CA1082505A - Feedback light amplifier - Google Patents

Abstract

ABSTRACT OF THE INVENTION
The image produced by an optical display apparatus is modified by an optical feedback arrangement whereby at least a portion of the image is directed through the feedback arrangement to the input of the display apparatus. By selectively controlling the feedback signal, the image characteristics of the display apparatus are manipulated for the desired results.

Description

51~5 BACKGROUND OF THE INVENTION
This invention relates to optical amplifiers in general, and, more specifically, to devices which employ feedback arrangements to modify optical signals.
There is known in the imaging art a broad class of imaging devices which record optical images by an imagewise distribution of photogenerated voltages or currents acting upon a voltage or current-alterable recording medium. Examples of devices which belong in this class are the Ruticon~and ~
FERICON devices as well as amplifiers or combinations of image amplifiers capable of utilizing readout illumination concurrently with actinic input. Typically, in these devices, imagewise activating radiation incident upon a photoconductor allows charge carriers to move in an externally applied electric field.

These charge carriers interact with a voltage or current-sensitive member which, in turn, modulates light. In the Ruticon family of devices described by Sheridon in IEEE Transactions on Electron Devices, September 1972, and U.S. Patent No. 3,716,359, the voltage-sensitive, light-modulating recording medium comprises a deformable elastomer layer in com-bination with the photoconductive material which is sometimes provided as a separate layer and at other times incorporated in the elastomer layer. Various embodiments for establishing an electric field across the elastomer layer are possible including the depositing of a thin flexible metallic conductive layer which serves as an electrode and reflective readout surface over the elastomer layer in the embodiment referred to as the Gamma Ruticon.
The Fericon devices are described in the May 1973 publication of the Society of Information Display in an article submitted by C. E. Land and W. D. Smith. The same two t r~ cl~ ,~ ar k -2-. ~ :

-~108~50S

authors published an article entitled "Reflective-Mode Ferro-electric-Photoconductor Image Storage Display Devices" in the Applied ~hysics Letter, Vol. 23, No. 2, 15 July 1973. Basically, these recorders rely on localized domains switching in PLZT
Ceramics which cause surface deformations corresponding to locally switched areas. Reflected light and Schlieren optics are used to readout the image information.
U.S. Patent No. 2,896,507 describes yet another imaging member which is a photoconductive layer and an elastically deformable layer sandwiched between a pair of electrodes, one of ~^7hich is a thin metallic layer overlying the deformable layer.
In operation, imagewise activating radiation is directed upon the member and an electric field is established across the photoconductive and deformable layers thus causing the deformable layer to deform in imagewise configuration. The member is described as being capable of functioning as an image intensifier since the deformation image may then be read out in a reflective mode with a high intensity light source and a Schlieren optical system.
Electro-optic imaging devices of the type described ~bove have been the subject of increasing attention since they ~re capable of providing highly satisfactory results. The RUTICON devices of Sheridon in particular have aroused great interest because of the excellent performance of which they are capable and the great many applications in which they are useful. Nevertheless, the devices of this type are capable of improvements which would make then even more va}uable in YarioUs applications. There is particular interest in improvement which will result in clear and discernible images from a minimum of optical input and in improvements which allow some manipulation of .

B~5V5 ...~

the image.

SUMM~RY OF THE INVENTION
-It is therefore an object of an aspect of the present invention to supply a method for modifying images produced by an optical display apparatus.
It is an object of an aspect of the present invention to furnish a method for amplifying images produced by an optical display apparatus wherein said method employs an image feedback means.
It is an object of an aspect of the present invention to afford an image modification method for use with an optical display apparatus wherein the light signal is altered during feedback.
These and other objects are accomplished by a method apparatus for modifying the image produced from original input by an optical display apparatus which comprises, generally speaking, directing at least a portion of the image through an optical feedback arrangement in order to provide subsequent input to the optical display apparatus. The image is modified 20 by the subsequent input. The modification sometimes includes ~-optical changes in the feedback portion of the image in order to alter the final~optical output signal.
In accordance with one aspect of this invention there is provided a method for modifying the image produced from original input by an optical display apparatus which comprises, directing at least a portion of said image through an optical feedback arrangement so as to provide subsequent input to said apparatus, whereby said image is modified by said subsequent input.
In accordance with another aspect of this invention there is provided an apparatus for modifying the image produced ~08Z505 from original input by an optical display apparatus which comprises: (a) an illumination means for making visible said image; and (b) a feedback means ~or directing at least a part of said image to said apparatus as subsequent modifying input.
BRIEF DESCRIPTION OF THE DRAWINGS :
The invention will now be described with reference to the accompanying drawings in which:
Fig. 1 is a schematic, cross-sectional view of an electro-optic imaging member useful with the instant invention;
Fig. 2 is a curve of exposure vs. efficiency for the RUTICON family of imaging members;
Figs. 3 and 4 are partially schematic, cross-sectional ~iews of positive feedback amplifier systems;
Fig. 5 shows schematically and in cross-section a transmission positive feedback system; and - 4a -:, : .
.. ..

