A laser utilizes a cavity design which allows the stable generation of high peak power pulses from mode-locked multi-mode fiber lasers, greatly extending the peak power limits of conventional mode-locked single-mode fiber lasers. Mode-locking may be induced by insertion of a saturable absorber into the cavity and by inserting one or more mode-filters to ensure the oscillation of the fundamental mode in the multi-mode fiber. The probability of damage of the absorber may be minimized by the insertion of an additional semiconductor optical power limiter into the cavity.

Mode-locked multi-mode fiber laser pulse source

Multi-mode fiber amplifier

The invention describes techniques for the control of the spatial as well as spectral beam quality of multi-mode fiber amplification of high peak power pulses as well as using such a configuration to replace the present diode-pumped, Neodynium based sources. Perfect spatial beam-quality can be ensured by exciting the fundamental mode in the multi-mode fibers with appropriate mode-matching optics and techniques. The loss of spatial beam-quality in the multi-mode fibers along the fiber length can be minimized by using multi-mode fibers with large cladding diameters. Near diffraction-limited coherent multi-mode amplifiers can be conveniently cladding pumped, allowing for the generation of high average power. Moreover, the polarization state in the multi-mode fiber amplifiers can be preserved by implementing multi-mode fibers with stress producing regions or elliptical fiber cores These lasers find application as a general replacement of Nd: based lasers, especially Nd:YAG lasers. Particularly utility is disclosed for applications in the marking, micro-machining and drilling areas.

Microchip-Yb fiber hybrid optical amplifier for micro-machining and marking

A method and apparatus using a gain medium in the form of a multiply clad gain fiber having an erbium-doped core. In some embodiments, aluminum and germanium are added to the silica core to make λ0 longer than the signal wavelength so the signal incurs normal dispersion. Optionally, a large-mode-area core amplifies primarily only one low-order mode because its NA is reduced by lowering the core's index of refraction (e.g., by adding fluorine) and/or by raising the index of the silica inner core (e.g., by adding germanium). Optionally, a thulium-doped region provides substantial loss at the first Raman-gain peak with respect to the signal wavelength but minimal loss at the signal or pump wavelength. Optionally, an inner cladding with a higher NA contains pump light within the outer boundaries of the cladding while allowing pump light to enter the core. In some embodiments, a triple cladding is provided.

Apparatus and method for an erbium-doped fiber for high peak-power applications

A method and apparatus is described that use an index-of-refraction profile having a significant central dip in refractive index (or another tailored index profile) within the core of a gain fiber or a gain waveguide on a substrate. The benefits of this central dip (more power with a given mode structure) are apparent when an input beam is akin to that of a Gaussian mode. In some embodiments, the invention provides a fiber or a substrate waveguide having an index profile with a central dip, but wherein the device has no doping. Some embodiments use a central dip surrounded by a higher-index ring in the index of refraction of the core of the fiber, while other embodiments use a trench between an intermediate-index central core portion and the ring, or use a plurality of rings and/or trenches. Some embodiments use an absorber in at least one core ring.

Apparatus and method for a waveguide with an index profile manifesting a central dip for better energy extraction

A self-tuning optical waveguide filter for attenuating a lower power light signal at λ1 more than a higher power signal at λ2 comprises a length of single core waveguide and a light injector for applying λ1, λ2 into the waveguide in two propagating modes subject to mode beating. The mode beating produces high intensity regions of λ1 physically displaced from high intensity regions of λ2. A portion of the waveguide is doped with a saturable absorber for disproportionately attenuating wavelengths at lower power levels. Advantageously the waveguide is a single-core fiber having its central core doped with rare-earth saturable absorber. In a preferred embodiment, the fiber is dimensioned to propagate λ1, λ2 in the LP01 and LP02 modes, and the saturable absorber is Erbium.

Jau-Sheng Wang

Papers

Self-tuning optical waveguide filter