JP2002092928A - Light source unit and optical pickup - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light source unit in which accuracy to be required for relative positioning a laser beam source and a beam shaping element is relieved than before, and to provide an optical pickup using the same. SOLUTION: The light source unit consists of a light source, and a beam shaping element which converts luminous flux emitted from the light source and diffusing at different flare angles based on axes orthogonal to each other and vertical to an optical axis into the luminous flux having nearly the same flare angle. A medium whose refractive index exceeds 1 is filled between the light source and the beam shaping element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a light source unit having a beam shaping element for converting a laser beam from a laser light source from a divergent beam having an elliptical cross section to a divergent beam having a substantially circular cross section, and uses the light source unit. It relates to an optical pickup.

[0002]

2. Description of the Related Art Conventionally, for example, a so-called CD (Compac
An optical recording / reproducing apparatus using an optical recording medium typified by an optical disc such as an optical disc such as a disc (t. Disc) or a DVD (Digital Versatile Disc) is required to have high light use efficiency. Therefore, it is necessary to convert a laser beam from a laser diode, which is a light source, having an elliptical cross section perpendicular to the optical axis into a laser beam having a substantially circular cross section.

As a result, the energy utilization efficiency of the laser beam is increased, the CN ratio is improved, and there is a margin in designing and manufacturing the optical pickup. In addition, since the laser beam can be focused small, the spot size on the optical recording medium can be reduced, thereby increasing the data capacity of the optical recording medium and reducing crosstalk during reproduction. Can be.

As described above, in order to convert a laser beam having an elliptical cross section into a laser beam having a substantially circular cross section,
Conventionally, a so-called anamorphic prism has been put to practical use. This is to convert a laser beam having an elliptical cross section, which has passed through the prism, into a laser beam having a substantially circular cross section by compressing the laser beam in one direction on a cross section perpendicular to the optical axis. However, such a prism needs to be used in a parallel light beam in order to prevent the occurrence of various aberrations. For this purpose, the laser beam must be collimated, and the optical system of the optical pickup is adjusted. And the miniaturization is limited.

On the other hand, a beam shaping element for converting a laser beam from a laser light source from a divergent beam having an elliptical cross section to a divergent beam having a substantially circular cross section has been put to practical use.
Since this can be arranged near the laser diode as the light source, it is effective for integration and miniaturization of the optical pickup. As such a beam shaping element, an element using an anamorphic lens or a diffraction element has been conventionally proposed. Further, as described in, for example, JP-A-6-294940, a beam shaping element having a cylindrical input surface and a toroidal output surface is disclosed.

[0006]

However, the conventional beam shaping element described above has a severe allowable wavefront aberration, and therefore, usually, the relative position of the laser diode as a light source and the beam shaping element in the optical axis direction is relatively low. However, there is a problem that the accuracy of the required positioning is increased. Further, in the configuration described in JP-A-6-294940, the relative position with respect to the irradiation source does not have to be strict, but the wavelength of the laser beam used is 800 nm.
Limited to a degree.

In particular, in a high-density optical recording / reproducing apparatus using a next-generation blue laser diode, the wavelength of a laser beam to be used is as short as about 400 nm, so that the allowable amount of wavefront aberration becomes more severe. As described above, the positioning accuracy of the beam shaping element in the optical axis direction is required.

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a light source unit in which the required accuracy of relative positioning between a laser light source and a beam shaping element is alleviated as compared with the related art, and an optical pickup using the same. With the goal.

[0009]

In order to achieve the above object, the present invention provides a light source and a light beam emitted from the light source and diverging at different diverging angles with respect to axes perpendicular to the optical axis and orthogonal to each other. And a beam shaping element for converting the beam into a light beam having substantially the same divergence angle. A light source unit characterized in that a medium having a refractive index of more than 1 is filled between the light source and the beam shaping element.

[0010] The beam shaping element has at least two anamorphic diffraction surfaces.
Alternatively, the beam shaping element has at least two anamorphic refractive surfaces.

Further, the present invention is characterized in that the following conditional expression is satisfied. n _D −n ≧ 0.2, where n _{D is} the refractive index of the beam shaping element and n is the refractive index of the medium.

Further, the medium is a photo-setting resin or a thermosetting resin.

The light source, the beam shaping element, and the medium are integrated and fixed to each other.

