Creation of super-length optical tube by phase modulated azimuthally polarized beam with multi-zone phase filter

We suggest a new approach to utilize a multi-zone phase filter along with a high NA lens axicon to accomplish a subwavelength focal hole with large uniform focal depth by means of azimuthally polarized Bessel–Gaussian beam. The intensity distributions are obtained and calculated based on the vector diffraction theory, the recommended system generates a subwavelength super-length optical tube with a sub diffraction beam size of 0.494 λ and long focal depth is approximately 63.6 λ in free space. We also established that the focal depth and sub diffraction beam size is dependent relative on focusing condition of the numerical aperture. The authors presume such a high intense tube beam may perhaps find the applications in atom optics, optical manipulations, optical trapping and optical processing technologies.