Quantum mechanically formulated fluctuation-characterization method using symmetric and asymmetric interferometers

A fluctuation-characterization method using an interferometer is ordinarily classically formulated by considering frequency fluctuations. However, it is preferable to treat it quantum mechanically because the method measures q-number quadrature fluctuations at the same time. We formulated an interferometric fluctuation-characterization method by treating quadrature fluctuations as q-number variables and frequency fluctuations as a c-number stochastic variable, and we gave the power spectral density of the fluctuations for pulse light. This method measures fluctuations that are calibrated with shot noise level, and it makes it possible to estimate the fluctuation angle in phase space, which is the quantity that determines transmission characteristics in optical communications. Fluctuations in a laser diode were characterized as an example of measurement.