New approach to polarization-independent integrated optical circuits: the bimodal polarization converter

Integrated optical circuits have to operate in a fiber network that does not preserve the polarization state. Therefore operations in the network should be polarization independent. In order to support both polarizations compromises are often made in design and realization. Such compromises can be avoided when incoming light of arbitrary polarization is converted into two identically polarized modes of different mode order. This is done with a passive bimodal polarization converter (BPC), which can be integrated in the circuit. The BPC is especially useful in combination with components that process both modes simultaneously (detectors, phased-array demultiplexers, multimode interference couplers, etc.) and for use with monomodal circuits mode splitters, e.g. asymmetrical Y-junctions, that enable separate processing of the modes. Design and simulations of the converter are performed for an InP/InGaAsP/InP heterostructure with a quaternary layer band gap of 1.3 μm. Coupled-mode expressions show that with 13 sections complete conversion is obtained with low loss (0.3 dB)