$O$ -Band Bismuth-Doped Fiber Amplifier With Double-Pass Configuration

A Bismuth-doped fiber amplifier (BDFA) in a double-pass configuration is proposed and demonstrated. The BDFA consists of a Bismuth-doped phosphogermanosilicate (BiPGeSiO
₂
) fiber pumped by a Titanium-Sapphire source at 810 nm. The BDFA has an amplified spontaneous emission (ASE) spectrum with a 3-dB bandwidth from 1220 to 1490 nm. The maximum gain of the proposed BDFA is 2.0 dB at an input signal wavelength of 1340 nm and is a gain enhancement of 100% over a similarly configured single-pass BDFA. The proposed BDFA has a higher gain enhancement of 1.7 dB at low input signal powers but decreases to as low as 0.5 dB as the input signal power increases.