Design of a compact silicon-based slot-waveguide crossing composed of an orthogonal strip multimode waveguide and four logarithmical mode converters

A compact silicon-based slot-waveguide crossing composed of a slot-to-strip mode converter (at each port) and an orthogonal strip multimode waveguide (SMW) is proposed and designed using a finite difference time domain method. With the mode converter based on logarithmically transitional tapers, the guided modes of the input slot waveguide are efficiently transformed to those of a strip one, and then enter into the SMW, where the fields converge at the centre of the intersection due to the self-imaging effect. As a result, the size of the input beam is much smaller than the width of the SMW at the crossing centre, leading to significant reductions in the crosstalk and radiation loss. The numerical results show that a slot-waveguide crossing operating at a wavelength of 1.55 µm with insertion loss, crosstalk and reflection of 0.131 dB, −37.44 dB and −35.47 dB, respectively, is achieved. Moreover, the fabrication tolerances to the structural parameters are investigated in detail. And the evolution of the injected field along the propagation distance through the slot-waveguide crossing is also demonstrated. (Some figures may appear in colour only in the online journal)