Contains research objectives and reports on five research projects.National Science Foundation (Grant ECS81-20637)U.S. Army Research Office - Durham (Contract DAAG29-80-K-0022)U.S. Navy - Office of Naval Research (Contract N00014-81-K-0662)U.S. Navy - Office of Naval Research (Contract N00014-80-C-0941

Bogler, Philip L.

Bondurant, Roy S.

Fratamico, John J.

Hakimi, Farhad

Kumar, Prem

Lau, Sun T.

Maeda, Mari W.

Mesite, Paula L.

Nguyen, Trung T.

Papurt, David M.

Rediker, Robert H.

Schloss, Robert P.

Shapiro, Jeffrey H.

Wagner, Stuart S.

Wong, Albert K.

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Communication Sciences and EngineeringOptical Propagation and Communication20. Optical Propagation and CommunicationAcademic and Research StaffProf. R.S. Kennedy, Prof. J.H. Shapiro, Dr. R.H. Rediker, Dr. P. KumarGraduate StudentsP.L. Bogler, R.S. Bondurant, J.J. Fratamico, F. Hakimi, S.T. Lau, M. Maeda, P.L.Mesite, T.T. Nguyen, J. Ocenasek, D.M. Papurt, J.J. Prisco, R.P. Schloss, P.D.Shapiro, S.S. Wagner, A.K. WongThe central theme of our programs has been to advance the understanding of optical andquasi-optical communication and radar systems. Broadly speaking, this has entailed: developingsystem-analytic models for important optical channels; using these models to derive the fundamentallimits on system performance; and identifying, and establishing the feasibility of, techniques anddevices which can be used to approach these performance limits.20.1 Atmospheric Optical Communication Systems for NetworkEnvironmentsNational Science Foundation (Grant ECS81-20637)Jeffrey H. Shapiro, Trung T. Nguyen, Albert K. WongA local computer network is prototypically a high-bandwidth (1-10 Mb/s) geographically compact(0.1-10 km diameter) packet-switched network that employs coaxial cable or fiber optics as itstransmission medium. Atmospheric optical communication links are a natural choice for certainhigh-bandwidth short-haul terrestrial transmission applications in which cable rights-of-way areunobtainable, or frequent link and network reconfiguration is necessary. Such links are thereforeattractive candidates for local network applications including bridges between buildings containingcable subnetworks, and temporary quick-connects for new outlying users for which cable runs areunavailable. This program addresses the problem of how best to employ atmospheric opticalcommunication links, which experience occasional outages due to local adverse weather conditions,in a local computer network, whose high-level protocols are designed to provide 100% end-to-endmessage reliability.The principal task for the past year has been the design and construction of a pair of 10 Mb/satmospheric optical communication transceivers to be used, in succeeding years, in local networkexperiments on the M.I.T. campus. Each transceiver will use a 2 mW semiconductor laser collimatorpen module in the transmitter, and an avalanche photodiode/preamplifier module in the receiver. InRLE P.R. No. 125127Optical Propagation and Communicationaddition to the optical transceiver work, we have begun analysis on how atmospheric optical links canbest be employed in various key network roles.20.2 Atmospheric Propagation Effects on Infrared RadarsU.S. Army Research Office - Durham (Contract DAAG29-80-K-0022)Jeffrey H. Shapiro, David M. Papurt, Sun T. Lau, Paula L. MesiteCompact coherent laser radars have the potential for greatly improved angle, range, and velocityresolution relative to their microwave-radar counterparts. This program is aimed at obtaining aquantitative understanding of target-reflection and atmospheric-propagation effects on theperformance of compact coherent laser radars through a combination of theory and experiments.Under a collaboration arrangement with the Optics Division of the M.I.T. Lincoln Laboratory, theexperimental portions of the research are being carried out on the compact C02-laser radars underdevelopment there.During the past year we have completed examination of the combined effects of turbulence andtarget speckle/glint on the performance of a 2-D pulsed-imager radar. 