Waveguide imaging system

A waveguide system includes a unitary elastomer waveguide means having radiation propagating therethrough. The unitary waveguide means is shaped to have at one end a coupling means and at the other end a plurality of individual waveguide means with field means for selectively attenuating the radiation in selected ones of the individual waveguide means. The system is positioned with respect to an imaging surface so that radiation emanating from the individual waveguide means strikes the imaging surface to form a line pattern of radiated and non-radiated bits.

BACKGROUND OF THE INVENTION 
The present invention relates generally to a system for making and 
recording light patterns. More particularly, the present invention 
pertains to a new and improved integrated optic image recorder. 
In the field of image recorders, especially laser image recorders, it has 
been the general practice to utilize a mechanical scanning system to scan 
a writing laser over the surface to be marked. Marking on the surface is 
generally accomplished as a result of the sensitivity of the surface to 
either the heat or light. 
Typically the laser is mechanically scanned across the imaging surface. 
During the scan, it may be modulated to leave a data path of light-struck 
and non-light-struck areas in each scan. The imaging surface is indexed 
between scans so that an image is built up on the surface line-by-line. 
Modulation is typically controlled by voltage pulses from a computer, or 
the like. 
Although excellent results have been achieved by such systems, they require 
high precision mechanical and optical equipment capable of operating 
accurately at high speeds. A system for addressing of an imaging surface 
which avoids the need for high precision and high speed mechanical 
scanning equipment is desirable. 
A variety of approaches to such a system have already been made. For 
example, the use of a linear array of light emitting diodes is disclosed 
by James E. Nucklos et al in U.S. Pat. No. 3,803,631 and by E. B. Neitzel 
in U.S. Pat. No. 3,438,057. Both systems have certain advantages; however, 
they are both limited by the intensity of the light available from light 
emitting diodes. Also, the size of commonly available such diodes can 
frustrate efforts to achieve high resolution patterns. 
An imaging system which enables the use of laser light is disclosed by John 
F. Ebersole in U.S. Pat. No. 3,841,733. Ebersole discloses the coupling of 
laser light into a waveguide configuration which comprises a parallel 
array of lithium niobate or tantalate waveguides which are contacted on 
one side by a common electrode and on the opposite side by individual 
electrodes. 
The lithium niobate or tantalate waveguides of Ebersole propagate TE waves 
while TM waves are absorbed by the contacting metal electrodes. When 
attenuation in a particular one of the parallel waveguides is desired, the 
individual electrode contacting that waveguide is activated. The field 
between the common electrode and the individual electrode changes the TE 
orientation of the propagating wave to TM orientation. The TM wave is then 
absorbed by the metal electrode. 
Ebersole discloses the use of such a system to project a line of 
information on an imaging surface. Each line comprises bits which 
correspond to individual ones of the waveguides. The bits are illuminated 
or not depending on whether a field is present across the individual 
waveguide. Ebersole discloses the use of a high speed buffer interface 
between the waveguide electrodes and the serial voltage pulses which 
control the electrodes. The buffer enables line-by-line parallel 
addressing of the waveguides responsive to serial input. 
The waveguide material of Ebersole, is expensive and easily damaged by 
radiation. A cheaper waveguide made from a material which is less 
susceptible to radiation damage is desirable. 
In the waveguide system of Ebersole, laser light is first coupled into a 
glass waveguide where it passes through a diverging lens and a collimating 
lens. Subsequently, the light is coupled into a parallel row of lithium 
niobate waveguides where it is modulated. 
The glass/lithium niobate interface of Ebersole causes reflection problems. 
An undesirable amount of light is reflected back into the glass from the 
interface. A waveguide means for producing a line of modulated bits of 
light while avoiding lithium niobate/glass interface problems is 
desirable. A convenient method for making such a waveguide means is also 
desirable. 
SUMMARY OF THE INVENTION 
It is an object of this invention to overcome the disadvantages of the 
prior art. 
It is also an object of this invention to furnish a waveguide system for 
forming a line pattern of bits of information on an imaging surface. 
It is a further object of this invention to supply such a system in which 
the problems of coupling interfaces within the waveguide system are 
avoided. 
It is another object of this invention to furnish a method for making a 
waveguide means which avoids the problems of coupling interfaces within 
the waveguide means while enabling line-by-line addressing of an imaging 
surface with modulated bits of light. 
It is yet another object of this invention to avoid the disadvantages of 
expensive waveguide means which are easily damaged by radiation. 
