Chapter 5
Recent Advances in Zero-Index
Photonics
In this chapter, we shall briefly describe a few important developments that have
taken place in the zero-index photonics during the past decade. These developments
are significant because they will show a path and become a foundation for zero-index
technologies for the future.
5.1 Moitra’s Design of Zero-Index Metamaterial
The first all-dielectric zero-index metamaterial proposed by Huang et al. was a 2D
photonic crystal made up of a square array of dielectric rods [27]. A two-dimensional
photonic crystal is infinite or practically very long in the third dimension compared
to other two. Erecting very long rods vertically on a substrate is extremely challenging with nanoscale fabrication techniques. So Moitra et al. suggested a more
plausible design [60] in which instead of erecting the rods vertically, they laid the
rods horizontally on the substrate (see Fig. 5.1). In this way, one could have rods of
any length without any difficulty, though there is a need for vertical spacer layers
between the rods. In their design, the rods were made of silicon, the spacer layer was
made of silica (SiO 2 ), and the whole device was embedded in polymethyl methacrylate (PMMA). Though Moitra’s design is significant from the fabrication point of
view, it lacks the compatibility to optical integration.
5.2 On-Chip Zero-Index Metamaterial
On-chip integration requires the structure to be periodic in the plane of the chip, and
the TM mode operation requires the cylinders to be infinitely long. The first condition
is achievable, but for the fulfillment of the second condition, Li et al. suggested an
indirect yet effective way [92]. They confined the structure between two parallel
metallic sheets, spread at the top and the bottom, as shown in Fig. 5.2a, so that the
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021
N. Shankhwar and R. K. Sinha, Zero Index Metamaterials,
https://doi.org/10.1007/978-981-16-0189-7_5
121
Recent Advances in Zero-Index
Photonics
In this chapter, we shall briefly describe a few important developments that have
taken place in the zero-index photonics during the past decade. These developments
are significant because they will show a path and become a foundation for zero-index
technologies for the future.
5.1 Moitra’s Design of Zero-Index Metamaterial
The first all-dielectric zero-index metamaterial proposed by Huang et al. was a 2D
photonic crystal made up of a square array of dielectric rods [27]. A two-dimensional
photonic crystal is infinite or practically very long in the third dimension compared
to other two. Erecting very long rods vertically on a substrate is extremely challenging with nanoscale fabrication techniques. So Moitra et al. suggested a more
plausible design [60] in which instead of erecting the rods vertically, they laid the
rods horizontally on the substrate (see Fig. 5.1). In this way, one could have rods of
any length without any difficulty, though there is a need for vertical spacer layers
between the rods. In their design, the rods were made of silicon, the spacer layer was
made of silica (SiO 2 ), and the whole device was embedded in polymethyl methacrylate (PMMA). Though Moitra’s design is significant from the fabrication point of
view, it lacks the compatibility to optical integration.
5.2 On-Chip Zero-Index Metamaterial
On-chip integration requires the structure to be periodic in the plane of the chip, and
the TM mode operation requires the cylinders to be infinitely long. The first condition
is achievable, but for the fulfillment of the second condition, Li et al. suggested an
indirect yet effective way [92]. They confined the structure between two parallel
metallic sheets, spread at the top and the bottom, as shown in Fig. 5.2a, so that the
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021
N. Shankhwar and R. K. Sinha, Zero Index Metamaterials,
https://doi.org/10.1007/978-981-16-0189-7_5
121