Fig. 1. Sketch of femtosecond Bessel beam direct writing device (LN：LiNbO₃)

Fig. 2. Schematic of microholes array fabrication

Fig. 3. Influence of average laser power on microholes morphological characteristics. (a)(d) Images of microhole entrance and corresponding cross-section at average laser power of 0.29, 0.62, 0.76, and 1.14 mW, respectively; (e) influence of average laser power on entrance diameter and average diameter of microhole; (f) influence of average laser power on depth and aspect ratio of microhole

Fig. 4. Simulation of intensity distribution of Bessel beam after focusing

Fig. 5. Influence of relative position of Bessel beam focus area and material on microhole morphology

Fig. 6. Femtosecond Bessel beam direct write periodic microhole arrays. (a) Optical microscope image of photonic-crystal based on microhole array; (b) optical microscope image and corresponded SEM image of microhole cross-section; (c) schematic of filtering performance test of photonic-crystal (the double arrows in the figure indicate polarization direction of the light); (d) test result of photonic-crystal filtering performance; (e) transmission spectra of photonic-crystal sample