Erbium-based optical coherent transient correlator for the 1.5-micron communication bands.

摘要

Correlators are needed in communications, memory, and signal processing applications to perform cross-correlations for tasks such as address-header decoding for data-packet switching, spread spectrum and code division multiple access communication, associative memory, database searching, and pattern recognition. Correlators based on optical coherent transients, Fourier theory, and holography can potentially perform real-time correlations with multi-phase encoded information at gigahertz bandwidths, a capability conventional electronics lack.; The first operation of spatial-spectral holographic correlators in the 1.5-gm communication bands was demonstrated at 1536 nm using Er3+:Y ₂SiO₅ and the correlator processed multi-phase encoded optical pulses. Real-time decoding of 20-bit binary-phase-shift key encoded address-header pulses is demonstrated using stimulated photon echoes in a phase-matched crossed-beam configuration; this function is required for coherent transient optical data routing and packet switching.; Optical 30-symbol quadriphase-shift keyed (QPSK) and binary-phase-shift keyed (BPSK) codes were processed, and the results demonstrated the ability of such correlators to process QPSK codes and BPSK codes with the same apparatus. The high-fidelity correlations exhibit the low sidelobe characteristics expected for the codes used.; The 4I_15/2 and 4I_13/2 crystal field levels of 0.005% Er3+:Y₂O₃ were measured by absorption and laser excited fluorescence on oriented samples. Site selective fluorescence distinguished transitions of Er3+ in crystallographic sites of C₂ and C_3i symmetry. The paramagnetic g-tensors for ions in sites of C₂ symmetry were measured by orientation dependent Zeeman absorption spectroscopy. For the lowest crystal field level of 4I_15/2 the g-tensor principal x-axis in the (100) plane is tipped +2.06° from [001] and principal g-values are: g_z = 11.93, g_x = 1.603, and g_y = 4.711. For the lowest crystal field level of 4I_13/2 the g-tensor principal x-axis in the (100) plane is tipped −11.7° from [001] and principal g-values are: g_z = 10.07, g_x, = 1.08, and g_y = 4.361. Two magnetic field orientations were identified for optimizing this material for optical coherent transient correlators: field along [111] and [110]. Fluorescence lifetimes of the lowest 4I _13/2 crystal field level were measured for ions in sites of C₂ and C_3i symmetry and they were 8.51 ms and 14.62 ms, respectively.