‘United States Patent ' [19*]v
`Shinosky, Jr.
`1
`-
`
`., [11]
`[4s]
`
`4,065,644
`' Dec.27, 1977
`
`[54] ELECI‘RQ-OPTICAL AND ELECTRONIC
`
`3,849,604 11/1974 7 Benes et al. ........................ .. 250/199
`
`
`
`3,852,640 12/1974 ‘ McCarthy 3,985,975 10/1976 Steensma ...................... .. 179/18 GF
`
`SWITCHING SYSTEMS
`\[76] Inventor: Leonard W. Shinosky, Jr., 3714
`White Pine Road, Apt. C, Baltimore,
`Md- 21220
`[211 App!‘ Nod 760,607
`‘[22]
`Filed:
`Jam 19’ 1977
`
`1631
`
`[56]
`
`OTHER PUBLICATIONS
`Lasers:Devices and Systems-Part II, Dulberger and
`Vogel, Electronics, Nov. 3, 1961, pp. 40-44.
`Primary Examiner-Thomas A. Robinson
`Attorney, Agent, or Firm-Grif?n, Branigan & Butler
`[57]
`ABSTRACT
`Related US. Application Data
`A switching system, speci?cally useful as a telephone
`Continuation-impart 01' Ser- NO- 573,177, April 30,
`central switching system, to establish a number of si
`1975' abandmled-
`'
`multaneOu-S but independent eemlnnnieatien links be
`Int. Cl.2 ............................................. .. H04B 9/00
`[51]
`tween selected lines, comprising (1) a CRT to transmit
`152] us. 01. ........................... .. 179/18 GF; 179/15 A;
`signals in the form of modulated light beams, (2) lenses
`250/199; 315/372
`to focus and direct the light generated, (3) an array of
`[581 Field of Search ........ .. 179/18 GF, 18 GE, 15 A,
`photosensors each connected to a different communica
`179/15 AT, 15 AZ; 250/199; 315/367, 374’
`372’ 30; 340/166 R, 147 R tion line, and (4) electronic controls to direct the beam
`_
`as required. Also disclosed are electronic embodiments
`References Clted
`of the foregoing; time division multiplex and composite
`U_S_ PATENT'DOCUMENTS
`systems to expand the basic system;_and also arrange
`ments to facilitate adaptation of the system to telephone
`,
`hhhlhhhhhh The syhhm hvhhh much of the hardware
`1331332 51328 £2211tiff,1:33:13:“71:33:11.313213;;
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`2/1964 Brooks et aL __
`179/18 GF and circuit complications of pnor switching systems.
`3,191,040
`6/1965 Critchlow ..... ..
`179/18 GF
`3,838,278
`9/1974 Duguay et a1. .................... .. 250/199
`
`42
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`US. Patent
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`Dec. 27, 1977
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`Sheet 1 of9
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`4,065,644
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`US. Patent
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`Dec. 27, 1977
`
`Sheet 3 of 9
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`4,065,644
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`US. Patent Dec. 27, 1977
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`Sheet 4 of9
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`U.S. Patent Dec. 27, 1977
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`Sheet 5 of9
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`U.S. Patent Dec. 27, 1977
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`US. Patent Dec. 27, 1977
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`Sheet 7 of9
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`
`US. Patent Dec. 27, 1977
`
`Sheet 8 of9
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`4,065,644
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`
`U.S. Patent
`
`Dec. 27, 1977
`
`Sheet 9 of9
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`4,065,644
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`
`ELECI‘RO-OPTICAL AND ELECTRONIC
`SWITCHING SYSTEMS
`RELATED PATENT APPLICATIONS
`This application is a continuation-in-part of aban
`doned application Ser. No. 573,177, entitled Electro
`Optical Switching Systems, ?led Apr. 30, 1975; and
`contains considerable common subject matter with said
`application, reliance upon which for credit as to ?ling
`date hereby being claimed.
`BACKGROUND OF THE INVENTION
`Field of the Invention
`This invention is concerned with a system which can
`achieve communication links between a plurality of
`spatially separated entities. In this sense, the device to
`be described herein could be applied to any circum
`stance which required this type of function. However,
`there is a speci?c context of application in which the
`capabilities of the invention are most clearly demon
`strated, and in which its utility and advantages over
`prior art can be most clearly presented. This said con
`text is that of a telephone central of?ce switching sys
`25
`tem, and therefore it is within this context that the use of
`the invention will be recommended, and its advantages
`over prior art pointed out.
