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 geometry, such a scheme can amplify images without deteriorating their signal-to-noise ratio thus working as a noiseless amplifier. Here we consider a configuration 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 physical 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 lens or a small displacement of the crystal) can improve the noise performance of the amplifier and bring it to the ultimate value achievable under given physical conditions. We discuss the possibility of using detectors with the area much smaller than the area of the input image elements. We compare our results with those obtained for the ring-cavity configuration. [S1050-2947(99)02209-X].