Piezo acoustic sensors are well known in the field of acoustic emission since the 20's but are considered as a common product since the 70's. Since that time, the number, type, shape and temperature range of AE sensors have been broaden to satisfy the industrial demands. When considering either high temperature and/or small size, piezo acoustic sensors have limits and an alternative technology has to be considered. In industrial applications with special requirements to high temperature tolerance, small size (< 150 μm), broad frequency response, insensitive to electromagnetic interference, opto-acoustic sensors including Fibre Bragg Grating (FBG) are very good candidates. FBG is an interferometric structure, imprinted inside the core of the optical fibre with unique spectral characteristics of reflectivity. The acoustic waves created during an industrial process result in periodical extension/compression of the optical fibre core and, consequently, the FBG structure. These momentary deformations affect the reflectivity properties of the FBG that follow the behaviour of the incoming pressure waves. This behaviour results in the intensity of the reflected light that encodes the momentary deformation states of the fibre core and so can be used for acoustic sensing. These sensors exhibit linear response in a broadband frequency range (from several Hz to tens of MHz) with potential detection upper limit of the order of several hundred MHz. In contrast, most piezo sensors have linear response in a limited bandwidth and lower detectable frequencies. In this work, we will focus on the fibre technology and compare the sensitivity of commercial FBG with several piezo acoustic sensors. We will also show how FBG's can be used as acoustic sensors in laser processing by analysing the data with state-of-the-art machine learning techniques, in particular for classification of laser power made from the sample itself which can be related to its quality.