Optical performance of Er³⁺/Yb³⁺ codoped core-cladding heterogeneous single-mode fiber amplifier

A high-concentration Er³⁺/Yb³⁺ codoped core-cladding heterogeneous single-mode phosphate fiber amplifier with a similar numerical aperture to the Corning SMF-28 standard single-mode optical fiber is described. Measurements and calculations are given for the device's optical absorption, strong infrared fluorescence, absorption, and emission cross-sections of Er ³⁺, Judd-Ofelt parameters, and spontaneous transition probabilities of Er³⁺ in the core glasses. The relative gain (the signal enhancement) of a 5.8-cm-long fiber amplifier was measured to be 32.3 dB, and after compensating for both the propagation loss and the absorption loss, a maximum internal gain of 2.6 dB/cm at 1.535 μm was obtained, which reveals an available core-cladding heterogeneous design strategy in developing high-gain amplifier devices.