JPS61116319A - Optical scanning device using hologram - Google Patents

Abstract

PURPOSE:To execute linear scanning by reproducing light having wavelength different from that of recording light by using two divergent or convergent spherical waves as recording light at the formation of a hologram and using a convergent spherical wave having wavelength different from that of the recording light as reproducing light. CONSTITUTION:Two divergent spherical waves of two convergent spherical waves having focuses 21, 22 on the image formation surface (scanning surface) 4 side are used recording light (reference light, substance light) at the formation of a hologram and a convergent spherical wave having wavelength different from that of the recording light is used as reproducing light at a reproducing (scanning) time. The positions of a recording light source and a reproducing light source are selected so that respective focuses 21, 22, 20 of the recording light and reproducing light are located on respectively different prescribed positions on a hologram surface upon which optical beams are made incident obliquely.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical scanning device that uses a hologram to deflect the direction of a light beam at high speed.

More specifically, the present invention is effective when used in a device that records/displays signals or images using optical signals, reduces the influence of eccentricity of a hologram disk, and enables linear scanning without aberration. This invention relates to an optical scanning device.

(Conventional Technique) FIG. 2 is a diagram showing the main part of a conventional optical scanning device using a hologram. This device uses holograms 3T and 32 that are exposed and produced using object light 1 as diverging light from a point light source and reference light 2 as parallel light (both shown by broken lines).
．． A parallel beam is incident on the hologram 33, and a reproduced image is obtained by the reproduction light 5 on the imaging plane 4, which is a scanning plane located behind the hologram 3.

(Problems to be Solved by the Invention) In the device configured as described above, the reproduced image obtained on the image forming surface 4 is shifted to the image forming surface 4 according to the rotation of the hologram disk 3.
Although it moves above, it scans on an arc as shown in the figure, which causes the problem that the image is distorted. Also optical scanning using semiconductor laser! Although the a position is very effective for laser printers and the like, there is no hologram photosensitive material sensitive to the wavelength of a semiconductor laser (for example, 0.78 μm), and there is no optical scanning device using a hologram for a semiconductor laser. Furthermore, when a hologram scanner is applied to a laser printer, pitch irregularities in scanning lines caused by eccentricity (deviation of the center of rotation) of the hologram disk become a major problem.

Here, the present invention uses a hologram to perform linear scanning with reproduction light (for example, semiconductor laser light) of a different wavelength from the recording light (reference light, object light) used when producing the hologram, and is affected by the eccentricity of the hologram disk. The objective is to realize an optical scanning device that has a convergence effect (lens effect) with no aberrations while reducing the amount of light.

(Means for Solving the Problems) An optical scanning device using a hologram according to the present invention is an optical scanning device a using a transmission type hologram disk. Two divergent spherical waves or two convergent spherical waves having a focus on the imaging plane (scanning plane) side are used, and a convergent spherical wave having a wavelength different from the recording light is used as the reproduction light used during reproduction (scanning). The recording light source and the reproduction light source are characterized in that the positions of the recording light source and the reproduction light source are selected so that the respective focal positions of the recording light and the reproduction light are at positions where the light beams obliquely enter the hologram surface and are at different predetermined positions.

(Function) According to the device having the above configuration, the change in the density of the lattice fringes of the hologram becomes small at the position where the reproduction light is incident, so that the imaging plane (
In addition to reducing the influence of the eccentricity of the hologram disk on the reproduced image on the scanning plane, the reproduced image on the imaging plane scans in a straight line and without aberration, and the incident angle of the reproduced light on the hologram satisfies the Bragg condition. It is possible to obtain high diffraction efficiency.

(Example) The present invention will be explained in detail below using the drawings.

3 and 1 are main part configuration diagrams showing an embodiment of the optical system according to the present invention, and FIG. 3 shows the overall state during recording (preparation) and reproduction (scanning). The perspective view, FIG. 1, is a side view of the hologram plate in FIG. 3. In these figures, 3 is a hologram disk;
Here, several holograms 31, 32, 33, . . . made of dry plates coated with a photosensitive material for holograms are installed in the rotating direction (direction indicated by arrow a). This hologram disk 3 rotates (moves) in the direction of arrow a, and one hologram performs one scan. 4 is an imaging plane.

