JP3034681B2 - Optical recording / reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording / reproducing apparatus for optically recording / reproducing information, and more particularly to an optical recording / reproducing apparatus having a plurality of light-emitting sources and recording / reproducing information in parallel. It is.

[0002]

2. Description of the Related Art Conventionally, optical means, for example, a laser beam, is used on a rotating disk-shaped information recording medium.
2. Description of the Related Art An optical recording / reproducing apparatus for recording / reproducing information concentrically or spirally is known. By the way, the amount of information handled with the development and spread of computers and the like has increased, and the optical recording / reproducing apparatus has also been required to improve the amount of information (transfer rate) capable of recording / reproducing per unit time. To improve the transfer rate, for example, a method of recording and reproducing information in parallel by using an array type semiconductor laser emitting a plurality of laser beams as disclosed in Japanese Patent Application Laid-Open No. 1-312747. There is. The configuration of this conventional example will be described below with reference to the drawings.

FIG. 7 is a plan view showing an optical system of a conventional optical recording / reproducing apparatus. In the figure, reference numeral 1 denotes a semiconductor laser array, which emits four laser beams 2 here. FIG. 8 is a perspective view of the semiconductor laser array 1. Four laser beams 2 of the semiconductor laser array 1 are emitted from the same active layer 3. Semiconductor laser array 1
In the laser beam emission direction, a collimator lens 4, a beam splitter 5, and an objective lens 6 are sequentially arranged, and four focused spots 2A are formed on the surface of the information recording medium 7 by the objective lens 6. Note that Japanese Patent Application Laid-Open
In Japanese Patent Publication No. 312747, of the four condensed spots, two central condensed spots are formed on a flat portion of the information recording medium 7 and two condensed spots at both ends are formed on a guide groove provided on the information recording medium 7. However, since such an arrangement is irrelevant to the object of the present invention, the information recording medium 7 is used here.
A description will be given on the assumption that four converging spots 2A are formed on four adjacent information tracks on the surface.
The four laser beams 2 reflected by the information recording medium 7 are
The light is reflected by the beam splitter 5 and further reflected by the composite prism 8.
Is separated into reflected light and transmitted light. The reflected light is
The light enters a photodetector 10 having at least four light receiving surfaces via a lens 9. A first prism 11 and a second prism 12 are disposed in the direction of the transmitted light, and the photodetector 1 is disposed in the transmission direction of the reflecting surfaces 11A and 12A of each prism.
3 and 14 are provided respectively. Note that, in the optical recording / reproducing apparatus shown in FIG. 7, a part constituted by optical components excluding the information recording medium 7 is generally called an optical head.

Next, the operation will be described. Objective lens 6
The four converging spots 2A formed on the surface of the information recording medium 7 are arranged on four adjacent information tracks, respectively. Therefore, the information transfer rate can be improved by recording and reproducing information in parallel with these four condensed spots 2A.

[0005] In order to record and reproduce information in parallel using the four converging spots 2A, it is necessary that each converging spot is properly arranged on a predetermined information track. In this conventional example, the following means is used to realize the above. First
Of the four laser beams 2 incident on the prism 11, only one of the two laser beams at both ends passes through the reflecting surface 11 </ b> A and enters the photodetector 13 due to the difference in the incident angle. The remaining three laser beams reflected by the reflecting surface 11A are incident on the second prism 12, but the other one of the two laser beams at both ends is also reflected by the reflecting surface due to the difference in the incident angle. 12
A passes through and enters the photodetector 14. Each of the two photodetectors 13 and 14 is a two-divided photodetector having two light receiving surfaces, and two laser beams at both ends are respectively provided with predetermined information by a known tracking error detection method called a so-called push-pull method. It is determined whether the vehicle is following the track correctly. If they do not follow correctly, the correction control is performed by a variable mechanism (not shown), and as a result, the four condensed spots 2A
Are sequentially arranged on adjacent information tracks.

The detection of a reproduction signal is performed by independently detecting each laser beam 2 reflected by the information recording medium 7 by a photodetector 10 having at least four light receiving surfaces. In this conventional example, information can be recorded / reproduced in parallel with four condensed spots, so that the information transfer rate can be improved four times.

[0007]

