JPS60194419A - Method and apparatus for scanning optical beam - Google Patents

Abstract

PURPOSE:To increase the allowable value of the surface vibration or the like of a disc and to attain highly accurate scanning by irradiating a substance wave and a reference wave symmetrically to a reproducing point of the disc and using a beam diffracted by the rotation of the disc on which a hologram is formed. CONSTITUTION:A reproducing point P is set up on a part obtained by dividing the disc 2 into plural parts and the substance wave 12 and the reference wave 14 both of which are divergent spherical waves are irradiated from the symmetrical positions to the surface normal passing the reproducing point P to form the hologram. The disc 2 on which the hologram is formed is rotated, a reproducing light beam 6 is irradiated and a screen 8 is scanned by using the diffracted projection light beam 7. Thus, the allowable value of the surface vibration or axial shift of the disc 2 can be increased and highly accurate light scanning can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a method and apparatus for scanning a light beam using a hologram.

Background of the Technology Recently, light beam scanning devices using holodrams, which have a simple structure and are easy to manufacture, have been used in place of complex and expensive rotating polygon mirrors for reading barcodes and scanning laser beams in laser printers. It's coming. Below, for simplicity,
The shape of the hologram will be explained as a disk, but of course it has 9 spherical surfaces, 9 cylinders, and 9 cones.

The following is exactly the same for a pyramidal shape.

FIG. 1 shows a schematic configuration diagram of a conventional example of a light beam scanning device using a hologram. As shown in the figure, hologram facets 3 in a predetermined pattern are formed on a transparent optical rotating disk 2 that rotates at high speed around a rotation axis 1, and are irradiated by a laser light source 4 through a lens 5. A reproduction light beam 6 is irradiated onto the hologram facet, and an output light beam 7 that is diffracted by interference fringes formed within the hologram facet becomes a scanning beam and scans a screen 8.

Conventional technology and problems Conventionally, in devices that perform high-precision linear scanning such as those used in laser printers using holograms as described above, in order to improve printing quality, the projection angle of the laser beam with respect to the sub-scanning direction is generally adjusted. It is required that the fluctuation be within ±10 seconds or less. This projection angle variation is due to slight variations such as surface wobbling or axis deviation of the rotating disk on which the hologram was created (
(on the order of several seconds or several micrometers), and it is extremely difficult and problematic to reduce this by increasing the mechanical precision of the rotating disk. Furthermore, the light usage efficiency of the hologram scanner was also low.

Regarding the conventional light beam scanning method mentioned above, please refer to the patent application filed in 1983.
It is described in the specification and drawings of No.-066145.

Purpose of the Invention In view of the above-mentioned problems with the conventional type, an object of the present invention is to create a hologram by irradiating an object wave and a reference wave from positions symmetrical to the surface normal passing through the reproduction point, and to generate a reproduction light beam. is irradiated onto the reproduction point so that the incident angle and the diffraction angle are equal, and a diverging spherical wave is used as the object wave and the reference wave. A hologram scanner with a large tolerance and high light usage efficiency can be obtained.
The purpose of this is to enable highly accurate scanning.

Structure of the Invention In one embodiment of the present invention, a reproduction point is set in a plurality of divided parts on the surface of a rotating body, and each of the reproduction points is set from a position symmetrical or almost symmetrical with respect to the surface normal passing through the reproduction point. A hologram is created in the area by irradiating an object wave and a reference wave, which are diverging spherical waves, and the object on which the hologram is created is rotated.
A light beam scanning method is provided for obtaining a diffracted output light beam for scanning.

In another form of the present invention, a rotating shaft is attached to the rotating shaft, and is attached to a plurality of shaped parts on the surface of the rotating body, symmetrically with respect to a surface normal passing through a reproduction point that is one point of the shaped part. Alternatively, a rotating object is provided with a hologram created by irradiating two diverging spherical waves from approximately symmetrical positions, and a reproduction light beam irradiation light source that irradiates a reproduction light beam, thereby diffracting the object according to the rotation of the rotating object. A light beam scanning device is provided in which the emitted light beam performs scanning.

Embodiments of the Invention Prior to a detailed description of the present invention, the conditions under which the permissible values for surface runout and axis misalignment of the rotating disk described above become large will be explained with reference to Figs. 2 and 3. FIG. 2 shows an optical path diagram of the reproduction optical system seen from the side of the optical beam scanning device using a hologram. Here, if the projection angle variation of the diffracted outgoing light beam 7 due to the surface wobbling dφ of the disk is dθd, then the following first-order approximation formula holds true.

dθd=±(cosθi/ 008θd-1)dφ・・
(1) Here, θI is the incident angle of incidence on the hologram, and θd is the diffraction angle by the hologram. From equation (1), it can be seen that in order to increase the allowable value of the surface runout of the disk, the incident angle and the diffraction angle should be set to be equal.

Also, projection angle fluctuation due to disc axis deviation dr
19d, the following linear approximation formula holds true.

dθd=±f'(RJλdr1008θd −・−・−
+21 Here, λ is the wavelength of the reproduction light beam in a light beam scanning device using a hologram, and f' (R, l is the radius R of the spatial frequency distribution f (rl (number of interference fringes per unit) of the hologram). is the differential value of.From equation (2),
In order to increase the tolerance for disk misalignment, f'(R
)=0. That is, it can be seen that the spatial frequency distribution f lr) only needs to have an extreme value at the radius R.