1-4 The principal conclusionsdrawn from this work are as follows. First, the compact radar system model must include beam jitter.Second, jitter-corrected glint target returns do show turbulence-induced lognormal scintillation.Third, turbulence-induced beam jitter is the cause for staring-mode speckle target decorrelation.The focus of our work has now shifted to moving-target indication (MTI) systems. In particular, wehave begun to study many of the same turbulence and speckle issues as they impact the LincolnLaboratory continuous-wave CO2 laser heterodyne-reception Doppler radar.5References1. J.H. Shapiro and S.T. Lau, "Turbulence Effects on Coherent Laser Radar Target Statistics," Appl.Opt. 21, 2395-2398 (1982).2. D.M. Papurt, "Atmospheric Effects on Heterodyne-Reception Optical Radars," Ph.D. Thesis,Department of Electrical Engineering and Computer Science, M.I.T., May 1982.3. S.T. Lau, "Decorrelation Time of Speckle Targets Observed with a Heterodyne-Reception OpticalRadar," S.M. Thesis, Department of Electrical Engineering and Computer Science, M.I.T.,June 1982.4. D.M. Papurt, J.H. Shapiro, and S.T. Lau, "Measured Turbulence and Speckle Effects in LaserRadar Target Returns," Proc. SPIE 415, (1983).5. D.G. Biron and B.E. Edwards, "Moving Target Imaging Radar Utilizing Both Intensity and VelocityInformation," CLEO 1982 Technical Digest, (Opt. Soc. of Am., Pheonix, Arizona, 1982)pp. 128-129.RLE P.R. No. 125 128Optical Propagation and Communication20.3 Improved Millimeter-Wave Communication Through RainU.S. Navy - Office of Naval Research (Contract N00014-81-K-0662)Jeffrey H. Shapiro, John J. Fratamico, Philip L. BoglerThe increased path loss due to rain has long been recognized as a key factor limiting the extensionof microwave satellite communications into the millimeter-wave spectral band. This program is aimedat understanding the extent to which millimeter-wave communication performance under severe rainconditions can be improved through exploitation of multiply-scattered radiation. Toward this end wehave developed efficient numerical procedures for solving the scalar transport equation for the totaltransmission, angular spread, multipath spread, and Doppler spread of the multiply-scatteredradiation. 1 Evaluation of these parameters has been performed for propagation at 35, 44, 95, 130,210, and 300 GHz in various rain rates.1We have combined the preceding propagation work with the appropriate communicationanalysis2,3 for the millimeter-wave channel and reached the following conclusions. In a heavyrainstorm a satellite-to-ground link at 95 GHz or above which has sufficient power for multi-Mb/scommunication in clear weather may have sufficient power for multi-Kb/s communication if adaptiveangle diversity reception of the scattered radiation is employed. Direct-beam reception will notfunction at these data rates, nor will nonadaptive angle diversity reception. The array needed for theadaptive combiner is far beyond the current state of the art, but may evolve out of the need for phasedarrays to be used in millimeter-wave radars.References1. J.J. Fratamico, "Millimeter-Wave Propagation through a Turbid Atmosphere," Ph.D. Thesis,Department of Electrical Engineering and Computer Science, M.I.T., November 1982.2. J.J. Fratamico, P.L. Bogler, and J.H. Shapiro, "Adaptive Diversity-Combining for ImprovedMillimeter-Wave Communication through Rain," IEEE J.Sel. Areas in Commun. SAC-I1,(1983).3. P.L. Bogler, "Electromagnetic Wave Propagation in Multiple-Scattering Atmospheres withApplications to Adaptive Communication," Ph.D. Thesis Proposal, Department of ElectricalEngineering and Computer Science, M.I.T., January 1983.20.4 Two-Photon Coherent State LightU.S. Navy -Office of Naval Research (Contract N00014-81-K-0662)Jeffrey H. Shapiro, Prem Kumar, Roy S. Bondurant, Mari Maeda, Stuart S. WagnerRecent theory has shown that the generation of light beams with quantum states of superiorfluctuation behavior may be possible. These states, called two-photon coherent states (TCS), areminimum