JPH0328713B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to electro-optic line printers, and more particularly to illumination nulls that occur between adjacent pixels printed by the printer.
The present invention relates to a device for reducing

Conventionally, electro-optic devices having multiple individually addressable electrodes have been used as multi-gate light valves for electro-optic line printers.
For example, U.S. Pat. There is. In addition, the 31st to 32nd issue of Electronic Design magazine published on July 19, 1979.
``Light Gate Gives Data Recorders Improved Hardcopy Resolution,'' Machine Design Magazine, July 26, 2008
“Polarizing filter that blots analog waveforms” described on page 62 of Volume 51, No. 17 (Design), and
Such a technique is similarly shown in "Data Recorder for Erasing Linear Problems" published on pages 56-57 of Design News magazine published on February 4, 1980.

Further, steady progress has been made in the development of multi-gate light valves of the above type and in the application of the light valves to electro-optic line printing. For example, US Patent Application No. 187911 (filed date: September 1980) by the present inventor.
17, an "electro-optical line printer") is a series of input data streams in which the displayed image is printed onto a standard photosensitive recording medium using a multi-gate light valve that is illuminated by a conventional light source. It has been shown that The same specification describes an input data sample and hold technique that minimizes the output power required by the light source.

Furthermore, a similar application was filed on September 17, 1980.
WDTurner Invention U.S. Patent Application No.
No. 187936, "Proximally Coupled Electro-Optical Device," states that the electrode and electro-optic element of a multi-gate light valve can be physically distinct components, and the two can be pressed together or rigidly integrated. It is disclosed that "proximity coupling" can be obtained by doing so. In addition, U.S. Patent Application No. 188171 (filing date: September 17, 1980, title of invention: "Integrated Electronics for Close Coupling Electro-Optical Devices") filed by the present applicant on the same day includes, for example, a VLSI silicon electrode actuation circuit. WDTurner discloses that electrical connections to the electrodes of the above-described close-coupled multi-gate light valve can be made relatively easily if the electrodes are formed by appropriately patterning the metallization layer of the WDTurner.
U.S. Patent Application No. 187916 (filing date;
September 17, 1980, the invention (titled "Differential Encoding for Ambient Field-Responsive Electro-Optical Line Printers") is based on the number of electrodes required by a multi-gate light valve in order for an electro-optic line printer to obtain the desired resolution. discloses that if the input data can be encoded differentially, it can be halved.

Additionally, the inventors' U.S. patent application no.
According to No. 248939 (filing date: March 30, 1981, title of invention: "Multilayer plug-in electrode for multi-gate light valve"), by using two or more layers of plug-in electrodes, multi-gate light valves are electro-optical. U.S. Pat. A gated light valve ("Gated Light Valve") is disclosed with respect to a convergent arrangement of electrodes that can simplify the imaging optics required for light valve applications in electro-optic line printers and the like. A previously filed application entitled "Nonuniformity Compensation for Multi-Gate Light Valve" by the present inventors discloses a technique for subtracting independent variables from data in the optical output of a multi-gate light valve.

Despite these advances, the characteristics of conventional electro-optic line printers result in undesirable illumination nulls between adjacent pixels of printed image lines. This illumination
Nulls cause discontinuities in printed images and significantly deteriorate image quality. Further, a straightforward method of removing illumination nulls by defocusing or blurring the printer's image forming system cannot generally be employed because electro-optic line printers rely on coherent image formation.

According to the invention, means are provided for coupling the light of a pixel, which is irradiated onto the image optical system of an electro-optical line printer, to an area adjacent to the pixel, thereby achieving a cross line movement of the recording medium. motion) and/or the limited resolution of the printing process can reduce, if not eliminate, illumination nulls. To achieve this, a tilted phase step is provided in or near the Fourier transform plane of the imaging optics, which transforms each illuminated pixel into a double spot diffraction pattern tilted with respect to the transverse motion of the recording medium. There is a means. Another method is to provide a light scattering element just in front of the image plane to scatter the light from the illuminated pixels, and to impart a high spatial frequency to the interference pattern created by this scattered light. There are means to prevent this from being resolved into the printing process.

Hereinafter, the present invention will be explained based on embodiments shown in the accompanying drawings. It should be noted that the present invention is not limited to these embodiments in any way, but includes all modifications and equivalent techniques included within the scope of the invention described in the claims.

Electro-optical line printer 11 is shown in Figures 1 and 2.
The electro-optical line printer 11 is shown schematically and includes a peripheral field-responsive multi-gate light valve 12 for printing an image on a photosensitive recording medium 13. As shown, the recording medium 13 is a photoconductively coated drum 14.
Then, it rotates in the direction of arrow 15 in the figure. Note that the means for rotating the drum 14 is not shown.

