Two-dimensional materials (2DMs) have been used widely in constructing photodetectors (PDs) because of their advantages in flexible integration and ultrabroad operation wavelength range. Specifically, 2DM PDs on silicon have attracted much attention because silicon microelectronics and silicon photonics have been developed successfully for many applications. 2DM PDs meet the imperious demand of silicon photonics on low-cost, high-performance, and broadband photodetection. In this work, a review is given for the recent progresses of Si/2DM PDs working in the wavelength band from near-infrared to mid-infrared, which are attractive for many applications. The operation mechanisms and the device configurations are summarized in the first part. The waveguide-integrated PDs and the surface-illuminated PDs are then reviewed in details, respectively. The discussion and outlook for 2DM PDs on silicon are finally given.

Our previous study demonstrated that transforming growth factor (TGF)-␤ activates ␤-catenin signaling through Smad3 interaction with ␤-catenin in chondrocytes. In the present studies, we further investigated the detailed molecular mechanism of the cross-talk between TGF-␤/Smad3 and Wnt/␤-catenin signaling pathways. We found that C-terminal Smad3 interacted with both the N-terminal region and the middle region of ␤-catenin protein in a TGF-␤-dependent manner. Both Smad3 and Smad4 were required for the interaction with ␤-catenin and protected ␤-catenin from an ubiquitin-proteasome-dependent degradation. In addition, the formation of the Smad3-Smad4-␤-catenin protein complex also mediated ␤-catenin nuclear translocation. This Smad3-mediated regulatory mechanism of ␤-catenin protein stability enhanced the activity of ␤-catenin to activate downstream target genes during chondrogenesis. Our findings demonstrate a novel mechanism between TGF-␤ and Wnt/␤-catenin signaling pathways during chondrocyte development.Endochondral bone formation is a tightly regulated process. The process starts from mesenchymal cell condensation with subsequent formation of chondrocytes and goes to chondrocyte proliferation and differentiation into hypertrophic chondrocytes. A number of growth factors and signaling molecules are involved in the regulation of chondrogenesis, including Sox9, Ihh, parathyroid hormone-related protein, bonemorphogenetic protein (BMP), 2 TGF-␤, and Wnt signaling proteins (1). ␤-Catenin is a central molecule in canonical Wnt pathway. In the absence of Wnt ligands, cytoplasmic ␤-catenin is constitutively phosphorylated by a multi-protein complex containing kinases such as GSK-3␤, CK1, and scaffolding proteins including Axins, APC, and Dsh. The phosphorylated ␤-catenin is recognized and modified by ubiquitin-protein isopeptide ligase complex, such as Skp1-␤-TrCP (2, 3), and finally degraded by the 26 S proteasome (4). During skeletal development, Wnt/␤-catenin signaling controls mesenchymal progenitor cells selectively to differentiate into osteoblasts. In the absence of ␤-catenin, the progenitor cells differentiate into chondrocytes instead of osteoblasts (5), indicating that ␤-catenin is required to suppress early mesenchymal cell differentiation into chondrocytes. However, the canonical Wnt pathway has also been reported to play a critical role in chondrocyte proliferation and hypertrophy. Chondrocyte-specific ␤-catenin deletion (targeted by Col2a1-Cre) leads to decreased chondrocyte proliferation and delayed hypertrophic chondrocyte differentiation (6, 7). In contrast, constitutive activation of ␤-catenin in chondrocytes through deletion of exon 3 of the ␤-catenin gene leads to severely compromised cartilage formation (6). Other signaling molecules could interact with ␤-catenin and indirectly regulate chondrocyte function (8, 9).The TGF-␤ signaling is involved in multiple cellular processes including cell proliferation, differentiation, and apoptosis. TGF-␤ ligand transduces its signal through binding with type II...

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Silicon photonics beyond the singlemode regime is applied for enabling ultralow-loss waveguide propagation for the fundamental mode even without any special fabrication process. Here a micro-racetrack resonator is fabricated with a standard 220-nm-SOI (silicon-on-insulator) multiproject-wafer foundry and shows a record high intrinsic quality factor of 1.02×10 7 , corresponding to an ultralow propagation loss of only 0.065 dB cm −1 , which is about 20 times less than that of regular 450-nm-wide waveguides on the same chip. A state-of-the-art microwave photonic filter on silicon is then realized with an ultranarrow 3-dB bandwidth of 20.6 MHz and a tuning range of ≈20 GHz for the first time. A 100-cm-long delayline employed the broadened waveguides is also demonstrated with compact 90°Euler-curve bends, and the measured average propagation loss is about 0.14 dB cm −1 . The concept of silicon photonics beyond the singlemode regime helps solve the issue of high propagation loss significantly. In particular, it enables silicon photonic devices with enhanced performances, which paves the way for realizing large-scale silicon photonic integration. This concept can be extended further to any other material platforms, such as silicon nitride and lithium niobate. This also brings numerous new opportunities for various applications such as nonlinear photonics, large-scale photonic integration, quantum photonics, microwave photonics, etc.

An ultra-broadband polarization beam splitter (PBS) with low excess loss (EL) and a high extinction ratio (ER) is proposed and demonstrated for the case with 340 nm thick silicon-on-insulator waveguides. Here the PBS is realized by using cascaded adiabatic dual-core tapers, which consist of a strip core and a subwavelength-grating core. For the designed PBS, which has a 33.6 µm long mode-evolution region, the ELs are <2007