Yixiao Gao

Nonvolatile optical switches based on phase-change materials (PCMs) are essential building blocks for reconfigurable photonic integrated circuits with reduced power consumption. However, the operating bandwidth of existing PCM optical switches is typically limited by modal dispersion. Here, we propose a broadband nonvolatile optical switch based on artificial-gauge-field-driven broadband 3 dB power splitters in a Mach-Zehnder interferometer (MZI) configuration. Although broadband power splitting is accompanied by phase dispersion across the 3 dB splitting bandwidth, this issue is addressed by introducing local dispersion control through asymmetric MZI arms. In addition, broadband differential phase tuning between the two arms is achieved by integrating a low-loss PCM into shallow-slot waveguides. The proposed device achieves an operating bandwidth of 170 nm with a switching extinction ratio exceeding 15 dB and an insertion loss below 0.78 dB. Our design provides a promising route toward compact, energy-efficient, and broadband optical routing for large-scale reconfigurable photonic integrated circuits.

The miniaturization of optical switches using phase-change materials (PCMs) holds broad prospects, and exploring various strategies to effectively integrate PCMs with integrated optical waveguides has become a fascinating research topic. This study proposes a compact silicon-waveguide three-port optical switch based on the phase-change material Sb ₂ Se ₃ . The device consists of the phase-change material Sb ₂ Se ₃ and an inverse-designed pixelated silicon-material structure. This pixelated structure can provide customized refractive indices unattainable by conventional materials or structures, thereby significantly reducing the device’s size and enabling automated device design. The ultra-compact device measures only 7.5µm×4.9µm and achieves three-port switching functionality by altering the state of the phase-change material. Simulation results demonstrate a high extinction ratio exceeding 13.0 dB in the C-band.

Active on-chip polarization control is essential for integrated photonic systems. Here, we propose reconfigurable on-chip polarizers based on a nonvolatile phase-change-material-assisted symmetric three-waveguide directional coupler. By exploiting the distinct coupling behaviors of TE and TM modes through controlled phase mismatch, the propagation path and attenuation of different polarizations can be independently engineered. Specifically, a TE-pass polarizer is realized by using Ge ₂ Sb ₂ Te ₅ (GST) as a phase-matching and loss-control medium on the side waveguides, while a TM-pass polarizer is achieved by introducing a resonant GST-loaded section in the central waveguide that selectively suppresses the TE mode with a high extinction ratio. The proposed polarizers demonstrate broadband operation from 1500 nm to 1600 nm, with polarization extinction ratios over 20 dB for both configurations. This work provides a compact, reconfigurable, and nonvolatile strategy for high-contrast polarization control in silicon photonic integrated circuits.

In this paper, we propose a switchable high-Q light absorber based on a reconfigurable metasurface enabled by a lowloss phase-change material (PCM). By leveraging the coupling between guided-mode resonance and Fabry-Perot modes, mediated by the phase-transition dynamics of the embedded PCM, the resonance Q factor can be actively tuned. This allows the system to switch from a perfect dark state, governed by the physics of bound states in the continuum, to a critically coupled resonance with a finite Q factor. Consequently, the metasurface exhibits perfect absorption in the amorphous state and a reflection-dominated response in the crystalline state. The proposed metasurface holds significant potential for diverse nanophotonic applications, including photodetection and thermal emission control.

In this paper, we propose a switchable high- Q light absorber based on a reconfigurable metasurface enabled by a lowloss phase-change material (PCM). By leveraging the coupling between guided-mode resonance and Fabry–Perot modes, mediated by the phase-transition dynamics of the embedded PCM, the resonance Q factor can be actively tuned. This allows the system to switch from a perfect dark state, governed by the physics of bound states in the continuum, to a critically coupled resonance with a finite Q factor. Consequently, the metasurface exhibits perfect absorption in the amorphous state and a reflection-dominated response in the crystalline state. The proposed metasurface holds significant potential for diverse nanophotonic applications, including photodetection and thermal emission control.

