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Publication numberUS796254 A
Publication typeGrant
Publication dateAug 1, 1905
Filing dateSep 15, 1904
Priority dateSep 15, 1904
Publication numberUS 796254 A, US 796254A, US-A-796254, US796254 A, US796254A
InventorsBruno Saenger, Raimund Wilhelm Hartmann
Original AssigneeArnold Franz
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Photophone.
US 796254 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

BRUNO SAENGER, OF BERLIN, GERMANY,

ADMINISTRATOR OF RAIMUND WILHELM HARTMANN, DEOEASED, ASSIGNOR TO FRANZ ARNOLD, OF

DEGGENDORP, GERMANY.

PHOTOPHONE.

Specification of Letters Patent.

Patented Aug. 1, 1905.

Application filed September 15, 1904. Serial No. 224,549.

T0 aZZ whom, it may concern.: l Beit known that I, BRUNO SAENGER, a citizen of the Empire of Germany, residing at l Berlin, in the Empire of Germany. am the administrator of the estate of RADIUND WIL- HELM HARTMANN, deceased, late a citizen of v the Empire of Germany, who did invent a new and useful Photophone, of which the following is a specification.

The hitherto-known photophones present the great disadvantage that they disperse too much the light, whereby the conveyance of l speech over very large distances and at dayl light is rendered impossible. The. only means l hitherto known for obtaining a pencil of rays l of light as parallel as possible is the parabolic 1 reliector. However, the more it is attempted to utilize the properties of the parabolic mirror the less will it be found possible to thereby increase the practical usefulness of the wireless telephony, which is now so much aimed at. For a mutual understanding over a distance of but a few kilometers already gigantic parabolic mirrors would be required, so that the use of such instruments would be quite impossible for military or sporting purposes. rlfhe hitherto-known photophones also present the defect that it is not possible to keep secret the conversation, since other receivers near the one to which speech is to be conveyed l from the sender are also capable of collecting l the dispersed rays of light and thereby receiving the intelligence. The receivers in such known photophones are, moreover, not adapted to receive only the rays of light from the right sender while excluding those from all other senders.

The present invention relates to improvements in photophones, whereby the conveyance of speech over greater distances than hitherto is rendered possible and the size and the weight of the photophone are kept within moderate limits, so that the latter can be easily transported, while a greater secrecy of the conversation both at the sending-station and at the receiving-station is insured.

The objects of the improvement are, first, to provide au elliptic mirror with a plane mirror covering it and having a narrow circularcentral hole; second, to provide as'ource of light in the focal point of the elliptic mirror; third, to provide a Bells mouthpiece at a convenient angle to the axis of the elliptic l mirror, its membrane being adapted to serve as a mirror for reflecting the pencil of rays of light from the elliptic mirror; fourth, to provide a sending-tube similar to an astronomical telescope and adapted for changing the pencil of rays reiected from the membrane to a beam of nearly parallel rays which pass through the space, all the parts hitherto named forming the sender of a photophone; fth, to provide a receiving-tube having at the rear end a bottom and at the front end an object-glass adapted to bend a beam of rays to the center;

sixth, to provide in the bottom of the receiving-tube a longitudinally-movable small camera obscura having a narrow circular central hole in the focal point of the object-glass;

i seventh, to provide within the small camera obscura a selenium cell or radiophone, and, eighth, to provide a circuit connectingl the selenium cell or radiophone with a telephone. These objects are attained by the photophone illustrated in the accompanying drawings, in which- Figure l is a vertical longitudinal section through a photophone comprising a sender and a receiver. Fig. 2 shows, on an enlarged scale in section, the bottom of the camera obscura in the receiving-tube and provided with the selenium cell. Fig. 3 is an elevation of the same; and Fig. 4 is a diagram, which will be referred to later on.

Similar characters of reference refer to similar parts throughout the several views.

