US2083995A - Television - Google Patents

Description

June 15, 1937. F. c. P. HENROTEAU TELEVI S ION 2 Sheets-Sheet 1 Filed Jan. 23, 1951 June 15, 1937. F. c. P. HENROTEAU TELEVISION Filed Jan. 23, 1931 '2 Sheets-Sheet 2 Arr-ya.

Patented June 15, 1937 PATENT- OFFICE TELEVISION Francois Charles Pierre Henroteau, Ottawa, 0n-

tarlo, Canada, assignor to Electronic Television Company, limited, Ottawa, Ontario, Canada Application January 23, 1931, Serial No. 510,705 In Canada January 20, 1931 13 Claims.

This invention relates to television, one object being to transmit either. by wire or by radio the moving images of scenes under ordinary illumination and at the same time provide that the image transmitted be exceedingly sharp and well defined, showing even the smallest details.

Another object of the invention is to permit the transmission of animate or still views under ordinary daylight illumination regardless, within limits, of the size of these views, that is to transmit all views which it is possible at present to photograph with a moving picture camera.

A further object of the invention is to provide a method whereby each point of the scene to be 15 televised can be impressed on the photoelectric surface for a greater time than has hitherto been possible.

A still further object of the invention is to provide a method whereby all the points of the scene to be televised are simultaneously projected on the transmitter and not successively projected thereon, as is the case with all practical methods of television now in use.

In all methods of television used at present the scene to be televised is divided into a number of elements according to the amount of detail required in the scene received. Each of these elements is then successively projected on the photoelectric transmitting cell and. sent to the receiving station. My method, however, differs radically from the above method in that all the elements of the sceneare simultaneously projected on the transmitter. If, according to the above method, it is desired to transmit an entire scene every sixteenth of a second and the scene is to be divided intoten thousand elements, then each element will be projected on the transmitting screen for only one one-hundred and sixty thousandth of a second. It is known that the electric energy liberated by photoelectric material is proportional to the amount of light falling on the material multiplied by the time during which this light acts. If, therefore, the light from each element of the scene is to remain on the transmitter for only one one-hundred and sixty thousandth of a second, a very strong illumination of this scene is necessary in order that the photoelectric material may emit enough energy for transmission and, for this reason, it is at present practically impossible to transmit scenes under ordinary daylight illumination.

According to my method, transmission is divided into three periods of equal length, the scene being projected on the transmitter during one of these periods. Since all the elements of the scene are simultaneously projected on the transmitter, the light from each element of the former falls on the latter for one third of one sixteenth of a second, that is for almost four thousand times longer than in known methods. If, however, the number of elements into which the scene is divided increases, then this proportion becomes still greater. In order to transmit the scene, a very strong spot of light is caused to scan the entire surface of the transmitting screen on which the scene has been projected. The time for which this scanning beam will act upon one element of the transmitter will be ten thousand times shorter than the time for which the light of the scene acts upon the same element. However, the light of the scanning beam can be made, on the average, ten thousand times greater than the light received from the scene. Therefore, the electric energy liberated from one element of the photoelectric material of the transmitter will be of the same order of magnitude as the energy liberated by the light of the scene which strikes that element. Thus, assuming the same illumination of the scene in transmission by my method and transmission by all other practical methods, the energy available for the transmission of the scene by my method will be, on the average, a number of thousand times greater than the energy available for the transmission of the scene by all practical methods.

It will be seen that by the use of my method,

-daylight television is made quite possible and,

since a very large number of elements may be formed in the particular transmitter which I use, a great wealth of detail in the transmitted scene is made possible.

The basic difference between my method of television and those now used is the simultaneous projection of all parts of the scene on the cathode, as has already been disclosed in my U. S. Patents Nos. 1,903,112 and 1,903,113. In the device as shown-in these patents, the cathode was divided into a multiplicity of tiny photoelectric elements insulated from one another. The view being projected on this cathode raised the individual elements thereof to different positive potentials, de-- pending upon the intensity of the light which struck these elements. The cathode was then scanned by a strong beam of light and a modulated electronic current was thus received by the anode. The interior of the photoelectric cell was coated with a layer of photoelectric material. In order to bring the various elements of the cathode back to a uniform potential, a strong beam of light was projected on the photoelectric coating Just mentioned, this light being of such wave length that the electrons which it detached from the coating had practically zero velocity and were thus attracted to any part of the cell which was at a positive potential. The anode and the grid being grounded, they were attracted to the cathode and neutralized the positive charges of the various elements thereof.

a certain part of the function of the cathode of my previous patents, namely, that of retaining an electrostatic reproduction of the view.

