WO2000045383A1 - Optical head - Google Patents

Abstract

Light rays separated by means (2) are converged on an information-recording medium (4) by means (3) for converging light. The means (2) comprises a first part for forming first light rays (5c) subjected to substantially no diffraction or deflection from the light from a light source (1) and a second part for forming second light rays (5b, 5d) diffracted or deflected. The second rays (5b, 5d) are derived from those portions of light (1) incident on the means (2), which are outside those portions that make the first rays (5c). As a result, the transmittance of the optical path for the main beam from the light source (1) to the information-recording medium (4) increases, and an optical head with a low-output light source is achieved.

Description

 Description Optical head Technical field

 The present invention relates to an optical head for optically recording or reproducing information on an information recording medium such as an optical disk. Background art

 Conventionally, a so-called three-beam method has been known as one of the typical tracking error signal detection methods for optical heads. Hereinafter, the conventional technology will be described while describing the three-beam optical head with reference to the drawings.

 FIG. 7 is a conceptual diagram of a conventional optical head. 100 (100a, 100Ob) is the optical axis of the optical system, 101 is a light source such as a semiconductor laser, 102 is a diffractive element having a uniform diffraction grating, 103 Is an objective lens, 104 is an information recording medium, 105 is a half mirror that transmits and reflects part of light, 106 is a detection lens formed of a cylindrical lens, etc., 107 Is a light receiving element and 110 is a track direction.

 The luminous flux emitted from the light source 101 is converted into three luminous fluxes by the diffractive element 102 as the 0th, + 1st, and-1st-order diffracted light, as represented by the light rays indicated by the arrows in the figure. Branched. These light beams pass through the half mirror 105 and are condensed on the information recording medium 104 by the objective lens 103, and three light spots are generated on the information recording medium 104.

The 0th-order diffracted light of the three light fluxes becomes a light spot (hereinafter, referred to as “main spot”) used for recording or reproducing information, and has an optical axis of 100 °. The first- and first-order diffracted lights are located on the two light spots (hereinafter, “sub-spots”) located at a distance from the optical axis 100 a as shown by the light ray 109 in the figure. It becomes.

 FIG. 8 is a diagram showing three light spots generated on the information track of the information recording medium 104. As shown in FIG. 8A is a plan view, and FIG. 8B is a cross-sectional view in a direction perpendicular to the track direction 110 of FIG. 8A. As shown in this figure, the two sub-spots 1 1 2 are separated from each other in the direction perpendicular to the track direction 1 1 0 by about 1 Z 4 of the continuous groove cycle, that is, the track cycle, about the main spot 1 1 1 Is located.

 The light reflected by the information recording medium 104 passes through the objective lens 103 again as shown in FIG. 7, is reflected by the half mirror 105, and is received by the light receiving element via the detection lens 106. Guided on 107. The detection lens 106 has a function of giving astigmatism to a light beam in order to detect a focus error signal by a known so-called astigmatism method.

 Light reflected from the main spot travels along the optical axes 100a and 100b, and is collected at the intersection of the light receiving element 107 and the optical axis 100b. The reflected light from the sub-spot is converged at a position away from the optical axis 100b as shown by a light ray 113. The light receiving element 107 has a light detection unit that receives each of these three light beams. The luminous flux from the main spot is used to detect the focus error signal and the information signal, and the luminous flux from the two sub-spots is used to detect the tracking error signal by differential calculation of the detection signals. Can be

Here, in the following description, for convenience, the light beam generating the main spot is referred to as a main beam, and the light beam generating the sub spot is referred to as a sub beam. FIG. 9 is a diagram illustrating the diffraction element 102. On the diffractive element 102, a diffraction grating having a uniform period with a stripe pattern is uniformly formed _; A circle 108 indicates a range through which light serving as a main beam passes. Such a diffraction grating having a uniform period spatially and uniformly divides a passing light beam into 0th, + 1st and 1st order diffracted lights.

 In a conventional optical head, a main beam and two sub beams are generated using such a diffraction element. The diffraction efficiency of the diffraction element was generally about 70% for the 0th order, and about 10% for each of the + 1st and 1st orders.

