JPS5942854B2 - Multiple beam simultaneous scanning device - Google Patents

Description

[Detailed description of the invention] The present invention relates to a simultaneous multiple beam scanning device.

A laser beam is incident on an AO modulation element, and this AO
A plurality of sets of signals are applied to the modulation element to emit a plurality of first-order diffracted light beams from the AO modulation element, and these are
A scanning method in which writing and scanning are performed on a photosensitive recording medium by simultaneous and periodic deflection has been proposed in connection with computer output devices, facsimile receiving and recording devices, copying devices, and the like. The plurality of sets of signals are placed on a plurality of high-frequency carriers each having a different frequency, and are applied to the AO modulation element.

The emission direction of the plurality of first-order diffracted light beams emitted from the AO modulation element is determined by the frequency of the corresponding high-frequency carrier. Adoption of such a scanning method has the following advantages. That is, since beam splitting and beam modulation are performed simultaneously by a single AO modulation element,
There is no need to provide a separate high-speed optical modulator, and the structure of the multiple beam simultaneous scanning device is simplified.Since multiple lines are simultaneously written and scanned using multiple beams, it is possible to use deflection means such as a rotating polygon mirror or a galvano mirror. Even if the deflection speed is slowed down, the scanning speed is reduced, and by slowing down the deflection speed, the accuracy of deflection can be improved.Since the beam is divided and modulated, the clock frequency of the image signal can be reduced. This means that signal processing becomes easier.

On the other hand, in order to perform beam splitting, the frequency band of the high frequency to be applied to the AO modulation element, the so-called width of the modulation frequency band △
f is limited by the applicable bandwidth ΔF determined as a characteristic of the AO modulation element itself, and is further limited by the propagation velocity V of the ultrasonic wave propagating in the AO modulation element and the laser beam Beam diameter ψ.

is limited accordingly.

As the modulation frequency bandwidth Δf becomes smaller, the modulation speed of the divided first-order diffracted light beam becomes slower. Therefore, in order to perform high-speed write scanning, it is necessary to ensure the above-mentioned Δf as wide as possible. For this reason, in general, the laser beam incident on the AO modulation element is focused by a focusing lens system, and the AO modulation element is placed at the focal point, thereby achieving the above-mentioned ψ.

is made smaller and △f is made larger. FIG. 1 shows such a situation. That is, laser light source 1
The laser beam L-B emitted from is focused by a focusing lens system 4, and its focus P. The light is incident on the AO modulation element 5 located at . It goes without saying that numerals 2 and 3 in the figure represent plane mirrors. A plurality of sets (four sets in this example) of image signals are applied to the transducer 5a of the AO modulation element 5. of individual image signals,
For example, COS2πFlt, COS2π
F2t, COS2πF3t, COS27cf4t, information signals for AM modulating these are a1(t), A2(t),
If a3(t) and A4(t), then the image signal. ΣAi(
t) Applied to the transducer 5a in the form of COS2πFitl=1.

Then, the first-order diffracted light beams LBl, LB2, LB3 are transmitted in directions corresponding to the frequencies f1 to F4 of the high-frequency carriers.
, LB4 are emitted, and these first-order diffracted light beams LBi(1
-1 to 4) are the corresponding information signals Ai(t)(1-1 to 4)
), the intensity is modulated by

The O-order light beam LBO, which is emitted from the AO modulation element 5 without being diffracted, is cut off by a stopper 6.

The first-order diffracted light beams LBl to LB4 are incident on the focusing lens system 7, and are focused onto the recording medium 8 in the photosensitive area by the focusing action of the lens system.

Of course, in reality, a deflection means such as a galvano mirror is interposed between the AO modulation element 5 and the recording medium, and the first-order diffracted light beam LBi is directed onto the recording medium 8.
Deflect so that scanning is done in a direction perpendicular to the drawing.
Now, the problem is as follows.

That is, each of the first-order diffracted light beams LBi conveys information for one line, and in order to simultaneously write four lines on the recording medium 8, these first-order diffracted light beams LBi must be Although they must be separated from each other by the line interval and focused on the recording medium 8, if a lens with normal optical characteristics is used as the focusing lens system 7, these first-order diffracted light beams LBi will become as shown in the figure. , 1 point q
This causes the light to coincide and converge again at the top, making beam splitting meaningless. In order to eliminate this inconvenience, if a lens with special optical characteristics is used as the focusing lens system 7, the manufacturing cost of the focusing lens system is high, resulting in the inconvenience of making the device expensive. Although it is possible to write four lines at the same time by slightly shifting the position of the surface of the recording medium 8 to the right or left side in the figure with respect to point q, in this case, the writing on the recording medium 8 is The spot diameter of the emitted beam becomes larger, and the resolution becomes significantly worse. SUMMARY OF THE INVENTION An object of the present invention is to improve a multiple beam simultaneous scanning device in order to eliminate such disadvantages.

