Asymmetric Millimeter-Wave Spectrum in Laser Mode Partition Noise Generated by Fiber Transmission

In this article, we report on the asymmetry of intensity noise spectrum at millimeter-wave (mm-wave) heterodyne carriers. Passively mode-locked laser diode (PMLLD) is employed for a low phase noise mm-wave photonic generation using direct detection. This optical source produces an excess intensity noise known by laser mode partition noise (LMPN) in which its spectrum usually appears as symmetric double side-bands around the beat-note. The propagation over a dispersive medium such as optical fiber can modify the spectral behavior and profile of the LMPN. This article explores the impact of fiber transmission on the distortions of the LMPN in optical and electrical spectrum. Experimental results reveal, for the first time, that the LMPN symmetry is converted to an asymmetric deformation on the generated beating carrier. The mathematical model and numerical simulation are presented to give hints for analyzing this phenomenon. The findings of the simulations and measurements demonstrate the main role of second- and third-order fiber dispersion on the LMPN profile.