Polarization control enabled by on-chip three-dimensional rotator

Precise polarization control is fundamental for applications such as optical communication and quantum information processing. Femtosecond-laser written photonic integrated circuits (PICs) offer the ability to both maintain and manipulate the state of polarization (SOP) on-chip, making them a promising platform for integrated and flexible polarization control. However, current polarization control devices are either inefficient in rotating polarization or limited to adjusting the birefringence and optical axis orientation of the waveguides. In this study, we introduce and demonstrate a new type of three-dimensional polarization rotator, built from composite waveguides with varied optical axis orientations. By varying the rotation length and angle of the rotators, we efficiently rotate the horizontal and vertical polarization states between 5° and 180°, achieving output SOPs with a linear polarization degree exceeding 99.5 %. Moreover, when other linear polarization states were introduced, the rotators not only preserved the rotation angle but also enabled additional control over the ellipticity of the output SOPs, ranging from -6° to 7° These novel waveguide rotators allow for both efficient polarization rotation and ellipticity control, marking a major advancement in on-chip polarization management and paving the way for full polarization utilization.