Fig. 1. (a) Schematic of the proposed PRS. Top: three-dimensional view, middle: overhead view, and bottom: cross- section view. The dotted lines encircling the region are the overlap of the two different waveguides. (b) The effective refractive indices of the first three modes of the L-waveguide as the function of the higher waveguide width (W2) and the lower waveguide width (W3). The calculation wavelength is 1550 nm. Mode 1, mode 2, and mode 3 are represented by the solid, dashed, and dotted lines, respectively.

Fig. 2. (a) Mode indices and profiles evolution along the L-waveguide with W2=450 and W3=400  nm at the wavelength of 1550 nm. (b) Average transmission efficiency varied with the L-waveguide length over a wavelength range from 1500 to 1600 nm.

Fig. 3. Average transmission efficiency varied with the radius of the S-bend waveguide of the asymmetrical Y-junction over a wavelength range from 1500 to 1600 nm.

Fig. 4. (a)–(d) Simulated field intensity distributions at 1310 and 1550 nm wavelengths. (e)–(f) Different modes’ outputs efficiencies as a function of the wavelength in the two output ports. Transmission efficiency below −40  dB is not shown.

Fig. 5. (a) Schematic of the proposed PRS. Top: before shortening, bottom: after shortening. (b)–(e) Simulated field intensity distributions of the shortened PRS at 1310 and 1550 nm wavelengths. (f)–(h) Different modes’ output efficiencies as a function of the wavelength in the two output ports of the shortened PRS. Transmission efficiencies below −40  dB are not shown.

Fig. 6. Simulated the transmission efficiencies varied with (a) the higher waveguide width deviation, (b) the lower waveguide width deviation, (c) the alignment error, and (d) the etching depth deviation. The transmission efficiencies of 1310 nm wavelength are the dashed line, and that of the 1550 nm wavelength are the solid line. The above figures are the TE0 input situation, and the bottom figures are the TM0 input situation. The inset in figure (c) demonstrates the alignment error, and the dashed–dotted line is the center line of the lower waveguide. The inset in figure (d) demonstrates the etching depth deviation, and the dashed–dotted line is the upper surface of the lower waveguide. Transmission efficiencies below −30  dB are not shown.