Gain dynamics of clad-pumped Yb-fiber amplifier and intensity noise control

Abstract

Gain dynamics study provides an attractive method to understand the intensity noise behavior in fiber amplifiers. Here, the gain dynamics of a medium power (5 W) clad-pumped Yb-fiber amplifier is experimentally evaluated by measuring the frequency domain transfer functions for the input seed and pump lasers from 10 Hz to 1 MHz. We study gain dynamic behavior of the fiber amplifier in the presence of significant residual pump power (compared to the seed power), showing that the seed transfer function is strongly saturated at low Fourier frequencies while the pump power modulation transfer function is nearly unaffected. The characterization of relative intensity noise (RIN) of the fiber amplifier is well explained by the gain dynamics analysis. Finally, a 600 kHz bandwidth feedback loop using an acoustic-optical modulator (AOM) controlling the seed intensity is successfully demonstrated to suppress the broadband laser intensity noise. A maximum noise reduction of about 30 dB is achieved leading to a RIN of -152 dBc/Hz (~1 kHz-10 MHz) at 2.5 W output power.

Intensity noise as a driver for transverse mode instability in fiber amplifiers

“…The results of our experimental investigations and simulations depict the described behavior and, thus, they are in good agreement with the physical understanding that has been revealed by the studies on the noise transfer in fiber amplifiers [20][21][22][23][24][25][26].…”

“…The experimental and theoretical findings of this work can be explained with the results presented in former studies [20][21][22][23][24][25][26], which have investigated the transfer functions of input pump-and seed-modulations to the modulations of the output-signal power in fiber amplifiers. All of these studies coincide in the same statement: the relative pump intensity-modulations in saturated fiber amplifiers are transferred to relative output-signal modulations following a low-pass behavior in the frequency domain.…”

Ultra-low intensity noise, all fiber 365 W linearly polarized single frequency laser at 1064 nm

“…It is known that the amplification process induces an excess of noise, especially at low frequencies, where the pump amplitude noise is converted in signal amplitude noise [25,26]. Different noise reduction techniques have been demonstrated in the past, one based on free-space acousto-optic modulators (AOM), but the one qualified for very high-power systems have a bandwidth limited at 100 kHz because of the inherent time delay [27,28].…”

Flexible all-PM NALM Yb:fiber laser design for frequency comb applications: operation regimes and their noise properties

“…The noise properties of each state are governed by a complex balance of various effects that need to be taken into account when interpreting these measurements, as will be discussed in the rest of this paragraph. The response properties of the gain medium alone can be separated from the oscillator dynamics by looking at the noise transfer function in amplifiers made of the same gain medium [50][51][52].…”