Zoé-Lise Deck-Léger

Optical isolation based on space-time engineered asymmetric photonic band gaps

Nonreciprocal electromagnetic devices play an important role in modern optical and microwave technologies. Conventional methods for realizing such systems are incompatible with integrated circuits. With recent advances in integrated photonics, the need for efficient on-chip magnetless nonreciprocal devices is more urgent than ever. This paper leverages space-time engineered asymmetric photonic bandgaps to generate optical isolation. It is shown that a properly designed space-time modulated slab is highly reflective/transparent for opposite directions of propagation. The proposed method requires a low modulation frequency, is magnetless and can achieve very high isolation levels. Experimental proof of concept at microwave frequencies is provided.

What is Nonreciprocity

This paper aims at providing a global perspective on electromagnetic nonreciprocity and clarifying confusions that arose in the recent developments of the field. It provides a general definition of nonreciprocity and classifies nonreciprocal systems according to their linear time-invariant (LTI), linear time-variant (LTV) or nonlinear nonreciprocal natures. The theory of nonlinear systems is established on the foundation of the concepts of time reversal, time-reversal symmetry, time-reversal symmetry breaking and related Onsager- Casimir relations. Special attention is given to LTI systems, as the most common nonreciprocal systems, for which a generalized form of the Lorentz reciprocity theorem is derived. The delicate issue of loss in nonreciprocal systems is demystified and the so-called thermodynamics paradox is resolved from energy conservation considerations. The fundamental characteristics and applications of LTI, LTV and nonlinear nonreciprocal systems are overviewed with the help of pedagogical examples. Finally, asymmetric structures with fallacious nonreciprocal appearances are debunked.

Space-time (ST) reflection focusing in dispersion-engineered medium

The space-time focusing of a pulse after reflection can be realized in a nonreciprocal dispersive medium. We show here how this task can be accomplished using a space-time (ST) periodic dispersive nonreciprocal medium.

Electromagnetic nonreciprocity and perfect mixing in space-time engineered asymmetric bandgaps

This paper leverages space-time engineered asymmetric electromagnetic bandgaps for generating magnetless electromagnetic nonreciprocity and perfect mixing. It is theoretically and experimentally demonstrated that a properly designed space-time modulated slab is highly reflective/transparent for opposite directions of propagation. The corresponding design is magnet-less, accommodates low modulation frequencies, and can achieve very high isolation levels. Moreover, the wave fully reflected from the space-time modulated slab exhibits frequency shifting, without any undesirable inter-modulation effects.

Scattering in superluminal space-time (ST) modulated electromagnetic crystals

Space-time (ST) modulated media manipulate the ST spectra, i.e. the k-ω frequencies, of waves. Here, we examine the scattering of electromagnetic waves from a superluminal periodic ST medium, or ST crystal. We rigorously solve, for the first time, the scattering problem for a single crystal period and explain the corresponding phenomenology using a geometrical construction in the Minkowski diagram. From these results, we infer the existence and locations of instabilities in the dispersion diagram of a ST crystal. FDTD-computed scattered fields are briefly described.

Sub/Super-luminal space-time slab: Fundamental scattering symmetries

Space-time (ST) media are regaining interest due to their capability to modify the ST spectra (k-ω) and amplitudes of waves, and their subsequent multiple potential applications. Many fundamental related problems have not been resolved yet, including the scattering of an oblique wave on a superluminal ST slab. Here, we address this problem for the first time and highlight fundamental symmetries in the deflection angles of sub- and super-luminal slabs. An insightful diagrammatic approach, conveying the symmetry information at a glance, is proposed.

Frequency generation in moving photonic crystals

In this paper, we discuss experimental feasibility and present several system designs that could be potentially used for generation of new frequencies by light waves interacting with moving photonic crystals. In particular, we first theoretically analyze multiple frequency generation when incident light is reflected or diffracted by the moving infinite 1D photonic crystals of different orientations. We then demonstrate frequency harmonics generation via leaky waves of a moving finite-size 1D photonic crystal. Finally, we study dispersion relations of modes guided in the hollow core of a moving waveguide. In particular, we demonstrate frequency comb generation inside of the hollow core of a moving 2D photonic crystal waveguide.

X wave transformation under time discontinuity

We study the transformation of X waves under time discontinuities. We find out that the wave splits into two X waves, that the spatial features are conserved, and that the time features are altered, the wave being either compressed or expanded depending on the indices of refraction before and after the discontinuity. We also find that one of the transformed waves is time-reversed. We expect this work will provide solutions in applications such as plasma science and metamaterials.