DE3321482A1 - Scanning device having a holographic deflecting device - Google Patents

Abstract

A scanning device, in which a holographic deflecting device is used, has a hologram which is recorded on a rotary disc, a device by means of which light beams are directed onto the hologram, and an optical device with a distortion which has the effect that light beams emerging from the hologram move linearly on a surface that is to be covered.

Description

Scanning device with a holographic Deflector

The invention relates to a scanning device with a holographic deflection device for deflecting light beams by means of a hologram for a scanning movement for use in a recorder never one Copier or a display device.

Generally used in a laser beam printer or a Laser beam display device for recording or Representation of an image by deflecting light rays to a scanning movement of a galvanometer mirror or a polygonal rotating mirror1 used. With a galvanometer mirror however, linear scanning is usually difficult to bring about at high speed, so that therefore normally a Galvanometerpiegei only for scanning

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is used at low speed. on the other hand must be in a system with a polygonal rotating mirror Heavy material such as glass or metal are put into circulation, so that there are problems with such a system occur when the moment of inertia becomes large and the Speed is limited, a surface deformation during rotation by gravity or centrifugal force and an improvement in performance such as leads to a very high cost in terms of the inclination angle of each surface or the surface accuracy.

As a method for solving these problems, JP-OS 161211/1980 known a method in which a holographic Deflector is used. This holographic

According to the illustration in FIG. 1 a spatial hologram or a relief hologram of the drawing 2 on a thin turntable 1 and deflects light beams for scanning movement by the fact that the disc is set in rotation about an axis of rotation 3; these

Deflector has attention as a light deflector energized, which are compact, lightweight, both for mass production and for high speed operation is suitable and inexpensive.

This holographic scanning device or deflection device, which has the advantages listed above, however, has the following shortcomings on the other hand:

(a) The direction of those falling on the hologram 2 .

Light rays is limited;

(b) when an imaging lens is used is the optical axis thereof inclined with respect to the surface of the hologram 2; and

.

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(c) the diffraction angle of the light rays is large and it is difficult to make a relief hologram.

That is, in this holographic deflector, the Angle of incidence 8i of the light rays falling on the hologram 2 Li limited to a special value, so that the linearity of the light rays emerging in the deflection direction Ld is complied with. This limitation with regard to the Einfallvi / inke Is 9i results in practical use Restriction with regard to the positional relationship between the light source and the holographic deflection device. Furthermore, the optical axis of the imaging lens is so too place them with the chief ray of the exit light rays Ld coincides and with respect to the axis of rotation 3 of the Turntable 1 is not parallel, but inclined; therefore, in the case of the heater equipment, the design is difficult and in some cases it is impossible to have a free space to ensure. Furthermore, in this holographic deflector, the angle of incidence Bi and the exit angle Bd with respect to the surface of the hologram 2 are approximately 45 ° and it is a deflection angle of about 90 ° with respect to the direction as the diffraction angle of the light of the incident light rays Li required so that for example in the case of the holographic deflection device with the design of the surface as a relief or grid the deflection angle is too large and such a deflector is difficult to manufacture. If the deflector can be produced anyway, it cannot be called practical because of the energy efficiency is very low.

The invention is based on the object of a scanning device with a holographic deflector / u create where the linearity of the deflection can be achieved

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is without the angle of incidence with respect to the hologram and the exit angle are restricted.

A further aim of the invention is to create a scanning device with a holographic scanner which enables a beam point sweeping over an area to be scanned to move at a uniform speed with respect to the rotation of the hologram.
^y

In the scanning device according to the invention with the holographic Deflection device is the non-linearity of the light rays emerging from the hologram are switched off in that the distortion of an optical imaging ο

systems is used. Furthermore, the uniformity of the

Speed achieved in that the hologram of

holographic deflector is designed non-linear.

The invention is explained below on the basis of exemplary embodiments explained in more detail with reference to the drawing.

Figure 1 is a representation of a holographic deflector -r-.

Figure 2 shows an embodiment of the scanning device with a holographic deflector.

QQ Figures 3A to 3G show distortion characteristics of the scanning device shown in FIG.

