• Advanced Photonics
  • Vol. 2, Issue 3, 036001 (2020)
Wange Song1、2, Hanmeng Li1、2, Shenglun Gao1、2, Chen Chen1、2, Shining Zhu1、2, and Tao Li1、2、*
Author Affiliations
  • 1Nanjing University, College of Engineering and Applied Sciences, National Laboratory of Solid State Microstructures, Key Laboratory of Intelligent Optical Sensing and Integration, Jiangsu Key Laboratory of Artificial Functional Materials, Nanjing, China
  • 2Collaborative Innovation Center of Advanced Microstructures, Nanjing, China
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    Abstract

    Self-imaging is an important function for signal transport, distribution, and processing in integrated optics, which is usually implemented by multimode interference or diffractive imaging process. However, these processes suffer from the resolution limit due to classical wave propagation dynamics. We propose and demonstrate subwavelength optical imaging in one-dimensional silicon waveguide arrays, which is implemented by cascading straight and curved waveguides in sequence. The coupling coefficient between the curved waveguides is tuned to be negative to reach a negative dispersion, which is an analog to a hyperbolic metamaterial with a negative refractive index. Therefore, it endows the waveguide array with a superlens function as it is connected with a traditional straight waveguide array with positive dispersion. With a judiciously engineered cascading silicon waveguide array, we successfully show the subwavelength self-imaging process of each input port of the waveguide array as the single point source. Our approach provides a strategy for dealing with optical signals at the subwavelength scale and indicates functional designs in high-density waveguide integrations.

    1 Introduction

    Precisely manipulating the optical field at the subwavelength scale is vital both in current imaging technology and on-chip photonic integrations. In pursuing super-resolution imaging, a striking design of a superlens based on negative index metamaterials (NIM) has been proposed;16 it is a revolutionary change in principle and quite different from the other strategies, such as fluorescence microscopy710 and structured light microscopy.1113 To circumvent the extreme difficulties in achieving the initially proposed NIM with negative permeability and permittivity, hyperbolic metamaterials were proposed in which multilayered metal–dielectric structures and metallic nanowires arrays were designed for two kinds of hyperbolic dispersions.1419 Unfortunately, these designs for superlens imaging remain unsatisfactory due to insurmountable manufacturing challenges and huge losses from impedance mismatch at the interface between these NIMs and a positive background. Therefore, demonstrations of a superlens in the optical regime were rarely reported.6,1719