Phase-Noise Analysis of Optically Generated Millimeter-Wave Signals With External Optical Modulation Techniques

In this paper, the phase-noise performance of optically generated electrical signals based on external optical modulation techniques is investigated theoretically and experimentally. Mathematical models are developed to represent perturbations on the transmitted optical signal caused by the phase fluctuations of the electrical drive signal applied to the external modulator and the optical carrier that feeds the external modulator. Closed-form expressions of the power spectral density (PSD) for the electrical signals, generated both locally and remotely, are derived. The calculated PSD of the locally generated electrical signal indicates that its phase noise is determined only by the phase noise of the electrical drive signal. The PSD of the remotely generated signal shows that its spectral quality is also affected by the chromatic dispersion of the fiber and the optical carrier linewidth. An experimental setup that can generate a millimeter-wave (mm-wave) signal, continuously tunable from 32 to 60 GHz using an electrical drive signal tunable from 8 to 15 GHz, is built. The spectra of the generated millimeter-wave signal are measured for both locally and remotely generated electrical signals, with optical carriers of different linewidths. The theoretical results agree with the experimental measurements