US1878711A - Electrooptical transmission system - Google Patents

Description

Sept. 26, 1932. F. w. REYNQLDS ELEcTRooPTIcAL TRANSMISSION SYSTEM Original Filed Feb. 18, 1927 2 Sheets-Sheet l IN VEN TOR By F. w. RE wvoL 05 A TTORNE V Lum .Sg-Qi.. E@ F. w. REYNQLDS ELECTROOPTIGAL TRANSMISSION SYSTEM Original Filed Feb. 18, 192'? 2 Sheets-Sheet 2 .m @Fi /NVENTOR E W REYNOLDS ATTORNEY Patented Sept. 20, 1932 UNiTsD STATES lPATENT .LoFi-ics FREDERICK W. REYNOLDS, OF GIR-ANTWOOD, NEW JERSEY, ASSIGNOR TO AMERICAN TELEPHONE AND' TELEGRAPH COMPANY, A CORPORATION OF NEW YORK ELECTROOPTIGL TRANSMISSION 'SYSTEM :Original application led February 18, 1927, Serial No. 169,322. Patent 1,773,119, dated August 19, 1930.

Divided and this application led July 17, 1930. Serial No. 468,702.

` rfhis invention relates .to electro-optical` paratus may be used for either transmission or reception, and hence the invention serves to simplify the terminal equipment which is used for the transmission of pictures over telephone circuits. j

In an embodiment of the invention selected for illustration a string or ribbon electro-` mechanical light valve such as disclosed'in Patent No. 1,667,805, May 1, 1928, of Herbert E. Ives, is positioned between a source of light and a holder 'for the transmitting or receiving film, depending upon whether transmission or reception is taking place. For picture transmission the light valve ribbon is vibrated by alternating current from a vacuum tube oscillator or other suitable source at a substantially constant frequency thereby generating a pulsating lightbeam which is hereinafter called a carrier light beam. This carrier light beam is modulated by the picture at the transmitter and is subsequently directed onto a photoelectric cell which in turn produces pulsating photoelectric currents representative of the light effects of the picture. By means of a transformer, these currents set up alternating current which constitutes the modulated carrier current for the line. For reception at the same terminal station, the oscillator is disconnected from the light valve and the incoming carrier picture currents are impressed upon this valve thereby4 causing to pass to the film holder, which now holds the receiving film, a'varying beam of light correspondingtothe light intensities of the elemental areas ofthe picture which is being transmitted from the distant station. The scanning at the terminals may be carried on in accordance with standard practice Well known in the art. A suitable 'scanning system is'dis'closed in Patent No. 1,7 06,032, March 19,1929 ofv M.V B.

lar parts of the apparatus.

Long. The level of the line carrier currents i may be raised at the transmitting terminal,

kto minimize the eiect of disturbances enternecting stations showing terminal -apparatus which may embody this invention. p

Fig. 2 is a detail, showing the lightvalve ribbon with relation to the light valveapertures when no current is flowing.

Fig. 3 is a curve, showing the variation in the intensity of the illumination of the picture at the transmitter with time. y

Fig. l is a curve,showing`-the'photoelectric current resulting from light modulation by the varying picture density plotted against time.

Fig. 5 is a general schematic arrangement of the terminal apparatus of one station, showing an embodimentV of the invention comprising apparatus which may replace certain parts of the apparatus of Fig; y

Similar reference characters refer to simi- In Fig. 1, in which two interconnected stations are shown'7 the terminal at the left,- designated station W, will be described asy a transmitting station and the switch at this station is :accordingly kthrown to the right; while the terminal at theright, designated station E, will be considered as a receiving station and the switch'lO of that station is also thrown to the right, thus connecting theterminal apparatus of kthe two Vstations for transmission Vand receptiomrespectively. y 4

VAt station W, light valve is positioned in the path of light obtained from Vany suitable source 21. f A suitable lens system 22, 23 and 24 land aperturedV members 25 'and 26 cause a beam of lightV to' passthrough-l the 'sticefinpicture transmissionssystemsfthereby causingtire light beam -to successively scan the elemental areas of the entire picture.

