arrangement similar to the arrangement of the polarizing beam splitter 25 of FIG. 11). Also by
A similar function can be obtained by appropriately setting the polarization direction.

FIG. 13 is a schematic configuration diagram of the detection optical system in this embodiment. The one-side dimension (effective diameter) D ′ of the polarization beam splitter 25 is larger than the one-side dimension (effective diameter) d ′ that is equal to the outermost diameter of the light flux (outer diameter that includes a plurality of light fluxes) when there is no light flux deviation. The size is generated in the entire moving range of the movable part, assuming that the angle error of the arrangement of the optical card 1, the accuracy error of the mechanical parts and the optical parts of the optical head, and the assembling error thereof occur to the maximum extent that is usually considered. The value of (D'-d ') is larger than the deviation of the luminous flux. That is, the effective diameter D ′ is larger than the light beam reachable range when the maximum light beam shift is taken into consideration.

For example, assuming that the light beam is inclined by 1 ° from a predetermined angle with respect to the optical system, the distance between the movable portion and the polarization beam splitter 25 of the detection optical system is 10 mm and 100 m.
In the case of m, the difference is (100-10) tan1 °
= 1.57 mm, and in an optical head in which the diameter of the light flux used is about 5 mmφ, there will be considerable fluctuations in the amount of light. In the present embodiment, the effective diameter is set so that even when the light beam incident on the polarization beam splitter 25 moves due to such movement of the movable portion, it falls within the effective diameter of the polarization beam splitter 25.

In FIG. 13, A shows an angular error in the arrangement of the optical card 1, accuracy errors of mechanical parts and optical parts, and a certain luminous flux when there is no assembly error thereof, and B shows the angle of the arrangement of the optical card 1. An error, an accuracy error of a mechanical component and an optical component, and a corresponding luminous flux when these assembly errors are large are shown.
The light beam A does not undergo vignetting even if the effective diameter of the polarization beam splitter 25 is d ', but the light beam B has vignetting at the shaded portion when the effective diameter of the polarization beam splitter 25 is d'. On the other hand, in the present embodiment, since the effective diameter of the polarization beam splitter 25 is D ', neither the luminous fluxes A nor B are vignetting.

Although the polarization beam splitter 25 of the detection optical system has been described here, the same applies to the outer diameter (effective diameter) of the convex spherical lens 40 and the cylindrical lens 41.

Further, in the present embodiment, the light flux reaches the cylindrical lens 41 from the polarization beam splitter 25 through the convex spherical lens 40, but the polarization beam splitter 2
The arrangement may be such that the lens 5 reaches the convex spherical lens through the cylindrical lens.

Instead of the polarization beam splitter 25,
A beam splitter can also be used.

In all of the above embodiments, the detection optical system uses the convex spherical lens 40 and the convex cylindrical lens 41 as optical components having a light converging function, but instead of the convex cylindrical lens 41 or the convex spherical lens 40. A toric lens may be used instead of the convex cylindrical lens 41.

Further, in all the above embodiments, since the diffraction gratings 11 and 11 'are arranged in the movable part, the positional relationship between the diffraction grating and the objective lens does not change even if the movable part moves. Therefore, the light beam divided by the diffraction grating is less likely to be vignetted as compared with the case where the diffraction grating is arranged in the fixed portion. Therefore, the reachable range of the light flux from the light spot on the recording medium is narrowed, and the effective diameter of the optical component forming the detection optical system can be set small.

[0071]

According to the present invention as described above, since the effective diameter of the optical component forming the detection optical system is larger than the reachable range of the light beam from the light spot on the recording medium, Vignetting of the light beam traveling toward the system can be avoided at the optical system fixing portion, which makes it less likely to cause disadvantages such as AT offset generation, reproduction signal strength reduction, and SN ratio reduction.

Further, in the present invention, by disposing the diffraction grating in the movable portion, the reachable range of the light beam from the light spot on the recording medium can be narrowed, and the effective diameter of the optical component forming the detection optical system can be minimized. It is possible to set it small.

[Brief description of drawings]

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

FIG. 2 is a schematic configuration diagram of a detection optical system in the embodiment of FIG.

FIG. 3 is a schematic configuration diagram of an embodiment of an optical head of an optical information recording / reproducing apparatus according to the present invention.

FIG. 4 is a schematic configuration diagram of an embodiment of an optical head of an optical information recording / reproducing apparatus according to the present invention.

5 is a plan view of the composite diffraction grating in the embodiment of FIG.

FIG. 6 is a diagram showing an optical card and a light spot formed thereon.

FIG. 7 is a diagram showing a light receiving element of a photodetector and a light spot formed thereon.

8 is a schematic configuration diagram of a detection optical system in the embodiment of FIG.

FIG. 9 is a schematic configuration diagram of an embodiment of an optical head of an optical information recording / reproducing apparatus according to the present invention.

