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In this letter, we propose a new experimental setup to extend the measurement range of frequencydomain low coherence interferometry (FD-LCI) from 3 mm to 2 cm. The FD-LCI can be extended to the technique of frequency domain optical coherence tomography by performing additional lateral scanning. This new and simple arrangement just attaches an extra interferometer before the spectrometer in a typical FD-LCI setup. With this configuration, it is possible to overcome the limitation of the dynamic range of the conventional technique. This allows us to measure the optical path difference of the sample of interest, which is outside the detection range of the spectrometer, using an extra interferometer as a tuner system. In addition, this tuning allows significant minimization of the effects produced by the fall-off. The accuracy of the new system is obtained by adding the FD-LCI and the tuning micrometric translator accuracies. In our experimental setup, this value is 20 μm.

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A low-cost long-range frequency domain low-coherence interferometry (LCI) detector is presented: time Fourier domain LCI (TFD-LCI). Combining ideas of time domain and frequency domain techniques, the TFD-LCI detects the analog Fourier transform of the optical interference signal with no limitation for the maximum optical path, measuring the thickness of several centimeters with micrometer resolution. A complete characterization of the technique is presented with a mathematical demonstration, simulations, and experimental results. An evaluation of repeatability and accuracy is also included. Measurements of small and large monolayer and multilayer thicknesses were done. Characterization of the internal and external thicknesses of industrial products such as transparent packages and glass windshield is presented, showing the potentiality of TFD-LCI for industrial applications.