Measurement of the pressure sensitivity of single-mode optical-fibre phase modulators

Theory predicts that, at a wavelength of 0.6328 ¿¿m, the pressure sensitivities of silica and borosilicate glass single-mode optical-fibre phase modulators are 6.4 rad/m interaction length per bar of pressure, and 44 rad/m/bar, respectively. The experimental technique described for measuring this pressure sensitivity uses a Raman-Nath water diffraction cell to produce an acoustic wave of calculable pressure amplitude, and a Mach-Zehnder heterodyning interferometer for measuring the fibre-optic phase-modulation index. The experimental measurements of pressure sensitivity are in sensible agreement with theory.