These and other objects are achieved by a novel waveguide system for 
forming a line pattern of radiated and non-radiated bits on an imaging 
surface. The system comprises, generally speaking, a unitary waveguide 
means having propagating therein radiation to which the imaging surface is 
sensitive and a field means for line-by-line attenuation of the radiation. 
The unitary waveguide member is shaped at an entrance end to receive a beam 
of organized light and to collimate the light across the width thereof. It 
is shaped at the exit end to form a plurality of separate waveguide means. 
The separate waveguide means are arranged substantially parallel to each 
other and in the same plane. The plane is oriented, with respect to the 
imaging surface, so that radiation emanating from the waveguide means 
impinges the imaging surface. The separate waveguide means are selected to 
attenuate propagating radiation by means of an electrical field. 
The field means includes individual electrodes associated with each 
separate waveguide means so that a field can be formed across the separate 
waveguide means responsive to electrical signals. In one embodiment, for 
example, the field means is a common electrode on one side of the 
waveguide means and individual electrodes on the opposite side. 
The attenuation of light propagating through individual ones of the 
waveguide means produces on the imaging surface a line pattern radiated 
and non-radiated bits. In a preferred embodiment, the system includes a 
means for line-by-line indexing the imaging surface with respect to the 
waveguide means. The indexing is coordinated with sequential line-by-line 
electrical signal input to the field means.

DETAILED DESCRIPTION 
Referring more specifically to FIGS. 1 and 2, there is shown a 
cross-section of one of the plurality of waveguide means. The arrangement 
of parts in FIGS. 1 and 2 is for ease in explaining the operation of the 
system. The relative sizes of the component parts as shown in FIGS. 1 and 
2 are also chosen for ease of illustration and is not intended to show 
commonly encountered size relationships of the parts. 
Laser radiation 1 is shown propagating in individual waveguide 2. Waveguide 
10 is suitably formed from a physically deformable material coated onto a 
suitable rigid support substrate 11. The relative thicknesses of waveguide 
10 and substrate 11 as shown in FIGS. 1 and 2 are not depicted in actual 
scale. Waveguide 10 is preferably substantially thinner than the substrate 
11, but is shown as being relatively thick for illustration purposes only. 
Waveguide 10 is preferably formed of polymer elastomer which has a greater 
index of refraction than support substrate 11. The elastomer should be one 
that is capable of being easily deformed when exposed to a force, such as 
that exerted by an electric field. 
A wide variety of elastomers may be selected which meets these 
requirements. Two such examples include phenylmethyl polysiloxane 
(n=1.54-1.55 at 6328 A) and dimethyl polysiloxane (N=1.40-1.41 at 6328 A) 
crosslinked to the desired elastomeric state. 
Likewise, a wide variety of materials for substrate 11 may be employed. The 
criteria for selection of such substrate material are that it possesses 
the requisite mechanical properties, e.g. strength and compatability with 
the waveguide 10, and that its index of refraction be lower than that of 
waveguide 10. 
By way of example, a Pyrex microscope glass (n=1.513 at 6328 A) is a 
suitable substrate where the phenylmethyl polysiloxane waveguide material 
is used. Lithium fluoride (N=1.39 at 6328 A) or sodium fluoride (n=1.38 at 
6328 A) may be used with dimethyl polysiloxane waveguides. 
Waveguide 10 can be of any suitable thickness. It is observed from 
experimental data that a preferred thickness is from about 4 to about 10 
microns. Such a range of waveguide diameters is readily modulated (as 
explained below) and produces a relatively high resolution image on 
imaging surface 12. 
The number of individual waveguides at the exit side of the waveguide 
system can vary greatly depending on the desired resolution. Resolution is 
generally considered to be satisfactory when 40 micron diameter separate 
waveguides are spaced at a frequency of at least about 40 per inch, 
although even fewer waveguides can be used as resolution is not important. 
Up to about 500 separate waveguides per inch are desirable for high 
resolution systems. 
A first electrode 13 and a second electrode 14 are positioned on either 
side of waveguide 10. The electrodes are connected through power source 15 
so that when switch 16 is closed, a field is created between electrodes 13 
and 14. The field draws electrode 14 toward electrode 13 to physically 
deform elastomeric waveguide 10 and to attenuate the propagating wave as 
shown in FIG. 2. When switch 16 is open, as shown in FIG. 1, waveguide 10 
is not deformed and the radiation propagates unattenuated to impinge 
imaging surface 12. 
