US3121866A

US3121866A - Magneto-optical analog to digital signal converter

Info

Publication number: US3121866A
Application number: US27092A
Authority: US
Inventors: Irving F Barditch
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1960-05-05
Filing date: 1960-05-05
Publication date: 1964-02-18
Anticipated expiration: 1981-02-18

Description

Feb. 18, 1964 I. F. BARDITCH MAGNETO-OPTICAL ANALOG TO DIGITAL SIGNAL CONVERTER Filed May 5, 1960 2 Sheets-Sheet 1 3s 37 l8 38 I6 32 39 AMPLIFIER 33 34 i- LQ as Flg. l.

3 5| I? 50 I3 l9 23 2| 27 STANDARD 25 DIRECT CURRENT 22 VOLTAGE 1 9 I'M? I 1| i 74 2G Fug. 2. 4% 4 l2' h 4 wnmzsses INVENTOR Irving F. Bordirch.

%(M; AW

ATTORNEY Feb. 18, 1964 F. BARDITCH 3,121,866

MAGNETO-OPTICAL ANALOG T0 DIGITAL SIGNAL CONVERTER Filed May 5, 1960 2 Sheets-Sheet 2 Fig. 4.

United States Patent "ice 3,121,866 MAGNETO-0PTICAL ANALOG T0 DIGITAL SIGNAL CONVERTER Irving F. Barditeh, Baltimore, Md., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed May 5, 1960, Ser. No. 27,092 19 Claims. (Cl. 340347) This invention relates to improvements in analog to digital converters, and more particularly to an improved magneto-optical analog to digital voltage converter.

Prior art devices for converting from analog to digital type of data presentation have been characterized by a number of disadvantages, and the apparatus of the instant invention overcomes these disadvantages by eliminating switching, differencing, counting, or any of the other previous techniques which have been employed. The device is capable of high speed operation and may be made in substantially monolithic form.

Accordingly, a primary object of the instant invention is to provide a new and improved analog to digital signal converter.

A further object is to provide a new and improved analog to digital voltage converter utilizing magneto-optical effects.

A further object is to provide a new and improved magneto-optical analog to digital voltage converter which may be made in substantially monolithic form.

These and other objects will become more fully apparent after a study of the following specification, when read in connection with the accompanying drawings, in which:

FIG. 1 is a diagrammatic View partially in perspective of apparatus according to the preferred embodiment of the invention;

FIG. 2. is a cross section of a portion of the apparatus of PEG. 1;

FIG. 3 is a diagrammatic view of a suitable source of polarized light for use in the invention; and,

FIG. 4 is a further view of a portion of the apparatus of PEG. 1 showing this portion in greater detail.

Referring now to the drawings for a more detailed understanding of the invention, in which like reference characters are used throughout to designate like parts, there is shown at It) a member composed of magnetooptically active material characterized by the magnetooptical effect. The term magneto-optical effect is applied to the rotation of the direction of the electric vector of plane-polarized light by interaction with a magnetic field while traversing a suitable medium. Member it} may be a film of yttrium or gadolinium iron garnet. Several ferrimagnetic oxides including yttrium or gadolinium iron garnet are transparent to light in the infrared and visible-light frequencies. The characteristic of yttrium iron garnet of particular interest to the instant invention is the property of the material while subjected to an electromagnetic field of altering the polarization of light passing through the material in the region where the magnetic field is active or is maintained. This characteristic of yttrium iron garnet has been described in the literature, for example, reference may be had to an article, entitled Ferromagnetic Resonance and Non-Linear Effects in Yttrium Iron Garnet, by Le Craw, Spencer, and Porter, Journal of Applied Physics, vol. 29, March 1958, pages 326-327. Additional articles in the same issue of the same periodical are entitled Trans-parent Ferromagnetic Light Modulator Using Yttrium Iron Garnet, by Porter, Spencer and Le Craw, pages 495 496, and Optical Properties of Several Ferrimagnetic Garnets, by Dillon, pages 539-541.

More particularly, magneto-optically active material 3,121,866 Patented Feb. 18, 1964 includes material characterized by either one or both of the effects of :faraday rotation or magnetic birefringence, the former of which will be discussed in more detail hereinafter.

As a result of the faraday rotation effect, a plane-polarized wave will undergo rotation on passing through a magnetic medium that is magnetized in the direction of propagation of the wave, i.e. the magnetic flux lines are parallel to the Poynting vector of. the light.

