  Due to that the polarization states in optical fibers change randomly during
transmission, polarization-independent (PID) devices are demanded to receive
lights with arbitrary polarization states. Compared with their orthogonal
polarization states, the optical profiles of various modes of the same
polarization are similar, and their directions of the main electric field are
same. Therefore, it's much easier to design PID devices using multi-modes of
one polarization state instead of orthogonal polarizations. This paper firstly
presents a scalable method to achieve PID devices and systems by transforming
the light orthogonal polarization states into one polarization with different
modes. Taking thermo-optical switches as an example, the PDL of the fabricated
2 x 2 switch cell was about 0.8 dB at 1300-1360 nm, and its extinction ratio
(ER) was larger than 19 dB for both polarizations. A 4 x 4 switch was also
demonstrated and its function of dual polarization switching was implemented,
whose ER was larger than 11 dB for both polarizations. This method has
potential in constructing PID on-chip systems for optical communications,
optical interconnections, etc.
