  Wavefront sensing from an extended object is a challenging task since the
phase to be sensed is disturbed by the phase generated from the structure of
the extended object. To address this problem, a general wavefront sensor was
proposed. The hardware of the sensor consists of a field lens, a collimating
lens, a lenslet array, and a camera. The idea for its algorithm is to eliminate
the phase caused by the extended object and reconstruct the point spread
function through each lenslet. As a result, the scenario of wavefront sensing
from an extended object has been converted to the conventional one from a point
source. Numerical simulations and experiments both verify the feasibility and
the accuracy of the proposed sensor.
