A butterfly MMI waveguides based polarization beam splitter etched on SOI platform

A polarization beam splitter is used for dividing transverse electric (TE) and transverse magnetic (TM) modes, in which a silicon on insulator platform based multimode interference coupler is etched depth by a butterfly form is proposed and designed by using the semi-vectorial three-dimensional beam-propagation method. The device is operated on quasi state mechanism that only four modes are excited in the multimode region. High birefringence property of the device incorporated with butterfly form allows to shortening the size. The polarization extinction ratio is smaller than 20 dB, and the excess loss is not excess 0.6 dB for both polarization modes. The splitter also has a relaxed fabrication tolerance. These attributes make it as a good candidate for polarization diversity circuits and compact photonic integrated circuits.