Use of single-mode fibers in an optical Interferometric array

Abstract

We have found that single-mode fiber optics can provide a simple and effective means of interfering the light collected by separate telescopes. Using several meters of fiber in each arm of a Mach-Zehnder interferometer, we observed the effects of dispersion, temperature, and birefringence on the broadband interference pattern. Dispersion and temperature effects are slow, differential (seen in each arm of the interferometer), and easily corrected. The much more serious problems caused by birefringence, which can have wavelength-dependent, wavelength-independent, and temporal components, can be eliminated by monochromatically monitoring the polarization in low-birefringence fiber or by using high-birefringence fiber. In the low-birefringence case, polarization control can be accomplished by elastooptically inducing birefringence,1 and in the high-birefringence case, two detectors, one for each eigenpo-larization, will be needed. In either case, the visibility of interference fringes can be made independent of effects introduced by the fiber optics.