Polarisation control

Abstract

A polarisation control device 10 having connected in sequence: an input waveguide 20, a first polarisation converter 100 having a first control element 132, a connecting waveguide 50, and a second polarisation converter 200 having a second control element 232. Each respective converter having separate cross-sectional structures perpendicular to a light propagation axis which determines the polarisation of respective modes (408 and 410, Fig. 4a and 4b). Each mode having a separate polarisation orientations. The first polarisation converter supports first and second modes; the second polarisation converter supports third and fourth modes. The first mode has a greater refractive index to the second mode; the third mode has a greater refractive index to the fourth mode. The first and second control elements are first and second electrical contact layers which, upon receiving first or second signals, modify the refractive indices of first and second modes, or third and fourth modes, respectively. The polarisation control device may be for a photonic integrated circuit 1001. Each converter cross-section may have separate widths. The connecting waveguide may be tapered. The control device may comprise a third polarisation converter 300 supporting fifth and sixth modes and comprise a third control element. [figure 14]