Theoretic And Experimental Research On Surface Plasma Wave Modulator

A new kind of modulator which is based on the theory of Surface Plasma Wave has been introduced in this thesis. Surface Plasmon oscillation is a phenomenon of physical optics, Evanescent Wave produced in the boundary of glass when Total Internal Reflection occur can be used to excitate the free charges at a metal surface to form Surface Plasma Wave which can propagate along a metal-vacuum interface. In the condition of proper incidence angle or wavelength, frequency and wavevector of Surface Plasma Wave are equal to Evanescent Wave, resonance occur. It is also be called Surface Plasmon Resonance. Here, incidence light is absorbed, energy of the reflection light decrease rapidly. Surface Plasma Wave light modulator just modulate with this theory. Surface Plasmon Resonance has two kind of modulation couple mode, one is prism-metal-vacuum Kretschmann configuration, the other is prism-vacuum-metal Otto configuration, experiment adopted Otto configuration. We can modulate by changing the incidence angle or air gap distance in Otto configuration, We make the numerical simulation In the situation of three kind of metal:Cu,Al,Ag and two wavelength value:1.064μm,0.532μm, result shows that reflectivity's variety can reach 0.8, modulation deepness can also reach 0.8. Experiment of Surface Plasma Wave modulator which is designed by ourselves proves that no matter we modulate Laser inside or outside the resonance cavity, effect is obvious. Modulation deepness can reach 0.8, the frequency of the best situation is 70k. A series of Laser pulse come into being when we modulate inside the cavity (Q-switch), current value of LD is 25A, modulation frequency is 70k, pulse width is about 100ns. All of the results are within the accepted error range and accord with the theory and numerical simulation. By the research on theory and experiment, it can be proved that modulation method basing on the theory of Surface Plasma Wave has excellent performance, if we continue to improve device and structure of the experiment, increase modulation deepness and expend frequency region, it can be applied in modulation of all kinds of continuous LASER and pulsed LASER.