The optical nonlinearity of safranin O dye in methanol solution at different concentrations and as a solid film with polymethylmethacrylate (PMMA) has been studied using cw Nd-YAG laser at 532 nm as the source of excitation. The optical responses were characterized by measuring the intensity dependent refractive index (n 2 ) of the medium using the Z-scan technique. The open aperture Z-scan trace of the dye in solution and solid sample displayed saturable absorption. The closed aperture Z-scan trace of the dye exhibited a negative (defocusing) nonlinearity. The nonlinear refractive index was found to vary with concentration. Optical limiting characteristics of the dye at various concentrations in solution were studied. The nonlinearity appears to be of thermal origin.
The realization of power electronic applications on hardware is a challenging task. The digital control circuit strategies are used to overcome the analog control strategies by providing great flexibility with simple equipment and higher switching frequencies. In this manuscript, an area optimized, modified digital space vector (DSV) pulse width modulation is designed and realized on low-cost FPGA. The modified digital space vector pulse width modulation (DSVPWM) uses a phase-locked loop (PLL) to generate clocks using the digital clock manager (DCM). These DCM clocks are used in the DSVPWM module to synchronize the other sub-modules. The voltage generation unit generates the three-phase (3-Ф) voltages and is used in the alpha-beta generation and sector determination unit. The reference active vectors are made by the reference generation unit and used in switching time calculation. The PWM pulses are generated using switching time generation, and lastly, the dead time occurrence unit generates the final SVPWM gate pulses. The modified DSVPWM is synthesized and implemented on Spartan-3E FPGA. The modified DSVPWM utilizes 17% slices, works at 102.45 MHz, and consumes 0.070 W total power. The simulation results and the resource utilization of modified DSVPWM are represented in detail. The modified DSVPWM is compared with existing PWM approaches on different Spartan-series FPGAs with better chip area improvement
Problem statement: The third order nonlinear optical properties of organic polymers are used in high speed telecommunication, optical limiters and optical computers. The purpose of the study was to determine the third order nonlinear characteristics and optical limiting effect of the organic dye, metanil yellow in liquid and solid medium. Approach: The samples were prepared by dissolving the dye in acetonitrile (liquid medium) at different concentration and thin film was prepared by bulk polymerization method. The nonlinear optical responses of the samples were studied by using single-beam Z-scan technique. The optical limiting effects of the samples were studied by using a CW, Nd: YAG laser at 532 nm. Results: The open aperture Z-scan of the solution and solid samples displayed reversible saturable absorption. The closed aperture Z-scan of the samples exhibited negative nonlinearity, which was larger in magnitude in solid film compared to that in solution. The third order nonlinear susceptibility was found to be 2.00 and 2.34×10-6 (e.s.u) for the dye in solution and film at 0.05 mM concentration. The saturated output power for the dye in solution and film was found to be 1.2 and 0.8 mW respectively at 1.0 mM concentration. Conclusion: The dye doped in polymer can be utilized in optical limiting, low-power degenerate four wave mixing, data storage and grating applications
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