All-fiber coherent beam combining with phase stabilization via differential pump power control

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.

Scalable Acoustical Frequency Tagging Coherent Beam Combining Based on Digital Signal Processing

“…The main reason for the amplifier's output phase instability is the change of its optical length. This phenomenon can even control the output phase without additional phase modulators necessary [16]. For designing a phase control system, there is the necessity to determine what typical phase shift changes speed is.…”

Practical technique for improving all-fiber coherent combination of multistage high-power ytterbium fiber amplifiers

“…Perfect coherent combination would null out the signal at the PD. Control of the phase is achieved by use of multidither feedback loops [2,3,13,14]. The pump currents of the first preamplifiers are dithered with different frequencies in the kilohertz range.…”

“…In most of the above demonstrations [4,5,11,12], a phase modulator, one of the major components that adds significant cost as well as loss, is required for phasing locking multiple beams. We explore here an all-fiber configuration scheme for realizing coherent combination via direct pump current modulation [3,13]. Compared with state-of-the-art dithering methods we eliminate the requirement of phase modulators in our fiber amplifiers.…”

Passive Phase Locking Coherent Combination of Solid-State Lasers through Stimulated Brillouin Scattering Effect

“…The above points, as long as one of them is not performed well, will affect the effect of coherent synthesis. Depending on the phase-locking method, coherent synthesis techniques can be divided into two categories: passive coherent synthesis [10] and active coherent synthesis [11]. Passive coherent synthesis realizes the phase locking of multiple lasers inside of the laser through the principle of self-organization, and its implementation methods mainly include the interferometer mode [12], non-linear selforganization mode [13], and evanescent wave coupling method [14].…”