The regeneration of the cell is performed according to my present invention in a manner entirely different from that disclosed by me in my prior patents. After the picture has been sent, it is necessary to bring the various elements of the grid back to a uniform potential. The photosensitive coating oi the cathode is of a material which is sensitive to light in the visible spectrum but practically insensitive to ultra-violet light, while the coating of the metallic elements of the grid is of a material which is insensitive to visible light but sensitive to ultra-violet light. Thus in order to bring the elements of the grid to a uniform potential, I cause a strong beam of ultra-violet light to be projected thereon, the

" cathode being practically unaffected by this beam. I may, if necessary. provide means for screening the cathode from the beam while exposing the grid thereto.

According to my present invention, I provide a cathode in the form of a plate having a coating of photo-sensitive material thereon. An anode is also provided within the cell, and between the anode and the cathode, very close to the latter,

is positioned a grid. This grid is formed of a large number of quartz fibres each fibre having a number of mutually insulated metallic elements thereon, the number of the fibres and the number of elements on each fibre depending upon the degree of detail desired in the final picture. Mounted on a shaft is a suitable shutter for admitting the light of. the view, the scanning beam and the ray of ultra-violet light through three different lenses, respectively. Mounted on the same shaft as the shutter are suitable commutators for effecting the various electrical connections necessary for the anode and cathode.

The transmission of a picture is divided into three different stages which may be briefly described as follows:-

(A) The cathode and anode are connected to a source of comparatively high negative potential, of equalvalue for both, so that the grid, which has no electrical connection, will be at a potential near zero and therefore positive with respect to the rest of the elements in the cell. At the same time theiimageof'a'. view 'is projected on the cathode. Different parts of the photo-sensitive coating of -this cathode will emit different numbers'of 'electronsdepending upon the degree of intensity of the light of the particular part of the view which strikes them. These electrons will be collected by the elements of the grid adjacent to the parts of the cathode from which they were emitted and these elements will thus attain varying degrees of negative potential, corresponding ductive elements i 2.

to the degree of intensity of the light which struck the adjacent parts of the cathode. In this manner an electrostatic reproduction of the view will be formed on the grid.

(B) The view is then interrupted and the cathode grounded, while the anode is connected to a source of comparatively high positive potential and to the grid of the first thermionic valve of a transmitter. At the same time a very strong beam of light from a cathode ray oscillograph is caused to scan the photo-sensitive surface of the cathode. The electrons emitted under the influence of this beam will be attracted to the anode by reason of its positive potential but their number in each instance will be controlled by the potential of the particular element of the grid adjacent to which they must pass. A modulated potential will thus be impressed on the grid of the first thermionic valve of the transmitter, and this potential will be proportioned in intensity to the intensity of the light of the various portions of the view which were originally projected on the cathode.

(C) The scanning beam is interrupted, the

cathode and anode are grounded and a strong beam of ultra-violet light is projected on the grid. Under the influence of this light, the metallic elements of the grid, which are composed of a metal, such as zinc, sensitive to ultraviolet light, will emit electrons until all the elements reach a uniform potential which will be very nearly zero. The emitted electronswill be captured by the cathode or by the anode.

The invention will be more fully understood by reference to the attached drawings in which:

Figure 1 is a general view of my apparatus partly in section.

Figure 2 is a plan view of the grid. Figure 3 is a plan view of the shutter showing the relation of the various lenses thereto, and

Figure 4 is a view showing a modification of the apparatus used for regenerating the grid.

In the drawings, l is a photoelectric cell which is formed with a flattened part 2 having a quartz window 3 therein and two lenses 4 and 5 mounted adjacent thereto, the centres of the two lenses and that of the quartz window being at the aploes of an equilateral triangle, as shown in Fig. 3. The part 2 is opaque except for the quartz window 3 and the parts directly behind the lenses 4 and 5. Mounted within the tube is an anode 6 and a screen 1 constituting a cathode and being formed of an electro-conductive plate 1a having thereon a layer 8 of material such as caesium sensitive to visible light but practically insensitive to ultraviolet light. This layer is preferably monomolecular, since it is well known that this enhances the photoelectric activity.

