Active phase control in fiber amplifiers is of considerable interest for low-noise single-frequency amplifiers and for coherent beam combining. We demonstrate phase control at 1064 nm by use of an erbium-doped fiber. We investigated the phase shift by guiding the beam through an erbium-doped fiber amplifier in a Mach-Zehnder configuration and applied the results to stabilize the relative phase of two ytterbium-doped fiber amplifiers. To the best of our knowledge, this is the first demonstration of an all-fiber coherent beam combining at 1064 nm employing an erbium-doped fiber as a phase actuator.
"As for the optical impact on the repetition rate change, there were two effects: (1) the interaction between the atoms of the gain media and electromagnetic radiation and (2) the nonlinear effect caused by the third-order susceptibility . Both of these two optical effects should be proportional to the occupation of the upper laser level . Therefore, the control bandwidth of the additional Er fiber would be mainly limited by the upper level lifetime. "
[Show abstract][Hide abstract] ABSTRACT: We demonstrated an all-optical stabilization of the repetition rate in an all-fiber picosecond fiber laser. An active Er-doped fiber was added in the Yb-doped fiber cavity as an optical length modulator via refractive index change with optical pumping at 976 nm to achieve repetition rate stabilization. The standard deviation of the residual fluctuation was 1.39 mHz in a 1 h measurement with a linewidth and phase noise of 1.6 mHz and 0.55 rad, respectively.
[Show abstract][Hide abstract] ABSTRACT: Gain dynamics and corresponding refractive index changes in fiber
amplifiers are important for low noise fiber amplifiers and when using
doped fibers as phase actuators. Furthermore self-induced refractive
index changes are a possible explanation for mode fluctuations in high
power fiber amplifiers, which currently present a major challenge for
high power fiber lasers. Since these processes are all time dependent, a
dynamic model of the refractive index change is very important. We will
present measurements of phase shift dynamics in a low power ytterbium
fiber amplifier. Using a simplified analytic model, which was originally
developed to predict power modulation in telecom amplifiers, we were
able to model the part attributed to the Kramers-Kronig-Relations and to
obtain a much better understanding of the involved timescales. This will
help modeling of phase noise in low noise amplifiers and possibly mode
fluctuations in fiber amplifiers.
Proceedings of SPIE - The International Society for Optical Engineering 02/2012; 8237:29-. DOI:10.1117/12.908316 · 0.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Coherent beam combining enables power scaling beyond the limits of single amplifiers. Therefore, improving the performance and simplicity of coherent combination techniques is of great interest for many high power applications. Here, we show all-fiber coherent beam combining of two ytterbium doped amplifiers with and without a dedicated phase actuator and a total output power up to 25 W. Instead of a dedicated phase actuator, we directly controlled the two ytterbium amplifiers to also stabilize their relative phase. We compared the performance of this method with phase stabilization using two piezo driven fiber stretchers. In both cases, power noise was dominated by the single amplifier.
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