JPH0682719A - Beam shaping optical element, manufacture thereof, and beam shaping method - Google Patents

Abstract

PURPOSE:To provide a new beam shaping optical element, by which adjustment of the optical path of an optical system accompanying beam shaping is facilitated. CONSTITUTION:This beam shaping optical element is constituted so that two flat reflecting planes 4, 5 are arranged in parallel with each other and closely arranged so as to have rectilinear edges and form a step difference of decided height 3, and against the incident direction of a parallel light flux 60 to be shaped, the reflecting planes 4, 5 are arranged so as to meet the rectilinear edges with each other at right angles and incline them at a decided angle of (delta) against the incident direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a beam shaping optical element, a method for manufacturing the beam shaping optical element, and a beam shaping method using the beam shaping optical element.

[0002]

2. Description of the Related Art Beam shaping is to convert the cross-sectional shape of a light beam (the shape of a light beam on a plane orthogonal to the direction of travel of the light beam), and has heretofore been used for optical information recording media such as optical disks in optical pickup devices. It is known to shape the cross section of a laser beam from a semiconductor laser in order to obtain a light spot having a desired shape.

FIG. 7 is an explanatory view showing an example of the above beam shaping. Anisotropic (far field pattern is elliptical) beam from the semiconductor laser 91 becomes a parallel light beam by the collimator lens 92. When the short-axis direction of the elliptical shape in the far field pattern is represented by an arrow P, the light flux diameter of the light flux converted into a parallel light flux by the collimator lens 92 is a light flux whose direction parallel to the drawing is perpendicular to the drawing. Shorter than diameter. Therefore,
The light flux converted into a parallel light flux by the collimator lens 92 is also “an anisotropic shape”.

This anisotropic parallel light beam is reflected by the prism 97.
By refracting and transmitting light, only the light beam diameter in the P direction is enlarged. By adjusting the apex angle and the incident angle of the prism 97, the parallel light flux after passing through the prism 97 can be made into a substantially isotropic parallel light flux. That is, the anisotropic parallel light flux is “beam-shaped” by the prism 97 into an isotropic parallel light flux.

The beam-shaped light beam is converted into an objective lens 93.
Is imaged on the recording surface 95 of the optical disc 94 by
A circular or isotropic light spot is formed. Such "beam shaping" is indispensable in order to form a light spot formed on an optical information recording medium such as an optical disc into a desired shape.

By the way, the beam shaping method of FIG. 10 has the following problems. That is, first, since the optical path is bent by the refraction by the prism 97, the optical path adjustment of the optical system is troublesome. Secondly, if the collimation lens 92 does not complete the parallel light flux, the prism 97 causes astigmatism, and when the objective lens 93 forms an image of the light spot, an asymmetric aberration occurs and the light spot shape is distorted. I will end up. Third, the elliptical long-axis / short-axis ratio that characterizes the far-field pattern emitted from the semiconductor laser that is the light source generally has "variation" between the individual semiconductor lasers, and when this "variation" is large, It is necessary to change the incident angle to the prism 97 for each semiconductor laser, and therefore it is necessary to readjust the entire optical system.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and a novel beam shaping optical element and a beam shaping optical element which can solve the above problems. An object of the present invention is to provide a manufacturing method and a beam shaping method using the above beam shaping optical element.

[0008]

A beam shaping optical system according to the present invention is a "beam shaping optical element for expanding the beam diameter of a parallel light beam in one predetermined direction" and has two plane reflecting surfaces. These two "flat reflective surfaces" are parallel to each other,
In addition, they are arranged in close contact with each other so as to form a step having a predetermined height with a straight edge. That is, the two flat reflecting surfaces are parallel to each other and form a step having a predetermined height, and the step portion forms a linear edge. The beam shaping optical element is arranged such that the straight edges are orthogonal to the incident direction of the parallel light flux to be beam shaped, and the reflecting surface is inclined at a predetermined angle with respect to the incident direction. Item 1).

As a concrete constitution of this beam shaping optical element, an "optical prism having a step on the reflecting surface" may be used (Claim 2), or a "planar mirror having a step on the reflecting surface". It is also possible (claim 3). Alternatively, it is also possible to adopt a configuration in which "a transparent parallel plate is bonded and integrated with a reflecting surface of an optical prism by an optical adhesive or an optical contact" (claim 4), and "two optical prisms are bonded by an optical adhesive or an optical contact". It is also possible to adopt a constitution in which the adhesive is integrated by "(claim 5),
A configuration in which two planar mirrors are bonded and integrated so as to form a step with each other (claim 6) or a configuration in which another planar mirror is bonded and integrated to a part of the reflecting surface of the planar mirror Good (Claim 7).

