A monotube CRT includes an envelope which comprises a first section that houses the electron gun and a second section that houses a fiber optics faceplate along a sidewall. An array of electromagnets is disposed along the second section for deflecting the electron beam from its longitudinal path through the envelope transversely to trace a linear scan on the faceplate. The first section of the envelope is a circular cylinder whose axis is coaxial with the longitudinal path of the electron flow. The second section of the envelope is essentially rectangular or elliptical in cross section and the undeflected beam flows adjacent one narrow sidewall opposite the sidewall housing the faceplate. Each electromagnet of the array includes a core portion adjacent said one narrow sidewall and pole pieces that flank the wide sidewalls of the section.

DETAILED DESCRIPTION 
FIGS. 1A and 1B illustrate the simplest form of cathode ray tube 20 of the 
monotube variety. The tube envelope 21 is a simple elongated glass 
cylinder of essentially circular cross section along substantially its 
entire length. Typically this cylinder may be about one and a half inches 
in diameter and about twenty inches in length to accommodate a fiber optic 
plate 22 that extends along a sidewall. One end of the tube includes the 
electron gun 23 that basically is of conventional design. Typically, it is 
designed to form an electron beam of circular cross section, initially 
about twenty five mils diameter, and to focus or converge this beam to a 
diameter of several mils at its focal point. Moreover, it will be 
advantageous to include provision in the electron beam for varying the 
focal point dynamically along the tube length for reasons to be discussed 
subsequently. 
The fiber optic faceplate 22 is positioned in a sidewall of the envelope 
primarily along the downstream half of the tube. In the usual fashion, the 
faceplate surface inside the envelope is coated with a phosphor while the 
surface outside the envelope is adapted to contact a recording medium, 
that is moved past the faceplate for recording the image formed in the 
faceplate in known fashion. 
The fiber optic face plate typically is about fourteen inches long and 
about a half-inch wide and includes bundles of fused fibers each about ten 
to fifteen microns in diameter, and the beam incident on the strip 
typically has a diameter of between two and three mils. Provision is made 
for periodically perturbing the beam in the vertical direction of the 
strip by several mils, as it sweeps along the length of the faceplate, to 
avoid excessive aging of the phosphor by repetitive traces along the exact 
same path. The movement of the recording medium advantageously is 
sufficiently slow relative to the speed of the scan to permit several 
repetitive scans of the same information on the strip to improve the 
signal-to-noise ratio based on the familiar principles that the noise will 
add on a random basis while the signal will add cumulatively. 
Additionally, multiple scans with a slight vertical perturbation will 
provide a desirable averaging effect that will reduce granularity and 
streaking. 
Additionally, the CRT 20 is provided with a plurality of electromagnets 27 
aligned in a linear array essentially along the same longitudinal portion 
of the envelope that includes the faceplate 22. Each of these 
electromagnets is so designed that, when energized, it will deflect the 
electron beam going there past from its longitudinal direction to a 
transverse direction for incidence on the portion of the faceplate 
alongside it. The electromagnets of the array are energized in turn so 
that the electron beam is deflected appropriately to scan the linear strip 
of optical fibers continuously from one end to the other at a smooth and 
uniform rate. 
As is known, the degree of deflection will depend both on the strength of 
the magnetic deflecting field, the velocity of the electrons in the beam 
at the time of deflection, and the distance the electrons go after 
deflection before incidence on their target. 
The strength of the deflecting field is controlled by varying the current 
supplied to the coils of the electromagnets. To this end, the deflecting 
array is driven by a power supply that provides on a cyclic basis a series 
of wave forms that are supplied in turn to the coils of the successive 
electromagnets of the array, so that each electromagnet is energized in 
turn. Moreover, each of the pulses has an amplitude that gradually 
decreases with time so that the deflection radius similarly decreases to 
provide a sweeping action along the target. 
Typically each electromagnet is used to control a length of about one a 
one-eight inches of the strip, so that for a strip fourteen inches long, 
about fifteen electromagnets should be assembled in the array, including 
two or three to establish the beginning of the deflecting field. 
In FIG. 1B there is seen in detail the basic structure of an individual 
electromagnet 27 of the array. It includes a core portion 29 about which 
is wound a coil 30 to which is supplied an energizing current. Pole pieces 
32 and 33, extending from opposite ends of the core 29 on opposite sides 
of the envelope 21, create a magnetic field that extends transversely 
across the envelope so that an electron beam flowing axially inside the 
envelope is deflected in a direction transverse to that flow and to the 
magnetic lines, for incidence on the faceplate 22 in the sidewall portion 
of the envelope equidistant from the two pole pieces as shown by lines 25. 
It is, of course, unnecessary that the beam be deflected at a ninety 
degree angle and, typically, the deflection angle will be between thirty 
and sixty degrees because of the shortness of the region over which the 
deflecting field acts. 