Further, any one of the light source units, an objective lens for condensing a light beam from the light source unit to form a converged spot on an optical recording medium, and the objective lens including information recorded from the optical recording medium. An optical pickup comprising: a detection optical system that converts return light of a light beam into an electric signal.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view schematically showing a basic configuration of a light source unit of the present invention. In FIG. 1, reference numeral 1 denotes a beam shaping element drawn in a cylindrical shape, and an optical axis corresponding to a central axis thereof is defined as a Z axis. P indicates the position of a laser light source (not shown) arranged on the Z axis in front of the beam shaping element 1. As an example, axes orthogonal to each other on the position P are defined as an X axis and a Y axis, and these axes are also orthogonal to the Z axis. A medium 2 having a refractive index exceeding 1 is filled between the beam shaping element 1 and the laser light source. This makes it possible to reduce the required accuracy of relative positioning between the laser light source and the beam shaping element 1. Details will be described later.

FIG. 1 shows a state in which a beam emitted from a laser light source enters a beam shaping element 1 from a position P via a medium 2 and is finally shaped and emitted. Here, of the beam from the laser light source, X-Z
The angles (spreading angles) formed by the marginal ray Lx on the cross section and the marginal ray Ly on the YZ cross section with the Z-axis differ from each other at the beginning when they are emitted from the laser light source. The light beams are emitted from the beam shaping element 1 at the same angle. That is,
This shows that the beam shaping element 1 converts a divergent beam having an elliptical cross section into a divergent beam having a substantially circular cross section.

FIG. 2 is a longitudinal sectional view schematically showing the basic structure of the light source unit of the present invention. As shown in the figure, a laser diode LD as a light source is disposed on the Z axis to the left of the beam shaping element 1. In the figure, an XZ section is drawn above the Z axis, and a YZ section is drawn below the Z axis. Note that the light source side surface of the beam shaping element 1 is denoted by r1, and the image side surface is denoted by r2. Further, between the light source side surface r1 of the beam shaping element 1 and the laser diode LD,
The medium 2 having a refractive index of more than 1 is filled.

FIG. 1 shows a state in which a beam emitted from a laser diode LD enters a beam shaping element 1 from a position P via a medium 2 and is finally shaped and emitted. Here, among the beams from the laser diode LD, the marginal rays Lx and Y on the XZ section
The angle formed by the marginal ray Ly on the -Z cross section and the Z axis is θx,
What was different from θy finally became almost the same angle θ '
And the state of being emitted from the beam shaping element 1. That is, the beam shaping element 1 converts a divergent beam having an elliptical cross section into a divergent beam having a substantially circular cross section.

FIG. 3 is an optical configuration diagram of the light source unit according to the first embodiment of the present invention, and shows a YZ section. FIG. 4 shows an XZ cross section. In this embodiment, the beam shaping element 1 is of a finite type, has first and second anamorphic diffraction surfaces r1 and r2 from the light source side, and a divergent beam having an elliptical cross section from a laser diode LD as a light source. Into a divergent beam having a substantially circular cross section. Here, as described above, the medium 2 having a refractive index exceeding 1 is filled between the laser diode LD and the first anamorphic diffraction surface r1 which is the light source side surface of the beam shaping element 1. This makes it possible to relax the required accuracy of relative positioning between the laser diode LD and the beam shaping element 1 in the Z-axis (optical axis) direction.

At this time, it is desirable to satisfy the following conditional expression (1). n _D −n ≧ 0.2 (1) where n _{D is} the refractive index of the beam shaping element and n is the refractive index of the medium.

If the lower limit of conditional expression (1) is not reached, the grating height h of the first anamorphic diffraction surface of the beam shaping element, which maximizes the diffraction efficiency, becomes high, making it difficult to form a diffraction surface. In addition, the diffraction efficiency for a laser beam having an angle with respect to the optical axis is reduced.

Here, the grid height h is determined by the following equation. h = λ / (n _D −n) where λ is the wavelength (μm) of the laser beam.

FIG. 5 is an optical configuration diagram of a light source unit according to the second embodiment of the present invention, and shows a YZ section. FIG. 6 shows an XZ cross section. In the present embodiment, the beam shaping element 1 is of a finite type, has first and second anamorphic refraction surfaces r1 and r2 from the light source side, and a divergent beam having an elliptical cross section from a laser diode LD as a light source. Into a divergent beam having a substantially circular cross section.

