Fig. 4: Forward Brillouin fibre lasing.
a Schematic illustration of the experimental setup of a forward SBS laser in a PM fibre. EDFA: erbium-doped fibre amplifier; PBS: polarisation beam splitter; PC: polarisation controller; FBG: fibre Bragg grating. b Power spectral density (PSD) of the detected beating between the slow-axis output of the PM fibre cavity and a local oscillator replica of the input pump wave. The optical pump power was 27.5 dBm. The trace was acquired by an electrical spectrum analyser (ESA) in max-hold mode over three minutes. A single peak at 68 MHz frequency is observed. This peak corresponds to forward SBS lasing through a guided acoustic mode with that cut-off frequency. c Same as panel b, with a pump power of 28 dBm. Four peaks are observed, representing forward SBS lasing through acoustic modes of 68, 169, 320 and 347 MHz cut-off frequencies (see Fig. 3a). d Same as panels b and c, with a pump power of 28.5 dBm. A large number of spectral peaks correspond to forward SBS lasing through multiple guided acoustic modes as well as inter-mixing products.
