In Part I of this three-part study it was shown that the use of two-photon coherent state (TCS) radiation may yield significant performance gains in free-space optical communication if the receiver makes a quantum measurement of a single field quadrature. In Part II it was shown that homodyne detection achieves the same signal-to-noise ratio as the quantum field quadrature measurement, thus providing a receiver which realizes the linear modulation TCS performance gain found in Part I. Furthermore, it was shown in Part II that if homodyne detection does exactly correspond to the field quadrature measurement, then a large binary communication performance gain is afforded by homodyne detection of antipodal TCS signals. The full equivalence of homodyne detection and single-quadrature field measurement, as well as that of heterodyne detection and two-quadrature field measurement, is established. Furthermore, a heterodyne configuration which uses a TCS image-band oscillator in addition to the usual coherent state local oscillator is studied. This configuration, termed TCS heterodyne detection, is shown to realize all the quantum measurements described by arbitrary TCS. The foregoing results are obtained by means of a representation theorem winch shows that photoemissive detection realizes the photon flux density measurement.
ASJC Scopus subject areas
- Information Systems
- Computer Science Applications
- Library and Information Sciences