As described above, the conventional optical recording / reproducing apparatus converts each of the four laser beams 2 emitted from the semiconductor laser array 1 into a collimator lens 4 as described above.
Is converted into a parallel beam by the light source, and is incident on the objective lens 6. Therefore, there is a problem as described below. This will be described with reference to FIGS. FIG.
FIG. 2 is a plan view of an optical system necessary for explaining a problem of a conventional optical recording / reproducing apparatus. In the figure, reference numerals 4 and 6 are the same as those in FIG. 7, and other optical system components are omitted. Reference numeral 15 denotes an optical axis of the optical system. In FIG. 1A, S1 is one light emitting point of the semiconductor laser array 1 on the optical axis 15. In this case, the parallel beam 16 emitted from the collimator lens 4 advances parallel to the optical axis 15 and
The light enters the center of the objective lens 6. On the other hand, in FIG. 3B, S2 is one light emitting point of the semiconductor laser array 1 which is off-axis by H with respect to the optical axis 15. In this case, the parallel beam 17 after exiting the collimator lens 4 is no longer parallel to the optical axis 15 and the principal ray 17 of the parallel beam 17
A enters the objective lens 6 shifted by D from the optical axis 15. Here, assuming that the focal length of the collimator lens is FC, the inclination U1 of the principal ray 17A with respect to the optical axis 15 is given by the following equation. U1 = H / FC (1) Assuming that the optical path length between the collimator lens 4 and the objective lens 6 is L, the deviation D of the principal ray 17A from the optical axis 15 at the position of the objective lens 6 is given by the following equation. D = L · U1-H = (L / FC−1) · H (2) In the above equation, if L / FC is sufficiently larger than 1, D = L · H / FC (3) Can be. When the semiconductor laser array 1 is used as a light source, all the light-emitting points except at least one light-emitting point are necessarily located outside the optical axis 15, so that each laser beam has a slight deviation D. become. Here, the shift D increases in proportion to the distance H of the light emitting point S2 from the optical axis 15 and the optical path length L1.
The ratio at which the light 7 enters the objective lens 6 is reduced. This means that a laser beam having a predetermined light intensity cannot be obtained on the surface of the information recording medium 7, and there is a possibility that information cannot be recorded and reproduced with high reliability.

[0008] By the way, the emission beam shape of a semiconductor laser generally has a characteristic that the radiation angle in the direction parallel to the active layer 3 is narrow and the radiation angle in the direction perpendicular to the active layer 3 is wide as shown in FIG. The same applies to semiconductor lasers. If the shape of the emitted beam is elliptical in this manner, the shape of the condensed spot formed on the surface of the information recording medium 7 will also be elliptical, or a part of the laser beam will be shaken by an optical component or the like. Occurs, leading to a loss of light intensity. Therefore, there is a method of correcting the elliptical beam shape to a substantially perfect shape by using a known means called beam shaping for the purpose of avoiding these.

FIG. 10 is a plan view of a main part of an optical system for explaining a problem which occurs in the conventional optical recording / reproducing apparatus using the beam shaping means as in FIG. 9B. In the figure, reference numerals 4, 6, and 15 are the same as those in FIG. 1
Reference numeral 8 denotes a beam shaping means for expanding the radiation angle of the semiconductor laser in a narrow direction (hereinafter, horizontal direction) so as to substantially coincide with the radiation angle in a wide direction (hereinafter, vertical direction). No. 53775. The beam shaping means 18 is disposed immediately behind the collimator lens 4. S2 is a light emitting point off-axis by H from the optical axis 15 as in FIG. 9B, and the parallel beam 19 emitted from the collimator lens 4 is not parallel to the optical axis 15. The distance between the collimator lens 4 and the beam shaping means 18 is L1, and the inclination between the principal ray 19A and the optical axis 15 between them is U1.
Assuming that 1, U1 = H / FC (4), and the principal ray 19A at the position of the beam shaping means 18
From the optical axis 15 is given by the following equation. D1 = L1 · U1-H = (L1 / FC−1) · H (5) Next, the parallel beam 19 transmitted through the beam shaping unit 18 is:
The inclination of the beam shaping means 18 with respect to the optical axis 15 changes depending on the beam diameter expansion rate M. Where the beam diameter expansion rate M
Is usually selected as a value of a ratio of a vertical radiation angle to a horizontal radiation angle of the semiconductor laser (hereinafter, referred to as an elliptic ratio). Assuming that the inclination between the principal ray 19B of the parallel beam 19 after passing through the beam shaping means 18 and the optical axis 15 is U2, U2 = U1 / M = H / FC / M (6) is generally satisfied. Chief ray 19 at
The deviation D2 of B from the optical axis 15 is given by the following equation. D2 = L2.U2-D1 = (L2 / FC / M- (L1 / FC-1)). H (7) where L2 is the distance between the beam shaping means 18 and the objective lens 6. Next, the distance L1 between the collimator lens 4 and the beam shaping means 18 is determined by the focal length FC of the collimator lens 4.
(7), equation (7) can be simplified to the following equation. D2 = L2 · H / FC / M (8) Therefore, by comparing the above equation with the equation (3), in the optical system using the beam shaping means 18, the main part of the laser beam whose emission point is off the optical axis is obtained. It can be seen that the shift amount of the light beam is reduced to one of the beam diameter enlargement ratio as compared with an optical system not using this. In general, the ratio of the radiation angle in the wide direction (vertical direction) to the radiation angle in the narrow direction (horizontal direction) of a semiconductor laser is 2
Therefore, the displacement can be reduced from か ら to １８ in the optical system using the beam shaping unit 18 as compared with the case where the optical system is not used. However, the shift amount is the optical path length L2
Therefore, unless L2 is kept sufficiently small, the amount of deviation cannot be ignored, and there is a possibility that a laser beam having a predetermined light intensity cannot be obtained.