- lOB~S~

Figs. 6 and 7 show schematically cross-sectional views of negative feedback amplifier systems.
DESCRIPTION OF THE PREFERRED ~MBODIMENTS

Referring more specifically to Fig. 1 there is shown R ~T I c l~ r~J,c ~ ~rk) B a ~i~on optical display device, frequently referred to as an optical recorder or light valve. Such a device is a useful optical display apparatus; and, for convenience, will be used throughout the present description as representative of the several well known such display apparatus which are useful.

Ruticon device 10 comprises a substantially transparent conductive substrate 11, such as NESA glass, which typically includes transparent support 12 and transparent conductive layer 13. Substrate 11 is adjacent photoconductive layer 14, and layer 14 is adjacent elastomer layer 15.

Elastomer layer 15 typically includes a layer of deformable elastomer 16 with conductive mirrored surface 17.
Conductive mirrored surface 17 and transparent conductive layer 13 are electrically connected through D.C. power source 18 so that a field is established across deformable elastomer 16 and photoconductive layer 14.
R~ n Optical display devices such as RU~ICON device 10 are well known in the art. Useful materials for the construction of such devices are disclosed in detail in U.S. Patent 3,716,359 to Sheridon.

Preferred embodiments of such optical display devices generally have a fine line pat~ern or other ruling pattern positioned between transparent conductive layer 13 and photoconductive layer 14 so that an optical image directed onto layer 14 through substrate 11 is broken into a corresponding pattern. When the patterned t~d~

~325~S
light strikes photoconductive layer 14 the field across elastomer layer 15 in the light struck areas is increased sufficiently to cause wrinkling or deformation of mirrored surface 17. The deformation corresponds to the image intensity. The imagewise deformation in mirrored surface 17 is made observable in reflected light when a quasi-Schlieren optical readout is employed.
Referring more specifically to Fig. 2, there is shown a generalized curve of Exposure vs. Percent Efficiency for reflection-type Ruticons. Most light valves or recorders of the type useful in this invention exhibit similar curves, some with greater slope, some with lesser. For a given exposure, a specific recorder will exhibit a specific efficiency or signal/noise ratio (~ ). In Fig. 2, for example, the efficiency value of ~ AI is exhibited where ~ AE is the exposure input. However, by using positive feedback amplification as taught herein, it is possible to move higher up the curve and thus to reduce the signal/noise ratio so that the efficiency is greatly increased. More specifically, the ef~iciency value ~ BI IS l~arger than the value ~ AI
even through the exposure inputs ~ AE and ABE are the same.
Thus, it is seen that the amplification method for optical displays described herein not only increases the brightness and visibility of the image output but also reduces the image/noise ratio.
Positive Feedback In the case of the conventional reflection-type Ruticon, it is possible to produce a positive or a negative image from a positive original by forming the image from either the reflected or diffracted light. If portions of the diffracted light are channeled back to the exposure side of the recorder and ~8Z~OS