The employment of an elliptic mirror in place of the parabolic mirror is based upon the well-known property of the ellipse (see Fig. 4) that the angle E E between the radius vector (Z from the one focus Z2 to any point (Z of the ellipse and the lengthened radius vector a c from the other focus L through the same point .Z is divided into two equal angles E and E by the tangent f g to the ellipse in (Z. 1f now in the center c a perpendicular Zt 'Z is raised, which intersects the radius vector a Z at lc, and a line c Z is drawn from Zt* to the point Z on the left of the perpendicular Z1. 1C at the same distance therefrom as the point (Z, of course the line Zt' Z will be equal to Zt' Z and t Z equals Z) ZZ, also angle a c ZL equals angle Z Zt' i. Now if the radius vector a Z be lengthened through the focus a to the point 1a of the ellipse and the latter point m.. be connected with the other focus Z by the radius vector m Z) intersecting the central perpendicular t i at n of course the line n a, drawn from the point n to the focus a, will be equal to n and also angle m yn equals angle a n z'. From an examination of Fig. -1 it will be seen that the distance n, c of the second intersection n from the center c is much smaller than that c of the first intersection k. It is also evident that when in a similar manner as before the line n a, be lengthened beyond the focus a to the ellipse and from the new intersection a radius vector be drawn to the right focus b intersecting the central perpendicular he' ata point the latter will be still nearer to the center c than the second interl section fn. It is further obvious that in an elliptic mirror covered by a plane mirror in the plane or' the central perpendicular /L z any ray of light ay k emanating from the focus a and striking the plane mirror at the point will be reiected to the point Z of the surface and from thence through the focus a to the opposite point m of the elliptic mirror, then from thence to the point yn oi' the plane mirror, and from the latter again through the focus ct to the respective point (not shown) of the elliptic mirror. In other words, this ray of light will constantly be reflected and more and more approach to the axis o e. The same is true for all the other rays of light produced by a source of light in the focus (t.

The photophone shown at Fig. 1 comprises a sender and a receiver. The sender is composed of an elliptic mirror 1, a plane mirror 2, a Bells mouthpiece 3 with the membrane 4, and a sending-tube 5. rlfhe receiver is composed of a receiving-tube6 and a small camera obscura 7. All the parts are shown as combined and supported by a table 8, provided with, preferably, three feet 9 9 and adjusting-screws 1() 10. rIhe two tubes 5 and 6 are parallel to each other and may be superposed and rigidly connected in any known and approved manner-for example, by means of the two frames 11 11, ailixed 0n the table 8 with convenient screws 12 12. The elliptic mirror 1 maybe supported on the table 8 with the aid of a suitable frame or casing 13 and is .connected with the plane mirror 2 by means of a thread 14e or otherwise. ror 2 is provided with a narrow circular hole 2T in the axis of the elliptic mirror 1. For g producing the rays of light within the elliptic mirror any convenient source of light;` may be employed. I have shown this to be an electric-arc light 15, produced by a convenient arc-lamp arranged in the frame or i casing 13. This lamp comprises two carbon pieces 16 and 1T, which pass through two opposite holes in the elliptic mirror 1 and may l be therein guided, while their external ends are secured in two holders or arms 18 and 19, respectively. feed-screw 20, parallel to the two carbon pieces 16 and 1T, is mounted to turn in the frame or casing 13 and provided l l i l l The plane mirwith two opposite threads of unequal pitch, the pitch of the one thread being about double that of the other thread. These two threads engage in correspondingly-threaded holes of the twoholders 18 and 19` which latter are guided by two horizontal rods 21 and 22, parallel to the feed-screw 2O and secured A small knurled in the frame or casing 13.

wheel 23 is fastened on the external end of the feed-screw 20, so that by turning this wheel 23 the twocarbon pieces 16 and 1T can be simultaneously and longitudinally shifted in opposite directions. rlhe two carbon pieces 16 and 17 are electrically connected by wires 24 and 25 with a battery 26 or other 1 source of electricity. It will be seen that the l striking of the arc can be effected by suitably i turning the knurled wheel 23 and that by l gradually turning the latter in proportion to the consumption of the carbon pieces the arc-light can be regulated and made steady. Owing to the unequal pitches ot' thetwo threads of the feed-screw 2O and from reasons well known, the arc-light 15 will remain in the focus of the elliptic mirror 1.

