JPH02222919A - Beam shape converting device - Google Patents

Abstract

PURPOSE:To eliminate the loss of the quantity of light which accompanies the cutoff of a light beam and to obtain a light beam which has a small beam diameter by separating a light beam into two light beams which leave each other completely and converging the two light beams on a focus position by a focus lens. CONSTITUTION:The device consists of a couple of conic lenses 2 and 3 which are equal in refracting power and a condenser lens 4 and when the laser beam 7 which is emitted by a semiconductor laser 5 and collimated by a collimator lens 6 is made incident on the device 1, this laser beam 7 is separated by the 1st conic lens 2 mutually into the two light beams which travel leaving each other. Then the beams are made parallel to each other by the 2nd conic lens 3 and converged on the focus position P of the condenser lens 4 by the condenser lens 4. Consequently, the problem of light quantity loss, etc., is eliminated and a beam spot is reduced in size by a super-resolving phenomenon.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a beam shape conversion device for obtaining a minute light beam spot, and more specifically, a beam shape conversion device that converts the intensity distribution of a light beam by utilizing a super-resolution phenomenon. This invention relates to a beam shape conversion device.

(Prior Art) In recent years, optical discs have attracted attention as high-density recording media, and various studies have been conducted to further increase their recording capacity. The first possible way to increase recording capacity is to reduce the recording light beam spot diameter and reduce the bit size on the disk, increasing the number of bits that can be formed. As a method to reduce the spot diameter of
a-ZD-6,7; NEC).

In other words, this technology blocks the central portion of a recording laser beam into a strip to form two parallel light beams, and uses an objective lens to focus the two parallel light beams onto the disk. This is to form an interference pattern with bright and dark areas separated on the disk. In this interference pattern, the central bright line (main lobe) has the highest light intensity,
The light intensity of the bright line (side lobe) farther away from the center becomes smaller, and the diameter of this main lobe is λ/NA (NA
is the numerical aperture, λ is the wavelength, and is a constant) (super resolution). Therefore, if this main lobe portion is used for optical recording, it becomes possible to reduce the spot diameter of the recording beam on the aforementioned optical disk. In addition, in this technique, since the light intensity of the side lobe is suppressed below the threshold of the recording light amount of the medium, there is no fear that information will be recorded on the disk by the side lobe. In addition, when reproducing signals from the disc using the main lobe, it is necessary to eliminate erroneous signals picked up by the side lobes, so after collecting the reflected light from the disc,
This reflected light is passed through a slit to cut off the sidelobe components and the signal is detected.

(Problem to be Solved by the Invention) However, in the prior art described in the above-mentioned publication, as described above, the central part of the light beam is blocked by a light-shielding band to cut off a part of the light amount, which makes recording difficult. The amount of beam light contributing to this decreases. For example, in order to make the main lobe diameter 80% of the original collimated beam diameter,
It is said that the width of the light-shielding band must be approximately 20% of the original beam diameter, and in this case a considerable part of the beam center is cut, so in order to secure the beam light intensity that contributes to recording, it is necessary to A higher output laser light source is required.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a beam shape conversion device that can reduce the beam spot by super-resolution phenomenon without blocking the light beam from the laser light source. It is something to do.

(Means for solving the problem) A beam shape conversion device according to claim 1 of the present invention includes:
A parallel light beam incident along the symmetry plane of a first prism having an isosceles triangular cross section is separated by this first prism into two light beams that travel apart from each other.
The two light beams emitted from the first prism and the first prism have an isosceles cross section with the same absolute value of refractive power.
The light beams are emitted parallel to each other by a rectangular second prism, and the light beams emitted from the second prism are focused at a predetermined position using a focusing lens.

Further, the beam shape converting device according to claim 2 of the present invention is a light beam separating member comprising an incidence surface and a reflection surface each having a dogleg-shaped cross section and having a common plane of symmetry and having the same absolute value of apex angles. Accordingly, one parallel light beam incident on this plane of incidence along this plane of symmetry is made to exit from the above-mentioned reflecting surface as two light beams separated into mutually parallel states, and this light beam separation It is characterized in that the light beam emitted from the shrine is focused on a predetermined position using a focusing lens.

Furthermore, in the beam shape conversion device according to claim 3 of the present invention, parallel light beams incident along a plane perpendicular to the grating surface and parallel to the grating lines are separated from each other by the first equal pitch grating element. The light beam emitted from the first equal-pitch grating element is separated into two traveling light beams, and the light beam emitted from the first equal-pitch grating element is split into two parallel light beams by the first equal-pitch grating element and the second equal-pitch grating element having the same pitch. The present invention is characterized in that the light beam is emitted as a regular light beam, and the light beam emitted from the second equal-pitch grating element is focused at a predetermined position using a focusing lens.

