JP2663948B2 - Light beam scanning device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] A light beam scanning apparatus using a hologram disc is provided. The object of the invention is to prevent a displacement of a scanning position due to a surface shake about a rotation center of the hologram disc. the divided portions of the rotating body surface to set the reproduction point, with respect to the normal plane passing through the regeneration ^{point, R / l · cos 2 θ} d = cosθ i -cosθ d However, the In the above formula, R = incidence radius of the reproduction point, l = imaging distance, θ _i =
Incident angle, θ _d = outgoing angle, S = λ ₂ (reproduced wave wavelength) / λ ₁
Irradiating a reference wave and an object wave, which are divergent spherical waves, from a position that satisfies the following conditions: (a created wave wavelength), F ₁ = normal distance from the rotating body surface to the reference wave point light source; The rotator on which the hologram is made incident at an incident angle that satisfies the above equation is rotated to obtain an output light beam that performs linear scanning.

[Industrial applications]

The present invention relates to a light beam scanning device that performs a linear scan using a hologram disk.

[Conventional technology]

In recent years, instead of a complicated and expensive rotary polygon mirror for reading a bar code or scanning a laser beam in a laser printer, a light beam scanning device using a hologram having a simple structure and easy manufacture has been studied.

FIG. 2 shows a basic configuration of a light beam scanning device using a hologram. As shown in the figure, a hologram facet 3 having a predetermined pattern is formed on a transparent optical rotating disk (hologram disk) 10 which rotates at high speed around a rotation axis 1. The hologram facet is irradiated with the reproduced light beam 6 irradiated by the irradiation, and the output light beam 7 diffracted by the interference fringes formed in the hologram facet becomes a scanning beam and scans on the screen 8.

Conventionally, in a device for performing high-precision linear scanning used in a laser printer or the like using a hologram as described above, in order to improve print quality, generally, a projection angle of a scanning line of a repetitive laser beam in a sub-scanning direction is used. ± 10 variation
It is required to be several seconds or less. This projection angle fluctuation is caused by slight fluctuation (about several seconds or several micrometers) such as surface deviation or axis deviation of the rotating disk on which the hologram is created, and increases and reduces the mechanical accuracy of the rotating disk. It was very difficult and problematic. Further, the light use efficiency of the porogram scanner is also low.

[Problems to be solved by the invention]

In order to solve the above-mentioned problems, the applicant of the present invention disclosed in Japanese Patent Application Laid-Open No. Sho 60-194419, an object wave and a reference wave (both diverging spherical waves) from a position symmetric with respect to a surface normal passing through a reproduction point. A hologram is created by irradiating the hologram disc with a reproduction light beam so as to make the incident angle and the diffraction angle equal to each other, thereby increasing the allowable values of surface deviation and axis shift of the hologram disc and light. A technique for obtaining a hologram scanner with high use efficiency has been disclosed.

That is, as shown in FIG. 4, a reproduction point P is set on a hologram facet on the hologram disk 10, and both points A ₁ and A ₂ are symmetric or almost symmetric with respect to a surface normal X passing through the reproduction point. to create a hologram partial reference wave W ₁ and the object wave W ₂ is a divergent spherical wave irradiated. By irradiating the reproduction light while rotating the object (hologram disk) 10 on which the hologram is created, a diffracted light emission light beam that scans on the imaging plane T in a predetermined direction is obtained. As described above, in the related art, the incident angle and the outgoing angle are equalized as described above in order to prevent the position from being changed due to the surface deflection. However, although this has a great effect on the surface contact with the beam incident position of the disk as the rotation center as shown in FIG. 3, the fluctuation of the scanning position with respect to the surface deflection (FIG. 1) with respect to the disk rotation center is sufficient. It was found that no significant effect was obtained.

SUMMARY OF THE INVENTION It is an object of the present invention to prevent a scanning position from changing with respect to a disk surface deflection with respect to a rotation center of a hologram disk.

[Means for solving the problem]

The inventor of the present application has noticed that the symmetry of the two generated divergent spherical waves is slightly broken, and has found a condition that can further reduce the position fluctuation due to the surface deflection with respect to the rotation center of the hologram disk. That is, according to the light beam scanning device of the present invention, a reproduction point is set on a portion on the rotating body surface divided into a plurality of parts, and a position satisfying the following expression with respect to a normal plane passing through the reproduction point is set. by irradiating a reference wave and the object wave is a divergent spherical wave, characterized in that so as to create a hologram ^{partial; R / l · cos 2 θ} d = cosθ i -cosθ d ... (1) where In the above formula, R = incidence radius of the reproduction point, l = imaging distance, θ _i =
Incident angle, θ _d = outgoing 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.

