JPH02222918A - 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 splitting 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. 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 leave each other after crossing each other temporarily. Then the beams are shaped cylindrically 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. A technique using super-resolution phenomenon is known as a method for reducing the spot diameter (Proceedings of the 49th Applied Physics Conference 4
a-ZD-6,7; Japan mki).

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 side lobe components and the r= sign 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, the curved part at the center of the beam is cut, so in order to secure the beam light intensity that contributes to recording. requires a higher output laser light source.

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 axis of rotational symmetry of the first conical lens is expanded into a conical tube shape by the first conical lens, and the light beam emitted from the first conical lens is The light beam is emitted in a cylindrical shape by a second conical lens whose absolute value is equal to that of the first conical lens, and the light beam emitted from this second conical lens is focused at a predetermined position using a converging lens. It is characterized by being focused.

Further, the beam shape conversion device according to claim 2 of the present invention uses a light beam separation member having first and second conical surfaces having a common axis of rotational symmetry and having the same absolute value of apex angles. One parallel light beam incident on the first conical surface along the axis of rotational symmetry is made to exit from the second conical surface as a parallel light beam having a cylindrical beam shape, and this This device is characterized in that the parallel light beam emitted from the light beam separation member is focused at a predetermined position using a focusing lens.

Furthermore, the beam shape conversion device according to claim 3 of the present invention converts the parallel light beam incident along the rotational symmetry axis of the first concentric equal pitch grating lens into the first
The light beam emitted from the first concentric constant pitch grating lens is expanded into a conical cylinder shape by the concentric constant pitch grating lens, and the light beam emitted from the first concentric constant pitch grating lens is expanded into a concentric circular pitch having the same concentric pitch as that of the first concentric constant pitch grating lens. The concentric circular pitch grating lenses are arranged to emit the same cylindrical shape, and this second
The parallel light beam emitted from the concentric circle equipitch grating lens is focused at a predetermined position using a focusing lens.

Moreover, the above-mentioned "conical cylindrical shape" shall mean a cone-like shape with a hollow interior.

(Function) According to the above configuration, one incident parallel light beam (collimated light beam) is first expanded into a conical tube shape, then formed into a cylindrical shape, and finally by a focusing lens. It is focused at the focal point of the lens. That is, the parallel light beam is expanded into a conical cylinder shape by each of the first conical lens, the first conical surface, and the first concentric constant pitch grating lens, and then expanded by the second conical lens and the second conical surface. is formed into a cylindrical shape by each of the conical surface and the second concentric equipitch grating lens. When observing this by taking a cross section along a plane that includes the central axis of the incident parallel light beam, within this cross section, the light beam is separated into two light beams that completely separate from each other, and then These two light beams are made parallel to each other, and these two parallel light beams are focused at the focal position of the focusing lens, and these two light beams are Since the conditions for interference are satisfied (emitted from the same light source at approximately the same time), interference fringes are formed at this focal point within this cross section. Such interference fringes appear in the same shape no matter what plane is taken in cross-section including the central axis of the incident parallel light beam, so in the end, when viewed three-dimensionally, they appear on all these cross-sections. A beam spot is formed that has an intensity distribution that resembles superimposed interference fringes, that is, an intensity distribution that is concentrically separated in brightness and darkness.

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, and for convenience of explanation, shows a cross section taken along a plane including the optical axis of the optical system. This device 1 consists of a pair of conical lenses 2.3 and a focusing lens 4 with equal refractive power, and when a laser beam 7 emitted from a semiconductor laser 5 and collimated by a collimating lens 6 enters the device 1, This laser beam 7 is first expanded into a conical cylindrical beam shape by a first conical lens 2 (in Fig. 1, the two light beams separated from each other are drawn as if they once intersected and then continued. ), then the beam is shaped into a cylindrical beam by the second conical lens 3 (in Figure 1, the two light beams are drawn in parallel), and finally by the focusing lens 4, the beam is shaped into a cylindrical beam. It is focused on the focal point P of 4. The laser beam 7 incident on the conical surface of the first conical lens 2 is refracted in the opposite direction across the rotational symmetry axis of the first conical lens 2 with respect to the incident position on the conical surface. In Figure 1, the portion above the optical axis that is incident on the first conical lens 2 is refracted below the optical axis, while the portion that is incident below the optical axis is refracted above the optical axis.) Further, at the position where the second conical lens 3 is disposed, the laser beam 7 is formed so that its cross section forms a complete ring, and then the second conical lens 3
Since the refractive power of the first conical lens 2 is set equal to that of the first conical lens 2, the laser beam 7, which has an annular cross section and is emitted from the second conical lens 3, passes through the focusing lens 4 without changing the diameter of the annular ring. incident on .

