arXiv subjects

Kaiwen Ji

Publications and source records attributed to Kaiwen Ji.

6 recordsLinked to original sources

arXiv2025

Twisted light from topological chiral exceptional points in a nanolaser array

We propose and experimentally demonstrate an orbital angular momentum (OAM) nanolaser array arranged in a ring geometry on an InP-based photonic crystal membrane. The device realizes a non-Hermitian extension of the Rice-Mele model, featuring alternating coupling strengths and imaginary on-site detunings. This configuration supports a symmetry-protected zero mode stabilized by non-Hermitian particle-hole symmetry, which enforces a uniform $π/2$ phase shift between adjacent nanolasers, establishing a coherent phase winding around the array. By adjusting the gain/loss contrast in a parity-time (PT)-like pumping scheme, the system can be tuned to a chiral exceptional point, where energy flows unidirectionally between nanocavities despite their reciprocal coupling. This symmetry-enforced, directional tunneling leads to far-field emission carrying non-zero OAM, providing a direct signature of the phase-structured lasing mode. Our results demonstrate a robust and scalable strategy for engineering compact, phase-locked laser arrays with controllable angular momentum output, and open new avenues for structured light generation in integrated photonic platforms.

physics.optics↗

arXiv2023

Non-Hermitian zero mode laser in a nanophotonic trimer

Symmetry-protected zero modes in arrays of coupled optical elements have attracted considerable attention because they are expected to be robust against coupling disorders. In the Hermitian limit, zero modes are dark ones, i.e. the intensity in one sublattice vanishes; yet, in a non-Hermitian counterpart, zero modes can be bright and feature π/2 phase difference between sublattices. In this work, we report on the direct observation of a lasing zero mode in a non-Hermitian three coupled nanocavity array. We show efficient excitation for nearly equal pump power in the two extreme cavities. Furthermore, its efficiency can be dynamically controlled by pumping the center cavity. The realization of zero mode lasing in large arrays of coupled nanolasers has potential applications in laser-mode engineering and it opens up promising avenues in optical computing.

physics.optics↗

arXiv2022

Tracking exceptional points above laser threshold

Recent studies on non-Hermitian optical systems having exceptional points (EPs) have revealed a host of unique characteristics associated with these singularities, including unidirectional invisibility, chiral mode switching and laser self-termination, to mention just a few examples. The vast majority of these works focused either on passive systems or active structures where the EPs were accessed below the lasing threshold, i.e. when the system description is inherently linear. In this work, we experimentally demonstrate that EP singularities in coupled semiconductor nanolasers can be accessed and tracked above the lasing threshold, where they become branch points of a nonlinear dynamical system. Contrary to the common belief that unavoidable cavity detuning will impede the formation of an EP, here we demonstrate that this same detuning is necessary for compensating the carrier-induced frequency shift, hence restoring the nonlinear EP in the lasing regime. Furthermore, unlike linear non-Hermitian systems, we find that the spectral location of EPs above laser threshold varies as a function of total pump power and can therefore be continuously tracked. Our work is a first step towards the realization of lasing EPs in more complex laser geometries, and enabling the enhancement of photonic local density of states through non-Hermitian symmetries combined with nonlinear interactions in coupled laser arrays.

physics.optics↗

arXiv2021

Anti-parity-time topologically undefined state

We constructed an anti-parity-time-symmetric photonic lattice by using perturbations. The results show the topological state will appear when the waveguide coupling constants $κ_1<κ_2$; Interestingly, a state with undefined winding numbers occurs when $κ_1=κ_2$, in which the light distributes only in the wide waveguides with equal magnitude distribution. Further studies show that the edge state will be strengthened by introducing defect for the topologically non-trivial case, while it will not affect the equal intensity transmission for the topologically undefined state. Our work provides a new way to realize the topological state and equally divided light transmission and might be applicable in optical circuits and optical interconnect.

physics.optics↗

arXiv2020

PT-symmetric topological near-zero interface state

Photonic systems with parity-time (PT) symmetry and topology are attracting considerable attentions. In this work, topological near-zero edge states are studied in PT-symmetric photonic lattice and the results indicate that the near-zero edge states can be broken spontaneously in spite of the unbroken PT symmetry. To achieve the stable topological near-zero mode, a binary lattice with carefully designed PT-symmetric is proposed. Further study shows such a structure supports a stable topological interface state experiences phase transition similar to the bulk states in infinite lattice and thus possess real-eigenvalues even with unbroken PT phase. Our study enriches the content of non-Hermitian topological physics and might have potential applications in the fields of topological lasing and quantum computation.

physics.optics↗

arXiv2020

Synthetic topological insulator with periodically modulated effective gauge fields

We study both theoretically and numerically the topological edge states in synthetic photonic lattice with finitely periodic gauge potentials. The effective gauge fields are implemented by tailoring the phase alternatively and periodically, which finally results in symmetric total reflection at two boundaries of the one-dimensional synthetic lattice. Further tuning the nearest-neighbor coupling anisotropically, topological edge states occur at the two boundaries. Our work provides a new way to study the topological physics of one-dimensional coupled waveguide arrays with synthetic photonic lattice.

physics.optics↗