JPH0478030A - Laser light converging optical device - Google Patents

Abstract

PURPOSE:To obtain an optional spot diameter by installing two zoneplates between a laser light source and an objective lens, and image-forming the positive and the negative first order light spots of the shape of a doughnut around a 0 order light spot, and making them interfere with each other. CONSTITUTION:Two zoneplates 12, 13 are installed between the objective lens 11 and the light source. Then, the intervals of these two zoneplates 12, 13 are set to be values different from each other so that 0 order light and positive and negative first order lights diffracted by the zoneplate 12 of one side are diffracted by the next zoneplate 13 so as to be nearly parallel with each other, and in addition, the positive and the negative first order lights are image-formed in the shape of a doughnut in the vicinity of and around the 0 order light spot on a medium through the objective lens 11, and these are made to interfere with each other. Thus, the spot diameter converged by the objective lens 11 is made the optional value.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention is applicable to optical pickups for recording and reproducing information on optical information recording media such as optical disks and optical cards, and laser microprocessing machines. This invention relates to a laser condensing optical device used in such applications.

(Prior Art) A laser condensing optical device used for the above-mentioned optical pickup etc. is conventionally constructed as shown in FIG. In other words, the laser collimated light having a similar intensity distribution is condensed by the objective lens 11 having no aberration. In this case, the intensity distribution of the spot at the focused focal point is as shown in the cross-sectional view in FIG. 3 and the perspective view in FIG.

1 (x) (2J+ (kNAx)/ (kNAx)) where,
J, is the first-order Heracel function, k=2π/λ0, λ. is the wavelength in vacuum, and NA is the numerical aperture of the lens 11.

As is clear from the above equation, the diameter of the spot focused by the objective lens 11 is uniquely determined when the objective lens is determined and the wavelength of the laser beam is determined, and it is not possible to obtain an arbitrary spot diameter. I can't.

In addition to the above-mentioned configuration, the laser focusing device is a device that provides a diffraction grating between the laser light source and the objective lens to form a main beam and two sub-beams in the three-spot method (for example, Japanese Patent Application Laid-Open No. 2-5231 ) or a device that separates reflected light from a recording medium into wavelengths using a diffraction grating (for example, Japanese Patent Application Laid-open No. 2-54434), but in both cases, the diameter of the spot focused by the objective lens is fixed; There is no consideration for obtaining arbitrary spot diameters.

(Problem to be solved by the invention) In this way, in conventional laser focusing optical devices, once the objective lens and the wavelength of the laser beam are determined, the spot diameter is also uniquely determined, and there is no degree of freedom regarding the spot diameter. .

An object of the present invention is to provide a laser focusing optical device that can set the diameter of a spot focused by an objective lens to an arbitrary value.

[Structure of the invention]

(Means for Solving the Problems) The present invention relates to a laser focusing optical device that focuses laser collimated light onto a medium using an objective lens to form an image of a spot. Two concentric diffraction gratings are provided, and the interval between these two concentric diffraction gratings is adjusted so that the 0th order light and ±1st order light diffracted by one concentric diffraction grating are diffracted by the next concentric diffraction grating so that they become almost parallel to each other. , and the above-mentioned ±
The values are set to be different from each other so that the primary light is imaged in a donut shape.

(Function) In the present invention, a 0th-order light spot is imaged on a medium, and ±1st-order light is focused in the vicinity of this 0th-order light spot in a donut shape, and these 0th-order light spots and ±1 Since the donut-shaped spot of the secondary light is made to interfere, an arbitrary spot diameter can be obtained depending on the distance relationship between the two concentric diffraction gratings, the diffraction efficiency of these two concentric diffraction gratings, etc.

(Example) Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

In FIGS. 1 and 2, two concentric diffraction gratings 12.1 are provided between the objective lens 11 and a laser light source (not shown).
3 will be provided.

In this embodiment, the spot light is divided into two concentric diffraction gratings 1
2. The case where the spot diameter is made smaller than the case where the spot diameter 13 is not provided is explained.

In the above configuration, the wavelength of the laser beam is λ, and the objective lens 1
Let the focal length of 1 be F and its numerical aperture be NA. Additionally, two concentric diffraction gratings 12. 13, the grating interval of one concentric diffraction grating 12 is set as Dl, and the grating interval of the other concentric diffraction grating 13 is set as D2, and these are set as shown in the following equation.

D2=SI! l[5IN-' (λ/D1)+
TAN-Mo, 61 Also, the ±1st-order diffracted light has a diffraction angle θ1.=
5IN-1 (λ/D1), and the -1st-order diffracted light is further diffracted at a diffraction angle θ2--3IN-' (λ/Di), and enters the other concentric diffraction grating 13.

The above-mentioned respective diffracted lights incident on the other concentric circular diffraction grating 13 are again diffracted into zero-order and ±1st-order diffraction lights, respectively. That is, 0th order light to 0th order light, +1st order light -1
The light is diffracted into second-order light, −1st-order light to +1st-order light, respectively. Here, the grating spacing of the concentric diffraction grating 13 is set to a slightly different value from the grating spacing of the concentric diffraction grating 12, as explained in the above formula, so that the O-th light to the O-th light,
The +1st-order light, the −1st-order light, and the -1st-order to +1st-order lights enter the objective lens 11 as nearly parallel light. The diffraction angle θ3 of the above +1st order light -1st order light is θ3TAN-' (0,6
1Xλ/ (NAxF)), and the primary light ~ +1
The diffraction angle θ4 of the order light is θ4TAN' (-〇, 61
xλ/(NAXF)l.