First, the object light 11 used when producing a hologram
122 uses a convergent spherical wave, and its convergence point is at the 0 point. Further, the reference light has the same wavelength as the object light source 22 (for example, the wavelength λC-O).

A convergent spherical wave of 63 μm) is used, and its focus is at point R. Both the object beam and the reference beam are installed so that the angle of incidence of the light beam on the hologram is at an angle other than 00 at the scanning center, that is, at an angle, and the light from each of these light sources causes the hologram to be 3+, 32.33...
・Record interference fringes on top.

The reproduction light used during reproduction (scanning) has a wavelength different from that of the reference light (for example, the wavelength λR-0 of a semiconductor laser beam).
, 78 μm) is used, and its focus is at point Q, which is at a different position from the focus R of the reference light source. The reproduction light beam converging on this focal point 20 is incident on the hologram disk 3 at an angle other than O'' at the scanning center, that is, at an angle, and the reproduction light from the hologram is
The light is diffracted with high diffraction efficiency by interference fringes recorded in advance on each hologram 3+, 32, 33, .

As the hologram disk 3 rotates (moves), this diffracted light forms a small light spot on the imaging surface 4, and the diffracted light is transmitted from S+→S2→
S3 and straight line, aberration-free scanning.

Here, in the present invention, the positions of the reference light focus 21, the reproduction light focus 20, WI&5, and the object light focus 22 are set at predetermined positions so as to satisfy the following equations (1) and (2). This enables straight-line, aberration-free scanning.

At the same time, the angle of incidence of the reproduction light on the hologram is selected to be equal to or close to the Bragg angle of incidence. That is, high diffraction efficiency is obtained by satisfying the Bragg condition of equation (3).

fc(Jrco, lrc g −'・θ・T・λ
C) Medium fg (1rRo, Ir'RR, r, θ, p
, λk)...(1) φc (lrcm, 1rcR', r, θ, ψ,
λC) medium φR(lrt+o, 1rRi, r, 8.p,
λR)...(2) θ7ki sin'(λR/2d')-(θob-θrer
)/2 ... (3) where fc: Spatial frequency φC of interference fringes recorded on the hologram surface by the object beam and reference target; Inclination fR of the interference fringes mentioned above: Convergence to a predetermined point on the imaging plane Spatial frequency φR of interference fringes formed on the hologram surface by the virtual light flux and reproduction light = Inclination of the interference fringes 1rco: Vector 1rcR indicating the focal position of the object light:
Vector indicating the focal position of the reference light FJo: Vector indicating the light source position of the virtual light flux Fig: Vector indicating the focal position of the reproduction light (r, θ): Coordinate P on the hologram disk surface
: Rotation angle λC of hologram disk: Wavelength of recording light (reference light, object light) λR: Wavelength of reproduction light and virtual light flux θr: Incident angle of reproduction light θob: Incident angle of object light θτef: Incident angle of reference light d ': Three-dimensional pitch of interference fringes on the hologram disk In the present invention, in FIG. 1, the center of rotation C of the hologram disk 3 and the hologram 3+.

The distance rB from the center P of 32..., from the point p to the imaging plane 4 (
When the distance 1d to the scanning position is given, the angle of incidence of the reproduction light satisfies the Bragg condition with respect to the lc interference fringe created at point P by the object light and reference light, and the linearity and convergence are The focal positions of the object light, reference light, and reproduction light are determined by equations (1) and (2) to obtain the best results.

It is obtained from equation (3). Here, equation (1), (
2) Equation is difficult to solve analytically, so (1) (2)
Equation (3) is replaced with an extreme value problem as described below, and this is solved by a numerical solution method using a computer. F c obtained by the method described below. +I'CR1rRR ultimately satisfies the above formula.

The focal point 2° of the reproduction light used during reproduction (scanning) must be at a different position from the focal point 21 of the reference beam, have different wavelengths, be a spherical wave, and be obliquely incident, and furthermore, the hologram 3 rotates.