 However, in the configuration of the conventional optical head as described above, a main beam and a sub-beam are generated by spatially and uniformly splitting a light beam using a diffraction element having a uniform diffraction grating. Therefore, the transmittance of the main beam in the optical path from the light source to the information recording medium is inevitably reduced by the zero-order diffraction efficiency of the diffraction element.

 In addition, since an increase in the 0th-order diffraction efficiency reduces the + 1st-order and −1st-order diffracted light, there is a limit to the increase in the 0th-order diffraction efficiency in order to obtain a sufficient amount of sub-beams. In other words, a semiconductor laser having a high light output was required as a light source in order to secure the amount of light necessary for recording information in the main beam. Disclosure of the invention

 SUMMARY OF THE INVENTION The present invention has been made to solve the conventional problems as described above, and an optical head which can improve the transmittance of a main beam in an optical path from a light source to an information recording medium and can obtain a sufficient amount of sub-beams. The goal is to realize it.

In order to achieve the above object, an optical head according to the present invention comprises: a light source; a light branching unit that branches light emitted from the light source into a plurality of light beams; and a light beam branched by the light branching unit. Focusing means for focusing on a recording medium; A first portion that forms a first light beam that is not substantially diffracted or deflected to the light emitted from the light source; and a second light beam that is diffracted or deflected. Wherein the second light flux, among the light emitted from the light source, passes on the light branching means outside the light that becomes the first light flux. It is characterized by being formed using light. According to the optical head as described above, the transmittance of the first light flux (for example, the main beam) in the optical path from the light source to the information recording medium can be improved, and the optical head using the light source with low light output can be improved. Can be realized. In the optical head, a width of the first portion in the track direction of the information recording medium is substantially equal to a light beam diameter on the light branching device of the light beam limited by the entrance pupil of the light collecting device. It is preferred that they have the same size. According to the optical head as described above, the first light flux restricted by the entrance pupil of the light condensing means is a light flux that has passed through the first portion, so that the transmittance of the first light flux is increased. Can be improved.

 In the light splitting means, it is preferable that the first portion is a portion where no diffraction grating is formed, and the second portion is a portion where a diffraction grating is formed.

 Further, when the second light flux passes through the light focusing means, the light source and the light source so that the area of the light flux occupying on the entrance pupil of the light focusing means is about half or more of the area of the entrance pupil. It is preferable that the light splitting means and the light collecting means are arranged. According to the optical head as described above, the light amount of the second light beam can be made sufficiently large, and the second light beam can be used as a sub-beam having a sufficient light amount necessary for detecting a tracking error signal. Further, it is preferable that the second portion is formed of two diffraction grating forming portions formed on both sides of the first portion in the track direction of the information recording medium with the first portion interposed therebetween. .

Further, the first light beam is used for recording information on the information recording medium or for recording information on the information recording medium. It is preferable that the second light beam is a light beam for performing tracking control at the time of recording or reproducing information on the information recording medium.

 Further, the second light beam has at least one pair of light beams, and the pair of light beams is collected on the information recording medium by the light condensing means at an interval obtained by multiplying about 1 Z2 of the track pitch by an integer. Preferably, the light is emitted and reflected by the information recording medium and used for detecting a tracking error. BRIEF DESCRIPTION OF THE FIGURES

 FIG. 1 is a configuration diagram of an optical head according to an embodiment of the present invention.

 FIG. 2 is a plan view of an optical branching element used for an optical head according to an embodiment of the present invention.

 FIG. 3 is a diagram illustrating an arrangement of a light source, a light splitting element, and an objective lens of an optical head according to an embodiment of the present invention.

 FIG. 4 is a view for explaining a sub beam generated by the optical branching device according to the embodiment of the present invention.

 FIG. 5 is a diagram illustrating a spot formed by the optical head according to one embodiment of the present invention.

 FIG. 6 is a diagram illustrating a spot formed by an optical head according to another embodiment of the present invention.

 Fig. 7 is a block diagram of an example of a conventional optical head.