imaged coincidently with the image of the original, an effective positive optical feedback amplifier is created.
There are two separate preferred modes of operation for the positive feedback amplifier. The first of these, or real-time mode, channels some or all of the readout illumination back to the input side of the imaging recorder concurrently with exposure. The second mode records a brief event of short exposure which may be low in light energy. Once recorded, the image is read out and some or all of the readout is channeled back to the input to enhance or amplify the image, subsequent to exposure, to be referred to as post exposure feedback.
Still another embodiment will allow an image recorder with a non-panchromatic photoreceptor to record and amplify input image information where the wavelength of the input image information lies in the low sensitivity range of the photoreceptor.
Using a readout light to enhance the image and further, to have its wavelength at the optimum sensitivity for the photo-receptor the image can be enhanced more readily. This accomplished, the readout source may be switched back to the standard source, perhaps white light, if desired.
Transmission-type image recorders do not lend themselves as well to feedback amplification; however, by using a second image recorder, as discussed further below, this is in fact possible.
Referring more specifically to Fig. 3, a specific arrangement of a real-time positive feedback amplifier is shown. Reflection type recorder 30 is addressed by input image 31 through lens 32, and the surface of recorder 30 deforms accordingly. Recorder 30 is similar in construction ~ ~ 10825~5 and operation to the Ruticon device 10 described in Fig. 1.
The image is reconstructed by a quasi-Schlieren system 33 which comprises light source 34, lens means 35, readout lens 36 and mirror 37. Mirror 37 includes an aperture to allow the zero order light to proceed to and to be reflected from recorder 30, returning to lens means 35.
Diffracted light originating at recorder 30 is reflected from mirror 37 onto second mirror 38, through shutter lO 39, lens 310 and variable density filter 311. Filter 311 is optional and generally controls the effect of the feedback on the recorder. The diffracted light then passes from third mirror 312 to fourth mirror 313 and, as subsequent input, onto the input side of recorder 30. The subsequent input improves the contrast in resulting image by intensifying the contrast between the information areas and the background areas.
The feedback image should be as near in registry with the original input image as possible to produce a more desirable final product and to avoid uneven magnification of the image. Oblique feedback to the recorder is illustrated, and is desirable when simultaneous inputting of original and subsequent input is used, but on-axis feedback is also possible. When the image on the recorder has been maximized, the shutter 39 is closed and the image on the recorder is viewed, projected or otherwise put to its intended use.

In the alternative, mirror 312 is sometimes a beam splitter which permits a portion of the incident radiation to be displayed at a viewing plane. Therefore, it is possible to view the image as it is being enhanced and visually adjust it to the desired characteristics.
` Referring more specifically to Fig. 4, a system is shown similar to that of Fig. 3 except that it is tailored 1~8'~ S

for post exposure feedback, i.e., the initial exposure is complete prior to feedback as opposed to simultaneous feedback and input. The basic difference lies in the function of mirror 40.
This mirror is excluded from the optical train (shown in dotted lines) when the original 41 is imaged into recorder 42 and moved into the position shown in solid lines thereafter.
The feedback image is generated as explained in connection with Fig. 3 except that the diffracted light is directed from mirror 43 onto mirror 40 and then to the input side of recorder 42.
Referring more specifically to Fig. 5, there is shown a positive feedback amplification arrangement which is useful with image recorders which are read out in a transmission mode.
Two transmissive image recorders 50 and 51 are necessary. Recorders 50 and 51 are sensitive to different wavelengths of light,~ 1 and ~ 2~ respectively. Original image 52, a transparency, for example, is addressed onto recorder 50 by illumination source 53 which emits radiation f ~ 1 wavelength. This recorded image is in turn read out with ~ 2 wavelength illumination from the source 54.
Diffracted image light of ~ 2 wavelength is focused using lens 55 onto recorder 51 which is sensitive to ~ 2 wavelength , but insensitive to~ 1 Non-diffracted zero order light is at the same time eliminated from the optical train by stop 56. The image recorded at recorder 51 is in turn read out with light of ~ 1 wavelength from source 57. Zero order undiffracted light is eliminated from the optical train by stop 58 while diffracted image light is collected by lens 59 and directed by means of lens 510, _9_ 5~S

