Many Methods have been developed to .easure displace.ent with high accuracy, for
exap1e, with a dual frequency laser interferometer (AC interferometer) and an classic
interferoseter (DC interferoeter) which use a stabilized laser and fringe counter, and
an AC interfero.eter has ore advantage over the DC one.
An AC interfero.eter with a Zee.an laser can get a high resolution, in the order of
nanoMeters, but its resolution extension liRited by nonlinear relation between phase and
displace.ent which caused by the two-frequency coRponents in interferoaeter. Because
the fundaaental length scale of the interferometer is the wavelength of the light source
in the air. The accuracy of an interferoeter is li.ited by the operating envireaent,
teRperature, husidity, pressure, etc. because the aiRs of interferoseters expose in the
air. A high resolution optical fiber heterodyne interfermeter is described in the paper.