For many years, thermoplastic composites have been conquering the technological market in commercial applications in civil and military structures, with particular emphasis on aircraft. One of their most attractive advantages is the potential to be repaired and welded in a short time. However, due to the lack of knowledge on the impact of process parameters (time, pressure, temperature) bonding thermoplastic composites remains a challenge. The combined action of force and temperature leads to intimate contact between the substrates, which is the prerequisite for macromolecular interdiffusion and welding. A polymer film named Energy Director (ED) can be set up at the interface between substrates to enable the process and to ensure the strength of the joint. This leads to the need for a temperature measurement technique to better understand the physics responsible for the best bonding parameters. The use of Fibre Bragg Grating (FBG) seems to be suitable for obtaining real-time temperature data during the joining. The present work is challenging this technique by means of a rheometer as a device for results validation. The considered bonded materials are carbon fibre-reinforced polyetheretherketone (CF/PEEK) and polyetherimide (PEI). The integration of PEI film on top of the CF/PEEK composite parts is studied. The FBG sensors respond to both temperature and longitudinal strain. Then two kinds of measurements are examined under the rheometer: the first response of the fibre as a function of temperature in static mode during processing and the second one as a function of torque loading. Wavelength shifts and spectral form changes induced by the contraction of the composite during cooling were observed. The use of a rheometer is suitable for the simulation of CF/PEEK composites joining processes such as welding. FBG method has a higher potential for temperature measurement than incorporated thermocouples (TC) as studied during ultrasonic (US) welding [1]. Its advantage is the possibility to allow several measurement points along the optical fibre. The ultimate goal is to provide temperature mapping in the welding zone. The results from both techniques: optical fibre sensors and thermocouples were compared.