The anode 6 is made in the form of a small sphere partly to prevent its interfering with the various beams of light through the lenses 3, 4, and 5 and partly to reduce its electrical capacity.

Mounted between the anode 6 and cathode I and very near the latter is a grid 9. This grid consists of a large number of quartz fibres ll stretched between posts ii and having thereon a multiplicity of mutually insulated electro-con- The elements of the grid are formed by silver plating an extremely thin quartz fibre, then electroplating the platedfibre with a metal, such as zinc, which, while insensitive to visible light is sensitive to ultra-violet light, and finally removing the entire metal plating from the quartz at regular intervals. by

some suitable process, such as dissolution, so that cent elements by a short length of bare quartz.

, The metallic elements-of the adjacent wires are preferably staggered with respect to one another, that is, the elements of one wire will occupy the 1, 3, 5 positions while the elements of the next wire will occupy the 2, 4, 6 positions.

A shutter I3, arranged opposite the flattened part 2 of the cell, has an opening I4 therein of such size that it will not uncover more than one transparent portion of the part 2 atone time. The shutter I3 is mounted on a shaft I5 and rotates therewith. Mounted on the same shaft and rotating therewith is a commutator I6 of insulating material having a metallic sector II thereon, this sector being connected to the anode 6 by means of a wire I8. Arranged around the commutator are three contacts I9, 20, and 2I, the contact I9 being connected to ground 22, the contact 20 being connected through negative battery 23 to ground 24 and the contact 2I being connected through resistance 25 and positive battery 26 to ground 21 and also to the grid 28 25 of the first thermionic valve 29 of a transmitter.

The contacts I9, 20 and 2| are arranged around thecommutator at the apices of an equilateral triangle and the angle subtended by the arc of the metallic sector I! is slightly less than 120 30 so that this sector connects-with only one contact at a time. A commutator 30 similar to the commutator I6 and having a metallic sector 3I similar to the metallic sector I1 is also mounted on the shaft I5, the sector 3| being connected to the cathode by a wire 32. Arranged around the commutator are three contacts 33, 34 and 35, the first being connected to ground 36, the second through negative battery 31 to ground 38 and the third to ground 39.

A cathode ray oscillograph '40 for scanning purposes is arranged in such a way that the light produced by the impact of its electronic stream on the fluorescent screen M will pass through the lens 5 and that its fluorescent screen M will be a conjugate plate to the cathode I with respect to this lens. In the embodiment shown the cathode ray oscillograph is arranged above the apparatus and its light is reflected by the mirror 42. If desired some other form of scanning means 50 might be used, the cathode ray oscillographhaving been shownmerely by Way of example and because it is thought to be the most suitable.

In Figure 1 the device for producing the ultraviolet light is shown by way of example as comprising an arc light 43 having in front thereof a piece of Jena glass 44 which will allow only the ultra-violet part of the light from the arc to pass.

Although the material with which the cathode is coated is practically insensitive to ultra-violet, it may be advisable to arrange the apparatus in such a manner that the ultra-violet light for regenerating the grid will be prevented from striking the cathode coating. This arrangement is illustrated in Fig. 4, in which only those parts directly relevant to it are shown.

What would correspond to a negative photographic reproduction of the grid 9 is formed on a plate 45 transparent to ultra-violet light so that this light may only traverse the plate at those points which correspond to the wires of the grid. In the drawings the black lines 46 represent the parts of the plate which correspond to the inter-wire spaces of the grid and are opaque 75 to ultra-violet light, while the white lines 41 repsensitive surface 8 of the cathode.

resent the parts of the plate which correspond to the wires of the grid and are transparent to ultra-violet light. The reproduction of the grid on the plate may.,be performed in any suitable manner, either photographically or otherwise. The finished plate is placed in such a position that it will form a conjugate plane to the grid 9 with respect to a quartz lens 48 which is used in this case instead of the quartz window 3. The

source of ultra-violet light is positioned so that The whole apparatus will be suitably magneti- 4 cally and electrically shielded.

