JPS6148813A - Photoscanning device using hologram - Google Patents

Abstract

PURPOSE:To obtain a photoscanning device which provides convergence having no aberration by installing light sources for recording light and reproducing light as spherical waves having different wavelengths at different positions where a light beam is incident on a hologram surface slantingly, and satisfying an equation. CONSTITUTION:The recording light used for the manufacture of the hologram and the reproducing light used for reproduction are divergent or convergent spherical waves having different wavelengths. Then, the light sources for those recording light and reproducing light are installed at different positions where the light beam strikes the hologram surface slantingly. Further, the equation holds, where Ir is the distance (mm.) between the light source for the reproducing light and a hologram disk, ra the distance (mm.) between the center of rotation of the hologram disk and the incidence position of the reproducing light, Id the distance (mm.) between the hologram disk and a scanning surface. Consequently, the photoscanning device of simple constitution which makes a linear scan, provides aberration-free convergence, and has high diffraction efficiency is realized.

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 relates to an optical scanning device that is effective for use in a device that records or displays signals, images, etc. using optical signals, and is capable of linear aberrationless scanning.

(Prior Art) FIG. 2 is a diagram illustrating a main part of an optical scanning device using a conventional photogram. This device consists of a hologram 31, which is made by exposing an object beam 1 as a diverging beam from a point light source, and a reference beam 2 as a parallel beam (both shown by broken lines).
A parallel beam is incident on 32.33..., and the hologram 3
On the imaging plane 4, which is the scanning plane located behind the
IL:! reproduced image by reproduction light 5. It is configured so that

(Problems to be Solved by the Invention) In the apparatus configured as described above, the reproduced image obtained on the imaging plane 4 moves on the imaging plane 4 according to the rotation of the hologram disk 32, but as shown in the figure There was a problem in that the scanning was performed on a circular arc and the image was distorted. Also, optical scanning devices using half-body lasers are very useful for laser printers, etc.
511J, but the wavelength of the semiconductor laser (for example, 0.
There is no hologram photosensitive material sensitive to 78 μm), and there is no optical scanning device using a hologram for semiconductor lasers.

Here, the present invention uses a hologram, and is capable of performing linear scanning with reproduction light (e.g., semiconductor laser light) of a wavelength different from the recording light (reference light, object light) used when producing the hologram, and has an aberration-free convergence effect ( The aim is to realize an optical scanning device that has a lens function.

(Means for Solving the Problems) The device used in the present invention uses a transmission or reflection type hologram plate, and uses recording light (reference light, object light) used during hologram production and reproducing (scanning) The reproduction light to be used is a spherical wave with different wavelengths, and the light source positions of the recording light and reproduction light are selected at different positions where the light beams are obliquely incident on the hologram surface, and at predetermined positions. It is configured to satisfy the relational expression.

(Function) According to the device configured as described above, the reconstructed image on the imaging plane can be scanned in a straight line and without aberration, and the incident angle of the reconstructed light to the hologram can satisfy the Bragg condition, resulting in high diffraction. You can gain efficiency.

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

Figure 3 J5 and Figure 1 are 1X diagrams of the main parts showing an embodiment of the MVfl (optical system) according to the present invention, and Figure 3 shows the state during recording (preparation) and reproduction (scanning). The overall perspective view shown in FIG. 1 is a view seen from the side of the hologram plate in FIG. 3. In these figures, 3 is a hologram disk, on which a plurality of holograms 3+, 32 made of a dry plate coated with a photosensitive material for holograms are shown.
．． 33... are stored in the rotational direction (direction indicated by arrow a). This hologram disk 3 rotates (moves) in the direction of arrow a, and one hologram performs one scan. Note that an example using a transmission hologram disk is not shown here. 4 is an imaging plane.

First, the object light source 2 used during hologram production
2 uses a convergent spherical wave, and its convergence point is at the 0 point. Further, the reference light source 21 uses a diverging spherical wave having the same wavelength as the object light source 22 (for example, wavelength λc=0°63 μm), and there is a point light source at point R. These object light sources 22
Both the reference light source 21 and the reference light source 21 are set so that the incident angle of the light beam emitted from them into the small program is at an angle other than 0° at the scanning center, that is, at an angle. The light from each light source creates a hologram 3.

