Silicon photonics 2  ×  2 trench coupler design and foundry fabrication

A 2×2 photonic coupler is realized at the intersection of two 480nm×220nm silicon on insulator waveguides. The designed 2×2 coupler is simulated in both High Frequency Simulator System (HFSS) and Lumerical and shows an equal split of an input signal into transmitted and reflected signals for a 45 deg, ∼100nmSiO₂ filled trench. The principle of operation of the coupler is frustrated total internal reflection. Thus, this behavior is reasonably flat across wavelength, which is confirmed by Lumerical simulations and by experiment. Also, it has been shown that this coupler has a flat behavior across trench thickness for the chosen geometry and material system, which makes it insensitive to fabrication variation and resolution. We are interested to make this coupler a part of silicon photonic foundry process development kits. Therefore, fabrication is done at the AIM Photonics Foundry to study the performance in the context of the foundry's design rules and process flow of the foundry. Good agreement between theory and experiment is reported herein. A 2×2 trench coupler is, when operated in the single photon or quantum regime, an integrated photonic realization of a Hadamard gate.