mirrors 511 and 512, to lens 513 which focuses in registry the image on recorder 50. Thus, the feedback loop is completed and the original image on recorder 50 is enhanced by a positive feedback.
Similarly, one can replace both stop 56 and stop 58 by an aperture. Such an aperture would serve to stop diffracted light while passing zero-order light. The image would, in this case, be recorded in sense for the i~aging on recorder 51 from the original but would be again reversed in ~ 1 light to coincide in sense with the original for feedback to recorder 50.
The arrangements thus presented have several important characteristics and capabilities, including the ability to increase output intensity for a weak input image resulting, for example, from a flash or spark exposure by post exposure feedback. Such arrangements also produce high contrast output for a given input by increasing the contrast between the information area of an image and the background area of the image as shown in Fig. 2.
The reduction of exposure time is an additional advantage of such arrangements as is the maintenance of a given output intensity without employing constant exposure to the original source image.
NEGATI~E FEEDBACK
With positive feedback, light is rechanneled to further expose the photoreceptor in previously exposed regions. This, in general, will serve to increase or intensify the contrast of the output.
To diminish this contrast one can either feedback light to the photoreceptor the light being reversed in its image sense - - . . .
-- ,- , . ' ,: -llV8;~5S~5 with respect to the original image or expose an element which becomes increasingly opaque with increasing intensity of actinic illumination such as a photochromic dye with the zero oder (negative) feedback image. Each of these methods tends to reduce the gray level separation between white and black areas by exposing with feedback light those areas not previously exposed or by diminishing feedback exposure in areas that were previously exposed. Both real time and post exposure negative feedback are possible.
There are two primary reasons for using negative feedback, the first being the reduction of contrast for im-proved continuous tone, or half-tone imaging applications.
The second application is that of regulation. For those situ-ations calling for a precise energy of exposure, a negative feedback is used to restrain the final output level to meet requirements. This can be useful for systems where the image amplifier is an intermediary ~buffer) for another photo-receptor, as in Fig. 5.
The structural arrangements of the negative feedback embodiments are the same as those shown in Figs. 3 and 4, with a minor difference. The Schlieren readout system does not stop the zero order reflected light, but rather lets it pass and stops the higher order diffracted light.
A negative feedback system employing transmissive-type image recorders can take the form shown in Fig. 5 with the exception that one of the steps, 56 or 58 allows the zero order to pass while blocking higher orders. As mentioned above, a useful negative feedback system can be constructed through a novel employment of a photochromic dye.
Attention is directed to Fig. 6 wherein such a structure is shown. ~eflective-type electro-optic image recorder 60 is 108~50S

addressed with an image from original 61, through lens 62.
Image readout light 63 is reflected from the modulated surface of recorder 60 through lens 610, stop 64 and onto mirror 65. Stop 64 prevents the higher order light from passing on, while at the same time permitting zero order to move along unimpeded.
The image modulated radiation incident upon mirror 65 is redirected onto the photochromic dye member 66. This member may take any suitable form but for purposes of discussion, will be considered to be a liquid dye solution evenly spread upon a glass. The behavior of the photochromic dye is such that the light struck areas become more opaque, as the intensity of the incident radiation increases.
The image modulated radiation which is passed to mirror 67 is thus reduced in intensity inversely with the input to member 66. The image on mirror 67 is then passed, via lens 68 and mirror 69, onto the input side of recorder 60 and in registry with the original input image.
Thusly, the readout image on recorder 60 is reduced in contrast by having the original lower intensity portions thereof increased in intensity relative to the higher original intensity portions.
For the purpose of regulation of input image intensity there is an alternate location for the photochromic filter.
By locating the photochromic filter in the input path, or at recorder 60, using a photochromic dye which is insensitive to the image light wavelength, one can feed back readout light which is either white light or light of a wavelength which activates the dye such that the continuous image light is attenuated concurrently with the development of the recorded image. Adjusting the -- 108Z5~5 intensity of the feedback light allows for any disparity in the sensitivity between the recorder and the photochrcmic dye.
Referring more specifically to Fig. 7, it is demonstrated that negative feedback ampllfication offers useful abilities, other than those set forth above, which provide for novel manipulations of image characteristics. For instance, the structure of Fig. 7 may be used to convert solid area original images into either black outlines on a white background or white outlines on a black background.
Original image 70 is addressed onto reflection-type recorder 71 through lens 72 which causes a phase image to develop upon the surface thereof. Radiation from readout ilIumination source 73 is focused through lens 74 onto the deformed surface of recorder 71 and reflected therefrom through lens 75, stop 76, lens 77 and onto mirror 78. Stop 76 lets only the zero order refl~cted light pass. The image modulated radiation incident upon mirror 78 is directed through shutter and/or variable density filter 79 and onto mirror 710. From mirror 710 the feedback image is directed through lens 711 onto mirror 712 and thence to the input side of recorder 71.
The final readout image may be either white lines on a dark background or dark lines on a bright background by selecting the proper readout light. As an example, if the original input image to the recorder consists of a black square surrrounded by a bright region and the negative feedback image is focused onto the recorder, in registration with the original image, but at a slightly lower magnification a line or outline image will result. Negative feedback imaging will expose most of the center .