It is advantageous that the scan of the faceplate by the beam be relatively 
smooth. However, a variety of scanning patterns are feasible. 
For example, for each scan the beam may be deflected in turn by successive 
electromagnets in the downstream direction of the electron flow, i.e., a 
line scan begins by deflection first by the uppermost electromagnet (i.e., 
the one closest to the electron gun). In this case for unidirectional scan 
by successive electromagnets, the degree of deflection introduced by any 
particular electromagnet needs to peak at the time such electromagnet 
takes over and to gradually reduce until the succeeding electromagnet 
takes over. This requires that the magnetizing current supplied to an 
individual coil have a pulse wave form which peaks at its leading edge and 
gradually reduces to its trailing edge. 
Alternatively, by appropriately processing the input signal applied to the 
CRT, there may be utilized a deflection arrangement in which the line scan 
moves in the direction opposite that of the electron flow. In this case, 
each line scan begins by deflection of the beam by the downmost 
electromagnet and is continued by deflection by its upstream neighbor. In 
this case, for a time-continuous unidirectional scan, the wave form of the 
magnetizing current to each coil should be a pulse whose amplitude 
increases between its leading the trailing edge. 
Moreover, it should be evident that by appropriate processing of the signal 
information before it is applied to the CRT for recording, a scanning 
pattern may be utilized in which the line scan comprises a succession of 
scans each in a given direction, either the same or opposite that of the 
beam, but the scan provided by successive electromagnets is not continuous 
with time in that each scan does not begin in time at the point in space 
where the preceding scan ended. With such a signal, it is feasible to 
begin the scan with the uppermost electromagnet and to supply a 
magnetizing current to each coil of pulses whose amplitude increases from 
its leading to trailing edge. 
For optimum reproduction quality, it is important that the electron beam be 
sharply focussed as it is swept along the faceplate. To this end, it is 
desirable that the electron beam be focused at the time that it is 
deflected. Since the path length of the beam from its source to the point 
of deflection is varying with time, it is advantageous to adjust the focus 
voltage continuously for optimum focus as a function of the beam 
deflection location. This technique, termed dynamic focusing, is well 
known in the art. However, it is also known that dynamic focusing 
typically provides a focused spot size that increases with increasing 
distance away from the source. For optimum reproduction quality, it is 
advantageous to use a scanning spot of relatively uniform size that is 
independent of its position of incidence along the faceplate. 
To this end, it is advantageous to apply a second correction to the dynamic 
focusing to compensate for the varying focused spot size. This can be 
achieved with an offsetting de-focusing wave form superimposed on the 
dynamic focus voltage, or by rapidly perturbing transversely the electron 
beam slightly, the amplitude of the perturbation decreasing with 
increasing distance from the source end to compensate for the increasing 
focused spot size with increasing distance along the beam path. 
Various techniques for such perturbation are described in my 
above-mentioned co-pending application, Ser. No. 151,438. 
In the monotube CRT just described, at the time of deflection, the beam is 
essentially centered along the axis of the envelope. This results in some 
inefficiency since little use is made for deflection of the radial 
separation of the beam from the envelope. A more efficient configuration 
is one in which the electron beam at the time of deflection is located 
proximate the core portion of each electromagnet. 
FIG. 2 illustrates one technique to this end. A pair of electromagnets 31 
are located just beyond the electron gun along the envelope, and they are 
used to displace the electron beam, launched initially in a direction 
along the central longitudinal axis of the envelope, for flow along a 
longitudinal path located near the bottom of the envelope, as shown by the 
lines 35, close to the core portions of the electromagnets. By so 
relocating the beam, it is apparent that there is increased effectively 
the distance over which the beam may be deflected before it is incident on 
the faceplate, thereby reducing the radius of the deflection and the 
strength of the magnetic field needed for the deflection. This similarly 
reduces the amount of energizing current needed to be supplied to the 
electromagnet. 
An alternative technique illustrated in the embodiment shown in FIGS. 3A 
and 3 B is to distort axial symmetry of envelope 41 by inclusion of the 
bend 42 in the envelope to divide the envelope into two sections 44 and 45 
whose central axes are displace, so that the beam, although not displaced 
in direction, will nevertheless proceed on a path close to the bottom of 
the envelope in the region 45 that includes the faceplate, although 
initially launched on a path along the central axis of the gun section 44 
of the envelope. In this figure, the electromagnets have not been shown to 
simplify the drawing. 
A related technique for effectively increasing the length of the deflection 
path available would include increasing the diameter of the envelope. This 
requires longer or larger magnetic pole pieces and consequently 
undesirably enlarges the entire assembly. 