However, other xerographic or non-xerographic recording media can be used as the recording medium, such as photosensitive film or paper, as well as photoconductively coated belts or plates. In general, the recording medium 13 can be regarded as a photosensitive medium that is exposed to light while traveling in a cross line direction or a line pitch direction with respect to the light valve 12.

A light valve 12 is shown in FIGS. 3 and 4 and is comprised of an optically transparent electro-optic element 17 and a plurality of individually addressable electrodes 18A-18I. At present, the most promising electro-optic materials for such light valves are LiNbO ₃ and LiTaO ₃ , but other materials include BSN, KDP, KD ^x P,
The use of Ba ₂ NaNb ₅ O ₁₅ and PLZT is also conceivable.
In this embodiment, the light valve 12 operates in TIR (total internal reflection) mode. Therefore, the electro-optical element 1
7 is preferably a Y-cut crystal of, for example, LiNbO ₃ , which Y-cut crystal has mutually opposing optically polished input faces 22 and output faces 23 and a similarly optically polished reflective face extending between the two faces. It has 21. In addition, the width of each electrode 18A to 18I is generally 1 to 1.
30 microns, and the electrode spacing is 1-30 microns.

With reference to FIGS. 1 to 4, the light valve 12
To briefly describe the effect of (An angle of incidence that is not larger than the critical angle of incidence for total internal reflection from the reflecting surface 21)
is transmitted from the input surface 22. input light beam 24
is diffused in the lateral direction (by means not shown), so that the entire width of the electro-optical element 17 can be illuminated substantially uniformly, passing through the electro-optical element 17 to the reflecting surface 21 in the substantially central part thereof. is focused (by means not shown) in a wedge shape on top. Next, the input light beam 24 is totally internally reflected from the reflecting surface 21 and becomes an output light beam 25, which exits the electro-optical element 17 via the output surface 23.

The phase plane or polarization of the output light beam 25 is
It is spatially modulated according to the data given to 8A to 18I. Specifically, according to the above data, the distance between each pair of adjacent electrodes, for example, electrodes 18B and 18C.
In between, when a voltage drop occurs, the peripheral electric field between the corresponding electrodes influences the electro-optical element 17, thereby making it possible to locally change the refractive index of the electro-optical element 17. In order to efficiently couple the above-mentioned peripheral electric field to the electro-optical element 17, each electrode 1
8A to 18I are provided on the upper surface of the reflective surface 21 or at positions close to the upper surface. In the illustrated embodiment, each electrode 18A-18I is preferably mounted on a suitable substrate, such as a VLSI silicon circuit 28;
This VLSI silicon circuit 28 is indicated by the arrow 29 in the figure.
The electrodes 18A to 18I are crimped or fixed to the electro-optical element 17 in the direction indicated by 30.
can be held in contact with, or at least in close proximity to, the reflective surface 21. With this configuration, the VLSI circuit 28 has an electrode 18A.
It has the advantage of being able to make the necessary electrical connections to ~18I. Alternatively, instead of the above, the electrodes 18A to 18I are connected to the reflective surface 2 of the electro-optical element 17.
It is also possible to arrange it on 1.

For purposes of explanation, it will be assumed that the phase front of output light beam 25 is spatially modulated according to data provided to electrodes 18A-18I. Schilleren central dark-area or bright-area imaging optics are therefore used to convert the phase front modulation of the output light beam 25 into a corresponding modulation intensity profile and to provide the magnification necessary to obtain an image of the required size. be able to.

More specifically, as shown, the central dark area imaging optical system 31 is comprised of a field lens 34, a central stop 35, and an imaging lens 36.
The field lens 34 is the output surface 23 of the electro-optic element 17.
and the central stop 35, and all zero-order diffraction components of the output light beam 25 are focused onto the central stop 35. However, the higher-order diffraction components of the output light beam 25 are scattered around the central stop 35, but this scattered light is focused by the image forming lens 36 and placed on the recording medium 35.
3, resulting in light bulb 12
An intensity modulated image is obtained.

Of course, once the input light beam 24 is polarized (by means not shown), the output light beam 25 is spatially modulated by the light valve 12 according to the data applied to the electrodes 18A-18I. In this case, a polarization analyzer (not shown) can be used to convert the spatial polarization modulation of the output light beam 25 into its corresponding modulation intensity profile.

Note that the phase plane modulation or polarization modulation of the output light beam 25 is referred to as "P-modulation" from a higher perspective.
In addition, the readout optical system 31 is assumed to be a "P-photosensitive image optical system."

