An end-point optical fiber interferometer using thin-film retroreflectors is introduced, which is very simple to construct and align. The use of single-mode and multimode fibers for illumination and signal reception, respectively, greatly increases optical efficiency and phase stability. In particular, measurements of essentially static phenomena are made possible. Limitations remaining on the use of thin-film retroreflectors as a coupling mechanism for interferometric fiber sensors are investigated. Error sources include finite numerical aperture effects, multiple beam interferences, and thermally pumped mechanical motions. © 1984 Optical Society of America.