:1~8;~5~S

of the square and just the edges of the square will remain unchanged. Thus, after proper feedback exposure is complete, one can select the diffracted light image to view a black line image on a bright background. Selecting the zero order image for viewing results in a bright line image on a black background.
The changes in magnification are easily accomplished by moving either, or both lens 77 or lens 711.
Post exposure feedback would be the preferred mode of operation.
The optical systems for all figures is for illustrative purposes and need not be literally representative of actual optlcal systems. The use of field lenses, dichroic filter/mirrors, image inverters, etc. is not illustrated but it is obvious that many systems would require such optical components to improve system performance. The feedback loops, of course, require some way to readout a final image, either at a viewing station, or to be recorded onto another material such as a selenium drum or photographic film. Various methods and/or components can obviously be used, including pivoting or rotating mirrors or beam splitters to extract the final readout image.
The two transmissive recorders may take most forms known in the art, for example, the gas or liquid Ruticons as taught by Sheridon.
The image modification methods and apparatus disclosed herein are not limited to the feedback-modification of a single image at any one time. It will be clear that a plurality of original images can be combined to form a composite final image. For example, referring again to Fig. 3, original 31 can be imaged on recorder 30 to the desired optical intensity;
and then at least one subsequent original 31 can be superimposed , 108Z~0~

onto the first image. A more specific example of such a method would be the first imaging of numerical lists and the subsequent superimposing of column lines to organize the listings.
It will be understood that various other changes of the details, materials, steps, arrangement of parts and uses which have been therein described and illustrated in order to explain the nature of the invention will occur to and may be made by those skilled in the art, upon a reading of this dis-closure, and such changes are intended to be included within the principles and scope of this invention.
For example, it should be appreciated that the Ruticon family of imaging members is used merely for purposes of demonstration, and that any reflection or transmission type of system where output illumination does not affect the activated photoreceptor through the device may benefit from the concepts herein disclosed. Some of these other system will obviously require modification; however, the instant disclosure would direct one of ordinary skill in the art to make such modifications.
Although specific components and process steps have been stated in the above description of the preferred embodiments of the invention, other suitable materials, elements of process steps as listed herein, may be used with satisfactory results in varying degrees of quality.

,. ............ . : . .

., .. . , :

Claims (11)

WHAT IS CLAIMED IS:

1. A method for modifying the image produced from original input by an optical display apparatus which comprises, directing at least a portion of said image through an optical feedback arrangement so as to provide subsequent input to said apparatus, whereby said image is modified by said subsequent input.

2. The method of Claim 1 wherein said subsequent input is additional positive input in substantial registration with said original input whereby said image is intensified in contrast.

3. The method of Claim 1 wherein said subsequent input is negative input in substantial registration with said original input whereby said image is reduced in contrast.

4. The method of Claim 1 wherein said subsequent input to said apparatus is not in registration with said original input whereby a modified image is produced.

5. The method of Claim 1 wherein said original input is terminated and said image is maintained by said subsequent input.

6. The method of Claim 1 including the subsequent step of providing a second original input to said apparatus while maintaining the modified image so that a composite image of said modified image and said second original input is produced.

7. An apparatus for modifying the image produced from original input by an optical display apparatus which comprises:
(a) an illumination means for making visible said image; and (b) a feedback means for directing at least a part of said image to said apparatus as subsequent modifying input.

8. The apparatus of Claim 7 wherein said feedback means provides subsequent modifying input having a positive image sense.

9. The apparatus of Claim 7 wherein said feedback means provides subsequent modifying input having a negative image sense.

10. The apparatus of Claim 7 wherein said feedback means provides subsequent modifying input not in registration with said original input.

11. The apparatus of Claim 7 further including a means for supplying a second original input to said optical display apparatus while said feedback means is operative.