An embodiment of an apparatus for estimating a parameter includes a light source configured to emit an optical signal, and an interferometer including a first reflector assembly having at least one reflective surface and a second reflector assembly having a plurality of individual reflective surfaces facing the at least one reflective surface. At least one of the first reflective assembly and the second reflector assembly is moveable in response to a stimulus, the plurality of individual reflective surfaces disposed at a fixed location relative to each other, each individual reflective surface defining a different optical cavity length relative to the first reflector assembly.