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As the demand for cheaper and faster computing continues to increase, the semiconductor industry has relied on transistor scaling to meet this demand. With transistor size approaching the atomic limit, there needs to be a fundamental change from the traditional improvement methods employed in the past. Improvement of data transfer between the microprocessor and other peripheral units could provide an immediate boost to computing in general. The bus lines connecting the CPU to other components are made up of metal interconnects. The speed of metal interconnects are highly limited due to parasitic effects. Switching to optical interconnects will eliminate most of the parasitic effects experienced with metal interconnects and will provide an immediate improvement in computing speed. Implementation of optical interconnect system will require nanoscale photodetectors and modulators. At 20nm scale and using a CMOS compatible process, Ge nanowire photodetectors could be integrated at the transistor level for interconnect applications. We have demonstrated a single 20nm diameter Ge nanowire photodetector with current gain of more than 〖10〗^3 and responsivity of 25A/W operating at 1.55um wavelength. Our device is based on the formation of an abrupt heterojunction between Ge nanowire and Si substrate. The device photocurrent is highly scalable based on the number of active nanowires connected in a parallel formation. We have also demonstrated a multilevel modulating device based on the integration of two memristors on a photonic crystal waveguide. Our device enabled the modulation of an optical channel by multiple electrical signals with distinct optical output for every combination of the modulating input signals. The device operation is based on the creation of optical extinction centers within the waveguide through the injection of silver clusters. By using a photonic crystal waveguide instead of traditional waveguide structure to build the device, we exploited the local resonances within the photonic crystal waveguide to tune the waveguide response and optical output characteristics of the device. The demonstrated device operates at the telecommunication wavelength of 1.55um and it is fabricated using CMOS compatible process.