uncertainty states of the electromagnetic field processing an asymmetric noise divisionRLE P.R. No. 125129Optical Propagation and Communicationbetween the quadratures. The purpose of this research is to generate TCS light via degeneratefour-wave mixing in sodium vapor, and to verify some of the predicted TCS fluctuation characteristicsvia photon counting measurements.During the past year we have: set up the mixer and verified conjugate-wave generation; developeda photon counting scheme for making accurate statistical measurements on nanosecond durationoptical pulses;1 and devised a pulse-conditioning technique to minimize excess noise in thefour-wave mixer output beams.2 Work is now proceeding on quantum-noise measurements.In addition to the main experimental effort we have begun analysis of the use of TCS light inphase-sensing interferometers3 and of fundamental limits in phase/amplitude heterodynemeasurements. 4References1. R.S. Bondurant, P. Kumar, J.H. Shapiro, and M.M. Salour, "Photon-Counting Statistics of PulsedLight Sources," Opt. Lett. 7, 529-531 (1982).2. P. Kumar and R.S. Bondurant, "Improving the Pulse Shape in Dye Laser Amplifiers: A NewTechnique," Appl. Opt. 22, 1284-1287 (1983).3. R.S. Bondurant, "Theoretical and Experimental Aspects of Quantum Noise Reduction andPrecision Measurement," Ph.D. Thesis Proposal, Department of Electrical Engineering andComputer Science, M.I.T., November 1982.4. S.S. Wagner, "An Investigation of the Uncertainties in Signal Energy and Phase in OpticalDetection," S.M. Thesis, Department of Electrical Engineering and Computer Science, M.I.T.,September 1982.20.5 Fiber-Coupled External-Cavity Semiconductor High-PowerLaserU.S. Navy -Office of Naval Research (Contract N00014-80-C-0941)Robert H. Rediker, Robert P. Schloss, Farhad HakimiDuring the past year an external cavity to contain five semiconductor gain elements operating inparallel has been designed and built. A photograph of this cavity is shown in Fig. 19-1. Starting fromleft to right the first plate attached to the four Super-Invar rods holds the micromanipulators andpiezo-electric elements which will be used to properly position the gain elements. In back of thisplate are the thermoelectric elements which are used to control individually the temperature of eachelement. The thermoelectric elements are connected to the gain elements by a flexible copper strap.The next plate will contain a lens which focuses all the collimated radiation from the gain elements onthe spatial filter to be held by the third plate from the left. The spatial filter which contains thirteen3 pim slits on 10.5 pm centers is the Fraunhoffer diffraction pattern of the gain elements' radiation ifthese elements are emitting in coherence. Filters have been built for us of blackened Si2N3 byintegrated circuit techniques. The single pass transmission of the filter for coherent radiation inputRLE P.R. No. 125 130Optical Propagation and Communicationfrom the five elements is -3 times that if the radiation is incoherent. The next plate will contain a lensto recollimate the radiation; the last plate will contain a partially reflecting mirror.Figure 20-1: Photograph of External CavityThermoelectric control circuits with sensors have also been built to control the temperature of eachsemiconductor gain element to 0.5 x 10.30C. (This temperature control is equivalent to controlling the820-nm wavelength of the gain element radiation to 3 x 10'5 nm.) This sophisticated control willenable us to tune and detune the output wavelength of each element if the element were operating byitself. We will thus be able to quantify the tolerance for "locking into coherence" to wavelengthvariations. The sophisticated positioning controls in the cavity shown in Fig. 20-1 will enable us toalso quantify the mechanical tolerances for "locking into coherence". These tolerances will give anindication of the ease with which this "high-power-laser" concept can be taken from laboratory togeneral use.RLE P.R. No. 125131RLE P.R. 125 132

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