The magnetic structure of the actual crystals of the yttrium iron garnet or gadolinium iron garnet material in its natural state may be broken up into magnetically discrete or saturated regions called domains. By proper processing or treatment of the material, the domains of the garnet crystal may be made to lie so that their mag- .etic moments are essentially perpendicular to the surface of the crystal, although they are not pointing in the same direction but generally in opposite directions, that is, the lines of force of the fields of adjacent domains may be parallel but the polarities may be opposite. Plane-polarized light normal to such a crystal surface will then be rotated in different portions of the crystal by amounts and in angular directions depending on whether the domain magnetic moment is parallel or antiparallel (polarity reversed) to the incident beam; some of the light will be rotated clockwise while some of the light will be rotated counterclockwise.

If a light analyzer, such for example as one known in the art as a Nicol prism analyzer, is set at degrees to a plane-polarized li ht wave, no light will emerge from the analyzer; in this orientation, the analyzer is said to be set at extinction. If a garnet crystal with domains creating magnetic moments normal to the surface is inserted between the plane-polarized light wave source and the analyzer, as previously stated some of the domains will rotate the light clockwise and some will rotate it counterclockwise. The light emerging from the crystal is now rotated in various portions of the beam with respect to the incident plane wave. The result is that some of these emerging parts of the beam are now oriented at such an angle that the Nicol prism is not set to extinction for them. Therefore, light is transmitted through the crystal and the Nicol prism. By rotating the analyzer with respect to the crystal, various of the domains may be set at essentially extinction, while others will not be. Accordingly, some light passes through the analyzer.

The Nicol prism or any other material such as is known by the name Polaroid which can polarize light may be used.

The domain magnetization direction of being parallel or antiparallel to the Poynting vector changes readily in the presence of a field produced by small magnets; a small external magnetic field may cause the magnetic fields or moments of all the domains to lie antiparallel to the direction of the Poynting vector of the light. Under these conditions, all the plane-polarized light passing through the garnet material can be blocked by an analyzer set at extinction for this particular condition. Removal of the field will allow the light to be transmitted again. In other words, the application of a small external magnetic field to the garnet material can change the light transmitted through the analyzer from on to off.

By cutting a yttrium-iron-garnet crystal (formula: 5Fe O 3Y O to yield a thin slice having given crys tallographic planes parallel to the surface, the magnetic moments of the domains may be arranged so that in zero applied field they are directed as desired.

The member 10 has disposed thereon or therein a plurality of preferably parallel transparent leads or condoctors of small diameter designated in FIG. 1 by the

reference numerals

11, 12, 13 and 14. Whereas for ease of illustration only four leads are shown in FIG. 1, it will be readily understood that any desired number may be employed depending upon the desired capacity of the analog to digital converter. The transparent leads 11, 12, 13 and 14 may be thin electrically conductive films of tin dioxide deposited and baked on garnet film 10.

There is shown at 18 an amplifier to which the analog voltage to be digitized is fed by any convenient means as by lead 16. The amplifier 18 develops an output voltage between ground 17 and each of leads 11-15 which is proportional either to variations in the analog quantity or signal, or which is a function of the value of the analog quantit as may be desired. It will be observed from FIG. 1 that one end of each of the

leads

11, 12, 13, 14 and 15 is connected to the aforementioned amplifier 18 output. It will be understood that the lead means 15 symbolically represents connections to any desired number of additional transparent leads in or on the member as may be desired. It is to be further noted that the amplifier 18 is of such design that each of the

leads

11, 12, 13, is fed so that none interacts with any of its neighbors and each in eifect is fed independently. Suitable amplifiers of this type have been built consisting of a level of voltage amplifier feeding a number of parallel emitter follower transistor stages each feeding its separate line 11, 12 etc.

It will be noted from FIG. 1 that the other end of each of

leads

11, 12, 13 and 14 is connected to spaced points 19,

2t

21 and 22 on a resistance voltage dividing network including the

resistors

28, 23, 24 and 25 and which is energized by way of resistor 9 and lead 26 by direct current potential from a standard voltage source 27 which develops a desired standard potential between lead 26 and ground 17. Again, these are so fed from suitable isolation sources, not shown, so as to make any currents drawn during operation unable to disturb the voltage distribution at any point elsewhere in the circuit. Terminal 19, which for purposes of illustration only is chosen as representing the lowest voltage to which the analog to digital converter is responsive, is connected by way of the aforementioned resistor 28 to ground 17.

