Contains research objectives and summary of research on four research projects.National Aeronautics and Space Administration (Grant NGR 22-009-013)U.S. Navy - Office of Naval Research (Contract N00014-76-C-0605)Joint Services Electronics Program (Contract DAAB07-76-C-1400)National Science Foundation (Grant ENG74-00131-AO2)U. S. Air Force - Electronic Systems Division (Contract F19628-76-C-0054)National Science Foundation (Grant ENG74-03996-A1

Kennedy, Robert S.

Shapiro, Jeffrey H.

Warde, Cardinal

Yuen, Horace P. H.

DSpace@MIT

COMMUNICATION SCIENCESANDENGINEERINGXVII. OPTICAL PROPAGATION AND COMMUNICATIONAcademic and Research StaffProf. Robert S. Kennedy Prof. Cardinal WardeProf. Jeffrey H. Shapiro Dr. Horace P. H. YuenGraduate StudentsM. Yousoof Burmawi Nam-Soo Myung Warren S. RossMarcel F. Coderch Woo Hyun Paik Steven V. SperryJesus A. Machado Mata Mahmoud TebyaniThe broad objectives of our program are to (i) formulate propagation models forimportant optical channels from the underlying physical processes, (ii) determine thefundamental limits on detection and communication performance that can be realizedwith these channels, (iii) develop techniques for optical detection and communicationwhich achieve or approach these limits, and (iv) establish, by means of experiment,the validity of the theoretical results and guide their further development.1. QUANTUM COMMUNICATION THEORYNational Aeronautics and Space Administration (Grant NGR 22-009-013)U. S. Navy - Office of Naval Research (Contract N00014-76-C-0605)Joint Services Electronics Program (Contract DAAB07-76-C-1400)Horace P. H. Yuen, Robert S. Kennedy, Jeffrey H. ShapiroOur main concern in this work is the extent to which commonly accepted conclusionsconcerning the limitations imposed by quantum effects upon system performance arecorrect. The issue is important because such effects often contribute the dominant"noise" in the optical communication systems that are now contemplated. Our goal isto determine whether the limits encountered thus far are fundamental in nature, ormerely associated with the specific systems that have been considered. If they are notfundamental, there may be opportunities for substantial improvement in the performanceof optical systems.To determine the extent of possible improvement in performance, three majorquestions are being addressed:(i) Assuming that we are only limited by physical laws rather than by present-daytechnology, what are the situations in which the performance of the systems now beingconsidered falls substantially short of the performance of an optimum system?(ii) What is the structure of the optimum quantum system for any given application,expressed in the abstract language of quantum physics?(iii) How can a desired optimum quantum system be realized or approximated inPR No. 119(XVII. OPTICAL PROPAGATION AND COMMUNICATION)situations wherein it offers a significant performance advantage?Our major effort during the past year was concentrated on determining the advan-tages of producing fields associated with two-photon coherent states and the advantagesof optimal quantum receivers for coded communication systems.The photodetection statistics for two-photon coherent states were determined forsingle-mode fields. It was also shown that ordinary homodyne detection is a realiza-tion of the optimum quantum measurement for these states.The practical possibilities of realizing two-photon coherent states, in the form ofultrashort pulses, were further developed during the past year. We found that dissipa-tion does not significantly alter the pulse formation, and that, to a first approximation,two-photon cascade systems, such as stimulated spin-flip Raman scattering, lead (bothclassically and quantum mechanically) to the desired two-photon behavior. This greatlyincreases the possibility of realizing stimulated two-photon emission experimentally.Detailed analysis of such cascade systems will be carried out during the coming year.We have developed the general theory of quantum field propagation between a trans-mitter and a receiver. This work, in combination with previous work on channelmodeling, yields a general framework for the representation of quantum channels. Theresults were applied to free-space propagation to obtain the two-photon results that wehave described. We are also determining the extent to which an optimum quantumdecoder can improve the performance of coded optical communication systems. A boundto the performance of such systems has been developed and will be compared with theperformance attainable with existing systems.2. IMPROVED LOW-VISIBILITY COMMUNICATIONNational Science Foundation (Grant ENG74-00131-AO2)U. S. Air Force - Electronic Systems Division (Contract F19628-76-C-0054)Robert S. Kennedy, Jeffrey H. Shapiro, Cardinal WardeThis investigation, which is carried out jointly with the M. I. T. Center for Materi-als Science and Engineering, is concerned with the performance of terrestrial line-of-sight communication systems under conditions of low visibility. Our aim is to determinethe extent to which performance can be improved through appropriate system design,and to develop the devices for achieving this improvement. The potential for improve-ment resides in the energy and information contained in the scattered component of thereceived field.The collection of data to establish the frequency, variability, and the regularity ofthe key channel parameters has been our major concern during the past year. Measure-ments taken on a 13-km line-of-sight path at 0. 