  Fringe-projection profilometry with 1 camera and 1 fringe-projector is a
well-known and widely used technique in optical metrology. Spatial-frequency
multiplexing interferometry with several spatial-carriers having
non-overlapping spatial-spectra is also well known and productive in optical
metrology. In this paper we propose temporal-multiplexing phase-shifting
interferometry applied to profilometry. That is, instead of having
fringe-patterns with well separated spatial-spectra, we propose instead to
separate the fringe information in the temporal-spectra. In other words, we may
have overlapping spatial-spectra, but separated in the temporal-spectra by
frequency multiplexing. Using 1-camera and several fringe-projectors one
minimizes the object shadows and specular reflections from the digitizing
solid. Temporal multiplexing profilometry allows us to illuminate the object
from several projectors turned-on simultaneously. In previous phase-shifting
co-phased profilometry, the projectors were turned-on and off sequentially. As
seen in this work temporal-multiplexing allow us to demodulate the several
fringe-patterns without crosstalk from other simultaneously projected fringes.
This is entirely analogous to having several television stations broadcasting
simultaneously, each TV-transmitter having its own broadcasting frequency. A
given TV-receiver tunes into a single TV-station and filter-out all other
broadcasters. Following this analogy, each fringe-projector must have its own
temporal broadcasting frequency to remain well separated from all other
projectors in the time-spectra domain. In addition to the general theory
presented, we assess its feasibility with experimental results.
