Optical amplifier noise-figure reduction using a variable polarisation beam splitter

A 3 dB noise figure (NF) reduction of an Er³⁺-doped fibre amplifier (EDFA) has been experimentally demonstrated using a variable polarisation beam splitter (VPBS). A VPBS controlled by two liquid crystal cells adequately separates half the amplified spontaneous emission (ASE) power of the optical output signal from the optical amplifier and reduces the NF by up to 3 dB. This technique is verified in an EDFA with a measured NF reduction of 3 dB. It yields an EDFA with an NF of 1.2-1.7 dB and gain of 32-34 dB over a wide spectral bandwidth