Junbo Chen

α-Ga₂O₃ has attracted significant attention for high-power electronics and deep ultraviolet optoelectronics. Herein, density functional theory calculations were employed to systematically investigate the effects of metal doping, including Cu, Ag, Zn, and Au, on the structural stability, electronic structure, and optical properties of α-Ga₂O₃. The formation energy analysis reveals that all metal dopants preferentially substitute at the octahedral Ga sites, with lower formation energies under O-rich conditions compared to Ga-rich conditions, among which Zn doping exhibits the lowest formation energy under O-rich conditions, followed closely by Cu, indicating that both Zn and Cu can be readily incorporated into the α-Ga₂O₃ lattice. Metal doping introduces impurity levels within the band gap through the strong hybridization between dopant d orbitals and O 2p orbitals near the Fermi level, significantly narrowing the effective band gap and transforming the material from a pristine n-type to a p-type semiconductor. The charge density difference analysis further confirms the electron transfer from dopant metal atoms to neighboring O atoms, generating holes as the dominant charge carriers. Among the four dopants, Zn introduces the shallowest acceptor level near the valence band maximum, making it the most promising candidate for achieving effective p-type conductivity, while Cu, Ag, and Au create relatively deeper acceptor states. Furthermore, the optical properties demonstrate that metal doping causes a pronounced red shift in the absorption edge from the ultraviolet to the visible light region, as the impurity levels provide additional electronic transition pathways at lower photon energies. The enhanced visible light absorption, combined with the increased static dielectric constant and modified reflectivity spectra, indicates improved light-harvesting capability of the doped systems. These findings provide important theoretical guidance for the design of α-Ga₂O₃-based optoelectronic devices.

Nonvolatile switching is emerging and shows potential in integrated optics. A compact nonvolatile reconfigurable mode converter implemented on a 4H-silicon-carbide-on-insulator (4H-SiCOI) platform with a footprint of 0.5 × 1 × 1.8 μm³ is proposed in this study. The functional region features an Sb₂S₃ film embedded in a 4H-SiC strip waveguide. The functionality is achieved through manipulating the phase state of the Sb₂S₃. The high refractive index contrast between the crystalline Sb₂S₃ and 4H-SiC enables high-efficiency mode conversion within a compact footprint. The incident TM0 mode is converted to the TM1 mode with a high transmittance (T) beyond 0.91 and a mode purity (MP) over 91.72% across the 1500–1600 nm waveband. Additionally, when the Sb₂S₃ transitions to its amorphous state, the diminished refractive index contrast efficiently mitigates the mode conversion effect. In this state, the TM0 mode propagates through the functional region with minimal perturbation, exhibiting T ≥ 0.99 and MP_TM0 ≥ 97.65% within a 1500–1600 nm waveband. Furthermore, the device performances were investigated under partially crystallized states of Sb₂S₃. The proposed structure offers a broad range of transmittance differences (−16.42 dB ≤ ΔT ≤ 17.1 dB) and mode purity differences (−90.91% ≤ ΔMP ≤ 96.11%) between the TM0 mode and TM1 mode. The proposed device exhibits a high robustness within ±20 nm Δl and ±10 nm Δw. We believe that the proposed multi-level manipulation can facilitate a large communication capacity and that it can be deployed in neuromorphic optical computing.

We investigate the phenomenology of spontaneous symmetry breaking (SSB) and spontaneous antisymmetry breaking (SASB) in the framework of a system of coupled nonlinear Schrödinger equations (NLSEs) with a combination of linear and nonlinear double-well potentials (DWPs), including self- and cross-phase-modulation (SPM and XPM) nonlinear terms. The DWP structure is represented by a symmetric pair of delta functions. This setup can be realized in optics and for matter waves in Bose-Einstein condensates. It is commonly known that SSB states are completely stable in the single one-dimensional NLSE with a combination of DWP and attractive SPM nonlinearity. The objective of the present work is to elaborate on the SSB and SASB phenomenology in the two-component system. One factor that affects the phenomenology (actually, the stability of stationary states) in this context is the relative sign of the two components, the states with identical/opposite signs defined as ones with in-phase/out-of-phase components. We demonstrate that the SSB/SASB, with both components originating from spatially symmetric or antisymmetric modes, of the out-of-phase type, in the coupled NLSEs including the SPM and XPM terms with opposite signs, are similar to their counterparts in the single NLSE. On the other hand, the SSB/SASB of in-phase states in the coupled NLSEs, including the SPM and XPM terms with opposite signs, are quite different from the ones in the single NLSE. In particular, we find that the in-phase SSB/SASB states are unstable in a part of the intervals of their propagation constant if the system includes SPM and XPM terms with opposite signs. As another feature that is possible only in the two-component system, we address mixed-parity states, originally built of spatially symmetric and antisymmetric components, and find that such states, featuring SSB or SASB, are stable in a part of their interval of the propagation constant. We clarify that the spatially antisymmetric component is a dominant one in determining the asymmetry of the established state if it is coupled to the symmetric one, in the case of the repulsive SPM. On the other hand, the symmetric component dominates if it is coupled to the antisymmetric one in the case of the attractive SPM.

We demonstrate the existence of two types of dark gap solitary waves—the dark gap solitons and the dark gap soliton clusters—in Bose–Einstein condensates trapped in a bichromatic optical superlattice with cubic–quintic nonlinearities. The background of these dark soliton families is different from the one in a common monochromatic linear lattice; namely, the background in our model is composed of two types of Gaussian-like pulses, whereas in the monochromatic linear lattice, it is composed of only one type of Gaussian-like pulses. Such a special background of dark soliton families is convenient for the manipulation of solitons by the parameters of bichromatic and chemical potentials. The dark soliton families in the first, second, and third bandgap in our model are studied. Their stability is assessed by the linear-stability analysis, and stable as well as unstable propagation of these gap solitons are displayed. The profiles, stability, and perturbed evolution of both types of dark soliton families are distinctly presented in this work.

Three ultracompact integrated photonic devices are proposed, assisted by etched structures. A mode-order converter (MOC) is achieved with a footprint of 0.85 × 1.4 μm², which exhibits high performances with insertion loss (IL) below 0.34 dB and mode purity (MP) above 90% within 100 nm waveband. Moreover, a mode blocking filter (MBF) is proposed based on a subwavelength grating with a footprint of 0.8 × 4.12 μm², which allows the propagation of TM0 mode but blocks the TM1 mode with a remarkably high extinction ratio of 31.6 dB at the wavelength of 1550 nm. Finally, a compact reciprocal optical diode (ROD) is presented by cascading the abovementioned MOC and MBF with a footprint of 0.85 × 5.9 μm². This ROD enables one-way transmissions for both TM0 mode and TM1 mode with contrast ratios of 19.74 dB and 32.04 dB, respectively. The design methodology paves a new way for mode manipulation in integrated multimode photonic circuits.