(Operation)

In FIG. 1, the imaging distance l is θ _i , the incident angle to the hologram is θ _i , the outgoing angle (diffraction angle by the hologram) is θ _d ,
Also, the surface deflection with respect to the rotation center is dφ. At this time,
When the deviation of the angle of diffraction with respect to the surface deflection and d [theta] _d primary approximate expression of the following are satisfied.

dθ _d = [cos θ _i / cos θ _d −1] dφ (1) On the other hand, if the deviation of the diffraction angle satisfies the following relationship, the change in position can be prevented.

∴dθ _d = R / [l / cos [theta] _d] · d.phi ... (2) Therefore, (1), the relationship of (2) the following equation from the equation (3) is obtained.

R / l ・ cos θ _d = cos θ _i / cos θ _d -1 (3) The following equation is obtained by rearranging equation (3).

_{^{R / l · cos 2 θ d}} = cosθ i -cosθ d ... (4) where (4) satisfies the equation, yet it is not obvious to perform a linear scan by the hologram disk. Next, it is described below that this is possible. Here, it is assumed that the incident angle satisfies the following equation (see FIG. 4).

Where λ ₂ / λ ₁ (λ ₁ : hologram creation wave wavelength, λ ₂ : hologram reproduction wave wavelength) F ₁ = vertical distance between point light source A _{1 of} reference wave and surface of disk 10 R = incidence radius of reproduction point P The incident angle condition (5) is generally selected so as to maximize the diffraction efficiency, that is, the Bragg angle, but is not limited thereto.

As described above, cos θ _i and cos θ _d are given by the following equations (6) and (7).

However, F = vertical distance between the vertical distance Y ₂ = A ₁ point and A ₂ points between the surface of the light source A ₂ and the disk 10 in terms of the object beam (6), Y ₂ = 2R in (7), It will be understood that the case where F ₁ = F _{2 corresponds} to the above-mentioned prior art, that is, the case where A ₁ and A ₂ are symmetrically arranged. In this case, θ _i
= A θ _d.

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

Here, θ _c is an important angle parameter that determines the linearity by the rotation angle of the hologram disc at a particular inflection point where the scanning trajectory rises while hanging.

The condition for maximizing the eccentric margin (allowable axis deviation) of the hologram disk is expressed by the following equation.

F ₂ ² [F ₁ ² + R ² ] ^3/2 = F ₁ ² [F ² + (R−Y ₂ ) ² ] ^3/2 …
(9) The method of deriving the above equation (9) is disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 60-194419.

In actually designed, specified disk entrance radius R, the wavelength ratio S, the image formation distance l, the theta _c to determine the optimal linear scan first. The remaining parameters are F ₁ , F ₂ , and Y ₂ , and these three parameters are obtained from the simultaneous equations (4), (8), and (9).
F ₁ , F ₂ and Y ₂ can be determined.

〔Example〕

 Examples (design values) will be described below.

λ ₂ : 787 nm (semiconductor laser), λ ₁ : 325 nm (He-Cd laser) R = 40 mm, Y ₂ = 83.969 mm θ _i = 41.956 °, θ _d = 48.90 °, l = 343 mm In this case, it was confirmed that good linear scanning within ± 0.15 mm over 252 mm was possible.

It was also found that when the permissible position fluctuation was within 20 μm, the surface runout was significantly reduced from ± 30 ″ to ± 60 ″ when the conventional symmetrical variation was within 20 μm. Needless to say, the above conditions can be applied to the reference wave and the object wave even if the reference wave and the object wave have a coma aberration wave for aberration correction.

〔The invention's effect〕

As described above, according to the present invention, it is possible to reliably prevent the scanning position shift caused by the surface shake about the rotation center of the hologram disk.

[Brief description of the drawings]

FIG. 1 is a view for explaining the prevention of fluctuation of a scanning position caused by surface runout by a hologram disk according to the present invention, FIG. 2 is a view for explaining a basic principle of a hologram canner, and FIG. FIG. 4 is a diagram for explaining a conventional hologram disc producing method. 10: Hologram disk, P: Reproduction point, X: Normal surface.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiroyuki Ikeda 1015 Uedanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fujitsu Limited (56) References JP-A-64-66617 (JP, A) JP-A-62-28708 (JP, A) JP-A-59-191007 (JP, A) JP-A-55-9595 (JP, A)

Claims (1)

(57) [Claims] 1. A reproduction point (P) is set on a surface of a rotating body (10) divided into a plurality of parts, and a divergent spherical wave satisfying the following equation with respect to a normal plane (X) passing through the reproduction point: And a hologram is created by irradiating a reference wave and an object wave that is a divergent spherical wave. light beam scanning device obtain outgoing light beam to ^{perform: R / l · cos 2 θ} d = cosθ i -cosθ d However, In the above formula, R = the radius of incidence of the rotating body at the reproduction point, l = the imaging distance,
θ _i = incident angle, θ _d = output angle, S = λ ₂ (reproduced wave wavelength)
/ Λ ₁ (creation wave wavelength), F ₁ = normal distance from the rotating body surface to the reference wave point light source.