Hereinafter, the present invention will be described by way of examples with reference to the drawings.

First, the principle portion of the present invention will be explained with reference to FIGS. 2 and 3.

However, in order to avoid complexity, it should be noted that the same reference numerals as in FIG. 1 are used for items that are unlikely to be confused. Now, first of all, considering the reason for the inconvenience that was a problem in the explanation based on Figure 1,
This means that the AO modulation element 5 is the focal point P of the laser beams L and B by the focusing lens system 4.

This is due to the fact that it was placed in That is, in this case, the beam splitting by the AO modulation element 5 is performed at the focal point P. The beam splitting occurs starting at the branching point and the convergence point P. This results in a match. Then, the first-order diffracted light beam LBi is at P as the position of its light source. We will share the points. The function of the focusing lens system 7 is to form an image of the light source that generates the first-order diffracted light beam LBi on the surface of the recording medium 8, so as long as the first-order diffracted light beam LBi shares the light source, the light source that generates the first-order diffracted light beam LBi focuses on one point. It is natural that the images overlap. Therefore, in the present invention, in order to solve this problem, the AO modulation element 5. (7) The arrangement position is a focal point P of the laser beams L and B by the focusing lens system 4.

, shift from the above focal point P. and the beam branching point. The arrangement position of the AO modulation element 5 is a point P.

There are two ways to shift from A.
One method is to shift the O modulation element 5 on the optical path of the laser beams L and B so that it approaches the focusing lens system 4 (FIG. 2), and the other method is to shift the O modulation element 5 in the direction away from the focusing lens system 4 on the optical path. This is the method of shifting (Figure 3). The distance at which the AO modulation element 5 is disposed is determined by considering other conditions.

By shifting from the point, the aforementioned ψo becomes larger, and △
Considering that f will be reduced, it goes without saying that the shift distance should be minimized within the range that can achieve the purpose. Due to the reduction of Δf described above, the modulation speed per divided beam becomes slower due to the implementation of the present invention, but considering that the scanning speed is originally sufficiently fast in simultaneous scanning of multiple beams, the present invention The implementation is
It will be easily understood that the influence on the scanning speed is not so great as to pose a problem in practice. Now, the AO modulation element 5 is placed at point P.

On the other hand, when arranged in the positional relationship shown in Figure 2, 1
After the second-order diffracted light beam LBi exits the AO modulator 5, it is focused at points Pl, P2, P3, etc., and further spreads from there. Therefore, the point Pl,
P2, P3, etc. come to play the role of a light source for generating the first-order diffracted light beam LBi. These points Pl, P2,
P3 is point P. and the same plane S. is on the point Pl,
Since P2 and P3 are separated from each other, even if the first-order diffracted light beam LBi is focused on the recording medium using a normal focusing lens system, the focusing points are separated from each other on the recording medium. The AO modulation element 5 is placed at a point P.

On the other hand, when the arrangement is as shown in FIG. 3, each of the first-order diffracted light beams LBi is at a point P. Points Pll, Pl2, P which are on the same plane S and are separated from each other.
13 is emitted as a virtual light source. Therefore, the first-order diffracted light beam LB is focused on the recording medium by a normal focusing lens system.
When i is focused, the focusing points, which are images of the virtual light source, are also separated from each other. In this way, by implementing the present invention, it has become clear that the focal points of the split beams can be separated on the recording medium even if a focusing lens system with normal optical characteristics is used.

However, in order to simultaneously scan multiple lines, the convergence points of the split beams must be located at equal line intervals on the recording medium.

For this purpose, first, the above Pl, P2, P3 points,
The three points Pll, Pl2, and P are the plane S.

Or they must be equally spaced on S. To achieve this objective, it is sufficient to correlate the frequencies of the high-frequency carriers under certain conditions. less than,
The above conditions will be explained. As is well known, the polarization angle θ of the first-order diffracted light beam LBi emitted from the AO modulator 5
i (see Figure 4) is the wavelength λ of the laser beams L and B,
The propagation velocity V1 of the ultrasonic wave transmitted through the AO modulation element 5 depends on the frequency Fi of the high frequency carrier, and is given by the following equation according to the so-called black condition.