I have shown the two tubes 5 and 6 as hori- Zontal and the axis of the elliptic mirror 1 as vertical-that is, the latter at right angles to the axis ofthe sending-tube 5. Consequently plane of the sending-tube 5 and ot' the elliptic mirror 1 and at an angle oi' forty-live degrees. The mirror 28 may bc made separately and affixed on the membrane 4 in any suitable or known manner, or it may be made in one piece with the membrane 4. or the mirror 28 may replace the membrane 4 altogether, it

Vlie mouthpiece 3 is placed in the vertical being made thin and elastic. The sendingtube 5 is similar to an astronomical telescope l and comprises a small tube 29 with two lenses i 30 and 31 near the mirror 28 and a large lens 32 on the external end. rl`he tube 29, with its g two lenses 30 and 31, is similar to an eyepiece ot' the said telescope and has a very g small focal distance, either positive or negative, while the large lens 32 has a very large i focal distance. The tube 29 is longitudinally l adjustable in the tube 5, and while this adl justment may be effected in any suitable way, as shown in the drawings, it is accoml plished by screwing the tube into the bottom 51 oi' the tube 5. Preferably the mouthpiece 3 is connected with the sending-tube 5 by means of a casing 33, and the latter is proi vided with a vertical tube 3-1 concentric with the elliptic mirror 1, which tube 34 can enx gage a similar tube 35 on the plane mirror 2.

i r1 hus the photophone can be put together and again taken to pieces, the sending-tube 5 being secured in the two frames 11 11 by means l of two detachable bows 36 36, so that it can Y, be vertically removed and again replaced. i The inside faces of the tubes 5, 29, 34, and l, 35, the bottom 51, and the casing 33 and the l outside faces of the tube 29 are preferably l l v blackened in the usual manner for absorbing l tain, though small, length, so that the theory all foreign rays of light, particularly the diffuse daylight.

The receiving-tube 6 is preferably made larger in diameter than the sending-tube 5 and is provided with a large lens 37, having a large focal distance. The small camera obscura 7 is a tube longitudinallyT adjustable in the bottom 38 of the tube 6 and provided with a front cover 39 and a bottom 40. The front cover 39 may be secured on the tube 7 by means of a threaded ring 42 or the like and is provided with a narrow circular central hole 41, and the tube 7 must be each time so adjusted as to bring the hole 41 exactly into the focus of the lens 37, as is indicated by the crossing lines in Fig. 1. 40 may be constructed in the manner shown at Fig. 2, so that it canl be screwed on the tube 7 and again taken off. It is to be remarked here that the tube 7 may be arranged to be longitudinally adjustable in any convenient manner. As shown in the drawings, the adjustment is effected by screwing the tube 7 into the bottom 38 of the tube 6. On the inside of the bottom 40 a selenium cell 43 or radiophone of any known construction is secured. I have shown this selenium cell as consisting of a ceramic plate and a Zigzagged selenium wire embedded in the surface of this plate. The two ends of this zigzagged selenium wire are connected with two hinding-posts 44 and .45 and the latter by two wires 46 and 47 with a telephone 48 and a battery 49. whereby a circuit is formed. The telephone 48 is not shown in the proper size, but merely diagrammatically, as its construction is immaterial for the present invention. The internal faces of the tubes 6 and 7 and the bottoms 38 and 40 and the faces of the cover 39 are also blackened for absorbing the diuse daylight.

The photo phone described so far is operated in the following manner: It is directed toward the respective receiving-station. After striking the arc this arc will emit rays of light in all directions; but only the rays in the axis of the elliptic mirror l and those very little deviating therefrom will be able to at once pass through the narrow circular hole 27 in the plane mirror 2. All the other rays of light will be reliected so many times by the surfaces of the elliptic mirror 1 and the plane mirror 2 as is necessary to bring them nearly into the axis of the elliptic mirror 1 in the manner explained above, when they will pass through the central hole 27 of the plane mirror 2. Thereby an intensive thin and very acute-angled pencil of rays of light is produced, which can easily be subjected to strong variations of the intensity. lt is to be remarked that the source of light, here the arclight, may not always be placed exactly in the focus of the elliptic mirror 1 and that it is not actually in the focus alone, since it has acer- The bottom g put forward above is not quite exact. However, the elliptic mirror in combination with the centrally-perforated plane mirror is specially suitable for collecting the rays emanating in all directions from a source of light in a single intense pencil of rays of a very restricted cross-section, which hitherto it was not possible to obtain by any known device.

