Towards 3D plasmonic circuits: Controlled coupling to multilevel plasmonic circuits

We propose a surface plasmon multilevel coupler based on the orthogonal junction coupling technique between silicon nanowires and plasmonic slot waveguides (PSWs). It couples light of different polarizations from a silicon nanowire into multilevel plasmonic networks. Two orthogonal PSWs are employed to guide each polarization to its respective port. The proposed structure splits the polarizations and allows for simultaneous processing at different horizontal layers. Our device overcomes inherent polarization limitation in plasmonic structures by providing multilevel optical signal processing. This ability of controlling polarization can be exploited to achieve 3-D multilevel plasmonic circuits and polarization controlled chip to chip channel. Our device is of a compact size and a wideband operation. The device utilizes both quasi-TE and quasi-TM polarizations to allow for increased optical processing capability. The crosstalk is minimal between the two polarizations propagating in two different levels. We achieve -4.5 dB transmission efficiency at a wavelength of 1.55 μm for the different polarizations in the respective ports. A transmission efficiency of -21 dB is achieved in the subsidiary port. We analyze and simulate the structure using the FDTD method. The proposed device can be utilized in integrated chips for optical signal processing and optical computations.