Experimental study of balanced optical homodyne and heterodyne detection by controlling sideband modulation

We experimentally study optical homodyne and heterodyne detections with a same setup, which is flexible to manipulate the signal sideband modulation. When the modulation only generate a single signal sideband, the light field measurement by mixing the single sideband at ω₀+Ω with a strong local oscillator at the carrier frequency ω₀ on a beam splitter become balanced heterodyne detection. When two signal sidebands at ω₀pmΩ are generated and the relative phase of the two sidebands is locked, this measurement corresponds to optical balanced homodyne detection. With this setup, we may confirm directly that the signal-to-noise ratio with heterodyne detection is two-fold worse than that with homodyne detection. This work will have important applications in quantum state measurement and quantum information.