Measurement of PDMS refractive index by low-coherence interferometry

We present a modification of the interferometric method for the measurement of the refractive index of the optical sample. The spectral low coherence interferometry technique utilizes an almost all-fiber Michelson interferometer with an air-path variable optical delay line. The length of the air-path variable optical delay line can be easily adapted to the various thickness and refractive indexes of investigated optical samples that is of particular importance for specialty optical sample characterisation. We record a series of spectral interferograms to measure the equalisation wavelength as a function of the path length difference. A second order polynomial fit is applied to the measured data. Comparing the fitting dependencies obtained for polydimethylsiloxane (PDMS) and reference fiber we get the spectral dependence of refractive index of PDMS. The described method can be practical tool for laboratories with the need of inexpensive and easily built set-up for measurement of refractive index of specialty optical samples in a broad spectral range.