Controlling light-with-light without nonlinearity

Abstract

According to Huygens' superposition principle, light beams traveling in a linear medium will pass though one another without mutual disturbance. Indeed, it is widely held that controlling light signals with light requires intense laser fields to facilitate beam interactions in nonlinear media, where the superposition principle can be broken. We demonstrate here that two coherent beams of light of arbitrarily low intensity can interact on a metamaterial layer of nanoscale thickness in such a way that one beam modulates the intensity of the other. We show that the interference of beams can eliminate the plasmonic Joule losses of light energy in the metamaterial or, in contrast, can lead to almost total absorbtion of light. Applications of this phenomenon may lie in ultrafast all-optical pulse-recovery devices, coherence filters and THz-bandwidth light-by-light modulators

Coherent perfect absorbers: linear control of light with light

“…It follows from Eq. (4) that the eigenvalues ofŜ are {−1, 1 + 2r}, thus satisfying r = −1/2 realizes a CPA: if the sheet is illuminated symmetrically with two coherent beams, it coincides with an anti-node of the electric field and absorption reaches 100% [8,21,51]. Conversely, for antisymmetric beams, the sheet is located at a node and the absorption vanishes.…”

“…A metasurface-based CPA was first demonstrated using a free-standing plasmonic metasurface (Fig. 2c) [21], which had thickness λ/13 (λ indicates the wavelength) and was tailored to function as a CPA at exactly λ = 1550 nm with normally-incident beams on each side. This system acts like the thin-film CPA described in Eq.…”

“…There is currently a considerable interest in using planar metamaterials -metasurfaces -to realize CPAs [21,22,[35][36][37][64][65][66]. The meta-atoms (unit cells of the metasurface) can be designed to tailor the electromagnetic properties at any desired frequency [67].…”

“…To achieve perfect absorption, it is essential to appropriately choose the values of the system parameters, the operating wavelength and the input waveform, including the intensities and relative phases of the input beams. The sensitivity of CPAs to the input waveform provides the opportunity to flexibly control light scattering and absorption [21][22][23]. The possibility of achieving perfect absorption at subwavelength lengthscales is extremely interesting for nanophotonic applications.…”

“…A coherent perfect absorber (CPA) [7] generalizes this phenomenon to arbitrary incoming waveforms that can consist of two or more waves, such as waves incident on opposite faces of an open slab or film [7,20,21]. To achieve perfect absorption, it is essential to appropriately choose the values of the system parameters, the operating wavelength and the input waveform, including the intensities and relative phases of the input beams.…”