Very Large Capacity Coherent Lightwave Communication

Osamu Hirota, Yoshihiro Yoshida, Masao Nakagawa +1 more

Lê Nguyên Bình

Richard E. Slusher, Bernard Yurke

Coherent lightwave communications systems are approaching a limit where the error rates and channel capacities are limited by the quantum properties of light. This is often referred to as the shot-noise limit. If ideal laser light is used in the system, there is no way to avoid this limit. However, new states of the light field called squeezed states have recently been developed that allow an improvement in error rates below the shot-noise limit. Squeezed light concepts and recent experiments are reviewed with emphasis on aspects important to coherent communications. It is shown that channel capacity can be improved using squeezed light by only a factor of two. Larger improvements are in principle possible for error rates, e.g. a factor of three reduction in the number of required photons per bit for a 10/sup -9/ bit error rate. An example of a recent high-performance system is described where optical losses and electronic noise reduce the improvement expected using squeezed light to the 10-20% level. It is concluded that squeezed light only offers significant improvement in bit error rates for very-high-efficiency systems.>

Shamsolah Salemian, Shahram Mohammadne

Abstract: An all optical method has been proposed for quantum Hadamard gate implementation. This quantum gate was realized by using Y-junction beam splitter. Normal modes in waveguides have been used as quantum bit. This all optical gate can be used in quantum computation and communication. The proposed Hadamard gate has potential of being more compact and easily realized compared to other optical implementations. By using planar lightwave circuit in implementation, the width of Y-junction input waveguide, width of each branch, angle of bend and length of bend were obtained 1 micron, 0.75 micron, 45º and 0.75 micron, respectively. By using planar lightwave circuit in implementation, the radius of large air holes and the radius of small holes were obtained 0.2 ands 0.1 micron, respectively. The index of substrate was 1.325. Implementation based on photonic crystal structures and planar lightwave circuit technology was used in integrated optics.

Murat Azizoá ̧¡lu

Bahaa E. A. Saleh, Malvin Carl Teich

Numerous schemes have been recently suggested for generating photon-number-squeezed light. In one class of technique, initially Poisson photons are modified (using methods such as deadtime deletion, decimation, coincidence decimation, and overflow count deletion) to yield sub-Poisson photons. In another class, feedback is applied (e.g., by control of the rate of generation of photoevents) so that the resultant point process is self-exciting instead of Poisson. Are such light sources useful for optical communication? Can the channel capacity C of a lightwave communication system based on photoevent point process observations be increased by use of photon-number-squeezed light?