Optimal Control of Quantum Noise (Optical Communications by Two-photon Laser Part II)

Osamu HIROTA  Isamu SHIOYA  Shikao IKEHARA  Yasuharu SUEMATSU  

IEICE TRANSACTIONS (1976-1990)   Vol.E61   No.4   pp.273-279
Publication Date: 1978/04/25
Online ISSN: 
Print ISSN: 0000-0000
Type of Manuscript: PAPER
Category: Optical and Quantum Electronics

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The problems for the controllability of the quantum state are considered for application to optical communications. The new optimization problems arise in the quantum communication theory in addition to problems considered up to now. The concrete example of the controllability problems is Two-photon coherent state (TCS) generated by Two-photon laser. The optimum conditions for the parameters of TCS, which minimize the error probability, are given when TCS is employed as the transmission state in the quantum optimum receiver of the binary system, and its numerical behavior is shown. Furthermore the noise behavior associated with the TCS in the several optical receivers are shown. As the result, the ultimate noise limit hitherto can be reduced by using TCS in the optical communication systems. The saving power, when we employ the TCS as the transmission state in the binary communication system, is about 3 dB in the direct photo detector, and it is 5 dB in the optical homodyne receiver. Furthermore the saving power in the quantum optimum receiver is 4 dB. The SNR of the direct photo detector is improved by more than 6 dB. The information performance of the homo dyne is superior to the heterodyne when TCS is employed, while the heterodyne is superior to the homodyne in general when an ordinary coherent state is employed. Thus, it is suggested for reduction of the noise problems that the Two-photon laser which will be realized in the future will convey the significant benefits to the optical communications.