In FIGS. 4 and 5, each electrode 18A to 18
I are individually addressable. Therefore, to print an image, differentially encoded data samples for successive rows of the image are transferred to electrodes 18A.
~18I. Specifically, each data sample, apart from the initial sample for each row of the image, differs in size from the previous differentially encoded sample by an amount corresponding to the size of a particular input data sample. It has a certain quality. The first differentially encoded sample in each row is at a predetermined potential, eg, ground potential. Thus, when differentially encoded data samples for any row of an image are applied to electrodes 18A-18I, the pixels of that row are faithfully represented by the voltage drop across the electrodes.

To provide differentially encoded data samples, a series of input data samples representing adjacent pixels of successive rows of an image are passed through a differential encoder 41 at a predetermined data rate.
is supplied to Encoder 41 differentially encodes these input samples row by row, and multiplexer 42 provides encoded data samples to electrodes 18A-18I at a ripple rate appropriate to the data rate. The controller 43 is this encoder 4
1 and the multiplexer 42. Of course, the input data can also be buffered (by means not shown) and adapted to the required ripple.

Alternatively, a set of ground plane electrodes (not shown, but defined as electrodes at the same potential level as the original input data sample) may be plugged with individually addressable electrodes, thereby allowing Therefore, the need for differential encoding can be eliminated. However, in general, the additional circuitry required for differential encoding is required given the benefit of reducing the number of electrodes required to obtain a given resolution.

As is clear from the above, a pair of adjacent electrodes (for example, electrodes 18B and 18 in FIG.
C) cooperates with the electro-optical element 17 and the readout optics 31 to effectively act as a local modulator to create the pixels at unique spatially predetermined positions along each line of the image. . However, due to the coherent nature of the optical system, the printer 11 described above
The configuration is similar to conventional line printers, with an illumination null or "blind spot" 45A between adjacent pixels 46A-46H in each row.
45G (Fig. 6). As shown in the figure, these illumination nulls line up in a line in the longitudinal direction of the image and form discernible stripes, degrading the quality of the printed image.

The electro-optic line printer according to the present invention directs the light from each modulator of the light valve 12 into an imaging optical system within an area on the recording medium 13 surrounding a spatially predetermined position of the pixels 46A-46H. It has means for coupling. Two embodiments of the invention are shown below, in which the same components are given the same numbers.

The above-mentioned FIGS. 1 and 2, as well as FIG. 7, show an application of the present invention to the printer 11. As shown, the image forming optical system 31 is generally a circular optical phase plate 61, and the phase plate 61 has two semicircular phase delay portions 62 and 63. The connection of the two phase lag sections 62, 63 also creates a phase step 64 of approximately 180 degrees. Phase plate 61 is located in the Fourier transform plane of imaging optics 31 (ie, in the focal plane of field lens 34) and supports stop 35. With this arrangement, the imaging lens 36 focuses the diffracted light from the light valve 12 onto the recording medium 13 (ie, the image plane of the light valve 12). The phase plate 61 creates a spatial phase distribution in the Fourier transform plane, and the pixels 46A to 46H that are illuminated by this phase distribution are illuminated with light spots 66AA and 66 that are approximately equally illuminated.
It appears on the image plane (ie, on the recording medium 13) as a pair of AB to 66HA and 66HB (FIG. 8). Diffraction spot 66AA, 66AB~6
The diameter and interval of 6HA, 66HB have an inverse relationship with the input lens aperture of the image forming lens 36, but each spot 66AA, 66AB to 66HA, 66HB
Their centers are aligned perpendicularly to the phase step 64. By tilting the phase step 64 preferably at about 45 degrees with respect to the axis along the direction in which each row is printed (hereinafter referred to as the "print axis"), the diffraction patterns 66AA, 66
AB~66HA, 66HB will be tilted at substantially the same angle with respect to the printing axis. Depending on the above conditions, diffraction spots 66AA, 66AB to 66
HA and 66HB intersect with each other on the recording medium 13, minimizing the illumination null. In particular, the cross line movement of the recording medium 13
Due to the exposure concentration caused by
Each gap between HAs may be substantially filled.

Here, the phase step 64 of the phase plate 61 is 180
These two values, ie, 45 degrees, and an angle of 45 degrees for the phase step 64 relative to the printing axis, are optimal values. Either or both of these two parameters may be determined by the diffraction spot 6.
The intensity and positional symmetry of 6AA, 66AB to 66HA, 66HB may be varied to the extent that it does not result in optical interference or other undesirable exposure disturbances.