It is preferable to mount-thelightvalve and thepicture holdingldrum so that the axis 'of' the light'valve ribbon andfthe drum are at right angles toea'ch'other.

The li ht beam, after passing through the l .picturqis .reflected 90 bya prism ormirror G01-:mdpassedthroughV aliens system 61- to the light sensitive cell lY0. "The -lightsensitive cell, .upon 'being' activated by the: varying light, causes varying electric" currents to be .transmitted .to the "amplifier 80. The amplifier connects throughthe sWitchSlto the cir- :cuit 82tvhich intur-nconnects throughblades Theoutgoing circuit 90 connects-through the filter 91 and the terminal .amplifier 92 lwith. the transmission linefleading V,to a receiving station.

- 'QT-he .lightbeam activating'the .light sensitive cell 470 v-is..a..pu'lsati.ng or carrier light .beam-andthe variationlzin the intensity of the/.beam isca'used by the light valve :20.

The ribbomofstheilight valve 20 is energized vbycan oscillator-'30 which generates a sinusoi dal lWave ofthe order Vof1000 to 2000 or more cycles per'second. -The voscillator 30 transmits its currents through blades 13- tand ,-1.4 of-fswitcl1l0-=and .a connecting .circuit Vto .the-amplilierliO Where the o'scillatingV current is amplified and the output current of .the iamplifienpassed through `the .ribbon 27 ofthe '.'valve thereby causing thezlightvalve '.-ribbonto oscillate .atla .substantially constant Afrequency.4 `liovernent of Athe light valve ribbon thus causesthelight lbeam-to rapidly vary .in `intensity in .accordance .with the frequency ofthe output current of the oscillator. Thebiasingbatteryl .and the high resi-stan ce 4.2 'afford:meansrtor adj ustmgl the relation of fthe light valveirbbon respect A tof .tli1e fl-ight valvefaperture.

. r-Ithas-.beenfound desirable 'iintheftransmission pictures .to z prOYde; for: festablishing` aldetinite rratio. between the maximum aand minimum picture currents transmitted, and to :provide for the transmission -olf V`a 'definite minimum carrier-current .at all times Yeven-.When no light.` reaches the `light sensitive cell. The purpose of this is to avoid-overloading fthe 'transmission circuit.- apparatus suchasfrepeatersfand also to avoid inducing "cross-talk :in :neighboring circuits, and .to yinsure 1 that the rlpi'cture -fcurrents transmitted i will be fat inne-energy sufficienti to2 Iavoid 4serious interference from noise currents. This may be accomplished as shown in Fig. 1 by using a part of the output current of the oscillator and adding it to the amplified picture currents, provision being made for adjusting .both'theg phase andthe magnitude of the former current With respect to the latter or vice versa.' 4One Way of adding a part of Lt'hefoscillator output .to the picture current tis Iicy: means of Lthe phase adjuster 85 and associated potentiometer 86, Which connect the'output"s'ide--ofthe amplifier 40 through the circuit comprisingrthe blades 15 and 16 yofthe switch'l'O andthe switch 87 to 'the circuit 82; I By means-of the phase adjuster Which may comprise Ma suitable network of variable im- .pedances arranged in accordance with principles Wellknownto the Aart,.a:nd the assofciated potentiometenthe outputfcurrent of the oscillator canbephased With the picture current,..and the necessary unmodulated carrier current of the proper amplitude im- .pressed upon` thetransmission circuit. y With such- .adjustment .the "shunted carrier andthe vvariable picture currents add directly. The variations in light shades or tones of the. pic- .ture varerepresented in this case by a current in the output circuit of the light sensiti-vefcell-70,Who'selfrequencyis the .frequency vof--th'e current impressed uponthe light valve ribbon and --Whose amplitude fatany instant Vis proportional to the light transmittedfby ntheypicture. t

If theflightvalveis adjustedso that When .there is no current flowing through its ribbon,'thezribbonguncovers one-half of the flight 1val-ve, aperture, then the illumination -will have :1a-sinusoidal form represented by sa. constantadded Vto a sine function, and at .the same 'frequency las the-current impressed `upon-"the light valve ribbon, but With a phase displacement-between its sine Vform com-pof nent and y the carrier -of approximately 180 4orlm-ultiple.thereof. The width of the light -valveribbonfshould-be equal to that of the light valvefaperturefand' its maximum ampli- VVtude ofv vibrationfshould be Within one-half itsl'vvidth.

