APPARATUS AND METHOD FOR NIGHTTIME AND LOW VISIBILITY ALIGNMENT OF COMMUNICATORS

Abstract: A method and apparatus associated therewith for acquiring and maintaining a high quality communication by communication means of the type that includes a detector (54) and focusing means (70) for directing encoded incoming radiation to said detector. Means (A, B, C, D, and 72-79) are provided for determining the location of said radiation upon said detector and for generating an electrical signal responsive to said location. Said electrical signal is applied to electroluminescent means (89, 90, 92, 94) so that there is produced for the user a pattern of illumination indicating the degree of alignment of said communication means with the incoming radiation.

Description: APPARATUS AND METHOD FOR NIGHTTIME AND LOW VISIBILITY ALIGNMENT OF COMMUNICATORS TECHNICAL FIELD The present invention relates to means for automatically aligning a receiver to an incoming laser transmission and, in particular, to means for achieving and maintaining good alignment between a pair of reciprocal tracking transmitter/receivers ^ in conditions of low visibility. BACKGROUND OF TEE INVENTION A hand-held optical communicator-*- presently avail¬ able is described in "Gallium Arsenide Laser Communicators for Hand-Held Voice or Fixed-Ease Voice/Data Optical Communications" by Robert J. Cinzori [Procs. Sixth Con¬ ference on Laser Technology, Department of Defense (1974)]. SUMMARY OF THE INVENTION It is an object of the present invention to provide means for establishing and maintaining a good line of sight between a pair of optical communicators, one or more of which is hand-held or has an otherwise unstable base. Another object of the present invention is to achieve the above object during periods of impaired visibility, such as nighttime, thereby increasing the utility of the hand-held communicator. Still another object of the invention is to improve the quality of signal transmission and reception by enabling the receiving communicator to continually improve the line-of-sight therebetween. These and other objects are achieved by the method and apparatus therefor disclosed herein. A distant transmission may be located and good quality maintained (avoiding receipt on the "edge" of the signal) by a listener utilizing a receiver having a detector according to the method of the present invention wherein the loca¬ tion of the point of incidence of said transmission upon said detector is first determined and an electrical signal generated in response thereto. This electrical signal is then applied to electroluminescent means comprising a plurality of electroluminescent devices arranged into a pattern corresponding to the geometry of the detector. The pattern of illumination generated thereby gives the listener an indication of the quality of the alignment of the receiver to the transmission and thereby provides continual guidance in the pointing of the receiver. The determination of the location of the received energy upon the detector is facilitated by the incorpora¬ tion of a detector comprised of a plurality of independent detector portions into the system. By the use of such a detector, as opposed to a unitary detector, each portion may correspond to a particular electroluminescent device of the aforementioned pattern. Apparatus incorporating the present invention may include a plurality of electroluminescent devices each mounted in a segment (defined by the reticle) of the eyepiece of a sighting monocular. The sighting monocular is mounted with the receiver so that movement thereof alters the pointing direction of the receiver. Detector portions generate a plurality of electrical signals, each of which controls the luminance of one device and OM indicates to the listener the present quality of reception so that any necessary correction may be done by repointing and transmission "drop out" thus avoided. Other and further aspects of the present invention will become apparent during the course of the following description and by reference to the accompanying draw¬ ings. BRIEF DESCRIPTION OF TEE DRAWINGS Referring now to the drawings, in which like numerals represent like parts throughout: FIG. 1 presents a conceptual view of a field communi¬ cation by means of a pair of optical communicators, each including the alignment apparatus of the present invention whereby a common line-of-sight therebetween is obtained; FIG. 2 is a partial sectional view of an optical communicator according to the present invention illus¬ trating the laser transceiver 28 and its orientation within the outer cylinder 26; FIG. 3 is an electromechanical schematic view of the line-of-sight detection system of the present invention; FIG. 4a is a side view of a communicator for use with the present invention illustrating the misalignment of the receiver in the vertical plane; FIG. 4b is