Telescope simulator using CGH and deformable mirror

Abstract

Test and characterization of the optical performance for the novel and advanced sub-optical-systems, as designed for large astronomical optical telescopes, often need to be carried out with the simulated telescope wavefront in the labs before working with the telescopes. Computer generated hologram (CGH) is a simple solution for monochromatic wavefront generation. Severely off-axis aberrated wavefront coming from the one-mirror or two-mirrors telescope can be generated by CGH with symmetric and un-symmetric terms of the Zernike polynomials. The chrome mask and/or the binary CGHs have been made as the CFH telescope simulator. The unused diffraction orders of the CGH can be completely eliminated by adding the carrier frequency on the phase function of the designed CGHs. The test results that are given with the fabricated CGH simulator have a good agreement with that of the simulation. The aberrated wavefront of the simulated telescope can be also generated by the ferrofluid deformable mirror (FDM) at low cost. A 100-mm FDM is designed and built with 271 actuators for performance evaluation. The revolution symmetric aberrated wavefront has been experimentally generated and proven by the FDM prototyping. The simulation and test results for the prototyping FDM are both given in this paper.