It Vis obvious-that vthe amplified photoelectric current VWilladd directly to vthe 1 shunted output current ofthe oscillator 'if the. phase Vofthe latter current is adjusted -relati-'vely'ztot'he former. The phase adjust- VV`-er185 '-isfadapted to bring -about the necessary phasev adjustment. This/arrangement of the -lfightzvalvein association with the light sen- ;sitive cel'l'fis such that the varying currents -fromfthe'icell -have'the-'same frequency as the variations of 'the flighttransmitted by the light valve andalso the same frequency asl :the current .from the oscillator operating the light' valve.. 'This arrangement is important forY if'fthe-.light :valve ribbon Were differently .adjusted respect to the light valveaperlli ture with no current flowing through the rib-A bon, a double, frequency in the light sensiwould make it more difficult to add` the de- Y sired carrier to the picture current.

In adjusting the apparatus for transmitting a picture it may be advantageous toascertain the amount of current transmitted by the brightest and by the darkest portions of the picture and f'or determining this a. measuring device 83 is arrangedso that by thro-wing switch 81 to its upper closed position the output circuit of the amplifier 8() may be connected to this measuring device. Upon placing in the light beam various portions of the fihn 50, or any other object of varying transparency, its transparency at different spots may be measured and indicated by the measuring device 83 in such units as may be desired. For example, the measuring device may have a scale calibrated to read in per cent of the total light. `When putting the apparatus in operation, the operator having ascertained the transparency of the lightest and the darkest portions of the picture may use this information in adjusting the apparatus for transmission.

The same measuring device 83, which may comprise a suitably arranged vacuum tube amplifier-detector unit, is also used for indicating when the phase difference between the photoelectric current and the shunted oscillator output current is zero. In making such a comparison, both the switches 81 and 87 are thrown into their upper closed position, thereby causing the out-put from both the light sensitive cell 70 and the phase adjuster 85 to be impressed simultaneously upon the measuring device 83. Also the ratio between the maximum and minimum picture currents, and the magnitude of the shunted oscillator output can be determined by the use of this measuring device 83 and proper manipulation of the switches 81 and 87 for connecting it to the two circuits. The magnitude of the picture current can be adjusted in a number of ways wellfknown to the art, such as, by varying the voltage impressed upon the light sensitive cell.

The descriptionso far has related primarilyv tothe apparatus arranged for transmitting. When arranged for reception, a part of the same apparatus as is `employed for transmission is used, and its connectionis shown in the terminalstation E at the right of Fig. 1. -The switch 11() is thrown right and the relation of the light valve ribbon 127 with respect to the light valve aperture arranged so that with no current flowing through the ribbon the light valve is closed.-

VlVhen the switch 110 is thrown to the right blades 111 and'112 are operative to connect the circuit 190 with the amplifier 140 and the light valve ribbon 127. Theother four blades 113, 114, 115 and 116 are inoperative to the and hence the oscillator 130 and the phase ad juster 185 are. disconnected from the oper ,ating circuit.

. The-proper relationship of the light valve ribbon to the light valve aperture may be established mechanically by adjustingV the light valve jaws or electrically by means of the biasing battery 141 and the potentiometer 142. The incoming picture current is ampli- `hed by the terminal amplifier 192 and then passed through the filter 191, the amplifier 140 and the light valve ribbon to control its movement in a manner to reproduce the light effects of the distant picture and cause a light beam to be impressed upon the photo-sensitive film 150 on the cylinder 151, which is mov-ed in synchronism and in phase with the picture at the transmitting stat-ion in accordance with standard practice-well known in the art. Light from a steady source 121' p be'required are employed for reception as are used for transmission and the principal adjustment necessary to put the terminal equipment into proper relationship for transmission or for reception are the circuit changes governed by the switches 10 and 110 at the terminals and the proper adjustments of the light valve ribbon with respectto the'light valve aperture when no current is fiowing. The interchangeability or dual use of the apparatus units for either transmission or reception simplifies the terminal equipment and its operation.

