JPH11232685A - Beam shaping element and optical pickup using the same - Google Patents

Abstract

(57) [Problem] To provide a beam shaping element which can be incorporated in an integrated optical pickup and which is resistant to wavelength fluctuation, and an optical pickup using the same. SOLUTION: A first shaping element 2 for generating astigmatism and a second shaping element 3 for canceling the astigmatism, and a set of focuses of a light beam having astigmatism after passing through the first shaping element 2 are provided. The lines 4 and 5 sandwich the light emitting point of the light source 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a beam shaping element for shaping the shape of light guided to a recording medium and an optical pickup using the same.

[0002]

2. Description of the Related Art In order to shorten the recording bit length and reduce crosstalk from adjacent tracks in response to the increase in the density of an optical disk, the spot diameter of the laser beam on the disk surface of the optical disk must be reduced. It is required that the shape be made as small as possible to make the shape almost a perfect circle. On the other hand, since the linear velocity of the optical disk increases in order to improve the data transfer speed, it is necessary to increase the power of the laser beam on the board required for recording.

In order to increase the power of the laser light on the board, it is necessary to increase the coupling efficiency between the LD (laser diode) used as a light source and the optical element to increase the amount of LD light taken in. However, the emission angle characteristics of the LD are small in a plane parallel to the bonding plane and large in a plane perpendicular to the LD, and the intensity distribution FFP (far-field pattern) of the LD light at a distance is elliptical. When the coupling efficiency between the LD and the optical element is small, only the central part where the intensity of the LD light is strong is used, so the difference in the light amount distribution between the direction parallel to the joining surface and the direction perpendicular to the joining surface is small, and the spot shape is almost circular However, when the coupling efficiency between the LD and the optical element is increased, the light is used up to the periphery of the LD light, so that the influence of the elliptical intensity distribution FFP (far field pattern) of the LD light at a long distance appears strongly. Therefore, the difference between the light amount distribution in the direction parallel to the bonding surface and the light amount distribution in the direction perpendicular to the bonding surface at the peripheral portion of the LD light is large, and as a result, the spot on the board surface becomes elliptical.

In order to solve the above problem, in the prior art, a beam shaping prism is provided in the parallel light between the collimator lens and the objective lens on the outward path, and the beam is shaped in one direction (in a direction parallel to the joining surface). The beam is enlarged to shape the elliptical beam into a circle. The conventional technique will be described below. FIG. 6 is a configuration diagram of an optical pickup using one conventional beam shaping prism. The light source 1 has a joining surface parallel to the paper surface, and the emitted light beam of the light source 1 is P-polarized light whose polarization surface is substantially parallel to the paper surface, and the intensity distribution (FFP) is such that the direction perpendicular to the paper surface is the short axis and the parallel direction. Has an elliptical shape that is the major axis. After the light emitted from the light source 1 is converted into parallel light by the collimator lens 62, it is incident on the incident surface 64 of the beam shaping prism 63, the path is bent by refraction, and is perpendicular to the light traveling direction and parallel to the paper. The beam is expanded in the direction toward the emission surface 65, and the beam expansion rate is determined by the magnitude of the prism vertex angle θa and the prism refractive index N. The expansion rate m is m = φb / φa = COS θa / (1− N ² SIN ² θa)
Given by ^1/2 . The exit surface 65 is arranged perpendicular to the parallel rays refracted by the entrance surface 64, and the parallel rays exit from the exit surface 65 without being refracted by the exit surface 65 and pass through the reciprocating beam splitter 66. , Objective lens 4
2 connects a spot on the recording medium 43. The light emitted from the light source 1 initially has an elliptical intensity distribution, but after passing through the beam shaping prism 63, the short axis side of the elliptical intensity distribution is elongated, and the intensity distribution becomes substantially circular. And the spot on the recording medium is also substantially circular. The return light reflected by the recording medium is guided to the sensor 69 by the reciprocating separation splitter 66, and signal detection is performed. Therefore, the return light does not pass through the beam shaping prism 63.
The spot on the sensor is also almost circular. In addition, a method of performing beam shaping by combining two beam shaping prisms and cylindrical lenses is also known.

[0005]

However, in a beam shaping element using a beam shaping prism, in a system using one beam shaping prism, the direction of the optical axis is changed before and after the beam shaping prism, and the beam shaping prism is used. In the method using two optical heads, displacement of the optical axis occurs, so that it is difficult to adjust the position of not only the beam shaping element but also the subsequent optical members. The width of the optical pickup becomes large. In addition, since a member used for beam shaping such as a prism is large, it is difficult to reduce the size of the optical pickup.

In recent years, in order to reduce the size of the optical pickup, an integrated optical pickup using an integrated element in which a light source and a sensor are housed in one package has been proposed.
In the integrated optical pickup, since the light source and the sensor are housed in one package, it is impossible to insert the beam shaping prism only in the forward path, and the beam shaping prism is inevitably inserted in the return path. This configuration is particularly problematic in magneto-optical recording. That is, in magneto-optical recording, the reproduced signal is detected from a slight change in the polarization state of the return light from the recording medium. The larger the light amount, the larger. The beam shaping prism has a polarization characteristic in which the transmittance of P-polarized light is large, but the transmittance of S-polarized light is small. The polarization is reduced, and the reproduced signal is reduced.
Therefore, in an integrated optical pickup for magneto-optical recording in which a light source and a detection sensor are integrated into one package, a beam shaping prism cannot be used as a beam shaping means.
There is a need for an effective beam shaping means that can replace the beam shaping prism.