Disposed in front of the member 10 (to the left as viewed in FIG. 1) is a suitable source of polarized light, the light being of a frequency or wavelength to which film 10 is transparent, which light source may include a light source 50, a polarizing element 51, and a collimating element '52. Disposed back of and adjacent to member 119 is an analyzer or filter member 30 for polarized light, which may be a light-polarizing film, and which is of the correct type to pass light waves having a predetermined polarization corresponding to the polarization of some of that light emanating from the source 5051 which passes through garnet film or member 10 in a region or area where there is substantially no external magnetic field. More specifically, the filter for polarized light 30 is set at extinction for light having a plane of polarization at a predetermined angle to the plane of polarization of light leaving source 50-51. Disposed adjacent to and back of member 311 are any desired number of photosensitive readout devices, five devices being shown in FIG. 1 and designated 31, 32, 33, 34 and 35.

Lead connections

36, 37, 33, 39 and 40 are made respectively to the upper ends of the photosensitive devices, and it will be understood that lead connections, not shown in FIG. 1, may be made to the lower ends of the devices.

In the operation of the apparatus of FIG. 1, it will be noted that the right-hand end of each of the

leads

11, 12, 13 and 14, as viewed in FIG. 1, is at a slightly different potential with respect to the other leads, as a result of the direct current source 27. For the purposes of this description and to facilitate an understanding of the invention, the amplifier 18 may be presumed .9 have an output impedance which is resistive in nature. Assume now by way of description that the amplifier 18 develops on leads 11-14 ajdirect current voltage as a result of some input thereto, and that this direct current voltage on leads 11-14 corresponds substantially to the voltage at one of the

points

19, 20, 21and 22. For purposes of illustration, let it be assumed that the volt age on the left-hand end of lead 12 is the same as the voltage at terminal or point 241. No current will flow in lead 12 whereas, because of a difference of potential between the two ends of each of the other leads 11, 13 and 14 a current will flow either from a left-to-right direction or from a right-to-left direction. The magnetic fields set up by these currents cause the magnetic moments of the domains to assume substantially uniform directions and polarities, so that all the light passing through member 10 in the areas adjacent the current carrying leads is rotated in the same angular direction to form a plane of polarization at an angle for which filter element 36 is set at extinction. Accordingly, no light passes through member 30 in the areas thereof back of

leads

11, 13 and 14. However, at the same time, no current is flowing in the lead 12 because the potentials at the two ends thereof are substantially equal in amplitude and of like polarity, and no magnetic field is set up in the area or region of member 10 adjacent lead 12. Accordingly, light from source 5li51 arriving at member 10 in the area adjacent lead 12 does not have the polarization of a portion thereof altered in an adverse manner, and this portion passes through the analyzer element 30 and impinges upon all of the

photosensitive readout devices

31, 32, 33, 34 and 35. Accordingly, light passes through

members

10 and 30 only in a rectangular area, zone or strip which corresponds to a particular voltage, and the member 10 may for purposes of analysis be thought of as constituting a number of parallel strips, each of which passes some light without altering the polarization thereof in a manner to be extinguished at 30 when a voltage of a particular amplitude is applied to leads 11-14 from amplifier 18.

Particular reference is made now to FIG. 4 which shows the

photosensitive readout devices

31, 32, 33, 34 and 35 in greater detail. The five

photosensitive devices

31, 32, 33, 34 and 35 provide for a binary notation or binary counting including five digits. It will be readily understood that five devices are used for ease of illustration and that any number of desired photosensitive devices may be utilized depending upon how high it is desired to count. Each of the rectangular zones, lying at intervals in a longitudinal direction, and extending transversely across the entire five devices, has five portions which are selectively masked in accordance with a binary coding pattern, so that the photosensitive devices are selectively energized in accordance with a binary code pattern. For example, in accordance with conventional binary code where five digits are employed, the number 1 would be represented by 00001. Accordingly, the rectangular zone 41 adjacent the lead 11 has the first four device portions (reading from left to right) masked in that zone by any suitable means, and the portion of the last photosensitive device 35 is unmasked. Light passing through member 16 in the area adjacent lead 11 and thence through member 30 and impinging upon only the zone 41 would therefore cause only the fifth or last photosensitive device 35 to produce an output signal on lead 40. The rectangular zone encompassing portions of the five devices lying adjacent the aforementioned lead 12 is designated 42, and in accordance with conventional binary coding, the number 2 is represented in binary notation by 00010. Accordingly, the portions in the rectangular zone 42 of

photosensitive devices

31, 32, 33 and 35 are masked in the areas thereof adjacent lead 12 while the adjacent portion of photo sensitive device 34 is unmasked, and when no potential difference exists between the ends. of lead 12, light passes s,121,see

through member and analyzer member and impinges upon only the unmasked portion of device 34 adjacent the lead 12, and only the output lead 39 of the five output leads has a signal produced thereon.

