JPH02199421A - Light beam scanner - Google Patents

Abstract

PURPOSE:To prevent the fluctuation in the scanning position occurring in the surface waving of a hologram disk by setting a reconstruction point to the part on the surface of a rotating body divided to plural pieces and irradiating the normal plane passing the reconstruction point with the reference wave specifying the specific equation and an object wave, thereby forming a hologram. CONSTITUTION:The reconstruction point P is set on the surface of the rotating body 10 divided to plural pieces and the normal plane X passing the reconstruction point P is irradiated with the reference wave W1 which is the divergent spherical wave from the position satisfying equation I and the object wave W2 to form the hologram in this part. A reconstructing light beam is made incident at the incident angle thetai satisfying equation I and the rotating body 10 formed with the hologram is rotated to obtain the exit light beam which makes linear scanning on an imaging plane T. The fluctuation in the scanning position occurring in the surface waving dphi with respect to the center of rotation of the hologram disk 10 is prevented is such a manner.

Description

[Detailed Description of the Invention] [Summary] Regarding a light beam scanning device using a hologram disk, the object is to prevent deviation of the scanning position due to surface wobbling around the rotation center of the hologram disk, and a plurality of light beam scanning devices are provided. A reproduction point is set on the part of the rotating body surface divided into R/l °cos with respect to the normal plane passing through the reproduction point.
”θd=cosoH−cosθdHowever, sin θ
, -3-UJE'P〒"'FIFTIn the above formula, R-incidence radius of reproduction point, !=imaging distance, θ,-incidence angle, θ4=
Output angle, S = λ2 (reproduced wave wavelength) / λ1 (created wave wavelength), normal distance from the F1 rotating body surface to the reference wave point light source, the reference wave and object wave, which are diverging spherical waves, are generated from a position that satisfies the following: The beam is irradiated to create a hologram in the area, and is incident at an incident angle that satisfies the above equation, rotating the rotating body on which the hologram was created to obtain an output light beam that performs linear scanning.

[Industrial Application Field] The present invention relates to a light beam scanning device that performs linear scanning using a hologram disk.

[Conventional technology]

Recently, a light beam scanning device using a hologram, which has a simple structure and is easy to manufacture, is being considered for bar code reading, laser beam scanning in a laser printer, etc. instead of a complicated and expensive rotating polygon mirror.

FIG. 2 shows the basic configuration of a light beam scanning device using a hologram. As shown in the figure, a transparent optical rotating disk (hologram disk) that rotates at high speed around the rotation axis 1
A hologram facet 3 having a predetermined pattern is formed on the hologram facet 10, and a reproduction light beam 6 irradiated from a laser light source 4 through a lens 5 is irradiated onto the hologram facet, and interference fringes are formed within the hologram facet. The emitted light beam 7 diffracted by the scanning beam 7 becomes a scanning beam and scans the screen 8.

Conventionally, in devices that perform high-precision linear scanning using the above-mentioned hologram and used in laser printers, etc., in order to improve printing quality, repeated scanning lines of laser light are projected in the sub-scanning direction in 111Q. ± angle fluctuation
It is required that the time be less than 10 seconds or less. This projection angle variation is caused by slight variations (on the order of a few seconds or several micrometers) such as surface wobbling or axis deviation of the rotating disk on which the hologram is created, and can impair the mechanical accuracy of the rotating disk. It was very difficult to reduce the amount of water, which was a problem. Furthermore, the light usage efficiency of the hologram scanner was also low.

[Problem to be solved by the invention]

In order to solve the above problems, the applicant of the present application proposed an object wave and a reference wave (
A hologram is created by irradiating a hologram (both divergent spherical waves) from a position symmetrical to the surface normal passing through the reproducing point, and by irradiating the reproducing light beam to the reproducing point so that the incident angle and the diffraction angle are equal. disclosed a technique for increasing the permissible values for surface runout and axis misalignment of a hologram disk, and for obtaining a hologram scanner with high light usage efficiency.

That is, as shown in FIG. 4, a reproducing point P is set on the facet of the vologram 1 on the vologram disk 10, and a position A is symmetrical or almost symmetrical with respect to the surface normal X passing through the reproducing point.
A reference wave W and an object wave W2, both of which are divergent spherical waves, are irradiated from A2 to create a hologram in the area. By irradiating the reproduction light while rotating the object (hologram disk) 10 on which the hologram l has been created in this way, a diffracted light output light beam that scans in a predetermined direction on the imaging plane T is obtained. As described above, conventionally, in order to prevent positional fluctuations due to surface runout, the incident angle and the exit angle were made equal as described above. However, although this has a large effect on surface runout with the beam incidence position of the disk as the center of rotation as shown in Figure 3, it is insufficient for fluctuations in the scanning position with respect to surface runout (Figure 1) with respect to the disk rotation center. It turned out that no significant effect could be obtained.

An object of the present invention is to prevent fluctuations in the scanning position, particularly with respect to disk surface runout with respect to the center of rotation of the hologram disk.