The present invention solves the above-mentioned conventional problems. Instead of the beam shaping prism, the present invention is applicable to an integrated optical pickup and uses a beam shaping element which enables downsizing of the optical pickup. It is intended to provide an optical pickup.

[0008]

In order to solve the above-mentioned problems, astigmatism is given to light emitted from a light source so that the light becomes substantially equivalent to light having a pair of virtual orthogonal focal lines. A first shaping element that acts, and a light emitting point that acts on light that has passed through the first shaping element to cancel the astigmatism given by the first shaping element and to be a virtual light emitting point different from the light emitting point And a second shaping element that acts so as to be substantially equivalent to the light emitted from the light source, and shapes the intensity distribution of the light emitted from the light source from an elliptical shape to a substantially circular shape.

[0009]

In the beam shaping element according to the first aspect of the present invention, the light emitted from the light source is provided with astigmatism,
A first shaping element that operates so as to be substantially equivalent to light having a set of orthogonal virtual focal lines, and a light that passes through the first shaping element and is provided by the first shaping element. A second shaping element that cancels out astigmatism and acts so as to be substantially equivalent to light emitted from a virtual light emitting point different from the light emitting point of the light source, and the intensity distribution of light emitted from the light source is elliptical. By shaping the beam shaping into a substantially circular shape, the size of the beam shaping element can be easily reduced while reducing the amount of aberration generated in the beam shaping element, and it can be incorporated in an integrated optical pickup.

According to a second aspect of the present invention, the light after passing through the first shaping element has a first virtual focal line and a second virtual focal line,
A ratio L2 / L0 of an optical path length L0 from the first shaping element to the light emitting point of the light source and an optical path length L2 from the first shaping element to the first virtual focal line is 1.1 or more and 2.0 or less. Accordingly, the influence of chromatic aberration generated in the beam shaping element when the wavelength of the light source fluctuates can be further reduced.

According to a third aspect of the present invention, the first virtual focal line and the second virtual focal line are positioned so as to sandwich the light emitting point of the light source, and the first virtual focal line is radiated by the light source. By being located in the opposite direction, the chromatic aberration generated in the beam shaping element when the wavelength of the light source fluctuates can be further reduced.

According to a fourth aspect of the present invention, there is provided a first shaping element and a second shaping element for converting the intensity distribution of incident light having a non-circular intensity distribution into a substantially circular shape and for performing the first shaping. By reducing the amount of aberration increased by the element by the second shaping element, the amount of aberration generated by the beam shaping element can be reduced.

According to a fifth aspect of the present invention, there is provided a first shaping element for giving an aberration to incident light and a second shaping element for giving an aberration to incident light, and an incident light having a non-circular intensity distribution. The first shaping element and the second shaping element such that the light intensity distribution is converted into a substantially circular shape, and that the aberration given by the first shaping element and the aberration given by the second shaping element almost cancel each other. By arranging (1) and (2), occurrence of aberration in the beam shaping element can be suppressed.

According to the sixth aspect of the present invention, since the shaping element is a transmission type or reflection type hologram element, the size and thickness of the shaping element can be reduced.

According to the seventh aspect of the present invention, since the diffracted light and the zero-order light travel in different directions, it is possible to eliminate the adverse effect due to the leakage of the zero-order light. Since the position of the second shaping element can be adjusted with respect to the shaping element, the allowable error of the mounting position of the light source can be greatly increased.

According to a ninth aspect of the present invention, by providing a light separating means between the first shaping element and the second shaping element, it is possible to prevent the return light from being incident on the first shaping element. Light can be given astigmatism.

According to the tenth aspect of the present invention, since the beam shaping element is formed on a substantially flat surface, the beam shaping element can be formed thinner than a case where the beam shaping element is formed with a curved surface. Can be reduced in size.

According to the eleventh aspect of the present invention, a beam shaping element having excellent optical characteristics can be provided by setting the amount of aberration generated by the beam shaping element to 0.03λ (RMS) or less.

According to a twelfth aspect of the present invention, there is provided a first shaping element and a second shaping element, both of which are formed in a substantially planar shape, and using the first shaping element and the second shaping element,
By converting the intensity distribution of the light emitted from the light source into a substantially circular shape, the beam shaping element can be formed very thin, so that the size of the beam shaping element can be further reduced.

According to a thirteenth aspect of the present invention, there is provided a light source, comprising:
A beam shaping element having a shaping element and a second shaping element, and converting the intensity distribution of incident light having a non-circular intensity distribution into a substantially circular shape using the first shaping element and the second shaping element; A light-condensing means for condensing light converted into a substantially circular intensity distribution on a recording medium, and a light detecting means for receiving light reflected by the recording medium and converting the light into an electric signal;
In at least one of the beam shaping element and the second beam shaping element, since the optical axis of the incident light and the optical axis of the outgoing light are substantially on a straight line, the alignment between the beam shaping element and other optical members is performed. Can be easily performed,
Further, the beam shaping element can be made smaller.

