The core of Ampliconyx’s technology is patented active tapered double clad fiber (T-DCF, US patent No. 8,433,168B2). T-DCF is an optical fiber with a core doped by rare-earth elements (Yb, Er, Tm etc.) and it is exploits as a gain element in high power amplifiers, both CW and pulsed. Core and cladding diameters of T-DCF are smoothly varying along length. Usually the core parameters (diameter and numerical aperture) are usually are chosen such that fundamental mode only is supported at the narrow part of T-DCF.
In the wide side, a T-DCF has a substantially larger core diameter (typically within range 50 to 200 μm), while the mode content and beam quality (M2) remains the same as it was in the narrow side. Thus, in the active T-DCF, a unique situation realized when only sole fundamental mode propagates in the core where hundreds of modes potentially are able to exsist. Thus, the tapering of the active fiber allows achieve an excitation and propagation of fundamental mode only in a multimode core with a diameter of several tens of microns.
The main advantages of active T-DCF are:
- Large mode field diameter (up to 100um) resulting in significant increasing nonlinear effects (SRS, SPM) threshold in fiber lasers and amplifiers;
- Large clad pump absorption (typically more than 20dB), which allow make amplifiers (lasers) shorter and thereby additionally (in comparison with a conventional fiber) increase the threshold for nonlinear effects;
- Immunity to the stimulated Brillouin scattering (SBS) due to modulation of the core diameter.