a planar view of the detector of the receiver of FIG. 4a, showing the movement of the blur circle thereon as a result of the alignment shown in FIG. 4a; FIG. 4c is a view of the monocular eyepiece of the present invention; FIG. 4d is a view of the monocular eyepiece as illuminated by the shifted blur circle of FIG. 4b; FIG. 5a is a top view of a communicator for use with the present invention illustrating the misalignment of the receiver in the horizontal plane; FIG. 5b is a planar view of the detector of the receiver of FIG. 5a showing the movement of the blur circle thereon as a result of the alignment shown in FIG. 5a; and FIG. 5c is a view of the monocular eyepiece as illustrated by the shifted blur circle of FIG. 5b. DETAILED DESCRIPTION OF THE INVENTION FIG. 1 presents a conceptual illustration of communication between a first (speaking or transmitting) operator 10 and a second (receiving or listening) operator 12 by means of the identical optical communicators 14, 16, respectively. It is seen that the communicators 14, 16 present relatively lightweight, compact units which may be hand-held during operation. Such units have been fabricated, generally cylindrical in nature, having a transceiver (not shown in FIG. 1) diameter of 1.6 inches and a length of approximately 7 inches positioned inside an outer cylinder, shown in FIG. 1, having a 3.7 inch diameter and a length of 10 inches. The communicators 14, 16 utilize the monoculars 22, 24 to obtain a line of sight 25 therebetween. Each operator is equipped with a headset having an earpiece 20, electrically coupled to the receiver electronics, and a microphone 18, elec- trically coupled to the transmitter electronics. Essentially, communication of voice is accomplished by transforming the voice of the transmitting operator 10 into a pulsed laser transmission over the optical path or ray 25. This "transformation" of voice or other data into a laser transmission is achieved by means of the modulation of the laser energy which travels over the path 25. The listening operator 12 receives the encoded laser transmission at the detector of his transceiver. The transmitted energy is converted into an electrical signal which, through standard transducer means, is "heard" after demodulation and decoding by the OM second operator 12 over his headset. Electronics appro¬ priate for the modulation and demodulation of such a pulsed transmission is disclosed, for a multiple signal case, in United States Patent No. 4,169,213 of R. A. Dye et al for "Apparatus and Method for Ordering Independent Signals", the property of the assignee herein. It is essential that the operators 10, 12 maintain both tran¬ sceivers housed within the communicators 14, 16 upon approximately coincident optical paths for the effective transmission and detection of the transmitted (laser) energy and associated signal content. It is additionally imperative that the line-of-sight 25 be held and main¬ tained as accurately as possible as a transmission on the "edge" of the field-of-view of the receiving communicator is subject to data loss through scintilla¬ tion, e.m.i. and related effects. The process by which the transmission path 25 of a first transceiver is utilized to orient a second, receiving transceiver is known in the art as "reciprocal tracking". Referring to FIG. 2, the (hollow) interior of the (outer) cylinder 26 is shown with the transceiver 28, secured by means of a holder 30, within the (outer) cylinder 26. The (inner) cylinder or optical transceiver 28 is secured to the holder 30 by the tensioning of a pair of fastening screws. The transceiver 28 may be seen in FIG. 2 to be divided internally into opposed transmitter and receiver sections 32, 34 separated by an internal partition 36. The transmitter electronics section 32 includes a ring up transformer 38 which provides power to pulser elec¬ tronics 40 mounted on a printed circuit board 42. The aforementioned serves to drive a compact GaAs laser diode 44 which is mounted on a heat sink 46 and a holding fixture 48. A transmitter lens system 50 serves to main- tain a predetermined solid angle of optical transmission. A conductor 52 provides electrical connection between the transmitter and the operator microphone. The optical center of the transmitter lens system 50 is intersected by the coincident axes of the cylinder 26 and the cylindrical transceiver 28. Also, coincident therewith, is the center of the IR quadrature (i.e., four equal segments) detector 54 of the receiver section 34. The detector 54 may be any of a number of well-known devices chosen principally for efficiency at the wave- length of interest. The selection of an appropriate detector technology hinges also upon signal-to-noise ratio considerations. For example, an avalanche detector is most desirable in low background noise applications, due to its internal current