Q-switched fibre laser using 21 cm Bismuth-erbium doped fibre and graphene oxide as saturable absorber

A compact, Q-switched fibre laser is proposed and demonstrated using a compact Bismuth-based erbium doped fibre (Bi-EDF) together with a Graphene Oxide (GO) Saturable Absorber (SA). The 21 cm long Bi-EDF has an erbium dopant concentration of 6300 ppm with absorption rates of about 83 and 133 dB/m at 1480 and 1530 nm. The SA is fabricated from graphene flakes dissolved in water, forming a GO film that is sandwiched between two FC/PC connectors. The Q-switched Bi-EDF laser has an Amplified Spontaneous Emission (ASE) spectrum of 120 nm, stretching from 1490 to 1610 nm and a Q-switching threshold power of about 65 mW. At the maximum pump power of 118 mW, the pulses are generated with an average output power and pulse energy of 0.11 mW and 4.3 nJ, with a repetition rate and pulse width of 27.2 kHz and 7.7 μs. The output can be tuned over the amplified spontaneous emission spectrum with an average peak power of about −16.8 dBm, and observation under a radio frequency spectrum analyser shows a highly stable output at 21.8 kHz. The proposed Bi-EDF laser will have substantial uses in applications requiring short and stable pulses such as rangefinding and sensing.