69 tm and 2 p m wavelengths have shownPR No. 119(XVII. OPTICAL PROPAGATION AND COMMUNICATION)little dispersion of the field, either in time or angle for optical thicknesses as large asten. Measurements at larger optical thicknesses have been limited by system sensitiv-ity. Efforts to correlate the experimental data with various propagation models arenow in progress.3. OPTICAL PROPAGATION AND COMMUNICATION THROUGHATMOSPHERIC TURBULENCENational Science Foundation (Grant ENG74-03996-A 1)Jeffrey H. ShapiroRandom spatiotemporal fluctuations in refractive index that result from turbulentmixing in the Earth' s atmosphere have a profound effect on optical wave propagation.In particular, turbulence-induced optical phase perturbations restrict the resolutionattainable in long-exposure telescopic photography to a few seconds of arc. The samephase perturbations gradually destroy the spatial coherence of a laser beam as it prop-agates through the atmosphere, and thus they limit the effectiveness of collimated orfocused laser transmitters in communication and radar systems. Furthermore, atmo-spheric optical receivers are subject to severe temporal fading caused by turbulence-induced optical amplitude fluctuations. We have been working to quantify the performancelimitations imposed by atmospheric turbulence on specific imaging and communicationsystems, and to develop system configurations that are immune to atmospheric fluctua-tions.During the past year, several advances have been made toward realizing the pre-1ceding objectives. In research for a Master' s thesis, Raymond J. Staron studied andsimulated phase-estimation procedures for mode-compression communication receiv-ers. This work provides a useful quantitative sensitivity analysis for direct-detectionlinear least-squares phase estimation, and includes computer simulation results thatoffer some valuable insights into the nonlinear phase estimation performance. In other2Master' s thesis research, Mahmoud Tebyani analyzed various diversity-combiningtechniques. His results have led us to an analytical framework for parametric per-formance comparisons between diffraction-limited, photon-bucket, channel matched-filter, and phase-compensated reception.3 Finally, we have prepared a review articlethat unifies recent results on propagation, imaging, and communication through atmo-spheric turbulence; 4 some novel results are presented in this article.In the coming year, we plan to develop Markov process (state-variable) models foratmospheric statistics, and use these models to study the ultimate limits on phase-tracking performance in imaging and communication systems.PR No. 119(XVII. OPTICAL PROPAGATION AND COMMUNICATION)References1. R. J. Staron, "Phase Estimators for Optical Communication Receivers," S.M.Thesis, Department of Electrical Engineering and Computer Science, M. I. T., May1976.2. M. Tebyani, "Robust Receivers for Optical Communication through AtmosphericTurbulence," S.M. Thesis, Department of Electrical Engineering and Computer Sci-ence, M. I. T., May 1976.3. J. H. Shapiro and M. Tebyani, "A Unified Analysis of PPM Error Rates for OpticalCommunication through the Turbulent Atmosphere," a paper presented at the 1976International Symposium on Information Theory, Ronneby, Sweden, June 21-24,1976.4. J. H. Shapiro, "Imaging and Optical Communication through Atmospheric Turbu-lence" (to appear in J. W. Strohbehn (Ed.), Laser Beam Propagation through theAtmosphere, Springer Verlag, Berlin).4. ULTRAVIOLET COMMUNICATIONJoint Services Electronics Program (Contract DAAB07-76-C-1400)Robert S. Kennedy, Horace P. H. YuenThis investigation is concerned with determining whether broadcast (omnidirectional)optical systems can operate in low-visibility scattering atmospheres. The potentialexists because in an omnidirectional system the power level at the receiving apertureis much less reduced by the presence of scattering than in a line-of-sight collimatedsystem. To utilize this power the field of view of the receiver must be increased withan attendant increase in collected noise power. By operating in the 0. 2-0. 3 .m wave-length region, where detector and background noise is negligible, the noise limitationis greatly relaxed and the major limitations become multipath spread and boundarylosses.During the past year, the magnitude of the multipath spread and the width of thereceived angular spectrum for omnidirectional scatter have been estimated theoretically.The angular spectrum broadens quickly to fill the hemisphere as the optical thicknessincreases to approximately one. The multipath spread is of the order of 3pr /c secondswhen there is no absorption. Here P is the scattering coefficient, r is the path length,and c is the velocity of light. A small amount of absorption changes this to approxi-mately 0. 5 F-7 [(a/P) 1]-3/4/c, where a is the extinction coefficient (absorption plusscatter).Our theoretical results will be extended to include other scattering functions. Apropagation experiment to confirm the results is also planned.PR No. 119

Optical Propagation and Communication

Contains reports on three research projects.National Aeronautics and Space Administration (Grant NGL 22-009-013)U.S. Navy - Office of Naval Research (Contract N00014-76-C-0605)Joint Services Electronics Program (Contract DAABO7-76-C-1400)National Science Foundation (Grant ENG74-00131-A03)U.S. Air Force - Electronic Systems Division (Contract F19628-76-C-0054)National Science Foundation (Grant ENG74-03996-A01

