Contents I. Introduction
Polarization states of incident light after propagation through the optical fiber are randomized, and connecting such a fiber directly to in-line components may disrupt proper operation of integrated chip [1]. One approach to overcome this problem is to divide incoming light into two separate polarization modes and process them separately, which increases size and adds complexity to the system [2]. Another approach is to properly design in-line components to make them polarization-insensitive. Such polarization-insensitive operation will be especially useful for on-chip optical interconnect applications, where there is no easy way to control the polarization modes [3]. Optical modulator, workhorse of integrated circuits, modify properties of light such as phase, amplitude or polarization by electro-refraction, electro-optic or electro-absorption modulation schemes have been intensively investigated over several decades [4] –[6]. However, the conventional modulator is always polarization-sensitive, which results in very large polarization-sensitive loss [7] . The traditional optical modulators, which are designed based on Pockels effect of silicon material, the light-silicon interaction is relatively weak [8]. The available effective mode index (EMI) change in silicon material is only on the order of 10–4 for the best record [8]. Thus, the modulator may have difficulties to be integrated on-chip due to relatively larger footprint [8], [9]. The modulator being polarization-insensitive should be compact and exhibit low insertion loss [10]. Therefore, the optical materials and architecture of polarization-insensitive modulators (PIMs) that can deliver the necessary leap in performance matrices are still lacking.
