Fresnel-assisted self-heterodyne detection for Brillouin gain spectrum characterisation in polymer optical fibres

It has been experimentally shown that by utilising the Fresnel-reflected light as the reference light, Brillouin signals in polymer optical fibres (POFs) can be observed with a higher signal-to-noise ratio (SNR) than those measured with standard self-heterodyne detection. This method is basically the same in setup as direct detection, leading to an additional advantage of system simplicity. Moreover, it has been demonstrated that the Brillouin signal in a 1 cm-long POF can be observed with a moderate SNR using this technique, indicating a potential feasibility of POF-based distributed Brillouin measurement with a millimetre-order spatial resolution.