Coherence and information in a fiber interferometer

Abstract: We present an experiment based on a fibered Mach-Zehnder interferometer. The aim is to familiarize students with fibered optics and interferometry, and to improve their understanding of optical amplification. The laboratory project has two parts: in a first part, the students modulate the optical path of the interferometer to study the spectra of light sources via Fourier Transform Spectroscopy. In a second part, an optical amplifier is placed in one or both arms of the interferometer. The set-up uses monomode, polarization-maintaining fibers that propagate light of 1.5 $\mu$m wavelength. In this article, we describe the set-up and the analysis of the measurements, and we present results from student reports. All components are part of standard optical catalogues. Even though the experiment is based on fibered optics, it is robust to manipulation (it is however relatively expensive $\sim \pounds 15\,000$): We describe our efforts to protect the components from damage. This experiment is now offered as a 2-week project for third-year Physics students. The experiment may likewise be of value in early graduate level laboratory courses.