According to a fourteenth aspect of the present invention, there is provided a light source, comprising:
A beam shaping element having a shaping element and a second shaping element, and converting the intensity distribution of incident light having a non-circular intensity distribution into a substantially circular shape using the first shaping element and the second shaping element; A light-condensing means for condensing the light converted into the substantially circular intensity distribution on a recording medium; and a light detecting means for receiving the light reflected by the recording medium and converting the light into an electric signal; In the element, by reducing the amount of aberration of light passing through the first shaping element by the second shaping element, it is possible to improve the optical characteristics of the optical system of the optical pickup, and , The light condensing characteristics of the light can be improved.

According to a fifteenth aspect of the present invention, a light source and a first light source are provided.
A beam shaping element having a shaping element and a second shaping element, and converting the intensity distribution of incident light having a non-circular intensity distribution into a substantially circular shape using the first shaping element and the second shaping element; Light collecting means for condensing light converted into a substantially circular intensity distribution on a recording medium; light detecting means for receiving light reflected by the recording medium and converting the light into an electric signal; Having an optical element that emits light guided from the light source toward a predetermined position, and an optical member that emits light reflected by a recording medium toward a predetermined position, By forming at least a part of the beam shaping element in the optical member, it is possible to integrate at least a part of the optical member that guides light from the light source to a predetermined position and the beam shaping element that adjusts the intensity distribution of the beam. Can be It can decrease, it is possible to simplify the assembly process such as positioning.

(Embodiment 1) First, Embodiment 1 of the present invention will be described.

FIG. 1A is a perspective view showing the configuration of the beam shaping element according to Embodiment 1 of the present invention. Reference numeral 1 denotes a light source, and the light source 1 has a strong linearity such as a semiconductor laser,
Often, coherent ones are used. The wavelength of the light emitted from the light source 1 is considered to be in a range from an infrared light region to a visible light region and an ultraviolet light region, and is preferably selected according to a recording medium to be used. Further, a plurality of light sources may be provided so as to support a plurality of recording media.

Reference numerals 2 and 3 denote a first shaping element and a second shaping element, respectively, which constitute a beam shaping element. First
The two shaping elements 2 and 3 can both be composed of a hologram, a birefringent member, or the like. Therefore, the first and second shaping elements 2, 3
Can be formed in a substantially planar shape, so that the first and second shaping elements 2 and 3 can be manufactured more easily. Also, for example,
(2) When the shaping elements 2 and 3 are formed on the surface (formed of a flat surface) of a thin translucent substrate, the volume can be significantly reduced as compared with the case where a conventional refractive optical member is used. , 2 shaping elements 2 and 3 can be reduced in size and thickness, and a small and thin beam shaping means can be realized.

The first shaping element 2 and the second shaping element 3 are arranged at any position in the path of the light emitted from the light source 1 and directed to the recording medium, and particularly arranged closer to the light source 1. Is preferred. With this arrangement, it is possible to make the light incident on the first and second shaping elements 2 and 3 before the diameter of the light emitted from the light source 1 and guided to the recording medium while diffusing becomes large. Because it is possible,
The shaping elements 2 and 3 can be made smaller, and the size of the optical pickup on which these members are mounted can be reduced.

In this embodiment, both the first shaping element 2 and the second shaping element 3 are formed by transmission holograms. Further, in the present embodiment, the first and second shaping elements 2 and 3 are formed as separate members, but may be formed on the front and back surfaces of the same substrate, or may be formed by a composite hologram.

Next, the operation of the first and second shaping elements 2 and 3 will be described. In the present embodiment, the first shaping element 2
The second shaping element 3 acts as a pair, and functions to expand the beam in one direction, in the case of the present embodiment, in the X direction shown in the drawing. For example, when the bonding surface of the light source 1 is in the XZ plane, after the light source 1 emits, the intensity distribution (FFP) of the beam at a distance has an elliptical shape whose major axis is in the Y-axis direction. First shaping element 2 and second shaping element 3
After passing through, the beam is expanded in the X-axis direction, resulting in a substantially circular intensity distribution.

This principle will be described with reference to the drawings. FIGS. 1B and 1C are diagrams showing the function of the beam shaping element according to the first embodiment of the present invention. In FIG. Second
The path of the light beam passing through the shaping element 3 is shown in the YZ plane, and FIG. 1C is shown in the XZ plane. Light source 1
Are arranged such that their joint surfaces are in the XZ plane, and the FFP has an elliptical shape with the Y axis as the major axis. Light rays emitted from the light source 1 enter the first shaping element 2. The first shaping element 2 gives astigmatism to the light beam from the light source 1, and the light beam after passing through the first shaping element is almost orthogonal (accurately, in many cases, a twisted relationship. (The plane including the optical axis of the light emitted from 1 and the focal line 4 is substantially orthogonal to the focal line 5). The rear focal line 5 is parallel to the X axis, and the front focal line 4 is parallel to the Y axis. When viewed in the YZ plane, the light beam that exits the light source 1 and enters the first shaping element 2 is deflected by the first shaping element 2 so that the virtual focal line 5 is set as a virtual light emitting point. Also,
When viewed in the X-Z plane, the light beam that exits the light source 1 and enters the first shaping element 2 is deflected by the first shaping element 2 so that the virtual focal line 4 is set as a virtual light emitting point. As a result, after passing through the first shaping element 2, the divergence angle of the light ray in the XZ plane is larger than that in the YZ plane, so that the light ray is To reach X
The beam is expanded in the direction. The second shaping element 3 functions to cancel the astigmatism given to the light beam by the first shaping element 2. The light beam whose path is bent by the first shaping element 2 and is incident on the second shaping element 3 is as if all the light rays are light rays emitted from one virtual light emitting point 6 by the second shaping element 3. You can bend that course.

