Panasonic Corporation

Osamu Hirota

Masaru Fuse

Masaki Souma

A dynamic range of intensity modulation is set to range from a maximum intensity Smax to a minimum intensity Smin. A difference &#x394;(=Smax&#x2212;Smin) between the maximum intensity Smax and the minimum intensity Smin is divided by the number 2M of multilevel signals. Thus, a distance (an intensity difference) between adjacent signals is [&#x394;/2M]. The number 2M of multilevel signals is selected such that the distance [&#x394;/2M] between adjacent multilevel signals (between an intensity Sand an intensity S) is sufficiently buried within a range of quantum fluctuations obtained when heterodyne measurements are made or buried within a range of quantum shot noise obtained when a direct detection is made. Bases of a basis group are each positioned for intensity signals so as to have a high intensity and a low intensity between which a distance is set to be a certain value smaller than a middle point intensity [&#x394;/2]. Note that adjacent bases are set to have an intensity signal transmitting a logical value '1' of transmission data and an intensity signal transmitting a logical value '0' of transmission data in an inverted manner.

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Kanagawa, Japan

Osamu Hirota