Particular reference is made now to FIG. 2 which is a cross section of a portion of the apparatus of FIG. 1 as it may be constructed in monolithic form. The leads 11' and 12' may be deposited leads of tin dioxide deposited on a film 10' of yttrium iron garnet and baked thereon. Adjacent the film 10' is a transparent backing plate 71 of any convenient or suitable material, which may be omitted if desired, and adjacent backing plate 71 is the analyzer element 30 which may as aforementioned be light-polarizing film of the correct type, whereas adjacent the back surface of member 30 is a partially filled space 72, which may be used if desired and may provide room for the masking material on the aforementioned photosensitive elements or devices, or the masking material may be deposited or otherwise applied to the elements so that no space 72 is required. Photosensitive element 31 is supported on the back thereof by any suitable mounting means 73. If desired, the readout devices may be selenium film or cadmium sulfide evaporated on the back of polaroid film 3t and portions of the analyzer 30 may be masked before evaporation of the photosensitive readout strips so that the same final result is achieved, that is, the provision of sensitive and insensitive portions.

Particular reference is made now to FIG. 3. A suitable source of palarized light may comprise a light source 74 disposed in the reflector means 75 and having a polarizing lens 76 adjacent thereto.

The number of degrees rotation of the polarization of the incident light on member 10, while not too sensitive to changes in the strengths of the magnetic fields set up at the leads, is, for any given magneto-optically active material, a function of the thickness of the material and the Wavelength of the light. The invention contemplates suitable choice of material, dimensions including thickness, and wavelength, to provide the desired manner of operation in accordance with the characteristics of the analyzer 30.

There has been provided then apparatus well suited to accomplish the aforedescribed objects of the invention. A variation in the voltage on leads 11-14 occurs as a result of changes in the input to amplifier 18 on lead means 16. Assuming one of the

leads

11, 12, 13 or 14 has no current flow therethrough as a result of the voltage developed on the lead, a change in the signal input on lead means 16 will cause a different one of the leads l1, 12, 13 and 14 to have substantially no current therethrough because of the equal potential existing at the two ends thereof, and as a result, another lead, for example, lead 13, having no current flow therethrough will cause a shift in the polarization of only a portion of the light arriving at the area adjacent thereto from source Sit-51 in a manner tobe excluded by analyzer 30, the remaining portion passing through analyzer 30. This last-named light portion is passed to the adjacent portions of the

photosensitive readout devices

31, 32, 33, 34 and 35, causing the output leads 36, 3'7, 38, 39 and 40, respectively, to have signals or no signals thereon in accordance with whether the sections or portions of the devices are masked in the particular areas where light falls thereon in accordance with the pattern of FIG. 4, and a direct readout on each of the aforementioned five output leads corresponding to whether that particular binary digit is O or 1 is obtained. No moving parts are required. The apparatus may be made sensitive to small changes in the potential or signal on lead 16, and by using any desired number of photosensitive readout devices with the corresponding required number of leads on member 10, the apparatus may be made to have a capacity of any desired binary count.

The invention includes the use of additional resist ance networks and isolation devices desired to insure uniform potential steps between adjacent leads on memher it), and to provide for operation in the manner intended.

The invention includes the use on? light guiding and shielding means Where desired to insure that light passing through any given portion of member 10 or member 30 arrives at only its intended destination.

Whereas the invention has been shown and described with reference to yttrium and gadoliniumdron garnet crystals, it will be understood that other suitable magneto optically active materials may be employed.

It will be understood that as an obvious adaptation the photosensitive devices could be coded to give a decimal readout as well as a binary readout; for example 19 adjacent readout devices could provide for decimal counting to 99, a suitable number of leads being provided on member 10.