Since the hologram is moving, by selecting the position of each focal point so as to satisfy the above equations (1) and (2), the reconstructed image created on the imaging plane 4 by the diffracted light from the hologram is Scans in a straight line and without aberration.

More specifically, convergent spherical waves are used for the reference beam and reproduction beam, the incident angle of the light on the hologram disk is selected to be an angle other than 0° at the scanning center, and as the hologram disk rotates, the reference beam The difference between the incident angles of the light and the reproduction light is relatively changed, and this angular difference is used to change the diffraction angle of the diffracted light, so that the optical axis of the diffracted light as seen from the side of the hologram disk 3 is set to P.

The angle θd (see Fig. 1) obtained by projecting onto a plane including Q and R (see Fig. 4 on the Y-Z plane) is projected onto the hologram disk 3.
It is always maintained constant regardless of the rotation of the image plane, thereby causing the reproduced image on the imaging plane to scan in a straight line.

Next, non-receivable scanning will be explained with reference to FIG. Here, no aberration refers to a case where the diameter of the optical spheroid created by the diffracted light on the imaging plane is at the diffraction limit or close to the diffraction limit and less than or equal to the target spot diameter.

As shown in FIG. 4, interference fringes are created on the hologram surface by a virtual light beam (ideal diffracted light) converging on a predetermined point on the imaging surface 4 of the diffracted light and the reproduction light, and the recording ( If the interference fringes created by the object light and the reference light during exposure are the same within the region of the reproduction beam width on the hologram surface, there will be no linear aberration. The fact that the interference fringes are the same can be considered as a necessary and sufficient condition that the spatial frequencies fc and fR and the inclinations φC and φR of the interference fringes are respectively the same. Further, even if the interference fringes are expressed by the rate of change or curvature of the spatial frequency depending on the position, the expression is exactly the same as the above expression. In equations (1) and (2), the left and right sides are not completely equal (because the recording light is composed of spherical waves to form interference fringes. By using beams, <1)(2)(
3) It is conceivable to make the difference between both sides of the equation smaller, but it is extremely difficult and impractical. ) Therefore, within the range of permissible linear aberration, solve the condition that they are approximately equal, and find the respective positions of the object beam, reference beam, and reproduction beam.

Next, an example of an actual calculation method will be explained. As shown in Figure 1, let us consider the x', y', z-coordinate system, and the y
-,z The convergence point position of the object light on one plane is 0 (0,'J+
, Z+ >, position of the focal point of the reference light R(0,'/2,
Z2), the respective phase distributions on the hologram plane placed on the x- and y planes can be expressed by equations (4) and (5).

φ+ ′(X′, V′) 2π x+y−V+) +
Z+ /λC...(4)φ2'(X-, V-)-
2π x+y'-Y2) +Z2/λC...(
5) Therefore, the phase difference distribution of the interference fringes recorded on the hologram dry plate, that is, the phase transfer function φH-(X-, y-) of the hologram scanner, can be calculated using the formula (6) % Formula % Next, the optical element design technique The reproduced light is analyzed using a ray tracing method, which is one of the methods. If the incident light on the hologram is regarded as a group of rays, the diffraction direction of any one ray can be calculated as follows.

As shown in Fig. 5, a light beam with a direction cosine of (1□n, min+ntn) enters a hologram on the X, y plane,
The first-order diffracted ray has the direction cosine (Iout, mout r
nout), the direction cosine of the diffracted light beam is expressed by the following equation using the direction cosine of the incident light beam and the phase transfer function φH(X, V) of the hologram.

1゜ut-ltn+(λtt/2π)φHX(XIy)
...(a) mou
t = mt n + (λtt / 2π)φ5y(X
.

y) ...(8)n
out" Out mout...(9) However, φHX (X+V) *φHr (X+V)
represent the partial differentiation of φH(X, V) with respect to x and y, respectively.

FIG. 6 is an explanatory diagram showing the characteristics analysis of a hologram scanner using ray tracing. In the figure, the hologram disk is on an xy plane defined by an xyz coordinate system fixed in space.