FIG. 4 shows distortion characteristics according to FIG. 3 in relation to the image height and the angle of incidence.

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Figure 5 is a graph showing the

Shows the relationship between the angle of incidence and the angle of exit of the holographic deflection device shown in FIG.
5

Figure 6 shows a holographic deflection device according to an embodiment of the scanning device.

FIG. 7 illustrates the design of the hologram of the holographic deflection device shown in FIG.

One describes the principle of operation of the holographic Deflection device according to FIG. 1, a hologram 2

a diffraction grating made up of straight lines with equal pitch 15

Such a hologram 2 can be a spatial Hologram or a surface design hologram of the Be lattice execution. It is now the respective pitch of the diffraction grating formed by the hologram 2 is denoted by ρ. When using the in Figure 1 of the coordinate system shown, the light ray vector of the incident light rays Li

IK = ( ΐ, m, n)

= (cos θϊ, sin Bi, 0) ... (1)

is defined, the wavelength of the light is' \ (μιη), the diffraction order is N, the angle of rotation of the hologram 2 is φ and the state in which the diffraction grating of the hologram 2 coincides with the Z axis is given by ^ = O , then the light ray vector IK ¹ of 30 results

emerging light rays Ld from the following equation:

IK ¹ = ( V , m ¹ , n ') ... (2)

where X ¹ , m ¹ and n ^{1 are given} by the following equations:
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V = Il - (m) ² - (n ') ² } ^1/2 ... (3) m = sin θί + (NA / p) cos φ ... (4) η = - (NX / p) sin φ ... (5)

If the diffraction order N is only the first order and the wavelength ^ is constant, the vector bzvi /. the direction IK ^{1 of} the exiting light rays Ld as a function of the angle of rotation Φ with the angle of incidence 8i of the incident light rays Li and the pitch ρ expressed as a parameter vi / earth.

On the other hand, there is between the pitch p, the Wavelength λ, the angle of incidence Si and the angle of exit 8d the following relationship:

sin ei + sin 9d = Νλ / ρ ... C6)

From this, ρ can be determined if Bi and Bd are determined are.

The Z and Y coordinates of a surface to be scanned such as a recording material a point at a distance F from the hologram 2 formed Photographs are given by:

Y = F. ImVA ¹ I ... (8)

Figure 2 shows an embodiment of the scanning device with the holographic deflection device. In Figure 2 etc. denote the same reference numerals in Figure 1 ' Identical elements are referenced.

In the embodiment of Figure 2 is on the house

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the step surface of the hologram 2 is an imaging lens 10
attached with an optical axis 0, which runs parallel to the axis of rotation of the turntable 1.

It is now assumed that the distortion properties the imaging lens 10 through

y = g (6) = F. (e + a ₃ e ³ + a ₅ e ⁵ + a _? e ⁷ + ..)

... (9)
are given, where θ is the angle of incidence at the imaging lens 10 and F is the focal length of the imaging lens bzu /. of the imaging lens. If 8 '= cos "(. £') applies, the position Y ^!, Z 'of a light image formed on the imaging plane is given by:

Ζ '- gt8') - n '. {( _M. ) ² + ( _η ·) ² Γ ^1/2 ^ _(ιΐ)

It can be seen from these equations that the position Y ', Z' of the light image is determined by the distortion properties
the imaging lens 10 is affected.

Figures 3A to 3G illustrate scan lines at

the scanning with the light image in this case, wherein in 25

In these figures, a deviation in the Y-axis direction with respect to the scanning range in the Z-axis direction with the exit angle Bd as a parameter for various Angle of incidence θι of the halogram 2 is plotted. at

"-. of this calculation, however, are the values F = 100 (mm),

Assuming Λ = 0.8 μπι and N = I, the origin of the Y-axis taking the position of the light image at ^ = O. Figures 3A to 3D relate to a case in which the distortion properties a, = a, - = a ₇ = 0,

ο, - while Figures 3E to 3G relate to a case

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that for the distortion properties a, = 0.5, a ,. = 0.33 and a- = 0 applies.

c FIG. 4 is a graphic representation in which the distortion that occurs is plotted. In FIG. 4, the image height y is plotted on the ordinate, while the angle of incidence Gi is plotted on the abscissa. A characteristic curve corresponds to the position Y, Z determined from equations jQ (7) and (8) and illustrates the case that y = F tan8 applies, a characteristic curve β illustrates the case that according to FIGS. 3A to 3Dy = FB applies, and a characteristic curve y illustrates the case in which, according to FIGS. 3E to 3G, y = F '(8 + Ο, 5Θ ³ + 0.338 ⁵ ) applies.