The beam expansion rate m in the beam shaping element configured by combining the two shaping elements as described above.
Is the optical path length from the first shaping element 2 to the light source 1 is L0, and the optical path length from the first shaping element 2 to the front focal point 4 is L1.
And the optical path length from the first shaping element 2 to the rear focal point 5 is L
2, and the optical path length from the first shaping element 2 to the second shaping element 3 is L3: m = ((L1 + L3) / L1) · (L2 / (L2 + L)
3)) given by

Next, the aberration generated due to the wavelength fluctuation of the light source 1 will be examined. FIG. 2 is a diagram illustrating the dependence of the wavelength variation and the aberration amount on the position of the shaping element according to the first embodiment of the present invention. Specifically, the ratio L2 / L0 of the optical path length L0 from the first shaping element 2 to the light emitting point 1 of the LD and the optical path length L2 from the first shaping element 2 to the virtual focal line 5, and the wavelength of the LD changes by 10 nm from the design wavelength. 6 shows the relationship with the increase amount of the wavefront aberration of the light beam after passing through the beam shaping element in the case of the above.

In general, an optical system using a hologram is vulnerable to wavelength fluctuation, and there is a problem that a large aberration occurs when the wavelength of the light source fluctuates due to a temperature change or the like.

The amount of aberration allowed in the optical system of the optical pickup is not absolutely certain due to differences in the wavelength of the light source 1 used, the spot diameter on the storage medium, and the like. In consideration of the above, the allowable range of the amount of wavefront aberration generated in the beam shaping element needs to be about 0.03λ (rms) or less. If the amount of wavefront aberration falls within this range, the convergence state of light on the recording medium can be improved, so that the light can be recorded on the recording medium without being affected by adjacent tracks or pits. Information can be accurately reproduced, the amount of light on the recording medium can be increased, and a highly reliable optical pickup capable of accurately recording information on the recording medium can be provided. it can.

As can be seen from FIG. 2, the ratio L2 / L0 of the optical path length L0 from the first shaping element 2 to the light emitting point 1 of the LD and the optical path length L2 from the first shaping element 2 to the virtual focal line 5 is 1. 1
It can be seen that when the wavelength is in the range from 2.0 to 2.0, the amount of increase in wavefront aberration due to wavelength fluctuation of the beam shaping element can be made 0.03λ (rms) or less.

When L2 / L0 is in the above range, the amount of generation of the wavefront aberration due to the wavelength variation becomes small because the condition of the first shaping element 2 is changed by the change of the wavefront aberration due to the wavelength variation of the first shaping element 2. This is considered to be because the change in the wavefront aberration due to the wavelength fluctuation of the second shaping element 3 is exactly canceled out, and the chromatic aberration generated in the beam shaping element when the wavelength of the light source fluctuates can be reduced.

In this embodiment, the number of shaping elements to be combined is two. However, three shaping elements may be combined, or four or more shaping elements may be combined. However, the smaller the number of combinations is, the easier it is to realize the miniaturization of the optical pickup which is a market need, which is preferable. Further, although the light source 1, the first shaping element 2, and the second shaping element 3 are provided continuously, another optical member may be provided between these members.

As described above, in the beam shaping element according to the present embodiment, the light emitted from the light source 1 having an elliptical FFP is formed on a straight line formed by the optical axis of the light emitted from the light source 1. In addition, since the FFP emitted from the virtual light emitting point 6 different from the light source 1 can be converted as if the FFP is substantially circular light, the optical axis of the light emitted from the light source 1 is Since it is not deflected or displaced, not only the beam shaping element but also the position of each optical member constituting the optical pickup can be easily adjusted, and the productivity of the optical pickup can be improved and the beam shaping can be performed. Since the element can be miniaturized, the miniaturization of the optical pickup equipped with the element can also be realized.

By using a hologram or the like, the first and second shaping elements 2 and 3 can be formed on the surface of the translucent substrate, so that the first shaping element 2 and the second shaping element 3 are extremely thin. Since it can be formed small, the size of the beam shaping element can be significantly reduced as compared with a beam shaping element using a conventional refractive optical system. In addition, it is possible to easily realize an optical pickup having a large light amount on a recording medium.

Further, by combining a plurality of shaping elements and canceling out the aberrations generated by each shaping element, the amount of aberrations generated by the beam shaping element can be greatly suppressed. An excellent optical pickup can be realized.

