Abstract

A system, which is able to determine pump induced phase modulation in Erdoped fibres for phase shifts ϕ_p ranging from ~ π/20 to several π, has been developed. The system (see Fig. 1) consists of a Mach–Zehnder interferometer using a polarization maintaining 3-dB fibre coupler. One arm of the interferometer includes an Er-doped fibre pumped by a 980-nm Ti:sapphire laser. Light from a tunable semiconductor signal laser (λ_s = 1.5 μm–1.6 μm) is coupled to both interferometric arms. A differential detection scheme improves the sensitivity and eliminates influence of amplified spontaneous emission. The phase in the reference arm is linearly modulated in time, ϕ_m = ωt, by means of a piezo-electric crystal.

© 1994 IEEE