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

Abstract

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.

Simplified setup for Brillouin scattering observation using variable reflectivity mirror and its polarisation characteristics

“…One of these efforts is the elimination of the independent reference light path. Thus far, several methods have been developed that use as reference light the Fresnel reflected light generated at the boundary between the open end of the FUT and air [11], and the boundary between the second port of the optical circulator and the proximal end of the FUT [12,13]. However, these methods present a challenge as the power of the Fresnel reflected light remains constant, hindering the maximisation of the signal-to-noise ratio (SNR) of the BGS through control mechanisms.…”

Long-term stability enhancement of Brillouin measurement in polymer optical fibers using amorphous fluoropolymer

“…In this configuration, without using an explicit reference light path, the Fresnel-reflected light operates as the reference light for BGS detection. 37) The temporal variations in the Fresnel-reflected light power, before immersing the open end of the PFGI-POF in water, while immersed in water, and shortly (1 min) after removing from water are depicted in Figs. 2(a), 2(b), and 2(c), respectively.…”

Brillouin frequency shift hopping in polymer optical fiber

“…The polycarbonate reinforcement overcladding layer (diameter of 490 lm) reduces micro-bending losses and increases the load-bearing capability. Instead of the standard experimental setup based on self-heterodyne detection, 17 we used a newly developed Fresnel-assisted setup, 24 which can detect the BGS in POFs with a higher signal-to-noise ratio. Large strain was applied to the POF with two computer-controlled motorized stages at a room temperature of 20 C.…”