Fig. 1. Schematics of DMEC coupling with dual-mode fiber in (a) 3D view and (b) top view; the silicon waveguides are in red, and the silicon oxide layer is in gray. The modes conversion process is also demonstrated. (c) Effective refractive index of the modes in each waveguide (WG0/WG1) of the mode-evolution counter-taper with tapering width from 1 µm/0.25 µm to 0.77 µm/0.48 µm.

Fig. 2. (a) Mode conversion loss for the input TE₀, TM₀, TE₁, and TM₁ modes, respectively, (b) transmission loss for the TE₀ and TM₀ modes in inverse taper (L₂), and (c) wavelength dependence of the transmission from ‘x₀’–‘x₁’.

Fig. 3. Cross-sectional schematics of the edge coupling area: (a) x–y direction; (b) y–z direction.

Fig. 4. (a) Simulated overlap integral of mode field between the FMF and SiO₂ cladding, (b) simulated coupling loss for different Wg, (c) spatial mode coupling (from ‘x₁’–‘x₂’), and (d) the lateral alignment tolerance of coupling efficiency (CE) for spatial mode coupling.

Fig. 5. (a) Total CE and (b) crosstalk of the FMEC in the span of 200 nm.

Fig. 6. Simulated electrical field mode profiles of (a) TE₀, (b) TM₀, (c) TE₁, and (d) TM₁ modes at position ‘x₀’ in Fig. 1(b); transmission profiles of the input (e) TE₀, (f) TM₀, (g) TE₁, and (h) TM₁ modes; mode profiles of the (i) TE₀, (j) TM₀, (k) TE₁, and (l) TM₁ modes in the SiO₂ waveguide; mode profiles of (m) LP_01,x, (n) LP_01,y, (o) LP_11a,x, and (p) LP_11a,y modes supported in FMF.

Fig. 7. Fabrication tolerance to deviation (a) of the waveguide width and thickness for TE₁ input mode, (b) of the waveguide width and thickness for TM₁ input mode, (c) of the tip width.

Table 1. Comparison of the Reported Multimode Edge Coupler and Coupler Proposed in This Work