In final summary, in the absence of a magnetic field, some domains of the yttrium iron garnet or other active material rotate a portion of the light passing therethrough in one angular direction while other domains rotate the remaining portion of the light in the opposite angular direction; one analyzer can be set to block only one portion, and the other portion passes to the photosensitive readout devices. A small external magnetic field causes the magnetic moments of all the domains to assume uniform directions and polarities; all the light passing through the active material is rotated in the same angular direction and is excluded by the analyzer. l

Whereas the invention has been shown and described with respect to an embodiment thereof which gives satisfactory results, it should be understood that changes may be made and equivalents substituted Without departing from the spirit and scope of the invention.

1 claim as my invention: 1

1. In analog to digital signal converter apparatus, in combination, a source of light having a predetermined plane of polarization, a plurality of light sensitive ele men-ts disposed in predetermined positions with respect to each other and with respect to said source out light, each of said light sensitive elements having sensitive and insensitive portions and generating an electrical output signal while light energy impinges only on a sensitive portion thereof, the sensitive and insensitive portions of all said plurality of light sensitive elements being arranged in a predetermined pattern whereby light reaching certain selected sensitive portions provides output signals from the light sensitive elements which are digitally coded to correspond to a quantity in accordance with the arrangement of the selected sensitive portions with respect to each other and light reaching certain other selected sensitive portions provides other ouput signals from the light sensitive elements which are digitally coded to correspond to another quantity in accordance with the arrangement of the other selected sensitive portions with respect to each other, light filtering means interposed between the source of light and the plurality of light sensitive elements and excluding only light having a plane of polarization at a predetermined angle with respect to said predetermined plane of polarization, and analog signal means including magneto optically active means interposed between the source of light and said light filtering means for selectively controlling the plane of polariza-tion of light reaching the light filtering means in selected areas thereof selected in accordance with the value of the analog signal to thereby variably select groups of sensitive portions to be illuminated in accordance with variations in the value of the analog signal.

2. In analog to digital signal converter apparatus, in combination, a plurality of lead means, means connected to all of said plurality of lead means for causing current flows in all but a selected one of said lead means selectively in accordance with the value of the analog signal to be digitized, magneto-optically active means disposed adjacent all of said lead means, those of said lead means having current flows therethrough creating magnetic fields in the adjacent regions of the magneto-optically active means, polarized light filter means disposed on one side thereof in predetermined position with respect to said magneto-critically active means, photo-sensitive means disposed on the other side of said polarized light filter means, and a source of polarized light disposed on the other side of said magneto-optically active means, said source of light having a wavelength at which said magnetooptically active means is transparent.

3. Analog to digital signal converter apparatus comprising, in combination, a plurality of photosensitive readout devices disposed adjacent each other, each of said readout devices being divided along the length thereof into an equal number of coextensive portions, each of said devices generating a signal While a sensitive portion thereof has light impinging thereon, corresponding coextensive portions of all of the photosensitive devices being selectively sensitive and insensitive in accordance with a binary code pattern whereby light impinging upon all the coextensive portions of all of said photosensitive devices in a selected zone of portions causes the generation of a signal in only selected ones of said devices in accordance with the location of the sensitive and insensitive portions thereof, a source of polarized light having a predetermined wavelength and plane of polarization, and means including magneto-optically active means and a filter for polarized light interposed in the order named between the source of light and the plurality of photosensitive devices for selectively passing light to selected portions of the devices in [accordance with variations in an analog signal to thereby selectively energize said plurality of photosensitive readout devices in a binary code patter-n corresponding to. the value of the analog signal.

I 4. In analog to digital voltage converte apparatus, in combination, a source of plane polarized light having a predetermined plane of polarization, a plurality of elongated photosensitive 1eadout devices disposed contiguous and substantially parallel to each other in predetermined positions with respect to the source of light, each of said readout devices generating an electrical signal while light energy reaches any portion thereof, each of said readout devices being divided along the length thereof into an equal number of coextensive substantially rectangular portions, corresponding portions of each of said plurality of devices being symmetrically located to form a plurality of substantially rectangular zones spaced along the length of the devices, each of said zones including a portion of each of the devices, the plurality of zones extending substantially transverse to the longitudinal axes of the devices, the portions of each zone being selectively masked and unmasked in accordance with a binary code pattern having a number of digits equal to the number of said readout devices, light impinging on any masked portion producing no signal in the readout device, polarized light analyzer means disposed with one side thereof adjacent said plurality of photosensitive readout devices and between the devices and the source of light for excluding only light having a plane of polarization at a predetermined angle to said predetermined plane of polarization, a transparent member of magneto-optically active material disposed adjacent the other side of said analyzer means between the analyzer means and the source Otf light, said magnetooptically active member having a plurality of leads extending thereacross at spaced intervals corresponding to the width of the zones extending across the photosensitive readout devices, the leads being centrally disposed with respect to the zones respectively, said active material normally in the absence of an external magnetic field applied thereto rotating the plane of polarization of a portion ot the light firom said source in a manner whereby said portion is excluded by the analyzer means and normally rotating the plane of polarization of another portion of light from said source whereby said other portion is not excluded by the analyzer means, a current flow in any one of said leads setting up a magnetic field in the area of the magneto-optically active member adjacent the last-named lead, said magnetic field causing a change in the polarization of said other portion of light passing through the member area adjacent the lead whereby said last-named light is not transmitted through the analyzer means to the zone of the photosensitive readout devices adjacent said last-named lead.

