We analyzed the light spectrum after passing through the encoding template element. Comparing the influence of the ideal coding template elements and coding template elements with rounded errors on the far-field spectrum. The far-field spectrum has a red offset. With the changing of the aperture error value r, the deviation of the far-field spectrum relative to the light source spectrum is slightly different, and the closer the aperture is to the circle, the smaller the deviation of the spectrum, that is, the closer the light source spectrum. Five different constituent units from the two-dimensional random coding template is found, and these five constituent units are randomly distributed. The far-field spectral distribution when the beam passes through two units at the same time is numerically calculated, and the analysis shows that the spectral deviation after passing through different types of coding units are obviously different. The analysis result will provide prior information for the target recovery of compressed-sampling hyperspectral imaging, and make the target recovery more accurate.
By using the finite difference method, the nonlinear effects of high repetition rate femtosecond pulse trains in silicon nanowire waveguides were analyzed. By numerically modeling the propagation of femtosecond pulse in silicon nanowire waveguides with the generalized nonlinear Schrödinger equation, the temporal and spectral properties of femtosecond pulses propagating are discussed, and the physical mechanisms of pulse evolution are demonstrated. The simulation results indicate that, owing to the remarkable nonlinear effect, the carriers in the silicon waveguide are rapidly excited with the increase of the input laser power, subsequently have significant modulation effects on the high repetition rate pulses train. For various repetition rate and power of the laser pulses train, the output pulsestrain will get different temporal compression and broadening under the dominance of different nonlinear effects. Furthermore, the results demonstrate that the spectrum evolution of pulse train with different transmission distances is similar to the calculated results of single pulse transmission. The results will provide an important reference for the design of optical sampling clock, microwave photonic radar system and the sweep of carriers in waveguide.
As a fundamental components for the integrated microwave photonic links, the nonlinear loss of the Silicon waveguides will significantly affect the links’ performance. We study the effects of the effective mode area (Aeff), two-photon absorption (TPA), free-carriers absorption (FCA), and linear propagation loss on the insertion loss in silicon waveguides. According to our simulations, the results show that it should be an efficient way to reduce the insertion loss of the silicon by combining the large mode area, small linear propagation loss and carriers sweep out techniques. And, we can also know that when the nonlinear loss will dominate with the coupled power becoming larger. Thus, the results can provide guidances on the gain, loss, and linear dynamic range of analog photonics links based on silicon waveguide.
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