The operation of the apparatus which has been described above is as follows:

Transmission takes place in three stages, each stage lasting approximately 1/50 of a second:

(A) The shaft I5 in its rotation connects the anode 6 through wire I8, sector I! and contact 20 to negative battery 23, this battery having a comparatively high potential, such as minus 100 volts. At the same time the cathode 1 is connected through wire 32, sector 3I and contact 34 to negative battery 31, this battery having the same potential as battery 23. Owing to the rotation of the shaft, the opening I4 of the shutter I3 is at this instant brought into registry with the lens 4 and the image of a view is projected through the opening and the lens onto the photo- Since both the cathode and the anode are at the same comparatively high negative potential and the grid is unconnected, the metallic elements of the latter are, therefore, positive with respect to the rest of the elements of the tube.

Under the influence of the light from the-view different parts of the cathode will emit diiferent numbers of electrons, depending upon the intensity of the light in the particular part of the view which is striking them. All the electrons emitted from any one point on the cathode will be collected by the nearest element I2 of the grid, which element will thus assume a certain negative potential. Owing to the small size of the elements and therefore their very low capacity, the negative potentials which they assume will be comparatively high even for the very small electronic emission which they receive. Each element of the grid receiving a difierent number of electrons will be raised to a difierent negative potential. It will thus be seen that the light of the view striking the cathode will produce an electrostatic reproduction of this view on the grid.

(B) The light from the view is interrupted and the rotation of the shaft I5 brings the opening I4 of the shutter I3 into registry with the lens 5. At the same time it connects the anode through the sector I! and contact 2I to the positive battery 26 and to the grid 28 of the first thermionic valve 29 of a transmitter and also connects the cathode through the sector 3| and contact 35 to ground 39. While the lens 5 is in registry with the opening I4 of the shutter I3, the beam of light from the cathode ray oscillograph 40 scans the photo-sensitive surface 8 of the cathode "I. The scanning beam of the cathode ray oscillograph is extremely strong and of constant intensity so that under its influence the same number of electrons will be detached from each successive point of the cathode which it strikes and attracted to the anode by reason of the comparatively high positive potential of the latter. One of the metallic elements I2 of the grid 9 will,

negative potentials of the different metallic elements of the grid, so that, in the result, the anode will receive an electronic currentmodulated in accordance with the intensityof the light of the different parts of the view which was originally projected on the cathode. The modulated electronic current received by the anode will modulateits potential and these potential modulations will be impressed on the grid 28 of the first thermionic valve 28 of the transmitter. From here transmission is by known methods.

It will be noticed, in connection with this operation, that the anode, being in the form of a small sphere, has a very low electric capacity and.

that its electrical connection to the grid 28 of the thermionic valve is made as short as possible in order to reduce the capacity of this connection also. Thus, in operation, the small variations of electronic current received by the anode will cause quite appreciable variations in its potential and thus cause the same variations of potential on the grid of the thermionic tube of the trans- 30 mltter.

(0) The rotation of the-shaft ls moves the opening ll of the shutter ll .into registry with the quartz window 3 and at the same time grounds both the anode and cathode at grounds 22 and 3 6 respectively. The ultra-violet light transmitted through the Jena glass will pass through the quartz window 8 and strike the metallic elements I 2 of the grid 9. It will also strike the photosensitive coating 8 of the cathode but since this coating is almost completely insensitive to ultraviolet light, the latter will have no effect on it. The zinc coating of the metallic elements II of the grid 9, however, being photo-sensitive to ultra-violet light, will emit electrons, which will be attracted by the cathode and also by the anode, since both these electrodes are grounded and therefore positive with respect to the various elements of the grid which are at various negative potentials. As soon as an element of the grid has emitted enough electrons to acquire a slight positive potential then any further electrons which it emits will be reattracted to it and it will retain the same potential. In this manner all the elements of the grid will be brought to a uniform potential which will be slightly positive.

If the regenerating arrangement shown in Figure 4 is used the operation is only slightly modified. When the opening I of the shutter l8 registers with the quartz lens 48, the ultra-violet light, which has passed through the screen 45 and'has been reflected by the mirror 49, passes through the lens 48 and strikes the wires of the grid 9. Owing to the construction of the screen 'the light is prevented from striking the cathode. The elements of the grid are brought to a uniform potential as described above.

