JPS6339045B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a light beam scanning device, and particularly to a light beam scanning device using a hologram for light deflection.

A light beam scanning device using a hologram uses the hologram as a diffraction grating, and deflects light by changing the diffraction angle by one-dimensionally moving the hologram, which has a distribution of grating periods within the hologram. In such a beam scanning device, the means for one-dimensionally moving the holograms is usually to arrange a plurality of holograms on the circumference of a disk and rotate the disk.

However, since the hologram is moved by rotating the disk, the hologram also rotates and moves.
Therefore, the scanning beam draws a scanning line curved in the shape of a circular arc. For this reason, a light beam scanning device using a disk-type hologram cannot be used in devices such as laser printers and facsimile devices that require high quality of recorded characters and images.

An object of the present invention is to provide a light beam scanning device in which a scanning beam performs linear scanning using a disk-type hologram.

The optical beam scanning device of the present invention has a phase distribution φ of φ=2π/λ _N 〓 ⁿ⁼¹ (√ ² + ² −fn) (1) (where λ is the wavelength of the light and r is the position on the hologram. A hologram disk with holograms recording interference fringes expressed by the following coordinates, _N 〓 ⁿ⁼¹ 1/fn is the reciprocal of the focal length F of the first-order diffracted light of the hologram, and N is an integer of 2 or more. a beam generator that generates light to irradiate the hologram; and means for rotating the hologram disk; and a beam generator that rotates the hologram disk; Letting the distance between the center of the hologram disk and the point r=0 of the hologram be Xc, the relationship between (Xc-R)/F and R/F is -0.15R/F+0.7<Xc-R/F< -0.15R/F+0.9
A light beam scanning device is characterized in that the hologram is arranged so as to satisfy the relationship (2).

Next, the present invention will be explained in detail with reference to the drawings. FIG. 1 is a diagram showing a light beam scanning device using a hologram disk. In the figure, a light beam 3 from a beam generator emitting light from a laser 1 and a lens 2 illuminates a hologram 5 disposed on the circumference of a hologram disk 4. The diffracted light 11 of the hologram 5 is scanned on the scanning surface 14 in the direction of the arrow 15 by rotating the hologram disk 4 in the direction of the arrow 13 by the motor 12, and the scanning locus becomes a curved line 16. The rotation of the motor 12 causes the holograms 5 to 10 to repeatedly scan.

FIG. 2 is a diagram schematically showing a hologram disk in which holograms are arranged on the circumference. Five to ten holograms are arranged with point 17 as the center of the disk. Regarding hologram 5, interference fringes are also schematically shown. Point 18 is the irradiation position of the light beam. The interference fringes of the hologram 5 are part of concentric circles centered on the point 19. In FIG. 2, the distance between the disk center 17 and the light beam irradiation position 18 is R, and the distance between the disk center 17 and the center 19 of the hologram interference fringe is Xc. Next, the relationship between R and Xc will be explained in detail.

FIG. 3 is a diagram for explaining the relationship between R and Xc. In Fig. 3, a hologram is formed on the disk with the coordinates (Xc, 0) of the center 19 of the concentric interference fringes of the hologram, with the origin 0 of the x-y coordinates being the center 17 of the disk, and the point 1 of the radius R of the disk.
A light beam is irradiated at step 8, and the disk is rotated to scan the light beam. To make the explanation easier to understand,
Instead of rotating the disk, the illumination beam and scanning surface are rotated to describe the scanning trajectory. Figure 3 shows the state in which the irradiation beam has been rotated by Θ _R , and the point 20
is the irradiation position of the light beam. A circular arc 21 indicates the locus of the irradiation point. The position R of the hologram irradiated at this point is determined by the following equation.

r ² =R ² +X ² c−2R・Xc・COSΘ _R (3) The arc 22 corresponds to one concentric interference fringe.

The illumination beam is diffracted from point 20 towards the central axis of the hologram (the axis passing through the center 19 of the interference fringes of the hologram and perpendicular to the xy plane). The angle Θr formed by the line segment connecting the light beam irradiation point 20 and the center 19 of the interference fringes of the hologram with the x-axis is determined by the following equation.

Θr＝COS ^{-1 ( r 2} + Θd is expressed by the following formula.

Considering a plane parallel to the xy plane and at a distance of 1 from the xy plane as the scanning plane, the length of the oblique shadow of the diffracted light on this scanning plane is =tanΘd (6). If the coordinates of the scanning point on this scanning plane are expressed in the x'-y' coordinate system rotated with the irradiation beam, x' = con (Θ _R + Θr) (7) y' = sin (Θ _R + Θr) (8) It is expressed as Therefore, the light beam diffracted by the hologram draws a scanning locus so as to satisfy the above equations (3) to (8). The curvature displacement Δx' of the scanning line is expressed by the following equation.