Compact, non-volatile optical switches on silicon platforms are essential for reconfigurable photonics, but the strong anisotropy of silicon waveguides leads to polarization-dependent performance. In this paper, we propose a polarization-independent, non-volatile optical switch utilizing low-loss phase change material (PCM) Sb₂S₃. By incorporating Sb₂S₃ into a multimode slot waveguide, multimode interference can be efficiently tuned for both TE and TM polarizations, owing to enhanced light–PCM interaction. Polarization-independent switching is achieved through the optimal design of the multimode slot waveguide region. The proposed non-volatile switch demonstrates a crosstalk (CT) < −21.9 dB and insertion loss (IL) < 0.12 dB at 1550 nm with a multimode section length of 9.67 µm, which may find promising applications in reconfigurable photonic circuits for on-chip optical signal processing.

Compact, non-volatile optical switches on silicon platforms are essential for reconfigurable photonics, but the strong anisotropy of silicon waveguides leads to polarization-dependent performance. In this paper, we propose a polarization-independent, non-volatile optical switch utilizing low-loss phase change material (PCM) Sb2S3. By incorporating Sb2S3 into a multimode slot waveguide, multimode interference can be efficiently tuned for both TE and TM polarizations, owing to enhanced light-PCM interaction. Polarization-independent switching is achieved through the optimal design of the multimode slot waveguide region. The proposed non-volatile switch demonstrates a crosstalk (CT) < -21.9 dB and insertion loss (IL) < 0.12 dB at 1550 nm with a multimode section length of 9.67 μm, which may find promising applications in reconfigurable photonic circuits for on-chip optical signal processing.

Achieving high-Q light absorption within a thin dielectric film is highly desired for optoelectronic applications. However, controlling the absorption linewidth remains challenging, as it requires simultaneous control over both radiative and non-radiative loss to satisfy the critical coupling condition. In this paper, we report the design of a metasurface-based, polarization-independent perfect light absorber with a tunable absorption Q factor. The radiative decay rate can be tuned by adjusting the lattice constant of the metasurface, leveraging the mechanism of degenerate merging bound states in the continuum (BICs). Meanwhile, the non-radiative loss rate is controlled by introducing a waveguiding layer that modulates the overlap between the resonant field and the absorbing medium. This dual-control mechanism enables the metasurface absorber to achieve arbitrarily high absorption Q factors at a desired wavelength under critical coupling. Our approach offers a versatile platform for narrowband light absorption with tunable spectral linewidths, opening new opportunities for photodetection and spectral sensing applications.

Achieving stable output and control of higher-order laser arrays has long been a challenge in the development of a passively Q-switched fiber laser. In this Letter, we reported a notable peak power of 14.9 kW alongside an average output power of 0.91 W in a passively Q-switched fiber laser. Particularly noteworthy is the observed evolution of laser modes into high-order laser arrays, extending to dimensions of up to 7 × 7 with increasing pump power. This advancement in generating high peak power laser arrays in the Q-switched states holds significant promise for applications, including optical communication and nanomicroscopic imaging.

Resonant metasurfaces driven by bound states in the continuum (BIC) offer an intriguing approach to engineer high-Q resonances. Merging multiple BICs in the momentum space could further enhance the Q-factor as well as its robustness to fabrication imperfections. Here, we report doubly-degenerate guided mode resonances (GMR) in a resonant metasurface, whose radiation losses could be totally suppressed due to merging BICs. We show that the GMRs and their associated accidental BICs can be evolved into degenerate merging BICs by parametric tuning of the metasurface. Significantly, these two GMRs share the same critical parameter (i.e. lattice constants or thickness) that the merging BICs occur. Interestingly, thanks to the degenerate property of two GMRs, a larger (smaller) period will split one of merging BICs into eight accidental BICs at off-Γ point, but annihilate the other. Such exotic phenomenon can be well explained from the interaction of GMRs and background Fabry-Perot resonances. Our result provides new strategies to engineering high-Q resonances in resonant metasurfaces for light-matter interaction.