Any suitable electrodes 13 and 14 can be used. Good results are observed 
when electrode 13 is a 300 A layer of gold which is sputtered or vacuum 
evaporated onto support substrate 11. Second electrode 14, in this 
embodiment, is a 10-25 micron diameter tungsten filament placed across 10 
micron waveguide 10. Electrodes 13 and 14, in this exemplary embodiment, 
are connected to a 50-250 V power source 15. 
A more detailed discussion of this arrangement for modulating radiation 
propagating in an elastomeric film-type waveguide can be found in the 
commonly assigned copending application U.S. Ser. No. 621,312, filed Oct. 
10, 1975 now U.S. Pat No. 4,106,848. 
Imaging surface 12 can be any suitable photosensitive surface. Any surface 
which is responsive to the radiation propagating in waveguide 10 is 
useful. Typically, imaging surface 12 is a uniformly charged 
photoconductive plate or a photographic plate. In a preferred embodiment, 
surface 12 is a grounded, conductive aluminum substrate having coated 
thereon a 60 micron layer of arsenic doped selenium, a well known 
photoconductor. 
In operation, the selenium layer is uniformly charged to a potential of 
about 1,000 volts. Radiation emanating from the exit end 17 of waveguide 
10 and impinging on surface 12, as shown in FIG. 1, will discharge surface 
12. There will be little or no discharge of the photoconductive surface in 
areas corresponding to waveguides in which the propagating light has been 
attenuated, as shown in FIG. 2. The discharged and non-discharged bits 
form a pattern on surface 12 which can subsequently be developed by any 
suitable one of the well known xerographic methods. 
It will be apparent that the end 17 of the individual waveguides should be 
placed sufficiently close to imaging surface 12 so that light 1 impinges 
surface 12 with usefully high definition and strength. The distance 
between end 17 and surface 12 is preferably equal to about the width of 
waveguide 10. 
Switch 16 is primarily for illustrative purposes. In a working embodiment, 
switch 16 is replaced by serial voltage pulses and can be controlled by a 
high speed buffer to enable parallel addressing. 
Referring more specifically to FIG. 3 there is shown an alternative 
individual waveguide means and an alternative field means useful in the 
present invention. 
The individual waveguide means in FIG. 3 is sputtered glass member 30 
coated with a nematic liquid crystal material 31. Nematic liquid crystal 
materials are those which exhibit optical uniaxiality. When the 
orientation of the liquid crystal molecules is parallel with the sputtered 
glass, radiation 32 propagates in the sputtered glass. When the 
orientation of the liquid crystal molecules is rotated away from the 
parallel position, radiation is attenuated. 
The field means comprises electrodes 33 and 34 which are connected to power 
source 35. A field is established across the waveguide by closing switch 
36. The field changes the orientation of the liquid crystals in coating 31 
so that sputtered glass member 30 is no longer internally reflective. As 
in FIGS. 1 and 2, switch 36 is primarily shown for illustrative purposes. 
The mechanism used to attenuate radiation propagating in sputtered glass is 
known in the art and has been described by J. P. Sheridan in his paper 
entitled "Liquid Crystals in Integrated Optics" given at the Topical 
meeting on Integrated Optics, New Orleans, January, 1974. 
Typical suitable liquid crystal materials for use in forming coating 31 on 
sputtered glass member 30 are disclosed in U.S. Pat. No. 3,687,515. Other 
suitable materials include cholesterics; mixtures of cholesterics and 
smectics; mixtures of nematics and cholesterics, such as about 80 percent 
by weight methoxybenzylidene-p-n-butylaniline (MBBA) and 20 percent 
cholesteryl chloride (CC); and mixtures of nematics and optically active 
non-mesomorphic materials such as 1-menthol; or d-camphor. These materials 
and mixtures typically exhibit optical characteristics of the cholesteric 
mesophase and will undergo phase transformation to the optically uniaxial 
nematic mesophase state in response to suitable stimuli such as, for 
example, electrical field induced phase transformation as disclosed in 
U.S. Pat. No. 3,652,148. 
An individual waveguide and field means combination such as the one shown 
in FIG. 3 can be constructed by vacuum coating a gold electrode on a Pyrex 
microscope slide and placing a Corning 7059 sputtered glass layer over the 
electrode. The free side of the sputtered glass layer is smeared with a 
cholesteric liquid crystal. The conductive coating of a NESA transparent 
electrode is pressed against the liquid crystal. The conductive coating on 
the NESA electrode and the gold electrode are connected through a suitable 
power source. 
Referring more specifically now to FIG. 4, there is shown in cross-section 
both a top and side view of the waveguide system making use of the 
waveguide modulating mechanism described in connection with FIGS. 1 and 2. 