Δx'=cos(Θ _R +Θr) - (9) FIG. 4 is a diagram showing an example of the calculation result of the scanning locus. The calculation can be normalized by the focal length F of the hologram. FIG. 4 shows the case where N=2 (f ₁ = f ₂ ) and R/F=2, and the scanning loci indicated by 23 to 25 are (Xc-
R)/F is 0.5200.527 and 0.529, respectively. 2
Regarding the scanning trajectory shown in 4, when the scanning length is |y′|<0.15, the curved displacement △x′ is 50×
10 ^-6 or less. The method for generating interference fringes expressed by equation (1) has already been proposed in Japanese Patent Application No. 11711-1983 and Japanese Patent Application No. 11711-1
- Filed under No. 78495.

That is, when N=2, the wave is generated by interference between a divergent spherical wave and a converging spherical wave, and when N≧3, the phase of a plurality of spherical waves is sequentially subtracted and the phases are combined to generate the wave. According to this, the scanning beam becomes aberration-free when the distance b ₀ between the hologram and the scanning surface is F×
This is the case for ^N2 . Therefore, let's convert the calculation example above to actual size. If R=100mm, then R/F=2, so F=50mm, and N=2, so b ₀ =
It will be 200mm. Therefore, the scanning length is ±300 mm and the bending displacement is 10 ⁻³ mm, or 1 μm. If this calculation example is used as an example, the bending displacement is 1 μm for a scanning length of ±300 mm, so it can be put to practical use as a light beam scanning device for a high-quality laser printer or facsimile machine.

FIG. 5 is a diagram showing the relationship of parameters for linear scanning. 26 is N=2, 27 is N=2
328 is a case where N=4, and 29 is a case where N=∞.

Dotted line 30 is (Xc-R)/F=-0.15R/F+
The straight line expressed by the relational expression 0.7, the dotted line 31, is (Xc
-R)/F=-0.15R/F+0.9.

By combining the parameters in the region between the dotted lines 30 and 31, a scanning line with a bending displacement small enough for practical use can be obtained.

According to the present invention, a disk-type light beam scanning device using a porogram that performs linear scanning can be obtained for various parameter combinations as shown in FIG. That is, by using the hologram disk with the combination of parameters shown in FIG. 5 as the hologram disk 4 in FIG. 1, the curved scanning line 16 becomes a straight scanning line.

[Brief explanation of the drawing]

Fig. 1 shows a light beam scanning device using a hologram disk, Fig. 2 schematically shows a hologram disk, and Fig. 3 shows the relationship between the irradiation position of the light beam and the center position of the interference fringes of the hologram. FIG. 4 is a diagram for explaining an example of a calculation result of a scanning locus, and FIG. 5 is a diagram showing a relationship between parameters for linear scanning. In the figure, 1 is a laser, 2 is a lens, 3 is an irradiation beam, 4 is a hologram disk, 5 to 10 are holograms, 11 is a diffracted light, 12
is the motor, 13 is the rotating direction of the disk, 14 is the scanning plane, 15 is the scanning direction, 16 is the scanning line, 17 is the center of the disk, 18 and 20 are the irradiation points of the light beam, 19 is the center of the hologram interference fringe, 21 is the trajectory of the irradiation beam, 22 is the concentric interference pattern, 23 to 25
are the calculation results of the scanning locus, 26 to 29 are relationship curves of parameters that result in linear scanning, and 30 and 31 represent the lower and upper limits, respectively, of the existence range of parameters that result in linear scanning.

Claims (1)

[Claims] 1 The phase distribution φ is φ=2π/λ _N 〓 ⁿ⁼¹ (√ ² + ² −fn) (where λ is the wavelength of the light, r is the coordinate indicating the position on the hologram, _N 〓 ^{n = 1} 1/fn is the reciprocal of the focal length F of the first-order diffracted light of the hologram, N is an integer of 2 or more) A hologram disk with holograms recording interference fringes expressed as 〓 n=1 arranged on the circumference and the holograms are irradiated. and a means for rotating the hologram disk; Assuming the distance from the point r=0 of the hologram to Xc, the relationship between (Xc-R)/F and R/F is -0.15R/F+0.7<Xc-R/F<-0.15R/F+0.9 A light beam scanning device characterized in that the hologram is arranged so as to satisfy the following relationship.