That is, in FIG. 1, the laser beams 7 separated above and below the optical axis enter 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. The one-dimensional light intensity distribution of the laser beam 7 in each part in FIG.
This is shown in Figures (a), (b), and (c). That is, the light intensity distribution of the laser beam 7 at the position immediately before entering the first conical lens 2 is shown in FIG. 2(a), and the light intensity distribution of the laser beam 7 after being emitted from the second conical lens 3 is shown in FIG. In FIG. 2(b), the light intensity distribution of the laser beam 7 at the condensing position P of the laser beam 7 is shown in FIG. 2(C), and from these figures, one light beam is separated, It can be seen how the light is then focused and an interference phenomenon occurs at this focal point.

As mentioned above, the pair of conical lenses 2 and 3 shown in FIG.
is arranged to expand the incident laser beam 7 into a conical cylinder shape and further form it into a cylindrical shape, so if the optical system has the same effect on the laser beam 7, the optical system can be called this one. It is possible to use it instead of the pair of conical lenses 2.3. In other words, the pair of conical lenses 2 and 3 shown in FIG. If the absolute values of the forces are equal to each other, one may have a convex surface and the other may have a concave surface, as shown in Figure 3 (a cross-sectional view taken along a plane including the optical axis). The first conical lens 2a may be formed with a concave surface facing inward, and the second conical lens 3a may be formed with a convex surface facing inward.

Further, in the optical system shown in FIG. 3, one side is a concave surface and the other side is a convex surface combined with this, which saves space in arranging the optical system. However, when the pair of conical lenses 2a and 3a are configured as shown in FIG. 3, the laser beam 7a emitted from the first conical lens 2a spreads out without intersecting on the way. The second conical lens 3 is used so that there is no vignetting of the beam 7a.
Care must be taken in determining the location and size of a.

In addition, FIGS. 4(a) and 4(b) show the laser beam 7b,
2 is a cross-sectional view showing a light beam separating member 8.9 which has the same effect as the pair of conical lenses 2.3 shown in FIG. 1 in relation to FIG. That is, the light beam separation member 8 shown in FIG. 4(a) has equal apex angle values and a common axis of rotational symmetry.
It is an optical member equipped with two four-convex conical surfaces 8a and b, and the parallel laser beam 7b incident on the first conical surface 8a along the axis of rotational symmetry is converted into a cylindrical beam shape and then transferred to the second conical surface. 8b (in FIG. 4(a), two light beams are drawn in parallel to each other). On the other hand, the light beam separating member 9 shown in FIG. Same as beam separation member 8.

However, while the light beam separating member 8 has two conical surfaces 8a and 8b that are both convex outward, in this light beam separating member 9, the first conical surface 9a is convex inward, and the second conical surface 9a is convex inward. Conical surface 9b
It is formed so that it is convex only to the outside. Due to this difference in structure, the laser beam 7b incident on the first conical surface of the light beam separation member 8 crosses once in this member 8 and then spreads out, whereas the laser beam 7b in the light beam separation member 9 The beam 7c will spread out within this member 9 without intersecting. In this way, when an integrated light beam separation member 8.9 is used, there is no need to consider changes over time in the alignment of optical members compared to the case where one consisting of multiple optical members is used, and design and maintenance are easier. etc. is easy.

Furthermore, FIGS. 5(a), (b), and (c) show a pair of concentric circles that have the same effect as the pair of conical lenses 2.3 shown in FIG. 1 on the laser beams 7d, e, and f'. FIG. 3 is a cross-sectional view showing an equal pitch grating lens. That is, these grating lenses loa, b, lla, b, L
2a.

b is a pair of concentric grating elements (grooves are formed in every other ring of concentric rings) configured coaxially and at equal pitches (corresponding rings have the same width); The one 10a in FIG. 5(a).

While b is a normal concentric grating lens without a blaze, the lenses 11a, b, 12a, and b shown in FIGS. 5(b) and (e) forcefully emit a light beam at a desired angle. It is a concentric blaze grating lens. 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. When the normal concentric grating lenses lOa and b shown in FIG. Figures (b), (c
) Grating lens lIa provided with the blaze shown in
, b, 12a, b, the laser beam 7c,
The entire f' will contribute to the interference phenomenon on the focal position P. By setting the direction of blaze, the incident laser beam 7e is emitted from the first grating lens lla and then expanded as it is, so as to be incident on the second grating lens llb, as shown in FIG. 5(b). It is also possible to do as shown in Figure 5 (C).
As shown in the figure, after the incident laser beam 7f is emitted from the first grating lens 12a, the incident laser beam 7f is crossed once and then spread out to the second grating lens 12b.
It is also possible to make the light incident on . In addition, a pair of grating lenses lOa, b, lla, b, 12a shown in FIGS. 5(a), (b), and (c)
.

These grating lenses 10a,
These pairs of grating lenses 1 are filled with the same material as that of b, lla, b, 12a, and b.
It is also possible to integrate 0a, b, lla, b, 12a, and b. In addition, these grating lenses 10a
, b, ILa, b, 12a, b may be protruding or embedded.

Furthermore, the surface with lattice grooves is shown in Fig. 5 (a), (b),
They may be arranged so as to face outward as shown in (c), or may be arranged so that only one or both of them face inward.