Since λFi is small compared to V, this equation can be written as θi2/1 in a good approximation.

Since V is a constant specific to the material of the AO modulation element 5, and λ is a constant specific to the laser beams L and B, in a practical device, the above deviation angle θi depends only on the frequency Fi of the high frequency carrier. Dependent.

Therefore, when applying multiple sets of information to the AO modulation element, if the frequencies of the high-frequency carriers that carry these signals are set in an arithmetic series, the first-order diffracted light beams will be shifted from each other by a constant angle. Shoot in the direction. Therefore, if the above fixed angle is made sufficiently small, points Pl, P2, and P3, which are the focusing points of the first-order diffracted light beam, and point Pll, which is a virtual focusing point, can be obtained.
, Pl2, and Pl3 are arranged at equal intervals on the SO plane and the S plane, respectively. Here, we will give a practical numerical example.
Now, assuming that a He-Ne laser is used as the laser light source 1 and PbMOO4 is used as the crystal for the modulation part of the AO modulation element 5, the above λ and V are respectively.

Therefore, suppose that six sets of information are simultaneously applied to the AO modulation element, and the frequencies of the high-frequency carriers that carry these are set to f1-175.5MHz, f2-184MHz, and f2, respectively.
3-192.5MHz, f4-201. MHz, f5-
209.5MHz, f6-218MHz, the declination angle for these frequencies is therefore, in this case,
The focusing lens 4 has a focal length of 120 mm, and the AO modulation element 5 is arranged as shown in FIG.
If placed 40 mm from the point, the convergence points of the six first-order diffracted light beams emitted from the AO modulation element according to the above frequency will be lined up at intervals of 601 tm on the SO plane.

Therefore, in order to simultaneously scan six lines on a recording medium with a line spacing of 125 μm, for example, a focusing lens is used to form an image of the convergent point on the recording medium using six first-order diffracted light beams. The system magnification should be set to 2.08 times.

If the above magnification is set to 1.33 times, the line spacing will be 83μ.
m, and the scanning line density is 1211nes/Mm
can be recorded. Here, we will briefly discuss the focusing lens system that focuses the first-order diffracted light beam onto the recording medium. The focusing lens system is composed of a single lens system or a plurality of lens systems, and the lens system as a component is composed of a single lens or a plurality of lenses. When the focusing lens system is a single set, its installation position is relative to the deflection output stage such as a galvanometer mirror, but this depends on the shape of the recording medium and the image signal. It is determined by the method of application of . If the recording medium is flexible, such as in the form of a sheet, a single set of focusing lens system is
It is arranged between the Q modulation element and the deflection means.

The recording medium is arranged to have a curvature at the focal position of the first-order diffracted light beam, with the center of curvature being the center of deflection of the beam by the deflecting means. When the recording medium is a so-called photoreceptor drum or the like as shown in Fig. 1, and the scanning section by the first-order diffracted light beam is linear, a single focusing lens system is a rotating polygon mirror or the like. It is interposed between the deflection means and the recording medium.

In this case, as a focusing lens system, the so-called f-θ
A lens system is used. When an f-θ lens system is not used as the focusing lens system, the timing of applying 6 pixel information in applying the image signal to the AO modulation element is determined according to the deflection angle α of the first-order diffracted light beam by the deflection means. COs2
It must be varied according to α. By the way, since the plurality of first-order diffracted light beams emitted from the AO modulation element are emitted radially from the branch point of beam splitting, the beam interval increases as they leave the AO modulation element, which is a problem due to the design of the device. In cases where the distance between the AO modulation element and a deflection mechanism such as a galvano mirror or a rotating polygon mirror becomes large, and in a method in which a focusing lens system is disposed between the deflection mechanism and the recording medium, the above-mentioned deflection mechanism The effective width of the mirror surface in the direction of the rotation axis must be increased. In order to avoid this, in this case, another set of focusing lens systems may be interposed between the AO modulation element and the deflection mechanism to suppress the beam spacing from increasing. In this case, the focusing lens system is composed of two sets of lens systems, and it goes without saying that in this case, the above-mentioned magnification means the combined magnification of the two sets of lens systems. FIG. 5 schematically depicts one embodiment of the invention.