5. Apparatus according to claim 4 including in addi tion a source of direct current potential, means including a voltage dividing network operatively connected to said source oi= direct current potential and energized there,

from for providing a plurality of graduated voltages, adjacent ends of said plurality of leads being operatively connected to different points on said voltage dividing network whereby a plurality of diiferent potentials are applied to the plurality of leads respectively, an amplifier having a variable input signal applied thereto and providing a variable direct current output which varies as a function of the input signal, and output means for the amplifier operatively connected to the other ends of all of said plurality of leads whereby a variably selected one of said leads has substantially no current flowing therethrough as a result of the balancing of potentials at the two ends thereof in accordance with the instant value of said input signal, all the other of said leads having current flows therethrough as a result of differences in potentials art the ends thereotf.

6. In an analog to digital voltage converter, in combination, amplifier means having the analog voltage applied thereto, a source of direct current potential, a resistance voltage dividing network having a plurality of resistors operatively connected in series to said source of direct current potential, a plurality of'leads connected at adjacent ends thereof to a plurality of different voltage points on said voltage dividing network, all the other ends of said plurality of leads being connected to the output of said amplifier means to receive a voltage therefrom, a selected one of 'said leads having no substantial potential diiference existing between the ends thereof in accordance with the instant output of the amplifier means whereby substantially no current flows therethrough, all the remainder of said plurality of leads carrying current flows during said instant, a thin fiat member composed of yttrium iron garnet, all of said plurality of leads being disposed at spaced intervals along the length of said member otf yttrium iron garnet, a source of plane polarized light of predetermined polarization disposed in predetermined position with respect to said yttrium iron garnet member whereby light from said source impinges upon said member in areas adjacent to all of said leads, said source of plane polarized light having a wavelength at which said yttrium iron garnet member is transparent, light analyzer means disposed on the other side of said garnet member for passing only polarized light which has a plane of polarization corresponding to the transmission characteristics of the light analyzer means, and photosensitive detector means disposed on the other side of said light analyzer means, flows of current in the remainder of said leads causing magnetic fields to be set up in the areas of the garnet member adjacent thereto, said magnetic fields changing the plane of polarization Otf light passing through the garnet member in said areas whereby said last-named light is not transmitted by said analyzer means to said photosensitive detector means, polarized light from said source which passes through the area of said garnet member adjacent said one lead having no magnetic field thereat having the plane of polarization of some out the light passing through said last-named area altered a predetermined amount so that some of the light passes through said light analyzer means to said photosensitive detector means.

7. In analog to digital voltage converter apparatus, in combination, a plurality of photosensitive elements, a

source of plane polarized light disposed in predetermined position with respect to said plurality of photosensitive elements, a member of magneto-optically active material disposed between said source of polarized light and said plurality of photosensitive elements, said source of light having a wavelength at which said magneto-optically active material is transparent, a filter element for polarized light disposed between said member of active material and said photosensitive elements, said filter element excluding only polarized light having a plane of polarization at a predetermined angle to the plane of polarization of the light emitted from said source, and means having the analog voltage applied thereto and operatively connected to the member of active material for selectively creating magnetic fields in portions of said member of active material which change the polarization of light passing through the member in said portions, said portions varying in position with variations in the instant value of the analog voltage.

8. Apparatus according to claim 7 wherein said plurality of photosensitive elements are additionally masked in predetermined patterns whereby the plurality of photosensitive elements provide a plurality of output voltages in digitally coded form which vary selectively in accord ance with variations in the areas of the member of active material in which the magnetic fields are set up.

