Abstract: A focal-length measuring apparatus for a sub-wavelength optical imaging device includes a laser, a beam-expanding and collimating system, a sub-wavelength optical imaging device, and a nanoscale stepped height standard sample block. The nanoscale stepped height standard sample block is connected to a power device, and the power device is connected to a computer control system. The nanoscale stepped height standard sample block is coated with a photoresist and includes a plurality of steps arranged at equal intervals Among all the steps, the heights of the steps gradually increase from a middle step to an upper side, and the values of the corresponding focal lengths decrease. While, the heights of the steps gradually decrease from the middle step to a lower side, and values of corresponding focal lengths increase. A wavelength of the laser is equal to a designed wavelength of an input light source of the sub-wavelength optical imaging device.

Abstract: A focal-length measuring apparatus for a sub-wavelength optical imaging device includes a laser, a beam-expanding and collimating system, a sub-wavelength optical imaging device, and a nanoscale stepped height standard sample block. The nanoscale stepped height standard sample block is connected to a power device, and the power device is connected to a computer control system. The nanoscale stepped height standard sample block is coated with a photoresist and includes a plurality of steps arranged at equal intervals Among all the steps, the heights of the steps gradually increase from a middle step to an upper side, and the values of the corresponding focal lengths decrease. While, the heights of the steps gradually decrease from the middle step to a lower side, and values of corresponding focal lengths increase. A wavelength of the laser is equal to a designed wavelength of an input light source of the sub-wavelength optical imaging device.