FIG. 5 is a graph showing the relationship between the angle of incidence Oi and the optimal exit angle 9d is applied. In FIG. 5, one corresponds to Curve B corresponds to the case according to FIGS. 3A to 3D, while a curve C corresponds to the case according to FIGS. 3E to 3G; on curve C is the value for the condition Bi = Bd 8i = Bd = 41 ° to be determined. From Figures 3, 4 and 5 the following conditions can be seen:

,

(d) The relationship between the angle of incidence θί

and the optimal exit angle Bd, which is the linearity the scan line of the light image changes with the distortion properties of the imaging lens 10;

^ου . (e) the optimum exit angle Sd becomes large as shown by the curve B in Fig. 5 when the distortion characteristic of the imaging lens 10 is negative;

(f) if the distortion characteristics never of the imaging lens 10 is negative, the deviation of the scan line becomes

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from the straight line large; and

(g) If the distortion characteristic of the imaging lens is positive, as illustrated by the characteristic y in FIG. 4, the angle of incidence θι and the optimal exit angle 8d become small and the deviation also becomes small.

From the above analysis it can be seen that in the jQ combination of the hologram 2 and the imaging lens 10 " the problems inherent in the prior art can be solved in that the imaging lens 10 has a positive distortion characteristic or positive distortion properties.

That is, it existed earlier as described above to achieve linearity solely by means of the hologram 2 under the influence of the effect of the inclination the only solution (Bi, 9d) = (45 °, 45 °), while to achieve the Linearity through a combination of the hologram 2 and the imaging lens 10 compared to the case that only the hologram 2 is used, the degree of freedom is increased is. As a result, in order to achieve linearity, each of the hologram 2 and the imaging lens 10 a curve of positive curvature (or negative curvature) and a curve of negative curvature (or positive curvature) be chosen so that they are offset from one another.

In the embodiment shown in Figure 2 runs although the optical axis 0 of the imaging lens 10 is parallel to the axis of rotation 3 of the turntable 1, but the optical Axis cannot always be parallel to the axis of rotation. That is, the imaging lens 10 can be arranged so that at the exit of the exit light rays emerging from the hologram 2 and falling on the imaging lens 10

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Ld from the imaging lens 10 related to the exit angle on the axial direction of the axis of rotation 3 becomes even greater.

There is now a method of achieving uniformity the speed described. If the scan line is linearized as described above, primarily the distortion properties of the imaging lens 10 determined. In the embodiment, taking into account of the distortion properties of the imaging lens 10, the uniformity of the speed of the light image achieved in that the change in the direction of incidence over time of the light rays falling on the imaging lens 10 is controlled with the circulation of the hologram. to

for this purpose, in the exemplary embodiment, the scanning 15

device the hologram on a group of non-linear, rather than linear, curves in the conventional manner.

Once the distortion properties of the imaging lens 10 are set, is with respect to the angle of rotation p.primarily the target exit direction of the light rays from the hologram is determined in order to increase the speed to keep the light image uniform at the imaging plane. Namely, as from the above equation (11)

"P. It can be seen, which represents the position of the light image on the surface to be swept, with defined distortion properties g (8) of the imaging lens 10, the values m ¹ and n ^{1 must} assume predetermined values so that the position of the light image on the area to be swept

QQ is a desirable location. The design of the hologram is used to freely set the values m 'and n ^1. Usually a linear hologram rotates through the angle P when the axis of rotation rotates through the angle Gi; through the non-linear design of holograms 2a, 2b, 2c, ...