[Means to solve the problem]

The inventor of the present invention paid attention to slightly breaking the symmetry of the two created diverging spherical waves, and thereby found conditions that could further reduce the fluctuation in position due to vibration with respect to the center of rotation of the hologram disk. That is, according to the light beam scanning device according to the present invention, a reproduction point is set at a portion on the surface of the rotating body divided into a plurality of parts, and the reproduction point is set from a position satisfying the following equation with respect to the normal plane passing through the reproduction point. The feature is that a hologram is created in the area by irradiating a reference wave and an object wave which are diverging spherical waves; R#!・cos2θ, = cosθi −CO3θd
... (1) However, sin θ1-3-R/, /-
m〒1]71η-In the above formula, R-Incidence radius of the reproduction point, l-
Imaging distance, θ, - human angle of incidence, θd=output angle, S=λ2 (
Reproduced wave wavelength)/λ, (Created wave wavelength), F, normal distance from the surface of the one-rotor body to the reference wave point light source.

[For production]

In Figure 1, the imaging distance! , the incident angle to the hologram is O1, the exit angle (diffraction angle by the hologram) is O4, and the surface deflection with respect to the center of rotation is dφ. At this time, if the deviation of the diffraction angle with respect to the surface runout is dθ4, the following first-order approximation formula holds true.

dθd−[CO5θ; / cos θd−1]dφ・
(1) On the other hand, if the deviation of this diffraction angle satisfies the following relationship, the positional fluctuation can be prevented.

ri, °, dθa = R/ Cj2/ cos θ6
] ・dφ ...(2) Therefore, (1),
From equation (2), the following equation (3) is obtained.

R/42・cos θd = CO5θt / cos
θa-i・ (a) Rearranging the equation (3) gives the following equation.

R/I! ,・cos2θd =CO3θi −CO3θ
a・(4) Here, it is not obvious that equation (4) is satisfied and linear scanning is performed using the hologram disk.

Next, it will be explained below that this is possible.

Here, it is assumed that the incident angle satisfies the following equation (see FIG. 4).

sin θ = S・
... (5), r [7 digits 7 However, S = λ2/λI (A1: hologram creation wave wavelength, S2: hologram reproduction wave wavelength) F, - Point light source A of the reference wave and Perpendicular distance R to the plane - incidence radius of the reproduction point P The incident angle condition (5) is generally selected to maximize the diffraction efficiency, that is, the Bragg angle, but is not limited thereto.

From the above, cosθi and CO3θ6 are calculated using the following formula (6), (
7) % formula % However, F2 - vertical distance between the point light source A2 of the object wave and the surface of the disk 10 Y z - A vertical distance between point r and point A2 (6),
It will be understood that the case where Y2=2R, F, -F2 in equation (7) corresponds to the above-mentioned conventional technique, that is, the case where A and A2 are arranged symmetrically. In this case, θ is -θ4.

On the other hand, it is known that the conditions for performing linear scanning on the scanning plane T are given by the following equation.

F2= 22-・CO3c”・(
8) Here, θゎ is the rotation angle of the hologram disk at the inflection point when the scanning locus rises from the drooping state, and is an important angle parameter that determines the linearity.

Further, the condition for maximizing the eccentricity margin (axis misalignment tolerance) of the hologram disk is expressed by the following equation.

Fz"CF+" +R2) "" = F+" (F
2+ (RY2)2) ””...(9) The method for deriving the above equation (9) is described in the above-mentioned Japanese Patent Application Laid-Open No. 60-19441.
9.

In actual design, the disk incidence radius R1 wavelength ratio S
, imaging distance! , θ to determine the optimal straight line scan. First determine. The remaining parameters are F, , F2. Y.

These three parameters F I+ F z and Y z can be determined from the three simultaneous equations (4), (8), and (9).

〔Example〕

Examples (design value examples) are shown below.

A2: 787nm (semiconductor laser), λI: 3
25 nm (He-Cd laser) R = 40 mm, Y2 = 83.969 mmθi
=41.956°, θ, =48.90°
, j2=343 mm In this case, it was confirmed that good linear scanning within ±0.15 mm over 252 mm was possible.

It has also been found that surface runout can be significantly reduced from ±30'' in the conventional symmetrical case to ±60'' when the allowable positional variation is within 20 tones.

It goes without saying that the above conditions can be applied to the reference wave and the object wave even if they are accompanied by a coma aberration wave for aberration correction.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to reliably prevent deviation of the scanning position due to surface wobbling about the rotation center of the hologram disk.

[Brief explanation of the drawing]

Figure 1 is a diagram illustrating how the hologram disk according to the present invention prevents fluctuations in scanning position due to surface runout, Figure 2 is a diagram explaining the basic principle of a hologram scanner, and Figure 3 is a diagram explaining the conventional countermeasure against surface runout. FIG. 4 is a diagram illustrating a conventional method for creating a hologram disk. 10... Hologram disk, P... Reproduction point, X... Normal plane.

Claims (1)

[Claims] A reproducing point (P) on the surface of the rotating body (10) divided into a plurality of parts.
, and create a hologram in that part by irradiating the normal plane (X) passing through the reproduction point with a reference wave that is a divergent spherical wave that satisfies the following equation, and an object wave that is a divergent spherical wave. , and a light beam scanning device that obtains an output light beam that enters at an incident angle that satisfies the following formula, rotates the rotating body on which the hologram is created, and performs linear scanning: (R/l)・cos＾2θ_d=cosθ_i− cos
θ_d However, sin θ_i=S・R/√(F_1^2+
R^2) In the above formula, R = radius of incidence of the rotating body at the reproduction point, l = imaging distance, θ_i = incident angle, θ_d = exit angle, S = λ_2
(Reproduced wave wavelength)/λ_1 (Created wave wavelength), F_1 = Normal distance from the rotating body surface to the reference wave point light source.