Also, aberrations caused by wavelength fluctuations of the light source 1 can be canceled by this configuration.
The optical pickup has a highly reliable optical pickup capable of minimizing the influence of the wavelength fluctuation occurring in the light source 1 and capable of accurately recording or reproducing information even if the wavelength fluctuation occurs in the light source 1.

(Embodiment 2) Next, Embodiment 2 of the present invention will be described.

FIG. 3 is a perspective view showing a configuration of a beam shaping element according to the second embodiment of the present invention. In the present embodiment, the first shaping element 2 is a reflection type hologram, and the second shaping element 3 is a transmission type hologram, and the concept of the first embodiment is applied.

Reference numeral 30 denotes an integrating prism,
Are a plurality of inclined surfaces 30 inclined with respect to the light emitting surface of the light source 1.
a, 30b, and 30c are formed from a plurality of light-transmitting substrates so as to be included therein, and an optical element having a predetermined function is previously formed at a predetermined position on an end surface of each substrate. . The number of slopes in the integrated prism 30 may be two, three, or more, and is determined by the number of optical elements to be formed, the positional relationship, and the like. In addition, it is preferable that the angle of the inclined surface be 30 ° to 60 °, since it is possible to further reduce the size of the integrating prism 30 when the same effect is achieved. Among them, in particular, by setting the angle to approximately 45 °, the deflection angle of the optical axis can be set to approximately 90 °, light can be guided most efficiently, and the degree of freedom in designing the integrated prism 30 can be increased. It is particularly preferable because it is possible.

As the light-transmitting substrate on which the integrated prism 30 is formed, an optical glass or a resin having a high light transmittance is often used.

Hereinafter, the optical element formed in the integration prism 30 will be described. The first shaping element 2 is provided as a reflection hologram on the second inclined surface 30 b of the integrating prism 30, which gives astigmatism to the light beam emitted from the light source 1 and is diffracted by the first shaping element 2. Of the light, the first-order diffracted light acts so as to be equivalent to a light beam having a virtual orthogonal set of focal lines 4 and 5, and further, the first shaping element 2 causes the focal lines 4 and 5 is disposed at a position sandwiching the light emitting point of the light source 1. The first shaping element 2 may be formed directly on the translucent substrate, or may be formed on a translucent substrate by forming an SiO ₂ film or the like thereon. Further, the shape of the hologram may be a sawtooth wave shape or a step shape.

The inclined surfaces 30a, 30 of the integrating prism 30
In b, reflecting elements 7a and 7b that reflect incident light are formed, respectively. The reflection element 7 is mainly made of Al, Ag
And the like, or a dielectric material having a different refractive index such as SiO ₂ or TiO ₂ is alternately combined.

Next, the second shaping element 3 includes an integrated prism 30
Separately from this, it is provided as a transmission hologram element on a substrate 44 provided closer to the recording medium than the integrating prism 30.

Here, the first shaping element 2 and the reflecting elements 7a, 7
b is formed on both end faces of one translucent substrate,
This is a preferable configuration because the light can be guided without being affected by the boundary of the substrates, particularly the bonding material for bonding between the substrates. Particularly, in the case of light traveling toward the recording medium, the size of the beam spot formed on the recording medium greatly contributes to the reproduction and recording quality of information. Is good.

In the beam shaping element having such a configuration,
A pair of virtual orthogonal focal lines 4 and 5 of the first-order diffracted light of the first shaping element 2 and the light emitting point of the light source 1 are close to each other. When used for an optical pickup, on a recording medium,
The imaging spot of the first shaping element 2 due to the zero-order light and the original imaging spot due to the first-order diffracted light are very close to each other,
The signal quality may be degraded due to the leakage of the zero-order light.

Therefore, in the present embodiment, in order to prevent this problem from occurring, the first shaping element 2 is inclined by about 1 degree from 45 degrees, which is the optimum inclination angle of the incident light from the light source 1 with respect to the optical axis. The first-order diffracted light is designed so as to give a predetermined astigmatism to the incident light and emit the light toward the second shaping element 3. On the other hand, the 0-order reflected light of the first shaping element 2 is
Since the first shaping element 2 is arranged at an angle of about 45 ° to 1 ° with respect to the optical axis of the incident light, it travels in a direction different from the traveling direction of the first-order diffracted light. Therefore, when a beam shaping element designed in this manner is used for an optical pickup, an image spot formed by the 0th-order light beam of the first shaping element 2 is formed at a position distant from an original image spot formed by the first-order diffracted light. 1. There is no adverse effect on the original imaging spot due to the first-order diffracted light.

In the present embodiment, the second shaping element 3 is provided on the substrate 44 provided as a separate member. However, the second shaping element 3 may be formed on the end face 30d of the integrated prism 30.
Further, the first shaping element 2 is connected to the incident end face 30 of the integrated prism 30.
e. Further, the first shaping element 2 may be formed between the light source 1 and the integrating prism 30, and the second shaping element 3 may be provided on the surface of the integrating prism 30 or inside thereof.

Further, both the first shaping element 2 and the second shaping element 3 are formed by reflection holograms,
May be formed on the surface or inside. By forming both of them on the integrated prism 30, the number of components can be reduced, so that an assembly process such as alignment between components can be simplified.