In the beam shaping optical element according to the present invention, the size of the step formed by the two plane reflecting surfaces can be adjusted when the prisms or the plane mirrors are bonded together. In order to perform the above, “each prism is provided with two prisms or two plane mirrors in one of the wavefront-divided light fluxes in the interferometer to reflect the light flux, and each reflected light by each reflection surface forming a step portion. However, it is possible to adjust the size of the step portion so that the other wavefront-divided light flux and the generated interference fringes match each other. " In the beam shaping optical element manufacturing method according to the eighth aspect, the prisms or the plane mirrors are bonded by adjusting the height of the step portion in this way.

A beam shaping method according to a ninth aspect is a beam shaping method using the beam shaping optical element according to the first to seventh aspects. That is, as described above, the beam shaping optical element according to any one of claims 1 to 7 is configured such that "the straight edges are orthogonal to the incident direction of the parallel light beam to be beam shaped, and the reflecting surface is the incident direction. The beam shaping is performed by arranging so as to incline by a predetermined angle.

[0012]

As described above, in the present invention, the direction of the light beam before and after the beam shaping by the beam shaping optical element is determined by reflection, not refraction. The light beam obliquely incident on and reflected by the beam shaping optical element is separated into two light beams by the step of the beam shaping optical element, and the amount of separation is determined by the height of the step and the angle of incidence on the beam shaping optical element.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, reference numeral 1 indicates a semiconductor laser which is a light source. A divergent laser beam from the semiconductor laser 1 (arrow P indicates the direction in which the divergence angle of the far field pattern is minimum) is collimated by the collimator lens 2. Parallelized light flux 6
0 is the light beam diameter: Di in the direction corresponding to the arrow P.
However, the light flux diameter: Di is smaller than the light flux diameter in the direction orthogonal to the drawing.

In FIG. 1, reference numeral 6 indicates a beam shaping optical element. This beam shaping optical element 6 has a step 3 on the reflecting surface.
An optical prism having (a height is “d”), which is an example of the optical prism described in claim 2. The reflecting surface is divided into two reflecting surfaces 4 and 5 by the step 3.
It goes without saying that these reflecting surfaces 4 and 5 are parallel to each other. The angle shown in the figure: α is 45 degrees. Now, the light flux 60 is made to enter at an angle of δ with the reflecting surfaces 4 and 5.
Are incident on the beam shaping optical element 6. At this time, the center of the incident light beam 60 is aligned with the edge of the step formed by the reflecting surfaces 4 and 5 (which is a straight line extending in the direction orthogonal to the drawing).

When the light beam is reflected by the reflecting surfaces 4 and 5 and emerges from the beam shaping optical element 6, the light beam diameter does not change before and after the beam shaping in the direction orthogonal to the drawing.
In the direction corresponding to the arrow P, the luminous flux diameter: Do (= Di + d
/ Sin δ). That is, the height d of the step is increased, the incident angle is increased, or a combination thereof is used to obtain the beam diameter Do after beam shaping.
Can be increased. Therefore, by adjusting the height: d, the magnitude relationship between the light beam diameter in the direction corresponding to the arrow P and the light beam diameter in the direction orthogonal to the drawing can be made desired.

The light beam shaped by the beam shaping optical element 6 is condensed by the objective lens 7 on the recording surface of the optical information recording medium 8 such as an optical disc to form a light spot. Since the light spot is formed by wavefront optics, in the beam-shaped light beam, the light beam reflected by the reflecting surface 4 and the light beam reflected by the reflecting surface 5 must be in phase with each other in the propagation direction. I won't.

The optical path length difference I between the two light beams is given by I = 2n · d · cos δ using the refractive index n of the beam shaping optical element 6, the height d of the step 3 and the incident angle δ. Of n, d, and δ, δ is determined by the layout of the optical system that uses the beam shaping optical element, and n is determined by the material of the beam shaping optical element. Therefore, m is mainly determined by adjusting the height of the step: d. The relationship: I = m · λ may be satisfied with a positive integer, λ being the wavelength of the laser beam.

For example, glass BK7 having a refractive index of n = 1.51 is used as the material of the beam shaping optical element 6, the height of the step 3 is 707.2 μm, and the diameter of the incident light beam is Di is 2 mm. When the wavelength: λ is 790 nm, the beam diameter after beam shaping: Do is about 3 mm.