(Function) According to the above configuration, one incident parallel light beam (collimated light beam) is first separated into two light beams that move away from each other, and then these two light beams are separated from each other. The two parallel light beams are finally focused by a focusing lens at the focal point of the lens. That is, the parallel light beam is
The prism, the entrance surface, and the first equal-pitch grating element separate the light beams into two light beams that travel away from each other, and then the two light beams pass through the second prism, the exit surface, and the first equal-pitch grating element. and the second equal pitch grating elements are formed in parallel to each other. In addition, since these two mutually parallel light beams that are focused meet the condition for interference (they are emitted from the same light source at approximately the same time), interference fringes are formed at this focusing point. .

In the above configuration, the light beams are reliably separated using the above-mentioned means for separating the light beams, instead of separating the light beams by blocking the central part of the beams as in the prior art described above. Therefore, all of the light intensity of the light beam emitted from the light source is focused at the focal point of the focusing lens, making it possible to reduce the beam spot due to the super-resolution phenomenon without causing problems such as light intensity loss. Become.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a beam shape conversion device according to an embodiment of the present invention.

This device 1 consists of a pair of prisms 2°3 with equal refractive power and a focusing lens 4, and when a laser beam 7 emitted from a semiconductor laser 5 and collimated by a collimating lens 6 is incident on the device 1, The laser beam 7 is first separated by the first prism 2 into two beams that move away from each other (these two light beams are formed so that they cross once and then continue), and then these two beams are separated. The beams are made parallel to each other by the second prism 3, and finally focused by the focusing lens 4 to the focal point P of this focusing lens 4. Among the laser beams 7 that have entered the bent surface of the first prism 2 having a dogleg shape in cross section, the light flux that has entered the prism 2 in the upper part of the optical axis is below the optical axis; The light beams incident on the lower part are each refracted above the optical axis. Also, the second
At the arrangement position of the prism 3, this -laser beam 7 is completely separated into two light beams, and the refractive power of the second prism 3 is set equal to the refractive power of the first prism 2. 2 is ejected from the second prism 3 because
The book light beam 7 enters the focusing lens 4 in a parallel state. This ensures that the laser beam 7 is focused on the focal point of the focusing lens 4. Further, the two prisms 2 and 3 are made of the same material, and are formed in the shape of a triangular prism having an isosceles triangle in cross section and having the same size or similar shapes to each other.
When parallel light is incident as shown in FIG. 2(a), the polarization angle of the incident light at the first prism 2 is δ, and the polarization angle of the incident light at the second prism 3 is Since the angle is also δ, the light emitted from the prism bear 2°3 becomes parallel. In fact, the two prisms 2.3 depicted in FIG. 1 are formed to have a pentagonal cross section, but in FIG.
), this pentagon is divided into a triangular part and the remaining rectangular part, and whether this rectangular part is present or not, the effect on the laser beam 7 as the prism 2.3 remains the same, and the effect is substantially the same. is an isosceles 3 with apex angle α' and base angle β'
It can be considered equivalent to something with a rectangular cross section. Note that FIG. 2(e) is a perspective view showing the three-dimensional shapes of the first and second prisms 2, 3. The light intensity distribution of the laser beam 7 in each part in FIG. 1 is shown in FIG. 3 (
Shown in a), (b) and (c). That is, the light intensity distribution of the laser beam 7 immediately before entering the first prism 2 is shown in FIG. The light intensity distribution of the laser beam 7 at the condensing position P of the laser beam 7 is shown in FIG. 3(C) in FIG. It can be seen that the interference phenomenon occurs at the post-focusing point.

As mentioned above, the pair of prisms 2.3 shown in FIG. Since the prisms 2 and 3 are arranged to provide the same effect, any optical system that has a similar effect on the laser beam 7 can be used in place of the pair of prisms 2.3. In other words, the pair of prisms 2.3 shown in Fig. 1 both have convex surfaces and are formed with the convex surfaces facing outward, but the absolute value of the refractive power for these pair of prisms is If they are equal to each other, one prism may have a convex surface and the other may have a concave surface, and as shown in FIG. 4, the first prism 2
a is the second prism 3 with its concave surface facing inward;
It is also possible to form a so that the convex surface faces inward. If the two prisms 2a and 3a are combined as shown in Figure 4, one has a concave surface and the other has a convex surface to be combined with it, so the space in the optical axis direction can be saved when arranging the optical system. It will save you money. However, one pair of prisms 2
When a and 3a are configured as shown in FIG. 4, the laser beam 7a emitted from the first prism 2a spreads without intersecting on the way.

Note that the beam diameter A when entering the beam shape converting device 7 and the beam diameter A when exiting the beam shape converting device 7.

