Abstract
In this paper, the metal–insulator–metal (MIM) plasmonic directional coupler (PDC) with 45° waveguide bends based on surface plasmon polaritons (SPPs) excitation has been analyzed by the finite-difference time-domain (FDTD) numerical method. Effects of the variations of the coupler length and the metal gap thickness on the output powers and the propagation loss at 1550 nm wavelength have been studied. By choosing proper coupler lengths, power splitters with various output power ratios at 1550 nm wavelength and multi/demultiplexers, as some applications of the directional couplers have been proposed and their performances have been simulated.
1. Introduction
Miniaturizing the size, increasing the speed and improving the performance of the optical devices have attracted many researchers' attentions in recent years. However, due to the optical diffraction limit, there is a basic limit for minimization of the size of the conventional optical devices [1,2]. For this purpose, photonic crystals (PCs) are the key components for photonic integrated circuits (PICs), in which the lightwave guidance through sharp bends with very low loss is possible. These structures are periodic structures and need at least five periods to acquire photonic band gap. Therefore, the dimensions of the PC devices are in the order of light wavelength [1].
4. Conclusion
In this paper, plasmonic directional coupler with 45° waveguide bends have been analyzed and simulated by the FDTD method. Effects of the variation of the coupler length and the metal gap thickness on the performance of the directional coupler, at the wavelength of 1550 nm, have been studied. It has been shown that by increasing the gap thickness, the amount of power coupled to the cross port increases and it reaches to its maximum value for d= 11 nm. By further increasing the metal gap thickness, as it approaches to the skin depth of silver at 1550 nm wavelength, the coupling to the cross waveguide is diminished, the coupler operates as a single waveguide and the interaction of lightwave and metal and hence the loss of the structure decreases.