FIG. 10 is a schematic configuration diagram of an embodiment of an optical head of an optical information recording / reproducing apparatus according to the present invention.

FIG. 11 is an explanatory diagram of the progress of light in the movable part of the optical system in the embodiment of FIG.

FIG. 12 is an explanatory diagram of a diffraction grating.

13 is a schematic configuration diagram of a detection optical system in the example of FIG.

FIG. 14 is a schematic diagram showing an optical head optical system of a conventional optical information recording / reproducing apparatus.

[Explanation of symbols]

1 Optical Card 2 Information Track 4 Tracking Track 11 Diffraction Grating 12 Polarizing Beam Splitter 13 Reflecting Prism 15 1/4 Wave Plate 16 Objective Lens 20 Optical System Fixing Part 21 Semiconductor Laser 22 Collimator Lens 23 Beam Shaping Prism 25 Polarizing Beam Splitter 26 Condensing Lens 27 Light amount monitor 30 Optical system movable part 31 Polarization beam splitter 32, 34, 36 Quarter wave plate 33 Reflecting mirror 33a Mirror 35 Reflective diffraction grating 37 Objective lens 40 Convex spherical lens 41 Convex cylindrical lens 42, 42 'Light detection 42a, 42b, 42c Light receiving elements D _AF , D _DV1 , D _DV2 , D _AT1 , D _AT2 , D _RF1 , D
_RF2 light receiving element S ₁ , S ₂ , S ₃ light spot Sa, Sb, Sc light spot S _AF , S _DV1 , S _DV2 , S _AT1 , S _AT2 , S _RF1 , S
_RF2 light spot _{S 'AF, S' DV1,} S 'DV2, S' AT1, S 'AT2, S' RF1,
_S'RF2 optical spot

Claims (13)

[Claims] 1. An optical head is provided which focuses a light beam from an irradiation optical system to irradiate the optical information recording medium as a light spot and guides the light beam from the light spot on the recording medium to a detection optical system. The optical head is composed of a fixed portion including the irradiation optical system and the detection optical system, and a movable portion that is movable with respect to the fixed portion and includes an objective lens. In an optical information recording / reproducing apparatus for recording information on the recording medium and / or reproducing the recorded information, the effective diameter of an optical component constituting the detection optical system is such that a light beam reaches from a light spot on the recording medium. An optical information recording / reproducing apparatus having a size larger than a possible range. 2. The optical head includes a diffraction grating that divides a light beam into a plurality of light beams, and a plurality of light beams are formed on the recording medium by the plurality of light beams divided by the diffraction grating. The optical information recording / reproducing apparatus according to claim 1. 3. The optical information recording / reproducing apparatus according to claim 2, wherein the diffraction grating is arranged in the movable portion. 4. The optical information recording / reproducing apparatus according to claim 2, wherein the diffraction grating has a plurality of diffraction areas having different grating pitches. 5. The diffraction grating has a plurality of diffraction regions having different grating pitch directions.
4. The optical information recording / reproducing device according to any one of 4 above. 6. The irradiation optical system and the detection optical system share a polarization beam splitter, and a light beam traveling from the irradiation optical system to the movable portion and a light beam traveling from the movable portion to the detection optical system. 6. The optical information recording / reproducing apparatus according to claim 1, wherein and pass through a common optical path from the polarization beam splitter to the movable portion. 7. The irradiation optical system and the detection optical system share a beam splitter, and a light beam traveling from the irradiation optical system to the movable part and a light beam traveling from the movable part to the detection optical system. Passing a common optical path from the beam splitter to the movable part.
5. The optical information recording / reproducing device according to any one of 5 above. 8. A reachable range of a light beam from a light spot on the recording medium includes an angular error of arrangement of the recording medium, an accuracy error of mechanical and optical parts of the optical head, an assembling error thereof and the movable error. The optical information recording / reproducing apparatus according to claim 1, wherein the optical information recording / reproducing apparatus is determined based on a moving range of the unit. 9. The reachable range of a light beam from a light spot on the recording medium is usually considered to be an angular error of the arrangement of the recording medium, an accuracy error of mechanical and optical parts of the optical head, and an assembly error thereof. 9. The optical information recording / reproducing apparatus according to claim 8, wherein the light beam is a range that the movable portion can reach when the movable portion moves within the entire movement range when it occurs to the maximum extent. 10. The optical information recording / reproducing apparatus according to claim 1, wherein the detection optical system includes an optical component having a light converging function. 11. The optical information recording / reproducing apparatus according to claim 10, wherein the optical component having the light converging function is a convex lens. 12. The optical component having the light converging action is a cylindrical lens.
An optical information recording / reproducing apparatus according to claim 1. 13. The optical information recording / reproducing apparatus according to claim 10, wherein the optical component having the light converging function is a toric lens.