gain. Unfor- tunately, the current gain of an avalanche detector acts upon both signal and noise. Thus, while signal current is multiplied by a factor M (set by adjusting the dc bias level of the quadrature detector 98), the detector noise current, which is a function of the background return and detector internal leakage current, is multi- plied M , where d can vary from 1.5 to 2. Therefore, as the multiplication factor of the detector 54 is increased, the system S/N ratio is decreased. Generally, the limit of multiplication a system can tolerate is reached when the detector noise (with background) equals the receiver preamplifier noise. As the field-of-view is increased, the background noise begins to increase proportionately with the square thereof, and a back¬ ground noise limiting situation is rapidly approached. A theoretical cross-over point, easily calculable, is then reached at which a PIN detector will provide a more favorable S/N ratio than a avalanche detector. The existence of such cross-over point is partially a reflection of the greater quantum efficiency of the PIN detector. The quadrature detector 54 is mounted upon a washer 56. The washer 56 and the associated detector 54 are manually positioned by adjustment of the alignment screws 58, 60 to assure that the detector 54 remains within a predetermined focal spherical surface 62 when rotated in the elevation plane. The output of the detec¬ tor 54 is applied to the preamplifier 64 mounted upon the printed circuit boards 66, 68. A composite conduc¬ tor 71 provides electrical paths to the receiver electronics and to light emitting diodes mounted in the monocular eyepiece which provide a significant aspect of the present invention. A spherical mirror 70 is positioned at the rear or closed end of the (outer) cylinder 26. The quadrature detector 54 is located at the focal plane 62 (approxi¬ mately one-half the radius of curvature) of the mirror 70. FIG. 3 is an electro-mechanical schematic view of the circuitry of the ' present invention. The quadrature detector 54, divided into the labeled segments A, B, C and D, is mounted concentrically with the cross sections of the transceiver 28 and the outer cylinder 26. The conductors 72, 74, 76 and 78 transmit the currents independently generated by the incidence of portions of the incoming radiation upon the individual segments. (The four conductors may be gathered, along with the conductor connecting the detector to the receiver electronics, into the composite conductor 71.) The currents therein are fed into the preamplifier elec¬ tronics 79 and then to four separate fast attack, slow decay pulse integrators 80, 82, 84 and 86 which produce the voltages that drive the LED's 88, 90 , 92, 94 mounted in the quadrants defined by the reticle 96 of the monocular eyepiece 98. The communication or data signal is extracted at the receiver electronics after the combination of the four (A, E, C and D) quadrant outputs ' in the OR gate 100 (after thresholding the signals through the comparators 102, 104, 106 and 108 to ascertain whether or not signal, as opposed to background noise, has been received). The output of the OR gate 100 is then applied to the listener's receiver demodulator electronics which may be located in the headset electronics. The operation and mode of use of the present invention may be observed by examining the situations illustrated in FIGS. 4(a), (b) and (c) and 5(a), (b) and (c) with respect to the electro-mechanical diagram of FIG. 3. In FIG. 4(a) there is illustrated a side view (similar to the view of FIG. 2) of the transceiver 28 mounted within the outer cylinder 26. Initially, the blur circle 110, which represents the location of the incident radiation upon the surface of the quadrature detector 54 after its reflection off the spherical mirror 70, is assumed to be centered upon the detector (shown by the solid circle in FIG. 4b) . The currents in the four conductors 72, 74, 76 and 78 and, therefore, the voltages applied to the LED's from the integrators 80, 82, 84 and 86, are equal. As a result, the four LED's 88, 90, 92 and 94 are equally illuminated as shown in FIG. 4(c). (The assumption that the blur circle 110 lies at the center of the detector 54, implies that rays of incident radiation such as the rays 112, 113 arrive at the communicator approximately perpendicular to the surface of the detector 54. As is well known in the field of optics, such rays, after reflection from the spherical mirror 70, will be focused upon the detector 54 at the center of the focal spherical plane. ) The dashed image of the communicator in FIG. 4a represents its position after an (inadvertent) amount of counterclockwise rotation has occurred. Such trans- lation of position might occur as a result of a bouncy platform, commonly incurred with ship-to-ship or , _- MPI ship-to-shore communications, or might result from the fact