We report for the first time on optical waveguides in zinc oxide (ZnO) crystals fabricated by femtosecond laser direct writing. The confocal Raman microscopy under 488 nm laser excitation is used to investigate the micro-modifications of the laser irradiation, and guiding properties are studied via the end-face coupling at 632.8 nm. The mode modulation has been achieved by the adjustment of laser writing parameters. A minimum propagation loss of ∼6 dB/cm is obtained for the double-line waveguide structures. A Y-branch waveguide beam splitter is also fabricated, reaching a splitting ratio of nearly 1:1. The original optical properties in the guiding region have been well preserved, according to the confocal Raman investigation, which suggests potential applications of the ZnO waveguides for integrated photonics and nonlinear optics.
The size‐ and shape‐dependent localized surface plasmon properties of metallic nanoparticles (NPs) enable nanoscale‐enhanced near‐field applications in a wide range of fields, including spectroscopy, nonlinear optics, and sensing. Orderly assembled NPs can construct plasmonic metamaterials for light manipulation at a subwavelength scale, exhibiting new collective properties in resonant modes regulated by plasmon coupling between their fundamental components. Despite the recognition of its significant advantages in photonics integration, plasmonic‐based tailored optical responses for practical applications have remained elusive due to limitations in scaling up processes, as neither etching nor assembly can design and fabricate embedded plasmonic devices into functional devices/structures. Here, the assembly of plasmonic NPs is demonstrated by ultrafast laser‐induced writing‐on‐demand inside solids, tailoring their distribution and sizes. By controlling the laser scanning speed, the in situ redistribution of NPs is observed. Plasmon mediated local energy deposition is considered as the main mechanism driving nano‐patterning at a subwavelength range. A direct nano‐printing is realized by utilizing the resonant optical response of laser‐modified NP structures/patterns. This work paves the way for directly induced NP composite structures inside transparent materials at a well‐defined and controlled depth for plasmonic applications.
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