32.3:1...The interference fringes are recorded on the top.

The reproduction light +1i;i20 used during reproduction (scanning) is
A diverging spherical wave with a wavelength different from that of the reference light (for example, the wavelength λR of the semiconductor light 11 light = 0.78 μm) is used, and its point light source is at point Q and is located at a different position from the point light source R of the reference light source. . The light beam from the reproduction light source 2o enters the hologram disk 3 at an angle of incidence other than 00 at the scanning center, that is, obliquely.The reproduction light from the holograms is transmitted to each hologram 3. + , 32.33...
・It is diffracted with high diffraction efficiency by interference fringes recorded in advance.

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

Here, in the present invention, the reference light source 21 and the reproduction light source 2
0 position and the focal position of the object light source 22 as follows (7>
A predetermined position is selected so as to satisfy Equation (2), thereby achieving linear, 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 (lrco, f”cR+ r, θ, ψ, λC)
:fB (lrl!o, lrq R, r, θ, ψ
, λR)...('1) φc (fco, lrcI2.r, θ, ψ・λC)kiφR(lrRo + lrRR+ r* θ, (1
), Atz >...(2) θ? −”5in−’(λR/ 2 d −) −(θo
b−θτer)/2 ...(
3) However, fc: Spatial frequency of interference fringes recorded on the hologram surface by the object light and reference light φC: Inclination of the interference fringes fR: Virtual light flux converging on a predetermined point on the image forming surface and reproduction light Therefore, the spatial frequency of interference fringes formed on the hologram surface is φR2. The inclination of the interference fringes is lrco: vector lr'cR, which does not indicate the light source position of the object light.
: Vector indicating the light source position of J illumination) rRo: Vector indicating the light source position of virtual light flux lrRR: Vector indicating the light source position of reproduction light (r, θ): Coordinate on the hologram disk surface ψ: Rotation angle λC of the hologram disk : Wavelength of recording light (reference light, object light) λR = Wavelength of reproduction light and virtual light flux θT: Incident angle θ of reproduction light. b = Incident angle of object light θyet: Incident angle of reference light d-: Three-dimensional pitch of interference fringes on hologram disk In the present invention, in FIG. 3+.

The distance ra from the center P of 32..., from the point P to the imaging plane 4 (
The pressure path 11d to the scanning position) is given 1! At J time,
For the interference fringes created at point P by the object beam and reference beam, the angle of incidence of the reproduction beam satisfies the Bragg condition, and the object beam, reference beam, and reproduction beam are Expressions (1) and (2) for each light source position.

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 the alltI solution method using a computer.IrcO, lrCR, lrRg obtained by the method described later
As a result, the above formula is satisfied.

The reproduction light 120 used during reproduction (scanning) is located at a different position from the reference light source 21, has different wavelengths, is a spherical wave, and is obliquely incident; rotate.

Since the hologram is moving, by selecting the position of each light source so as to satisfy the above equations (7) 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, a diverging spherical wave is used for the reference beam and the reproduction beam, the incident angle of the light on the hologram disk is selected to be an angle other than 00 at the scanning center, and as the hologram disk rotates, the reference beam and The difference in the incident angle with 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. 3) obtained by projecting onto a plane including Q and R (see Fig. 4 for Y-Z) is always maintained constant regardless of the rotation of the hologram disk 3, and thereby the imaging plane The reproduced image above is scanned in a straight line.

Next, aberration-free scanning will be explained with reference to FIG. Here, no aberration refers to a case where the diameter of a light spot created by diffracted light on the imaging plane is at the diffraction limit or close to the diffraction limit and smaller 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 beam and the nine illumination beams during exposure (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 f, J) and the slopes φC and φR of the interference fringes are the same, respectively. In addition, even if the interference fringes are expressed as changes depending on the position of the spatial frequency (hi rate or curvature, etc.), the above expression remains the same (
be the same. (1) and (2), the left and right sides are not completely equal (in order to form interference fringes, the recording light is composed of a converging spherical wave and a diverging spherical wave). To be there.

