A general procedure for determining the optimum placement of filters in Nd3+-doped ZBLANP fibres is presented. Extra gain of 5 dB per filter is predicted for the first four filters, yielding 20 dB of gain with 125 mW of pump power using three filters.

The viability of using mode coupling notch filters to suppress the amplified spontaneous emission around 1050 nm in Nd3+ doped ZBLAN fibres was demonstrated. A gain value of 9.2 dB was observed at 1328 nm using one pump at 795 nm and one mode coupling filter.

A model for Nd3+-doped ZBLANP fibres is verified. The model predicts high gain improvements by suppressing the 1050 nm amplified spontaneous emission. The gain in dB can be more than tripled and a gain to pump power ratio of 0.16 dB/mW is obtained independently of the pump power.

Gain values of 4 to 5 dB were observed between 1310 and 1370 nm in a Nd-doped bimoded ZBLAMP fibre pumped at the diode laser compatible wavelength of 795 nm. The magnitude of the gain was shown to be limited by saturation due to amplified spontaneous emission from 1050 nm radiation. The excited state absorption spectrum was mapped.<>