Non-Conventional Modulation Schemes

This chapter presents several non-conventional silicon-based integrated circuits realizing optical modulators as well as other functionalities such as logic gates. Although the presented concepts are in the state of pure research and yet far from being industrially implemented, they show the potential as well as a different point of view of how to allocate existing resources for achieving the desired goal. It presents a nano-scale miniaturized waveguide Mach–Zehnder interferometer (MZI) realized on a silicon chip. By illuminating the MZI structure with visible light, one varies the silicon (Si) refraction index and consequently the Si absorption coefficient for an infra-red (IR) information beam passing through it. The visible light illumination is the control command that turns the modulator to its ON and OFF states. In our case, the structure is illuminated in a spatially non-uniform way, therefore breaking the symmetry or the balance between the two arms of the interferometer. The advantage of this approach is that it results in a high contrast, since when the arms are balanced, no output is obtained, whereas even the slightest imbalance will produce an output signal. Therefore, a very small-scale device can produce the desired outcome. This approach differs from the one in which external visible illumination is applied directly on the optical waveguide that guides the IR beam, where one needs a long interaction length to obtain a high contrast, because there is no balancing mechanism.