We report on the theoretical analysis of an optical parametric oscillator i
n which a succession of parametric amplifications takes place to achieve mo
re than 200% quantum efficiency at the wavelength of interest. The first in
teraction generates the desired radiation, which we call the signal, whatev
er its wavelength, and its complement, which we called the idler. When the
idler is of no particular interest it is used as the pump in a second inter
action to amplify the same signal, increasing the quantum efficiency for th
is radiation. The same type of process can be applied again until the maxim
um efficiency is reached. (C) 1999 Optical Society of America [S0740-3224(9
9)02410-8].