In FIG. 2, the curve indicated by reference numeral I shows the light intensity distribution in the light beam 60 incident on the beam shaping optical element 6. As shown by the solid line O, the intensity distribution of the light flux after beam shaping has a shape in which the intensity distribution of the incident light flux is divided into two at the symmetry axis, and the intensity at the center of the light flux becomes zero. As described above, since the light intensity at the center of the light flux becomes 0, there is an effect of "super-resolution", and the light intensity when condensed by the objective lens has a distribution 2A shown by a solid line in FIG. A distribution 1A indicated by a broken line is a light intensity distribution when the light flux is condensed when the light flux center portion of the distribution of the solid line O in FIG. 2 also has light intensity and has a Gaussian intensity distribution as a whole. The light intensity distribution of the light spot formed by the light beam shaped by the beam shaping optical element 6 exceeds the diffraction limit when a light beam having a Gaussian distribution having a light beam width equivalent to this is condensed and the spot diameter is small. Become.

FIG. 4 shows another embodiment. In order to avoid complication, the same reference numerals as those in FIG. 1 are used for those which are considered to have no possibility of confusion. The beam shaping optical element indicated by reference numeral 16 is a "planar mirror having a step on the reflecting surface", and is therefore an embodiment of the beam shaping optical element according to claim 3.

In the beam shaping optical element 16, a flat plate is polished to form a metal film on the surface on which the step 13 is formed by vapor deposition.
The reflecting surfaces 14 and 15 are used. For forming the reflecting surface, a dielectric multilayer film may be used instead of the metal film. When the inclination angle of the light beam to be beam-shaped with respect to the traveling direction is δ, the height of the step: d, m is a positive integer, and the wavelength is λ, and the relation “m · λ = 2 · d · cos δ” is satisfied. To be set.

FIG. 5 shows four modified embodiments of the beam shaping optical element. In the example of FIG. 5A, the reflecting surface 18 of the prism 17 has the same refractive index as the prism 17 and a predetermined thickness: d.
An example of the beam shaping optical element according to claim 4 is an example in which a transparent parallel flat plate 19 having a is bonded and integrated with an optical adhesive. Needless to say, an optical adhesive having a refractive index substantially the same as that of the prism 17 is used. As the optical adhesive, for example, an ultraviolet curable adhesive can be used. Instead of using the adhesive material, the adhesion may be performed by “optical contact” in which the adhesive surface is polished and annealed at a high temperature. The use of the optical contact can reduce the influence of the bonded portion as compared with the case of bonding with the optical adhesive.

Beam shaping optical element 25 shown in FIG.
Is an embodiment of the beam shaping optical element according to claim 5, wherein the two optical prisms 20 and 21 are connected to the prism surface 2.
3 and 24 are combined so as to form a step as a reflecting surface, and are bonded and integrated by an optical adhesive or an optical contact.

The beam shaping optical element 34 shown in FIG.
Is an embodiment of the beam shaping optical element according to claim 6, wherein the two plane mirrors 29, 30 are connected to the reflecting surfaces 32, 33.
Are integrally bonded so as to form a step 31 therebetween.

The beam shaping optical element 28 shown in FIG.
Is an embodiment of the beam shaping optical element according to claim 7, and is constructed by bonding another flat mirror 27 to a part of the reflecting surface of the flat mirror 26. Figure 5 (C)
In (D), the adhesive may be a normal adhesive because the adhesive does not affect the beam shaping.

In the four examples shown in FIG. 5, the steps are formed by adhesion, and it is not necessary to polish the reflection surface to form the steps. Therefore, compared with the embodiments of FIGS. 1 and 4, , Easy to manufacture.

The beam shaping optical element of the type shown in FIGS. 5B and 5C uses the reflecting surfaces of these two prisms or plane mirrors when the two prisms 20 and 21 or plane mirrors 29 and 30 are bonded. The size of the formed step must be adjusted in units of wavelength so that the wavefronts of the light beams reflected by the reflecting surfaces are aligned with each other. This adjustment can be performed as follows.

In FIG. 6A, the coherent light from the laser light source denoted by reference numeral 41 is collimator lens 4
The light beam is converted into a parallel light beam by 2 and is wavefront-divided into two light beams equivalent to each other by the half mirror 43. One of the light beams divided into the wavefront is incident on the imaging lens 46 via the mirror 44 and the half mirror 45, and is imaged on the CCD camera 47. On the other hand, the other of the light fluxes divided into the wavefronts is incident on the beam shaping optical element 25 (each prism has not been bonded yet) which is a combination of two prisms, and each of the reflection surfaces 23, 2
It is reflected by 4, and enters the image forming lens 46 through the half mirror 45 and forms an image on the CCD camera 47. The light flux passing through the mirror 44 and the light flux passing through the reflecting surfaces 23 and 24 interfere with each other to form “interference fringes” on the light receiving surface of the CCD camera 47. That is, the optical system of FIG. 5 constitutes a Mach-Zehnder interferometer as a whole.

