Interferometer having a short coherence length light source and means for identifying interference fringes

A measuring device comprising a short coherence length light source, interferometer means arranged to receive light from said source and to produce a first and second sequential series of interference fringes in which the contrast between bright and dark fringes varies along each of the series, the contrast in said first series varying in the opposite sequential sense to that in said second series, first means for detecting said fringes of said first series and for providing a first signal having a first value which is derived from different fringes in said first series for different values of a measurand and whose first value varies as a function of the brightness of the fringes from which said first signal is derived, second means for detecting said fringes in said second series and for providing a second signal having a second value which is derived from different fringes in said second series for different values of said measurand and whose second value varies as a function of the brightness of the fringes from which said second signal is derived, and means for identifying from said first and second values of said first and second signals the identity of the fringes from which said first and second signals are derived and for providing, on the basis of said identity, an indication of the value of said measurand.

A measuring device comprising a short coherence length light source, interferometer means arranged to receive light from said source and to produce a first and a second series of interference fringes, whose contrast between adjacent bright and dark fringes varies over a measuring range as a function of a measurand, said contrast in one of said series varying with said measurand in the sense opposite to said contrast in the other said series, means for detecting said fringes, and means for deriving from said detecting means a signal which is a function of the value of said contrast in each said series within said measuring range and is thereby indicative of the value to be measured.