Analysis of coupling length for symmetrical SOI rib waveguide

In this paper, the optical directional coupler based on symmetrical silicon-on-insulator (SOI) rib waveguide is successfully simulated and analysed using Beam Propagation Method with the communication wavelength of 1.55 m. The geometry structure is 6 μm rib height (H) while rib width (W), slab height (h) and rib depth (d) are varied accordingly. The ratio of slab height to rib height (r) is fixed to 0.5, 0.6, 0.7 and 0.8. In general, the coupling length (Lc) between two symmetrical rib waveguide increases with the increment of waveguide spacing (S). However, the rib based coupler with r = 0.7 and 0.8 at the waveguide spacing above 4.5 μm are most recommended due to the normalized output power is almost 100 per cent.