The relation of the light valve ribbon to the light valve aperture when no current is flowing is such that for transmission the light valve is half open and for reception the light valve is substantially closed as is shown at T and R, respectively, in Fig, 2. The primary reason'for the half open position when no current is flowing whe-ntransmitting, as

already explained, is to produce a varying illumination which when impressed on a light sensitive cell causes the latterV to set up a varying photoelectric current of the same freis necessitated by the fact that the photoelectric current approaches zero when a dark Y portion of the picture isbeing transmitted and a maximum when the lightest porton of the picture is being transmitte Adjustment of the relationship betweenV the `light .valve ribbon and the light valve aperture, yas described in connection with Fig.

1, is effected by passing the properbiasing current through the light valve ribbon to cause to takel up the proper Yposition `'forv "transmission .or for reception. This requires adjusting the biasing current When the'light valve is Vchanged from transmitting to receiving or vice versa. f

I-nFig. 2 isshoWn a mechanical means for making this-change. Tivo light valve Vapertures Tand'R are used and permanently pofio . arrangement such as the opaque shutter 29r sitioned inthe apertured member 28 in proper relationship tothe light valve ribbon. Only one of these apert-ures isopen at a'time. This .may be mechanically eected vby any suitable capable of being positionedzini front. of either v adjusted, is approximately alinear-function of the current input to the lightvalve ribbon so that the distortion from this source ,is negligible. v'This pulsating illumination has been described herein'as producinga carrier light vvbeam' andl as already explainedit is impressed by means of a suitable'optical .system upon elementalareas of the picture `Whose image is "lio being transmitted. One reason for employing a pulsating carrier light beam is to make possible the kuse of an alternating current amplilier, and thus Vuse a `.pliotoelectric` current under conditions Which permit of its being ampliedwith ordinary voicefrequency alternating current vacuum tube amplifiers. 'Iheemployment of such apparatuspermits its use on existing telephone crothertrans- 'mission circuits.

The pulsating carrier light beam in passing through the picture at the transmitter is modulated in accordance Withthe light density of the elemental areas of thepicture and the cur- 4rent Yvariations resulting from` the modulated light beam being impressed upon, the photosensitive cell at the transmitting station may be representedby a curve having asubstantially uniforml fundamental frequency'but of .varying amplitude as shown in Fig. 4. :The .fundamental frequency ofthe photoelectric current as heretofore explained is the same as that of the illumination.

g The unmodulated Vcarrier current which is impressed upon the transmission circuit at -all times, irrespective of the photoelectric current, may be obtained as vdescribed in Fig.

'l by shunting a part of the oscillator output current to .the outgoing circuit.

In accordance With this invention. an optical arrangement 'for supplying the modulatedV carrier is shown in Fig. 5. In vthis ar-` rangement, a part of the. carrierv light beam is diverted'byvvmeans ofapartially transpar- Sent mirror 210, positioned in? the'path'of the light beam, in such relation that it diverte a small percentage ofy the totalr lightjto'tlie light sensitive cell`70. `In the path ofthe light diverted to the -light l.sensitive cell, is

afplane or preferably' a concave mirror 211 and an adjustable aperture 212 arrangedv for directing and controlling the diverted light.

By such any optical arrangement the major portion f the carrier light beam passes through the mirror l210 to the picture, and a minor portion of the light is diverted tothe light sensitive cell which is thereby actuated t0 produce unmodulated current of carrier.y

frequency. Whenv the .apparatusis used Vfor receiving, the semi-transparent mirror 210 is moved out of the path of the light beam into the v position` indicated at 213. 'The current produced inthe light sensitive cell vby the tivo parts of the light beam ivill be in synchronisin andy in-pliase and.y consequently add directly to each other. Themagnitude of the carrier `current'prod-uced bythe deflected vpart of the light beam may be adjusted vby means of the-` aperture 212.

