Coherent light generators – Optical fiber laser
Patent
1990-03-09
1992-01-28
Davie, James W.
Coherent light generators
Optical fiber laser
372 66, 372 75, 359333, H01S 330
Patent
active
050848828
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a phased-array laser oscillator/amplifier system consisting of looped fibre whose two optically polished end faces are stacked together to form a single output aperture near to which is positioned a single laser mirror in the case of the laser oscillator configuration of the invention or an optical window in the case of the laser amplifier configuration, which is index matched to said output aperture, the said fibre bundle laser medium being optically excited via the said single aperture composed of the fibre ends. In the case of the laser oscillator configurations of the invention, the single laser mirror is partially transmitting and allows the output laser beam to emerge as a phase-locked beam formed by adding together all the outputs from the individual fibre laser ends. In the amplifier configuration of the invention, the input beam to be amplified passes into the said amplifier as a polarized beam via an optical window which is anti-reflection coated on its outside surface and index-matched to the output aperture of the invention from the other side.
The invention has application as a scaleable laser beam generator in the industrial, medical and defence fields.
SUMMARY OF THE PRIOR ART
Prior art, fibre bundle based, phased-array lasers consisted of doped optical fibre laser oscillators stacked together so that each of the said fibre laser oscillators were excited along the whole, or a portion of their length with the excitation light being coupled into the fibre along part of its length via optical coupling devices as known in the art or simply by direct, side excitation of said prior art lasers.
It was not possible to efficiently excite such prior art phased-array, fibre bundle based lasers via their output apertures because the cross-section area of the doped fibre core represented only a small portion of the total area of the said end faces most of whose area was taken up by the cross-sectional area of the fibre cladding. To achieve efficient coupling of the excitation light into the fibre laser bundle end face of prior art fibre bundle based, phased-array lasers would have required the use of complex and expensive arrays of micro-lenses, each one positioned so as to focus its portion of the excitation light into its own matching fibre core. Prior art phased-array lasers also suffered from multilobbed output beams, and, in the case of such prior art phased-array lasers formed by stacking together semi-conductor laser diodes, from severe heating of the output aperture due to the fact that over 60% of their electrical energy input was deposited within the body of the array itself.
This invention overcomes the defects and operating problems of prior art fibre bundle based, phased-array lasers by using fibres whose core diameters are comparable to or greater than their cladding thickness, ideally, using optical fibres which contain a multitude of cores within a given cladding so that the core diameters are much greater than their separation from each other. In a preferred embodiment, the present invention uses multi-cored optical fibres doped with the appropriate lasing ion. This configuration allows for most of the laser light incident on the aperture face constructed from the optically polished ends of such fibres to pass into the fibre cores. For example, a well collimated beam of narrow optical bandwidth excitation light emitted from a stack of temperature tuned phase-locked laser diodes can be injected into the invention via its end face with high efficiency.
The invention also allows for the plane of polarization of the laser light propogating within said fibres to be magnetically rotated.
BACKGROUND OF THE INVENTION
Pioneering work on fibre bundle lasers was undertaken by the inventor at the Royal Radar Establishment, UK in 1963 when laser light was propogated through optical fibre bundles that were commercially available at that time. The early goal was to use bundles of coherently packed optical fibres to inter-connect laser rod media to
REFERENCES:
patent: 3471215 (1979-10-01), Smitzer
patent: 4682335 (1987-07-01), Hughes
Davie James W.
Phased Array Lasers Pty. Ltd.
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