Showing papers by "Jeffrey H. Shapiro published in 1978"

Optical communication with two-photon coherent states--Part I: Quantum-state propagation and quantum-noise

Abstract: Recent theoretical work has shown that novel quantum states, called two-photon coherent states (TCS), have significant potential for improving free-space optical communications. The first part of a three-part study of the communication theory of TCS radiation is presented. The issues of quantum-field propagation and optimum quantum-state generation are addressed. In particular, the quantum analog of the classical paraxial diffraction theory for quasimonochromatic scalar waves is developed. This result, which describes the propagation of arbitrary quantum states as a boundary-value problem suitable for communication system analysis, is used to treat a number of quantum transmitter optimization problems. It is shown that, under near-field propagation conditions, a TCS transmitter maximizes field-measurement signal-to-noise ratio among all transmitter quantum states; the performance of the TCS system exceeds that for a conventional (coherent state) transmitter by a factor of N_{s} + 1 , where N_{s} is the average number of signal photons (transmitter energy constraint). Under far-field propagation conditions, it is shown that use of a TCS local oscillator in the receiver can, in principle, attenuate field-measurement quantum noise by a factor equal to the diffraction loss of the channel, if appropriate spatial mode mixing can be achieved. These communcation results are derived by assuming that field-quadrature quantum measurement is performed. In part II of this study, photoemissive reception of TCS radiation will be considered; it will be shown therein that homodyne detection of TCS fields can realize the field-quadrature signal - to-noise ratio performance of part I. In part III, the relationships between photoemissive detection and general quantum measurements will be explored. In particular, a synthesis procedure will be obtained for realizing all the measurements described by arbitrary TCS.

Quantum Statistics of Homodyne and Heterodyne Detection

Abstract: There are three basic techniques that may be employed to detect optical radiation: photon detection, homodyne detection, and heterodyne detection (see Fig. 1). From the photocounting theory of Kelley and Kleiner [1], one can readily show that photon detection, in the limit of unity quantum efficiency, can be interpreted as the quantum measurement of the total photon number operator N for any quantum state of a quasi-monochromatic input field. No similar quantum description is as yet available for homodyne or heterodyne detection. In this paper, we shall derive the abstract quantum description of homodyne detection. Because heterodyne detection involves the more complicated concept of simultaneous measurement of non-commuting observables, its quantum description will only be briefly discussed.

Propagation experiments in low-visibility atmospheres.

Abstract: An experimental program aimed at measuring critical channel parameters of atmospheric optical communication channels under low-visibility weather conditions is described. Multipath and angular spectrum measurements made under a variety of weather conditions over a 13.6-km line-of-sight propagation path are reported. The latter measurements are used to examine the dependence of scattered plus unscattered optical transmission on optical thickness.