The objective lens 11 condenses these O-order light to 0-order light, +1st-order light, -1st-order light, and -1st-order light to +1st-order light, and forms an image on a medium (not shown). Here, as shown in the cross-sectional view in FIG. 3 and the perspective view in FIG. 4, the O-th to 0th-order lights condensed by the objective lens 11, as in the conventional case shown in FIG.
T (x) (2J, (kNAx)/' (k, NAx
)) The image is formed in a spot shape of 2.

On the other hand, the +1st order light - which is focused by the objective lens 11
The primary light is r (x) − (2J.

(k NA x-0, 61k NA) / (k NA
An image is formed at x-0,61 in a spot shape of NA)l 2. Furthermore, −1st order light to +1st order light are I (x)
= (2J(k, NA x +0.61k NA)
/ (k NA x +0.61, NA,))2 is imaged. These composite intensity distributions are shown in a line cross-sectional view in FIG. 5 and a perspective view in FIG.

Here, the above-mentioned +1st order light -1st order light and 1st order light ~+
The phase of the first-order light is shifted by 180 degrees with respect to the 0th-order light to the 0th-order light. This is set by the distance between the two concentric diffraction gratings 12,13.

In addition, the spot image of the 0th-order light ~ 0th-order light and the −+−1st-order light ~
−1st order light and 11st order light to +1st order light spot images,
1-The intensity distribution before crossing is 0 as shown in Figure 7.
Order light ~ 0th order light, +1st order light ~ 1st order light, -1st order light ~ ↓1
The amplitude ratio of the light with the next light, 0th order light ~ 0th order light ↓1st order light -
1st order light -1st order light to +1st order light -1-:0.2:0.2 Concentric circular diffraction grating 12. Set the diffraction efficiency of i3. Note that the intensity ratio is intensity ratio = (amplitude ratio) pa, so 0th-order light to O-order light: +1st-order light to -1st-order light -1
Next light to +first order light -1-:o, oi:o, 04.

FIG. 8 shows the spot intensity distribution (-dotted chain line) after the above-mentioned 0th-order light spot and ±1st-order light spot interfere,
Spot intensity distribution without conventional interference (solid line)
It is shown in comparison.

Here, since there is a phase difference of 180° between the 0th order light spot and the ±1st order light spot shown in FIG. , which compensate for the difference between them, result in a spot intensity distribution as shown by the dashed line in FIG. 8. That is, it is possible to obtain a spot diameter smaller than the conventional spot diameter shown by the solid line.

FIG. 9 shows the amplitude ratio from 0th order light to 0th order neat 1st order light to −
1st order light knee 1st order light to +1st order light -10, If-35:0.
135, the spot intensity distribution after interference is shown. The spot diameter is defined as the diameter that is 1/e2 of the maximum intensity, so in the case of FIG. /e2 or less, and the spot diameter is reduced by more than ten percent compared to the conventional method.

In this way, two concentric diffraction gratings 12. are provided between the laser light source and the objective lens 11. 13 is provided, and donut-shaped ±1st order light spots are formed in the vicinity of the 0th order light spot, and these are made to interfere. Set the phase relationship between the secondary light spot and the ±1st-order light spot,
Additionally, two concentric diffraction gratings 12. By setting the amplitude ratio according to the diffraction efficiency of 13, an arbitrary spot diameter can be obtained. When an arbitrary spot diameter is obtained in this way, in the case of optical pickup, it is possible to record and reproduce information on an optical information recording medium at high density, and to perform transparentization with high efficiency. In addition, when applied to a laser processing machine,
Even finer processing can be performed.

〔Effect of the invention〕

As described above, according to the present invention, even if the wavelength of the objective lens or laser beam is determined, the spot diameter is not fixed by these factors, and it is possible to obtain a degree of freedom regarding the spot diameter. Can you get the diameter?

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a laser focusing optical device according to the present invention, FIG. 2 is a perspective view of the device shown in FIG. 1, and FIGS. 3 and 4 show the intensity of the zero-order light spot. A line cross-sectional view and a perspective view showing the distribution, Figures 5 and 6 are a line cross-sectional view and a perspective view showing the intensity distribution of the ±1st-order light spot, and Figure 7 shows the O-order light spot and the ±1st-order light spot. Figures 8 and 9 are line cross-sectional views showing the intensity distribution before interference between the 0th-order light spot and the ±1st-order light spot. FIG. 11. Objective lens, 12.13. Concentric diffraction grating. "[U"

Claims (1)

[Claims] (1) In a laser focusing optical device that focuses laser collimated light onto a medium using an objective lens to image a spot, two concentric circular diffraction gratings are provided between the objective lens and the light source, and these two concentric circular diffraction gratings are The spacing between the gratings is set such that the 0th-order light and the ±1st-order light diffracted by one concentric diffraction grating are diffracted by the next concentric diffraction grating so that they become almost parallel to each other, and the 0th-order light and ±1st-order light are diffracted by the next concentric diffraction grating, and are transmitted onto the medium through the objective lens. A laser condensing optical device characterized in that the ±1st-order light beams are set to different values so that the ±1st-order light beams are imaged in a donut shape in the vicinity of the secondary light spot.