It is to be understood, however that the modulating system shown in FIG. 3 
could also be used. The modulating system of FIGS. 1 and 2 is preferred 
because of its ease of fabrication, which will be explained in greater 
detail below. 
Waveguide systems 40 of FIG. 4 comprises shaped unitary waveguide means 41 
supported on substrate 42. Waveguide means 41 is shaped to have grating 43 
for coupling laser light into waveguide means 41. 
Waveguide means 41 is also shaped to include aspheric diverging lens 44 and 
aspheric collimating lens 45. The use of such aspheric lenses in 
waveguides is well known in the application of waveguides to practical 
use. See, for example, U.S. Pat. No. 3,841,733 to Ebersole. 
The functions of grating 43 and lenses 44 and 45 are to couple laser 
radiation 46 into waveguide means 41 and to spread it to substantially the 
width of the waveguide. 
Waveguide means 41 is shaped on its exit side to form individual waveguide 
means 47. Individual means 47 are arranged substantially parallel to each 
other in the same plane. They are positioned with respect to imaging 
surface 48 so that light 46 emanating from the ends of individual means 47 
impinge surface 48 in substantially a straight line. 
Means for attenuating light 46 in individual waveguides 47 includes 
individual electrodes 49 and common electrode arrangement 410. Arrangement 
410 in FIG. 4 is a parallel array of electrode wires 411. Electrodes 49 
operate together to attenuate light 46 in individual waveguide means 47 
substantially as described in connection with FIG. 1. 
There are a variety of electrical control mechanisms well known in the art 
useful for providing voltage pulses to individual electrodes 49. Typical 
of such mechanisms are computers including a high speed buffer to convert 
the serial computer output to parallel (line-by-line) output. 
Surface 48 can be indexed synchronously with the line-by-line input. Such 
indexing can be accomplished by any suitable means, exemplified by 
stepping motor 412 and friction wheel 413. 
The embodiment of FIG. 4 is assembled by first vacuum coating the desired 
number of electrodes 49 on glass plate 42 at the locations shown in FIG. 
4. The electrodes are vacuum coated to a thickness of about 300 A. The 
electrodes can be plated to extend onto the end of plate 42 for ease of 
connection with voltage pulse input connectors (not shown). Vacuum coating 
is through a mask having openings corresponding to the desired number of 
individual waveguides 47. 
Gold and silver are useful materials for electrodes 49 because of their 
electrical conductivity, resistance to corrosion and compatability with 
vacuum deposition techniques. 
The electroded substrate 42 is then coated with a layer of ultraviolet (UV) 
polymerizable liquid. One useful such liquid is polydimethylsiloxane 
(PDMS). The liquid is cured by exposure to UV radiation through a 
projection mask. The mask prevents UV radiation from striking the PDMS in 
the areas between electrodes 49. 
The PDMS layer on substrate 42 is UV cured (polymerized) except in the 
masked areas. The unpolymerized PDMS is washed away with benzene. The 
polymerized material forms unitary waveguide 41 with individual waveguide 
meams 47 at the exit end. 
The waveguide means 41 is then coated with a second layer of liquid PDMS 
which is exposed to UV radiation through a second projection mask. The 
second mask is shaped to enable UV curing of the PDMS so as to form 
aspheric lenses 44 and 45 and grating 43. Once again the unpolymerized 
PDMS is removed with a benzene wash. 
Tungsten wires are placed across the ends of individual waveguides 47 to 
form common electrode 411. 
In the embodiment of FIG. 4, waveguide system 40 can be made to have any 
useful number of individual waveguides 47. Typically, such systems have 
from about 50 to about 500 individual waveguides, depending primarily on 
the resolution desired in the data line projected on surface 48. 
Connectors to electrically couple electrodes 49 with voltage pulse 
suppliers, such as computers or interfacing high speed buffers, are 
commonly available in lower frequencies. Higher frequency connectors (such 
as 500 per inch) are within the capability of large scale integrated 
circuit technology and are compatible with thin film transistors commonly 
used in integrated optical circuitry. 
It can be seen that waveguide system 40 avoids an undesirable internal 
interface while enabling the projection on surface 48 of a data line 
comprising illuminated and non-illuminated bits. 
The above description and drawings will be sufficient to enable one skilled 
in the art to make and use the present invention and to distinguish it 
from other inventions and from what is old. It will be appreciated that 
other variations and modifications will occur to those skilled in the art 
upon reading the present disclosure. These are intended to be within the 
scope of this invention.