采用内、外曲线分别为圆形弯曲和欧拉-圆形弯曲曲线，以及内、外曲线分别为欧拉-圆形弯曲和欧拉弯曲曲线，提出并优化了两种曲率与宽度双渐变的硅基单模弯曲光波导结构。采用有限时域差分对提出的两种弯曲光波导结构进行了仿真优化，并与圆形弯曲、欧拉弯曲、欧拉-圆形弯曲和贝塞尔弯曲光波导的性能进行了比较。结果表明在等效弯曲半径为2 μm时，内、外曲线分别为圆形弯曲和欧拉-圆形弯曲的弯曲光波导损耗值仅为0.005 6 dB/90°，且具有低的损耗波长相关性。

Photonic structures with topological edge states and resonance loops are both important in optical communication systems, but they are usually two separate structures. In order to obtain a photonic system combining properties from both, we design multiple-layer nested photonic topological structures. The nested topological loops not only have topological protection immune to structural disorder and defects, but also possess both the properties of unidirectional propagation and loop resonance. Through mode analysis and simulations, we find that the transport can form diverse circulation loops. Each loop has its own resonance frequencies and can be solely excited in the nested layered structure through choosing its resonance frequencies. As a result, this work shows great application prospects in the area of reconfigurable photonic circuits.

We investigate femtosecond laser trapping dynamics of two-photon absorbing hollow-core nanoparticles with different volume fractions and two-photon absorption (TPA) coefficients. Numerical simulations show that the hollow-core particles with low and high-volume fractions can easily be trapped and bounced by the tightly focused Gaussian laser pulses, respectively. Further studies show that the hollow-core particles with and without TPA can be identified, because the TPA effect enhances the radiation force, and subsequently the longitudinal force destabilizes the trap by pushing the particle away from the focal point. The results may find direct applications in particle sorting and characterizing the TPA coefficient of single nanoparticles.

Understanding the nonlinear optical effect of novel materials plays a crucial role in the fields of photonics and optoelectronics. Herein, we theoretically and experimentally investigate the simultaneous presence of third-order locally refractive nonlinearity and thermally induced nonlocal nonlinearity saturation. We present analytical expressions for the closed-aperture Z-scan trace and the number of spatial self-phase modulation (SSPM) rings, which allows one to unambiguously and conveniently separate the contributions of local and nonlocal nonlinear refraction in the case that both effects occur simultaneously. As a test, we study both the local and thermally induced nonlocal nonlinear refraction in fullerene/toluene solution by performing continuous-wave Z-scan and SSPM measurements at two different wavelengths. This work enriches the understanding of the physical mechanism of the optical nonlinear refraction effect in solution dispersions of nanomaterials, which can be exploited for nonlinear photonic devices.

Due to the excellent electro-optic properties of lead lanthanum zirconium titanate ((Pb,La)(Zr,Ti)O3, PLZT), compact 1×2 and 1×4 PLZT optical switches with a high response speed are proposed and fabricated successfully in this Letter. By introducing a thin isolating layer between the waveguides and the electrodes, the absorption loss of the fabricated 1×2 PLZT switch caused by the electrodes is reduced 8.9 dB with a relatively low driving voltage. The 1×2 PLZT switch shows an insertion loss of 18.3 dB and crosstalk of 20.5 dB at an applied voltage of 9.5 V. The fabricated 1×4 switch array shows an insertion loss of 20.7 dB and a crosstalk of 20.5 dB at an applied voltage of 13 V. The response time of the switches is less than 27 ns, and the device’s size is only 15 mm×6 mm. The switches can be used in optical communication systems.