Furthermore, a somewhat broader interpretation of the invention is that the light valve 1 along an axis oblique to the printing axis
It can be seen that a phase plate that tends to blur the image of the recording medium 13 reduces illumination nulls due to motion blur created by cross line motion of the recording medium 13. For example, if the light valve 12 has a ground plane electrode in addition to the individually addressable electrodes 18A-18I, a tilted cylinder lens can be used for the phase plate 61. However, in this case, when the light valve 12 is operated by encoded data, the cylinder lens is not particularly effective since it does not give the same blur to pixels in both positive and negative electric fields. In any case, if the image of the light valve 12 is blurred to reduce the illumination null, care must be taken to avoid creating unnecessary visible optical interference patterns. For this reason,
The image of light bulb 12 is approximately
The blurring was done along an axis tilted at 45 degrees.

Additionally, if necessary, the phase plate 61 can be used not only to reduce illumination nulls between pixels, but also to adjust the energy profile of the pixels. This is achieved by giving the phase plate 61 a preset non-uniform phase or absorption profile at the expense of some of the light that can be used for printing.

Pixels 46A to 46H (sixth
Another means of coupling the light from FIG.

This light scattering element 7 is optically aligned with the image forming lens 36 and located immediately in front of the recording medium 13. The light scattering element 71 is the light valve 12
has a light scattering profile that can blur illumination nulls that have a substantial effect on the image. Although the scattered light is somewhat overlapping in nature, the random phase relationship of the scattered light causes the secondary optical interferogram to have a high spatial frequency and is not resolved by the printing process. Although the readout optical system 31A of the printer 11A does not include a phase plate, other configurations are the same as the readout optical system 31 of the embodiment described above.
Further, the printer 11A is the same as the printer 11 except for the above-mentioned differences.

As described above, the device according to the present invention can reduce the illumination null between pixels that degrades the image quality of electro-optic line printers. Also, based on the above example, illumination
The null-reducing phase plate can also be used to shape the energy profile of the illuminated pixel.

[Brief explanation of the drawing]

1 is a side view schematically showing an electro-optical line printer equipped with an image forming optical system having an inclined phase step used in the present invention; FIG. 2 is a partially enlarged bottom plan view of the line printer of FIG. 1; Figure 3 is
Figure 4 is an enlarged cutaway bottom view of the light valve of Figure 3 showing the individually addressable electrodes; Figure 5 is an enlarged side view of the TIR multi-gate light valve showing the individually addressable electrodes; A block diagram of a system that provides encoded input data samples;
FIG. 6 is a diagram schematically showing a line image generated by a conventional electro-optic line printer, and FIG.
FIG. 8 is an enlarged front view of a phase plate for the image forming optical system of the line printer shown in FIG.
The figure is a side view schematically showing another embodiment of the present invention. 11: Electro-optical line printer, 12: Light valve, 13: Recording medium, 14: Drum, 17:
Electro-optical element, 18A to 18I: electrode, 21: reflective surface, 22: input surface, 23: output surface, 28:
VLSI silicon circuit, 31: Readout optical system, 34:
Field lens, 35: Central stop, 36:
Image forming lens, 41: Differential encoder, 42: Multiplexer, 43: Controller, 45A-4
5G: Illumination Null, 46A-46
H: Pixel, 61: Phase plate, 62, 63: Phase delay portion, 64: Phase step, 66AA, 66AB
~66HA, 66HB: Diffraction spot, 71: Light scattering element.

Claims (1)

[Scope of Claims] 1. A recording medium, a multi-gate light valve for printing pixels at spatially predetermined positions along a printing axis, means for irradiating the multi-gate light valve with coherent light, and the above-mentioned means arranged optically in a straight line between the multi-gate light valve and the recording medium to image the emitted light from the multi-gate light valve on the recording medium; an electro-optical line printer having means for advancing the recording medium in a linear direction, wherein the imaging means has a phase plate provided in a Fourier transform plane of the imaging means, and the phase plate The spatial phase distribution is structured so that the phase changes approximately 180 degrees in a step-like manner, and the straight line in the phase plate indicating the step-like changing part is relative to the arrangement direction in which the multi-gate light valves are arranged. an electro-optic line characterized in that the line is tilted, thereby converting light from the illuminated pixels into a double spot diffraction pattern tilted with respect to the print axis to reduce illumination nulls between the pixels; printer. 2. Claim 1, wherein the straight line in the phase plate indicating the step-like changing portion is inclined at approximately 45 degrees with respect to the direction in which the multi-gate light valves are arranged. The electro-optical line printer described.