A PROCESS FOR THE FABRICATION OF YTTERBIUM-DOPED CLADDING-PUMPED AIR-CLAD FIBER FOR USE AS HIGH POWER LASER SOURCE IN THE INFRA-RED WAVELENGTH REGION

摘要

Confinement of high power pump light into the active core of laser fiber is an important issue that can be overcome by ytterbium- doped cladding-pumped air-clad fiber (ACF) operating in infrared wavelength range. The present invention describes an improvised version of such fiber where fabrication steps and drawing conditions of the ACFs are optimized in silica matrix. The air clad surrounded by low index silica offers a high index contrast and hence high numerical aperture (NA) of the primary cladding which helps to confine the pump light well within the inner silica cladding (primary cladding) and enables efficient coupling of the pump light to the rare earth doped fiber core. ACFs were drawn maintaining feed rate in the range of 5-15 mm/min and high drawing speed of 24-50 m/min during fiber drawing in order to ensure proper air-clad structure with elongated air holes separated by very narrow silica bridges. The core diameter of the ACFs ranged between 9-11 �m and the bridge width was 1 �m. High power laser output was observed from the fabricated Yb-doped ACF at about 1 �m using a standard cavity set-up with bulk optical components. For an optimized fiber length of 1.9 m of the ACF, the lasing performance of the fiber was reasonably good with output power of greater than 5 W and slope efficiency as high as 82%.