 FIG. 8 is a diagram illustrating a spot formed by an optical head. FIG. 9 is a diagram illustrating an example of a diffraction element of a conventional optical head.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of an optical system of an optical head according to an embodiment of the present invention. 1 is a light source such as a semiconductor laser, 2 is a diffraction element as a light splitting means, 3 is an objective lens, 4 is an information recording medium, 5a to 5e are light beams split by the diffraction element 2, and 6 is an optical system. The optical axis, 8 is a detection lens formed of a cylindrical lens or the like, 9 is a light receiving element, 15 is a track direction, and D 1 is the diameter of the aperture (entrance pupil) of the objective lens 3.

 FIG. 2 is a conceptual diagram of a diffraction grating formed on the diffraction element 2. The striped regions 2a and 2b indicate the regions where the diffraction grating is formed. No diffraction grating is formed in the portion sandwiched between the regions 2a and 2b in the track direction 15. The region 10 is a part of the region where the diffraction grating is not formed. The area 10 indicates an area inside the circle 10a, and the main beam passes through the area 10a. The diameter D2 of the circle 10a, which is the outer periphery of this area 10, is equal to the diameter of the light beam on the light branching means 2 for the light beam limited by the aperture of the diameter D1 corresponding to the entrance pupil of the objective lens 3. .

 That is, the distance d3 between the regions 2a and 2b is approximately equal to the diameter D2 of the circle 10a. As a result, the light beam corresponding to the main beam passes through the region on the diffraction element 2 where no diffraction grating is formed.

The light emitted from the light source 1 enters the diffraction element 2 and is split into a plurality of light beams. Of these light beams, the light beam used as the main beam is the diffraction grating of the diffraction grating 2 like the light beam 5c. This is a light beam that passes through the non-formed portion. The luminous flux used as the sub-beam is, for example, the + 1st-order diffracted light in the area 2a as a light beam 5a, the first-order diffracted light as a light beam 5b, and the + 1st-order diffracted light in the area 2b as a light beam 5d. If the first-order diffracted light is a light beam 5e, it is two diffracted light beams branched in the directions indicated by the light beams 5b and 5d. The main beam and the two sub-beams pass through the half mirror 7 and are focused on the information recording medium 4 by the objective lens 3 to generate three light spots. The reflected light from these light spots passes through the objective lens 3 again, is reflected by the half mirror 17, and is guided to the light receiving element 9 via the detection lens 8. The position of each light beam guided to the light receiving element 9 and a method of detecting a focus error signal, a tracking error signal, and an information signal using these light beams are the same as in the conventional example, and therefore description thereof is omitted. I do. Further, the diffracted lights indicated by the light beams 5a and 5e do not pass through the aperture of the objective lens 3, and thus become unutilized light beams.

 Here, if the diffraction grating for generating the sub-beam is located at a position away from the optical axis as in the areas 2a and 2b in Fig. 2, the sub-beam will pass through the aperture of the objective lens sufficiently. In this case, the distance between the light source 1 and the diffraction element 2 needs to be sufficiently close to satisfy a certain condition. This condition will be described with reference to FIG.

 FIG. 3 is a configuration diagram illustrating an arrangement of a light source, a light splitting element, and an objective lens in an optical head according to an embodiment of the present invention. Elements having the same configurations as those in FIG. 11 is a surface set up at the light source position. When the information recording medium 4 is regarded as the object plane, the conjugate image plane formed by the objective lens 3 is the plane 11.

The conjugate image height of the objective lens 3 of one of the sub spots generated on the information recording medium 4 is y1, the distance between the boundary between the diffraction grating forming portion and the non-forming portion and the optical axis is y2, yl, The height at which the extension of the straight line connecting the point 1 'and the point y2' at the tip of 2 intersects the aperture of the objective lens 3 is h, the distance between the light source 1 and the diffraction element 2 is d1, and the diffraction is Assuming that the distance between the element 2 and the aperture surface of the objective lens 3 is d2, and the upward direction on the paper is positive, the following expression (1) is satisfied. However, the thickness of the diffraction grating 2 is not taken into account. Equation (1) h = y2-(y1-y2) * d2Zd1

 For example, the condition that the sub-beam passes through more than half of the aperture area of the objective lens 3 is, for example, the following equation (2) when the upper part of FIG.

