Passive erbium-doped fiber seed photon generator for high-power Er³⁺-doped fiber fluorescent sources with an 80-nm bandwidth

A novel structure that converts wasted backward amplified spontaneous emission (ASE) to seed photons for the amplifier stage is suggested for a high-power erbium-doped fiber (EDF) broadband source. A considerable increase in output power and bandwidth extension was achieved by placement of a segment of passive EDF in front of the amplifier stage, thus recycling backward ASE as the secondary pumping source for the passive EDF seed photon generator. Experimental results showed a dramatic increase in output ASE power of more than 10 dB for most radiation bands from 1540 to 1620 nm with the simple addition of an unpumped EDF segment to the ordinary fluorescence-source structure.