Mach-Zehnder fiber interferometer for measuring the spectral characteristics of single-frequency semiconductor lasers of the 1.32-μm and 1.55-μm range

This paper describes the design of a Mach-Zehnder fiber interferometer based on a single-mode optical fiber with a path difference from 2 m to 10.3 km. The phase modulator of the interferometer is made in the form of a coil of fiber on a metallic cylinder, in which acoustic vibrations are excited a piezoelectric converter. The results of interferometric studies are presented for commercial single-frequency semiconductor lasers with fiber Bragg gratings (FBGs) of the 1.32 and 1.55-mu m range. It is shown that the short-term line width (a few seconds to a few tens of seconds) of the spectrum of semiconductor lasers with fiber Bragg reflectors is less than 20 kHz; in this case, such lasers are not strictly single-frequency lasers and based at several (two or more) closely spaced spectral lines. (c) 2008 Optical Society of America.