Next, using a specific example, the shift amount of the principal ray and the accompanying decrease in the transmittance of the optical system will be described. FIG. 11 is a graph showing the relationship between the optical path length, the principal ray, and the transmittance of the optical system in the optical system using the beam shaping means 18. The optical path length L2 on the horizontal axis is the distance shown in FIG. The shift amount of the principal ray represented by the equation 8), and the vertical axis on the right side is the transmittance of the optical system. The calculation conditions are also shown in the figure. The radiation angle in the horizontal direction of the semiconductor laser is 10 degrees (full width at half maximum). The radiation angle in the vertical direction of the semiconductor laser is 30 degrees (full width at half maximum). Distance from optical axis H = 0.2 mm Beam expansion rate of beam shaping means M = 3 Focal length of collimator lens FC = 7 mm Focal length of objective lens FO = 4 mm Opening radius of objective lens RO = 2 mm The transmittance of the optical component was 100%. In the calculation of the optical system transmittance, the laser beam intensity profile of the semiconductor laser was assumed to be Gaussian. When the light emitting point is on the optical axis, the condition is the same as the optical path length L2 = 0. In this case, the shift of the principal ray does not occur, and the transmittance of the optical system is 57.5%. On the other hand, when the optical path length L2 = 100 mm under the above conditions, the shift of the principal ray is D2 =
0.95 mm and the transmittance is reduced to 51.0%.

To summarize the above problems, a conventional optical recording / reproducing apparatus using a semiconductor laser array has:
In a laser beam whose emission point is outside the optical axis, a shift between the principal ray and the optical axis occurs at the position of the objective lens. This shift amount is proportional to the distance of the light emitting point from the optical axis and the optical path length. Therefore, among the light emitting points of the semiconductor laser array, the loss of the light amount becomes larger as the laser beam is emitted from the outer light emitting point. In the optical system using the beam shaping means 18, the above-mentioned shift amount is inversely proportional to the beam diameter expansion rate. Therefore, if the beam diameter enlargement ratio is increased, it is possible to reduce the shift amount. However, if the beam diameter in the horizontal direction is increased beyond the elliptic ratio of the radiation angle of the light source, the shaking of the incident laser beam by the objective lens increases, causing a problem of a loss of light quantity of the beam emitted from the objective lens. In addition, in the optical recording / reproducing apparatus in which the optical path length cannot be shortened since the deviation amount is proportional to the output optical path length, a serious problem occurs in that the laser beam whose light emitting point is off the optical axis has a light quantity loss. .

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems. In an optical recording / reproducing apparatus using a semiconductor laser array, a laser beam having a light-emitting point outside the optical axis has a large optical path length. It is another object of the present invention to provide an optical recording / reproducing apparatus which can reduce the loss of the light quantity of the beam emitted from the objective lens whose emission point is off the optical axis even in the optical system.

[0013]

An optical recording / reproducing apparatus according to a first aspect of the present invention focuses and irradiates a laser beam from a laser array having a plurality of light emitting points to an information recording medium via an optical system. In an optical recording / reproducing apparatus for recording or reproducing information, the optical recording / reproducing apparatus is disposed immediately after a collimator lens with respect to the laser beam emission direction, and has a beam diameter expanding function in a horizontal direction in which the plurality of light emitting points are arranged, and , Shaping
The beam diameter of the subsequent laser beam in the horizontal direction is
The beam diameter in the vertical direction perpendicular to the horizontal direction is smaller than the specified value.
A first beam shaping unit having an upper large elliptical shape , disposed in front of the objective lens with respect to the laser beam emitting direction, having a beam diameter reducing action in the horizontal direction in which the plurality of light emitting points are arranged, and A second beam shaping means having a beam diameter reduction ratio set so that the laser beam diameter becomes a substantially perfect circle immediately before the objective lens by the beam diameter reduction action. In addition, the
An optical recording / reproducing apparatus according to claim 2 is the optical recording / reproducing apparatus according to claim 1.
In the optical recording / reproducing apparatus, the predetermined value is a value of 2 or more.
That's what I did.

According to a third aspect of the present invention, there is provided an optical recording / reproducing apparatus according to the first aspect, wherein:
A semiconductor laser array is used as the laser array.

According to a fourth aspect of the present invention, there is provided an optical recording / reproducing apparatus according to the first aspect, wherein:
As optical components constituting first beam shaping means disposed immediately after the collimator lens and second beam shaping means disposed immediately before the objective lens, a triangular prism, an achromatic triangular prism, or a cylindrical prism In this case, a lens is used.

An optical recording / reproducing apparatus according to a fifth aspect of the present invention provides an optical system for transmitting laser beams from a plurality of light sources having an isotropic radiation angle distribution or an isotropic two-dimensional intensity distribution to an optical system. In an optical recording / reproducing apparatus for recording or reproducing information by condensing and irradiating an information recording medium through the laser beam, the optical recording / reproducing apparatus is disposed immediately after a collimator lens with respect to the laser beam emitting direction, and is arranged in a direction in which the plurality of light emitting points are arranged. First beam shaping means for enlarging the laser beam diameter; and a beam diameter reducing function disposed in front of the objective lens with respect to the laser beam emission direction and having a beam diameter reducing function in a direction in which the plurality of light emitting points are arranged. A second beam shaping means having a beam diameter reduction ratio set so that the laser beam diameter becomes a substantially perfect circle by the reduction action.