`It is the basic function of a telephone switching sys
`tem to achieve a communications link between two or
`more telephones. In the performance of this function,
`various automatic systems have evolved; but all of these
`systems can be grouped into two general categories:
`I. space division systems: which use physically dis
`tinct paths to achieve communication between
`telephones;
`II. time division systems: which use a time-shared
`common path between telephone terminations at
`the switching system itself.
`‘
`This discourse will ?rst concern itself with the differ
`ent types of space division systems. These can be di
`vided into two general catagories:
`l. electro-mechanical
`2. electronic
`The electro-mechanical systems,‘ of course, preceded
`the electronic systems, and even some of the earlier
`types of electro-mechanical systems are still in wide
`spread use today. The ?rst type of electro-mechanical
`system that was of major signi?cance was the step-by
`step system. This system used banks of the Strowger
`rotary-type switch along with the appropriate support
`ive equipment to achieve the required switching func
`tions.
`Increased numbers of subscribers posed problems of
`maintaining satisfactory speed in the switching process
`itself, and of dealing adequately with the inherent com
`55
`plexity of a larger sized system. As a result, a number of
`other electro-mechanical systems evolved. These sys
`tems used various switching arrangements, and various
`types of electromechanical components. The crossbar
`system is one such system, and features a trend that was
`developed extensively in the later‘electronic systems:
`that of common or centralized control of the switching
`process.
`I
`The search for a system that could handle ever in
`creasing numbers of subscribers and traf?c loading con
`ditions, and also possessed the possibility of ful?lling
`long term anticipated increased subscriber demands, led
`to the development of electronic switching systems.
`
`4,065,644
`2
`Systems of this type feature an electronic central pro
`cessor which functions as a centralsupervisory control
`unit for the entire switching system. The #1 BS8, de
`veloped by Bell Telephone Laboratories, is a good
`representative example of such a system. In addition to
`an electronic centralized control, this system featured a
`new switching element, the ferreed cross-point switch.
`This switch hadlmagnetic retentive properties which
`allowed it to remain in a closed position upon the appli
`cation of a momentary pulse. This fact facilitated its use
`as a switching element within the network of the sys
`tem. Also of signi?cance was the E88 technique for
`detecting the off-hook status of a subscriber telephone.
`Off-hook detection is one of the basic functions that
`must be performed by a telephone switching system.
`The ESS utilized a new type of magnetic sensing de
`vice, the ferrod sensor, which reacted to a change in
`impedance of the subscriber line. Banks of these sensors
`were used, and they were repeatedly scanned by the
`central processor unit to detect an off-hook status.
`The electronic systems outperformed their electro
`mechanical counterparts in a number of areas:
`1. They had improved speed, which is very important
`for a large and complex system.
`.
`2. They had improved versatility. This was realized
`in two areas:
`'
`‘
`a. Adaptability of the system to different operating
`requirements: This adaptability arises from the fact
`that the control functions in an electronic systems
`are not “hard-wired,” but rather are a part of a
`stored program, and hence machine operation can
`be altered simply by changing the program.
`b. If it became desireable to increase the size of a
`given installation, much easier implementation of
`this was available with an electronic system.
`3. Their overall traffic handling capability was in
`creased.
`4. Maintenance features were improved due to diag
`nostic routines included in the central processor pro
`grams.
`-
`On an initial cost basis, electronic systems tend to
`exceed the cost of electro-mechanical systems, but it is
`widely held that thisfact is adequately compensated for
`by the long term advantage of ?exibility andlow main
`tenance cost provided for by an electronic switching
`system.
`Upon observing the. above cited systems, it can be
`seen that there have beena series of improvements
`which have increased both the speed and versatility of
`the systems. Among these improvements are more du
`rable and more sophisticated components, and the use
`of centralized electronic control. Nevertheless, all of
`these systems actually achieve telephone-telephone
`interconnection by closing the proper combination of
`electro-mechanical switching elements, which individ
`ual elements are part of a switching network. The use of
`individual switching elements structured into a network
`results in an of?ce which is very complex for any sys
`tem of appreciable ‘size. Furthermore, the whole ap
`proach of achieving central of?ce function in this way
`encounters inherent problematic factors. The following
`paragraphs will discuss these factors.