Also, assume that the X-, y'', and z-coordinate systems are fixed on the hologram disk, and the angle between the y-axis and the y'-axis, that is, the rotation angle of the hologram, is ψ.The scanning plane is p- 0
It is assumed to be perpendicular to the central ray of the reproduction ray group when ,
X in the plane as shown.

Assume that the Y coordinate is taken. Here, the y-axis is on the yz plane. Here, the phase transfer function φH (X, V, 5') in the xy2 coordinate system of the hologram scanner is obtained from equation (6) as follows: φH (X * Y + F) ... (10) Reproduction (incident) ray group Once the phase transfer function of the hologram disk is determined, the group of diffracted rays can be found using equations (7) to (9), and the group of intersections between the group of diffracted rays and the constant surface can be found as shown in Figure 6. can.

That is, once the relative positions of Irco, Fcg, IrgR, and rB and the distribution of reproduction light on the hologram disk 3 are determined, it is possible to draw a spot diagram corresponding to the rotation of the hologram disk on an appropriate scanning plane. can.

Based on this spot diagram, by an iterative method,
lr CO*IrCR, FiR, Ir12o+ ra, which optimizes linearity and convergence and increases diffraction efficiency
The predetermined position of can be found.

Ray tracing is then used to define functions to evaluate the convergence, linearity, and diffraction efficiency of the hologram scanner.

In Figure 6, the reproduction light irradiates a circle with radius rb centered on the coordinates (0, ra, O) on the hologram disk, and each ray of the reproduction light beam group is numbered from 1 to N. to distinguish each ray. When the hologram disk is rotating p, the position vector in the xY coordinate system within the scanning plane of the intersection of the diffracted beam corresponding to the i-th reproduction beam and the scanning plane is expressed as Fi (F'), and its elements are (Xl (
95).

Yl <9F)). At this time, the convergence evaluation function Ea is defined by the following equation.

However, F (95J) = Σ1rL(9''')/N
'-1...(12) i-1, 2,..., N. Here, when 95J is the element of F IPj> (also <ψj), Y (95J)) and the scanning width of the scanner is L, ×(Pl)=L/2. Nu (9'M) = L/
2...(13) is satisfied, Pl and ψ. Indicates the value of each dividing point when the area is divided into M-1 equal parts, and ? 'J=9'++(J~1)(S'M-ψ+)/(M'
1) It is expressed as (14).

Equation (11) above is a relatively strict planning equation, but in order to simplify the calculation, let us represent the reproduction ray group by ray C' passing through the center of the reproduction ray group and rays passing through four points in the periphery. It becomes as follows.

/4.M.-<15>Tatatari rc (Pj) is a position vector representing the intersection of the central ray C' with the scanning plane.

The linearity evaluation function E1 is defined as follows.

El-! i'(9(fi'J)-7)2/M...(
16)j-Also, Equation 16) is also a relatively strict equation, but in order to simplify the calculation, the reproduction beam group is represented by its central ray C' as described above, and the following equation is obtained.

however Ru.

When the hologram used is a two-dimensional hologram, there is no need to consider the Bragg incidence condition, but when a three-dimensional hologram is used, the highest diffraction efficiency is obtained when the angle of incidence of the incident light beam is equal to the Black angle. The difference between the angle of incidence of the i-th reproduction beam on the hologram and the Bragg angle of incidence is Δθa1
(Pj), the evaluation function Eb regarding the Bragg incidence condition can be defined as follows.

Equation (20) is also a relatively strict equation, and in order to simplify the calculation, the reproduction ray group is represented by the central ray C-, and the following equation is used instead of Equation (20)... (21) Using each of the above evaluation functions, the overall evaluation function is defined as follows.

E-Wa E@+Wt Et +Wb Eb ・= (
22> However, W@, Wl, and Wb are weighting constants and the incident position (0, ra, O) of the reproduction light in FIG.

When the irradiation radius rb of the reproduction light on the hologram disk, the distance +d between the hologram disk and the scanning surface, and the scanning width are determined by the required specifications, the exposure light that minimizes the evaluation function E shown in equation (22) m and the position of the reproduction light source are set to optimal design values.

The minimum value of the evaluation function is determined by repeated calculations using the maximum slope method or the like.

