Fabrication of Fresnel zone plate in chalcogenide glass and fiber end with femtosecond laser direct writing

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• High quality Ge-As-S glass and low loss fibers were prepared. • FZP working in visible and near infrared bands was fabricated on Ge-As-S glasses surface by laser direct writing. • With a well-designed FZP on the fiber end face, ChG fiber can achieve excellent self-focusing effect without the collimating and focusing lens. Chalcogenide glass (ChG) has excellent optical properties in the mid-infrared range. The micro-optical fiber devices made of ChG play a strong part in various infrared sensing and detection fields. In this work, Fresnel zone plate (FZP) was fabricated on the Ge-As-S ChG surface and the end face of ChG fiber through femtosecond laser direct writing. FZP with high optical quality was obtained by optimizing the laser writing parameters. Clear focusing pattern can be observed in the visible and infrared bands with the prepared FZP. The full width at half maximum (FWHM) of laser beam with wavelength of 1550 nm is recorded to be 10.39 μm at the focus of FZP, and the numerical aperture (NA) is 0.122. With a well-designed FZP on the fiber end face, the ChG fiber can achieve a self-focusing effect without the collimating and focusing lens. The FWHM of the 1550 nm laser beam at the focus is measured to be 7.46 μm, and NA is 0.162. The combination of FZP and ChG fiber can make the structure of the optical fiber more compact and has potential application value in enhancing the interaction between light and material in the infrared band.