Further, the optical recording / reproducing apparatus according to the invention of claim 6 of the present application is the optical recording / reproducing apparatus according to claim 1, wherein the optical head, which is an optical system part of the optical recording / reproducing apparatus, comprises a fixed part and a movable part. Wherein the first beam shaping means having a beam diameter enlarging function in a direction in which the plurality of light emitting points are arranged in the fixed portion, and in a direction in which the plurality of light emitting points are arranged. The second beam shaping means having a beam diameter reducing action is arranged on the movable part.

[0018]

In the invention according to claim 1 of the present application, the beam diameter is enlarged in the direction in which the light emitting points of the light source are arranged in the above-described configuration, so that the main part of the laser beam whose light emitting point is off the optical axis. Since the deviation of the light beam from the optical axis is reduced, and the beam diameter is reduced in the direction in which the light emitting points of the light source are arranged immediately before the objective lens, the cross-sectional shape of the laser beam becomes almost a perfect circle. In the invention according to claim 2 of the present application,
As described above, the first beam shaping means
Is the beam in the horizontal direction of the laser beam after shaping
The beam diameter is larger than the beam diameter in the vertical direction orthogonal to the horizontal direction by 2
Since the shape is an elliptical shape larger by the above-mentioned predetermined value,
The cross-sectional shape of the beam is almost perfect and light is emitted off the optical axis.
The light quantity loss of a laser beam having a point is reduced. Further, in the invention according to claim 3 of the present application, with the above configuration, in the case where the semiconductor laser array is used as the laser array, the beam diameter is enlarged in the direction in which the light emitting points of the light source are arranged, so that the light emission The deviation of the chief ray of the laser beam whose point is off the optical axis from the optical axis is reduced, and the beam diameter is reduced in the direction in which the light emitting points of the light source are arranged immediately before the objective lens. It becomes a perfect circle. Further, in the invention according to claim 4 of the present application, with the above configuration, the first beam shaping means disposed immediately after the collimator lens and the second beam shaping means disposed immediately before the objective lens In the case where a triangular prism, an achromatic triangular prism, or a cylindrical lens is used as an optical component constituting the shaping means, the beam diameter is enlarged in the direction in which the light emitting points of the light source are arranged, so that the light emitting point is off the optical axis. Since the deviation of the principal ray of the laser beam from the optical axis is small, and the beam diameter is reduced in the direction in which the light emitting points of the light source are arranged immediately before the objective lens, the cross-sectional shape of the laser beam becomes almost a perfect circle.

Further, in the invention according to claim 5 of the present application, the above configuration makes it possible to expand the beam diameter in the direction in which the light emitting points are arranged even in a light source having an isotropic radiation angle. The deviation of the principal ray of the laser beam whose point is off the optical axis from the optical axis is reduced, and the beam diameter is reduced in the direction in which the light emitting points are arranged immediately before the objective lens. Is kept.

Further, in the invention according to claim 6 of the present application, with the configuration described above, even if the optical recording / reproducing apparatus has a configuration in which the optical head includes a fixed portion and a movable portion, Due to the second beam shaping means arranged on the movable part side, there is almost no influence of the optical path length fluctuation accompanying the movement of the movable part.

[0021]

【Example】

Embodiment 1 FIG. FIG. 1 is a plan view showing an optical system of an optical recording / reproducing apparatus according to one embodiment of the present invention. In the figure, reference numerals 1, 2,
2A, 4 to 7 are the same as the conventional example shown in FIG. Reference numeral 20 denotes first beam shaping means, which is disposed immediately after the collimator lens 4 with respect to the laser beam emission direction so as to have a beam diameter expanding function in a direction in which the light emitting points of the semiconductor laser array 1 are arranged. Reference numeral 21 denotes a second beam shaping means, which is similarly disposed immediately before the objective lens 6 so as to have a beam diameter reducing action in a direction in which the light emitting points of the semiconductor laser array 1 are arranged. The first beam shaping means 20 and the second
There are various types of beam shaping means 21. Here, triangular prisms 20A and 20B and 21A and
4 shows a method using B. Reference numeral 23 denotes a detection optical system that detects light reflected from the surface of the information recording medium 7 and reproduces information signals and the like, but details thereof are omitted.

