Compact topological polarization beam splitter based on all-dielectric fishnet photonic crystals.

Conventional polarization beam splitters (PBSs) suffer energy loss and signal distortion due to backscattering caused by disturbances. Topological photonic crystals provide backscattering immunity and anti-disturbance robustness transmission owing to the topological edge states. Here, we put forward a kind of dual-polarization air hole-type fishnet valley photonic crystal with a common bandgap (CBG). The Dirac points at the K point formed by different neighboring bands for transverse magnetic and transverse electric polarizations are drawn closer via changing the filling ratio of the scatterer. Then the CBG is constructed by lifting the Dirac cones for dual polarizations within a same frequency range. We further design a topological PBS using the proposed CBG via changing the effective refractive index at the interfaces which guide polarization-dependent edge modes. Based on these tunable edge states, the designed topological PBS (TPBS) achieves efficient polarization separation and is robust against sharp bends and defects, verified by simulation results. The TPBS's footprint is approximately 22.4 × 15.2 µ m 2, allowing high-density on-chip integration. Our work has potential application in photonic integrated circuits and optical communication systems.

Dirac cones with zero refractive indices in phoxonic crystals.

In this paper, simultaneous zero refractive indices (ZRIs) for both sound and light are realized on the basis of a 2D triangular lattice phoxonic crystal (PxC) with C6v symmetry. For the phononic mode, accidental phononic Dirac degeneracy at the center of Brillouin zone (BZ) occurs at a relatively high frequency which leads to the failure of the efficient medium theory; hence, it is no longer applicable to the realization of acoustic ZRI. We thus turn to a low-frequency phononic Dirac cone located at K point, the corner of the BZ, which shows in-phase pressure field oscillations in expanded unit cells. Using zone folding, we further reveal the cause for the characteristic of acoustic ZRI. For the photonic mode, a low-frequency photonic Dirac-like cone can be achieved by adjusting the geometric parameter due to the high contrast permittivity between scatterers and the matrix. When the phononic and photonic low-frequency Dirac dispersions coexist, the PxC can be mapped into a zero-index material for both sound and light at the same time. The new mechanism for simultaneously controlling sound and light helps to achieve acousto-optic synchronous cloaking and unidirectional transmission, which are numerically demonstrated.

Protein quality control by the proteasome and autophagy: A regulatory role of ubiquitin and liquid-liquid phase separation.

Degradation of dysfunctional, damaged, or misfolded proteins is a crucial component of the protein quality control network to maintain cellular proteostasis. Dysfunction in proteostasis regulation due to imbalances in protein synthesis, folding, and degradation challenges the integrity of the cellular proteome and favors the accumulation of aggregated proteins that can damage cells by a loss of their functions and/or a gain of adverse functions. Ubiquitination is an essential player in proteostasis regulation but also in orchestrating signaling pathways in response to various stress conditions. Both cellular degradation systems, the proteasome and autophagy, employ ubiquitin for selection and targeting of substrates to the degradative machineries. Here we summarize the manifold functions of ubiquitin in protein degradation and discuss its emerging role in the formation of biomolecular condensates through liquid-liquid phase separation, which allows spatiotemporal regulation of protein quality control.