 Equation (2) h <0

Therefore, when the condition for limiting the distance d1 is derived from the equation (1), it is expressed by the following equation (3).

 Equation (3) d l <(y l / y 2-l) * d 2

 Further, assuming that the main beam does not pass through the diffraction grating forming area at all, assuming that the numerical aperture on the light source 1 side of the objective lens 3 is NA, the condition expressed by the following equation (4) is added. , Dl, d 2

 Equation (4) y 2> NA * d 1

 FIG. 4 is a diagram showing a state where the sub-beam generated by such a diffraction element passes through the aperture of the objective lens 3 as viewed from the light source 1 side. The hatched portion 12 diffracts in the region 2a in FIG. 2 and the sub-beam represented by the light beam 5b in FIG. 1.The hatched portion 13 diffracts in the region 2b in FIG. 2 and the light beam in FIG. The sub-beam represented by 5d is shown. The cross-hatched portion at the center indicates an area where the two sub-beams overlap. Circle 14 indicates the aperture (diameter D1) of the objective lens. FIG. 4 shows that each of the two sub-beams passes through at least half of the aperture of the objective lens 3. If the area of the passing light beam occupies more than half of the objective lens aperture, the numerical aperture in the direction perpendicular to the track can be secured, so the focused sub-beam is small enough to detect the tracking error signal. It becomes a sub spot.

Equations (1) to (4) are equations derived from the relationship between the light source, the diffraction element, and the objective lens. However, the equations (1) to (4) are optical systems having other lenses such as a collimated lens. However, it is clear that a similar idea can be applied. is there.

 As described above, the transmittance of the main beam is improved by using the diffraction element having the diffraction grating non-forming portion in the area where the main beam passes, and the + 1st-order and 1st-order beams in the diffraction grating forming portion are improved. The secondary diffraction efficiency can be set arbitrarily irrespective of the main beam intensity by adjusting the arrangement of the elements, so that a sufficient sub-beam intensity can be obtained.

 In the above-described embodiment, the case where a diffraction element having a normal diffraction grating is used as the light branching unit has been described. However, the diffraction grating is blazed, and the light beams 5b and 5d shown in FIG. 1 are used. If a diffraction element with an increased diffraction efficiency of the diffracted light is used, the light amount of the sub-beam can be further increased. As a result, the quality of the tracking error signal can be further improved.

 In addition, it is also possible to form a prism or the like in the regions 2a and 2b shown in FIG. 2 instead of the diffraction grating and use an optical element that deflects light in the directions of the light beams 5b and 5d in FIG. Similar effects can be obtained.

 Further, in the above embodiment, as shown in FIG. 8, an example has been described in which two sub-spots are arranged at an interval of 1 Z 2 of the track pitch in a direction perpendicular to the track. However, the present invention is not limited to such a subspot arrangement. Figures 5 and 6 show other examples of subspot arrangements. FIGS. 5 (a) and 6 (a) are plan views of a part of the information recording medium, and FIGS. 5 (b) and 6 (b) are the tracks of FIGS. 5 (a) and 6 (a), respectively. 2 shows a cross-sectional view in a direction perpendicular to the direction.

 For example, as shown in Fig. 5 (a), the optical system has a structure in which two sub-spots 18 are arranged at an interval of the information track 16's track pitch (1/2 of the track pitch). May be used.

Such an optical head has a main spot 17 and a sub spot 18 Divides each light beam by the far field to detect a signal

It is well known that this is realized using a tracking error detection method known as a “differential push-full method”.

 Also, as shown in FIG. 6 (a), the two sub-spots 18 are arranged at an interval of twice the track pitch of the information track 16 (four times the track pitch of 1Z2), The present invention can also be applied to an optical disc device in which information is recorded and reproduced on three information tracks 16 at the same time by the main spot 17 and the two sub spots 18.