The operation of the present invention will be described. In FIG. 1, a laser beam 2 converted into a parallel beam by a collimator lens 4 is incident on a slope of a triangular prism 20A. Here, the laser beam 2 that has been subjected to the refraction action is emitted almost vertically on the emission surface of the triangular prism 20A. Therefore, the diameter of the laser beam in the direction parallel to the incident surface is enlarged by refraction at the incident surface. A beam shaping means using such a triangular prism is disclosed, for example, in JP-B-61-537.
No. 75. In the first beam shaping means 20 shown in FIG. 1, a triangular prism 20B of the same shape is arranged behind a triangular prism 20A, and the triangular prism 20A
The beam diameter in the direction parallel to the incident surface of the laser beam 2 enlarged by the above is enlarged again. Second beam shaping means 2
1 operates in a reverse manner to the first beam shaping means 20. That is, the laser beam 2 is made to enter the triangular prism 21A almost perpendicularly, and the laser beam diameter in the direction parallel to the incident surface is reduced by the refraction effect received when the laser beam 2 is emitted from the triangular prism 21A. In this case, similarly, two-stage beam diameter reduction is performed using the two triangular prisms 21A and 21B. Here, it is assumed that the elliptic ratio of the radiation angle of the semiconductor laser array 1 is M, and the beam diameter expansion rate of the first beam shaping means 20 is T · M. T is a number greater than 1 and will be referred to as the beam expansion factor. On the other hand, the beam diameter expansion rate of the second beam shaping means 21 is set to 1 / T. As a result, the beam diameter expansion rate of the laser beam 2 transmitted through the first beam shaping unit 20 and the second beam shaping unit 21 eventually becomes M, and can match the elliptic ratio of the radiation angle.
That is, after the first beam shaping unit 20 enlarges the beam diameter to be larger than the elliptic ratio of the radiation angle, the second beam shaping unit 21 performs reduction so as to match the elliptic ratio of the radiation angle.

The shift of the principal ray at the position of the objective lens is determined by the optical system shown in FIG. FIG. 2 is a plan view of a main part of an optical system for obtaining a shift of a principal ray. S2 is a light-emitting point that is H off-axis from the optical axis 15. The parallel beam 24 emitted from the collimator lens 4 is inclined with respect to the optical axis 15, the inclination of the principal ray 24A between the collimator lens 4 and the first beam shaping means 20 is U1, the interval is L1, and the first beam shaping is performed. The inclination of the chief ray 24B between the means 20 and the second beam shaping means 21 is U2, and the inclination of the chief ray 24C between the second beam shaping means 21 and the objective lens 6 is U3. The distance between the first beam shaping means 20 and the objective lens 6 is L2, and a number K (referred to as a distance coefficient) larger than 0 and smaller than 1 is introduced. The distance between the beam shaping means 21 is K · L2,
The distance between the second beam shaping means 21 and the objective lens 6 is defined as (1−K) · L2.

Principal rays 24A, 24B, 24C at each position
Are expressed as follows. U1 = H / FC (9) U2 = H / FC / T / M (10) U3 = H / FC / M (11) Deviation of the principal ray 24A from the optical axis 15 at the position of the first beam shaping means 20 D1 is given by the following equation. D1 = L1 · U1-H = L1 · H / FC−H = (L1 / FC−1) · H (12) The deviation D2 of the principal ray 24B from the optical axis 15 at the position of the second beam shaping means 21 is It is given by the following equation. D2 = K · L2 · U2 + D1 · T · M (13) The deviation D3 of the principal ray 24C from the optical axis 15 at the position of the objective lens 6 is given by the following equation. D3 = (1−K) · L2 · U3 + D2 / T (14) Here, similarly to the conventional example, the distance L1 is set to the collimator lens 4.
D1 in equation (12) becomes zero when the focal length FC is equal to the focal length FC. D3 = (1−K) · L2 · U3 + K · L2 · U2 / T = ((1−K) + K / T / T) · H · L2 / FC / M (15) where distance and magnification are related P = (1-K) + K / T / T (16) is defined as a factor. If there is no second beam shaping means 21, K = 1 and T = 1 in the above equation, and P =
As a result, the expression (15) matches the expression (8) derived in the conventional example. If P can be made smaller than 1, the shift D of the principal ray
3 also decreases, and it can be seen that it is sufficient to increase both the distance coefficient K and the beam expansion coefficient T. In order to increase the distance coefficient K, the distance between the second beam shaping means 21 and the objective lens may be reduced. In order to increase the beam expansion coefficient T, the expansion ratio of the first beam shaping means 20 may be set to be larger than the elliptic ratio of the radiation angle of the semiconductor laser array.

