Multi-Wavelength Phase Unwrapping: A Versatile Tool For Extending The Measurement Range, Breaking The Nyquist Limit, And Encrypting Optical Communications

Multi-wavelength phase unwrapping techniques have traditionally been used to unwrap the phase at the shortest measurement wavelength, where numerous techniques have been developed with distinct advantages for a given application. Nevertheless, multi-wavelength techniques are more than phase unwrapping approaches: super-sensitive multi wavelength interferometers have a lower uncertainty than conventional interferometers, multi-wavelength techniques can break the Nyquist limit and thereby relax the requirements on the measurement system, and multi-wavelength techniques have also unconventional applications as e.g. optical encryption. This work discusses different multi-wavelength techniques, derives new noise criteria with no approximations, and outlines important, but still little researched areas of multi -wavelength phase unwrapping techniques.