As described above, the beam shaping element according to the present embodiment can be easily incorporated into an optical system using the integrated prism 30 which has been put into practical use in recent years. It is possible to realize an optical system having excellent optical characteristics that can convert the light intensity distribution into a substantially circular shape while minimizing the aberration, and can also suppress the amount of aberration generated in the optical system to a small value.

In particular, since the first shaping element 2 is formed of a reflection type hologram and the second shaping element 3 is formed of a transmission type hologram, a part of the beam shaping element can be provided in the integrated prism 30. it can. Also, since the transmission type shaping element has a larger tolerance for error than the reflection type shaping element,
The allowable assembly error of the shaping element 3 with respect to the first shaping element 2 can be increased, and the yield of the beam shaping element can be improved.

As described above, according to the beam shaping element of this embodiment, various optical elements can be easily integrated, and the positional accuracy of the integrated various optical elements can be improved.

(Embodiment 3) Next, Embodiment 3 of the present invention will be described.

FIG. 4 is a diagram showing a configuration of an optical pickup according to Embodiment 3 of the present invention, wherein the first shaping element 2 is a transmission hologram and the second shaping element 3 is a transmission hologram. , Both are formed outside the integrated prism 50, and apply the concept of the first embodiment. By using transmission holograms for both the first and second shaping elements 2 and 3, it is possible to increase the assembly tolerance, so that the yield of the beam shaping elements can be improved and the optical pickup using the same can be improved. Since the tolerance can be increased, the yield of the optical pickup can be improved.

In the optical pickup of this embodiment, the light source 1 and the plurality of inclined surfaces (the inclination angle is 45 degrees) 50a, 50b, 5
An integrated prism 50 having a light receiving portion 0c and a light detection sensor 20 having a plurality of light receiving portions are housed in a single package 40. Further, the inside of the package 40 includes an inert gas such as a nitrogen gas or an argon gas, dry air, or the like. Is preferable because deterioration of the light source 1 and the light detection sensor 20 can be prevented.

The package 40 is formed of metal, resin, ceramics, or the like. In this case, it is possible to cut off external noise, and to improve the output of the light source 1 and the signal characteristics from the light detection sensor 20 with good stability. It is preferable to use a metal material that can be used.

The second shaping element 3 is provided on the substrate 44 at a position outside the package 40 from the recording medium, and the substrate 44 is attached to the position adjusting device 45. And by using this position adjusting device 45,
The position of the second shaping element 3 with respect to the light source 1 can be easily adjusted. Accordingly, even if the mounting position of the light source 1 is displaced, the installation position of the second shaping element 3 can be changed, and the optical system can be optimized. An optical pickup having excellent optical characteristics can be realized.

The integrating prism 50 has inclined surfaces 50a and 50a.
b, 50c, and the reflection element 7a on the slope 50a.
However, the reflecting element 7b, the first beam splitter 8, and the astigmatism generating means 10 are formed on the slope 50b, and the second beam splitter 9 is formed on the slope 50c.

The light emitted from the light source 1 enters the integration prism 50, is reflected by the reflection elements 7a and 7b, respectively, is further reflected by the first beam splitter 8, and has an end face 50d of the integration prism 50. The light is diffracted and passed by the first shaping element 2 formed in the above, further passes through the translucent member 41 closing the opening of the package 40, and is diffracted and passed by the second shaping element 3. Although the intensity distribution of the LD light beam emitted from the light source 1 is elliptical, the first shaping element 2
And the light passes through the second shaping element 3 to be shaped substantially circularly.

The light beam that has passed through the second shaping element 3 is focused on the data surface of the recording medium 43 by the objective lens 42,
The spot has a substantially circular shape. The light beam reflected by the recording medium 43 passes through a path opposite to the above and passes through the second shaping element 3.
The light that has passed through the first beam splitter 8 passes through the first beam splitter 8 and enters the integrated prism 50 through the first shaping element 2.
Are split into two beams by the beam splitter 9, one of which reaches the light detection sensor 20 as it is, the RF reproduction signal is detected by the light detection sensor 20, and the other is reflected by the astigmatism generation means 10. Later, the light reaches the light detection sensor 20 and is used to form a focus error signal and a track error signal. In this embodiment, a focus error signal is obtained by the astigmatism method, and a track error signal is obtained by the push-pull method.

As described above, in the optical pickup of this embodiment, by performing beam shaping, it is possible to realize a small optical pickup while realizing good optical characteristics. Therefore, it is an excellent optical pickup that can satisfy both the needs of the market for securing the amount of light on the recording medium and miniaturization of the apparatus.

In the present embodiment, the opening of the package 40 is closed by the translucent member 41 and is provided separately from the substrate 44. However, the opening of the package 40 may be closed by the substrate 44. .

(Embodiment 4) FIG. 5 is a diagram showing a configuration of an optical pickup according to Embodiment 4 of the present invention, wherein the first shaping element 2 is a reflection hologram and the second shaping element 3 is a transmission hologram. This is an application of the concept of the second embodiment.