Next, the shift amount of the principal ray and the transmittance of the optical system will be described using a specific example. FIG. 3 is a graph showing the relationship between the beam expansion coefficient and the optical system transmittance in an optical system using the first beam shaping unit 20 and the second beam shaping unit 21. The horizontal axis indicates the beam expansion coefficient T, and the left side. The vertical axis represents the factor P, and the right vertical axis represents the transmittance of the optical system. The calculation conditions are also shown in the figure. The radiation angle in the horizontal direction of the semiconductor laser is 10 degrees (full width at half maximum). The radiation angle in the vertical direction of the semiconductor laser is 30 degrees (full width at half maximum). Distance from the optical axis H = 0.2 mm Beam magnification ratio M = 3 Focal length of collimator lens FC = 7 mm Focal length of objective lens FO = 4 mm Opening radius of objective lens RO = 2 mm Transmission of optical parts Rate 100% ・ Distance L2 = 10 between collimator lens 4 and objective lens 6
0 mm A distance coefficient K = 0.2 was used. In the calculation of the optical system transmittance, the laser beam intensity profile of the semiconductor laser was assumed to be Gaussian. The case where the beam expansion coefficient T is 1 corresponds to the case where the second beam shaping means 21 is not provided as described above, and the optical system transmittance is 51%. If T = 2, the factor P is 0.3
8. The optical system transmittance is 56.4%, and when T = 3, the factor P is 0.29 and the optical system transmittance is 56.9%. By the way, from FIG. 11, the transmittance of the optical system when the light emitting point is on the optical axis is 57.5%. Therefore, if T is set to 2 or more, the loss of the light quantity can be greatly improved, and furthermore, the light on the optical axis can be improved. A transmittance substantially equal to the light emitting point is obtained.

Embodiment 2 FIG. FIG. 4 is a plan view showing an optical system of an optical recording / reproducing apparatus according to another embodiment of the present invention. In the figure,
Reference numerals 1, 2, 4 to 7, 23 are the same as those in FIG.
Reference numeral 20C denotes a triangular prism constituting first beam shaping means, which is disposed immediately after the collimator lens 4 with respect to the laser beam emission direction so as to have a beam diameter expanding function in a direction in which the light emitting points of the semiconductor laser array 1 are arranged. You. 21C
Is a triangular prism constituting a second beam shaping means, which is similarly disposed immediately before the objective lens 6 so as to have a beam diameter reducing action in the direction in which the light emitting points of the semiconductor laser array 1 are arranged. Embodiment 1 FIG. Now we have two triangular prisms
What was configured in stages is the same as in Example 2. Here is a one-stage.

Embodiment 3 FIG. In the first and second embodiments, the triangular prisms 20A, 20B, 20C, 21A,
If the achromatized 1B and 21C are used, it is possible to eliminate the angular deviation of the principal ray caused by the fluctuation of the oscillation wavelength at each light emitting point of the semiconductor laser array 1 and the deviation of the oscillation wavelength between the light emitting points.

Embodiment 4 FIG. FIG. 5 is a plan view showing an optical system of an optical recording / reproducing apparatus according to another embodiment of the present invention. In the figure,
Reference numerals 1, 2, 4 to 7, 23 are the same as those in FIG.
In the first and second embodiments, a configuration using a triangular prism is used. However, a cylindrical lens may be used. Reference numeral 24 denotes a first beam shaping unit including a cylindrical concave lens 24A and a cylindrical convex lens 24B. The lenses 24A and 24B are arranged so as to have a lens function in the direction in which the light emitting points of the semiconductor laser array 1 are arranged. . 25 is a cylindrical convex lens 25A
And a cylindrical concave lens 25B.
Beam shaping means. Similarly, each of the lenses 25A and 25A
B is disposed so as to have a lens function in the direction in which the light emitting points of the semiconductor laser array 1 are arranged. As for beam shaping using a cylindrical lens, there is a known technique disclosed in, for example, Japanese Patent Publication No. 62-32532. Although FIG. 5 shows a combination of a cylindrical concave lens and a convex lens, beam shaping can be performed by combining two cylindrical convex lenses.

Embodiment 5 FIG. FIG. 6 is a plan view showing an optical system of an optical recording / reproducing apparatus according to another embodiment of the present invention. In the figure,
Reference numerals 1, 2, 4, 6, 7, 20, and 21 are the same as those in FIG. Reference numeral 26 denotes a fixing portion of the optical head, which includes the semiconductor laser array 1, the collimator lens 4, the first beam shaping means 20, the detection optical system (not shown), and the like among the components constituting the optical head. Reference numeral 27 denotes a movable portion of the optical head, which includes the objective lens 6, the reflection mirror 28, the second beam shaping means 21 and the like among the components constituting the optical head. The movable section 27 is positioned at a predetermined position on the surface of the information recording medium 7 by the moving mechanism 29. In this manner, by separating the optical head into the fixed portion 26 and the movable portion 27, the weight of the movable portion 27 can be reduced, and the positioning can be speeded up. In such a configuration,
The distance between the collimator lens 4 and the objective lens 6 fluctuates as needed depending on the position of the movable portion 27, and at the same time, the shift amount of the principal ray given by the expression (15) also fluctuates. However, by arranging the first beam shaping means 20 on the fixed part 26 close to the collimator lens 4 and arranging the second beam shaping means 21 on the movable part 26 close to the objective lens 6, the light emitting point Can reduce the amount of deviation of the principal ray of the laser beam off the optical axis and the amount of fluctuation thereof. Therefore, the fluctuation of the light amount due to the movement of the movable section 27 can be suppressed to be small.