FIG. 3 shows a diagram similar to FIG. 2, showing the irradiation conditions when creating a hologram on a Tiskuch. Although the optical path of the stable light beam is omitted in this figure, point P indicates the reproduction point. The disks are arranged along the r-axis perpendicular to the y-axis. An object wave 12 is emitted from the object wave light source 11 to the reproduction point P, and a reference wave light source 13 irradiates the reproduction point P.
A reference wave 14 is irradiated to the target. A hologram is created on the disk by irradiation from these two light sources.

In this case, f(FLI) is given by the following equation when the two light sources are divergent spherical waves.

λ here! is the wavelength of the created wave (object wave and reference wave), R is the r coordinate value of the reproduction point, the r coordinate of the reference wave light source is 0,
The object wave light source whose y coordinate is fAs has an r coordinate of y2 and a y coordinate of f
Suppose it is B. The condition for f'(R)-o is obtained by differentiating and transforming equation (3) to obtain equation (4) shown below, that is, (4)
When the condition (fA, fn, y21R) satisfies the formula, the axis misalignment tolerance becomes maximum.

In order to satisfy the condition (1), that is, the angle of incidence on the hologram and the angle of diffraction are equal, the object wave and the reference wave must be symmetrical about the straight line PPl passing through point P and parallel to the y-axis. In order to satisfy both equations 1) and (4), it is sufficient that s fA'''B and y2=2R.

FIG. 4 shows hologram creation conditions and reproduction light beam irradiation conditions for an apparatus that performs a light beam positioning method as an embodiment of the present invention. FIG. 4 is a diagram similar to FIG. 3, but shows the reproduction light beam 6 and the diffraction optical path of the reproduction light beam by the hologram, that is, the optical path of the output light beam 7. In this embodiment, for the purpose of linear scanning, R=
60wa, fA=fB=180mm, Yg=120 groups, hologram creation wavelength λ+=325nm, and reproduction light beam wavelength λ=760nm. The reason why the production wavelength and reproduction wavelength are different is because linear scanning is performed. A divergent spherical wave H, -Od laser is used as the light source for creating the hologram, and a laser diode is used as the light source for the reproduction light beam. The angle of incidence of the reproduction light beam on the hologram disk is 417 degrees. At this time, the linearity is within ±0.1 rttm over a scanning width of 260, which is good. In addition, in order to keep the projection angle fluctuation within the permissible value (within ±10 seconds), the disk surface runout must be approximately ±1 minute, and the axis misalignment must be ±1 minute.
It can be seen that a value within 00 μm is largely permissible.

This embodiment has advantages such as a high diffraction efficiency (up to 75%) due to Bragg angle incidence, and no influence of swelling, contraction, etc. since the hologram interference fringes are vertical.

Further, in this embodiment, a diverging spherical wave is used as the created wave, but a spherical wave accompanied by spherical aberration may also be used. This can be realized by a deflection element such as a prism 19 or a lens, as shown in FIG. This spherical aberration wave may be used for either one or both of the created waves.

Also, although the figure shows a disk, the hologram is spherical.

It goes without saying that the cylinder may be shaped like a cone or a pyramid.

Effects of the Invention According to the present invention, when performing scanning with a light beam using a hologram, it is possible to increase the permissible values for surface wobbling and axis misalignment of the rotating object on which the hologram is created, and to increase the optical measurement efficiency. A hologram scanner with a high level of accuracy can be obtained, thereby realizing highly accurate scanning with a laser beam.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a schematic configuration of a conventional example of a light beam scanning device using a hologram, and FIG. 2 is a diagram showing the optical path of a reproduction optical system seen from the side of the light beam scanning device for explaining the present invention in detail. 3 is an optical path diagram of a hologram creation wave similar to that shown in FIG. 2, and FIG. 4 is a hologram creation condition and reproduction light beam irradiation conditions of an apparatus that performs a light beam scanning method as an embodiment of the present invention. FIG. 5 is a diagram showing another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Rotation axis, 2... Rotating disk, 3... Hologram facet, 4... Laser light source, 5... Lens, 6... Reproduction light beam, 7... Emission light beam , 8... Screen, 11... Object wave light source, 12... Object wave, 13... Reference wave light source, 14... Reference wave, 19... Prism, P... Reproduction point. (11) Figure 1, Figure 2 [1 Powder

Claims (1)

[Claims] 1. A reproducing point is set in a plurality of divided parts on the surface of the rotating body, and a diverging spherical wave is generated from a position symmetrical or almost symmetrical with respect to the surface normal passing through the reproducing point. A light beam scanning method in which a hologram is created at a core by irradiating an object wave and a reference wave, and the object on which the hologram is created is rotated to obtain a diffracted output light beam for scanning. 2. A rotating shaft, which is attached to the rotating shaft and has a plurality of shaped parts on the surface of the rotating body, which are symmetrical or nearly symmetrical with respect to the surface normal passing through the reproduction point, which is one point of the shaped part. 2 from position
The rotating object includes a hologram created by irradiating two divergent spherical waves, and a reproduction light beam irradiation light source that irradiates a reproduction light beam, whereby the output light beam diffracted according to the rotation of the rotating object is scanned. A light beam scanning device designed to 3. Is the reproduction incident angle and diffraction angle of the reproduction light beam equal?
Or, the second claim characterized in that they are substantially equivalent.
The optical beam scanning device described in 2. 4. The light beam scanning device according to claim 2, wherein the hologram creation wave and the reproduction wave have different wavelengths. 5. The light beam scanning device according to claim 2, wherein one or both of the hologram creation waves have spherical aberration. 6. The light beam scanning device according to claim 2, wherein the rotating object is a disk, a cone, a sphere, a pyramid, or a cylinder.