The optical pickup of the present embodiment has a light source 1
The integrated prism 60 having a plurality of 45-degree slopes and the light detection sensor 20 are housed in one package 40. In the present embodiment, the first shaping 2 is provided on the integrated prism 60, and the second shaping element 3 is
The position of the second shaping element 3 can be adjusted by adjusting the position adjusting device 45, which is provided near the recording medium 43 external to the recording medium 43.

The integrating prism 60 has inclined surfaces 60a and 60a.
b, 60c, and the reflective element 7 is provided on the slope 60a.
However, the first beam splitter 8 and the first beam splitter 8
The shaping element 2 has a second beam splitter 9 formed on the slope 60c.

The light emitted from the light source 1 is
0, and diffracted by the first reflection type hologram element 2.
The light source 1 is reflected, reflected by the reflecting element 7, further reflected by the first beam splitter 8, transmitted through the translucent member 41 closing the opening of the package 40, and passing through the second shaping element 3. Has an elliptical shape after passing through the first shaping element 2 and the second shaping element 3, and is shaped into a substantially circular shape. The light beam that has passed through the second shaping element 3 is condensed on the data surface of the recording medium 43 by the objective lens 42, and has a substantially circular spot shape.

The light reflected by the recording medium 43 passes through the reverse path, passes through the second shaping element 3, enters the integrating prism 60, and passes through the first beam splitter 8. Then, the light reaches the light detection sensor 20, and the RF reproduction signal and the servo signal are detected by the light detection sensor 20. In a configuration having a separating mechanism (first beam splitter 8) for forward light and backward light between the first shaping element 2 and the second shaping element 3 as in the present embodiment, the integrated prism 60
Since the return light to pass through the second shaping element 3 but does not pass through the first shaping element 2, the astigmatism generated in the second shaping element 3 remains in the return light to the integration prism 60. The focus error signal can be detected by the astigmatism method using the astigmatism remaining in the returning light beam to the integrating prism 60. There is no need to provide astigmatism generating means, so that the structure of the integrating prism 60 can be simplified, and the productivity of the integrating prism 60 can be improved. Note that the second shaping element 3 is used instead of the reflecting element 7
May be formed by a reflection hologram. By doing so, the beam shaping element can be completely provided inside the integrated prism 60, so that the size of the optical pickup can be further reduced, and the number of parts in the assembly process of the optical pickup can be reduced. It can be simplified.

[0071]

As described above, according to the present invention,
The light emitted from the light source 1 having an elliptical FFP is assumed to be on a straight line formed by the optical axis of the light emitted from the light source 1 and emitted from a virtual light emitting point different from the light source. Since it can be converted as if it were substantially circular light, the optical axis of the light emitted from the light source does not deflect or shift, so not only the beam shaping element,
Since the position of each optical member constituting the optical pickup can be easily adjusted, the productivity of the optical pickup can be improved, and the beam shaping element can be downsized. Can also be reduced in size.

Also, by using a hologram or the like, a shaping element can be formed on the surface of the translucent substrate, and the first shaping element and the second shaping element can be formed very thin and small. Compared to a beam shaping element using an optical system, the size of the beam shaping element can be remarkably reduced. Pickup can be easily realized.

Further, by combining a plurality of shaping elements and canceling out the aberrations generated in each shaping element, the amount of aberrations generated in the beam shaping element can be greatly suppressed. An excellent optical pickup can be realized.

Also, aberrations caused by the wavelength fluctuation of the light source can be canceled by this configuration, so that the influence of the wavelength fluctuation generated in the light source can be minimized. Even if the wavelength fluctuation occurs in the light source, This is a highly reliable optical pickup capable of accurately recording or reproducing information.

Also, a pair of virtual orthogonal focal lines of the light beam after passing through the first shaping element is arranged at a position sandwiching the light emitting point of the light source, and the optical path length from the first shaping element to the light emitting point of the light source. The ratio L2 / L0 of the optical path length L2 from L0 to the virtual focal line behind the light emitting point of the light source among a pair of virtual orthogonal focal lines from the first shaping element is 1.1 or more and 2.0 By the following, the change of the wavefront aberration due to the wavelength variation of the first shaping element and the change of the wavefront aberration due to the wavelength variation of the second shaping element have a relationship to cancel each other out. Can be reduced.

Further, since the traveling directions of the diffracted light of the first shaping element and the zero-order light that has not been diffracted are different, the first-order element can eliminate the adverse effect due to the leakage of the zero-order light.
The position of the second shaping element with respect to the shaping element can be adjusted, and the tolerance of the mounting position of the light source can be greatly increased.

Further, by providing the light separating means between the first shaping element and the second shaping element, since the return light incident on the sensor has astigmatism from the beginning, the astigmatism method is used. The focus error signal can be easily detected, and the structure of the integrated optical pickup can be simplified.

[Brief description of the drawings]

FIG. 1A is a diagram illustrating a configuration of a beam shaping element according to a first embodiment of the present invention. FIG. 1B is a diagram illustrating a function of the beam shaping element according to the first embodiment of the present invention. The figure which shows the function of the beam shaping element in Embodiment 1.

FIG. 2 is a diagram showing the wavelength fluctuation and the amount of aberration depending on the position of a shaping element according to the first embodiment of the present invention;

FIG. 3 is a perspective view showing a configuration of a beam shaping element according to a second embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of an optical pickup according to a third embodiment of the present invention.