Embodiment 6 FIG. In the above embodiment, the case where the radiation angle of the semiconductor laser array 1 is different depending on the direction, that is, elliptical, has been described. However, the present invention is also effective when the radiation angle is isotropic. That is, even if the emission angle is isotropic, the beam diameter is expanded with respect to the emission angle in the direction in which the light emitting points are arranged, and the beam diameter is reduced in this direction immediately before the objective lens 6 so that the light emitting point is increased. The displacement of the principal ray of the laser beam located off the optical axis can be reduced. In such a case, it is sufficient to set M = 1 in the calculation after the expression (9).

[0031]

As described above, according to the optical recording / reproducing apparatus according to the first aspect of the present invention, a laser beam from a laser array having a plurality of light emitting points is applied to an information recording medium via an optical system. In an optical recording / reproducing apparatus that records or reproduces information by condensing and irradiating, it is disposed immediately after a collimator lens with respect to the laser beam emitting direction, and has a beam diameter enlarging action in a horizontal direction in which the plurality of light emitting points are arranged. In the horizontal direction of the shaped laser beam
Beam diameter in the vertical direction where the beam diameter is perpendicular to the horizontal direction
A first beam shaping means for a large elliptical shape or a predetermined value than, disposed immediately in front of the objective lens relative to the laser beam emitting direction, the horizontal direction <br/> direction in which the plurality of light emitting points are arranged A second beam shaping means having a beam diameter reducing function, and having a beam diameter reducing ratio set so that the laser beam diameter becomes substantially a perfect circle immediately before the objective lens by the beam diameter reducing function. By providing the semiconductor laser beam emitted from the collimator lens, after expanding the beam diameter in a direction in which the light emitting points are arranged to be larger than the elliptic ratio of the radiation angle, the beam diameter becomes isotropic immediately before incidence on the objective lens. Since the beam diameter in the above direction is reduced, the deviation of the principal ray of the laser beam whose emission point is off the optical axis on the incidence surface of the objective lens can be reduced, and the optical recording of the multi-beam system can be performed. There is an effect that can reduce the optical loss of the laser beam emitting point is outside the optical axis in a living system. Also,
According to the optical recording / reproducing apparatus according to the invention of claim 2 of the present application,
2. The optical recording and reproducing apparatus according to claim 1, wherein the predetermined value is
Since the value was set to 2 or more, the emission point was off the optical axis.
This has the effect of reducing the light amount loss of the laser beam. Further, according to the optical recording / reproducing apparatus according to the third aspect of the present invention, in the optical recording / reproducing apparatus according to the first aspect, the semiconductor laser array is used as the laser array. In the multi-beam optical recording / reproducing device using a semiconductor laser array, the loss of the light amount of the laser beam whose emission point is off the optical axis can be minimized. Has the effect of reducing Claim 4 of the present application
According to the optical recording / reproducing apparatus of the present invention, in the optical recording / reproducing apparatus according to claim 1, the first beam shaping means arranged immediately after the collimator lens and the second beam shaping means arranged immediately before the objective lens. A triangular prism, an achromatic triangular prism, or a cylindrical lens is used as an optical component constituting the beam shaping means, so that a laser beam whose emission point is off the optical axis is mainly incident on the objective lens incident surface. Ray shift can be kept small,
In a multi-beam optical recording / reproducing apparatus, the effect of using a triangular prism, an achromatic triangular prism, or a cylindrical lens as an optical component to reduce the light quantity loss of a laser beam whose emission point is off the optical axis. There is. Further, according to the optical recording / reproducing apparatus according to the invention of claim 5 of the present application, laser beams from a plurality of light sources having an isotropic radiation angle distribution or an isotropic two-dimensional intensity distribution are transmitted through an optical system. In an optical recording / reproducing apparatus for recording or reproducing information by condensing and irradiating an information recording medium with a laser beam, the laser is disposed immediately after a collimator lens with respect to the laser beam emission direction, and is arranged in a direction in which the plurality of light emitting points are arranged. First beam shaping means for expanding a beam diameter, and a beam diameter reducing function arranged in a direction in which the plurality of light emitting points are arranged immediately before the objective lens with respect to the laser beam emission direction,
A second beam shaping means having a beam diameter reduction ratio set so that the laser beam diameter becomes substantially a perfect circle by the beam diameter reduction action, so that the laser beam whose emission point is off the optical axis is provided. In a multi-beam optical recording / reproducing device having a light source having an isotropic radiation angle distribution or an isotropic two-dimensional intensity distribution, the light emission point can be reduced. Has the effect of reducing the light quantity loss of the laser beam off the optical axis.

According to the optical recording / reproducing apparatus according to the sixth aspect of the present invention, in the optical recording / reproducing apparatus according to the first aspect, an optical head which is an optical system part of the optical recording / reproducing apparatus is provided.
A separation type optical head comprising a fixed portion and a movable portion, wherein the first beam shaping means having a beam diameter expanding function in a direction in which the plurality of light emitting points are arranged is arranged on the fixed portion; By arranging the second beam shaping means having a beam diameter reducing action in the direction in which the points are arranged in the movable section, the first beam shaping means is arranged in the fixed section in the separation type optical head, and the movable section is provided. Since the second beam shaping means is arranged in the optical path, even if the optical path length changes due to the movement of the movable part, the light quantity fluctuation of the laser beam whose emission point is off the optical axis can be suppressed, and the light quantity is constant. There is an effect that you can get something.

