1 3 12 even fanout using multimode interference optical beam

Introduction: Efficient optical beam splitters are a key component in photonic integrated circuits (PICs). Multimode interference (MMI) couplers have the advantages of compact size, low loss, stable splitting ratio, large optical bandwidth, and good fabrication tolerances [1, 2]. One of the major applications of MMI couplers is power splitters. To date, high performance in output uniformity is difficult to achieve for MMIs with a large number of output ports N owing to the modal phase errors, which have been shown to scale with N [3]. Acoleyen et al. have shown a 16 port optical phased array but this is achieved by cascading 1 × 2 MMI couplers, thereby creating multiple stages of MMIs [4]. The majority of MMI couplers based on silicon-on-insulator (SOI) have used a ridge waveguide structure. Until recently, few devices employing a strip waveguide structure for the input and output have been presented. Using strip waveguides, submicron cross-sectional areas of the waveguide core are possible while still maintaining singlemode operation at 1550 nm wavelength owing to the large refractive index contrast between silicon (nSi 1⁄4 3.5) and silicon dioxide (nSiO2 1⁄4 1.45) which provides excellent light confinement. In addition, the strong lateral confinement of strip waveguides allows the bending radius to be shrunk down to the micron range [5], whereas the slab region of ridge waveguides does not provide such confinement and thus requires large bending radius to achieve low loss propagation. Ultimately, the overall device size is increased by using ridge waveguides and this limits their use in ultracompact photonic integrated circuits, such as on-chip optical interconnects. In this Letter, we demonstrate a single stage optical beam splitter with a large number of outputs that avoids multiple insertion loss by using a 1 × 12 MMI on SOI with a rib waveguide structure, which shows the smallest device size for a 1 × 12 waveguide beam splitter at a wavelength of 1550 nm.