The intense thin and very acute-angled pencil of rays of light passing through the central hole 27 strikes the mirror 28 and is therefrom deflected to the lens 30. The beam of parallel rays passing' from the lens 3() to the other lens 31 converges to the focus 50 and thence diverges to the large lens 32, from which nearly parallel rays of light pass through the space, so that this beam is capable of producing an image in a telescope at a very distant station. Of course the receiving-tube is made sufficiently large in diameter for receiving the full image. \Vhen assuming the tube 6 to be at the receiving-station and its lens 37 to receive the beam of rays from the lens 32 of the sending-station, the rays will be bent toward the center and made to converge to the focus-e7. e., the central hole 41 in the cover 39-after which they will diverge and produce the image on the face of the selenium cell 43 or radiophone.

lfVhen the operator talks immediately in 'front of the mouthpiece 3, the membrane 4, and with it the mirror 28, will be thrown into a complicated state of vibration, which represents the three elements of the speakers voice-namely, pitch` intensity, and quality. The pencil of rays of light will of course be subjected to these vibrations by the mirror Q8, and these vibrations will be transmitted with the rays through the space to the lens 37 of the distant receiving-tube 6 and produce variations in the resistance of the selenium cell 43 or radiophone. rIhe currents circulating in the circuit 46 47 of the battery 49 and the telephone 48 will register all the peculiarities of the speakers voice and produce changes in the magnetism of the magnet and of the membrane in the telephone 48. The operator at the distant receiving-station placing his ear to the membrane of the telephone 48 will therefore hear the vcry sounds given out by the speaker at the sending-station.

The sender of the new photophone presents the important advantage that it does not emit any7 lateral rays of light-that is to Say, the image of the source of light can only be pcrceived by an eye in or close to the optical axis of the sending-tube, so that the speech can be conveyed only to a distantreceivingtube 6 which is in line with the axis of the sending-tube In a similar manner the receiver of the new photophone presents the advantage that owing to its small camera obscura 7 it does not receive any other rays of light but the beam of rays emanating from a l n l l sured, which hitherto was not possible with v the known photophones.

It is evident that if both photophones at the sending-station and at the receiving-station have two superposed tubes the sendingtube of the one photophone and the receiving-tube of the other photoplione require to be above, while the receiving-tube of the former photophone and the sending-tube of the latter photophone require to be placed below. In other words, with the one photophone the sending-tube is above and the receiving-tube below, while with the other photophone the Leyer is the case.

`Where so preferred, the sending and the receiving tubes of a photo phone may be placed side by side in a horizontal plane, so that the two photophones at the sending and the receiving stations may be made alike, as the sending-tube of the one photophone will be opposite to the receiving-tube of the other photophone, and vice versa. The elliptic mirror of each photophone may also be placed horizontally, and the two carbon pieces of the arc-lamp may be placed either horizontallyv or vertically or at any angle. I have shown the knurled wheel 23 as arranged to be turned by hand; but it may also be automatically turned by any known mechanism. rIhe arc-lamp may be of any known and approved construction. The supportingtable 8, with the three legs 9 9, may be replaced by any convenient support.

\Vhere so preferred, the sender, comprising the elliptic mirror l, the plane mirror Q, the arc-lamp, the tube 5, and the mouthpiece 3, with the membrane 4 and the mirror 28, may be Iliade separately and supported by a convenient table 8, while the receiver, comprising the tube 6 andthe small camera obscura 7, may equally be made separately, supported `by a convenient table.

The angle between the axes of the elliptic mirror and the sending-tube may be varied. The phot-ophone may be varied in its construction without deviating from the spirit of the present invention.

That is claimed, and desired to be secured by Letters Patent, is-

1. In a system of photophony, the combination wit-h a device emitting an intense, thin and very acute angled pencil of rays of light, of means for subjecting this pencil of rays to the action of the voice, a sending-telescope adapted to change the pencil of varied rays to a beam of nearly parallel rays passing through the space, a receiving-tube with a lens adapted to bend the rays of this beam toward the center, a small second camera obscura in the receiving-tube and having a narrow circular central hole in the focus of the lens, a radiophone on the bottom of the small camera obscura and adapted to increase and decrease its electrical resistance und er the action of the beam of bent and varied rays of light, a circuit connected with the radiophone, and a telephone in this circuit.

2. In a photophone, the combination of an elliptical mirror, a plane mirror covering the elliptical mirror and provided with a small hole in the axis of the elliptical mirror, a source of light in the Jfocus of the elliptical mirror, means for subjecting the rays of light passing through the hole of the plane mirror to sound-waves, and means for transmitting the varying rays through space.