Immediately after this last operation is completed the cycle of operations A, B, C is repeated many times. In each case operation C brings the metallic elements of the grid to the same uniform potential. v

' The irequency'band necessary for transmission might be narrowed if, instead of using only one apparatus where the whole cycle of operations is completed in one sixteenth of a second, three on the receiver.

-- thereof.

aosspos apparatuses were used. In this case while the first apparatus was performing operation 'A the second would be performing operation B and the third, operation C. Thus, though a picture would be transmitted every 1" second, each operation could last instead of only 1/50 of a second. This would be of importance in transmitting the picture since this operation could then be spread over three times the period which could be allowed when only one apparatus was used and the frequency band for transmission thus narrowed.

Very strong, enlarged and contrasted images of very faint, still objects could be produced with my system owing to electrical amplification. The shutter I3 would be brought to a position to allow the view to fall on screen 8 for a suitable length of time. The shutter would then be rotated to a position to allow scanning of the screen and this scanning could be repeated without any intermediate operation for as long as desired since the electrostatic image of the object would always remain on the grid. My device could for instance be attached .to a powerful astronomical telescope and, while the image focussed would be large and weak, a very vivid strong image would appear The device could also be attached to a microscope andpermit hitherto invisible objects to be seen.

The effect produced by the scanning beam'of the cathode ray oscillograph may be achieved in a modification of my invention by another arrangement.

In this modification, the cathode is formed of a an extremely thin plate of aluminium or berylium, the latter being preferred owing to its low density. This plate is coated on one side with a monomolecular layer of photo-sensitive material such as caesium, this side of the plate facing toward the grid. The plate itself forms the screen of a cathode ray oscillograph, the electronic stream of the latter being directed against the uncoated side of the plate, namely that facing away from the grid.

At the appropriate time for the scanning operation the cathode ray oscillograph comes into operation to cause an electronic stream to scan the uncoated side of the plate. The electrons in this stream are moving at an extremely high speed and will pass through the plate. In so doing, however, their speed will be considerably reduced so that after their passage they will be moving with approximately the same speed as the electrons emitted from the photo-sensitive surface 8 as described in connection with Figure 1. The berylium plate, being of uniform thinness and density, the speed of the electronic stream, after its passage therethrough, will be uniform for all points. After they have passed through the plate the electrons will be attracted by-the anode, the number reaching the latter from any point of the cathode being controlled in each instance by the potential of the metallic element of the grid near which they must pass.

.Thus the same result will be produced by this arrangement as would be produced by the scanning arrangement disclosed above.

' Various modifications might be made in the apparatus disclosed for carrying out my invention without departing from the spirit or scope Thus for instance, it is not necessary that the shutter l8 and commutators l8 and ll be all mountedon the same shaft, this particular arrangement having been disclosed merely because it was thought to be the most convenient. 7

quence, causing said stream to be modulated by said electrostatic reproduction, and picking up the modulated stream at an anode.

2. A method or electrical image transmission 15 which comprises impressing an image upon a photosensitive surface, collecting the electronic emission from said surface to form an electrostatic reproduction of said image on means other than said surface, causing an electronic stream 20 to be emitted from every point of said surface in sequence, causing said stream to be modulated by said electrostatic reproduction, picking up the modulated stream at an anode, and finally causing said electrostatic reproduction to disappear.

3. A method of electrical image transmission which comprises impressing an image upon a uniformly electro-conductive and uniformly photosensitive surface, collecting the electronic emission from said surface to form an, electro- 30 static reproduction of said image on means distinct from said surface, causing an electronic stream to be emitted from every point of said surface in sequence, causing said stream to be modulated by said electrostatic reproduction and 35 causing the modulated stream to be attracted by an anode.

4. A method of electrical image transmission which comprises impressing an image upon a surface photosensitive only to visible light, collecting the electronic emission from the said surface to form an electrostatic reproduction of said image on means distinct from said surface and photosensitive only to ultraviolet light, causing an electronic stream to be emitted from every point of said surface in sequence, causing said stream to be modulated by said electrostatic reproduction, picking up the modulated stream at an anode, and finally causing said electrostatic reproduction to disappear by means of ultraviolet light.

