Abstract
Quantum stochastic calculus is an operator analogue of classical Ito's stochastic calculus which was originally developed for treating quantum noise. However, it turned out to be also useful in other cases of open systems, as in the case of measurement theory in quantum mechanics and in the treatment of quantum input and output channels. In the present paper, this calculus is used for developing a theory of direct, homodyne and heterodyne detection in quantum optics.