Optical Phase Unwrapping in the Presence of Branch Points
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH
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Strong turbulence causes phase discontinuities known as branch points in an optical field. These discontinuities complicate the phase unwrapping necessary to apply phase corrections onto a deformable mirror in an adaptive optics AO system. This paper proposes a non-optimal but effective and implementable phase unwrapping method for optical fields containing branch points. This method first applies a least-squares LS unwrapper to the field which isolates and unwraps the LS component of the field. Four modulo-2-pi-equivalent non-LS components are created by subtracting the LS component from the original field and then restricting the result to differing ranges. 2-pi phase jumps known as branch cuts are isolated to the non-LS components and the different non-LS realizations have different branch cut placements. The best placement of branch cuts is determined by finding the non-LS realization with the lowest normalized cut length and adding it to the LS component.