By using aspheric waves and electron beams, (1) (
2) Although it is conceivable to make the difference between both sides of equation (3) smaller, it is extremely difficult and impractical. ) Therefore, within the range of permissible straight-line aberration, solve the approximately equal line 1 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 Fig. 4, it is assumed that the X, Y, Z coordinate system is used, and the IQ position of the reference light source (0, Vr, Zr) and the position of the convergence point of the object light (
0, O, Zo), the phase term of each electric field strength distribution on the hologram surface can be expressed as Equation (4), (
5) It can be expressed by the formula.

exp(-+ k x + y yr +
-, r) )...(4) exp(ik X +y + 0)... (
5) However, k is the phase term of the light intensity distribution of interference fringes recorded on the wave number hologram dry plate, which is expressed by equation (6).

cos(k(x +y +
. + 4--nuko17--1=V Yr
+Zτ2)) (6) From this, the spatial frequency t'c of the interference fringe and the slope φC of the interference fringe are as shown in equations (7) and (8).

fc= YΦ + y−yT a + a
+b)”x2/λCa −b −(7)φ
c-arctan((V-b+a(V!/r))/
[x(a+b))) -ψ...(8) However, a=
inψ y=R-r11cosψ R, rl: See Figures 3 and 4 In Figure 4, the relationship between the incident angle and the diffraction angle of light diffraction due to interference fringes recorded on the hologram 3 is
The direction cosine for the axis is m, and the direction cosine for the y axis is n2.
If the direction cosines of the diffracted light with respect to the
1o) The equation is as follows.

m−−m=I)−fc−λcosφc”(9)n−−m
=p-fc, λsinφc-(10) However, p is the order of the diffracted light, usually considering the first-order diffracted light.

lrc o, lrc R, lrRR, rQf) MJ
Once the relative fjx position &Ti and the distribution of the reproduction light on the hologram disk 3 are determined, a spot diagram corresponding to the rotation of the hologram disk can be drawn on an appropriate scanning plane. Based on this spot diagram, an iterative method yields lrco, lrc R, lrRR,
The predetermined position of lrRO*rQ can be determined.

As a more specific method, the linearity evaluation FA@E+Jj shown in equation (11), the evaluation function Ea that opens to convergence according to equation (12), and the comprehensive evaluation function E shown in equation (13) are determined, respectively. , Ir Co+lrcR, FRR+
Find the predetermined position of Fio+ra.

y) 2J/Nψi...(11) However, ψt: (i-1, 2,..., Nψ1) is one value of the rotation angle ψ of the hologram disk, which is appropriately sampled. A proverb is a sum that makes ψ1.

Ir (ψ) is a two-dimensional vector on the scanning plane and indicates the position of the diffracted light on the scanning plane. The subscript C of Irc (ψ) indicates the diffracted light from the center of the reproduction light distribution on the hologram disk, (Ir (ψ)) y is the component in the direction perpendicular to the scanning direction of Ir (ψ), (bottom y=2. (lrc(ψ)) y/
NΦ1ψ1.

/ N p t r7 cho] ]0-Σ) rpi (ψ) / NptI However, pi of F p□ (ψ)<i-1, 2,...
.

Np+) indicates diffracted light from one sample point that appropriately samples the distribution of reproduction light on the hologram disk. Σ accepts the sum with respect to pi.

The overall evaluation function that combines linearity and convergence is (13)
The formula is as follows.

E=ω+E+±ω2E2 (13) However, ω1. ω2 is the m-mirror constant.Next, a specific method of determining the Bragg condition will be explained.

In the case of a three-dimensional hologram, if the plaque condition of equation (3) is satisfied, high diffraction efficiency is given by It is sufficient that the angle of incidence is V around the Bragg condition.The diffraction efficiency under this condition is the 5th
As shown in the figure, although the high diffraction efficiency is reduced by 1, the diffraction efficiency decreases at the periphery of scanning. Another method is ψ−
The Bragg condition is satisfied by ±ψB (ψB~0). The diffraction efficiency under this condition is shown in FIG. 6, which shows relatively flat characteristics. As an example of a specific 4T calculation method, the evaluation of diffraction efficiency t311 is expressed by the formula (14), E3 = 6 days'' - (14) where θB = angle of deviation of the incident angle of the reproduced light from the Bragg condition E is the evaluation O1I number that combines linearity, convergence, and diffraction efficiency.
-ω+'E+ +ω2E2 +ωko Eko...
(13) However, ω1. ω, ω3 may be a weighting constant.