3. In a photophone the combination of an elliptic mirror, a plane mirror covering said elliptic mirror and provided with a small circular hole in the axis of said elliptic mirror, a source of light in the focus of said elliptic mirror, so that the rays of light emanating in all directions from said source of light are several times reiiected by said elliptic mirror and said plane mirror, until they pass through the small hole of the latter in an intense, thin and very acute angled pencil, a mouthpiece having a vibrating and reflect-ing membrane standing at an angle to the axis of the elliptical mirror, and a telescope into which the pencil-rays are deected.

4. In a photophone the combination of an elliptic mirror, a plane mirror covering said elliptic mirror and provided with a small circular hole in the axis of said elliptic mirror, an arc-lamp, the carbon pieces of which pass through holes in said elliptic mirror and are adapted to form the arc-light in the focus, so that the rays of light emanating in all directions from said arc-light are several times refiected by said elliptic mirror and said plane mirror, until they pass through the small hole of the latter in an int-ense, thin and very acute angled pencil, a mouthpiece arranged at an angle to the axis of the elliptical mirror and having a vibrating and reiecting membrane, and a telescope into which the pencil-rays are deiected.

5. In a sender of a photophone, the combination with an elliptic mirror, of a plane mirror covering said elliptic mirror and provided with a small circular hole in the axis of said elliptic mirror, a source of light in the focus of said elliptic mirror, so that the rays oi' light emanating in all directions from said source of light are several times reiiected by said elliptic mirror and said plane mirror, until they pass through the small hole of the latter in an intense, thin and very acute angled pencil, a Bells mouthpiece at an angle to the axis of said elliptic mirror and having a membrane which is adapted to vibrate under the action of the voice and to reflect the pencil of rays, a telescope adapted for changing the pencil of refiected and varied rays of light to a beam of nearly-parallel rays which pass through the space, and means for supporting all said parts.

6. In a sender of a photophone, the combination with an elliptic mirror, ot' a plane mirror covering' said elliptic mirror and provided with a small circular hole in the axis of said elliptic mirror an arc-lamp, the carbon pieces ot' which pass through holes in said elliptic mirror and are adapted to form the arc-light in the focus, so that the rays of light emanating in all directions from said arc-light are several times reflected by said elliptic mirror and said plane mirror, until they pass through the small hole of the latter in an intense, thin and very acute angled pencil, a Bells mouthpiece at an angle to the axis of said elliptic mirror and having a membrane which is adapted to vibrate under the action of the voice and to reflect the pencil of rays, a telescope adapted for changing the pencil ot' reflected and varied rays ot' light to a beam of nearly-parallel rays which pass through the space, and means for supporting all said parts.

T. In a receiver ot' a photophone, the combination with a tube, of a bottom closing the one end ot' said tube, an object-glass closing the other end ot' said tube and adapted to bend a beam of rays of light toward the center, a small camera obscura longit-udinally adjustable in said bottom and having a small circular hole in the focus of said object-glass, a radiophone in said small camera obscura and adapted to increase and decrease its electrical resistance under the action of the bent rays ot light, a telephone, and a circuit connecting said radiophone with said telephone.

8. In a receiver ot' a photophone, the combination with a tube, ot' a bottom closing the one end ot' said tube, an object-glass closing the other end of said tube and adapted to bend a beam ot' rays of light toward the center, a small tube longitudinally movable in said bottom, a cover closing the internal end of said small tube and having a small central hole, a small bottom closing the external end ot' said small tube, means for adjusting said small tube in said bottom to bring the small central hole in said cover into the focus ot' said object-glass, a radiophone on the inside ot' said small bottom and adapted to increase and decrease its electrical resistance under the action of the bent rays of light, a telephone, and a circuit connecting said radiophone with said telephone.

9. In a receiver of a photophone, the combination with a tube, of a bottom closing the one end of said tube, an object-glass closing the other end of said tube and adapted to bend a beam of rays of light toward the center, a small tube longitudinally movable in said bottom, a cover closing the internal end of said small tube and having a small central hole, a small bottom closing the external end of said small tube, means for adjusting said small iai/i1 rliildi 796,254 5 tube in said bottom to bring the small central hole in said cover into the focus of said object-glass. a selenium cell on the inside of said small bottom and adapted to increase and decrease its electrical resistance under the action of the bent rays of light, a telephone, and a circuit connecting said selenium cell with said telephone.

