Nonlinear polarization switching and logic operation with rocking filter fibers.

Abstract

This dissertation investigates experimentally as well as theoretically several all-optical switching configurations in a rocking filter fiber. It is shown experimentally that the rocking filter can be used as an intensity dependent polarization switch at the resonant wavelength. Up to 70% of the input power consisting of 30 ps pulses could be switched between the orthogonal polarization axes of a 2 long fiber. Stimulated Raman scattering and pulse break-up led to the saturation of the self-switching response. Off-resonant self-switching was shown to yield an enhanced response at shorter wavelengths with lower critical powers than for the resonant case. At longer wavelengths switching was initially inhibited but could still be implemented at powers significantly larger than for shorter wavelengths. This result implies that switching is noreciprocal which is a useful and necessary condition for operating a device as a logic gate. Controlling an intense signal pulse by a weak control pulse through a variable phase delay was successfully demonstrated. In excess of 55% of the input energy could be switched by controlling the phase difference between the two pulses. The phase-sensitive response suffered just as for the self-switching response from Raman scattering and pulse break-up. When combining the nonreciprocity due to wavelength detuning with the phase-sensitive response, logic operation with rocking filters can be implemented. By choosing the proper operating conditions of the device. e.g. input power, phase delay, and wavelength detuning, it is shown that XOR, OR, and AND gates can be realized. The contrast between a logic 0 and 1 state was shown to be as low as 0.3 and 0.7, respectively. Strong pump controlled switching of a weak signal beam produced the best switching characteristics of this dissertation. Up to 90% of the signal pulse could be switched between polarization states. This result was accomplished by using a pump pulse at a different wavelength which had a pulsewidth three times as large than that of the signal pulse.