`Upon considering the relationship between the cen
`tral control of a switching system and the switching
`network itself, a number of factors must be taken into
`account for both electro-mechanical and electronic
`systems.
`i
`
`45
`
`50
`
`65
`
`

`
`3
`DISTRIBUTION OF CONTROL SIGNALS
`a. The circuitry in an electro-mechanical system must
`distribute the control signals to the individual switch
`ing elements comprising the switching network.
`b. The problem of spatial distribution of control signals
`is also true for electronic systems, although here it
`can be achieved with greater speed.
`
`In both types of systems, electro-mechanical and
`electronic, substantial circuitry must be provided to
`distribute control signals to the switching network.
`
`SENSING AND LOCATING FREE
`PATHWAYS-RETENTION OF PATHWAY
`INFORMATION
`In any system utilizing a switching network, a con
`nection pathway through this network must be formed
`in order to achieve a communications link between two
`telephones. This requires the control units to perform
`20
`several functions:
`
`15
`
`1. checking to see if a given switching element is avail
`able for use,
`2. constructing a pathway of free switching elements,
`3. applying the necessary control signals to these
`switching elements to close the pathway and establish
`a communications link, and
`4. retaining this information so as to free these particular
`elements upon the completion of a call and to aid in
`the determination of available pathways for other
`calls which might be initiated in the interim.
`
`25
`
`30
`
`4,065,644
`4
`designate these digits. Signaling is provided at a number
`of points during the progress of a call such as the dial
`tone, a ringing signal, and a busy signal. Consequently,
`additional equipment is required to:
`
`1. connect these special-purpose devises to an individual
`subscriber path. This equipment essentially consists
`of additional network circuitry to establish the re
`quired connection.
`2. distribute the necessary control signals to the con
`necting network circuitry mentioned immediately
`above.
`
`These circuitry requirements hold true for both elec
`tronic and electro-mechanical systems and are another
`demonstration of some of the inherent aspects of imple
`menting a switching system using a spatially distributed
`network of individual elements.
`
`RESULTANT COST-PERFORMANCE
`LIMITATIONS
`Since the requirements of a large telephone office
`demand complex operations, the amount of equipment
`becomes great and consequently becomes expensive.
`Because of this, the design of any such system becomes
`a trade-off between cost and switching capability. The
`systems are designed to handle calls on a probabilistic
`demand basis in order to economize upon the massive
`amounts of equipment that would otherwise be needed
`to provide theoretical complete call handling capabil
`ity. This type of compromise results in systems which:
`
`In electro-mechanical systems, this requires a sub
`stantial amount of equipment. Although electronic
`equipment performs these functions in a superior man
`ner, the system must still incur substantial equipment
`requirements and the consequent cost in:
`
`35
`
`1. the necessary information storage equipment to retain
`the pathway information through the network;
`2. the necessary information storage equipment to store
`the program instructions that achieve the complex
`processes of determining connection pathways
`through the switching network.
`45
`
`For electronic systems, the advantages gained by
`electronic circuitry are also partially compromised by
`requirements for adequate interfacing circuitry between
`the central processor and the switching network ele
`ments themselves. This problem arises in two areas:
`
`50
`
`1. interfacing the high-speed central processor equip
`ment with the relatively slow speeds of electro
`mechanical devices;
`2. providing the necessary interfacing in regard to elec
`trical parameters such as voltage, current, and imped
`ance.
`
`55
`
`CONNECTION OF SPECIAL PURPOSE
`DEVICES DURING CALL PROCESSING
`In the performance of standard telephone call pro
`cessing, it is necessary to connect sensing, recording,
`and signaling devices to the line at various stages in the
`progress of a call. Sensing is primarily used to detect the
`on-off hook status of a given line. Recording must be
`accomplished when a subscriber dials the digits of the
`number he wishes to call, or uses a tone sequence to
`
`65
`
`1. must be continually monitored with respect to tele
`phone traf?c conditions. The results of the traf?c
`monitoring studies must be acted upon and appropri
`ate corrective actions must be taken to ensure that the
`system can provide satisfactory service at all times,
`including periods of peak load.
`2. suffer from localized network blockage. This is a
`localized effect, resulting not from an overall high
`usage rate, but from a spurious concentration of sub
`scriber line use in one physical area of the system,
`resulting in tie-ups in that area.
