Search

Dynamic localization (DL) refers to a wavefunction confinement effect of electrons in periodic lattices under an ac electric field driving. Recent studies have transplanted DLs from electronic to photonic systems using periodically curved waveguide lattices, where the ac electric field is mimicked by the waveguide's bending curvature. However, due to the severe limitations of bending losses and poor tunability for highly curved, arbitrarily shaped waveguides, present studies mainly focus on DL under the simplest sinusoidal‐wave driving; its extension to an arbitrary‐wave driving remains challenging. Here, by constructing a synthetic temporal lattice with a coupled fiber‐loop circuit, the limitations of spatially curved waveguides are circumvented and generalized DLs are experimentally demonstrated under arbitrary‐wave driving. First, by applying band‐collapse criteria, the general conditions for the driving field's symmetry to achieve DLs are revealed. Then, two representative even‐function driving fields of square‐ and triangle‐waveforms are chosen, and wave‐packet revivals are observed as signatures of DLs. As a counter‐example, the breakdown of DL is also verified using odd‐function driving field of sawtooth‐waveform. The work reveals the conditions for realizing generalized DLs and experimentally verifies them using synthetic lattice schemes. This paradigm may find potential applications in versatile temporal‐waveform reshaping, pulse manipulations for optical communications, and signal processing. [ABSTRACT FROM AUTHOR]

Dynamically encircling the exceptional point (EP) of an anti‐parity‐time (anti‐PT) symmetric system can achieve chiral mode switching between symmetry‐broken eigenmodes, which is especially important for developing nanophotonic devices. However, the realization of anti‐PT‐symmetric systems on a chip still remains significantly challenging as precisely controlling the parameters of nanophotonic structures is difficult. Herein, a novel anti‐PT‐symmetric system is designed and constructed on a silicon‐on‐insulator chip by taking advantage of subwavelength gratings to help engineer nanophotonic structures. Consequently, on‐chip chiral switching between symmetry‐broken eigenmodes is experimentally realized by dynamically encircling the EP in parametric space of the proposed anti‐PT‐symmetric system. Moreover, the achieved chiral mode switching exhibits high output power ratios (≥ 6.4 dB) at 1550 nm, wide‐band response that covers C‐band completely, and great thermal stability up to 90 °C, which indicate desirable performance features for practical applications in optical communication. This study paves an avenue for realizing on‐chip chiral switching between symmetry‐broken modes, which shows great promise for developing nanophotonic devices, such as optical switching, logic gates, and isolators, in optical telecommunication bands. [ABSTRACT FROM AUTHOR]