that human pointing errors of less than +1° are considered unrealistic. Such a small pointing error, although often admirable and satisfactory in many applications, can quickly bring a transmission to the "edge" when a narrow field-of-view is necessitated. The movement of the outer cylinder 26 to the dashed posi¬ tion produces a rotation of the mirror 70. The result of such movement is thus: rays of the incoming trans- mission lying above the transceiver 28, such as the ray 112, contact the mirror 70 (after rotation) at a point such that the distance traveled to the mirror 70 is shorter than before, as a result of which the ray 112 contacts the mirror's surface at a more acute angle than previously. The reflected ray, of course, identi¬ cally contacts the mirror at a more acute angle, the net result of which is a greater divergence of the reflected beam 112 from the incident beam 112'. Likewise, portions of the transmission which lie below the transceiver 28 travel a greater distance before striking the mirror 70 than before. This results in a less acute angle of incidence than before and a smaller divergence of incident ray 113 from reflected ray 113'. The sum of these effects can be seen in* FIG. 4b where there is indicated (by arrow and dashed circle) the downward rotation of the blur circle 110 on the surface of the detector 54 that accompanies the movement illus¬ trated in FIG. 4a. Referring back to FIG. 3, this movement of the blur circle 110 results in a diir.inuition of the currents carried along the conductors 72, 78 and an increase in the currents along the conductors 74, 76. Consequently, the voltages applied to the LED's 88, 90 by the integrators 82, 84 will exceed those applied to the LED's 92, 94 by the integrators 86, 80 respectively. The corresponding state of the eyepiece 98 of the monocular, as shown in FIG. 4d, 1 thus comprises a fully illuminated .pair of upper half LED's 88, 90, and an unilluminated or lesser intensity pair of lower half LED's 92, 94. The operator, viewing such a pattern, is informed that he is now receiving 5 a transmission "on the edge" and hence directed to rotate the communicator's outer cylinder 26 upward (in the direction of the illuminated LED's) to restore a good field-of-view with the transmitting communicator. In such a manner, easily learned by the listener, a ° nighttime communication can be kept on target so that transmission "drop out" - a very serious error in terms of nighttime corrections and/or compensation - can be avoided. In FIG. 5a, a top view of a communicator, the 5 outer cylinder 26 is seen to have become misaligned with respect to the incoming transmission as the result of an unintended clockwise rotation or torque. Once again optical effects, analogous to those described above, act upon the incident radiation to cause the 0 ray 114 to the right of the transceiver 28 to diverge upon reflection from the mirror 70 less than before while the ray 115, arriving on the left hand side of the transceiver 28, diverges, upon reflection from the mirror, a greater amount than before. The net result 5 of these effects is indicated in FIG. 5b by the arrow and dashed circle indicating the rightward movement of the blur circle 110 on the surface of the detector 54. As a result of this movement, the currents carried by the conductors 72, 74 increase while those carried 0 by the conductors 76, 78 decrease. The relative current values result in a greater voltage output from the inte¬ grators 80, 82 than from the integrators 84, 86 and a corresponding increase in the illumination afforded by the LED's 88, 94 relative to that afforded by the 5 LED's 90, 92. The pattern thereby superimposed upon the eyepiece of the monocular is shown in FIG. 5c to OjVΪRI consist of a brightly illuminated pair of LED's 88, 94 to the left hand side of the reticle 96 and a dimly (if at all) illuminated pair of LED's 90, 92 to the right hand side of the reticle 96. Once again, the listener is notified that his hand movements and the like have moved the communicator off center and he is now at the "edge" and close to transmission drop out. To correct therefor, he must rotate the front of the communicator toward the illuminated half of the eye- piece (that is, counterclockwise) until the full complement of eyepiece LED's is illuminated as before. Thus, it is seen that the present invention affords the user (listener) of a communication system of the nature described an easily understood and implemented apparatus and method for maintaining a "good" line-of- sight so that maximum transmission/reception quality can be maintained. The apparatus of the present inven¬ tion, which employs, inter alia, illuminative elements, solves critical nighttime communication problems by allowing the user a convenient, non-distracting means for analyzing the varying quality of communication and may be employed to