An example of specific numerical values of the hologram scanner obtained as described above is shown below.

Wavelength of reproducing light λR: Q, 78 [μm] Wavelength of recording light λ
c: o, 63 [μm] Distance ra between the center of rotation of the hologram disk and the incident position of the reproduction light: 40 [mm] Angle of incidence of the reproduction light on the hologram disk θT: 45 Ide9] Rotation angle ψ of the hologram disk Diffraction angle θa of the reproduction light when -0: 45 [deg] Distance lr from the incident position of the reproduction light to the focal point of the reproduction light: 510 [mm] Distance between disk scanning surfaces 1d: 300 [mm] Scanning width L: 300 [mml Recording convergent spherical wave 1 focal point position (On yr + Z+)
:(0,123,113 recording convergent spherical wave two focal points IF (0, Y2, Z2):
(0, −51, 3, 136> Reproduction convergent spherical wave focal position! (0, yr, Zτ): (0, −
315, 366) However, the unit of the constant without a unit symbol is [mml] In the above optical scanning device, the focal position of the two recording beams used at hologram 11 is the perpendicular to the hologram disk surface at the incident position of the reproduction beam. The position is asymmetrical.

In addition, here, some analysis assumes a two-dimensional hologram,
However, in reality, three-dimensional holograms are often used because they provide high diffraction efficiency.

Analysis of three-dimensional holograms is complex, and as described here, even when analyzed with two-dimensional holograms, good results that are generally in good agreement can be obtained.

In the apparatus shown in FIG. 1 constructed as described above, the influence of eccentricity (misalignment of the central axis, also referred to as axis deviation) of the hologram disk is extremely small as shown below.

For simplicity, consider the case where the rotation angle ρ of the hologram scanner is O. The diffraction grating on the hologram scanner is perpendicular to the plane of incidence of the reproduction light, its spatial frequency is f, the wavelength of the incident light is λ, and the diffraction angle is θd.The change in the diffraction angle Δθd with respect to the eccentricity Δy is Δθci− (λR/CO8θd) (df/dV)・Δy
...(23). Therefore, the pitch unevenness ΔY on the scanning surface is equal to the pitch unevenness ΔY on the disk scanning surface fi
Using lld, ΔY"ldΔθd = (1dλR/CO8θd) (df/dy)・Δy
...(24). For the hologram scanner in Figure 1, df, /dy-λc-'
[Z+ 2 (Z+ 2+ (''/V+)')
"Z2 '(Z2" + (V-Vz)2
)-3/2
...
-(25), and ΔY/Δy=0.217. When diverging light is used as the reference light and reproduction light under similar conditions, ΔY/Δy=7.12, which indicates a significant improvement. This is because the change in the spatial frequency of the diffraction grating CJf, /CJy (density change in the radial direction of interference fringes) can be made smaller by using a convergent spherical wave than by using a diverging spherical wave for the reproduction light. . As a result,
When the allowable range of pitch unevenness on the scanning plane is ±20 μm, eccentricity is allowed up to 92 μm, which means that very rough fitting is sufficient, and processing is simplified. This is particularly effective when a hologram scanner is applied to a laser printer.

FIGS. 7 and 8 are characteristic diagrams in which the linearity error and convergence spot diameter of the scanning spot obtained on the imaging plane 4 were investigated in ¥ff11F according to the present invention. Within a scanning width of 300 mm, linearity of ±110 μm and maximum spot diameter of 200 μm were obtained. Scanning width 200m
m, the maximum spot diameter is 100 μm.

Further, in the above embodiment, two converging spherical waves are used as the recording light, but the present invention is not limited to this, and two diverging spherical waves may also be used. In this case, the light source position of the recording light becomes the focal position, and the light source of the diverging spherical wave may be provided at the focal position of the convergent spherical waves of the two recording lights in the embodiment shown in FIG.