 The case where the two sub-spots are arranged at intervals of 1, 2, and 4 times the integer multiple of 1 Z 2 of the track pitch has been described above. The present invention can be similarly applied to the case where they are arranged at intervals.

 Furthermore, the example of using a + 1st- or 1st-order diffracted light from a diffraction element to generate a subbeam has been described. However, two or more subbeams are generated using second- or higher-order diffracted light. The same concept as described above can be applied to the optical branching means. Industrial applicability

 As described above, according to the present invention, of the light beams emitted from a light source, a light beam other than a light beam used for recording or reproducing information is generated by using a light beam in a range not conventionally used. However, the ratio of using the light emitted from the light source can be improved.

 For this reason, the present invention can be used for an optical head of a type that operates by condensing a plurality of light beams on an information recording medium, and an optical head using a light source with a smaller light output than before. Can be realized.

Claims

The scope of the claims 1. A light source, a light branching unit that branches light emitted from the light source into a plurality of light beams, and a light collecting unit that collects a light beam branched by the light branching device on an information recording medium. The light branching unit forms a first portion that forms a first light beam that is not substantially diffracted or deflected to light emitted from the light source, and forms a second light beam that is diffracted or deflected. The second light flux uses, of the light radiated from the light source, light that passes outside the light that becomes the first light flux on the light branching unit. An optical head characterized by being formed.  2. The width of the first portion in the track direction of the information recording medium is substantially the same as the light beam diameter on the light branching device of the light beam restricted by the entrance pupil of the light collecting device. An optical head according to item 1 of the range.  3. The optical head according to claim 1, wherein in the light branching unit, the first portion is a portion where no diffraction grating is formed, and the second portion is a portion where a diffraction grating is formed. 4.The light source and the light source such that the area of the light beam occupying on the entrance pupil of the light condensing means is about half or more of the area of the entrance pupil when the second light beam passes through the light condensing means. The optical head according to claim 1, wherein the light branching unit and the light collecting unit are arranged.  5. The second portion is formed by two diffraction grating forming portions formed on both sides of the first portion in the track direction of the information recording medium with the first portion interposed therebetween. 2. The optical head according to item 1. 6. The first light beam is a light beam for recording or reproducing information on or from the information recording medium, and the second light beam is a tracking beam when recording or reproducing information on the information recording medium. 2. The optical head according to claim 1, wherein the optical head is a light beam for control. 7. The second light flux has at least one pair of light fluxes, and the pair of light fluxes is collected on the information recording medium by the light condensing means at an interval obtained by multiplying about 12 track pitches by an integer. 7. The optical head according to claim 6, wherein the optical head is illuminated and reflected by the information recording medium and used for detecting a tracking error. Claim of amendment [May 24, 2000 (24.05.00) Accepted by the International Bureau: Application  The first claims 1, 4 and 6 have been amended; the first claims 2,  5 and 7 have been withdrawn; new claims 8-12 have been added  Other claims remained unchanged. (Page 3)]  1. (after correction) a light source, a light branching unit that branches light emitted from the light source into a plurality of light beams, and a light-collecting unit that focuses the light beams branched by the light branching device on an information recording medium. Wherein the light branching means comprises: a first portion forming a first light beam substantially not diffracted or deflected to light emitted from the light source; and a second portion diffracted or deflected. A second portion forming a light beam, wherein the second light beam is a light beam, which is emitted from the light source and which passes on the light branching unit outside the light beam that becomes the first light beam. The width of the first portion in the track direction of the information recording medium is substantially the same as the light beam diameter on the light branching means of the light beam limited by the entrance pupil of the light condensing means. An optical head characterized in that: 2. (Delete)  3. The optical head according to claim 1, wherein in the light branching unit, the first portion is a portion where no diffraction grating is formed, and the second portion is a portion where a diffraction grating is formed. 