TDFA-band (2-μm waveband) has been considered as a promising optical window for the next generation of optical communication and computing. Absorption modulation, one of the fundamental reconfigurable manipulations, is essential for large-scale photonic integrated circuits. However, few efforts have been involved in exploring absorption modulation at TDFA-band. In this work, variable optical attenuators (VOAs) for TDFA-band wavelengths were designed and fabricated based on a silicon-on-insulator (SOI) platform. By embedding a short PIN junction length of 200 μm into the waveguide, the fabricated VOA exhibits a high modulation depth of 40.49 dB at 2.2 V and has a fast response time (10 ns) induced by the plasma dispersion effect. Combining the Fabry-Perot cavity effect and plasma dispersion effect of silicon, the attenuator could achieve a maximum attenuation of more than 50 dB. These results promote the 2-μm waveband silicon photonic integration and are expected to the future use of photonic attenuators in crosstalk suppression, optical modulation, and optical channel equalization.
We propose the squeezing of hyperbolic polaritonic rays in cylindrical lamellar structures with hyperbolic dispersion. This efficient design is presented through conformal mapping transformation by combining with circular effective-medium theory (CEMT) that is adopted to predict the optical response of concentric cylindrical binary metal-dielectric layers. The volume-confined hyperbolic polaritons supported in these cylindrical lamellar structures could be strongly squeezed when they propagate toward the origin since their wavelength shortens, and velocity decreases. To demonstrate the importance of using CEMT for engineering highly-squeezed hyperbolic polaritons, both CEMT and planar effective-medium theory (PEMT) are utilized to design the cylindrical lamellar structures. It is shown that the PEMT-based design is unable to achieve hyperbolic polaritons squeezing even with a sufficiently large number of metal-dielectric binary layers. Remarkably, this study opens new opportunities for hyperbolic polaritons squeezing, and the findings are promising for propelling nanophotonics technologies and research endeavours.
This article contains a digest of the theory of electromagnetism and a review of the transformation between inertial frames, especially under low speed limits. The covariant nature of the Maxwell's equations is explained using the conventional language. We show that even under low speed limits, the relativistic effects should not be neglected to get a self-consistent theory of the electromagnetic fields, unless the intrinsic dynamics of these fields has been omitted completely. The quasi-static limits, where the relativistic effects can be partly neglected are also reviewed, to clarify some common misunderstandings and imprecise use of the theory in presence of moving media and other related situations. The discussions presented in this paper provide a clear view of why classical electromagnetic theory is relativistic in its essence.