Further, in the above embodiment, a photoresist is used as the photosensitive material, and after exposure and development, the substrate is etched by oblique ion etching to form an echelette-shaped grating to improve the diffraction efficiency. In this case, equation (1), (
It is sufficient to perform exposure under conditions that satisfy only formula 2).Alternatively, a 3i crystal or the like may be used as the substrate and an echelette-shaped lattice may be formed by anisotropic etching. Furthermore, the above-mentioned echelette-shaped grid may be used as an original, and a replica may be made using transparent plastic or the like.

(Effects of the Invention) As explained above, according to the present invention, the hologram disk has a simple configuration, a large eccentricity tolerance range, straight-line scanning, and a highly diffraction-efficient light beam with an aberration-free convergence effect. A scanning device can be realized.

In addition, since the wavelengths of the recording light (object light, reference light) and reproduction light are different, when producing a hologram, it is necessary to use He-
A Ne laser or an Ar laser can be used, and a semiconductor laser can be used during reproduction.

[Brief explanation of the drawing]

1 and 3 are main part configuration diagrams showing an example of the device according to the present invention, FIG. 1 is a side view of the state during recording and reproduction, FIG. 3 is a perspective view of the whole, Fig. 2 is a configuration diagram of the main parts of an optical scanning device using a conventional hologram, Figs. 4 to 6 are explanatory diagrams for explaining aberration-free scanning, and Figs. 7 and 8 are diagrams according to the present invention. It is a characteristic line diagram in an apparatus. 3... Hologram disk, 20... Reproduction light focus,
21...Reference light focus, 22...Object light focus, 4...
・Imaging plane.

Claims (5)

[Claims] (1) In an optical scanning device using a transmission hologram disk, two diverging spherical waves or two convergent waves having a focus on the imaging plane (scanning plane) are used as recording lights (reference light, object light) used during hologram production. A convergent spherical wave having a different wavelength from the recording light is used as the reproduction light used during reproduction (scanning), and the focal position of each of the recording light and reproduction light is a position where the light beam is obliquely incident on the hologram surface. By selecting the positions of the recording light source and the reproduction light source so that they are at different predetermined positions, the reproduction image on the imaging plane (scanning plane) is less affected by eccentricity of the hologram disk, and linear and aberration-free scanning is possible. An optical scanning device using a hologram, characterized in that: (2) Convergence of the reference light focus, object light focus, and reproduction light focus;
An optical scanning device using a hologram according to claim 1, which is provided at a position that minimizes an evaluation function regarding linearity and Bragg incidence conditions. (3) Light using a hologram according to claim 1, in which the reference beam focus, the object beam focus, and the reproduction light focus are set at predetermined positions satisfying the following formula in the area on the hologram surface where the reproduction light is incident. scanning device. f_C(■_C_O, ■_C_R, γ, θ, ψ, λ_C
)≒f_R(■_R_O, ■_R_R, γ, θ, ψ, λ
_R) φ_C (■_C_O, ■_C_R, γ, θ, ψ,
λ_C)≒φ_R(■_R_O, ■_R_R, γ, θ,
ψ, λ_R) where f_C: Spatial frequency of interference fringes recorded on the hologram surface by the object light and reference light φ_C: Inclination of the interference fringes f_R: Virtual light flux converging to a predetermined point on the image plane and reproduction Spatial frequency of interference fringes created on the hologram surface by the light φ_R: Inclination of the interference fringes ■_C_O: Vector indicating the focal position of the object light ■_C_
R: Vector indicating the focal position of the reference light ■_R_O: Vector indicating the light source position of the virtual light beam ■_R_R: Vector indicating the focal position of the reproduction light (γ, θ): Coordinates on the hologram disk surface ψ: Rotation of the hologram disk Angle λ_C: Wavelength of recording light (reference light, object light) λ_R: Wavelength of reproduction light and virtual light flux (4) Using the hologram according to claim 1, in which the incident angle θr of the reproduction light on the hologram disk and the diffraction angle θ_d of the reproduction light when the rotation angle ψ of the hologram disk is 0 are as follows. An optical scanning device. θ_r-45[deg] θ_d-45[deg] (5) Optical scanning using the hologram according to claim 1, in which the focal positions of the two recording beams used during hologram production are set at positions asymmetrical with respect to the perpendicular to the hologram disk surface at the incident position of the reproduction beam. Device.