Infrared broadband all-fiber light source based on high-concentration Er³⁺/Yb³⁺ composite double-clad fiber

We report characteristics of an infrared broadband all-fiber light source based on a high-concentration Er³⁺/Yb³⁺ co-doped phosphate core silica cladding fiber as a gain medium. The fiber blank was fabricated by the 'rod-in-tube' technique. The concentrations of rare-earth ions in a phosphate glass for the fiber core were 1.7  ×  10²¹ cm⁻³ of Yb³⁺ and 1.3  ×  10²⁰ cm⁻³ of Er³⁺. The source demonstrated a maximum output power about 20 mW with a fiber length of only 50 cm. Maximum bandwidth at the  −10 dB level was 16.39 nm at a fiber length of 80 cm. Results from experiment indicate that using composite fiber offers good possibilities in achieving a broadband emission with a gain medium length several times shorter than that of silica fibers. (letter)