4. (after correction) a light source, a light branching unit for branching the light emitted from the light source into a plurality of light beams, and a light collecting unit for collecting the light beam branched by the light branching device on an information recording medium. Wherein the light branching means comprises: a first portion forming a first light beam substantially not diffracted or deflected to light emitted from the light source; and a second portion diffracted or deflected. A second portion forming a light beam, wherein the second light beam is a light beam, which is emitted from the light source and which passes on the light branching unit outside the light beam that becomes the first light beam. When the second light beam passes through the light collecting means, the area of the light beam occupying on the entrance pupil of the light collecting means is about half or more of the area of the entrance pupil. The light source, the light branching means, and the light condensing means are arranged. Optical head to be featured. 13 Papers captured (Article 19 of the Convention) 5. (Deleted)  6. (After Correction) The first light beam is a light beam for recording or reproducing information on the information recording medium, and the second light beam is for recording information on the information recording medium or A light flux for tracking control during reproduction, and has at least one pair of light fluxes, and the pair of light fluxes has a track pitch of about 12 on the information recording medium by the condensing means. 2. The optical head according to claim 1, wherein the optical head is collected at intervals of several times and reflected by the information recording medium to be used for detecting a tracking error.  7 (deleted)  8. (Addition) A light source, a light splitting unit that splits light emitted from the light source into a plurality of light beams, and a light condensing unit that condenses the light beam split by the light splitting device on an information recording medium. A first portion that forms a first light beam that is not substantially diffracted or deflected to the light emitted from the light source; and a second light beam that is diffracted or deflected. Wherein the second light flux is, among the light rays emitted from the light source, a light ray that passes on the light splitting means and passes outside the light beam that becomes the first light flux. An optical head formed by using the optical head, wherein the light source and the light branching unit are arranged close to each other.  9. (Addition) A light source, a light splitting unit that splits light emitted from the light source into a plurality of light beams, and a light condensing unit that condenses the light beam split by the light splitting device on an information recording medium. A first portion that forms a first light beam that is not substantially diffracted or deflected to the light emitted from the light source; and a second light beam that is diffracted or deflected. Wherein the second light flux is, among the light rays radiated from the light source, a light ray that passes on the light splitting means and passes outside the light that becomes the first light flux. 14 Amended paper (Article 19 of the Convention) The optical head, wherein the second light flux is a first-order or second-order or higher-order diffracted light.  10. (Addition) The light beam splitting means according to claim 4, 8 or 9, wherein the first portion is a diffraction grating non-forming portion, and the second portion is a diffraction grating forming portion. Optical head.  (Addition) The width of the first portion in the track direction of the information recording medium is substantially the same as the light beam diameter on the light branching device of the light beam restricted by the entrance pupil of the light condensing device. 10. The optical head according to claim 4, 8 or 9, which has a size.  12. (Addition) The distance between the light source and the light splitting means is d1, the distance between the light splitting means and the entrance pupil of the light collecting means is d2, and the second light flux is changed by the light collecting means. The conjugate image height of the light spot formed by focusing on the information recording medium with respect to the focusing means is y1, the boundary between the first portion and the second portion, and radiated from the light source. Assuming that the distance between the light and the optical axis is y2,  d 1 <(y 1 / y 2-1) * d 2 The optical head according to claim 11, wherein the optical head satisfies the following relationship: 15 Papers captured (Article 19 of the Convention) Statements under Article 19 of the Convention Deleted claim 2, paragraph 2, merged it into claim 1, and rewrote claim 4, into independent form.  In the invention according to claim 1 of the present application, the width of the first portion in the track direction of the information recording medium is substantially the same as the light beam diameter on the light branching device of the light beam limited by the entrance pupil of the light condensing device. With this size, the transmittance of the first light beam can be improved. The invention according to claim 4 of the present application is characterized in that, when the second light beam passes through the light collecting means, the area of the light beam occupying on the entrance pupil of the light collecting means is about half or more of the area of the entrance pupil. By arranging the light source, the light branching unit, and the condensing unit such that the second light flux can be used as a sub-beam having a sufficient light amount. These are not described in the reference.  In addition, the configuration in which the light source of claim 8 and the branching means are arranged close to each other, and the second light flux of the added claim 9 is a primary light beam and a second-order or higher light beam The configuration that is diffracted light is not described in the cited reference.