Miljana G. Stojanović

Demand for densely packed wavelength demultiplexers has increased due to the rapid developments in information systems and sensing for biomedical and space applications. The required miniaturisation is problematic due to the crosstalk in high-density photonic circuits, while the feature size complicates design at sub-micrometer wavelengths. As a solution, we propose wavelength demultiplexers based on wavelength-dependent self-imaging in linearly coupled finite optical lattices. The novel semi-analytical design allows for intuitive and efficient control of their spectral characteristics, notably the bandwidth control by changing the number of waveguides in the lattice. The principle is validated using femtosecond laser fabrication of visible/near-infrared demultiplexers in borosilicate glass. The insertion loss did not exceed 0.43 dB with 0.1–0.15 dB for most devices and the crosstalk was lower than 30 dB. The applicability of the proposed design to other fabrication platforms and wavelength ranges is demonstrated by numerical simulations of silicon-on-insulator demultiplexers at telecom wavelengths with highly competitive insertion loss and crosstalk of 0.13 dB and −82 dB, respectively.

We propose a novel approach to design of wavelength demultiplexers based on self-imaging of light in optical lattices and validate it experimentally. It applies to all fabrication platforms, enabling scalability, spectral control and low loss.

Tuning the values of artificial flux in the two-dimensional octagonal-diamond lattice drives topological phase transitions, including between singular and non-singular flatbands. We study the dynamical properties of nonlinear compact localized modes that can be continued from linear flatband modes. We show how the stability of the compact localized modes can be tuned by the nonlinearity strength or the applied artificial flux. Our model can be realized using ring resonator lattices or nonlinear waveguide arrays.

Two-dimensional dice lattice can be dressed by artificial flux to host the Aharonov-Bohm (AB) caging effect resulting in the occurrence of a fully flatband spectrum. Here, we focus on the dynamics of flatband compact localized eigenmodes shared by a few unit cells in two snowflake configurations. We numerically show the possibility of dynamically stable propagation of two types of compact localized complexes by tuning the nonlinearity. The caging is imprinted in complexes dynamics regardless of the type and strength of nonlinearity. On the other hand, nonlinearity can only affect the appearance of the caged complex. These findings open a new route for the manipulation of structured light in photonic systems.

We investigate analytically and numerically the existence and dynamical stability of different localized modes in a two-dimensional photonic lattice comprising a square plaquette inscribed in the dodecagon lattices. The eigenvalue spectrum of the underlying linear lattice is characterized by a net formed of one flat band and four dispersive bands. By tailoring the intersite coupling coefficient ratio, opening of gaps between two pairs of neighboring dispersive bands can be induced, while the fully degenerate flat band characterized by compact eigenmodes stays nested between two inner dispersive bands. The nonlinearity destabilizes the compact modes and gives rise to unique families of localized modes in the newly opened gaps, as well as in the semi-infinite gaps. The governing mechanism of mode localization in that case is the light energy self-trapping effect. We have shown the stability of a few families of nonlinear modes in gaps. The suggested lattice model may serve for probing various artificial flat-band systems such as ultracold atoms in optical lattices, periodic electronic networks, and polariton condensates.

We consider a two-dimensional octagonal-diamond network with a fine-tuned diagonal coupling inside the diamond-shaped unit cell. Its linear spectrum exhibits coexistence of two dispersive bands (DBs) and two flat bands (FBs), touching one of the DBs embedded between them. Analogous to the kagome lattice, one of the FBs will constitute the ground state of the system for a proper sign choice of the Hamiltonian. The system is characterized by two different flat-band fundamental octagonal compactons, originating from the destructive interference of fully geometric nature. In the presence of a nonlinear amplitude (on-site) perturbation, the single-octagon linear modes continue into one-parameter families of nonlinear compact modes with the same amplitude and phase structure. However, numerical stability analysis indicates that all strictly compact nonlinear modes are unstable, either purely exponentially or with oscillatory instabilities, for weak and intermediate nonlinearities and sufficiently large system sizes. Stabilization may appear in certain ranges for finite systems and, for the compacton originating from the band at the spectral edge, also in a regime of very large focusing nonlinearities. In contrast to the kagome lattice, the latter compacton family will become unstable already for arbitrarily weak defocusing nonlinearity for large enough systems. We show analytically the existence of a critical system size consisting of 12 octagon rings, such that the ground state for weak defocusing nonlinearity is a stable single compacton for smaller systems, and a continuation of a nontrivial, noncompact linear combination of single compacton modes for larger systems. Investigating generally the different nonlinear localized (noncompact) mode families in the semi-infinite gap bounded by this FB, we find that, for increasing (defocusing) nonlinearity the stable ground state will continuously develop into an exponentially localized mode with two main peaks in antiphase. At a critical nonlinearity strength a symmetry-breaking pitchfork bifurcation appears, so that the stable ground state is single peaked for larger defocusing nonlinearities. We also investigate numerically the mobility of localized modes in this regime and find that the considered modes are generally immobile both with respect to axial and diagonal phase-gradient perturbations.