Here, as described above, the first anamorphic refraction surface r1 which is the light source side surface of the beam shaping element 1
A medium 2 having a refractive index of more than 1 is filled between the laser diode LD and the laser diode LD. This makes it possible to relax the required accuracy of relative positioning between the laser diode LD and the beam shaping element 1 in the Z-axis (optical axis) direction. At this time, it is desirable that the conditional expression (1) is satisfied. If the lower limit of conditional expression (1) is not reached, the curvature of the first anamorphic refracting surface of the beam shaping element will be small, and it will be difficult to make it.

The beam shaping element as shown in each of the above embodiments can be mass-produced by molding with a precision mold using a material such as glass or plastic. Also, after adjusting the laser diode and beam shaping element integrally,
By adopting a fixed configuration, the light source unit can be used in an integrated type optical pickup including a laser diode, and a further reduction in size and thickness can be achieved. In particular, the material to be filled as a medium is provided with a function as an adhesive, thereby facilitating adjustment, and thereby, the laser diode and the beam shaping element can be fixed.

Incidentally, positioning in the Z-axis direction is a very important performance factor for a beam shaping element that converts a divergent beam having an elliptical cross section into a divergent beam having a substantially circular cross section. This is because the amount of fluctuation of the lens back when the distance between the laser diode and the beam shaping element slightly changes differs between the X direction and the Y direction.
At this time, an astigmatic difference occurs on the optical axis.

Such an axial astigmatic difference causes a so-called increase in wavefront aberration when the light source unit is particularly applied to an optical pickup or the like. Moreover, since the astigmatic difference is a difference generated due to a difference in direction, it is extremely difficult to correct the astigmatic difference behind the beam shaping element.

Conventionally, an optical pickup has a wavelength of 8
Although a laser beam of about 00 nm has been used, a high-density optical recording / reproducing apparatus using a blue laser beam having a wavelength of about 400 nm for an optical pickup has recently been put into practical use. In this case, assuming that the allowable wavefront aberration amount in the optical pickup is the same, if simply calculated,
The required accuracy of positioning of the beam shaping element in the Z-axis direction is about twice that of the conventional art, and it is extremely difficult to adjust it.

As a method for solving such a problem,
Filling a medium having a refractive index of more than 1 between the first anamorphic surface, which is the light source side surface of the beam shaping element, and the laser diode. Assuming that the refractive index of such a medium is n, the amount of astigmatism can be reduced to 1 / n when the medium is filled, with respect to the same amount of change in the distance between the laser diode and the beam shaping element.

The principle of the present invention will be described below. In general,
The following Newton's formula holds as the imaging equation. zz '=-(n' / n) f^Two  Here, z: distance from the object to the object-side focal point z ': distance from the image to the image-side focal point n: object-side refractive index n': image-side refractive index f: focal length of the optical system.

When the above equation is differentiated by z, δz ′ = (n ′ / n) (f / z) ² δz = (n ′ / n) from the geometric similarity of the optical path between the light source side and the image side. ) (Θ / θ ′) ² δz. Where θ: the angle of the marginal ray with the optical axis on the object side (light source side) (incident side angle) θ ′: the angle of the marginal ray with the optical axis on the image side (exit side angle).

In general, beam shaping is performed so that the directions of NA (emission angle) on the emission side are substantially equal, that is, a divergent beam having a substantially circular cross section. When the distance from the beam shaping element changes by δz, the astigmatic difference after beam shaping is represented by the following equation. AS _z = (n ′ / n) (θ _x / θ ′) ² (1-M ² ) δz

Here, M is a shaping magnification, and is represented by the following equation.
Given. M = θ_y/ Θ_x  Where θ_y> Θ_xAnd θ_y, Θ_xIs the Y direction
Direction, the value of θ in the X direction. Generally, M = about 2-3
Yes, from laser diode and beam shaping element specifications
It is determined.

