High-precision method for submicron-aperture fiber point-diffraction wavefront measurement.

It is a key issue to measure the point-diffraction wavefront error, which determines the achievable accuracy of point-diffraction interferometer (PDI). A high-precision method based on shearing interferometry is proposed to measure submicron-aperture fiber point-diffraction wavefront with high numerical aperture (NA). To obtain the true shearing point-diffraction wavefront, a double-step calibration method based on three-dimensional coordinate reconstruction and symmetric lateral displacement compensation is proposed to calibrate the geometric aberration in the case of high NA and large lateral wavefront displacement. The calibration can be carried out without any prior knowledge about the system configuration parameters. With the true shearing wavefront, the differential Zernike polynomials fitting method is applied to reconstruct the point-diffraction wavefront. Numerical simulation and experiments have been carried out to demonstrate the accuracy and feasibility of the proposed measurement method, and a good measurement accuracy is achieved.