Lensless low coherence interferometer fibre-deployed metrology for in-situ measurements

The need for increased geometric complexity and accuracy in manufactured parts is being industrially driven by sectors such as automotive, aerospace, medical, and energy generation. It is important to not only have traceable measurement systems in place for component geometry and tolerance conformance verification, but also to aid in the control of the material removal process in real-time on machine. Low Coherence Interferometry (LCI) has been developed and primarily used in the biomedical imaging domain for the past 20 years as Optical Coherence Tomography (OCT). During this period, it has been shown to be a powerful imaging modality with the ability to operate down to micrometre resolution for depth measurements in non-ideal environments. However, literature defining the effectiveness of lensless LCI/OCT systems operating outside of the biomedical domain is more sparse. Furthermore, the impact of system component choice on key output parameters has not been considered. In this work, the characterisation of a lensless, fibre deployed LCI system in a common path configuration is performed whilst varying system components. Geometric measurements are demonstrated both in air and in water, with analysis of the impact of system design and componentry on output performance metrics. Relative and absolute traceability of results are produced from calibration grade gauge blocks and Renishaw XL-80 calibration experiments to determine and underpin metrological statements of operating characteristics of the system.