10. In a photophone, the combination of an elliptical mirror, a plane mirror covering the elliptical mirror and having a small hole in the axis ot' the elliptical mirror, a source of in the focus of the elliptical mirror,

meansl'or su bjectingt 1e rays of light passing through the hole of the plane mirror to sound- Waves. means for transmitting the varying rays through space, a receiver having means for producing audible sounds, and a telephone connected With the sound-producer of the receiver.

11. In a photophone, the combination with an elliptic mirror, of a plane mirror covering said elliptic mirror and provided with a small circular hole in the axis ot' said elliptic mirror, a source ot' light in the focus ot' said elliptic mirror, so that the rays of light emanating in all directions from said source of light are several times reflected by said elliptic mirror and said plane mirror, until they pass through the small hole of the latter in an intense, thin and very acute angled pencil, a lBells mouthpiece at an angle to the axis of said elliptic mirror and havinga membrane which is adapted to vibrate under the action of the voice and to reflect the pencil of rays, a telescope adapted for changing the pencil ot' reflected and varied rays of light to a beam of nearly-parallel rays which pass through the space, a receivingtube, a bottom closing the one end ot' said receiving-tube, an object-glass closing the other end of said receiving-tube and adapted to bend a beam ot' rays of light toward the center, a s inall camera obscura longitudinally adjustable in said bottom and having a small circular hole in the focus of said object-glass, a radiophone in said small camera obscura and adapted to increase and decrease its electrical resistance under the action of the bent rays ot' light. means for supporting all said parts, a telephone, and a circuit connecting said radiophone with said telephone.

12. In a photophone, the combination with an elliptic mirror, ot' a plane mirror covering said elliptic mirror and provided-With a small circular hole in the axis of said elliptic mirror, an arc-lamp, the carbon pieces of which pass through holes in said elliptic mirror and are adapted to form the arc-light in the focus, so that the rays of light emanating in all directions t'rom said arc-light are several times reected by said elliptic mirror and said plane mirror, until they pass through the small hole ot' the latter in an intense, thin and very acute angled pencil, a Bells mouthpiece at an angle to the axis ot' said elliptic mirror and having a membrane which is adapted to vibrate under l crease and decrease its electrical resistance the action ofthe voice and to reflect. the pencil l under the action of the bent rays of light, of rays` a telescope adapted for changing the means for supporting all said parts. a telepencil of reflected and varied rays of light to l phone, and a circuit connecting said radioa beam of nearly-parallel rays which pass phone with said telephone.

through the space,areceivingtube, abottonl 1 In testimony whereof I have signed my closing the one end of said receiving-tube, an name to this specification in the presence of object-glass closing` the other end of Said rel two subscribing witnesses.

ceiving-tube and adapted to bend a beam of BRUNO SAENGER, rays oflight toward thecentenasrnall camera. l Admvz'n/szwlzfor of zf/u; csf/zie of Raimund obscura longitudinally adjustable in said botl lVZ/ielm, 11min/mm, Zee/fwd?.

tom and having a small circular hole in the Yitnessesz focus of said object-glass, a radiophone in l HEXRY HASPER,

said small camera obscura and adapted to in- I WILLIAM MAYNER.

Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2466000 *Jun 12, 1945Apr 5, 1949Brown Chester LPhotophone
US2494645 *Sep 15, 1944Jan 17, 1950Rca CorpTwo-way light communication system
US2702859 *Oct 30, 1945Feb 22, 1955Robinson Charles VConical reflector
US2754425 *Sep 13, 1952Jul 10, 1956Froemel John GX-ray microscope
US3290503 *May 6, 1963Dec 6, 1966Raytheon CoLight communication system
US3740559 *Jun 29, 1971Jun 19, 1973Singer CoVoice communication system
US4187404 *Jul 20, 1978Feb 5, 1980Thomson-CsfTelephone set for optical fibers lines
US4882772 *Jul 30, 1987Nov 21, 1989Telescript Industries, Inc.Electro-optical light beam signal transmission system
Classifications
Cooperative ClassificationH04B10/11