Metalens, a novel class of optical devices based on metasurfaces, exhibit exceptional optical properties and superior wavefront control capabilities. These characteristics have enabled the development of ultra-thin devices with broad applications in imaging, spectroscopy, optical communications, and photodetection. This paper presents the realization of a near-infrared (IR) metalens used as a beam expander. Our approach effectively achieves optical beam expansion functionality. Initially, we designed the geometric structure of the metalens on a silicon platform, leveraging its design principles. Numerical simulations confirmed that the proposed structure can achieve effective lens focusing. Subsequently, we fabricated the metalens using micro-nanofabrication techniques and validated its performance with a customized testing system. The results demonstrate that the near-IR metalens exhibits excellent focusing performance at a working wavelength of 1550 nm. It can expand and collimate the output beam of a single-mode fiber, thereby verifying the effectiveness and practicality of our design. This design can replace traditional lenses in fiber beam expansion, achieving a thinner profile. Additionally, arrayed metalenses can provide a solution for beam expansion in multi-core fibers, reducing alignment workload and enhancing alignment precision.
We propose and analyze a novel compact modulator on a silicon-on-insulator (SOI) waveguide with the modulation mechanisms of free-carrier plasma dispersion effect. The free carriers are produced by two-photon absorption (TPA) effect, and to understand the change process of free carriers in the silicon, we carried out theoretical simulation and calculation on it, which based on the coupling wave propagation equation and boundary conditions. Free carriers density of 2.5×1017/cm3 could be obtained under pump power of 50 mW and the refractive index change Δn of 9.24×10-4 are achieved. The result indicates that TPA-induced free carriers could be effectively change the effective refractive index of the silicon and further realize the modulation application in silicon modulators.
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