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.
Highlights
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;[1,2,3,4,5,6] it is a revolutionary change in principle and quite different from the other strategies, such as fluorescence microscopy[7,8,9,10] and structured light microscopy.[11,12,13]
We propose a cascaded straight and curved 1-D silicon waveguide array to access subwavelength self-imaging, where the curved waveguides array works as a negative index material with a well-engineered negative dispersion,[32] while the straight part acts as normal positive index material
Summary
Manipulating the optical field at the subwavelength scale is vital both in current imaging technology and on-chip photonic integrations. Photonic waveguide arrays are widely used for the flexible control of light.[20,21,22,23,24,25,26,27,28,29,30,31,32,33] Negative refraction, deep-subwavelength focusing, and reconstruction of initial state have been demonstrated.[21,22,23,24,25,26,27,28,29] a waveguide array bears similarities with metamaterials as its lattice is much smaller than the wavelength in the effective medium regime. The multilayer nanofilms or the arrayed-nanorod metamaterials [Fig. 1(b)] can be treated as planar [one-dimensional (1-D)] or cylindrical [two-dimensional (2-D)] waveguides arrays. Structures can be greatly simplified while many of their unusual properties and functionalities can be preserved, for example, imaging beyond the diffraction limit
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