The ratio Az/A1 is the refractive power of both prisms 2.3 and the distance #i! between both prisms 2.3. 2. This beam diameter A2 is further limited by the effective diameter of the condenser lens 4. Therefore, it is necessary to determine the distance between the two prisms 2.3, the refractive power, and the effective diameter of the condenser lens 4 so that there is no vignetting of the laser beam 7.

In addition, FIGS. 5(a) and 5(c) show the laser beam 7b,
2 is a cross-sectional view showing a light beam separating member 8.9 that has the same effect as the pair of prisms 2.3 shown in FIG.
FIGS. 5(b) and 5(d) are perspective views showing the entirety of these separating members 89, respectively. That is, FIG. 5(a),
The light beam separation member 8 shown in (b) is an optical member having an entrance surface and an exit surface 8a, b, each having a four-convex dogleg cross section and having a common plane of symmetry with equal apex angle values ψ. The parallel laser beam 7b incident on the incident surface 8a along the plane of symmetry is separated into two mutually parallel beams and emitted from the exit surface 8b. On the other hand, the light beam separation member 9 shown in FIGS. 5(c) and 5(d) is an optical beam splitting member 9 having an entrance surface and an exit surface 9a, b having the same absolute value of the apex angle and a common plane of symmetry. Although it is similar to the first beam separation member 8 in terms of the member, the entrance surface and the exit surface 8a, b of the light beam separation member 8 are both outwardly convex, whereas the entrance surface of this light beam separation member 9 is The surface 9a is convex inward, and only the exit surface 9b is convex outward. Due to this difference in configuration, the laser beam 7b incident on the incident surface of the light beam separation member 8
The laser beams 7c cross once in this member 8 and then spread out, whereas in the light beam separation member 9, the laser beam 7c spreads out without crossing in this member 9. When such integrated light beam separation members 8 and 9 are used, there is no need to consider changes over time in the alignment of optical members compared to when a combination of a plurality of optical members is used. Design, maintenance, etc. are the details.

Furthermore, FIG. 6(a) = (b), (c) shows a pair of equal pitch gratings that have the same effect as the pair of prisms 2 and 3 shown in FIG. 1 on the laser beams 7d, c, and f. FIG. 3 is a cross-sectional view showing the element. That is, these grating elements 10a, b, 11a, b, 12a, and b are a pair of diffraction gratings that have a common plane of symmetry and are arranged at equal pitches, and the gratings lOa and b in FIG. 6(a) are In contrast to the normal grating elements without blazes, those shown in FIGS. 6(b) and 6(c) 11a, b, 12a
, b are blaze grating elements that forcefully emit a light beam at a desired angle. Note that blaze means that the surface of the groove has a certain inclination with respect to the surface of the diffraction grating, and the cross section thereof has a sawtooth shape. Figure 6 (a
), only the ±1st-order diffracted light of the laser beam 7d contributes to the interference phenomenon on the focal position P; however, as shown in FIG. 6(b), ( Grating lenses 11a, b, 12a provided with the blaze shown in c).

If the laser beam 7e is used, the entire laser beam 7e will contribute to the interference phenomenon on the focal point P.

In addition, depending on the setting of the direction of blaze, the result shown in Fig. 6(b)
As shown in FIG. 3, the incident laser beam 7e may be made into two beams that are emitted from the first grating element 11a and then made incident on the second grating element flb by widening the beam interval. , as shown in FIG. 6(e), the incident laser beam 7f is converted into two beams and is connected to the first grating element 1.
It is also possible to make the beams intersect once after being emitted from 2a, and then to widen the beam interval and make them incident on the second grating element 12b. Furthermore, the space between the pair of grating elements 10a, b, lla, b, 12a, b shown in FIGS.
These pairs of grating elements 10a, b, 12a, b are filled with the same material as the constituent material of grating elements 10a, b,
It is also possible to integrate 11a, b, 12a, b. In addition, these grating elements 10a, b, lla
, b, 12a, and b may protrude from the element surface or may be embedded. Further, the surface with lattice grooves is shown in FIG. 6(a).

They may be arranged so that they face outward as shown in (b) and (c), or they may be arranged so that only one or both of them face inward.

Incidentally, instead of the blazed grating lenses shown in FIGS. 6(b) and 6(c), a Bragg grating lens that forcibly emits a light beam in a predetermined direction using Bragg diffraction may be used, and the laser beam 7 can be separated into two light beams.

Note that if the beam shape conversion device 1 is applied in the θ direction where the laser beam 7 emitted from the semiconductor laser light source 5 has a large divergence angle, the diameter of the beam spot at the fish collection position P of the focusing lens 4 can be minimized. Therefore, it is preferable.

