Quantum fluctuations in traveling-wave amplification of optical images

We investigate amplification of optical images by means of a traveling-wave optical parametric amplifier. As shown recently for a cavity-based geometr y, such a scheme can amplify images without deteriorating their signal-to-n oise ratio thus working as a noiseless amplifier. Here we consider a config uration without cavity, which is more realistic for a possible experimental realization. We study in detail the quantum fluctuations of the amplifier and formulate criteria for its noiseless performance. We investigate physic al features of noiseless amplification, which take place for both traveling -wave and ring-cavity configurations. We demonstrate how the optimum phase matching of a phase-sensitive wave front of an image (by means of a thin le ns or a small displacement of the crystal) can improve the noise performanc e of the amplifier and bring it to the ultimate value achievable under give n physical conditions. We discuss the possibility of using detectors with t he area much smaller than the area of the input image elements. We compare our results with those obtained for the ring-cavity configuration. [S1050-2 947(99)02209-X].