As described above, the astigmatic difference AS _z is inversely proportional to the square of the injection side angle θ ′. The optical path difference OPD due to the astigmatism is given by the following equation. Where n '= 1
And OPD = AS _z NA ^2/2

Since the effective value of the wavefront aberration amount W (waves) is approximately given by W _rms λ ≒ OPD / 3.5, λ = 400 nm = 0.4 μm, NA
= Sin θ ′ ≒ θ ′, the following equation is obtained. W _rms = 0.357 (1 / n) θ _x ² (1-M ² ) δz

Here, θ _x and M are determined from the specifications of the laser diode and the beam shaping element, respectively. Therefore, it can be seen that in order to reduce the influence of the change in the distance between the laser diode and the beam shaping element on the wavefront aberration, n should be larger than 1 for the same specification. That is, the space between the laser diode and the beam shaping element may be filled with a medium having a refractive index.

With such a configuration, it is possible to reduce the required accuracy of the relative positioning of the laser diode and its beam shaping element in the optical axis direction. Accordingly, the above-described configuration suppresses an increase in the positioning error sensitivity in the optical axis direction due to a shorter wavelength using a blue laser beam and a stricter level of wavefront accuracy in the high-density optical recording / reproducing apparatus described above. It is possible to do.
Then, the light source unit and the optical pickup can be easily assembled and adjusted.

As a specific numerical example, θ _x = 0.1
5, In the case of M = 2.3, in order to satisfy the wavefront aberration amount of 0.02λ, when the air is between the laser diode and the beam shaping element, the positioning accuracy in the z-axis direction is on the order of submicrons. This makes assembly adjustment difficult. Therefore, if the space between the laser diode and the beam shaping element is filled with, for example, a medium having a refractive index of 1.5 or more, the allowable error can be reduced to 1.5 times or more.

Hereinafter, the configuration of the optical system of the light source unit according to the present invention will be described more specifically with reference to construction data, aberration diagrams, and the like. In addition, the following Example 1,
2 corresponds to the above-described first and second embodiments, respectively, and the optical configuration diagrams (FIGS. 3, 4, 4, 5, and 6) representing the first and second embodiments correspond to the corresponding embodiments. Examples 1 and 2
Are shown respectively. Note that each embodiment has a configuration of θ _y > θ _x .

In each embodiment, ri (i = 1,2) indicates the i-th surface counted from the light source side and its curvature radius (unit: mm), and di (i = 0,1) indicates the light source side. The i-th axis upper surface interval (unit: mm) counted from the above is shown. Ni (i = 0, 1) indicates the refractive index of the i-th optical member (here, the medium and the beam shaping element) counted from the light source side, and the wavelengths are 410.00 nm and 405.00 nm from the left, respectively. , 400.00n
m for a laser beam. OB
J indicates a laser diode LD.

<Embodiment 1> In this embodiment, the anamorphic diffraction surface is defined by a phase difference function based on an XY polynomial and is represented by the following equation. φ (X, Y) = (2π / HWL) (Σ _{m, n} C _j X ^m Y ⁿ ) where j = {(m + n) ² + m + 3n} / 2, (m, n = 1,
2,...) HWL: Defined wavelength of the diffraction surface. In this embodiment, the emission side N of the laser diode
A (in the air) is 0.35 in the X direction and 0.15 in the Y direction, and the NA on the emission side is about 0.23. The space between the laser diode and the beam shaping element is filled with a UV curable resin.

HWL = 405.00nm [radius of curvature] [interval of axial top surface] [refractive index (N)] OBJ ∞ d0 = 0.1535 N0 = 1.534053, 1.534659, 1.535160 r1 = ∞ d1 = 1.000000 N1 = 1.909821, 1.913418, 1.917218 r2 = ∞

[Phase coefficient of the first surface (r1)] (diffraction order) = 1 C3 = 2.5000 C5 = -2.0000 C10 = -5.9033 × 10 ² C12 = 3.4967 × 10 ² C14 = 5.2217 × 10 C21 = -2.5560 × 10 ⁵ [Phase coefficient of the second surface (r2)] (diffraction order) = 1 C3 = -2.5000 × 10 ^-3 C5 = 1.2060 × 10 ^-1 C10 = -3.5653 × 10 ^-1 C12 = -1.1856 C14 = -5.3615 × 10 ^-1 C21 = 1.8995 C23 = 2.0634 C25 = 3.0842 C27 = 9.3097 × 10 ^-1

