Real-time imaging of standing-wave patterns in microresonators.

Real-time characterization of microresonator dynamics is important for many applications. In particular, it is critical for near-field sensing and understanding light-matter interactions. Here, we report camera-facilitated imaging and analysis of standing wave patterns in optical ring resonators. The standing wave pattern is generated through bidirectional pumping of a microresonator, and the scattered light from the microresonator is collected by a short-wave infrared (SWIR) camera. The recorded scattering patterns are wavelength dependent, and the scattered intensity exhibits a linear relation with the circulating power within the microresonator. By modulating the relative phase between the two pump waves, we can control the generated standing waves' movements and characterize the resonator with the SWIR camera. The visualized standing wave enables subwavelength distance measurements of scattering targets with nanometer-level accuracy. This work opens broad avenues for applications in on-chip near-field (bio)sensing, real-time characterization of photonic integrated circuits, and backscattering control in telecom systems.

Geometry optimization for dark soliton combs in thin multimode silicon nitride microresonators.

Silicon nitride (Si3N4) has been well established as an ultralow-loss material for integrated photonics, particularly for the generation of dissipative Kerr soliton frequency combs, enabling various applications for optical metrology, biological imaging, and coherent telecommunications. Typically, bright soliton generation in Si3N4 devices requires thick (>600 nm) films to fulfill the condition of anomalous dispersion at telecom wavelengths. However, thick films of ultralow-loss Si3N4 (>400 nm) often suffer from high internal stress, leading to cracks. As an alternative approach, thin Si3N4 films (<400 nm) provide the advantage of one-step deposition and are widely applied for commercial use. Here, we provide insights into engineering an integrated Si3N4 structure that achieves optimal effective nonlinearity and maintains a compact footprint. A comparative analysis of Si3N4 resonators with varying waveguide thicknesses is conducted and reveals that a 400-nm thin Si3N4 film emerges as a promising solution that strikes a balance among the aforementioned criteria. Based on a commercially available 400-nm Si3N4 film, we experimentally demonstrate the generation of low-noise coherent dark pulses with a repetition rate of 25 GHz in a multimode Si3N4 resonator. The compact spiral-shaped resonator has a footprint of 0.28 mm2 with a high-quality factor of 4 × 106. Our demonstrated dark combs with mode spacings of tens of GHz have applications in microwave photonics, optical spectroscopy, and telecommunication systems.

Optimal Bezier curve transition for low-loss ultra-compact S-bends.

S-bends with a widening of the width at the mid-bend and a Bezier curve transition are proposed and demonstrated for low-loss S-bends. The increased optical confinement and reduced transition loss enable low insertion loss (IL) and compact S-bends with longitudinal offsets as small as 2.5 µm and a wide operating bandwidth (∼100nm) on a 220 nm thick silicon-on-insulator platform. The simulation results show ILs less than (0.22, 0.20, 0.20, 0.20) dB in the wavelength range of (1.5-1.6) µm, while the minimum ILs are (0.13, 0.13, 0.15, 0.16) dB for lateral offsets of (3, 6, 9, 12) µm. The experimental results show that ILs remain less than (0.41, 0.38, 0.36, 0.39) dB for the mid-bend widening Bezier (MWB) S-bends.

Inverse design of multi-band and wideband waveguide crossings.

Photonic integrated circuits for wideband and multi-band optical communications will need waveguide crossings that operate at all the wavelengths required by the system. In this Letter, we use the modified gradient decedent method to optimize the dual-wavelength band (DWB) crossings on both single- and double-level platforms. On the single-level platform, the simulation results show insertion losses (ILs) less than 0.07 and 0.11 dB for a crossing working at a DWB of 1.5-1.6 and 1.95-2.05 µm. ILs are less than 0.1 and 0.2 dB for a crossing operating in the DWB of 1.5-1.6 and 2.2-2.3 µm. On the double-layer platform, the simulated results show IL less than 0.08 dB across the wavelength range of 1.25-2.25 µm. We experimentally demonstrate the DWB crossing operating at 1.5-1.6 and 2.2-2.3 µm to have IL less than 0.3 and 0.4 dB and crosstalk of -28 and -26dB in the two bands, respectively.

Construction of a novel cell-free tracheal scaffold promoting vascularization for repairing tracheal defects.

