A new achromatic optical phase shifter based on a frequency-domain delay line

Summary form only given. In many interferometric optical systems, a controllable or variable phase delay between interfering beams is required. Conventionally, such a phase delay is generated by variation of the optical length difference between two paths in an interferometer. The resulting phase delay depends on wavelength, which is undesirable in many broadband interferometric schemes such as white-light interferometry. Pancharatnam proposed and demonstrated an alternative method of generating a (geometric) phase delay through the effect of an analyzer on two coherent light beams with different states of polarization. We propose and demonstrate a novel alternative with important advantages over previous implementations of the geometric phase shifter including high-speed, polarisation insensitivity, and generation of a phase delay that can always be determined absolutely and has a large, bounded maximum value.