However, it should be noted that even in this figure, the same reference numerals as in FIG. 1 are used for parts that are unlikely to be confused. The device uses a 6-line simultaneous write/scan method, uses a He-Ne laser as the laser light source 1, uses PbMOO4 as the crystal of the AO modulation element 5, and uses a focusing lens system 4 with a focal length of 120 mm. The frequencies of the high-frequency carrier are f1-175.5MHz, f2-184MHz, and f2, respectively.
3-192,5MHz, f4-201MHz, f5-2
09.5MHz, f6-218MHz is used.

Then, from the focusing lens system 4, there is a distance of 80 m71L on the optical axis.
Six first-order diffracted light beams LBl, LB2,...LB6 emitted from the AO modulation element 5 disposed at the positions of
(To avoid clutter, LBl, LB3, LB
Only 6 is shown. ) is S. Focus on the surface at 60 μm intervals. The code 9 indicates a beam expander,
The beam diameters of the laser beams L and B are once expanded by a beam expander 9, and then they enter a focusing lens system 4.

Reference numeral 71 is a lens system, and reference numeral 72 is an f-θ lens system, which constitute a focusing lens system.

Although not shown, a rotating polygon mirror serving as a deflecting means is provided between the lens system 71 and the f-theta lens system indicated by the reference numeral 72. A first-order diffracted light beam L is formed by a focusing lens system composed of a lens system 71 and an f-θ lens system 72.
Bi (1-1 to 6) is 83μ on the recording medium 8
In order to focus at intervals of m, the combined magnification in the above focusing lens system must be 1.33 times.

As the lens system 71, one with a focal length of 184 mm was used, and as the f-θ lens system 72, a focal length of 245.8 mm was used.
When using a lens system in which the distance between the first lens surface and the second principal point is 33 degrees, the object-world side focal plane of the lens system 71 must be S to satisfy the above condition.

The distance between the lens system 71 and the image field side principal point of the f-θ lens system 72 is set to 200 mu, and the scanning plane of the recording medium 8 is aligned with the image field side focal plane of the f-θ lens system 72. The position of the recording medium 8 may be determined so that they match. The rotating polygon mirror serving as the deflecting means is arranged so that the center of beam deflection is located 30 mm from the object-field side lens surface of the f-theta lens system 72. The recording medium 8 is a photoconductive photoreceptor drum, and by rotating its charged surface in the direction of the arrow while performing write scanning in a direction perpendicular to the drawing, six lines at a time,
An electrostatic latent image is formed according to an image signal.

By making the electrostatic latent image thus formed visible with toner, and transferring and fixing the resulting visible image onto a recording sheet, a recorded image corresponding to the image signal can be obtained.

By adjusting the beam diameter expansion rate in the beam expander 9, the spot diameter of the beam focal point on the recording medium can be finely adjusted, and the frequency of the high frequency carrier applied to the AO modulation element or the lens system can be adjusted. 7
1 or by moving the position of the f-θ lens diameter 72 by a minute distance on the optical axis, the line spacing of the writing scan can be finely adjusted. According to the present invention, the structure is simple and the cost is low. A low cost, multiple beam simultaneous scanning device can be provided.

Of the n first-order diffracted light beams emitted from the AO modulation element,
Among them, write-out scanning is performed using m books, and (n-m) books are
Needless to say, it can be used for beam intensity correction and for detecting the timing to start writing.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining a conventionally known beam splitting method and problems when applying it to simultaneous scanning of multiple beams, and FIGS. 2 to 4 illustrate the principle of the present invention. FIG. 5, which is a diagram for explaining the parts, is an optical layout diagram schematically showing only the main parts of one embodiment of the present invention. 1... Laser light source, 4... Focusing lens system, 5... AO modulation element, 71...
Lens system, 72... f-θ lens system, 8...
...Photosensitive recording medium, 9...Beam expander.

Claims (1)

[Claims] 1. An AO modulation element to which n signals having n (≧2) high-frequency waves having different frequencies as carriers are applied, and a first focusing lens that focuses the beam diameter of a laser beam incident on this AO modulation element. Depending on the system and the above signals,
A deflection means for simultaneously and periodically deflecting m of the n first-order diffracted light beams emitted from the AO modulation element in mutually different directions;
A second focusing lens system is provided on the photosensitive recording medium and is placed close to each other and focuses the laser beam at a predetermined interval;
A multiple beam simultaneous scanning device characterized in that the arrangement position of the AO modulation element is determined so that the branch points of n first-order diffracted light beams by the O modulation element are separated from each other.