however, according to the illustration in FIG. 6, it is possible to use the

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Angle of rotation of the holograms in relation to the angle of rotation D

the axis of rotation 3 to change. FIG. 7 is an enlarged view showing the configuration of that shown in FIG Shows holograms. According to the illustration in FIG. 5

7, the structure of the hologram consists of one group

curves arranged at the same pitch ρ, the concave surfaces or parts of which face the axis of rotation are. The design of group 11 of the curves is determined as follows: If as described above 10

the distortion properties of the imaging lens 10 are determined, the desired light beam vector IK ¹ = (m ¹ , n ¹ , i! ¹ ) is determined with respect to the angle of rotation β of the holographic deflection device. To achieve the values m ^1, n 'and ^ ^1, the angle B thereby advertising bestirnt,

that the value ρ in equations (3), (4) and (5) is replaced by (ß - B) to achieve the desired values m ¹ , n ¹ and l ^{f as} follows:

m '= sin 9i + (Νλ / ρ) «cos (φ - 0) ... (12) 20th

η ¹ = - (Νλ / ρ) «βίηίφ - 0) ... (13)

where the actual angle β is used. As a result, the envelope of a sequence of data for this 25th

Angle θ be the group 11 of the curves of the diffraction grating.

That is, the choice is made such that at a point where the incident eight rays Li are incident when the HoIo-OQ grams 2a, 2b, 2c ... are rotated by $ , the group 11 of the curves are regarded as a linear diffraction grating can, which is inclined essentially by (0 - Θ); this achieves speed uniformity.

ο, - In the above description, with regard to the

:::: · ::.: J ό I I ^ ö z

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In order to achieve the uniformity of speed, consider a case where the ^{angle Θ 'formed between the light ray vector IK 1} and the optical axis of the imaging lens 10 of the equation Θ ¹ = cos £'

corresponds, namely the optical axis 0 of the imaging lens 10 and the direction of the X-axis shown in Figures 1 and 2 coincide with one another; if, however, too / regard the optical axis of the imaging lens 10 and the direction of the rotation axis 3 of deflector a predetermined angle "ψ is, the design of the curve group can be prepared by the skilled person easily in this case are defined by the fact that the system of coordinates by the angle ψ is pivoted so that the optical axis of the imaging lens 10 and the X-axis over-

. . .

agree.

The group 11 of curves can easily be replaced by an expedient numerical calculation can be determined based on the above equations, however, the Ge-20

shaping this group of curves into a complex one

Function equation if the design is to be determined precisely. Considering the method of manufacture however, of the actual diffraction grating, it is convenient and practical to approximate it by an arc of a circle 25th

make the center of which lies in the direction of the axis of rotation of the deflector. In this case it is necessary with the help of a computer to bring about such a division that the deviations from linearity and the uniformity of speed are minimal.

A scanning device that uses a holographic deflector is used, comprises a hologram recorded on a rotatable disk, a device with the light rays are quenched onto the hologram, and

an optical device with a distortion on it, dir

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causes the move light rays emerging from the hologram linearly

Claims (5)

Claims 1. Scanning device with a holographic deflection device, characterized in that a non-linearity the scan line of the means of the holographic deflection device device (1, 2) deflected light rays by the distortion properties of an imaging lens (10) is corrected, whereby the scan line is linearized. 2. Scanning device according to claim 1, characterized in that that the imaging lens (10) has distortion properties through which the angle formed by the light rays emerging from the imaging lens with respect to the The axis of rotation (3) of the deflection device (1, 2) is formed larger than the angle u / ird, which is formed by the on the imaging lens falling light rays with respect to the axis of rotation of the Deflector is formed. 3. Scanning device according to claim 1 or 2, characterized characterized in that the optical axis (0) of the imaging lens (10) essentially parallel to the axis of rotation (3) of the Deflection device (1, 2) runs. 4. Scanning device according to one of claims 1 to 3, characterized in that the hologram (2) the holograph! see deflection device (1, 2) non-linear under the same - 2 - DE 3082 Pitch is designed. 5. Scanning device according to claim 4, characterized in that that the hologram (2) has a group (11) of arc curves, the centers of which in the direction the axis of rotation (3).