The Interference Phase Loop is an interferometer with feedback of the
output intensity to a phase modulator in one of the interferometer arm
s. When a spatial optical phase modulator is used, the modulator phase
distribution approximates to the conjugate of the spatial phase distr
ibution in the interferometer, and so the device has potential for app
lication in adaptive optics. We have implemented an interference phase
loop using a high-resolution liquid crystal spatial light modulator (
PAL-SLM) and a common path radial shearing interferometer. We show how
the system can be analysed in simple terms, derive some design and op
erating criteria, and demonstrate diffraction-limited real-time aberra
tion correction of arbitrary input wavefronts using the system. Becaus
e of the nature of the interferometer used, our system has the potenti
al to operate in white light.