In this way, according to the device of this embodiment, it is possible to obtain a laser beam 7 having a region with a low level of light intensity distribution in the center without blocking the laser beam 7. This allows the laser beam 7 to be focused at the focal position P of the focusing lens 4. It becomes possible to form an interference pattern. The intensity distribution of this interference pattern is shown in Figure 3 (C
), the pattern has a main lobe with the highest light intensity in the center, and on the outside there are multiple side lobes with lower light intensity than the main lobe (which gradually become smaller towards the outside). ) is formed. The beam diameter of this main lobe is considerably smaller than that of the laser beam 7 (shown in FIG. 3(a)) when it is incident on the beam shape conversion device 1, and its light intensity is There is not much difference. Therefore, if this main lobe is used as recording light for an optical recording medium, the spot diameter of the recording beam can be made smaller, and therefore the recording bits can be made smaller, so that the recording capacity of the optical recording medium can be increased.

Next, the spot diameter (width of the distribution corresponding to the intensity of 1/e2 of the maximum intensity) when the light beam 7g having the shape of the intensity profile of the beam cross section as shown in FIG. 7 is focused by the focusing lens is: How this changes depending on the ratio of the outer diameter to the inner diameter of the light beam was calculated based on the equation of light wave diffraction, and the values are shown in the table below. Furthermore, D! and D2 are the outer diameter and inner diameter of this light beam 7g.

As is clear from the above table, the larger the ratio of the width of the low-level light intensity region at the center of the light beam, the smaller the spot diameter of the main lobe becomes.

(Effects of the Invention) As explained above, according to the beam shape conversion device of the present invention, a pair of prisms, or a light beam separation member having an incident surface and a reflection surface having a dogleg cross section, or a pair of prisms, One parallel light beam is separated into two beams using equal-pitch grating elements, and these two separated light beams create an interference pattern at a predetermined position, causing a super-resolution phenomenon. , it becomes possible to obtain a light beam with a small beam diameter without causing problems such as loss of light amount due to light beam blocking as in the prior art.

[Brief explanation of the drawing]

FIG. 1 is a side view showing a beam shape converting device according to an embodiment of the present invention, and FIGS. 2(a), (b), and (c) are cross-sectional views for explaining the prism shown in FIG. Perspective views, Figures 3 (a), (b), and (c) are graphs showing the light intensity distribution of the laser beam at each position in Figure 1, respectively, and Figure 4 is a graph showing a pair of laser beams shown in Figure 1. A side view showing a pair of prisms according to another combination, which is an example of a modification of the prisms;
Figures 5(a), (c) and (b), (d) are respectively
A side view showing a light beam separation member as an example of a modification of the pair of prisms shown in FIG. 1, and FIGS. 1 as an example
FIG. 7 is a side view showing a pair of equal pitch grating elements, and FIG. 7 is a graph showing a beam intensity profile model for calculating the spot diameter of a light beam. 1... Beam shape conversion device 2.2a... First prism 3.3a... Second prism 4... Focusing lens 5... Semiconductor laser light source 6... Collimator lens 7.7a -4...Laser beam 7g...Light beam 8.9...Light beam separation member 8a, 9a...Incidence surface 8b, 9b...
- Emission surfaces 10a, lla, 12a...first equal pitch grating elements fob, llb, 12b...second equal pitch grating elements 5r! jA (d)

Claims (3)

[Claims] (1) A first prism with an isosceles triangular cross section that separates a parallel light beam incident along a plane of symmetry into two light beams that travel away from each other and emit them; and from this first prism. a second prism having an isosceles triangular cross-section and having absolute values of refractive power equal to those of the first prism, which make the two emitted light beams parallel to each other; What is claimed is: 1. A beam shape conversion device comprising: a focusing lens that focuses a light beam at a predetermined position. (2) A single parallel light beam that is provided with an entrance surface and an exit surface that have a dogleg-shaped cross section and that have the same absolute value of apex angles and have a common plane of symmetry, and that is incident on the entrance surface along the plane of symmetry. A light beam separating member for emitting a beam from the exit surface as two parallel light beams, and a focusing lens for focusing the light beam emitted from the light beam separating member at a predetermined position. Characteristic beam shape conversion device. (3) a first equal-pitch grating element that separates a parallel light beam incident along a plane perpendicular to the grating surface and parallel to the grating lines into two light beams that travel apart from each other and emit them; The first equal-pitch grating element causes the two light beams emitted from the first equal-pitch grating element to be emitted in parallel to each other.
A beam characterized by comprising: a second equal-pitch grating element having the same pitch as the equal-pitch grating element; and a focusing lens that focuses the light beam emitted from the second equal-pitch grating element at a predetermined position. Shape conversion device.