Novel mode control method based on transmission matrix characteristics of a photonic lantern

Abstract

Photonic lanterns can control beam modes by tuning phase, amplitude and polarization of multiple beam inputs, providing new methods to overcome mode instability in high-power large-mode area fiber lasers. The initial amplitude input of photonic lanterns are usually preset to be equal or random. The beam mode is then adaptively controlled by evaluating the beam output profile. This method can easily realize stable light output, but it sometimes runs into local optimum solutions. In this work, we propose a novel method to preset the initial amplitudes to realize better beam mode control. Based on the waveguide characteristics of the photonic lantern structure, we inversely work out the initial amplitude requirement of the input channels for controlling a certain mode using its transmission matrix. Taking 3×1 photonic lantern as an example, our simulation results show that this method can realize any mode control of LP₀₁, LP_11e, LP_11o with their mode power ratios all above 99%, better than those preset methods to be equal or random. Our simulation method can be utilized in beam control experiments to achieve better beam control in photonic lantern-based fiber lasers