Functional vascularization is crucial for maintaining the long-term patency of tissue-engineered trachea and repairing defective trachea. Herein, we report the construction and evaluation of a novel cell-free tissue-engineered tracheal scaffold that effectively promotes vascularization of the graft. Our findings demonstrated that exosomes derived from endothelial progenitor cells (EPC-Exos) enhance the proliferation, migration, and tube formation of endothelial cells. Taking advantage of the angiogenic properties of EPC-Exos, we utilized methacrylate gelatin (GelMA) as a carrier for endothelial progenitor cell exosomes and encapsulated them within a 3D-printed polycaprolactone (PCL) scaffold to fabricate a composite tracheal scaffold. The results demonstrated the excellent angiogenic potential of the methacrylate gelatin/vascular endothelial progenitor cell exosome/polycaprolactone tracheal scaffold. Furthermore, in vivo reconstruction of tracheal defects revealed the capacity of this composite tracheal stent to remodel vasculature. In conclusion, we have successfully developed a novel tracheal stent composed of methacrylate gelatin/vascular endothelial progenitor exosome/polycaprolactone, which effectively promotes angiogenesis for tracheal repair, thereby offering significant prospects for clinical and translational medicine.

Broadband high-Q multimode silicon concentric racetrack resonators for widely tunable Raman lasers.

Multimode silicon resonators with ultralow propagation losses for ultrahigh quality (Q) factors have been attracting attention recently. However, conventional multimode silicon resonators only have high Q factors at certain wavelengths because the Q factors are reduced at wavelengths where fundamental modes and higher-order modes are both near resonances. Here, by implementing a broadband pulley directional coupler and concentric racetracks, we present a broadband high-Q multimode silicon resonator with average loaded Q factors of 1.4 × 106 over a wavelength range of 440 nm (1240-1680 nm). The mutual coupling between the two multimode racetracks can lead to two supermodes that mitigate the reduction in Q factors caused by the mode coupling of the higher-order modes. Based on the broadband high-Q multimode resonator, we experimentally demonstrated a broadly tunable Raman silicon laser with over 516 nm wavelength tuning range (1325-1841 nm), a threshold power of (0.4 ± 0.1) mW and a slope efficiency of (8.5 ± 1.5) % at 25 V reverse bias.

Inhibition of proliferation and transforming growth factor beta3 protein expression by peroxisome proliferators-activated receptor gamma ligands in human uterine leiomyoma cells.

BACKGROUND: Rosiglitazone is known as the most potent and specific peroxisome proliferators-activated receptor gamma (PPAR-gamma) ligand. It has potentially far-reaching effects on pathophysiological processes, from cancer to atherosclerosis and diabetes. However, it is not clear whether rosiglitazone affects the protein expression of transforming growth factor beta3 (TGF-beta3) and the cell proliferation in human uterine leiomyoma cells in vitro. METHODS: Human uterine leiomyoma tissues were dissected and cultured. Cells were divided into 5 groups: one control group and other four groups with different concentrations of rosiglitazone (10(-7), 10(-8), 10(-9) and 10(-10) mol/L). Cells were cultured for 72 hours in serum-free Dulbecco's modified Eagle's medium. MTT reduction assay was used to detect the cell proliferation. Reverse transcription polymerase chain reaction (RT-PCR) was used to detect the mRNA expression of PPAR-gamma and TGF-beta3. Immunofluorescence staining was used to detect the expressions of PPAR-gamma and TGF-beta3 proteins. RESULTS: MTT reduction assay indicated that the treatment with rosiglitazone (from 10(-7) to 10(-9) mol/L) resulted in an inhibition of the cell growths after 72 hours (P < 0.01). RT-PCR analysis revealed that 10(-7) mol/L rosiglitazone significantly affected the gene expression at 72-hour: PPAR-gamma mRNA expression was up-regulated and TGF-beta3 mRNA was down-regulated and rosiglitazone at the concentration of 10(-7) mol/L affected these most effectively (P < 0.01). Immunofluorescence staining demonstrated that treatment with 10(-7) mol/L rosiglitazone resulted in the significant changes of PPAR-gamma and TGF-beta3 protein expressions compared with the other treatment groups and the control group at 72-hour (P < 0.01). All the effects of rosiglitazone on uterine leiomyoma cells were dose- and time-dependent in vitro. CONCLUSIONS: The present study demonstrates that the PPAR-gamma activator, rosiglitazone, inhibits the cell proliferation partly through the regulations of PPAR-gamma and TGF-beta3 expressions. The cross-talk between the signal pathways of PPAR-gamma and TGF-beta3 may be involved in the process.