We present a brief overview of the recent developments in quantum opti
cs concerning the control and reduction of quantum noise. The achievem
ents on squeezing, quantum non-demolition measurement and noiseless op
tical functions are summarized. The present limitations in quantum per
formance are discussed. We particularly stress the role of nonlinear o
ptics and point out the advantages expected from the implementation of
new artificially phase-matched materials, in different configurations
including cascaded second-order nonlinearities.