Phase measurement through sinusoidal excitation with application to multi-wavelength interferometry

In this paper we present a novel approach to obtain interference phase measurements using sinusoidal modulation in order to obtain high resolution data at high temporal bandwidths. The use of classical phase stepping techniques generates ringing in PZT-based phase modulators and hence limits the temporal bandwidth at which reliable phase data can be obtained. Signal processing techniques are introduced to extract intensity measurements at any required phase step and hence offer compatibility with existing linear phase shifting interferometry algorithms. It was found that, under high frequency and/or high amplitude sinusoidal excitation, the PZT phase modulator could exhibit a nonlinear response. Strategies are introduced to mitigate these effects on the calculated interference phase. Experimental data is presented demonstrating a phase resolution of 1/600th of a fringe at a temporal bandwidth of 8150 Hz when using the Carre phase stepping algorithm. Data from a multi-wavelength fibre interferometer with sinusoidal modulation to obtain the wrapped phase measurements are also presented where a dynamic range of 1 part in 2 × 106 was achieved.