FIG. 5 is a diagram showing a configuration of an optical pickup according to a fourth embodiment of the present invention.

FIG. 6 is a configuration diagram of an optical pickup using one conventional beam shaping prism.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source 2 1st shaping element 3 2nd shaping element 4 Focal line 5 Focal line 6 Virtual light emitting point 7 Reflective element 8 Beam splitter 9 Beam splitter 10 Astigmatism generation means 20 Light detection sensor 30 Integrated prism 30a, 30b Slope 40 Package 41 Translucent member 42 Objective lens 43 Recording medium 50 Integrated prism 50a, 50b, 50c Slope 60 Integrated prism 60a, 60b, 60c Slope

Claims (15)

[Claims] (1) Astigmatism is given to light emitted from a light source,
A first shaping element that operates so as to be substantially equivalent to light having a set of orthogonal virtual focal lines, and a light that passes through the first shaping element and is provided by the first shaping element. And a second shaping element that acts to cancel out astigmatism and become substantially equivalent to light emitted from a virtual light emitting point different from the light emitting point of the light source, and an intensity distribution of light emitted from the light source. A beam shaping element for shaping the beam into a substantially circular shape. 2. The light after passing through the first shaping element has a first virtual focal line and a second virtual focal line, and an optical path length L0 from the first shaping element to a light emitting point of a light source and the second virtual focal line. The ratio L2 / L0 of the optical path length L2 from the first shaping element to the first virtual focal line is 1.
2. The structure according to claim 1, wherein the value is not less than 1 and not more than 2.0.
3. A beam shaping element according to claim 1. 3. A first virtual focal line and a second virtual focal line are located so as to sandwich a light emitting point of the light source, and the first virtual focal line is located in a direction opposite to a radiation direction of the light source. 3. The beam shaping element according to claim 2, wherein: 4. A method according to claim 1, further comprising a first shaping element and a second shaping element, wherein the first shaping element and the second shaping element are used to reduce the intensity distribution of incident light having a non-circular intensity distribution. And a second shaping element that reduces an increased amount of aberration in light transmitted through the first shaping element. 5. A non-circular intensity distribution of an incident light having a first shaping element for giving an aberration to incident light and a second shaping element for giving an aberration to incident light, wherein the intensity distribution of the incident light is substantially circular. And the first shaping element and the second shaping element are arranged such that the aberration given by the first shaping element and the aberration given by the second shaping element almost cancel each other. Beam shaping element 6. The beam shaping element according to claim 4, wherein the shaping element is a transmission type or reflection type hologram element. 7. The beam shaping element according to claim 6, wherein the traveling directions of the diffracted light and the undiffracted light (zero-order light) of the first shaping element are different. 8. The method according to claim 4, wherein the position of the second shaping element with respect to the first shaping element can be adjusted.
The beam shaping element as described. 9. The method according to claim 4, further comprising a light separating means between the first shaping element and the second shaping element.
Optical pickup as described. 10. The beam shaping element according to claim 4, wherein the beam shaping element is formed substantially in a plane. 11. The amount of aberration generated by the beam shaping element is set to 0.1.
The beam shaping element according to claim 4, wherein the beam shaping element is equal to or smaller than 03λ (RMS). 12. A light-emitting device comprising a first shaping element and a second shaping element, both of which are formed in a substantially planar shape, and using the first shaping element and the second shaping element, light emitted from a light source. A beam shaping element for converting an intensity distribution into a substantially circular shape. 13. A light source, a first shaping element and a second shaping element, wherein the first shaping element and the second shaping element are used to calculate the intensity distribution of incident light having a non-circular intensity distribution. A beam shaping element for converting the light into a substantially circular shape, a light condensing means for condensing the light converted to a substantially circular intensity distribution on a recording medium, and receiving the light reflected by the recording medium and converting the light into an electric signal Light detecting means, wherein at least one of the first beam shaping element and the second beam shaping element has an optical axis of incident light and an optical axis of outgoing light existing substantially on a straight line. Optical pickup. 14. A light source, a first shaping element and a second shaping element, wherein the first shaping element and the second shaping element are used to reduce the intensity distribution of incident light having a non-circular intensity distribution. A beam shaping element for converting the light into a substantially circular shape, a light condensing means for condensing the light converted to a substantially circular intensity distribution on a recording medium, and receiving the light reflected by the recording medium and converting the light into an electric signal An optical pickup comprising: a light detecting means; wherein the second beam shaping element reduces an amount of aberration of light passing through the first beam shaping element in the beam shaping element. 15. A light source, a first shaping element and a second shaping element, wherein the first shaping element and the second shaping element are used to reduce the intensity distribution of incident light having a non-circular intensity distribution. A beam shaping element for converting the light into a substantially circular shape, a light condensing means for condensing the light converted to a substantially circular intensity distribution on a recording medium, and receiving the light reflected by the recording medium and converting the light into an electric signal Light detection means, having a plurality of optical elements inside or on the surface,
An optical member that emits light guided from the light source toward a predetermined position and emits light reflected by a recording medium toward a predetermined position, at least a part of the beam shaping element Is formed on the optical member.