Abstract

Si photonics have attracted great attention due to their high-dense integrability of optical components, and even, a network on chip can be composed. One of the key component is a polarization converter (PC), which can rotate the state of polarization 90 degree. A PC based on Si taper waveguide [1] is structurally simple and compact, however, its loss is relatively large (over 1.0 dB). In this paper, a PC based on Si modulated taper waveguide is proposed to improve the performance further. The waveguide width geometry is designed by newly developed full-vector wavefront matching (WFM) method [2, 3]. WFM is a kind of optimization algorithm based on beam propagation method (BPM) and has been widely used for planar photonic components, such as Y-branch and multimode interference waveguides. However, its application was limited to only scalar analysis (only one electromagnetic field is considered), and full-vector version is necessary to treat polarization conversion, in which all of the electromagnetic fields are involved. Here, we developed WFM based on full-vector BPM. In WFM, beam propagation from input port to output port (forward propagating field) and from output port to input port (backward propagating field) are calculated by BPM and a coupling coefficient, η, between forward and backward fields are evaluated as $\eta ={\left|{\int }_s\left(E_{in}\left(z\right)\times H_{out}^{*}\left(z\right)\right)\cdot i_{z}dS\right|}^2$, where i_z is the unit vector along the propagation direction, E_in(z) represents the input electric field vector that propagates to z, H_out(z) represents the ideal output magnetic field vector that propagates to z, and superscript * represents the complex conjugate. Evaluating the magnitude of η, the width of the waveguide is changed according to wavefront matching theory [2, 3].

© 2015 IEEE