We report over 2 W of single spatial-mode output power at 1.5 microm from an 8-cm-long, large-core phosphate fiber laser. The fiber has a numerical aperture of approximately equal to 0.17 and a 25-microm-wide core, heavily doped with 1% Er(+3) and 8% Yb(+3). The laser utilizes a scalable evanescent-field-based pumping scheme and can be pumped by as many as eight individual multimode pigtailed diode laser sources at a wavelength of 975 nm. Nearly diffraction-limited laser output with a beam quality factor M2 approximately equal to 1.1 is achieved by use of a simple intracavity all-fiber spatial-mode filter. Both spectrally broadband and narrowband operation of the laser are demonstrated.
"For instance, the fundamental mode can be selected by means of an external free space cavity . Tapers are also known to perform efficient modal filtering  . Fibre bending techniques introduce losses on high order modes but "
[Show abstract][Hide abstract] ABSTRACT: We propose new laser architecture to improve the spatial emission of a multimode fibre amplifier (MMFA) by using a self-imaging process. Interference between the different modes of the MMFA is filtered by a single-mode fibre section which serves as feedback in a unidirectional ring cavity. The laser self-adjusts its frequency to ensure self-imaging between opposite faces of the multimode fibre. The laser output pattern and longitudinal modes depend on the single-mode fibres' end face position with respect to the MMFA centre axis. As a proof of principle we report experimental results which are in good agreement with numerical simulations.
Journal of Optics A Pure and Applied Optics 09/2008; 10(11):115303. DOI:10.1088/1464-4258/10/11/115303 · 1.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Raman fiber lasers (RFLs) and Raman fiber amplifiers (RFAs) in multimode fibers were explored. The RFL based on a graded-index fiber was shown to be very efficient relative to RFLs based on singlemode fibers. Several configurations of the RFL were examined; the beam quality of the Stokes beam depended on the reflectivity of the output coupler and the Stokes power. When used as a beam combiner, the RFL was a highly efficient brightness converter. RFL configurations which used dichroic mirrors were shown to be potentially useful for RFLs based on very large fibers. The forward- and backward-seeded geometries of an RFA based on a graded-index fiber were examined. The beam quality of the output was observed to depend on the beam quality of the input. A numerical model explains this behavior in terms of mode competition and explains why beam cleanup occurs in graded-index fibers but not in step-index fibers. The spectrum of the forward-seeded geometry was superior to the spectrum of the backward-seeded geometry. The RFA was used as a beam combiner.
[Show abstract][Hide abstract] ABSTRACT: This multi-disciplinary research effort developed new classes of compact, highly-doped Er/Yb phosphate-doped glass fibers as high power, low noise single wavelength, single mode oscillators. Three world record powers in low-noise, single frequency laser oscillators at the eyesafe wavelength of 1.55 micrometers were reported. The project vertically integrated fabrication, testing, and optimization of all components necessary for manufacturing of fiber laser units including highly doped specialty glasses, fiber preforms, fiber drawing techniques, fiber Bragg gratings, fiber facet coatings, and fusion splicing of fiber components. A novel stack and draw technique produced single and multicore geometries including index guides and micro-structured single and multiple core fibers. Ulltra-short pulse generation in these phosphate fibers yielded world record peak intensities and novel applications. The MIT partners developed a novel class of surface emitting fiber lasers based on 1D photonic bandgap confinement. A new class of optically-pumped high-power, high brightness semiconductor vertical-external-cavity surface emitting laser emitting around 980nm were designed using a novel epitaxial quantum design approach and demonstrated experimentally. Power scaling methods such as spectral beam combining and cascaded intra-cavity semiconductor chips were demonstrated as well as visible light generation via intra-cavity second harmonic generation. Over 70 articles were published in peer-reviewed journals.
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