A Photonic Method for Measuring the AM Noise of Periodic Electrical Signals

In this work, we demonstrate mode partition noise in the radio-frequency spectra of periodic signals generated using electrical pattern generators that are often used in digital optical communications and error testing. This effect makes the measurement of the amplitude modulation noise of the repetitive signal through its single sideband (SSB) power spectral density (PSD) at its fundamental frequency inaccurate. This is demonstrated for a square wave, where the dependence of the SSB PSD on the duty cycle of the signal is experimentally shown. To alleviate this ambiguity, we propose and experimentally demonstrate a photonic up-convert and down-convert method that results in invariant SSB power spectra at the signal´s fundamental frequency.