Low-Attenuation Variable Mode Control Using Twist Processing for Step-Index Optical Fiber Loops

We propose a method of variable mode control that generates an equilibrium modal distribution (EMD) in step-index multimode fibers. The proposed method can control the modal power distribution variably from a low-order mode distribution to a high-order mode distribution (including EMD) by twisting fiber loops. The attenuation of the controller for EMD generation is five times smaller than those of conventional EMD generation methods. As a reference light source with high measurement reproducibility, the EMD light source obtained by the variable mode control method can be used to evaluate hard polymer cladding fiber link systems. The proposed method is applicable to all types of step-index multimode optical fibers, including all-glass fibers, hard polymer cladding fibers, and plastic optical fibers.