Method for extending focal depth based on amplitude modulation, polarization and phase modulation and device thereof

The invention discloses a method for extending focal depth, including that: Bessel-Gauss radial polarized light passes through an annular diaphragm, so as to modulate amplitude and split the light into two light beams; one light beam is subject to 0-Phi phase coding and then are incident into the same optical beam combining device with the other light beam after optical reflex, so as to form a combined coaxial light beam, and then lens focusing is carried out, thus obtaining the extended focal depth spot. The invention also discloses a device for extending focal depth, comprising a light source generating Bessel-Gauss radial polarized light, an annular diaphragm, a beam splitter, a 0/Phi phase plate, an optical reflex device, an optical beam combining device and an apochromatism focusing lens. In the method and device, Bessel-Gauss laser is taken as a work light beam, the focal depth of extended focal spot is more than 8lambda, the focal spot can be less than diffraction limit of system, and light distributio