[Brief description of the drawings]

FIG. 1 is a plan view showing an optical path system of an optical recording / reproducing apparatus according to Embodiment 1 of the present invention.

FIG. 2 is a plan view of a main part of an optical system of the optical recording / reproducing apparatus according to the first embodiment of the present invention.

FIG. 3 is a graph showing a relationship between a beam expansion coefficient and an optical system transmittance of the optical recording / reproducing apparatus according to the first embodiment of the present invention.

FIG. 4 is a plan view showing an optical system of an optical recording / reproducing apparatus according to Embodiment 2 of the present invention.

FIG. 5 is a plan view showing an optical system of an optical recording / reproducing apparatus according to Embodiment 4 of the present invention.

FIG. 6 is a plan view showing an optical system of an optical recording / reproducing apparatus according to Embodiment 5 of the present invention.

FIG. 7 is a plan view showing an optical system of a conventional optical recording / reproducing apparatus.

FIG. 8 is a perspective view showing a semiconductor laser array.

FIG. 9 is a plan view of a main part of an optical system for explaining a problem of an optical system of a conventional optical recording / reproducing apparatus.

FIG. 10 is a plan view of a main part of an optical system for describing a problem of an optical system including a beam shaping unit in a conventional optical recording / reproducing apparatus.

FIG. 11 is a diagram illustrating a relationship between a shift amount of a principal ray with respect to an optical path length and an optical system transmittance in a conventional optical recording / reproducing apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser array 2 Laser beam 2A Focusing spot 4 Collimator lens 6 Objective lens 7 Information recording medium 20, 24 First beam shaping means 20A, 20B, 20C Triangular prism 21, 25 Second beam shaping Means 21A, 21B, 21C Triangular prism 24A, 25B Cylindrical concave lens 24B, 25A Cylindrical convex lens 26 Fixed part 27 Movable part

Continuation of front page (56) References JP-A-64-84450 (JP, A) JP-A-2-91832 (JP, A) JP-A-62-32532 (JP, A) JP-A-2-183430 (JP, A) , A)

Claims (6)

(57) [Claims] 1. An optical recording / reproducing apparatus for recording or reproducing information by irradiating a laser beam from a laser array having a plurality of light emitting points onto an information recording medium via an optical system. It is arranged immediately after the collimator lens with respect to the direction, has a beam diameter expanding action in the horizontal direction in which the plurality of light emitting points are arranged, and, after shaping,
The beam diameter in the horizontal direction is orthogonal to the horizontal direction
An elliptical shape larger than the beam diameter in the vertical direction by a predetermined value or more
A first beam shaping means, which is disposed immediately before the objective lens with respect to the laser beam emission direction, has a beam diameter reducing function in the horizontal direction in which the plurality of light emitting points are arranged, and An optical recording / reproducing apparatus comprising: a second beam shaping means having a beam diameter reduction ratio set so that the laser beam diameter becomes a substantially perfect circle immediately before the objective lens by an action. 2. The optical recording / reproducing apparatus according to claim 1, wherein the predetermined value is two or more . 3. An optical recording / reproducing apparatus according to claim 1, wherein said laser array is a semiconductor laser array . 4. An optical recording / reproducing apparatus according to claim 1,
And a first beam shaper disposed immediately after the collimator lens.
A shaping means, and a second arranged immediately before the objective lens
As an optical component constituting the beam shaping means, a triangular prism, or an achromatic triangular prism, or
An optical recording / reproducing device using a cylindrical lens . 5. An isotropic radiation angle distribution, or an isotropic radiation angle distribution.
Laser beams from multiple light sources with two-dimensional intensity distribution
To the information recording medium via the optical system,
In an optical recording / reproducing apparatus that performs recording or reproduction, a collimator lens is arranged with respect to the laser beam emission direction.
A laser that is placed immediately after and in the direction in which the multiple light emitting points are lined up
First beam shaping means for enlarging the beam diameter, and immediately before the objective lens with respect to the laser beam emission direction.
Beam diameter reduction in the direction in which the plurality of light emitting points are arranged
The laser beam is reduced by the beam diameter reducing function.
The beam diameter reduction rate is set so that the beam diameter is approximately a perfect circle.
An optical recording / reproducing apparatus comprising: a second beam shaping means . 6. An optical recording / reproducing apparatus according to claim 1,
The optical head, which is the optical system part of the optical recording / reproducing device,
And a movable part, and has a beam diameter expanding function in a direction in which the plurality of light emitting points are arranged.
Disposing the first beam shaping means on the fixed portion, and has a beam diameter reducing action in a direction in which the plurality of light emitting points are arranged.
The second beam shaping means is arranged on the movable part.
An optical recording and reproducing apparatus characterized by the following.