`
`RELIABILITY PROBLEMS
`Any system with a large number of components will
`suffer from random component malfunction to some
`extent. However, the electronic systems utilizing a cen
`tral processor, must again pay for their performance
`advantages in terms of substantial duplicate equipment,
`since the failure of the main control unit would cause
`the entire system to be inoperative.
`
`SYSTEM MAINTENANCE
`Electro-mechanical systems require sufficient staffs
`of trained technical personnel to maintain them. This
`problem is made more difficult by the inherent com
`plexity of large networks.
`Electronic systems can overcome this to a significant
`degree by providing comprehensive diagnostic pro
`grams, but the advantage thus gained incurs costs result
`ing from the storage equipment needed for the neces
`sary program instructions in the central processor mem
`ory.
`
`SUMMARY
`The above paragraphs have considered the major
`inherent problems encountered in space division type
`
`

`
`DESCRIPTION OF THE PRIOR ART
`This invention is ‘believed to be basically unique in
`that switching is accomplished by selectively pointing a
`beam of radiation at sensors connected in the receiving
`line; the radiation being modulated with signal informa
`tion. The prior art does show wireless switching by
`frequency selection at the central of?ce and, in a very
`crude early embodiment, by physically moving a sound
`tube to connect two points to the audio signal. Neither
`approach is considered directly or closely pertinent to
`that described in this disclosure.
`
`SUMMARY OF THE INVENTION
`This invention is a switching system, and it speci?
`cally relates to the functions performed by a switching
`network such as those networks typi?ed in a telephone
`central of?ce system. In the central of?ce format, the
`network function is to establish a number of simulta
`neous but independent communication links between
`specifically designated signal line terminations. The
`inter-connections between line terminations are estab
`lished according to control information which has been
`entered into the system. This invention accomplishes
`the functions of a network by employing a selectively
`directed, modulated beam, the primary or preferred
`embodiments being implemented by:
`
`4,065,644
`6
`5
`more apparent after a description of basic concepts of
`systems. These problems can be summarized as all stem
`ming from the inherent aspects involved in implement
`the invention itself.
`I
`ing a switching system using a spatially differentiated
`network of switching elements. It is an object of this
`invention to substantially reduce the magnitude of these
`problems.
`TIME DIVISION MULTIPLEX
`The following is concerned with time division multi
`plex systems (abbreviated TDM). The class of time
`division systems encounters different problems due to
`the fact that it approaches the generic problem of con
`structing a telephone switching system from a com
`pletely different point of view. The time division system
`utilizes a “common highway” or “talking bus” along
`which all conversation travels when within the system
`itself. This type of approach can be used because it has
`been determined that the continuous throughput of a
`signal is not inherently necessary for the effective trans
`mission of human voice signals. The signal need only be
`sampled on a repetitive bases. The pulse samples can be
`used to reconstruct the original waveform by appropri
`ate equipment. Thusly, each subscriber signal is sam
`pled, and assigned a time slot in the overall repetitive
`sampling sequence. In order for two subscribers to talk
`to one another, the control equipment simply assigns
`both telephones to the same time slot so that both sig
`nals are simultaneously gated into the “talking bus” and
`pulse-samples are transferred between these two gates
`for that particular time slot.
`'
`Time division systems, however, suffer from their
`own set of disadvantages. One of these is that time
`division systems require substantial equipment on a
`per-line basis as opposed to space division systems
`which can have commonly used equipment. The other
`key limitation of the time division system is the total
`number of subscribers that such a system can service;
`this number remains relatively small in comparison to
`space division systems on a competitive applications
`basis. The primary reason for this size-effectiveness
`limitation is that only a limited number of subscribers
`can be time-shared on a given “common highway.”
`This number is 100 or less conversations, implying a
`possible 200 full access subscribers. The Bell System
`#101 E88, has only 25 time slots per highway, allowing
`45
`for 25 possible simultaneous conversations. Therefore,
`TDM systems due to the inherent aspects of their ap
`proach to the problem of switching, lend themselves to
`approximately several hundred line terminations, be
`these subscriber terminations or trunk line terminations.
`Therefore, if it is desired to provide for a large num
`ber of subscribers using TDM techniques, then exten
`sive provisions must be made for trunk line connections
`between the many small-sized TDM of?ces. But, this
`becomes prohibitive, in terms of equipment cost effec
`tiveness. Consequently, TDM systems are employed as
`small PBX units‘ which are interfaced with regular
`space division large central offices.
