Polarization Splitter-Rotator (PSR)

The Polarization Splitter-Rotator (PSR) is a photonic integrated device composed of an adiabatic taper, an asymmetric directional coupler (ADC), and a multimode interference (MMI) mode filter. The adiabatic taper enables effective mode conversion from the launched TM0 mode in a wide waveguide to the TE1 mode. It is then coupled to the TE0 mode of a narrow waveguide via the ADC. Meanwhile, the launched TE0 mode undergoes no direct mode conversion and is transmitted through the port. The MMI mode filter cascades at the through port to filter out residual power from the TE1 mode, significantly improving the PSR extinction ratio.

When polarized light passes through the adiabatic tapered waveguide, the wide waveguide converts the launched TM0 mode to an effective TE1 mode. The TE1 mode is then coupled to the narrow waveguide’s TE0 mode via the ADC. Meanwhile, the launched TE0 mode undergoes no direct mode conversion and is transmitted through the port. The MMI mode filter cascades at the through port, filtering out residual TE1 mode power and improving the PSR extinction ratio.

The PSR design starts with a straight input port of width $W_{\text{in}}=1\mu \text{m}W\_\{\backslash text\{in\}\}\; =\; 1\; \backslash \; \backslash mu\backslash text\{m\}$, followed by an adiabatic taper waveguide of length $48\mu \text{m}48\; \backslash \; \backslash mu\backslash text\{m\}$ (composed of multiple taper segments). It then connects to an ADC of length $L_{\text{dc}}=8.9\mu \text{m}L\_\{\backslash text\{dc\}\}\; =\; 8.9\; \backslash \; \backslash mu\backslash text\{m\}$, with widths $W_3=0.75\mu \text{m}W\_3\; =\; 0.75\; \backslash \; \backslash mu\backslash text\{m\}$ and $W_4=0.367\mu \text{m}W\_4\; =\; 0.367\; \backslash \; \backslash mu\backslash text\{m\}$. This is followed by an MMI filter structure with length $L_{\text{MMI}}=5.2\mu \text{m}L\_\{\backslash text\{MMI\}\}\; =\; 5.2\; \backslash \; \backslash mu\backslash text\{m\}$ and width $W_{\text{MMI}}=1.8\mu \text{m}W\_\{\backslash text\{MMI\}\}\; =\; 1.8\; \backslash \; \backslash mu\backslash text\{m\}$. The output port of the straight section has a width $W_2=0.7\mu \text{m}W\_2\; =\; 0.7\; \backslash \; \backslash mu\backslash text\{m\}$. The gap between the bent and straight ADC sections is $W_{\text{gap}}=0.12\mu \text{m}W\_\{\backslash text\{gap\}\}\; =\; 0.12\; \backslash \; \backslash mu\backslash text\{m\}$, with the bent section's output port width $W_4=0.367\mu \text{m}W\_4\; =\; 0.367\; \backslash \; \backslash mu\backslash text\{m\}$. The PSR structure is placed on a silicon substrate $3.5\mu \text{m}3.5\; \backslash \; \backslash mu\backslash text\{m\}$ thick (top surface at $Z=0\mu \text{m}Z\; =\; 0\; \backslash \; \backslash mu\backslash text\{m\}$).

The device structure used in this simulation is based on [1]. The total PSR length is $70\mu \text{m}70\; \backslash \; \backslash mu\backslash text\{m\}$, and the fabricated PSR achieves an extinction ratio of $20\text{ dB}20\; \backslash \; \backslash text\{dB\}$ over a broadband range of $15471547$–$1597\text{ nm}1597\; \backslash \; \backslash text\{nm\}$.

In this simulation, monitors were placed at all PSR ports to observe $SS$ parameters and transmission spectra under different mode excitations.