Orthogonal Pump Research Articles

Perturbative analysis of self-oscillation in degenerate four-wave mixing

Self-oscillation of two counterpropagating waves in four-wave mixing under orthogonal pump configuration is analyzed perturbatively, taking into account the pump depletion and the refractive-index variation. A number of threshold pump intensities corresponding to different oscillating field distributions are obtained. Certain values of pump intensity permit multiple solutions for the oscillating field distribution and the corresponding output power of the oscillating waves, indicating a possibility of multistability.

Stimulated Raman amplification characteristics in long span single-mode silica fibers

Spectral Raman amplification characteristics have been measured directly for a tunable pumping source, taking the relative polarization states of pump and signal waves into consideration. Raman amplification has been observed, even with an orthogonal polarization pump, in a long span single mode fiber. Raman amplification causes significant crosstalk in wave-length-multiplexed systems.

Grain-Size Average and Distribution Effects on the Magnetic Losses and Threshold Fields in Nickel Ferrites at Microwave Frequencies

Nickel ferrites with scaled average grain sizes and lognormal size distributions were prepared by hot-pressing and subsequent annealing and by conventional firing. Average grain sizes ranged from less than 1 to 10 μ. The dielectric loss, saturation magnetization, bulk density, and linewidth measurements confirmed that almost all samples were good nickel ferrites. Lognormal distributions allow with easy calculations to evaluate for each sample the fraction of grains having diameters below certain values that are critical for the loss mechanism. Orthogonal and parallel pump measurements of threshold fields at X band showed a very regular behavior with average grain sizes: ∥ hcrit varied from 80 Oe for 0.9-μ sample to 8 Oe for a 10-μ sample with a dependence of the type hcrit≈x̄−2 for x̄<2 μ, hcrit≈x̄−0.5 for x̄>2 μ. An analysis of the distribution of grains shows that ∥ hcrit increases steeply for samples having about 80% or more of the number of grains with sizes less than 3 μ. Regular behaviors of the imaginary part of the permeability (at Hdc≈4πMs/3) with average sizes are found at 9.23, 12.12, and 19.75 GHz: losses increase with decreasing grain sizes but not as much as threshold fields, with a dependence of the type μ″min≈x̄−0.5. The high-power figure of merit F*, measured on spheres at X band, increases with decreasing grain size from 0.07 to 0.26, thus encouraging the fine grain approach for microwave device applications.

Ferrimagnetic Resonance with Orthogonal and Parallel Pumping

An rf magnetic field of sufficient amplitude gives rise to a nonlinear absorption caused by the unstable growth of certain spin waves. We have calculated the threshold for the case in which an rf field of frequency ω0 is applied orthogonally to the dc field and another rf field at frequency 2ω0 is simultaneously applied parallel to the dc field. We find that under these conditions the wave number of the spin waves with the lowest instability threshold varies discontinuously with the ratio of the two rf magnetic fields. If the orthogonal rf field is relatively small, the unstable spin waves have wavelength comparable with the sample dimensions. In this region the critical parallel field decreases linearly with the square of the orthogonal field.