Patent ID: 8908263

Claim:
An optical waveguide amplifier assembly comprising: a signal source for providing signal light at a wavelength of between 1050 nm and 1120 nm; and an active optical waveguide coupled to the signal source, the active optical waveguide comprising: a core for guiding the signal light, wherein the core is doped with neodymium ions at a concentration of at least 0.1% by weight; a first cladding surrounding the core, for guiding pump light, wherein the first cladding has a refractive index structure to confine the signal light within the core, wherein in operation, the signal light is amplified by the neodymium ions when a population inversion is created in the neodymium ions upon absorption of the pump light; and a second cladding surrounding the first cladding, having an effective refractive index lower than an effective refractive index of the first cladding, for confining the pump light to the first cladding and the core; wherein the refractive index structure of the first cladding is such that a fundamental spatial mode of the signal light has an area of at least 500 square micrometers; wherein the neodymium ions in the core have a concentration to provide a net optical absorption of at least 3 dB/m for the pump light at a wavelength of 795 to 815 nm or 883 to 887 nm.