  Based on Planck's blackbody equation it is argued that a single mode light
pulse, with a large number of photons, carries one entropy unit. Similarly, an
empty radiation mode carries no entropy. In this case, the calculated entropy
that a coded sequence of light pulses is carrying is simply the Gibbs mixing
entropy, which is identical to the logical Shannon information. This approach
is supported by a demonstration that information transmission and
amplification, by a sequence of light pulses in an optical fiber, is a classic
Carnot machine comprising of two isothermals and two adiabatic. Therefore it is
concluded that entropy under certain conditions is information.
