Fig. 1. (a) Schematic of the polarization rotator-splitter (PRS). In each taper section, the top widths of Branch 1 (Branch 2) are labeled in red (orange); lengths are labeled in yellow. (b) Optical eigenmode profiles (electric field intensity, viewed from the receiving end) at different locations along the PRS. Top (Mode 1) and bottom (Mode 2) profiles correspond to mode evolutions for TE0 input and TM0 input, respectively. (c), (d) Effective index (neff) evolution for the three lowest-order modes along the PRS in (c) Step I and (d) Step II, respectively, at the wavelength of 1550 nm. Inset of (c): optical intensity profile of the supermode at the avoided crossing between TM0 and TE1 modes in Step I.

Fig. 2. (a), (b) Simulated electric field intensity evolution along the PRS for (a) TE0 input and (b) TM0 input at 1550 nm wavelength. Waveguide structure profiles are shown as white dashed lines. The y and z axes are not shown in the same scale for better viewing. (c), (d) Simulated electric field distributions (Ez) at the output facets of the Step II splitter for (c) TE0 input and (d) TM0 input.

Fig. 3. Scanning electron microscope (SEM) images of (a) the polarization splitter (Step II) and the output bends, and the zoom-in views of (b) the adiabatic coupler and (c) the output straight waveguide.

Fig. 4. (a) Experimental setup for output mode characterization. The free-space fiber-bench polarization controller (FFBPC) consists of a quarter-wave plate (QWP), a linear polarizer (LP), and a second QWP. (b) Infrared camera images of the mode profiles at the device output facet in cases of various input polarization states. The top row (i, ii, and iii) shows the output from a device with Step I only (objective lens NA=0.45), while the bottom row (iv, v, and vi) shows the output from a full device with Step I+Step II (objective lens NA=0.30).

Fig. 5. Measured optical transmission spectra at the PRS output (a) Port 1 and (b) Port 2 in the wavelength range of 1500–1630 nm. Black and red curves correspond to TE0 and TM0 input polarizations, respectively.

Fig. 6. Simulated mode hybridization points as functions of wavelength in (a) Step I rotator and (b) Step II splitter. The shaded area indicates the actual tapering regions in our device.