Note that although the partial analysis and calculations were made assuming a two-dimensional hologram, in reality, three-dimensional holograms are often used because of their high diffraction efficiency (q).

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

The object beam and the reference light source are placed at predetermined positions that satisfy lrco, lrcp, and ra thus obtained, and are recorded (exposed) over a plurality of areas on the hologram. After developing this and performing bleaching treatment to improve the diffraction efficiency as necessary, if the light source of the reproduction light is placed Jλ at a predetermined position that satisfies lrgR and reproduced, the diffracted light will be transmitted to the imaging surface. 4 above'? L line.

Non-abrasive pressure scanning will be performed.

In this way, in the device according to the present invention, first,
The scanning width is determined, the distance ra from the center of rotation of the hologram disk to the incident position of the reproduction light, and the distance 1d from the hologram disk to the scanning surface are determined, and using the above-mentioned evaluation 13!1 failure, This is to find the optimal position of each light source. The calculation results will be explained below. However, the fog light source is a He-Ne ray Ff (wavelength λ-0, 63 μm).
), the reproduction light source is a rod conductor laser (wavelength λ = 0.78μ
m) shall be used.

FIG. 7 shows the scanning plane (imaging plane) from the hologram disk 3.
Let the distance 1d at the end of 4 be 300 (mm>), and the distance from the reproduction light source to the hologram disk ~tlr is hl ill
This is a diagram in which the optimum value of lα calculated as described in 11ff is plotted on + and 611 axis, the distance ra (!-611) from the center of rotation of the hologram disk to the incident position of the reproduction light.

Further, FIG. 8 is a diagram in which the optimum Iff is plotted with rQ=5QIT1m, 1τ on the vertical axis and 1d on the horizontal axis.

In these diagrams, if IT is considered as a function of 1d and ra, it turns out that the characteristic lr represented by the broken line can be expressed by the following equation.

IT-<9. 4 x 10 °2 r a
+22 exp (2゜6 x 10'
I d) - (16) However,
The units of 1τ+'a and Id are mm.

9 and 10 are scaled diagrams in which the optimum IFfi is plotted, with the incident angle θr of the reproduction light on the hologram disk taken on the vertical axis instead of lr, and ra, Id, and 9 on the horizontal axis, respectively.

In these diagrams, if θr is considered as a function of ra and ld, it was found that the characteristic θτ represented by the broken line can be expressed by equation (17).

θr=<0.22'/ra+4.4X10-")ld
+7.5 (17) However, the unit of θr is degrees.

Similarly, FIGS. 11 and 12 are diagrams in which the vertical axis represents the reproduction light diffraction angle θd, the horizontal axis represents rB and Id, and the optimum values are plotted.

In these diagrams, if θd is considered as a function of ra and ld, it was found that the characteristic θd represented by the broken line can be expressed by equation (18).

θd-(2,2/ra+1.7xlO-")ld+22
...(18) However,
θd is the diffraction angle when the rotation angle of the hologram disk is such that the diffracted light scans the center on the scanning line, and I'l
The first place is degree.

FIGS. 13 to 15 are characteristic diagrams in which the linearity error, convergence spot diameter, and diffraction efficiency of the scanning spot formed on the imaging plane 4 were examined, respectively, in the apparatus according to the present invention. In this experiment, the wavelength λC is 0 as the reference light source.
．． A 63 μm He-Ne Rayleigh and a semiconductor radar with a wavelength λk of 0° and 78 μm were used as the light source for the reproduction light, and a scanning width of ±150 mm was obtained. Within this range, the linearity was ±100 μm and the maximum spot diameter was 100 μm.
.

The diffraction efficiency ψ-〇 is about 45% (this depends on the processing conditions of the hologram dry plate), which is the result of ;n less than 1;7.

Note that although a transmission type hologram disk is used in the above embodiment, an anti-Q'l type hologram may be used instead. Furthermore, using a 7-photoresist as a photosensitive material, the substrate can be etched by exposure, development, and oblique ion etching to form an echelette-shaped grating to improve the diffraction efficiency. In this case, exposure may be performed under conditions that satisfy only equations (1) and (2). In addition, the substrate is made of Si.
It is also possible to create an echelette-shaped lattice by anisotropic etching using crystals or the like. Roughly, the above-mentioned esh (knot-shaped lattice) may be used as the 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 simple (11
With a single structure, it is possible to realize an optical scanning device that can perform linear scanning, has an aberration-free convergence effect, and has high diffraction efficiency.