`It is an object of this invention to improve upon the
`information handling capability of a switching system
`by utilizing time division multiplexing techniques but
`without the usual size limitations that are imposed upon
`such systems in the prior art.
`In general, the system proposed in this invention will
`utilize both time division and space division techniques,
`but the resulting system will have advantages that nei
`ther of these approaches has realized on its own in the
`prior art. The advantages of this invention will become
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`l. transmitting the signals in the form of modulated light
`beams,
`2. collimating said beams to achieve selective communi
`cation links,
`‘
`3. directing the thusly collimated beams to speci?cally
`designated points according to input control informa
`tion, and
`4. detecting said light signals by photosensor devices
`with appropriate provisions for signal ampli?cation.
`
`Consequently, this invention functions as a switching
`network; but in total contrast to prior art which is in
`widespread use today, it is both wireless and switchless.
`The actual physical structure used to achieve this com
`prises:
`
`l. a CRT with appropriate control circuitry for control
`ling both the deflection and intensity of the electron
`beam,
`2. optical means for focusing the light generated by the
`CRT screen, and
`3. an array of photosensors with each photosensor hav
`, ing provisions for amplifying any signal it might re
`ceive.
`
`The light signals are generated and modulated by the
`CRT; are collimated by the focusing action of the opti
`cal system; and are directed to a speci?c photosensor by
`controlling the position of the CRT’s electron beam.
`From a systems viewpoint, the physical structure
`thus described functions as a multi-position switch that
`can direct a single input signal to one of a number of
`output signal ?ow paths. Additional circuitry is added
`to this basic structure so that the teclmiques of time
`division multiplexing can be used to enable the thusly
`augmented system to in effect transmit a number of
`signals simultaneously.
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`A further increase in system performance is attained
`sponsive to electron radiation with a multiple beam
`by introducing the concept of a composite system in
`CRT.
`which a number of CRT’s, each with its associated
`FIG. 4 illustrates a system employing an array of
`circuitry, are used with a common photosensor array.
`light emitting diodes as optical generators to function as
`In this con?guration means are provided to enable each
`a multiplexing unit with appropriate supportive gating
`circuitry.
`CRT unit to function normally, despite the off-set posi
`tion of any individual unit with respect to the photosen
`FIG. 5A illustrates the basic telephone system with
`sor array.
`the line interfacing unit; FIG. 58 illustrates a block
`A device is also described which uses an electro-opti
`diagram of the line interfacing unit.
`cal approach to achieve the function of time division
`FIG. 6 illustrates a basic telephone system including
`multiplexing individual signals onto a common time
`the data unit for station selection.
`shared path. This device is considered for possible use
`FIG. 7 illustrates the overall basic telephone system.
`in a time division multiplexed CRT unit, and is also
`considered for use as a line status sensing device in the
`speci?c application as part of a telephone switching
`system. The device is comprised of:
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`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`Statement Of Function— Basic Distributive Unit
`The ?rst functional unit to be described is a switching
`device which has as its input only a single signal flow
`path, and is capable of switching signals entering the
`system on this single input path to one of a number of
`output signal flow paths.
`It should be noted that the restriction of a single input
`path is not made due to inherent necessity, but is chosen
`at this point for convenience of explanation of the in
`vention by developing the concept of a basic functional
`unit.
`The device to be described has a basic capability of
`transmitting audio frequency signals, and hence it has
`the capacity of being used in transmitting the human
`voice signals comprising a telephone conversation.
`It should be noted, however, that the frequency re
`sponse of the device is not limited to the audio fre
`quency range, and higher frequency signals can be
`transmitted if so desired.
`Description Of The System Elements
`As shown in FIG. 1, this device consists of three basic
`units:
`
`1. an array of modulated light sources and associated
`gating control circuitry
`2. a converging lens
`3. a photosensor and ampli?er
`
`In the context of application of this invention as the
`switching network of a central office telephone switch
`ing system, additional means are provided for:
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`l. interfacing the switching device itself with both the
`supervisory control equipment, and the external lines
`and associated telephone equipment;
`2. providing two-way communication between inter
`connected subscribers.
`
`A description is given of the relationship of the
`switching device itself to the other major systems in the
`telephone central of?ce such as:
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`l. the central supervisory control unit;
`2. special purpose devices such as sensing, signaling,
`and recording units.
