Patent ID: 8532150

Claim:
A method for generating laser light, comprising: directing laser light first into a passive large mode area fiber that supports a first fundamental fiber mode and first higher order fiber modes and then into an active large mode area fiber that supports a second fundamental fiber mode and second higher order fiber modes and is doped to amplify light to produce amplified laser light, the passive large mode area fiber and the active large mode area fiber being spliced to connect to each other; coiling the passive large mode area fiber to have a coiling portion that selects light in the first fundamental fiber mode to transmit through the passive large mode area fiber into the active large mode area fiber for amplification while suppressing first higher fiber modes in light output by the passive large mode area fiber; and coiling the active large mode area fiber to have a coiling portion that selects light in the second fundamental fiber mode to transmit through, and to be amplified by, the active large mode area fiber while suppressing light in the second higher fiber modes in light output by the active large mode area fiber.