Analysis of Erbium-doped segmented-cladding fiber for optical amplification

A segmented-cladding fiber (SCF) has a uniform core of high refractive index and a cladding consisting of alternating high and low refractive-index angular segments. It is known that such a fiber can be designed to provide effective single-mode operation with an ultra-large core size. In this paper, we analyze a SCF that is doped with erbium ions in its high-index regions (i.e., the core and the high-index cladding segments). The core of the fiber has a diameter of 20 μm and the cladding consists of 8 segments of equal size. The concentration of the erbium ions is 1×10²⁶. We calculate the mode-field distributions in the fiber at the signal (1530 nm) and the pump (980 nm) wavelength with the finite-element method. We obtain the gain characteristics and the pump efficiency of the fiber by solving the propagation rate equations. Assuming an initial signal power of 1 μW, the threshold pump power required is 102 mW for a 30-cm long fiber. The optimal gain of the fiber is 25 dB, which can be achieved with a fiber length of 26 cm and a pump power of 150 mW. Our results confirm that a properly designed SCF can provide highly efficient optical amplification with a short length.