Optical fiber laser

Claim 1

An optical fiber laser comprising: a gain cavity including a single mode optical fiber of given length having a core with a given index of refraction and a cladding surrounding said core and having an index of refraction lower than that of said core, said core comprising a host glass having incorporated therein a laser gain material with a fluorescence spectrum having at least one broadband region in which there is at least one peak emission line; filter means optically coupled to one end of said gain cavity and reflective to radiation emitted from said gain material over a predetermined wavelength interval about said peak emission line to provide feedback in said gain cavity; an etalon filter section butt coupled to the remaining end of said gain cavity optical fiber, said etalon filter section comprising a pair of filters spaced apart in parallel by a predetermined length of material transparent to any radiation emitted from by said gain cavity, one of said parallel filters being in direct physical contact with said core and perpendicular to the longitudinal axis of said core with the other of said parallel filters serving as the emitting end of said laser, said predetermined length of said transparent material in combination with the reflection characteristics of said pair of parallel filters being such that etalon filter section operates as a Fabry-Perot resonator in reflection with a periodic reflectivity characteristic having a peak reflectivity centered at said peak emission line of said gain material and gradually dropping to no reflectivity on either side of said peak reflectivity, said etalon filter section and the resonant characteristics of said gain cavity being structured and arranged with respect to one another to jointly operate to enhance laser action at said peak emission line and to preclude it beyond a wavelength interval centered about said peak emission line, said predetermined length of said transparent material being such that said etalon filter section is no longer than the distance over which the wave train energy from said fiber core remains substantially planar so that said etalon filter section is inside the divergent region from said fiber core to enhance feedback in said gain cavity; and means for pumping energy into said gain cavity to raise the interval energy level of said gain material such that only a small part of the ion population thereof, corresponding to a predetermined bandwidth about said peak emission line, is raised above laser threshold for said gain material so that said laser emits radiation only over narrow lines over a narrow wavelength interval centered about said peak emission line.