Note that instead of the concentric blazed grating lenses shown in FIGS. 5(b) and 5(c), a concentric Bragg grating lens that forcibly emits a light beam in a predetermined direction using Bragg diffraction may be used to prevent the laser beam 7. can be formed into a similar beam shape.

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. When this interference pattern is viewed one-dimensionally, the intensity distribution has a shape as shown in Figure 2 (C), with the main lobe having the highest light intensity in the center of this pattern, and the areas outside of it that are smaller than the main lobe. A plurality of side lobes (gradually smaller toward the outside) with lower light intensity are formed. This main lobe is the laser beam 7 when it is incident on the beam shape converter 1 (see Fig. 3(a)).
The beam diameter is considerably smaller than that shown in Figure 1), and there is not much difference in the light intensity. Therefore, if this main lobe is used as the recording light of an optical recording medium, the spot of the recording beam can be made two-dimensionally smaller, and therefore the recording bit can be made smaller, thereby increasing the recording capacity of the optical recording medium. Can be done.

Next, the spot diameter (width of the distribution corresponding to the intensity of 1/e2 of the maximum intensity) when the light beam 7g whose beam cross section has the shape shown in FIG. 6 is focused by a focusing lens is as follows. 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. Note that Dl and Dl are the outer diameter and inner diameter of this light beam 7g. Further, the actual intensity profile has a shape when the intensity distribution shown in FIG. 6 is rotated about the central axis, that is, a cylindrical shape.

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

(Effects of the Invention) As explained above, according to the beam shape conversion device of the present invention, a pair of conical lenses, a light beam separating member having a pair of conical surfaces, or a pair of concentric circles with equal pitches are used. A lens is used to separate parallel light beams three-dimensionally, and the separated light beams create an interference pattern at a predetermined position to create a super-resolution phenomenon, making it possible to block light beams unlike conventional technology. It becomes possible to obtain a light beam with a small beam diameter without causing problems such as light quantity loss.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing a beam shape conversion device according to an embodiment of the present invention, FIG. 2 is a graph showing the light intensity distribution of the laser beam at each position in FIG. 1, and FIG. 3 is the same as that shown in FIG. FIGS. 4(a) and 4(b) are cross-sectional views showing another combination of the pair of conical lenses, which is a modified example of the pair of conical lenses shown in FIG.
are the modified example of the pair of conical lenses shown in FIG. 1 and L2, respectively.
FIGS. 5(a), 5(b), and 5(c) are cross-sectional views showing a light beam separating member having a pair of conical surfaces, respectively.
A sectional view showing a pair of concentric equal pitch grating lenses as a modification of the pair of conical lenses shown in FIG.
FIG. 6 is a graph showing a beam intensity profile model for calculating the spot diameter of the light beam. 1... Beam shape conversion device 2.2a... First conical lens 3.3a... Second conical lens 4... Focusing lens 5... Semiconductor laser light source 6... Collimator lens 7 .7a-1'... Laser beam 7g... Light beam 8.9... Light beam separating member 8a, 9a... First conical surface 8L+, 9b... Second conical surface 10a, 11a, 12a = First concentric circle equal pitch grating lens 10b, 11b, 12b... Second concentric circle equal pitch grating lens Relationship with the Beam Shape Conversion Si Correction Case Patent Applicant Address 210 Nakanuma, Minamiashigara City, Kanagawa Prefecture Name
520) Fuji Photo Film Co., Ltd. 4, Agent Address: 7W4 Hauraiya Pill, 5-2-1 Roppongi, Minato-ku, Tokyo 6, "Detailed Description of the Invention" column 7 of the specification to be amended, Contents of the amendment l) The table on page 18, lines 15 to 20 of the specification is corrected as follows. 5. Voluntary correction of the date of the 4th order

Claims (3)

[Claims] (1) A first conical lens that expands a parallel light beam incident along the axis of rotational symmetry into a conical shape and emits it; and a first conical lens that emits the light beam emitted from the first conical lens in a cylindrical shape. A second conical lens having the same absolute value of refractive power as the first conical lens, and a focusing lens that focuses the light beam emitted from the second conical lens at a predetermined position. Beam shape conversion device. (2) comprising first and second conical surfaces having the same absolute value of apex angles and having a common axis of rotational symmetry; one beam incident on the first conical surface along the axis of rotational symmetry; It is characterized by comprising a light beam separation member that converts a parallel light beam into a cylindrical light beam and outputs it from the second conical surface, and a focusing lens that focuses the light beam emitted from the light beam separation member at a predetermined position. Beam shape conversion device. (3) A first concentric equal-pitch grating lens that spreads a parallel light beam incident along the axis of rotational symmetry into a conical cylinder shape and emits the light beam; a second concentric constant pitch grating lens having a concentric pitch equal to that of the first concentric constant pitch grating lens, which is emitted in a cylindrical shape; and a light beam emitted from the second concentric constant pitch grating lens to a predetermined position. 1. A beam shape conversion device comprising: a focusing lens that focuses the beam on the beam;