Abstract
Abstract Manipulating on-chip optical modes via components in analogy with free-space devices provides intuitional light control, and this concept has been adopted to implement single-lens–assisted spot size conversion using integrated device. However, the reported schemes have been demonstrated only for fundamental mode, while high-order or irregular modes are preferred in specific applications. The 4-f system is widely used in Fourier optics for optical information processing. Under the inspiration of the 4-f system and the beam expander in bulk optics, a spot size converter (SSC) with two metamaterial-based graded-index waveguides is proposed and demonstrated. The proposed device is capable of widening an arbitrary mode while preserving its profile shape. Compared with conventional SSC using adiabatic taper, the footprint can be reduced by 91.5% under a same intermode crosstalk. Experimentally, an expansion ratio of five is demonstrated for regular modes. Furthermore, for an irregular mode, the functionality is numerically verified without structure modification. This work offers a universal solution to on-chip spot size conversion and may broaden the on-chip application prospects of Fourier optics.
Highlights
On-chip photonic devices exhibit tremendous potentials in many applications, including communication, microwave photonic signal processing, quantum information, sensing and computing [1,2,3,4,5,6]
The optical information processing capability for these systems has been proved to be remarkable for computational applications, it can inspire other unique functionalities demanded on a chip
In this work, inspired by the 4-f system and the beam expander in bulk optics, we propose and demonstrate an on-chip arbitrary-mode spot size converter (SSC) (AM-SSC) using the silicon-oninsulator (SOI) platform
Summary
On-chip photonic devices exhibit tremendous potentials in many applications, including communication, microwave photonic signal processing, quantum information, sensing and computing [1,2,3,4,5,6]. In high-order mode cases, the shape of this spectrum is normally different from that of the incident mode, resulting in the shape distortion In this work, inspired by the 4-f system and the beam expander in bulk optics, we propose and demonstrate an on-chip arbitrary-mode SSC (AM-SSC) using the silicon-oninsulator (SOI) platform. From the viewpoint of wave optics, if a mode propagates along the GRINWG for a distance of fGRINWG, the FT is performed on it [20]. In this scenario, the AM-SSC can be analyzed using FT (see Supplementary Material). For an input mode profile Ei(y), the output at the end of the GRINWG2 can be expressed as
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