If the wavefronts of the light beams reflected by the reflecting surfaces 23, 24 are displaced in the traveling direction, the reflecting surfaces 23, 24
The interference fringes generated by the interference of the reflected light fluxes from 24 with the light flux passing through the mirror 44 are displaced from each other as shown in FIG. 6 (B). In this state, the height of the step between the reflecting surfaces 23 and 24 of the two prisms is adjusted. By this adjustment, when the wavefronts of the light reflected by the reflecting surfaces 23, 24 are aligned in the traveling direction, the interference fringes are also aligned as shown in FIG. 6C. Therefore, this state may be fixed by a jig or the like and then bonded.

Since the beam diameter after beam shaping is determined by the height d of the step and the incident angle: δ, the height of the step: d and / Alternatively, it will be clear that the incident angle: δ may be adjusted.

Needless to say, the beam shaping optical element of the present invention can also be applied to beam shaping of a light beam other than the semiconductor laser light beam converted into a parallel light beam as described above.

[0032]

As described above, according to the present invention, it is possible to provide a novel beam shaping optical element, its manufacturing method and beam shaping method. Since the beam shaping optical element of the present invention performs beam shaping by reflection rather than refraction, the direction of the light beam before and after beam shaping is easily determined by the law of reflection. Therefore, beam shaping for an optical device that requires beam shaping is possible. It is easy to adjust the position of the optical system when incorporating the optical element. Further, since refraction is not used for beam shaping, astigmatism does not occur even when the light beam to be beam shaped is not highly parallelized. According to the manufacturing method of the eighth aspect, the size of the step can be set extremely easily. Further, according to the method of claim 9, beam shaping can be performed easily and surely.

[Brief description of drawings]

FIG. 1 is a diagram for explaining one embodiment of the present invention.

FIG. 2 is a diagram for explaining beam diameter expansion according to the above embodiment.

FIG. 3 is a diagram for explaining a super-resolution effect of a light beam whose beam diameter is enlarged according to the above embodiment.

FIG. 4 is a diagram for explaining another embodiment.

FIG. 5 is a diagram for explaining four modified examples.

FIG. 6 is a drawing for explaining the manufacturing method according to claim 8;

FIG. 7 is a diagram for explaining conventionally known beam shaping.

[Explanation of symbols]

 1 Semiconductor Laser 2 Collimating Lens 3 Step 4 Reflecting Surface 5 Reflecting Surface 6 Beam Shaping Optical Element 7 Objective Lens 8 Optical Information Recording Medium

Claims (9)

[Claims] 1. A beam shaping optical element for expanding the diameter of a parallel light beam in one predetermined direction, wherein two plane reflecting surfaces are parallel to each other and have a predetermined height with straight edges. Are arranged in close contact with each other so as to form a step, the straight edges are orthogonal to the incident direction of the parallel light beam to be beam-shaped, and the reflecting surface is inclined at a predetermined angle with respect to the incident direction. A beam shaping optical element, which is arranged so as to be peeled. 2. A beam shaping optical element according to claim 1, wherein the beam shaping optical element is an optical prism having a step on a reflecting surface. 3. The beam shaping optical element according to claim 1, wherein the beam shaping optical element is a plane mirror having a step on a reflecting surface. 4. A beam shaping optical element according to claim 1, wherein a transparent parallel plate is bonded and integrated with a reflecting surface of an optical prism by an optical adhesive or an optical contact. 5. The beam shaping optical element according to claim 1,
A beam shaping optical element characterized in that two optical prisms are bonded and integrated with an optical adhesive or optical contact. 6. The beam shaping optical element according to claim 1,
A beam shaping optical element, characterized in that two planar mirrors are formed as a step and are bonded and integrated. 7. A beam shaping optical element according to claim 1, wherein another flat mirror is bonded and integrated with a part of the reflecting surface of the flat mirror. 8. A method for manufacturing a beam shaping optical element according to claim 5 or 6, wherein two prisms or two plane mirrors are provided in one of the wavefront-divided light beams in the interferometer. By adjusting the height of the step portion so that the reflected light from each of the reflection surfaces forming the step portion and the reflected fringes generated by the reflecting surfaces that form the step portion and the interference fringes generated by the other light flux are equal to each other. A method of manufacturing a beam shaping optical element, which is characterized by being performed. 9. A beam shaping method using the beam shaping optical element according to claim 1, 2 or 3 or 4 or 5 or 6 or 7.