Polarization independent microphotonic circuits

Abstract

Microphotonic circuits have been proposed for applications ranging from optical switching and routing to optical logic circuits. However many applications require microphotonic circuits to be polarization independent, a requirement that is difficult to achieve with the high index contrast waveguides needed to form microphotonic devices. Chief among these microphotonic circuits is the optical add/drop multiplexer which requires polarization independence to mate to the standard single-mode fiber forming today's optical networks. Herein, we present the results of an effort to circumvent the polarization dependence of a microphotonic add/drop multiplexer with an integrated polarization diversity scheme. Rather than attempt to overcome the polarization dependence of the microphotonic devices in the circuit directly, the arbitrary polarization emanating from the fiber is split into orthogonal components, one of which is rotated to enable a single on-chip polarization. The outputs are passed through identical sets of devices and recombined at the output through the reverse process.

(cont.) While at the time of this publication the full polarization diversity scheme has yet to be implemented, the sub-components have demonstrated best-in-class performance, leaving integration as the remaining task. We present the results of a significant effort to design integrated polarization rotators, splitters, and splitter-rotators needed to implement the integrated polarization diversity scheme. Rigorous electromagnetic simulations were used to design these devices along with the microring-resonator based filters used to form the optical add/drop multiplexer microphotonic circuit. These device designs were passed onto fabrication, and the fabricated devices were characterized and the results compared to theoretical predictions. The integrated polarization rotators and splitters demonstrated broadband, low loss, and low cross-talk performance while the integrated polarization splitter-rotators demonstrated equally impressive performance and represent the first demonstrations of a device of this kind. Similarly impressive performance was exhibited by the microring-resonator filters which achieved the deepest through port extinction and largest free-spectral-range of a functioning high order microring-resonator filter.