)1 Radio and Optical Communications Research Laboratory, School of Electronic Engineering, Dublin City University, Glasnevin Dublin 9, Ireland; [EMAIL_ADDRESS] (Y.L. ); [EMAIL_ADDRESS] (L.B. )1 Radio and Optical Communications Research Laboratory, School of Electronic Engineering, Dublin City University, Glasnevin Dublin 9, Ireland; [EMAIL_ADDRESS] (Y.L. ); [EMAIL_ADDRESS] (L.B. )1 Radio and Optical Communications Research Laboratory, School of Electronic Engineering, Dublin City University, Glasnevin Dublin 9, Ireland; [EMAIL_ADDRESS] (Y.L. ); [EMAIL_ADDRESS] (L.B. )1 Radio and Optical Communications Research Laboratory, School of Electronic Engineering, Dublin City University, Glasnevin Dublin 9, Ireland; [EMAIL_ADDRESS] (Y.L. ); [EMAIL_ADDRESS] (L.B. )1 Radio and Optical Communications Research Laboratory, School of Electronic Engineering, Dublin City University, Glasnevin Dublin 9, Ireland; [EMAIL_ADDRESS] (Y.L. ); [EMAIL_ADDRESS] (L.B. )1 Radio and Optical Communications Research Laboratory, School of Electronic Engineering, Dublin City University, Glasnevin Dublin 9, Ireland; [EMAIL_ADDRESS] (Y.L. ); [EMAIL_ADDRESS] (L.B. )1 Radio and Optical Communications Research Laboratory, School of Electronic Engineering, Dublin City University, Glasnevin Dublin 9, Ireland; [EMAIL_ADDRESS] (Y.L. ); [EMAIL_ADDRESS] (L.B. )1 Radio and Optical Communications Research Laboratory, School of Electronic Engineering, Dublin City University, Glasnevin Dublin 9, Ireland; [EMAIL_ADDRESS] (Y.L. ); [EMAIL_ADDRESS] (L.B. )1 Radio and Optical Communications Research Laboratory, School of Electronic Engineering, Dublin City University Glasnevin Dublin 9, Ireland; [EMAIL_ADDRESS] (Y.L. ); [EMAIL_ADDRESS] (L.B. )1 Radio and Optical Communications Research Laboratory, School of Electronic Engineering, Dublin City University, Glasnevin Dublin 9, Ireland; [EMAIL_ADDRESS] (Y.L. ); [EMAIL_ADDRESS] (L.B. )1 Radio and Optical Communications Research Laboratory, School of Electronic Engineering, Dublin City University, Glasnevin Dublin 9, Ireland; [EMAIL_ADDRESS] (Y.L. ); [EMAIL_ADDRESS] (L.B. )1 Radio and Optical Communications Research Laboratory, School of Electronic Engineering, Dublin City University, Glasnevin Dublin 9, Ireland; yi. this paper we shall refer to this noise as excess FM-noise, because this noise is in addition to the usual Schawlow-Townes-Henry phase noise present in all semiconductor lasers [23]. For communication systems that employ such tunable lasers, the digital signal processing in the receiver needs to account for the instantaneous frequency drifts that occur on microsecond timescales. Adopting second-order phase-locked loops [19] or employing doubly differential phase encoding [17] can overcome the random frequency offsets caused by the excess FM-noise of DBR-style tunable lasers. Despite the numerous observations of this excess frequency noise, the spectral profile of this frequency noise follows the same dynamics as the modulation capabilities of the tunable passive sections. We have postulated this in previous work, and attributed contributions from shot noise and dynamic carrier generation to this excess FM-noise [18]. Apart from a detailed simulation work that includes shot noise and random carrier generation [20], to date there has been no explicit confirmation that quantifies the contribution from carrier recombination and shot noise to the FM-noise of tunable lasers. \"Shot noise\" refers to the randomness of the electronic current arising from the discreetness of electronic charge, and \"random carrier recombination\" refers to random recombination of electrons and holes within the laser waveguide. In this study, we quantified the contribution from current shot noise and carrier recombination in the passive tuning sections to the FM-noise of tunable lasers. We numerically solved for the carrier density rate equation in the passive tuning sections, and invoked quasi-static laser dynamics to transform the calculated carrier noise fluctuations into FM-noise spectral density (SD) calculations.