<Embodiment 2> In this embodiment, anamorph
The refractive surface is represented by the following equation. z = (CUXx^Two+ CUYy^Two) / [1 + √ ｛1- (1+
KX) CUX^Twox^Two− (1 + KY) CUY^Twoy^Two｝] + AR
｛(1-AP) x^Two+ (1 + AP) y^Two｝^Two+ BR ｛(1
-BP) x^Two+ (1 + BP) y^Two｝^Three+ CR ｛(1-C
P) x^Two+ (1 + CP) y^Two｝^Four+ DR ｛(1-DP) x^Two
+ (1 + DP) y^Two｝^Five  Where z: displacement of the surface in the Z-axis direction CUX, CUY: curvature in the X and Y directions respectively KX, KY: conical constant in the X and Y directions AR, BR, CR, DR: fourth, sixth, respectively 8th,
Of the deformations from the 10th order cone, the non-rotationally symmetric
Spherical coefficients AP, BP, CP, DP: 4th, 6th, 8th,
Represents the rotationally asymmetric part of the deformation from the 10th order cone
The aspheric coefficient is

In this embodiment, the emission side NA (in the air) of the laser diode is 0.35 in the X direction and 0.15 in the Y direction, and the NA on the emission side is about 0.24. The space between the laser diode and the beam shaping element is filled with a UV curable resin. Note that RDX, RD in the data
Y indicates the radius of curvature in the X and Y directions, respectively, and is the reciprocal of CUX and CUY, respectively.

[Curvature radius] [Axis top surface interval] [Refractive index (N)] OBJ ∞ d0 = 0.1000 N0 = 1.534053, 1.534659, 1.535160 r1 RDY = ∞ RDX = -0.02000 d1 = 1.000000 N1 = 1.909821, 1.913418, 1.917218 r2 RDY = -2.00000 RDX = -1.60900

[Coefficient of first surface (r1)] KY = 0.000000 KX = 0.000000 AR = 0.000000 BR = 0.000000 CR = 0.000000 DR = 0.000000 AP = 0.000000 BP = 0.000000 CP = 0.000000 DP = 0.000000 [Second surface (r2) KY = 4.470844 KX = 1.671833 AR = 0.514456 × 10 ^-2 BR = 0.117540 × 10 ^-1 CR = 0.000000 DR = 0.000000 AP = 0.100000 × 10 BP = 0.100000 × 10 CP = 0.100000 × 10 DP = 0.100000 × 10

FIGS. 7 and 8 are lateral aberration diagrams of the optical systems of Examples 1 and 2, respectively. In each figure, (a), (b)
Represents aberrations in the Y and X directions, respectively, and curves a, b, and c represent wavelengths of the laser beam of 410
nm, 405 nm, and 400 nm. The unit of the scale is mm. As shown in each figure, good chromatic aberration correction is possible and the wavefront aberration is suppressed to a small value in a wavelength variation range to be considered when a blue laser beam is used.

In the first embodiment, when the distance between the laser diode and the beam shaping element (first surface) is increased by 1.5 μm from the designed value of 0.1535 mm, the amount of astigmatism is about 1.6 μm. In this case, the residual wavefront aberration is about 0.02, which is within the allowable range. When air is present between the laser diode and the beam shaping element as in the related art, the accuracy required for adjustment in the z-axis direction to satisfy the wavefront aberration of about 0.02 is 1 μm or less.
In the second embodiment, when the distance between the laser diode and the beam shaping element (first surface) is increased by 1.5 μm from the designed value of 0.1 mm, the astigmatism amount is about 1.4 μm. Is within an allowable range of about 0.02.

FIG. 9 is a diagram schematically showing a configuration example of an optical pickup using the light source unit of the present invention. In the figure, a laser diode LD and a beam shaping element 1
Are united. From the beam shaping element 1, a beam L having a substantially circular cross section diverges and is emitted. This beam L
After passing through the polarizing beam splitter 3, the light is collimated by a collimating lens 4 and further passes through an objective lens 5 to form a condensed spot on an optical recording medium 6.

Since information by bits is recorded on the optical recording medium 6, the beam L reflected at this portion is
Is reflected by the polarizing beam splitter 3 as return light,
The light is split by another beam splitter 7 and detected by the photodetector PD. As shown in the figure, since the laser diode LD and the beam shaping element 1 are integrated, there is no need to arrange a beam shaping prism or the like after the collimating lens 4,
The optical pickup can be made thinner and smaller.

