Nonlinear coupling of relative intensity noise from pump to a fiber ring laser mode-locked with carbon nanotubes

Abstract

Pump relative intensity noise (RIN) has been recognized as a major source of noise in mode-locked lasers. The coupling of RIN from the pump to the output of a passively mode-locked fiber laser (PMFL) is systematically investigated using a pump modulation technique. It is found that the linear RIN coupling ratio from pump to PMFL is decreased with an increase in modulation frequency and is independent of modulation power. Moreover, the nonlinear RIN coupling from pump to PMFL is clearly demonstrated with a square wave modulated pump. The nonlinear RIN coupling ratio is noise power dependent. An exponential decay model based on the view of gain modulation is proposed and explains well the behavior of the nonlinear coupling phenomena.

Frequency Response of the Noise Conversion From Relative Intensity Noise to Phase Noise in the Photodetection of an Optical Pulse Train

“…The pump DC bias current is 780 mA, so that the modulation depth is 2.56%. Due to the gain modulation effect in the mode-locked laser, noise spurious peaks at harmonic frequencies of can be observed in the RIN spectrum [14]. Similar noise spurious peaks can also be observed in the phase noise spectrum.…”

“…Also, the measurement setup is complicated due to the requirement of an additional AOM. In this letter we adopt pump modulation method [14] to characterize the frequency response of the relative-intensity-noise (RIN)-to-phase-noise conversion in the photodetection process. This method provides an effective way to investigate the noise conversion with respect to the offset frequency.…”

Noise conversion from pump to the passively mode-locked fiber lasers at 15 μm

“…This pump RIN then transfers to the RIN and the phase noise of the MLLs through various mechanisms, such as gain modulation effect [10]. After an isolator, the output of the lasers is fed into an acousto-optic modulator (AOM) and then into a 2 GHz photodetector (PD).…”

“…Various studies have been done on the quantum noise limits [3][4], pulse dynamics [5], noise reduction [6][7][8], and noise measurement, [9] etc. It has been known that the relative intensity noise (RIN) of the pump converts to the RIN and phase noise of the MLL through various mechanisms [4,10,11]. The phase noise in this paper refers to the timing jitter of the MLLs.…”

“…The noise conversion from the pump RIN to the RIN and phase noise in Ti:Sapphire lasers has been experimentally measured [11,12]. We have also investigated the nonlinear noise conversion from the pump RIN to the laser RIN [10]. However, there is no reported work yet investigating in detail the noise conversion from the pump RIN to the laser RIN and laser phase noise for the MLLs at 1.5 μm.…”