Another technique is illustrated in FIGS. 4A and 4B. In this case, the 
envelope is made in two separate cylindrical circular glass sections 51, 
52, each of which is fused to a transition section 54 and aligned to 
provide an effective step in the resulting envelope, and the electron beam 
flows along the path shown by the solid line 56. Accurate assembly in the 
desired alignment is readily achieved by facing the ends of the two 
sections on a 90 degree glass grinder and by providing a precision jig to 
hold the two parts in the designed alignment during the sealing steps. 
As an added advantage of this geometry, the high voltage connection 58 to 
the conductive coating included in the inside walls of the envelope used 
for accelerating the beam can be brought out, as shown, near the 
transition 54. 
In FIGS. 5A and 5B, there is shown a monotube CRT 60 that uses the 
presently preferred geometry for the tube envelope. In this case, the 
envelope, typically also of glass, again includes two separate sections 
61, 62 each of transition section 64, as with the tube shown in Figs, 4A 
and 4B. The first section 61 that houses the electron gun 65 is preferably 
circularly cylindrical and the electron gun is aligned to provide a 
longitudinal path for the electron beam along the axis of this section. As 
best seen in Fig. 5B, the section 62 is essentially rectangular in cross 
section with a pair of relatively narrow side walls 66A, 66B and a pair of 
relatively wide side walls 66E, 66D. One of the narrow side walls 66A 
includes an elongated fiber optics faceplate 68 of the size and kind 
previously described. This faceplate 68 preferably essentially serves as 
the sidewall 66A. Section 62 is aligned with respect to section 61 so that 
the longitudinal path 69 of the undeflected electron beam in section 62 is 
close to the narrow sidewall 66B and centered between the wide walls 66C 
and 66D. 
Positioned along the length of section 62 is the array of electromagnets 70 
for providing the transverse deflection of the electron beam as it flows 
therepast to provide the desired repetitive linear scan of the faceplate 
68 in the manner previously discussed. 
FIG. 5B shows more the basic structure of an individual electromagnet 70 of 
the array. Each electromagnet 70 includes a core 72, adjacent sidewall 
66b, and about which is wound a coil 73 to which is supplied an energizing 
current of appropriate waveform as previously discussed Pole pieces 74 and 
75, adjacent wide sidewalls 66C, 66D, respectively, create a magnetic 
field that extends transversely across the envelope between sidewalls 66C, 
66D. This field is used to deflect the electron beam flowing inside the 
envelope along sidewall 66B transversely to the magnetic field for 
incidence on the faceplate 68 in the opposite sidewall 66A. Again it is 
unnecessary nor desirable that the beam be deflected at a ninety degree 
angle and preferably the deflection angle varies between thirty and sixty 
degrees. 
It is characteristic of this structure that is provides a highly efficient 
magnetic deflection system since it concentrates the magnetic field in a 
short gap where the electron beam flows. 
In one embodiment, Syntronic coil type C-15600-1 has been used for the 
electromagnets centered at 1.2" intervals. Of course, other sizes and 
different spacings are feasible. 
In practice, for ease of manufacture, the narrow side wall 66B is not 
perfectly plane but curved. Similarly, for ease of fabrication the wider 
sidewalls 66C and 66D need not be perfectly plane but also may be slightly 
curved particularly where they merge with the narrow side walls. 
Accordingly, the second section also may be viewed as having an elliptical 
cross section of which the major axis is the wide spacing between walls 
66A and 66B and minor axis the spacing between walls 66C and 66D. 
Typically, it may be advantageous to include one or more electromagnets 
(not shown) immediately after the electron gun along section 61 for 
positioning the beam and for minor deflection of the beam in the plane of 
the drawing of FIG. 5B to include the noise reduction multiple scan 
techniques previously mentioned. Additionally, such deflection would be 
important if a color display is to be provided at faceplate 68 by 
providing it with a typical R G B (red, green, blue) phosphor arrangement. 
In this CRT 60, typical dimensions for the second section 62 compatible 
with a first section 61 of about 1.5 inches diameter and a faceplate at 
least fourteen inches long and about 0.5 inches wide would be a spacing of 
about 0.5 inches between wide walls 66C and 66D and about 1.5 inches 
between walls 66A and 66B. Again the array might comprise fifteen magnets 
spaced apart about 1.2 inches for use with the 14 inch faceplate. For a 
longer facplate, more magnets would be included. 
It is to be understood that the specific design described is merely 
illustrative of the general principles and that various modifications are 
feasible consistent with the spirit of the invention. In particular, if a 
color display is desired, the electron gun can be designed to provide 
there parallel electron beams; one for each of the three primary colors, 
each modulated separately and deflected transversely in unison for 
incidence on an appropriate three color faceplate. 
Additionally, the endplate 74 shown in FIG. 5A may be treated i the manner 
described in aforementioned patent application Ser. No 151,439 to be 
provided with an electron sensitive coating (not shown) for use in 
monitoring the total current and/or position of the undeflected beam for 
use in adjusting the amount of current or position of the beams.