FIG. 10 is an explanatory diagram schematically showing an example of a procedure for producing the light source unit of the present invention. First, as shown in FIG. 1A, in the beam shaping element 1, diffraction surfaces (or refraction surfaces) r1 and r2 are formed on the light source side and the image side, respectively. In particular, the diffraction surface r1 is formed at the bottom of the concave portion 1a provided at the light source side end of the beam shaping element 1. Next, as shown in FIG. 3B, for example, a laser diode LD attached to an end of the substrate 8 is brought close to the diffraction surface r1.

In this state, as shown in FIG. 3C, the concave portion 1a is filled with the UV curable resin 9, and the space between the laser diode LD and the beam shaping element 1 is filled. In this state, a beam L is emitted from the laser diode LD, and while monitoring the cross-sectional shape of the beam L, the laser diode LD is directed in the optical axis direction or in the direction perpendicular thereto as shown by an arrow A so that the beam L becomes substantially circular. Adjust the positioning. After positioning, (d)
As shown by the arrow, the UV curable resin 9 is irradiated with ultraviolet rays as shown by the arrow UV and solidified, thereby fixing the laser diode LD to the beam shaping element 1. Instead of the UV curable resin, another light curable resin, a thermosetting resin, or the like may be used.

[0054]

As described above, according to the present invention,
It is possible to provide a light source unit in which the required relative positioning accuracy between the laser light source and the beam shaping element is relaxed as compared with the related art, and an optical pickup using the same.

Further, it is possible to obtain a finite type beam shaping element in which the positioning accuracy in the optical axis direction is reduced.

Further, since the laser diode and the beam shaping element are adhered and fixed by the medium, the stability to the surrounding environment is increased.

Further, since the beam shaping element can be arranged near the laser diode, a small and highly efficient optical pickup can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing a basic configuration of a light source unit of the present invention.

FIG. 2 is a longitudinal sectional view schematically showing a basic configuration of a light source unit of the present invention.

FIG. 3 is an optical configuration diagram (YZ section) of the light source unit according to the first embodiment.

FIG. 4 is an optical configuration diagram (XZ cross section) of the light source unit according to the first embodiment.

FIG. 5 is an optical configuration diagram (YZ section) of a light source unit according to a second embodiment.

FIG. 6 is an optical configuration diagram (XZ cross section) of a light source unit according to the second embodiment.

FIG. 7 is a lateral aberration diagram of the optical system according to the first embodiment.

FIG. 8 is a lateral aberration diagram of the optical system according to the second embodiment.

FIG. 9 is a diagram schematically illustrating a configuration example of an optical pickup.

FIG. 10 is an explanatory view schematically showing an example of a procedure for producing a light source unit of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Beam shaping element 2 Medium 3 Polarization beam splitter 4 Collimating lens 5 Objective lens 6 Optical recording medium 7 Beam splitter 8 Substrate 9 UV curing resin Lx PD Photo Detector

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H087 KA13 LA26 LA28 PA01 PA17 PB01 QA01 QA03 QA07 QA13 QA17 QA33 QA37 RA07 RA42 RA45 RA46 UA01 5D119 AA32 AA35 AA39 EC27 JA08 JB03

Claims (7)

[Claims] 1. A light source, and a beam shaping element for converting light beams emitted from the light source and diverging at different divergence angles with respect to axes perpendicular to the optical axis and orthogonal to each other, into light beams having substantially the same divergence angle. A light source unit, wherein a medium having a refractive index of more than 1 is filled between the light source and the beam shaping element. 2. The light source unit according to claim 1, wherein the beam shaping element has at least two anamorphic diffraction surfaces. 3. The light source unit according to claim 1, wherein the beam shaping element has at least two anamorphic refractive surfaces. 4. The light source unit according to claim 1, wherein the following conditional expression is satisfied: n _D −n ≧ 0.2, where n _{D is a} beam shaping element. Refractive index n: Refractive index of the medium. 5. The light source unit according to claim 1, wherein the medium is a photocurable resin or a thermosetting resin. 6. The light source unit according to claim 1, wherein the light source, the beam shaping element, and the medium are integrated and fixed to each other. 7. The light source unit according to claim 1, further comprising: an objective lens configured to collect a light beam from the light source unit to form a focused spot on an optical recording medium; An optical pickup comprising: a detection optical system that converts return light of the light flux including recording information from a recording medium into an electric signal.