We experimentally study optical homodyne and heterodyne detections with the same setup, which is flexible to manipulate the signal sideband modulation. When the modulation only generates a single signal sideband, the light field measurement by mixing the single sideband at ω 0 ± Ω with a strong local oscillator at the carrier frequency ω 0 on a beam splitter becomes balanced heterodyne detection. When two signal sidebands at ω 0 ± Ω 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. homodyne detection, heterodyne detection, sideband modulation, the signal-to-noise ratio PACS number(s): 01.50.Pa, 03.65.Ta, 42.50.Lc Citation: Li W, Yu X D, Meng Z M, et al. Experimental study of balanced optical homodyne and heterodyne detection by controlling sideband modulation. Sci