9. An analog to digital voltage converter comprising, in combination, a plurality of photosensitive devices each generating a signal While light impinges on a sensitive portion thereof, said plurality of photosensitive devices being disposed adjacent each other, each of said photosensitive devices being divided along the length thereof into an equal number of coextensive portions, the portions of each of said photosensitive devices being selectively insensitive and sensitive to provide a total pattern corresponding to a binary code having a number of digits equal to the number of said photosensitive devices, filter means for polarized light disposed with one side thereof adjacent said plurality of photosensitive devices for excluding only polarized light having a predetermined plane of polarization, yttrium iron garnet film disposed adjacent said filter means on the other side thereof, a source of plane polarized light disposed on the other side of said yttrium iron garnet film in predetermined position with respect thereto and having a wavelength at which said garnet film is transparent, polarized light from said source passing through said film in the absence of an external magnetic field applied thereto with predetermined changes in the polarization thereof and with at least a portion of the light passing through said filter means and impinging on said photosensitive devices, a plurality of leads extending at spaced intervals and in substantially parallel lines across the suriace of said garnet film, each of said leadscreating an external magnetic field in the area of the film adjacent thereto while current flows in the lead, analog voltage input means operatively connected to all of said leads, means operatively connected to all of said leads for applying graduated voltages thereto whereby only one of said leads has no current flow therein in accordance with the instant value of an analog voltage, light passing through the area of said garnet film adjacent said last-named lead and impinging upon said plurality of photosensitive devices causing signals to be generated therein in accordance with the pattern of sensitive and insensitive portions of said devices adjacent the area of the film through which the light passes, light impinging on the other areas of the garnet film having the polarization thereof shifted to said predetermined plane whereby light passing through said other areas does not pass through the filter means to the photosensitive devices.

10. In an analog to digital voltage converter, in combination, means forming a film of yttrium iron garnet, means operatively connected to said film for setting up a plurality of magnetic fields at spaced intervals along said film, said intervals corresponding to discrete changes in the value of the analog voltage, no magnetic field being set up in the film at a position corresponding to the instant value of the analog voltage, a source of polarized light disposed in predetermined position with respect to said garnet film on one side thereof, said source of light having a wavelength at which said garnet film is transparent, filter means for polarized light disposed adjacent said garnet film on the other side thereof, and a plurality of photosensitive devices disposed on the other side of said filter means, the magnetic fields in the areas of the garnet film causing light passing through the areas of the garnet film in which the magnetic fields exist to be shifted in polarization and not to pass through the filter means to the photosensitive devices, light from said source which passes through the area of the garnet film having no external magnetic field created therein passing through the filter means to the photosensitive devices.

11. Apparatus according to claim 2 wherein said magneto-optically active means is composed of yttrium iron garnet.

12. Apparatus according to claim 3 wherein said magnetic-optically active means is composed of yttrium iron garnet.

13. Apparatus according to claim 4 wherein said magneto-optically active member is composed of yttrium iron garnet.

14. Apparatus according to claim 2 wherein said magneto-optically active means is composed of gadolinium iron garnet.

15. Apparatus according to claim 3 wherein said magneto-optically active means is composed of gadolinium iron garnet.

16. Apparatus according to claim 4 wherein said magneto-optically active member is composed of gadolinium iron garnet.

17. Apparatus according to claim 4 wherein said magneto-optically active member is additionally characterized as containing discrete magnetic domains normally characterized by magnetic moments of both polarities with re spect to a selected direction of measurement, a magnetic moment of one polarity rotating the electric vector of the light in one angular direction and a magnetic moment of the opposite polarity rotating said vector of the light in the opposite angular direction, the application of an exernal magnetic field causing substantially all the magnetic moments to assume the same polarity whereby all the light has the vector thereof rotated in the same angular direction to provide a plane of polarization at said predetermined angle.

18. Analog-to-digital signal converter apparatus comprising a source of polarized light, a plurality of elongated photosensitive readout elements disposed adjacent each other, masking means for excluding light from portions of all of said readout elements in accordance with a binary code pattern thereby providing a pattern of areas that are responsive and non-responsive, respectively, to light in accordance with a binary code, an analyzer disposed between said light source and said photosensitive elements, said analyzer being oriented at an angle of extinction with respect to the plane of polarization of said source of polarized light, and magneto-optical means disposed between said source of polarized light and said analyzer means for selectively rotating the polarization of a portion of said light in accordance with the value of the analog signal to be digitized to selectively enable light to pass through selected portions of said analyzer.

