Abstract
We have investigated balanced heterodyne detection in applications where laser intensity fluctuations are the dominant noise source, as, for example, in laser Doppler velocimetry with a He-Ne laser. The suppression of excess noise in comparison with a single receiver detection system is analysed theoretically. In our heterodyne experiment we have compared two different fibre-optic Mach-Zehnder interferometers, both with single-mode polarization-preserving fibres, one in integrated form using a directional coupler, the other one with a dielectric beam-splitter as the optical mixing element. With the former we have verified the theoretical results; with the latter we have demonstrated that with a good balance the fundamental short noise detection limit can be reached.
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