5. Apparatus for the electrical transmission of images comprising a cell, a photosensitive surface within said cell, means for impressing an image on said surface, separate means in the form of a grid also within said cell, formed with a multiplicity of mutually insulated electroconductive elements, for retaining an electrostatic reproduction of said image, means for thereafter causing said photosensitive surface to emit an electronic stream from every point thereof in sequence, and an anode for receiving said electronic stream modulated by said electrostatic reproduction.

6. Apparatus for the electrical. transmission of images comprising a cell, a photosensitive surface within said cell, means for impressing an image on said surface, separate means in the form of a grid also within said cell, composed of a number of'insulating fibres each having a number of mutually insulated electroconductive elements thereon, for retaining an electrostatic reproduction of said image, scanning means for causing said photosensitive surface to emit an electronic stream from every point thereof in sequence, and an anode for receiving'said electronic stream modulated by said electrostatic reproduction.

7. Apparatus for the electrical transmission of images comprising a cell, a surface within said cell, photosensitive only to visible light, means for impressing an image on said surface, a grid also within said cell formed witha multiplicity of mutually insulated electro-conductive elements, said elements being photo-sensitive only to ultra-violent light, said grid serving to retain an electrostatic reproduction of said image, means for causing said photosensitive surface to emit an electronic stream from every point thereof in sequence, and means for thereafter projecting ultraviolet light on said grid to neutralize said electrostatic image.

8. Apparatus for the electrical transmission of images comprising a cell, a photosensitive surface within said cell, a grid also within said cell composed of a multiplicity of mutually insulated electroconductive elements, said elements being sensitive only to light of a different wave length from that to which said surface is sensitive, means for impressing an image on said surface, means for causing the elements of said grid to collect the resulting electronic emission from the adjacent portions of said surface and thus assume various negative potentials, means for scanning said surface with a beam of light, and means for causing another electrode in said cell to attract the resulting electronic stream, the electroconductive elements of said grid serving to modulate the last mentioned electronic stream.

9. Apparatus for the electrical transmission of images comprising a cell, a surface within said cell, photosensitive only to visible light, means for impressing an image on said surface, a grid also .within said cell formed with a multiplicity of mutually insulated electroconductive elements, said elements being photo-sensitive only to ultraviolet light, said grid serving to retain an electrostatic reproduction of said image, means for cause ing said photosensitive surface to emit an electronic stream from every point thereof in sequence, means for thereafter projecting ultraviolet light on said grid to neutralize said electrostatic image, and means for shielding said photosensitive surface from said ultraviolet light.

10. Apparatus for the electrical transmission of images, comprising a cell, a photosensitive surface within said cell, means for causing an electronic stream to be emitted from every point of said surface in sequence, means for impressing an image on said surface, separate means in said cell for retaining an electrostatic reproduction of said image and for modulating the emitted electronic stream in accordance with the electrostatic reproduction, and an anode for receiving the modulated stream.

11. Apparatus for the electrical transmission of images, comprising acell, a photosensitive surface within said cell, means for causing an electronic stream to be emitted from every point of said surface in sequence, means for impressing an image on said surface, separate means in said cell for retaining an electrostatic reproduction of said image and for modulating the emitted electronic stream in accordance with the electrostatic reproduction, an anode for receiving the modulated stream, and means for causing the electrostatic reproduction to disappear.

12. In a method of electrical image transmission the steps which comprise impressing an image upon a photosensitive surface, collecting the electronic emission from said surface on means comprising a multiplicity oi! mutually insulated e1ectroconductive elements, to form an electrostatic reproduction 01' said image thereon, scanning a surface to cause an electronic current of substantialiy constant intensity to be emitted from areas of said surface successively scanned, modulating said electronic current by said electrostatic reproduction, picking up the modulated current at an anode, and controlling the operation '01 a 10 transmitting device in accordance with the successive changes in value of said modulated current.

13. In apparatus for the electrical transmission of images, means for scanning a screen to cause an electronic stream to be emitted therefrom. means separate and distinct from said screen tor modulating the electronic stream in accordance .with the intensity of thedight 0! an image, and

an anode for picking up the modulated stream.

FRANCOIS CHARLES HEHRO'IIAU. l0

Images