guard against the transmission drop out that would otherwise greatly degrade the night¬ time usefulness of such apparatus. in actual nighttime operation, the present inven¬ tion might be employed in conjunction with an acquisition or "hailing" system such as that described in "GaAs Laser Communicator acquisition System" by R. A. Dye and C. R. Berry (Santa Barbara Research Center Information Paper, March 1974) which determines the absence or presence of transmitting activity in the sector of interest. The system described in the above paper includes, inter alia, apparatus for performing scanning and filtering functions in conjunction with a "maximum likelihood" detection scheme whereby the presence of an active (transmitting) communicator in the sector of interest can be determined. Once such a determination has been made, the listener need only scan the horizon while observing the illumination pattern of the LED's of the monocular in accordance with the teachings herein to obtain (and maintain) a good (full reception) line-of-sight with the transmitting communicator. "gϋR O

Claims: CLAIMS What is Claimed is: 1. Apparatus for aligning a communication means having a detector to incoming radiation, said communica¬ tion means including focusing means for directing said incoming radiation to said detector, said apparatus comprising: a) means for determining the location of said radiation upon said detector, and for generating an electrical signal responsive thereto; and b) electroluminescent means responsive to said electrical signal. 2. Apparatus as defined in Claim 1 wherein said electroluminescent means is further characterized by a plurality of electroluminescent devices arranged into a pattern corresponding to the geometry of said detector so that there may be illuminated thereby a pattern indicative of the location of said transmission upon said detector. 3. Apparatus as defined in Claim 2 which addition¬ ally includes: a) a monocular having an eyepiece, said monoc¬ ular being mounted with respect to said receiver so that its movement directly effects the pointing direction of said receiver; and b) said eyepiece having a reticle defining a plurality of eyepiece segments, each of said segments having an electroluminescent device associated therewith. 14 4. Apparatus as defined in Claim 3 wherein said detector comprises a plurality of independent detector portions, each of said detector portions corresponding to a segment of said eyepiece as defined by said reticle. 5. A method for aligning a communication means having a detector to incoming radiation during conditions of low visibility comprising the steps of: a) receiving said radiation upon said detector; b) determining the point of incidence of said radiation signal upon said detector; c) generating an electrical signal in response to the location of said point of incidence; d) arranging a plurality of electroluminescent devices into a pattern corresponding to the geometry of said detector; e) applying said electrical signal to said plurality of electroluminescent devices so that said pattern is illuminated in response to the location of said radiation upon said detector; and f) pointing said communication means in response to the illumination of said pattern. 6. The method defined in Claim 5 further charac¬ terized in that the location of the point of incidence of said radiation upon said detector is determined by separating said detector into a plurality of independent detector portions and generating a corresponding plurality of independent electrical signals in response thereto, the relative magnitudes of said signals serving as an indication of the location of said point of incidence. OMPI 7. The method defined in Claim 6 characterized by the additional steps of: a) arranging the plurality of independent detector portions into a pattern; and b) arranging said plurality of electro¬ luminescent devices into a corresponding pattern. 8. The method defined in Claim 7 characterized by the additional steps of: a) locating said plurality of electro¬ luminescent devices in the eyepiece of a monocular; and b) engaging said monocular to said communi¬ cation means so that the movement of said monocular produces a corresponding movement of said means. 9. A method for acquiring a communication at night by aligning a communicator having a detector to incoming radiation comprising the steps of: a) scanning an area with said communicator so that said incoming radiation falls upon said detector; b) generating an electrical signal in response to the presence of said radiation upon said detector; and c) applying said electrical signal to electro¬ luminescent means so as to indicate the presence of said radiation and the direction of its source. O PI

Inventors: CINZORI R
Applicants: HUGHES AIRCRAFT CO
Application year: 1981
Main classification: G01B11
IPC codes: G01B11, H04B10