In addition, since the recording light (object light, reference light) and reproduction light have different wavelengths, when producing a hologram, it is necessary to
E-Nc lasers and Ar rays can be used, and
When playing back J3, the semiconductor laser is not used.

[Brief explanation of the drawing]

Figures 1a3 and 3 show main parts 4j and 4 of an example of the device according to the present invention, and Figure 1 is a side view of the state during recording and playback, and Figure 3 is the overall view of the same. A perspective view, FIG. 2 shows the main groove formation of an optical scanning device using a conventional hologram, FIG. 4 is an explanatory diagram for explaining aberration-free scanning, and FIGS. 5 to 15
The figure is a characteristic diagram of the device according to the present invention. 3... Hologram disk, 20... Reproduction light source, 2
1... E1 (((light exclusion, 22... object light source, 4...
・Imaging plane. Non-5-figure M6-figure flagger IUji) King car enters! ■I fL @ ra Tisfu hi front surface distance d Reproduction light incident fl 11 ra Reproduction light incidence IQ tl ra Tisfu further surface opening distance id Atsushi 13 rotation figure 14 figure 15 removal ヱ [i II

Claims (3)

[Claims] (1) In an optical scanning device using a transmission or reflection type hologram disk, the recording light (reference light, object light) used during hologram production and the reproduction light used during reproduction (scanning) are connected to a diverging spherical surface with different wavelengths. wave or convergent spherical wave, and the light source positions of the recording light and the reproducing light are selected at different predetermined positions where the light beams are obliquely incident on the hologram surface, and the position of the reproducing light source and the hologram disk are selected. An optical scanning device using a hologram, characterized in that the reproduced image on the imaging plane (scanning plane) scans in a straight line and without aberration by determining the distance from the hologram to satisfy the following formula. lr=(9.4×10^-^2ra+22)exp(2
．． 6×10^-^3ld) Where, lr: Distance between the light source of the reproduction light and the hologram disk (unit [mm]) ra: Distance between the center of rotation of the hologram disk and the incident position of the reproduction light (unit [mm]) ]) ld: Distance between the hologram disk and the scanning surface (unit [mm]) (2) In an optical scanning device using a transmission or reflection type hologram disk, the recording light (reference light, object light) used during hologram production and the reproduction light used during reproduction (scanning) are connected to a diverging spherical surface with different wavelengths. wave or convergent spherical wave, and the light source positions of the recording light and the reproducing light are selected at different predetermined positions where the light beams are obliquely incident on the hologram surface, and the reproducing light is transmitted to the hologram disk. An optical scanning device using a hologram, characterized in that the reproduced image on the imaging plane (scanning plane) scans linearly and without aberration by setting the incident angle to satisfy the following formula. θr=(0.22/ra+4.4×10^-^3)ld
Where, θr: Angle of incidence of the reproduction light on the hologram disk (unit: [°]) ra: Distance between the center of rotation of the hologram disk and the incident position of the reproduction light (unit: [mm]) ld: Hologram disk and scanning Distance to surface (unit [mm]) (3) In an optical scanning device using a transmission or reflection type hologram disk, the recording light (reference light, object light) used during hologram production and the reproduction light used during reproduction (scanning) are connected to a diverging spherical surface with different wavelengths. waves or convergent spherical waves, and the respective light source positions of the recording light and the reproducing light are selected at different predetermined positions where the light beams are obliquely incident on the hologram surface, and the rotation angle of the hologram disk is When the diffracted light is at an angle that scans the center of the scanning line, the reproduced image on the imaging plane (scanning plane) is scanned in a straight line and without aberration by setting the diffraction angle so that it satisfies the following formula. . θd=(2.2/ra+1.7×10^-^3)ld+
22 However, θd: Diffraction angle (unit [°]) when the rotation angle of the hologram disk is such that the diffracted light scans the center on the scanning line ra: The rotation center of the hologram disk and the incident position of the reproduction light distance (unit [mm]) ld: distance between hologram disk and scanning surface (unit [mm])