`'Iheterminal apparatus shown in Fig. 5 with the exception oft-lie` omission of the electrical sliunt'and the substitution-r.ofv the optical shunt, above described for impressingV carriercurrent on the outgoing circuit, is the sameas Fig. 1, and with the exception ofthese I differences, the same description applies to both figures.

lVhat is claimed is:

1. In an electro-opticall system, a source of*y steady light, meansto intermittentlyvary a beam'from said source, means to further vary said beam in accordance with signals, means toproduceza signal modulated carrier cur.

rent from said beam, and means dependent upon the operation of said intermitten beam varying means to control the amplitude of the component of carrier frequency in said modulated carrier current. v

V2. In Aan electro-optical transmissionV sys-H tem, a transmission circuit, alight beam, ia light interrupterrapidly and regularly interrupting saidbeai'n at a substantially uniform frequency thereby producing carrier f pulsations, a light modulating picture fpositioned in the of the said light beam,l alight sensitive element excited by-the 'said Ylight beam subsequent ato the said picture iio modulating the said lightbeam, and .anoptiv cal shunt passingpulsating light aroundfthe said light modulating picture for `applying -uninodulated carrier light pulsations producedv .by said light interrupter to the said light sensitive element." l

3. An electro-optical system comprising a sourcer of steadyy light, meansV for cyclically varying a light'beamsupplied by said' source and for producing an auxiliary light beam therefrom,'means for varying said Vfirst menl tioned beam in accordance-With signals, "and l means upon which said signal varied and auxiliary beams are incident to produce signal modulated carrier current. A

4. An electro-optical system comprisinga source of steady light, means for cyclically varying a light beam supplied by said source, means for diverting light radiations from said beam to produce an auxiliary beam, means for varying said first mentioned beam in accordance with signals, and means upon which said signal varied and auxiliary beams are incident to produce signal modulated carrier current.

5. In an electro-optical transmission system, a transmission circuit, an analyzing light beam, a light interrupter in the pathof said light beam, means for controlling the said light beam to produce a modulated carrier current in said circuit, and means acted upon by said analyzing beam to produce a second light beam for controlling the production of unmodulated carrier currentto establish a minimum transmission level in said circuit.

6. In an electro-optical transmission system, a transmission circuit, an analyzing light beam, a light interrupter in the path of said light beam, a picture whose image is to be transmitted, means for controlling the said light beam to produce a modulated carrier current in said circuit varying according to the lights and shades of the said picture, and means acted upon by said analyzing beam to produce a. second light beam for controlling the establishment of a definite ratio between the maximum and minimum current representing the darkest and lightest areas of said picture.

7 The method of carrier current signaling which comprises producing two beams of light from a single source of light which is modulated at carrier frequency, impressing a signal upon one only of said beams, and simultaneously utilizing said beams to set up a carrier current modulated in accordance with said signal.

8. A signaling system comprising a source of uniformly periodically varying light, means for modulating light in accordance with signals, means for directing light from said light source to said last mentioned means, light sensitive electric means receiving signal modulated light from said modulating means, and means for simultaneously impressing upon said last mentioned means light from said source which is not modulated in accordance with signals.

9. A signaling system comprising means for producing two uniformly periodically varying separate beams of light, the variations of said beams being in phase with each other, means for modulating one only of said beams in accordance with signals, and light sensitive electric means simultaneously receiving said signal modulated beam and said beam which is not signal modulated.

10. In an electro-optical system, means to produce a. uniformly periodically varying beam of light, means to vary said beam in accordance with signals, means to produce a signal modulated carrier current from said beam, and means to control the amplitude of the component of carrier frequency in said modulated carrier currentcomprising light sensitive electric means and means for impressing thereupon a second beam of light having uniform periodic variations similar to and in phase with thoserof the first beam.

In testimony whereof, I have signed my name to this specification this 16th day of July 1930.

FREDERICK W. REYNOLDS.

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