COMMUNICATION SCIENCESANDENGINEERINGXX. OPTICAL PROPAGATION AND COMMUNICATIONAcademic and Research StaffProf. Robert S. Kennedy Prof. Cardinal Warde Dr. Vincent ChanProf. Jeffrey H. Shapiro Dr. Horace P. H. YuenGraduate StudentsM. Yousoof Burmawi Jesus A. Machado-Mata Diane C. SimmonsMarcel F. Coderch Nam-Soo Myung Steven V. SperryPaul J. Curlander Woo Hyun Paik Mahmoud TebyaniWarren S. RossThe broad objectives of our program are to (i) formulate propagation models forimportant optical channels from the underlying physical processes, (ii) determine thefundamental limits on detection and communication performance that can be realizedwith these channels, (iii) develop techniques for optical detection and communicationwhich achieve or approach these limits, and (iv) establish, by means of experiment, thevalidity of the theoretical results and guide their further development.1. QUANTUM COMMUNICATION THEORYNational Aeronautics and Space Administration (Grant NGL 22-009-013)U. S. Navy - Office of Naval Research (Contract N00014-76-C-0605)Joint Services Electronics Program (Contract DAABO7-76-C- 1400)Horace P. H. Yuen, Jeffrey H. Shapiro, Robert S. KennedyThe long-range goal of this investigation is to realize improved optical communica-tion, detection, and estimation in the space environment. Such improvement may bepossible through the use of quantum measurements (optical receivers) that are superiorto those now considered and the use of quantum states other than coherent states.1 Ourmajor goal during the next year is to design an experiment which will demonstrate thatthe desired quantum states, which are called two-photon coherent states, can be pro-duced.References1. R. S. Kennedy, "Problems in Quantum Communication and Information Theory,"presented at the 1975 IEEE-USSR Joint Workshop on Information Theory, Moscow,1975 (Proceedings published by IEEE, 75CH1167-61T), pp. 105-110.PR No. 120(XX. OPTICAL PROPAGATION AND COMMUNICATION)2. IMPROVED LOW-VISIBILITY COMMUNICATIONNational Science Foundation (Grant ENG74-00131-A03)U. S. Air Force - Electronic Systems Division (Contract F19628-76-C-0054)Robert S. Kennedy, Jeffrey H. Shapiro, Cardinal WardeThis investigation, which is carried out jointly with the M. I. T. Center for MaterialsScience and Engineering, is concerned with the performance of terrestrial line-of-sightcommunication systems under conditions of low visibility. Our aim is to determine theextent to which performance can be improved through appropriate system design, andto develop the devices for achieving this improvement. The potential for improvementresides in the energy and information contained in the scattered component of the re-ceived field.The collection of data to establish the frequency, variability, and the regularity ofthe key channel parameters has been a major concern during the past year. Measure-ments taken on a 13-km line-of-sight path at 0. 69 1im and 2 lm wavelengths have shownlittle dispersion of the field, either in time or angle, for optical thicknesses as large asten. Up to that optical thickness, the results are well approximated by the predictedunscattered field.1 Recently we have installed new 1.06 4m and 0.54 Lm lasers withwhich we expect to be able to operate at lower visibilities.References1. W. H. Paik, M. Tebyani, D. J. Epstein, R. S. Kennedy, and J. H. Shapiro, "Prop-agation Experiments in Low-Visibility Atmospheres" (to appear in Applied Optics).3. OPTICAL PROPAGATION AND COMMUNICATION THROUGHATMOSPHERIC TURBULENCENational Science Foundation (Grant ENG74-03996-A01)Jeffrey H. ShapiroIn this investigation, we have sought to quantify the performance limitationsimposed by atmospheric turbulence on specific imaging and optical communicationsystems, and to develop system configurations that are immune to atmospheric fluctu-ations. Our work in previous years has established a rigorous analytical frameworkfor parametric performance comparisons among various imaging and communicationsystem alternatives.1 During the past year, we have focused our attention on channel/signal estimation structures and their performance. In particular, we have examinedthe design and performance of focal-plane detection arrays using a state-variablePR No. 120 100(XX. OPTICAL PROPAGATION AND COMMUNICATION)atmospheric propagation model that includes both drift and evolution terms in its tem-poral behavior. These results, which will appear in Marcel F. Coderch's S.M. thesis, 2comprise the final work done under this program.References1. J. H. Shapiro, "Imaging and Optical Communication through Atmospheric Turbu-lence" (to appear in J. W. Strohbehn (Ed.), Laser Beam Propagation through theAtmosphere, Springer Verlag, Berlin).2. M. F. Coderch, "Focal Plane Optical Detection for Turbulent Channels," S.M. thesisproposal, Department of Electrical Engineering and Computer Science, M.I. T., May1977.PR No. 120 101

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