l9. Analog-to-digital signal converter apparatus comprising a source of polarized light, a plurality of elongated photosensitive readout elements disposed adjacent each other, masking means for excluding light from portions of all of said readout elements in accordance with a binary code pattern thereby providing a pattern of areas that are responsive and non-responsive, respectively, to light in ac- 11 cordance with the binary code, an analyzer disposed between said source of polarized light and said photosensitive elements, said analyzer being oriented at an angle of extinction with respect to the polarization of light from said light source, and magneto-optical means disposed between said light source and said analyzer means, said magneto-optical means comprising a magneto-optically active film and a plurality of lead means disposed adjacent thereto, means connected to all of said plurality of lead means for causing current flow in all but a selected one of said lead means selectively in accordance with the value of the analog signal to be digitized, those of said lead'means having current flowing therein creating magnetic fields in the adjacent regions of said magneto-optition ofa selected portion of the light from said source to selectively enable light to pass through selected portions of said analyzer.

References Cited in the file of this patent UNITED STATES PATENTS 2,834,005 Ketchledge May 6, 1958 2,855,539 Hoover Oct. 7, 1958 2,968,799 Smith Ian. 17, 1961 OTHER REFERENCES Magnetic Domains by Longitudinal Kerr Effect, by Chas. A Fowler, Jr., and Edward M. Fryer, Physical Recally active film to selectively rotate the plane of polariza- 15 view, April 1, 1954, pages 5256.

Claims

1. IN ANALOG TO DIGITAL SIGNAL CONVERTER APPARATUS, IN COMBINATION, A SOURCE OF LIGHT HAVING A PREDETERMINED PLANE OF POLARIZATION, A PLURALITY OF LIGHT SENSITIVE ELEMENTS DISPOSED IN PREDETERMINED POSITIONS WITH RESPECT TO EACH OTHER AND WITH RESPECT TO SAID SOURCE OF LIGHT, EACH OF SAID LIGHT SENSITIVE ELEMENTS HAVING SENSITIVE AND INSENSITIVE PORTIONS AND GENERATING AN ELECTRICAL OUTPUT SIGNAL WHILE LIGHT ENERGY IMPINGES ONLY ON A SENSITIVE PORTION THEREOF, THE SENSITIVE AND INSENSITIVE PORTIONS OF ALL SAID PLURALITY OF LIGHT SENSITIVE ELEMENTS BEING ARRANGED IN A PREDETERMINED PATTERN WHEREBY LIGHT REACHING CERTAIN SELECTED SENSITIVE PORTIONS PROVIDES OUTPUT SIGNALS FROM THE LIGHT SENSITIVE ELEMENTS WHICH ARE DIGITALLY CODED TO CORRESPOND TO A QUANTITY IN ACCORDANCE WITH THE ARRANGEMENT OF THE SELECTED SENSITIVE PORTIONS WITH RESPECT TO EACH OTHER AND LIGHT REACHING CERTAIN OTHER SELECTED SENSITIVE PORTIONS PROVIDES OTHER OUTPUT SIGNALS FROM THE LIGHT SENSITIVE ELEMENTS WHICH ARE DIGITALLY CODED TO CORRESPOND TO ANOTHER QUANTITY IN ACCORDANCE WITH THE ARRANGEMENT OF THE OTHER SELECTED SENSITIVE PORTIONS WITH RESPECT TO EACH OTHER, LIGHT FILTERING MEANS INTERPOSED BETWEEN THE SOURCE OF LIGHT AND THE PLURALITY OF LIGHT SENSITIVE ELEMENTS AND EXCLUDING ONLY LIGHT HAVING A PLANE OF POLARIZATION AT A PREDETERMINED ANGLE WITH RESPECT TO SAID PREDETERMINED PLANE OF POLARIZATION, AND ANALOG SIGNAL MEANS INCLUDING MAGNETO OPTICALLY ACTIVE MEANS INTERPOSED BETWEEN THE SOURCE OF LIGHT AND SAID LIGHT FILTERING MEANS FOR SELECTIVELY CONTROLLING THE PLANE OF POLARIZATION OF LIGHT REACHING THE LIGHT FILTERING MEANS IN SELECTED AREAS THEREOF SELECTED IN ACCORDANCE WITH THE VALUE OF THE ANALOG SIGNAL TO THEREBY VARIABLY SELECT GROUPS OF SENSITIVE PORTIONS TO BE ILLUMINATED IN ACCORDANCE WITH VARIATIONS IN THE VALUE OF THE ANALOG SIGNAL.