Single Mode High Power Fiber Laser System

A fiber comprising a MM core capable of supporting substantially a single fundamental mode at a given wavelength, the core being configured with a refractive index profile provided a dip, the dip being configured to transform an intensity profile of the fundamental mode between Gaussian and ring intensity profiles as the fundamental mode propagates along the core.

A high power SM fiber laser system comprising;

• an active fiber provided with a MM core, the MM core having a double bottleneck-shaped cross-section configured to guide substantially only a fundamental mode without excitation of HOMs, the core being configured to receive the fundamental mode with a substantially Gaussian shape, further shape the Gaussian mode into a ring shape of the fundamental mode and back into the Gaussian shape;
• and
• a passive delivery fiber provided with a SM core configured with a narrow uniformly dimensioned input end region receiving the fundamental mode with the substantially Gaussian shape from the active fiber, and a frustoconical region guiding the fundamental mode into a central region of the passive fiber.