`
`In this systems perspective, the function of the inven
`tion as a switching unit is described as part of the entire
`call processing functions of the telephone central office
`system.
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`1. A CRT 1
`2. a lens or lens system 2
`3. an array 3 of photosensors and an ampli?er associated
`with each photosensor.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`These and other objects, features, characteristics, and
`advantages of the invention will be apparent by consid
`eration of the following description of the peferred
`embodiments, as illustrated by the accompanying draw
`mgs.
`FIG. 1 illustrates the basic switching system, utilizing
`a single, conventional CRT.
`FIG. 2 illustrates a basic switching system also incor
`porating a time division multiplex feature.
`FIG. 2A shows an improvement on the basic system
`shown in FIG. 2.
`FIGS. 2B and 2C show illustrative diagrams and data
`charts describing the performance the systems of FIG.
`2 and FIG. 2A, respectively.
`FIG. 3 illustrates a composite system employing a
`plurality of CRT beams.
`FIG. 3A illustrates an alternative embodiment using
`sensors responsive to electron radiation employed in a
`TDM single CRT con?guration with the reallocation
`circuitry of FIG. 2A. FIG. 3B illustrates an alternative
`embodiment of a composite system using sensors re
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`The lens is placed between the CRT 1 and the photo
`sensor array 3, and the photosensor array 3 is positioned
`so that any light emitted from the screen of the CRT is
`focused on the array.
`Integral to the CRT itself are:
`
`l. a phosphor coated screen LA
`2. an electron gun l-B
`3. means for modulating the intensity of the electron
`beam (z-axis control). This device is internal to the
`CRT itself and consequently is not otherwise shown.
`
`The electron gun functions as both a source of elec
`trons and a collimating device which forms the elec
`trons into a narrow beam of particles.
`Not shown in FIG. 1, but also conventional and basic
`to CRT operation are:
`
`l. a power supply unit for producing the high voltage
`levels used to accelerate the electrons to the CRT
`screen, and for producing power for other CRT
`associated units.
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`Associated with the CRT as external equipment is the
`control unit 1-C which applies the proper voltage to the
`de?ection apparatus thereby directing the electron
`beam in the desired manner.
`In the photosensor array, the individual photosensor
`elements 3-A are drawn as small, squares. In actual use
`the system would have an ampli?er associated with
`each photosensor, but for the purposes of description
`only one ampli?er 3-C is shown and is connected to the
`photosensor labeled 3-A-1. The individual photosensors
`3-A in the array 3 are contiguous and closely packed so
`as to permit light beams to be selectively directed from
`one CRT to any particular photosensor in the array as
`may be desired.
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`these factors is begun by considering the focusing ac
`2. means for de?ecting the electron beam such as elec
`trostatic plates or magnetic coils.
`tion of the lens 2 which focuses any light emitted from
`the surface of the screen of the CRT 1 onto the surface
`occupied by the photosensor array 3. This means that
`the divergent light emanating from a speci?c point on
`the CRT screen is caused to converge on a correspond
`ing speci?c point on the surface of the array. Thus, the
`lens solves the problem of selectivity, i.e., of con?ning
`the light signal which is essentially omnidirectional as it
`leaves the CRT screen so that it will strike a single
`photosensor and not a number of photosensors.
`The focusing action of the lens, which action pro
`duces a speci?c point target area on the array for a
`speci?c point source on the CRT, holds true for any
`point on the CRT screen. This generates a one-to-one
`correspondence between points on the CRT screen and
`points on the surface of the array. Since the action of
`the electron beam striking the phosphor on the CRT
`screen generates what is essentially a point source of
`light, it can be seen that it is only necessary to control
`the beam target position on the screen in order to direct
`the resultant light signal to a particular spot on the
`photosensor array. The control of the beam target posi
`tion is of course achieved by de?ecting the beam, and
`this can be accomplished by employing the standard
`electrostatic or electro-magnetic techniques. As shown
`in FIG. 1, the representative points on the CRT screen
`labeled l-A-l, 1-A-2, and 1-A-3, respectively, emit the
`diverging cones of light L-l, L-2, and L-3. These di
`verging signals propagate outward to the lens where
`they are focused by the lens and are shown on the other
`side of the lens 2 by the converging cones of light also
`labeled L-1, L-2, and L-3, respectively. These conver